Abstract 2079: Enhanced potency of the polymeric fluoropyrimidine CF10 to KRAS-mutant colorectal cancer cells
Authors: Gmeiner William H. , Manandhar Mandira , Hinds Amanda M. , Holmes Julija , Vidi Pierre , Tsunoda Toshiyuki , Shirasawa Senji 
Published: August 2019

Background: Mutant KRAS is a key stratification factor in determining colorectal cancer (CRC) treatment. Nearly 50% of CRC tumors have KRAS mutations and these patients are unlikely to respond to anti-EGFR therapy. 5-fluorouracil (5-FU)-based chemotherapy is the preferred treatment for CRC patients with KRAS mutations; however, response rates remain very low for patients with advanced disease. Further, a sub-set of patients treated with 5-FU-based regimens suffers from serious side effects resulting from RNA-directed effects that do not contribute to the anti-cancer activity. We are developing polymeric fluoropyrimidines, such as CF10, to treat CRC more effectively and with reduced side effects. CF10 is &gt;300-fold more potent than 5-FU across the NCI 60 cell line screen with particularly strong potency to KRAS-mutant CRC cells. We investigate the role of KRAS mutation on CF10 and 5-FU response as part of an overall effort to determine if CF10-based regimens can more effectively treat CRC patients for whom 5-FU-based regimens are currently the preferred treatment option.

Methods: HKe3-wtKRAS and HKe3-mtKRAS were generated from HCT-116 human CRC cells (ATCC) by transfection with the pMSCVpuro vector encoding HA-tagged mutant or wild-type KRAS. Cytotoxicity was determined using an Alamar blue assay. Thymidylate synthase (TS) inhibition was evaluated by detecting ternary complex formation by Western blot and using a TS activity assay. Topoisomerase 1 cleavage complex (Top1cc) was evaluated using a RADAR assay and by immunofluorescence. DNA double strand breaks were detected by IF for γH2AX.

Results: CF10 is highly potent to CRC cells regardless of KRAS mutation status. In isogenic cell lines that differ only in KRAS, CF10 is more potent to KRAS-mutant relative to wild type cells. The improved potency of CF10 relative to 5-FU and increased sensitivity of KRAS-mutant cells is enhanced for cells grown in 3D culture. CF10 cytotoxicity is mediated by TS inhibition and Top1cc formation that induces DNA DSBs and activates apoptosis. In vivo, CF10 displays significantly improved anti-tumor activity relative to 5-FU in HCT-116 orthotopic tumors and causes minimal systemic toxicity.

Conclusions. KRAS mutation confers increased sensitivity to the DNA-directed fluoropyrimidine CF10. The overall mechanism of CF10 cytotoxicity to CRC cells is similar in both KRAS-WT and KRAS-MT CRC cells and involves TS inhibition, and misincorporation of FdU into DNA followed by generation of Top1-mediated DNA DSBs. Our studies indicate FP polymers are likely to be effective in CRC regardless of KRAS-mutation. The increased sensitivity of KRAS-mutant CRC to CF10 together with the very low systemic toxicity indicates that CRC patients currently being treated with 5-FU-based therapy could more effectively be treated with CF10-based regimens.

Citation Format: William H. Gmeiner, Mandira Manandhar, Amanda M. Hinds, Julija Holmes, Pierre Vidi, Toshiyuki Tsunoda, Senji Shirasawa. Enhanced potency of the polymeric fluoropyrimidine CF10 to KRAS-mutant colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2079.