Synergistic Antiproliferative Activity Research Articles

Abstract 1924: Therapeutic potential of inhibitor of apoptosis protein (IAP) inhibitor APG-1387 combined with DR5 agonist monoclonal antibody (mAb) CTB-006 in preclinical models of solid tumors

Abstract TNF-related apoptosis-inducing ligand (TRAIL) receptor (DR4 or DR5) agonists are promising agents for cancer therapy because they induce apoptosis selectively in cancer cells. However, their clinical effect is hampered by either primary or acquired resistance in cancer cells. Second mitochondria-derived activator of caspase (Smac) mimetics that antagonize the IAPs potently sensitize cancer cells to TRAIL-induced apoptosis in a caspase-8-dependent manner. We evaluated antitumor effects of small-molecule IAP antagonist APG-1387combined with an agonist mouse mAb directed against TRAIL death receptor type 5 (DR5) termed CTB-006 in the preclinical setting. Both agents are in phase I/II clinical development for patients with solid tumors. In vitro the combination treatment showed synergy in a dose-dependent manner across various cancer cell lines, as evidenced by synergistic antiproliferative activity and enhanced induction of caspase-3 cleavage. Potential synergistic in vivo antitumor activity of the combination was then assessed in human triple negative breast cancer (TNBC) xenograft models in mice. Specifically, in MDA-MB-231 and 2LMP TNBC xenograft models, either APG-1387 or CTB-006 single agent exhibited limited antitumor activity, with T/C (%) values of >35% (T, tumor volume in the treatment group; C, tumor volume in the vehicle control group). Only one tumor showed partial regression (PR) by DR5 treatment. Addition of APG-1387 potentiated this effect, with the combination treatment leading to T/C values of 3% to 15%, and complete regression, PR, or stable disease in all treated tumors. In summary, our results suggest great potential of combination therapy with APG-1387 and CTB-006 for solid tumor therapy and deserves further clinical investigation. Citation Format: Qiang Li, Douglas D. Fang, Zhe Li, Dajun Yang, Fengqi Cao, Yifan Zhai. Therapeutic potential of inhibitor of apoptosis protein (IAP) inhibitor APG-1387 combined with DR5 agonist monoclonal antibody (mAb) CTB-006 in preclinical models of solid tumors [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 1924.

Abstract 1271: In vitro and in vivo characterization of BI 1823911 - a novel KRASG12C selective small molecule inhibitor

Abstract KRASG12C mutations are predominantly found in non-small cell lung cancer (NSCLC, 13%), in colorectal cancer (CRC, 3%), and with a lower prevalence in pancreatic ductal adenocarcinoma (PDAC, 1%). The amino acid exchange at position 12 from glycine to cysteine renders RAS insensitive to GAP-catalyzed hydrolysis but not to intrinsic hydrolysis and consequently, KRASG12C is still dependent on GEF stimulation to achieve full activation. The active GTP-loaded form of KRASG12C is favored and leads to activation of downstream signaling and proliferation. A number of recent publications has shown that targeting this mutant form of KRAS, using several covalent KRASG12C inhibitors binding to the inactive GDP-KRASG12C form, leads to anti-proliferative effects and induction of apoptosis in KRASG12C mutant cancer cell lines, CDX and PDX models. Early clinical data for AMG 510 and MRTX849 revealed a response rate of 35-45% in NSCLC and of 7-17% in CRC patients. Here, we show that BI 1823911 has potent anti-proliferative activity in a panel of KRASG12C mutant cancer cell lines with higher or similar potency compared to these two most advanced compounds in clinical development. In a panel of KRASG12C NSCLC cell lines, treatment with BI 1823911 results in downregulation of MAPK pathway-responsive genes, such as DUSP6 and CCND1, and the extent of pathway modulation correlates with sensitivity. Likewise, we observe strong and sustained inactivation of the MAPK pathway at the protein level using p-ERK as a pharmacodynamic (PD) biomarker. A MIA PaCa-2 cell line-derived pancreatic cancer xenograft model was selected for extensive PK/PD/efficacy analyses in vivo. Briefly, BI 1823911 tested at 60 mg/kg showed similar anti-tumor activity compared to both competitor compounds dosed at clinically relevant exposures. Results of the ongoing in-depth PK/PD/efficacy analysis will be shared. Furthermore, BI 1823911 was tested with a daily oral dose of 60 mg/kg in a panel of NSCLC or CRC CDX or PDX mouse models and showed comparable efficacy to AMG 510 and MRTX849, respectively. Preclinical and clinical data suggest that monotherapy with a KRASG12C inhibitor will not be sufficient to achieve durable response. Combination therapy of a KRASG12C inhibitor may therefore lead to enhanced anti-tumor efficacy and may address adaptive resistance mechanisms. Therefore, we selected a panel of KRASG12C mutant cancer cell lines and tested a large set of compounds in combination with BI 1823911 to identify synergistic anti-proliferative activity. Among other MAPK and PI3K pathway inhibitors, a SOS1::KRAS inhibitor was confirmed as promising combination partner. We will show results from in vitro and in vivo combination studies in NSCLC and CRC tumor models that show deep and durable responses upon combination of BI 1823911 with SOS1::KRAS inhibitor BI 1701963 providing a strong rationale for clinical investigation of this combination. Citation Format: Fabio Savarese, Andreas Gollner, Dorothea Rudolph, Jesse Lipp, Johannes Popow, Marco H. Hofmann, Heribert Arnhof, Jörg Rinnenthal, Francesca Trapani, Michael Gmachl, Daniel Gerlach, Joachim Broeker, Peter Ettmayer, Andreas Mantoulidis, Jason Phan, Christian A. Smethurst, Matthias Treu, Alex G. Waterson, Hengyu Lu, Annette Machado, Joseph Daniele, Stephan W. Fesik, Christopher P. Vellano, Timothy P. Heffernan, Joseph R. Marszalek, Darryl B. McConnell, Mark Petronczki, Norbert Kraut, Irene C. Waizenegger. In vitro and in vivo characterization of BI 1823911 - a novel KRASG12C selective small molecule inhibitor [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 1271.

