Abstract 1814: Novel ABC transport inhibitor as a treatment for pancreatic and prostate cancers

Abstract ABC transporters are the active transport systems of the cell involved in the export or import of a wide variety of molecules. We discovered that a member of the ABC transporter family called ABCC3 has a critical role in pancreatic cancer. ABCC3 blockade using genetic knockdown inhibits pancreatic cancer growth in vitro and in vivo. In addition, we demonstrate that knockdown of ABCC3 reduces cell proliferation by inhibition of STAT3 and HIF1α signalling pathways, which are key regulators of pancreatic cancer progression. A focused chemical library of indenes was screened for ABCC3 inhibition using ABCC3 expressing pancreatic tumour cells. A drug development candidate, designated as S3, emerged following extensive chemical modification to optimize target selectivity and oral bioavailability. Oral administration of S3 significantly inhibited tumour growth and increased survival in several mouse models of pancreatic cancer without discernible toxicity. Interestingly, using the KPC transgenic mouse model that closely mimics human pancreatic cancer, we identified a dual activity of S3 to inhibit the growth of the primary tumour and impact the surrounding stroma. Strikingly, a significant increase in survival was achieved with S3 treatment compared to vehicle treated KPC mice. A two-fold increase in lifespan was observed from 72.5 days (median survival) in the control group to 146.5 days in the treatment group. Importantly, we observed no overt toxicity from S3 treatment at a dosage of 50 mg/kg, which generated plasma levels exceeding growth inhibitory IC50 values. Furthermore, we show that stromal cells in pancreatic tumours, which actively participate in cancer progression, are enriched for ABCC3, and that its inhibition may contribute to stroma reprogramming. In other studies, we found that S3 inhibits the closely related transporter, ABCC1, and that pharmacological inhibition of ABCC1 reduced prostate cancer cell growth in vitro and potentiated the effects of Docetaxel in vitro and in mouse models of prostate cancer in vivo. Mechanistically, we have shown that ABCC3, is overexpressed in pancreatic cancer cells and can efflux the bioactive lipid lysophosphatidylinositol (LPI) which, in turn, activates its receptor G protein-coupled receptor 55 in an autocrine mitogenic loop. Similarly, ABCC1 mediates LPI efflux in prostate cancer cells. The fact that both ABCC1 and ABCC3 transport LPI and are inhibited by S3 is not surprising considering that they share a high primary sequence identity and are known to have overlapping substrate specificity. Interestingly, unlike known ABC inhibitors, S3 has anticancer activity as a single agent. Our goal is to further study the antitumor activity of S3 alone and in combination with conventional chemotherapy or molecular targeted drugs used for the treatment of pancreatic and prostate cancer. Citation Format: Marco Falasca, Xi Chen, Gary Piazza. Novel ABC transport inhibitor as a treatment for pancreatic and prostate 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 1814.