The Role of All-trans Retinoic Acid (ATRA) As A Potential Downregulator of Integrin α5β1 Mediated Signalling in Melanomas

Integrin α5β1 plays an important role in promoting tumour metastasis in melanomas which have the highest mortality rate among all dermatological cancers. Interactions of fibronectin with integrin α5β1 activates cellular signalling through phosphatidylinositol 3’ kinase (PI3K) and extracellular signal regulated kinase (ERK) pathways. Synthetic inhibitors have been used for targeting integrins and integrin mediated signalling pathways but such therapies are often hindered by toxicity or by a lack of efficacy. In our present study, the effects of the phytochemical all-trans retinoic acid (ATRA) on integrin α5β1α5β1-fibronectin interactions and integrin α5β1 mediated signalling were studied using the metastatic murine melanoma cell line B16F10 as a model. Molecular docking indicated ATRA has higher binding affinity to integrin α5β1 (Δ ΔG = - 6.89 kcal/mole) in comparison to its synthetic inhibitor ATN-161 (ΔΔG = - 4.83 kcal/mole). ATRA also showed higher binding affinity to ERK and equal binding affinity to PI3K compared to their synthetic inhibitors ravoxertinib and alpelisib respectively. Treatment of B16F10 cells with ATRA (20 μM/ml) for 24 hours significantly inhibited integrin α5β1α5β1-fibronectin interactions (as shown by cell adhesion assays), integrin α5 expression, phosphorylation of ERK, PI3K and MMP-2 expression (as shown by ELISA). Treatment of cells with ATRA (20 μM/ml) also inhibited MMP-2 activity but increased expression of the MMP inhibitor TIMP-2. Inhibition of integrin α5β1α5β1-fibronection interactions and α5β1 mediated signalling through PI3K and ERK upon ATRA treatment could lower invasive potential of tumour cells by inhibiting MMP-2 expression and activity. Our studies thus indicate that ATRA has excellent potential as an inhibitor of integrin α5β1 and targeting integrin α5β1α5β1-fibronectin interactions and integrin α5β1 mediated signalling pathways for modulation of MMP-2 with ATRA could show good therapeutic potential for melanoma treatment.