Nanoparticle targeting of neutrophil glycolysis prevents lung ischemia-reperfusion injury

Neutrophils exacerbate pulmonary ischemia-reperfusion injury (IRI) resulting in poor short and long-term outcomes for lung transplant recipients. Glycolysis powers neutrophil activation, but it remains unclear if neutrophil-specific targeting of this pathway will inhibit IRI. Lipid nanoparticles containing the glycolysis flux inhibitor 2-deoxyglucose (2-DG) were conjugated to neutrophil-specific Ly6G antibodies (NP-Ly6G[2-DG]). Intravenously administered NP-Ly6G(2-DG) to mice exhibited high specificity for circulating neutrophils. NP-Ly6G(2-DG)-treated neutrophils were unable to adapt to hypoglycemic conditions of the lung airspace environment as evident by the loss of demand-induced glycolysis, reductions in glycogen and ATP content, and an increased vulnerability to apoptosis. NP-Ly6G(2-DG) treatment inhibited pulmonary IRI following hilar occlusion and orthotopic lung transplantation. IRI protection was associated with less airspace neutrophil extracellular trap generation, reduced intragraft neutrophilia, and enhanced alveolar macrophage efferocytotic clearance of neutrophils. Collectively, our data show that pharmacologically targeting glycolysis in neutrophils inhibits their activation and survival leading to reduced pulmonary IRI.

Fatty acid binding proteins in multiple myeloma

Fatty acid binding proteins (FABPs) transport fatty acids (FA) into cells as an energy source, and their inhibition suppressed tumor proliferation in solid tumors. Multiple myeloma (MM) is a hematologic malignancy, known for disrupted protein metabolism including high proteasome activity, where proteasome inhibitors made a dramatic improvement in its treatment. Recent discovery found FABPs as a novel metabolic pathway in MM, which will have an impact on understanding the biology and on therapeutic application in MM.

Proceedings from the Blood and Marrow Transplant Clinical Trials Network Myeloma Intergroup Workshop on Immune and Cellular Therapy in Multiple Myeloma

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) Myeloma Intergroup conducted a workshop on Immune and Cellular Therapy in Multiple Myeloma on January 7, 2022. This workshop included presentations by basic, translational, and clinical researchers with expertise in plasma cell dyscrasias. Four main topics were discussed: platforms for myeloma disease evaluation, insights into pathophysiology, therapeutic target and resistance mechanisms, and cellular therapy for multiple myeloma. Here we provide a comprehensive summary of these workshop presentations.

BRD9 degraders as chemosensitizers in acute leukemia and multiple myeloma

Bromodomain-containing protein 9 (BRD9), an essential component of the SWI/SNF chromatin remodeling complex termed ncBAF, has been established as a therapeutic target in a subset of sarcomas and leukemias. Here, we used novel small molecule inhibitors and degraders along with RNA interference to assess the dependency on BRD9 in the context of diverse hematological malignancies, including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and multiple myeloma (MM) model systems. Following depletion of BRD9 protein, AML cells undergo terminal differentiation, whereas apoptosis was more prominent in ALL and MM. RNA-seq analysis of acute leukemia and MM cells revealed both unique and common signaling pathways affected by BRD9 degradation, with common pathways including those associated with regulation of inflammation, cell adhesion, DNA repair and cell cycle progression. Degradation of BRD9 potentiated the effects of several chemotherapeutic agents and targeted therapies against AML, ALL, and MM. Our findings support further development of therapeutic targeting of BRD9, alone or combined with other agents, as a novel strategy for acute leukemias and MM.

Tumor-associated macrophages in multiple myeloma: advances in biology and therapy

Multiple myeloma (MM) is a cancer of plasma cells in the bone marrow (BM) and represents the second most common hematological malignancy in the world. The MM tumor microenvironment (TME) within the BM niche consists of a wide range of elements which play important roles in supporting MM disease progression, survival, proliferation, angiogenesis, as well as drug resistance. Together, the TME fosters an immunosuppressive environment in which immune recognition and response are repressed. Macrophages are a central player in the immune system with diverse functions, and it has been long established that macrophages play a critical role in both inducing direct and indirect immune responses in cancer. Tumor-associated macrophages (TAMs) are a major population of cells in the tumor site. Rather than contributing to the immune response against tumor cells, TAMs in many cancers are found to exhibit protumor properties including supporting chemoresistance, tumor proliferation and survival, angiogenesis, immunosuppression, and metastasis. Targeting TAM represents a novel strategy for cancer immunotherapy, which has potential to indirectly stimulate cytotoxic T cell activation and recruitment, and synergize with checkpoint inhibitors and chemotherapies. In this review, we will provide an updated and comprehensive overview into the current knowledge on the roles of TAMs in MM, as well as the therapeutic targets that are being explored as macrophage-targeted immunotherapy, which may hold key to future therapeutics against MM.

Liposomal phytohemagglutinin: In vivo T-cell activator as a novel pan-cancer immunotherapy

Immunotherapy is an attractive approach for treating cancer. T‐cell engagers (TCEs) are a type of immunotherapy that are highly efficacious; however, they are challenged by weak T‐cell activation and short persistence. Therefore, alternative solutions to induce greater activation and persistence of T cells during TCE immunotherapy is needed. Methods to activate T cells include the use of lectins, such as phytohemagglutinin (PHA). PHA has not been used to activate T cells in vivo, for immunotherapy, due to its biological instability and toxicity. An approach to overcome the limitations of PHA while also preserving its function is needed. In this study, we report a liposomal PHA which increased PHA stability, reduced toxicity and performed as an immunotherapeutic that is able to activate T cells for the use in future cancer immunotherapies to circumvent current obstacles in immunosuppression and T‐cell exhaustion.

A pilot study of 3D tissue-engineered bone marrow culture as a tool to predict patient response to therapy in multiple myeloma

Cancer patients undergo detrimental toxicities and ineffective treatments especially in the relapsed setting, due to failed treatment attempts. The development of a tool that predicts the clinical response of individual patients to therapy is greatly desired. We have developed a novel patient-derived 3D tissue engineered bone marrow (3DTEBM) technology that closely recapitulate the pathophysiological conditions in the bone marrow and allows ex vivo proliferation of tumor cells of hematologic malignancies. In this study, we used the 3DTEBM to predict the clinical response of individual multiple myeloma (MM) patients to different therapeutic regimens. We found that while no correlation was observed between in vitro efficacy in classic 2D culture systems of drugs used for MM with their clinical efficacious concentration, the efficacious concentration in the 3DTEBM were directly correlated. Furthermore, the 3DTEBM model retrospectively predicted the clinical response to different treatment regimens in 89% of the MM patient cohort. These results demonstrated that the 3DTEBM is a feasible platform which can predict MM clinical responses with high accuracy and within a clinically actionable time frame. Utilization of this technology to predict drug efficacy and the likelihood of treatment failure could significantly improve patient care and treatment in many ways, particularly in the relapsed and refractory setting. Future studies are needed to validate the 3DTEBM model as a tool for predicting clinical efficacy.

