Durable Tumor Regression Research Articles

A phase I study of a mutant KRAS-targeted long peptide vaccine combined with ipilimumab/nivolumab in resected pancreatic cancer and MMR-proficient metastatic colorectal cancer.

TPS814 Background: Novel strategies are needed to improve immune responses in “cold” tumors such as pancreatic ductal adenocarcinoma (PDAC) and mismatch repair-proficient colorectal cancer (MMRp CRC). As a frequent oncogenic driver, mutant KRAS (mKRAS) neoantigens are attractive targets to augment anti-tumor immunity in both diseases. Recently, adoptive transfer of mKRAS G12D-specific T cells has shown durable tumor regressions in patients with metastatic CRC and PDAC (Tran et. al., 2020; Leidner et. al., 2022). Furthermore, our preclinical work has demonstrated that combining a mKRAS neoantigen vaccine with immune-modulating agents prevents progression of premalignant lesions to PDAC in mice (Keenan et. al., 2014). Based on this rationale, our study pairs a pooled synthetic long peptide (SLP) mKRAS vaccine with dual checkpoint blockade to assess safety and immunogenicity in patients with resected PDAC and chemorefractory MMRp CRC. Methods: This is a first-in-human, single-arm, open-label phase I trial evaluating a pooled SLP mKRAS vaccine combined with ipilimumab/nivolumab (ipi/nivo) in patients with resected PDAC (Cohort A, n = 12) and MMRp metastatic CRC (Cohort B, n = 12) The vaccine consists of poly-ICLC adjuvant admixed with SLPs corresponding to six common mKRAS subtypes: G12D, G12R, G12V, G12A, G12C, and G13D. In priming phase, the mKRAS vaccine is given on days 1, 8, 15, and 22 along with ipi/nivo. In boost phase, the mKRAS vaccine is given on weeks 13, 21, 29, 37, and 45 along with nivo alone. Cohort A patients who remain disease-free can continue to receive boost vaccines in a 12-month extended treatment phase. Eligible patients must have molecular tumor testing that demonstrates one of the six KRAS mutations listed above. Cohort A patients must be disease-free following completion of adjuvant chemotherapy within 6 months prior to study entry. Cohort B patients must have confirmed MMRp status, exposure to ≥ 2 prior lines of standard chemotherapy, and measurable disease amenable to biopsies at baseline and week 7. The co-primary endpoints of this study are safety and T cell response. Adverse events will be graded per NCI CTCAE v5.0. T cell response will be determined by the maximal percent change in IFNγ-producing mKRAS-specific T cell density within 16 weeks post-vaccination compared to baseline. Secondary endpoints include disease control and objective response rates at 16 weeks per RECIST v1.1/iRECIST (Cohort B only) as well as disease-free/progression-free and overall survival. Correlative studies will examine treatment-associated changes in T cell receptor (TCR) repertoire diversity by next-generation TCR sequencing of peripheral blood and tumor specimens. Patient accrual began in May 2020 and is completed for Cohort A. Enrollment is currently ongoing for Cohort B. Study drug support provided by Bristol Myers Squibb. Clinical trial information: NCT04117087 .

Efficacy of a Small-Molecule Inhibitor of KrasG12D in Immunocompetent Models of Pancreatic Cancer.

Pharmacologic inhibition of KRASG12D in pancreatic cancer models with an intact immune system stimulates specific, potent, and durable tumor regressions. In the absence of overt toxicity, these results suggest that this and similar inhibitors should be tested as potential, high-impact novel therapies for patients with PDAC. See related commentary by Redding and Grabocka, p. 260. This article is highlighted in the In This Issue feature, p. 247.

Paclitaxel, gemcitabine, oxaliplatin regimen in induction therapy of patients with relapsed and refractory germ cell tumors before high-dose chemotherapy: results of a pilot study

Purpose: to evaluate the efficacy of TGO (paclitaxel, gemcitabine, oxaliplatin) regimen as induction therapy for hematopoietic stem cells mobilization (HSC) before high-dose chemotherapy (HDCT) in patients with recurrent nonseminomatous germ cell tumors (NSGCT).Patients and methods: the study enrolled patients with relapsed and/or refractory NSGCT after frontline chemotherapy. Modified TGO regimen (paclitaxel 100 mg/m2 on day 1 + gemcitabine 1000 mg/m2 on day 1 + oxaliplatin 130 mg/m2 on day 1, once every 14 days) was administered with filgrastim support 10 mcg/kg subcutaneous from day 8 and until the completion of leukapheresis. Maximum 3 cycles of TGO regimen was administered. After harvesting the required volume of CD34+ cells, HDCT was initiated which consisted of 3 cycles of the CE regimen (carboplatin AUC8 on day 1–3 + etoposide 400 mg/m2 on day 1–3) with further HSC autologous stem cell transplantation (ASCT).Results: Five patients with NSGCT with poor IGCCCG prognosis according were enrolled. All of them received ifosfamide-containing chemotherapy as initial treatment. The required HSC were collected for three cycles of HDCT in all patients (100 %); in four (80 %) patients the required number of cells was collected after the 1st cycle of TGO. Four (80 %) patients started the HDCT phase, one patient prematurely terminated treatment due to the rapid progression. One patient who received full planned therapy demonstrated complete and durable tumor regression at the time of data analysis (with 37 months follow-up).Conclusions: the TGO regimen can be used to collect PBSC from patients with relapsed and/or refractory NSGCT before HDCT, further study of this approach is required.

