Expression of a flt-4 (VEGFR3) splicing variant in primary human prostate tumors. VEGF D and flt-4tΔ773–1081 overexpression is diagnostic for sentinel lymph node metastasis

Utilizing a cDNA expression library established from human prostate PC-3ML tumor cells, we have cloned a truncated flt-4 gene, termed flt-4t(Delta773-1081). We have then utilized RNase protection and ELISA to measure the relative levels of VEGF B, C, D and flt-1, KDR, flt-4 and flt-4t(Delta773-1081) expression in freshly isolated benign prostatic hyperplasia or BPH tissue (n=21), primary prostate cancers (n=82) and matching sentinel lymph node metastases from stage T2a-T2b/T3 tumors (n=52). Comparisons of the primary tumors with BPH showed that there was a significant upregulation of VEGF-B (P=0.003), VEGF D (P=0.005), flt-1 (P=0.003), KDR (P=0.002), flt-4 (P=0.007), and flt-4t(Delta773-1081) (P=0.001), but not VEGF-C (P=0.543). There was no correlation between VEGF-B and its receptor flt-1 (P=0.545), or VEGF-C and flt-4 (P=0.16) and KDR (P=0.23) receptor expression in tumor specimens. Conversely, there was no significant relationship between VEGF-D and the flt-4t(Delta773-1081) receptor (P=0.516) expression. Statistical analysis further showed that there was no significant correlation between VEGF-B, VEGF-C, VEGF-D, flt-1, KDR, flt-4 and flt-4t(Delta773-1081) with patient age (P>0.10), stage (P>0.10), PSA value (P>0.15) or tumor size (P>0.15). Likewise, there was no significant correlation between VEGF-B, VEGF-C, flt-1, KDR, and flt-4 with Gleason score (P>0.15). In comparison, flt-4t(Delta773-1081) levels clearly increased significantly in Gleason score 7 and Gleason score 8-10 tumors as well as in stage T2a-T2b/T3 tumors. The studies were extended to compare gene expression profiles in T2a-T2b and T3 tumors with (n=26) and without (n=26) matching sentinel lymph node metastases. The data showed that VEGF D and flt-4t(Delta773-1081) expression levels were significantly elevated in primary tumors with sentinel lymph node involvement compared to those lacking lymph node involvement (P>0.0022 and 0.006, respectively). These data suggest that targeting VEGF D and flt-4t(Delta773-1081) receptors may be particularly effective in the prevention of lymph node metastases.