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Biomedical subjects

D W Chan

Publications and source records attributed to D W Chan.

At least 19 recordsLinked to original sources
PubMed1997

Recommended prostate-specific antigen testing intervals for the detection of curable prostate cancer.

OBJECTIVE: To evaluate prostate-specific antigen (PSA) testing intervals that maintain the detection of curable cancer and reduce unnecessary testing. DESIGN AND PATIENTS: Historical prospective study of serial PSA measurements at 2- and 4-year intervals from frozen serum samples of 40 men who eventually developed prostate cancer and 272 men without prostate cancer who were participants in a prospective aging study (Gerontology Research Center of the National Institute on Aging, the Baltimore Longitudinal Study of Aging) and the case series of 389 consecutive men treated surgically for nonpalpable prostate cancer. MAIN OUTCOME MEASURES: Probability of a PSA conversion to 4.1 to 5.0 ng/mL and to greater than 5.0 ng/mL at 2 and 4 years and probability of detecting curable prostate cancer by age and PSA level. RESULTS: When the pretreatment PSA level was less than or equal to 4.0 ng/mL, nonpalpable prostate cancers were highly likely (34/36, 94%) to be curable (organ-confined or capsular penetration with Gleason score < 7 and negative margins), and the majority (25/36, 69%) were small cancers (confined tumor < or = 0.5 cm3 with no Gleason pattern 4 or 5). When the pretreatment PSA level was greater than 4.0 ng/mL and less than or equal to 5.0 ng/mL, cancers were highly likely to be curable (32/36, 89%), and a minority were small cancers (12/36, 33%). When the pretreatment PSA level was greater than 5.0 ng/mL, 96 (30%) of 317 cancers were noncurable. The PSA conversion (for cancer cases) to a level at which cure is less likely (> 5.0 ng/mL) is rare (0%) after 2 or 4 years when the initial PSA is less than 2.0 ng/mL. PSA conversion to a range at which cancers are likely to be curable and less likely to be small (4.1-5.0 ng/mL) is rare after 2 years (0%-4%) when the baseline PSA level is less than 2.0 ng/mL but common when the baseline PSA level is between 2.1 and 3.0 ng/mL (27%) or 3.1 and 4.0 ng/mL (36%). CONCLUSIONS: These data suggest that for men with no cancer suspected on digital rectal examination, a PSA level of 4.0 to 5.0 ng/mL is an acceptable range for maintaining the detection of curable prostate cancer and a 2-year PSA testing interval is not likely to miss a curable prostate cancer when the initial PSA level is less than 2.0 ng/mL. Recognizing that 70% of a screened population between the ages of 50 years and 70 years have PSA levels less than 2.0 ng/mL, elimination of annual PSA testing for these men would result in large health care cost savings.

Aged↗
PubMed1997

Prostate-specific antigen in men born with bladder exstrophy.

OBJECTIVES: To determine serum levels of prostate-specific antigen (PSA) in men born with bladder exstrophy and to investigate the clinical utility of this test in the bladder exstrophy population. METHODS: Ten men aged 19 to 45 years with a history of bladder exstrophy underwent digital rectal examination and free and total serum PSA determinations. Immunohistochemistry for PSA and prostate-specific acid phosphatase (PSAP) was performed on archival prostate tissue from 1 man with bladder exstrophy. RESULTS: Free and total serum PSA levels for all patients were measurable and below the upper limit for established age-specific reference ranges for normal men. Both PSA and PSAP were detectable by immunohistochemistry in prostate epithelial cells of a man with bladder exstrophy. CONCLUSIONS: Men born with bladder exstrophy have detectable serum PSA levels. However, because prostate cancer in men with bladder exstrophy has not been reported, whether PSA will have a clinical role as a serum tumor marker for prostate cancer in this population remains to be determined. If so, the PSA reference range for men with the exstrophy condition will need to be defined. Because prostate histology in men with exstrophy resembles that of normal men, careful clinical monitoring for benign and malignant tumors should not be overlooked in this particular population.

