Synthesis, antiproliferative activity and molecular docking studies of neo- and isocryptolepine conjugates

A series of twelve conjugates 9a-c, 10a-c, 11a-c, and 12a-c based on naturally occurring neo- and isocryptolepines I and II were synthesized and characterized. The synthetic pathways involved nucleophilic substitution reaction of the preprepared amines 4a-c and 5a-c with 1-(4-bromobutyl)indole derivatives 8a and 8b, respectively, in aprotic solvent under heating. The structures of the synthesized conjugates were elucidated by FTIR, ¹H NMR, ¹³C NMR, and MS spectrometry and showed data consistence with the expected structures. The antiproliferative activity of 9a-c, 10a-c, 11a-c and 12a-c was evaluated against HepG-2 and HCT-116 cancer cell lines using normal cells and reference drug paclitaxel. The screening results revealed that 9b and 9c were the most active conjugates against HepG-2 and HCT-116 cancer cell lines with IC₅₀: 8.49, 9.52, 16.87, 21.75 µM, respectively, using paclitaxel as a reference drug. It is worth noting that 9b and 9c were more selective toward cancer cells versus normal Vero cells. To rationalize the anticancer activity and selectivity of 9b and 9c, we have performed molecular docking study against human topoisomerases I and II for better understanding of their anticancer activities in atomic level. Molecular docking studies revealed that the presence of planar indoloquinoline fused four rings and a flexible side chain pharmacophores together improve DNA-intercalation and inhibition of DNA-Topo isomerases activity.