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Historically, phenotypic-based drug discovery has yielded a high percentage of novel drugs while uncovering new tumor biology. CC-671 was discovered using a phenotypic screen for compounds that preferentially induced apoptosis in triple-negative breast cancer cell lines while sparing luminal breast cancer cell lines. Detailed in vitro kinase profiling shows CC-671 potently and selectively inhibits two kinases—TTK and CLK2. Cellular mechanism of action studies demonstrate that CC-671 potently inhibits the phosphorylation of KNL1 and SRp75, direct TTK and CLK2 substrates, respectively. Furthermore, CC-671 causes mitotic acceleration and modification of pre-mRNA splicing leading to apoptosis, consistent with cellular TTK and CLK inhibition. Correlative analysis of genomic and potency data against a large panel of breast cancer cell lines identifies breast cancer cells with a dysfunctional G1–S checkpoint as more sensitive to CC-671, suggesting synthetic lethality between G1–S checkpoint and TTK/CLK2 inhibition. Furthermore, significant in vivo CC-671 efficacy was demonstrated in two cell line–derived and one patient tumor-derived xenograft models of triple-negative breast cancer (TNBC) following weekly dosing. These findings are the first to demonstrate the unique inhibitory combination activity of a dual TTK/CLK2 inhibitor that preferably kills TNBC cells and shows synthetic lethality with a compromised G1–S checkpoint in breast cancer cell lines. On the basis of these data, CC-671 was moved forward for clinical development as a potent and selective TTK/CLK2 inhibitor in a subset of patients with TNBC. Mol Cancer Ther; 17(8); 1727–38. ©2018 AACR.

Supplementary Figures S1-S3, Tables S1-S7. Suppl. Figure S1: Prolif. Curves, PC3 Cell Cycle & solid tumor apoptosis Suppl. Figure S2: PK/PD Model Performance and eIF4E In Vivo Biomarker Suppl. Figure S3: HCT-116, MBA MD231 & A549 Efficacy Studies Suppl. Table S1: Kinase Selectivity Suppl. Table S2: Cellular Biomarker with SEM Suppl. Table S3: Cellular Proliferation with SEM Suppl. Table S4: Hematological Panel Suppl. Table S5: IRF4 Gene and Protein Data Suppl. Table S6: PK/PD Data PK Data Suppl. Table S7: In Vivo Efficacy Across Tumor Types

SUPPLEMENTAL METHODS • Correlative analysis of CC-671 sensitivity data with genomic features in the 240 Oncopanel • Correlative analysis of CC-671 sensitivity data with genomic features or tumor subtypes in 49 breast cancer cell lines • Molecular of action studies • Xenograft efficacy studies SUPPLEMENTAL DATA • Table S1. Primer sequences for PCR • Table S2. Invitrogen kinase panel data • Table S3. Growth inhibition (IC50 and AUCR Values) of CC-671 in breast cancer panel • Table S4. CC-671 effects on cancer cell proliferation, apoptosis, and cell cycle • Table S5. Cell lines in Oncopanel with mutations in CTNNB1 exon 3 • Table S6. Correlation between CC-671 IC50 values and mutations in CTNNB1 exon 3 in cancer cell lines • Table S7. Correlation of CDKN2A and TP53 mutations with sensitivity or resistance to CC-671 in lung and melanoma cell lines from the Oncopanel • Figure S1. CLK2 knockdown by siRNA reduced phosphorylation of SRp75 in CAL51 cells • Figure S2. Induction of apoptosis in vivo with a single dose of CC-671 in MDA-MB-231 tumors • Figure S3. Antitumor activity of CC-671 in CAL51 and MDA-MB-231 TNBC xenograft models • Figure S4. CC-671 potently and selectively inhibits proliferation and induces apoptosis in cancer cell lines from different anatomic origins • Figure S5. Cancer cell lines with CTNNB1 exon 3 mutations tend to be more sensitive to CC-671 in Oncopanel, but the correlation does not reach statistical significance • Figure S6. TTK expression and CC-671 potency correlate with the growth rates (t0) of cell lines in both breast cancer panel and Oncopanel

