Discovery of novel 2-aryl-4-benzoyl-imidazoles targeting the colchicines binding site in tubulin as potential anticancer agents

Abstract

A series of 2-aryl-4-benzoyl-imidazoles (ABI) was synthesized as a result of structural modifications based on the previous set of 2-aryl-imidazole-4-carboxylic amide (AICA) derivatives and 4-substituted methoxylbenzoyl-aryl-thiazoles (SMART). The average IC(50) of the most active compound (5da) was 15.7 nM. ABI analogues have substantially improved aqueous solubility (48.9 μg/mL for 5ga vs 0.909 μg/mL for SMART-1, 0.137 μg/mL for paclitaxel, and 1.04 μg/mL for combretastatin A4). Mechanism of action studies indicate that the anticancer activity of ABI analogues is through inhibition of tubulin polymerization by interacting with the colchicine binding site. Unlike paclitaxel and colchicine, the ABI compounds were equally potent against multidrug resistant cancer cells and the sensitive parental melanoma cancer cells. In vivo results indicated that 5cb was more effective than DTIC in inhibiting melanoma xenograph tumor growth. Our results suggest that the novel ABI compounds may be developed to effectively treat drug-resistant tumors.

Figure 1

General structures of AICA, SMART and ABI

Figure 2

In vivo study of 5cb against B16-F1 melanoma tumors in C57/BL mice

Figure 3

A. Effect of ABI compounds on tubulin polymerization in vitro. Tubulin (0.4 mg/assay) was exposed to 10 μM ABI compounds (vehicle control, 5% DMSO). Absorbance at 340 nm was monitored at 37°C every minute for 15 min; B. [³H]-colchicine competition-binding scintillation proximity assay showed that ABI compounds competitively bound to tubulin colchicine binding site.

Figure 4

Proposed binding mode of ABI analogs in the colchicine binding site.

Figure 5

SAR relationship of the ABI analogs

Scheme 1

Reagents and conditions: (a) t-BuOH, I₂, Ethylenediamine, K₂CO₃, reflux; (b) PhI (OAc)₂, K₂CO₃, DMSO; (c) DBU, CBrCl₃, DMF; (d) NaH, PhSO₂Cl, THF, 0°C − rt; (e) t-BuLi, substituted benzoyl chloride, THF, −78°C; (f) Bu₄NF, THF, rt;

Scheme 2

Reagents and conditions: (a) NH₄OH, oxalaldehyde, Ethanol, rt; (b) NaH, PhSO₂Cl, THF, 0°C − rt; (c) t-BuLi, substituted benzoyl chloride, THF, −78°C; (d) Bu₄NF, THF, rt; (e) BBr₃, CH₂Cl₂; (f) c-HCl, AcOH, reflux;

Scheme 3

Reagents and conditions: (a) NaH, substituted benzoyl chloride, THF.