Tissue-specific thresholds of mutation burden associated with anti-PD-1/L1 therapy benefit and prognosis in microsatellite-stable cancers

Immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 or its ligand (PD-1/L1) have expanded the treatment landscape against cancers but are effective in only a subset of patients. Tumor mutation burden (TMB) is postulated to be a generic determinant of ICI-dependent tumor rejection. Here we describe the association between TMB and survival outcomes among microsatellite-stable cancers in a real-world clinicogenomic cohort consisting of 70,698 patients distributed across 27 histologies. TMB was associated with survival benefit or detriment depending on tissue and treatment context, with eight cancer types demonstrating a specific association between TMB and improved outcomes upon treatment with anti-PD-1/L1 therapies. Survival benefits were noted over a broad range of TMB cutoffs across cancer types, and a dose-dependent relationship between TMB and outcomes was observed in a subset of cancers. These results have implications for the use of cancer-agnostic and universal TMB cutoffs to guide the use of anti-PD-1/L1 therapies, and they underline the importance of tissue context in the development of ICI biomarkers.

Differential landscape of immune evasion in oncogenic RAS-driven primary and metastatic colorectal cancers

Oncogenic drivers such as KRAS extensively modulate the tumor inflammatory microenvironment (TIME) of colorectal cancer (CRC). The influence of KRAS on modulating immune cell composition remains unclear. The objective of this study was to identify signatures of infiltrative immune cells and distinctive patterns that differ between RAS wild-type (WT) and oncogenic mutant (MT) CRC that explain immune evasion in MT tumors. A total of 7,801 CRC specimens were analyzed using next-generation DNA sequencing, whole-exome sequencing, and/or whole transcriptome sequencing. Deficiency of mismatch repair (dMMR)/microsatellite instability (MSI) and tumor mutation burden (TMB) were also assessed. KRAS mutations were present in 48% of CRC, similarly distributed in patients younger than vs. 50 years and older. In microsatellite stable (MSS) KRAS MT tumors, composition of the TIME included higher neutrophil infiltration and lower infiltration of B cells. MSI-H/dMMR was significantly more prevalent in RAS WT (9.1%) than in KRAS MT (2.9%) CRC. In MSS CRC, TMB-high cases were significantly higher in RAS MT (3.1%) than in RAS WT (2.1%) tumors. KRAS and NRAS mutations are associated with increased neutrophil infiltration, with codon-specific differences. These results demonstrate significant differences in the TIME of RAS mutant CRC that match previous reports of immunoevasive characteristics of such tumors.

Abstract 3241: IC50-Seeding Density Slope (ISDS)-measurement as a standardized methodology for assessing anti-cancer therapeutic activity in vitro

The 50% inhibitory concentration (IC50) is a widely used measure of how effective a given anti-cancer therapeutic is at reducing cancer cell viability in vitro. It is known that IC50 of a given therapeutic agent is dependent on the seeding density of the treated cells (in that more densely-seeded cells tend to be more resistant to therapeutic agents). We performed experiments using the CellTiter Glo cell viability assay to assess the cytotoxicity of various chemotherapeutic drugs towards various cancer cell lines. To elucidate the role the extracellular environment of densely-seeded cells plays in cancer cell chemoresistance, we tested conditioned media from cells cultured at high density on cells seeded at low densities. The resulting impact on the IC50 of the low-density cells was determined. The IC50 of the various therapeutic agents tested was cell density-dependent in each cancer cell line examined. Based on this analysis, we propose the IC50-seeding density slope (ISDS), which relates seeding density to the effectiveness of a drug and that we believe could be a standardized quantitative measurement of how a given cancer cell line responds to a given therapeutic treatment. Our results from the conditioned media experiments consistently indicated that the environment of densely-seeded tumor cells conferred chemoresistance to sparsely-seeded cells, suggesting that extracellular cytokines and growth factors may be involved in density-dependent chemoresistance mechanisms. We are currently exploring the effect of serum deprivation on in vitro chemoresistance, in order to further understand how the presence of extracellular nutrients impacts observed IC50 trends. In addition, we are examining the role that cell-cell contact, integrin and FGF signaling pathways play in giving rise to density-dependent chemoresistance. Moreover, to analyze the manner in which conditioned media gives rise to chemoresistance and how this effect relates to intracellular survival pathways, we are performing cytokine profiling experiments. Overall, we describe density-dependent IC50 variations as a hallmark of cancer cells and propose that ISDS may serve as a standardized method of assessing chemosensitivity.

Citation Format: Ujwal Punyamurtula, Shengliang Zhang, Thomas Brown, Arielle De La Cruz, Alexander Raufi, Jillian Strandberg, Lindsey Carlsen, Lanlan Zhou, Wafik El-Deiry. IC50-Seeding Density Slope (ISDS)-measurement as a standardized methodology for assessing anti-cancer therapeutic activity in vitro [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 3241.

Abstract 4166: Small-molecule inhibition of glycogen synthase kinase-3 (GSK-3) increases the efficacy of anti-PD-L1 therapy in a murine model of microsatellite stable colorectal cancer (CRC); Therapeutic response correlates with T cell ratios and serum cytokine profiles in mice

Immune checkpoint blockade (ICB) with αPD-1/PD-L1 has impressive efficacy in microsatellite unstable (MSI+) CRC but no significant activity in the 85% of CRC cases that are microsatellite stable (MSS). Our group previously demonstrated that 9-ING-41, a small-molecule inhibitor of GSK-3 in clinical development, stimulates both NK and T cell activity. This project characterizes the effects of 9-ING-41 in combination with ICB in vivo. In a syngeneic murine colon carcinoma BALB/c model using MSS cell line CT-26, we compared isotype, 9-ING-41 (70 mg/kg 2x/wk), αPD-1 (10 mg/kg 2x/wk), αPD-L1 (10 mg/kg 2x/wk), 9-ING-41 + αPD-1, and 9-ING-41 + αPD-L1 treatment groups. The median overall survival was 19 days (d) with 9-ING-41 (hazard ratio for death (HR) 0.12; 95% confidence interval (CI), 0.03-0.54; p=0.008), 16 d for 9-ING-41 + isotype (HR 0.40; 95% CI, 0.08-1.9; p=0.14), 20.5 d for αPD-1 (HR 0.15; 95% CI, 0.03-0.67; p=0.0185), 18 d for αPD-L1 (HR 0.21; 95% CI, 0.05-0.89; p=0.0559), 17 d for 9-ING-41 + αPD-1 (HR 0.37; 95% CI, 0.09-0.1.5; p=0.29), and 45.5 d for 9-ING-41 + αPD-L1 (HR 0.08; 95% CI, 0.02-0.36; p=0.0019), compared to 16 d for the isotype control group. Tumor response rates observed were 33.3% in the 9-ING-41 + αPD-L1 group, 16.6% in the αPD-1 group, and a 0% for all other treatment groups. We hypothesize that the 9-ING-41-mediated upregulation of PD-L1 in CRC cells (HCT-116, HT-29) observed via both flow cytometry (FC) and western blot analysis may contribute to the increased efficacy of combination therapy with αPD-L1, as compared to αPD-1. Significant differences between responders and non-responders in intratumoral and splenic natural killer (NK) and T cell subsets 14-days post-treatment initiation were shown by multi-color FC. Compared to non-responders, regardless of treatment group, responders had lower percentages of splenic CD4+ (p=0.0145) and CD8+ T cells (p=0.0001), increased percentages of splenic CD69+ activated T cells (p=0.0070) and FOXP3+ regulatory T cells (p=0.001), and increased percentages of tumor-infiltrating CD3+ (p=0.0006) and CD4+ T cells (p<0.0001). Responders had lower splenic CD8+/Treg (p=0.0007) and CD4+/Treg (p=0.001) ratios and higher intra-tumoral CD8+/Treg (p=0.0032) and CD4+/Treg (p=0.0001) ratios. Murine serum cytokine profiling showed that responders had lower concentrations of tumorigenic cytokines (BAFF, CCL7, CCL12, VEGF, VEGFR2, CCL21) and higher concentrations of immunomodulatory cytokines (CCL4, TWEAK, GM-CSF, CCL22, IL-12p70) compared to non-responders. These results demonstrate that small-molecule inhibition of GSK-3 with 9-ING-41 may increase the anti-tumor effects of ICB and improve response in patients with MSS CRC via modulation of anti-tumor immunity and cytokine signaling.

Citation Format: Kelsey E. Huntington, Anna Louie, Lanlan Zhou, Benedito A. Carneiro, Wafik El-Deiry. Small-molecule inhibition of glycogen synthase kinase-3 (GSK-3) increases the efficacy of anti-PD-L1 therapy in a murine model of microsatellite stable colorectal cancer (CRC); Therapeutic response correlates with T cell ratios and serum cytokine profiles in mice [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 4166.

Abstract 2593: Combined ATR+PARP inhibition exhibits potent synergy in colorectal and pancreatic cancer cytotoxicity

Precision medicine continues to expand treatment options for patients tailored to tumor phenotype. In homologous recombination (HR) deficient cancers like those with BRCA1/2-mutations, inhibition of poly (ADP-ribose) polymerase (PARP) has shown improved mortality compared to older gold standard therapies like DNA damaging agents. Unfortunately estimates upward of 40% of patients develop resistance to PARP inhibitor monotherapy during the course of their treatment. We explored potential synergistic drug combinations to re-sensitize tumors with acquired PARP inhibitor resistance in pancreatic and colorectal cancer. We hypothesized that dual inhibition of the DDR pathway through PARP and Ataxia telangiectasia and Rad3 related (ATR) inhibition would combine synergistically especially in cell lines with existing HR deficiencies through a synthetic lethality-mediated response. The ATR inhibitor Ceralasertib was selected for its potent antagonism of the DDR pathway, a key pathway associated with cell survival through DNA repair. Pancreatic and colorectal cell lines were carefully selected based on their varying mutational profiles to study differences in response to dual treatment. CellTiter-Glo® (CTG) was used after drug treatment to quantify IC-50. CTG synergy and combination indices were used to study drug combinations, and western blotting identified changes in protein expression among key mediators of cell survival and apoptosis. Colony forming assays and cytokine profiling using Luminex technology (and single cell cytokine profiling) were performed to study changes within the tumor microenvironment. We observed strong synergy and cytotoxicity in addition to increased apoptosis and cellular disassembly following treatment with dual ATR+PARP inhibition compared to monotherapy alone. Western Blot showed upregulation of cleaved PARP and cleaved Caspase 8 with combination therapy, and cytokine profiles provided insights into immune-suppressive versus stimulatory TME after drug treatment. There is potent synergy when ATR inhibitors are added to PARPi therapy in the context of pancreatic and colorectal cancers. Ongoing research efforts are further characterizing the mechanisms underlying these observed synergies in the same and additional tumor types such as prostate and ovarian cancer.

Citation Format: Anna M. Ochsner, Kelsey E. Huntington, Lanlan Zhou, Benedito Carneiro, Wafik El-Deiry. Combined ATR+PARP inhibition exhibits potent synergy in colorectal and pancreatic cancer cytotoxicity [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 2593.

