The bone ecosystem facilitates multiple myeloma relapse and the evolution of heterogeneous drug resistant disease

Multiple myeloma (MM) is an osteolytic malignancy that is incurable due to the emergence of treatment resistant disease. Defining how, when and where myeloma cell intrinsic and extrinsic bone microenvironmental mechanisms cause relapse is challenging with current biological approaches. Here, we report a biology-driven spatiotemporal hybrid agent-based model of the MM-bone microenvironment. Results indicate MM intrinsic mechanisms drive the evolution of treatment resistant disease but that the protective effects of bone microenvironment mediated drug resistance (EMDR) significantly enhances the probability and heterogeneity of resistant clones arising under treatment. Further, the model predicts that targeting of EMDR deepens therapy response by eliminating sensitive clones proximal to stroma and bone, a finding supported by in vivo studies. Altogether, our model allows for the study of MM clonal evolution over time in the bone microenvironment and will be beneficial for optimizing treatment efficacy so as to significantly delay disease relapse.

How circulating tumor cluster biology contributes to the metastatic cascade: from invasion to dissemination and dormancy

Circulating tumor cells (CTCs) are known to be prognostic for metastatic relapse and are detected in patients as solitary cells or cell clusters. Circulating tumor cell clusters (CTC clusters) have been observed clinically for decades and are of significantly higher metastatic potential compared to solitary CTCs. Recent studies suggest distinct differences in CTC cluster biology regarding invasion and survival in circulation. However, differences regarding dissemination, dormancy, and reawakening require more investigations compared to solitary CTCs. Here, we review the current state of CTC cluster research and consider their clinical significance. In addition, we discuss the concept of collective invasion by CTC clusters and molecular evidence as to how cluster survival in circulation compares to that of solitary CTCs. Molecular differences between solitary and clustered CTCs during dormancy and reawakening programs will also be discussed. We also highlight future directions to advance our current understanding of CTC cluster biology.

γδ-Enriched CAR-T cell therapy for bone metastatic castrate-resistant prostate cancer

Immune checkpoint blockade has been largely unsuccessful for the treatment of bone metastatic castrate-resistant prostate cancer (mCRPC). Here, we report a combinatorial strategy to treat mCRPC using γδ-enriched chimeric antigen receptor (CAR) T cells and zoledronate (ZOL). In a preclinical murine model of bone mCRPC, γδ CAR-T cells targeting prostate stem cell antigen (PSCA) induced a rapid and significant regression of established tumors, combined with increased survival and reduced cancer-associated bone disease. Pretreatment with ZOL, a U.S. Food and Drug Administration-approved bisphosphonate prescribed to mitigate pathological fracture in mCRPC patients, resulted in CAR-independent activation of γδ CAR-T cells, increased cytokine secretion, and enhanced antitumor efficacy. These data show that the activity of the endogenous Vγ9Vδ2 T cell receptor is preserved in CAR-T cells, allowing for dual-receptor recognition of tumor cells. Collectively, our findings support the use of γδ CAR-T cell therapy for mCRPC treatment.

Abstract 276: Delineating the role of vesicular glutamate transporter SLC17A7 in osteosarcoma

Osteosarcoma (OS) frequently metastasizes to lung where it greatly contributes to patient mortality. Frustratingly, OS treatment options have remained static due to a paucity of strong pre-clinical evidence to motivate clinical trials. To identify therapeutic targets, we assessed a number of FDA approved therapies for their cytotoxic effects. We found that histone deacetylase (HDAC) inhibitors (panobinostat and romidepsin) limited OS viability at low nM and were highly effective for the treatment of lung metastatic disease in vivo. Although clinically approved, HDAC inhibitors have noted toxicities. Therefore, we next examined the potential mechanisms through which HDAC controlled OS growth. Gene expression analyses on romidepsin treated OS cells revealed key up and downregulated targets. We found that SLC17A7, a vesicular glutamate transporter, was highly and consistently induced in response to romidepsin (greater than 100 fold more than base line) across multiple OS cell lines. Functionally, SLC17A7 traps glutamate in cytoplasmic synaptic vesicles that are then released via exocytosis. Our data show that HDAC inhibition reduces glutamate secretion from OS cells while SLC17A7 overexpression significantly impaired OS viability. Further, we showed that the glutamate export inhibitor, riluzole, significantly impairs the OS growth in vitro and is highly effective for the treatment of lung metastatic OS in vivo. Taken together, we conclude that HDAC1/2 suppression of SLC17A7 ensures high cytoplasmic glutamate levels that can be leveraged for OS growth. We posit that targeting glutamate usage by OS cells using FDA approved inhibitors such as riluzole will be highly effective for the treatment of lung metastatic OS.

Citation Format: Niveditha Nerlakanti, Jeremy McGuire, Ryan T. Bishop, Diana Yu, Damon R. Reed, Conor C. Lynch. Delineating the role of vesicular glutamate transporter SLC17A7 in osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 276.

Abstract 1767: Biodistribution of zoledronate and effects on gd PSCA-CAR T cells in a model of bone metastatic prostate cancer

Background: Metastatic castrate resistant prostate cancer (mCRPC) is frequently manifested in the bone, leading to increased morbidity and mortality. We have previously demonstrated that γδ Chimeric Antigen Receptor (CAR) T cells targeting prostate stem cell antigen (PSCA) led to significant regression of established prostate cancer cells in the bone. Regression was further increased by combination with the bisphosphonate zoledronate (ZOL), routinely administered to mCRPC patients to prevent bone loss. To further optimize the use of γδ CAR T cells for mCRPC, we aimed to determine the kinetics of γδ CAR T cell in a mouse model of bone metastatic prostate cancer, either as single treatment or in combination with ZOL. In addition, we identified the sites of systemic ZOL accumulation in an immune competent model that could potentially induce off-target effects of γδ CAR T cells.

Methods: Male NSG mice were injected with C4-2B prostate cancer cells expressing PSCA and luciferase in the left tibia, while the right tibia received PBS. ZOL (25 μg/kg) was injected every other day subcutaneously in half of the mice and was discontinued one day prior to administering T cells. When tumors were established, mice received γδ PSCA-CAR T cells, γδ untransduced (UT) T cells or were left untreated. Bone marrow from tumor-bearing tibia, tumor-naive tibia, femur, spleen and blood were recovered at multiple time points, and the number of γδ T cells was analyzed by flow cytometry. To determine systemic ZOL uptake, C57BL/6 mice were injected with PTE-82 prostate cell line in both tibias. One week after injection, mice received ZOL-AF647 every other day for 2 weeks. Bone marrow, liver, kidney, peritoneal lavage, skin-draining lymph nodes, Peyer’s patches and spleen were recovered and analyzed by flow cytometry.

Results: γδ CAR T cells showed a rapid accumulation in the bone marrow recovered from tumor-bearing tibias, with 3 times more cells than those from mice treated with γδ UT cells (p=0.0002). The number of γδ T cells peaked at 5 days post infusion and were still detected after 21 days. Increased γδ CAR T cell accumulation was not observed in tumor-free bones or in spleen or blood, suggesting a preferential localization of γδ CAR T cells at tumor sites. Treatment with ZOL did not significantly affect the number or phenotype of γδ T cells accumulated in bone. Analysis of ZOL distribution showed significant uptake by macrophages, specially from liver and peritoneal lavage (p<0.0001), with an average of 30% and 70% of macrophages showing positive staining for ZOL-AF647, respectively (p<0.0001).

Conclusion: γδ PSCA-CAR T cells accumulate and get activated at tumor sites with limited distribution outside the bone, while their kinetics is not affected by ZOL treatment in the NSG xenograft model. Additional studies will be necessary to determine the impact of ZOL uptake by myeloid cells on γδ CAR T cells migration.

Citation Format: Leticia Tordesillas, Junior Cianne, Jeremy S. Frieling, Xiomar Bustos, Conor C. Lynch, Daniel Abate-Daga. Biodistribution of zoledronate and effects on gd PSCA-CAR T cells in a model of bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1767.

Abstract 61: PRDM16 is key for promoting bone metastatic prostate cancer cell survival during entry into dormancy

Recurrent metastatic prostate cancer (PC) typically manifests in the skeleton. Despite our knowledge that DTCs give rise to incurable bone metastatic PC, the molecular mechanisms underpinning their entry into dormancy and exit, remain under-investigated. To address this, we developed a novel in vitro model of PC dormancy as determined by increased entry into G0/G1 state (flowcytometry) and increased p38/ERK activity ratio & p27 (immunoblotting). Interestingly, we also observed dormancy entry resulted in the formation of clusters that remained dormant for long periods (21 days) and could be reawakened via serum addition. RNASeq and bioinformatic analysis of control vs. dormant cells revealed PRDM16 to be significantly elevated during entry into dormancy across mouse (RM1) and human cell lines (LAPC4, 22RV1). In vitro, we observed that genetic silencing of PRDM16 leads to a significant reduction in the ability of PC cells to enter dormancy. Analyses show that PRDM16 increases the expression of anti-apoptotic proteins including BCL-2 while inhibiting pro-apoptotic proteins such as BIM and NOXA. Our preliminary data shows that PRDM16 expression in CRPC cells can be induced by BMP7 and conversely decreased by the BMP signaling antagonist, noggin, factors with known critical roles in regulating bone homeostasis. In vivo, we used intrailiac-artery technique to deliver actively growing RM1 cells or dormant RM1 clusters (D-RM1) to the hind limbs (n = 8) of syngeneic mice (C57BL/6). Bioluminescence shows that D-RM1 remains dormant for more than 30 days. Subsequent histological analyses show that D-RM1 home preferentially to the endosteal niche where, compared to RM1 controls, they remain largely negative for ki-67 and cleaved caspase 3 and exhibit high expression of PRDM16. In conclusion, our data points to PRDM16 as a key regulator of survival pathways during PC entry into dormancy.

Citation Format: Mostafa Nasr, Tao Li, Ryan T. Bishop, Conor C. Lynch. PRDM16 is key for promoting bone metastatic prostate cancer cell survival during entry into dormancy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 61.

Abstract 452: Novel autophagy inhibitory strategies to overcome chemotherapy resistance in multiple myeloma

Multiple myeloma (MM) is an incurable disease. Classical chemotherapeutics including bortezomib, melphalan, lenalidomide and thalidomide have greatly enhanced survival times. Unfortunately, patients typically relapse and become refractory with an average survival of 5 years post-diagnosis. Our emerging studies demonstrate a novel role for ULK3 in regulating autophagy in MM, a key program that sustains cell survival under times of stress and has been implicated as a major mechanism of proteasome inhibitor (PI) resistance. MM is known to be highly dependent on autophagy and, currently, specific ULK3 inhibitors are lacking. We posit that by targeting this marker in chemotherapy resistant MM patients, we can circumvent alternative metabolic routes and resensitize to standard of care proapoptotic therapy. We performed RNASeq analysis of CD138+ MM cells derived from patients across the disease stages spectrum (n=815) to confirm the role of ULK3 in disease progression and resistance to chemotherapy. We developed novel inhibitors SG3014/MA9060 that target multiple kinases including ULK3 (EC50 90nM) as well as BRD4. BRD4 is a known driver of MYC and its expression is increased in refractory MM. The BRD4 inhibitor, JQ1, effectively impairs the tumorigenic potential of MM but resistance has also been noted. We determined the efficacy of MA9060 for the treatment of CD138+ MM isolated from naive and refractory patients using a novel ex vivo high throughput platform developed at Moffitt.ULK3 is highly associated with MM stage of the disease. Refractory MM patients have increased autophagy activity with significantly higher expression of ULK3 in refractory patients and in drug resistant cell lines (immunoblotting U266 vs U266-PSR; RPMI-8226 vs RPMI-8226-B25; ABNL vs V10 resistant cells).Genetic ablation of ULK3 by siRNA in U266 and 8226 cell lines results in rapid cessation of the downstream autophagy proteins (ULK1, ATG13, pATG13) and MM cell death within 72h of transduction. Increased concentrations of autophagy inhibitors MA9060/SG3014 progressively decreased CMYC and ULK3 levels, as measured by immunoblotting in U266 cells. In vivo preclinical model of U266Luc tail vein injection proved our drugs are highly effective in reducing tumor dissemination and extending overall survival (CTRL untreated n=65 days vs MA9060 n=110). Importantly, we noted no overt toxicity and protected effect against myeloma-induced bone disease. This novel class of drug works synergistically with PI and can re-sensitize PI resistant disease to these effective therapies. We also show by EMMA ex vivo platform that MA9060 is highly effective for the treatment of CD138+ MM cells isolated from patients with refractory disease.ULK3 represents a novel target for treatment of MM refractory disease. Our dual inhibitors can increase overall survival in vivo and ex vivo, therefore we expect to quickly translate our novel molecules to the clinic.

