Flow cytometric measurement of proliferating cell nuclear antigen (PCNA) in solid tumors

Purpose: The importance of cell kinetic parameters for prognosis and therapeutic strategy is widely accepted in oncology. Repopulation is a major problem in radiotherapy of head and neck tumors. Various assays exist for measuring the proliferation characteristics of individual tumors. However, the existing methods have several drawbacks. Materials and Methods: PCNA (proliferating cell nuclear antigen) is expressed in a cell cycle dependent manner. There is a DNA-bound, S-phase specific fraction and a nucleoplasmatic, extractable fraction, which is detectable in all phases except G0. We describe a method for simultaneous measurement of PCNA and DNA in solid tumors using flow cytometry. The assay was applied to three different sublines (AT1, HI, H) of the Dunning rat prostate tumor R3327 and biopsies of twelve human head and neck squamous cell carcinomas. The PCNA-assay was compared to the standard BrdUrd-assay (bromodeoxyuridine) by simultaneous measurement of PCNA and BrdUrd in the animal tumors. Results: Percentages of PCNA-positive cells of 29 ± 4% (AT1), 25 ± 7% (HI) and 3 ± 1% (H) were calculated for the animal tumors with good rank correlation with the BrdUrd-LI. The PCNA-indices for human tumors ranged from 5 ± 1% up to 70 ± 9%. Conclusion: The flow cytometric PCNA-assay can be applied to standard biopsy material and yields reproducible results with an intratumor variation of about 5% which is small compared to the wide range of PCNA-indices in our series. The method may enhance the pretherapeutic assessment of tumor proliferation kinetics.