Abstract 1823: Imipridones show pre-clinical efficacy in MYCN-amplified and MYCN non-amplified neuroblastoma cell lines

Neuroblastoma is the most common extracranial solid tumor of childhood, accounting for 15% of all pediatric cancer-related deaths, with around 63% survival for high-risk patients. Treatment remains limited for advanced disease, calling for the development of novel therapies. We investigated the anti-tumor effect of three imipridones (ONC201, ONC206, and ONC212), a promising new class of small molecules, in the treatment of neuroblastoma. Imipridones are potent anticancer drugs that have previously shown efficacy for a variety of adult and pediatric malignancies. ONC201 and ONC206 are antagonists of dopamine receptor D2 (DRD2), while ONC212 is an agonist of GPR132, both of which are overexpressed in many cancers. We performed drug treatment with ONC201, ONC206, and ONC212 on established MYCN-amplified SK-N-BE(2) and MYCN non-amplified SH-SY5Y pediatric neuroblastoma cell lines in vitro. Cell viability assays were performed 72 hours post-treatment to generate dose responses curves. The IC50s for ONC201, ONC206, and ONC212 were 17.82 uM, 547 nM, and 70 nM for SK-N-BE(2), and 997 nM, 314 nM, and 6 nM for SH-SY5Y. Imipridones demonstrated greater efficacy for the non-MYCN-amplified cell line. Using protein quantification studies and downstream target analysis on drug-treated cells, we investigated the mechanisms of how these therapies caused cell death. We showed that imipridones inactivate cell proliferation kinases Akt/ERK and induce cell death through the pro-apoptotic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). They also induce tumor cell apoptosis by modifying the mitochondrial Clp protease complex, decreasing expression of chaperone subunit ClpX and activating mitochondrial proteolysis. Histone deacetylases (HDACs) play a role in controlling MYCN function, which is amplified in more aggressive neuroblastoma; HDAC activity and MYCN are also upregulated in chemotherapy-resistant neuroblastoma. Cell viability assays with HDAC inhibitors Vorinostat and Panobinostat demonstrated single-agent efficacy in vitro. The IC50s for Vorinostat and Panobinostat were 609 nM and 5.51 nM for SK-N-BE(2), and 884 nM and 6.13 nM for SH-SY5Y. However, further investigation is needed to determine synergy and mechanisms of synergy when histone deacetylase (HDAC) inhibitors are used in novel combinations with imipridones. Overall, our data reveals promise in imipridone therapy for neuroblastoma, and future studies are proposed to explore potential novel therapeutic combinations in this difficult-to-treat pediatric cancer.

Citation Format: Claire Lin, Wen-I Chang, Joshua N. Honeyman, Lanlan Zhou, Varun V. Prabhu, Joshua Allen, Wafik El-Deiry. Imipridones show pre-clinical efficacy in MYCN-amplified and MYCN non-amplified neuroblastoma cell lines [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 1823.

Molecular Targets for Novel Therapeutics in Pediatric Fusion-Positive Non-CNS Solid Tumors

Chromosomal fusions encoding novel molecular drivers have been identified in several solid tumors, and in recent years the identification of such pathogenetic events in tumor specimens has become clinically actionable. Pediatric sarcomas and other rare tumors that occur in children as well as adults are a group of heterogeneous tumors often with driver gene fusions for which some therapeutics have already been developed and approved, and others where there is opportunity for progress and innovation to impact on patient outcomes. We review the chromosomal rearrangements that represent oncogenic events in pediatric solid tumors outside of the central nervous system (CNS), such as Ewing Sarcoma, Rhabdomyosarcoma, Fibrolamellar Hepatocellular Carcinoma, and Renal Cell Carcinoma, among others. Various therapeutics such as CDK4/6, FGFR, ALK, VEGF, EGFR, PDGFR, NTRK, PARP, mTOR, BRAF, IGF1R, HDAC inhibitors are being explored among other novel therapeutic strategies such as ONC201/TIC10.

Abstract 1044: ONC201 as a novel anti-cancer therapeutic via modulation of inhibitors of apoptosis and up-regulation of DR5 in gastric adenocarcinoma

Gastric adenocarcinoma is commonly asymptomatic early in its course, leading to late-stage diagnosis at a time when patients are inoperable. Currently available chemotherapy options are non-targeted and highly toxic, leading to a poor 5-year survival of only 31.5%. ONC201 is a small molecule imipridone anti-cancer therapy discovered by our lab that induces cell death in a variety of malignant tumors via a multitude of mechanisms including activation of the integrated stress response (ISR) leading to up-regulation of TNF-related apoptosis-inducing ligand (TRAIL), which induces apoptosis after binding to the death receptor 5 (DR5). We investigated the ability of ONC201 to induce cell death in gastric adenocarcinoma cells when used in combination with recombinant human TRAIL (rhTRAIL), and its affect on DR5 cell surface expression and expression of inhibitors of apoptosis (IAP) in order to further establish mechanism of action. AGS (caspase 8, KRAS, PIK3CA mutant, HER2 amplified), SNU-1 (KRAS and MLH1 mutant, microsatellite instable), SNU-5 (p53 mutant) and SNU-16 (p53 mutant) gastric adenocarcinoma cell lines were treated with ONC201 and rhTRAIL and viability assays were performed to determine cell line sensitivities. All lines were then treated with combination therapy based on sensitivities and viability assays were performed in order to determine combination indices. Cell death was verified with sub-G1 analysis via flow cytometry and protein expression was established via western blotting. All cell lines exhibited strong synergy in response to dual therapy with ONC201 and rhTRAIL, with combination indices <0.6 at doses that did not induce cell death in normal fibroblast cells. Synergy was confirmed via flow cytometry analysis with increased cells in the sub-G1 phase of the cell cycle with dual therapy in excess of what would be expected from an additive effect. On western blot analysis, apoptosis was confirmed with increased cleavage of PARP, caspase 8 and caspase 3 after dual treatment with ONC201 and rhTRAIL. Flow cytometry revealed increased cell surface expression of DR5 with ONC201 therapy, and western blot analysis showed that ONC201 lead to up-regulation of ATF-4 and CHOP, indicating activation of the ISR, and down-regulation of anti-apoptotic CIAP-2 and XIAP in all cell lines except AGS, as well as FLIP in all cell lines except SNU-16. These in vitro results suggest that ONC201 in combination with rhTRAIL may be an effective and non-toxic option for the treatment of gastric adenocarcinoma by inducing apoptosis via activation of the ISR, increased cell surface expression of DR5 and down-regulation of inhibitors of apoptosis. We are currently applying this regimen to an organoid model, as well as a murine sub-cutaneous xenograft model using AGS and SNU-1 cells.

Citation Format: Cassandra Susan Parker, Lanlan Zhou, Varun Prabhu, Josh Allen, Wafik El-Deiry. ONC201 as a novel anti-cancer therapeutic via modulation of inhibitors of apoptosis and up-regulation of DR5 in gastric adenocarcinoma [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 1044.

HGG-42. PEDIATRIC H3K27M MUTANT DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG) SHOWS ROBUST RESPONSE TO IMIPRIDONE BASED COMBINATION THERAPY

ONC201 is a first-in-class small molecule imipridone therapy, which is known to selectively induce apoptosis of cancer cells independent of p53. This novel chemotherapeutic, as well as its analogs ONC206 and ONC212, has been shown to have potent preclinical efficacy against H3K27M mutant diffuse intrinsic pontine glioma (DIPG). We sought to identify synergy between imipridones and other FDA-approved chemotherapeutics. Seven patient-derived DIPG cell lines, six H3.3K27M mutant (SU-DIPG-IV, SU-DIPG-13, SU-DIPG-25, SUDIPG-27, SU-DIPG-29, SF8628), and one H3.1K27M mutant (SU-DIPG-36) were grown in culture and exposed to first and second generation imipridones, both as monotherapies and in combination with histone de-acetylase inhibitors [HDACi], Marizomib, Etoposide, and Temozolomide. A dose dependent response was demonstrated across all cell lines, with increased potency of ONC206 and ONC212 as compared to ONC201, with half maximal inhibitory concentration (IC₅₀) of 0.11 µM, 0.03 µM, and 1.46 µM respectively. Strong synergy is demonstrated between ONC201 and Panobinostat with best combination index (CI) of 0.01. ONC201 similarly shows strong synergy with Romidepsin with best CI of 0.02, and Marizomib with best CI of 0.18. Combination of ONC201 and Etoposide or Entinostat shows some synergy, with best CI of 0.53 and 0.71 respectively. When combined with Temozolomide, some synergy is evident, however, there is overall poor efficacy, with lack of cell death even at the highest doses of Temozolomide. Second generation imipridones show a similar pattern of strong synergy with Panobinostat, Romidepsin, and Marizomib. Immunoblotting showed evidence of apoptosis, as measured by the induction of PARP cleavage, with a combination of imipridones and Panobinostat, as well as induction of integrated stress response with a combination of imipridones and Romidepsin. These results are indicative of promising synergy between imipridones and Panobinostat, Romidepsin, or Marizomib against H3K27M mutant DIPG, combinations which should be considered for future clinical trials.

DIPG-62. PRECLINICAL EVALUATION OF IMIPRIDONE-BASED COMBINATION THERAPIES IN PEDIATRIC H3K27M MUTANT DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG)

Imipridones induce apoptosis in cancer via p53 independent upregulation of TNF-related apoptosis inducing ligand (TRAIL) pathway and its proapoptotic receptor DR5. ONC201, a first-in-class imipridone, is being evaluated alone and with radiotherapy for children with H3K27M mutant diffuse glioma. We sought to determine if ONC201 and its imipridone analogs (ONC206, ONC212) are synergistic with other chemotherapy agents. Seven patient-derived DIPG cell lines, six H3.3K27M mutant (SU-DIPG-IV, SU-DIPG-13, SU-DIPG-25, SU-DIPG-27, SU-DIPG-29, SF8628) and one H3.1K27M mutant (SU-DIPG-36) were grown in culture and exposed to ONC201, ONC206, and ONC212 alone and in combination with histone de-acetylase inhibitors (HDACi) or etoposide. A dose-dependent response to ONC201, ONC206, and ONC212 was demonstrated in all cell lines, with mean IC50 values of 1.46 µM, 0.11 µM, and 0.03 µM respectively. ONC206 and ONC212 induced apoptosis measured by increased expression of cleaved PARP and ISR by increased expression ATF4. In two cell lines, synergy studies revealed combination indices (CI) < 1 for ONC206 and etoposide, with a best CI of 0.62 in SU-DIPG-IV and 0.46 in SU-DIPG-25. Synergy was also observed between ONC201 and etoposide (CI 0.46) and ONC201 and panobinostat (CI 0.01). Imipridones and analogs were superior to panobinostat and etoposide in triggering apoptosis as measured by sub-G1 phase content. Additional synergy and mechanistic analyses are ongoing and will be reported. Our results suggest that H3K27M mutant DIPG cells demonstrate increased sensitivity to imipridone analogs (ONC206 and ONC212) when compared to ONC201. Combinational strategies with etoposide or HDACi should be considered for clinical translation.

DDRE-16. SYNERGISTIC TUMOR SUPPRESSION FROM COMBINATION OF ONC201 AND EPIGENETIC MODULATORS EZH2 OR HDAC INHIBITOR PROVIDES A NOVEL TREATMENT STRATEGY FOR GBM AND DMG

ONC201 is a promising anti-cancer agent that kills tumor cells by triggering an integrated stress response (ISR) dependent on ATF4. ONC201 demonstrated tumor regression and prolonged disease stability in patients with histone H3K27M-mutated midline glioma. The Enhancer of Zeste Homolog 2 (EZH2), a subunit of the polycomb repressive complex 2 (PRC2), is a histone methyltransferase that tri-methylates H3K27 (H3K27me3) and silences target genes. EZH2 inhibitors (EZH2i) reduce global H3K27 methylation. Based on the fact that the H3K27 mutation reduces H3K27 dimethylation (H3K27me2) and trimethylation (H3K27me3), we hypothesized that ONC201 sensitivity and tumor cell death may be enhanced by reducing H3K27 methylation with EZH2i as a mimic of H3K27M-mutation and by increasing H3K27 acetylation with histone deacetylase inhibitors (HDACi). We evaluated synergy of EZH2i EPZ-6438 or HDACi vorinostat with ONC201 against GBM cell lines, U251 and T98G-1 and DMG cell line, SF8638. Cell viability was determined with the Cell Titer Glo assay. Apoptosis was evaluated through immunoblotting of cleaved PARP and flow cytometry analysis of cell distribution. ISR activity was evaluated using immunoblotting of ATF4. Our result demonstrate that ONC201 synergistically reduced cell viability with vorinostat in U251, T98G-1 and SF8628 cell lines, induced apoptosis in combination with vorinostat in U251 and SF8628. ONC201 synergistically reduced cell viability and induced apoptosis with EPZ-6438 in U251. The immunoblotting detected no enhancement of ATF4 by addition of EPZ-6438 to ONC201. Immunoblotting analysis showed that EPZ-6438 reduced H3K27me3 in U251. Our results unravel potent synergy between ONC201 and EZH2i or HDACi in GBM and DMG cell lines, and provide further insights into the role of H3K27me3 in ONC201 drug sensitivity.

