Francine Hebert

Potentiation of the inhibitory effect of growth hormone-releasing hormone antagonists on PC-3 human prostate cancer by bombesin antagonists indicative of interference with both IGF and EGF pathways

In view of the involvement of various neuropeptides and growth factors in the progression of androgen‐independent prostate cancer, we investigated the effects of antagonists of growth hormone‐releasing hormone (GHRH) alone or in combination with an antagonist of bombesin/gastrin‐releasing peptide (BN/GRP) on PC‐3 human prostate cancers.

Antagonists of growth hormone-releasing hormone (GH-RH) inhibit IGF-II production and growth of HT-29 human colon cancers

Insulin-like growth factors (IGFs) I and II are implicated in progression of various tumours including colorectal carcinomas. To interfere with the production of IGFs, we treated male nude mice bearing xenografts of HT-29 human colon cancer with various potent growth hormone-releasing hormone (GH-RH) antagonists. Twice daily injections of antagonist MZ-4-71, 10 μg intraperitoneally or 5 μg subcutaneously (s.c.) resulted in a significant 43–45% inhibition of tumour growth. Longer acting GH-RH antagonists, MZ-5-156 and JV-1-36 given once daily at doses of 20 μg s.c. produced a 43–58% decrease in volume and weight of cancers. Histological analyses of HT-29 cancers demonstrated that both a decreased cell proliferation and an increased apoptosis contributed to tumour inhibition. GH-RH antagonists did not change serum IGF-I or IGF-II levels, but significantly decreased IGF-II concentration and reduced mRNA expression for IGF-II in tumours. In vitro studies showed that HT-29 cells produced and secreted IGF-II into the medium, and addition of MZ-5-156 dose-dependently decreased IGF-II production by about 40% as well as proliferation of HT-29 cells. Our studies demonstrate that GH-RH antagonists inhibit growth of HT-29 human colon cancers in vivo and in vitro. The effect of GH-RH antagonists may be mediated through a reduced production and secretion of IGF-II by cancer cells.

Antagonists of growth hormone-releasing hormone (GH-RH) inhibit in vivo proliferation of experimental pancreatic cancers and decrease IGF-II levels in tumours.

Insulin-like growth factors (IGF-I and IGF-II) are implicated in the pathogenesis of pancreatic carcinoma. Antagonists of growth hormone-releasing hormone (GH-RH) suppress the GH-RH-GH-IGF-I axis and also act directly on tumours to reduce production of IGF-I or II. The aim of this study was to investigate the effects of two potent GH-RH antagonists in two experimental models of pancreatic cancer. Syrian golden hamsters with nitrosamine-induced pancreatic tumours were treated with 10 micrograms/day of GH-RH antagonist MZ-4-71 for 60 days. The therapy reduced the number of tumorous animals, decreased the weight of tumorous pancreata by 55%, and lowered AgNOR numbers in tumour cells. In two other experiments, GH-RH antagonists MZ-4-71 and MZ-5-156 significantly inhibited growth of SW-1990 human pancreatic cancers xenografted into nude mice, as shown by a reduction in tumour volume and tumour weights, and a decrease in AgNORs in cancer cells. IGF-I levels in serum and in pancreatic cancer tissue remained unchanged after therapy, suggesting that an effect on IGF-I is not involved in tumour inhibition. In contrast, IGF-II concentrations in tumours were significantly reduced by 50-60% after treatment with the GH-RH antagonists as compared with controls. In vitro studies showed that the concentration of IGF-II in the culture medium was increased after seeding of SW-1990 cells, indicating that this pancreatic cancer cell line produced and released IGF-II. This finding was also supported by the expression of IGF-II mRNA in the SW-1990 cells. Addition of 3 x 10(-6) M of GH-RH antagonist MZ-5-156 to the reduced-serum medium decreased cell proliferation, IGF-II mRNA expression in the cells and IGF-II concentration in the medium. Our findings indicate that inhibitory effects of GH-RH antagonists on the growth of experimental pancreatic cancers, may result from a decrease in the production and concentration of IGF-II in the tumours.

A targeted cytotoxic somatostatin (SST) analogue, AN-238, inhibits the growth of H-69 small-cell lung carcinoma (SCLC) and H-157 non-SCLC in nude mice

Recently, we developed a cytotoxic analogue of somatostatin (SST), AN-238, in which the SST carrier peptide RC-121 was linked to 2-pyrrolinodoxorubicin (2-pyrrolino-DOX) (AN-201), a potent derivative of doxorubicin. AN-238 can be targeted to SST receptors (SSTRs) on tumours. In the present study, we evaluated the effects of AN-238 on the growth of H-69 small-cell lung carcinoma (SCLC) and H-157 non-SCLC xenografted into nude mice. High affinity binding sites for SST are present in H-69 SCLC and were now detected in H-157 non-SCLC xenografts, but not in H-157 cells. A strong expression of the human SSTR subtype 2 (hSSTR-2) and a weaker expression of subtype 5 (hSSTR-5) was found in H-69 SCLC cells, but not in H-157 non-SCLC cells. However, a strong expression of mRNA for mouse (m)SSTR-2 could be detected in H-157 xenografts. AN-238 effectively inhibited the growth of H-69 SCLC tumours in nude mice. Twenty-six days after a single injection of AN-238 at 200 nmol/kg, the volume of H-69 tumours was decreased by approximately 55% (P<0.05) compared with the controls, while AN-201 at the same dose was highly toxic and produced only a minor tumour inhibition. To evaluate the potency of multiple doses of AN-238, nude mice bearing H-69 SCLC received three injections of AN-238 at 150 nmol/kg on days 1, 12 and 28. In the period of 42 days after the first injection, the growth rate of H-69 tumours was approximately 50% lower than that of controls. In nude mice bearing H-157 non-SCLC tumours, a single i.v. administration of AN-238 at 200 nmol/kg inhibited tumour volume by 91% after 28 days (P<0.01 compared with controls). AN-201 was toxic and ineffective at the same dose. Two injections of AN-238 at 150 nmol/kg given on days 1 and 18 produced 83% inhibition of H-157 tumour growth (P<0.01 versus controls). AN-238 given as a single dose of 200 nmol/kg induced necrosis, while two injections of 150 nmol/kg induced apoptosis in the tumour tissue. Our results indicate that targeted cytotoxic SST analogue AN-238 could be considered for therapy of both SCLC and non-SCLC.

Inhibition of growth of MX-1, MCF-7-MIII and MDA-MB-231 human breast cancer xenografts after administration of a targeted cytotoxic analog of somatostatin, AN-238

Since somatostatin (sst) receptors are expressed in a high percentage of human breast cancers, we studied the effects of a targeted cytotoxic somatostatin analog (AN‐238) formed by linking the highly active doxorubicin (DOX) derivative 2‐pyrrolino‐DOX (AN‐201) to octapeptide RC‐121 (D‐Phe‐Cys‐Tyr‐D‐Trp‐Lys‐Val‐Cys‐Thr‐NH2) in 3 human breast cancer models. The models included estrogen‐independent MDA‐MB‐231 and MX‐1 and estrogen‐sensitive MCF‐7‐MIII tumors. Nude mice bearing xenografts of these cancers were injected i.v. with 250 nmol/kg doses of cytotoxic radical AN‐201, cytotoxic analog AN‐238 or the unconjugated mixture of AN‐201 and sst analog RC‐121. Significant inhibition of growth of MDA‐MB‐231, MX‐1 and MCF‐7‐MIII tumors was observed 1 week after injection of a single dose of cytotoxic analog AN‐238. The volume of MDA‐MB‐231 tumors remained significantly decreased 3 weeks after treatment. The volumes and weights of MCF‐7‐MIII tumors continued to be significantly reduced 60 days after therapy with AN‐238. AN‐238 also caused complete regression of MX‐1 tumors in 5 of 10 animals, which remained tumor‐free 60 days after treatment. In contrast, after treatment with cytotoxic radical AN‐201, MDA‐MB‐231 and MCF‐7‐MIII tumors grew steadily and the regression of MX‐1 tumors was only transitory in most animals. Toxicity of AN‐201 was much greater than that of AN‐238, as measured by animal deaths, loss of body weight and leukopenia. High‐affinity sst receptors and mRNA for both sst2 and sst5 subtypes were found in all 3 tumor lines. Expression of sst receptors was not significantly affected by treatment with AN‐238. Our results indicate that the cytotoxic somatostatin analog AN‐238 efficaciously inhibits growth of human breast cancers expressing sst receptor subtypes 2 and 5. Int. J. Cancer 82:592–598, 1999.