Citation Format: Marilena Tauro, Tao Li, Mark Meads, Praneeth R. Sudalagunta, Raghunandan R. Alugubelli, Nicholas J. Lawrence, Ernst Schonbrunn, Harshani Lawrence, Kenneth H. Shain, Conor C. Lynch. Novel autophagy inhibitory strategies to overcome chemotherapy resistance in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 452.

Abstract 988: Epigenetic upregulation of neuropilin-1 promotes osteosarcoma progression and metastasis

Background: Osteosarcoma (OS) frequently metastasizes to lung and the prognosis for these patients is grim with 5-year overall survival rates as low as 30%. There has been little change in the treatment paradigm for this disease and new targeted therapies are an urgent and unmet clinical need. Previously, we showed that the epigenetic regulators, histone deacetylase 1 and 2 (HDAC1 and 2) are key mediators of OS progression and lung metastasis and that the HDAC1/2 selective inhibitor (romidepsin) significantly prevented OS lung metastasis in vivo. Yet, inhibition of HDACs by romidepsin has noted toxicities in humans and here we define the potential mechanisms through which HDAC1/2 mediate their effects in a bid to identify additional therapeutic targets.

Methods: Human OS cell lines were treated with vehicle or romidepsin for 24h before undergoing RNA/protein isolation for microarray/proteomics to identify differentially regulated genes. Standard siRNA, proliferation, migration and molecular analyses were preformed to investigate the role of candidate genes in OS malignant behavior.

Results: Microarray/proteomics analyses on romidepsin treated OS cells identified neuropilin-1 (NRP1), a membrane bound co-receptor for vascular endothelial growth factor, to be highly downregulated in response to romidepsin; (<70% compared to vehicle in multiple OS cell lines). NRP1 knockdown (siRNA) led to reduced cell proliferation and interestingly, increased cell migration. Further, a phosphokinase array revealed increased phosphorylation in eNOS, ERK 1/2 and β-catenin in NRP1 knockdown cells that is consistent with a role for NRP1 in regulating OS migration. Based on this data, we hypothesize that NRP1 is a significant regulator of OS proliferation and migration. Our next steps will be to dissect the role of NRP1 silencing in OS invasion and metastasisin vivo and the potential role of NRP1 in OS differentiation.

Conclusions: HDAC1/2 contributes to OS growth potentially via the upregulation of NRP1, a therapeutically actionable target.

Citation Format: Niveditha Nerlakanti, Jeremy Mcguire, Diana Yu, Damon Reed, Conor C. Lynch. Epigenetic upregulation of neuropilin-1 promotes osteosarcoma progression and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 988.

Abstract A031: Dissecting the role of the bone ecosystem and intrinsic resistance in the evolution of refractory multiple myeloma

Multiple myeloma (MM) is a largely incurable cancer characterized by the expansion of plasma cells in the bone marrow. A key component of MM growth involves the establishment of a “vicious cycle” of enhanced bone resorption and tumor growth, resulting in extensive bone destruction and osteolytic lesions. Although there are many approved therapies that contribute to the long-term survival of patients, MM ultimately become refractory to treatment. The evolution of resistance is in part due to the bone ecosystem, which protects MM cells during treatment through interactions between the tumor cells and mesenchymal stem cells and cytokines secreted during bone resorption. The acquisition of refractory disease has also been attributed to intrinsic drug resistance, which allows for MM clones with inherent resistance to become the dominant population due to treatment-imposed selective pressures. While both the protective bone microenvironment and intrinsic drug resistance contribute to refractory disease, the role of the bone microenvironment in the development of cell intrinsic resistance has not been established and remains difficult to assess using current in vitro and in vivo methods alone. However, integration of cancer and evolutionary biology with computational modeling allows a unique insight into the spatiotemporal aspects of myeloma evolution and how treatment impacts the evolutionary dynamics of the disease. To explore these evolutionary dynamics, we developed a hybrid agent-based model that incorporates key cellular species that drive normal bone remodeling and, in the context of cancer, create an environment that provides protection. We use published data as well as our own to calibrate parameters such as the bone mineralization rate and to compare cell population dynamics to model outputs. Furthermore, we incorporate spatial data from immunofluorescence imaging of bone to motivate model assumptions on the localization of dividing and dying MM cells. We show that our model captures two key features: normal bone homeostasis, and the myeloma-bone vicious cycle. We then examine how the bone ecosystem impacts the growth dynamics of MM cells and the degradation of bone under standard of care treatments such as bortezomib, an anticancer therapy. Specifically, we test how the spatial distribution of the cells and factors that provide protection, as well as the timing and dose of treatment, impacts treatment response. Our data demonstrates that resistant disease cannot develop without myeloma intrinsic mechanisms, however, protection from the bone microenvironment dramatically increases the likelihood of intrinsic resistance developing. This model provides a foundation to explore how ecological and evolutionary dynamics in the bone ecosystem and MM contribute to drug resistance and tumor growth which ultimately has the potential to help improve treatment strategies.

Citation Format: Anna K. Miller, Ryan T. Bishop, Tao Li, Conor C. Lynch, David Basanta. Dissecting the role of the bone ecosystem and intrinsic resistance in the evolution of refractory multiple myeloma [abstract]. In: Proceedings of the AACR Special Conference on the Evolutionary Dynamics in Carcinogenesis and Response to Therapy; 2022 Mar 14-17. Philadelphia (PA): AACR; Cancer Res 2022;82(10 Suppl):Abstract nr A031.

Integrated computational and in vivo models reveal Key Insights into macrophage behavior during bone healing

Myeloid-derived monocyte and macrophages are key cells in the bone that contribute to remodeling and injury repair. However, their temporal polarization status and control of bone-resorbing osteoclasts and bone-forming osteoblasts responses is largely unknown. In this study, we focused on two aspects of monocyte/macrophage dynamics and polarization states over time: 1) the injury-triggered pro- and anti-inflammatory monocytes/macrophages temporal profiles, 2) the contributions of pro- versus anti-inflammatory monocytes/macrophages in coordinating healing response. Bone healing is a complex multicellular dynamic process. While traditional in vitro and in vivo experimentation may capture the behavior of select populations with high resolution, they cannot simultaneously track the behavior of multiple populations. To address this, we have used an integrated coupled ordinary differential equations (ODEs)-based framework describing multiple cellular species to in vivo bone injury data in order to identify and test various hypotheses regarding bone cell populations dynamics. Our approach allowed us to infer several biological insights including, but not limited to,: 1) anti-inflammatory macrophages are key for early osteoclast inhibition and pro-inflammatory macrophage suppression, 2) pro-inflammatory macrophages are involved in osteoclast bone resorptive activity, whereas osteoblasts promote osteoclast differentiation, 3) Pro-inflammatory monocytes/macrophages rise during two expansion waves, which can be explained by the anti-inflammatory macrophages-mediated inhibition phase between the two waves. In addition, we further tested the robustness of the mathematical model by comparing simulation results to an independent experimental dataset. Taken together, this novel comprehensive mathematical framework allowed us to identify biological mechanisms that best recapitulate bone injury data and that explain the coupled cellular population dynamics involved in the process. Furthermore, our hypothesis testing methodology could be used in other contexts to decipher mechanisms in complex multicellular processes.

Myeloid-derived monocytes/macrophages are key cells for bone remodeling and injury repair. However, their temporal polarization status and control of bone-resorbing osteoclasts and bone-forming osteoblasts responses is largely unknown. In this study, we focused on two aspects of monocyte/macrophage population dynamics: 1) the injury-triggered pro- and anti-inflammatory monocytes/macrophages temporal profiles, 2) the contributions of pro- versus anti-inflammatory monocytes/macrophages in coordinating healing response. In order to test various hypotheses regarding bone cell populations dynamics, we have integrated a coupled ordinary differential equations-based framework describing multiple cellular species to in vivo bone injury data. Our approach allowed us to infer several biological insights including: 1) anti-inflammatory macrophages are key for early osteoclast inhibition and pro-inflammatory macrophage suppression, 2) pro-inflammatory macrophages are involved in osteoclast bone resorptive activity, whereas osteoblasts promote osteoclast differentiation, 3) Pro-inflammatory monocytes/macrophages rise during two expansion waves, which can be explained by the anti-inflammatory macrophages-mediated inhibition phase between the two waves. Taken together, this mathematical framework allowed us to identify biological mechanisms that recapitulate bone injury data and that explain the coupled cellular population dynamics involved in the process.

Abstract PD3-10: Dual epigenetic/autophagy inhibition as a novel strategy to tackle triple negative breast cancer

Clinical Significance: Despite initial response to therapies, patients with triple negative breast cancer (TNBC) have the highest risk of metastatic relapse within 5 years of diagnosis. There is an urgent need for better treatments for this deadly disease. To this end, understanding the molecular drivers can reveal novel therapeutic targets. Background: The TNBC oncogenic program is known to be driven by MYC. MYC expression is regulated by bromodomain proteins and several bromodomain inhibitors such as JQ1 have proven effective at inhibiting MYC expression. However, resistance can occur rapidly upon activation of alternative cell survival mechanisms, such as autophagy. TNBC is noted for its elevated basal autophagy. Interestingly, publicly available datasets show that ULK3, an initial effector of the autophagy program, is upregulated in TNBC patients while the opposite is observed for the classical autophagy initiator ULK1. Moreover, TNBC patients with low ULK3 expression levels tend to achieve longer relapse free survival (RFS) than higher expression cohort, in opposition to ULK1. Importantly, ULK3 has not been investigated to date in regulating TNBC cell intrinsic autophagy and no drugs exist that can inhibit ULK3. Methods and Results: Given the importance of MYC and ULK3 in TNBC progression, our team developed a novel class of small molecules, namely dual BRD4/ULK3 inhibitors, that are superior to JQ1 alone in limiting TNBC viability. In vitro data demonstrate that TNBC cells are more sensitive to the cytotoxic activity of the dual inhibitors compared to other breast cancer subtypes. Further investigation through western blot analysis confirms the effectiveness of these novel dual inhibitors in abrogating MYC expression overtime, and completely blocking the autophagy program (measured by downstream ULK3, ULK1, LC3B, p62 protein levels), resulting in cell death. Interestingly, the human cell line SUM159R, that is resistant to BRD4 inhibitor JQ1 and cross-resistant to standard chemotherapeutics (doxorubicin) is also highly sensitive to our dual inhibitors, implying their potential use for the treatment of refractory TNBC disease. Excitingly, and for the first time, using a genetic silencing approach (shULK3 in SUM159), we demonstrated that ULK3 is critical for TNBC autophagy and cell survival. As a proof of concept, we reproduced the same genetic silencing experiment in a different cell line, namely WM1366-LC3BmCherry-GFP, an LC3B conveniently engineered system used to visualize proper autophagosome formation and material degradation through autophagy. We verified that both genetic ablation and pharmacologic inhibition of ULK3 are strategies that lead to cancer cell death. Conclusions: In conclusion, we 1) characterized a novel class of dual BRD4/kinase compounds, capable of inhibiting BRD4 activity and autophagy, and superior to the BRD4 inhibitor, JQ1. 2) showed that ULK3 is over-expressed in TNBC. 3) demonstrated that silencing ULK3 blocks autophagy in TNBC cell lines and results in significantly lower cell viability. 4) found that our dual inhibitors present a double bind for TNBC cells that results in increased cytotoxicity and potentially will be useful for the treatment of resistant TNBC. Clinically, we also posit that our dual inhibitors could be easily administered as a single agent, avoiding the potential complication of pharmacokinetics/pharmacodynamics associated with administering multiple therapies.

Citation Format: Marilena Tauro, Tao Li, Conor C Lynch. Dual epigenetic/autophagy inhibition as a novel strategy to tackle triple negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD3-10.

