BACKGROUND.
The growth of breast carcinoma is promoted by autocrine growth factors such as the bombesin (BN)-like peptides and epidermal growth factor (EGF). The stimulatory action of BN-like peptides can be blocked by the use of BN/gastrin-releasing peptide (GRP) antagonists.
METHODS.
The authors investigated the effects of synthetic BN/GRP antagonists RC-3095 and RC-3940-II on tumor growth and the expression of mRNA for EGF receptors and three BN receptor subtypes in MDA-MB-468 human breast carcinoma. Athymic nude mice with xenografts of MDA-MB-468 human breast carcinoma were injected subcutaneously for 6 weeks with RC-3940-II at doses of 20 or 40 g/day. In another study, the effects of RC-3940-II and RC-3095 were compared.
RESULTS.
RC-3940-II caused a significant and dose-dependent growth inhibition of MDA-MB-468 tumors in nude mice; therapy with either dose of RC-3940-II significantly (P Ͻ 0.01) reduced the mean final tumor volume and weight compared with controls. RC-3940-II induced a persistent regression of Ͼ 50% of all tumors. One of 3 tumors treated with 20 g of RC-3940-II and 3 of 5 tumors treated with 40 g were found to have regressed completely by the end of the study. When RC-3940-II and RC-3095 were compared at the dose of 20 g/day, both powerfully suppressed growth of MDA-MB-468 tumors, with RC-3940-II causing a complete regression of 2 tumors and RC-3095 a complete regression of 1 tumor. Receptor analyses of untreated MDA-MB-468 tumors revealed an overexpression of EGF receptors and two classes of binding sites for BN/GRP. mRNAs for receptors of GRP, neuromedin B, and BN receptor subtype-3 were detected by reverse transcriptase-polymerase chain reaction.
CONCLUSIONS.
A virtual arrest of growth or regression of MDA-MB-468 human breast carcinoma after therapy with RC-3940-II and RC-3095 indicates that these BN/GRP antagonists could provide a new treatment modality for breast tumors expressing BN and EGF receptors.