Modulation of Navitoclax Sensitivity by Dihydroartemisinin-Mediated MCL-1 Repression in BCR-ABL+ B-Lineage Acute Lymphoblastic Leukemia

Abstract

Purpose BCR-ABL+ B-ALL leukemic cells are highly dependent on the expression of endogenous anti-apoptotic MCL-1 to promote viability and are resistant to BH3-mimetic agents such as navitoclax (ABT-263) that targets BCL-2, BCL-XL, and BCL-W. However, the survival of most normal blood cells and other cell types are also dependent on Mcl-1. Despite the requirement for MCL-1 in these cell types, initial reports of MCL-1-specific BH3-mimetics have not described any overt toxicities associated with single-agent use, but these agents are still early in clinical development. Therefore, we sought to identify FDA-approved drugs that could sensitize leukemic cells to ABT-263. Experimental Design A screen identified dihydroartemisinin (DHA), a water-soluble metabolite of the anti-malarial artemisinin. Using mouse and human leukemic cell lines, and primary patient-derived xenografts, the effect of DHA on survival was tested and mechanistic studies were carried out to discover how DHA functions. We further tested in vitro and in vivo whether combining DHA with ABT-263 could enhance the response of leukemic cells to combination therapy. Results DHA causes the down-modulation of MCL-1 expression by triggering a cellular stress response that represses translation. The repression of MCL-1 renders leukemic cells highly sensitive to synergistic cell death induced by ABT-263 in a mouse model of BCR-ABL+ B-ALL both in vitro and in vivo. Furthermore, DHA synergizes with ABT-263 in human Ph+ ALL cell lines, and primary patient derived xenografts of Ph+ ALL in culture. Conclusions Our findings suggest that combining DHA with ABT-263 can improve therapeutic response in BCR-ABL+ B-ALL.

Heme-Sensing Pathway Modulates Susceptibility of Poor Prognosis B-Lineage Acute Leukemia to BH3-Mimetics

“…Our lab has previously shown that the anti-malarial drug dihydroartemisinin (DHA) can repress MCL-1 translation and synergize with the BH3-mimetic ABT-263 (22). Here, we show mechanistically that DHA induces the repression of MCL-1 through activation of a Heme-sensing pathway dictates apoptotic response 5 cellular heme-sensing pathway that results in eIF2α phosphorylation and subsequent attenuation of protein translation.…”

“…Previous efforts to mechanistically address how DHA triggered the repression of MCL-1 revealed a gene expression signature consistent with the induction of the endoplasmic reticulum (ER) stress pathway (22). To further interrogate this pathway, the three canonical branches of the cellular ER stress pathway were genetically ablated in mouse p185 + Arf-null B-ALL (hereafter referred to as BCR-ABL + B-ALL) using CRISPR/Cas9 targeting (Sup.…”

“…1F). Since DHA acts to repress MCL-1 translation in leukemic cells (22), we tested whether pharmacological manipulation of cellular heme levels could affect MCL-1 repression in response to DHA treatment. The combination of ALA and DHA caused even greater MCL-1 repression than that observed with DHA alone (Fig.…”

“…These data indicate that DHA can disrupt the HRI-heme interaction in a cell-free system. Our previous studies demonstrated that DHA-induced repression of MCL-1 renders BCR-ABL + B-ALL cells susceptible to synergistic cell death induced by the BH3-mimetic drug ABT-263 (22). Since HRI is responsible for mediating the repression of MCL-1 in response to DHA treatment, we assessed whether HRI-deficient BCR-ABL + B-ALL cells would exhibit less synergistic cell death in response to combination treatment of DHA with BH3-mimetic drugs.…”

“…Aminolevulinic acid (ALA), a precursor of heme synthesis, or succinylacetone (SA), an inhibitor of heme synthesis, (both from Sigma) were solubilized in water and added at indicated concentrations to alter cellular heme levels (30). Cell viability was determined by staining with Annexin-V-APC and propidium iodide (BD Biosciences) and measured by flow cytometry as previously described (22).…”