Abstract 5407: Novel imipridone combination therapies targeting oncohistone H3K27M mutant diffuse midline glioma (DMG)

Malignant glioma including diffuse midline glioma (DMG) is the leading cause of cancer related death in children. Recent advances in sequencing have identified the oncohistone H3K27M mutation in ~80% of pediatric DMG, which represents a target for new therapeutics. ONC201 is a first-in-class small molecule which upregulates TNF-related apoptosis inducing ligand (TRAIL) and its proapoptotic receptor DR5, independent of p53, selecting for apoptosis/growth arrest of many different tumor types including H3K27M mutant DMG. While single agent ONC201 along with RT is currently being tested in clinical trials for newly diagnosed and refractory DMG, there is an urgent need to evaluate ONC201 and other imipridone analogs in combination with other agents. Patient derived H3K27M mutant DMG cell lines (SU-DIPG-IV, SU-DIPG-13, SU-DIPG-25, SU-DIPG-27, SU-DIPG-29, SU-DIPG-36, and SF8628), were grown in culture and exposed to imipridones (ONC201, ONC206 and ONC212) alone, and in combination with other chemotherapeutic agents that have demonstrated pre-clinical activity against DMG (HDAC inhibitors and etoposide). Response to treatment was determined by Cell Titer-Glo cell viability assays as well as Western Immunoblotting for evidence of apoptosis and integrated stress response (ISR) activation. All H3K27M-mutant DMG cell lines tested to date exhibit a dose-dependent response to imipridone therapy. Mean IC50 values were significantly lower with the imipridone analogs ONC206 (0.11 µM) and ONC212 (0.03 µM) as compared to ONC201 (1.46 µM) when used as a single agent. ONC206 and ONC212 were associated with robust induction of apoptosis evidenced by increased expression of cleaved PARP, and ISR by increased expression ATF4. In the SU-DIPG-IV cell line, combination studies of ONC201 and panobinostat demonstrated a synergistic effect of both agents, as calculated by CompuSyn software. Combination indices below one were observed at concentrations of 0.003 - 0.05 µM of panobinostat with ONC201 at 0.156 - 5 µM, with the best combination index of 0.22. We similarly observed synergy between either ONC201 or ONC206 with Etoposide. Additional combination testing and synergy analysis is ongoing and will be presented. Our findings suggest that H3K27M DMG cells demonstrate increased sensitivity to imipridones ONC206 and ONC212 as single agents and combinational strategies with HDAC inhibitors and etoposide, and provide insights into novel therapies for further clinical testing.

Citation Format: Robyn Borsuk, Lanlan Zhou, Rishi Lulla, Wafik El-Deiry. Novel imipridone combination therapies targeting oncohistone H3K27M mutant diffuse midline glioma (DMG) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5407.

Abstract 2959: Glycogen synthase kinase 3-β expression in prostate cancer (PCa) correlates with aggressive pathological features and its blockade with 9-ING-41 inhibits viability of PCa cell lines

Castration-resistant prostate cancer (CRPC) represents a lethal stage of disease with limited treatment options beyond androgen receptor (AR) inhibitors and chemotherapy. GSK-3β is a serine/threonine kinase established as a therapeutic target in several solid tumors. GSK-3β inhibitors reduce prostate cancer cell growth and inhibit AR-V7 transcriptional activity in vitro (Rinnab L et al 2008; Schütz SV et al 2011; Nakata et al 2017). This study aimed to characterize the GSK-3β expression in molecular subtypes of PCa and the antitumor activity of 9-ING-41, a selective small molecule GSK-3β inhibitor currently in phase 1/2 clinical studies (NCT03678883). We hypothesized that GSK3-β expression may correlate with sensitivity to GSK3-β inhibition as well as suppression of anti-apoptotic pathways. We evaluated the expression of GSK-3β in a tissue microarray of 134 specimens of PCa tumors from radical prostatectomies (median age 69, serum PSA 10.5 ± 7.6 ng/ml; grade groups (GG): 18 - GG 1 (13.4%), 67 - GG 2 (48.5%), 29 - GG 3 (21.4%), 7 - GG 4 (5.2%), 13 - GG 5 (9.7%); 72 patients (54.9%) had pT2 tumors, and 52 (39,1%) were pT3. Seven patients (5.7%) had positive lymph node (pN1 disease). ERG expression and PTEN loss were observed in 52% (71/134) and 42%, respectively. The GSK-3β histologic score (% of positive tumor cells multiplied by intensity 0-3) correlated with higher Gleason grade (p&lt;0.05), extraprostatic extension (pT3a, p&lt;0.05), but not with serum PSA, tumor volume, margin status or size of index nodule. Cases with predominant nuclear localization of GSK-3β (5%; N=7) had higher Gleason score, pathologic stage, and all but one had PTEN loss. The antiproliferative effect of 9-ING-41 in four PCa human cell lines (PC3, DU145, LNCAP and 22rV1) was investigated using Cell-Titer-Glo (CTG) viability assay. 9-ING-41 demonstrated a dose-dependent decrease in proliferation of AR positive (IC50s 0.3 μM LNCAP; 0.8 μM 22rV1) and AR negative cell lines (IC50 0.6 μM PC3, 0.2 μM DU145). 9-ING-41 induced robust apoptosis (cleaved PARP) in LNCAP and PC3 cells, but not in DU145. All four cell lines expressed GSK-3β, the target of 9-ING-41 and its level were not altered by treatment. 9-ING-41 decreased the expression of phosphorylated NF-kβ (Ser536), anti-apoptotic proteins MCL-1 and BCL-2 by western immunoblotting. Interestingly, the most sensitive cell line, DU145, had lower levels of NF-kβ and suppressed both MCL-1 and BCL-2 after exposure to 9-ING-41. Our current work is evaluating the extent of apoptosis versus growth arrest, especially in the DU145 cell line, where PARP cleavage was not observed. We are also evaluating the effects of the 9-ING-41 on cellular targets of GSK-3β as potential markers of drug efficacy. 9-ING-41 has potent anti-proliferative activity against PCa cell lines. These data support the inclusion of patients with CRPC in clinical studies of 9-ING-41 and its further investigation for the treatment of CRPC.

Citation Format: Fabio Tavora, Tamara Lotan, Marclesson Alves, Lanlan Zhou, Ali Amin, Navaraj Arunasalam, Andre De Souza, Anthony Mega, Dragan Golijanin, Frank Giles, Wafik El-Deiry, Benedito Carneiro. Glycogen synthase kinase 3-β expression in prostate cancer (PCa) correlates with aggressive pathological features and its blockade with 9-ING-41 inhibits viability of PCa cell lines [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2959.

Abstract 1836: ONC201 shows synergistic effect with the androgen receptor AR-inhibitor darotulamide in prostate cancer models

Prostate cancer (PC) is the most frequently diagnosed cancer among men in the United States and is the 3rd cause of cancer mortality. Despite advances in the treatment and understanding of pathogenesis, patients with metastatic PC invariably progress to a lethal stage of castration-resistant prostate cancer (CRPC). Inhibition of androgen signaling remains crucial for the treatment of CRPC, but novel treatment strategies are urgently needed. ONC201 is a first-in-class, selective inhibitor of dopamine receptor D2 that upregulates death-receptor 5 and induces apoptosis. ONC201 induced apoptosis in PC cell lines and showed synergy with enzalutamide, docetaxel and everolimus (Lev A Mol Cancer Res 2018). Darolutamide (DARO) is a novel androgen receptor (AR) antagonist approved for treatment of patients with non-metastatic CRPC. DARO has higher affinity to AR and preclinical activity against enzalutamide-resistant PC cell lines including AR variants associated with enzalutamide agonism (Borgmann H Eur Urol 2018). We treated human PC cell lines (LNCAP [castration sensitive, AR wild-type], 22Rv1 [castration-resistant cell line that expresses AR splice variant AR-V7], DU145 [AR negative], PC3 [AR negative]) with DARO alone and combined with ONC201. Single-agent DARO decreased PC cell viability in Cell-Titer-Glo assays (IC50s of 10 and 693 nM for LNCAP and DU145, respectively). ONC201 showed strong synergism with DARO in LNCAP cells (combination indices &lt; 1 at concentrations of 156, 312, 625 nM, and 1.25 µM of DARO with 2.5 μM ONC201). ONC201 induced robust apoptosis in 22Rv1 as measured by PARP cleavage, which was partially amplified by DARO. PARP cleavage was also observed in LNCAP cells with less intensity and not potentiated by DARO. ONC201 reduced the expression of phospho-AR (p-AR) in both 22Rv1 and LNCAP. The combination of ONC201 and DARO had a significant additive effect in reducing p-AR in 22Rv1, but not in LNCAP. ONC201 reduced PSA protein levels in LNCAP cells while DARO alone did not cause any significant change in PSA. Immunofluorescence experiments showed that DARO caused significant reduction of AR nuclear translocation in both 22rV1 and LNCAP cells. The combination with ONC201 potentiated this inhibition of AR translocation in both cell lines. ONC201 showed strong antiproliferative activity against PC cells lines independent of AR status. Combination of ONC201 with DARO demonstrated synergy in enzalutamide resistant 22Rv1 cells expressing AR-V7 with marked reduction of nuclear localization of AR. Our studies provide preclinical rationale for combination of ONC201 with DARO as a novel therapy of PC.

Citation Format: Fabio Tavora, Lanlan Zhou, Ali Amin, Safran Howard, Navaraj Arunasalam, Andre de Souza, Anthony Mega, Dragan Golijanin, Wafik El-Deiry, Benedito Carneiro. ONC201 shows synergistic effect with the androgen receptor AR-inhibitor darotulamide in prostate cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1836.

EXTH-57. PRECLINICAL COMBINATION OF ONC201 WITH RADIOTHERAPY OR TEMOZOLOMIDE IN GBM, DIPG AND ATRT CELL LINES RESULTS IN DOPAMINE RECEPTOR ANTAGONISM, ATF4 INDUCTION AND CELL DEATH

CNS tumors are one of the most lethal cancers in children and young adults. We previously reported that first-in-class small-molecule imipridone ONC201 can antagonize dopamine receptor D2 (DRD2), inactivate ERK/AKT, induce the integrated stress response (ISR), upregulate pro-apoptotic TRAIL receptor DR5, deplete cancer stem cells, and induce growth arrest or cell death in tumor cells. ONC201 crosses the blood-brain barrier and has induced durable tumor regressions in adult and pediatric H3K27M-mutant glioma patients. We hypothesized that ONC201 may synergize with radiotherapy or temozolomide in brain tumors. Glioblastoma (GBM: SNB19, T98G and U251), diffuse intrinsic pontine glioma (DIPG: SF8628) and atypical teratoid rhabdoid tumor (ATRT: BT-12, BT-16) cell lines were tested using cell viability or colony formation assays with ONC201 up to 20 μM alone or in combination with radiotherapy up to 8 Gy or temozolomide up to 100 μM. We observed synergy between ONC201 and radiation or temozolomide by multiple assays. We observed induction of PKA substrate phosphorylation as a marker of DRD2 antagonism, induction of ATF4 as a marker of ISR activation, and multiple markers of cell death in treated brain tumor cells. We are evaluating the relevance of mitochondrial protease ClpP, a recently described binding target of ONC201, in ONC201-induced glioma cell death. We have observed that knockdown of ClpP strongly protects multiple human cancer cell lines from ONC201-mediated cytotoxicity. Thus, we are exploring the potential interplay between ClpP, dopamine receptors, the ISR and TRAIL signaling pathways after single agent or combinatorial treatments. Our data suggests that ONC201 may be combined synergistically with temozolomide or radiation to address gliomas, along with potential pharmacodynamic biomarkers.

