Markers of angiogenesis and response to VEGF pathway-targeted therapy in renal cell carcinoma Free

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Background: Therapies that target the vascular endothelial growth factor (VEGF) pathway are effective in a significant fraction of patients with metastatic clear cell renal cell carcinoma (cRCC). The identification of molecular markers that predict response to these therapies will greatly help physicians with treatment decisions.

Methods: RNA was extracted from formalin-fixed, paraffin-embedded (FFPE) and frozen samples and analyzed by quantitative PCR (qPCR). 44 tumors with matched pairs of FFPE and frozen samples for each tumor was used to initially compare SYBR Green and Taqman qPCR assays. 18 of the matched pairs of tumors were then used to validate the relative expression of 26 candidate genes and three housekeeping genes (HSKs) by SYBR Green. FFPE primary tumor blocks were obtained from an independent set of 52 patients prior to treatment for metastatic cRCC. Patients were treated with SU11248, AG013736, or IFNA and bevacizumab at the UCSF Comprehensive Cancer Center. RNA was extracted and analyzed using the validated SYBR Green assays. Protein expression for a subset of candidate genes was also assessed by immunohistochemical (IHC) analysis of FFPE sections.

Results: SYBR Green assays gave better Spearman rank correlations than Taqman when comparing expression in matched frozen and FFPE samples, and were therefore used for subsequent qPCR analyses. Expression of VEGF, VEGFR, CAIX, CP, and HIF2alpha was significantly associated with response to anti-angiogenic therapy. IHC data also indicated expression of VEGFR2and CD34/microvessel density was associated with response to therapy. Correlations between gene expression, IHC, and VHL mutation data were also examined. CAIX showed the strongest correlation between gene expression and IHC, while HIF2alpha and VEGFR-2 were moderately correlated. No association between VHL mutation and expression of candidate genes or proteins was observed.

Conclusions: Response to VEGF pathway-targeted therapy in metastatic cRCC appears to be associated with expression of several candidate genes, including the angiogenic targets VEGF and VEGFR. At the protein level, increased expression of VEGFR2 and CD34 reflects increased vascularization and response to anti-angiogenic therapies as well. Such analyses of angiogenic markers help in understanding the biology of and clinical response to VEGF pathway-targeted agents.