Chromene ring truncation-based structure optimization of SH-1242, an antitumor agent inhibiting HSP90 (Heat Shock Protein 90)

Abstract

Heat Shock Protein 90 (HSP90), one of the molecular chaperones, promotes proper folding and transcription of various proteins associated with the tumor signaling network for cancer progression. As inhibition of HSP90 can regulate many client proteins related to cancer hallmarks, it has gained much attention as a target mechanism to overcome resistance to anticancer agent. In previous study, it was revealed that SH-1242, well known as a HSP90 inhibitor, facilitates rapid degradation of oncogenic client proteins like Hypoxia inducible factor-1α (HIF-1α) by binding to the C-terminal ATP-binding pocket of HSP90, and has in vivo potent anticancer activity in mice bearing human non small cell lung cancer (NSCLC) cell-derived xenograft tumor as well as in vitro activity in various NSCLC cell lines and drug resistant NSCLC cell lines. However, SH-1242 is predicted to have low bioavailability because of its physicochemical property and metabolic unstability, and posseses chromene moiety which has already been known as privileged structure of many bioactive compounds. For these reasons, there are limitations in developing SH-1242 as novel HSP90 targeting anticancer agent. In this study, therefore, we designed and synthesized chromene ring truncated analogues to improve not only physicochemical property and metabolic stability but also structural novelty. Sulforhodamine B assay (SRB assay) using A549 cell line, KRAS mutated NSCLC cell, was utilized as the first screening method to evaluate inhibition of cancer growth and analyze structure-activity relationship (SAR). HIF-1α western blot assay of the selected analogue was also conducted to verify HIF-1α inhibition. The analogues were designed to introduce various substituents into each of the three parts of the chromene truncated scaffold of SH-1242, and we named these three parts as A, B and C part. Synthetic pathways were optimized to include two key steps. One was synthesis of common scaffold via tandem claisen condensation-decarboxylation sequence in one pot reaction. The other was late stage differentiation via Buchwald-Hartwig coupling between aryl triflate and various amines. The structure optimization of analogues was performed in order of A, B and C parts. In the A part cyclohexylmethylamine group showed most potent activity, and the methoxy group in B part and the fluorine group in C part were found to be the best substituents. According to these results, we identified SH-333 as the best analogue which showed most potent anticancer activity through SRB assay in A549 cell line (IC50 = 0.80 µM). In addition we conducted preliminary HIF-1α westernblot assay of SH-314 (IC50 = 1.70 µM in SRB assay) and verified the HIF-1α inhibition of the chromene truncated SH-1242 analogue which had been confirmed to have anticancer activity in SRB assay.