Adult↗
PubMed1997

Percentage of free prostate-specific antigen in sera predicts aggressiveness of prostate cancer a decade before diagnosis.

OBJECTIVES: To evaluate serial measurements of free and total prostate-specific antigen (PSA) as a predictor of prostate cancer aggressiveness. METHODS: Twenty men diagnosed with adenocarcinoma of the prostate in the pre-PSA era had serum PSA measurements made on multiple stored frozen sera samples available for up to 18 years prior to diagnosis. Subjects were categorized as having aggressive cancer (n = 12) based on the presence of clinical Stage T3, or nodal or bone metastases (N+, M+), or pathologic positive-margin disease, or a Gleason score of 7 or greater; nonaggressive cancer (n = 8) was identified by the absence of these criteria. RESULTS: There was no statistically significant difference in free PSA levels among men with aggressive and nonaggressive prostate cancers from 0 to 15 years before diagnosis. Total PSA levels were significantly different between the groups by 5 years before diagnosis (P = 0.04). At a time when total PSA levels were not different between groups (10 years before diagnosis), there was a statistically significant difference in the percentage of free PSA between aggressive and nonaggressive cancers (P = 0.008). Among 14 men who had sera available for analysis at 10 years before diagnosis, all 8 men with aggressive cancers had a percent free PSA of 0.14 or less; this compares with only 2 of 6 men (33%) with nonaggressive cancer. CONCLUSIONS: These data suggest that the percentage of free PSA in sera is predictive of tumor behavior at a time when total PSA levels provide no information on tumor aggressiveness. Evaluation of the percentage of free serum PSA may be helpful in making the decision between expectant management and treatment for those men who are diagnosed with early prostate cancers by PSA testing.

Adenocarcinoma↗
PubMed1997

Prostate-specific antigen. Its discovery and biochemical characteristics.

The search for a more sensitive and specific marker for prostate cancer as well as for use in forensic investigations led to the discovery of PSA. Utilization of the purified protein resulted in the development of many immunoassays that are now in widespread use and have been applied successfully to the detection and monitoring of prostate cancer. Subsequent investigation into the biochemical characteristics of PSA revealed free and complexed forms of PSA in serum whose measurement now may provide additional clinical benefit. Further research into the molecular and biochemical properties of PSA as well as improvements in measurement techniques no doubt will lead to new applications and enhanced clinical use for this important tumor marker.

Humans↗
PubMed1996

Interleukin-1 beta-converting enzyme-like protease cleaves DNA-dependent protein kinase in cytotoxic T cell killing.

Cytotoxic T cells (CTL) represent the major defense mechanism against the spread of virus infection. It is believed that the pore-forming protein, perforin, facilitates the entry of a series of serine proteases (particularly granzyme B) into the target cell which ultimately leads to DNA fragmentation and apoptosis. We demonstrate here that during CTL-mediated cytolysis the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), an enzyme implicated in the repair of double strand breaks in DNA, is specifically cleaved by an interleukin (IL)-1 beta-converting enzyme (ICE)-like protease. A serine protease inhibitor, 3,4-dichloroisocoumarin (DCl), which is known to block granzyme B activity, inhibited CTL-induced apoptosis and prevented the degradation of DNA-PKcs in cells but failed to prevent the degradation of purified DNA-PKcs by CTL extracts. However, Tyr-Val-Ala-Asp-CH2Cl (YVAD-CMK) and other cysteine protease inhibitors prevented the degradation of purified DNA-PKcs by CTL extracts. Furthermore, incubation of DNA-PKcs with granzyme B did not produce the same cleavage pattern observed in cells undergoing apoptosis and when this substrate was incubated with either CTL extracts or the ICE-like protease, CPP32. Sequence analysis revealed that the cleavage site in DNA-PKcs during CTL killing was the same as that when this substrate was exposed to CPP32. This study demonstrates for the first time that the cleavage of DNA-PKcs in this intact cell system is exclusively due to an ICE-like protease.

Amino Acid Sequence↗
PubMed1996

DNA-dependent protein kinase catalytic subunit: a target for an ICE-like protease in apoptosis.