Abstract B033: LP-184, a tumor site activated small molecule therapeutic, is synthetically lethal in pancreatic cancers with DNA damage repair defects

Abstract Biomarker-based therapeutic strategies associated with increased efficacy, manageable toxicity and extended disease-free survival are urgently needed in pancreatic cancer (PaCa). 15-20% of PaCa carry mutations in DNA repair pathways (BRCA1/BRCA2/PALB2/RAD51/ATR/ATM/FANCD2). Additionally, mutations in nucleotide excision repair (NER) genes (ERCC2/3/4/5/6) have been reported in ~5% of PaCa. LP-184 is an acylfulvene analog that is converted to an active alkylating agent in the strict dependency on the oxidoreductase, prostaglandin reductase 1 (PTGR1). LP-184 induced tumor cell kill is enhanced in the presence of DNA damage repair (DDR) defects. Mutation or expression driven TC-NER and/or HR deficiency is expected to predispose PaCa cells to increased sensitivity to LP-184. To test the idea of LP-184 activity in DNA repair-deficient tumors, we evaluated the anti-tumor effects of LP-184 in mouse subcutaneous PDX models harboring pathogenic frameshift mutations in ATR (CTG-1522 model) or BRCA1 (CTG-1643 model) representing HR deficiency in PaCa. Two cycles of LP-184 treatment in CTG-1522 resulted in 140% tumor growth inhibition (TGI), relative to 80% TGI with gemcitabine in this FOLFIRONOX non-responder. Similarly, complete and durable tumor regression with 112% TGI was observed in CTG-1643 with single agent LP-184. There was <5% body weight loss and no significant hematological toxicity in both these models during or after LP-184 treatment. In selected PaCa models, we determined LP-184 efficacy to be synergistic in combination with multiple treatment modalities including standard of care agent gemcitabine, and ERCC3 degrader spironolactone in vitro, and with radiation therapy (RT) in vivo. Overall Bliss synergy scores (score > 10 indicates synergy) of 12.37 for LP-184 + gemcitabine in Capan-1, and 14.08, 16.47 and 15.52 for LP-184 + spironolactone in Capan-1 (BRCA2 loss), Hs766t (ATR mutant) and Panc03.27 cell lines respectively were achieved. Taking advantage of the transcriptional regulation underlying the NRF2 mediated anti-oxidant response pathway, we reasoned that induction of PTGR1 expression, a downstream NRF2 target gene, in irradiated PaCa tumors would thereafter poise them for LP-184 treatment. Indeed, we found that Panc03.27 xenograft tumors treated with 3 mg/kg i.p. LP-184 + 4 Gy RT once weekly for 3 weeks were significantly smaller than those receiving LP-184 alone or RT alone, thus capitalizing on the opportunity to increase PTGR1 expression (and linked LP-184 anti-tumor cytotoxicity) selectively in irradiated tumors. Increased PTGR1 expression has emerged as a promising biomarker for LP-184 cytotoxicity. Moreover, LP-184 can become synthetically lethal in multiple contexts when combined with genetic or pharmacologic DDR pathway aberrations, or with RT. Based on these properties, we anticipate that LP-184 will extend therapeutic opportunities to a large subset of PaCa patients. Citation Format: Aditya Kulkarni, Diana Restifo, Troy Dos Santos, Dusica Cvetkovic, Joseph McDermott, Kishor Bhatia, Panna Sharma, Charlie Ma, Igor Astsaturov. LP-184, a tumor site activated small molecule therapeutic, is synthetically lethal in pancreatic cancers with DNA damage repair defects [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B033.

Development of KT-253, a Highly Potent and Selective Heterobifunctional MDM2 Degrader for the Treatment of Acute Myeloid Leukemia

The murine double minute 2 (MDM2) oncoprotein is a key E3 ubiquitin ligase that degrades and thereby inactivates the tumor-suppressor p53. Targeting of the MDM2/p53 interaction with reversible small molecule inhibitors (SMI) to stabilize p53 and induce apoptosis in wildtype (WT) p53 tumors has been an emerging therapeutic approach in AML and in other WT p53 hematologic and solid tumor malignancies. However, recent clinical trials with MDM2 inhibitors, especially in R/R AML, have resulted in suboptimal clinical activity, highlighting the need for novel therapeutic approaches. KT-253 is a novel, highly potent heterobifunctional MDM2 degrader that suppresses p53-dependent MDM2 protein upregulation that is known to be triggered by the MDM2 SMIs and thereby limits their clinical activity. Previously, we have shown that KT-253 has superior activity compared to MDM2 SMIs, demonstrating >200-fold improvements in both in vitro cell growth inhibition and apoptosis. Because of its superior pharmacological profile, a single dose of KT-253 was sufficient to induce rapid apoptosis and sustained tumor regression in the MV4;11 AML and RS4;11 ALL cell line-derived (CDX) mouse xenograft models, supporting an intermittent dosing schedule of KT-253. Because of the initial promising clinical activity of SMIs in AML, and the potential for KT-253 to provide superior activity, we assessed the activity of KT-253 in AML patient-derived xenograft (PDX) models. In vivo, KT-253 administered once every 3 weeks at 1 mg/kg led to tumor regression in a variety of these models, including CTG-2227 (Figures 1A and B). In addition, in an AML CDX model resistant to venetoclax such as MOLM13, KT-253 administered in combination with venetoclax once every three weeks showed more substantial activity than the single agents alone and led to sustained tumor regression. In summary, intermittent dosing of the clinical candidate KT-253 achieved tumor regression in a variety of AML PDX and CDX models. Combination of KT-253 with the AML standard of care treatment venetoclax achieved durable tumor regression in additional AML xenograft models that are resistant to standard of care, suggesting potential benefit to an expanded patient population. In addition, we have identified hematological and solid tumor indications that respond acutely to MDM2 degradation, we plan to share more details at upcoming meetings. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

