Identification of cytosolic aldehyde dehydrogenase 1 from non-small cell lung carcinomas as a flavopiridol-binding protein

The synthetic flavone flavopiridol can be cytostatic or cytotoxic to mammal ian cells, depending on the concentration of the drug and the duration of e xposure. It has been shown to inhibit the cyclin-dependent kinase (CDK) fam ily of cell cycle regulatory enzymes. However, the existence of additional potential targets for drug action remains a matter of interest to define, T o identify cellular targets, flavopiridol was immobilized. CDKs, particular ly CDK 4, bound weakly to immobilized flavopiridol when ATP was absent but not in its presence. Two proteins with molecular weights of 40 kDa and 120 kDa had high affinities to the immobilized flavopiridol independent of the presence of ATP, They were present in all cell lines analyzed: cervical (He La), prostate and non-small cell lung carcinoma (NSCLC) cell lines. A 60-kD a protein, which was present only in NSCLC cells and bound similarly well t o immobilized flavopiridol, was identified as cytosolic aldehyde dehydrogen ase class 1 (ALDH-1). The level of this protein correlated with the resista nce of NSCLC cell lines to cytotoxicity caused by 500 nM flavopiridol but n ot higher flavopiridol concentrations, Despite binding to ALDN-1, there was no inhibition of dehydrogenase activity by flavopiridol concentrations as high as 20 mu M and flavopiridol was not metabolized by ALDH-1. The results suggest that high cellular levels of ALDH-1 may reduce cytotoxicity of fla vopiridol and contribute to relative resistance to the drug. This is the fi rst report that flavopiridol binds to proteins other than CDKs, (C) 1999 Fe deration of European Biochemical Societies.