Cellular kinetics of murine lung: model system to determine basis for radioprotection with keratinocyte growth factor.
OBJECTIVE
Normal tissue toxicity remains a dose limitation for cancer radiotherapy and chemoradiotherapy. Growth factors offer a novel means of mitigating normal tissue radiotoxicity. In particular, keratinocyte growth factor (rHuKGF), whose proliferative activity is restricted to epithelial cells, holds promise on the basis of the findings of preclinical models of epithelial cytoprotection and the clinical developments to date. We report the radioprotection of murine lung by an increase in tissue cellularity after rHuKGF-induced proliferation.


METHODS
Flow cytometric and image analysis techniques after bromodeoxyuridine labeling were used to estimate proliferative parameters. Our specialized analytical methods measure not only labeling indexes, but also the durations of S and G(2)+M phases, potential doubling times, and the net cell production rate. Image analysis techniques were used to identify the specific cell types that were proliferating (type II pneumocytes).


RESULTS
Lung labeling index control values (0.5%) rose to a maximum (5.5%) at 3 days after intratracheal rHuKGF, returning to normal by Day 7. The potential doubling time fell from 66 days to 4.4 days. The net cell production rate rose from a control value of 1%/d to >15%/d by Day 3. This resulted in a nearly twofold increase in alveolar epithelial cellularity, which remained significantly elevated on Day 7. Saline-treated control animals exhibited no significant changes in the proliferative parameter values or cellularity. On the basis of these data, mice were irradiated, solely to the thorax, with ranges of single doses of 250 kVp X-rays 7 days after either intratracheal administration of 5 mg/kg rHuKGF or phospate-buffered saline. This interval was chosen because the proliferative response of the type II cells was finished but the cellularity of the lung remained increased. Pretreatment with rHuKGF extended the latent period before onset of pneumonitis after all radiation doses. rHuKGF treatment 7 days before thoracic irradiation significantly protected against pneumonitis (median effective dose 13.7 Gy, 95% confidence limit 13.4-14.0) compared with the control pretreatment with phosphate-buffered saline (median effective dose 12.8 Gy, 95% confidence limit 12.6-13.1).


CONCLUSIONS
The data showed that an increase in tissue cellularity, caused by rHuKGF treatment before irradiation, protected the lung from damage due to pneumonitis.
Terry
Nicholas H A
NH
Department of Experimental Radiation Oncology, Box 066, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. ntflow@odin.mdacc.tmc.edu
Brinkley
John
J
Doig
Andrew J
AJ
Ma
Jun
J
Patel
Nalini
N
White
R Allen
RA
Mahajan
Nitin
N
Kang
Yun
Y
D000465:Algorithms; D000818:Animals; D001973:Bromodeoxyuridine / Q000032:analysis; D002455:Cell Division / Q000187:drug effects; D004307:Dose-Response Relationship, Radiation; D004847:Epithelial Cells / Q000187:drug effects* / Q000528:radiation effects; D051523:Fibroblast Growth Factor 7; D005346:Fibroblast Growth Factors / Q000494:pharmacology*; D005434:Flow Cytometry; D051379:Mice; D023421:Models, Animal; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D017564:Radiation Pneumonitis / Q000517:prevention & control*; D011835:Radiation Protection; D011994:Recombinant Proteins / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology
C496454:Fgf7 protein, mouse; D011994:Recombinant Proteins; D051523:Fibroblast Growth Factor 7; D012965:Sodium Chloride; D005346:Fibroblast Growth Factors; D001973:Bromodeoxyuridine