Nude mice bearing xenografts of HT-29 human colon cancer cell line were treated for 4 weeks with a [d-Trp6] agonist of luteinizing hormone releasing hormone (LH-RH), somatostatin analogue (RC-160), and bombesin/gastrin releasing peptide antagonist (RC-3095). Some inhibitory effect of [d-Trp6] LH-RH microcapsules releasing 25 µg/day on tumor growth was observed that could be due to sex steroid deprivation, but the inhibition was not statistically significant. Microcapsules of RC-160, releasing 50 µg/day, significantly reduced tumor volume after 21 and 24 days of treatment, but at the end of the experiment the inhibition in tumor volume and weight was not significant. Bombesin/gastrin releasing peptide antagonist RC-3095, at a dose of 20 µg/day administered by daily s.c. injections or by continuous infusion using Alzet osmotic minipumps, had the greatest inhibitory effect on tumor growth. Tumor volume, percentage change in tumor volume, and tumor weights were significantly decreased in both groups treated with RC-3095. This is the first report on inhibition of human colon cancer growth in vivo by bombesin antagonists.
This work was supported by NIH Grant CA 40077 and the Medical Research Services of the Veterans Affairs, all to A. V. S.