(S)-Gossypol is the isomer of a natural product Gossypol. (S)-Gossypol binds to the BH3-binding groove of Bcl-xL and Bcl-2 proteins with high affinity.

The natural racemic Gossypol has two enantiomers, namely the (-)-Gossypol and (S)-Gossypol ((+)-Gossypol) enantiomers. (+)-Gossypol and (-)-Gossypol binds to Bcl-2 or Bcl-xL with similar binding affinities. (-)-Gossypol is more potent than (+)-Gossypol in inhibition of cell growth and induction of apoptosis. 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].

• [1]. Oliver CL, et al. In vitro effects of the BH3 mimetic, (-)-Gossypol, on head and neck squamous cell carcinoma cells. Clin Cancer Res. 2004 Nov 15;10(22):7757-63.