Abstract 262: Anti-tumorigenic effect of ONC201 is enhanced by combination treatment with TRAIL or a DR5 agonist in endometrial cancer in vitro

ONC201 is a well-tolerated, orally active small molecule in the novel imipridone class that has anti-tumorigenic properties in a number of solid tumors, but not in non-neoplastic cells. ONC201 has demonstrated promising activity as a single agent in patients with advanced endometrial cancer in the first-in-human clinical trial with Phase II trials in endometrial cancer patients now underway. Although the mechanism of action in endometrial cell pathology has not been well studied, ONC201’s anti-tumor effect has been shown in other model systems to be p53-independent and mediated through activation of the integrated stress response (ISR) leading to DR5 activation and through induction of cell death or growth arrest. ONC201 inhibits ERK and AKT leading to upregulation of TRAIL in many systems. We hypothesized that ONC201 upregulation of DR5 could sensitize tumor cells to TRAIL and that TRAIL could convert growth arrest to cell death in ONC201-treated cells. Three endometrial cancer cell lines AN3CA, HEC1A and KLE were treated with ONC201 alone or in combination with TRAIL, or a DR5 agonist. Effects on cell viability were assessed by the Cell Titer-Glo cell viability assay, colony formation assays and cell cycle analysis by propidium iodide staining. QPCR and Western blot analysis were used to evaluate mRNA and protein expression, respectively. Assessment of TRAIL and DR5 cell surface expression was evaluated by surface staining using flow cytometry and FlowJo data analysis. ONC201 decreased the cell viability of all three endometrial cancer cell lines at clinically achievable low micro-molar concentrations. ONC201 activated the ISR and an anti-proliferative effect involving a G1 phase arrest and little cell death as indicated by increased Sub-G1 analysis and PARP cleavage. DR5 mRNA and protein expression at the cell surface were induced by ONC201. All three endometrial cancer cell lines were resistant to TRAIL alone, however, pre-treatment with ONC201 sensitized the AN3CA and KLE to TRAIL and a DR5 agonist, leading to potent cell death induction. The combination of ONC201 plus TRAIL did not cause appreciable cell death in normal human fibroblast. ONC201 decreases cell viability in endometrial cancer cells lines primarily through growth arrest while the combination of ONC201 and TRAIL or a DR5 agonist promotes cell death in AN3CA and KLE cells but not in HEC1A endometrial cancer cells. Our results suggest a novel cancer therapeutic strategy that can be exploited in the clinic.

Citation Format: Jocelyn Ray, Marie Ralff, David Dicker, Wafik El-Deiry. Anti-tumorigenic effect of ONC201 is enhanced by combination treatment with TRAIL or a DR5 agonist in endometrial cancer in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 262.

Abstract 1866: Small molecule NSC59984 is a radio-sensitizer dependent on ERK2 and DDR but independent of wild-type p53

Radiotherapy is a common and effective therapeutic strategy applied to various types of tumors. Mutations that commonly occur in p53 as a tumor suppressor gene, are a hallmark of tumor, and confer cellular radio-resistance. Targeted therapy is considered as a promising approach to increase efficacy and specificity of radiotherapy. We explore utilization of a small molecule targeting mutant p53 to enhance efficacy of radiotherapy in colorectal cancer. Colorectal cancer cells carrying with mutant p53 were treated with NSC59984 followed by ionizing radiation treatment. Combined NSC59984 with radiation significantly reduced colony formation in mutant p53-expressing colorectal cancer cells in a dose-dependent manner, suggesting that NSC59984 enhances the efficacy of radiotherapy. NSC59984 induces mutant p53 degradation via the ERK2 pathway. We investigated the role of ERK2 in the efficacy of the combination of NSC59984 and radiation treatment. ERK2 blockade partially abrogated the effect of NSC59984 on the radio-sensitivity, and this correlated with the rescue of mutant p53. Our results suggest that NSC59984 increases the efficacy of radiotherapy via activation of ERK2 or ERK2-dependant mutant p53 degradation. Mutant p53 and ERK2 are important regulators involved in repair of DNA double-strand breaks. We examined the DNA damage response (DDR) system and found that reduced Rad51 protein in cells treated with NSC59984, and the Rad51 protein was increased by the blockade of the ERK2 pathway. On the basis of the above results, we conclude that small-molecule NSC59984 enhances cancer cell sensitivity to radiotherapy via the ERK2 pathway and effects on DDR.

Citation Format: Shengliang Zhang, Lanlan Zhou, Niklas Finnberg, Wafik El-Deiry. Small molecule NSC59984 is a radio-sensitizer dependent on ERK2 and DDR but independent of wild-type p53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1866.

Abstract A060: Targeting DRD2 dysregulation in recurrent glioblastoma with imipridone ONC201: predictive and pharmacodynamic clinical biomarker analyses

Background: ONC201, an imipridone that is a selective antagonist of the G protein-coupled receptors dopamine receptor D2 (DRD2) and D3 (DRD3), has exhibited biologic activity and an exceptional safety profile in a phase II study in bevacizumab-naïve recurrent glioblastoma (Arrillaga et a.l, 2017). Single-agent ONC201 efficacy has been observed in preclinical glioblastoma models in addition to robust penetrance of the blood-brain barrier (Allen et al., 2013). DRD2 antagonism induces tumor cell apoptosis via the same signaling pathways affected by ONC201. In addition, DRD2 is expressed on NK and other immune cells and DRD2 antagonism can induce their activation. Methods: Cell viability assays were performed with ONC201 in &gt;1000 Genomic of Drug Sensitivity in Cancer (GDSC) cell lines and NCI60. Immunohistochemistry staining of DRD2/DRD5 was performed in glioblastoma tissue microarrays and archival tumor tissues. Whole exome sequencing was performed in RKO cells with acquired resistance to ONC201. DRD5 wild-type and mutant constructs were generated for overexpression studies. ELISA was used to quantitate serum prolactin and immune effector (perforin) levels. Intratumoral drug concentrations were evaluated by LC-MS assays conducted on glioblastoma tissue resected from patients following the second dose of 625mg ONC201. Results: Evaluation of ONC201 in GDSC cell lines confirmed broad anticancer efficacy with high sensitivity (~1-3 µM) in human brain cancer. The Cancer Genome Atlas (TCGA) revealed that DRD2 is highly expressed in glioblastoma relative to other dopamine receptors and that genetic aberrations are rare. High expression of DRD2 occurred in primary, rather than secondary, glioblastoma and was associated with a poor prognosis. Immunohistochemistry of tissue microarrays revealed DRD2 overexpression in glioblastoma relative to normal brain. A linear correlation between DRD2 mRNA and ONC201 GI50 was observed among glioblastoma cell lines in the NCI60 panel. Interestingly, expression of DRD5, a D1-like dopamine receptor that counteracts DRD2 signaling, was significantly inversely correlated with ONC201 potency in the NCI60 and GDSC datasets (P &lt;.05). Furthermore, a missense DRD5 mutation was identified in cancer cells with acquired resistance to ONC201. Resistance could be recapitulated with overexpression of the mutant or wild-type DRD5 gene. A significant induction of serum prolactin, a surrogate biomarker of target engagement, was detected upon ONC201 administration to recurrent glioblastoma patients. Intratumoral drug concentrations surpassed therapeutic levels, ranging from ~0.6-10µM at 24 hours post-dose. Immune effector levels in the serum correlated with the kinetics of a durable objective response observed in a patient with an H3.3 K27M glioma. Among the 15 available archival tumor tissue specimens, all had expression of DRD2 and 8/17 patients had low expression of DRD5. Patients with PFS&gt;5 month had no detectable expression of DRD5, unlike those with PFS&lt;5 months. In addition, 4/8 DRD2+DRD5- and 0/7 DRD2+DRD5+ patients are still alive with a median follow-up of 47.4 weeks. Conclusion: The dopamine receptor pathway is a novel therapeutic target that is dysregulated in glioblastoma and provides predictive and pharmacodynamic biomarkers of tumor sensitivity to ONC201.

Citation Format: Varun Vijay Prabhu, Neel Madhukar, C. Leah B. Kline, Rohinton Tarapore, Wafik El-Deiry, Olivier Elemento, Faye Doherty, Alexander VanEngelenburg, Jessica Durrant, Andrew Zloza, Cyril Benes, Isabel Arrillaga, Wolfgang Oster, Joshua E. Allen. Targeting DRD2 dysregulation in recurrent glioblastoma with imipridone ONC201: predictive and pharmacodynamic clinical biomarker analyses [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A060.

Abstract 3990: Use of 3D tumoroid systems to define immune and cytotoxic therapeutic responses based on tumoroid and tissue slice culture molecular signatures

Historically, the successful establishment of exponentially growing viable in vitro tumor cell cultures has been found to occur from a minority of tumor tissues following artificial selection of a sub-population of tumor cells. Such limitations make it difficult to model patient variability in drug responses in vitro. Moreover, the lack of stromal cells that play a critical role in tumor viability, growth and drug response in vivo make the prediction of tumor response of immune-based therapeutics challenging. Through recent advances in three-dimensional (3D) culture (“tumoroid”) methodologies some of these hurdles are beginning to be addressed. However, it is currently unclear to what extent such models can be engineered to retain important phenotypic properties of infiltrating immune cells from the tumor tissue of origin. To better understand these limitations, we have developed 3D tumoroids and tumor slice in vitro cultures from tumors derived from patients with colorectal cancer (CRC) to evaluate immune cell populations infiltrating cultured CRC tissues. Furthermore, we have developed a system whereby the patient’s immune cells are re-incorporated into tumoroid in vitro cultures to evaluate the ability of the culture to mimic an immunosuppressive tumor microenvironment (ITM). Here we demonstrate the development of a propagating 3D epithelial tumoroid culture system from resected CRC tissue where we assessed the response to standard FDA approved therapy within weeks of surgical resection. Interestingly, tumoroid cultures from a CRC patient were highly sensitive to the thymidylate synthase inhibitor fluorouracil (adrucil) but less sensitive to the combination of the nucleoside analog trifluridine and the thymidine phosphorylase inhibitor tipiracil (Lonsurf). We isolated approximately four (4) million immune cells using Percoll density gradient centrifugation and flow cytometry. Re-introduction of isolated immune cells derived from surrounding and infiltrating tumor tissue and CD45+ tumor infiltrating hematopoietic cells displayed prolonged (&gt;10 days) survival in co-culture. Moreover, established tumor slice cultures contained both an outer epithelial and inner stromal cell compartment mimicking tumor structure in vivo. Collectively, these data suggest that CRC tumoroid in vitro assays can be used for the assessment of some therapeutic responses. While further work is required to optimize this system, 3D tumoroid and slice culture assays may represent a novel in vitro approach to assess therapeutic efficacy of novel therapeutics and evaluate mechanisms of therapy resistance in general as well as for patient-specific response.

