Establishment and characterization of patient-derived xenograft of a rare pediatric anaplastic pleomorphic xanthoastrocytoma (PXA) bearing a CDC42SE2-BRAF fusion

Pleomorphic xanthoastrocytoma (PXA) is a rare subset of primary pediatric glioma with 70% 5-year disease free survival. However, up to 20% of cases present with local recurrence and malignant transformation into more aggressive type anaplastic PXA (AXPA) or glioblastoma. The understanding of disease etiology and mechanisms driving PXA and APXA are limited, and there is no standard of care. Therefore, development of relevant preclinical models to investigate molecular underpinnings of disease and to guide novel therapeutic approaches are of interest. Here, for the first time we established, and characterized a patient-derived xenograft (PDX) from a leptomeningeal spread of a patient with recurrent APXA bearing a novel CDC42SE2-BRAF fusion. An integrated -omics analysis was conducted to assess model fidelity of the genomic, transcriptomic, and proteomic/phosphoproteomic landscapes. A stable xenoline was derived directly from the patient recurrent tumor and maintained in 2D and 3D culture systems. Conserved histology features between the PDX and matched APXA specimen were maintained through serial passages. Whole exome sequencing (WES) demonstrated a high degree of conservation in the genomic landscape between PDX and matched human tumor, including small variants (Pearson's r = 0.794-0.839) and tumor mutational burden (~ 3 mutations/MB). Large chromosomal variations including chromosomal gains and losses were preserved in PDX. Notably, chromosomal gain in chromosomes 4-9, 17 and 18 and loss in the short arm of chromosome 9 associated with homozygous 9p21.3 deletion involving CDKN2A/B locus were identified in both patient tumor and PDX sample. Moreover, chromosomal rearrangement involving 7q34 fusion; CDC42SE-BRAF t (5;7) (q31.1, q34) (5:130,721,239, 7:140,482,820) was identified in the PDX tumor, xenoline and matched human tumor. Transcriptomic profile of the patient's tumor was retained in PDX (Pearson r = 0.88) and in xenoline (Pearson r = 0.63) as well as preservation of enriched signaling pathways (FDR Adjusted P < 0.05) including MAPK, EGFR and PI3K/AKT pathways. The multi-omics data of (WES, transcriptome, and reverse phase protein array (RPPA) was integrated to deduce potential actionable pathways for treatment (FDR < 0.05) including KEGG01521, KEGG05202, and KEGG05200. Both xenoline and PDX were resistant to the MEK inhibitors trametinib or mirdametinib at clinically relevant doses, recapitulating the patient's resistance to such treatment in the clinic. This set of APXA models will serve as a preclinical resource for developing novel therapeutic regimens for rare anaplastic PXAs and pediatric high-grade gliomas bearing BRAF fusions.

Abstract 5498: SHP2 inhibition enhances antitumor effect of mirdametinib in a pediatric brain tumor model bearing CDC42SE2BRAF fusion by rewiring the proteome and phosphoproteome landscape

Pediatric gliomas are the most common type of pediatric brain tumors representing wide range of molecularly and clinically heterogenous subtypes. The hyperactivity of mitogen-activated protein kinases (MAPK) pathway has been identified in the majority of pediatric glioma suggesting its therapeutic potential. However, pharmacologic targeting single MAPK pathway’s component is limited due to the development of drug resistance and differential response associated with tumor molecular landscape. Therefore, effective combination strategy in the framework of precision medicine is needed. Here we report combination benefit and molecular underpinning therapeutic response of brain penetrant MEK inhibitor (mirdametinib) and SHP2 inhibitor (SHP099) in a pediatric patient derived xenograft (PDX) and xenoline developed at our institution. Our model was derived from a pediatric patient who was diagnosed with rare high-grade subtype of glioma, anaplastic pleomorphic xanthoastrocytoma, and did not respond to MEK inhibitor, trametinib. Integrative multi-omics revealed molecular fidelity between our model and its patient tumor counterpart including the presence of 7q35 fusion, CDC52SE2-BRAF, CDKN2A/B loss, and MAPK pathway hyperactivation. In vitro studies using our xenoline IU-X128 demonstrated synergy between SHP099 and mirdametinib to curtail cell proliferation (p&lt;0.05). Moreover, this combination was well tolerated in our PDX, IU-RHT128, and potentiated anti-tumor effect of the single agent within clinically achievable doses. Reverse Phase Proteome Array (RPPA) identified MAPK reactivation via Mushasi RNA binding protein-PI3K-AKT crosstalk as a potential innate resistance mechanism to single agent MEK inhibitor in the PDX tumor. Further, tandem mass tags (TMT)-LC-MS/MS profiling on tumor treated with single agent SHP099 or mirdametinib and their combination revealed that combination therapy does not only revert certain proteome and phosphoproteome reprogramming from single agent treatment but also created a novel landscape which can be associated with anti-tumor effect. In this case, kinase network reprograming leading to MAPK reactivation was identified in mirdametinib treated tumor which was attenuated in the combination treatment. In summary, our results demonstrated that combination SHP099 and mirdametinib is superior to single agent alone in the pediatric A-PXA brain tumor model with proteome and phosphoproteome reprogramming of multiple networks as potential molecular mechanisms underlying therapeutic benefit of combination therapy. Ultimately, clinical translation of this finding will potentially benefit patient of this malignant rare pediatric glioma subset which currently does not have standard therapy.

Citation Format: Nur P. Damayanti, Anthony Alfonso, Josue D. Ordaz, Erika Dobrota, M. Reza Saadatzadeh, Pankita Pandya, Barbara J. Bailey, Khadijeh Bijangi-Vishehsaraei, Harlan E. Shannon, Kathy Coy, Melissa Trowbridge, Anthony L. Sinn, Rosa Gallager, Julia Wulfkuhle, Emanuel Petricoin, Amber Mosley, Mark S. Marshall, Alex Lion, Michael J. Fergusson, Karl Balsara, Karen E. Pollok. SHP2 inhibition enhances antitumor effect of mirdametinib in a pediatric brain tumor model bearing CDC42SE2BRAF fusion by rewiring the proteome and phosphoproteome landscape. [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 5498.

Abstract 6728: Osteosarcoma patient-derived xenografts derived from naive and pretreated metastatic patients with high-risk CDK4/6 hyperactivation signatures are sensitive to dual inhibition of CDK4/6 and PI3K/mTOR

Precision genomics studies have demonstrated hyperactivation of cyclin-dependent kinases 4 and 6 (CDK4/6) as a top actionable marker in children, as well as adolescents and young adults (AYA) with osteosarcoma (OS). CDK4/6 binds to cyclin D resulting in a complex that mediates RB phosphorylation leading to cell cycle progression. Preclinical modeling approaches are critical for identification of tumor adaptive responses to CDK4/6 inhibitors (CDK4/6i) as well as validation of alternative or combination therapies. Although CDK4/6i are clinically well-validated, cytostatic effects make combination treatments essential. Moreover, concomitant dysregulation of CDK4/6 and PI3K/mTOR pathways are observed in aggressive OS. Multiple positive feedback loops between these pathways exacerbate the hyperactivation of CDK4/6 and PI3K/mTOR signaling. Thus, we hypothesize that dual inhibition of CDK4/6 and PI3K/mTOR will be efficacious in RB+ OS PDXs. In this study, OS PDX models TT2-77 (pretreated patient) and HT96 (treatment-naïve patient) with molecular signatures indicative of therapeutic sensitivity to palbociclib (RB+, CDKN2A null, CCND3 amplified) were treated long-term with CDK4/6i (palbociclib) (50 mg/kg), PI3K/mTOR inhibitor (PI3K/mTORi; voxtalisib) (50 mg/kg) or combination palbociclib+voxtalisib. In both PDXs, growth was significantly reduced in single-agent and combination groups compared to vehicle (p&lt;0.05, two-way ANOVA). Importantly, combination palbociclib + voxtalisib was more efficacious than single-agents following prolonged treatment and well tolerated based on histological analyses. Kinome profiling analysis of long-term treated HT96 PDX demonstrated that compared to single agents, dual inhibition of CDK4/6+PI3K/mTOR significantly decreased PI3K pathway activity, including downregulation of Pik3ca, mTOR, and the G2 to M transition regulator CDK1 (-log10[p] ≥1.3). OS metastatic lesion 143B model indicated increased survival based on body scoring criteria in combo versus single agent. In RB+ OS cell lines and TT2-77 xenoline, palbociclib+voxtalisib caused additive-to-synergistic cell growth inhibition, G1 arrest, and minimal apoptosis at clinically relevant doses. Increased activity of senescence biomarker beta-galactosidase indicated that inhibition of CDK4/6 but not PI3K/mTOR induced significant levels of senescence in OS cells. Mechanistic siRNA RB studies indicated CDK4/6i effect was partially dependent on RB status. These data provide evidence that combination palbociclib+voxtalisib therapy is safe, efficacious, and increases CDK4/6i efficiency in both pretreated and naive PDX models of OS. These studies provide rationale for earlier therapeutic intervention in pediatric and AYA OS patients with CDK4/6 hyperactivation signatures.

