Inhibition of Tumor Angiogenesis by Phloroglucinol Figure 3. Effect of phloroglucinol on tubule-like structure formation of EPCs. (A) Representative tubular network structure of VEGF- stimulated outgrowths of ECs treated with or without phloroglucinol. Bevacizumab was used as a positive control. Bar: 500 mm. (B, C) Tube branches and total tube length were quantified using MacBiophotonics Images J software. Bar graph represents the number of intact loops in the capillary networks. Graph represents the length of tubes in the capillary networks (*P,0.05, **P,0.01). doi:10.1371/journal.pone.0033618.g003 Further studies are needed to investigate if the mechanical cascade underlying the phloroglucinol-dependent inhibition of tumor-mediated EPC mobilization during tumor angiogenesis can provide clues regarding cancer spread and metastatic growth since blockage of the process by phloroglucinol may be a significant target for therapeutic treatments [34,35]. Interestingly, we recently observed that the effect of phloroglucinol on EPC mobilization seems to involve in altered VEGF dependent actin reorganization, not decreased VEGF levels in blood by phloroglucinol, suggesting that phloroglucinol might affect the bioactivities of EPCs including cytoskeletal changes (Figure S3). In particular, tumor cell- associated proteinases such as matrix metalloproteinases MMP2 and MMP9 [36,37,38] might play a role in the decline of mechanical barriers represented by extracellular matrices and may be closely related to the incorporation process and importance of EPCs during tumor angiogenesis. PLoS ONE | www.plosone.org 5 April 2012 | Volume 7 | Issue 4 | e33618