EXTH-104. ROLE OF CLPP AND MITOCHONDRIAL METABOLISM IN THE ANTI-CANCER EFFECTS OF IMIPRIDONE ONC201 AND ONC206 IN GLIOBLASTOMA AND DIPG

Abstract ONC201 is the first bitopic dopamine receptor D2 (DRD2) antagonist and allosteric mitochondrial protease ClpP agonist. 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, is also a bitopic DRD2 antagonist and ClpP agonist with enhanced nanomolar potency relative to ONC201. We evaluated in vitro efficacy, mechanism(s) of action and acquired resistance for ONC201 and ONC206 in glioblastoma (GBM) (T98G, A172, U87MG), H3.3 K27M mutant DIPG (SF8628, SF7761) and astrocytoma (H4, U118MG) cell lines. ONC206 was more potent than ONC201 in cell viability assays for all line. A mutation in ClpP has previously been associated with resistance to imipridones. Accordingly, SF8628 cells with a CRISPR-mediated ClpP knockout were resistant to both ONC201 and ONC206. Polyclonal resistant cell lines were generated through prolonged passaging in increasing concentrations of ONC201 (SF8628 and T98G cells) or ONC206 (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. Whole genome sequencing revealed ClpP mutations in both ONC201Res and ONC206Res T98G cells. RNAseq analysis revealed upregulation of the integrated stress response, apoptosis pathways, and amino acid metabolism with imipridone treatment in T98G parental cells but not resistant clones. Depleting glucose in the media enhanced cell viability inhibition by imipridones, indicating mitochondrial metabolism may contribute to their mechanism of action. Our results identify ClpP and mitochondrial metabolism as key aspects for the mechanism of action of ONC201 and ON206 in DIPG and GBM cell lines.

233 (PB113) - TNG908 is a brain-penetrant, MTA-cooperative PRMT5 inhibitor for the treatment of MTAP-deleted cancer

TNG908 is a clinical stage MTA-cooperative PRMT5 inhibitor that leverages the synthetic lethal interaction between PRMT5 inhibition and MTAP deletion. TNG908 was discovered using structure-based design following an initial high-throughput screening campaign. TNG908 is 15X selective for MTAPnull cell lines over isogenic MTAPWT cell lines and has marked selectivity for MTAP-deleted cancer cell lines independent of lineage in a large, diverse cell line panel. Oral administration of TNG908 drives dose-dependent, MTAPnull-selective antitumor activity in xenograft models, including durable tumor regressions in models representing glioblastoma, non-small cell lung cancer (adenocarcinoma and squamous), mesothelioma, cholangiocarcinoma, urothelial carcinoma, and others.

Sustained Aurora Kinase B Expression Confers Resistance to PI3K Inhibition in Head and Neck Squamous Cell Carcinoma.

Aurora B signaling facilitates resistance to PI3K inhibition in head and neck squamous cell carcinoma, suggesting that combined inhibition of PI3K and Aurora kinase is a rational therapeutic strategy to overcome resistance.

1488MO Initial results of phase II/III trial of AL102 for treatment of desmoid tumors (DT)

AL102 is a potent, orally available, selective gamma secretase inhibitor (GSI) under investigation as an antineoplastic agent. GSIs have antitumor activity against DT, including AL101 (2 confirmed PRs >3.5 years and >1 year; 1 stable disease for 1 year). There remains an unmet need for effective systemic therapy in DT, associated with durable tolerability, tumor regression, and symptom improvement.

Personalized neoantigen vaccine combined with PD-1 blockade increases CD8+ tissue-resident memory T-cell infiltration in preclinical hepatocellular carcinoma models

BackgroundPersonalized neoantigen vaccine could induce a robust antitumor immune response in multiple cancers, whose efficacy could be further enhanced by combining with programmed cell death 1 blockade (α-PD-1). However, the...

STUB1 is an intracellular checkpoint for interferon gamma sensing

Immune checkpoint blockade (ICB) leads to durable and complete tumour regression in some patients but in others gives temporary, partial or no response. Accordingly, significant efforts are underway to identify tumour-intrinsic mechanisms underlying ICB resistance. Results from a published CRISPR screen in a mouse model suggested that targeting STUB1, an E3 ligase involved in protein homeostasis, may overcome ICB resistance but the molecular basis of this effect remains unclear. Herein, we report an under-appreciated role of STUB1 to dampen the interferon gamma (IFNγ) response. Genetic deletion of STUB1 increased IFNGR1 abundance on the cell surface and thus enhanced the downstream IFNγ response as showed by multiple approaches including Western blotting, flow cytometry, qPCR, phospho-STAT1 assay, immunopeptidomics, proteomics, and gene expression profiling. Human prostate and breast cancer cells with STUB1 deletion were also susceptible to cytokine-induced growth inhibition. Furthermore, blockade of STUB1 protein function recapitulated the STUB1-null phenotypes. Despite these encouraging in vitro data and positive implications from clinical datasets, we did not observe in vivo benefits of inactivating Stub1 in mouse syngeneic tumour models—with or without combination with anti-PD-1 therapy. However, our findings elucidate STUB1 as a barrier to IFNγ sensing, prompting further investigations to assess if broader inactivation of human STUB1 in both tumors and immune cells could overcome ICB resistance.