Radiosensitive cell lines derived from X-ray cross complementing group 5 (XRCC5), SCID mice and a human glioma cell line lack components of the DNA-dependent protein kinase, DNA-PK, suggesting that DNA-PK plays an important role in DNA double-strand break repair. Another enzyme implicated in DNA repair, poly(ADP-ribose) polymerase, is cleaved and inactivated during apoptosis, suggesting that some DNA repair proteins may be selectively targeted for destruction during apoptosis. Here we demonstrate that DNA-PKcs, the catalytic subunit of DNA-PK, is preferentially degraded after the exposure of different cell types to a variety of agents known to cause apoptosis. However, Ku, the DNA-binding component of the enzyme, remains intact. Degradation of DNA-PKcs was accompanied by loss of DNA-PK activity. One cell line resistant to etoposide-induced apoptosis failed to show degradation of DNA-PKcs. Protease inhibitor data implicated an ICE-like protease in the cleavage of DNA-PKcs, and it was subsequently shown that the cysteine protease CPP32, but not Mch2alpha, ICE or TX, cleaved purified DNA-PKcs into three fragments of comparable size with those observed in cells undergoing apoptosis. Cleavage sites in DNA-PKcs, determined by antibody mapping and microsequencing, were shown to be the same for CPP32 cleavage and for cleavage catalyzed by extracts from cells undergoing apoptosis. These observations suggest that DNA-PKcs is a critical target for proteolysis by an ICE-like protease during apoptosis.

Animals↗
PubMed1996

The DNA-dependent protein kinase is inactivated by autophosphorylation of the catalytic subunit.

The DNA-dependent protein kinase (DNA-PK) requires for activity free ends or other discontinuities in the structure of double strand DNA. In vitro, DNA-PK phosphorylates several transcription factors and other DNA-binding proteins and is thought to function in DNA damage recognition or repair and/or transcription. Here we show that in vitro DNA-PK undergoes autophosphorylation of all three protein subunits (DNA-PKcs, Ku p70 and Ku p80) and that phosphorylation correlates with inactivation of the serine/threonine kinase activity of DNA-PK. Significantly, activity is restored by the addition of purified native DNA-PKcs but not Ku, suggesting that inactivation is due to autophosphorylation of DNA-PKcs. Our data also suggest that autophosphorylation results in dissociation of DNA-PKcs from the Ku-DNA complex. We suggest that autophosphorylation is an important mechanism for the regulation of DNA-PK activity.

Adenosine Triphosphate↗
PubMed1996

Detection of T-cell receptor delta gene rearrangement in T-cell malignancies by clonal specific polymerase chain reaction and its application to detect minimal residual disease.

A clonal-specific polymerase chain reaction technique to detect T-cell receptor delta gene rearrangement in acute lymphoblastic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL) was evaluated. It was applied to detect minimal residual disease. A sensitive and specific technique to detect minimal residual disease for T-cell malignancies was explored. Southern analysis and polymerase chain reaction (PCR) were used to detect the rearranged V-D-J segment of T-cell receptor delta (TCR delta) gene from malignant cell specimens of patients with leukemia and lymphoma of T-cell lineage. The PCR product was sequenced and from the DNA sequences of the V-D-J region, a 3' anti-sense primer was designed and synthesized for clonal specific PCR (CS-PCR). T-cell receptor delta (TCR-delta) gene rearrangement was studied in 40 cases of acute leukaemia and lymphoma of T-cell lineage at diagnosis. Using Southern analysis, the positive rates were 28 and 32% for the 18 T-lymphoma and 22 T-ALL, respectively. A one stage Polymerase Chain Reaction (PCR) technique was used to detect the rearrangement in Southern positive cases and the PCR positive rates were 80 and 86%, respectively. The PCR technique had a sensitivity of 0.1%. Serial follow-up marrow specimens were available from 4 T-ALL patients following chemotherapy for monitoring of minimal residual disease. Their PCR products were DNA sequenced. A 3' primer was designed for each case for a clonal specific (CS) PCR. The technique had a sensitivity of 0.003%. It was applied to detect minimal residual disease in serial follow-up marrow samples. The first patient had persistent negative CS-PCR results and enjoyed continuous remission for more than 3 years. The second patient with negative one stage PCR but positive CS-PCR results had eventual relapse of leukaemia. The other two patients never achieved a morphological remission. These preliminary results appeared to support the usefulness of these PCR techniques in detecting minimal residual disease and predicting relapses for ALL. However, further clinical correlation in larger populations of patients is necessary.

