However, there was only slightly reduction of MDSCs, but no statistical significance was observed in both sunitinib and rapamycin groups. Compared with other groups, combination treatment substantially reduced the MDSCs, and there was less than 30% MDSCs in the spleen ( Figure 3, A and B). Together, the combinational strategy significantly decreased MDSC proportion in the spleen. To determine whether the combined therapy reduced the cancer metastasis, we examined the metastasis macroscopically and microscopically. Unexpectedly, though the combination of sunitinib and rapamycin retarded the tumor growth,

it also promoted lung metastasis. Selleckchem VE822 The enhanced metastasis was assessed on the day-21 of post-therapy by gross evaluation (Figure 4A) and further confirmed by the microscopical examination ( Figure 4B). There was apparent lung metastasis in both rapamycin monotherapy and the combination group more lung metastasis was observed in the combination group ( Figure 4C). These data indicated that rapamycin could induce metastasis in cancer therapy and make it more severe once combined selleck with antiangiogenic therapy. To investigate the possible mechanism of metastasis induced by the combination therapy, immunohistochemistry

of pimonidazole (Hypoxyprobe™-1, HPI Inc., Burlington, MA) adducts for hypoxic cells was evaluated in tumor sections. The results showed that significantly larger hypoxic areas exist in the tumors after antiangiogenic therapy with sunitinib or rapamycin compared with the control group (Figure 5). Versican secreted

by MDSCs has been shown to accelerate lung metastasis. To investigate whether versican participates in rapamycin and sunitnib–induced lung metastasis, we examined the versican levels in the lungs with reverse transcription–PCR (RT-PCR) Thymidylate synthase assay. Rapamycin markedly upregulated versican expression in the lungs and even more once combined with sunitinib (Figure 6A). We then assessed whether the increased versican was due to increased MDSCs in the lungs. Unexpectedly, MDSCs were decreased in the combination group ( Figure 6B), which suggested other sources of versican. Next, we evaluated the immunosuppressive molecules and cytokines in the lungs of tumor-bearing mouse. Arginase 1, IDO, and IL-6 expression in the lungs was increased after treatment with rapamycin alone or together with sunitinib (Figure 6C). Sunitinib alone was not sufficient to induce arginase 1, IDO, and IL-6, in which it induced more TGF-β and IL-10, two other immunosuppressive cytokines. Rapamycin also significantly increased TGF-β and IL-10 expression in the lungs, whereas the combination of two drugs only induced TGF-β expression but not IL-10 ( Figure 6C). We further examined those molecules in the tumor tissues. Both sunitinib and rapamycin could decrease IL-10 in the tumor microenvironment but not arginase 1 (Figure 6D).