Highly Antiproliferative Latonduine and Indolo[2,3‑c]quinoline Derivatives: Complex Formation with Copper(II) Markedly Changes the Kinase Inhibitory Profile

A series of latonduine and indoloquinoline derivatives HL¹–HL⁸ and their copper­(II) complexes (1–8) were synthesized and comprehensively characterized. The structures of five compounds (HL⁶, [CuCl­(L¹)­(DMF)]·DMF, [CuCl­(L²)­(CH₃OH)], [CuCl­(L³)]·0.5H₂O, and [CuCl₂(H₂L⁵)]­Cl·2DMF) were elucidated by single crystal X-ray diffraction. The copper­(II) complexes revealed low micro- to sub-micromolar IC₅₀ values with promising selectivity toward human colon adenocarcinoma multidrug-resistant Colo320 cancer cells as compared to the doxorubicin-sensitive Colo205 cell line. The lead compounds HL⁴ and 4 as well as HL⁸ and 8 induced apoptosis efficiently in Colo320 cells. In addition, the copper­(II) complexes had higher affinity to DNA than their metal-free ligands. HL⁸ showed selective inhibition for the PIM-1 enzyme, while 8 revealed strong inhibition of five other enzymes, i.e., SGK-1, PKA, CaMK-1, GSK3β, and MSK1, from a panel of 50 kinases. Furthermore, molecular modeling of the ligands and complexes showed a good fit to the binding pockets of these targets.