mTOR is a serine/threonine kinase that regulates cell growth, metabolism, proliferation, and survival. mTOR complex-1 (mTORC1) and mTOR complex-2 (mTORC2) are critical mediators of the PI3K–AKT pathway, which is frequently mutated in many cancers, leading to hyperactivation of mTOR signaling. Although rapamycin analogues, allosteric inhibitors that target only the mTORC1 complex, have shown some clinical activity, it is hypothesized that mTOR kinase inhibitors, blocking both mTORC1 and mTORC2 signaling, will have expanded therapeutic potential. Here, we describe the preclinical characterization of CC-223. CC-223 is a potent, selective, and orally bioavailable inhibitor of mTOR kinase, demonstrating inhibition of mTORC1 (pS6RP and p4EBP1) and mTORC2 [pAKT(S473)] in cellular systems. Growth inhibitory activity was demonstrated in hematologic and solid tumor cell lines. mTOR kinase inhibition in cells, by CC-223, resulted in more complete inhibition of the mTOR pathway biomarkers and improved antiproliferative activity as compared with rapamycin. Growth inhibitory activity and apoptosis was demonstrated in a panel of hematologic cancer cell lines. Correlative analysis revealed that IRF4 expression level associates with resistance, whereas mTOR pathway activation seems to associate with sensitivity. Treatment with CC-223 afforded in vivo tumor biomarker inhibition in tumor-bearing mice, after a single oral dose. CC-223 exhibited dose-dependent tumor growth inhibition in multiple solid tumor xenografts. Significant inhibition of mTOR pathway markers pS6RP and pAKT in CC-223–treated tumors suggests that the observed antitumor activity of CC-223 was mediated through inhibition of both mTORC1 and mTORC2. CC-223 is currently in phase I clinical trials. Mol Cancer Ther; 14(6); 1295–305. ©2015 AACR.

PDF file - 2080K, Tunable expression of EGFRvIII in genetically modified models correlates with autophagy induction upon CC214-1 treatment.

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PDF file - 5300K, CC214-1 synergizes at low doses with rapamycin. Quantification of the blots shown in Fig. 2B. PTEN detection on DEAL captured GBM39 cells upon CC214-1 treatment.

PDF file - 3457K, Time course dependent CC214-1 treatment in a panel of isogenic GBM cell lines, U87EGFRvIII, U251 and LN229.

PDF file - 1554K, Cap-dependent translation is enhanced by EGFRvIII expression and CC214-1 strongly inhibits P-4E-BP1 phosphorylation.

PDF file - 2561K, Treatment with CC214-1, leads to induction of autophagy in GBM39 cells and genetic inhibition of autophagy sensitizes U87EGFRvIII cells to apoptosis.

PDF file - 5321K, In vitro and in vivo pharmacological inhibition of autophagy sensitizes U87EGFRvIII cells and orthotopic xenografts to CC214-1/CC214-2 mediated apoptosis.

Purpose: mTOR pathway hyperactivation occurs in approximately 90% of glioblastomas, but the allosteric mTOR inhibitor rapamycin has failed in the clinic. Here, we examine the efficacy of the newly discovered ATP-competitive mTOR kinase inhibitors CC214-1 and CC214-2 in glioblastoma, identifying molecular determinants of response and mechanisms of resistance, and develop a pharmacologic strategy to overcome it.Experimental Design: We conducted in vitro and in vivo studies in glioblastoma cell lines and an intracranial model to: determine the potential efficacy of the recently reported mTOR kinase inhibitors CC214-1 (in vitro use) and CC214-2 (in vivo use) at inhibiting rapamycin-resistant signaling and blocking glioblastoma growth and a novel single-cell technology—DNA Encoded Antibody Libraries—was used to identify mechanisms of resistance.Results: Here, we show that CC214-1 and CC214-2 suppress rapamycin-resistant mTORC1 signaling, block mTORC2 signaling, and significantly inhibit the growth of glioblastomas in vitro and in vivo. EGFRvIII expression and PTEN loss enhance sensitivity to CC214 compounds, consistent with enhanced efficacy in strongly mTOR-activated tumors. Importantly, CC214 compounds potently induce autophagy, preventing tumor cell death. Genetic or pharmacologic inhibition of autophagy greatly sensitizes glioblastoma cells and orthotopic xenografts to CC214-1- and CC214-2–induced cell death.Conclusions: These results identify CC214-1 and CC214-2 as potentially efficacious mTOR kinase inhibitors in glioblastoma, and suggest a strategy for identifying patients most likely to benefit from mTOR inhibition. In addition, this study also shows a central role for autophagy in preventing mTOR-kinase inhibitor-mediated tumor cell death, and suggests a pharmacologic strategy for overcoming it. Clin Cancer Res; 19(20); 5722–32. ©2013 AACR.