EphA2 Is a Clinically Relevant Target for Breast Cancer Bone Metastatic Disease

EphA2 receptor tyrosine kinase (RTK) is highly expressed in breast tumor cells across multiple molecular subtypes and correlates with poor patient prognosis. In this study, the potential role of EphA2 in this clinically relevant phenomenon is investigated as metastasis of breast cancer to bone is a major cause of morbidity and mortality in patients. It was found that the EphA2 function in breast cancer cells promotes osteoclast activation and the development of osteolytic bone disease. Blocking EphA2 function molecularly and pharmacologically in breast tumors reduced the number and size of bone lesions and the degree of osteolytic disease in intratibial and intracardiac mouse models, which correlated with a significant decrease in the number of osteoclasts at the tumor-bone interface. EphA2 loss of function in tumor cells impaired osteoclast progenitor differentiation in coculture, which is mediated, at least in part, by reduced expression of IL-6. EPHA2 transcript levels are enriched in human breast cancer bone metastatic lesions relative to visceral metastatic sites; EphA2 protein expression was detected in breast tumor cells in bone metastases in patient samples, supporting the clinical relevance of the study's findings. These data provide a strong rationale for the development and application of molecularly targeted therapies against EphA2 for the treatment of breast cancer bone metastatic disease. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Quantification and Optimization of Standard-of-Care Therapy to Delay the Emergence of Resistant Bone Metastatic Prostate Cancer

BACKGROUND

Bone metastatic prostate cancer (BMPCa), despite the initial responsiveness to androgen deprivation therapy (ADT), inevitably becomes resistant. Recent clinical trials with upfront treatment of ADT combined with chemotherapy or novel hormonal therapies (NHTs) have extended overall patient survival. These results indicate that there is significant potential for the optimization of standard-of-care therapies to delay the emergence of progressive metastatic disease.

METHODS

Here, we used data extracted from human bone metastatic biopsies pre- and post-abiraterone acetate/prednisone to generate a mathematical model of bone metastatic prostate cancer that can unravel the treatment impact on disease progression. Intra-tumor heterogeneity in regard to ADT and chemotherapy resistance was derived from biopsy data at a cellular level, permitting the model to track the dynamics of resistant phenotypes in response to treatment from biological first-principles without relying on data fitting. These cellular data were mathematically correlated with a clinical proxy for tumor burden, utilizing prostate-specific antigen (PSA) production as an example.

RESULTS

Using this correlation, our model recapitulated the individual patient response to applied treatments in a separate and independent cohort of patients (n = 24), and was able to estimate the initial resistance to the ADT of each patient. Combined with an intervention-decision algorithm informed by patient-specific prediction of initial resistance, we propose to optimize the sequence of treatments for each patient with the goal of delaying the evolution of resistant disease and limit cancer cell growth, offering evidence for an improvement against retrospective data.

CONCLUSIONS

Our results show how minimal but widely available patient information can be used to model and track the progression of BMPCa in real time, offering a clinically relevant insight into the patient-specific evolutionary dynamics of the disease and suggesting new therapeutic options for intervention.

TRIAL REGISTRATION

NCT # 01953640.

FUNDING

Funded by an NCI U01 (NCI) U01CA202958-01 and a Moffitt Team Science Award. CCL and DB were partly funded by an NCI PSON U01 (U01CA244101). AA was partly funded by a Department of Defense Prostate Cancer Research Program (W81XWH-15-1-0184) fellowship. LC was partly funded by a postdoctoral fellowship (PF-13-175-01-CSM) from the American Cancer Society.

Mesenchymal stem cell-derived interleukin-28 drives the selection of apoptosis resistant bone metastatic prostate cancer

Bone metastatic prostate cancer (PCa) promotes mesenchymal stem cell (MSC) recruitment and their differentiation into osteoblasts. However, the effects of bone-marrow derived MSCs on PCa cells are less explored. Here, we report MSC-derived interleukin-28 (IL-28) triggers prostate cancer cell apoptosis via IL-28 receptor alpha (IL-28Rα)-STAT1 signaling. However, chronic exposure to MSCs drives the selection of prostate cancer cells that are resistant to IL-28-induced apoptosis and therapeutics such as docetaxel. Further, MSC-selected/IL-28-resistant prostate cancer cells grow at accelerated rates in bone. Acquired resistance to apoptosis is PCa cell intrinsic, and is associated with a shift in IL-28Rα signaling via STAT1 to STAT3. Notably, STAT3 ablation or inhibition impairs MSC-selected prostate cancer cell growth and survival. Thus, bone marrow MSCs drive the emergence of therapy-resistant bone metastatic prostate cancer yet this can be disabled by targeting STAT3.

Host-Derived Matrix Metalloproteinase-13 Activity Promotes Multiple Myeloma-Induced Osteolysis and Reduces Overall Survival

Multiple myeloma promotes systemic skeletal bone disease that greatly contributes to patient morbidity. Resorption of type I collagen-rich bone matrix by activated osteoclasts results in the release of sequestered growth factors that can drive progression of the disease. Matrix metalloproteinase-13 (MMP13) is a collagenase expressed predominantly in the skeleton by mesenchymal stromal cells (MSC) and MSC-derived osteoblasts. Histochemical analysis of human multiple myeloma specimens also demonstrated that MMP13 largely localizes to the stromal compartment compared with CD138⁺ myeloma cells. In this study, we further identified that multiple myeloma induces MMP13 expression in bone stromal cells. Because of its ability to degrade type I collagen, we examined whether bone stromal-derived MMP13 contributed to myeloma progression. Multiple myeloma cells were inoculated into wild-type or MMP13-null mice. In independent in vivo studies, MMP13-null mice demonstrated significantly higher overall survival rates and lower levels of bone destruction compared with wild-type controls. Unexpectedly, no differences in type I collagen processing between the groups were observed. Ex vivo stromal coculture assays showed reduced formation and activity in MMP13-null osteoclasts. Analysis of soluble factors from wild-type and MMP13-null MSCs revealed decreased bioavailability of various osteoclastogenic factors including CXCL7. CXCL7 was identified as a novel MMP13 substrate and regulator of osteoclastogenesis. Underscoring the importance of host MMP13 catalytic activity in multiple myeloma progression, we demonstrate the in vivo efficacy of a novel and highly selective MMP13 inhibitor that provides a translational opportunity for the treatment of this incurable disease. SIGNIFICANCE: Genetic and pharmacologic approaches show that bone stromal-derived MMP13 catalytic activity is critical for osteoclastogenesis, bone destruction, and disease progression. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/9/2415/F1.large.jpg.

Abstract PO-044: Epigenetic silencing of SLC17A7 promotes osteosarcoma growth

Osteosarcoma is an orphan disease with only 900 patients diagnosed each year in US. Most patients are adolescents with small number of older patients. The 5-survival rates for those with metastatic disease is only 30%. Frustratingly, there has been little change in treatment options (chemotherapy, surgery and radiotherapy) due to the difficulty of conducting clinical trials in this rare but deadly cancer. To address this, strong pre-clinical trial information is required to motivate clinical trial design. In vitro and in vivo, we identified that the pan-HDAC inhibitor, panobinostat is highly effective in limiting osteosarcoma growth and metastasis. Panobinostat is approved for the treatment of other malignancies but has noted toxicities. Therefore, to identify therapeutic targets, we explored the HDACs responsible for driving osteosarcoma metastasis and the specific genes through which those HDACs mediated their effects. Our data shows that HDAC1 and HDAC2 are key for osteosarcoma survival using siRNA approaches. Use of the HDAC1/2 selective inhibitor romidepsin in vitro and in vivo supported this finding. To identify targets being regulated by HDAC1/2, we performed microarray and proteomics analyses on romidepsin treated osteosarcoma cells. We found and validated independently that, SLC17A7, a metabolic vesicular glutamate transporter to be highly induced in response to romidepsin treatment; >100 fold more than base line in multiple osteosarcoma cell lines. Functionally, SLC17A7 allows entry of glutamate into the synaptic vesicles from cytoplasm and releases the glutamate from the cells via exocytosis. In our studies, we have seen that romidepsin treatment leads to reduced glutamate levels in the conditioned media and cell death indicating key roles for SLC17A7 in driving osteosarcoma progression and metastasis. In conclusion, our data shows that HDAC1/2 suppression of SLC17A7 is a novel means of promoting osteosarcoma progression and metastasis.

Citation Format: Niveditha Nerlakanti, Jeremy McGuire, Diana Yu, Damon R. Reed, Conor C. Lynch. Epigenetic silencing of SLC17A7 promotes osteosarcoma growth [abstract]. In: Abstracts: AACR Special Virtual Conference on Epigenetics and Metabolism; October 15-16, 2020; 2020 Oct 15-16. Philadelphia (PA): AACR; Cancer Res 2020;80(23 Suppl):Abstract nr PO-044.

Modeling Osteocyte Network Formation: Healthy and Cancerous Environments

Advanced cancers, such as prostate and breast cancers, commonly metastasize to bone. In the bone matrix, dendritic osteocytes form a spatial network allowing communication between osteocytes and the osteoblasts located on the bone surface. This communication network facilitates coordinated bone remodeling. In the presence of a cancerous microenvironment, the topology of this network changes. In those situations, osteocytes often appear to be either overdifferentiated (i.e., there are more dendrites than healthy bone) or underdeveloped (i.e., dendrites do not fully form). In addition to structural changes, histological sections from metastatic breast cancer xenografted mice show that number of osteocytes per unit area is different between healthy bone and cancerous bone. We present a stochastic agent-based model for bone formation incorporating osteoblasts and osteocytes that allows us to probe both network structure and density of osteocytes in bone. Our model both allows for the simulation of our spatial network model and analysis of mean-field equations in the form of integro-partial differential equations. We considered variations of our model to study specific physiological hypotheses related to osteoblast differentiation; for example predicting how changing biological parameters, such as rates of bone secretion, rates of cancer formation, and rates of osteoblast differentiation can allow for qualitatively different network topologies. We then used our model to explore how commonly applied therapies such as bisphosphonates (e.g., zoledronic acid) impact osteocyte network formation.

Arginine vasopressin receptor 1a is a therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) recurs after androgen deprivation therapy (ADT) and is incurable. Reactivation of androgen receptor (AR) signaling in the low androgen environment of ADT drives CRPC. This AR activity occurs through a variety of mechanisms, including up-regulation of AR coactivators such as VAV3 and expression of constitutively active AR variants such as the clinically relevant AR-V7. AR-V7 lacks a ligand-binding domain and is linked to poor prognosis. We previously showed that VAV3 enhances AR-V7 activity to drive CRPC progression. Gene expression profiling after depletion of either VAV3 or AR-V7 in CRPC cells revealed arginine vasopressin receptor 1a (AVPR1A) as the most commonly down-regulated gene, indicating that this G protein-coupled receptor may be critical for CRPC. Analysis of publicly available human PC datasets showed that AVPR1A has a higher copy number and increased amounts of mRNA in advanced PC. Depletion of AVPR1A in CRPC cells resulted in decreased cell proliferation and reduced cyclin A. In contrast, androgen-dependent PC, AR-negative PC, or nontumorigenic prostate epithelial cells, which have undetectable AVPR1A mRNA, were minimally affected by AVPR1A depletion. Ectopic expression of AVPR1A in androgen-dependent PC cells conferred castration resistance in vitro and in vivo. Furthermore, treatment of CRPC cells with the AVPR1A ligand, arginine vasopressin (AVP), activated ERK and CREB, known promoters of PC progression. A clinically safe and selective AVPR1A antagonist, relcovaptan, prevented CRPC emergence and decreased CRPC orthotopic and bone metastatic growth in mouse models. Based on these preclinical findings, repurposing AVPR1A antagonists is a promising therapeutic approach for CRPC.