Citation Format: Farinaz Barghi, M. Reza Saadatzadeh, Erika Dobrota, Rada Malko, Barbara J Bailey, Courtney Young, Harlan E. Shannon, Ryli Justice, Niknam Riyahi, Khadijeh Bijangi-Vishehsaraei, Melissa Trowbridge, Kathy Coy, Felicia M Kennedy, Anthony L Sinn, Amber Mosley, Steve Angus, Michael J. Ferguson, Pankita H. Pandya, Karen E. Pollok. Osteosarcoma patient-derived xenografts derived from naive and pretreated metastatic patients with high-risk CDK4/6 hyperactivation signatures are sensitive to dual inhibition of CDK4/6 and PI3K/mTOR. [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 6728.

Peanut allergen inhibition prevents anaphylaxis in a humanized mouse model

Peanut-induced allergy is an immunoglobulin E (IgE)-mediated type I hypersensitivity reaction that manifests symptoms ranging from local edema to life-threatening anaphylaxis. Although there are treatments for symptoms in patients with allergies resulting from allergen exposure, there are few preventive therapies other than strict dietary avoidance or oral immunotherapy, neither of which are successful in all patients. We have previously designed a covalent heterobivalent inhibitor (cHBI) that binds in an allergen-specific manner as a preventive for allergic reactions. Building on previous in vitro testing, here, we developed a humanized mouse model to test cHBI efficacy in vivo. Nonobese diabetic-severe combined immunodeficient γc-deficient mice expressing transgenes for human stem cell factor, granulocyte-macrophage colony-stimulating factor, and interleukin-3 developed mature functional human mast cells in multiple tissues and displayed robust anaphylactic reactions when passively sensitized with patient-derived IgE monoclonal antibodies specific for peanut Arachis hypogaea 2 (Ara h 2). The allergic response in humanized mice was IgE dose dependent and was mediated by human mast cells. Using this humanized mouse model, we showed that cHBI prevented allergic reactions for more than 2 weeks when administered before allergen exposure. cHBI also prevented fatal anaphylaxis and attenuated allergic reactions when administered shortly after the onset of symptoms. cHBI impaired mast cell degranulation in vivo in an allergen-specific manner. cHBI rescued the mice from lethal anaphylactic responses during oral Ara h 2 allergen-induced anaphylaxis. Together, these findings suggest that cHBI has the potential to be an effective preventative for peanut-specific allergic responses in patients.

Characterization and Function of Cryopreserved Bone Marrow from Deceased Organ Donors: A Potential Viable Alternative Graft Source

Despite the readily available graft sources for allogeneic hematopoietic cell transplantation (alloHCT), a significant unmet need remains in the timely provision of suitable unrelated donor grafts. This shortage is related to the rarity of certain HLA alleles in the donor pool, nonclearance of donors owing to infectious disease or general health status, and prolonged graft procurement and processing times. An alternative hematopoietic progenitor cell (HPC) graft source obtained from the vertebral bodies (VBs) of deceased organ donors could alleviate many of the obstacles associated with using grafts from healthy living donors or umbilical cord blood (UCB). Deceased organ donor-derived bone marrow (BM) can be preemptively screened, cryogenically banked for on-demand use, and made available in adequate cell doses for HCT. We have developed a good manufacturing practice (GMP)-compliant process to recover and cryogenically bank VB-derived HPCs from deceased organ donor (OD) BM. Here we present results from an analysis of HPCs from BM obtained from 250 deceased donors to identify any substantial difference in composition or quality compared with HPCs from BM aspirated from the iliac crests of healthy living donors. BM from deceased donor VBs was processed in a central GMP facility and packaged for cryopreservation in 5% DMSO/2.5% human serum albumin. BM aspirated from living donor iliac crests was obtained and used for comparison. A portion of each specimen was analyzed before and after cryopreservation by flow cytometry and colony-forming unit potential. Bone marrow chimerism potential was assessed in irradiated immunocompromised NSG mice. Analysis of variance with Bonferroni correction for multiple comparisons was used to determine how cryopreservation affects BM cells and to evaluate indicators of successful engraftment of BM cells into irradiated murine models. The t test (with 95% confidence intervals [CIs]) was used to compare cells from deceased donors and living donors. A final dataset of complete clinical and matched laboratory data from 226 cryopreserved samples was used in linear regressions to predict outcomes of BM HPC processing. When compared before and after cryopreservation, OD-derived BM HPCs were found to be stable, with CD34+ cells maintaining high viability and function after thawing. The yield from a single donor is sufficient for transplantation of an average of 1.6 patients (range, 1.2 to 7.5). CD34+ cells from OD-derived HPCs from BM productively engrafted sublethally irradiated immunocompromised mouse BM (>44% and >67% chimerism at 8 and 16 weeks, respectively). Flow cytometry and secondary transplantation confirmed that OD HPCs from BM is composed of long-term engrafting CD34+CD38-CD45RA-CD90+CD49f+ HSCs. Linear regression identified no meaningful predictive associations between selected donor-related characteristics and OD BM HPC quality or yield. Collectively, these data demonstrate that cryopreserved BM HPCs from deceased organ donors is potent and functionally equivalent to living donor BM HPCs and is a viable on-demand graft source for clinical HCT. Prospective clinical trials will soon commence in collaboration with the Center for International Blood and Marrow Research to assess the feasibility, safety, and efficacy of Ossium HPCs from BM (ClinicalTrials.gov identifier NCT05068401).

Integrative Multi-OMICs Identifies Therapeutic Response Biomarkers and Confirms Fidelity of Clinically Annotated, Serially Passaged Patient-Derived Xenografts Established from Primary and Metastatic Pediatric and AYA Solid Tumors

Establishment of clinically annotated, molecularly characterized, patient-derived xenografts (PDXs) from treatment-naïve and pretreated patients provides a platform to test precision genomics-guided therapies. An integrated multi-OMICS pipeline was developed to identify cancer-associated pathways and evaluate stability of molecular signatures in a panel of pediatric and AYA PDXs following serial passaging in mice. Original solid tumor samples and their corresponding PDXs were evaluated by whole-genome sequencing, RNA-seq, immunoblotting, pathway enrichment analyses, and the drug−gene interaction database to identify as well as cross-validate actionable targets in patients with sarcomas or Wilms tumors. While some divergence between original tumor and the respective PDX was evident, majority of alterations were not functionally impactful, and oncogenic pathway activation was maintained following serial passaging. CDK4/6 and BETs were prioritized as biomarkers of therapeutic response in osteosarcoma PDXs with pertinent molecular signatures. Inhibition of CDK4/6 or BETs decreased osteosarcoma PDX growth (two-way ANOVA, p < 0.05) confirming mechanistic involvement in growth. Linking patient treatment history with molecular and efficacy data in PDX will provide a strong rationale for targeted therapy and improve our understanding of which therapy is most beneficial in patients at diagnosis and in those already exposed to therapy.

Abstract 2017: Therapeutic induction of replication stress in the context of salvage therapy in osteosarcoma

Osteosarcoma (OS) is an aggressive pediatric cancer with ~35% of patients developing metastasis over time. The survival rate for metastatic and relapsed OS patients is &lt;30% and there is currently no standardized salvage therapy. Lack of efficacy is attributed to extensive genetic complexity present in OS that is partly due to moderate levels of replication stress (RS). While high levels of RS can induce cell death, moderate RS levels may cause genomic instability that contributes to progression of OS. Therefore, induction of RS to high levels, especially in genetically complex cancers like OS, could be a promising therapeutic strategy. Bromodomain and extra-terminal domain (BET) proteins (BRD2,3,4) are a family of epigenetic readers that not only regulate gene expression networks, but also regulate DNA replication and RS. BRD4 directly regulates major factors involved in DNA replication and checkpoint signaling. Thus, disruption of BRD4 function should exacerbate RS to levels that cause cell death. The objective of this study is to test the hypothesis that BET inhibition potentiates the efficacy of current salvage therapy through RS induction in aggressive OS. The effects of BET inhibitors (BETi), AZD5153 and OTX-015, as single agents and in combination with drugs used in salvage therapy such as topotecan were evaluated for effects on OS cell growth, PARP cleavage, and the DNA damage repair network. BET knockdown experiments were performed to evaluate target selectivity and dependency. In vivo efficacy and safety studies focused on patient-derived xenografts (PDXs) of relapsed OS. TT2-77 xenoline, Saos2, G292, and U2OS cell lines were selected for in vitro experiments. Combination index and Bliss independence analyses demonstrated additive to synergistic cell growth inhibition upon treatment with clinically relevant concentrations of BETi+topotecan. Significant increase in PARP cleavage was observed in the combination compared to single agent, indicating enhancement of apoptosis. Moreover, Western analyses demonstrated that BETi induces its effect, at least partly, via decreased CHK1 activation and increased DNA damage. Selective siRNA treatments illustrated that transient knockdown of individual BET proteins was not sufficient for potentiation of topotecan-induced cell death in OS cells, indicating that simultaneous knockdown of BETs may be required. Dose-finding studies of AZD5153 in relapsed OS PDXs that harbor replication stress signatures (TT2-77 and PDX96) indicated that daily doses of 1.25 or 2.5 mg/kg AZD5153 were well tolerated and effective in partially suppressing tumor growth compared to vehicle (p&lt;0.05, Two-way ANOVA; Holm-Sidak). In vivo combination treatments of BETi+topotecan are in progress. These data collectively suggest that BET inhibition alongside salvage therapy holds promise as a novel treatment strategy for inducing RS-mediated cell death in aggressive OS.

