Durable Tumor Regression Research Articles

Tumor sensitization to PARP inhibitors by DNA damaging synthetically lethal acylfulvenes.

e15123 Background: 20-30% of solid tumors (ovarian, breast, pancreatic, prostate cancers) harbor some level of deficiency in DNA Damage Repair (DDR) pathways. Such cancers become dependent on alternative DDR pathways to maintain genome integrity, making them selectively vulnerable to DNA damaging agents. The concept of synthetic lethality has been leveraged to treat subsets of such tumors. Clinically, PARP inhibitors (PARPi) have been successful in Homologous Recombination Deficiency (HRD) cancers. LP-100 and LP-184 are acylfulvene (AF) class small molecule prodrugs that are metabolized to active compounds by prostaglandin reductase 1 (PTGR1) that is often elevated in solid tumors. AF-induced DNA lesions are likely selectively processed by repair pathways including BRCA1/2 mediated Homologous Recombination (HR). Methods: Cell Titer Glo based 10 day cell viability assays were used to generate drug IC50 values in vitro. Bliss synergy scores were computed with scores ≥ 10 reflecting synergy. Drug-induced DNA double strand breaks (DSB) were detected and quantified with STRIDE (SensiTive Recognition of Individual DNA Ends) assay in cancer cells. A subcutaneous tumor xenograft model was used to determine tumor volumes in control and drug treated mice. Results: In a BRCA2 mutant ovarian cancer cell line OVCAR3, LP-184 and olaparib co-treatment in vitro showed synergistic effects (Bliss score 10). Similarly in a BRCA2 mutant prostate cancer cell line 22Rv1, LP-100 combination with rucaparib was synergistic (Bliss score 18). 400 nM LP-184 showed a time dependent increase in DNA DSB signals in vitro, 1.7X more so in BRCA2 mutant vs wild type (WT) DLD-1 isogenic colon cancer cell lines up to 24 hours. To validate the hypothesis that AF-induced DSBs remain unresolved if exposed to and further synergize with PARPi in vivo, we tested LP-100 plus olaparib in a DU145 (BRCA2 mutant) prostate cancer xenograft model. LP-100 + olaparib treatment resulted in sustained, durable tumor regression indicating in vivo synergy whereas either agent alone did not produce tumor shrinkage. Day 42 tumor growth inhibition was 66% for 2.5 mg/kg LP-100 alone, 34% for 40 mg/kg olaparib alone and 108% for the combination. Moreover, LP-184 treatment resulted in early onset and complete tumor regression in 7 PDX models of PARPi resistant triple negative breast cancers (TNBC) harboring BRCA1/2 loss whereas olaparib/ niraparib remained entirely ineffective in these. Conclusions: AF response is influenced by tumor DNA repair competence. LP-100 and LP-184 are synthetically lethal resulting from their abilities to cause unresolvable DNA damage where tumor cells express high PTGR1 and are deficient in the HR pathway. LP-184 single agent was superior to PARPi in TNBC and LP-100 combination made an olaparib resistant tumor highly sensitive, thereby facilitating a path to extend the opportunities for both AFs and PARPis and enhance the clinical utilization of PARPi.

Initial results from the phase 2A trial of visugromab (CTL-002) + nivolumab in advanced/metastatic anti-PD1/-L1 relapsed/refractory solid tumors (The GDFATHER-TRIAL).

2501 Background: Increasing evidence has emerged that Growth and Differentiation Factor 15 (GDF-15) plays a critical role in tumoral immunosuppression. Apart from blocking immune-cell entry into the tumor microenvironment, GDF-15 also has a major impact on the formation of the immune synapse. Many tumors overexpress GDF-15 and have hijacked this mechanism to block immunotherapy success. Here we report initial results of the phase 2a part of the GDF-15 neutralizing antibody visugromab (CTL-002) in combination with nivolumab. Methods: At cut-off date (06-Feb-2023), a total of 79 pts with advanced/metastatic solid tumors have been enrolled and were treated with visugromab 10 mg/kg Q2W in combination with nivolumab 240 mg Q2W in the phase 2a expansion part of the CTL-002-001 phase 1/2 trial (NCT04725474). The primary endpoint of the phase 2a expansion is the Objective Response Rate (ORR) according to RECIST v1.1. Tumor assessments were performed every 8 weeks and patients had to be relapsed/refractory to a minimum of 12 weeks continuous prior anti-PD1/-PD-L1-containing therapy, with relapse or progression after initial response to have occurred on continued anti-PD1/PDL1 therapy. Phase 2a contained several indication-specific expansion cohorts (e.g. NSCLC, Bladder Cancer, HCC, Melanoma), following a Simon 2-stage design, and two cohorts were already expanded to stage 2 in light of initial responses observed. An additional expansion cohort is a pan-tumor basket cohort with sequential tumor biopsies for biomarker analyses. A key component of this multi-arm trial is an extensive translational research program to identify response-predictive tumor and immunologic marker and pattern. Results: Across several expansion cohorts, durable tumor regressions were observed, including several partial responses (PR) and one complete response (CR) in heavily pretreated patients with a median of 3 prior lines of systemic therapy for advanced/metastatic cancer, including at least one prior line of anti-PD1/-PD-L1 therapy and being relapsed/refractory to it. In NSCLC, so far 13 pts underwent at least one tumor assessment. Of these, two experienced a PR (one confirmed), three additional tumor shrinkage > 5% (TS) and one longer-term SD (LT-SD) were seen. In bladder cancer, 7 patients underwent at least one tumor assessment with 1 confirmed CR, 1 TS and 1 LT-SD. The treatment was overall well tolerated. Conclusions: These initial phase 2a results demonstrate promising clinical activity for the combination of visugromab and nivolumab in heavily pretreated anti-PD1/-PD-L1 refractory/relapsed solid tumor patients across various indications, including induction of confirmed partial and complete responses. Extensive biomarker evaluations are ongoing to further evaluate potential response-predictive markers identified during phase 1 development. Clinical trial information: NCT04725474 .

Abstract ND12: TNG260: A novel, orally active, CoREST-selective deacetylase inhibitor for the treatment of STK11-mutant cancers

