We previously had reported that Western blot analysis of HDJ 2 could be used as a surrogate for farnesylation sta tus in hematopoietic cells. We therefore applied that assay to peripheral blood T cells. As shown in Figure 3 for three representative patients, accumulation nearly of non farnesylated Inhibitors,Modulators,Libraries HDJ 2 was easily detected in T cells at the week 7 time point. These results indicate that farnesyla tion was inhibited in peripheral blood T cells as it had been in the tumor tissue. To gauge whether T cell func tion could be affected by this inhibition of protein farne sylation, IFN production was assessed on T cells stimulated ex vivo with the polyclonal stimulus, SEA. The combined data from all available patients are Inhibitors,Modulators,Libraries shown in Figure 4. Significant inhibition of IFN production was observed in the week 7 samples compared to pre treatment specimens.
These results suggest that R115777 hibition may be required, these results nonetheless sug gest that inhibition of Inhibitors,Modulators,Libraries FT alone will not be sufficient for clinical activity in melanoma. One caveat of this inter pretation is that, while pre treatment samples were analyzed by pathology to confirm the presence of melan oma, given the large amount of tissue needed to perform the correlative analyses, post treatment samples were not routinely assessed for viable tumor. It is Inhibitors,Modulators,Libraries therefore technically possible that the decrease in FT activity Inhibitors,Modulators,Libraries seen in the post treatment samples could be due to inad equate tumor in the sampled tissue, as a result of either necrosis or contamination with adjacent normal tissue.
Given that marked FT inhibition was seen in multiple clinically evident lesions post therapy, and that no clin ical responses were observed, it is most likely that these results reflect true sellectchem target inhibition. A recent clinical trial in patients with acute myelogen ous leukemia has shown that patients whose tumor cells have a high ratio of expression of two genes, RASGRP1 and APTX, are more likely to respond to R115777. Therefore, in future trials it might be of interest to de termine if this gene expression ratio is also indicative of the dependence of melanoma tumors on farnesylation. Therefore, the selection of patients whose melanoma tumors express such a high ratio may have a greater likelihood of clinical responses. Understanding the mu tation status of RAS, BRAF and PI3K may also be in formative for predicting tumor sensitivity resistance and would be important for future work. The mechanism of anti tumor activity of FTIs when they are effective is incompletely understood, and the majority of FTI trials have failed to demonstrate mean ingful clinical activity, despite confirmation that FTase or another intended target was inhibited. Multiple mechanisms of resistance and escape have been pro posed.