Citation Format: Niknam Riyahi, Pankita H. Pandya, M. Reza Saadatzadeh, Khadijeh Bijangi-Vishehsaraei, Barbara J. Bailey, Erika A. Dobrota, Courtney Young, Melissa A. Trowbridge, Kathy Coy, Henry Mang, Reagan K. Wohlford, Anthony L. Sinn, Emily S. Sims, Matt J. Repass, Nuri Damayanti, Farinaz Barghi, Harlan E. Shannon, Michael J. Ferguson, Jamie L. Renbarger, Karen E. Pollok. Therapeutic induction of replication stress in the context of salvage therapy in osteosarcoma [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 2017.

Multispecific targeting of glioblastoma with tumor microenvironment-responsive multifunctional engineered NK cells

Tumor antigen heterogeneity, a severely immunosuppressive tumor microenvironment (TME) and lymphopenia resulting in inadequate immune intratumoral trafficking, have rendered glioblastoma (GBM) highly resistant to therapy. To address these obstacles, here we describe a unique, sophisticated combinatorial platform for GBM: a cooperative multifunctional immunotherapy based on genetically engineered human natural killer (NK) cells bearing multiple antitumor functions including local tumor responsiveness that addresses key drivers of GBM resistance to therapy: antigen escape, immunometabolic reprogramming of immune responses, and poor immune cell homing. We engineered dual-specific chimeric antigen receptor (CAR) NK cells to bear a third functional moiety that is activated in the GBM TME and addresses immunometabolic suppression of NK cell function: a tumor-specific, locally released antibody fragment which can inhibit the activity of CD73 independently of CAR signaling and decrease the local concentration of adenosine. The multifunctional human NK cells targeted patient-derived GBM xenografts, demonstrated local tumor site-specific activity in the tissue, and potently suppressed adenosine production. We also unveil a complex reorganization of the immunological profile of GBM induced by inhibiting autophagy. Pharmacologic impairment of the autophagic process not only sensitized GBM to antigenic targeting by NK cells but promoted a chemotactic profile favorable to NK infiltration. Taken together, our study demonstrates a promising NK cell-based combinatorial strategy that can target multiple clinically recognized mechanisms of GBM progression simultaneously.

Abstract 3043: Targeting CDK4/6 inhibitor resistance in relapsed osteosarcoma via PI3 Kinase inhibition

Osteosarcoma (OS) is the most common primary bone malignancy in children as well as in adolescents and young adults (AYA). Approximately 35% of OS patients develop metastases and relapse after first-line treatment emphasizing the need for new therapies. Our objective was to use patient -omics analyses to prioritize models of relapsed pediatric and AYA OS to investigate an unexplored combination therapy. Genomic data from pediatric and AYA patients enrolled in the Precision Genomics program at Riley Hospital for Children, Indiana University Health indicate that dysregulation of cyclin-dependent kinases 4 and 6 (CDK4/6) is one of the top actionable signatures. The cyclin D-CDK4/6 complex regulates retinoblastoma protein (RB)-E2F transcription factor interactions. Upon cyclin D-CDK4/6-mediated RB phosphorylation, the RB-E2F complex dissociates, and cell cycle progression ensues. CDK4/6 inhibitors (CDK4/6i) typically induce cell cycle arrest rather than cell death and can activate compensatory pathways such as PI3K. Moreover, aberrant PI3K activation has been reported in OS. Our hypothesis is that inhibition of CDK4/6 and PI3K pathways will be efficacious and well-tolerated in RB1-proficient (RB+) OS models exhibiting hyperactivation of the cyclin D-CDK4/6 complex. Cell growth response to CDK4/6i (Palbociclib or Abemaciclib) and a PI3K/mTOR inhibitor (PI3K/mTORi, Voxtalisib) was evaluated in RB+ OS cell lines and an RB+ patient-derived xenograft (PDX)-derived xenoline (TT2-77). Combination index and Bliss independence analyses indicated that CDK4/6i+PI3K/mTORi resulted in additive to synergistic inhibition of growth in RB+ OS cell lines at clinically relevant concentrations. In the TT2-77 PDX, whole genome sequencing indicated that the original OS biopsy and the TT2-77 PDX generated from a resection sample harbor signatures associated with CDK4/6 pathway up-regulation. Global and phosphoproteome analysis were conducted on TT2 PDX tumors from NOD/SCIDγnull mice treated with vehicle vs. Palbociclib for 5 days. Modulation of 6226 phosphopeptides and 3870 total proteins were observed and included downregulation of phosphopeptides and total protein levels of CDK1 as well as DNA replication proteins in Palbociclib-treated TT2-77 PDX mice. Furthermore, TT2-77 PDX mice were treated with Palbociclib daily (10-120 mg/kg) for 3 weeks. TT2-77 PDX growth was completely blocked by high dose Palbociclib. While all mice survived, clinical observation criteria indicated that this dose was not optimal. In TT2-77 PDX mice treated with 50 mg/kg Palbociclib, tumor growth significantly decreased compared to vehicle (p&lt;0.01) and was well tolerated. However, tumors progressed over time while still on treatment; evaluation of PI3K pathway activation is in progress. These data provide an opportunity to evaluate efficacy of targeting CDK4/6i-induced compensatory pathways in relapsed pediatric and AYA OS.

Citation Format: Farinaz Barghi, Pankita H. Pandya, M. Reza Saadatzadeh, Khadijeh Bijangi-Vishehsaraei, Barbara J. Bailey, Erika A. Dobrota, Courtney Young, Melissa A. Trowbridge, Kathy Coy, Anthony L. Sinn, Harlan E. Shannon, Jamie L. Renbarger, Karen E. Pollok. Targeting CDK4/6 inhibitor resistance in relapsed osteosarcoma via PI3 Kinase inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3043.

The neurotransmitter receptor Gabbr1 regulates proliferation and function of hematopoietic stem and progenitor cells

Hematopoietic and nervous systems are linked via innervation of bone marrow (BM) niche cells. Hematopoietic stem/progenitor cells (HSPCs) express neurotransmitter receptors, such as the γ-aminobutyric acid (GABA) type B receptor subunit 1 (GABBR1), suggesting that HSPCs could be directly regulated by neurotransmitters like GABA that directly bind to GABBR1. We performed imaging mass spectrometry and found that the endogenous GABA molecule is regionally localized and concentrated near the endosteum of the BM niche. To better understand the role of GABBR1 in regulating HSPCs, we generated a constitutive Gabbr1-knockout mouse model. Analysis revealed that HSPC numbers were significantly reduced in the BM compared with wild-type littermates. Moreover, Gabbr1-null hematopoietic stem cells had diminished capacity to reconstitute irradiated recipients in a competitive transplantation model. Gabbr1-null HSPCs were less proliferative under steady-state conditions and upon stress. Colony-forming unit assays demonstrated that almost all Gabbr1-null HSPCs were in a slow or noncycling state. In vitro differentiation of Gabbr1-null HSPCs in cocultures produced fewer overall cell numbers with significant defects in differentiation and expansion of the B-cell lineage. To determine whether a GABBR1 agonist could stimulate human umbilical cord blood (UCB) HSPCs, we performed brief ex vivo treatment prior to transplant into immunodeficient mice, with significant increases in long-term engraftment of HSPCs compared with GABBR1 antagonist or vehicle treatments. Our results indicate a direct role for GABBR1 in HSPC proliferation, and identify a potential target to improve HSPC engraftment in clinical transplantation.