Abstract STK11 loss of function mutations occur in 12-15% of lung adenocarcinoma and have been shown to drive resistance to immune checkpoint blockade in patients and preclinical models. STK11-deficient syngeneic mouse tumor models reflect this biology and are insensitive to anti-PD1 treatment. Informed by in vivo CRISPR-based screens, histone deacetylase 1 (HDAC1) was identified as a target gene, which when knocked out in tumor cells, reverses anti-PD1 resistance driven by STK11 tumor suppressor gene loss. Here, we describe the discovery and development of TNG260 as a potent and selective inhibitor of the HDAC1-containing complex CoREST. TNG260 inhibits CoREST deacetylase activity with 500-fold selectivity over the other HDAC1-containing complexes, NuRD and Sin3, and the HDAC3-containing complex NCoR. In preclinical studies, selective CoREST inhibition by TNG260 results in transcriptional reprogramming of STK11-mutant tumor cells, altering tumor cell cytokine secretion and markedly reducing recruitment of suppressive Treg cells to STK11-mutant tumors. Moreover, TNG260, in combination with anti-PD1 treatment, drives durable tumor regressions in multiple syngeneic STK11-mutant xenograft models. TNG260 has no anti-tumor efficacy in athymic mice, indicating the responses with TNG260 are mediated by T cells. Unlike previously developed pan-HDAC inhibitors, which are directly cytotoxic to cancer (and immune) cells, IND-enabling toxicology studies in rat and dog showed that TNG260 was well-tolerated at exposures predicted to be efficacious in humans, with bone marrow suppression only detectable at doses where TNG260 is no longer selective for CoREST inhibition. TNG260 clinical development will be among the first to combine the power of genetic patient selection and immunotherapy, evaluating patients with STK11 mutant cancers in a trial combining TNG260 and a checkpoint inhibitor. Citation Format: Leanne G. Ahronian, Minjie Zhang, Chengyin Min, Alice W. Tsai, Jacques Ermolieff, Patrick McCarren, Margaret Wyman, David Guerin, Ye Wang, Alborz Bejnood, Kenjie Amemiya, Brian McMillan, Nikitha Das, Preksha Shahagadkar, Brian Doyon, Andre Mignault, Colin Liang, Vassil Elitzin, Samuel R. Meier, Ashley Choi, Yi Yu, John P. Maxwell, Brian B. Haines, Jannik N. Andersen, Heather DiBenedetto, Aaron Weitzman, Alan Huang, Xinyuan Wu. TNG260: A novel, orally active, CoREST-selective deacetylase inhibitor for the treatment of STK11-mutant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr ND12.

Abstract ND05: The discovery and characterization of CFT1946: A potent, selective, and orally bioavailable degrader of mutant BRAF for the treatment of BRAF-driven cancers

Abstract The BRAF kinase plays a critical role in the MAPK signaling pathway and is mutated in ~8% of all human cancers including melanoma (~60%), thyroid (~60%), and lung adenocarcinoma (~10%). The most common mutation in BRAF is V600E (Class I), which is found in >70% in these cancers. Despite the clinical success of approved small molecule inhibitors of BRAF V600E (vemurafenib, dabrafenib and encorafenib), this remains an area of unmet medical need because nearly all patients progress, due to either primary or acquired resistance. A bifunctional degradation activating compound (or BiDACTM degrader) may address the liabilities of approved drugs by overcoming, or preventing the emergence of, resistance to BRAF inhibitors. Here we describe CFT1946, an orally bioavailable cereblon-based BiDAC degrader of BRAF V600 mutant proteins, and provide an overview of the medicinal chemistry path leading to its discovery. CFT1946 degrades BRAF V600 mutant proteins, while maintaining exquisite selectivity against the proteome, sparing wild type BRAF (BRAF-WT), ARAF, and CRAF. In A375 cells, CFT1946 potently degraded BRAF V600E and inhibited ERK phosphorylation and cell growth while having no effect in the mutant KRAS, BRAF-WT driven cell line HCT116. In the A375 xenograft model, oral delivery of CFT1946 at 10 mg/kg PO BID resulted in deeper and more durable tumor regression compared to a clinically relevant dose of encorafenib. Further evaluation of CFT1946 in an engineered, clinically relevant BRAFi-resistant A375 cell line (endogenous BRAF V600E + engineered expression of NRAS Q61K) demonstrated that CFT1946 both degraded BRAF V600E and caused a loss of viability in these cells, while treatment with encorafenib had no effect. In xenografts derived from this BRAFi-resistant cell line, oral dosing of CFT1946 as a single agent led to tumor growth inhibition, while treatment with a clinically relevant dose of encorafenib had no effect on tumor growth. Furthermore, dosing CFT1946 in combination with the MEK inhibitor, trametinib, resulted in significant tumor regression, whereas combining encorafenib with the same dose of trametinib had no effect. The medicinal chemistry campaign resulting in CFT1946 focused on the improvement of in vivo pharmacokinetics and rational linker design to achieve high oral bioavailability in a beyond Rule of 5 heterobifunctional degrader. The preclinical data presented herein support the planned Phase 1/2 clinical trial of CFT1946 for the treatment of BRAF-V600 mutant solid tumors. Citation Format: Yanke Liang, Mathew E. Sowa, Katrina L. Jackson, Jeffrey R. Simard, Bridget Kreger, Ping Li, Laura Poling, Joelle Baddour, Andrew Good, Hongwei Huang, Scott Eron, Christopher G. Nasveschuk, Robert Yu, Mark Fitzgerald, Victoria Garza, Morgan W. O’Shea, Gesine Veits, Jeremy L. Yap, Moses Moustakim, Ashley Hart, Roman V. Agafonov, Grace Sarkissian, Joe S. Patel, Richard Deibler, Kyle S. Cole, David Cocozziello, Fazlur Rahman, Andrew J. Phillips, Elizabeth Norton, Adam S. Crystal, Roy M. Pollock, Stewart L. Fisher. The discovery and characterization of CFT1946: A potent, selective, and orally bioavailable degrader of mutant BRAF for the treatment of BRAF-driven cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr ND05.

Abstract CT070: Double-blind placebo-controlled trial of AL102 for treatment of progressing desmoid tumors: the RINGSIDE phase 3 study design

Abstract Background: There is an unmet need for effective systemic therapy for desmoid tumors (DT, aggressive fibromatosis) that provides durable tolerability, symptom improvement, and tumor regression. Gamma secretase inhibitors (GSIs) demonstrate antitumor activity against DT. AL102 is a potent, orally available, selective GSI under investigation as an antineoplastic agent. Methods: RINGSIDE (AL-DES-01) is a 2-part Phase 2/3 study. In the open-label Phase 2 study (Part A), adults with progressing DT (≥10% unidimensional growth within 18 months or DT-related pain requiring non-opioid medication) were randomized to three dosing regimens: 1.2 mg once daily, 2 mg intermittent BIW (2 days on 5 days off), or 4 mg intermittent BIW. RINGSIDE Phase 3 (Part B) is a double-blind, placebo-controlled study evaluating the chosen dose regimen from Phase 2 (1.2 mg once daily) in adults and adolescents (≥12 years of age) with recurrent or treatment-naïve histologically confirmed progressing DT per investigator. For eligibility, progression is defined as ≥20% measured by MRI or CT scan according to RECIST v1.1 within 12 months of the screening visit. Planned enrollment is for ≈156 subjects globally to be randomized 1:1 to either AL102 1.2 mg once daily or placebo. Randomization will be stratified according to tumor location: intra-abdominal vs. extra-abdominal (including abdominal wall). Subjects will undergo MRI or CT scans (using the same modality throughout the study) every 12 weeks to assess tumor response according to RECIST v1.1 by blinded independent central review (BICR). The primary endpoint is progression-free survival (PFS) by BICR based on RECIST v1.1. Primary and secondary endpoints are summarized in Table 1. The trial is currently enrolling. Table 1. RINGSIDE Phase 3 Study Endpoints Objectives Endpoints Primary Evaluate effects of AL102 on disease progression PFS defined as time from randomization until date of assessment of progression (assessed by BICR based on RECIST v1.1) or death by any cause Secondary Evaluate additional effects of AL102 on tumor response • ORR (CR and PR) by BICR based on RECIST v1.1 • DOR defined by time from CR or PR (by BICR based on RECIST v1.1) until first documentation of disease progression or death from any cause Evaluate effects of AL102 on quality of life • Change from baseline in quality of life as determined by: • GOunder/Desmoid Tumor Research Foundation (DTRF) DEsmoid Symptom Scale and Impact Scale (GODDESS) • Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function • EuroQol 5-Dimensional (EQ-5D-3L) questionnaire • Patient’s Global Impression of Change (PGI-C) • Change from baseline in pain assessment using Brief Pain Inventory (BPI) short form Evaluate safety and tolerability of AL102 • Frequency, duration and severity of treatment-emergent adverse events (TEAEs) and serious AEs • Time to treatment discontinuation due to TEAE BICR: blinded independent central review; CR: complete response; DOR: duration of response; ORR: objective response rate; PR: partial response; PFS: progression-free survival; RECIST: Response Evaluation Criteria in Solid Tumors Citation Format: Mrinal Gounder, Robin L. Jones, Jonathan Yovell, Gary Gordon, Bernd Kasper. Double-blind placebo-controlled trial of AL102 for treatment of progressing desmoid tumors: the RINGSIDE phase 3 study design [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT070.