Novel Affibody Molecules Targeting the HPV16 E6 Oncoprotein Inhibited the Proliferation of Cervical Cancer Cells.

Despite prophylactic vaccination campaigns, high-risk human papillomavirus (HPV)-induced cervical cancer remains a significant health threat among women, especially in developing countries. The initial occurrence and consequent progression of this cancer type primarily rely on, E6 and E7, two key viral oncogenes expressed constitutively, inducing carcinogenesis. Thus, E6/E7 have been proposed as ideal targets for HPV-related cancer diagnosis and treatment. In this study, three novel HPV16 E6-binding affibody molecules (ZHPV16E61115, ZHPV16E61171, and ZHPV16E61235) were isolated from a randomized phage display library and cloned for bacterial production. These affibody molecules showed high binding affinity and specificity for recombinant and native HPV16 E6 as determined by surface plasmon resonance, indirect immunofluorescence, immunohistochemistry, and near-infrared small animal optical imaging in vitro and in vivo. Moreover, by binding to HPV16 E6 protein, ZHPV16E61235 blocked E6-mediated p53 degradation, which increased the expression of some key p53 target genes, including BAX, PUMA and p21, and thereby selectively reduced the viability and proliferation of HPV16-positive cells. Importantly, ZHPV16E61235 was applied in combination with HPV16 E7-binding affibody ZHPV16E7384 to simultaneously target the HPV16 E6/E7 oncoproteins, and this combination inhibited cell proliferation more potently than either modality alone. Mechanistic studies revealed that the synergistic antiproliferative activity depends primarily on the induction of cell apoptosis and senescence but not cell cycle arrest. Our findings provide strong evidence that three novel HPV16 E6-binding affibody molecules could form a novel basis for the development of rational strategies for molecular imaging and targeted therapy in HPV16-positive preneoplastic and neoplastic lesions.

Anticancer activity of repurposed hemostatic agent desmopressin on AVPR2-expressing human osteosarcoma.

Osteosarcoma is the most prevalent primary bone malignancy. Due to its high aggressiveness, novel treatment strategies are urgently required to improve survival of patients with osteosarcoma, especially those with advanced disease. Desmopressin (dDAVP) is a widely used blood-saving agent that has been repurposed as an adjuvant agent for cancer management due to its antiangiogenic and antimetastatic properties. dDAVP acts as a selective agonist of the vasopressin membrane receptor type 2 (AVPR2) present in the microvascular endothelium and in some cancer cells, including breast, lung, colorectal and neuroendocrine tumor cells. Despite the fact that dDAVP has demonstrated its antitumor efficacy in a wide variety of tumor types, exploration of its potential anti-osteosarcoma activity has, to the best of our knowledge, not yet been conducted. Therefore, the aim of the present study was to evaluate the preclinical antitumor activity of dDAVP in osteosarcoma. Human MG-63 and U-2 OS osteosarcoma cell lines were used to assess in vitro and in vivo therapeutic effects of dDAVP. At low micromolar concentrations, dDAVP reduced AVPR2-expressing MG-63 cell growth in a concentration-dependent manner. In contrast, dDAVP exhibited no direct cytostatic effect on AVPR2-negative U-2 OS cells. As it would be expected for canonical AVPR2-activation, dDAVP raised intracellular cAMP levels in osteosarcoma cells, and coincubation with phosphodiesterase-inhibitor rolipram indicated synergistic antiproliferative activity. Cytostatic effects were associated with increased apoptosis, reduced mitotic index and impairment of osteosarcoma cell chemotaxis, as evaluated by TUNEL-labeling, mitotic body count in DAPI-stained cultures and Transwell migration assays. Intravenous administration of dDAVP (12 µg/kg; three times per week) to athymic mice bearing rapidly growing MG-63 xenografts, was indicated to be capable of reducing tumor progression after a 4-week treatment. No major alterations in animal weight, biochemical or hematological parameters were associated with dDAVP treatment, confirming its good tolerability and safety. Finally, AVPR2 expression was detected by immunohistochemistry in 66% of all evaluated chemotherapy-naive human conventional osteosarcoma biopsies. Taking these findings into account, repurposed agent dDAVP may represent an interesting therapeutic tool for the management of osteosarcoma. Further preclinical exploration of dDAVP activity on orthotopic or metastatic osteosarcoma models are required.

