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:

Semi-Synthetic Mithramycin SA Derivatives with Improved AntiCancer Activity. Mithramycin (MTM) is a potent anti-cancer agent that has recently garnered renewed attention. This manuscript describes the design and development of mithramycin derivatives through a combinational approach of biosynthetic analogue generation followed by synthetic manipulation for further derivatization. Mithramycin SA is a previously discovered analogue produced by the M7W1 mutant strain alongside the improved mithramycin analogues mithramycin SK and mithramycin SDK. Mithramycin SA shows decreased anti-cancer activity compared to mithramycin and has a shorter, two carbon aglycon side chain that is terminated in a carboxylic acid. The aglycon side chain is responsible for an interaction with the DNA-phosphate backbone as mithramycin interacts with its target DNA. It was therefore decided to further functionalize this side chain through reactions with the terminal carboxylic acid in an effort to enhance the interaction with the DNA phosphate backbone and improve the anti-cancer activity. This side chain was modified with a variety of molecules increasing the anti-cancer activity to a comparable level to mithramycin SK. This work shows the ability to transform the previously useless mithramycin SA into a valuable molecule and opens the door to further functionalization and semi-synthetic modification for the development of molecules with increased specificity and/or drug formulation.
{"Chemical": ["mithramycin SK", "Mithramycin", "mithramycin", "carbon", "carboxylic acid", "Mithramycin SA", "MTM", "mithramycin SDK", "mithramycin SA", "phosphate"]}