Citation Format: Niklas K. Finnberg, Prashanth Gokare, Avital Lev, Alexander W. MacFarlane, Kerry S. Campbell, Karen Kaputa, Jeffrey Farma, Luigi Grasso, Nicholas C. Nicolaides, Wafik El-Deiry. Use of 3D tumoroid systems to define immune and cytotoxic therapeutic responses based on tumoroid and tissue slice culture molecular signatures [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 3990. doi:10.1158/1538-7445.AM2017-3990

Abstract 3245: Preclinical evaluation of the imipridone family of small molecules, including analogues of clinical-stage anti-cancer small molecule ONC201, reveals potent anti-cancer effects of ONC212

We previously identified a novel, potent anti-cancer small molecule ONC201, which upregulates the integrated stress response (ISR) through ATF4/CHOP/DR5 and acts as a dual inactivator of Akt and ERK, leading to TRAIL gene activation. After completing a first-in-human phase I clinical trial that revealed exceptional safety, therapeutic pharmacokinetic (PK) profile and tumor engagement, ONC201 is under investigation in several advanced cancer Phase I/II trials. Given the unique imipridone core chemical structure of ONC201, we synthesized a family of analogues in an effort to identify additional chemical family members with distinct therapeutic properties. Based on in vitro potency improvements in human cancer cell lines and therapeutic window approximations with normal human fibroblasts, select analogues were investigated in animals for toxicity, maximum tolerated dose (MTD), and antitumor efficacy. ONC212 is one of the most promising new imipridones that was further evaluated to establish the PK profile, oral bioavailability, and efficacy in tumor types that are less sensitive to ONC201. Compared to ONC201, we noted distinct and more rapid kinetics of activity as well as improved potency in multiple human cancer cell lines in vitro. ONC212 has a broad therapeutic window, an acceptable PK profile, and is orally well-tolerated in mice. With no evidence of toxicity at efficacious doses in both colon and triple negative breast cancer, we have begun further evaluation of antitumor efficacy studies in ONC201-resistant tumor types. Efficacy studies with ONC212 are ongoing in melanoma models that are sensitive to ONC212 but less sensitive to ONC201 in vitro. Preliminary data indicates potent tumor growth reduction by ONC212 in vivo in ONC201-resistant melanoma xenografts. With a wide safety margin, potent antitumor activity in ONC201-insenstive tumors, and drug-like characteristics, ONC212 is being further developed as a drug candidate from the new imipridone class of compounds that complements the spectrum of activity of ONC201.

Citation Format: Jessica Wagner, C. Leah Kline, Gary Olson, Bhaskara Nallaganchu, Richard Pottorf, Varun Prabhu, Martin Stogniew, Joshua Allen, Wafik El-Deiry. Preclinical evaluation of the imipridone family of small molecules, including analogues of clinical-stage anti-cancer small molecule ONC201, reveals potent anti-cancer effects of ONC212 [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 3245. doi:10.1158/1538-7445.AM2017-3245

Abstract 5636: Targeting of NOXA overexpression in anaplastic thyroid cancer (ATC)

Anaplastic thyroid cancer (ATC) is a rare, aggressive and fatal cancer with a median survival of 3-5 months after diagnosis. Our long-term goal is to develop better therapies based on the biology of ATC that contributes to improved tumor response and a reduced risk of potential side-effects. We recently showed that the anti-apoptotic BCL2 family member MCL1 is overexpressed in a subset of ATC and that targeting of MCL1 with quinacrine leads to increased sensitization to the BRAF inhibitor sorafenib. To further investigate the importance of BCL2 family proteins in ATC, we analyzed gene expression data from several published independent gene expression studies. We discovered that both papillary thyroid cancer (PTC) and ATC surprisingly overexpress the mRNA of the pro-apoptotic BCL2 family member NOXA. However, despite the observed overexpression of NOXA mRNA in several ATC cell lines, we find that NOXA protein expression, by contrast, is low. NOXA protein has previously been shown to be subject to ubiquitination and proteasomal degradation. Indeed, through bioinformatics, we find overexpression of several ubiquitin enzymes in ATC suggesting that the half-life of NOXA protein may be selectively reduced in this tumor type. We are further assessing differences in the turnover of NOXA protein in ATC cells and are investigating if restoring NOXA protein expression may synergize with the pharmacologic targeting of MCL1 and other anti-apoptotic BCL2 family members. Interestingly, through TCGA analysis, we discovered that BCL2 overexpression is associated with a poor prognosis in thyroid cancer (THCA) patients. Indeed, treatment with the BCL2/BCLXL inhibitor navitoclax showed encouraging efficacy and synergized with the neddylation inhibitor MLN4924 in the ATC cell line 8505C. This was based on the expectation that MLN4924 would rescue NOXA protein expression. We are pursuing mechanistic studies in a larger panel of thyroid cancer cell lines and in vivo efficacy and toxicity studies. We conclude that restoring NOXA protein expression can together with the rational targeting of anti-apoptotic BCL2 family members may allow for the expansion of the limited ATC-selective treatment strategies currently available.

Citation Format: Niklas K. Finnberg, Junaid Abdulghani, Hormoz Ehya, Wafik El-Deiry. Targeting of NOXA overexpression in anaplastic thyroid cancer (ATC) [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 5636. doi:10.1158/1538-7445.AM2017-5636

Abstract 4147A: Potent anti-cancer activity of the imipridone ONC206: A selective dopamine D2-like receptor antagonist

DRD2 is a G protein-coupled receptor (GPCR) that is overexpressed in many cancers, controls an array of pro-survival signaling pathways, and its antagonism causes anti-cancer effects. ONC201, the founding member of the imipridone class of anti-cancer compounds, is a small molecule DRD2 antagonist that is in Phase I/II advanced cancer clinical trials. In this study, we evaluated the binding target and antitumor activity of ONC206, a chemical analogue of ONC201.

An orphan small molecule target prediction algorithm revealed that ONC206, like ONC201, antagonizes DRD2. Experimental GPCR profiling using the PathHunter® β-Arrestin assay, determined that ONC206 selectively antagonizes the D2-like (DRD2/3/4), but not the D1-like (DRD 1/5), subfamily of dopamine receptors. ONC206 possesses a ~10-fold increased affinity for DRD2 compared to ONC201 with a Ki of ~320nM with selectivity that was superior to approved antipsychotics. The increased association rate for the ONC206-DRD2 interaction was responsible for the increased affinity, whereas the dissociation rate was similar to ONC201 and atypical antipsychotics that are well tolerated.

TCGA analysis and immunohistochemistry of patient-derived tissue microarrays revealed DRD2 was overexpressed in neuroblastoma, sarcoma and pheochromocytoma specimens relative to normal tissues. In vitro efficacy profiling of ONC206 in the Genomic of Drug Sensitivity in Cancer collection of cell lines revealed broad efficacy across most tumor types (GI50 &lt;78-889nM). Bone cancer and neuroblastoma were identified as the most ONC206-responsive solid tumor types that were comparatively less responsive to ONC201. Within bone cancer cell lines, Ewing’s sarcoma (n=16) was the most sensitive to ONC206 with nanomolar sensitivity (GI50 168-303nM) that was superior to ONC201. ONC206 was highly efficacious in neuroblastoma (n=35, GI50 87-589nM) including cell lines derived from metastatic sites and with MYCN amplification associated with poor prognosis. In the PC12 rat pheochromocytoma cell line ONC206 (GI50 200nM) was superior to ONC201. ONC206 time-course experiments revealed anti-cancer effects occurring at 48-72 post-treatment, similar to ONC201. In support of a wide therapeutic window, ONC206 reduced the viability of normal fibroblasts (HFF-1) at relatively high doses (GI50 &gt; 5µM). Efficacy evaluations in MHH-ES-1 athymic nude mice xenografts demonstrated that ONC206 (100 mg/kg PO every 10 days) causes significant tumor growth inhibition that was comparable to methotrexate (400 mg/kg, IP) while being better tolerated.

In summary, ONC206 is an imipridone that acts as a selective antagonist of DRD2 at nanomolar concentrations and has broad-spectrum anti-tumor activity. ONC206 may address tumor types where the properties of ONC201 do not permit for complete therapeutic engagement in vivo.

Citation Format: Varun Vijay Prabhu, Neel Madhukar, Jessica Wagner, Rohinton Tarapore, Mathew Garnett, Ultan McDermott, Cyril Benes, Neil Charter, Sean Deacon, Alexander VanEngelenburg, Olivier Elemento, Wafik El-Deiry, Martin Stogniew, Wolfgang Oster, Joshua Allen. Potent anti-cancer activity of the imipridone ONC206: A selective dopamine D2-like receptor antagonist [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 4147A. doi:10.1158/1538-7445.AM2017-4147A

Abstract 3213: Antagonism of D2-like dopamine receptors plays a role in Onc201’s anticancer effects

ONC201/TIC10 is a first-in-class small molecule inducer of TRAIL that causes early activation of the integrated stress response and inactivates both Akt and ERK. Its promising safety profile and broad spectrum efficacy in vitro has been confirmed in Phase I/II trials in several advanced malignancies. Biochemical and reporter assays have shown that ONC201 is a selective and competitive antagonist of the D2-like receptors, specifically, dopamine receptor D2 (DRD2) and dopamine receptor D3 (DRD3) with a KD value of ~3 µM. The theme that dopamine and dopamine receptors are important in cancer has emerged in the literature. We hypothesize that ONC201’s interaction with DRD2 is critical for ONC201’s anticancer effects. Co-treating HCT116 and RKO colorectal cancer cells with ONC201 and dopamine or the selective D2-like receptor agonist sumanirole partially abrogated ONC201-induced ATF4/CHOP expression and apoptosis. Knocking down DRD2 expression using siRNA negated ONC201’s effects on viable cell count. Overexpressing DRD2 in a cancer cell line that has very low levels of DRD2, increased ONC201-induced PARP cleavage. Quantitative RT-PCR analyses showed that cells that have acquired resistance to ONC201 did not express detectable mRNA levels of the D2-like receptors. To further determine the anti-tumor potential of targeting the D2-like receptor, we treated different cancer cell lines with other D2-like receptor antagonists. Similar to ONC201, the D2-selective antagonist L-741,626 decreased cell viability and induced apoptosis in a number of cancer cell lines. In contrast to ONC201, however, L-741,626 has a poor therapeutic index. Our findings show that the ability of ONC201 to inhibit D2-like receptors contributes to ONC201’s antiproliferative and pro-apoptotic activity. Ongoing work is aimed at elucidating the mechanisms by which antagonism of D2-like receptors can promote apoptotic cell death, especially with regard to ATF4/CHOP/DR5 and Akt/ERK/Foxo3a/TRAIL, which have been shown to be stimulated in ONC201-treated and -sensitive tumor cells.

Citation Format: Christina Leah B. Kline, Amriti Lulla, Jessica Wagner, David Dicker, Marie Baumeister, Sophie Oster, Wafik El-Deiry. Antagonism of D2-like dopamine receptors plays a role in Onc201’s anticancer effects [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 3213. doi:10.1158/1538-7445.AM2017-3213

Abstract 124: Imipridone ONC201 promotes intra-tumoral accumulation of CD3+/NK+ cells that contribute to its anti-tumor efficacy

ONC201, a first-in-class oral anti-tumor agent, upregulates the pro-apoptotic immune cytokine TRAIL and activates the integrated stress response leading to upregulation of death receptor 5 in bulk tumor and cancer stem cells. We previously demonstrated that ONC201 exerts a dose- and schedule-dependent effect on tumor progression in vivo while suppressing Akt/ERK signaling in tumors in a dose/frequency-dependent manner (Wagner et al., AACR, 2016). We also provided evidence that ONC201 exhibits a potent anti-metastatic effect (Wagner et al., AACR, 2016). We observe accumulation and activation of TRAIL-secreting NK+ cells within ONC201-treated tumors in C57/BL6, Balb/c, and athymic nude tumor-bearing mice. Importantly, ONC201 exerts in vivo anti-tumor efficacy on tumor cell lines that are ONC201-resistant in vitro, including acquired stable resistance. Using the NK-depleting antibody GM1, we demonstrate that the activation and TRAIL secretion of NK cells by ONC201 significantly contributes to in vivo anti-tumor efficacy, including TRAIL/ONC201-resistant tumors. We are currently investigating how ONC201 recruits NK cells to the tumor by examining NK-recruiting chemokine factors within the tumor site. We have also demonstrated upregulation of CD3+ T cells by ONC201 in syngeneic mice. Finally, we observed an increase in activated TRAIL-secreting NK cells in the peripheral blood of patients upon ONC201 administration in the clinic. Our results demonstrate novel and potentially significant increases in cytotoxic NK cell recruitment to tumors. The results offer a unique pathway of immune stimulation for cancer therapy that may be combined with immune checkpoint or targeted cancer therapy strategies. We are currently investigating the role of NK cells and CD3+ cells in ONC201’s ability to inhibit metastasis by using a metastatic model that involves surgically removing the primary tumor and allowing metastases to grow in vivo before treatment. These findings indicate that ONC201 possess immunomodulatory activity and provide a rationale for combining ONC201 with PD-1/PDL-1 inhibitors, a combination we are currently testing in syngeneic immunocompetent mouse models.

