Inhibition of Mitochondrial Matrix Chaperones and Antiapoptotic Bcl-2 Family Proteins Empower Antitumor Therapeutic Responses.

Rational therapeutic approaches based on synthetic lethality may improve cancer management. On the basis of a high-throughput drug screen, we provide preclinical proof of concept that targeting the mitochondrial Hsp90 chaperone network (mtHsp90) and inhibition of Bcl-2, Bcl-xL, and Mcl-1 is sufficient to elicit synthetic lethality in tumors recalcitrant to therapy. Our analyses focused on BH3 mimetics that are broad acting (ABT263 and obatoclax) or selective (ABT199, WEHI-539, and A1210477), along with the established mitochondrial matrix chaperone inhibitor gamitrinib-TPP. Drug combinations were tested in various therapy-resistant tumors in vitro and in vivo in murine model systems of melanoma, triple-negative breast cancer, and patient-derived orthotopic xenografts (PDX) of human glioblastoma. We found that combining BH3 mimetics and gamitrinib-TPP blunted cellular proliferation in a synergistic manner by massive activation of intrinsic apoptosis. In like manner, suppressing either Bcl-2, Bcl-xL, or Mcl-1 recapitulated the effects of BH3 mimetics and enhanced the effects of gamitrinib-TPP. Mechanistic investigations revealed that gamitrinib-TPP activated a PERK-dependent integrated stress response, which activated the proapoptotic BH3 protein Noxa and its downstream targets Usp9X and Mcl-1. Notably, in the PDX glioblastoma and BRAFi-resistant melanoma models, this drug combination safely and significantly extended host survival. Our results show how combining mitochondrial chaperone and Bcl-2 family inhibitors can synergize to safely degrade the growth of tumors recalcitrant to other treatments. Cancer Res; 77(13); 3513-26. ©2017 AACR.

Karpel-Massler G ，Ishida CT ，Bianchetti E ，Shu C ，Perez-Lorenzo R ，Horst B ，Banu M ，Roth KA ，Bruce JN ，Canoll P ，Altieri DC ，Siegelin MD ... -  《-》

BH3-mimetics and BET-inhibitors elicit enhanced lethality in malignant glioma.

Ishida CT ，Bianchetti E ，Shu C ，Halatsch ME ，Westhoff MA ，Karpel-Massler G ，Siegelin MD ... -  《Oncotarget》

CDK inhibitors upregulate BH3-only proteins to sensitize human myeloma cells to BH3 mimetic therapies.

BH3 mimetic drugs induce cell death by antagonizing the activity of antiapoptotic Bcl-2 family proteins. Cyclin-dependent kinase (CDK) inhibitors that function as transcriptional repressors downregulate the Bcl-2 family member Mcl-1 and increase the activity of selective BH3 mimetics that fail to target this protein. In this study, we determined whether CDK inhibitors potentiate the activity of pan-BH3 mimetics directly neutralizing Mcl-1. Specifically, we evaluated interactions between the prototypical pan-CDK inhibitor flavopiridol and the pan-BH3 mimetic obatoclax in multiple myeloma (MM) cells in which Mcl-1 is critical for survival. Coadministration of flavopiridol and obatoclax synergistically triggered apoptosis in both drug-naïve and drug-resistant MM cells. Mechanistic investigations revealed that flavopiridol inhibited Mcl-1 transcription but increased transcription of Bim and its binding to Bcl-2/Bcl-xL. Obatoclax prevented Mcl-1 recovery and caused release of Bim from Bcl-2/Bcl-xL and Mcl-1, accompanied by activation of Bax/Bak. Whether administered singly or in combination with obatoclax, flavopiridol also induced upregulation of multiple BH3-only proteins, including BimEL, BimL, Noxa, and Bik/NBK. Notably, short hairpin RNA knockdown of Bim or Noxa abrogated lethality triggered by the flavopiridol/obatoclax combination in vitro and in vivo. Together, our findings show that CDK inhibition potentiates pan-BH3 mimetic activity through a cooperative mechanism involving upregulation of BH3-only proteins with coordinate downregulation of their antiapoptotic counterparts. These findings have immediate implications for the clinical trial design of BH3 mimetic-based therapies that are presently being studied intensively for the treatment of diverse hematopoietic malignancies, including lethal multiple myeloma.

Chen S ，Dai Y ，Pei XY ，Myers J ，Wang L ，Kramer LB ，Garnett M ，Schwartz DM ，Su F ，Simmons GL ，Richey JD ，Larsen DG ，Dent P ，Orlowski RZ ，Grant S ... -  《-》

Mitochondrial matrix chaperone and c-myc inhibition causes enhanced lethality in glioblastoma.

Ishida CT ，Shu C ，Halatsch ME ，Westhoff MA ，Altieri DC ，Karpel-Massler G ，Siegelin MD ... -  《Oncotarget》

Inhibition of Bcl-2/Bcl-xL and c-MET causes synthetic lethality in model systems of glioblastoma.

Zhang Y ，Ishida CT ，Shu C ，Kleiner G ，Sanchez-Quintero MJ ，Bianchetti E ，Quinzii CM ，Westhoff MA ，Karpel-Massler G ，Siegelin MD ... -  《Scientific Reports》