To evaluate the potential application of
somatostatin (SST) analogs as an adjuvant treatment for
prostate cancer, we characterized the binding sites for SST octapeptide analogs on
prostate cancers in patients treated with radical
prostatectomy. The affinity and density of binding sites for SST analog
RC-160 on 80 surgical specimens of
prostate cancers were determined by
ligand competition assays. The expression of messenger
ribonucleic acid (
mRNA) for SST receptor subtype 1 (
SSTR1), subtype 2 (SSTR2), and subtype 5 (SSTR5) was also investigated in 22 samples by RT-PCR. Fifty-two of 80 specimens (65%), showed a single class of specific binding sites for
RC-160 with a mean dissociation constant (K(d)) of 9.44 nmol/L and a mean maximal binding capacity of 754.8 fmol/mg
membrane protein. The
mRNA for
SSTR1 was detected in 86% of samples, whereas the incidences of
mRNA for SSTR2 and SSTR5 were 14% and 64%, respectively. The expression of SSTR2 and/or SSTR5 was 100%, consistent with the presence of
RC-160 binding. In patients at high risk of
cancer recurrence (stage pT3 and/or Gleason score of 8-10), the incidence of
RC-160 binding (65.7%) was similar to that observed in the low risk group (64.3%). The demonstration of the high incidence of octapeptide-preferring SSTRs in organ-confined and locally advanced
prostate cancers supports the merit of further investigations of the application of SST analogs and their
radionuclide and cytotoxic derivatives for adjuvant treatment of patients at high risk of
cancer recurrence after radical
prostatectomy. Such approaches could be also considered for patients with advanced
prostate cancer at the time of relapse.