Targeted cytotoxic analogue of bombesin/gastrin-releasing peptide inhibits the growth of H-69 human small-cell lung carcinoma in nude mice.

Recently, we developed a powerful cytotoxic analogue of bombesin AN-215, in which the bombesin-like carrier peptide Gln-Trp-Ala-Val-Gly-His-Leu-psi(CH2-NH)-Leu-NH2 (RC-3094) is conjugated to a potent derivative of doxorubicin, 2-pyrrolinodoxorubicin (AN-201). Small-cell lung carcinomas (SCLCs) are known to express high levels of bombesin receptors. We evaluated whether these receptors could be used for targeting cytotoxic bombesin analogue to H-69 SCLC cells. H-69 cells were xenografted into male nude mice, which then received an intravenous injection of AN-215, cytotoxic radical AN-201, the carrier peptide RC-3094 alone or unconjugated mixture of RC-3094 and AN-201. The levels of mRNA for bombesin receptor subtypes were evaluated by reverse transcription-polymerase chain reaction. In vitro, both the analogue AN-215 and the radical AN-201 showed strong antiproliferative effects on H-69 cells, AN-215 requiring more time to exert its action at 10(-8) M concentration than AN-201. In vivo, the growth of H-69 SCLC tumours was significantly inhibited by the treatment with 200 nmol kg(-1) of AN-215, while equimolar doses of the cytotoxic radical AN-201 or the mixture of AN-201 and the carrier peptide were toxic and produced only a minor tumour inhibition as compared with control groups. mRNA for bombesin receptor subtypes 2 (BRS-2) and 3 (BRS-3) was detected in H-69 tumours. The mRNA levels for BRS-3, but not for BRS-2, were lower in the AN-215-treated tumours as compared with controls. Our results demonstrate that the cytotoxic bombesin analogue AN-215 could be considered for targeted therapy of tumours, such as SCLC, that express bombesin receptors.