Abstract 1136: Targeting DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer

Abstract DHX9 is a multifunctional DEAH-box ATP-independent RNA helicase which has been reported to play important roles in replication, transcription, translation, RNA splicing and RNA processing which contribute to DHX9’s role in maintenance of genomic stability. Functionally, DHX9’s role involves binding to as well as unwinding and/or resolving double-stranded and single-stranded DNA/RNA, DNA/RNA hybrids (R-loops), circular RNA and DNA/RNA G quadraplexes. Overexpression of DHX9 is evident in multiple cancer types, including colorectal cancer (CRC) and lung cancer. In addition, microsatellite instable (MSI) tumors exhibiting defective mismatch repair (dMMR) show a strong dependence on DHX9, making this helicase an attractive target for oncology drug discovery. Here we describe data supporting targeting DHX9 in MSI CRC as a novel therapeutic, and the first identification of potent and selective in vitro and in vivo small molecule inhibitors of DHX9. We demonstrate that DHX9 inhibition in MSI CRC, delivered either through siRNA knockdown or compound treatment, leads to an increase in RNA/DNA secondary structures such as R-loops and circRNA (i.e. circBRIP1) inducing replication stress. Cell lines that are dMMR (i.e. MSI) are unable to resolve this replication stress, resulting in prevention of DNA replication in S phase and later onset of apoptosis. We were able to confirm this selective dependency in a panel of 20 CRC cell lines; anti-proliferative effects mediated by DHX9 inhibition were dependent on cell line dMMR status in a 10-day proliferation assay. Furthermore, compound 1, an orally bioavailable DHX9 inhibitor was used to investigate in vivo efficacy in MSI CRC (LS411N) and MSS CRC (SW480) xenograft models. Compound 1 was well tolerated across the 28-day treatment period with robust and durable tumor regression (TGI = 105 %) observed in the LS411N tumor xenograft model only. In addition, following cessation of treatment, minimal tumor regrowth was observed in a 28-day post treatment window. Tumor and plasma concentrations of compound 1 and changes in pharmacodynamic markers of DHX9 inhibition, such as circBRIP1 mRNA, were measured and resulting PK and PD data were highly correlated. Together, these preclinical data validate DHX9 as a tractable new target with potential utility as a novel treatment for patients with MSI CRC. Citation Format: Jennifer Castro, Matthew H. Daniels, Chuang Lu, David Brennan, Deepali Gotur, Young-Tae Lee, Kevin Knockenhauer, April Case, Jie Wu, Shane M. Buker, Julie Liu, Brian A. Sparling, E. Allen Sickmier, Stephen J. Blakemore, P. Ann Boriack-Sjodin, Kenneth W. Duncan, Scott Ribich, Robert A. Copeland. Targeting DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1136.

Abstract 2013: Oxidized anthracycline payloads induce anti-tumor immunogenic cell-death and show linker-dependent tolerability when delivered as ADCs

Abstract Novel payloads with orthogonal mechanisms of action (MOAs) to established ADC technologies are important for expanding the utility of antibody-drug conjugates (ADCs) in cancer treatment. Anthracyclines, a class of cytotoxic small molecules that include important clinical chemotherapeutics such as doxorubicin, have long been of interest to the ADC field due to their high potency and unique MOA. Interest in anthracyclines has increased in recent years due to their status as canonical inducers of immunogenic-cell death (ICD), a feature that may lead to more durable tumor regressions and increased synergy with immune checkpoint blockade. In this work, we investigate several drug-linkers based on oxidized derivatives of the highly potent anthracycline analogue PNU-159682. Resultant ADCs are potent and immunologically specific with linker-dependent bystander activity in co-culture cytotoxicity assays displaying heterogeneous antigen (Ag+/Ag-) expression. Rodent in vivo anti-tumor activity and tolerability are shown with significant differences emerging between the toxicity profile of the cleavable and non-cleavable analogues. In vitro, tumor cells treated with anthracycline ADCs showed key hallmarks of ICD including markers of endoplasmic reticulum (ER) stress and the induction of ICD damage-associated molecular patterns (DAMPs) such as HMGB1 and ATP. In vivo mouse xenograft studies show increased tumoral F4/80+ macrophage infiltration by IHC in anthracycline ADC treated animals relative to controls. ADCs delivering monomethyl auristatin E (MMAE) show comparable activity in ICD assays, confirming MMAE as an ICD inducing ADC payload alongside canonical inducers such as anthracyclines. Our results indicate there is a therapeutic window in rodents alongside ICD induction by anthracycline ADCs, positioning anthracyclines as a potentially impactful class of ADC payloads. Citation Format: Joseph Z. Hamilton, Kerry Klussman, Rebecca Mahzereh, Jessica Simmons, Michelle Ulrich, Shyra J. Gardai, Peter D. Senter, Patrick J. Burke. Oxidized anthracycline payloads induce anti-tumor immunogenic cell-death and show linker-dependent tolerability when delivered as ADCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2013.

