OSU-A9, An Indole-3-Carbinol Derivative, Induces Cytotoxicity In Acute Myeloid Leukemia Through Reactive Oxygen Species-Mediated Apoptosis

Indole-3-carbinol (I3C) is a broadly targeted phytochemical shown to prevent carcinogenesis in animal studies and to suppress the proliferation of cancer cells of human breast, colon, prostate, and endometrium. Here we aim to test the anticancer effect of OSU-A9, an I3C derivative with improved potency, in acute myeloid leukemia (AML).

The in vitro activity of OSU-A9 was evaluated in AML cell lines (HL-60 and THP-1) and primary leukemia cells from 18 AML patients. THP-1 xenograft tumors in athymic nude mice was used for in vivo study.

OSU-A9 mediates cytotoxicity in AML cell lines and primary leukemia cells from AML patients in a dose-responsive manner. The IC₅₀ at 24 h for 18 patients was 1.63 μM. Normal human bone marrow cells were much less sensitive to OSU-A9 with an IC₅₀ at 24 h greater than 8 μM. OSU-A9 causes cytotoxicity dependent on caspase activation, as evidenced by caspase-3 and PARP cleavage, and induces autophagy but not autophagic cell death. Interestingly, pretreatment of AML cell lines and primary AML cells with N-acetylcysteine or glutathione rescues them from apoptosis (and concomitant PARP cleavage) and Akt hypophosphorylation, implicating a key role of reactive oxygen species (ROS) in OSU-A9-related cytotoxicity. To investigate the anti-leukemia effect of OSU-A9 in vivo, fifteen male athymic nude mice were xenografted with THP-1 cells. Briefly, the anticancer utility of OSU-A9 is extended in vivo as it, administered intraperitoneally, suppresses the growth of THP-1 xenograft tumors in athymic nude mice without obvious toxicity. For biomarker analysis in the THP-1 xenografts, protein extracts were obtained from the tumors and immunoblotted for Akt levels. The tumors from OSU-A9 treated mice exhibited down regulation of Akt phosphorylation compared with those from placebo-controlled mice.

This study shows that ROS-mediated apoptosis contributes to the anticancer activity of OSU-A9 in AML cell lines and primary AML cells, and thus should be considered in the future assessment of its translational value in AML therapy.

No relevant conflicts of interest to declare.