Kurmi, Kiran

Abstract BRCA1 plays a key role in homologous recombination (HR) DNA repair. Accordingly, changes that downregulate BRCA1, including BRCA1 mutations and reduced BRCA1 transcription, due to promoter hypermethylation or loss of the BRCA1 transcriptional regulator CDK12, disrupt HR in multiple cancers. In addition, BRCA1 has also been implicated in the regulation of metabolism. Here, we show that reducing BRCA1 expression, either by CDK12 or BRCA1 depletion, led to metabolic reprogramming of ovarian cancer cells, causing decreased mitochondrial respiration and reduced ATP levels. BRCA1 depletion drove this reprogramming by upregulating nicotinamide N-methyltransferase (NNMT). Notably, the metabolic alterations caused by BRCA1 depletion and NNMT upregulation sensitized ovarian cancer cells to agents that inhibit mitochondrial metabolism (VLX600 and tigecycline) and to agents that inhibit glucose import (WZB117). These observations suggest that inhibition of energy metabolism may be a potential strategy to selectively target BRCA1-deficient high-grade serous ovarian cancer, which is characterized by frequent BRCA1 loss and NNMT overexpression. Significance: Loss of BRCA1 reprograms metabolism, creating a therapeutically targetable vulnerability in ovarian cancer.

Abstract Many important metabolic processes such as energy homeostasis, regulation of reactive oxygen species (ROS) levels, production of signaling metabolites, and synthesis of precursors for macromolecules occur in mitochondria of cancer cells. However, targeting mitochondrial metabolism in cancer has been challenging due to toxicity in normal cells, which also depend on mitochondrial metabolism. Therefore, identification of tumor specific mitochondrial metabolic alterations would be crucial to develop drugs that can selectively target cancer cells while sparing normal tissue. Here, by using targeted metabolite profiling and mitochondria-specific phospho-proteomics approach, we identified Mitochondrial Creatine Kinase (MtCK) 1 as a metabolic target in HER2+ breast cancer cells. We show that the oncogenic HER2-ABL axis stabilizes MtCK1 through tyrosine 153 (Y153) phosphorylation to activate the PCr energy shuttle pathway that transfers ATP from mitochondria to cytosol. Inhibition of the PCr energy shuttle pathway either by genetically depleting MtCK1 or by pharmacologically with a creatine analogue cyclocreatine, decreases proliferation of trastuzumab-sensitive and -resistant HER2+ cancer cells and reduces tumor growth in vivo without obvious toxicity. These findings suggest that, once ATP is produced in the mitochondria, it is equally important for breast cancer cells to transfer this energy from mitochondria to the cytosol for maintenance of various biochemical processes and tumor growth. In summary, our study reveals MtCK1 stabilization by Y153 phosphorylation as a key molecular mechanism underlying the intersection between oncogenic HER2 signaling and mitochondrial energy metabolism, which creates a druggable metabolic vulnerability in cancer. Since cyclocreatine has been used as a dietary sport supplement, cyclocreatine might be able to inhibit trastuzumab-resistant tumors with much less toxicity in patients as compared to conventional anticancer drugs. Citation Format: Taro Hitosugi, Kiran Kurmi. Oncogenic activation of mitochondrial phosphocreatine energy shuttle creates a druggable metabolic liability in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-250.

ABSTRACT High-fat diet (HFD)-fed mouse models have been widely used to study early type 2 diabetes. Decreased β-cell glucokinase (GCK) expression has been observed in HFD-induced diabetes. However, owing to its crucial roles in glucose metabolism in the liver and in islet β-cells, the contribution of decreased GCK expression to the development of HFD-induced diabetes is unclear. Here, we employed a β-cell-targeted gene transfer vector and determined the impact of β-cell-specific increase in GCK expression on β-cell function and glucose handling in vitro and in vivo. Overexpression of GCK enhanced glycolytic flux, ATP-sensitive potassium channel activation and membrane depolarization, and increased proliferation in Min6 cells. β-cell-targeted GCK transduction did not change glucose handling in chow-fed C57BL/6 mice. Although adult mice fed a HFD showed reduced islet GCK expression, impaired glucose tolerance and decreased glucose-stimulated insulin secretion (GSIS), β-cell-targeted GCK transduction improved glucose tolerance and restored GSIS. Islet perifusion experiments verified restored GSIS in isolated HFD islets by GCK transduction. Thus, our data identify impaired β-cell GCK expression as an underlying mechanism for dysregulated β-cell function and glycemic control in HFD-induced diabetes. Our data also imply an etiological role of GCK in diet-induced diabetes. This article has an associated First Person interview with the first author of the paper.