Quantifying intracellular radioresponse diversity in irradiated sandwich cultures via micronucleus expression.
Determining the degree of diversity in therapeutic sensitivity exhibited by a tumour population is of considerable clinical importance. In addition to being a contributor to radiation resistance, diversity is the basis for variation in sensitivity over the course of treatment. To study intrapopulation diversity in radiosensitivity following gamma-irradiation (2 Gy), distributions of the number of micronuclei/binucleate cell were obtained for human cervix carcinoma sandwich populations. Cell-to-cell diversity in radioresponse (micronucleus expression) was quantified using the overdispersion index ((variance/mean)--1). As measured by this index, the radioresponse diversity of sandwich cultures sharply increased after introduction of oxygen/nutrients to the cultures, mimicking tumour reperfusion. In addition, a strong correlation was found between this measure of diversity and the extent to which the fraction of cells without micronuclei exceeds that expected from a Poisson distribution. This correlation indicates that for a diverse population there can be a significant departure of the aggregate population sensitivity (determined, for instance, by log-survival in a clonogenic assay) from that inferable from simply averaging per-cell sensitivities (reflected, e.g. by mean number of chromosome aberrations/cell). Our experimental results suggest a model attributing diversity in a population to its being a mixture of distinct subpopulations, each biologically homogeneous with respect to micronucleus expression, and each contributing an individual Poisson-distributed micronucleus response. We demonstrate how such radiodiversity may be quantified and show that reoxygenation of a microenvironmentally heterogeneous population leads to an increase in its radiobiological diversity.
Hlatky
L
L
Joint Center for Radiation Therapy, Harvard Medical School, Boston 02115, MA, USA.
Van Buren
T
T
Hahnfeldt
P
P
D002453:Cell Cycle; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005720:Gamma Rays; D006801:Humans; D066298:In Vitro Techniques; D015162:Micronucleus Tests; D010100:Oxygen; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*
D010100:Oxygen