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:

Chemopreventive effects of Ginkgo biloba extract in estrogen-negative human breast cancer cells. Excessive level of estrogen is considered as a main cause of breast cancer, therefore, many studies have focused on estrogen receptor (ER)-positive breast cancer, even though ER-negative cancer has a poor prognosis than ER-positive breast cancer. We evaluated the anti-cancer effects of Ginkgo biloba extract (GBE) in estrogen-independent breast cancer. GBE has been traditionally used as a platelet activating factor, a circulatory stimulant, a tonic, and anti-asthmatic drug, and anti-cancer agent. However, anti-cancer effects of GBE on ER-negative breast cancer have not been proved yet. In this study, we tested chemotherapeutic potential of GBE in the MDA-MB-231 (ER-negative) human breast cancer cell line. Our results showed that cytotoxicity effects of GBE in MDA-MB-231 lead to DNA fragmentation at high concentrations (500 and 1,000 μg/ml). Caspase-3 was significantly activated and mRNA levels of apoptosis-related genes (Bcl-2 and Bax) were altered. These results indicate that GBE induces apoptosis in MDA-MB-231 cells. It is presumed that GBE has chemopreventive effects in ER-independent breast cancer through anti-proliferation and apoptosis-inducing activities.
{"Chemical": ["estrogen"]}