PDF file - 1694K, EGFRvIII expression sensitizes cells to CC214-1 mediated inhibition of proliferation and to autophagy.

CC-91516 (also called CC0776314), a selective and potent inhibitor of ERK1/2 and NLK, was discovered via a phenotypic screen of a kinase-focused library for compounds that synergize with mTOR kinase inhibitor CC-223 to induce apoptosis in combination with CC-223. Broad kinase selectivity profiling identified ERK1/2 and NLK as targets of CC-91516. Crystal structure of CC-91516 in complex with ERK2 reveals that its 2, 4, 6-trichlorophenyl moiety binds to a unique back pocket of the adenosine-5′-triphosphate (ATP) binding site of ERK2, which is not accessible to other ERK inhibitors such as BVD-523 and GDC-0994. This unique binding mode of CC-91516 leads to a slow off-rate for its ERK binding with long residence time disrupting both the active and inactive ERK forms. Consequentially, CC-91516 causes sustained inhibition of the MAPK pathway in BRAF mutant colorectal cancer cells. In addition, CC-91516 also regulates Wnt/β-catenin and YAP pathways in multiple cancer cell lines. CC-91516 shows potent yet selective anti-proliferative activity against a large panel of cancer cell lines. Activating mutations in BRAF or CTNNB1 gene associate with sensitivity to CC-91516-mediated anti-proliferative activity while mutations in RB and PI3K/PTEN pathway associate with resistance. CC-91516 inhibits ex vivo colony formation of PDX models with BRAF and CTNNB1 mutations. In addition, CC-91516 potently induces apoptosis, inhibits survival, and overcomes resistance to MEK inhibitor trametinib of BRAF or CTNNB1 mutant cancer cells in long-term culture assay in vitro. CC-91516 has good oral bioavailability and shows excellent anti-tumor activity in vivo against both BRAF and CTNNB1 mutant xenograft models. DMPK and toxicology studies showed robust oral exposure across preclinical species. In summary, CC-91516 has demonstrated preclinical anti-tumor activities and DMPK and safety profiles in support of its clinical development. Citation Format: Shuichan Xu, Tam Tran, Dan Zhu, Tao Shi, David Mikolon, Jim Leisten, Philip Chamberlain, Laurie LeBrun, Sogole Bahmanyar, Ning Jiang, Jingjing Zhao, Mehnaz Malek, Ellen Filvaroff, Heather Raymon, Robert Hubbard, John Boylan. Discovery of CC-91516, a potent and selective ERK/NLK inhibitor, with anti-tumor activity in preclinical cancer models harboring BRAF or CTNNB1 mutation [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 1180.