MNK1 and MNK2 enforce expression of E2F1, FOXM1, and WEE1 to drive soft tissue sarcoma

Soft tissue sarcoma (STS) is a heterogeneous disease that arises from connective tissues. Clinical outcome of patients with advanced tumors especially de-differentiated liposarcoma and uterine leiomyosarcoma remains unsatisfactory, despite intensive treatment regimens including maximal surgical resection, radiation, and chemotherapy. MAP kinase-interacting serine/threonine-protein kinase 1 and 2 (MNK1/2) have been shown to contribute to oncogenic translation via phosphorylation of eukaryotic translation initiation factor 4E (eIF4E). However, little is known about the role of MNK1/2 and their downstream targets in STS. In this study, we show that depletion of either MNK1 or MNK2 suppresses cell viability, anchorage-independent growth, and tumorigenicity of STS cells. We also identify a compelling antiproliferative efficacy of a novel, selective MNK inhibitor ETC-168. Cellular responsiveness of STS cells to ETC-168 correlates positively with that of phosphorylated ribosomal protein S6 (RPS6). Mirroring MNK1/2 silencing, ETC-168 treatment strongly blocks eIF4E phosphorylation and represses expression of sarcoma-driving onco-proteins including E2F1, FOXM1, and WEE1. Moreover, combination of ETC-168 and MCL1 inhibitor S63845 exerts a synergistic antiproliferative activity against STS cells. In summary, our study reveals crucial roles of MNK1/2 and their downstream targets in STS tumorigenesis. Our data encourage further clinical translation of MNK inhibitors for STS treatment.

Synergism of AZD6738, an ATR Inhibitor, in Combination with Belotecan, a Camptothecin Analogue, in Chemotherapy-Resistant Ovarian Cancer.

Epithelial ovarian cancer remains the leading cause of mortality among all gynecologic malignancies owing to recurrence and ultimate development of chemotherapy resistance in the majority of patients. In the chemotherapy-resistant ovarian cancer preclinical model, we investigated whether AZD6738 (an ataxia telangiectasia and Rad3-related (ATR) inhibitor) could synergize with belotecan (a camptothecin analog and topoisomerase I inhibitor). In vitro, both chemotherapy-resistant and chemotherapy-sensitive ovarian cancer cell lines showed synergistic anti-proliferative activity with a combination treatment of belotecan and AZD6738. The combination also demonstrated synergistic tumor inhibition in mice with a chemotherapy-resistant cell line xenograft. Mechanistically, belotecan, a DNA-damaging agent, increased phospho-ATR (pATR) and phospho-Chk1 (pChk1) in consecutive order, indicating the activation of the DNA repair system. This consequently induced G2/M arrest in the cell cycle analysis. However, when AZD6738 was added to belotecan, pATR and pChk1 induced by belotecan alone were suppressed again. A cell cycle analysis in betotecan showed a sub-G1 increase as well as a G2/M decrease, representing the release of G2/M arrest and the induction of apoptosis. In ascites-derived primary cancer cells from both chemotherapy-sensitive and -resistant ovarian cancer patients, this combination was also synergistic, providing further support for our hypothesis. The combined administration of ATR inhibitor and belotecan proved to be synergistic in our preclinical model. This combination warrants further investigation in a clinical trial, with a particular aim of overcoming chemotherapy resistance in ovarian cancer.

Nitidumpeptins A and B, Cyclohexapeptides Isolated from Zanthoxylum nitidum var. tomentosum: Structural Elucidation, Total Synthesis, and Antiproliferative Activity in Cancer Cells.

Nitidumpeptins A and B (1 and 2), two novel cyclic hexapeptides, were isolated from the herb Zanthoxylum nitidum var. tomentosum. Their planar structures were elucidated based on NMR and MS spectrometric analysis, and the absolute configurations were determined by the Marfey's method. Structurally, 1 is a unique peptide with a backbone bearing a pyrrolidine-2,5-dione unit, which is the first occurrence moiety specifically in a naturally occurring cyclohexapeptide. The total synthesis of 1 and 2 was achieved by solution-phase in parallel with solid-phase peptide synthesis, and their absolute configurations were further confirmed. The combination of 2 with gefitinib exhibited synergistic antiproliferative activity in acquired gefitinib-resistant non-small cell lung cancer cells (HCC827-gef). The underlying mechanism for the antiproliferative activity of 2 was in part associated with the suppression of YAP expression in HCC827-gef cells.

The structure and biosynthesis of heinamides A1-A3 and B1-B5, antifungal members of the laxaphycin lipopeptide family.

Laxaphycins are a family of cyclic lipopeptides with synergistic antifungal and antiproliferative activities. They are produced by multiple cyanobacterial genera and comprise two sets of structurally unrelated 11- and 12-residue macrocyclic lipopeptides. Here, we report the discovery of new antifungal laxaphycins from Nostoc sp. UHCC 0702, which we name heinamides, through antimicrobial bioactivity screening. We characterized the chemical structures of eight heinamide structural variants A1-A3 and B1-B5. These variants contain the rare non-proteinogenic amino acids 3-hydroxy-4-methylproline, 4-hydroxyproline, 3-hydroxy-d-leucine, dehydrobutyrine, 5-hydroxyl β-amino octanoic acid, and O-carbamoyl-homoserine. We obtained an 8.6-Mb complete genome sequence from Nostoc sp. UHCC 0702 and identified the 93 kb heinamide biosynthetic gene cluster. The structurally distinct heinamides A1-A3 and B1-B5 variants are synthesized using an unusual branching biosynthetic pathway. The heinamide biosynthetic pathway also encodes several enzymes that supply non-proteinogenic amino acids to the heinamide synthetase. Through heterologous expression, we showed that (2S,4R)-4-hydroxy-l-proline is supplied through the action of a novel enzyme LxaN, which hydroxylates l-proline. 11- and 12-residue heinamides have the characteristic synergistic activity of laxaphycins against Aspergillus flavus FBCC 2467. Structural and genetic information of heinamides may prove useful in future discovery of natural products and drug development.

