The role of metabolic reprogramming in the sensitivity of breast cancer to chemo- and immunotherapy

Background: Breast cancer exhibits metabolic reprogramming, in which it hijacks the metabolic pathways, aerobic glycolysis (Warburg effect) and oxidative phosphorylation, alternatively, to avail fuel needed for tumor growth and proliferation. This characteristic of breast cancer is associated with resistance to chemotherapy and immunotherapy, in addition to tumor aggressiveness. Multidrug resistant breast cancer cells are enriched with cancer stem cells population and are characterized with high rate of aerobic glycolysis and high activity of ATP-binding cassette (ABC) transporters. Furthermore, breast cancer is a highly heterogenous disease, by which different breast cancer subtypes acquire distinct metabolic profiles. Therefore, deeper understanding of metabolic characteristics of breast cancer subtypes would support the individualization of treatment with anticancer metabolic agents. In addition, tackling breast cancer resistance through targeting metabolic regulators would improve the sensitivity of breast cancer to chemo and immuno- therapy. Methods and Results: To Sensitize multi-drug resistant breast cancer cells to chemotherapy using glycolysis inhibitor as OSU-CG5 compound, MCF-7 and MDA-MB231 resistant cells were developed as models for multidrug resistance. Their resistance characteristics were verified via evaluating ABC transporters and stemness markers expressions using Western blot analysis and Flow cytometry, respectively. Synergy between Doxorubicin (Dox) and OSU-CG5 was observed using MTT cell viability assay and the mechanism of synergy was investigated via Western blot analysis, PCR, and mitochondrial functions related assays. To discover a novel anticancer agent with metabolic regulatory effect, a library of compounds was generated in Sharjah institute for medical research, and SIMR1281 compound was recognized as the most potent compound in a panel of cancer cell lines including breast and colorectal cancers. Several in vitro assays, including DARTS proteomic study, Western blot and enzymatic assay revealed SIMR1281 mechanism of action in disrupting thioredoxin and glutathione antioxidant systems. In addition, in vivo studies revealed significant reduction of tumor volume while maintaining a high in vivo safety profile at a high dose. Furthermore, the expression of the metabolic gatekeeper, PDH-E1A and its inactive form (P-PDH-E1A) was investigated in breast cancer cell lines and tissues via Western blot and immunohistochemistry, respectively. Correlation of PDH-E1A and P-PDH-E1A expressions with the clinicopathological characteristics and molecular subtyping of breast cancers was determined. In addition, analysis revealed the prognostic value of PDH-E1A. Findings were further confirmed in transcriptomics data of breast cancer patients subtracted from cancer genome atlas. To boost cancer chemotherapy and immunotherapy effectiveness in breast cancer, CPI-613, a PDH-E1A inhibitor, was combined with Dox and the immune checkpoint inhibitor, anti-PDL1, in resistant breast cancer cells and 4T1 Balb/c breast cancer mouse model, respectively. CPI-613 synergized Dox anticancer effect in breast cancer cells as indicated by MTT cell viability assay, Western blot and mitochondrial assays. However, no significant change in tumor proliferation was observed upon CPI-613 combination with anti-PDL1. While the percent of tumor infiltrated lymphocytes was modulated following CPI-613 and anti-PD1 treatments as indicated by flow cytometry analysis. Conclusion: This work highlighted OSU-CG5 as a promising adjuvant to revert the resistance to Dox chemotherapy, through hampering intracellular ATP stores, modulation of NADP+/NADH redox ratio, and induction of ROS generation with subsequent activation of mitochondrial apoptosis. In addition, it revealed the discovery of SIMR1281compound which had shown a promising anticancer activity in vitro and in vivo while maintaining a high in vivo safety profile. The unique activity of SIMR1281 in inhibiting the thioredoxin and glutathione antioxidant systems, suggests SIMR1281 as a promising anticancer agent that warrants testing in clinical settings. Furthermore, the observed association between PDH-E1A/P-PDHE1 and clinicopathological characteristics and molecular subtyping of breast cancers suggests PDH-E1A/P-PDHE1 as a prognostic factor in breast cancer. Finally, targeting PDH-E1A using CPI-613 compound in combination with dox is a promising therapeutic approach in breast cancer, while its combination with anti-PDL1 demands further investigations.