Abstract A49: Modeling “decathlon winner” cancer cells that drive therapy resistance and metastasis in triple-negative breast cancer
Authors: Singh Balraj , Sarli Vanessa N. , Lucci Anthony 
Published: August 2018

Abstract
Introduction: There is a pressing need for reliable models for testing potential therapeutic drugs that accurately predict how drugs will act in cancer patients. Cancer resembles an evolution-like process in the body involving epigenetic and genetic alterations in tumor cells accompanied by a selection for their fitness to survive multiple challenges in the body. Therefore, we are developing an approach designed to test whether a therapy would affect most adaptable/evolvable cancer cells. We hypothesize that there is a two-way linkage between the regulatory state and the metabolic state, which can be exploited for selecting highly adaptable “decathlon winner” cancer cells.
Methods: To model the intrinsic resistance in triple-negative breast cancer that often overwhelms currently offered therapies, we selected rare cancer cells (0.01% in population) based on their ability to survive a severe metabolic challenge, i.e., a prolonged lack of glutamine in culture medium of SUM149 and FC-IBC02 triple-negative Inflammatory Breast Cancer (IBC) cell lines. The rationale is that if a cancer cell can survive such a severe challenge, it can survive all other challenges encountered in the body.
Results: The rare metabolically adaptable (MA) cancer cells, which survive and grow without glutamine indefinitely, are resistant to chemotherapeutic drugs, and highly metastatic to multiple organs—lungs, liver, brain, and skin—from fat pad xenografts in nude mice (Singh et al., PLoS ONE, 2012). The MA cells are resistant to most drugs tested thus far as single agent, supporting the validity of our cell-based model for testing new therapies (Singh et al., PLoS ONE, 2014). We have strong evidence of epithelial-to-mesenchymal transition (EMT) in MA cells, as indicated by reduced expression of GRHL2, increased expression of ZEB1, and reduced expression of ESRP1 (epithelial splicing regulatory protein 1) and a consequently increased level of CD44s, to name a few critical alterations. There is a strong correlation between EMT and a progenitor-like cell state. Investigating the molecular characteristics of SUM149-MA cells, we found that MA cells produced a very low level of TET2 methylcytosine dioxygenase (5- to 10-fold reduction) compared with the parental SUM149 cell line. TET2 could represent a link between the metabolic state and the epigenetic state in progenitor-like MA cells; its activity could be regulated both in terms of expression levels and by allosteric regulation with metabolites. We have recently reported that an RNA demethylase, FTO, which is important in organismal survival under food shortages and also controls obesity, plays an important role in the survival of MA cells (Singh et al., PLoS ONE, 2016). We also observed that SUM149-MA cells overexpress ADARB2, an RNA-editing adenosine deaminase converting adenosine to inosine, which is interestingly associated with extreme old age in humans. ADARB2 can also influence lifespan in Caenorhabditis elegans. These investigations of MA cells revealed how resistant cancer cells can exploit the regulatory molecular networks that evolution has selected for organismal fitness. We are currently evaluating therapeutic strategies that will eradicate or disable MA cells.
Conclusions: A highly abnormal and highly adaptable subpopulation of cancer cells modeled through our approach is ideally suited for evaluating combination therapies that are required for combating a heterogeneous and evolving disease. Such studies are likely to improve outcomes for breast cancer patients with high-risk of relapse, e.g., those with triple-negative breast cancer and IBC.
Supported by a State of Texas Grant for Rare and Aggressive Cancers.
Citation Format: Balraj Singh, Vanessa N. Sarli, Anthony Lucci. Modeling “decathlon winner” cancer cells that drive therapy resistance and metastasis in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A49.