Effective treatment of metastatic MDA-MB-435 human estrogen-independent breast carcinomas with a targeted cytotoxic analogue of luteinizing hormone-releasing hormone AN-207

A highly potent derivative of doxorubicin, 2-pyrrolinod-oxorubicin (AN-201) , was linked to [D-Lys(6)]luteinizing hormone-releasing hormone (LH-RH) to form a cytotoxic analogue, AN-207, that can be targeted to LH-RT-I receptor s, The effects of AN-207 were investigated in MDA-MB-435 human estrogen-ind ependent breast carcinomas, which express LB-RH receptors, In experiment I, nude mice bearing orthotopically implanted tumors received a single i.v. i njection of AN-207, AN-201, or the carrier at 250 nmol/kg, Five weeks after administration of AN-207, tumor volume was significantly decreased by 66% (P < 0.001) and tumor burden by 71% (P < 0.05) as compared with controls, b ut no significant effects occurred in other groups. Six of eight (75%) cont rol animals and 37.5% of mice treated with AN-201 developed metastases in t he lymph nodes, whereas no lymphatic spread was found in any of the mice th at received injections of AN-207, The antitumor effect of AN-207 could be p artially blocked by pretreatment of the tumor-bearing mice with high doses of agonist [D-Trp(6)]LH-RH,which suggests that AN-207 acts on LH-RH recepto rs on tumors. The mortality due to toxicity was 25% in the group receiving AN-201 and 12.5% in the AN-207-treated group. Radioligand binding assays re vealed the presence of high-affinity binding sites for LH-RH on tumor membr anes, and mRNA for LH-RH receptors was demonstrated by reverse transcriptio n-PCR, In experiment 2, two i.v. injections of AN-207 or AN-201 at 150 nmol /kg were given on days 0 and 28 to mice bearing orthotopic xenografts of MD A-MB-435, The outcome of the treatment was similar to that observed in expe riment 1, but without any toxicity-related deaths, Tumor growth inhibition and prevention of metastatic disease suggest that cytotoxic LH-RH analogue AN-207 could be considered for the treatment of human estrogen-independent breast cancers expressing receptors for LH-RH.