Abstract 2904: CAT-179, an allogeneic NK cell product expressing HER2-CAR, IL-15 and TGFβ dominant negative receptor, durably regresses HER2-expressing xenograft tumors in mice

Abstract While chimeric antigen receptor (CAR)-engineered immune cell therapies have been at the forefront of cancer immunotherapy for hematological malignancies, patients with solid tumors have yet to benefit from such therapies. Engineered, off-the-shelf, allogeneic natural killer (NK) cells are particularly attractive as cell therapies for solid tumors given their clinical safety, efficacy, and multimodal recognition of tumor cells. We describe here the pre-clinical pharmacokinetics, efficacy, biodistribution and safety of CAT-179, a novel allogeneic, cryopreserved CAR-NK cell therapy, in naïve animals as well as multiple xenograft models of HER2-amplified ovarian and gastric cancer. CAT-179 cells are engineered to express an optimized HER2-directed CAR to effectively target tumor cells, a transforming growth factor b (TGFβ) dominant negative receptor (DNR) to protect against TGFβ-mediated immunosuppression, and interleukin-15 (IL-15) to enhance NK cell persistence. A single intravenous (IV) dose of CAT-179 resulted in IL-15-dependent (p<0.0001) expansion and persistence of CAT-179 cells for at least 140 days in NOD-scid IL2Rgnull (NSG) mice, peaking at approximately 15,000 cells/µL of blood (by day 60). Persisting CAT-179 NK cell levels at day 60 were functionally active and significantly reduced tumor burden when challenged intraperitoneally (IP) with HER2+ SKOV3-luc tumor cells. No significant changes in body weight or condition were observed during this study. The therapeutic anti-tumor activity of CAT-179 against established tumors was assayed using two different xenograft models. In the first model, NSG mice were given an IP dose of 1 million SKOV3-luc tumor cells (derived from ovarian cancer) followed by either 4 million CAT-179 or control NK cells on days 4, 11 and 18. CAT-179 dosed animals showed a rapid and sustained 95% decline in tumor burden (p<0.0001) and a significant extension in survival relative to animals dosed with control NK cells (p<0.0001). In the second model, 1 million HER2+ N87 cancer cells (derived from gastric cancer) were implanted subcutaneously into the right flank of NSG mice. When tumors reached 70mm3, a single IV dose of 2M CAT-179 or control NK cells was administered. CAT-179 dosed animals showed a 96% durable tumor regression and significant survival benefit relative to animals dosed with control NK cells (p<0.0001). Efficacy strongly correlated with the circulating levels of CAT-179, which significantly infiltrated the tumor xenograft. Our pre-clinical results demonstrate the potential of CAT-179 as a novel, durable, and off-the-shelf cell therapy to overcome the challenges associated with solid tumors and provide quantitative insights into pharmacokinetics, pharmacodynamics and anti-tumor activity of engineered NK cells expressing CAR, TGFb DNR and IL-15. Citation Format: Bashar Hamza, Angela Nunez, Marilyn Marques, Alexia Barandiaran, Henry Moreno, Finola Moore, Meghan Walsh, Eugene Choi, Kisha Pradhan, Krista Daniel, Jennifer Johnson, Charlotte Franco, Andres Alvarez, Karl Malakian, Keith H. Wong, Joseph Gold, Vipin Suri, Dominic Picarella. CAT-179, an allogeneic NK cell product expressing HER2-CAR, IL-15 and TGFβ dominant negative receptor, durably regresses HER2-expressing xenograft tumors in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2904.

Abstract 6241: LP-184, an acylfulvene class small molecule therapeutic, is synthetically lethal in DNA damage repair deficient cancers

Abstract As many as one third of solid tumors (ovarian, breast, pancreatic, prostate cancers) harbor deficiency in some DNA Damage Repair (DDR) pathways. Such cancers become dependent on alternative DDR pathways to maintain genome integrity, making them selectively vulnerable to DDR inhibitors. The concept of synthetic lethality has been successfully applied to develop strategies to treat subsets of such tumors. Clinically, PARP inhibitors (PARPi) have been successful particularly in Homologous Recombination Deficiency (HRD) cancers. Other agents have also been designed to target these DDR deficiencies in cancer cells and have potential to be clinically beneficial. LP-184 is a next generation acylfulvene prodrug metabolized to an active compound by prostaglandin reductase 1 (PTGR1) that is often elevated in multiple tumors. LP-184-induced DNA lesions are likely repaired by the Nucleotide Excision Repair (NER) and Homologous Repair (HR) pathways. Reduced activities of multiple DDR-related pathways in solid tumor models correlated with increased sensitivities to LP-184 as indicated by Gene Set Enrichment Analysis. Chinese Hamster Ovary cells with NER mutations (ERCC1/2/6) were at least 4 fold more sensitive to LP-184 relative to otherwise isogenic parental cells. ERCC2 or BRCA2 depletion enhanced LP-184 sensitivity 5-8X in a metastatic prostate cancer cell line. LP-184 showed ~120 fold higher potency (IC50 77 nM) compared to Olaparib in HRD prostate cancer organoid model LuCaP 96 (BRCA2/CHEK2 inactivating mutations). Across 14 patient-derived pancreatic, lung and prostate tumor models harboring HR mutations (BRCA1/2, CHEK1/2, ATM/ATR, PALB2, PARP1/2, RAD51, FANCA/B), LP-184 showed ex vivo IC50s in the range of 30-300 nM, whereas Olaparib IC50s ranged from 1700-6900 nM. LP-184 treatment resulted in complete tumor regression (107-141% TGI) in 10/10 HR deficient triple negative breast cancer PDX models of which 7/10 were resistant Olaparib/Niraparib and to Doxorubicin/Cyclophosphamide. LP-184 treatment resulted in complete and durable tumor regression in HRD (BRCA1/ATR mutant) pancreatic cancer PDX models (112-140% TGI). In the ovarian cancer cell line OVCAR3 having HRD/NERD phenotype, LP-184 IC50 was 13 nM, Olaparib IC50 was 145 nM and their combination Bliss Synergy Score was 16 indicating synergy. LP-184 is synthetic lethal resulting from its abilities to cause unresolvable DNA damage if tumor cells express high PTGR1 and are deficient in NER/HR genes. Unlike PARPi, LP-184 has striking activity in both NERD as well as HRD cancers. These strong data have prompted the development of a soon to be launched clinical trial to translate the broad preclinical anticancer activity of LP-184 in solid tumors with HR/NER pathway defects, such as pancreatic, prostate, ovarian and breast cancers. Citation Format: Aditya Kulkarni, Jianli Zhou, Neha Biyani, Kishor Bhatia, Panna Sharma. LP-184, an acylfulvene class small molecule therapeutic, is synthetically lethal in DNA damage repair deficient cancers. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6241.

Abstract 4434: A PD-1-targeted, receptor-masked IL-2 immunocytokine with maintained potential to engage endogenous IL-2Ra drives selective stimulation of PD-1+ T cells and robust anti-tumor efficacy

Abstract Interleukin-2 (IL-2) is a key cytokine for T cell proliferation, differentiation, and effector function. Recombinant IL-2 has been used for the treatment of metastatic melanoma and renal cell carcinoma, and induced complete, durable tumor regression in some patients. ​However, its broader use in cancer immunotherapy has been limited by severe toxicity. A new generation of IL-2 therapies with decreased binding to IL-2 receptor α-chain (IL-2Rα) is being developed to reduce toxicity and Tregs expansion yet with limited clinical success so far. Here, we show that the ability to engage IL-2Rα is critical for maximal anti-tumor activity of a systemic IL-2 therapy, and an alternative approach to circumvent systemic toxicity is to deliver IL-2 specifically to tumor-reactive T cells. We developed REGN10597, a PD-1-targeted, receptor-masked IL-2 immunocytokine with attenuated systemic IL-2 activity but maintained capacity to engage endogenous IL-2Rα on PD-1+ T cells. Compared to WT IL-2, receptor masked IL-2 shows improved PK and diminished systemic toxicity in mice. REGN10597 shows PD1-targeting-dependent IL-2 activity in vitro and drives selective expansion of tumor-infiltrating PD-1+ CD8 T cells with vigorous effector functions in vivo. In preclinical syngeneic tumor models in PD-1 humanized mice, REGN10597 demonstrates robust anti-tumor efficacy both as a single agent and in combination with PD-1 or PD-L1 blocking antibodies. These findings highlight the therapeutic potential of REGN10597 as a novel targeted and receptor masked WT IL-2 therapy, supporting its clinical development for the treatment of cancer. Citation Format: Jiaxi Wu, Nicolin Bloch, Aaron Chang, Ramandeep Bhavsar, Supriya Patel, Qingqing Wang, Hassan Shakil Ahmed, Vidur Garg, Michael Amatulli, Yuetian Yan, Shunhai Wang, Drew Dudgeon, Willy Ramos, Pamela Krueger, Ashique Rafique, Tammy Huang, Erica Ullman, Aynur Hermann, William Olson, John Lin, Eric Smith, Tong Zhang. A PD-1-targeted, receptor-masked IL-2 immunocytokine with maintained potential to engage endogenous IL-2Ra drives selective stimulation of PD-1+ T cells and robust anti-tumor efficacy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4434.