CD47-targeting antibodies as a novel therapeutic strategy in hematologic malignancies

CD47 is a surface glycoprotein expressed by host cells to impede phagocytosis upon binding to macrophage SIRPα, thereby represents an immune checkpoint known as the "don't-eat-me" signal. However, accumulating evidence shows that solid and hematologic tumor cells overexpress CD47 to escape immune surveillance. Thus, targeting the CD47-SIRPa axis by limiting the activity of this checkpoint has emerged as a key area of research. In this review, we will provide an update on the landscape of CD47-targeting antibodies for hematological malignancies, including monoclonal and bi-specific antibodies, with a special emphasis on agents in clinical trials and novel approaches to overcome toxicity.

Nanoparticle T cell engagers for the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common type of leukemia and has a 5-year survival rate of 25%. The standard-of-care for AML has not changed in the past few decades. Promising immunotherapy options are being developed for the treatment of AML; yet, these regimens require highly laborious and sophisticated techniques. We create nanoTCEs using liposomes conjugated to monoclonal antibodies to enable specific binding. We also recreate the bone marrow niche using our 3D culture system and use immunocompromised mice to enable use of human AML and T cells with nanoTCEs. We show that CD33 is ubiquitously present on AML cells. The CD33 nanoTCEs bind preferentially to AML cells compared to Isotype. We show that nanoTCEs effectively activate T cells and induce AML killing in vitro and in vivo. Our findings suggest that our nanoTCE technology is a novel and promising immuno-therapy for the treatment of AML and provides a basis for supplemental investigations for the validation of using nanoTCEs in larger animals and patients.

Bispecific T Cell Engagers for the Treatment of Multiple Myeloma: Achievements and Challenges

MM is the second most common hematological malignancy and represents approximately 20% of deaths from hematopoietic cancers. The advent of novel agents has changed the therapeutic landscape of MM treatment; however, MM remains incurable. T cell-based immunotherapy such as BTCEs is a promising modality for the treatment of MM. This review article discusses the advancements and future directions of BTCE treatments for MM.

3D tissue engineered plasma cultures support leukemic proliferation and induces drug resistance

Chronic myeloid leukemia (CML), acute myeloid leukemia (AML), and chronic lymphocytic leukemia (CLL) are hematological malignancies that remain incurable despite novel treatments. In order to improve current treatments and clinical efficacy, there remains a need for more complex in vitro models that mimic the intricate human leukemic microenvironment. This study aimed to use 3D tissue engineered plasma cultures (3DTEPC) derived from CML, AML and CLL patients to promote proliferation of leukemic cells for use as a drug screening tool for treatment. 3DTEPC supported the growth of primary CML, AML and CLL cells and also induced significantly more drug resistance in CML, AML and CLL cell lines compared to 2D. The 3DTEPC created a more physiologically relevant environment for leukemia cell proliferation, provided a reliable model for growing leukemia patient samples, and serves as a relevant tool for drug screening and personalized medicine.

Targeting E-selectin to Tackle Cancer Using Uproleselan

E-selectin is a vascular adhesion molecule expressed mainly on endothelium, and its primary role is to facilitate leukocyte cell trafficking by recognizing ligand surface proteins. E-selectin gained a new role since it was demonstrated to be involved in cancer cell trafficking, stem-like properties and therapy resistance. Therefore, being expressed in the tumor microenvironment, E-selectin can potentially be used to eradicate cancer. Uproleselan (also known as GMI-1271), a specific E-selectin antagonist, has been tested on leukemia, myeloma, pancreatic, colon and breast cancer cells, most of which involve the bone marrow as a primary or as a metastatic tumor site. This novel therapy disrupts the tumor microenvironment by affecting the two main steps of metastasis-extravasation and adhesion-thus blocking E-selectin reduces tumor dissemination. Additionally, uproleselan mobilized cancer cells from the protective vascular niche into the circulation, making them more susceptible to chemotherapy. Several preclinical and clinical studies summarized herein demonstrate that uproleselan has favorable safety and pharmacokinetics and is a tumor microenvironment-disrupting agent that improves the efficacy of chemotherapy, reduces side effects such as neutropenia, intestinal mucositis and infections, and extends overall survival. This review highlights the critical contribution of E-selectin and its specific antagonist, uproleselan, in the regulation of cancer growth, dissemination, and drug resistance in the context of the bone marrow microenvironment.

Localized Delivery of Cisplatin to Cervical Cancer Improves Its Therapeutic Efficacy and Minimizes Its Side Effect Profile

PURPOSE

Cervical cancer represents the fourth most frequent malignancy in the world among women, and mortality has remained stable for the past 4 decades. Intravenous cisplatin with concurrent radiation therapy is the standard-of-care for patients with local and regional cervical cancer. However, cisplatin induces serious dose-limiting systemic toxicities and recurrence frequently occurs. In this study, we aimed to develop an intracervical drug delivery system that allows cisplatin release directly into the tumor and minimize systemic side effects.

METHODS AND MATERIALS

Twenty patient biopsies and 5 cell lines treated with cisplatin were analyzed for platinum content using inductively coupled plasma mass spectrometry. Polymeric implants loaded with cisplatin were developed and evaluated for degradation and drug release. The effect of local or systemic cisplatin delivery on drug biodistribution as well as tumor burden were evaluated in vivo, in combination with radiation therapy.

RESULTS

Platinum levels in patient biopsies were 6-fold lower than the levels needed for efficacy and radiosensitization in vitro. Cisplatin local delivery implant remarkably improved drug specificity to the tumor and significantly decreased accumulation in the blood, kidney, and other distant normal organs, compared with traditional systemic delivery. The localized treatment further resulted in complete inhibition of tumor growth.

CONCLUSIONS

The current standard-of-care systemic administration of cisplatin provides a subtherapeutic dose. We developed a polymeric drug delivery system that delivered high doses of cisplatin directly into the cervical tumor, while lowering drug accumulation and consequent side effects in normal tissues. Moving forward, these data will be used as the basis of a future first-in-human clinical trial to test the efficacy of localized cisplatin as adjuvant or neoadjuvant chemotherapy in local and regional cervical cancer.

