Rocaglamide Selectively Eradicates Human Leukemia Stem Cells and Synergizes with Multiple Agents to Target AML Cells

Abstract 1338

Recent evidence suggests that myeloid leukemia is initiated and maintained by Leukemia Stem Cells (LSCs). Standard chemotherapy however, does not efficiently ablate LSCs. Consequently, even for leukemia patients who attain a clinical remission, LSCs are generally not destroyed and are thought to be responsible for subsequent relapse of the disease. Therefore, new treatment regimens are necessary to improve therapeutic outcomes. Nearly half of the agents used in cancer therapy today are either natural products or derivatives of natural products. The present studies demonstrate that rocaglamide, a compound derived from the traditional Chinese medicinal plants Aglaia induces robust apoptosis in primary human AML cells while sparing normal hematopoietic cells. Further analysis of progenitor cells using in vitro colony assays, as well as stem cells using the NOD Scid Gamma (NSG) xenograft model, show that rocaglamide also preferentially targets AML progenitor and stem cell populations.

Methionine metabolic labeling experiments show that rocaglamide inhibits the translation of nascent protein synthesis within twenty-four hours and this inhibition results in the rapid loss of short-lived survival proteins such as c-myc, Mcl-1, and Bcl-xl. These results are consistent with previous work showing rocaglamide, and members of the rocaglamide family of compounds, inhibit translation. To investigate further the molecular mechanism of LSC-specific cell death induced by rocaglamide we performed next generation sequencing on 5 AML specimens treated with rocaglamide. Bioinformatic analysis and subsequent experiments showed that rocagalmide leads to P53 activation, NFkB inhibition, cell cycle inhibition as well as defects in mitochondrial integrity and energy metabolism. In addition to efficacy as a single agent, pre-treatment of leukemia cells with rocaglamide significantly sensitizes the cells to several anti-cancer compounds, including cytarabine and daunorubicin two of the front-line chemotherapuetic drugs for AML patients. Importantly, we show that many of the mechanistic features of rocaglamide as a single agent play a role in its ability to synergize. In comparison with translational inhibitors that are used clinically to treat AML patients, temsirolimus and ribovarin, rocaglamide is significantly more toxic to leukemia cells. Interestingly, this increased cytotoxicity does not directly correlate with ability of the compounds to inhibit translational inhibition. Temsirolimus, inhibits translation at levels equal to or greater than rocaglamide however it has a cytostatic effect on leukemia cells in contrast to the cytotoxic effects of rocaglamide. Temsirolimus also does not synergize with anti-cancer compounds to the same degree as rocaglamide. These results suggest that rocaglamide's ability to modulate several key pathways in addition to inhibiting translation are critical to the activity of rocagalmaide and may suggest ways to improve the efficacy of translational inhibitors currently used in the clinic. These studies along with preliminary in vivo pharmacodynamic and pharmacokinetic experiments indicate that rocaglamide may be a promising candidate for the development of a new class of compounds for the treatment of leukemia and for increasing the efficacy of treatments designed to specifically target AML cells.