Influence of freeze-drying on the recovery of the tumour invasion markers uPA and PAI-1 from prostate cancer resections

Abstract

Background: Urokinase plasminogen activator (uPA) and its inhibitor (PAI-1) have been shown to be of merit as biomarkers for a variety of cancers. Prostate tissue resections from patients with prostate cancer (PCa) and benign prostatic hyperplasia were analysed to determine the influence of freeze-drying on the recovery of uPA and PAI-1 and their predictive performance. Methods: Prostate tissue was frozen in liquid nitrogen and homogenised into a fine powder in a precooled stainless steel punch homogeniser. One aliquot of the powder was extracted directly, and a second aliquot was freeze-dried overnight and then extracted. The extracts were analysed by FEMTELLE assay to determine the concentrations of uPA and PAI-1. uPA/PAI-1 ratios were calculated for each sample, and the mean ratios for the frozen and the lyophilised tissue were compared. Results: The concentrations of uPA measured for the frozen and lyophilised samples are strongly correlated (R¼0.90± 0.05). The same applies to the PAI-1 measured (R¼0.89± 0.03). The uPA/PAI-1 ratios for the lyophilised and frozen samples were strongly correlated. The uPA/PAI-1 ratios for frozen and lyophilised samples were found to be essentially the same with values of 0.0344± 0.0066 and 0.0340± 0.0068, respectively (P¼0.9633). Conclusion: The recovery of uPA and PAI-1 from a deep frozen prostate tissue homogenate followed by freeze-drying proceeds with a loss of 10 and 11%, respectively, with no influence on the uPA/PAI-1 ratio. Lyophilisation is a safe procedure for the preservation of frozen prostate tissue samples as it permits recovery of the markers without compromising their use for diagnostic purposes.