Camptothecin and its Analogues as Putative Bruton Tyrosine Kinase (BTK) Inhibitors in Cancer Therapy - Biophysical Simulations of Wild Type and C481S Mutation

Abstract

Camptothecin (CPT) and its derivatives are extracted from the Chinese tree Camptotheca acuminata and have been long known for their significant antitumor activity. The widely reported primary mechanism of their anti-cancer activity is through inhibition of topoisomerase I (Topo I), a key anticancer target. However, there is a lack of research on other possible mechanisms of action of CPT and its analogues (CPT/analogues). In this report, we investigated the potential inhibitory mechanism of CPT/derivatives against Bruton’s tyrosine kinase (BTK) ‒ a crucial protein for regulating various cellular functions and is essential for B-cell growth and cyclical division. The binding mechanism of CPT and its analogues (Irinotecan, Diflomotecan, and Topotecan) against BTK was investigated using molecular docking, molecular dynamics simulations and thermodynamic binding free energy calculations. NRX-0492, a potent orally active degrader of both wild-type and mutant BTK, was used as a reference/control inhibitor. We also included a set of active binders (actives) and non-binders (inactives) to distinguish between effective binders and false positives to ensure the validity of our results. Binding affinity analysis suggested that CPT and its analogues could potentially bind to BTK comparably to NRX-0492. The studied compounds demonstrated stable binding with the protein throughout the simulation time via hydrogen bonds, π-π interactions, van der Waals forces and π-sulfur interactions. Irinotecan exhibited a binding affinity of ΔG_binding = –42.4±5.3 kcal/mol, closely matching that of NRX-0492 (ΔG_binding = –48.8±3.4 kcal/mol). Furthermore, the activity of CPT/derivatives was examined against the C481S mutant. Although the activity was slightly decreased due to the mutation, the compounds retained a promising binding affinity when compared to the results of NRX-0492. The findings of this study provide foundation for future experimental investigation of unexplored potential anti-cancer mechanism of CPT/derivatives and offer a new perspective on repurposing of natural products in cancer therapy.