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:

Structural requirements within protoporphyrin IX in the inhibition of heat shock protein 90. Porphyrins are used for photodynamic therapy for their light-absorbing properties, and some of them were approved for the treatment of certain types of cancers. Porphyrins prevent activation of hypoxia inducible factor-1α (HIF-1α) by inhibiting heat shock protein 90 (HSP90). This study investigated the structural requirements within protoporphyrin IX (PPIX) for the inhibition of HSP90 activity. In HCT116, HT29 and DLD-1 cells, PPIX treatment directly hindered the binding between HSP90 and HIF-1α; PPIX treatment inhibited the chaperone activity of HSP90, accelerating protein degradation of HIF-1α. In addition, PPIX treatment suppressed cancer cell migration, endothelial cell tube formation, and aortic ring sprouting, being consistent with its anti-tumor and anti-angiogenic activities. In silico analysis, molecular docking model indicated that a tetrapyrrole macrocycle and two propionate chains within PPIX are necessary for the binding to the adenosine triphosphate (ATP)-binding pocket of HSP90. The predicted structural requirement was verified by the differential inhibitory effects of PPIX analogs, or the precursor of PPIX, on HIF-1α; compounds lacking either the tetrapyrrole macrocycle or the propionate chains were inactive. Our results show that a tetrapyrrole macrocycle and two attached propionate chains in PPIX coordinately interact with the ATP-binding pocket of HSP90, offering structural information on the inhibitory effect of porphyrins on angiogenesis.
{"Chemical": ["Porphyrins", "adenosine triphosphate", "tetrapyrrole macrocycle", "ATP", "protoporphyrin IX", "propionate", "PPIX"]}