Gossypol acetic acid ((±)-Gossypol-acetic acid), a natural product isolated from cottonseeds and roots, binds to Bcl-xL protein and Bcl-2 protein with K_is of 0.5-0.6 μM and 0.2-0.3 mM, respectively. IC50 & Target: Ki: 0.5-0.6 μM (Bcl-xL), 0.2-0.3 mM (Bcl-2)^[1] In Vitro: Gossypol, a natural product isolated from cottonseeds and roots that has been studied as an anticancer agent. The racemic form of Gossypol [(±)-Gossypol] is tested in several clinical trials and is well tolerated. The racemic form Gossypol ((±)-Gossypol) binds to Bcl-xL protein with a K_i of 0.5 to 0.6 μM. (±)-Gossypol also potently binds to Bcl-2 protein with a K_i value of 0.2-0.3 mM. The natural racemic Gossypol has two enantiomers, namely the (-)-Gossypol and (+)-Gossypol enantiomers. The racemic form and each of the enantiomers of Gossypol are tested against UM-SCC-6 and UM-SCC-14A in 6-day MTT assays. (-)-Gossypol exhibits greater growth inhibition relative to (±)-Gossypol than (+)-Gossypol in both cell lines tested (P<0.001). An intermediate growth inhibitory effect is observed with (±)-Gossypol but this effect is only observed at the higher dose of Gossypol (10 μM, P<0.0001)^[1].