Somatostatin receptor subtypes in hormone-refractory (castration-resistant) prostatic carcinoma.
ABSTRACT The aim of this study was to examine the tissue expression and localisation of the somatostatin receptors (SSTRs) in hormone-refractory (HR) prostate cancer (PCa). Five SSTRs were evaluated immunohistochemically in 20 radical prostatectomies (RPs) with Gleason score (GS) 3+3=6 PCa, in 20 RPs with GS 4+4=8 and 4+5=9 PCa, and 20 transurethral resection of the prostate specimens with HR PCa. The mean values in the cytoplasm (all five SSTRs were expressed), membrane (only SSTR3 and SSTR4 were expressed) and nuclei (only SSTR4 and SSTR5 were expressed) of the glands in HR PCa were 20-70% lower than in the other two groups, the differences being statistically significant. All five SSTRs were expressed in the smooth muscle and endothelial cells of HR PCa, the mean values being lower than in the other two groups. In conclusion, this study expands our knowledge on the expression and localisation of five SSTRs in the various tissue components in the HR PCa compared with hormone-sensitive PCa.
- [show abstract] [hide abstract]
ABSTRACT: Background. Advanced adenocarcinoma of the prostate after hormonal manipulation has been noted to be a relatively chemotherapeutic nonresponsive tumor. Earlier reviews have reported objective responses, that is, complete and partial remissions in 6.5% of 3184 patients, and the current review examines the efficacy of new agents.Methods. The current review consists of 26 new drug trials culled from papers and abstracts published between 1987–1991.Results. Results of these 26 drug trials found a similar trend, 8.7% (95% confidence interval, 6.4–9.0%), indicating that hormone-resistant adenocarcinoma of the prostate still fails to respond to most cytotoxic agents. The most interesting of the new therapeutic agents is the combination of vinblastine plus estramustine. Only six agents had an objective response rate greater than 10%, such as vinblastine by continuous infusion, trimetrexate, mitoguazone, and estramustine. The recent introduction of radioactive-labeled monoclonal antibodies is intriguing and these will undoubtably be used as carriers for radiotherapeutic and cytotoxic compounds.Conclusions. Although multidrug resistance may explain the marginal efficacy of cytotoxic drugs, methods to overcome such resistance and, more importantly, new classes of agents must be developed. In addition, reliable disease markers must be found for osseous and visceral metastases to avoid the prevailing confusion in evaluating more precisely the destruction of prostate cancer cells.Cancer 01/1993; 71(S3):1098 - 1109. · 5.20 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Receptors for somatostatin (SST) that are found on prostate cancers might be used for targeting of chemotherapeutic agents. Thus, doxorubicin derivative 2-pyrrolinodoxorubicin (AN-201) can be linked to SST analogue RC-121 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2) to form targeted cytotoxic SST analogue AN-238. In this study, we evaluated the effects of AN-238 on the growth of SST receptor (SSTR)-positive androgen-independent Dunning R-3327-AT-1 prostate cancers in Copenhagen rats. The dose range and tumor growth-inhibitory effects of AN-238 and AN-201 were investigated in preliminary experiments. Administration of cytotoxic radical AN-201 at single i.v. doses of 110, 125, and 150 nmol/kg resulted in 0, 77.7, and 100% mortality, respectively, within 6-10 days. Four weeks after the injection of 110 nmol/kg AN-201, mean tumor volume was reduced by 35.1 % (P < 0.05), as compared with controls. In contrast, a single i.v. injection of analogue AN-238 at a dose of 300 nmol/kg was nontoxic and remarkably potent in inhibiting the growth of Dunning AT-1 tumors, resulting in a 85.9% (P < 0.01) reduction in tumor volume after 4 weeks. Treatment with AN-238 extended the survival time of tumor-bearing rats from 52.0+/-3.75 to 91.8+/-3.70 days, corresponding to a 76.5% (P < 0.01) increase. In a comprehensive experiment, we compared the effects of radical AN-201 at 115 nmol/kg, analogue AN-238 at 115 and 300 nmol/kg, carrier SST analogue RC-121 at 300 nmol/kg, and a mixture of AN-201 and RC-121 at doses of 300 nmol/kg administered i.v. Administration of AN-201 at 115 nmol/kg led to 90.0% mortality in 12 days, but animals treated with 115 nmol/kg of AN-238 showed no signs of toxicity, their tumor volume was reduced by 40.0% (P < 0.05), and their tumor weight was reduced by 42.8% (P < 0.01) after 4 weeks, as compared with controls. The dose of 300 nmol/kg of AN-238 was also nontoxic and diminished tumor volume by 80.9% (P < 0.01) and tumor weight by 82.0% (P < 0.01). No reduction in tumor growth or toxic effects was observed with carrier RC-121, but after the injection of unconjugated mixture of AN-201 and RC-121 at doses of 300 nmol/kg, all rats died within 4 days. Specific high-affinity receptors for SST were found on Dunning R-3327-AT-1 tumor membranes by radioligand binding assay and were identified by reverse transcription-PCR as SSTR2. Our study indicates that cytotoxic SST analogue AN-238 can be targeted to SSTRs on tumors and produces a powerful inhibition of the growth of Dunning-AT-1 rat prostate cancer at doses that are nontoxic, whereas its cytotoxic component, 2-pyrrolinodoxorubicin, is toxic and ineffective.Cancer Research 10/1998; 58(18):4132-7. · 8.65 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Doxorubicin (DOX) was conjugated to a monoclonal antibody (mAb 425) directed against the human epidermal growth factor receptor. The immunoreactivity of these conjugates, with an average of six to eight molecules of DOX per antibody, was largely conserved, and their in vitro cytotoxicity against metastatic human melanoma cells (M24 met) was improved over that of free DOX. An evaluation of the therapeutic efficacy of mAb 425-DOX indicated that this immunoconjugate suppressed the growth of primary and secondary M24 met tumors in mice with severe combined immunodeficiency and prolonged the life span of these animals, whereas an equivalent dose of free DOX was ineffective. Conjugation of DOX to an irrelevant mAb also increased its antitumor effect over that of equivalent amounts of free drug but to a lesser extent than that achieved by the mAb 425-DOX conjugate. These results demonstrate targeted delivery and striking antitumor activity of DOX immunoconjugates in a preclinical model of spontaneous, metastatic human melanoma that was insensitive to free DOX.Cancer Research 07/1995; 55(11):2352-6. · 8.65 Impact Factor