Andarine (S-4) is a selective androgen receptor (AR) antagonist with a Ki value of approximately 4 nM indicating strong receptor-binding affinity It functions by selectively targeting androgen receptors nuclear receptors involved in DNA-mediated transcription and gene expression regulation In vitro studies using AR-driven transcription assays illustrate Andarine s capacity to modulate AR activity at nanomolar concentrations Animal model studies in male Sprague-Dawley rats suggest Andarine administration induces a dose-dependent increase in tissues responsive to androgen activity including prostate gland seminal vesicles and levator ani muscle Due to its receptor specificity and manageable pharmacodynamics Andarine is widely investigated in biomedical research related to androgen receptor signaling pathways endocrine regulation and therapeutic responses involving AR-mediated mechanisms