Abstract 3597: Direct targeting of KRASG12X mutant cancers with RMC-6236, a first-in-class, RAS-selective, orally bioavailable, tri-complex RASMULTI(ON) inhibitor

Abstract Mutant RAS is common in pancreatic carcinoma (PDAC), non-small cell lung cancer (NSCLC) and colorectal cancer (CRC) and exists predominantly in the GTP-bound (RAS(ON)) state, leading to excessive downstream oncogenic signaling. KRASG12C(OFF) inhibitors have provided clinical proof of concept for targeting mutant KRAS. Preclinical data suggests inhibition of RAS(ON) may be a superior therapeutic strategy. In addition, KRASG12 mutations such as KRASG12D and KRASG12V remain unserved.RMC-6236 is a first-in-class, potent, oral tri-complex RASMULTI(ON) small molecule inhibitor designed to treat cancers driven by a variety of RAS mutations. RMC-6236 non-covalently binds to an abundant intracellular chaperone protein, cyclophilin A (CypA), resulting in a binary complex that engages RAS(ON) to form a high-affinity, RAS-selective tri-complex that sterically inhibits RAS binding to effectors. Exposure to RMC-6236 suppressed ERK phosphorylation and cell growth, and induced apoptosis in multiple human RAS-addicted cancer cell lines in vitro.RMC-6236 induced dose-dependent, deep, and durable suppression of RAS pathway activation up to 48 hours in preclinical xenograft models in vivo. Prolonged exposure in tumors was observed relative to blood and various healthy tissues, likely mediated by high affinity binding of RMC-6236 to tumor CypA.RMC-6236 at tolerable doses induced profound and durable tumor regressions in multiple cell line-derived (CDX) and patient-derived (PDX) RASMUT xenograft models, including NSCLC, CRC and PDAC. Anti-tumor activity was particularly notable in KRAS position 12 (G12X) mutant tumors, particularly KRASG12D, KRASG12V, and KRASG12R, with significant tumor regressions observed. Tumor growth inhibition was durable even in tumors that did not regress. Intermittent scheduling of RMC-6236 was active and permitted a higher dose intensity than daily dosing.RMC-6236 promoted anti-tumor immunity in vivo and was additive with anti-PD1 antibodies, driving durable complete responses and immunologic memory in a KRAS mutant CRC model. Furthermore, RMC-6236 treatment reversed oncogenic RAS-driven immune evasion mechanisms in a checkpoint blockade refractory KRAS mutant model, significantly transforming the tumor microenvironment in favor of anti-tumor immunity.These preclinical results support the inclusion of NSCLC, PDAC, and CRC patients in our planned clinical trial of RMC-6236 in patients with KRASG12X advanced solid tumors. Citation Format: Elena S. Koltun, Meghan A. Rice, W. Clay Gustafson, David Wilds, Jingjing Jiang, Bianca J. Lee, Zhengping Wang, Stephanie Chang, Mike Flagella, Yunming Mu, Nuntana Dinglasan, Nicole Nasholm, James W. Evans, Yingyun Wang, Kyle Seamon, Yang Liu, Cristina Blaj, John Knox, Rebecca Freilich, Elsa Quintana, Jim Cregg, Alun Bermingham, Adrian L. Gill, Jacqueline Am Smith, Mallika Singh. Direct targeting of KRASG12X mutant cancers with RMC-6236, a first-in-class, RAS-selective, orally bioavailable, tri-complex RASMULTI(ON) inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3597.

Abstract 3697: Exploiting patient-derived xenografts and organoids to tackle apoptotic dependencies in EGFR-inhibited colorectal tumours

Abstract Treatment with EGFR-targeted therapies, such as the EGFR monoclonal antibody cetuximab, has improved the outcome of patients with metastatic colorectal cancer (mCRC). However, EGFR inhibition is mainly cytostatic and does not lead to tumor eradication: subsets of drug-tolerant cancer cells often persist even after maximal response to therapy and foster residual disease, leading to relapse. Importantly, drug-tolerant cells are less prone to undergo apoptosis, and thus constitute a reservoir of treatment-refractory persisters that are difficult to extinguish. Here we aimed to investigate the mechanisms by which apoptosis escape mediates survival of cetuximab-tolerant mCRC cells as a means to find new therapeutic strategies for limiting residual disease and delaying disease recurrence. By performing an innovative functional assay named Dynamic BH3 Profiling in cetuximab-sensitive patient-derived organoids (PDOs), we found that antibody treatment increased the “apoptotic priming”, i.e. decreased the distance of cells from the apoptotic threshold without eliciting overt cell death. To start investigating the mechanisms of this increased apoptotic priming, protein levels of the major anti-apoptotic molecules (BCL2, BCL-XL, MCL1) and the pro-apoptotic molecule BIM were evaluated by Western blot in cetuximab-treated PDOs. BIM was consistently upregulated by cetuximab in all tested models. Increased BIM was sequestered by the anti-apoptotic BCL-XL, suggesting that EGFR blockade may render mCRC residual cells dependent on BCL-XL to elude cell death and, consequently, more susceptible to its inhibition. We therefore challenged a panel of 14 PDOs with different BH3 mimetics currently in preclinical or clinical development and found that only the combination of cetuximab with BH3 mimetics against BCL-XL strongly reduced cell viability and induced apoptosis. BCL-XL blockade enhanced cetuximab efficacy also in mCRC patient-derived xenografts, which displayed more durable tumor regression that was maintained also after treatment discontinuation. Notably, the combination of cetuximab with BCL-XL inhibitors was effective in vivo in all tested models except for one, which was characterized by low basal expression of BIM. Mechanistically, unleashed apoptosis by combination therapy was due to cetuximab-induced BIM upregulation concomitantly with its displacement from BCL-XL by the BH3 mimetic. Overall, this study offers new insights into the molecular mechanisms assisting residual disease after cetuximab treatment in mCRC, providing hints to design rational strategies that may convert the cytostatic effect of cetuximab into a cytotoxic, fully apoptotic outcome. Basal expression of BIM could be exploited as a predictive biomarker to enrich for potential responders to the combination of cetuximab and BH3 mimetics. Citation Format: Simonetta Maria Leto, Irene Catalano, Martina Ferri, Valentina Vurchio, Francesca Cottino, Eugenia Rosalinda Zanella, Francesco Sassi, Giorgia Migliardi, Andrea Bertotti, Livio Trusolino. Exploiting patient-derived xenografts and organoids to tackle apoptotic dependencies in EGFR-inhibited colorectal tumours [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3697.