Abstract 4914: Role of ClpP in the anti-cancer effects of imipridone ONC201 and ONC206

Abstract ONC201 is the first bitopic dopamine receptor D2 (DRD2) antagonist and allosteric mitochondrial protease ClpP agonist. Downstream of target engagement, ONC201 activates the integrated stress response pathway resulting in selective tumor cell death. ONC201 is well tolerated and induces durable tumor regressions in H3 K27M-mutant glioma patients. ONC206, a derivative of ONC201 currently in Phase I trials for adult and pediatric brain tumors, is also a bitopic DRD2 antagonist and ClpP agonist with nanomolar potency. We further evaluated in vitro efficacy and mechanism of action specific to ClpP for ONC206 and investigated acquired resistance to ONC201 and ONC206. FITC-casein and peptide degradation assays confirmed that ONC206 acts as an agonist of human ClpP with enhanced potency relative to ONC201. Broad efficacy in the nanomolar range for ONC206 (GI50 <78-889nM, 72h) was observed in 1,088 Genomics of Drug Sensitivity in Cancer (GDSC) cancer cell lines with increased sensitivity in cell lines exhibiting high ClpP mRNA expression. Among solid tumors, nervous system-related cell lines were particularly sensitive. Gene Expression Profiling Interactive Analysis (GEPIA) database analysis showed ClpP mRNA was overexpressed in glioblastoma cells relative to normal cells. GDSC observations were confirmed in glioblastoma (GBM) (T98G, A172, U87MG), H3.3 K27M mutant diffuse intrinsic pontine glioma (DIPG) (SF8628, SF7761) and astrocytoma (H4, U118MG) cell lines. ONC206 was more potent than ONC201 in cell viability assays for all glioma lines tested. SF8628 cells with a CRISPR-mediated ClpP knockout were shown to demonstrate resistance to both ONC201 and ONC206. Polyclonal resistant cell lines were generated through prolonged passaging in increasing concentrations of ONC201 or ONC206 (SF8628 and T98G cells). Cells with acquired resistance to ONC201 (ONC201Res) or ONC206 (ONC206Res) showed cross resistance to both imipridones. Time-stability of resistance was confirmed by removing drug for 2 to 4 weeks and retesting. RNAseq analysis revealed upregulation of the integrated stress response with imipridone treatment in T98G parental cells but not resistant clones. Whole genome sequencing revealed ClpP mutations in both ONC201Res and ONC206Res cells. Our results confirm the role of ClpP in the mechanism of action of ONC201 and ONC206 in tumor cells. Citation Format: Andrew Lee, Cristina Maranto, Scott Foster, Sara Morrow, Joshua E. Allen, Randall Lanier, Phiroze Sethna, Varun V. Prabhu. Role of ClpP in the anti-cancer effects of imipridone ONC201 and ONC206. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4914.

Abstract 4165: A systemically administered killed bacteria-based multiple immune receptor agonist for pulsed anti-tumor immunotherapy

Abstract Systemic activation of multiple immune receptors, such as Toll-like (TLR), NOD-like (NLR) and Stimulator of Interferon Genes (STING) is essential for efficient innate and adaptive immune responses. Attempts to use single receptor agonists for advanced cancers have not produced approved products. Limitations include insufficient immune activation and dose-limiting toxicities associated with continuous exposure. Gram-negative bacteria (G-NB) contain multiple TLR, NOD and STING agonists. Potential utility of G-NB for cancer immunotherapy is supported by observation of tumor regression in the setting of infection and Coley’s Toxins. Coley reported that i.v. administration was likely most effective but produced toxicity. The discovery of TLRs, particularly the broad/potent activities of the TLR4 agonist lipopolysaccharide (LPS) suggest that it may be both a critical active ingredient and a dose-limiting feature of i.v. G-NB. Non-pathogenic E. coli were treated with polymyxin to achieve ~90% reduction of LPS activity without lysis and were then killed and stabilized with glutaraldehyde. The resulting product, Decoy10, was shown to contain multiple TLR, NOD and STING agonists and exhibited reduced i.v. toxicity (mice, rabbits) relative to unprocessed cells. Surprisingly, despite reduction in LPS activity and toxicity, Decoy10 induced secretion of similar or higher levels of most cytokines/chemokines by peripheral blood mononuclear cells, compared to unprocessed bacteria. Higher cytokine/chemokine induction was also observed compared to monospecific TLR agonists. Administration of 4 to 8 weekly or twice a week i.v. doses of Decoy10 to mice with established s.c., orthotopic or metastatic syngeneic breast, colorectal, hepatocellular, pancreatic carcinomas or syngeneic or human non-Hodgkin’s lymphoma was well-tolerated and produced single agent anti-tumor activity and/or combination-mediated durable tumor regressions, with induction of immunological memory. Regressions were observed, without significantly increased toxicity, when Decoy10 was combined with chemotherapy, a non-steroidal anti-inflammatory drug, anti-PD-1 therapy or rituximab. Tumor regressions were associated with activation of innate and adaptive immune pathways in tumors after one dose of Decoy10 and were mediated by NK, CD4+ and CD8+ T cells. Published studies have demonstrated that systemic bacteria are engulfed by and activate immune cells in the liver and spleen, with rapid clearance in mice, rabbits, and humans. Systemic bacteria have also been shown to accumulate in or around tumors. We have taken advantage of these phenomena to produce a detoxified but potent multiple immune agonist that induces systemic innate and adaptive anti-tumor immune activation without requirement for continuous systemic exposure. A Decoy product has been cleared by the US FDA for a Phase 1 oncology trial. Citation Format: Michael J. Newman. A systemically administered killed bacteria-based multiple immune receptor agonist for pulsed anti-tumor immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4165.

