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Inhibition of Metastatic Renal Cell Carcinomas Expressing Somatostatin Receptors by a Targeted Cytotoxic Analogue of Somatostatin AN-238¹

Endocrine, Polypeptide and Cancer Institute, Veterans Administration Medical Center, New Orleans, Louisiana 70112-1262 [A. P., A. V. S., A. N., H. K., F. H., G. H.], and Section of Experimental Medicine, Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112-2699 [A. P., A. V. S., A. N., H. K., G. H.]

The effectiveness of chemotherapy targeted to somatostatin (SST) receptors based on cytotoxic SST analogue AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201) linked to SST carrier octapeptide, was investigated in human renal cell carcinomas (RCCs). SST receptors, which showed high-affinity binding for AN-238, were found in the SW-839 RCC line with sst_2A subtype and in the 786-0 RCC line, which expressed the sst₅ subtype. CAKI-1 RCC, which does not express sst_2A or sst₅, was used as a negative control for testing the specificity of SST receptor targeting. Using microsatellite analysis, AN-238 was shown to selectively inhibit the proliferation of 786-0 line, but not the CAKI-1 RCC line in vitro. The effects of three i.v. injections of 150 nmol/kg of AN-238 or AN-201, given on days 1, 8, and 21, were evaluated in groups of nude mice bearing s.c. xenografts of SW-839 and 786-0 RCC. After 5 weeks, the volumes of SW-839 and 786-0 RCC tumors were decreased by 67.2 (P < 0.05) and 78.3% (P < 0.01), respectively, whereas AN-201 had no significant effect on tumor growth. The inhibition of SST receptor-negative CAKI-1 tumors by AN-238 was only marginal. To investigate the efficacy of SST receptor-targeted chemotherapy in metastatic RCC, three i.v. injections of AN-238 or AN-201 at 150 nmol/kg were given at biweekly intervals to nude mice implanted with 786-0 tumors under the renal capsule. After 6 weeks, the weight of orthotopic tumors treated with AN-238 (55.3 ± 44.3 mg) was significantly lower (87% reduction; P < 0.001) than that in the control group (414.2 ± 41.0 mg) or in animals given AN-201 (270.2 ± 60.3 mg; P < 0.05). Five of six animals (83%), both in the control and the AN-201 group, developed metastases to lymph nodes, but only one of seven mice (14%) given AN-238 showed lymphatic spread. Lung metastases were found in 83% of controls and 50% of AN-201 treated animals, but none occurred in mice treated with AN-238. This study demonstrates that targeted cytotoxic SST analogue AN-238 provides an effective therapy for chemoresistant neoplasms such as RCC. Because most clinical RCCs express SST receptors, this treatment modality might be beneficial to patients with metastatic disease.

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