Historically, phenotypic-based drug discovery has yielded a high percentage of novel drugs while uncovering new tumor biology. CC-671 was discovered using a phenotypic screen for compounds that preferentially induced apoptosis in triple-negative breast cancer cell lines while sparing luminal breast cancer cell lines. Detailed in vitro kinase profiling shows CC-671 potently and selectively inhibits two kinases—TTK and CLK2. Cellular mechanism of action studies demonstrate that CC-671 potently inhibits the phosphorylation of KNL1 and SRp75, direct TTK and CLK2 substrates, respectively. Furthermore, CC-671 causes mitotic acceleration and modification of pre-mRNA splicing leading to apoptosis, consistent with cellular TTK and CLK inhibition. Correlative analysis of genomic and potency data against a large panel of breast cancer cell lines identifies breast cancer cells with a dysfunctional G1–S checkpoint as more sensitive to CC-671, suggesting synthetic lethality between G1–S checkpoint and TTK/CLK2 inhibition. Furthermore, significant in vivo CC-671 efficacy was demonstrated in two cell line–derived and one patient tumor-derived xenograft models of triple-negative breast cancer (TNBC) following weekly dosing. These findings are the first to demonstrate the unique inhibitory combination activity of a dual TTK/CLK2 inhibitor that preferably kills TNBC cells and shows synthetic lethality with a compromised G1–S checkpoint in breast cancer cell lines. On the basis of these data, CC-671 was moved forward for clinical development as a potent and selective TTK/CLK2 inhibitor in a subset of patients with TNBC. Mol Cancer Ther; 17(8); 1727–38. ©2018 AACR.

mTOR is a serine/threonine kinase that regulates cell growth, metabolism, proliferation, and survival. mTOR complex-1 (mTORC1) and mTOR complex-2 (mTORC2) are critical mediators of the PI3K–AKT pathway, which is frequently mutated in many cancers, leading to hyperactivation of mTOR signaling. Although rapamycin analogues, allosteric inhibitors that target only the mTORC1 complex, have shown some clinical activity, it is hypothesized that mTOR kinase inhibitors, blocking both mTORC1 and mTORC2 signaling, will have expanded therapeutic potential. Here, we describe the preclinical characterization of CC-223. CC-223 is a potent, selective, and orally bioavailable inhibitor of mTOR kinase, demonstrating inhibition of mTORC1 (pS6RP and p4EBP1) and mTORC2 [pAKT(S473)] in cellular systems. Growth inhibitory activity was demonstrated in hematologic and solid tumor cell lines. mTOR kinase inhibition in cells, by CC-223, resulted in more complete inhibition of the mTOR pathway biomarkers and improved antiproliferative activity as compared with rapamycin. Growth inhibitory activity and apoptosis was demonstrated in a panel of hematologic cancer cell lines. Correlative analysis revealed that IRF4 expression level associates with resistance, whereas mTOR pathway activation seems to associate with sensitivity. Treatment with CC-223 afforded in vivo tumor biomarker inhibition in tumor-bearing mice, after a single oral dose. CC-223 exhibited dose-dependent tumor growth inhibition in multiple solid tumor xenografts. Significant inhibition of mTOR pathway markers pS6RP and pAKT in CC-223–treated tumors suggests that the observed antitumor activity of CC-223 was mediated through inhibition of both mTORC1 and mTORC2. CC-223 is currently in phase I clinical trials. Mol Cancer Ther; 14(6); 1295–305. ©2015 AACR.

