Abstract 1811: Dithiazanine Iodide suppresses mitochondrial function to strongly inhibit pancreatic ductal adenocarcinoma growth in-vitro and in-vivo, producing a marked increase in survival

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDAC) is an aggressive recalcitrant cancer with a uniquely austere tumor microenvironment (TME). It is hypovascularized, hypoxic, and poor in nutrients. These features, which are critical due to the increased energetic demand in continuously replicating cancer cells, drive metabolic reprograming to support the continued activity. Thus leading to a vulnerability in the form of energy restriction - a vulnerability further exacerbated by the nutrient-poor pancreatic cancer TME. We have recently shown mitochondrial inhibition to have great potential in in-vitro inhibition of PDAC cells. Since repurposing of FDA-approved drugs holds great promise in terms of faster and safer drug development, we selected to investigate the effect of mitochondrial inhibition on pancreatic cancer cells through assessment of the previously FDA-approved antimicrobial Dithiazanine Iodide (CDI). CDI is a fluorescent, orally bioavailable, small molecule. In-vitro, it has been previously shown to preferentially localize to the mitochondria, bind proteins and nucleic acids, and have a yet to be discerned inhibitory effect on the electron transport chain. We demonstrated CDI had low IC50s (30-300 nM) in multiple PDAC and other GI cancer cell lines. In an agnostic, unbiased manner, we assessed metabolomic and transcriptomic perturbations caused by CDI. These revealed a profound 92% decrease in the abundance of mitochondrial-encoded transcripts (P<0.05), decreased mitochondrial beta-oxidation, and a reduction in the ATP/ADP ratio. We have therefore hypothesized that the anti-cancer effects of CDI may be related to disruption of mitochondrial processes and we proceeded to characterize its mechanism of action. CDI treatment reduced protein expression of electron transport chain complexes I, II, III, and IV. Treatment with CDI in hypoglycemic conditions resulted in a 3-4 fold increase in sensitivity (P<0.05) and ATP quantification showed a marked >90% decrease in cellular ATP (P<0.05). Furthermore, mitochondria-depleted PDAC cell lines were 4-fold more resistant to CDI treatment (P<0.05). In-vivo, oral CDI treatment resulted in a 2-fold decrease in mouse xenograft tumor growth compared to gemcitabine treatment. RNA-sequencing from the in-vivo samples showed a 60% reduction in the abundance of mitochondrial-encoded transcripts (P<0.05). Examination of the mitochondrial sequences revealed the existence of putative G-Quadruplex sequences. Fluorescence shift and stop-PCR assays confirmed CDI to be a G-Quadruplex binder of mitochondrial sequences. Citation Format: Avinoam Nevler, Christopher W. Schultz, Aditi Jain, Saed Khalilieh, Grace McCarthy, Harish Lavu, Wilbur Bowne, Charles J. Yeo, Jonathan R. Brody. Dithiazanine Iodide suppresses mitochondrial function to strongly inhibit pancreatic ductal adenocarcinoma growth in-vitro and in-vivo, producing a marked increase in survival [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 1811.