Preclinical and Translational Support for Clinical Development of Iberdomide in Combination with Proteasome Inhibitors: Mechanism of Synergy in Clinical Trial CC-220-MM-001

Preclinical and Translational Support for Clinical Development of Iberdomide in Combination with Proteasome Inhibitors: Mechanism of Synergy in Clinical Trial CC-220-MM-001

A first-in-class CDK4 inhibitor demonstrates in vitro, ex-vivo and in vivo efficacy against ovarian cancer

IntroductionCyclin-dependent kinases 4 and 6 (CDK4/6) are fundamental drivers of the cell cycle and are involved in the initiation and progression of various cancers. Deregulation of the CDK4/6-cyclin D-retinoblastoma (Rb) pathway is common in ovarian cancer and is associated with an aggressive phenotype and poor prognosis. Patients with advanced ovarian cancer whose tumor demonstrates Rb-positivity, a low expression of p16 and overexpression of cyclin D1 are most likely to benefit from CDK4/6 inhibition. Materials and methodAnti-proliferative activity and mechanistic investigations for CDDD2–94, employing palbociclib as comparator, were evaluated by MTT assay, cell cycle and apoptosis analysis, western blotting as well as senescence and colony formation assay. In vivo safety and efficacy studies were done in A2780 tumor-bearing nude mice. Combinations of CDDD2–94 with mTOR, MEK, PI3K or PARP inhibitors were evaluated in A2780 and OVCAR5 ovarian cancer cells. ResultsConsistent with a CDK4-targeted mechanism, CDDD2–94 arrested the G1/G0 cell cycle, induced senescence and inhibited the proliferation of Rb-proficient ovarian cancer cells. CDDD2–94 exhibited synergistic anti-proliferative activities with mTOR, MEK, PI3K or PARP inhibitors. Importantly, unlike palbociclib which caused significant reductions in the number of lymphocytes and neutrophils, CDDD2–94 had little effect. CDDD2–94, as single agent and in combination with everolimus, delayed tumor growth and significantly increased survival of mice. ConclusionGiven its high specificity in targeting CDK4 and excellent anti-tumor efficacy with low toxicity, CDDD2–94 has potential to be developed as a standalone agent or in combination with targeted therapeutics for the treatment of ovarian cancer.

Abstract 5270: HSP90 identified by a proteomic approach as druggable target to reverse platinum-resistance in ovarian cancer

Abstract INTRODUCTION: Epithelial ovarian cancer (EOC) represents the gynecologic cancer with the highest mortality rate. Despite a high initial response to platinum (PT)-based chemotherapy, the majority of patients with advanced EOC relapses and develops chemo-resistance that results in treatment failure and poor prognosis. Therefore, understanding the mechanisms underlying PT-resistance and finding strategies to overcome them are urgently needed. METHODS: Three isogenic models of PT-resistance generated by our group from EOC cell lines (TOV-112D, OVSAHO and MDAH) (Sonego M. et al, 2017), were characterized by a proteomic approach taking advantage of two-dimensional differential in gel electrophoresis (2-D DIGE) followed by Mass Spectrometry. Proteomics data were also analyzed by the ingenuity pathway analysis (IPA) software. Synergistic anti-proliferative activity was evaluated by calculating combination indexes (CI) by the Chou-Talalay method and colony formation assay. Apoptosis was measured by flow-cytometry and by western blotting evaluation of caspase-3 and PARP cleavage. In vivo experiments were performed on xenograft model in athymic mice. RESULTS: We identified 23, 24 and 20 differentially expressed proteins in PT-resistant TOV-112D, OVSAHO and MDAH respectively, compared with parental cells. A relevant relationship between all the identified proteins in the three models was highlighted by IPA. Interestingly, eight of the identified proteins, HSP7C, HNRPL, ATPA, EFTU, PHB, HNRPK, LMNA and PHGDH, shared at least within two cell lines, are all included in one main network related with cancer. Notably, the protein chaperone HSP90 emerged as a central hub of this network and its up-regulation was observed in all the PT-resistant cell lines compared with parental counterparts. Further molecular characterization also showed overexpression of HSF1 transcription factor, a relevant HSP90 activator and client protein, in PT-resistant cells. On this bases, we evaluated the effect of cisplatin in combination with two HSP90 inhibitors (17AAG or ganetespib), both in phase II/III clinical development in cancer patients, observing synergistic anti-proliferative activity and reduced colony formation, particularly in PT-resistant cells. These data were confirmed in primary cultures from PT-Resistant ovarian cancer patients. Furthermore we confirmed for the first time in vivo the synergistic antitumor effect of cisplatin and ganetespib combination in TOV112D PT-resistant xenograft model. Increased pro-apoptotic effect and DNA-damage induction by the combination treatment compared to untreated or single agents treated tumors was confirmed both in vitro and in vivo. CONCLUSIONS: Our data suggest an innovative antitumor strategy based on the combination of platinum compounds with HSP90 inhibitors, to re-challenge PT-resistant EOC, that warrants further clinical evaluation. Citation Format: Rita Lombardi, Maura Sonego, Laura Addi, Federica Iannelli, Francesca Capone, Maria Serena Roca, Maria Rita Milone, Alice Costa, Francesca Bruzzese, Biagio Pucci, Gustavo Baldassarre, Alfredo Budillon. HSP90 identified by a proteomic approach as druggable target to reverse platinum-resistance in ovarian cancer [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 5270.

