Delineating the interaction of combretastatin A-4 with αβ tubulin isotypes present in drug resistant human lung carcinoma using a molecular modeling approach

Abstract

Tubulin isotypes are known to regulate microtubule dynamic instability and contribute to the development of drug resistance in certain types of cancers. Combretastatin-A4 (CA-4) has a potent anti-mitotic, vascular disrupting and anti-angiogenic activity. It binds at the interface of αβ tubulin heterodimers and inhibits microtubules assembly. Interestingly, the CA-4 resistant human lung carcinoma shows alteration of βI and βIII isotype levels, a higher expression of βI tubulin isotype and a decreased expression of βIII tubulin isotypes has been reported in drug resistant cell lines. However, the origin of CA-4 resistance in lung carcinoma is not well understood. Here, we investigate the interaction and binding affinities of αβI, αβIIb, αβIII and αβIVa tubulin isotypes with CA-4, employing molecular modeling approaches. Sequence analysis shows that variations in residue composition at the CA-4 binding pocket of βI, βIII and βIVa tubulin isotypes when compared to template βIIb isotype. Molecular docking result shows that the CA-4 prefers ‘cis’ conformation in all αβ-tubulin isotypes. Molecular dynamics simulation reveal role of H7 helix, T7 loop and H8 helix of β-tubulin in lower binding affinity of αβI and αβIII isotypes for CA-4. The order of binding energy for CA-4 is αβIIb > αβIVa > αβI > αβIII. This suggest that drug resistance is induced in human lung carcinoma cells by altering the expression of β-tubulin isotypes namely βI and βIII which show lowest binding affinities. Our present study can help in designing potential CA-4 analogs against drug-resistant cancer cells showing altered expression of tubulin isotypes.

Abbreviations:
CA-4	=	combretastatin-A4
MD	=	molecular dynamics
RMSD	=	root mean square deviation
DSSP	=	dictionary of secondary structure of proteins
VMD	=	visual molecular dynamics

Communicated by Ramaswamy H. Sarma

Keywords:

• Microtubule
• tubulin isotypes
• anticancer drug resistance
• combretastatin
• molecular dynamics simulations

Acknowledgment

BVK and VVB are thankful for the Indian Institute of Technology Bombay for Post-Doctoral Fellowship.

Additional information

Funding

DP is supported by Tata Innovation fellowship from Department of Biotechnology, Government of India. AK is supported by Pilot Project Grants, Program for young investigators in cancer biology (Grant No. 6242-P12/RGCB/PMD/DBT/AMBK/2015).