Histone deacetylase inhibition prevents the growth of primary and metastatic osteosarcoma

Overall survival rates for patients with advanced osteosarcoma have remained static for over three decades. An in vitro analysis of osteosarcoma cell lines for sensitivity to an array of approved cancer therapies revealed that panobinostat, a broad spectrum histone deacetalyase (HDAC) inhibitor, is highly effective at triggering osteosarcoma cell death. Using in vivo models of orthotopic and metastatic osteosarcoma, here we report that panobinostat impairs the growth of primary osteosarcoma in bone and spontaneous metastasis to the lung, the most common site of metastasis for this disease. Further, pretreatment of mice with panobinostat prior to tail vein inoculation of osteosarcoma prevents the seeding and growth of lung metastases. Additionally, panobinostat impaired the growth of established lung metastases and improved overall survival, and these effects were also manifest in the lung metastatic SAOS2-LM7 model. Mechanistically, the efficacy of panobinostat was linked to high expression of HDAC1 and HDAC2 in osteosarcoma, and silencing of HDAC1 and 2 greatly reduced osteosarcoma growth in vitro. In accordance with these findings, treatment with the HDAC1/2 selective inhibitor romidepsin compromised the growth of osteosarcoma in vitro and in vivo. Analysis of patient-derived xenograft osteosarcoma cell lines further demonstrated the sensitivity of the disease to panobinostat or romidepsin. Collectively, these studies provide rationale for clinical trials in osteosarcoma patients using the approved therapies panobinostat or romidepsin.

CAR-T Engineering: Optimizing Signal Transduction and Effector Mechanisms

The adoptive transfer of genetically engineered T cells expressing a chimeric antigen receptor (CAR) has shown remarkable results against B cell malignancies. This immunotherapeutic approach has advanced and expanded rapidly from preclinical models to the recent approval of CAR-T cells to treat lymphomas and leukemia by the Food and Drug Administration (FDA). Ongoing research efforts are focused on employing CAR-T cells as a therapy for other cancers, and enhancing their efficacy and safety by optimizing their design. Here we summarize modifications in the intracellular domain of the CAR that gave rise to first-, second-, third- and next-generation CAR-T cells, together with the impact that these different designs have on CAR-T cell biology and function. Further, we describe how the structure of the antigen-sensing ectodomain can be enhanced, leading to superior CAR-T cell signaling and/or function. Finally we discuss how tissue-specific factors may impact the clinical efficacy of CAR-T cells for bone and the central nervous system, as examples of specific indications that may require further CAR signaling optimization to perform in such inhospitable microenvironments.

Abstract 2016: HDAC inhibition significantly reduces primary and lung metastatic osteosarcoma progression

Osteosarcoma (OS) is the most common bone malignancy in adolescents. At the time of initial diagnosis, approximately 15% of the patients present with metastatic disease in lungs. Prognosis for this cohort is grim with 5-year overall survival rates at 30%. Frustratingly, these statistics have changed little over the past three decades, in part due to the lack of progress in identifying effective therapies and difficulty in coordinating robust clinical trials in this relatively rare malignancy. To address this, we previously screened 54 FDA approved drugs against 5 different OS cell lines and identified the histone deacetylase inhibitor (HDAC), panobinostat (Pano) as having potent effects in vitro. Here, we explore whether Panobinostat is effective in preventing multiple stages of OS progression in vivo using the K7M2 and SAOS2LM7 pre-clinical models of the disease. Pano prevents the growth of primary OS and lung metastasis. Mice were intratibially inoculated with K7M2-Luc cells and then treated with vehicle (n=11) or panobinostat (n=10; 10 mg/kg for all in vivo studies). Tumor growth was measured by bioluminescence (RLU). The clinical endpoint was 1x106RLU (IVIS-200). Primary OS growth was significantly slower in the panobinostat treated group (p<0.05 by day 17) with the median time to clinical endpoint being 2.5-fold longer than the controls (control median: 21 days vs. Pano median: 53 days, p<0.05). Micro-CT analysis demonstrated panobinostat limited OS induced bone disease. Panobinostat also impacted spontaneous lung metastasis (Time to detection; control, 10 days vs. Pano, 21 days). Histological analyses showed significantly lower metastatic burden and growth rates (pHistone-H3/cleaved caspase-3) in the panobinostat group. Pano pretreatment prevents OS lung seeding. Mice were pretreated with vehicle (n=9) or panobinostat (n=5) for 5 days prior to tail vein inoculation of 1x106K7M2-Luc cells. Bioluminescence demonstrated that panobinostat significantly (p<0.05) delayed tumor growth compared to control animals. This translated into higher overall survival rates (Control median: 54 days vs. Pano median: 93 days, p<0.05). Despite halting panobinostat treatment at day 38, 44% (4/9) of the mice remained alive at day 100. Pano halts the growth of established lung metastases. Mice were tail-vein inoculated with 1x106K7M2-Luc cells and randomized after three days into control (n=12) and panobinostat (n=15) treated groups. Bioluminescence readings demonstrated that panobinostat significantly reduced the growth of established OS lung metastases (p<0.05). These data were confirmed using the SAOS2LM7 model. Mechanistically, we are now exploring the contribution of individual HDACs to the progression of OS. Taken together we demonstrate that panobinostat is effective for the treatment of OS and our findings provide rationale for the initiation of broad spectrum HDAC inhibitor focused clinical trials.

Citation Format: Niveditha Nerlakanti, Jeremy McGuire, Diana Yu, Damon R. Reed, Conor C. Lynch. HDAC inhibition significantly reduces primary and lung metastatic osteosarcoma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2016.

Abstract 934: γδ CAR T-cell therapy significantly mitigates bone metastatic castrate-resistant prostate cancer

Bone metastasis is a frequent complication in advanced prostate cancer, with the resultant lesions significantly contributing to patient morbidity and mortality. While next generation hormone ablation therapies and bone protecting bisphosphonates alleviate these symptoms, the disease remains incurable, and new therapeutic approaches are of urgent need. In this regard, we have focused on tapping the tumor-seeking potential of chimeric antigen receptor (CAR) T cells. CAR T cells have shown remarkable anti-tumor responses in hematologic malignancies, but unique physical and biological challenges have hindered their activity in solid tumors. Interestingly, patients treated with bisphosphonates such as zoledronate exhibit enhanced recruitment and activation of the γδ subset of T cells in bone due intracellular accumulation of isopentenyl pyrophosphate (IPP) phosphoantigen. Whereas conventional CAR T cell therapies utilize αβ T cells, we posit that designing γδ CAR T cells could improve homing to bone metastases when administered with bisphosphonates. First, to test the impact of prostate specific stem cell antigen (PSCA)-specific γδ CAR T cells against bone metastatic prostate cancer in vivo, NSG mice (n=10) were intratibially injected with PSCA/luciferase-expressing C4-2B (2x105) castrate resistant prostate cancer cells. Tumors were allowed to establish for 10 days and then randomized into control or γδ CAR T (1.5x107 via tail vein) groups. Subsequent bioluminescent imaging indicated a rapid and significant (p=0.0006) regression of tumors in the γδ CAR T cell group, leading to increased overall survival (5/5 γδ CAR T vs. 0/5 control after 68 days, p=0.0002). Ex vivo bone morphometry analysis also demonstrated the significant protective effect of γδ CAR T associated bone disease. To determine whether bisphosphonates could further enhance the homing of γδ CAR T to bone, NSG mice (n=30) were intratibially injected with C4-2B (2x105), and randomized into control and zoledronate (30µg/kg) groups. After 10 days, mice received γδ T cells (3x106). Subsets were sacrificed at 1, 3, and 5 days post-T cell administration, and peripheral blood, tibia bone marrow, and spleens isolated. CD3-Vδ2 flow cytometry indicated increased γδ T cells in the tibia bone marrow from zoledronate groups (Day 1=61%, Day 3=32%, and Day 5=57%). Furthermore, decreased tumor growth rates were observed in the zoledronate group, suggesting that increased homing of γδ T cells induced anti-tumor effects. Our data to date demonstrate that γδ CAR T cells significantly mitigate bone metastatic prostate cancer and associated bone disease. Further, bisphosphonates (already used in the clinical setting) enhance the homing of γδ CAR T cells to the tumor-bone microenvironment. We posit that γδ CAR T will be an effective immunotherapy approach for the treatment of men with incurable bone metastatic prostate cancer.

Citation Format: Jeremy Steven Frieling, Maria Cecilia Ramello, Ismahene Benzaid, Emiliano Roselli, Chen Hao Lo, Conor C. Lynch, Daniel Abate-Daga. γδ CAR T-cell therapy significantly mitigates bone metastatic castrate-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 934.

Proteolytic Regulation of Parathyroid Hormone-Related Protein: Functional Implications for Skeletal Malignancy

Parathyroid hormone-related protein (PTHrP), with isoforms ranging from 139 to 173 amino acids, has long been implicated in the development and regulation of multiple tissues, including that of the skeleton, via paracrine and autocrine signaling. PTHrP is also known as a potent mediator of cancer-induced bone disease, contributing to a vicious cycle between tumor cells and the bone microenvironment that drives the formation and progression of metastatic lesions. The abundance of roles ascribed to PTHrP have largely been attributed to the N-terminal 1-36 amino acid region, however, activities for mid-region and C-terminal products as well as additional shorter N-terminal species have also been described. Studies of the protein sequence have indicated that PTHrP is susceptible to post-translational proteolytic cleavage by multiple classes of proteases with emerging evidence pointing to novel functional roles for these PTHrP products in regulating cell behavior in homeostatic and pathological contexts. As a consequence, PTHrP products are also being explored as potential biomarkers of disease. Taken together, our enhanced understanding of the post-translational regulation of PTHrP bioactivity could assist in developing new therapeutic approaches that can effectively treat skeletal malignancies.

Inhibition of Human Dendritic Cell ER Stress Response Reduces T Cell Alloreactivity Yet Spares Donor Anti-tumor Immunity

Acute graft- vs. -host disease (GVHD) is an important cause of morbidity and death after allogeneic hematopoietic cell transplantation (HCT). We identify a new approach to prevent GVHD that impairs monocyte-derived dendritic cell (moDC) alloactivation of T cells, yet preserves graft- vs.-leukemia (GVL). Exceeding endoplasmic reticulum (ER) capacity results in a spliced form of X-box binding protein-1 (XBP-1s). XBP-1s mediates ER stress and inflammatory responses. We demonstrate that siRNA targeting XBP-1 in moDCs abrogates their stimulation of allogeneic T cells. B-I09, an inositol-requiring enzyme-1α (IRE1α) inhibitor that prevents XBP-1 splicing, reduces human moDC migration, allo-stimulatory potency, and curtails moDC IL-1β, TGFβ, and p40 cytokines, suppressing Th1 and Th17 cell priming. B-I09-treated moDCs reduce responder T cell activation via calcium flux without interfering with regulatory T cell (Treg) function or GVL effects by cytotoxic T lymphocytes (CTL) and NK cells. In a human T cell mediated xenogeneic GVHD model, B-I09 inhibition of XBP-1s reduced target-organ damage and pathogenic Th1 and Th17 cells without impacting donor Tregs or anti-tumor CTL. DC XBP-1s inhibition provides an innovative strategy to prevent GVHD and retain GVL.

Fractionated follow-up chemotherapy delays the onset of resistance in bone metastatic prostate cancer

Prostate cancer to bone metastases are almost always lethal. This results from the ability of metastatic prostate cancer cells to co-opt bone remodeling leading to what is known as the vicious cycle. Understanding how tumor cells can disrupt bone homeostasis through their interactions with the stroma and how metastatic tumors respond to treatment is key to the development of new treatments for what remains an incurable disease. Here we describe an evolutionary game theoretical model of both the homeostatic bone remodeling and its co-option by prostate cancer metastases. This model extends past the evolutionary aspects typically considered in game theoretical models by also including ecological factors such as the physical microenvironment of the bone. Our model recapitulates the current paradigm of the "vicious cycle" driving tumor growth and sheds light on the interactions of heterogeneous tumor cells with the bone microenvironment and treatment response. Our results show that resistant populations naturally become dominant in the metastases under conventional cytotoxic treatment and that novel schedules could be used to better control the tumor and the associated bone disease compared to the current standard of care. Specifically, we introduce fractionated follow up therapy - chemotherapy where dosage is administered initially in one solid block followed by alternating smaller doeses and holidays - and argue that it is better than either a continuous application or a periodic one. Furthermore, we also show that different regimens of chemotherapy can lead to different amounts of pathological bone that are known to correlate with poor quality of life for bone metastatic prostate cancer patients.

