A targeted cytotoxic somatostatin (SST) analogue, AN-238, inhibits the growth of H-69 small-cell lung carcinoma (SCLC) and H-157 non-SCLC in nude mice

Recently, we developed a cytotoxic analogue of somatostatin (SST), AN-238, in which the SST carrier peptide RC-121 was linked to 2-pyrrolinodoxorubicin (2-pyrrolino-DOX) (AN-201), a potent derivative of doxorubicin. AN-238 can be targeted to SST receptors (SSTRs) on tumours. In the present study, we evaluated the effects of AN-238 on the growth of H-69 small-cell lung carcinoma (SCLC) and H-157 non-SCLC xenografted into nude mice. High affinity binding sites for SST are present in H-69 SCLC and were now detected in H-157 non-SCLC xenografts, but not in H-157 cells. A strong expression of the human SSTR subtype 2 (hSSTR-2) and a weaker expression of subtype 5 (hSSTR-5) was found in H-69 SCLC cells, but not in H-157 non-SCLC cells. However, a strong expression of mRNA for mouse (m)SSTR-2 could be detected in H-157 xenografts. AN-238 effectively inhibited the growth of H-69 SCLC tumours in nude mice. Twenty-six days after a single injection of AN-238 at 200 nmol/kg, the volume of H-69 tumours was decreased by approximately 55% (P < 0.05) compared with the controls, while AN-201 at the same dose was highly toxic and produced only a minor tumour inhibition. To evaluate the potency of multiple doses of AN-238, nude mice bearing H-69 SCLC received three injections of AN-238 at 150 nmol/kg on days 1, 12 and 28. In the period of 42 days after the first injection, the growth rate of H-69 tumours was approximately 50% lower than that of controls. In nude mice bearing H-157 non-SCLC tumours, a single i.v. administration of AN-238 at 200 nmol/kg inhibited tumour volume by 91% after 28 days (P < 0.01 compared with controls). AN-201 was toxic and ineffective at the same dose. Two injections of AN-238 at 150 nmol/kg given on days 1 and 18 produced 83% inhibition of H-157 tumour growth (P < 0.01 versus controls). AN-238 given as a single dose of 200 nmol/kg induced necrosis, while two injections of 150 nmol/kg induced apoptosis in the tumour tissue. Our results indicate that targeted cytotoxic SST analogue AN-238 could be considered for therapy of both SCLC and non-SCLC.