ELEVATED LEVELS OF PRO-CATHEPSIN-D IN THE PLASMA OF BREAST-CANCER PATIENTS

Changes in the expression and processing of cathepsin D (CD) have been shown to be associated with cancer invasion and metastasis. However, the value of CD as a prognostic marker remains controversial. Most stu dies have used immunological methods to measure the mature form of CD, although it is the precursor (pro-CD) that appears to be abnormally s ecreted by breast cancer cells. A sandwich-type ELISA has been develop ed that is specific for pro-CD. The assay employs a monoclonal antibod y to mature CD as the capture reagent and a rabbit polyclonal to the p ro fragment as the detector. The assay is specific for pro-CD and capa ble of quantitating this antigen in biological samples. Pro-CD levels were measured in plasma samples from 76 breast cancer patients and com pared with 36 samples from normal control individuals. The plasmas of breast cancer patients showed elevated levels of pro-CD; 12% were more than two standard deviations above the mean for the normal samples. I mmunoblots of the plasma samples using a CD monoclonal antibody reveal ed a band at the appropriate size for pro-CD that corresponded in inte nsity with the ELISA results. Affinity adsorption of breast cancer pla smas with pepstatin agarose followed by immunoblot analysis revealed a single protein band that correlated with pro-CD. Only trace amounts w ere detected in the normal control plasmas. These results demonstrate that cathepsin D is present in the plasma of breast cancer patients pr imarily in its precursor form and that it may be a useful prognostic i ndicator.