Multifaceted Roles for Macrophages in Prostate Cancer Skeletal Metastasis

Bone-metastatic prostate cancer is common in men with recurrent castrate-resistant disease. To date, therapeutic focus has largely revolved around androgen deprivation therapy (ADT) and chemotherapy. While second-generation ADTs and combination ADT/chemotherapy approaches have been successful in extending overall survival, the disease remains incurable. It is clear that molecular and cellular components of the cancer-bone microenvironment contribute to the disease progression and potentially to the emergence of therapy resistance. In bone, metastatic prostate cancer cells manipulate bone-forming osteoblasts and bone-resorbing osteoclasts to produce growth and survival factors. While osteoclast-targeted therapies such as bisphosphonates have improved quality of life, emerging data have defined important roles for additional cells of the bone microenvironment, including macrophages and T cells. Disappointingly, early clinical trials with checkpoint blockade inhibitors geared at promoting cytotoxic T cell response have not proved as promising for prostate cancer compared to other solid malignancies. Macrophages, including bone-resident osteomacs, are a major component of the bone marrow and play key roles in coordinating normal bone remodeling and injury repair. The role for anti-inflammatory macrophages in the progression of primary prostate cancer is well established yet relatively little is known about macrophages in the context of bone-metastatic prostate cancer. The focus of the current review is to summarize our knowledge of macrophage contribution to normal bone remodeling and prostate-to-bone metastasis, while also considering the impact of standard of care and targeted therapies on macrophage behavior in the tumor-bone microenvironment.

Size Matters: Metastatic Cluster Size and Stromal Recruitment in the Establishment of Successful Prostate Cancer to Bone Metastases

Prostate cancer (PCa) impacts over 180,000 men every year in the USA alone, with 26,000 patients expected to succumb to the disease ( cancer.gov ). The primary cause of death is metastasis, with secondary lesions most commonly occurring in the skeleton. Prostate cancer to bone metastasis is an important, yet poorly understood, process that is difficult to explore with experimental techniques alone. To this end we have utilized a hybrid (discrete-continuum) cellular automaton model of normal bone matrix homeostasis that allowed us to investigate how metastatic PCa can disrupt the bone microenvironment. Our previously published results showed that PCa cells can recruit mesenchymal stem cells (MSCs) that give rise to bone-building osteoblasts. MSCs are also thought to be complicit in the establishment of successful bone metastases (Lu, in Mol Cancer Res 4(4):221-233, 2006). Here we have explored the aspects of early metastatic colonization and shown that the size of PCa clusters needs to be within a specific range to become successfully established: sufficiently large to maximize success, but not too large to risk failure through competition among cancer and stromal cells for scarce resources. Furthermore, we show that MSC recruitment can promote the establishment of a metastasis and compensate for relatively low numbers of PCa cells seeding the bone microenvironment. Combined, our results highlight the utility of biologically driven computational models that capture the complex and dynamic dialogue between cells during the initiation of active metastases.

Selective inhibition of matrix metalloproteinase-2 in the multiple myeloma-bone microenvironment

Multiple myeloma is a plasma cell malignancy that homes aberrantly to bone causing extensive skeletal destruction. Despite the development of novel therapeutic agents that have significantly improved overall survival, multiple myeloma remains an incurable disease. Matrix metalloproteinase-2 (MMP-2) is associated with cancer and is significantly overexpressed in the bone marrow of myeloma patients. These data provide rationale for selectively inhibiting MMP-2 activity as a multiple myeloma treatment strategy. Given that MMP-2 is systemically expressed, we used novel “bone-seeking” bisphosphonate based MMP-2 specific inhibitors (BMMPIs) to target the skeletal tissue thereby circumventing potential off-target effects of MMP-2 inhibition outside the bone marrow-tumor microenvironment. Using in vivo models of multiple myeloma (5TGM1, U266), we examined the impact of MMP-2 inhibition on disease progression using BMMPIs. Our data demonstrate that BMMPIs can decrease multiple myeloma burden and protect against cancer-induced osteolysis. Additionally, we have shown that MMP-2 can be specifically inhibited in the multiple myeloma-bone microenvironment, underscoring the feasibility of developing targeted and tissue selective MMP inhibitors. Given the well-tolerated nature of bisphosphonates in humans, we anticipate that BMMPIs could be rapidly translated to the clinical setting for the treatment of multiple myeloma.

Abstract P3-06-02: Tackling bone metastatic breast cancer growth with novel bone-seeking matrix metalloproteinase-2 inhibitors

Background. Despite medical advances, currently there is no treatment for breast to bone metastasis. The progression of bone metastatic breast cancer is critically dependent on interactions with the surrounding microenvironment. Therefore, identifying the underpinning molecular mechanisms is vital for the development of new therapies.

Rationale. Gene expression analysis and validation in human and murine specimens of bone metastases revealed matrix metalloproteinases, such as MMP-2, are highly expressed in the bone metastatic microenvironment. Genetic ablation of MMP-2 demonstrated the importance of this MMP in driving the growth of the osteolytic bone metastatic breast cancer by regulating the bioavailability of transforming growth factor β (TGFβ). These data support the rationale for the development of a highly specific MMP-2 inhibitor for the eradication of active bone metastatic breast cancer.

Methods. We utilized a novel chemical approach to synthesize bone seeking MMP inhibitors (BMMPIs) on a bisphosphonic backbone, with specificity for MMP-2 in the nanomolar range (IC50=140 nM).

In vitro, we tested the effect of BMMPIs at varying doses (1nM-100μM) on the viability of the major cellular components of the cancer-bone microenvironment, namely breast cancer cells (PyMT, 4T1), osteoblasts (MC3T3) and osteoclasts (primary monocytes and RAW 264.7). In vivo, mice were intratibially inoculated with either luciferase expressing 4T1 or PyMT (1x105) cells. Mice (n=10/group) then received vehicle, zoledronate (1 mg/kg) or BMMPIs (1 mg/kg). Tumor growth was determined via luminescence quantitation. Cancer induced bone disease was measured ex vivo by μCT, Xray and histomorphometry. MMP activity in vivo and ex vivo was determined via specific activatable MMP probes. Pharmacokinetic and pharmacodynamic studies were performed. Plasma and bone marrow supernatants were collected from PyMT-R221A tumor bearing mice treated with ML115 (5mg/Kg) at 0.25, 0.5, 1, 2, 4, 8, 24 hours and three weeks (n=3 mice/time point).

Currently, we are investigating the BMMPIs ability to impact the metastatic process through an in vivo model of intracardiac inoculation.

Results. BMMPIs significantly impacted the viability of breast cancer cells and osteoclasts in vitro (p<0.05) compared to control. In vivo, BMMPIs significantly reduced the growth of bone metastatic breast cancer compared to control and the standard of care bisphosphonate, zoledronate. MMP activity was also lower in the BMMPI treated groups (using tumor burden to normalize values). μCT/Xray/Histomorphometry analysis also illustrated the significant beneficial effects of the BMMPIs in reducing the size of osteolytic lesions (up to 80% by μCT; p<0.05).

ML115 is rapidly cleared from the plasma and accumulates selectively in the bone marrow microenvironment over time.

Conclusions. MMP-2 specific BMMPIs prevent bone metastatic breast cancer growth by impacting cancer cell viability and cancer induced osteolysis. Given that bisphosphonates are well tolerated in the clinical setting, we predict that BMMPIs could be translated to the clinical setting for the treatment and eradication of bone metastatic breast cancer.

Citation Format: Tauro M, Laghezza A, Tortorella P, Soliman HH, Lynch CC. Tackling bone metastatic breast cancer growth with novel bone-seeking matrix metalloproteinase-2 inhibitors [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-06-02.

Matrix metalloproteinase processing of PTHrP yields a selective regulator of osteogenesis, PTHrP1-17

Parathyroid hormone-related protein (PTHrP) is a critical regulator of bone resorption and augments osteolysis in skeletal malignancies. Here we report that the mature PTHrP_1-36 hormone is processed by matrix metalloproteinases to yield a stable product, PTHrP_1-17. PTHrP_1-17 retains the ability to signal through PTH1R to induce calcium flux and ERK phosphorylation but not cyclic AMP production or CREB phosphorylation. Notably, PTHrP_1-17 promotes osteoblast migration and mineralization in vitro, and systemic administration of PTHrP_1-17 augments ectopic bone formation in vivo. Further, in contrast to PTHrP_1-36, PTHrP_1-17 does not affect osteoclast formation/function in vitro or in vivo. Finally, immunoprecipitation-mass spectrometry analyses using PTHrP_1-17-specific antibodies establish that PTHrP_1-17 is indeed generated by cancer cells. Thus, matrix metalloproteinase-directed processing of PTHrP disables the osteolytic functions of the mature hormone to promote osteogenesis, indicating important roles for this circuit in bone remodelling in normal and disease contexts.

Potent Dual BET Bromodomain-Kinase Inhibitors as Value-Added Multitargeted Chemical Probes and Cancer Therapeutics

Synergistic action of kinase and BET bromodomain inhibitors in cell killing has been reported for a variety of cancers. Using the chemical scaffold of the JAK2 inhibitor TG101348, we developed and characterized single agents which potently and simultaneously inhibit BRD4 and a specific set of oncogenic tyrosine kinases including JAK2, FLT3, RET, and ROS1. Lead compounds showed on-target inhibition in several blood cancer cell lines and were highly efficacious at inhibiting the growth of hematopoietic progenitor cells from patients with myeloproliferative neoplasm. Screening across 931 cancer cell lines revealed differential growth inhibitory potential with highest activity against bone and blood cancers and greatly enhanced activity over the single BET inhibitor JQ1. Gene drug sensitivity analyses and drug combination studies indicate synergism of BRD4 and kinase inhibition as a plausible reason for the superior potency in cell killing. Combined, our findings indicate promising potential of these agents as novel chemical probes and cancer therapeutics. Mol Cancer Ther; 16(6); 1054-67. ©2017 AACR.

Abstract P6-12-10: Bone seeking matrix metalloproteinase-2 inhibitors prevent bone metastatic breast cancer growth

Bone metastasis is a common event during breast cancer progression. The resultant lesions are painful and currently, despite medical advances, are incurable. The progression of bone metastatic breast cancer is critically dependent on interactions with the surrounding microenvironment. Therefore, identifying the underpinning molecular mechanisms is vital for the development of new therapies.

Rationale: Gene expression analysis and validation in human and murine specimens of bone metastases revealed that matrix metalloproteinases, such as MMP-2, are highly expressed in the bone metastatic microenvironment and significantly associated with aggressive breast cancer and poorer overall survival. In bone, tumor or host derived MMP-2 contributes to breast cancer growth and does so by processing substrates including type I collagen and transforming growth factor beta (TGFβ) latency proteins. These data provide strong rationale for the application of MMP-2 inhibitors to treat the disease. However, in vivo, MMP-2 is systemically expressed. Therefore, to overcome potential toxicities noted with previous broad-spectrum MMP inhibitors (MMPIs), we used highly selective bisphosphonic based MMP-2 inhibitors (BMMPIs) that allowed for specific bone targeting.

Methods: We utilized a novel chemical approach to synthesize bone seeking MMP inhibitors (BMMPIs) on a bisphosphonic backbone, with specificity for MMP-2 in the nanomolar range (IC50=140 nM).

Results: In vitro, we tested the effect of BMMPIs at varying doses (1nM-100μM) on the viability of the major cellular components of the cancer-bone microenvironment, namely breast cancer cells, (PyMT, 4T1, MDA-MB-231, MCF-7), osteoblasts (MC3T3) and osteoclasts (primary monocytes and RAW 264.7). In vivo, we demonstrated using two bone metastatic models (PyMT-R221A-Luc and 4T1-Luc) that BMMPI treatment significantly reduced tumor growth and tumor associated bone destruction. Additionally, BMMPIs are superior in promoting tumor apoptosis compared to the standard of care bisphosphonate, zoledronate. MMP activity was also lower in the BMMPI treated groups (using tumor burden to normalize values). μCT/Xray/Histomorphometry analysis also illustrated the significant beneficial effects of the BMMPIs in reducing the size of osteolytic lesions (up to 80% by μCT; p<0.05). We demonstrated MMP-2 selective inhibition in the bone microenvironment using specific and broad spectrum MMP probes. Further, compared to zoledronate, BMMPI treated mice had significantly lower levels of TGFβ signaling and MMP generated type I collagen carboxy-terminal (ICTP) fragments. Taken together, our data show the feasibility of selective inhibition of MMPs in the bone metastatic breast cancer microenvironment.