Abstract 3425: The discovery and characterization of CFT1946: A potent, selective, and orally bioavailable degrader of mutant BRAF for the treatment of BRAF-driven cancers

Abstract The BRAF kinase plays a critical role in the MAPK signaling pathway and is mutated in ~8% of all human cancers including melanoma (~60%), thyroid (~60%), and lung adenocarcinoma (~10%). The most common mutation in BRAF is V600E (Class I), which is found in >70% in these cancers. Despite the clinical success of approved small molecule inhibitors of BRAF V600E (vemurafenib, dabrafenib and encorafenib), this remains an area of unmet medical need because nearly all patients progress, due to either primary or acquired resistance. A bifunctional degradation activating compound (or BiDACTM degrader) may address the liabilities of approved drugs by overcoming, or preventing the emergence of, resistance to BRAF inhibitors. Here we describe CFT1946, an orally bioavailable cereblon-based BiDAC degrader of BRAF V600 mutant proteins, and provide an overview of the medicinal chemistry path leading to its discovery. CFT1946 degrades BRAF V600 mutant proteins, while maintaining exquisite selectivity against the proteome, sparing wild type BRAF (BRAF-WT), ARAF, and CRAF. In A375 cells, CFT1946 potently degraded BRAF V600E and inhibited ERK phosphorylation and cell growth while having no effect in the mutant KRAS, BRAF-WT driven cell line HCT116. In the A375 xenograft model, oral delivery of CFT1946 at 10 mg/kg PO BID resulted in deeper and more durable tumor regression compared to a clinically relevant dose of encorafenib. Further evaluation of CFT1946 in an engineered, clinically relevant BRAFi-resistant A375 cell line (endogenous BRAF V600E + engineered expression of NRAS Q61K) demonstrated that CFT1946 both degraded BRAF V600E and caused a loss of viability in these cells, while treatment with encorafenib had no effect. In xenografts derived from this BRAFi-resistant cell line, oral dosing of CFT1946 as a single agent led to tumor growth inhibition, while treatment with a clinically relevant dose of encorafenib had no effect on tumor growth. Furthermore, dosing CFT1946 in combination with the MEK inhibitor, trametinib, resulted in significant tumor regression, whereas combining encorafenib with the same dose of trametinib had no effect. The medicinal chemistry campaign resulting in CFT1946 focused on the improvement of in vivo pharmacokinetics and rational linker design to achieve high oral bioavailability in a beyond Rule of 5 heterobifunctional degrader. The preclinical data presented herein support the planned Phase 1/2 clinical trial of CFT1946 for the treatment of BRAF-V600 mutant solid tumors. Citation Format: Yanke Liang, Mathew E. Sowa, Katrina L. Jackson, Jeffrey R. Simard, Bridget Kreger, Ping Li, Laura Poling, Joelle Baddour, Andrew Good, Hongwei Huang, Scott Eron, Christopher G. Nasveschuk, Robert Yu, Mark Fitzgerald, Victoria Garza, Morgan W. O’Shea, Gesine Veits, Jeremy Y. Yap, Moses Moustakim, Ashley Hart, Roman V. Agafonov, Grace Sarkissian, Joe S. Patel, Richard Deibler, Kyle S. Cole, David Cocozziello, Fazlur Rahman, Andrew J. Phillips, Elizabeth Norton, Adam S. Crystal, Roy M. Pollock, Stewart L. Fisher. The discovery and characterization of CFT1946: A potent, selective, and orally bioavailable degrader of mutant BRAF for the treatment of BRAF-driven cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3425.

Abstract 2263: Complete remission of a patient with Merkel cell carcinoma treated with durvalumab

Abstract Merkel cell carcinoma (MCC) is a rare, cutaneous, neuroendocrine tumor that is highly aggressive. It is the second leading cause of death from skin cancer, after melanoma, despite accounting for less than 1% of malignant skin tumors. Due to the characteristic histopathological neuroendocrine features of the neoplasm, cases of MCC are often misdiagnosed as undifferentiated skin cancers or other tumors with small blue cell types. Clinical examination fails to establish the diagnosis in 99% of cases and pathological assessment by biopsy with immunohistochemistry is essential to confirm MCC diagnosis. Historically, cytotoxic chemotherapy combinations with platinum-based agents (Carboplatin or Cisplatin) plus Etoposide or Cyclophosphamide, Epirubicin, and Vincristine (CAV) agents were the primary systemic treatment for advanced cases. Despite available evidence sensitivity of MCC to chemotherapy, responses are not durable, and the literature is not supportive of combination chemotherapy (NCCN guidelines). The introduction of immunotherapy such as checkpoint inhibitors (ICI) particularly PD-1/PD-L1 blockers increased overall survival and achieved durable tumor regression in clinical trials leading to FDA approval in locally advanced and metastatic disease. Permbrluzimab and Avelumab are the only two FDA-approved ICIs as first-line standard-of-care treatments for MCC patients. What we are missing is data or trials examining the efficacy of other ICI such as Durvalumab, (anti-PD-L1) in MCC. We hereby report an unprecedented case of an 84-year-old female MCC patient with extensive axillary nodal involvement achieving complete remission after treatment with Durvalumab combined with Carboplatin and Etoposide. Citation Format: Saad Sabbagh, Barbara Dominguez, Houssein Abdul Sater. Complete remission of a patient with Merkel cell carcinoma treated with durvalumab [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2263.

Abstract 1644: Dual inhibition of MAT2A and PRMT5 delivers synergistic anti-tumor responses in preclinical models of MTAP-deleted cancer

Abstract Approximately 15% of all tumors harbor deletions in the 9p21 locus that encompass CDKN2A and MTAP. MTAP fuels the adenine and methionine salvage pathways by converting MTA into precursors of building blocks for protein and DNA production. In MTAP-deleted (MTAPdel) tumors, cellular MTA accumulates and partially inhibits the essential protein methyl transferase, PRMT5, through direct displacement of the cofactor S-adenosyl methionine (SAM) from the PRMT5 active site. This context provides therapeutic opportunities, currently under clinical evaluation, to selectively extinguish PRMT5 activity in tumor cells with MAT2A inhibitors that limit SAM synthesis or with direct PRMT5 inhibitors that are MTA-cooperative. Preclinical modeling of these synthetic lethal relationships, and elucidation of their cellular mechanisms of action, suggests efficacy can vary depending upon the extent of MTA accumulation and/or adaptive compensation to PRMT5 inhibition. To potentially maximize therapeutic activity among mechanistically heterogenous MTAPdel tumors, we evaluated combinatorial pathway suppression with MAT2A and PRMT5 inhibitors in MTAPWT and MTAPdel tumor models in vitro and in vivo. We noted synergistic antiproliferative effects when the potent and selective MAT2A inhibitor IDE397 was combined with any of multiple MTA-cooperative PRMT5 inhibitors in MTAPdel cell lines that exhibit sensitivity to each single agent. In vivo, the combination of IDE397 and MTA-cooperative PRMT5 inhibitors were well tolerated, and induced durable tumor regressions, including complete responses, at dose levels well below the maximally efficacious preclinical dose of each individual agent in MTAPdel lung adenocarcinoma and pancreas cancer models H838 and BXPC3. Pharmacodynamic target engagement in the tumor was evaluated by quantitative assessment of symmetric dimethyl arginine (SDMA), as detected by IHC, and indicated earlier onset and greater extent of PRMT5 inhibition by combination treatment as compared to either agent alone. The potentiation of the antitumor response with the combination did not occur in the MTAPWT setting. Thus, combined inhibition of MAT2A and PRMT5 potentially offers a compelling dual synthetic lethal opportunity to address unmet need for the many patients afflicted with MTAPdel cancers. Citation Format: Marcus M. Fischer, Kimberline Gerrick, Brian Belmontes, Katherine Slemmons, Yevgeniy Freyman, Jay Jain, Steve Federowicz, Isaac Bishof, Arjun A. Rao, Melissa Fleury, Zineb Mounir, Mark R. Lackner, Paul E. Hughes, Mike White, Claire L. Neilan. Dual inhibition of MAT2A and PRMT5 delivers synergistic anti-tumor responses in preclinical models of MTAP-deleted cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1644.