Citation Format: Jessica Wagner, C. Leah Kline, Lanlan Zhou, Andrew Zloza, Charles Chesson, Jenna Newman, Howard Kaufman, Joseph Bertino, Mark Stein, Wafik El-Deiry. Imipridone ONC201 promotes intra-tumoral accumulation of CD3+/NK+ cells that contribute to its anti-tumor efficacy [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 124. doi:10.1158/1538-7445.AM2017-124

Abstract 327: Anti-tumor effect and destabilization of R175H-mutant p53 by CB002, a p53-pathway restoring small molecule that stimulates autophagy

Tumor suppressor p53 is a master regulator of genotoxic and cellular stress signals, controlling cell fate by transcriptionally activating genes involved in DNA repair, cell cycle arrest, and apoptosis. p53 is mutated in over half of human cancers and this is associated with tumor development and chemotherapy resistance. TP53 gene mutations can result in the abolishment of p53 contact with DNA and disruption of p53 structural conformation. These mutations not only prevent p53 to exert its normal tumor suppressive functions but can result in gain-of-function activity, acquiring oncogenic characteristics. Therefore, altering the stability of mutant p53 protein is an attractive therapeutic strategy in cancer cells. We investigated small molecules that modulate mutant p53 stability and restore the p53-signaling pathway. We identified a small molecule, CB002, as a candidate for restoration of the p53 pathway in mutant p53-bearing cancer cells. Three colorectal cancer cell lines: SW480, DLD-1, HCT116-R175H and the RXF393 renal cancer cell line, were treated with different concentrations of CB002 at various time points. Cell lines exposed to CB002 showed an increase in apoptotic and cell death markers, such as NOXA/DR5 induction, cleaved caspases and PARP, as early as 16 hrs. CB002 decreased mutant p53 stability in structural conformation-mutant bearing cells (HCT116 R175H and RXF393). Our data suggests that CB002 stimulates an increase of p53 target genes and promotes expression of pro-apoptotic proteins. R175H p53 mutant protein expression was largely rescued by the co-treatment with MG132, a proteasomal inhibitor, implicating a role for the ubiquitin proteasome system. Furthermore, we observed significant autophagy induction upon CB002 treatment, as indicated by LC3 conversion and p62 levels. Autophagy inhibition decreased levels of cell death markers and increased the stability of the R175H-mutant p53, suggesting that autophagy might be required for CB002-induced cell death and mutant p53 turnover. Therefore, we hypothesize that CB002 is capable of degrading mutant p53 and restoring the p53 pathway through p53 family members in colorectal cancer cells. Currently we are investigating p53 degradation mechanism by CB002, the role of p53 family members in the restoration of the pathway and autophagy on mutant p53 stability. Hence, our results provide an insight on effective p53 pathway activation through the use of small molecules.

Citation Format: Liz J. Hernandez Borrero, Shengliang Zhang, David Dicker, Wafik El-Deiry. Anti-tumor effect and destabilization of R175H-mutant p53 by CB002, a p53-pathway restoring small molecule that stimulates autophagy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 327.

Abstract 3706: p53 represses pyrimidine catabolic gene dihydropyrimidine dehydrogenase (DPYD) expression following thymidylate synthase (TS) inhibition

Nucleotide catabolism by cancer cells can influence malignant behavior and intrinsic resistance to therapy. The rate-limiting enzyme in the pyrimidine catabolic pathway, dihydropyrimidine dehydrogenase (DPYD) contributes to the pharmacokinetics of fluorouracil (5-FU). Using in silico/chromatin-immunoprecipitation (ChIP) analysis we identify a conserved p53 DNA-binding site (p53BS) downstream of the DPYD gene with increased p53 occupancy following 5-FU. Histone H3K9 acetylation marks at the DPYD promoter is diminished concomitantly with reduced expression of DPYD mRNA and protein in a p53-dependent manner. Notably we find that the P72 allele of p53 suppresses DPYD expression more than the R72 p53 allele following 5-FU treatment in mouse embryo fibroblasts. Mechanistic studies reveal inhibition of DPYD expression by p53 is augmented following thymidylate synthase (TS) inhibition by 5-FU, methotrexate (MTX), raltitrexed and siRNA in cancer cells in vitro as well as in mice in vivo. DPYD repression by p53 is dependent on DNA-PK and ATM-signaling since pharmacologic targeting of these kinases reverses the transcriptional repression of DPYD by p53. Mice lacking p53 in their livers have increased conversion of 5-FU to 5-FUH2 in plasma and elicit a diminished 5-FU therapeutic response in syngeneic colorectal tumor xenografts as compared to littermates with an intact p53 allele consistent with increased DPYD-activity. Our data suggest that p53 plays an important role in controlling pyrimidine catabolism through its ability to regulate DPYD, particularly following metabolic stress imposed by nucleotide imbalance. The findings have implications for the toxicity and efficacy of the cancer therapeutic 5-fluorouracil.

Citation Format: Prashanth Ravishankar Gokare, Niklas Finnberg, Jenny Dai, Maureen Murphy, Wafik El-Deiry. p53 represses pyrimidine catabolic gene dihydropyrimidine dehydrogenase (DPYD) expression following thymidylate synthase (TS) inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3706.

Abstract PR03: P53 inhibits the expression of the pyrimidine catabolic gene Dihydropyrimidine dehydrogenase (DPYD)

Fluorouracil (5-FU) a widely used chemotherapeutic drug whose unpredictable pharmacokinetics is controlled by the pyrimidine catabolic gene dihydropyrimidine dehydrogenase (DPYD), that has recently also been shown to be a gatekeeper of the epithelial-to-mesenchymal transition (EMT) in breast cancer. Relatively little is known about the transcriptional control of DPYD and here we show for the first time an interaction between p53 and DPYD (involved in catabolism of pyrimidines as well as 5-FU) where p53 represses both the base-line expression of DPYD and that following 5-FU administration in vitro and in vivo. This mechanism affects the catabolic conversion of 5-FU to 5-FUH2 in mice in vivo. Using an in-silico approach we also identified several putative p53 binding sites (P53DBS) in and around ~20Kb upstream and downstream of the mouse DPYD gene. In-vivo ChIP from mice livers identified a key p53DBS binding site downstream (chr3: 119451237-11941257) of the gene to which p53 binds to at about 1.8 ± 0.05 fold over untreated control following a single IV bolus of 5-FU (150 mg/kg bw). Interestingly DPYD mRNA and protein levels were decreased by 1.8 and 1.5 fold respectively (P&lt; 0.0005) in a p53-dependent manner in the liver. Similarly DPYD-repression was documented at both the mRNA and protein levels in the wild-type (WT) p53-expressing cancer cell lines H460, HCT-116, and A569. To further characterize the functional effect of DPYD repression in vivo, we utilized mice with a liver specific deletion of p53 (Albcre p53Δ/Δ) which showed ~2-fold (p≤0.03 wilcoxon rank-sum test) decrease plasma ratio of 5-FUH2/5-FU to mice with an intact allele of p53 in their livers (Albcre p53Δ/+). Increased plasma concentrations of 5-FU caused a significant tumor growth delay (TGD) in mouse colon cancer cells implanted in syngeneic Albcre p53Δ/+ versus Albcre p53Δ/Δ mice (TGD 11 vs 8.93 days). Our data also suggest a possible feedback mechanism of DPYD repression by p53 due to thymidylate synthase (TS) inhibition, a key mediator for supplying thymidine for DNA replication and itself a target for regulation by 5-FU. The addition of exogenous thymidine abrogated the p53-dependent repression of DPYD expression following siRNA-mediated targeting of TS. Further cross-validation experiments using the specific TS inhibitors raltitrexed and methotrexate showed similar effects. Furthermore treatment with the ATM (KU-55933) or DNA-PK (NU7026) inhibitors reversed the p53-dependent repression of DPYD-expression indicating a specific DNA damage feedback mechanism following TS inhibition. Taken together our data suggest that p53 plays an important role in controlling pyrimidine catabolism, particularly following metabolic stress imposed by nucleotide imbalances. In light of more recent discoveries of the role of DPYD in malignant progression, it is plausible that the relationship between p53 and DPYD can have implications beyond influencing the pharmacokinetics of 5-FU and may extend to control of EMT and metastasis. Thus our current efforts are focused on exploring short- and long-term consequences of p53-dependent DPYD-repression as part of p53⊠s tumor suppressor function as well as understanding cellular context for the observed link in vitro and in vivo.

Citation Format: Prashanth Ravishankar Gokare, Niklas Finnberg, Jenny Dai, Wafik El-Deiry. P53 inhibits the expression of the pyrimidine catabolic gene Dihydropyrimidine dehydrogenase (DPYD). [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr PR03.

Abstract 2643: Small molecule identification for the restoration of p53 pathway through p73 and by degradation of mutant p53

One of the most explored cancer targets has been the tumor suppressor p53. p53 is mutated in more than half of all human tumors and therefore provides an attractive way to selectively target cancer cells that harbor the mutant protein. Mutant p53 protein can acquire a gain-of-function activity, losing its normal tumor suppressor properties and gaining oncogenic characteristics. Various approaches have been taken to restore the p53 pathway in mutant p53 expressing cells including the modulation of mutant p53 conformation to wild-type, and through the upregulation of p53 family members i.e. p73. Unlike p53, p73 is not commonly mutated in cancer cells and thus confers restoration of the p53 pathway through pharmacological stimulation. We characterized a small molecule that restores the p53 pathway through p73. A high-throughput cell-based screen identified small molecule CB002 as a potential candidate for the restoration of the p53 pathway in mutant p53 containing human colorectal cancer cells. Two colorectal cancer cell lines: SW480, DLD-1, and the RXF393 renal cancer cell line, were treated with different concentrations of CB002 for various time points. SW480 cells treated with CB002 for 8 hrs showed a decrease in p53 followed by an increase in DR5 expression at 16 hrs. DLD-1 cells treated with CB002 showed a decrease in p53 expression at 8 hrs. Although no change was observed in proteins involved in cell cycle arrest or cell death that were tested, colony formation was suppressed as compared to control. RXF393 cells treated with CB002 for 48 hrs showed decreased expression of p53 levels and increased levels of p21. These data suggest that CB002 is able to decrease mutant p53 protein expression, increase p53 target genes and promote expression of proteins involved in apoptosis, such as p21 and DR5, respectively. It appears that the CB002 mechanism is different depending on the cell line tested. We hypothesize that CB002 is capable of degrading mutant p53 and restoring the p53 pathway through p73 in colorectal cancer cells. Current undergoing experiments are focused on unraveling the p73 dependence through p73 knockdown and the mechanism of action involved in each cell line. The following project will aid in the understanding of the role of p73 in pharmacological restoration of the p53 pathway in cancer therapy.

