Abstract B012: Validation of the OncoSignature assay, an ACR-368-tailored response-predictive quantitative multiplexed immunofluorescent assay for prediction of sensitivity to the CHK1/2 inhibitor ACR-368 in individual patients with cancer

Abstract

Abstract Background: The CHK1/2 kinase inhibitor ACR-368 (Prexasertib) demonstrated durable single-agent efficacy in a subset of patients with high grade serous ovarian, anal and head and neck cancers in past trials. Using a quantitative phospho-proteomics approach, we identified three orthogonal candidate biomarkers tailored to predict tumor response to ACR-368 treatment. The OncoSignature® assay is based on immunofluorescent staining of biomarkers in FFPE tumor sections with image acquisition, analysis, and scoring of biomarkers. The sample is OncoSignature positive if all three biomarker scores are above their thresholds. We validated the OncoSignature® assay to predict response to ACR-368 in cancer cell lines and ovarian cancer PDX models. Here, we further validated OncoSignature® assay in novel cancer indications and in patient biopsy samples from ACR-368 clinical trials. Methods: Multiple cancer types were tested with the OncoSignature® assay for prevalence of potential ACR-368 responders. For validation, endometrial cancer PDX models were tested in anACR-368 efficacy study. Blinded untreated PDX tumors were analyzed in the OncoSignature® assay and results locked prior to unblinding and statistical analysis. Adapted [CS1] Oncosignature assay was applied to frozen pretreatment ovarian cancer biopsies from a single center ACR-368 monotherapy Ph2 trial (NCT02203513). OncoSignature® assay was also applied to FFPE pretreatment ovarian cancer biopsies from a multi-center ACR-368 monotherapy Ph 2 trial (NCT03414047) and from the NCT02203513 trial. After biomarker scores were generated and locked, patient treatment outcomes were unblinded and ACR-368 response was compared with OncoSignature prediction. Results: Evaluation of multiple cancer indications revealed a concordance between OncoSignature-predicted prevalence of ACR-368 responders and results of ACR-368 treatment observed in clinical trials. Metastatic ovarian cancer had 30% of predicted responders and 30% and 14% observed RECIST responses the above-cited trials. Squamous lung cancer had no predicted responders and no RECIST responses in a clinical trial. Endometrial and bladder cancer had a high prevalence of predicted responders with 40% and 36%, respectively. The endometrial cancer PDX efficacy study had multiple complete responses predicted by OncoSignature® assay with an AUC of 0.88. For frozen and FFPE patient biopsy samples from Phase 2 ACR-368 trials, OncoSignature positive groups had highly significant response enrichment to 47% and 57%, respectively, and significant increases in progression free survival time. Conclusions: Bladder and endometrial cancers were identified as novel indications with high prevalence of predicted ACR-368 responders. The OncoSignature® assay significantly predicted response in endometrial PDX models and in samples from ovarian cancer patients treated with ACR-368. OncoSignature® assay driven clinical trial (NCT05548296) in ovarian, endometrial and bladder cancers was initiated to test benefit to patients. Citation Format: Ayesha Murshid, Christina Noe, Kailash Singh, Sibgat Choudhury, Jayakumar Nair, James Dunyak, Michail Shipitsin, Jung-Min Lee, Peter Blume-Jensen. Validation of the OncoSignature assay, an ACR-368-tailored response-predictive quantitative multiplexed immunofluorescent assay for prediction of sensitivity to the CHK1/2 inhibitor ACR-368 in individual patients with cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B012.