Abstract 5853: Identification of TSC1 and TSC2 as potential determinants of sensitivity to trastuzumab emtansine

Abstract Trastuzumab emtansine (T-DM1, Kadcyla) is an antibody-drug conjugate used in the treatment of HER2-positive breast cancer. However, its use is limited by acquired and intrinsic resistance, the mechanisms of which are not well understood. Further knowledge of T-DM1 resistance may provide new combination strategies or therapeutic targets to overcome resistance or new predictive biomarkers to identify the patients most likely to benefit from T-DM1 therapy. To discover genes responsible for T-DM1 sensitivity and resistance in an unbiased manner, we have conducted CRISPR/Cas9 functional genomics screens by a two-stage process. Firstly, we performed whole genome screens in MDA-MB-361 and MDA-MB-453 cells transduced with Cas9 and the GeCKOv2 lentiviral library that were exposed to T-DM1 and its effector DM1 for 8-13 weeks. Gene knockouts enriched or depleted in response to T-DM1 or DM1 treatment in either cell line were identified by sequencing of genomic DNA and differentially expressed genes by RNA sequencing, revealing 599 candidate genes of T-DM1 sensitivity. For high-throughput validation of the 599 genes, we developed a custom library of 2539 guide RNAs (gRNAs) to target these 599 genes, plus non-targeting controls. Cas9-expressing MDA-MB-361 cells were transduced with the custom library and exposed to T-DM1 for 28 days. MAGeCK analysis of gRNA sequencing revealed 11 genes that were significantly enriched and one gene that was significantly depleted at a false discovery rate (FDR) of <0.1. Two of the top hits in the secondary screen were two genes whose loss is known to promote T-DM1 resistance: ERBB2 (HER2) and SLC46A3 (P<8 × 10−5; FDR <0.007). Other top hits were TSC1 and TSC2 (P<3 × 10−6; FDR= 0.0004); which are both tumor suppressor genes and negative regulators of mTOR complex 1 (mTORC1). For subsequent validation, we have generated TSC2 knockout cell pools, which were more resistant to T-DM1 than wildtype cells in a competition growth assay. Knockout clones have been isolated and are being tested for T-DM1 resistance. Since mTOR inhibitors can phenocopy TSC1 and TSC2 by inhibiting mTORC1 activity, we have also evaluated T-DM1 in combination with the mTOR inhibitor KU-0063794 in a sulforhodamine B assay in MDA-MB-361 and MDA-MB-453 cells. Each agent potently inhibited cell proliferation and demonstrated synergistic anti-proliferative activity in combination. Together, our results suggest that TSC1 and TSC2 knockout may promote T-DM1 resistance and that targeting mTOR may be an effective strategy to overcome T-DM1 resistance. Citation Format: Francis W. Hunter, Barbara A. Lipert, Kyla N. Siemens, Aziza Khan, Hilary R. Barker, Troy W. Ketela, William R. Wilson, Tet-Woo Lee, Stephen M. Jamieson. Identification of TSC1 and TSC2 as potential determinants of sensitivity to trastuzumab emtansine [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 5853.

Targeting Casein Kinase 1 Delta Sensitizes Pancreatic and Bladder Cancer Cells to Gemcitabine Treatment by Upregulating Deoxycytidine Kinase.

Although gemcitabine is the cornerstone of care for pancreatic ductal adenocarcinoma (PDA), patients lack durable responses and relapse is inevitable. While the underlying mechanisms leading to gemcitabine resistance are likely to be multifactorial, there is a strong association between activating gemcitabine metabolism pathways and clinical outcome. This study evaluated casein kinase 1 delta (CK1δ) as a potential therapeutic target for PDA and bladder cancer, in which CK1δ is frequently overexpressed. We assessed the antitumor effects of genetically silencing or pharmacologically inhibiting CK1δ using our in-house CK1δ small-molecule inhibitor SR-3029, either alone or in combination with gemcitabine, on the proliferation and survival of pancreatic and bladder cancer cell lines and orthotopic mouse models. Genetic studies confirmed that silencing CK1δ or treatment with SR-3029 induced a significant upregulation of deoxycytidine kinase (dCK), a rate-limiting enzyme in gemcitabine metabolite activation. The combination of SR-3029 with gemcitabine induced synergistic antiproliferative activity and enhanced apoptosis in both pancreatic and bladder cancer cells. Furthermore, in an orthotopic pancreatic tumor model, we observed improved efficacy with combination treatment concomitant with increased dCK expression. This study demonstrates that CK1δ plays a role in gemcitabine metabolism, and that the combination of CK1δ inhibition with gemcitabine holds promise as a future therapeutic option for metastatic PDA as well as other cancers with upregulated CK1δ expression.

