Mitsunobu R. Kano

Ligand-mediated drug delivery systems have enormous potential for improving the efficacy of cancer treatment. In particular, Arg-Gly-Asp peptides are promising ligand molecules for targeting αvβ3/αvβ5 integrins, which are overexpressed in angiogenic sites and tumors, such as intractable human glioblastoma (U87MG). We here achieved highly efficient drug delivery to U87MG tumors by using a platinum anticancer drug-incorporating polymeric micelle (PM) with cyclic Arg-Gly-Asp (cRGD) ligand molecules. Intravital confocal laser scanning microscopy revealed that the cRGD-linked polymeric micelles (cRGD/m) accumulated rapidly and had high permeability from vessels into the tumor parenchyma compared with the PM having nontargeted ligand, "cyclic-Arg-Ala-Asp" (cRAD). As both cRGD/m- and cRAD-linked polymeric micelles have similar characteristics, including their size, surface charge, and the amount of incorporated drugs, it is likely that the selective and accelerated accumulation of cRGD/m into tumors occurred via an active internalization pathway, possibly transcytosis, thereby producing significant antitumor effects in an orthotopic mouse model of U87MG human glioblastoma.

Transforming growth factor (TGF)-beta plays a pivotal role in regulation of progression of cancer through effects on tumor microenvironment as well as on cancer cells. TGF-beta inhibitors have recently been shown to prevent the growth and metastasis of certain cancers. However, there may be adverse effects caused by TGF-beta signaling inhibition, including the induction of cancers by the repression of TGF-beta-mediated growth inhibition. Here, we present an application of a short-acting, small-molecule TGF-beta type I receptor (TbetaR-I) inhibitor at a low dose in treating several experimental intractable solid tumors, including pancreatic adenocarcinoma and diffuse-type gastric cancer, characterized by hypovascularity and thick fibrosis in tumor microenvironments. Low-dose TbetaR-I inhibitor altered neither TGF-beta signaling in cancer cells nor the amount of fibrotic components. However, it decreased pericyte coverage of the endothelium without reducing endothelial area specifically in tumor neovasculature and promoted accumulation of macromolecules, including anticancer nanocarriers, in the tumors. Compared with the absence of TbetaR-I inhibitor, anticancer nanocarriers exhibited potent growth-inhibitory effects on these cancers in the presence of TbetaR-I inhibitor. The use of TbetaR-I inhibitor combined with nanocarriers may thus be of significant clinical and practical importance in treating intractable solid cancers.

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that regulates cell growth, differentiation, and apoptosis of various types of cells. Autophagy is emerging as a critical response of normal and cancer cells to environmental changes, but the relationship between TGF-beta signaling and autophagy has been poorly understood. Here, we showed that TGF-beta activates autophagy in human hepatocellular carcinoma cell lines. TGF-beta induced accumulation of autophagosomes and conversion of microtubule-associated protein 1 light chain 3 and enhanced the degradation rate of long-lived proteins. TGF-beta increased the mRNA expression levels of BECLIN1, ATG5, ATG7, and death-associated protein kinase (DAPK). Knockdown of Smad2/3, Smad4, or DAPK, or inhibition of c-Jun NH(2)-terminal kinase, attenuated TGF-beta-induced autophagy, indicating the involvement of both Smad and non-Smad pathway(s). TGF-beta activated autophagy earlier than execution of apoptosis (6-12 versus 48 h), and reduction of autophagy genes by small interfering RNA attenuated TGF-beta-mediated growth inhibition and induction of proapoptotic genes Bim and Bmf, suggesting the contribution of autophagy pathway to the growth-inhibitory effect of TGF-beta. Additionally, TGF-beta also induced autophagy in some mammary carcinoma cells, including MDA-MB-231 cells. These findings show that TGF-beta signaling pathway activates autophagy in certain human cancer cells and that induction of autophagy is a novel aspect of biological functions of TGF-beta.