SOMATOSTATIN ANALOG RC-160 AND LH-RH ANTAGONIST SB-75 INHIBIT GROWTH OF MIA PACA-2 HUMAN PANCREATIC-CANCER XENOGRAFTS IN NUDE-MICE

Nude mice bearing xenografts of the MIA PaCa-2 human pancreatic cancer cell line were treated with sustained-release formulations (microcapsules) of luteinizing hormone releasing hormone (LH-RH) agonist [D-Trp6]-LH-RH, somatostatin analogue RC-160 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2), or combination of both analogues. Other groups of mice received daily subcutaneous injections of LH-RH antagonist SB-75 [Ac-D-Nal(2)1,D-Phe(4Cl)2,D-Pal(3)3.D-Cit6,D-Ala10-LH-RH] or bombesin antagonist RC-3095. At necropsy, in mice given microcapsules releasing 25 mug/day Of [D-Trp6]-LH-RH, tumor weight and volume were decreased, but not significantly, as compared with control mice. Microcapsules of RC-160, releasing 25 mug/day, significantly reduced tumor volume, percentage change in tumor volume, and tumor weight. Combination of RC-160 and [D-Trp6]-LH-RH inhibited tumor growth to a somewhat greater extent than RC-160 alone. Bombesin antagonist RC-3095, at a dose of 25 mug/day, did not influence the growth of tumors. In mice receiving 100 mug/day of antagonist SB-75, there was a significant decrease in tumor weight and volume and a significant reduction in the weight of ovaries and uteri. Specific binding of [I-125]RC-160 and [I-125][D-Trp6]-LH-RH, but not [I-125]Tyr4-bombesin, was found on MIA PaCa-2 cells in culture. [D-Trp6]-LH-RH, SB-75, and RC-160 inhibited the growth of MIA PaCa-2 cells in vitro. Neither bombesin nor RC-3095 influenced the growth of MIA PaCa-2 cells in cultures. The results indicate that the LH-RH antagonist SB-75 could be tried for treatment of pancreatic cancer. Our findings confirm the efficacy of somatostatin analogue RC-160 in inhibiting the growth of pancreatic cancers and suggest that the combination of RC-160 and agonist [D-Trp6]-LH-RH might possibly increase the therapeutic response.