Citation Format: Liz J. Hernandez Borrero, Shengliang Zhao, David T. Dicker, Wafik El-Deiry. Small molecule identification for the restoration of p53 pathway through p73 and by degradation of mutant p53. [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 2643. doi:10.1158/1538-7445.AM2015-2643

Abstract 2942: TRAIL pathway inducer ONC201/TIC10 primes multiple myeloma cells (MM) for apoptosis by downregulating X-linked inhibitor of apoptosis

MM cells inherently have a high protein turnover rate that makes them heavily dependent on the proteasome and uniquely sensitive to ER stress induction. Proteasome inhibitors, such as bortezomib, are used in front-line therapy for MM to elicit the ER stress response that results in apoptosis of MM cells. Despite significantly improved clinical outcomes in MM patients treated with proteasome inhibitors, resistance to therapy invariably emerges and MM remains an incurable disease. The objective of this study is to assess the utility of the TRAIL pathway inducer ONC201/TIC10 in MM due to preliminary evidence that suggests ONC201/TIC10 activates the integrated stress response (ISR) in tumor cells. We found that MM cells are uniquely sensitive to ONC201/TIC10, with EC50 values in the nanomolar range. In addition, ONC201/TIC10 was effective as a single agent against bortezomib-resistant MM cells and exhibited an additive effect with bortezomib against these cells. Sub-G1 analyses of MM cells co-treated with ONC201/TIC10 and a pan-caspase inhibitor indicated that MM cells undergo ONC201/TIC10-induced apoptosis in a caspase-dependent manner. Given that ONC201/TIC10 can inactivate both Akt and ERK signaling pathways, we assessed Akt and ERK phosphorylation in ONC201/TIC10-treated KMS18 and MM1S MM cells. These MM cell lines showed no inhibition of Akt and ERK phosphorylation or decrease in the downstream phosphorylation of Fox3a in response to ONC201/TIC10 treatment. These results suggested that alternative mechanisms of cytotoxicity are operative in myeloma cells treated with ONC201/TIC10. Given that downregulation of X-linked inhibitor of apoptosis (XIAP) has been linked to the ISR, we assessed the effect of ONC201/TIC10 treatment on XIAP expression. In agreement with ISR activation, XIAP levels were significantly downregulated in MM cells in response to ONC201/TIC10. Ongoing experiments are unraveling the mechanistic basis for lowered XIAP expression in ONC201/TIC10-treated MM cells. In summary, our results indicate that ONC201/TIC10 is highly effective in preclinical MM models by engaging antitumor mechanisms that include the ISR and downstream attenuation of XIAP expression. ONC201/TIC10 appears to have significant therapeutic potential in MM as a monoagent and in combination with bortezomib.

Citation Format: Christina Leah Kline, Amriti R. Lulla, David Dicker, Joshua E. Allen, Wafik El-Deiry. TRAIL pathway inducer ONC201/TIC10 primes multiple myeloma cells (MM) for apoptosis by downregulating X-linked inhibitor of apoptosis. [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 2942. doi:10.1158/1538-7445.AM2015-2942

Abstract 5387: ONC201/TIC10 is effective as a monoagent and synergizes with chemotherapy to induce cell death in non-Hodgkin's lymphoma

Outcome for non-Hodgkin's lymphoma (NHL) patients using conventional treatment standards remains unsatisfactory, particularly in advanced stage/ relapsed disease creating an imminent need for investigating novel treatment strategies. ONC201/TIC10 is a small molecule (Allen et al, 2013) that induces p53-independent cell death in tumor cells while sparing normal cells through inactivation of the prosurvival kinases Akt and ERK. ONC201 is currently entering Phase I/II clinical trials as a monoagent in adult advanced cancers. We have previously shown that ONC201 induces significant cytotoxicity in preclinical models of human lymphomas (Talekar et al, ASPHO 2014). Here, we show that ONC201 is not only effective as a monoagent across several NHL cell lines, but that it also synergizes with several chemotherapeutic agents to cooperatively induce cell death in vitro.

We found that ONC201 induces significant apoptosis in a diverse panel of human NHL cell lines at low micromolar concentrations (1.3 to 5.06 uM). Increased surface TRAIL and surface DR5 expression was noted in a dose-dependent manner across representative cell lines. The increase in surface TRAIL correlated with increase in sub-G1 DNA content, which suggests that TRAIL may serve as a potential biomarker of response to ONC201. ONC201-induced apoptosis was inhibited using a pan-caspase inhibitor and was blocked by an anti-TRAIL antibody RIK-2, which indicate induction of TRAIL-dependent cell death. Western blot analysis of ONC201-treated NHL cells suggests ERK inhibition and Foxo3a activation as a potential mechanism of cytotoxicity via TRAIL induction. In agreement with this notion, we also observed upregulation of PARP & DR5 and caspase-3 activation in response to ONC201 treatment.

We further found that ONC201 synergizes to potentiate cytotoxicity with several chemotherapeutic agents approved for NHL treatment, particularly anthracyclines (doxorubicin), nitrogen mustard (bendamustine), antimetabolite (cytarabine) and proteasome inhibitor (bortezomib) via cell viability experiments that were corroborated by apoptosis assays. Together these results suggest that ONC201 is a potent antitumor agent in NHL as monoagent and in combination with several approved therapies that may be explored in phase Ib/II trials.

Citation Format: Mala Kiran Talekar, David Dicker, Joshua Allen, Wafik El-Deiry. ONC201/TIC10 is effective as a monoagent and synergizes with chemotherapy to induce cell death in non-Hodgkin's lymphoma. [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 5387. doi:10.1158/1538-7445.AM2015-5387

Abstract B95: Is ethanol required for cyst ablation in patients with premalignant type pancreatic cysts?

Background: Mucinous pancreatic cystic lesions have the propensity to progress into pancreatic cancer. Currently radiographic surveillance or surgical resection is recommended for this premalignant type of cyst, both of which have significant limitations. Recently, endoscopic ultrasound-guided cyst ablation has emerged as an innovative and promising alternative treatment approach.

Previous studies have shown that EUS-guided ethanol lavage of pancreatic cysts is safe and results in complete cyst resolution in 1/3 of patients. Subsequent studies demonstrated marked increases in rates of ablation with infusion of paclitaxel following ethanol lavage, which raises the question of whether alcohol is necessary for effective ablation. This is important, since ethanol extravasation is felt to have caused two complications in previous trials, abdominal pain and pancreatitis.

This study hypothesizes that the removal of alcohol lavage prior to chemotherapy infusion will not impair ablation rates and will decrease complication rates. A secondary aim of this study is to assess whether a custom chemoablation cocktail tailored to pancreatic neoplasia (paclitaxel+gemcitabine) will improve ablation rates overall. Gemcitabine was chosen because it dilutes paclitaxel for injection and has been the standard in pancreatic cancer chemotherapy. Recently, the combination of paclitaxel and gemcitabine was shown to improve response rates and progression-free survival when compared with gemcitabine alone.

Methods: Patients with mucinous or indeterminate type pancreatic cysts of 1-5cm’s without signs of malignancy were randomized to undergo either EUS-guided lavage with 80% alcohol or normal saline followed by infusion of 3 mg/ml paclitaxel + 19mg/ml gemcitabine (both arms). 9 patients were enrolled in this initial pilot study and evaluated post op, at 72 hours, with two week lab tests and by CT scan at 3, 6, and 12 months to assess response rates and for any complications.

Results: The initial 9 patients of this trial (expected to have an N of 78 when complete) were randomized for this pilot study with 8 patients then able to be treated. Pancreatic cysts ranged in maximum diameter from 2.2cm to 3.8 cm (mean 2.9 cm). Location included body (n=4), head (n=2), neck (n=1) and tail (n=1). The overall reduction in cyst surface area was 67% at 3 months and 82% at 6 months. At 6 months size reduction was 81% in the alcohol infusion arm and 83% in the alcohol-free arm. Complications were mild abdominal pain (1) in the alcohol free arm (12.5%), moderate abdominal pain (1), and mild pancreatitis (1) in the alcohol arm (25%).

Conclusion: The treatment of mucinous type pancreatic cysts with either alcohol or saline lavage followed by gemicitabine-paclitaxel infusion is feasible and safe in this limited pilot study. Initial results indicate that alcohol-free ablation does not impair ablation efficacy and is associated with fewer complications although the full sample size will be required to prove this hypothesis with any certainty.

Citation Format: Matthew T. Moyer, Setareh Sharzehi, Charles E. Dye, Wafik El-Deiry, Thomas J. McGarrity, Abraham Mathew, Niraj Gusani, Raquel E. Davila, Brooke Ancrile. Is ethanol required for cyst ablation in patients with premalignant type pancreatic cysts? [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B95.

ER stress response regulates the fate of myeloid-derived suppressor cells through TRAIL receptors mediated apoptosis (TUM4P.907)

We studied the fate of myeloid-derived suppressor cells (MDSC) in cancer. Unexpectedly, MDSC had lower viability and a shorter half-life than their control counterparts neutrophils and monocytes. This effect was due to increased apoptosis mediated by the changes in TRAIL receptors (TRAIL-R) expression. Targeting TRAIL-R did not affect myeloid cells from naïve mice, but dramatically reduced the presence of MDSC and improved the immune responses in tumor-bearing mice. Pro-inflammatory cytokines did not affect TRAIL-R expression. However, induction of ER stress recapitulated changes in TRAIL-R expression observed in tumor-bearing hosts. ER stress response was detected in MDSC isolated from cancer patients and tumor-bearing mice, but not in control neutrophils or monocytes. Block of ER stress abrogated changes in TRAIL-R. Thus, MDSC pathophysiology is linked to ER stress, which shortens their lifespan in the periphery and promotes their expansion in bone marrow. In conclusion, TRAIL-R can be considered for selective targeting of MDSC.

Abstract 1176: Pharmacokinetic monitoring of 5-FU appears beneficial in stage II-IV colorectal cancer patients treated with different 5-FU-based chemotherapeutic regimens

The mainstay of colorectal cancer chemotherapy has been 5-fluorouracil (5-FU) alone or in combination with other agents. Unfortunately, therapeutic plasma 5-FU levels are achieved in only 20-30% of patients, in response to administration of 5-FU doses calculated from the patient's body surface area. Pharmacokinetic (PK) monitoring of 5-FU has been found to be beneficial for metastatic colorectal cancer patients. However, its utility among Stage II and III patients has not been reported. Purpose: We examined the impact of pharmacokinetic monitoring of 5-FU in colorectal patients with Stage II- Stage IV disease, receiving different 5-FU-based chemotherapy regimens, in terms of therapeutic response and safety. Methods: The study involved 73 colorectal cancer patients. The patients received different 5-FU based regimens; namely, FOLFOX6, mFOLFOX, FOLFIRI, and capecitabine. Thirty-five patients received 5-FU doses based on the traditional body surface area (BSA) method, which takes into account the patient's height and weight. On the other hand, in 38 patients, their 5-FU dose was adjusted based on their plasma 5-FU levels from their previous cycle. 5-FU plasma levels were measured using the commercially available OnDose test (Myriad Genetic Laboratories Inc., Salt Lake City, UT). The 5-FU levels were monitored per cycle and administered doses were adjusted accordingly until a target plasma AUC level of 20-24 mg.h/L was achieved. Results: Pharmacokinetic monitoring among Stage IV patients (n=17) had a trend toward improved survival. Out of the 8 patients that needed at least one dose adjustment, 7 of them involved increasing the 5-FU dose. 5-FU doses were not increased in the patients that did not have their 5-FU levels monitored. The ability to maximize the 5-FU dose administered without risking toxicity with PK monitoring may explain at least in part the trend towards prolonged survival in patients that underwent pharmacokinetic dose adjustment. Among Stage II and III patients, toxicities were markedly reduced by pharmacokinetic dose adjustment of 5-FU. In patients that had their doses adjusted by the BSA method, 38% experienced (7 out of 18 patients) dose-limiting toxicities, that included Grade III diarrhea, fatigue, nausea and vomiting, and cardiotoxicity. In contrast, none of the patients (n=19) that underwent pharmacokinetic monitoring experienced dose-limiting toxicity (Fisher's exact test, p=0.0031). The toxicities observed in the BSA group were not among the patients that received capecitabine. Conclusions: 5-FU dose adjustment in response to pharmacokinetic monitoring results in a trend towards improved survival of Stage IV patients. Moreover, dose-limiting toxicities are reduced in Stage II and III patients. The results presented point to the benefits of pharmacokinetic dose adjustment of 5-FU in clinical practice.

