The Effect of Proliferation Heterogeneity on Idodeoxyuridine Uptake by Glioma Cells Cultured as Monolayer and Spheroids Measored by Flowcytometry

Herogeneous proliferative activity of glioma cells (ie non-cycling cells) is on of the main barriers to the therapeutic of radiolabelled IudR. Therefore it is important to evaluate the proliferative heterogeneity on IUdR theoretical because theoretical calculation suggests that this could be the dominant factor in the efficacy of treatment. The uptake of IUdR in solutions of conceteration ranging from 10µM to 100 µM was studied using UVW glioma cell line cultured as monolayer in exponential and plateau phases also spheroids in different range of size (100-200 µm) and 700-1000 µm diameter) and different incubation times, from one to four doubling times by was studied by flow cytometry. The results of the study confirm that there is an inverse relationship between the proportion of cycling cells and spheroid diameter. In monolayer cultures, more than 95% of exponentially growing cells and 62% of plateau phase cells, were labelled with IudR after one doubling time. However, the labelling index in the small spheroids (100-200 µm) was approximately 76% and 28% for large spheroids (700-1000 µm) after one volume doubling time incubation (52 hours). The proporetion of cells that incorporate IUdR in small and large sizes of spheroids inceased with the increasing of the incubation period with IUdR from one to four volume doubling times. Cunclusion: The success of curative targeting strategies is governed by the ability to sterilise all clonogens. Therefore, theraputic regimes must be designed to overcome the limitations imposed by proliterative heterogenety, including the presence of viable tumour cells that are temporarily out of cycle or cycling very slowly.