Abstract 516: Discovery and preclinical characterization of AMG 650, a first-in-class inhibitor of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers

Abstract Chromosomal instability (CIN) is a hallmark of human cancers and is caused by persistent errors in chromosome segregation during mitosis. Aggressive types of human cancer such as high-grade serous ovarian cancer and triple-negative breast cancer have elevated levels of CIN and frequently harbor TP53 gene alterations and are poorly served by current treatment options. These two CIN+ cancer types also share mutually exclusive genetic alterations in BRCA1 and CCNE1 cancer genes. KIF18A is a mitotic kinesin motor protein that localizes to the plus-end tips of kinetochore microtubule (MT) spindle fibers, where it regulates chromosome alignment during cell division. KIF18A is overexpressed in a subset of human cancers, and its elevated expression is associated with tumor aggressiveness. Recent reports provide compelling evidence that genetic ablation of KIF18A reduced the viability of CIN cancer cells (Marquis et al. Nature Com 2021, Quinton et al. Nature 2021, Cohen-Sharir et al. Nature 2021). Here, we report the discovery and preclinical characterization of AMG 650, a potent and selective inhibitor of KIF18A with a compelling anti-cancer profile distinct from other cell cycle and anti-mitotic drug targets. Structural insights gained by cryo-EM illustrate the unique binding mode of AMG 650 to an allosteric pocket at the interface of KIF18A motor α4 and α6 helices and α-tubulin. AMG 650 selectively inhibits KIF18A MT-ATPase motor activity (IC50 = 48 nM) and exhibits specificity against a panel of diverse motor proteins. In cells, AMG 650 is active at double-digit nM concentrations and phenocopies KIF18A genetic KD/KO dependencies across a panel of DNA-barcoded cancer cell lines. AMG 650 selectively activates the mitotic checkpoint resulting in multipolarity and apoptosis in breast and ovarian cancer cell lines enriched with CIN features. Notably, AMG 650 has minimal effects on proliferating human bone marrow mononuclear cells in culture at concentrations active on sensitive cancer cells (>100X window). In vivo, AMG 650 has low clearance, long half-life, and good oral bioavailability across preclinical species. In mice, oral administration of AMG 650 induces a dose-dependent pharmacodynamic response (pH3 mitotic marker) that is sustained for 24 hours in OVCAR-3 tumor model. Importantly, continuous once-daily dosing with AMG 650 shows robust anti-cancer activity with evidence of durable tumor regressions in a subset of human ovarian and breast CDX/PDX tumor models at well-tolerated doses. Lastly, the combination of AMG 650 with PARP inhibitor Olaparib enhances anti-cancer activity relative to single agent alone in BRCA1- and CCNE1-altered tumor models at well-tolerated doses. Collectively, our results provide a rational therapeutic strategy for selective targeting of CIN cancers via AMG 650, a first-in-class KIF18A inhibitor. Citation Format: Brian Belmontes, Jodi Moriguchi, Grace Chung, Jan Sun, Maria Stefania S. Ninniri, Kelly Hanestad, Kui Chen, John D. McCarter, Upendra P. Dahal, Sudipa Ghimire-Rijal, Yue Hao, Christopher P. Mohr, Xinchao Yu, Matthew G. Rees, Melissa Ronan, Jennifer Roth, Sheroy Minocherhomji, Jennifer R. Allen, Matthew P. Bourbeau, Paul E. Hughes, Nuria A Tamayo, Marc N. Payton. Discovery and preclinical characterization of AMG 650, a first-in-class inhibitor of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 516.

Merkel cell carcinoma: epidemiology, clinical features, diagnosis and treatment of a rare disease

Merkel cell carcinoma is a rare skin cancer with neuroendocrine differentiation. The risk factors include sun exposure, advanced age, immunosuppression (such as transplant recipients, patients with lymphoproliferative neoplasms, or patients with HIV), and Merkel cell polyomavirus infection. Clinically, Merkel cell carcinoma appears as a cutaneous or subcutaneous plaque or nodule, but this tumor diagnosis is rarely made clinically. Therefore, histopathology and immunohistochemistry are usually necessary. Primary tumors without evidence of metastases are treated with complete surgical excision and appropriate surgical margins. The presence of occult metastasis in a lymph node is frequent and a sentinel lymph node biopsy should be performed. Postoperative adjuvant radiotherapy increases local tumor control. Recently, agents that block the PD-1/PD-L1 pathway have shown objective and durable tumor regression in patients with advanced solid malignancies. The first anti-PD-L1 antibody used in patients with Merkel cell carcinoma was avelumab, but pembrolizumab and nivolumab have also shown efficacy. This article describes the current state of knowledge of the epidemiology, diagnosis, and staging of Merkel cell carcinoma, as well as new strategies for its systemic treatment.

Abstract P6-10-07: CDK2 inhibition with BLU-222 in combination with ribociclib demonstrates robust antitumor activity in pre-clinical models of CDK4/6 inhibitor-naïve and -resistant HR+/HER2- breast cancer

