Indibulin

Indibulin, a microtubule-depolymerizing agent, produces minimal neurotoxicity in animals. It is also less cytotoxic toward differentiated neuronal cells than undifferentiated cells. We found that the levels of β-III tubulin, acetylated tubulin, and polyglutamylated tubulin were significantly increased in differentiated neuroblastoma cells (SH-SY5Y). Since neuronal cells express β-tubulin isotypes differently from other cell types, we explored the binding of indibulin to different β-tubulin isotypes. Our molecular docking analysis suggested that indibulin binds to β-III tubulin with lower affinity than to other β-tubulin isotypes. We therefore studied the implications of different β-tubulin isotypes on the cytotoxic effects of indibulin, colchicine, and vinblastine in differentiated SH-SY5Y cells. Upon depletion of β-III tubulin in the differentiated cells, the toxicity of indibulin and colchicine significantly increased, while sensitivity to vinblastine was unaffected. Using biochemical, bioinformatics, and fluorescence spectroscopic techniques, we have identified the binding site of indibulin on tubulin, which had not previously been established. Indibulin inhibited the binding of colchicine and C12 (a colchicine-site binder) to tubulin and also increased the dissociation constant of the interaction between tubulin and colchicine. Indibulin did not inhibit the binding of vinblastine or taxol to tubulin. Interestingly, indibulin antagonized colchicine treatment but synergized with vinblastine treatment in a combination study performed in MDA-MB-231 cells. The results indicate that indibulin is a colchicine-site binder and that the efficacy of colchicine-site binders is affected by the β-III tubulin levels in the cells.

The synthesis of some novel 4‐azaindole‐1,2,4‐oxadiazole hybrids ( 5 a–5 q ) from the reaction between 1H‐pyrrolo[3,2‐b]pyridine‐3‐carbonitrile and readily available aromatic carboxylic acids using was described herein. All these hybrids were evaluated for their in vitro anticancer activity against three human cancer cell lines namely A375 (melanoma), MCF7 (breast) and A549 (lung) using MTT assay and outcomes revealed that three compounds like 5 c , 5 f and 5 m displayed superior inhibitory activities against all the cell lines than the standard. In those, predominantly, the compound 5 m showed outstanding activity in MCF‐7 cell line possessing IC 50 values 0.48 μM. In addition, the in silico studies of three potent compounds 5 c , 5 f and 5 m were carried out to identify the interactions against EGFR receptor and found that the energy calculations were in good agreement with the obtained IC 50 values. Furthermore, the compounds 5 c , 5 f and 5 m exhibited promising inhibitory activity against tyrosine kinase EGFR. Among them, the compounds 5 f and 5 m displayed superior activity against tyrosine kinase EGFR when compared with the standard Erlotinib.