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Theranostics 2021; 11(19):9180-9197. doi:10.7150/thno.60503 This issue Cite

Research Paper

BCL-XL blockage in TNBC models confers vulnerability to inhibition of specific cell cycle regulators

Olivier Castellanet^1*, Fahmida Ahmad^1*, Yaron Vinik², Gordon B. Mills³, Bianca Habermann¹, Jean-Paul Borg^4,5, Sima Lev², Fabienne Lamballe^1✉, Flavio Maina^1✉

1. Aix Marseille Univ, CNRS, Developmental Biology Institute of Marseille (IBDM), Turing Center for Living Systems, Parc Scientifique de Luminy, Marseille (France).
2. Weizmann Institute of Science, Department of Molecular Cell Biology, Rehovot (Israel).
3. Knight Cancer Institute, Portland, OR 97201, USA.
4. Aix Marseille Univ, Centre de Recherche en Cancérologie de Marseille (CRCM), Equipe labellisée Ligue 'Cell polarity, cell signaling and cancer', Inserm, CNRS, Institut Paoli-Calmettes, Marseille (France).
5. Institut Universitaire de France (IUF).
*Co-first authors.

✉ Corresponding authors: Flavio Maina & Fabienne Lamballe shared senior authorship. fabienne.lamballefr; flavio.mainafr.

Abstract

Cell cycle regulators are frequently altered in Triple-Negative Breast Cancer (TNBC). Emerging agents targeting these signals offer the possibility to design new combinatorial therapies. However, preclinical models that recapitulate TNBC primary resistance and heterogeneity are essential to evaluate the potency of these combined treatments.

Methods: Bioinformatic processing of human breast cancer datasets was used to analyse correlations between expression levels of cell cycle regulators and patient survival outcome. The MMTV-R26^Met mouse model of TNBC resistance and heterogeneity was employed to analyse expression and targeting vulnerability of cell cycle regulators in the presence of BCL-XL blockage. Robustness of outcomes and selectivity was further explored using a panel of human breast cancer cells. Orthotopic studies in nude mice were applied for preclinical evaluation of efficacy and toxicity. Alterations of protein expression, phosphorylation, and/or cellular localisation were analysed by western blots, reverse phase protein array, and immunocytochemistry. Bioinformatics was performed to highlight drug's mechanisms of action.

Results: We report that high expression levels of the BCL2L1 gene encoding BCL-XL and of specific cell cycle regulators correlate with poor survival outcomes of TNBC patients. Blockage of BCL-XL confers vulnerability to drugs targeting CDK1/2/4, but not FOXM1, CDK4/6, Aurora A and Aurora B, to all MMTV-R26^Met and human TNBC cell lines tested. Combined blockage of BCL-XL and CDK1/2/4 interfered with tumour growth in vivo. Mechanistically, we show that, co-targeting of BCL-XL and CDK1/2/4 synergistically inhibited cell viability by combinatorial depletion of survival and RTK/AKT signals, and concomitantly restoring FOXO3a tumour suppression actions. This was accompanied by an accumulation of DNA damage and consequently apoptosis.

Conclusions: Our studies illustrate the possibility to exploit the vulnerability of TNBC cells to CDK1/2/4 inhibition by targeting BCL-XL. Moreover, they underline that specificity matters in targeting cell cycle regulators for combinatorial anticancer therapies.

Keywords: cancer mouse model, triple-negative breast cancer, cell cycle regulators, BCL-XL, MET

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