Honokiol-Chlorambucil Co-Prodrugs Selectively Enhance the Killing Effect through STAT3 Binding on Lymphocytic Leukemia Cells In Vitro and In Vivo

The broad-spectrum DNA alkylating therapeutic, chlorambucil (CBL), has limited safety and shows lower therapy effect because of a short half-life while used in the clinic. Therefore, it is very necessary to develop a more efficient and safer type of CBL derivate against tumors with selective targeting of cancer cells. In addition, the natural product of honokiol (HN), the novel potent chemo-preventive or therapeutic entity/carrier, can target the mitochondria of cancer cells through STAT3 to prevent cancer from spreading and metastasizing. In this study, we designed and synthesized the honokiol–chlorambucil (HN–CBL) co-prodrugs through carbonate ester linkage conjugating with the targeted delivery help of the HN skeleton in cancer cells. Biological evaluation indicated that HN–CBL can remarkably enhance the antiproliferation of human leukemic cell lines CCRF-CEM, Jurkat, U937, MV4-11, and K562. Furthermore, HN–CBL can also selectively inhibit the lymphocytic leukemia (LL) cell survival compared to those mononuclear cells derived from healthy donors (PBMCs), enhance mitochondrial activity in leukemia cells, and induce LL cell apoptosis. Molecular docking and western blot study showed that HN–CBL can also bind with the STAT3 protein at some hydrophobic residues and downregulate the phosphorylation level of STAT3-like HN. Significantly, HN–CBL could dramatically delay leukemia growth in vivo with no observable physiological toxicity. Thus, HN–CBL may provide a novel and effective targeting therapeutic against LL with fewer side effects.