Although Sirt1-3 are closely related sirtuin isoforms [83], optimized Sirtris Sirt1 STACs SRT1460, SRT1720 (Table 1), and SRT2183 displayed up to 833- and 1875-fold selectivity for Sirt1 over Sirt2/3 in vitro, and demonstrated a Sirt1-dependent decrease in p53 acetylation in the U2OS osteosarcoma cell line [59]. The gene discussed is SIRT1; the disease is osteosarcoma.