Conclusions. MMP-2 specific inhibition was achieved in the bone microenvironment. BMMPIs significantly inhibit breast cancer growth in bone, they are able to induce breast cancer cell apoptosis and prevent cancer induced bone destruction. Given that bisphosphonates are well tolerated in the clinical setting, we predict that BMMPIs could be translated to the clinical setting for the treatment and eradication of bone metastatic breast cancer.

Citation Format: Tauro M, Laghezza A, Tortorella P, Lynch CC. Bone seeking matrix metalloproteinase-2 inhibitors prevent bone metastatic breast cancer growth [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-12-10.

Abstract A13: Predictive computational modeling to define effective treatment strategies for bone metastatic prostate cancer

The ability to rapidly assess the efficacy of therapeutic strategies for incurable bone metastatic prostate cancer is an important and urgent need. Pre-clinical in vivo models provide insights yet are limited in their capacity to interrogate temporal multi-cellular interactions occurring in the cancer-bone microenvironment. Computational and mathematical models that integrate and, are validated experimentally, can overcome this limitation and accelerate biological research. Here, we describe how a biologically driven discrete continuum hybrid cellular automaton (HCA) model approach can dissect the pleiotropic effects of inhibiting putative therapeutic targets such as, TGFβ. Using our HCA model, we tested five different therapeutic doses delivered in two therapeutic windows. In silico results predict that TGFβ inhibition, applied prior to tumor seeding acts by directly impacting prostate cancer cell viability but also by simultaneously restricting osteoclast formation and unexpectedly, promoting osteoblast differentiation. This effect was dependent on the prostate cancer cell expression of TGFβ receptors. In silico predictions were validated with two independent in vivo models of bone metastatic prostate cancer (PAIII and C4-2B). Using immunohistochemical information from human bone metastatic prostate cancer samples, we also demonstrate how the HCA can be used to predict the evolution of heterogeneous disease in response to applied therapies. Collectively, these data underscore the power of a combined HCA/biological approach in optimizing the efficacy of applied therapies and measuring their impact on bone metastatic prostate cancer.

Citation Format: Leah Cook, Arturo Araujo, Julio Pow-Sang, Mikalai Budzevich, David Basanta, Conor C. Lynch. Predictive computational modeling to define effective treatment strategies for bone metastatic prostate cancer. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A13.

Bone-Seeking Matrix Metalloproteinase-2 Inhibitors Prevent Bone Metastatic Breast Cancer Growth

Bone metastasis is common during breast cancer progression. Matrix metalloproteinase-2 (MMP-2) is significantly associated with aggressive breast cancer and poorer overall survival. In bone, tumor- or host-derived MMP-2 contributes to breast cancer growth and does so by processing substrates, including type I collagen and TGFβ latency proteins. These data provide strong rationale for the application of MMP-2 inhibitors to treat the disease. However, in vivo, MMP-2 is systemically expressed. Therefore, to overcome potential toxicities noted with previous broad-spectrum MMP inhibitors (MMPIs), we used highly selective bisphosphonic-based MMP-2 inhibitors (BMMPIs) that allowed for specific bone targeting. In vitro, BMMPIs affected the viability of breast cancer cell lines and osteoclast precursors, but not osteoblasts. In vivo, we demonstrated using two bone metastatic models (PyMT-R221A and 4T1) that BMMPI treatment significantly reduced tumor growth and tumor-associated bone destruction. In addition, BMMPIs are superior in promoting tumor apoptosis compared with the standard-of-care bisphosphonate, zoledronate. We demonstrated MMP-2-selective inhibition in the bone microenvironment using specific and broad-spectrum MMP probes. Furthermore, compared with zoledronate, BMMPI-treated mice had significantly lower levels of TGFβ signaling and MMP-generated type I collagen carboxy-terminal fragments. Taken together, our data show the feasibility of selective inhibition of MMPs in the bone metastatic breast cancer microenvironment. We posit that BMMPIs could be easily translated to the clinical setting for the treatment of bone metastases given the well-tolerated nature of bisphosphonates. Mol Cancer Ther; 16(3); 494-505. ©2017 AACR.

Abstract 3282: Host-derived MMP-13 mediates multiple myeloma-induced osteolysis

Myeloma cells promote osteolysis and suppress osteogenesis in the bone microenvironment by regulating osteoclasts (OCL) and osteoblasts (OBL), respectively. Patients often suffer painful, osteoporotic bone status as diseases progresses. Bone consists of 90% type-I collagen, which is degraded by OCL derived cathepsin K during regular bone remodeling. While bisphosphonates delay pathological fracture, they have little impact on overall survival; therefore, development of new therapies is crucial. Matrix metalloproteinase-13 (MMP-13) is an enzyme involved in type-I collagen degradation and resorption. Immunohistochemical staining of a panel of human myeloma biopsies (n = 15) show high MMP-13 expression predominantly in bone stroma and to a lesser extent in the myeloma compartment. Consistent with previous reports, MMP-13 expression localizes to mesenchymal stromal cells (MSC) and OBLs rather than OCLs. Further supporting these observations, analysis of publically available data sets revealed upregulation of MMP-13 expression in MSCs co-cultured with myeloma cells (1.81 LogFC, p<0.05). Based on this rationale, we examined whether stromal MMP-13 plays a role in myeloma progression.

To test our hypothesis, we generated immune-compromised MMP-13-null mice on a C57BL/6 background for ex vivo and in vivo studies. Mouse myeloma cell line, 5TGM1, homes to the skeleton and progresses upon tail vein injection in this model. Our in vivo studies showed that 5TGM1-bearing MMP-13-null mice had significantly improved overall survival compared to wild-type controls (Mean 39 vs. 43 days; p<0.05). Interestingly, we detected no difference in tumor burden between wild-type and MMP-13-null groups, by bioluminescence or IgG2b quantification. We observed significantly less bone degradation in the MMP-13 null mice compared to controls as determined by μCT and histomorphometry. Surprisingly, however, tartrate-resistant acid phosphatase (TRAP) staining in bone sections showed no difference in OCL numbers and size in vivo, but ex vivo OCL differentiation cultures demonstrated fewer (Mean 89 vs. 16; p<0.05) and smaller (Mean 29 vs. 20 μm; p<0.05) OCLs in the MMP-13-null group. Furthermore, we note that OCLs derived from MMP-13-null bone marrow have a reduced capacity to resorb bone mimetic (24% reduction; p<0.05). Time course analyses indicate OCL formation is delayed in MMP-13-null cultures, and may partially explain observed differences between groups in vivo. Mechanistically, we are assessing MMP specific cross-linked carboxy-terminal telopeptide of type-I collage (ICTP) fragments in sera of tumor-bearing MMP-13-null and wild-type animals. Taken together, the data suggests that host stroma-derived MMP-13 contributes to myeloma progression and bone turnover, by regulating the formation and functionality of OCLs. The outcomes of our study provide rationale for the use of MMP-13 specific inhibitors in the treatment of multiple myeloma.

Citation Format: Chen Hao Lo, Gemma Shay, Conor C. Lynch. Host-derived MMP-13 mediates multiple myeloma-induced osteolysis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3282.

Abstract 749: Betaglycan-mediated regulation of mesenchymal stromal cell behavior in the prostate tumor-bone microenvironment

Prostate cancer frequently metastasizes to bone, resulting in increased risk of fractures and severe pain that significantly impacts patient quality of life. Bone metastatic prostate cancer is currently incurable with standard of care therapies being mainly palliative. In bone, prostate cancer generates extensive osteogenic lesions by promoting osteoblast activity. Osteoblasts are specialized bone forming cells derived from mesenchymal stem cells. In a bid to find new molecular targets through which prostate cancer induces osteogenesis, we incubated naïve MSCs with osteogenic bone metastatic prostate cancer cell line C4-2B conditioned media. Gene expression analysis revealed a 3-fold increase in expression of the TGFâ co-receptor, betaglycan. Given the critical role of TGFâ in the context of bone metastatic disease, we examined the role of betaglycan in MSC behavior. To this end, we utilized shRNA to knockdown betaglycan gene expression in mouse bone marrow-derived primary MSCs. Reduced betaglycan expression in knockdown (KD) MSCs had little to no impact on the expression of TGFâ signaling receptors, TGFâRI and TGFâRII, or pan-TGFâ ligand expression. However, using PAI promoter activity, a readout for TGFâ signaling, we observed a 3-fold increase in luminescence in KD-MSCs compared to controls. Likewise, phosphorylated Smad 2 was significantly increased in Betaglycan KD-MSCs in response to TGFâ treatment, collectively demonstrating increased TGFâ signaling in MSCs with reduced betaglycan expression. Using modified Boyden chamber assays, we found that 50% more Betaglycan-KD MSCs migrated towards recombinant TGFâ than controls (100 KD-MSCs cells migrated towards recombinant TGFâ vs. 50 control cells); this change was reversed with the addition of recombinant betaglycan. Using osteogenic differentiation assay, we found that Betaglycan KD-MSC differentiation was reduced by approximately 70% compared to control MSCs as measured by alizarin red staining. Addition of recombinant TGFâ further suppressed differentiation in both KD-MSCs and Control MSCs. This phenomenon was rescued by the addition of recombinant betaglycan, suggesting that MSC-derived betaglycan is critical for driving the osteogenic program. We are currently determining the impact of betaglycan on MSC behavior in the tumor bone microenvironment using in vivo models of bone metastatic prostate cancer. Collectively, these findings suggest that prostate cancer-induced MSC osteogenic programs are regulated in part via the induction of betaglycan.

Citation Format: Leah M. Cook, Jeremy J. McGuire, Conor C. Lynch. Betaglycan-mediated regulation of mesenchymal stromal cell behavior in the prostate tumor-bone microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 749.

Abstract P6-16-02: Treatment of skeletal metastatic breast cancer with bone seeking matrix metalloproteinase inhibitors

Background. Breast to bone metastasis is a common event during breast cancer progression. The resultant lesions are painful and currently, despite medical advances, are incurable. The progression of bone metastatic breast cancer is critically dependent on interactions with the surrounding microenvironment. Therefore, identifying the underpinning molecular mechanisms is vital for the development of new therapies.

Rationale. Gene expression analysis and validation in human and murine specimens of bone metastases revealed matrix metalloproteinases, such as MMP-2, are highly expressed in the bone metastatic microenvironment. Genetic ablation of MMP-2 demonstrated the importance of this MMP in driving the growth of the osteolytic bone metastatic breast cancer by regulating the bioavailability of transforming growth factor β (TGFβ). These data support the rationale for the development of a highly specific MMP-2 inhibitor for the eradication of active bone metastatic breast cancer.

Methods. Given that previous broad-spectrum MMP inhibitor (MMPI) trials were unsuccessful due to dose limiting systemic side effects, we utilized a novel chemical approach to synthesize bone seeking MMP inhibitors (BMMPIs) on a bisphosphonic backbone, with specificity for MMP-2 in the nanomolar range (IC50=140 nM). In vitro, we tested the effect of BMMPIs at varying doses (1nM-100μM) on the viability of the major cellular components of the cancer-bone microenvironment, namely breast cancer cells (PyMT, 4T1), osteoblasts (MC3T3) and osteoclasts (primary monocytes and RAW 264.7). In vivo, mice were intratibially inoculated with either luciferase expressing 4T1 or PyMT (1x105) cells. Mice (n=10/group) then received vehicle, zoledronate (1 mg/kg) or BMMPIs (1 mg/kg). Tumor growth was determined via luminescence quantitation. Cancer induced bone disease was measured ex vivo by μCT, Xray and histomorphometry. MMP activity in vivo and ex vivo was determined via specific activatable MMP probes.

Results. BMMPIs significantly impacted the viability of breast cancer cells and osteoclasts in vitro (p<0.05) compared to control. In vivo BMMPIs significantly reduced the growth of bone metastatic breast cancer compared to control and the standard of care bisphosphonate, zoledronate. MMP activity was also lower in the BMMPI treated groups (using tumor burden to normalize values). μCT/Xray/Histomorphometry analysis also illustrated the significant beneficial effects of the BMMPIs in reducing the size of osteolytic lesions (up to 80% by μCT; p<0.05).

