Effects of the novel vascular targeting agent MDS-11P on tumor vascularity and its antitumor activity

Vascular disrupting agents show selective effects on tumor established vasculature, and achieve encouraging results in both pre-clinical and clinical experiments. In the present study, we investigated the effects of a new CA4 derivative MDS-11 and its prodrug MDS-11P on vascular disrupting activity in vitro and in vivo. Surface plasmon resonance (SPR) and tubulin polymerization assay showed that MDS-11 interacted with tubulin directly and inhibited tubulin polymerization in a cell free system, and western blot assay further confirmed the action in the cellular level. MDS-11 was found to significantly disrupt the microtubulin skeleton in proliferating HUVECs than quiescent ones determined by confocal microscopy. Furthermore, MDS-11 was found to damage the HUVEC-formed tube quickly, but did not influence structures of microvessels from aortic ring possessing pericytes and smooth muscle cells until 3 h treatment. In A549 xenograft mice, immunohistochemistry staining of tumor sections revealed that a single dose of MDS-11P led to large areas of necrosis within tumor and reduced the number of tumor vessels, which was consolidated by perfused vascular volume assay. Pharmacokinetic studies of MDS-11P indicated that MDS-11P rapidly converted to the active form, MDS-11, and exhibited a much faster elimination in mice. The antitumor analysis using H22 and A549 mice xenograft models revealed that the growth inhibition rates of MDS-11P at 50 mg/kg (twice a day for three weeks) reached 59.4%, 60.5% respectively without obvious weight loss. Taken together, these results suggest that MDS-11 is a potential vascular disrupting agent for further development of antitumor drug.