HIF1A and neoplasm: To examine whether the effect of tanshinone-1 on VEGF is correlated with its effect on p-705-Stat3 and/or HIF-1α protein in tumor cells, we used specific siRNA against hif-1α (siHIF-1α-1 and -2), stat3 (siStat3-1 and -2) or both to downregulate the expression of the corresponding genes in MCF-7 cells (Figure 5C).