Abstract A50: Lapatinib potentiates the antitumor effects of paclitaxel treatment in resistant ovarian cancer cells

Abstract Introduction: Frontline treatment regimens for ovarian cancer routinely consist of repeated cycles of paclitaxel/platinum doublets; however, chemotherapy resistance frequently leads to recurrent or refractory disease. Novel therapeutic strategies aimed at circumventing or preventing resistance are needed for improved disease control. Experimental Procedures: Multiple paclitaxel-resistant ovarian cancer cell line models were established via repeated cycles of paclitaxel treatment in vitro. Resistance to paclitaxel was assessed using dose response cell viability assays with CellTiter-Glo 2.0 and calculation of IC50 values using a 4-parameter logistic regression model. RNAseq and whole-exome sequencing were used to examine genomic variation distinguishing resistant lines from their sensitive counterparts. Recurrent expression differences associated with paclitaxel resistance were identified, a subset of which were selected for further validation. Candidate genes and pathways associated with paclitaxel resistance were manipulated using siRNA and/or small-molecule inhibitors and assessed for the ability to alter the resistant phenotype. Synergistic interactions for drug combinations were evaluated using the Loewe Additivity model. Results: Paclitaxel-resistant ovarian cancer cell lines were derived from TOV-21G, OVCAR-3, and UWB1.289 cells. Resistant cell lines exhibited increases in paclitaxel IC50 ranging from 6.5 to 94-fold over their parental control cells. RNAseq analysis identified the transcript encoding P-glycoprotein (P-gp), ABCB1, among the most highly upregulated genes in the resistant TOV-21G and OVCAR-3 cells while no such induction of expression was seen in resistant UWB1.289 cells. Previous reports have shown several different tyrosine kinase inhibitors (e.g., lapatinib, neratinib, dasatinib, etc.) have the ability to inhibit P-gp function. We tested a panel of tyrosine kinase inhibitors for the ability to sensitize resistant P-gp-overexpressing ovarian cancer cells to paclitaxel. The most potent synergistic antiproliferative activity was observed when lapatinib was combined with paclitaxel treatment of resistant TOV-21G and OVCAR-3 cells; however, a similar interaction was not observed in resistant UWB1.289 cells that do not overexpress P-gp. The dependence of this synergistic effect on P-gp expression was confirmed by using siRNA to inhibit P-gp expression in paclitaxel-resistant TOV-21G and OVCAR-3 cells, significantly reducing paclitaxel IC50 by 20.7 and 6.2-fold, respectively, and eliminating cytotoxic synergy. Conclusions: Paclitaxel and lapatinib have synergistic anticancer properties when used to treat P-gp-overexpressing ovarian cancer cells. The addition of lapatinib to second-line dose-dense paclitaxel therapy could be an effective strategy for a subset of ovarian cancer patients with recurrent disease and warrants further clinical exploration. Citation Format: Rob McCorkle, Justin W. Gorski, Abigail Anderson, Jill M. Kolesar. Lapatinib potentiates the antitumor effects of paclitaxel treatment in resistant ovarian cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A50.

Salinomycin and Sulforaphane Exerted Synergistic Antiproliferative and Proapoptotic Effects on Colorectal Cancer Cells by Inhibiting the PI3K/Akt Signaling Pathway in vitro and in vivo.

BackgroundBoth salinomycin (SAL) and sulforaphane (SFN) exert their antitumorigenic effects in various types of cancer We investigated whether combining salinomycin (SAL, an antibiotic ionophore) with sulforaphane (SFN, a phytochemical) exerted synergistic antiproliferative and proapoptotic activities in colorectal cancer (CRC) cells in vitro and in vivo by evaluating the proliferative and apoptotic responses of two CRC cell lines.Materials and MethodsThe combination index (CI) was calculated using the Chou-Talalay method, and the effects of the synergistic combination (CI<1) of lower doses of SAL and SFN were selected for further studies. Anti-tumor effect of the combination of SAL and SFN was tested both in vitro and in vivo.ResultsCotreatment effectively inhibited proliferation, migration and invasion and enhanced apoptosis. The xenograft model also showed similar results. Furthermore, we evaluated the molecular mechanism behind SAL- and SFN-mediated CRC cell apoptosis. The combination treatment induced apoptosis in Caco-2 and CX-1 cells by inhibiting the PI3K/Akt pathway, which increased the expression of the tumor suppressor protein p53. The treatment also decreased the expression of the survival protein Bcl-2 and increased the expression of the proapoptotic protein Bax, which increased the Bax/Bcl-2 ratio, as well as enhanced poly ADP-ribose polymerase (PARP) cleavage. Upon inhibiting the PI3K/Akt pathway with LY294002 prior to cotreatment, we detected enhanced PARP cleavage compared to that in the cotreatment only group.ConclusionWe investigated whether the combination of SAL and SFN had antiproliferative and proapoptotic effects in CRC cells both in vitro and in vivo. Cotreatment also significantly decreased migration and invasion compared to that of the control and SAL or SFN monotherapies. This novel combination of SAL and SFN might provide a potential strategy to treat CRC.

