Inhibition of prostate carcinoma establishment and metastatic growth in mice by an antiangiogenin monoclonal antibody.

A neutralizing monoclonal antibody (MAb) 26-2F to human angiogenin, a potent inducer of neovascularization, has been shown previously to prevent or delay the appearance of angiogenin-secreting human colon, fibrosarcoma and lung tumor cell xenografts implanted subcutaneously (s.c.) into athymic mice. In an analogous model system, we report here that the antibody also prevents the establishment of PC-3 androgen-independent human prostate cancer tumors in, on average, 40% of treated mice (p < 0.0001, survivor analysis). Intriguingly, combining MAb 26-2F together with cisplatin and suramin, 2 therapeutic agents that together showed little antitumor activity in the aforementioned model, resulted in an even greater degree of protection (71% protected, p = 0.009 compared to antibody treatment alone). This protective effect persisted several weeks after cessation of treatment. Additionally, prophylactic systemic administration of MAb 26-2F dramatically reduced by 50% the formation of spontaneous regional metastasis originating from primary growth in the prostate gland of PC-3M cells, highly metastatic variants of PC-3. Protection from metastasis was still significant when treatment with MAb 26-2F was delayed until after the primary tumor was well established. The antibody is not directly cytotoxic to either cell type, both of which secrete angiogenin in vitro and when growing as tumors in vivo, but changes the pattern of vascularity in primary tumors growing orthotopically. These findings, together with the observation that angiogenin protein and mRNA are apparently overexpressed in cancerous vs. normal human prostate tissues, demonstrate that angiogenin antagonism represents a promising new approach for preventing progression and metastasis of clinical prostate cancer.