Moreover, tumor cell dependence on VEGFA as a sur vival factor was explored via the quantification of apop tosis by cleaved PARP and confirmed by FACS analysis, which did not produce evidence that bevacizumab had an effect on cellular survival. It has been shown that de pletion of VEGFA or VEGFR1 through knock down ex periments can interfere with the autocrine feedback loop and more bonuses survival of tumor cells, but only where VEGFR1 is present at nuclear membranes and therefore inaccessible to extracellular ligands or bevacizumab. Our experi ments show that the use of a VEGFA targeted antibody is not able to mimic this phenomenon in our cell lines as there is no Inhibitors,Modulators,Libraries evidence of a significant increase in apop totic cells upon single agent treatment.
VEGFA stimulated proliferation induced by hypoxia was not inhibited by bevacizumab treatment and rem ained more or less unchanged in most tumor cells ex cept HT 29. The decrease in proliferation noted in HT 29, could Inhibitors,Modulators,Libraries not be attributed to changes in VEGFA related gene or protein regulation and may be related to other downstream components of the HIF response. Small molecule receptor tyrosine kinases targeted to the VEGFA pathway in HT 29 xenografts have shown some tumor cell effects in other studies suggesting this path way does play a critical role in cell survival, however per haps only clearly evident when there are multiple receptor targets. The lack of proliferation changes in the other cell lines was consistent at each time point investigated with only minor decreases or increases.
In contrast, endothelial cells showed a significant decrease in proliferation rate after bevacizumab treatment. There has been some limited Inhibitors,Modulators,Libraries analysis of individual cell lines treated with bevacizumab in the literature, overall con curring with our results of a lack of major effects on proliferation, or even a slight increase in prolifera tion when treated with bevacizumab alone. The role of VEGFA in generating endothelial cell changes is well established, with the inhibition of VEGFA leading to changes in tumor vasculature. However, patient outcomes using bevacizumab have implied that VEGFA antibodies may also differentially Inhibitors,Modulators,Libraries affect the tumor cells or the tumors microenvironment. Even with inherent difficulties of in vitro studies, our data suggest that tumor cells themselves are not intrinsically affected in an adverse manner by bevacizumab monotherapy based on the selec tion of assays performed.
In addition, the angiogenic po tential mediated through the VEGFA pathway was not significantly altered in the tumor cell lines. The effect be yond vasculature permeability, remodeling and pruning of an anti VEGFA Inhibitors,Modulators,Libraries based therapy, is likely to be a complex interaction of tumor vasculature, tumor stroma, immune cells as well as the tumor selleck cells.