Conclusions. MMP-2 specific BMMPIs prevent bone metastatic breast cancer growth by impacting cancer cell viability and cancer induced osteolysis. Given that bisphosphonates are well tolerated in the clinical setting, we predict that BMMPIs could be translated to the clinical setting for the treatment and eradication of bone metastatic breast cancer.

Citation Format: Tauro M, Laghezza A, Tortorella P, Lynch CC. Treatment of skeletal metastatic breast cancer with bone seeking matrix metalloproteinase inhibitors. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-16-02.

Dissecting the multiple myeloma-bone microenvironment reveals new therapeutic opportunities

Multiple myeloma is a plasma cell skeletal malignancy. While therapeutic agents such as bortezomib and lenalidomide have significantly improved overall survival, the disease is currently incurable with the emergence of drug resistance limiting the efficacy of chemotherapeutic strategies. Failure to cure the disease is in part due to the underlying genetic heterogeneity of the cancer. Myeloma progression is critically dependent on the surrounding microenvironment. Defining the interactions between myeloma cells and the more genetically stable hematopoietic and mesenchymal components of the bone microenvironment is critical for the development of new therapeutic targets. In this review, we discuss recent advances in our understanding of how microenvironmental elements contribute to myeloma progression and, therapeutically, how those elements can or are currently being targeted in a bid to eradicate the disease.

Abstract 398: Specific skeletal targeting of MMP-2 inhibitors for the treatment of bone metastatic breast cancer

Background. Bone metastatic breast cancer promotes extensive bone destruction/osteolysis and is currently incurable. Progression of the disease is critically dependent on cancer-bone interaction. Defining the molecular mechanisms underlying this communication can lead to the identification of new therapeutic targets that will eradicate the disease.

Rationale. Gene expression analysis and validation in human and murine specimens of bone metastases revealed that matrix metalloproteinases (MMPs) such as MMP-2 are highly expressed in the bone metastatic microenvironment. Genetic ablation of MMP-2 highlighted the importance of this MMP in driving the growth of the osteolytic breast cancer lesions. We subsequently found that MMP-2 regulation of transforming growth factor β (TGF β) bioavailability was a major mechanism through which MMP-2 mediated this effect. These data support the rationale for the development of selective MMP inhibitors and imply that MMP-2 inhibition would be a successful strategy for the eradication of active bone metastatic breast cancer.

Methods. To address systemic dose limiting side effects noted in previous broad spectrum MMP inhibitor trials, we utilized a novel chemical approach to generate bone-targeting, highly selective MMP-2 inhibitors grafted onto a bisphosphonic backbone. In vitro, we tested the effect of BMMPIs at varying doses (1nM-100μM) on the viability of the major cellular components of the cancer-bone microenvironment, namely breast cancer cells (PyMT, 4T1), osteoblasts (MC3T3) and osteoclasts (primary monocytes and RAW 264.7). In vivo, mice were inoculated with either luciferase expressing 4T1 or PyMT (100,000) cells. Mice (n = 10/group) then received vehicle, zoledronate (1 mg/kg) or BMMPIs (1 mg/kg). Tumor growth was determined via luminescence quantitation. Cancer induced bone disease was measured ex vivo by μCT, Xray and histomorphometry. MMP activity in vivo and ex vivo was determined via an activatable MMP probe.

Results. BMMPIs significantly impacted the viability of breast cancer cells and osteoclasts in vitro (p<0.05) compared to control. In vivo BMMPIs significantly reduced the growth of bone metastatic breast cancer compared to control and the standard of care bisphosphonate, zoledronate. MMP activity was also lower in the BMMPI treated groups (using tumor burden to normalize values). μCT/Xray/Histomorphometry analysis also illustrated the significant beneficial effects of the BMMPIs in reducing the size of osteolytic lesions (up to 80% by μCT; p<0.05).

Conclusions. MMP-2 specific BMMPIs prevent bone metastatic breast cancer growth by impacting cancer cell viability and cancer induced osteolysis. Given that bisphosphonates are well tolerated in the clinical setting, we predict that BMMPIs could be translated to the clinical setting for the treatment and eradication of bone metastatic breast cancer.

Citation Format: Marilena Tauro, Antonio Laghezza, Paolo Tortorella, Conor C. Lynch. Specific skeletal targeting of MMP-2 inhibitors for the treatment of bone metastatic breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 398. doi:10.1158/1538-7445.AM2015-398

Abstract 2386: MMP processing of bone metastatic prostate cancer-derived PTHrP yields novel osteogenic peptides

Introduction: Bone metastatic prostate cancer lesions are incurable and contain areas of extensive osteoblast (osteogenic) and osteoclast (osteolytic) activity. Understanding how prostate cancer cells elicit these bone effects can identify new therapeutic targets.

Rationale/Hypothesis: Parathyroid hormone-related peptide (PTHrP) stimulates osteoblasts to promote osteoclast mediated bone resorption. Mature PTHrP consists of 36 amino-acids and is susceptible to proteolytic processing. For the first time, we demonstrate that matrix metalloproteinases (MMP-2, -3, -7, and 9), can process PTHrP1-36 into distinct peptides (PTHrP 1-17, PTHrP 18-26, and PTHrP 27-36). We posit that MMP generated PTHrP peptides possess distinct, biological properties and focused our efforts on osteoblasts and osteoclasts based on the well documented effects of tumor derived PTHrP 1-36 on these cell types.

Methods: Osteoblast proliferation was determined by trypan blue and MTT assay. Boyden chamber assays were used to study PTHrP peptide effects on mesenchymal stem cell (MSC) and osteoblast (MC3T3) migration. Morphological changes (10nM peptides for 1 hour) were determined by confocal imaging of actin (phalloidin-488). ERK activity was analyzed by Western blot while cyclic AMP and calcium flux assays were used to examine PTHrP signaling. In vitro osteogenic assays were carried out for 16-days in the presence of PTHrP peptides (10nM) followed by alizarin red staining/quantification. For in vivo calvarial assays, 2μg of PTHrP peptide was injected over the calvaria every 6 hours for 72 hours. Calvariae were subsequently isolated and processed for histological analysis.

Results: MMP generated peptides did not impact osteoblast proliferation. However, migration assays demonstrated that PTHrP 1-17 and PTHrP 1-36 significantly enhanced MSC and MC3T3 migration compared to control (p<0.05) and had profound effects on morphology whereas PTHrP 18-26 and PTHrP 27-36 had no effect on these processes. Focusing further on PTHrP 1-17, we observed rapid ERK phosphorylation and calcium flux within 10 minutes of peptide treatment (10nM), indicating potent biological activity of PTHrP 1-17. PTHrP 1-17 and PTHrP 1-36 also significantly stimulated osteoblast differentiation compared to control (1.6 and 2-fold respectively, p<0.05), but had little or no effect on direct osteoclast formation or activity in vitro. However, in vivo we observed that PTHrP 1-36 induced a robust osteolytic response, an effect that was not observed with PTHrP 1-17.

Conclusion: Our data demonstrate that MMPs can generate distinct PTHrP peptides, of which PTHrP 1-17 significantly stimulates osteoblast migration and differentiation. However, unlike PTHrP 1-36, PTHrP 1-17 does not impact osteoclast activity suggesting a novel role for MMPs in regulating the osteolytic-osteogenic responses commonly observed in bone metastatic prostate cancer.

Citation Format: Jeremy Steven Frieling, Gemma Shay, Conor C. Lynch. MMP processing of bone metastatic prostate cancer-derived PTHrP yields novel osteogenic peptides. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2386. doi:10.1158/1538-7445.AM2015-2386

Abstract 2605: The geranylgeranyltransferase I inhibitor GGTI-2418 suppresses multiple myeloma malignancy in the 5TMG1 mouse model

Little is known about the contributions of geranylgeranylated proteins to multiple myeloma (MM) malignancy, and whether targeting geranylgeranyltransferase I (GGT-1) is a viable therapeutic approach in myeloma is yet to be explored. In this study, we investigated the effects of GGTI-2418, a GGT-1 inhibitor that has reached phase I clinical trials, on MM malignancy in the 5TMG1 mouse model, where GGTI-2418 effects were assessed in the confines of the bone microenvironment that recapitulates the clinical disease in humans. GGTI-2418 treatment significantly decreased the serum levels of the MM biomarker IgG2B (M-protein) as well as the percentage of MM tumors within the tibia as demonstrated by H&E staining. X-ray and micro-CT analyses also identified that GGTI-2418 prevented MM induced bone disease with significantly lower tumor induced osteolysis and trabecular bone volume loss noted. Furthermore, treatment of mice with GGTI-2418 resulted in a significant activation of caspase 3 (apoptosis induction), accumulation of nuclear p27Kip in MM tumors (a positive prognostic biomarker for MM patients), and reduction of α-SMA levels in myofibroblasts surrounding the sinusoidal vasculature, suggesting decreased vascularization of marrow blood vessels. Importantly, GGTI-2418 treatment resulted in a significant increase in mouse median survival and delay in the onset of limb paralysis. In cell culture studies, GGTI-2417, the methylester pro-drug of GGTI-2418 that is better taken up by cultured cells, inhibited MM proliferation, increased p27kip levels, induced apoptosis and sensitized MM cells to bortezomib. Taken together, our preclinical studies suggest targeting GGT-1 as a viable therapeutic approach in MM, and warrant the investigation of GGTI-2418 in the clinic.

Citation Format: Hua Yang, Michael F. Emmons, Christopher Cubitt, Ken Shain, Domenico Coppola, Daniel Sullivan, Conor C. Lynch, Lori Hazlehurst, Said M. Sebti. The geranylgeranyltransferase I inhibitor GGTI-2418 suppresses multiple myeloma malignancy in the 5TMG1 mouse model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2605. doi:10.1158/1538-7445.AM2015-2605

Abstract 3751: Defining the temporal effects of TGFβ inhibition on the cellular heterogeneity of the bone metastatic prostate cancer microenvironment

Introduction. Bone metastatic prostate cancer is currently incurable. Traditional in vivo experimentation has provided insight into the circuitry driving the osteolytic and osteogenic nature of the disease but is limited in its ability to interrogate multiple simultaneous interactions occurring in the tumor-bone microenvironment. We hypothesize that this limitation can be overcome by combining the power of predictive computational modeling with biological approaches. To this end, we developed a clinically relevant hybrid cellular automaton model of bone metastatic prostate cancer to test the impact of putative targeted therapies. Herein, we examined the impact of inhibiting transforming growth factor beta (TGFβ) because of its well-described pleiotropic effects on the tumor-bone microenvironment.

Results. In silico, simulations of 250 days (n = 27) were performed for five different levels of TGFβ inhibition (0-100%), applied either pre- or post- metastatic seeding. The computational outputs predicted that TGFβ inhibition will only work if administered as a pre-treatment. In this scenario, TGFβ inhibition (at 80% inhibition); 1) reduced tumor cell number by ∼25%, 2) prevented osteoclast precursor infiltration and maturation by 40% and surprisingly, 3) reduced tumor-induced osteogenesis by ∼14%; all data were significant with p<0.0001. Next we tested these predictions in vivo with an osteogenic and TGFβ responsive model of bone metastatic prostate cancer (PAIII). Pre-treatment of mice (n = 9/group) with a TGFβ inhibitor (1D11) prior to intratibial inoculation of luciferase expressing PAIII cells remarkably validated computational model predictions while post-treatment (n = 7/group) with 1D11 had little or no effect. Unlike our homogeneous in vivo model, analysis of human clinical specimens (n = 20) of bone metastatic prostate cancer revealed heterogeneous expression of TGFβ ligand and receptor in prostate cancer cells. Again, computational modeling is a powerful way to address the issue of heterogeneity and using TGFβ as an example, the computational model was seeded with equal ratios of TRP (ligand and receptor-producing), TR (receptor-expressing), and TN (neutral) cells. In silico control simulations (n = 30) reveal that TR cancer cells are the dominant population. However, application of a TGFβ inhibitor in silico results in the eventual emergence (∼100 days later) of the TN population. These data suggest that adaptive application of an inhibitor such as TGFβ could prevent the emergence of resistant populations over time.

Conclusions. Integration of computational and biological approaches can be a powerful tactic in determining the temporal impact of putative therapies on heterogeneous tumor microenvironments. Further, the computational model can be of major benefit in optimizing treatments for the eradication of bone metastatic prostate cancer.