Inactivation of NF1 Promotes Resistance to EGFR Inhibition in KRAS/NRAS/BRAFV600 -Wild-Type Colorectal Cancer.

Through the use of an unbiased, genome-scale CRISPR modifier screen, we identified NF1 suppression as a mechanism of resistance to EGFR inhibition in NRAS/KRAS/BRAFV600 -wild-type colorectal cancer cells. Reduced NF1 expression permitted sustained signaling through the MAPK pathway to promote cell proliferation in the presence of EGFR inhibition. Targeting of MEK in combination with EGFR inhibition leads to synergistic antiproliferative activity. Human KRAS/NRAS/BRAFV600 -wild-type colorectal cancer cell lines with NF1 mutations displayed reduced NF1 mRNA or protein expression and were resistant to EGFR blockade by gefitinib or cetuximab. Cooccurring loss-of-function mutations in PTEN were associated with resistance to dual EGFR/MEK inhibition but cotreatment with a PI3K inhibitor further suppressed proliferation. Loss of NF1 may be a useful biomarker to identify patients that are less likely to benefit from single-agent anti-EGFR therapy in colorectal cancer and may direct potential combination strategies. IMPLICATIONS: This study suggests that further clinical validation of NF1 status as predictor of response to anti-EGFR targeting antibodies in patients with colorectal cancer with KRAS/NRAS/BRAFV600 -wild-type tumors is warranted.

The Novel ATR Inhibitor BAY 1895344 Is Efficacious as Monotherapy and Combined with DNA Damage-Inducing or Repair-Compromising Therapies in Preclinical Cancer Models.

The DNA damage response (DDR) secures the integrity of the genome of eukaryotic cells. DDR deficiencies can promote tumorigenesis but concurrently may increase dependence on alternative repair pathways. The ataxia telangiectasia and Rad3-related (ATR) kinase plays a central role in the DDR by activating essential signaling pathways of DNA damage repair. Here, we studied the effect of the novel selective ATR kinase inhibitor BAY 1895344 on tumor cell growth and viability. Potent antiproliferative activity was demonstrated in a broad spectrum of human tumor cell lines. BAY 1895344 exhibited strong monotherapy efficacy in cancer xenograft models that carry DNA damage repair deficiencies. The combination of BAY 1895344 with DNA damage-inducing chemotherapy or external beam radiotherapy (EBRT) showed synergistic antitumor activity. Combination treatment with BAY 1895344 and DDR inhibitors achieved strong synergistic antiproliferative activity in vitro, and combined inhibition of ATR and PARP signaling using olaparib demonstrated synergistic antitumor activity in vivo Furthermore, the combination of BAY 1895344 with the novel, nonsteroidal androgen receptor antagonist darolutamide resulted in significantly improved antitumor efficacy compared with respective single-agent treatments in hormone-dependent prostate cancer, and addition of EBRT resulted in even further enhanced antitumor efficacy. Thus, the ATR inhibitor BAY 1895344 may provide new therapeutic options for the treatment of cancers with certain DDR deficiencies in monotherapy and in combination with DNA damage-inducing or DNA repair-compromising cancer therapies by improving their efficacy.

Abstract A063: TAS1553, a novel class of RNR inhibitor, demonstrates synergistic antitumor efficacy in combination with nucleoside analogues

Abstract Background: Ribonucleotide reductase (RNR) is an essential metabolic enzyme that catalyzes a rate-limiting step for de novo dNTP biosynthesis via converting ribonucleotides to deoxyribonucleotides. dNTPs are also supplied through nucleoside salvage pathway in which dNTP is synthesized from extracellular nucleoside. The salvage pathway is also utilized for conversion of several nucleoside analogues to their active metabolites. Given the previous report showing that the inhibition of de novo pathway activates salvage pathway at least in vitro, RNR is considered as a promising target for combination therapy with nucleoside analogues. However, in vivo efficacy of selective RNR inhibitor in combination with nucleoside analogues has not been clarified yet. Previously, we reported a novel class of RNR inhibitor TAS1553, which is a selective and orally available small molecule abrogating protein-protein interaction between RNR subunits. Here, we evaluated the synergistic activity of TAS1553 and several nucleoside analogues in vitro as well as in vivo studies. Material and methods: Antiproliferative activity was assessed by CellTiter-Glo® 2.0 assay. Intracellular and intratumoral ara-CTP amounts were measured by HPLC analysis. Antitumor efficacy was evaluated in athymic nude mice bearing MV-4-11 (human AML) and CFPAC-1 (human pancreatic cancer) cell line. Results: To examine whether TAS1553 plus nucleoside analogues combination shows synergistic efficacy, we evaluated antiproliferative activity of TAS1553 in combination with some nucleoside analogues (cytarabine, gemcitabine, decitabine, and 2F-ara-A) to calculate the combination index (CI). TAS1553 exhibited synergistic antiproliferative activity (CI &amp;lt; 1) against cancer cell lines in combination with all of the tested nucleoside analogues. Then, to analyze the mechanism underlying the synergistic effect, we asked whether treatment with TAS1553 augments the activity of salvage pathway by measuring ara-CTP, which is an active metabolite of cytarabine. The results showed that treatment with TAS1553 significantly increased ara-CTP accumulation in MV-4-11 cells implying that TAS1553 activates nucleoside salvage pathway by inhibiting de novo nucleotide synthesis. Importantly, when analyzing the timing of treatment for the combination, prior or simultaneous treatment with TAS1553 increased ara-CTP amount more than post treatment. Consistently with in vitro result, co-administration of TAS1553 and cytarabine caused significant increase of intratumoral ara-CTP compared with cytarabine administration in MV-4-11 mouse xenograft model. Following this result, the combination of TAS1553 (100 mg/kg/day, q.d.) and cytarabine (10 mg/kg/day, 5 consecutive days) showed superior antitumor efficacy to MV-4-11 tumor than each monotherapy while the combination did not cause intolerable body weight change. Furthermore, TAS1553 also demonstrated the striking anittumor efficacy in combination with gemcitabine (20 mg/kg/day, q.wk.) on CFPAC-1 mouse xenograft model. Conclusions: TAS1553, a novel class of RNR inhibitor, has synergistic antitumor efficacy in combination with nucleoside analogues. These combination therapy could be promising therapeutic options for cancer patients. Citation Format: Takuya Hoshino, Hiroyuki Ueno, Wakako Yano, Sayaka Tsukioka, Seiji Miyahara, Takamasa Suzuki, Kazutaka Miyadera, Teruhiro Utsugi, Takeshi Sagara. TAS1553, a novel class of RNR inhibitor, demonstrates synergistic antitumor efficacy in combination with nucleoside analogues [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A063. doi:10.1158/1535-7163.TARG-19-A063

