Abstract
Almost all highly metastatic tumor cells possess high platelet aggregating abilities, thereby form large tumor cell-platelet aggregates in the microvasculature. Embolization of tumor cells in the microvasculature is considered to be the first step in metastasis to distant organs. We previously identified the platelet aggregation-inducing factor expressed on the surfaces of highly metastatic tumor cells and named as Aggrus. Aggrus was observed to be identical to the marker protein podoplanin (alternative names, T1α, OTS-8, and others). Aggrus is frequently overexpressed in several types of tumors and enhances platelet aggregation by interacting with the platelet receptor C-type lectin-like receptor 2 (CLEC-2). Here, we generated a novel single-chain antibody variable region fragment (scFv) by linking the variable regions of heavy and light chains of the neutralizing anti-human Aggrus monoclonal antibody MS-1 with a flexible peptide linker. Unfortunately, the generated KM10 scFv failed to suppress Aggrus-induced platelet aggregation in vitro. Therefore, we performed phage display screening and finally obtained a high-affinity scFv, K-11. K-11 scFv was able to suppress Aggrus-induced platelet aggregation in vitro. Moreover, K-11 scFv prevented the formation of pulmonary metastasis in vivo. These results suggest that K-11 scFv may be useful as metastasis inhibitory scFv and is expected to aid in the development of preclinical and clinical examinations of Aggrus-targeted cancer therapies.
Highlights
Metastasis is the major cause of cancer-related mortality, accounting for approximately 90% of cancer deaths [1]
Using the purified KM10 scFv, we analyzed its binding to the human Aggrus-derived P4262 peptide, which had been used as an immunogen to generate MS-1 monoclonal antibody (mAb) [10]
We further examined the reactivity of KM10 scFv to Aggrus protein using CHO cells that had been transfected with Aggrus-expressing plasmids (CHO/Aggrus), H226, and PC-10 cells [10]
Summary
Metastasis is the major cause of cancer-related mortality, accounting for approximately 90% of cancer deaths [1]. Because the process of metastasis is complicated, an optimal treatment strategy remains uncertain. It is well recognized that the interaction between platelets and tumor cells plays an important role in successful hematogenous metastasis [2, 3]. The main function of platelets under physiological conditions is to stop the bleeding after tissue trauma and vascular injury [2, 4]. Under pathological conditions, platelets enhance survival of tumor cells by protecting them from immunological assault within the circulation or from shear stress [2]. Antiplatelet or anticoagulant drugs extend progression-free survival in patients with progressive cancer [5, 6]. It is impossible to administrate such antiplatelet or anticoagulant drugs to some cancer patients with thrombocytopenia induced by antitumor drug treatment [5]
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