Citation Format: Leah M. Cook, Arturo Araujo, David Basanta, Conor C. Lynch. Defining the temporal effects of TGFβ inhibition on the cellular heterogeneity of the bone metastatic prostate cancer microenvironment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3751. doi:10.1158/1538-7445.AM2015-3751

Integrating new discoveries into the "vicious cycle" paradigm of prostate to bone metastases

In prostate to bone metastases, the "vicious cycle" paradigm has been traditionally used to illustrate how metastases manipulate the bone forming osteoblasts and resorbing osteoclasts in order to yield factors that facilitate growth and establishment. However, recent advances have illustrated that the cycle is far more complex than this simple interpretation. In this review, we will discuss the role of exosomes and hematopoietic/mesenchymal stem/stromal cells (MSC) that facilitate the establishment and activation of prostate metastases and how cells including myeloid-derived suppressor cells, macrophages, T cells, and nerve cells contribute to the momentum of the vicious cycle. The increased complexity of the tumor-bone microenvironment requires a system level approach. The evolution of computational models to interrogate the tumor-bone microenvironment is also discussed, and the application of this integrated approach should allow for the development of effective therapies to treat and cure prostate to bone metastases.

Moving targets: Emerging roles for MMPs in cancer progression and metastasis

Matrix metalloproteinases have long been associated with cancer. Clinical trials of small molecule inhibitors for this family of enzymes however, were spectacularly unsuccessful in a variety of tumor types. Here, we discuss some of the newer roles that have been uncovered for MMPs in cancer that would not have been targeted with those initial inhibitors or in the patient populations analyzed. We also consider novel ways of using cancer-associated MMP activity for clinical benefit.

Current and emerging therapies for bone metastatic castration-resistant prostate cancer

BACKGROUND

A paucity of therapeutic options is available to treat men with metastatic castration-resistant prostate cancer (mCRPC). However, recent developments in our understanding of the disease have resulted in several new therapies that show promise in improving overall survival rates in this patient population.

METHODS

Agents approved for use in the United States and those undergoing clinical trials for the treatment of mCRPC are reviewed. Recent contributions to the understanding of prostate biology and bone metastasis are discussed as well as how the underlying mechanisms may represent opportunities for therapeutic intervention. New challenges to delivering effective mCRPC treatment will also be examined.

RESULTS

New and emerging treatments that target androgen synthesis and utilization or the microenvironment may improve overall survival rates for men diagnosed with mCRPC. Determining how factors derived from the primary tumor can promote the development of premetastatic niches and how prostate cancer cells parasitize niches in the bone microenvironment, thus remaining dormant and protected from systemic therapy, could yield new therapies to treat mCRPC. Challenges such as intratumoral heterogeneity and patient selection can potentially be circumvented via computational biology approaches.

CONCLUSIONS

The emergence of novel treatments for mCRPC, combined with improved patient stratification and optimized therapy sequencing, suggests that significant gains may be made in terms of overall survival rates for men diagnosed with this form of cancer.

Abstract 5330: Defining the role of TGFB in osteogenic prostate cancer to bone metastases: An integrated biological/mathematical modeling approach

Almost 90% of patients that succumb to prostate cancer will have evidence of bone metastases. These metastases are incurable with patients often experiencing intense pain. In bone, prostate cancer cells derive factors necessary for growth and survival by manipulating bone forming osteoblasts and bone resorbing osteoclasts, resulting in areas of excessive osteogenesis and osteolysis, respectively. Our group and others have defined transforming growth factor beta (TGFβ) as being a key factor in the progression of bone metastases. Using semi-quantitative immunohistochemical analysis, we have found in human specimens that TGFβ signaling is much higher in the cancer cells relative to the surrounding bone stroma. Therapeutic inhibition of TGFβ however, presents a dilemma since TGFβ can have differential effects on cell types in the tumor-bone microenvironment. Furthermore, current biological approaches are limited in their ability to assess multicellular parallel interactions over time but this can be overcome via the power of computational modeling. Thus, we have developed an integrated approach where biological results inform a predictive mathematical model, allowing for exploration of complex parallel and multicellular interactions mediated by TGFβ. The model was parameterized with empirical and published data. Simulations of the prostate cancer-bone microenvironment over a 208 day period generated a clinically relevant pathophysiological model with the following outputs: 1) that TGFβ is key for coordinating prostate cancer- induced phases of osteolysis and osteogenesis and 2) that mesenchymal stem cells (MSCs) are crucial for the osteogenic component of the disease. To test these hypotheses, we performed biological studies using a TGFβ antibody-based inhibitor (1D11) that demonstrated: 1) TGFβ in prostate cancer cell conditioned media significantly contributes to MSC and osteoblast precursor recruitment and, 2) using an intratibial model of prostate cancer-induced osteogenesis (PAIII), we identified that TGFβ regulates prostate cancer induced osteolysis and osteogenesis (μCT, histomorphometry). Histological analyses of in vivo specimens will further test the predicted outcomes of the mathematical model. Future studies are focused on evolving the model to incorporate tumor heterogeneity. We believe that integrated computational and biological approaches are key to the development of powerful models that can be used for the delivery of precision medicine to cure prostate to bone metastases.

Citation Format: Leah M. Cook, Arturo Araujo, David Basanta, Conor C. Lynch. Defining the role of TGFB in osteogenic prostate cancer to bone metastases: An integrated biological/mathematical modeling approach. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5330. doi:10.1158/1538-7445.AM2014-5330

Abstract 4877: MMP-3 generates a novel PTHrP peptide that impacts osteoblast behavior and contributes to metastatic tumor growth in bone

Prostate cancer commonly metastasizes to bone, generating incurable mixed lesions that are both osteolytic and osteogenic. To identify new therapeutic targets we performed gene expression analysis and found that matrix metalloproteinase-3 (MMP-3), also known as stromelysin-1 was highly expressed in the prostate tumor-bone microenvironment. In keeping with the literature, immunohistochemical analysis of human bone metastases revealed MMP-3 was largely localized to the stromal compartment. To test whether stromal/host derived MMP-3 contributed to prostate cancer progression in bone, we generated immunocompromized MMP-3 null mice.

Using an in vivo intratibial model of prostate to bone metastases (PaIII), we found that tumor growth, as measured by luminescence, and tumor-induced bone remodeling (μCT, histomorphometry) were significantly mitigated (p<0.05) in MMP-3 null mice compared to wild type controls. Using a candidate approach to examine potential mechanisms, we focused on parathyroid hormone-related protein (PTHrP), a powerful regulator of osteoblast behavior in the vicious cycle. We identified that MMP-3 processes mature PTHrP1-36 to yield unique PTHrP1-17, PTHrP18-26, and PTHrP27-36 fragments in vitro. To test the biological significance of the fragments we focused on testing their impact on stromal cell behavior. Using Boyden chamber migration assays, we observed a significant increase in migration of murine MSCs and MC3T3-E1 pre-osteoblasts in response to 10nM PTHrP1-17 compared to that of PTHrP1-36. Further analysis via confocal microscopy revealed a reduction in actin stress fibers as well as variations in lamellipodia and vinculin organization of pre-osteoblasts and primary osteoblasts treated with PTHrP1-17, and live cell microscopy indicated that these effects were transient with the cells reverting to the usual phenotype in a 24-hour period. Reduced phosphorylation of Rho-associated protein kinase (ROCK) substrates such as the myosin light chain suggest that PTHrP1-17 may mediate pre-osteoblast migration by modulating ROCK activity.

Our data demonstrate that host MMP-3 contributes to prostate tumor growth and tumor induced changes in bone remodeling in vivo. Further, we have identified that mature PTHrP1-36 is subject to cleavage by MMP-3 resulting in PTHrP1-17, PTHrP18-26, and PTHrP27-36 fragments of which PTHrP1-17 significantly stimulates migration of murine MSCs and MC3T3-E1 pre-osteoblasts. Collectively, these data indicate that specific inhibition of MMP-3 and/or targeting MMP generated neo-epitopes would be efficacious for the treatment of prostate to bone metastases.

Citation Format: Jeremy Steven Frieling, Lizzie Atomi Pamen, Shengyu Yang, Conor C. Lynch. MMP-3 generates a novel PTHrP peptide that impacts osteoblast behavior and contributes to metastatic tumor growth in bone. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4877. doi:10.1158/1538-7445.AM2014-4877

Abstract 4858: A novel strategy for the selective and tissue specific inhibition of MMPs in active breast cancer to bone metastases

Bone metastasis is a common event during breast cancer progression: The delicate balance between bone matrix synthesizing osteoblasts and bone resorbing osteoclasts activities is typically subverted by the presence of tumor cells at the bone site. The resulting incurable lesions cause extensive osteolysis and severely impact the patient's quality of life. Understanding how active breast-to-bone metastases manipulate the bone microenvironment is critical for the development of new therapies to treat the disease. We have recently shown in preclinical animal models of breast to bone metastases that MMP-2 proteolytic activity is critical for the growth of the tumor and the associated osteolysis. We therefore hypothesized that the selective inhibition of MMP-2 at the tumor site would be a potent means through which to prevent the progression of the malignancy. Given that previous broad-spectrum MMP inhibitor (MMPI) trials were unsuccessful mainly because of consistent side effects, we took a novel chemical approach to generate a selective MMPI that would preferentially target the skeleton. To this end, we utilized a bisphosphonate backbone (tiludronate) to synthesize an MMPI (BMMPI) with high specificity for MMP-2 (IC50 0.14± 0.04μM). To test the efficacy of the BMMPI in vivo, we inoculated 6-week old immunocompromized female mice with a luciferase expressing osteolytic breast cancer cell line, PyMT-Luc (105 cells). Following tumor injection, mice (n=6/group) received saline, tiludronate (25mg/kg, to control for bisphosphonate effects) or BMMPI (25mg/kg) sub-cutaneously, twice weekly. Tumor growth was measured by quantitating luminescence over time. Our results show that application of the BMMPI significantly reduced the breast cancer growth over a two-week period (p<0.05). Furthermore, using Faxitron analysis to determine the extent of tumor induced bone destruction, we observed significantly less osteolysis in the tibia images of BMMPI treated mice compared to the control group. Our initial studies also suggest that BMMPIs perform better than clinically used bisphosphonates such as tiludronate. We are currently following up our in vivo/ex vivo analyses with histomorphometrical and histology approaches. In conclusion, our data thus far demonstrate that an MMP-2 specific BMMPI may be an effective means to prevent the progression of breast to bone metastases while at the same time eliminating some of the noted off-target effects of broad-spectrum MMP inhibitors. Since bisphosphonates are well tolerated in the clinical setting, we predict that BMMPIs could be rapidly translated to the patient.

Citation Format: Marilena Tauro, Antonio Laghezza, Paolo Tortorella, Conor C. Lynch. A novel strategy for the selective and tissue specific inhibition of MMPs in active breast cancer to bone metastases. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4858. doi:10.1158/1538-7445.AM2014-4858

An integrated computational model of the bone microenvironment in bone-metastatic prostate cancer

Bone metastasis will impact most men with advanced prostate cancer. The vicious cycle of bone degradation and formation driven by metastatic prostate cells in bone yields factors that drive cancer growth. Mechanistic insights into this vicious cycle have suggested new therapeutic opportunities, but complex temporal and cellular interactions in the bone microenvironment make drug development challenging. We have integrated biologic and computational approaches to generate a hybrid cellular automata model of normal bone matrix homeostasis and the prostate cancer-bone microenvironment. The model accurately reproduces the basic multicellular unit bone coupling process, such that introduction of a single prostate cancer cell yields a vicious cycle similar in cellular composition and pathophysiology to models of prostate-to-bone metastasis. Notably, the model revealed distinct phases of osteolytic and osteogenic activity, a critical role for mesenchymal stromal cells in osteogenesis, and temporal changes in cellular composition. To evaluate the robustness of the model, we assessed the effect of established bisphosphonate and anti-RANKL therapies on bone metastases. At approximately 100% efficacy, bisphosphonates inhibited cancer progression while, in contrast with clinical observations in humans, anti-RANKL therapy fully eradicated metastases. Reducing anti-RANKL yielded clinically similar results, suggesting that better targeting or dosing could improve patient survival. Our work establishes a computational model that can be tailored for rapid assessment of experimental therapies and delivery of precision medicine to patients with prostate cancer with bone metastases.