Pentoxifylline modulates cell surface integrin expression and integrin mediated adhesion of B16F10 cells to extracellular matrix components.

Our previous studies demonstrated that Pentoxifylline (PTX), a phosphodiesterase inhibitor, could inhibit the lung homing of B16-F10 melanoma cells in C57BL/6 mice. In this study we have looked at the effect of PTX on cell surface integrin expression and integrin mediated adhesion of B16-F10 melanoma cells. B16-F10 cells treated with PTX when injected through the tail vein of mice showed a 75% reduction in pulmonary nodules as compared to control untreated cells. PTX brought about a significant reduction in the integrin mediated adhesion of F10 cells to Fibronectin and Vitronectin (58.75% +/- 3.4 S.E and 60% +/- 1.7 S.E respectively if control was considered as 100%). This inhibition in adhesion was evident up to four hours only and treatment for 24 hours brought about an increase in adhesion (135.5% +/- 0.5 S.E). Flow cytometric analysis showed higher surface expressions of alphav, alpha5 and alphaIIb integrin subunits in B16-F10 as compared to the low metastatic cell line B16-F1 suggesting a role for these integrins in determining the metastatic potential. PTX brought about a significant decrease in the cell surface expression of alpha5, alphaIIb and beta1 integrin subunits but not that of the alphav subunit on B16-F10 cells. PTX also brought about a reduction in the total cellular protein levels of beta1 and alphav integrin subunits. Various isoforms of Protein Kinase C (PKC) has been shown to regulate integrin expression, localization and activity. Hence we looked at the effect of PTX on total cellular PKC activity. PTX brought about a significant reduction in total cellular PKC activity (82.66 +/- 0.593). Collectively our results indicate that the antimetastatic action of PTX is mediated, at least in part through its effects on adhesion and the surface expression of specific integrin receptors.