Abstract CT186: Pharmacokinetic (PK) profile of a novel IKZF1/3 degrader, CFT7455, enables significant potency advantage over other IKZF1/3 degraders in models of multiple myeloma (MM) and the results of the initial treatment cohort from a first-in-human (FIH) phase 1/2 study of CFT7455 in MM

Abstract Introduction: CFT7455 is a highly potent and novel Ikaros Family Zinc Finger Protein 1/3 (IKZF1/3) degrader. In xenograft models, CFT7455 has more potent IKZF1/3 degradation compared to other degraders. Early observations from the FIH clinical trial (NCT04756726) along with supporting translational studies are presented here. Methods: Pre-clinical studies comparing CFT7455 and CC-92480 in both in vitro and xenograft models were performed. The pre-clinical studies’ results coincided with observations from the on-going clinical trial. The clinical trial is an open-label, Phase 1/2, multi-center, FIH study in heavily pretreated relapsed/refractory (R/R) MM and non-Hodgkin’s lymphoma (NHL) patients evaluating safety, tolerability, and PK of CFT7455. Eligible MM patients are R/R to therapy and are not candidates for regimens known to provide clinical benefit. A starting dose of 50 μg QD 21 days on/7 days off (21/7) in 28-day cycles was administered. Results: CFT7455 and CC-92480 showed similar cereblon binding profiles and in vitro IKZF1/3 degradation kinetics, translating into sub-nanomolar GI50 values in proliferation assays across a panel of MM cell lines. In the NCI-H929 xenograft model, 100 μg/kg/day of CFT7455 resulted in durable tumor regressions, while 1000 μg/kg/day of CC-92480 gave tumor stasis. Similar results were seen in a systemic model of MM, MM1.S. Both compounds achieved >95% IKZF3 degradation in tumors 4h post dose. At 48h post dose, CFT7455 was more effective than CC-92480 in maintaining IKZF3 degradation (65% vs. 6% respectively). When levels of CFT7455 and CC-92480 in plasma and tumor were compared, CFT7455 concentrations were > DC80 in tumor 48h post dose, while CC-92480 levels were undetectable in tumor and plasma, demonstrating CFT7455 has longer exposure resulting in sustained IKZF1/3 degradation in pre-clinical models. In cohort A, 5 heavily pre-treated MM patients (pts) received single agent CFT7455. 4 pts have received at least 3 cycles, with 2 pts receiving 5 cycles. Neutropenia (grade 4) was observed in 3/5 pts without coincident fever or infection. Additionally, a 2-4 fold accumulation in plasma CFT7455 exposure at steady state was observed. Early pharmacodynamic (PD) data demonstrates deep persistent degradation of IKZF3 (~100%) and serum free light chain reduction (up to 72%) in response to treatment. Stable disease has been observed in 34 pts, suggesting clinical benefit. Conclusions: While CFT7455 showed clinical benefit at 50 ug with deep target degradation, neutropenia was dose limiting. PK/PD modeling suggests alternative dosing regimens may result in increased tolerability with preserved efficacy, and evaluation of them is underway. Updated results will be presented at the meeting. Citation Format: Sagar Lonial, Shambavi Richard, Jeffrey V Matous, Andrew J. Yee, Urvi Shah, Neha Mehta-Shah, Thomas Martin, Eli Muchtar, Sikander Ailawadhi, Paul G. Richardson, Manisha Bhutani, Samantha Perino, Jason Kirby, Roman V. Agafonov, Prasoon Chaturvedi, Bradley Class, Matthew Schnaderbeck, Michael R. Palmer, Cathleen Gorman, Oliver Schoenborn-Kellenberger, Amanda Hoerres, Stewart L. Fisher, Roy M. Pollock, Adam Crystal, Michelle Mahler, Jesus Bardeja. Pharmacokinetic (PK) profile of a novel IKZF1/3 degrader, CFT7455, enables significant potency advantage over other IKZF1/3 degraders in models of multiple myeloma (MM) and the results of the initial treatment cohort from a first-in-human (FIH) phase 1/2 study of CFT7455 in MM [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT186.