Abstract Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are standard of care in combination with endocrine therapy in advanced hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) breast cancer. Despite improved progression-free and overall survival, almost all patients develop CDK4/6 inhibitor resistance and experience disease progression on treatment. Aberrant activation of CDK2/cyclin E is a key resistance mechanism by which tumors can evade CDK4/6 blockade. Therefore, patients with HR+/HER2- breast cancer could benefit from treatment with a selective CDK2 inhibitor in combination with CDK4/6 inhibitors both in the resistant and first-line (1L) settings. BLU-222 is a novel, potent, and selective small-molecule inhibitor of CDK2 with favorable pharmacokinetic properties when administered orally, currently in early-stage clinical development. In pre-clinical studies using the MCF-7 xenograft model of HR+ CDK4/6-responsive breast cancer, treatment with BLU-222 combined with the CDK4/6 inhibitor ribociclib led to pronounced and durable tumor regression superior to ribociclib alone. In a derived palbociclib resistant MCF-7 xenograft model, ribociclib had no anti-tumor activity while BLU-222 led to a strong and durable anti-tumor response (83% tumor growth inhibition [TGI]) that was further improved when given in combination with ribociclib (110% TGI). To further explore the mechanism of aberrant CDK2 activation in CDK4/6 resistant, HR+ breast cancer, we engineered isogenic T47D cell lines to overexpress cyclin E1 (CCNE1) with or without p16, an endogenous inhibitor of CDK4/6 activity. In in vitro proliferation assays, co-expression of CCNE1 and p16 sensitized T47D cells to BLU-222 by approximately 10-fold compared to the parental control (110 nM vs 1078 nM, respectively). CDK4/6 inhibition with ribociclib had no anti-proliferative effect in the CCNE1 overexpressing cell lines regardless of p16 expression status. In vivo, treatment of the empty vector control T47D xenografts with ribociclib led to tumor stasis, while ribociclib in combination with BLU-222 led to tumor regression. T47D xenografts overexpressing both CCNE1 and p16 were resistant to ribociclib however CDK2 inhibition with BLU-222 single-agent treatment led to tumor regression. Finally, the activity of BLU-222 was evaluated in a patient-derived xenograft (PDX) model of CDK4/6 inhibitor-resistant HR+/HER2- breast cancer where the patient had progressed on 1L palbociclib/fulvestrant and 2L abemaciclib/fulvestrant therapy. In this PDX model, BLU-222 in combination with ribociclib led to tumor stasis, even in the absence of fulvestrant. In conclusion, these data support CDK2/cyclin E activation as a key vulnerability in CDK4/6 resistant, HR+/HER2- breast cancer and provide a rationale for the study of BLU-222 in patients with disease progression following CDK4/6 inhibitor treatment. Additionally, the improved durability of response when BLU-222 is combined with CDK4/6 inhibitors in the CDK4/6-naïve setting supports the combination of these agents as 1L treatment. BLU-222 is currently under investigation in VELA (NCT05252416), a phase 1/2, first-in-human trial for patients with cyclin E aberrant cancers and HR+/HER2- breast cancer. Citation Format: Victoria Brown, Nealia House, Phil Ramsden, Karen Ho, Hsin-Jung Wu, Erik Wilker, Jian Guo, Maxine Chen, Douglas Wilson, Neil Bifulco, Steve Wenglowsky, Yoon Jong Choi, Kerrie Faia. CDK2 inhibition with BLU-222 in combination with ribociclib demonstrates robust antitumor activity in pre-clinical models of CDK4/6 inhibitor-naïve and -resistant HR+/HER2- breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-07.

Abstract OT3-23-01: VELA: A first-in-human phase 1/2 study of BLU-222, a potent, selective cyclin-dependent kinase (CDK) 2 inhibitor in patients with cyclin E1 gene (CCNE1)-amplified or CDK4/6 inhibitor-resistant advanced solid tumors

Abstract Background The regulation of cell growth and proliferation is dependent on cyclins and CDKs. The formation of the cyclin D-CDK4/6 complex increases the expression of cyclin E1 and E2. Cyclin E1 and E2 bind to and activate CDK2; this results in a cyclin E/CDK2 complex that assists with downstream expression of DNA synthesis machinery. The use of CDK4/6 inhibitors such as palbociclib or ribociclib is an effective treatment in patients with hormone receptor-positive (HR+), human epithelial growth factor receptor-2 negative (HER2-) breast cancer; however, resistance to treatment eventually occurs. Aberrant cyclin E/CDK2 activity has been identified as a potential resistance mechanism by which tumors can evade CDK4/6 inhibitors. BLU-222 is an oral, investigational, potent, and selective CDK2 inhibitor. In preclinical studies, BLU-222 treatment in combination with ribociclib led to durable tumor regression in both CDK4/6-resistant and sensitive models of HR+HER2- breast cancer. Trial design VELA (NCT05252416) is an international, open-label, first-in-human phase 1/2 study evaluating the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy of BLU-222 in adult patients with CCNE1-amplified tumors or with HR+HER2- breast cancer with disease progression on CDK4/6 inhibitors. In phase 1 and 2, patients aged ≥18 years with an Eastern Cooperative Oncology Group performance status 0–2 are eligible. In phase 2, all patients must have ≥1 measurable target lesion per Response Evaluation Criteria in Solid Tumors version 1.1. Primary endpoints include assessing the safety of BLU-222 as a single agent or BLU-222 in combination with either carboplatin or ribociclib and/or fulvestrant (phase 1 and 2), identifying the maximum tolerated dose and/or recommended phase 2 dose (phase 1), and determining the objective response rate (phase 2). In the phase 1 dose-escalation part, patients with any advanced solid tumor with progression on standard of care (SOC) will receive BLU-222; patients with gastric or endometrial cancer (EC) with progression on ≥2 prior therapies (including ≥1 platinum-based therapy) or with CCNE1-amplified platinum-resistant/refractory ovarian cancer (OC) will receive BLU-222 and carboplatin; patients with HR+HER- breast cancer with progression on CDK4/6 inhibitors will receive BLU-222, ribociclib, and fulvestrant. In the phase 2 dose-expansion part, patients with CCNE1-amplified tumors including EC (progression on ≥2 prior therapies), platinum-resistant/refractory OC, or other advanced solid tumors (progression after SOC) will receive BLU-222 monotherapy; patients with CCNE1-amplified platinum-resistant/refractory OC will receive BLU-222 and carboplatin; and patients with CDK4/6 inhibitor-resistant HR+HER2- breast cancer will receive BLU-222 and fulvestrant with/without ribociclib. Pharmacokinetic parameters will be calculated using standard non-compartmental methods from the plasma concentration–time data. Tissue biopsies will be collected during cycle 1 to assess the phosphorylation of retinoblastoma 1 (Rb1) protein which will be used as a pharmacodynamic marker to assess target inhibition. Dose escalation is ongoing and approximately 50 sites are anticipated to enroll patients across North America, Europe, and the Asia/Pacific region. Citation Format: Manish R Patel, Dejan Juric, Brian S Henick, Kathleen N Moore, Doreen Do, Joshua Chapman, Hui Zhang, Maria Roche, Kate J Newberry, Mikael Rinne, Timothy A Yap. VELA: A first-in-human phase 1/2 study of BLU-222, a potent, selective cyclin-dependent kinase (CDK) 2 inhibitor in patients with cyclin E1 gene (CCNE1)-amplified or CDK4/6 inhibitor-resistant advanced solid tumors [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-23-01.

Targeting tumor-associated macrophages with STING agonism improves the antitumor efficacy of osimertinib in a mouse model of EGFR-mutant lung cancer.

Despite the impressive clinical response rate of osimertinib, a third-generation EGFR-TKI, as a frontline treatment for patients with EGFR-mutant non-small-cell lung cancer (NSCLC) or as a salvage therapy for patients with T790M mutation, resistance to osimertinib is common in the clinic. The mechanisms underlying osimertinib resistance are heterogenous. While genetic mutations within EGFR or other cancer driver pathways mediated mechanisms are well-documented, the role of tumor cell and tumor immune microenvironment in mediating the response to osimertinib remains elusive. Here, using a syngeneic mouse model of EGFR-mutant lung cancer, we show that tumor regression elicited by osimertinib requires activation of CD8+ T cells. However, tumor-associated macrophages (TAMs) accumulated in advanced tumors inhibit CD8+ T cell activation and diminish the response to osimertinib. These results are corroborated by analyses of clinical data. Notably, reprogramming TAMs with a systemic STING agonist MSA-2 reinvigorates antitumor immunity and leads to durable tumor regression in mice when combined with osimertinib. Our results reveal a new mechanism of EGFR-TKI resistance and suggest a new therapeutic strategy for the treatment of EGFR-mutant tumors.