Blocking angiogenesis is an effective approach to cancer therapy. Proliferation of endothelial cells (EC) serves as the basis of angiogenesis. In particular, tumor angiogenesis depends on the paracrine network in which a variety of angiogenic growth factors secreted by tumor cells stimulate endothelial cell proliferation. In the present study, the effects of lidamycin (LDM, C-1027), an antitumor antibiotic composed of an enediyne chromophore and an apoprotein of 110 amino acid residues, on tumor angiogenesis and the growth of prostatic carcinoma xenograft were investigated. Results: (1) Determined by Western blot analysis, LDM down-regulated VEGF expression and the signaling pathway of ERK in EC and tumor cells; by comparison, no similar effect was found by treatment with mitomycin and pingyangmycin. This effect was mainly executed by the enediyne chromophore. (2) By MTT assay, LDM showed extremely potent efficacy to suppress the proliferation of EC and tumor cells. The IC50 values for human umbilical vein endothelial cells (HUVEC), human cord blood endothelial progenitor cells (EPC), human prostatic carcinoma DU 145 cells, and human hepatoma HepG2 cells were 3.88×10-12 M, 7.63×10-12 M, 2.06×10-11 M, and 7.74×10-11 M, respectively. Notably, the chemosensitivity of EC was higher than that of tumor cells. (3) LDM at 0.1 nM significantly induced apoptosis in EC. LDM blocked tube formation of EC, and significantly inhibited the migration of EC and tumor cells, as examined by Wound Healing Assay, Transwell assay. By zymography, LDM inhibited the secretion of MMP-2 and MMP-9. (4) LDM activated the signaling pathway of apoptosis in both EC and tumor cells, including increase of p53 level, inhibition of Bcl-2 and RB expression, and activation of caspase-9 and caspase-3. (5) Gene chip assay showed that LDM caused changes in a number of genes of HUVEC that are related to apoptosis, cell cycle, and angiogenesis. (6) A monoclonal antibody directed against LDM was prepared. As observed with immunofluorescence assay, LDM was found in the cytoplasm of cells but not in their nucleus. (6) Determined in co-culture condition, marrow stem cells and fibroblasts cells were less sensitive to LDM than EC and tumor cells. (7) LDM at the dosage of 0.02 mg/kg and 0.04 mg/kg (iv, weekly, x 2) suppressed the growth of human prostatic carcinoma DU145 xenografts in nude mice by 53.3% and 76.5% (P < 0.01), respectively. Examined with frozen sections, LDM significantly reduced VEGF level and microvessel density in the tumor. Results suggest that LDM shows highly potent activity in blocking paracrine network related tumor angiogenesis and suppressing EC proliferation. LDM might be potentially useful in treatment of prostatic carcinoma.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA