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 ALDH3A1 in colon tumor homogenates and surrounding tissue fragments were measured, using isozyme- selective, fluorimetric assays. The assays are based on two fluorogenic substrates, 6-methoxy-2-naphthaldehyde and 7-methoxy-1-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.