Magnus E. Jakobsson (Lund / SE), Michail Shipitsin (Watertown, MA / US), Caroline Wigerup (Lund / SE), Ayesha Murshid (Watertown, MA / US), Lei Shi (Watertown, MA / US), Dorte Bekker-Jensen (Copenhagen / DK), Sibgat Choudry (Watertown, MA / US), Christina Noe (Watertown, MA / US), Kailash Singh (Watertown, MA / US), Jayakumar Nair (Bethesda, MD / US), James Dunyak (Watertown, MA / US), David A. Proia (Watertown, MA / US), J.-M. Lee (Bethesda, MD / US), S. MacLaughlan (Chicago, IL / US), D. Matei (Chicago, IL / US), M. Song (Duarte, CA / US), L. Brubaker (Aurora, CO / US), B. Rimmel (Los Angeles, CA / US), R. Eskander (La Jolla, CA / US), C. Kyi (New York, NY / US), H. Williams (Little Rock, AR / US), L. Duska (Charlottesville, VA / US), F. Musa (Seattle, WA / US), R. Coleman (The Woodlands, TX / US), B. Slomovitz (Miami, FL / US), Eric Gamelin (Watertown, MA / US), J.-M. Cuillerot (Watertown, MA / US), M. Phadnis (Watertown, MA / US), B. Guercio (Rochester, NY / US), S. Crafton (Pittsburgh, PA / US), P. Konstantinopoulos (Boston, MA / US), Jesper Velgaard Olsen (Copenhagen / DK), Kristina Masson (Lund / SE), Peter Blume-Jensen (Watertown, MA / US)
Introduction
ACR-368 (prexasertib) is a potent and selective CHK1/2 inhibitor with demonstrated durable, single-agent activity in patients with advanced solid tumors. Genomic biomarkers have been unsuccessful in predicting response to ACR-368 due in part to the complex genetic changes in cancer that translate into dysregulated protein signaling pathways. To address this challenge, we sought to identify and clinically validate protein-based predictive biomarkers that measure the ACR-368-sensitive dysregulated signaling driving tumorigenesis using our proprietary approach, termed Acrivon Predictive Precision Proteomics (AP3).
Methods
Ovarian cancer cells with differential ACR-368 sensitivity were profiled with phosphoproteomics. Kinase activity inference and signaling pathway activity analyses were conducted to uncover ACR-368-regulated pathways associated with tumorigenesis and biomarkers predictive of drug sensitivity. A quantitative, multiplexed immunofluorescent (IF) assay was developed based on three biomarkers, termed ACR-368 OncoSignature™, and validated in prospective clinical studies.
Results
AP3 phospho-proteomic profiling of ACR-368-sensitive and non-sensitive cells exposed to ACR-368 uncovered >17,000 confidently localized phospho-sites (localization probability > 0.75), with 8272 being significantly regulated by ACR-368 (FC > 1.5, Q-value < 0.05, Limma t-test). Upon ACR-368 treatment, annotated ATM/ATR and CDK1/2 substrate consensus sites were strongly upregulated and CHK1 substrates downregulated. Global phospho-pathway analyses revealed three functionally orthogonal biomarkers that were assembled into a predictive quantitative multiplex in situ assay, ACR-368 OncoSignature™, developed for routine-processed FFPE biopsy tissue to provide a direct readout of a tumor"s dependency on the signaling axis inhibited by ACR-368.
The ACR-368 OncoSignature™ test was robustly validated in preclinical studies, including 2 prospectively designed, blinded studies on biopsies from past ACR-368 Phase 2 trials on platinum-resistant ovarian cancer. The test demonstrated segregation of responders from non-responders across studies, including an ORR enrichment to 47% (p=0.01, Wilcoxon), and significant increase in progression free survival (p=0.006, CoxPH) in biopsies from Phase 2 trials at NCI.
Acrivon has shown initial prospective validation of the AP3-based ACR-368 OncoSignature™ test in the ongoing, registrational-intent Phase 2b clinical trial in ovarian and endometrial cancers (NCT05548296), demonstrating clear segregation of RECIST responders in the OncoSignature™-positive (50% confirmed ORR in 10 patients) versus OncoSignature™-negative (0% ORR in 16 patients) arms (p-value=0.0038).
Conclusions
Employing AP3, we have developed a response-predictive test for the CHK1/2 clinical stage inhibitor, ACR-368, and demonstrated initial prospective validation for patient responder identification in the ongoing Phase 2 registrational intent trial.