Novel Mitochondrial Inhibitors Hold Promise For The Eradication Of Lung Cancer Stem Cells

Lung cancer therapy failure is attributed not only to the genetic heterogeneity of tumors, but is also promoted by the functional and phenotypic plasticity of different cell populations. The cancer stem cell (CSC) theory postulates that an under-represented population of cells with different growth- and drug-sensitivity properties is responsible for metastatic dissemination and post-therapy relapse. The detailed molecular and phenotypical analysis of CSCs in primary human lung cancers has been limited however, because CSCs have poor proliferative capacity when placed in culture and eventually undergo terminal differentiation. We have developed a novel culturing system that permits the rapid expansion of patient-derived cancer samples and is allowing us to rapidly build a collection of non-small-cell (NSCLC) lung cancers for real-time drug screening as well as for molecular and phenotypical characterization. Compared to other known culturing conditions, this system leads to a stark enrichment of CSCs, defined as such based on the expression of stem cell markers, the ability to differentiate towards multiple lineages and to form tumors at limiting dilutions in immuno-deficient mice. Because CSCs tend to be refractory to targeted or untargeted therapies, we have studied these CSC populations with respect to their metabolic vulnerabilities. CSCs reside in stem cell niches that are deprived of nutrients and of glucose and are characterized by low radical oxygen species (ROS) levels, thus likely relying upon different metabolic requirements relative to other cancer cells which represent the “bulk” of the tumor mass. We found that CSCs populations derived from tumors harboring diverse mutational profiles share, as a common feature, the reliance upon mitochondrial respiration for growth and expansion. We show that this metabolic aberration is sustained, for the most part, by the mitochondrial citrate transporter SLC25A1, whose expression levels are elevated in NSCLC predicting poorest prognostic outcome. SLC25A1 is required for the expansion of CSCs where it promotes the homeostatic energetic output of the mitochondria via oxidative phosphorylation, while overcoming the glycolytic addition, thus essentially reverting the Warburg effect which has been thus far considered a hallmark of tumor cells. We have also developed two chemical inhibitors of SLC25A1 activity and we demonstrate that these inhibitors target lung CSCs by blocking mitochondrial respiratory activity, by inducing mitochondrial dysfunction and by altering the redox environment. These alterations lead to energetic crisis and to cell death. These agents show remarkable anti-tumor activity as single agents in xenograft experiments in mice and they enhance sensitivity to platinum-based chemotherapy. In conclusion we have identified a novel class of agents that specifically targets the mitochondrial metabolism of cancer stem cells. We propose that such activity may permit eradication of the cell population primarily responsible of drug resistance and metastatic dissemination regardless of the mutational status of the tumor of origin. These findings could set the ground for clinical trials employing mitochondrial inhibitors as a rescue-treatment after failure with currently available targeted or untargeted therapies. Citation Format: Harvey Fernandez, Shreyas Grade, Kyu Ah Kim, Mayalin Laforteza, Yuwen Zhang, Chris Albanese, Mikell Paige, Giuseppe Giaccone, Maria L. Avantaggiati. Novel mitochondrial inhibitors hold promise for the eradication of lung cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-229.