Cellular Uptake and Transport Characteristics of FL118 Derivatives in Caco-2 Cell Monolayers

In the evaluation of the druggability of candidate compounds, it was vital to predict the oral bioavailability of compounds from apparent permeability (Papp) across Caco-2 cell-culture model of intestinal epithelium cultured on commercial transwell plate inserts. The study was to investigate the transport characteristics and permeability of FL118 (10, 11-Methylenedioxy-20(S)-camptothecin) derivatives 7-Q6 (7-(4-Ethylphenyl)-10, 11-methylenedioxy-20(S)-camptothecin) and 7-Q20 (7-(4-Trifluoromethylphenyl)-10, 11-methylenedioxy-20(S)-camptothecin). Transport characteristics and permeability of the tested compounds to the small intestine were assessed at different concentrations (0.5, 1 µM) via Caco-2 cell monolayers model in vitro. Uptake studies based on Caco-2 cells, including temperatures, concentrations, and the influence of efflux transporters, were combined to confirm the transport characteristics of the tested compounds. Furthermore, cytotoxicity results showed that the concentrations used in the experiments were non-toxic and harmless to cells. In addition, The Papp of 7-Q6 was (3.69 ± 1.07) × 10-6 cm/s with efflux ratio (ER) 0.98, while the Papp of 7-Q20 was (7.78 ± 0.89) × 10-6 cm/s with ER 1.05 for apical-to-basolateral (AP→BL) at 0.5 µM, suggesting that 7-Q20 might possess higher oral bioavailability in vivo. Furthermore, P-glycoprotein (P-gp) was proved to slightly affect the accumulations of 7-Q20, while the absorption of 7-Q6 was irrelevant with P-gp and breast cancer resistant protein (BCRP) based on the cellular uptake assays. Accordingly, 7-Q6 was completely absorbed by passive diffusion, and 7-Q20 was mainly dependent on passive diffusion with being effluxed by P-gp slightly. Meanwhile, both 7-Q6 and 7-Q20 were potential antitumor drugs that might exhibit high oral bioavailability in the body.