CC-671 is a potent and selective TTK1 (Mps1) and CLK2 inhibitor. In support of a phase I proof of concept, we used an image-based, multiplex cell assay to evaluate the antiproliferative impact of CC-671 across a broad panel of cancer cell lines representing tumors from various anatomic origins. CC-671 potently and selectively inhibited proliferation and induced apoptosis. Cell lines representing leukemia, lymphoma, colorectal cancer (CRC), head and neck (H&N), and bladder cancers were uniformly sensitive to CC-671 while the cell lines from other tumor types, such as breast and lung cancers, were differentially sensitive to CC-671. Cell cycle analysis using phospho-histone H3 (pHH3) as a mitosis biomarker suggested that CC-671 had cell line-specific mitotic effects. CC-671 accelerated mitotic exit in 120 cell lines while causing mitotic block in 37 cell lines at concentrations < 1 μM. Custom gene expression signatures correlating with sensitivity or resistance were generated. Mapping these signatures to a gene expression database of clinical tumor samples identified additional CC-671 sensitive tumor types including Wilms tumor, superficial bladder cancer, triple-negative, and luminal Btype breast cancer, and several squamous cell carcinomas (lung, esophageal, cervical, H&N). To identify a breast cancer patient selection profile, the CC-671 antiproliferative activity was assessed in a panel of 49 breast cancer cell lines. CC-671 potently inhibited the growth of breast cancer cell lines with 50% inhibitory concentrations (IC50 values) < 100 nM in 14 lines and > 10 μM in 21 lines. Triple-negative breast cancer (TNBC) cell lines were significantly more sensitive to CC-671 than non-TNBC (ER+/PR+ and/or HER2+) lines. Within TNBC, the mesenchymal (M) and basal-like 1 (BL1) subtypes were more sensitive to CC-671. In addition, TNBC lines with cancer stem cell (CSC)-like properties were also sensitive, indicating a potential role of TTK1 and CLK2 in cancer stem cells. Interestingly, mutations in several genes (phosphatidylinositol-4,5-bisphosphate 3kinase 110 kDa catalytic subunit alpha [PIK3CA], serine/threonine kinase 11 [STK11], and phosphatase and tensin homolog [PTEN]) in the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway tend to associate with CC-671 TNBC sensitivity. These mutational correlates are being confirmed in additional TNBC lines. Citation Format: Shuichan Xu, Tam Tran, Tao Shi, Ning Jiang, Dan Zhu, Jennifer R. Riggs, John Boylan. Identification of a patient enrichment strategy supporting development of a potent and selective dual TTK/CLK2 inhibitor CC-671 [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 A043.

The protein cereblon is part of the CRL4-CRBN E3 ubiquitin ligase complex, and has been shown to be the molecular target for the drugs lenalidomide and pomalidomide. These drugs bind to the surface of cereblon, triggering the recruitment of substrate proteins to the ligase complex where they can be ubiquitinated and subsequently degraded by the proteosome. By this mechanism, lenalidomide and pomalidomide cause the degradation of the zinc finger transcription factors Ikaros and Aiolos, which mediate the antimyeloma activity of these compounds. Here we describe the discovery of CC-885, a novel cereblon modulator with potent and broad-spectrum antiproliferative activity against a panel of tumor cell lines. Acute myeloid leukemia (AML) cell lines and patient-derived AML cells show particular sensitivity to CC-885 treatment. CC-885 achieves this activity by causing the degradation of G1 to S phase transition 1 (GSPT1), a translation termination factor required for the release of nascent peptides from the ribosome. A crystal structure of cereblon in complex with the ligase adapter protein DDB1, as well as CC-885 and GSPT1, reveals that GSPT1 interacts with both CC-885 and the surface of cereblon. The principal molecular feature on GSPT1 that binds to cereblon is a beta-hairpin incorporating a glycine residue that docks against CC-885. Surprisingly, we found evidence that a similar molecular feature mediates Ikaros recruitment, even though there is no common structural fold or sequence homology other than the key glycine residue. We thereby define the common molecular feature, or degron, shared by the known cereblon neomorphic substrates. We further describe a novel therapeutic target, GSPT1, with promise in cancer such as AML. These results further show that cereblon-mediated protein degradation can be directed against new proteins and that this mechanism enables the targeting of multiple protein classes that may be considered undruggable with conventional approaches. Citation Format: Mary Matyskiela, Gang Lu, Takumi Ito, Barbra Pagarigan, Chin-Chu Lu, Karen Miller, Wei Fang, Nai-Yu Wang, Derek Nguyen, Jack Houston, Gilles Carmel, Tam Tran, Mariko Riley, Lyn'Al Nosaka, Gabriel Lander, Svetlana Gaidarova, Shuichan Xu, Alexander Ruchelman, Hiroshi Handa, James Carmichale, Thomas O. Daniel, Brian E. Cathers, Antonia Lopez-Girona, Philip Chamberlain. Ligand-directed degradation of GSPT1 by a novel cereblon modulator drives potent antitumor 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 SY37-02. doi:10.1158/1538-7445.AM2017-SY37-02

