Betulinic Acid ω-Triphenylphosphonium Alkyl Esters: Antiproliferative Activities and In Silico Pharmacokinetic Profiles.

Background: Betulinic acid (BA) and some derivatives are well-known antiproliferative compounds. Literature precedents suggest that incorporating triphenylphosphonium (TPP+) salts on this triterpenoid scaffold enhances its biological activity. In the present study, we carried out a simple synthesis of C-28 ester derivatives of this triterpenoid conjugated with TPP+ bromide salts through 4- to 6-carbon chains via nucleophilic substitution of the corresponding ω-TPP+bromoalkanes. Tests for antiproliferative activity in nine cancer cell lines and normal human fibroblasts showed that TPP+ incorporation enhanced the potency of BA by more than an order of magnitude, up to 100-fold. BA-C4-TPP+Br-, with a four-carbon chain separating the TPP+ moiety from the BA, showed remarkable antiproliferative effects, sometimes more potent than the reference drug (Etoposide). This compound exhibited the strongest mitochondrial uncoupling effect in human cancer cells. No significant LDH release was noted in colorectal carcinoma cells at low micromolar concentrations of BA-C4-TPP+Br-, and sub-micromolar concentrations were sufficient for inducing apoptosis. The in silico prediction of pharmacokinetic properties suggested high oral absorption (88%), as well as a non-inhibitor and non-substrate profile vs. cytochrome isoenzymes. These results point to this compound as a promising lead for the development of novel anticancer drugs.