Tumor Vascular Maturation and Improved Drug Delivery Induced by Methylselenocysteine Leads to Therapeutic Synergy with Anticancer Drugs

Purpose: Our previously reported therapeutic synergy between naturally occurring seleno-amino acid methylselenocysteine (MSC) and anticancer drugs could not be shown in vitro . Studies were carried out to investigate the potential role of MSC-induced tumor vascular maturation and increased drug delivery in the observed therapeutic synergy in vivo . Experimental Design: Mice bearing s.c. FaDu human head and neck squamous cell carcinoma xenografts were treated with MSC (0.2 mg/d × 14 days orally). Changes in microvessel density (CD31), vascular maturation (CD31/α-smooth muscle actin), perfusion (Hoechst 33342/DiOC 7 ), and permeability (dynamic contrast-enhanced magnetic resonance imaging) were determined at the end of the 14-day treatment period. Additionally, the effect of MSC on drug delivery was investigated by determining intratumoral concentration of doxorubicin using high-performance liquid chromatography and fluorescence microscopy. Results: Double immunostaining of tumor sections revealed a marked reduction (∼40%) in microvessel density accompanying tumor growth inhibition following MSC treatment along with a concomitant increase in the vascular maturation index (∼30% > control) indicative of increased pericyte coverage of microvessels. Hoechst 33342/DiOC 7 staining showed improved vessel functionality, and dynamic contrast-enhanced magnetic resonance imaging using the intravascular contrast agent, albumin-GdDTPA, revealed a significant reduction in vascular permeability following MSC treatment. Consistent with these observations, a 4-fold increase in intratumoral doxorubicin levels was observed with MSC pretreatment compared with administration of doxorubicin alone. Conclusion: These results show, for the first time, the antiangiogenic effects of MSC results in tumor growth inhibition, vascular maturation in vivo , and enhanced anticancer drug delivery that are associated with the observed therapeutic synergy in vivo .