Bombesin antagonists inhibit growth of MDA-MB-435 estrogen-independent breast cancers and decrease the expression of the ErbB-2/HER-2 oncoprotein and c-jun and c-fos oncogenes

Previous studies showed that antagonists of bombesin (BN)/gastrin-releasing peptide (GRP) inhibit the growth of various cancers by interfering with the growth-stimulatory effects of BN-like peptides and down-regulating epidermal growth factor receptors on tumors. Because the overexpression of the human epidermal growth factor receptor-2 (ErbB-2/HER-2/neu) oncogene plays a role in the progression of many breast cancers, we investigated whether BN/GRP antagonists can affect HER-2 in mammary tumors. Female nude mice bearing orthotopic xenografts of MDA-MB-435 human estrogen-independent breast cancers were treated daily with BN/GRP antagonists RC-3095 (20 μg) or RC-3940-II (10 μg) for 6 weeks. The expression of BN/GRP receptors on tumors was analyzed by reverse transcription–PCR and immunoblotting. We also evaluated whether the mRNA expression for the c-jun and c-fos oncogenes is affected by the therapy. Both BN/GRP antagonists significantly inhibited growth of MDA-MB-435 cancers; RC-3095 reduced tumor volume by 40% and RC-3940-II by 65%. The GRP receptors (subtype 1) were detected in MDA-MB-435 tumors, showing that they mediate the inhibitory effect of the antagonists. Tumor inhibition was associated with a substantial reduction in the expression of mRNA and protein levels of the ErbB/HER receptor family as well as with a decrease in the expression of c-jun and c-fos oncogenes. BN/GRP antagonists RC-3940-II and RC-3095 could be considered for endocrine therapy of estrogen-independent breast cancers that express members of the ErbB/HER receptor family and the c-jun and c-fos oncogenes.

Inhibition of growth of ES-2 human ovarian cancers by bombesin antagonist RC-3095, and luteinizing hormone-releasing hormone antagonist Cetrorelix

We evaluated the effects of the bombesin/gastrin-releasing peptide (GRP) antagonist RC-3095, and the luteinizing hormone-releasing hormone (LH-RH) antagonist Cetrorelix, administered singly or in combination, on the growth of human ovarian carcinoma cell line ES-2, xenografted into nude mice. RC-3095 at a dose of 20 microg/day and Cetrorelix (100 microg/day), significantly reduced the volume of ES-2 tumors by 63.0% (P<0.01) and 38.0% (P<0.05) respectively, after 44 days of treatment, as compared with controls. The combination of RC-3095 with Cetrorelix inhibited the growth of ES-2 tumors by 66.2% (P<0.01). Serum levels of LH were significantly decreased in the groups treated with Cetrorelix alone and/or in combination with RC-3095. RT-PCR analyses revealed that the expression of mRNA for receptors of GRP (GRPR/BRS-1) and Neuromedin B (NMBR/BRS-2) on tumors was significantly decreased in all the treated groups. The expression of mRNA for epidermal growth factor receptors (EGFR) on tumors was reduced by 36.5 % (P<0.05) in the animals treated with Cetrorelix and by 72.5% (P<0.05) in the group that received the combination of RC-3095 with Cetrorelix. Our results indicate that the bombesin antagonist RC-3095 and the LH-RH antagonist Cetrorelix inhibit effectively the growth of ES-2 ovarian cancers in nude mice. These antagonists and their combination could be considered for the therapy of patients with ovarian cancer.