TY - JOUR
T1 - Specific and efficient peptide substrates for assaying the proteolytic activity of prostate-specific antigen
AU - Denmeade, Samuel R.
AU - Lou, Wei
AU - Lövgren, Janita
AU - Malm, Johan
AU - Lilja, Hans
AU - Isaacs, John T.
PY - 1997/11/1
Y1 - 1997/11/1
N2 - Prostate-specific antigen (PSA) is a serine protease secreted by hath normal prostate glandular celts and prostate cancer cells. The major proteolytic substrates for PSA are the gel-forming proteins in semen, semenogelin (Sg) I and II. On the basis of the PSA cleavage map for Sg I and II, a series of small peptides (ie., ≤ 7 amino acids) was synthesized and coupled at the COOH terminus to 7-amino-4-methyl coumarin. Using these fluorescently tagged substrates, K(m)s and k(cm)s were determined for PSA hydrolysis, and the substrates were also tested for activity against a panel of purified proteases. Previously, a variety of chymotrypsin substrates have been used to assay the enzymatic activity of PSA. The present studies have identified a peptide sequence with a high degree of specificity for PSA (i.e., no detectable hydrolysis by chymotrypsin) and improved K(m)s and k(cat)s over previously used substrates. On the basis of these parameters, the best peptide substrate for PSA has the amino acid sequence HSSKLQ. Using PC-82 human prostate cancer xenografts and human prostate tissues, this PSA substrate was used to document that prostate cancer cells secrete enzymatically active PSA into the extracellular fluid but that once in the blood, PSA is not enzymatically active. On the basis of this information, it should be possible to use the HSSKLQ peptide as a carrier to target peptide- coupled prodrugs for selective activation within sites of PSA-secreting, metastatic prostate cancer cells and not within the blood or other nonprostatic normal tissues.
AB - Prostate-specific antigen (PSA) is a serine protease secreted by hath normal prostate glandular celts and prostate cancer cells. The major proteolytic substrates for PSA are the gel-forming proteins in semen, semenogelin (Sg) I and II. On the basis of the PSA cleavage map for Sg I and II, a series of small peptides (ie., ≤ 7 amino acids) was synthesized and coupled at the COOH terminus to 7-amino-4-methyl coumarin. Using these fluorescently tagged substrates, K(m)s and k(cm)s were determined for PSA hydrolysis, and the substrates were also tested for activity against a panel of purified proteases. Previously, a variety of chymotrypsin substrates have been used to assay the enzymatic activity of PSA. The present studies have identified a peptide sequence with a high degree of specificity for PSA (i.e., no detectable hydrolysis by chymotrypsin) and improved K(m)s and k(cat)s over previously used substrates. On the basis of these parameters, the best peptide substrate for PSA has the amino acid sequence HSSKLQ. Using PC-82 human prostate cancer xenografts and human prostate tissues, this PSA substrate was used to document that prostate cancer cells secrete enzymatically active PSA into the extracellular fluid but that once in the blood, PSA is not enzymatically active. On the basis of this information, it should be possible to use the HSSKLQ peptide as a carrier to target peptide- coupled prodrugs for selective activation within sites of PSA-secreting, metastatic prostate cancer cells and not within the blood or other nonprostatic normal tissues.
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M3 - Article
C2 - 9354459
AN - SCOPUS:0030728733
SN - 0008-5472
VL - 57
SP - 4924
EP - 4930
JO - Cancer Research
JF - Cancer Research
IS - 21
ER -