Base Sequence↗
PubMed1996

Pattern of T-cell receptor delta gene rearrangement by Southern blotting and polymerase chain reaction technique in Hong Kong Chinese patients with non-T-cell hematological malignancies.

It has been recognized that clonal T-cell receptor delta (TCR delta) gene rearrangement is present in both T-and B-cell malignancies. The highly sensitive polymerase chain reaction (PCR) technique may be applicable to cases of leukemia and lymphoma of non-T-cell origin for detection of minimal residual disease (MRD). A PCR technique was used in this study to investigate the pattern of clonal TCR delta gene rearrangement in Hong Kong Chinese patients with non-T-cell hematological malignancies. Seventy-three patients with the diagnosis of acute leukemia and non-Hodgkin's lymphoma of non-T-cell origin were included in this study. There were 20 patients with common ALL (cALL), seven precursal B-cell ALL (PreB-ALL), 23 acute myeloid leukemia (AML), and 23 non-Hodgkin's lymphoma of B-lineage (B-NHL). Clonal rearrangement was detectable by Southern analysis using a J delta 1 probe in 41 per cent of ALL of B-lineage but in none of the B-NHL or AML. The samples were also studied further by monoclonal PCR amplification for TCR delta gene rearrangement. Three different sets of primers were employed to detect clonal rearrangement of the TCR delta gene. The V delta 1(D)J delta 1 recombination typically seen in T-cell malignancies were not seen in any of the of the non-T-cell malignancies. The V delta 2 (D) D delta 3 recombination was found exclusively in ALL of B-lineage and was seen in 73 per cent of the Southern positive cases. Although clonal TCR delta gene rearrangement was undetectable by Southern analysis in our AML cases, 26 per cent had a V delta 2(D)J delta 1 recombination found by the PCR technique. Sensitivity of the PCR technique was determined by serial mixing and was up to 5-10 leukemic cells per 10(4) nucleated cells. It was apparent from this study that it was feasible to detect clonal TCR delta gene rearrangement by the PCR technique in a proportion of the cases of non-T-cell hematological malignancies. The PCR technique can be applied to detect residual leukemic cells in marrow of patients in an apparent morphological complete remission. The value of this application requires further clinical evaluation and correlation.

Acute Disease↗
PubMed1996

Longitudinal analysis of serial measurements of free and total PSA among men with and without prostatic cancer.

OBJECTIVES: Evaluation of free and total serum prostate specific antigen (PSA) levels before diagnosis of prostate cancer. METHODS: Free and total PSA levels were measured on frozen sera samples of 26 men with no history of prostate disease (controls), 29 men with a histologic diagnosis of benign prostatic hyperplasia (BPH) made at simple prostatectomy (BPH cases), and 23 men with a histologic diagnosis of prostatic cancer (cancer cases). Longitudinal regression analysis was used to evaluate PSA levels as a function of years before diagnosis of prostate disease. RESULTS: On average, mean total serum PSA was statistically significantly greater for subjects with cancer (5.0 ng/mL +/- 0.9) versus BPH (2.8 ng/mL +/- 0.3) and control subjects (0.8 ng/mL +/- 0.1) by 4 years before diagnosis, whereas free PSA levels were similar among groups at 4 years before diagnosis. The ratio of free to total serum PSA continuously decreased among cancer cases over the decade before cancer diagnosis. At a time when mean total and free PSA levels were similar among groups (8 years before diagnosis), the ratio of free to total PSA was statistically significantly lower for cancer cases (0.13 +/- 0.01) compared with BPH (0.17 +/- 0.01) and control cases (0.21 +/- 0.02). Use of a free to total PSA ratio of < or = 0.12 when total PSA was between 4.0 and 10.0 ng/mL resulted in the highest sensitivity (76%) and specificity (94%) for diagnosis among subjects with and without cancer. Lowering the reflex range to 2.5 ng/mL increased false positive tests more than it increased sensitivity. CONCLUSIONS: The ratio of free to total PSA is the earliest serum marker predicting a subsequent diagnosis of prostate cancer. Measurement of the free to total serum PSA ratio would appear to reduce false positive results among men without prostate cancer.

