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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: BACKGROUND, METHODS, RESULTS. Meshes: Animals, Breast Neoplasms, Bridged Bicyclo Compounds, Heterocyclic, Cell Line, Tumor, Down-Regulation, Female, Humans, Mice, Mice, Nude, Receptors, Estrogen, Selective Estrogen Receptor Modulators, Xenograft Model Antitumor Assays.
user
Is thiochroman derivative CH4986399 , a new nonsteroidal estrogen receptor down-regulator , effective in breast cancer models? Context: Tamoxifen, a selective estrogen receptor modulator, and fulvestrant, a selective estrogen receptor down-regulator (SERD), are now available for estrogen receptor-positive breast cancer patients. However, these patients acquire drug-resistance during the treatments. We identified a new orally active nonsteroidal SERD, CH4986399, which is structurally unrelated to fulvestrant and tamoxifen. We examined the oral antitumor activity and down-regulation of ER by CH4986399 in human breast cancer Br-10 and ZR-75-1 xenografts. In the Br-10 xenografts, CH4986399 (100 mg/kg p.o.) as well as fulvestrant (3 mg/body s.c.) strongly reduced tumor weight. In the ZR-75-1 xenografts, CH4986399 (100 mg/kg p.o.) strongly reduced tumor weight and ER content without agonistic activity. In contrast, tamoxifen (100 mg/kg p.o.) showed only moderate antitumor activity and no ER down-regulation.
assistant
With a chemical structure different from both fulvestrant and tamoxifen, CH4986399, may help overcome drug resistance from the endocrine treatment sequence for breast cancer patients. Final Decision: yes