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:

DNA Adducts in Aldehyde Dehydrogenase-Positive Lung Stem Cells of A/J Mice Treated with the Tobacco Specific Lung Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Lung cancer is the leading cause of cancer death in the world. Evidence suggests that lung cancer could originate from mutations accumulating in a subpopulation of self-renewing cells, lung stem cells. Aldehyde dehydrogenase (ALDH) is a marker of stem cells. To investigate the presence of DNA modifications in these cells, we isolated ALDH-positive lung cells from A/J mice exposed to the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. Using LC-NSI-HRMS/MS-PRM, O(6)-methyl-G, 7-POB-G, and O(2)-POB-dT were positively identified in ALDH-positive cell DNA. This is the first example of detection of carcinogen-DNA adducts in lung stem cells, supporting the hypothesis of their role in lung carcinogenesis.
{"Chemical": ["NNK", "O(6)-methyl-G", "4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone", "O(2)-POB-dT", "Aldehyde", "7-POB-G", "4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone"]}