Aged↗
PubMed1996

Multicenter comparison of the diagnostic performance of free prostate-specific antigen.

OBJECTIVES: This study examined the multicenter clinical performance of noncomplexed (free) prostate-specific antigen (PSA) in men presenting with total PSA values between 2.5 to 20 ng/mL. METHODS: Prebiopsy serum samples were obtained from 1,081 consecutively accrued, histologically diagnosed men between the ages of 40 and 75 years with total PSA values falling between 2.5 and 20 ng/mL. Total PSA was determined by either the Tosoh AIA-1200 or Hybritech method. Free PSA values were determined using the Dianon PSA II immunoradiometric method. Free PSA was expressed as a percentage of total PSA. Immunochemistry was performed at each accrual site. RESULTS: Among men diagnosed with prostate cancer (CaP), only 4% (21/520) had proportions of free to total PSA values > 25%. Conversely, among men with benign prostatic disease, only 2% (13/561) had proportions of free to total PSA values < 7%. These results confirm those of previous research. Differences among sites were found in age and prostate volume. CONCLUSIONS: These data confirm that free PSA values < 7% are highly suspicious for CaP whereas free PSA values > 25% suggest absence of malignancy. The data also suggest that age and/or prostate volume influences the serum level of free PSA but does not affect the diagnostic cutoff points of 7% and 25%. Future analysis is needed to confirm that younger men with small prostates are at higher risk for CaP.

Adult↗
PubMed1996

The role of free/total prostate-specific antigen ratio in the prediction of final pathologic stage for men with clinically localized prostate cancer.

OBJECTIVES: The combined use of total prostate-specific antigen (PSA), clinical stage, and Gleason score accurately predicts final pathologic stage for men with clinically localized prostate cancer. Recently, the free/ total PSA ratio has been proposed as an adjunct for early detection of prostate cancer. We examined the association between free/total PSA and pathologic stage. METHODS: In a prospective study, 301 consecutive men with clinically localized prostate cancer (average age 58.8 years, range 45-72) underwent a staging pelvic lymphadenectomy and radical prostatectomy. Total PSA and free PSA were measured from preoperative sera. Pathologic stage was determined as organ-confined (OC, n = 169), capsular penetration (CP+, n = 108), seminal vesicle involvement (SV+, n = 13) and lymph node involvement (LN+, n = 11). RESULTS: Overall, 292/301 (97%) of the free/total PSA values were < 25%, and thus suspicious for prostate cancer. Combination of total PSA, Gleason score, and clinical stage predicted well OC (P = 0.00001) and LN+ (P = 0.023); whereas, replacing total PSA with free/total PSA ratio did not improve the prediction of OC (P = 0.0007) nor LN+ (P = 0.03). CONCLUSIONS: The free/total PSA ratio cutoff point of 25% had high sensitivity for prostate cancer among a group of men with clinically localized disease. The free/total PSA ratio did not significantly improve the prediction of pathologic stage provided by total PSA when used alone or in combination with Gleason score and clinical stage. These preliminary data demonstrate that free/total PSA levels provide no additional information for pathologic stage prediction when combined with Gleason score and clinical stage in men with clinically localized prostate cancer.

Aged↗
PubMed1996

Analysis of percent free prostate-specific antigen (PSA) for prostate cancer detection: influence of total PSA, prostate volume, and age.