Tumor microenvironment-targeted nanoparticles loaded with bortezomib and ROCK inhibitor improve efficacy in multiple myeloma

Drug resistance and dose-limiting toxicities are significant barriers for treatment of multiple myeloma (MM). Bone marrow microenvironment (BMME) plays a major role in drug resistance in MM. Drug delivery with targeted nanoparticles have been shown to improve specificity and efficacy and reduce toxicity. We aim to improve treatments for MM by (1) using nanoparticle delivery to enhance efficacy and reduce toxicity; (2) targeting the tumor-associated endothelium for specific delivery of the cargo to the tumor area, and (3) synchronizing the delivery of chemotherapy (bortezomib; BTZ) and BMME-disrupting agents (ROCK inhibitor) to overcome BMME-induced drug resistance. We find that targeting the BMME with P-selectin glycoprotein ligand-1 (PSGL-1)-targeted BTZ and ROCK inhibitor-loaded liposomes is more effective than free drugs, non-targeted liposomes, and single-agent controls and reduces severe BTZ-associated side effects. These results support the use of PSGL-1-targeted multi-drug and even non-targeted liposomal BTZ formulations for the enhancement of patient outcome in MM.

The tumour microenvironment (TME) has a major role in chemoresistance in multiple myeloma. The authors show that a nanoparticle targeted to TME and loaded with bortezomib (BTZ) and Y27632 is more effective than free drugs, non-targeted and single-agent controls and reduces BTZ-related side effects.

Abstract B01: Nanoparticle multispecific T-cell engagers for the treatment of multiple myeloma

Introduction: Multiple myeloma (MM) is the second most prevalent hematologic malignancy. Chimeric antigen receptor (CAR)-T cells and bispecific T-cell engagers targeting BCMA, CS1, and CD38 are promising approaches for MM. However, using these targets individually limits the efficacy of these immunotherapy options due to the variable expression levels of these markers, leading to inefficient eradication of MM. Studies have attempted to develop CAR-T cells and T-cell engagers with multispecific targeting; however, these are still technically very challenging and are highly expensive. In this study, we developed nanoparticles with monovalent or multivalent specificity against MM targets and engage T cells, by chemical conjugation of monoclonal antibodies against each molecule to the surface of the liposome. Bi-specific nanoparticles with anti CD38/CD3, BCMA/CD3 or CS1/CD3 were termed nanoBiTEs, while the multispecific particles with anti BCMA/CS1/CD38/CD3 were termed nanoMuTEs.

Methods: Liposomes were prepared using the thin-film hydration method followed by extrusion. nanoBiTEs and nanoMuTEs were developed by chemical conjugation of monoclonal antibodies against BCMA, CS1, and/or CD38; together with anti CD3 onto the liposomes. We have tested the expression of BCMA, CS1, and CD38 antigens in MM cell lines and primary MM patient samples, and we analyzed the binding of the CD38/CD3, BCMA/CD3, and CS1/CD3 nanoBiTEs, as well as the BCMA/CS1/CD38/CD3 nanoMuTEs to these cells by flow cytometry and confocal microscopy. Binding specificity was assessed by blocking the target with corresponding free antibodies. CD25 expression, a T-cell activation marker, was assessed for CD8 and CD4 T cells when incubated with or without nanoBiTEs and nanoMuTEs. Moreover, we tested the efficacy of the nanoBiTEs and nanoMuTEs against MM cells in vitro using the 3D tissue engineered bone marrow (3DTEBM) myeloma model. Finally, we tested the efficacy of the nanoBiTEs and nanoMuTE against MM tumors in vivo in xenograft MM models.

Results: The expression of BCMA, CS1 and CD38 was variable in MM cell lines and patient samples, and so was the binding of each nanoBiTEs, while the binding of the nanoMuTE was higher and more universal than each nanoBiTE. Similar patterns were observed in activation of CD8 T cells (no significant activation was observed in CD4 T cells) and in eradication of MM cell lines and primary patient samples in vitro. In vivo, the nanoBiTEs extended the survival and reduced the tumor burden in the MM bearing mice compared to untreated and T cell alone groups, and nanoMuTE experiments are still ongoing.

Conclusions: The nanoBiTEs and nanoMuTEs were bound specifically to MM cells and initiated CD8 T-cell activation that resulted in MM eradication in vitro and in vivo, while the effect of the nanoMuTEs was more universal and efficacious than each nanoBiTE. These nanoparticles are an inexpensive method of engaging T cells for the treatment of MM and represent a new class of immunotherapy that can be expanded to other tumors.

Citation Format: Kinan Alhallak, Jennifer Sun, Barbara Muz, Christopher Egbulefu, Pilar de la Puente, Cinzia Federico, Justin King, Danny Kohnen, Ravi Vij, Samuel Achilefu, Abdel Kareem Azab. Nanoparticle multispecific T-cell engagers for the treatment of multiple myeloma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B01.

Abstract A27: Endothelial progenitor cells as drug-delivery Trojan horses for treatment and imaging of cancer

Introduction: Endothelial progenitor cells (EPCs) are a subtype of stem cells capable of differentiating into mature endothelial cells. Tumor-derived paracrine signals activate the bone marrow-residing EPCs to home to the tumor to promote angiogenesis. The aim of this study was to utilize the EPCs and their specific pathophysiologic homing to tumors as a biologically targeted drug-delivery system, as a novel “Trojan horse” cellular immunotherapy in cancer.

Methods: To test the specificity of EPCs’ homing to cancer, chemotaxis of EPCs towards conditioned media derived from a series of cancer cell lines or towards nonconditioned media was performed in vitro using Boyden Chamber. In vivo biodistribution of EPCs was studied in diverse tumor models (localized and disseminated) of different cancers (myeloma, lymphoma, leukemia, breast, lung, pancreatic and glioma) after injecting EPCs intravenously, by analysis of the accumulation of EPCs in the tumors and other organs. To enhance the ability of EPCs to home to tumors, EPCs were “primed” in vitro by exposing them to conditioned media from hypoxic (1% O2) tumor cells, followed by testing the homing of “primed” EPCs to tumors, both in vitro and in vivo. Next, EPCs were loaded with LS-542 (NIR imaging dye), and with Titanocene (Tc) (a nontoxic compound used in phototherapy that can be activated by positrons to become toxic) and tested for the effect of the loading on viability and functionality of EPCs, using MTT and migration assays, respectively. Also, we tested the effect of Tc-loaded EPCs on killing of cancer cells when activated by 18FDG/PET.

Results: We found that EPCs specifically homed to tumors in vitro and in vivo, in tumor size-dependent and time-dependent manner, and that EPCs selectively accumulated in tumor tissues, with significantly negligible amounts in other organs. Moreover, EPCs homed to primary tumors and followed the metastatic pattern of the tumor. Hypoxia “priming” of EPCs significantly improved their homing to cancer in vitro and in vivo. Loading EPCs with LS-542 or with Tc did not affect their viability or functionality. Additionally, Tc-loaded EPCs, when activated by 18FDG, induced a dose-dependent killing of cancer cells.