Melanoma LAMP-2C Modulates Tumor Growth and Autophagy

Autophagy plays critical but diverse roles in cellular quality control and homeostasis potentially checking tumor development by removing mutated or damaged macromolecules, while conversely fostering tumor survival by supplying essential nutrients during cancer progression. This report documents a novel inhibitory role for a lysosome-associated membrane protein, LAMP-2C in modulating autophagy and melanoma cell growth in vitro and in vivo. Solid tumors such as melanomas encounter a variety of stresses in vivo including inflammatory cytokines produced by infiltrating lymphocytes directed at limiting tumor growth and spread. Here, we report that in response to the anti-tumor, pro-inflammatory cytokine interferon-gamma, melanoma cell expression of LAMP2C mRNA significantly increased. These results prompted an investigation of whether increased melanoma cell expression of LAMP-2C might represent a mechanism to control or limit human melanoma growth and survival. In this study, enhanced expression of human LAMP-2C in melanoma cells perturbed macroautophagy and chaperone-mediated autophagy in several human melanoma lines. In vitro analysis showed increasing LAMP-2C expression in a melanoma cell line, triggered reduced cellular LAMP-2A and LAMP-2B protein expression. Melanoma cells with enhanced LAMP-2C expression displayed increased cell cycle arrest, increased expression of the cell cycle regulators Chk1 and p21, and greater apoptosis and necrosis in several cell lines tested. The increased abundance of Chk1 protein in melanoma cells with increased LAMP-2C expression was not due to higher CHEK1 mRNA levels, but rather an increase in Chk1 protein abundance including Chk1 molecules phosphorylated at Ser345. Human melanoma cell xenografts with increased LAMP-2C expression, displayed reduced growth in immune compromised murine hosts. Melanomas with high LAMP-2C expression showed increased necrosis and reduced cell density upon histological analysis. These results reveal a novel role for LAMP-2C in negatively regulating melanoma growth and survival.

Abstract 2814: Effect of kif14 overexpression on tumor formation in mice in a lifespan study

KIF14 is a mitotic kinesin and microtubule-associated molecular motor that plays an essential role in the last stages of cytokinesis. In multiple cancer types, KIF14, overexpression in tumors correlates with stage, aggressiveness, and poor patient outcomes. There is considerable interest in KIF14 as a possible oncogene, since the KIF14 locus is in a common region of genomic gain in multiple cancers.

In this study, wild type BDF-1 mice and a strain constitutively overexpressing Kif14, known as Kif14-Tg mice, were evaluated at the end of their natural lifespan, specifically for the occurrence of tumors. There were approximately fifty mice per genotype, and eighty of these mice have died. These mice were necropsied and the following tissues were collected: kidney, liver, lung, spleen, seminal vesicles, ovary, mammary gland, bone marrow, pituitary gland, eye, and brain. Any gross nodules were also collected. These tissues were then fixed in 10% neutral buffered formalin, processed, sectioned, and stained with hematoxylin and eosin.

Although there was no significant difference in mouse weights through the lifespan or in the survival curve between the Kif14-Tg and their wild type littermates, a significant increase in follicular lymphoma and diffuse large B cell lymphoma was seen in Kif14-Tg mice compared to the wild type mice. Thirty-three mice developed either a follicular lymphoma or a diffuse large B cell lymphoma, and twenty-four of those mice were Kif14-Tg mice. These were the two most common tumors in Kif14-Tg mice. Other lesions and tumors that were seen in both strains included thymic lymphoma, sarcomas, myeloid dysplasia, and other carcinomas. Nontumorous lesions were seen in both strains of mice including hydronephrosis and telangiectasia in multiple organs. Ballooning degeneration of the lens of the eyes was observed in five mice from the strain Kif14-Tg.

Our finding of increased follicular lymphoma and diffuse large B cell lymphoma proves the first evidence that Kif14 can promote tumor formation in a wild-type background. This is the first evidence that Kif14 may have a role in lymphoma, but complements our earlier finding that Kif14 overexpression can accelerate tumor formation in a mouse model of retinoblastoma. Together, these outcomes further support Kif14’s potential as an oncogene.

Citation Format: Natalie Pitt, Kamakshi Sishtla, Mehdi Shadmand, Rania Sulaiman, Anthony L. Sinn, Keith Condon, George E. Sandusky, Timothy W. Corson. Effect of kif14 overexpression on tumor formation in mice in a lifespan study [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 2814. doi:10.1158/1538-7445.AM2017-2814

Potentiation of Carboplatin-Mediated DNA Damage by the Mdm2 Modulator Nutlin-3a in a Humanized Orthotopic Breast-to-Lung Metastatic Model

Triple-negative breast cancers (TNBC) are typically resistant to treatment, and strategies that build upon frontline therapy are needed. Targeting the murine double minute 2 (Mdm2) protein is an attractive approach, as Mdm2 levels are elevated in many therapy-refractive breast cancers. The Mdm2 protein-protein interaction inhibitor Nutlin-3a blocks the binding of Mdm2 to key signaling molecules such as p53 and p73α and can result in activation of cell death signaling pathways. In the present study, the therapeutic potential of carboplatin and Nutlin-3a to treat TNBC was investigated, as carboplatin is under evaluation in clinical trials for TNBC. In mutant p53 TMD231 TNBC cells, carboplatin and Nutlin-3a led to increased Mdm2 and was strongly synergistic in promoting cell death in vitro. Furthermore, sensitivity of TNBC cells to combination treatment was dependent on p73α. Following combination treatment, γH2AX increased and Mdm2 localized to a larger degree to chromatin compared with single-agent treatment, consistent with previous observations that Mdm2 binds to the Mre11/Rad50/Nbs1 complex associated with DNA and inhibits the DNA damage response. In vivo efficacy studies were conducted in the TMD231 orthotopic mammary fat pad model in NOD.Cg-Prkdc(scid)Il2rg(tm1Wjl)/SzJ (NSG) mice. Using an intermittent dosing schedule of combined carboplatin and Nutlin-3a, there was a significant reduction in primary tumor growth and lung metastases compared with vehicle and single-agent treatments. In addition, there was minimal toxicity to the bone marrow and normal tissues. These studies demonstrate that Mdm2 holds promise as a therapeutic target in combination with conventional therapy and may lead to new clinical therapies for TNBC.

Abstract 4961: Longitudinal bioluminescence imaging of primary versus abdominal metastatic tumor growth in orthotopic pancreatic tumor models in NOD/SCIDγ(-/-) mice

Pancreatic ductal adenocarcinoma (PDAC) has a very poor prognosis and is currently the fourth leading cause of cancer death in the United States. The lethal nature of PDAC is strongly associated with metastases to distant organs. The purpose of the present study was to develop and validate noninvasive bioluminescence imaging methods for differentially monitoring the kinetics of primary and abdominal metastatic tumor growth in mouse orthotopic models of pancreatic cancer. A semiautomated maximum entropy segmentation method was implemented for the primary tumor region-of-interest (ROI), and a rule-based method for manually drawing an ROI for the abdominal metastatic region also was developed. The two ROI methods were first validated by having two observers independently construct ROIs for the tumors of animals implanted orthotopically with Panc-1 cells, and the results compared with the number of mesenteric lymph node metastatic nodules counted upon necropsy. The findings were extended to orthotopic tumors of the more metastatic MIA PaCa-2 and AsPC-1 cells where different groups of animals were implanted with different numbers of cells. When the data were expressed as the total photon flux (Ph/sec) in the ROIs for the primary tumor and metastases, the total flux within the metastasis ROI was larger in magnitude than the total flux from the primary tumor ROI, at times by as much as several orders of magnitude. However, when the data were expressed as the average flux density (Ph/sec*mm2) within the ROIs, the density of the flux within the smaller primary tumor ROI was larger in magnitude than the density of the flux from the larger metastasis ROI, by as much as several orders of magnitude. Interobserver assessments for total flux and flux density from ROIs for both the primary tumors and metastatic region were highly concordant, with correlation coefficients of r &gt; 0.98, coefficients of variation of ≤ 0.02, and limits of agreement within &lt;5%. Further, there were statistically significant differences in the growth kinetics of AsPC-1 and MIA PaCa-2 orthotopic tumors when mice were implanted with different numbers of cells for each cell line. The present results demonstrated that the segmentation methods were highly reliable, reproducible and robust, and allowed statistically significant discrimination in the growth kinetics of primary and abdominal metastatic tumors of different cell lines implanted with different cell numbers. Thus, primary tumors and abdominal metastatic foci in orthotopic pancreatic cancer models can be reliably monitored separately and noninvasively over time with bioluminescence imaging. The novel segmentation methods reported here will facilitate investigations of the biology of primary and metastatic tumor growth, as well as the effects of novel treatments, over time, in individual animals.

