Abstract 1275: Suppression of platelet aggregation and tumor metastasis by anti-podoplanin mAbs recognizing a novel CLEC-2 binding domain

Tumor-induced platelet aggregation promotes tumor growth and hematogenous metastasis by secreting growth factors from platelets, by avoiding immune system and shear stress, and by stimulating the formation of tumor emboli in microvasculature. Thus, tumor-platelet interaction could be a promising target for cancer therapy. We previously identified a sialoglycoprotein podoplanin, also known as Aggrus, as a key factor in tumor-induced platelet aggregation enhancing tumor metastasis. Podoplanin is expressed in various cancers and reported to be a candidate for cancer stem cell marker. Podoplanin-induced platelet aggregation depends on binding to its platelet receptor CLEC-2. Here, we report the discovery of a novel platelet aggregation-stimulating domain PLAG4 in human podoplanin critical for the binding to CLEC-2. Mutant analyses indicated that PLAG4 exhibits a predominant CLEC-2 binding ability and platelet-aggregating function when compared to the previously reported PLAG3. Moreover, mutation of both PLAG3 and PLAG4 domains could almost completely attenuate its CLEC-2 binding ability and its platelet-aggregation activity. To validate the inhibitory effect against PLAG4 domain, we established anti-PLAG4-neutralizing monoclonal antibodies (mAbs), PG4D1 and PG4D2. Both mAbs recognized PLAG4 domain and exhibited a high affinity to podoplanin. We confirmed those neutralizing ability against PLAG4-CLEC-2 interaction and platelet aggregation. Remarkably, the administration of each mAbs significantly suppressed pulmonary metastasis of podoplanin expressing tumor. Taken together, we suggest that PLAG4 is the novel CLEC-2 binding and platelet aggregation-stimulating domain on podoplanin and has a role in podoplanin-mediated metastasis formation. Blocking the podoplanin-CLEC-2 interaction targeting PLAG3 or PLAG4 would be a promising strategy for suppressing hematogenous metastasis. Citation Format: Takaya Sekiguchi, Ai Takemoto, Naoya Fujita. Suppression of platelet aggregation and tumor metastasis by anti-podoplanin mAbs recognizing a novel CLEC-2 binding domain. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1275.