A single in vivo administration of bombesin antagonist RC-3095 reduces the levels and mRNA expression of epidermal growth factor receptors in MXT mouse mammary cancers

Abstract

Epidermal growth factor (EGF) and its receptors (EGFR) play important roles in tumorigenesis. In various experimental cancers, treatment with antagonists of bombesin͞ gastrin-releasing peptide (BN͞GRP) produces a reduction in EGFRs, concomitant to inhibition of tumor growth. To investigate the mechanisms involved, we monitored concentrations of BN͞GRP antagonist RC-3095 in serum of mice, rats, and hamsters given a single subcutaneous or intravenous injection of this analog. In parallel studies, we measured levels and mRNA expression of EGFRs in estrogen-dependent and independent MXT mouse mammary cancers, following a single subcutaneous administration of RC-3095 to tumor-bearing mice. Peak values of RC-3095 in serum were detected 2 min after intravenous or 15 min after subcutaneous injection. The levels of RC-3095 declined rapidly and became undetectable after 3-5 hr. In the estrogendependent MXT tumors, the concentration of EGF receptors was reduced by about 60% 6 hr following injection and returned to original level after 24 hr. Levels of mRNA for EGFR fell parallel with the receptor number and were nearly normal after 24 hr. In the hormone-independent MXT cancers, the number of EGFRs decreased progressively, becoming undetectable 6 hr after injection of RC-3095, and returned to normal values at 24 hr, but EGFR mRNA levels remained lower for 48 hr. Thus, in spite of rapid elimination from serum, BN͞GRP antagonist RC-3095 can induce a prolonged decrease in levels and mRNA expression of EGFRs. These findings may explain how single daily injections of BN͞GRP antagonists can maintain tumor growth inhibition.

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

“…In accord with our previous findings in MDA-MB-231 and MDA-MB-468 human mammary tumors and MXT mouse mammary cancers (11,12,14), the treatment with our BN͞GRP antagonists RC-3095 and 3940-II results in a marked reduction in growth of MDA-MB-435 human mammary cancers in nude mice. RC-3940-II at doses of 10 g͞day proved to be more powerful than RC-3095 at 20 g͞day.…”

“…Accordingly, in addition to decreasing the levels of EGFR, as it was reported in previous studies (11)(12)(13)(14), BN͞GRP antagonists also induce down-regulation of other members of the ErbB͞ HER family. The expression of mRNA for EGFR and HER-2, -3, and -4 in general was well correlated with receptor protein levels, although Western blot analyses revealed a somewhat greater decrease in HER-2 and HER-3 protein levels after treatment with BN͞GRP antagonists.…”

“…BN͞GRP antagonists RC-3095 and RC-3940-II, synthesized in our laboratory (9), inhibit growth of various experimental tumors including small cell lung carcinoma (SCLC) and breast cancers xenografted into nude mice (2,8,10,11). Tumor growth inhibition was invariably associated with a significant down-regulation of EGFRs in tumors (11)(12)(13)(14). In previous studies, we evaluated the effects of BN͞GRP antagonists RC-3095 and RC-3940-II on MDA-MB-231 and MDA-MB-468 estrogen-independent human breast cancers (11,14).…”

Mitogenic effects of gastrin-releasing peptide in head and neck squamous cancer cells are mediated by activation of the epidermal growth factor receptor

“…Indirect evidence suggests the potential involvement of EGFR in GRP or BLP signaling. In several in vivo tumor models (including SCLC and estrogen-dependent and estrogen-independent MTX mouse mammary cancers), treatment with a synthetic bombesin/GRP antagonist, RC-3095, resulted in the downregulation of EGFR mRNA expression levels (Pinski et al, 1994;Halmos and Schally, 1997;Szepeshazi et al, 1997;Koppan et al, 1998). Moreover, Liebow et al showed that bombesin and EGF seemed to promote phosphorylation of similar substrates (Liebow et al, 1994).…”

Growth inhibition of non-small-cell lung carcinoma by BN/GRP antagonist is linked with suppression of K-Ras, COX-2, and pAkt

“…BN/GRP antagonists synthesized in our laboratory have already been shown to be effective against a wide range of solid tumors, including SCLC; breast, ovarian, and prostatic cancers; renal cell carcinomas; and brain tumors (2, 7, 21) Although pseudononapeptide BN/GRP antagonists are rapidly eliminated from the blood stream after a single administration, EGF-Rs remain down-regulated for many hours (2,22). This finding explains how daily single injections of the antagonists can maintain tumor growth inhibition (2,22). An antiproliferative effect of BN/GRP antagonists against NSCLC has not been demonstrated previously (2, 7).…”