Abstract 3939: Preclinical development of embryonic ectoderm development (EED) inhibitor APG-5918/EEDi-5273 for cancer therapy

Abstract Three core components constitute the polycomb repressive complex 2 (PRC2), a multiprotein complex that catalyzes methylation of histone H3 at lysine 27 (H3K27): (1) enhancer of zeste homolog 2 (EZH2), (2) EED, and (3) suppressor of zeste 12 protein homolog (SUZ12). Dysregulated function of PRC2 is implicated in the development of various cancer types. With regulatory approval of EZH2 inhibitor tazemetostat, a potentially effective successful cancer therapeutic strategy is now available for patients with epitheloid sarcoma and relapsed or refractory follicular lymphoma. However, EZH2 inhibitor activity might be reduced because of acquired resistance through secondary mutations in EZH2 or its inability to inhibit paralogs of EZH2 (including EZH1). Because binding of EED with trimethylated H3K27 (H3K27me3) is required to activate methyltransferase activity of EZH2, allosterically targeting EED is emerging as a novel approach to inhibit PRC2 (Qi et al, Nat Chem Biol 2017). APG-5918/EEDi-5273 is a well-documented, investigational, novel, bioactive, and potent EED inhibitor (Rej et al, JMC 2021). The aim of this study was to further characterize the anticancer therapeutic activity of APG-5918 in the preclinical setting. APG-5918/EEDi-5273 showed high-affinity binding to EED protein in a biochemical assay (IC50 = 1.2 nM). It also exerted potent antiproliferative activity in several EZH2 mutant (EZH2mut) diffuse large B-cell lymphoma (DLBCL) cell lines, with IC50 values in the nanomolar range and inhibitory effects that were approximately 5 times lower than those with tazemetostat. In a mouse xenograft model derived from EZH2mut KARPAS-422 DLBCL cells, single-agent APG-5918 conferred potent and dose-dependent antitumor activity, resulting in durable complete tumor regression that correlated with inhibition of H3K27me3, induction of PRC2 target genes, and drug exposure in tumors. In summary, our results provide scientific rationale for the clinical development of APG-5918/EEDi-5273 in EZH2mut lymphomas and, potentially, other hematologic malignancies and solid tumors. Citation Format: Saijie Zhu, Douglas D. Fang, Qiang Li, Dongmei Yang, Shoulai Gu, Shaomeng Wang, Dajun Yang, Yifan Zhai. Preclinical development of embryonic ectoderm development (EED) inhibitor APG-5918/EEDi-5273 for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3939.

Abstract 3945: Novel antagonists of TEAD palmitoylation inhibit the growth of Hippo-altered cancers in preclinical models

Abstract Background: The Hippo pathway is an evolutionarily conserved signaling cascade whose deregulation can promote excessive cell proliferation and tumor development. Pathway output is mediated by the YAP and TAZ transcriptional co-activators, which bind to TEAD family transcription factors to drive target gene expression. Genomic aberrations in Hippo pathway components result in constitutive activation of YAP/TAZ, as seen with NF2 mutations in subsets of mesothelioma and other cancers. Hyperactivation of YAP/TAZ has also been associated with resistance to a variety of targeted agents, including EGFR and CDK4/6 inhibitors, suggesting that targeting the pathway may have utility as part of rationally selected combinations, in addition to genomically-informed monotherapy applications. Activity of the YAP/TAZ-TEAD complex thus represents a compelling pharmacologic target, due to its essential role in the pathway, and the presence of a conserved druggable site in TEAD that is required for transcriptional function. Results and Discussion: Using biophysical techniques, we identified novel small molecules that bind to the TEAD auto-palmitoylation pocket. Initial hits were optimized for antagonism of TEAD-based transcription and drug-like properties, ultimately producing highly potent and orally bioavailable TEAD inhibitors. These compounds selectively inhibited the proliferation of cancer cell lines harboring genomic alterations in the Hippo pathway with low nM potency. In vivo models of Hippo pathway-altered xenografts showed consistent monotherapy activity, with dose-dependent and durable tumor regressions achieved at well-tolerated doses. Further characterization of these compounds as monotherapies and as part of rationally-designed combination regimens is ongoing. Citation Format: Adeela Kamal, Aurélie Candi, Matthias Versele, Bart Vanderhoydonck, Arnaud Marchand, Ron de Jong, Thuy Hoang, Georg Halder, Patrick Chaltin, Stephen L. Gwaltney, Mike Burgess. Novel antagonists of TEAD palmitoylation inhibit the growth of Hippo-altered cancers in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3945.

Abstract 5333: Pancreatic cancer enhances HER2 signaling through DUSP6 to circumvent therapeutic MAPK inhibition