Conclusions: EPCs have a highly specific and efficient biologic machinery to target tumors in as a pan-cancer phenomenon, especially when “primed” with hypoxic tumor media. Loading EPCs with LS-542 or Tc did not change their viability and functionality; thus, both are promising molecules for imaging and therapy of cancer. These results provide a proof of concept that EPCs can be used as a novel cellular immunotherapy for specific and efficacious delivery of theranostic agents in cancer. Also, unlike engineered/targeted immunotherapies such as cellular (CAR-T cells), bispecific T cell engagers, or monoclonal antibodies that target specific molecules on a specific tumor type, EPCs can be used as a pan-cancer “Trojan horse” drug-delivery platform due to the universality of (angiogenesis) in all cancer types.

Citation Format: Barbara Muz, Pilar de la Puente, Shruti Shah, Cinzia Federico, Feda Azab, Justin King, Mark Fiala, Rui Tang, Partha Karmakar, Ravi Vij, Samuel Achilefu, Abdel Kareem Azab. Endothelial progenitor cells as drug-delivery Trojan horses for treatment and imaging of cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A27.

Abstract PR06: Targeting CD47 as a novel immunotherapy for multiple myeloma

Introduction: CD47 is an immune checkpoint highly expressed on the surface of various cancer cells, allowing cells to escape innate immune response by sending inhibitory signals to macrophages, which further hinders the antitumor response by the adaptive immune system. This CD47 “don’t-eat-me signal” has been identified as a novel therapeutic target in cancers. Targeted reprogramming of this interaction using anti-CD47 monoclonal antibodies (mAbs) represents a new class of checkpoint inhibitors that attack tumors via coordinating the innate and adaptive immune systems. Multiple myeloma (MM) is a cancer of plasma cells in the bone marrow (BM). The objective of this study is to investigate the inhibition of CD47 using anti-CD47 mAbs as a novel checkpoint immunotherapy for the treatment of MM.

Methods: We performed analysis of CD47 mRNA expression in healthy, MGUS (pre-condition of MM), and MM subjects. We measured CD47 protein expression on MM cell lines by flow cytometry, labeling MM cells with Vx1000R (anti-human CD47 mAb). We also investigated the effect of hypoxia (1% O2), stromal cells, and 3D tissue engineered bone marrow (3DTEBM) cultures on CD47 expression in MM cells. Next, we tested the cytotoxic activity of Vx1000R on MM cells alone by MTT assay. Additionally, we investigated the effect of Vx1000R on phagocytosis and killing of MM cells (GFP+) by primary macrophages (labeled with DiD dye) at 4 and 24 hours with or without Vx1000R, in 2D cultures and in 3DTEBM cultures. Phagocytosis was determined as GFP+ DiD+ cells and MM survival was analyzed by counting GFP+ by flow cytometry. Moreover, we performed real-time live confocal imaging on 3DTEBM cultures of GFP-MM cells and DiD-macrophages, with or without treatment of Vx1000R, to further visualize the effect of Vx1000R.

Results: CD47 gene expression was increased with MM progression (healthy<MGUS<MM). CD47 protein was highly expressed in MM cells lines (MM.1S, H929, and U266) and primary MM cells. The expression of CD47 was not affected by hypoxia or co-culture with stromal cells in 2D cultures; however, 3DTEBM significantly increased CD47 expression. Vx1000R alone (without macrophages) did not result in direct killing of MM cells in 2D culture or in the 3DTEBM. Vx1000R treatment in presence of macrophages in 2D resulted in mild effect on killing of MM cells, while cultures in 3DTEBM resulted in extensive killing of MM cells (50% killing at 4 hours and 95% killing at 24 hours).

Conclusions: Myeloma cells express high levels of CD47, and this expression is not affected by hypoxia or TME in 2D, but significantly increases in 3DTEBM cultures. Blocking CD47 on MM cells with anti-CD47 mAbs enhanced MM phagocytosis and killing by macrophages, especially in 3DTEBM. These results suggest that anti-CD47 mAbs are applicable for MM treatment, and further studies are warranted to examine the effect of anti-CD47 mAbs as a novel checkpoint immunotherapy to target MM in vivo and in patients.

This abstract is also being presented as Poster A88.

Citation Format: Jennifer Sun, Barbara Muz, Kinan Alhallak, Christopher Egbulefu, Justin King, Danny Kohnen, Mark Fiala, Benjamin Cappocia, Pamela Manning, Samuel Achilefu, Ravi Vij, Abdel Kareem Azab. Targeting CD47 as a novel immunotherapy for multiple myeloma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr PR06.

CXCR4-targeted PET imaging using 64Cu-AMD3100 for detection of Waldenström Macroglobulinemia

Objective:  Waldenström Macroglobulinemia (WM) is a rare B-cell malignancy characterized by secretion of immunoglobulin M and cancer infiltration in the bone marrow. Chemokine receptor such as CXCR4 and hypoxic condition in the bone marrow play crucial roles in cancer cell trafficking, homing, adhesion, proliferation, survival, and drug resistance. Herein, we aimed to use CXCR4 as a potential biomarker to detect hypoxic-metastatic WM cells in the bone marrow and in the circulation by using CXCR4-detecting radiopharmaceutical.Methods: We radiolabeled a CXCR4-inhibitor (AMD3100) with ⁶⁴Cu and tested its binding to WM cells with different levels of CXCR4 expression using gamma counter in vitro. The accumulation of this radiopharmaceutical tracer was tested in vivo in subcutaneous and intratibial models using PET/CT scan. In addition, PBMCs spiked with different amounts of WM cells ex vivo were detected using gamma counting.Results: In vitro, ⁶⁴Cu-AMD3100 binding to WM cell lines demonstrated a direct correlation with the level of CXCR4 expression, which was increased in cells cultured in hypoxia with elevated levels of CXCR4, and decreased in cells with CXCR4 and HIF-1α knockout. Moreover, ⁶⁴Cu-AMD3100 detected localized and circulating CXCR4^high WM cells with high metastatic potential.Conclusions: In conclusion, we developed a molecularly targeted system, ⁶⁴Cu-AMD3100, which binds to CXCR4 and specifically detects WM cells with hypoxic phenotype and metastatic potential in the subcutaneous and intratibial models. These preliminary findings using CXCR4-detecting PET radiopharmaceutical tracer indicate a potential technology to predict high-risk patients for the progression to WM due to metastatic potential.

Thermal Sensitive Liposomes Improve Delivery of Boronated Agents for Boron Neutron Capture Therapy

PURPOSE

Boron neutron capture therapy (BNCT) has the potential to become a viable cancer treatment modality, but its clinical translation requires sufficient tumor boron delivery while minimizing nonspecific accumulation.

METHODS

Thermal sensitive liposomes (TSLs) were designed to have a stable drug payload at physiological temperatures but engineered to have high permeability under mild hyperthermia.