Citation Format: Harlan E. Shannon, Melissa L. Fishel, Jingwu Xie, Dongsheng Gu, Brian P. McCarthy, Amanda A. Riley, Anthony L. Sinn, Jayne M. Silver, Mark R. Kelley, Helmut Hanenberg, Murray Korc, Karen E. Pollok, Paul R. Territo. Longitudinal bioluminescence imaging of primary versus abdominal metastatic tumor growth in orthotopic pancreatic tumor models in NOD/SCIDγ(-/-) mice. [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 4961. doi:10.1158/1538-7445.AM2014-4961

Abstract 1680: Modulation of MDM2 in context of DNA damage enhances cell death in a metastatic breast-to-lung xenograft model

Metastatic breast cancer is highly refractive to current treatment strategies, and new multi-targeted treatments need to be elucidated. In metastatic disease, inhibiting key protein-protein interactions with the murine double minute 2 (MDM2) could be beneficial for developing new treatment modalities since this signaling pathway is a critical regulatory point in cancer progression. Inhibition of protein binding to the hydrophobic pocket of MDM2 by Nutlin-3a can activate pro-apoptotic proteins such p73 and E2F1 as well as decrease pro-angiogenic Hif-1α. Since the DNA damaging agent carboplatin is currently being studied in clinical trials of triple-negative breast cancers (TNBCs), our objective was to evaluate the effects of carboplatin and Nutlin-3a in combination in TNBC in a mutant p53 background. Using a TNBC cell line TMD231 derived from the MDA-MB-231 human breast cancer cell line, we performed combination studies using different ratios of carboplatin to Nutlin-3a in vitro to evaluate the range of carboplatin-mediated DNA damage required to obtain synergism with inhibition of MDM2 function. A fixed ratio of 1:1 carboplatin:Nutlin-3a was strongly synergistic with a combination index of &lt;0.5. In cell proliferation assays there was increased sensitivity to the drugs when given in combination (p&lt;0.05). TMD231 cells implanted into the mammary fat pad of NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice showed enhanced tumor growth, and metastasis was evident in the lungs. Dose-finding studies were performed to determine an optimal carboplatin dosing schema. NSG mice were randomized based on fluorescent imaging of E2-crimson expressing TMD231 cells allowing for a sensitive measurement of early tumor burden. Following Nutlin-3a and carboplatin combination treatment in vivo, there was a statistically significant reduction in tumor volume and lung metastases compared to vehicle and single drug treated mice (p&lt;0.001). Following Kaplan-Meier analysis, the combination treated mice had a significant increase in survival, (54.3±1.5 days) compared to the vehicle (39.3±0.6 days) and each single drug (Nutlin-3a: 39±1 and carboplatin: 47.5±1.8 days) (p&lt;0.001). While there was a decrease in bone-marrow cellularity, this did not lead to bone-marrow aplasia, and body weights recovered to normal levels within 7 days post-treatment. Pharmacodynamic studies are ongoing to further understand at the molecular level how the DNA damage response and repair is modulated by MDM2 resulting in a robust synergistic response. These studies will lead to a better understanding of how to potentiate DNA damage and may lead to new clinical therapies in the future for metastatic breast cancer.

Citation Format: Eva Tonsing-Carter, Harlan E. Shannon, Barbara J. Bailey, Anthony L. Sinn, Kacie M. Peterman, Lindsey D. Mayo, Karen E. Pollok. Modulation of MDM2 in context of DNA damage enhances cell death in a metastatic breast-to-lung xenograft model. [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 1680. doi:10.1158/1538-7445.AM2014-1680

A heterobivalent ligand inhibits mast cell degranulation via selective inhibition of allergen-IgE interactions in vivo

Current treatments for allergies include epinephrine and antihistamines, which treat the symptoms after an allergic response has taken place; steroids, which result in local and systemic immune suppression; and IgE-depleting therapies, which can be used only for a narrow range of clinical IgE titers. The limitations of current treatments motivated the design of a heterobivalent inhibitor (HBI) of IgE-mediated allergic responses that selectively inhibits allergen-IgE interactions, thereby preventing IgE clustering and mast cell degranulation. The HBI was designed to simultaneously target the allergen binding site and the adjacent conserved nucleotide binding site (NBS) found on the Fab of IgE Abs. The bivalent targeting was accomplished by linking a hapten to an NBS ligand with an ethylene glycol linker. The hapten moiety of HBI enables selective targeting of a specific IgE, whereas the NBS ligand enhances avidity for the IgE. Simultaneous bivalent binding to both sites provided HBI with 120-fold enhancement in avidity for the target IgE compared with the monovalent hapten. The increased avidity for IgE made HBI a potent inhibitor of mast cell degranulation in the rat basophilic leukemia mast cell model, in the passive cutaneous anaphylaxis mouse model of allergy, and in mice sensitized to the model allergen. In addition, HBI did not have any observable systemic toxic effects even at elevated doses. Taken together, these results establish the HBI design as a broadly applicable platform with therapeutic potential for the targeted and selective inhibition of IgE-mediated allergic responses, including food, environmental, and drug allergies.

Soypeptide lunasin in cytokine immunotherapy for lymphoma

Immunostimulatory cytokines can enhance anti-tumor immunity and are part of the therapeutic armamentarium for cancer treatment. We have previously reported that post-transplant lymphoma patients have an acquired deficiency of signal transducer and activator of transcription 4, which results in defective IFNγ production during clinical immunotherapy. With the goal of further improving cytokine-based immunotherapy, we examined the effects of a soybean peptide called lunasin that synergistically works with cytokines on natural killer (NK) cells. Peripheral blood mononuclear cells of healthy donors and post-transplant lymphoma patients were stimulated with or without lunasin in the presence of IL-12 or IL-2. NK activation was evaluated, and its tumoricidal activity was assessed using in vitro and in vivo tumor models. Chromatin immunoprecipitation assay was performed to evaluate the histone modification of gene loci that are regulated by lunasin and cytokine. Adding lunasin to IL-12- or IL-2-stimulated NK cells demonstrated synergistic effects in the induction of IFNG and GZMB involved in cytotoxicity. The combination of lunasin and cytokines (IL-12 plus IL-2) was capable of restoring IFNγ production by NK cells from post-transplant lymphoma patients. In addition, NK cells stimulated with lunasin plus cytokines displayed higher tumoricidal activity than those stimulated with cytokines alone using in vitro and in vivo tumor models. The underlying mechanism responsible for the effects of lunasin on NK cells is likely due to epigenetic modulation on target gene loci. Lunasin represents a different class of immune modulating agent that may augment the therapeutic responses mediated by cytokine-based immunotherapy.

Human proangiogenic circulating hematopoietic stem and progenitor cells promote tumor growth in an orthotopic melanoma xenograft model

We previously identified a distinct population of human circulating hematopoietic stem and progenitor cells (CHSPCs; CD14(-)glyA(-)CD34(+)AC133(+/-)CD45(dim)CD31(+) cells) in the peripheral blood (PB) and bone marrow, and their frequency in the PB can correlate with disease state. The proangiogenic subset (pCHSPC) play a role in regulating tumor progression, for we previously demonstrated a statistically significant increase in C32 melanoma growth in NOD.Cg-Prkdc (scid) (NOD/SCID) injected with human pCHSPCs (p < 0.001). We now provide further evidence that pCHSPCs possess proangiogenic properties. In vitro bio-plex cytokine analyses and tube forming assays indicate that pCHSPCs secrete a proangiogenic profile and promote vessel formation respectively. We also developed a humanized bone marrow-melanoma orthotopic model to explore in vivo the biological significance of the pCHSPC population. Growth of melanoma xenografts increased more rapidly at 3-4 weeks post-tumor implantation in mice previously transplanted with human CD34(+) cells compared to control mice. Increases in pCHSPCs in PB correlated with increases in tumor growth. Additionally, to determine if we could prevent the appearance of pCHSPCs in the PB, mice with humanized bone marrow-melanoma xenografts were administered Interferon α-2b, which is used clinically for treatment of melanoma. The mobilization of the pCHSPCs was decreased in the mice with the humanized bone marrow-melanoma xenografts. Taken together, these data indicate that pCHSPCs play a functional role in tumor growth. The novel in vivo model described here can be utilized to further validate pCHSPCs as a biomarker of tumor progression. The model can also be used to screen and optimize anticancer/anti-angiogenic therapies in a humanized system.

Dichloroacetate reverses the hypoxic adaptation to bevacizumab and enhances its antitumor effects in mouse xenografts

Inhibition of vascular endothelial growth factor increases response rates to chemotherapy and progression-free survival in glioblastoma. However, resistance invariably occurs, prompting the urgent need for identification of synergizing agents. One possible strategy is to understand tumor adaptation to microenvironmental changes induced by antiangiogenic drugs and test agents that exploit this process. We used an in vivo glioblastoma-derived xenograft model of tumor escape in presence of continuous treatment with bevacizumab. U87-MG or U118-MG cells were subcutaneously implanted into either BALB/c SCID or athymic nude mice. Bevacizumab was given by intraperitoneal injection every 3 days (2.5 mg/kg/dose) and/or dichloroacetate (DCA) was administered by oral gavage twice daily (50 mg/kg/dose) when tumor volumes reached 0.3 cm(3) and continued until tumors reached approximately 1.5-2.0 cm(3). Microarray analysis of resistant U87 tumors revealed coordinated changes at the level of metabolic genes, in particular, a widening gap between glycolysis and mitochondrial respiration. There was a highly significant difference between U87-MG-implanted athymic nude mice 1 week after drug treatment. By 2 weeks of treatment, bevacizumab and DCA together dramatically blocked tumor growth compared to either drug alone. Similar results were seen in athymic nude mice implanted with U118-MG cells. We demonstrate for the first time that reversal of the bevacizumab-induced shift in metabolism using DCA is detrimental to neoplastic growth in vivo. As DCA is viewed as a promising agent targeting tumor metabolism, our data establish the timely proof of concept that combining it with antiangiogenic therapy represents a potent antineoplastic strategy.

