Table 1 Expression of the 5 multidrug resistance proteins in the tumor cells Multidrug resistance protein n – + ++ +++ Strongly positive rate (%) P-gp 30 4 18 8 0 26.67 Topo II 30 13 10 7 0 23.33 GST-π 30 10 15 5 0 16.67 MRP 30 28 1 1 0 3.33 LRP 30 26 3 1 0 3.33 In tumor cells, the strongly positive rate of P-gp, Topo II, GST-π, LRP and MRP were 26.67%,23.33%,16.67%,3.33% and 3.33%, respectively.

This difference was statistically significant (Rank sum test, ABT-263 mouse P < 0.05) However, in our study, the expression of P-gp is weak in tumor cells but strongly positive in capillary vessels (Fig 1a, b and Fig 1c). Low positive expression of LRP, MRP, GST-π and Topo II was observed in capillary vessels (Tab 2). In the normal brain tissues, the expression of P-gp was strongly positive in the tissues surrounding the cerebral vessels, but no positive expression was observed in capillary vessels. The BBB contains capillary endothelial 3-Methyladenine mw cells, basement membrane and the IGF-1R inhibitor end-feet of astrocytes. The accurate structure is difficult to distinguish using ordinary light microscopy. In order to confirm the expression of P-gp in the end-feet of astrocytes, the S-100 protein was used to locate the

end-feet of astrocytes by immunohistochemistry. The expression of the S-100 protein was positive in the capillary walls (Fig 1d). These findings suggest P-gp expression in the microvasculature is found at both the endothelium as well at the astrocyte end-feet at the microvasculature. In addition, the same results were observed

in the interstitial cells. Figure 1 The expression of P-gp and S-100 in brain tumors (astrocytoma),(×400). (a, b, c) The expression of P-gp is weak in tumor cells (red arrow), but strongly positive in capillary vessels (black arrow). (c) The expression of P-gp in the interstitial cells was related to the distance from the capillary wall. The expression of P-gp was stronger the nearer the P-type ATPase cell was to the capillary wall (green arrow). (d) The expression of S-100 in brain tumors. Our study shows the expression of P-gp and S-100 are co- localized in the capillary endothelial cells and interstitial cells of tumor tissues. These findings suggest P-gp expression at the microvasculature is found at both the endothelium as well at the astrocyte end-feet at the microvasculature. Table 2 Expression of the 5 multidrug resistance proteins in the capillary walls of tumor tissues Multidrug resistance protein n – + ++ +++ Strongly positive rate (%) P-gp 30 3 6 12 9 70.00 Topo II 30 23 5 2 0 6.67 GST-π 30 26 3 1 0 3.33 MRP 30 27 2 1 0 3.33 LRP 30 27 3 0 0 0.00 The expression of P-gp is strongly positive in capillary vessels. Low positive expression of LRP, MRP, GST-π and Topo II was observed in capillary vessels. This difference was statistically significant (Rank sum test, P < 0.01) Otherwise, we find the expression of resistance proteins in interstitial cells are similar to the tumor cells.