Introduction: PIK3CA and PTEN are among the top five most frequently mutated genes in breast cancer. Activating mutation of PIK3CA or loss of function mutation in PTEN leads to constitutive activation of AKT and mTOR driving multiple downstream metabolic and proliferative pathways important to oncogenesis. There is also cross-talk between the PI3K/AKT/mTOR pathway and ER signaling and activation of the PI3K/AKT/mTOR pathway is associated with resistance to endocrine therapy. CC-223 is a potent and selective ATP-competitive mTOR kinase inhibitor, targeting both TORC1 and TORC2 complexes. Results: Pre-clinically, CC-223 potently inhibits the growth of breast cancer cell lines with GI50 values below 1 uM in 38 of 43 lines. Luminal-derived cell lines are more sensitive to CC-223 than basal-derived lines. Within the luminal subset, ER+, HER2+, PIK3CA mutant, or wild-type TP53 cell lines are more sensitive to CC-223; PTEN loss is not associated with increased CC-223 sensitivity. During the dose escalation part of the phase I clinical trial, 3 pts with breast cancer were enrolled. One pt with HR+/Her2- breast cancer had a durable PR (31 weeks). An expansion cohort of HR+/Her2- breast cancer enrolled 17 pts at a CC-223 dose of 45 mg QD in 28-day cycles and 13 pts were evaluable for tumor response. Deep sequencing of tumors for multiple cancer-related genes was performed. The most common (> 20%) related adverse events (all grades) reported in the breast cancer cohort were nausea, stomatitis, fatigue, anorexia, diarrhea, vomiting, hyperglycemia, rash, and thrombocytopenia. Exposure-dependent TORC1 (p4EBP1) and TORC2 (pAKT) inhibition was observed in blood cells; analysis of paired tumor biopsies is ongoing. Reduction in glucose uptake (> 25% decrease in SUV) on PET imaging at day 15 was observed in 4 of 8 patients with PET imaging data currently available. Three pts demonstrated RECIST PR in target lesions (one categorized as PD due to a new bone lesion); PIK3CA mutations were present in all 3 subjects. Of the two additional pts with PIK3CA mutations, one had SD > 6 months. The one PIK3CA mutated subject with PD at first restaging had a concurrent p53 mutation. Additional genetic abnormalities in mTOR and related pathways in subjects with target lesion PR involved PTEN, Rictor, and IGFR1 genes. Six subjects had SD after 2 cycles, with minor target lesion regression (0 to -30%) in 5 of 6, and with SD > 24 weeks in 1 of 6. Conclusion: The safety profile of CC-223 is typical for drugs targeting the mTOR pathway. Preclinical and clinical data support the activity of CC-223 in HR+ positive breast cancer, particularly in tumors with PIK3CA mutations. Breast Cancer Accrual: Cedars-Sinai (Mita): 4; SCRIL (Arkenau): 4; IGR (Varga): 4; SCRI (Bendell): 3 (all Part A); Moffitt (Mahipal): 2; UCSF (Munster): 1; JSOM (Paz-Ares): 1; ICR (DeLord): 1. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A68. Citation Format: Monica M. Mita, Hendrik-Tobias Arkenau, Johanna C. Bendell, Pamela N. Munster, Amit Mahipal, Jean-Pierre Delord, Luis G. Paz-Ares, Jean-Charles Soria, Shuichan Xu, Tam Tran, Tao Shi, Xiaoling Wu, Rajesh Chopra, Kristen Hege, Andrea Varga. Activity of the TORC 1/2 kinase inhibitor, CC-223, in hormone receptor positive (HR+) breast cancer cell lines and patients (pts) with genetically characterized HR+ breast cancer in a Phase I clinical trial. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A68.

