Differential expression of insulin-like growth factor binding proteins in high versus low Gleason score prostate cancer

Purpose: The insulin-like growth factor (IGF) system appears to be important in human prostate cancer biology. Expression of specific IGF binding proteins (IGFBPs) by prostate cancer tissues may modulate IGF cellular actions, and possibly determine both ICE-dependent tumor growth and biological aggressiveness in vivo. The purpose of this study was to examine the differential expression of all six IGFBP genes in benign and malignant prostate tissue samples. Materials and Methods: Using RNAse protection assays, we examined expression of IGFBPs 1 through 6 in 23 paired benign and neoplastic prostate tissue samples obtained from the same prostatectomy specimen. RNA expression levels on each tissue sample were determined densitometrically and groups compared using standard Student's t test. Results: We found expression of IGFBPs 2 through 6, but not IGFBP-1, in both malignant and benign tissues. A statistically significant differential expression of IGFBPs 2, 3 and 5 was found between tumors with high Gleason score and those with low scores and benign tissues. Expression of IGFBPs 2 and 5 was higher (p = 0.002 and 0.04, respectively) while that of IGFBP-3 was lower (p = 0.05) in high versus low Gleason score cancer specimens. Expression of IGFBPs 4 and 6 was no different between tumors (p = 0.052 and 0.25, respectively). No significant differences in IGFBP expression were evident between benign and tumor tissues when tumor grade was not considered. Conclusion: Our results indicate that differential expression of certain IGFBPs in human prostate cancer correlates with tumor Gleason score. Thus, expression of certain IGFBPs in prostate cancer may be used as a surrogate marker of aggressive clinical behavior.