Abstract 2081: NUC 3373 induces endoplasmic reticulum stress in colorectal cancer cells

Abstract

Abstract Background Although 5-fluorouracil-based (5-FU) chemotherapies remain the cornerstone of combination therapies for colorectal cancer (CRC), their clinical utility is limited by key cancer resistance mechanisms associated with breakdown, transport, and activation. This includes the intracellular conversion of 5-FU into its active metabolite, fluorodeoxyuridine-monophosphate (FUDR-MP), before core anti-cancer activity can be exerted via inhibition of the enzyme thymidylate synthase (TS). NUC-3373, a phosphoramidate transformation of FUDR-MP, is designed to bypass the key resistance mechanisms associated with 5-FU, resulting in a potentially more effective and safer treatment option. In a Phase I dose-finding study, plasma obtained from patients with advanced cancers revealed that NUC-3373 has a longer half-life than 5-FU (9.7 hours vs 8-14 minutes). Herein, we aimed to investigate the potential role of endoplasmic reticulum (ER) stress pathways in the cancer cell response to NUC-3373. Methods IC50 values for NUC-3373 were established in nine CRC cell lines by sulforhodamine B assay, after which one sensitive (HCT116) and one resistant (SW480) cell line were selected for further characterization. Control experiments were conducted with thapsigargin and tunicamycin. Cells were examined by transmission electron microscopy and, using stereological principles, changes in cell ultrastructure were quantified. Expression of the ER chaperone protein binding immunoglobulin protein (BiP) was detected by Western blot analysis. Results Ultrastructural analysis revealed that NUC-3373 had differential effects on ER stress that were dependent on cell line sensitivity to the drug. Following treatment, NUC-3373-sensitive HCT116 cells responded by dilation of their ER, while the SW480 resistant cells responded by lengthening of ER but without dilation. These changes were reflected with the two classical ER stress inducers, thapsigargin and tunicamycin. NUC-3373 activated the unfolded protein response (UPR), as evidenced by upregulation of BiP. Both the magnitude and the duration of the BiP response were higher in SW480 cells. Conclusions This study supports a novel mechanism of action for NUC-3373-induced anti-cancer activity through modulation of cell stress. NUC-3373 induces UPR and ER stress in colorectal cancer cells. Results of the ultrastructural analysis suggest that the sensitivity of cells to NUC-3373 may be determined by the differential adaptation of ER to stress conditions. Citation Format: Fiona G. McKissock, Asmithaa Prabhakaran, Peter Mullen, David J. Harrison. NUC 3373 induces endoplasmic reticulum stress in 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 2081.