AbstractBackground: The reported incidence of prostate cancer (PCa) has increased in recent years due to the aging of the population and increased testing; however mortality rates have remained largely unchanged. Studies have shown deficiencies in predicting patient outcome for both of the major PCa diagnostic tools, namely prostate specific antigen (PSA) and trans rectal ultrasound ‐guided biopsy (TRUS). Therefore, serum biomarkers are needed that accurately predict prognosis of PCa (indolent vs. aggressive) and can thus inform clinical management.
Aim: This study uses surface enhanced laser desorption/ionization time of flight mass spectrometry (SELDI‐TOF‐MS) analysis to identify differential serum protein expression between PCa patients with indolent vs. aggressive disease categorised by Gleason grade and biochemical recurrence.
Materials and Methods: A total of 99 serum samples were selected for analysis. According to Gleason score, indolent (45 samples) and aggressive (54) forms of PCa were comparedusing univariate analysis. The same samples were then separated into groups of different recurrence status (10 metastatic, 15 biochemical recurrence and 70 nonrecurrences)and subjected to univariate analysis in the same way. The data from Gleason score and recurrence groups were then analysed using multivariate statistical analysis to improve PCa biomarker classification. Using gel‐electrophoresis technique, candidate biomarkers were separated and identified by LC‐MS/MS and validated using optimised Western blot (WB) immunoassay against 100 PCa serum samples from the Wales Cancer Bank (50 as indolent group & 50 as aggressive group).
Results: The comparison between serum protein spectra from indolent and aggressive samples resulted in the identification of twenty‐six differentially expressed protein peaks (p<0.05), of which twenty proteins were found with 99% confidence. A total of 18 differentially expressed proteins (p<0.05) were found to distinguish between recurrence groups; three of these were robust with P<0.01. Sensitivity and specificity within the Gleason score group was 73.3% and 60% respectively and for the recurrence group 70% and 62.5%. Four candidate biomarkers (categorised by Gleason score) were identified using a novel 1 D LC‐MS/MS technique. The candidate biomarker with m/z of 9.3 kDa was found to be upregulated in aggressive PCa patients, and was identified as Apolipoprotein C‐I (ApoC‐I). Another three candidate biomarkers (22.2, 44.5 and 79.1 kDa) were found downregulated in the aggressive group and up‐ regulated in the indolent group and identified as apolipoprotein D (ApoD), putative uncharacterised protein (PUP) and Transferrin (TF), respectively. The utility of the putative biomarkers was examined by Western blot (WB) analysis of 100 blinded PCa serum samples. None of the three SELDI identified biomarkers were able to statistically identify PCa patients’ progression.
Conclusion: The use of SELDI to identify potential PCa progression biomarkers has been confirmed in PCa patients. However, immunovalidation of prospective biomarkers in blinded PCa serum samples was unsuccessful. This study demonstrates the importance of validation in ascertaining the true clinical applicability of a cancer biomarker.
|Date of Award||Jan 2011|
|Supervisor||Claire Aukim-Hastie (Supervisor) & Jeremy Mills (Supervisor)|