GP88 induces AC1 cell proliferation in vitro. 5 × 104 cells/plate (35 mm well plates) MCF-7AC1 cells were plated in PRF medium supplemented with 5% Charcoal treated FBS overnight. The next day, medium was removed and serum free medium was added without or with increasing concentration of GP88: 150 ng/ml (P-150), 300 ng/ml (P-300) and 600 ng/ml (P-600) or 25 nM androstenedione (AD). After 6 days, cells were trypsinized and cell number was determined by counting cells with a hemocytometer. Experiment was performed three times in triplicate.