Design, synthesis, and antiproliferative activity of novel thiazole-based derivatives as tubulin polymerization inhibitors targeting the colchicine binding site

Abstract

The development of novel microtubule-targeting medicines (MTAs) remains a crucial strategy in cancer treatment, as they combat drug resistance and systemic toxicity. A novel series of thiazole-based derivatives was synthesized, characterized, and evaluated as antitubulin agents endowed with antiproliferative action. An IC₅₀ experiment was performed to assess the efficacy of novel compounds 9a–o in suppressing tubulin activity. The antiproliferative effects of the most potent compounds were evaluated. The levels of initiator caspases (Caspase-8 and Caspase-9) and executioner caspase (Caspase-3) were examined to ascertain the degree of apoptosis. Additionally, the expression levels of the mitochondrial regulatory proteins Bax and Bcl-2 were examined to ascertain the importance of the intrinsic apoptotic pathway. Compound 9k exhibited significant inhibition of tubulin with an IC₅₀ of 1.56 µM and showed potent activity against HeLa (cervical), HCT-116 (colorectal), and A-549 (lung) cancer cell lines. The apoptotic assays revealed that 9k effectively triggered the apoptotic cascade, leading to a ninefold increase in Caspase-3 and a significant twenty-onefold rise in Caspase-9, surpassing the effects of the reference Staurosporine. Caspase-8 was activated by an elevenfold increase, primarily via the intrinsic pathway. This was confirmed by a substantial change in the mitochondrial “rheostat”: 9k induced a 38-fold increase in pro-apoptotic Bax and a 5-fold decrease in anti-apoptotic Bcl-2. Molecular docking studies showed that 9k exhibited a favorable binding mode consistent with its tubulin-inhibition profile. In silico ADMET predictions further supported 9k as a drug-like lead with acceptable oral exposure and a beneficial P-gp–related transporter profile. The enhanced apoptotic effects of 9k compared with Staurosporine make 9k an attractive lead candidate for further development as an anti-cancer drug targeting the colchicine-binding site.