Abstract LB-397: SMIP004-7: A novel oxidative phosphorylation inhibitor selectively kills Breast Cancer Stem-Like Cells with metabolic vulnerabilities
Authors: JAIN SHASHI , Wolf Dieter A. 
Published: August 2018

Background The manifestation of metastases from &lt;1% of the leftover subset of cells after apparently successful initial therapy is predictive of stem cell like properties such as self-renewal capacity, slow proliferation, and drug resistance. These “cancer stem cells” (CSCs) appear to drive relapse and form clinically relevant macro-metastases by establishing themselves in the microenvironment of distal sites. The aggressive nature of Triple Negative Breast Cancer (TNBC) may be explained by the presence of breast cancer stem cells (BCSCs) within TNBC tumors that are resistant to conventional therapies. Recent studies have shown an unexpected common denominator of these scenarios of therapy-selected quiescence is metabolic reprogramming to upregulate OXPHOS genes and increase oxygen consumption and ATP production. Efforts to target BCSCs have therefore focused on specific vulnerabilities of these cells. Multicellular tumor spheroid (MCTS) is one such 3D model that has been suggested to provide a more clinically relevant in vivo model. MCTS not only simulate the harsh conditions present in poorly vascularized tumors but also closely simulate the microenvironment with respect to glucose, oxygen, and lactate distribution thus enriched cancer cell phenotype. To counter this aggressive aspect of MCTS, we employed SMIP004-7 (N-(4-butyl-2-methyl-phenylaniline), a novel OXPHOS inhibitor in this study.

Methods and Results Mammosphere assay (3D culture) for the enrichment of CD133+ CSCs in established breast cancer cell lines was performed. Overexpression of CD133+, as determined by flow cytometric analysis and immunoblot, correlated with an increased colonogenic, chemo-resistant, and invasive potential in vitro. This phenotype is concordant to that of CSCs in vivo. Our novel compound SMIP004-7, showed enhanced anti-cancer activity in 3D culture compared to its respective 2D monolayer cells in cytotoxicity assay. More specifically, we demonstrated that SMIP004-7 treatment of breast cancer cells inhibited oxygen-consumption and metabolically induced aerobic glycolysis, as well as oxidative stress determined through DCFH-DA, Glucose starvation experiment and OCR and ECAR assay. Remarkably, SMIP004-7 potently inhibited the propagation of TNBC-derived CSCs, with an IC50 of 1 μM, as measured using the mammosphere assay. Importantly, these results indicated that glycolysis itself is not sufficient to maintain the proliferation of CSCs, which is instead strictly dependent on mitochondrial function.

Conclusions/Significance In conclusion, our mechanistic and pharmacokinetic insights are relevant to understanding and developing the role of SMIP04-7 using mammosphere cultures, we propose that mitochondria are new therapeutic targets for eradicating cancer stem cells, to prevent tumor recurrence, metastasis and poor clinical outcome in breast cancer patients. Our findings are in accordance with the hypothesis on dormant cells being CSCs.

Citation Format: SHASHI JAIN, Dieter A. Wolf. SMIP004-7: A novel oxidative phosphorylation inhibitor selectively kills Breast Cancer Stem-Like Cells with metabolic vulnerabilities [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-397.