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The ABCA5 Protein: A Urine Diagnostic Marker for Prostatic Intraepithelial Neoplasia

Authors' Affiliations: ¹ Drexel University College of Medicine, Philadelphia, Pennsylvania and ² GTx, Inc., Memphis, Tennessee

Requests for reprints: Mark E. Stearns, Department of Pathology, Drexel University College of Medicine, 245 North Broad Street, Philadelphia, PA 19102-1192. Phone: 215-762-1597; Fax: 215-246-5918; E-mail: stearnsm1{at}aol.com.

Purpose: To develop a urine diagnostic test for preneoplastic intraepithelial neoplasia of the prostate.

Experimental Design: We have used a DNA-binding assay and electrophoretic mobility shift assays (EMSA) to screen for novel duplexed DNA-binding sequences, which bind protein(s) overexpressed in crude protein extracts from high-grade prostatic intraepithelial neoplasia (HGPIN). EMSAs, immunohistochemistry, and ELISAs were used to measure expression of the ABCA5 protein identified as a specific marker in prostate tissue and patient urine.

Results: Following screening of 4,096 sequences, an 8-bp dsDNA sequence (i.e., TCCAGCGA) was identified, which binds the ABCA5 protein, a member of the ATP-binding cassette multidrug resistant family. EMSAs showed that ABCA5 was overexpressed in HGPIN tissue (n = 11/11) and in the urine of patients with HGPIN (n = 18/18) but was not expressed in prostate cancer, benign prostatic hyperplasia, or stroma. Immunohistochemistry indicated that ABCA5 was overexpressed in foci of intermediate basal cells in normal glands and in HGPIN. ABCA5 was faintly expressed in prostate cancer glands. ELISAs showed in ‘blinded studies’ that ABCA5 was a highly sensitive (>98% sensitivity) urine diagnostic marker for HGPIN in biopsy-positive patients (n = 107) at a ‘cutoff’ of 25 ng/mL. ABCA5 was present at very low levels (i.e., <25 ng/mL) in the urine of patients diagnosed with benign prostatic hyperplasia (n = 79) or prostatitis or kidney and bladder cancer (>86% specificity).

Conclusions: The data indicate that ABCA5 might be a specific urine marker for diagnosis of patients with HGPIN.