Abstract 2599: Targeted delivery of a colchicine analogue provides synergy with ATR inhibition
Authors: Barnieh Francis M. , Morais Goreti Ribeiro , Loadman Paul M. , Falconer Robert A. 
Published: June 2022

Abstract
Introduction: Vascular disrupting agents (VDA) are an important class of therapeutic that have yet to reach their clinical potential. Colchicine is representative of the class and is an effective disruptor of microtubule dynamics. Microtubules play an important role in the maintenance of vascular integrity, hence the ability of these agents to collapse tumour blood vessels, and consequently cause tumour necrosis. Colchicine, in addition to its vascular disrupting properties, is known to induce G2/M arrest and trigger apoptosis. ICT2588 is a non-toxic, tumour targeted prodrug of a potent colchicine analogue with reduced potential for toxicity, (cardiotoxicity in particular) due to its metabolic stability in plasma and normal tissues. The preclinical evaluation of ICT2588 to-date has been focused solely on its selective tumour vascular disrupting ability and subsequent antitumour activity. The aim of this current study was to investigate the cellular metabolism of ICT2588, examine its G2/M cell cycle arrest potential, and to explore mechanisms of synergy between ICT2588 and ATR inhibition.
Method: The cellular mechanism of uptake and MT1-MMP-selective metabolism of ICT2588 was studied in MT1-MMP positive (HT1080) and negative (MCF-7) cell lines using LCMS based metabolism assays. Flow cytometry was used to analyse the effect of ICT2588 and active azademethylcolchicine (the ‘warhead’) on G2/M cell cycle arrest in both MT1-MMP positive and negative cell lines. The growth inhibitory effects of ICT2588 and its warhead either alone or in combination with ceralasertib (AZD6738, ATR inhibitor) were performed using an MTT assay in MT1-MMP positive cell lines (HT1080, MDA-MB-231, and SH-SY5Y). Synergy Finder (https://synergyfinder.fimm.fi) was used to evaluate combinations.
Results: The expression of MT1-MMP correlates with selective metabolism of ICT2588 and subsequent selective release of its warhead in HT1080 cells, but not MCF-7 cells. This metabolism is inhibited by an MT1-MMP inhibitor. Metabolism of ICT2588 induced G2/M arrest and triggered apoptosis in HT1080 cells, but not in MCF-7 cells, though the warhead induced G2/M arrest and triggered apoptosis in both cell lines. ICT2588 was synergistic with AZD6738 in all MT1-MMP positive cell lines, contrary to the antagonism observed with the warhead and AZD6738. These findings will be explored.
Conclusion: ICT2588 is metabolised by only MT1-MMP expressing cells, releasing the potent colchicine analogue in a targeted-manner, which synergised with ATR inhibition in a way not observed when the warhead was administered alone. This in vitro data has important potential implications for possible combinations of ICT2588 and DNA damage repair inhibitors in the clinic.
Citation Format: Francis M. Barnieh, Goreti Ribeiro Morais, Paul M. Loadman, Robert A. Falconer. Targeted delivery of a colchicine analogue provides synergy with ATR inhibition [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 2599.