Exploring the role and potential of anti-viral drugs to sensitize cancer cells to chemotherapy - PROJECT SUMMARY Chemotherapy remains the most used systemic treatment for cancers. However, despite significant improvement in chemotherapy agents, chemoresistance remains the major problem in cancer management. Recently, we discovered that the selective inhibitors of hepatitis C virus (HCV) NS5A replication complex elbasvir (Elb) and daclatasvir (Dac), an analog of Elb, may be used to sensitize and re-sensitize solid and hematologic cancer cells to chemo-drugs. We screened 1855 FDA-approved drugs and found that Elb was among the top drugs that significantly sensitized multiple myeloma (MM) cells to carfilzomib (Cfz, proteasome inhibitor), dexamethasone (Dex, corticosteroid), and melphalan (Mel, alkylating agent). Elb and Dac could also re-sensitize Cfz- or Dex-resistant MM cells to Cfz or Dex respectively. In addition, we observed that Elb and Dac enhanced chemosensitivity and re-sensitized different types of cancers such as pancreatic ductal adenocarcinoma to 5-fluorouracil and gemcitabine (Gem), estrogen receptor‑positive breast cancer (BC) cells to tamoxifen, and triple negative BC cells to Gem. Moreover, in the presence of Elb or Dac, lower doses of chemo-drugs were required to induce similar cancer cell death compared to chemotherapy drugs alone. We discovered that Elb and Dac significantly enhanced drug retention in cancer cells by inhibiting drug efflux through ATPase phospholipid transporting 9B (ATP9B). Importantly, although tumor microenvironment (TME) components such as tumor-associated stromal cells (TASCs) and tumor-associated macrophages (TAMs) can protect cancer cells from chemotherapy-induced cell death, Elb and Dac abrogated TASC and TAM protective effects by suppressing pro-tumor lipid secretion, reprogramming them to secrete type-I-IFNs for sensitizing MM cells to Cfz, and inhibiting TAM release of deoxycytidine for overcoming Gem resistance in solid tumors. Finally, Elb and Dac significantly improved the therapeutic efficacy of chemotherapies in MM in vivo without increased toxicity to normal tissues. Therefore, we hypothesize that HCV NS5A inhibitors Elb and Dac can be developed into cancer therapeutic agents due to their ability to (re)sensitize cancer cells to chemotherapies by enhancing chemo-drug retention in tumor cells and removing TME-provided protection. To minimize the scope of this application, we will focus on human MM (hematological malignancy) and use human MM cell lines and primary MM cells from patients and MM PDX mouse models to test the hypothesis. Aim 1 will elucidate the role and mechanism of Elb and Dac in sensitizing tumor cells to chemotherapy by inhibiting chemotherapeutic drugs efflux through ATP9B and Aim 2 will elucidate the role and mechanisms of Elb and Dac in overcoming TME-mediated extrinsic resistance by inhibiting ATP9B-mediated cholesterol uptake and deoxycytidine efflux. Accomplishing these aims will provide the justification and tools for developing novel and effective strategies for targeting both cancer drug efflux and TME to improve the therapeutic efficacy of chemotherapy.