RESULTS

We found that TSLs improved the tumor-specific delivery of boronophenylalanine (BPA) and boronated 2-nitroimidazole derivative B-381 in D54 glioma cells. Uniquely, the 2-nitroimidazole moiety extended the tumor retention of boron content compared to BPA.

CONCLUSION

This is the first study to show the delivery of boronated compounds using TSLs for BNCT, and these results will provide the basis of future clinical trials using TSLs for BNCT.

Enhancing proteasome-inhibitory activity and specificity of bortezomib by CD38 targeted nanoparticles in multiple myeloma

The establishment of more effective treatments that can circumvent chemoresistance in Multiple Myeloma (MM) is a priority. Although bortezomib (BTZ) is one of the most potent proteasome inhibitors available, still possesses limitations related to dose limiting side effects. Several strategies have been developed to improve the delivery of chemotherapies to MM by targeting different moieties expressed on MM cells to nanoparticle delivery systems (NPs), which have failed mainly due to their heterogeneous expression on these cells. Our goal was to test CD38 targeted chitosan NPs as novel targeting moiety for MM to improve the potency and efficacy of BTZ in MM cells and reduce the side effects in healthy tissue. We have showed preferential BTZ release in tumor-microenvironment, specific binding to MM cells, and an improved drug cellular uptake through BTZ diffusion from the surface and endocytosed NPs, which translated in enhanced proteasome inhibition and robust cytotoxic effect on MM cells when BTZ was administered through anti-CD38 chitosan NPs. Furthermore, the anti-CD38 chitosan NPs specifically delivered therapeutic agents to MM cells improving therapeutic efficacy and reducing side effects in vivo. The anti-CD38 chitosan NPs showed low toxicity profile allowing enhancement of proteasome-inhibitory activity and specificity of BTZ by endocytosis-mediated uptake of CD38 representing a promising therapy in MM.

Injectable Hydrogels for Localized Chemotherapy and Radiotherapy in Brain Tumors

Overall survival of patients with newly diagnosed glioblastoma (GBM) remains dismal at 16 months with state-of-the-art treatment that includes surgical resection, radiation, and chemotherapy. GBM tumors are highly heterogeneous, and mechanisms for overcoming tumor resistance have not yet fully been elucidated. An injectable chitosan hydrogel capable of releasing chemotherapy (temozolomide [TMZ]) while retaining radioactive isotopes agents (iodine, [¹³¹I]) was used as a vehicle for localized radiation and chemotherapy, within the surgical cavity. Release from hydrogels loaded with TMZ or ¹³¹I was characterized in vitro and in vivo and their efficacy on tumor progression and survival on GBM tumors was also measured. The in vitro release of ¹³¹I was negligible over 42 days, whereas the TMZ was completely released over the first 48 h. ¹³¹I was completely retained in the tumor bed with negligible distribution in other tissues and that when delivered locally, the chemotherapy accumulated in the tumor at 10-fold higher concentrations than when delivered systemically. We found that the tumors were significantly decreased, and survival was improved in both treatment groups compared to the control group. Novel injectable chemo-radio-hydrogel implants may potentially improve the local control and overall outcome of aggressive, poor prognosis brain tumors.

Abstract 5005: Inhibition of E-selectin or E-selectin together with CXCR4 resensitizes multiple myeloma to treatment

INTRODUCTION: Multiple myeloma (MM) is a plasma cell malignancy localized in the bone marrow. Selectins and CXCR4 play a pivotal role in homing, adhesion, and proliferation of MM. Herein, we tested the role of E-selectin in the pathophysiology of MM by using a specific E-selectin antagonist (GMI-1271) and a dual E-selectin/CXCR4 antagonist (GMI-1359) on the proliferation and cell trafficking of MM in vitro and in vivo.

PROCEDURES: Endothelial cells (HUVECs), stromal cells (HS5), MM patient-derived stromal cells (MSP1), and MM cell lines (MM1s, H929, U266 and RPMI8226) were tested for expression of E-selectin, CLA (E-selectin ligand) and CXCR4 by flow cytometry. The effect of GMI-1271 and GMI-1359 was studied on MM cell adhesion to stroma; chemotaxis to stromal media or SDF1; and MM cell survival by MTT assay, where MM cells were treated with lenalidomide or carfilzomib; in the presence, or absence of GMI-1271 or -1359. In a xenograft mouse model, the sensitivity of MM was tested in mice treated with vehicle, lenalidomide, GMI-1271, or a combination of GMI-1271 and lenalidomide (n=10 mice/group); and tumor growth was monitored weekly using bioluminescence imaging.

SUMMARY: Expression of E-selectin was high in HUVECs, MSP1 and HS5; CLA was high only in RPMI8226; and CXCR4 was high in all MM cells. MM1s cell adhesion to stroma was decreased by GMI-1271 and even more profoundly decreased by GMI-1359 in a dose-dependent manner. Chemotaxis of MM1s cells towards conditioned media or SDF1 was modestly affected by GMI-1271, but greatly reduced by GMI-1359. MM cell proliferation was significantly inhibited by GMI-1359, only when MM cells were co-cultured with stroma, but not alone. Stroma-induced drug resistance of MM cells to carfilzomib and lenalidomide was reduced in the presence of the GMI compounds, while the effect of GMI-1359 was stronger than GMI-1271. In vivo, GMI-1271 and lenalidomide as single agents delayed tumor growth compared to vehicle by 40% and 35%, respectively; however, a combination treatment delayed tumor growth more profoundly than vehicle by 64% (p=0.04).

CONCLUSIONS: GMI-1271 and GMI-1359 disrupt the interaction between MM cells and bone marrow microenvironment as determined by reduction of adhesion, chemotaxis and microenvironment-induced drug resistance in vitro. However, the dual inhibition of E-selectin and CXCR4 produced more profound effects compared to E-selectin alone. Moreover, GMI-1271 sensitized MM cells to lenalidomide by alleviating chemoresistance and delayed tumor growth in vivo.

Citation Format: Barbara Muz, Henna Y. Bazai, Anita Sekula, William E. Fogler, Ted Smith, John L. Magnani, Abdel Kareem Azab. Inhibition of E-selectin or E-selectin together with CXCR4 resensitizes multiple myeloma to treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5005. doi:10.1158/1538-7445.AM2017-5005

Selinexor Overcomes Hypoxia-Induced Drug Resistance in Multiple Myeloma

Increased levels of the nuclear export protein, exportin 1 (XPO1), were demonstrated in multiple myeloma (MM) patients. Targeting XPO1 with selinexor (the selective inhibitor of nuclear export; SINE compound KPT-330) demonstrates broad antitumor activity also in patient cells resistant to bortezomib; hence, it is a promising target in MM patients. Hypoxia is known to mediate tumor progression and drug resistance (including bortezomib resistance) in MM cells. In this study, we tested the effects of selinexor alone or in combination with bortezomib in normoxia and hypoxia on MM cell survival and apoptosis in vitro and in vivo. In vitro, selinexor alone decreased survival and increased apoptosis, resensitizing MM cells to bortezomib. In vivo, we examined the effects of selinexor alone on tumor initiation and tumor progression, as well as selinexor in combination with bortezomib, on tumor growth in a bortezomib-resistant MM xenograft mouse model. Selinexor, used as a single agent, delayed tumor initiation and tumor progression, prolonging mice survival. In bortezomib-resistant xenografts, selinexor overcame drug resistance, significantly decreasing tumor burden and extending mice survival when combined with bortezomib.

