Combination Treatment of Retinoic Acid Plus Focal Adhesion Kinase Inhibitor Prevents Tumor Growth and Breast Cancer Cells Metastasis

All-trans retinoic acid (RA) is the primary metabolite of vitamin A and controls the development and homeostasis of organisms and tissues. RA and its natural and synthetic derivatives, known as retinoids, are promising agents in treating and chemoprevention different neoplasias, including breast cancer (BC). Focal adhesion kinase (FAK) is a crucial regulator of cell migration, and its overexpression is associated with the metastatic behavior of tumors. Thus, pharmaceutical FAK inhibitors (FAKi) have been developed to counter its action. In this work, we hypothesize that RA plus FAKi (RA+FAKi) approach could improve inhibition of tumor progression. By in silico analysis, we confirmed RARA, SRC, and PTK2 (encoding RARα, Src, and FAK, respectively) overexpression in all breast cells tested. In metastatic BC cells, we reveal that genes encoding proteins that FAK directly or indirectly modulates are deregulated compared to normal cells. We showed a different pattern of genes up/down-regulated between RA-resistant and RA-sensitive BC cells. In addition, we demonstrated that both RA-resistant BC cells (MDA-MB-231 and MDA-MB-468) display the same behavior after RA treatment, modulating the expression of genes involved in Src-FAK signaling. Furthermore, we demonstrated that although RA and FAKi administered separately decrease viability, adhesion, and migration in mammary adenocarcinoma LM3 cells, their combination exerts a higher effect. We also evidenced that RA effects are extrapolated to other cancer cells, including the human cervical carcinoma cells HeLa. In an orthotopic assay of LM3 tumor growth, RA and FAKi administered separately reduce tumor growth; however, the combined treatment induces the more potent inhibition increasing mice survival. Moreover, in an experimental metastatic assay, RA significantly reduces metastatic lung dissemination of LM3 cells. Overall, these results indicate that RA resistance would reflect deregulation of most RA-target genes, including genes encoding components of the Src-FAK pathway. Our study demonstrates that RA plays an essential role in disrupting BC tumor growth and metastatic dissemination in vitro and in vivo by controlling FAK expression and localization. RA plus FAKi exacerbated these effects suggesting that the sensibility to RA therapies could be increased with FAKi coadministration in BC tumors.