冨澤 聡史

PURPOSE: Semaphorins, axon guidance cues in neuronal network formation, have been implicated in cancer progression. We previously identified semaphorin 3 C (SEMA3C) as a secreted protein overexpressed in pancreatic ductal adenocarcinoma (PDAC). We, therefore, hypothesized that SEMA3C supports PDAC progression. In this study, we aimed to investigate the clinical features of SEMA3C, especially its association with chemo-resistance and peritoneal dissemination. METHODS: In resected PDAC tissues, we assessed the relationship between SEMA3C expression and clinicopathological features by immunohistochemistry. In vitro studies, we have shown invasion assay, pancreatosphere formation assay, colony formation assay, cytotoxicity assay, and activation of SEMA3C downstream targets (c-Met, Akt, mTOR). In vivo, we performed a preclinical trial to confirm the efficacy of SEMA3C shRNA knockdown and Gemcitabine and nab-Paclitaxel (GnP) in an orthotopic transplantation mouse model and in peritoneal dissemination mouse model. RESULTS: In resected PDAC tissues, SEMA3C expression correlated with invasion and peritoneal dissemination after surgery. SEMA3C promoted cell invasion, self-renewal, and colony formation in vitro. We further demonstrated that SEMA3C knockdown increased Gem-induced cytotoxicity by suppressing the activation of the Akt/mTOR pathway via the c-Met receptor. Combination therapy with SEMA3C knockdown and GnP reduced tumor growth and peritoneal dissemination. CONCLUSIONS: SEMA3C enhances peritoneal dissemination by regulating putative cancer stemness and Gem resistance and activates phosphorylation of the Akt/mTOR pathway via c-Met. Our findings provide a new avenue for therapeutic strategies in regulating peritoneal dissemination during PDAC progression.

Glycoproteins produced by tumor cells are involved in cancer progression, metastasis, and the immune response, and serve as possible therapeutic targets. Considering the dismal outcomes of pancreatic ductal adenocarcinoma (PDAC) due to its unique tumor microenvironment, which is characterized by low antitumor T-cell infiltration, we hypothesized that tumor-derived glycoproteins may serve as regulating the tumor microenvironment. We used glycoproteomics with tandem mass tag labeling to investigate the culture media of three human PDAC cell lines, and attempted to identify the key secreted proteins from PDAC cells. Among the identified glycoproteins, prosaposin (PSAP) was investigated for its functional contribution to PDAC progression. PSAP is highly expressed in various PDAC cell lines; however, knockdown of intrinsic PSAP expression did not affect the proliferation and migration capacities. Based on the immunohistochemistry of resected human PDAC tissues, high PSAP expression was associated with poor prognosis in patients with PDAC. Notably, tumors with high PSAP expression showed significantly lower CD8+ T-cell infiltration than those with low PSAP expression. Furthermore, PSAP stimulation decreased the proportion of CD8+ T cells in peripheral blood monocytes. Finally, in an orthotopic transplantation model, the number of CD8+ T cells in the PSAP shRNA groups was significantly increased, resulting in a decreased tumor volume compared with that in the control shRNA group. PSAP suppresses CD8+ T-cell infiltration, leading to the promotion of PDAC progression. However, further studies are warranted to determine whether this study contributes to the development of a novel immunomodulating therapy for PDAC.