OBJECTIVES: To determine whether the use of the free-to-total PSA ratio (percent free PSA) could increase the specificity of PSA testing for prostate cancer detection in men with serum PSA concentrations between 4.0 and 10.0 ng/mL, and to assess the influence of total PSA, prostate volume, and age on percent free PSA. METHODS: Sera were obtained from 217 men with histologically confirmed diagnoses (139 prostate cancer, 78 benign). Free and total PSA concentrations were determined using Hybritech Tandem assays. RESULTS: Use of percent free PSA increased PSA specificity: 29% of negative biopsies would be spared while retaining 95% sensitivity. Percent free PSA increased with increasing age and prostate volume. Percent free PSA decreased as total PSA increased. A significant relation exists between percent free PSA and the probability of a positive biopsy; in this cohort, a patient with a low percent free PSA (< or = 10%) had a higher probability of cancer (63 +/- 9%) than a patient with a high percent free PSA (> or = 26%) (probability 2 +/- 3%). CONCLUSIONS: Percent free PSA may be used as an aid in distinguishing prostate cancer from benign disease in men with a total PSA between 4.0 and 10.0 ng/mL. Large prospective multicenter trials are required to develop consistent recommendations and determine the appropriate cutpoints and risk probabilities, controlling for total PSA, prostate volume, age, and biopsy history.

Adult↗
PubMed1996

Purification and characterization of the double-stranded DNA-activated protein kinase, DNA-PK, from human placenta.

The double-stranded DNA-activated protein kinase (DNA-PK) is a serine-threonine protein kinase that is composed of a large catalytic subunit (p350) and a DNA-binding protein of 70 and 80 kDa subunits known as the Ku autoantigen. When targeted to DNA by free DNA ends, DNA-PK phosphorylates many DNA-binding proteins and transcription factors. Previously, DNA-PK had only been purified and characterized from transformed human tissue culture cells. Here we report that DNA-PK is an abundant protein in human placenta and lymphocytes. We have purified the placental DNA-PK to homogeneity and show that its biochemical properties are similar to those of the HeLa cell enzyme.

Blotting, Western↗
PubMed1996

Clearance rate of serum-free and total PSA following radical retropubic prostatectomy.

BACKGROUND: Our objective was to determine the clearance rate of free and total serum PSA following radical retropubic prostatectomy. METHODS: Sera were obtained from 10 men with localized prostate cancer prior to and 1, 4, 8, 24, 48, and 72 hr after radical prostatectomy. No patient received any postoperative blood transfusion. Free and total PSA were measured using the Hybritech Tandem-R (total PSA) and radioimmunometric free PSA assay. Postsurgery serum-free and total PSA concentrations were modeled using a "two-compartment" pharmacokinetic model. RESULTS: The pharmacokinetic model with an initial constant "infusion" suggests that, following release from the prostate, both free and total PSA are taken up into a second compartment for metabolism. The movement of PSA between these compartments was accurately modeled. Following surgery, there is a shift of both free and total PSA best modeled as a constant infusion into the serum at a rate of 1.97 and 1.60 ng/ml, respectively, for a period of approximately 1 hr. Following this initial constant infusion, the half-life estimations for free and total PSA are initially 1.2 and 0.75 hr, respectively, which then increase to 22 and 33 hr, respectively. CONCLUSIONS: Serum free and total PSA are cleared from the circulation following a "two-compartment" model with an initial constant "infusion." The constant "infusion" is most likely a consequence of surgical manipulation. The initial half-life estimates are < 2 hr for both free and total PSA, and later increase to 22 and 33 hr, respectively.

Aged↗
PubMed1995

Absence of p350 subunit of DNA-activated protein kinase from a radiosensitive human cell line.

The radiosensitive rodent mutant cell line xrs-5 is defective in DNA double-strand break repair and lacks the Ku component of the DNA-activated protein kinase, DNA-PK. Here radiosensitive human cell lines were analyzed for DNA-PK activity and for the presence of related proteins. The radiosensitive human malignant glioma M059J cell line was found to be defective in DNA double-strand break repair, but fails to express the p350 subunit of DNA-PK. These results suggest that DNA-PK kinase activity is involved in DNA double-strand break repair.

Amino Acid Sequence↗