Abstract B003: Combinatorial therapies of neratinib for HER2-amplified cancer

Abstract Activation of HER2 signaling by amplification or overexpression of ERBB2 (HER2) is associated with the development and progression of breast cancer. Neratinib is an irreversible, pan-HER tyrosine kinase inhibitor which selectively inhibits EGFR, HER2 and HER4. In this preclinical study, we explored the therapeutic efficacy of neratinib in combination with other clinically relevant targeted agents for HER2-amplified breast cancer in in vitro and in vivo models. HER2-amplified cell lines BT-474, SK-BR-3, and HCC-1954 were sensitive to neratinib with low nanomolar IC50s. Cell viability and colony formation assays demonstrated synergistic anti-proliferative activity of neratinib in combination with multiple targeted agents, including the MEK inhibitor trametinib, the PI3Ka inhibitor alpelisib, the mTOR inhibitors everolimus and sapanisertib, and CDK4/6 inhibitor palbociclib. We tested combinatorial efficacy of neratinib with everolimus, trametinib, and palbociclib in vivo on five HER2-amplified PDXs (two breast, two colorectal and one gastric-esophageal junction cancer), four derived from patients with previous HER2-targeted therapy. The combination of neratinib with everolimus or trametinib led to at least a 100% increase in median time for tumor doubling in 25% (1 of 4) and 60% (3 of 5) models respectively and was associated with decreased tumor volumes in 50% (2 of 4) and 20% (1 of 5) of the models respectively. The combination of neratinib with palbociclib significantly enhanced antitumor efficacy compared to single agent treatment in all five PDX models. The combination achieved treatment/control volume ratios of 0.03-0.16 and increased time for tumor doubling more than 100% in all five models. Taken together, our results provide solid preclinical evidence for targeting combinatorial therapies of neratinib for HER2-amplified cancer. Citation Format: Ming Zhao, Stephen Scott, Kurt Evans, Erkan Yuca, Turcin Saridogan, Mehmet E Demirhan, Bryce P Kirby, Scott Kopetz, Irmina Diala, Alshad S Lalani, Sarina A Piha-Paul, Funda Meric-Bernstam. Combinatorial therapies of neratinib for HER2-amplified cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B003. doi:10.1158/1535-7163.TARG-19-B003

Synergistic anticancer effects of electrospun nanofiber-mediated codelivery of Curcumin and Chrysin: Possible application in prevention of breast cancer local recurrence

To decrease the locoregional recurrence of breast cancer, the in vitro anticancer efficacy of electrospun nanofibers (NFs) co-loaded with Curcumin (Cur) and Chrysin (Chr), as natural anticancer compounds, against T47D breast cancer cells was evaluated. According to FE-SEM results, the randomly oriented bead-free CurChr co-loaded PLGA/PEG fibers presented more interconnection among the fibers with increased average diameter to around 800 nm. Also, co-loading Cur and Chr into the NFs improved mechanical properties than single drug-loaded NFs. The in vitro release profile indicated the almost identical and prolonged release profile of drugs from CurChr-NFs that were lower than that from Cur-NFs and Chr-NFs. Based on MTT, CurChr-loaded PLGA/PEG NFs displayed effectively synergistic antiproliferative activities than the single drug-loaded NFs. Among loading different non-constant ratios of Cur and Chr in polymeric NFs, 10:5% (wt:wt%) CurChr-NFs exhibited the best synergistic cytotoxicity against the cells and could further altered the mRNA levels of bax, bcl-2, p53, Cyclin D1, caspase-3, caspase-7, and hTERT genes. In conclusion, the dual drug-loaded NFs showed an excellent capacity to inhibit T47D breast cancer cells in vitro than the single drug-encapsulated NFs. Therefore, the fabricated dual drug-encapsulated NFs may achieve a safe and suitable application for breast cancer relapse rate after surgery.