CC-223 is a potent and selective mTOR kinase inhibitor currently undergoing Phase 1 clinical evaluation. We evaluated combinatorial effect of CC-223 with 5-Aza and erlotinib at three different ratios of the two combining agents in three different orders of addition in eight NSCLC lines. Combinational indices (CIs) were calculated based upon published method (Chou and Talalay, 1984). CC-223 synergized with azacitidine (CI Citation Format: Tam Tran, Kristen Hege, Deborah Mortensen, Heather Raymon, Shuichan Xu. CC-223, a selective and potent mTOR kinase inhibitor, synergizes with 5-Aza and Erlotinib in eight NSCLC lines in vitro. [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 5252. doi:10.1158/1538-7445.AM2013-5252

Three-dimensional (3D) in vitro models have been used in cancer research to overcome limitations of 2D systems. 3D in vitro models recapitulate many aspects of actual tumors including hypoxia, metabolism, proliferation gradients, cell-cell and cell-matrix interactions and closer clinical gene expression profiles than those seen in 2D. Importantly, some cancer drugs showed high potency only in the 3D environment compared to 2D (Muranen, et al, Cancer Cell, 2012). In order to identify improved cancer drugs, we established a simple and versatile 3D spheroid culture approach for high-throughput screening for compounds that selectively kill cancer cells with certain genetic backgrounds. We used HCT116 (parental: HCT116/KRas-mut) and an isogenic counterpart that expresses a genetically modified KRas gene (HCT116/KRas-wt) for 3D cell culture. To validate this approach, HCT116/KRas-mut and HCT116/KRas-wt were cultured separately, treated with 15 selected tool compounds and viability was measured using a caspase 3/7 assay. We found 4 compounds that induced caspase 3/7 activity only in 3D culture of HCT116/KRas-mut and not in 2D. Furthermore, 5 compounds were predominantly sensitive to HCT116/KRas-wt cells in 3D culture, but not in HCT116/KRas-mut 3D culture. These results indicate that the more physiological relevant 3D synthetic lethal screen is an attractive approach to cancer drug discovery and may identify compounds missed in conventional 2D culture model screens. Citation Format: Toshiya Tsuji, Lisa M. Sapinoso, I-Lin Lin, Shuichan Xu, John F. Boylan. Development of a 3-dimensional synthetic lethality screening approach targeting KRas-mut cells. [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 3839. doi:10.1158/1538-7445.AM2013-3839

mTOR pathway hyper activation is a common feature in many cancers, including in nearly 90% of Glioblastomas. mTOR exists in two multiprotein complexes, which differ in regulation, function, and response to the allosteric mTOR inhibitor rapamycin. The failure of glioblastomas to clinically respond to rapamycin appears to be mediated both by inability of rapamycin to inhibit mTORC2 signaling, and by failure to fully suppress p4E-BP1, a critical effector of mTORC1. The new generation of mTOR kinase inhibitors (mTORki) has emerged as a new class of targeted cancer therapies capable of blocking mTOR more potently than rapalogs (such as Rapamycin). Here we demonstrate that CC214-1 and CC214-2, mTOR kinase inhibitors, have potent effects on the growth of glioblastoma in vitro and in vivo. Across a panel of GBM cell lines, CC214-1 was significantly more effective at suppressing 4E-BP1 phosphorylation and protein translation, and mTORC2 signaling than rapamycin, resulting in significantly more growth inhibition at equal levels of suppression of S6 phosphorylation. EGFRvIII, the constitutively active EGFR mutant frequently detected in GBMs strongly activates mTORC1 and mTORC2 signaling, potently sensitizing tumors to CC214-1. In contrast, PTEN expression suppressed mTOR signaling and reduced the response to CC214-1. In vivo CC214-2 significantly inhibited mTORC1 and mTORC2 signaling, significantly suppressing tumor growth by 50%. CC214-1 also potently activated autophagy. Addition of chloroquine suppressed autophagy resulting in significant CC214-1-dependent apoptotic cell death. These results demonstrate the potential activity of mTOR kinase inhibitors in GBM, and identify EGFRvIII expression and PTEN loss as molecular determinants of response. These data also suggest that mTOR kinase inhibitors, alone or in combination with autophagy inhibiting agents, are likely to have significant anti-tumor efficacy in GBM patients. 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 1923. doi:1538-7445.AM2012-1923