Citation Format: Christina Leah B. Kline, Angelique Schiccitano, Jay Zhu, Cheryl Beachler, Hassan Sheikh, Harold Harvey, Heath Mackley, Walter Koltun, Kevin McKenna, Lisa Poritz, Evangelos Messaris, David Stewart, Jeffrey Sivik, Wafik El-Deiry. Pharmacokinetic monitoring of 5-FU appears beneficial in stage II-IV colorectal cancer patients treated with different 5-FU-based chemotherapeutic regimens. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1176. doi:10.1158/1538-7445.AM2013-1176

Abstract 5102: Analysis of CTCs enriched from whole blood samples of Breast, Lung and Colorectal cancer patients with a flexible microspring array device

The process by which metastatic cancers release cells that detach from a primary tumor, spread through the circulatory system and invade distant organs accounts for over 90% of cancer related deaths. A fundamental challenge with analysis of these circulating tumor cells (CTCs) in blood samples is the fact that they are so rare, with only a few tumors cells occurring among billions of blood cells. We have developed a flexible micro spring array (FMSA) that employs mechanical separation to effectively enrich CTCs in a nondestructive manner that does not compromise cell viability. The FMSA device geometric design and applied filtration pressures have been optimized to maximize capture efficiency, enrichment against leukocytes, and tumor cell viability. We have successfully enriched and detected varying numbers of CTCs (min=1, max=101) in 7.5mL whole blood samples obtained from Breast, Lung and Colorectal cancer patients. CTCs were analyzed qualitatively and quantitatively based on immunocytochemical determination of phenotype and cell morphological characteristics. Aggregate clusters of cells were observed in all assayed cancer types that comprised of multiple attached CTCs (min=2, max=20) and occasionally leukocytes as well.

Citation Format: Ramdane Harouaka, Ming-Da Zhou, Yin-Ting Yeh, Cristina Truica, Avisnata Das, Jussuf Kaifi, Wafik El-Deiry, Xin Liu, Chandra Belani, Tara Baney, Jeffrey Allerton, Si-Yang Zheng. Analysis of CTCs enriched from whole blood samples of Breast, Lung and Colorectal cancer patients with a flexible microspring array device. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5102. doi:10.1158/1538-7445.AM2013-5102

Abstract 1020: VRC2, a novel bortezomib re-sensitizing compound for the treatment of multiple myeloma

The development of novel agents including the proteasome inhibitor bortezomib (Btz) has significantly improved treatment outcomes in multiple myeloma (MM). Despite these advances, resistance to therapy invariably emerges and MM remains an incurable disease. The objective of this study was to identify new therapeutic agents and combinations with the ability to overcome resistance to Btz in MM cells. We developed a high throughput drug screening (HTS) assay system to discover small molecules that selectively target Btz resistant MM cells as single agents and/or re-sensitize resistant cells to Btz. For HTS we used isogenic pairs of Btz sensitive (595 P) and resistant (595 VR) cells derived from iMycCα/Bcl-xL transgenic mouse model of MM. Cell viability was the HTS assay read-out, and 3 treatment groups (595 P, 595 VR, and 595 VR + Btz) were included to identify compounds with selective activity against Btz resistant cells as single agents, and compounds that restore Btz sensitivity in the presence of Btz. Our screening of multiple publically-available compound libraries identified several chemical structures with selective activity against Btz resistant cells. One compound in particular showed modest but significant selectivity for Btz resistant cells as a single agent, and most notably, exhibited potent Btz re-sensitizing activity when the 2 drugs were combined. We named this compound Velcade Re-sensitizing Compound 2, or VRC-2 for short. The Btz re-sensitizing activity of VRC-2 was confirmed using multiple human and mouse cell lines that had been selected for Btz resistance in vitro. IC50s for VRC-2 in normal mouse and human fibroblasts were 100-fold higher than that observed in MM cells, suggesting it may have a low toxicity profile in vivo. We are currently evaluating the activity of VRC-2 in animal models of MM, alone and in combination with Btz, and conducting molecular studies to identify its precise mechanism of action. This study establishes the proof-of-principal for our HTS approach and demonstrates the potential of VRC-2 in Btz refractory MM.

Citation Format: Amriti Lulla, Holly Stessman, David Dicker, Brian Van Ness, Wafik El-Deiry, Nathan G. Dolloff. VRC2, a novel bortezomib re-sensitizing compound for the treatment of multiple myeloma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1020. doi:10.1158/1538-7445.AM2013-1020

Extracellular protease imaging for cell mass tracking of xenografted human malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is locally aggressive and challenging to quantitate non-invasively in vivo, particularly in orthotopic models of disease. We describe imaging of extracellular protease activity, typically elevated in locally aggressive tumors, as a novel method for tracking MPM in vivo. Mice bearing human MPM subcutaneous flank xenografted tumors were imaged with ProSense 680, an optical imaging agent of extracellular cysteine protease activity. The relative contribution of extracellular cysteine proteases to the ProSense tumor signal was estimated using RT-PCR quantitation of cysteine protease RNA expression of the MPM cell lines and compared to ArrayExpress microarray RNA expression data from human MPM tumors. Feasibility of orthotopic intraperitoneal MPM cell mass tracking with fluorescence signal was evaluated using CellVue Maroon-coated MSTO-211H and compared to bioluminescent signal using luciferase-transfected MSTO-211H cells. ProSense 680 yielded a robust tumor signal in MPM subcutaneous grafts, primarily resulting from MPM secretion of cathepsin L demonstrated not only by RT-PCR data on MPM cell lines but also by microarray expression data from resected human patient tumors. CellVue Maroon intraperitoneal tumor signal was robust and durable indicating feasibility of intraperitoneal cell mass tracking of orthotopically-xenografted MPM. Optical imaging of extracellular cysteine protease activity is useful for tracking MPM tumor cell mass in vivo. Intraperitoneal MPM cell mass tracking of fluorescently labeled tumor is feasible.

Compartmentalization of tumor cells to the CSF or peripheral blood of a breast cancer patient with CNS metastasis

e11544

Background: We recently adapted the CellSearch system to detect cerebrospinal fluid tumor cells (CSFTCs) in breast cancer patients with CNS metastases and found that the CSFTCs correlate with disease burden. Here, we present the enumeration of CSFTCs and peripheral blood tumor cells (PBTCs) in a patient with metastatic breast cancer during treatment with intrathecal (IT) chemotherapy. Methods: We enumerated CSFTCs and PBTCs in a patient with ER+, Her2-, BRCA2+ breast cancer and CNS metastases who received IT chemotherapy and systemic chemoradiation. The patient was initially diagnosed with locally advanced breast cancer and underwent bilateral mastectomies followed by AC-T one year prior to CNS relapse. Tumor cell enumeration was conducted every 1-2 weeks from 7.5mL of peripheral blood or 9mL of CSF along with CSF cytology, Karnofsky performance status (KPS), neurologic examination and radiographic studies during the IT chemotherapy and subsequent systemic chemoradiation. Results: At the beginning of the IT chemotherapy the patient presented with diplopia, gait ataxia, 7th facial nerve palsy, confusion, and intractable headaches, an initial burden of 19570 CSFTCs and 10-45 PBTCs, a KPS of 80, and no systemic disease. Tumor cell counts dropped rapidly in response to IT therapy alone to 0-1 CSFTCs and 3 PBTCs, all neurologic symptoms resolved, and the KPS increased to 90. The patient subsequently suffered progression of systemic disease with development of bone and brachial plexus metastases. PBTCs rose from 3 to 64 during this same period, whereas CSFTCs remained at 0-1. The CA 27-29 level increased from 111 to 214. CSF cytology and neuro-radiographic imaging cleared in the face of progressive systemic disease. Conclusions: There was a compartmentalization of metastatic tumor cells to either the blood or the CSF in this patient. We hypothesize that tumor cells in the CSF or peripheral blood migrate to the untreated compartment during compartmentalized therapy, resulting in disease recurrence in the untreated compartment. Preliminary data on other patients supports this hypothesis, which may represent an important mechanism for disease recurrence in patients with potentially curable disease.

Abstract 5665: Multiplexing markers of response to sorafenib/mapatumumab combination therapy in hepatocellular carcinoma circulating tumor cells

Hepatocellular carcinoma (HCC) accounts for approximately 600,000 deaths per year worldwide. Effective therapeutic strategies for advanced stage patients are lacking, and the median survival rate for patients who are not eligible for surgical resection is a mere 6 months. Circulating tumor cells (CTCs) are detectable in the peripheral blood of cancer patients, are accessible through a minimally invasive procedure, and may provide a source of tumor tissue for analyzing molecular markers of therapeutic response that may help guide treatment protocols. To demonstrate this potential, we developed a system for imaging and quantifying multiplexed molecular markers of response to sorafenib/mapatumumab combination therapy in an HCC CTC model. The sorafenib/mapatumumab combination regimen is currently in phase 2 clinical trials for the treatment of HCC, and molecular markers that mediate the synergistic anti-tumor activity of this combination have been identified. These markers include phospho-p42/44 MAPK (p-ERK), Mcl-1, c-IAP2, and apoptotic markers such as cleaved caspase-3. We developed a technical approach using MultiSpectral Imaging (MSI) to quantitatively measure multiplexed fluorescent signals from primary antibodies specific to phospho-ERK, Mcl-1, c-IAP-2, and cleaved caspase-3 that had been conjugated to quantum dots (Qdots) with distinct fluorescence emission spectra. We first confirmed the ability to modulate marker expression and uncouple multiplexed Qdot signals by MSI in cultured HCC cells that had been treated with sorafenib or sorafenib/mapatumumab combinations. We then applied this detection system to HCC cells that were spiked into human blood and recovered using FDA-approved CTC isolation technology (CellSearch CTC Test by Veridex). Our data demonstrate the potential for studying molecular markers of therapeutic response in CTCs. Information gained from this technology may be used to guide therapeutic decisions or serve as pharmacokinetic/pharmacodynamic endpoints in experimental clinical protocols.

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 5665. doi:1538-7445.AM2012-5665

Abstract 3187: Ex vivo characterization of CTCs isolated using the FMSA device

Although technological advances in recent years have enabled isolatation of circulating tumor cells (CTCs), only the VeridexCellSearch System has been approved by the FDA for assessment of patient prognosis in metastatic breast, colon, and prostate cancers. A fundamental challenge with the CellSearch System is that the technique it uses to enrich and detect CTCs, EpCAM-basedimmunomagnetic isolation, fixates captured cells and prevents further molecular characterization by functional assays and primary cell culture. Progress in addressing these issues may help with progress with a variety of clinical needs including further characterization of the biology of individual patient tumors as well as their potential response top various therapeutics. In this study, we use the Flexible Micro Spring Array (FMSA) Device —a novel portable microfluidic device that captures and isolates viable CTCs by two physical parameters: size and flexibility—to capture, culture, and further characterize CTCs.GFP-labeled HCT-116 cells were spiked into healthy samples of donor blood to mimic blood samples of metastatic cancer patients. This spiked blood was filtered using the FMSA device, and the recovered cells were expanded in cell culture. A series of experiments were carried out to characterize these cells and investigate the effect of chemotherapy on the resulting cultures. Studies are ongoing to evaluate the potential of using this model to culture CTCs from patients and to evaluate the response of these cells to chemotherapies using high-throughput methodologies. The isolation of viable CTCs from human blood using the FMSA device provides a novel means for studying viable CTCs and for testing drug efficacy ex vivo. The analysis and identification of CTC-specific characteristics and their relation to chemotherapy susceptibility suggests a potential paradigm shift toward personalized and targeted cancer therapy based on the specific genetic defects of each patient's malignancy and CTCs.

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 3187. doi:1538-7445.AM2012-3187