Tetrahydroisoquinoline Sulfamates as Potent Microtubule Disruptors: Synthesis, Antiproliferative and Antitubulin Activity of Dichlorobenzyl-Based Derivatives, and a Tubulin Cocrystal Structure

Abstract

Tetrahydroisoquinoline (THIQ) 6-O-sulfamate-based anticancer agents, inspired by the endogenous steroid 2-methoxyestradiol and its sulfamate derivatives, are further explored for antiproliferative and microtubule disruptor activity. Based on recently designed C3-methyl C7-methoxy-substituted THIQ derivatives, compounds with mono- and dichloro-substitutions on the pendant N-benzyl ring were synthesized and evaluated. Although improved antiproliferative activity was observed, for example, 4a versus 4b and 4b versus 8c, it was relatively modest. Compound 8c, a 2′,5′-dichlorobenzyl derivative was, however, identified as a promising antiproliferative agent with in vitro activities exceeding that of the parent steroid (e.g., GI50 90 nM in DU-145 cells) and was highly potent against a range of tumor cell lines (e.g., GI50 26 nM for OVCAR-3). 8c inhibited the polymerization of tubulin in vitro with an IC50 only twofold less potent than combretastatin A-4 and inhibited colchicine binding to tubulin. Tubulin polymerization assays showed the parent THIQ 4a to be only a very weak inhibitor, but a striking potency difference was seen between compounds with C2′ methoxy and chloro substituents, whereas this was much smaller when these substituents were positioned at C5′. To confirm the target in atomic detail and because 8c is a racemic mixture, an achiral parent THIQ 6-O-sulfamate derivative 10 was successfully cocrystallized with the αβ-tubulin heterodimer. The derivative 10 binds at the colchicine site on tubulin, the first example of this compound class investigated in such detail, with its sulfamate group interacting with residues beyond the reach of colchicine itself, similar to a recently reported quinazolinone sulfamate derivative, 6a. The structure also suggests that for racemic C3-methyl-substituted THIQ derivatives, such as 8c, the (S)-enantiomer is likely to be preferentially accommodated within the colchicine site for steric reasons. The results further confirm the potential of nonsteroidal THIQ sulfamate derivatives for oncology and suggest that the mechanism of microtubule destabilization for the THIQ compound class is to prevent the curved-to-straight conformational transition of tubulin required for polymerization.

Cell Fate following Irradiation of MDA-MB-231 and MCF-7 Breast Cancer Cells Pre-Exposed to the Tetrahydroisoquinoline Sulfamate Microtubule Disruptor STX3451

“…Previous studies reported that STX3451 exposure abrogated microtubule structure and function in MDA-MB-231 cells, resulting in a metaphase block [21,43]. STX3451 was successfully co-crystallized with the αβ-tubulin heterodimer, showing its binding to the colchicine site in atomic detail and its sulfamate group interacting with residues beyond the reach of colchicine itself [35].…”

Nonsteroidal sulfamate derivatives as new therapeutic approaches for Neurofibromatosis 2 (NF2)

“…This is the first atomic level demonstration of such an interaction for a sulfamate ester. Associated crystallographic work has also demonstrated the effectiveness of STX3451 in binding to the colchicine site [55].…”

Synthesis and Biological Evaluation of 1-(Diarylmethyl)-1H-1,2,4-triazoles and 1-(Diarylmethyl)-1H-imidazoles as a Novel Class of Anti-Mitotic Agent for Activity in Breast Cancer

“…A number of approaches to the design of dual targeting breast cancer agents have been reported e.g., ER/tubulin [ 78 ], tubulin/HSP90 [ 79 ], tubulin/HSP27 [ 80 ], ER/AI e.g., norendoxifen [ 81 , 82 ], and endoxifen [ 83 ], sulfatase/AI [ 84 ], tubulin/sulfatase [ 85 , 86 ] and tubulin/angiogenesis (vascular endothelial growth factor receptor-2 (VEGFR2) [ 87 ]. We now report the synthesis and biological evaluation of a series of 1-(diarylmethyl)-1 H -1,2,4-triazoles, 1-(diarylmethyl)-2 H -1,2,3-triazoles, and 1-(diarylmethyl)-1 H -imidazoles, which are designed as hybrid scaffolds derived from the benzophenone structure of the tubulin targeting phenstatin 7a , together with the 1,2,4-triazole of the aromatase inhibitor letrozole 2 [ 88 ].…”