You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

In vitro antiproliferative effect of a water-soluble Laminaria japonica polysaccharide on human melanoma cell line A375. A water-soluble polysaccharide WPS-2-1, purified from Laminaria japonica, has been found to have antitumor activity. In this study, WPS-2-1 exhibited high anti-proliferative activity on A375 cells in a dosedependent manner. Further investigation indicated that WPS-2-1 induced A375 cells apoptosis. Moreover, WPS-2-1-induced apoptosis was associated with the alteration in expressions of Bcl-2 family proteins. Mitochonadrial apoptotic pathway was involved in WPS-2-1-induced apoptosis, which included the loss of mitochondrial membrane and activation of caspase-3/9. The results in this study suggested that WPS-2-1 could effectively inhibit proliferation of A375 cells in vitro and induce apoptosis via mitochondrial apoptotic pathway. It might serve as a potential anti-tumor agent.
{"Chemical": []}