Effect of long-term treatment with low doses of the LHRH antagonist Cetrorelix on pituitary receptors for LHRH and gonadal axis in male and female rats.

Our previous studies showed that treatment of female rats with large doses of Cetrorelix, an antagonist of luteinizing hormone-releasing hormone (LHRH), reduces levels of serum LH, estradiol, progesterone, and the concentration of pituitary LHRH receptors (LHRH-Rs) and their mRNA expression. Serum LH and testosterone levels and pituitary LHRH-R in male rats are also decreased by high doses of Cetrorelix. This approach can be used for therapy of sex hormone-dependent cancers. However, in conditions where an incomplete hormone deprivation is indicated, lower doses of Cetrorelix may suffice. Thus, we investigated the effect of a 30-day treatment with a low-dose depot formulation of Cetrorelix (20-24 microg per kg per day) on the pituitary-gonadal axis of male and female rats. In both sexes, lower serum LH levels were observed on day 4 after administration. In males, LH returned to control levels by day 10, whereas in females, a rebound LH elevation occurred. Testosterone levels in male rats were decreased up to day 20, but on day 30, the values were similar to controls. In females, serum estradiol was reduced on day 4; however, by day 10 it returned to normal. Progesterone levels were diminished through the entire period. Female rats showed diestrous smears during the first week of treatment and prolonged estrous periods thereafter. The weights of testes and ovaries were significantly lower, but not the weights of prostate, seminal vesicles, and uterus. Pituitary LHRH-R mRNA and LHRH-R protein levels were not significantly different from the controls. Thus, the treatment with low doses of Cetrorelix did not seriously impair gonadal functions. The results suggest that Cetrorelix in low doses induces only a partial pituitary-gonadal inhibition and might be indicated for treatment of endometriosis, leiomyomas, and benign prostatic hyperplasia.

Preclinical evaluation of therapeutic effects of targeted cytotoxic analogs of somatostatin and bombesin on human gastric carcinomas.

BACKGROUND: New modalities are necessary for the treatment of patients with unresectable gastric carcinoma. The authors investigated whether receptors for somatostatin and bombesin were present in human gastric carcinoma lines and tested the antitumor effects of cytotoxic somatostatin analog AN-238 and cytotoxic bombesin conjugate AN-215. METHODS: Nude mice bearing AGS, Hs 746T, and NCI-N87 human gastric carcinomas were treated with AN-238, AN-215, or their cytotoxic moiety 2-pyrrolinodoxorubicin (AN-201). Tumor growth reduction and tumor doubling times were calculated, and histologic characteristics of cell proliferation and apoptosis were examined. The expression of mRNA for somatostatin and bombesin receptors in tumors was investigated by reverse transcriptase-polymerase chain reaction. Subtypes 2 and 5 of somatostatin receptor proteins (sst2 and sst5, respectively) were analyzed using immunohistochemistry and immunoblotting. Binding assays were performed with radiolabeled somatostatin and bombesin analogs. RESULTS: Cytotoxic bombesin analog AN-215 powerfully inhibited the growth of AGS carcinomas that expressed high-affinity subtype 1 bombesin receptors. All three carcinomas expressed high-affinity sst2 and sst5 receptors. Cytotoxic somatostatin analog AN-238 exerted a strong inhibitory effect on NCI-N87 and Hs 746T carcinomas, which exhibited high concentrations of somatostatin receptors, but had a weaker effect on AGS tumors, which expressed the lowest receptor levels. AN-201 had only nonsignificant effects. CONCLUSIONS: Experimental human gastric carcinomas that expressed high-affinity subtype 1 bombesin receptors were inhibited by cytotoxic bombesin analog AN-215, and tumors with high concentrations of sst2 or sst5 somatostatin receptors were suppressed by cytotoxic somatostatin analog AN-238. These findings suggest that this class of targeted compounds should be considered for the therapy of patients with advanced gastric carcinoma.

Effective treatment of H838 human non-small cell lung carcinoma with a targeted cytotoxic somatostatin analog, AN-238.

The accumulation of radioactive somatostatin analog [111In]pentetreotide in non-small cell lung cancer (non-SCLC) during scintigraphy of patients provides a rationale for investigating the efficacy of somatostatin receptor-based chemotherapy in non-SCLC. Consequently, in this study, we evaluated the antitumor effects of cytotoxic somatostatin analog AN-238 on H838 human non-SCLC xenografted into nude mice in comparison with its cytotoxic radical, 2-pyrrolinodoxorubicin (AN-201). The expression of messenger RNA (mRNA) for human somatostatin receptor subtypes 2 (hsst2) and 5 (hsst5) in H838 cells, and tumors was also investigated using reverse-transcription polymerase chain reaction (RT-PCR). Somatostatin receptors on H838 tumors were characterized by ligand competition assay using radiolabeled somatostatin analog, RC-160. Three i.v. injections of AN-238 at 150 nmol/kg, given on days 1, 7 and 21, resulted in a significant (p<0.05) tumor growth inhibition, the final tumor volume being 60% smaller than in the controls. The tumor doubling time was also extended significantly (p<0.05) from 9.65+/-0.56 days in the controls to 17.52+/-3.3 days. Only one of 8 mice died due to toxicity. In contrast, cytotoxic radical AN-201 was ineffective and more toxic, killing 2 of 7 animals. mRNA for hsst2 was found in H838 xenografts, but not in H838 cells from which the xenografts originated. Interestingly, H838 cells grown in a special, serum-free medium did express mRNA for hsst2. mRNA for hsst5 was not found in any samples tested. Binding studies demonstrated the presence of high affinity (K(d) = 7.3+/-1.2 nM) binding sites for RC-160 with a mean maximal binding capacity (B(max)) of 953.3+/-45.3 fmol/mg protein. AN-238 at 3.14+/-0.93 nM concentration displaced 50% of radiolabeled RC-160 binding to somatostatin receptors in H838 tumors. Our results indicate that patients with inoperable non-SCLC may benefit from chemotherapy targeted to somatostatin receptors based on AN-238.