Activities of cytosolic aldehyde dehydrogenase isozymes in colon cancer: determination using selective, fluorimetric assays.

Activities of two principal cytosolic forms of human aldehyde dehydrogenase, ALDH1A1 and ALDH3AI in colon tumor homogenates and surrounding tissue fragments were measured, using isozymeselective, fluorimetric assays. The assays are based on two fluorogenic substrates, 6-methoxy-2-naphthaldehyde and 7-methoxy-l-naphthaldehyde, and are independent of NADH determinations. The results show high variability of ALDH levels in colon tumors, with several samples below sensitivity level (< 0.01 units per gram protein), while the highest activities of both ALDH1A1 and ALDH3A1 in tumor tissue were close to 0.5 U/g. Correlation coefficients between tumor and colon tissue activities were found to be below 0.5 for both ALDH activities examined, but the average activities were similar. and close to 0.1 U/g. thus similar to that found in the thyroid fragments. It is concluded that ALDH probably cannot be directly responsible for oxazaphosphorine resistance in colon cancer.