Small-molecule inhibition of the uPAR·uPA interaction: synthesis, biochemical, cellular, in vivo pharmacokinetics and efficacy studies in breast cancer metastasis

The uPAR·uPA protein-protein interaction (PPI) is involved in signaling and proteolytic events that promote tumor invasion and metastasis. A previous study had identified 4 (IPR-803) from computational screening of a commercial chemical library and shown that the compound inhibited uPAR·uPA PPI in competition biochemical assays and invasion cellular studies. Here, we synthesize 4 to evaluate in vivo pharmacokinetic (PK) and efficacy studies in a murine breast cancer metastasis model. First, we show, using fluorescence polarization and saturation transfer difference (STD) NMR, that 4 binds directly to uPAR with sub-micromolar affinity of 0.2 μM. We show that 4 blocks invasion of breast MDA-MB-231, and inhibits matrix metalloproteinase (MMP) breakdown of the extracellular matrix (ECM). Derivatives of 4 also inhibited MMP activity and blocked invasion in a concentration-dependent manner. Compound 4 also impaired MDA-MB-231 cell adhesion and migration. Extensive in vivo PK studies in NOD-SCID mice revealed a half-life of nearly 5h and peak concentration of 5 μM. Similar levels of the inhibitor were detected in tumor tissue up to 10h. Female NSG mice inoculated with highly malignant TMD-MDA-MB-231 in their mammary fat pads showed that 4 impaired metastasis to the lungs with only four of the treated mice showing severe or marked metastasis compared to ten for the untreated mice. Compound 4 is a promising template for the development of compounds with enhanced PK parameters and greater efficacy.

Abstract 1409: Real-time in vivo imaging for sensitive detection of primary and metastatic disease in a human breast-to-lung orthotopic model

Orthotopic mouse models of human disease are absolutely essential for validating therapeutic targets and assessing efficacy of emerging therapies. Early detection of in vivo tumor growth is a critical benchmark in humanized mouse models, for it reveals tumor take at a time of reasonable tumor burden. To develop an optimal mouse model of human metastatic breast cancer, we utilized TMD231 breast cancer cells (derived from MDA-MB-231) that have a high propensity to metastasize to the lung. TMD231 tumor take and improved kinetics of tumor growth and metastatic foci formation appeared more consistently and at a faster rate in NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) versus NOD/SCID mice. For in vivo detection of small tumor burden at study initiation and metastatic lesions over time, TMD231 breast cancer cells were transduced with lentiviral vectors that express either mCherry or E2-Crimson fluorescent proteins (FPs). Flow cytometric analysis indicated transduction efficiencies for the lentiviral vectors expressing mCherry and E2-Crimson in the TMD231 cells was &gt;99% and &gt;80%, respectively. TMD231 cells expressing either the mCherry or E2-Crimson FPs were implanted into NSG mice and were imaged weekly using the Optix MX3 (ART Technologies, Montreal, Canada) to assess to what degree fluorescently tagged cells could be longitudinally and non-invasively visualized at primary and secondary sites within the NSG mice. While photon emission from TMD231 tumors expressing mCherry could be detected, levels were low and did not correlate with tumor growth overtime. In contrast, high levels of photon emission were detected using TMD231-E2-Crimson cells. Non-palpable tumors expressing the E2-Crimson FP could be detected in NSG mice as early as 7 days post-implant into the mammary fat pad. Additionally, metastatic foci in the lung were detected via optical imaging as early as 2-3 weeks post-implant. Following imaging analysis, TMD231-E2-Crimson tumor size correlated to increased fluorescent intensity, tumor depth, and fluorescent concentration longitudinally. In vitro imaging analysis of TMD231-E2-Crimson cells confirmed the in vivo imaging results showing a linear relationship between cell number and fluorescent intensity. The discrepancy in the in vivo detection of mCherry versus E2-Crimson proteins is most likely due to the greater brightness of E2-Crimson, as well as the closer alignment of the excitation/emission spectra of E2-Crimson with the laser/filter set of the Optix MX3 imaging system. To confirm optical imaging results, H&E staining indicated the presence of numerous foci in the lungs post-mortem. The optimized orthotopic model described here is being used to investigate mechanisms of metastasis as well as novel therapeutic strategies in metastatic breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1409. doi:1538-7445.AM2012-1409

Virtual screening targeting the urokinase receptor, biochemical and cell-based studies, synthesis, pharmacokinetic characterization, and effect on breast tumor metastasis

Virtual screening targeting the urokinase receptor (uPAR) led to (±)-3-(benzo[d][1,3]dioxol-5-yl)-N-(benzo[d][1,3]dioxol-5-ylmethyl)-4-phenylbutan-1-amine 1 (IPR-1) and N-(3,5-dimethylphenyl)-1-(4-isopropylphenyl)-5-(piperidin-4-yl)-1H-pyrazole-4-carboxamide 3 (IPR-69). Synthesis of an analogue of 1, namely, 2 (IPR-9), and 3 led to breast MDA-MB-231 invasion, migration and adhesion assays with IC(50) near 30 μM. Both compounds blocked angiogenesis with IC(50) of 3 μM. Compounds 2 and 3 inhibited cell growth with IC(50) of 6 and 18 μM and induced apoptosis. Biochemical assays revealed leadlike properties for 3, but not 2. Compound 3 administered orally reached peak concentration of nearly 40 μM with a half-life of about 2 h. In NOD-SCID mice inoculated with breast TMD-231 cells in their mammary fat pads, compound 3 showed a 20% reduction in tumor volumes and less extensive metastasis was observed for the treated mice. The suitable pharmacokinetic properties of 3 and the encouraging preliminary results in metastasis make it an ideal starting point for next generation compounds.

Impact of APE1/Ref-1 redox inhibition on pancreatic tumor growth

Pancreatic cancer is especially a deadly form of cancer with a survival rate less than 2%. Pancreatic cancers respond poorly to existing chemotherapeutic agents and radiation, and progress for the treatment of pancreatic cancer remains elusive. To address this unmet medical need, a better understanding of critical pathways and molecular mechanisms involved in pancreatic tumor development, progression, and resistance to traditional therapy is therefore critical. Reduction-oxidation (redox) signaling systems are emerging as important targets in pancreatic cancer. AP endonuclease1/Redox effector factor 1 (APE1/Ref-1) is upregulated in human pancreatic cancer cells and modulation of its redox activity blocks the proliferation and migration of pancreatic cancer cells and pancreatic cancer-associated endothelial cells in vitro. Modulation of APE1/Ref-1 using a specific inhibitor of APE1/Ref-1's redox function, E3330, leads to a decrease in transcription factor activity for NFκB, AP-1, and HIF1α in vitro. This study aims to further establish the redox signaling protein APE1/Ref-1 as a molecular target in pancreatic cancer. Here, we show that inhibition of APE1/Ref-1 via E3330 results in tumor growth inhibition in cell lines and pancreatic cancer xenograft models in mice. Pharmacokinetic studies also show that E3330 attains more than10 μmol/L blood concentrations and is detectable in tumor xenografts. Through inhibition of APE1/Ref-1, the activity of NFκB, AP-1, and HIF1α that are key transcriptional regulators involved in survival, invasion, and metastasis is blocked. These data indicate that E3330, inhibitor of APE1/Ref-1, has potential in pancreatic cancer and clinical investigation of APE1/Ref-1 molecular target is warranted.

