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. B16F10 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 upto 4 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 αv, α5 and αIIb 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 α5, αIIb and β1integrin subunits but not that of the αv subunit on B16-F10 cells. PTX also brought about a reduction in the total cellular protein levels of β1 and αv 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