Is there still a role for prostatic acid phosphatase? CSCC Position Statement. Canadian Society of Clinical Chemists

Changes in tissue prostatic acidic phosphatase during endocrine treatment of patients with prostatic carcinoma

OBJECTIVE

We have previously developed methods for the quantification of different macromolecules in aspiration biopsy material and described the changes in prostate-specific antigen (T-PSA) during cancer treatment. We have now studied the changes in tissue prostatic acidic phosphatase (T-PAP) in 58 endocrine-treated patients with prostatic carcinoma and compared these data with cancer development data and tissue PSA (T-PSA) levels.

MATERIAL AND METHODS

PAP and PSA were quantified in aspiration biopsies taken before treatment and after 6 and 12 months of treatment. Patients were followed until death or for >98 months.

RESULTS

Pretreatment T-PSA was more strongly associated with survival than T-PAP. Both T-PSA and T-PAP decreased in responders during treatment. In non-responders, T-PSA and T-PAP increased after 12 months in 17/18 and 7/13 patients, respectively. Estrogen-treated responders had significantly higher T-PSA, but not T-PAP, treatment values than those treated with orchidectomy or gonadotropin-releasing hormone.

CONCLUSIONS

The inferiority of serum PAP compared to PSA for monitoring cancer treatment may reflect its less pronounced changes at the tissue level, indicating different in vivo regulation of the two markers. Estrogen stimulation of PSA synthesis in vivo may underlie the higher PSA levels observed during estrogen treatment.

From gene to protein: Prostatic acid phosphatase: Structure and expression of gene and protein*

A set of classes for medical students is designed to reinforce an understanding of the basic laboratory methods of molecular biology and protein biochemistry in the context of a clinically important problem, prostate gland pathology. Students examine the gene coding for prostatic acid phosphatase and they assay expression of the gene in different lines of prostate cancer cell cultures (LNCaP and PC-3). The three-dimensional structure of the expressed protein is also investigated, in relation to its catalytic function. Students are encouraged to collect data for their experiments and to perform laboratory exercises on their own. The theory and practice should stimulate the students' discussion of various fields of biochemistry and molecular biology.

Suppression of LNCaP prostate cancer xenograft tumors by a prostate-specific protein tyrosine phosphatase, prostatic acid phosphatase

BACKGROUND

Although the molecular mechanism of androgen-independent prostate cancer growth and progression has been gradually elucidated, there is limited effective treatment for this prevalent disease. Human prostatic acid phosphatase (PAcP), a major protein tyrosine phosphatase in prostate epithelium, plays a critical role in regulating the growth of prostate cancer cells. In prostate carcinomas, the expression of cellular PAcP decreases. To explore directly the possible therapeutic potential of cellular PAcP, we investigated the suppression effect of PAcP by utilizing cDNA direct intratumoral administration in androgen-independent LNCaP xenograft tumors.

METHODS

An androgen-independent LNCaP cell model (C-33 and C-81 cells) and stable subclones of PAcP cDNA-transfected C-81 cells (LNCaP-23 and LNCaP-34 cells) were used for the experiments. We examined the growth property and expression of PAcP and c-ErbB-2 of these different LNCaP cells in vitro and in vivo. We subsequently investigated the growth suppression effect of PAcP cDNA intratumoral injection in pre-established C-81 xenograft tumors, and analyzed the expression of PAcP, prostate-specific antigen (PSA), proliferating cell nuclear antigen (PCNA), and c-ErbB-2 in the tumors by immunohistochemistry and Western blotting.

RESULTS

The different LNCaP cells exhibited different growth property and tumorigenicity, both in cell culture and xenograft. Biochemical characterizations revealed that the level of cellular PAcP correlated negatively with the growth property of different LNCaP cells, while the level of tyrophosphorylated c-ErbB-2 had an inverse correlation with cellular PAcP. The single intratumoral administration of the wild type PAcP cDNA showed a significant suppression effect on C-81 xenograft tumor growth, compared to vector alone-injected control (P<0.05). In the tumors injected with this PAcP cDNA, the PAcP expression was detected 1 week (wk) after injection, but was undetectable at 6 wk, which inversely correlated with the level of tyrophosphorylated c-ErbB-2 and the degree of cell proliferation indicated by PCNA staining.

CONCLUSIONS

Our results clearly demonstrated that cellular PAcP has a suppression effect on the growth of androgen-independent LNCaP xenograft tumors. This effect occurs at least partly through the dephosphorylation of c-ErbB-2 by PAcP, the prostate-specific protein tyrosine phosphatase. The data indicates that human PAcP could be utilized in the corrective gene therapy for a subgroup of androgen-independent human prostate cancer cells that lack cellular PAcP expression.

Screening for prostate cancer with prostate-specific antigen: beware the biases

BACKGROUND

The evidence relating to the use of prostate-specific antigen (PSA) as a screening test is a highly controversial, as demonstrated by the lack of agreement among experts. There may be biases associated with various studies.

ISSUES

The main controversy is the relatively high prevalence of prostate cancer (PC) found at autopsy compared with the relatively low death rate from the disease. The lack of modifiable risk factors has led to early detection as a strategy to reduce mortality, as there is evidence for a significant burden of disease. Important issues are the accuracy of current screening tests, some attempts to improve on them, and whether there are good prognostic markers. The consequences of PSA testing (usually further testing including biopsy) and outcomes of treatment are presented in terms of mortality and morbidity; quality of life (QOL) must also be considered. Also important are the benefits from, and the difficulties associated with the "informed choice" approach to PSA screening.

CONCLUSION

There is evidence to suggest that biases can have a significant impact on the utility of PSA as a screening test for PC.