Abstract 2543: Humanized bone-marrow mouse model as a pre-clinical tool to assess therapy-mediated hematotoxicity

Murine xenograft models are one of the primary tools used for screening of new therapeutic compounds and regimens. However, one major limitation of utilizing murine xenograft studies to assess therapeutic efficacy is that significant inter-species differences in drug sensitivity can exist between mice and humans. It is possible that the levels of a therapeutic compound reached in a mouse xenograft model may not be achievable in humans due to differential toxicity profiles. There is a growing need for in vivo models that can simulate efficacy of promising therapeutic regimens but at the same time can evaluate the potential for off-target human toxicity. Since bone-marrow toxicity can be a major life-threatening side effect of treatment, models to screen for the impact of treatment on human hematopoiesis would improve our ability to select compounds with decreased off-target toxicities. In this study, a xenograft model containing humanized bone marrow is utilized as an in vivo assay to monitor hematotoxicity. As a proof-of-concept, the impact of a combination therapy consisting of O6-benzylguanine and temozolomide (O6-BG/TMZ) on human hematopoiesis in vivo was investigated since this regimen is currently being evaluated in clinical trials and the main dose-limiting toxicity in these patients is myelosuppression. A dose-intensive O6-BG/TMZ-dosing regimen that requires stem-cell rescue was developed that significantly inhibits the growth of human-glioblastoma xenografts in NOD/SCID/γchainnull mice. To monitor human hematotoxicity profiles, NOD/SCID/gammanull mice were next transplanted with human CD34+ cells and reconstitution confirmed one month post-transplantation by peripheral blood analysis. The dose-intensive regimen was then administered to NOD/SCID/gammanull mice reconstituted with human hematopoietic cells and the impact of treatment on human hematopoiesis evaluated. Flow cytometric analyses indicated that the human bone-marrow cells were significantly more sensitive to treatment than the murine bone-marrow cells in vivo, and that the regimen was highly toxic to human-derived hematopoietic cells of all lineages (CD34+ progenitor, CD45+CD19+ lymphoid, and CD33+ myeloid). This proof-of-concept study indicates that use of NOD/SCID/γchainnull mice with humanized bone marrow can be used as an in vivo toxicity measure of human hematopoiesis. This model holds promise as a new approach for monitoring the impact of anti-cancer therapies on human hematopoiesis and could lead to subsequent refinement of therapies prior to clinical evaluation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2543. doi:10.1158/1538-7445.AM2011-2543

Humanized bone marrow mouse model as a preclinical tool to assess therapy-mediated hematotoxicity

PURPOSE

Preclinical in vivo studies can help guide the selection of agents and regimens for clinical testing. However, one of the challenges in screening anticancer therapies is the assessment of off-target human toxicity. There is a need for in vivo models that can simulate efficacy and toxicities of promising therapeutic regimens. For example, hematopoietic cells of human origin are particularly sensitive to a variety of chemotherapeutic regimens, but in vivo models to assess potential toxicities have not been developed. In this study, a xenograft model containing humanized bone marrow is utilized as an in vivo assay to monitor hematotoxicity.

EXPERIMENTAL DESIGN

A proof-of-concept, temozolomide-based regimen was developed that inhibits tumor xenograft growth. This regimen was selected for testing because it has been previously shown to cause myelosuppression in mice and humans. The dose-intensive regimen was administered to NOD.Cg-Prkdc(scid)IL2rg(tm1Wjl)/Sz (NOD/SCID/γchain(null)), reconstituted with human hematopoietic cells, and the impact of treatment on human hematopoiesis was evaluated.

RESULTS

The dose-intensive regimen resulted in significant decreases in growth of human glioblastoma xenografts. When this regimen was administered to mice containing humanized bone marrow, flow cytometric analyses indicated that the human bone marrow cells were significantly more sensitive to treatment than the murine bone marrow cells and that the regimen was highly toxic to human-derived hematopoietic cells of all lineages (progenitor, lymphoid, and myeloid).

CONCLUSIONS

The humanized bone marrow xenograft model described has the potential to be used as a platform for monitoring the impact of anticancer therapies on human hematopoiesis and could lead to subsequent refinement of therapies prior to clinical evaluation.

Preclinical activity of a novel multiple tyrosine kinase and aurora kinase inhibitor, ENMD-2076, against multiple myeloma

ENMD-2076 is a novel, orally-active molecule that has been shown to have significant activity against aurora and multiple receptor tyrosine kinases. We investigated the activity of ENMD-2076 against multiple myeloma (MM) cells in vitro and in vivo. ENMD-2076 showed significant cytotoxicity against MM cell lines and primary cells, with minimal cytotoxicity to haematopoietic progenitors. ENMD-2076 inhibited the phosphoinositide 3-kinase/AKT pathway and downregulated survivin and X-linked inhibitor of apoptosis as early as 6 h after treatment. With longer treatment (24-48 h), ENMD-2076 also inhibited aurora A and B kinases, and induced G(2)/M cell cycle arrest. In non-obese diabetic/severe combined immunodeficient mice implanted with H929 human plasmacytoma xenografts, oral treatment with ENMD-2076 (50, 100, 200 mg/kg per day) resulted in a dose-dependent inhibition of tumour growth. Immunohistochemical staining of excised tumours showed significant reduction in phospho-Histone 3 (pH3), Ki-67, and angiogenesis, and also a significant increase in cleaved caspase-3 at all dose levels compared to tumours from vehicle-treated mice. In addition, a significant reduction in p-FGFR3 was observed on Western blot. ENMD-2076 shows significant activity against MM cells in vitro and in vivo, and acts on several pathways important for myeloma cell growth and survival. These results provide preclinical rationale for clinical investigation of ENMD-2076 in MM.

Abstract 5373: Modulation of temozolomide-mediated DNA damage in glioblastoma multiforme by the HDM2 antagonist, nutlin3

Development of efficacious strategies for eradication of glioblastoma multiforme (GBM) remains a significant challenge. While treatment of GBM with radiation and temozolomide (TMZ) has improved clinical outcome, lack of long-term efficacy can be due to the ability of GBM to acquire resistance to therapy by modulation of signaling pathways that control DNA repair and cell survival. The HDM2 antagonist, Nutlin3, blocks interactions of HDM2 with key signaling molecules such as p53, p73α, and HIF1α, and modulates their downstream effector function. A panel of human GBM cell lines is currently being used to monitor the extent to which Nutlin3 can sensitize cells to TMZ. In vitro survival assays indicate that Nutlin3 potentiates TMZ-mediated cell death; analysis of cell survival data using Dose Effect CalcuSyn software indicates that the combination index value was &lt; 1 and indicative of a synergistic effect between Nutlin3 and TMZ. Western analyses of p53 wild-type GBM indicated increased p53 stabilization and activation of down-stream targets in cells treated with the combination of Nutlin3/TMZ compared to vehicle, TMZ, or Nutlin3. In addition, time-course studies indicated that U87-MG cells treated with Nutlin3/TMZ in comparison to single agent resulted in increased γ-H2AX and DNA-strand breaks. Efficacy studies using ectopic U87-MG xenografts indicated that 2 cycles of 5-consecutive days of Nutlin3/TMZ led to a significant decrease in tumor growth compared to vehicle or single agent (p &lt; 0.001) with no signs of off-target toxicity. Regulation of DNA repair was further analyzed using the primary GBM.10 line that when grown as an ectopic xenograft, expresses the direct-reversal repair protein, O6-methylguanine DNA methyltransferase (MGMT) and proteins involved in base-excision repair (BER). In vivo target-validation studies using GBM.10 xenografts confirmed that repair of TMZ-mediated DNA damage is modulated in the presence of Nutlin3. GBM.10 xenografts were treated with vehicle, TMZ, nutlin3, or TMZ/Nutlin3 and modulation of critical targets determined by Western analyses. Increases in total p53, p53 phosphorylated at residue serine16, p73α, and substantial decreases in MGMT and the BER protein, APE-1, were observed following treatment with Nutlin3/TMZ compared to vehicle or single-agent exposure. Busso et al (Oncogene 2009) recently reported that HDM2 can monoubiquitinate APE-1 leading to proteosomal-mediated degradation. In addition, recombinant activity assays in our laboratory indicate that HDM2 directly monoubiquitinates recombinant MGMT and may play a role in its degradation. These data suggest that DNA repair proteins required for repair of TMZ-mediated DNA damage can be downregulated by altering HDM2-mediated signaling. Combination therapy that targets the p53-HDM2 E3 ligase network and DNA repair represents a novel approach towards improving treatment of GBM.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5373.

Abstract 1954: Human circulating progenitor cells of hematopoietic origin promote tumor growth in melanoma xenograft models

The tumor microenvironment contains various cell sub-populations of hematopoietic and endothelial origin. These cells are recruited by the tumor and can play an integral role in regulating tumor growth and metastasis. However, the heterogeneity of these cells has made it difficult to study their specific function in tumorigenesis. We recently developed a detailed polychromatic flow cytometric (PFC) protocol to isolate and characterize the phenotype of the hematopoietic versus endothelial circulating progenitor cells (CPCs) found in peripheral blood (PB). Transplantation of CPC populations into NOD/SCID mice indicated that a purported endothelial CPC subset largely consisted of in vivo engrafting hematopoietic stem cells and myeloblasts, and not endothelial cells. Additionally, our recent PFC studies indicate that hematopoietic CPCs can be subdivided into two cell populations based upon AC133 expression (ViViD−CD14−glyA−CD34+AC133+CD45dimCD31+ and ViViD−CD14−glyA−CD34+AC133−CD45dimCD31+ cells), and will be referred to as primitive CPCs and mature CPCs respectively. To date, the functional role of hematopoietic CPCs in tumor growth is not known. We hypothesize that primitive CPCs home to the tumor bed and secrete pro-angiogenic factors to promote tumor growth. To address this hypothesis, we have developed two in vivo modeling approaches. In the first approach, primitive and mature CPCs were isolated from umbilical cord blood CD34+ cells and intravenously injected into NOD/SCID mice harboring C32 human melanoma xenografts that secrete high levels of vascular endothelial growth factor. Tumor growth was monitored for 7 weeks and a statistically significant increase in melanoma growth and weight was observed in mice injected with the primitive CPCs compared to control mice (p&lt;0.001, primitive CPCs vs mature CPCs, phosphate buffered saline or non-sorted CD34+ cells). Histological analyses did not detect human CD34+, AC133+, or CD31+ cells in the tumor xenograft tissue at week 7. Time-course studies are in progress to determine if human hematopoietic cells can be found in the tumor bed during the early stages of tumor growth. In the second approach, sub-lethally irradiated NOD/SCID mice were first transplanted with human CD34+ cells and detectable levels of primitive CPCs in the PB were observed at one month post-transplantation. C32 melanoma cells were then injected subcutaneously into the flank and tumor growth monitored. At 3-4 weeks post-tumor implantation, melanoma xenografts began to grow more rapidly in mice previously transplanted with human CD34+ cells compared to melanoma xenografts in sub-lethally irradiated, non-transplanted mice. Taken together, these data indicate that primitive human CPCs of hematopoietic origin play a functional role in tumorigenesis and the in vivo models developed here can be used to delineate how hematopoietic CPCs regulate tumor progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1954.

