IC50 values were calculated and ranged from 4.2 to 70 ��M, with most cell lines having values <11 ��M (Fig. 2A). To demonstrate that CRA could induce and vandetanib could inhibit RET phosphorylation, neuroblastoma tumor cells were treated with CRA for 48 hours, <a href="http://www.selleckchem.com/products/PLX-4032.html
">learn more followed by treatment with vandetanib for 90 minutes. Phosphorylated RET was dramatically increased after CRA treatment, and this phosphorylation could be blocked with subsequent treatment with vandetanib (Fig. 2B). We then examined the effects of vandetanib, CRA, and the combination on the histologic appearance of neuroblastoma cells in vitro. CRA exposure for 48 hours resulted in neural differentiation with neurite outgrowth in SK-N-SH, SK-N-AS, SMS-KCNR, and SH-SY5Y cell lines (Fig. 2D and data not shown). Treatment with vandetanib resulted in cell rounding and detachment from the cell surface within 8 hours, consistent with cell death (Fig. 2E). Treatment with the combination of vandetanib and CRA also resulted in a similar Ku-0059436
degree of cell rounding and detachment (Fig. 2F). To determine the effect of vandetanib, CRA, and the combination on the viability of neuroblastoma tumor cells, we treated the cells for 48 hours with either drug or the combination and then stained the cells with PI and analyzed the cells by flow cytometry for PI exclusion. CRA had no effect on the percentage of cells remaining viable, whereas vandetanib treatment resulted in a 75% reduction in cell viability (P < .01, Fig. 3A). The combination of vandetanib and CRA resulted in a significantly lower percentage of remaining viable cells, with only 14% PI-negative Pomalidomide
cells (P < .01 vs untreated, P < .05 vs vandetanib, Fig. 3A), compared with either drug alone. Although CRA treatment had no effect on neuroblastoma cell viability by PI staining, CRA did result in reduced cell number at the end of treatment and a lower percentage of cells in the S/G2/M phases of the cell cycle, demonstrating G0/G1 growth arrest (Fig. 3B and C). The combination of vandetanib and CRA also resulted in reduced total cell number and percentage of cycling cells (Fig. 3B and C). To determine whether the decreased viability after treatment with vandetanib plus CRA was the result of apoptosis, we performed assays to assess for caspase-3 cleavage and for DNA ladder formation. Caspase-3 cleavage, with characteristic 17- and 19-kDa products, was apparent in multiple neuroblastoma cell lines after treatment with vandetanib (Fig. 4A), confirming activation of the caspase-mediated apoptotic pathway. Furthermore, DNA ladders consistent with apoptosis were also clearly evident in tumor cells treated as early as 24 hours after treatment with either vandetanib or the combination of vandetanib and CRA, but only minimally present after 48 hours of CRA treatment (Fig. 4B).