Design, synthesis, and biological evaluation of indole carboxylic acid esters of podophyllotoxin as antiproliferative agents

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A series of indole carboxylic acid conjugates of the podophyllotoxin were synthesized and evaluated as antiproliferative agents against two human chronic myeloid leukemia cell lines. Several compounds (In-2, In-8 and In-9) not only showed antiproliferative activity against normal K562 cells but also exhibited potent antineoplastic effect against resistant K562/VCR cells. The indole-6-formyl conjugate, In-9, revealed potent cytotoxic activity against K562 and K562/VCR cell lines, with IC50 values of 0.100 ± 0.008 and 0.227 ± 0.011 μM, respectively. Preliminary mechanism studies indicated that In-9 could disrupt the microtubule network in K562/VCR cells via occupying the colchicine binding site of the tubulin. Molecular dynamics simulation results revealed that the complex of In-9 and tubulin were stable. Furthermore, In-9 induced intracellular ROS generation, apoptosis, and cycle arrest at the G2 phase by inhibition of CDKs, loss of mitochondrial membrane potential and cleavage of caspase. In-9 simultaneously induced K562/VCR cells autophagy by upregulating the levels of Beclin1 and LC3-II, and exhibited anti-MDR ability by downregulating the levels of P-gp and MRP1. Finally, In-9 activated the AMPK and JNK signaling, and inhibited the ERK, P38, and PI3K/AKT/mTOR signaling in K562/VCR cells. In silico prediction indicated that In-9 mainly obeyed Lipinski rule for druglikeness. Together, In-9 possessed potent antiproliferative activity, and may be a promising agent for the potential treatment of resistant leukemia cancer.