Antiangiogenic ruthenium(ii) benzimidazole complexes, structure-based activation of distinct signaling pathways

Abstract

Antiangiogenic therapy is considered to be a promising strategy for the treatment of cancers. VEGF and its receptors are important angiogenic factors involved in tumor growth. In the present study, the new ruthenium(II) complexes containing 2,6-bis(benzimidazolyl)pyridine have been identified as potent antiangiogenic agents in vitro and in vivo, through activation of distinct antiangiogenic signaling pathways. Specifically, [Ru(bbp)(p-mpip)Cl]ClO₄ (complex 2, bbp = 2,6-bis(benzimidazolyl)pyridine; p-mpip = 2-(4-methylphenyl)imidazo[4,5-f]-1,10-phenanthroline) exhibited the highest antiangiogenic activity, as evidenced by significant suppression of neovessel formation in chick chorioallantoic membranes and blockage of the angiogenesis in a matrigel plugs assay, which are significantly higher than those of the most accepted anti-metastasis ruthenium-based drug NAMI-A. Generally, these kinds of complexes induced the G0/G1cell cycle by inhibiting the formation of a Cyclin D1/CDK4 complex and CDK2 activation, through up regulation of the expression levels of p15^INK4B, p21^Cip1 and p27^Kip1. Moreover, the complexes also triggered intracellular DNA damage, and thus activated the phosphorylation of ATM, ATR, CHK1, Histone and p53. The suppression of Akt and ERK1/2 pathways reinforced the cell cycle perturbation effects of the complexes. Interestingly, complex 2 displayed strong inhibition on the activation of VEGF and VEGFR-2 phosphorylation, which blocked the transmission of the mitogenic signal through Akt and ERK1/2 pathways, and thus enhanced cell cycle arrest. In contrast, we found that the most accepted anti-metastasis ruthenium based drug NAMI-A exerted lower antiangiogenic activity via activation of the DNA damage-mediated pathway, but showed no effects on VEGF and VEGFR-2 phosphorylation. Taken together, this study clearly demonstrates the distinct antiangiogenic mechanisms of metal complexes, and these kinds of complexes can be further developed as anti-vascularized drugs and as alternative agents of NAMI-A for the treatment of cancers.