Tariquidar sensitizes multiple myeloma cells to proteasome inhibitors via reduction of hypoxia-induced P-gp-mediated drug resistance

Multiple myeloma (MM) presents a poor prognosis and high lethality of patients due to development of drug resistance. P-glycoprotein (P-gp), a drug-efflux transporter, is upregulated in MM patients post-chemotherapy and is involved in the development of drug resistance since many anti-myeloma drugs (including proteasome inhibitors) are P-gp substrates. Hypoxia develops in the bone marrow niche during MM progression and has long been linked to chemoresistance. Additionally, hypoxia-inducible transcription factor (HIF-1α) was demonstrated to directly regulate P-gp expression. We found that in MM patients P-gp expression positively correlated with the hypoxic marker, HIF-1α. Hypoxia increased P-gp protein expression and its efflux capabilities in MM cells in vitro using flow cytometry. We reported herein that hypoxia-mediated resistance to carfilzomib and bortezomib in MM cells is due to P-gp activity and was reversed by tariquidar, a P-gp inhibitor. These results suggest combining proteasome inhibitors with P-gp inhibition for future clinical studies.

Nanoparticle delivery systems, general approaches, and their implementation in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy that remains incurable, with relapse rates >90%. The main limiting factor for the effective use of chemotherapies in MM is the serious side effects caused by these drugs. The emphasis in cancer treatment has shifted from cytotoxic, non-specific chemotherapies to molecularly targeted and rationally designed therapies showing greater efficacy and fewer side effects. Traditional chemotherapy has shown several disadvantages such as lack of targeting capabilities, systemic toxicity, and side effects; low therapeutic index, as well as most anticancer drugs, has poor water solubility. Nanoparticle delivery systems (NPs) are capable of targeting large doses of chemotherapies into the target area while sparing healthy tissues, overcoming the limitations of traditional chemotherapy. Here, we review the current state of the art in nanoparticle-based strategies designed to treat MM. Many nanoparticle delivery systems have been studied for myeloma using non-targeted NPs (liposomes, polymeric NPs, and inorganic NPs), triggered NPs, as well as targeted NPs (VLA-4, ABC drug transporters, bone microenvironment targeting). The results in preclinical and clinical studies are promising; however, there remains much to be learned in the emerging field of nanomedicine in myeloma.

The eIF2-alpha kinase HRI is a novel therapeutic target in multiple myeloma

Dexamethasone (dex) induces apoptosis in multiple myeloma (MM) cells and is a frontline treatment for this disease. However resistance to dex remains a major challenge and novel treatment approaches are needed. We hypothesized that dex utilizes translational pathways to promote apoptosis in MM and that specific targeting of these pathways could overcome dex-resistance. Global unbiased profiling of mRNA translational profiles in MM cells treated with or without dex revealed that dex significantly repressed eIF2 signaling, an important pathway for regulating ternary complex formation and protein synthesis. We demonstrate that dex induces the phosphorylation of eIF2α resulting in the translational upregulation of ATF4, a known eIF2 regulated mRNA. Pharmacologic induction of eIF2α phosphorylation via activation of the heme-regulated eIF2α kinase (HRI) induced apoptosis in MM cell lines and in primary MM cells from patients with dex-resistant disease. In addition, co-culture with marrow stroma failed to protect MM cells from apoptosis induced by targeting the eIF2 pathway. Combination therapy with rapamycin, an mTOR inhibitor, and BTdCPU, an activator of HRI, demonstrated additive effects on apoptosis in dex-resistant cells. Thus, specific activation of the eIF2α kinase HRI is a novel therapeutic target in MM that can augment current treatment strategies.

Direct measurement of hypoxia in a xenograft multiple myeloma model by optical-resolution photoacoustic microscopy

Using photoacoustic microscopy (PAM), we evaluated non-invasively oxygenation and vascularization in vivo due to multiple myeloma (MM) progression. Mice injected with MM.1S-GFP were monitored with a fluorescence microscope for tumor progression. In vivo PAM of the cerebral bone marrow quantified the total oxygen saturation (sO₂). At 28 days after the MM cell injection, the total sO₂ had decreased by half in the developing tumor regions, while in the non-tumor regions it had decreased by 20% compared with the value at one day post MM injection. The blood vessel density was reduced by 35% in the developing tumor regions, while in the non-tumor regions it was reduced by 8% compared with the value at one day post MM injection. Hence, PAM corroborated the development of hypoxia due to MM progression and demonstrated decreased vascularization surrounding the tumor areas.

The role of hypoxia in cancer progression, angiogenesis, metastasis, and resistance to therapy

Hypoxia is a non-physiological level of oxygen tension, a phenomenon common in a majority of malignant tumors. Tumor-hypoxia leads to advanced but dysfunctional vascularization and acquisition of epithelial-to-mesenchymal transition phenotype resulting in cell mobility and metastasis. Hypoxia alters cancer cell metabolism and contributes to therapy resistance by inducing cell quiescence. Hypoxia stimulates a complex cell signaling network in cancer cells, including the HIF, PI3K, MAPK, and NFĸB pathways, which interact with each other causing positive and negative feedback loops and enhancing or diminishing hypoxic effects. This review provides background knowledge on the role of tumor hypoxia and the role of the HIF cell signaling involved in tumor blood vessel formation, metastasis, and development of the resistance to therapy. Better understanding of the role of hypoxia in cancer progression will open new windows for the discovery of new therapeutics targeting hypoxic tumor cells and hypoxic microenvironment.

Drug Delivery Approaches for the Treatment of Cervical Cancer

Cervical cancer is a highly prevalent cancer that affects women around the world. With the availability of new technologies, researchers have increased their efforts to develop new drug delivery systems in cervical cancer chemotherapy. In this review, we summarized some of the recent research in systematic and localized drug delivery systems and compared the advantages and disadvantages of these methods.

A Hypoxia-Targeted Boron Neutron Capture Therapy Agent for the Treatment of Glioma

PURPOSE

Boron neutron capture therapy (BNCT) has the potential to become a viable cancer treatment modality, but its clinical translation has been limited by the poor tumor selectivity of agents. To address this unmet need, a boronated 2-nitroimidazole derivative (B-381) was synthesized and evaluated for its capability of targeting hypoxic glioma cells.

