Mcl1 downregulation sensitizes neuroblastoma to cytotoxic chemotherapy and small molecule Bcl2-family antagonists

Abstract

Neuroblastoma (NB) is a common, highly lethal pediatric cancer, with treatment failures largely attributable to the emergence of chemoresistance. The pro-survival Bcl2 homology (BH) proteins critically regulate apoptosis, and may represent important therapeutic targets for restoring drug sensitivity in NB. We used a human NB tumor tissue microarray to survey the expression of pro-survival BH proteins Mcl1 and Bcl2, and correlated expression to clinical prognostic factors and survival. Primary NB tumors heterogeneously expressed Mcl1 or Bcl2, with high expression correlating to high-risk phenotype. Co-expression is infrequent (11%), but correlates to reduced survival. Using RNA interference, we investigated the functional relevance of Mcl1 and Bcl2 in high-risk NB cell lines (SK-N-AS, IMR-5, NLF). Mcl1 knockdown induced apoptosis in all NB cell lines, while Bcl2 knockdown inhibited only NLF, suggesting functional heterogeneity Finally, we determined the relevance of Mcl1 in resistance to conventional chemotherapy (etoposide, doxorubicin) and small molecule Bcl2-family antagonists (ABT-737 and AT-101). Mcl1 silencing augmented sensitivity to chemotherapeutics 2- to 300-fold, while Bcl2 silencing did not, even in Bcl2-sensitive NLF cells. Resistance to ABT-737, which targets Bcl2/-w/-x, was overcome by Mcl1 knockdown. AT-101, which also neutralizes Mcl1, had single-agent cytotoxicity, further augmented by Mcl1 knockdown. In conclusion, Mcl1 appears a predominant pro-survival protein contributing to chemoresistance in NB, and Mcl1 inactivation may represent a novel therapeutic strategy. Optimization of compounds with higher Mcl1 affinity, or combination with additional Mcl1 antagonists, may enhance the clinical utility of this approach.

Dual Targeting of Wild-Type and Mutant p53 by Small Molecule RITA Results in the Inhibition of N-Myc and Key Survival Oncogenes and Kills Neuroblastoma Cells In Vivo and In Vitro

“…Among others, these include PPM1D, which encodes oncogenic phosphatase Wip1 (wild-type p53 induced phosphatase 1), increased expression of which is likely to be associated with 17q gain, a predictor of poor prognosis (5). Recent studies have shown a correlation between high expression of antiapoptotic factors Mcl-1 and Bcl-2 and resistance to therapy in neuroblastoma (6). Mcl-1 depletion via RNA interference induced apoptosis in neuroblastoma cell lines and sensitized them to cytotoxic chemotherapy, suggesting that Mcl-1, as well as Bcl-2, might be promising targets for neuroblastoma treatment (6,7).…”

Purified cranberry proanthocyanidines (PAC-1A) cause pro-apoptotic signaling, ROS generation, cyclophosphamide retention and cytotoxicity in high-risk neuroblastoma cells

“…All these cellular targets of PAC-1A are of interest in the search for alternative drugs to treat NB. Aberrant Bcl-2 family protein expression promotes chemo-refractory high-risk NB and selective inhibitors against pro-survival proteins of the Bcl-2 family have been developed to treat NB (37,38). Induction of the extrinsic pathway of apoptosis is generally initiated by ligation of transmembrane death receptors such as the TNF receptor family.…”

A Novel Eg5 Inhibitor (LY2523355) Causes Mitotic Arrest and Apoptosis in Cancer Cells and Shows Potent Antitumor Activity in Xenograft Tumor Models

“…Furthermore, phosphorylation of Bcl2 and rapid degradation of Mcl1 observed in cells mitotically arrested by LY2523355 may also contribute to induction of apoptosis. Indeed, recent studies that shows CDK1-mediated phosphorylation of Bcl-xL/ Bcl2 to be a functional link between mitotic arrest and apoptosis (38), and that suppression of Mcl1 sensitizes cancer cells to the treatment of anticancer agents, including an Eg5 inhibitor (ARRY-520), in human multiple myeloma (39)(40)(41). Consistent with Eg5 biology and mode of action of LY2523355 as discussed above, we demonstrated that anticancer activity of LY2523355 is highly schedule-dependent and has an optimal threshold exposure level and duration to achieve significant anticancer activity.…”