Abstract PO-036: LP184, a novel alkylating agent, is highly effective in pancreatic cancers with DNA damage repair defects

Abstract

Abstract Biomarker-based chemotherapy with increased efficacy and prolonged disease-free survival are urgently needed in pancreatic cancer (PDAC). A 15-20% subset of PDAC tumors carry mutations in DNA repair pathway (BRCA1/BRCA2/PALB2/RAD51/ATM/FANCD2). Additionally, mutations in nucleotide excision repair (NER) genes (ERCC2/3/4/5/6) have been reported in ~5% of PDAC. LP184 is a novel synthetic small molecule acylfulvene analog. Using precise synthetic chemistry, we determined that only a negative enantiomer of LP184 is converted to an active alkylating agent in the strict dependency on oxidoreductase, prostaglandin reductase 1 (PTGR1). By computational analyses, we demonstrate a strong positive correlation of LP184 sensitivity with PTGR1 transcript levels (r=0.89, p<10−15) in a broad panel of cancer cell lines. Once activated by PTGR1, highly reactive LP-184 nucleophile creates covalent DNA adducts that are selectively repaired via Nucleotide Excision Repair (NER) mechanism coupled to transcription (TC-NER) and/or homologous recombination (HR). We reasoned that mutation or expression driven TC-NER and HR deficiency would predispose PDAC cells to increased sensitivity to LP184. To test the idea of LP184 activity in DNA repair-deficient tumors, we evaluated LP184 chemosensitivity in genetically defined PDAC models in vitro, ex vivo, and in xenografts. Testing in six different pancreatic cancer cell lines (Capan-1, CFPAC-1, Panc1, MiaPaCa2, Panc03.27 and BxPC-3) resulted in very potent inhibition with LP184 IC50 values ranging from 114 to 182 nM. In this cell line panel, LP184 sensitivity correlated negatively with transcript levels of an NER pathway gene ERCC8 (r = -0.94). In comparison to these PDAC cell lines, a normal pancreatic epithelial cell line HPNE was 3-6 times less sensitive to LP184 (IC50 670 nM). Ex vivo cultures of 4 out of 5 low-passage patient-derived xenografts with HR deficiency showed nanomolar sensitivity to LP184 with IC50s ranging from 45 to 270 nM. These tumor graft models which were at least 6 times less sensitive to olaparib in the same assay. Depletion of ERCC4 enhanced sensitivity to LP184 about 2-fold relative to the parental cell line. To define PTGR1 as a biomarker for LP184 activity, we used CRISPR/Cas9-mediated gene editing to deplete PTGR1 expression. We found PTGR1-null Capan-1 cell line-derived xenografts were poorly sensitive to LP184, whereas PTGR1-expressing xenografts showed near complete tumor regression in all LP184 treated animals with 109% tumor growth inhibition relative to the control group in this study. Furthermore, PTGR1 depleted cells were completely resistant to LP184 in vitro. Our preclinical data demonstrate that PDAC models carrying a range of DNA repair pathway mutations are highly sensitive to LP-184 in vitro and in vivo. Increased PTGR1 expression is a validated biomarker for LP184 cytotoxicity, and is the exclusive convertase of LP184 to an active alkylator drug. We anticipate LP184 will extend the therapeutic opportunities to a large subset of PDAC patients carrying these genetic alterations. Citation Format: Diana Restifo, Aditya Kulkarni, Caleb Schimke, Joseph McDermott, Umesh Kathad, Kishor Bhatia, Panna Sharma, Igor Astsaturov. LP184, a novel alkylating agent, is highly effective in pancreatic cancers with DNA damage repair defects [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-036.