MRx102, a triptolide derivative, has potent antileukemic activity in vitro and in a murine model of AML

Triptolide, isolated from the herb Tripterygium wilfordii, has been shown to potently induce apoptosis in various malignant cells by inhibiting RNA synthesis and nuclear factor-kappa B activity. Previously, we showed that triptolide promotes apoptosis in acute myeloid leukemia (AML) cells via the mitochondria-mediated pathway, in part, by decreasing levels of the antiapoptotic proteins XIAP and Mcl-1. MRx102 is a triptolide derivative, currently in preclinical development. Here we show that MRx102 potently promoted apoptosis in AML cell lines, with EC50 values of 14.5+/-0.6 nM and 37.0+/-0.9 nM at 48 h for OCI-AML3 and MV4-11 cells, respectively. MRx102, at low nanomolar concentrations, also induced apoptosis in bulk, CD34(+) progenitor, and more importantly, CD34(+)CD38(-) stem/progenitor cells from AML patients, even when they were protected by coculture with bone marrow derived mesenchymal stromal cells. MRx102 decreased XIAP and Mcl-1 protein levels and inhibited RNA synthesis in OCI-AML3 cells. In vivo, MRx102 greatly decreased leukemia burden and increased survival time in non-obese diabetic/severe combined immunodeficiency mice harboring Ba/F3-ITD cells. Collectively, we demonstrated that MRx102 has potent antileukemic activity both in vitro and in vivo, has the potential to eliminate AML stem/progenitor cells and overcome microenvironmental protection of leukemic cells, and warrants clinical investigation. Leukemia (2012) 26, 443-450; doi:10.1038/leu.2011.246; published online 9 September 2011