Cell kinetic analysis of murine squamous cell carcinomas: a comparison of single versus double labelling using flow cytometry and immunohistochemistry.

The study was originally set up to measure accurate cell kinetic parameters in two murine squamous cell carcinomas (scc) for comparison with radiobiological data on proliferation during radiotherapy. The tumours, AT84 and AT478, were both moderately well differentiated aneuploid scc. In the course of the study, several comparisons of techniques were made in two different centres. This paper reports on the results of those comparisons involving two different detection methods (flow cytometry and immunohistochemistry), single vs double labelling, and in vivo and in vitro labelling, the latter using tissue slices incubated under high pressure oxygen. Pulse labelling studies with bromodeoxyuridine (BrdUrd) showed that the labelling indices (LI) were not significantly different after in vitro or in vivo labelling. In addition, the flow cytometry (FCM) and immunohistochemistry (IHC) methods also gave labelling indices which were not significantly different. Only tumour cells were analysed in these studies by selecting cells on the basis of aneuploidy (FCM) or morphology (IHC). The DNA synthesis time of the tumour cells were analysed by both techniques. For FCM, the Relative Movement method was used (Begg et al., 1985). For IHC, a double labelling method was used, employing BrdUrd and triated thymidine (3H-TdR) administered several hours apart, detected simultaneously using immunoperoxidase and autoradiography, respectively. When both labels were administered in vivo, there was good agreement for Ts between the FCM and IHC methods. Attempts were also made to measure Ts in vitro using both techniques. With double labelling, it was found that cells did not take up the second label, implying a failure of cycle progression. This was confirmed by FCM results, showing no movement of labelled cells through the S-phase, despite an initially high uptake. This could not be influenced by lowering the DNA precursor concentration or by adding foetal calf serum. This indicates that DNA synthesis times are difficult or impossible to measure in vitro in fresh tumour explants. Finally, the double labelling IHC method allowed intratumoural variations of both LI and Ts to be studied. Both parameters were found to vary markedly throughout the tumour volume, particularly for larger tumours (600 mg), giving calculated local potential doubling time values (Tpot) ranging from 1-7 days.