c-FLIP gene silencing eliminates tumor cells in breast cancer xenografts without affecting stromal cells

Cellular FLICE-like inhibitory protein (c-FLIP) is an inhibitor of death receptor-mediated apoptosis and exerts its anti-apoptotic function by blocking the activation of caspase-8. We recently showed that the siRNA-mediated knockdown of c-FLIP in MCF-7 breast cancer cells growing in vitro triggered apoptosis. The aim of this study was to determine if the in vivo knockdown of c-FLIP in MCF-7 breast cancer xenografts affected tumor viability. Immunohistochemical detection of c-FLIP in the tumor sections revealed that the knockdown of c-FLIP eliminated the neoplastic cells within the breast cancer xenografts without affecting the normal stromal and fibroblastic cells. These results indicate that c-FLIP is required for breast cancer growth and is a relevant therapeutic target for the treatment of breast cancer.

Enhanced homing and engraftment of fresh but not ex vivo cultured murine marrow cells in submyeloablated hosts following CD26 inhibition by Diprotin A

OBJECTIVE

We recently reported that murine marrow cultured ex vivo for gamma-retrovirus transduction engrafts approximately 10-fold less well than fresh marrow upon transplantation into submyeloablated hosts. Here, we evaluated homing efficiency as a potential mechanism for this engraftment disparity, and whether CD26 inhibition with the tripeptide Diprotin A (DipA) would enhance engraftment of ex vivo cultured cells in submyeloablated hosts.

MATERIALS AND METHODS

Homing and engraftment of fresh and ex vivo cultured lineage-negative (lin(-)) marrow cells in submyeloablated congenic hosts with and without DipA treatment was evaluated. Expression of CXCR4 and CD26 on fresh and cultured lin(-) marrow cells was compared.

RESULTS

Homing of lin(-) cells cultured for gamma-retrovirus transduction was at least threefold less than that of fresh lin(-) cells 20 hours after transplantation into submyeloablated hosts. DipA treatment of fresh lin(-) cells resulted in at least twofold increased homing and engraftment in submyeloablated hosts. DipA treatment, however, did not significantly improve homing or engraftment of cells undergoing a 3-day culture protocol for gamma-retrovirus transduction in submyeloablated hosts. CXCR4 expression on lin(-) cells was significantly decreased following 3 days of culture; CXCR4 expression was not significantly altered following overnight culture.

CONCLUSIONS

Ex vivo culture of lin(-) cells for gamma-retroviral transduction downregulates CXCR4 expression and markedly impairs homing and engraftment of murine lin(-) marrow in submyeloablated hosts. While inhibition of CD26 activity with DipA increases homing and engraftment of fresh lin(-) cells, DipA treatment does not improve homing and engraftment of cultured lin(-) marrow cells in submyeloablated congenic hosts.

In vivo selection of hematopoietic stem cells transduced at a low multiplicity-of-infection with a foamy viral MGMT(P140K) vector

OBJECTIVE

Using a clinically relevant transduction strategy, we investigated to what extent hematopoietic stem cells in lineage-negative bone marrow (Lin(neg) BM) could be genetically modified with an foamy virus (FV) vector that expresses the DNA repair protein, O(6)-methylguanine DNA methyltransferase (MGMT(P140K)) and selected in vivo with submyeloablative or myeloablative alkylator therapy.

MATERIALS AND METHODS

Lin(neg) BM was transduced at a low multiplicity-of-infection with the FV vector, MD9-P140K, which coexpresses MGMT(P140K) and the enhanced green fluorescent protein, transplanted into C57BL/6 mice, and mice treated with submyeloablative or myeloablative alkylator therapy. The BM was analyzed for the presence of in vivo selected, MD9-P140K-transduced cells at 6 months post-transplantation and subsequently transplanted into secondary recipient animals.

RESULTS

Following submyeloablative therapy, 55% of the mice expressed MGMT(P140K) in the BM. Proviral integration was observed in approximately 50% of committed BM-derived progenitors and analysis of proviral insertion sites indicated up to two integrations per transduced progenitor colony. Transduced BM cells selected with submyeloablative therapy reconstituted secondary recipient mice for up to 6 months post-transplantation. In contrast, after delivery of myeloablative therapy to primary recipient mice, only 25% survived. Hematopoietic stem cells were transduced because BM cells from the surviving animals reconstituted secondary recipients with MGMT(P140K)-positive cells for 5 to 6 months.

CONCLUSIONS

In vivo selection of MD9-P140K-transduced BM cells was more efficient following submyeloablative than myeloablative therapy. These data indicate that a critical number of transduced stem cells must be present to produce sufficient numbers of genetically modified progeny to protect against acute toxicity associated with myeloablative therapy.

A novel competitive repopulation strategy to quantitate engraftment of ex vivo manipulated murine marrow cells in submyeloablated hosts

OBJECTIVE

Standard competitive repopulation assays have proven valuable in evaluating engraftment potential in ablated hosts, permitting comparisons between various test cell populations. However, no similar method exists to compare engraftment of test cells in submyeloablated hosts, which would be helpful given the applications of reduced-intensity conditioning for hematopoietic gene-replacement therapy and other cellular therapies. Here, we developed a novel assay to quantitate engraftment of hematopoietic stem cells in submyeloablated hosts.

MATERIALS AND METHODS

Engraftment of murine marrow cells transduced with retroviral vectors using two separate protocols was compared to engraftment of fresh untreated competitor cells within low-dose radiation-conditioned hosts using a "three-way" marking system, so that test, competitor, and host cell chimerism could be reliably determined posttransplantation.

RESULTS

We demonstrate that the repopulating ability of marrow cells transduced using two distinct protocols was reduced approximately 10-fold compared to fresh competitor cells in submyeloablated hosts utilizing the novel "three-way" transplant assay.

CONCLUSIONS

Murine marrow cells transduced using a clinically applicable protocol acquire an engraftment defect in submyeloablated hosts, similar to cells transduced using a research protocol. We conclude that the submyeloablative competitive repopulation assay described here will be of benefit to comparatively assess the engraftment ability of manipulated hematopoietic stem cells using various culture protocols, such as to test the impact of modifications in transduction protocols needed to attain therapeutic levels of gene-corrected blood cells, or the effect of ex vivo expansion protocols on engraftment potential.

Granulocyte colony-stimulating factor prior to nonmyeloablative irradiation decreases murine host hematopoietic stem cell function and increases engraftment of donor marrow cells

The use of nonmyeloablative conditioning prior to bone marrow transplantation is an important component of transplantation-based therapies for nonmalignant blood diseases. In this study, treatment of recipient mice with granulocyte colony-stimulating factor (G-CSF) prior to low-dose total body irradiation (LD-TBI) enhanced long-term engraftment of freshly isolated congenic marrow 1.5- to 2-fold more than treatment with LD-TBI alone. This combined regimen was also evaluated in a mouse model of X-linked chronic granulomatous disease (X-CGD), where neutrophils have a defective NADPH oxidase due to genetic deletion of the gp91(phox) subunit. Long-term engraftment of male X-CGD bone marrow cells cultured ex vivo for retroviral transduction of gp91(phox) was enhanced by approximately 40% when female X-CGD recipients were pretreated with G-CSF prior to 300 cGy. These data confirm that sequential treatment with G-CSF and LD-TBI prior to transplantation increases long-term engraftment of donor marrow, and they extend this approach to transplantation of murine donor marrow cultured ex vivo for gene transfer. Additional studies showed that the administration of G-CSF prior to LD-TBI did not alter early homing of donor marrow cells. However, the combined regimen significantly decreased the content of long-term repopulating cells in recipient marrow compared with LD-TBI alone, as assessed in competitive assays, which may contribute to the enhanced engraftment of donor marrow cells. Disclosure of potential conflicts of interest is found at the end of this article.