Abstract Background: Oncogenic KRAS is present in almost all cases of pancreatic ductal adenocarcinoma (PDAC). However, targeting KRAS or its canonical signaling cascades, especially the mitogen-activated protein kinase (MAPK) pathway, remains clinically unsuccessful. Targeting ERK kinases has recently emerged as a promising therapeutic strategy and combinatorial strategies should be developed. Aim: Identify adaptive mechanisms to ERK inhibition that can be co-targeted to achieve effective tumor inhibition in multiple patient-derived xenograft (PDX) models. Methods: Reverse-phase protein array (RPPA) was used in early-passage patient-derived cell lines (PDCLs) to identify potential resistance mechanisms. These were confirmed using RNA interference and overexpression in PDAC cell lines and PDCLs. The promising combinations were tested in 30 early-passaged PDAC PDXs. Results: RPPA showed dramatic downregulation of DUSP4 and DUSP6 phosphatases following MEK and ERK inhibition, which coincided with upregulation of phospho-HER2 and -HER3. Knockdown of DUSP6, but not DUSP4, was sufficient in phosphorylation of HER2. Conversely, overexpression of DUSP6 curbed HER2 and ERK activation. Downregulation of DUSP4 and DUSP6 induced by ulixertinib, an ERK inhibitor now in clinical development, was reversed by bortezomib, suggesting DUSP4 and DUSP6 are proteosomally degraded. Combined ulixertinib plus PI3K inhibitor copanlisib, or pan-HER inhibitor afatinib slowed but did not arrest PDX tumor growth in vivo, and addition of gemcitabine was required to achieve tumor regression or durable growth arrest. Alternatively, ulixertinib or MEK inhibitor (trametinib) in combination with trastuzumab deruxtecan (DS-8201a), an anti-HER2 conjugated topoisomerase I inhibitor, were extremely effective, leading to complete and durable tumor regression for all tested PDX models. We showed that upregulation of HER2 expression following MEK or ERK inhibitor treatment provides a conduit for enhanced internalization of DS-8201a. Conclusions: Our study provided novel mechanistic insight on how PDAC cells evade MAPK inhibition via enhancing HER2 signaling. We demonstrated that the combination of MEK or ERK inhibitor plus DS-8201a is extremely effective, leading to complete tumor regression in multiple PDAC PDX models. This combination should be advanced as a clinical trial for PDAC patients. Keys: DS-8201a, DUSP6, HER2, KRAS, ulixertinib, pancreatic ductal adenocarcinoma Citation Format: Ashenafi Shiferaw Bulle, Kuljeet Seehar, Sapana Bansod, Yali Chen, Chen Hung-Po, Paarth B. Dodhiawala, Lin Li, Vikas Somani, Jacqueline Mudd, Ryan C. Fields, Deborah Knoerzer, Andrea Wang-Gillam, Lim Kian-Huat. Pancreatic cancer enhances HER2 signaling through DUSP6 to circumvent therapeutic MAPK inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5333.

Abstract 2306: BLU-222, an investigational, potent, and selective CDK2 inhibitor, demonstrated robust antitumor activity in CCNE1-amplified ovarian cancer models

Abstract Background: Cyclin-dependent kinases (CDK) are a class of enzymes that, along with their regulatory cyclin binding partners, drive cell cycle progression. Cell cycle dysregulation is a hallmark of cancer and targeting its genetic drivers can confer therapeutic benefits. Cyclin E1 (CCNE1) gene alterations are common in patients with ovarian cancer and can be found in ~20% of high-grade serous ovarian cancer cases, which tend to be platinum therapy resistant and therefore represent a high medical need. Cyclin E1 is the canonical binding partner of CDK2, which becomes constitutively active when CCNE1 is amplified and overexpressed. Selectively inhibiting CDK2 is an attractive therapeutic option for CCNE1-amplified tumors and may limit off-target CDK-driven toxicities. Here we report preclinical validation studies leading to the development of an orally available CDK2 inhibitor, BLU-222, for the treatment of ovarian cancer harboring a CCNE1 amplification. Methods: BLU-222 selectivity was measured by enzyme assays, cellular target engagement assays (NanoBRET), and proliferation assays in a panel of ovarian cancer cell lines. In vitro cellular potency was assessed by phospho-Rb levels. In vivo antitumor activity of BLU-222 as a single agent or in combination with carboplatin was measured in an OVCAR-3 cell line-derived xenograft (CDX) tumor model harboring a CCNE1 amplification. Results: BLU-222 demonstrated selectivity, both biochemically and in cells, with low nanomolar potency for CDK2 vs other CDK family members (CDK1, -4, -6, -7, and -9). In a panel of ovarian cancer cell lines, those with CCNE1 amplifications were highly sensitive to BLU-222. Consistent with the in vitro profiling, BLU-222 exhibited significant antitumor activity in the OVCAR-3 CDX model. While administration of single-agent carboplatin led to stasis in vivo, the combination of BLU-222 + carboplatin induced durable tumor regression even after treatment cessation. Conclusions: These data provide a strong rationale for advancing BLU-222 towards clinical development in patients with CCNE1-amplified ovarian cancer. Citation Format: Victoria Brown, Phil Ramsden, Nealia House, Richard Vargas, Jian Guo, Ruduan Wang, Riadh Lobbardi, Maxine Chen, Douglas Wilson, Joseph Kim, Neil Bifulco, Michelle Maynard, Emanuele Perola, Dean Zhang, Steve Wenglowsky, Yoon Jong Choi. BLU-222, an investigational, potent, and selective CDK2 inhibitor, demonstrated robust antitumor activity in CCNE1-amplified ovarian cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2306.

Abstract 327: Antitumor efficacy of trastuzumab deruxtecan in combination with adavosertib in HER2-expressing Cyclin E amplified gastroesophageal cancers