METHODS

B-381 has been synthesized from a 1-step reaction. Using D54 and U87 glioma cell lines, the in vitro cytotoxicity and cellular accumulation of B-381 has been evaluated under normoxic and hypoxic conditions compared to L-boronophenylalanine (BPA). Furthermore, tumor retention of B-381 was evaluated in vivo.

RESULTS

B-381 had low cytotoxicity in normal and cancer cells. Unlike BPA, B-381 illustrated preferential retention in hypoxic glioma cells compared to normoxic glioma cells and normal tissues in vitro. In vivo, B-381 illustrated significantly higher long-term tumor retention compared to BPA, with 9.5-fold and 6.5-fold higher boron levels at 24 and 48 h, respectively.

CONCLUSIONS

B-381 represents a new class of BNCT agents in which their selectivity to tumors is based on hypoxic tumor metabolism. Further studies are warranted to evaluate B-381 and similar compounds as preclinical candidates for future BNCT clinical trials for the treatment of glioma.

Spotlight on ixazomib: potential in the treatment of multiple myeloma

Despite the significant therapeutic advances achieved with proteasome inhibitors (PIs) such as bortezomib and carfilzomib in prolonging the survival of patients with multiple myeloma, the development of drug resistance, peripheral neuropathy, and pharmacokinetic limitations continue to pose major challenges when using these compounds. Ixazomib is a second-generation PI with improved activity over other PIs. Unlike bortezomib and carfilzomib, which are administered by injection, ixazomib is the first oral PI approved by US Food and Drug Administration. This review discusses the biochemical properties, mechanisms of action, preclinical efficacy, and clinical trial results leading to the US Food and Drug Administration approval of ixazomib.

A CD138-independent strategy to detect minimal residual disease and circulating tumour cells in multiple myeloma

CD138 (also termed SDC1) has been the gold-standard surface marker to detect multiple myeloma (MM) cells for decades; however, drug-resistant residual and circulating MM cells were shown to have lower expression of this marker. In this study, we have shown that residual MM cells following bortezomib treatment are hypoxic. This combination of drug exposure and hypoxia down-regulates their CD138 expression, thereby making this marker unsuitable for detecting residual or other hypoxic MM cells, such as circulating tumour cells, in MM. Hence, we developed an alternative biomarker set which detects myeloma cells independent of their hypoxic and CD138 expression status in vitro, in vivo and in primary MM patients. The new markers were able to identify a clonal CD138-negative population as minimal residual disease in the bone marrow and peripheral blood of MM patients. Further investigation to characterize the role of this population as a prognostic marker in MM is warranted.

The role of hypoxia in cancer progression, angiogenesis, metastasis, and resistance to therapy

Hypoxia is a non-physiological level of oxygen tension, a phenomenon common in a majority of malignant tumors. Tumor-hypoxia leads to advanced but dysfunctional vascularization and acquisition of epithelial-to-mesenchymal transition phenotype resulting in cell mobility and metastasis. Hypoxia alters cancer cell metabolism and contributes to therapy resistance by inducing cell quiescence. Hypoxia stimulates a complex cell signaling network in cancer cells, including the HIF, PI3K, MAPK, and NFĸB pathways, which interact with each other causing positive and negative feedback loops and enhancing or diminishing hypoxic effects. This review provides background knowledge on the role of tumor hypoxia and the role of the HIF cell signaling involved in tumor blood vessel formation, metastasis, and development of the resistance to therapy. Better understanding of the role of hypoxia in cancer progression will open new windows for the discovery of new therapeutics targeting hypoxic tumor cells and hypoxic microenvironment.

3D tissue-engineered bone marrow as a novel model to study pathophysiology and drug resistance in multiple myeloma

PURPOSE

Multiple myeloma (MM) is the second most prevalent hematological malignancy and it remains incurable despite the introduction of several novel drugs. The discrepancy between preclinical and clinical outcomes can be attributed to the failure of classic two-dimensional (2D) culture models to accurately recapitulate the complex biology of MM and drug responses observed in patients.

EXPERIMENTAL DESIGN

We developed 3D tissue engineered bone marrow (3DTEBM) cultures derived from the BM supernatant of MM patients to incorporate different BM components including MM cells, stromal cells, and endothelial cells. Distribution and growth were analyzed by confocal imaging, and cell proliferation of cell lines and primary MM cells was tested by flow cytometry. Oxygen and drug gradients were evaluated by immunohistochemistry and flow cytometry, and drug resistance was studied by flow cytometry.

RESULTS

3DTEBM cultures allowed proliferation of MM cells, recapitulated their interaction with the microenvironment, recreated 3D aspects observed in the bone marrow niche (such as oxygen and drug gradients), and induced drug resistance in MM cells more than 2D or commercial 3D tissue culture systems.

CONCLUSIONS

3DTEBM cultures not only provide a better model for investigating the pathophysiology of MM, but also serve as a tool for drug development and screening in MM. In the future, we will use the 3DTEBM cultures for developing personalized therapeutic strategies for individual MM patients.

Tris DBA palladium overcomes hypoxia-mediated drug resistance in multiple myeloma

Despite recent progress in novel and targeted therapies, multiple myeloma (MM) remains a therapeutically challenging incurable disease. The regulation of important cellular processes and its link to cancer presented Src as an attractive target for MM. We suggest a novel strategy to improve the treatment of MM and overcome the drug resistance for the current therapeutic agents by specific inhibition of Src in MM cells by Tris (Dibenzylideneacetone) dipalladium (Tris DBA). Tris DBA reduces proliferation, induces G1 arrest and apoptosis in MM cells. Tris DBA showed additive effect with proteasome inhibitors reducing proliferation, cell cycle signaling, and increasing apoptosis more than each drug alone. Tris DBA overcame hypoxia-induced effects such as enhanced chemotaxis or drug resistance to proteasome inhibitors by inhibition of HIF1α expression. Moreover, we found that Tris DBA is an effective anti-myeloma agent alone or in combination with other targeted drugs and that it reverses hypoxia-induced drug resistance in myeloma.

Identification of ILK as a novel therapeutic target for acute and chronic myeloid leukemia

Current treatment options as well as clinical efficacy are limited for chronic myelogenous leukemia (CML), Ph+ acute lymphoblastic leukemia (ALL), and acute myeloid leukemia (AML). In response to the pressing need for more efficacious treatment approaches and strategies to override drug resistance in advanced stage CML, Ph+ ALL, and AML, we investigated the effects of inhibition of ILK as a potentially novel and effective approach to treatment of these challenging malignancies. Using the small molecule ILK inhibitor, Cpd22, and ILK knockdown, we investigated the importance of ILK in the growth and viability of leukemia. Our results suggest that the ILK inhibition may be an effective treatment for CML, Ph+ ALL, and AML as a single therapy, with ILK expression levels positively correlating with the efficacy of ILK inhibition. The identification of ILK as a novel target for leukemia therapy warrants further investigation as a therapeutic approach that could be of potential clinical benefit in both acute and chronic myeloid leukemias.

Abstract 5305: Predicting relapse using CD138-independent strategy to detect residual myeloma plasma cells

Introduction: Despite the introduction of novel therapies, majority of multiple myeloma (MM) patients relapses. The major reason for the relapse in MM is the presence of a minimal residual disease (MRD) population that remains after treatment. MM cells are defined as CD138+; however, the presence of clonogenic CD138-negative MM cells and hypoxia-driven CD138 decrease in expression were previously shown. We propose a novel set of biomarkers (independent of CD138) to detect MRD in MM in order to predict patient relapse.

Procedures: We tested the effect of hypoxia on CD markers expression in MM cell lines. We developed new method to detect MM cells by flow cytometry based on CD38(APC+) gating and negatively selecting other leukocytes including T cells, B cells, monocytes, NK cells, and dendritic cells using CD3, CD19, CD14, CD16, and CD123, respectively (FITC-conjugated), the MM cells were defined as APC+/FITC-. We compared traditional method (CD138-based) with the new set of biomarkers (1) to detect normoxic and hypoxic MM cells, (2) to detect MM cells in the peripheral blood (PB) and the bone marrow (BM) from MM patients, confirming cell clonality by internal staining with Kappa/Lambda light chain antibodies, and (3) to predict relapse in MM patients whose BM was defined a CD138-negative.

Summary of data: We found that hypoxia decreased the expression of CD138 by ∼50%, while CD38 was not altered by hypoxia in MM cells. The use of CD138+ as a marker for MM detected only 60-75% of hypoxic MM cells, whereas APC+/FITC- strategy detected close to a 100% of the hypoxic MM cells in vitro. In patient samples, all patients had a higher number of BM-derived and circulating MM cells as detected by APC+/FITC- strategy compared to CD138+. In addition, the clonality of the APC+/FITC- population in BM negative fractions was the same as the original disease (CD138+ cells). Moreover, studies conducted on 16 patients with BM defined as a CD138-negative, showed that the novel APC+/FITC- strategy was more successful than CD138-based method or histology in predicting recurrence and time to relapse. The median time-to-progression with <2% or ≥2% of MM cells detected by novel strategy was 40 and 20 months, respectively. Moreover, patients who relapsed within 2 years had an average 4.4% of APC+/FITC- cells, while patients who relapse in more than 2 years had an average of 1.6% APC+/FITC- cells in their BM.

Conclusion: CD138 cannot be used as a universal marker to detect MM cells, especially when they are hypoxic. A novel set of biomarkers CD38+/CD3-/CD19-/CD14-/CD16-/CD123- (APC+/FITC-) was designed to detect MM cells independent of CD138 expression and hypoxic status. This strategy was able to detect a clonal CD138-negative MM cell population in the BM and PB from MM patients. Moreover, this strategy predicted tumor recurrence and relapse in MM patients more accurately compared to traditional methods such as CD138-based or histology.

Citation Format: Barbara Muz, Feda Azab, Pilar de la Puente, Justin King, Micah Luderer, Ravi Vij, Abdel Kareem Azab. Predicting relapse using CD138-independent strategy to detect residual myeloma plasma cells. [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 5305. doi:10.1158/1538-7445.AM2015-5305

Abstract 5468: Tirapazamine as a strategy to prevent cell dissemination and overcome drug resistance

Introduction: Multiple myeloma (MM) and Waldenström's macroglobulinemia (WM) are lymphoplasmacytic malignancies which are characterized by continuous spread through cell trafficking in and out of the BM. We have recently shown that the spread process in these diseases is mediated by hypoxia. Moreover, despite the introduction of novel therapies, cancer patients relapse due to the development of a drug-resistant stem cell-like subpopulation, which we recently found to be, at least in part, promoted by hypoxia. Therefore, in this study we aimed to overcome spread and drug resistance in MM and WM by inhibition of the hypoxic responses in these cells. Tirapazamine (TPZ) is a hypoxia-activated pro-drug causing cell apoptosis, which has been shown to improve cancer patient outcome when combined with radiotherapy. We use TPZ for the first time in hematologic malignancies to target the drug-resistant cancer cells and sensitize them to therapy.

Procedures: Cell survival was tested on MM (MM1.s, H929, OPM1, RPMI8226) and WM (BCWM.1, MWCL.1) cell lines exposed to normoxia (21% O2) or hypoxia (1% O2) for 24hrs in the presence of bortezomib and carfilzomib, different concentrations of TPZ (in order to obtain an IC50), or combination of those drugs using MTT assay. For adhesion assay, cancer cells were pre-labeled with calcein-AM, treated with TPZ, applied to unlabeled endothelial cells, non-adherent cells were washed after 1hr, and adherent cells were analyzed by a fluorescent reader. Chemotactic properties of cells were tested using a transwell chamber and the migrated cells were counted by flow cytometry. For in vivo study, 5 × 106 MM1s-Luc-GFP cells were injected i.v. into 6 SCID mice and tumor progression was monitored for 3 weeks by bioluminescent imaging. All mice were treated with (1) high-dose bortezomib (1.5mg/kg) only (n = 3), or (2) bortezomib and TPZ (40mg/kg; n = 3), all administered i.p. sequentially twice a week. Bone marrow and peripheral blood were collected and analyzed for the presence of GFP+ cells by flow cytometry.

Summary of data: We found that hypoxia induced drug resistance to bortezomib and carfilzomib of MM and WM cells, and that TPZ was active in a dose-dependent manner only in hypoxic conditions. Combination of TPZ with bortezomib and carfilzomib, resensitized cancer cells to death in hypoxia. Addition of TPZ increased adhesion of cancer cells to endothelial cells, and decreased chemotactic properties of cancer cells in hypoxia in vitro. Moreover, post-treatment residual cancer cells were further decreased using TPZ, preventing recurrence of MM in vivo.

Conclusion: We report that TPZ prevents hypoxia-induced metastasis and overcomes hypoxia-induced drug resistance in MM and WM. This is the first study to show the efficacy of TPZ in hematologic malignancies in general and in MM and WM in particular. This data provide a preclinical basis for future clinical trials testing efficacy of TPZ in MM and WM.

Citation Format: Barbara Muz, Pilar de la Puente, Feda Azab, Micah Luderer, Abdel Kareem Azab. Tirapazamine as a strategy to prevent cell dissemination and overcome drug resistance. [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 5468. doi:10.1158/1538-7445.AM2015-5468