Abstract Purpose: Trastuzumab deruxtecan (T-DXd) is a HER2-directed antibody-drug conjugate approved for patients with HER2-positive gastric/gastroesophageal junction (GEJ) cancers. Amplification of CCNE1, which encodes cyclin E, has been proposed as a mechanism of resistance to HER2-targeted therapies. The Wee1 kinase inhibitor adavosertib (AZD1775) has demonstrated enhanced antitumor activity in the setting of cyclin E overexpression. We investigated the efficacy of T-DXd in combination with adavosertib in HER2-expressing cancers with and without co-amplification of CCNE1. Methods: Frequency of CCNE1 amplification was determined among patients with ERBB2 amplification in a clinical genomic database at the MD Anderson Cancer Center (MDACC) and within The Cancer Genome Atlas (TCGA). Sulforhodamine B assay, western blotting, and Annexin V staining were used to determine the effects of T-DXd and DXd in combination with adavosertib in vitro. Four HER2-expressing gastric/GEJ patient-derived xenograft (PDX) models with or without co-amplification of CCNE1 were tested with T-DXd in combination with adavosertib in vivo. Tumor volume and body weights were measured twice weekly and treatment responses were assessed by the relative treatment-to-control ratio, waterfall plots, and event-free survival (event defined as the day which tumors doubled in size from baseline). Results: Of 515 patients identified at MDACC with ERBB2 amplification, 60 (11.6%) had co-amplification of CCNE1. Of the 405 patients identified within the TCGA with ERBB2 amplification, 43 (10.6%) had co-amplification of CCNE1. Tumor types with the highest frequency of ERBB2/CCNE1 co-amplification were gastric/GEJ (38.1% MDACC, 31.0% TCGA), endometrial (25.0% MDACC, 29.6% TCGA), and ovarian (15.4% MDACC, 15.4% TCGA). Adavosertib was synergistic in combination with DXd in four cell lines with ERBB2 amplification, CCNE1 amplification, or ERBB2/CCNE1 co-amplification. Both DXd and T-DXd upregulated cyclin E and γH2AX protein expression at 24 and 96 hours, and the combination of DXd or T-DXd with adavosertib enhanced apoptosis. T-DXd induced durable tumor regression in two HER2 amplified and HER2 overexpressing gastroesophageal PDX cancer models with HER2 amplification/3+ overexpression and concomitant cyclin E amplification/expression. Adavosertib enhanced the antitumor activity of T-DXd in two HER2 low, cyclin E amplified gastroesophageal cancer PDX models (one with an ERBB2 G778A mutation). Conclusions: ERBB2 and CCNE1 are frequently co-amplified. Our findings provide supporting rationale for combining T-DXd with adavosertib in HER2-expressing cancers with CCNE1 co-amplification. Further study is needed to determine if therapeutic induction of cyclin E with DXd may sensitize to Wee1 kinase inhibition in patients without cyclin E amplification as well. Citation Format: Timothy P. DiPeri, Kurt W. Evans, Gabriela Raso, Yasmeen Q. Rizvi, Xiaofeng Zheng, Bryce Kirby, Kathleen Kong, Khandan Keyomarsi, Jaffer A. Ajani, Timothy A. Yap, Funda Meric-Bernstam. Antitumor efficacy of trastuzumab deruxtecan in combination with adavosertib in HER2-expressing Cyclin E amplified gastroesophageal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 327.

Phase 1 study of KT-333, a targeted protein degrader, in patients with relapsed or refractory lymphomas, large granular lymphocytic leukemia, and solid tumors.

TPS3171 Background: The signal transducer and activator of transcription 3 (STAT3) protein is activated by cytokines and growth factors resulting in tumor growth and promotion and hindering antitumor immunity. Approximately 70% of human cancers including both hematological malignancies and solid tumors exhibit increased levels of phosphorylated STAT3 (pSTAT3). There is evidence of constitutive activation of STAT3 through genetic mutations or aberrant cellular signaling pathways in tumors such as large granular lymphocytic leukemia (LGL-L), peripheral T-cell lymphoma (PTCL), and cutaneous T-cell lymphomas (CTCL). Hyperactivation of STAT3 has been reported in a variety of solid tumors. In several of these cancers, the levels of pSTAT3 and/or activated STAT3 have been shown to correlate with poor clinical prognosis. As with other transcription factors, selective inhibition of STAT3 has been proven to be difficult with conventional therapeutic approaches. KT-333 is a potent highly selective, heterobifunctional small molecule degrader of STAT3. In preclinical studies, durable tumor regressions were seen with weekly KT-333 administration in STAT3-dependent T cell lymphomas, and antitumor activity was seen in solid tumors in combination with anti-PD1 (ASH 2021, SITC 2021). Methods: KT-333 is being evaluated in an open-label, dose escalation (Phase 1a, n = 40) study in patients with lymphomas relapsed or refractory (R/R) to at least two prior systemic treatments or for whom standard therapies are unavailable. Dose escalation will be conducted by accelerated titration followed by a 3+3 design in ascending doses of intravenous KT-333 administered once weekly in 28-day cycles to evaluate safety and define the maximum tolerated dose (MTD)/recommended Phase 2 dose (RP2D) (primary endpoint). Secondary endpoints include pharmacokinetics (PK) in plasma and urine and preliminary pharmacodynamic effects (PD) of KT-333 using blood (peripheral blood mononuclear cells [PBMCs], plasma/serum) and tumor tissue. After confirming the MTD/RP2D in patients with lymphoma, patients with advanced solid tumors will be enrolled in a separate Phase 1a cohort at the MTD/RP2D. In Phase 1b (n = 80), patients with PTCL, CTCL, LGL-L (T-cell LGL-L or chronic lymphoproliferative disorder of natural killer-cells), or solid tumors R/R to at least one prior systemic standard of care treatment or for whom standard therapies are not available, will be enrolled in separate 20 patient cohorts. This will further characterize safety, PK, PD and evaluate the clinical activity of KT-333. Treatment with KT-333 will continue until disease progression, unacceptable toxicity, or patient refusal. KT333-TL-101 began enrolling in January 2022. Clinical trial information: NCT05225584.