Hypersensitivity to low single doses and split-dose recovery: two manifestations of induced resistance that might be related

Purpose: To study retrospectively the relationship between intrinsic radios ensitivity (SF2), and both the low-dose inducible response (alpha(s)/alpha( r)) and the amount of split-dose recovery (beta(RR)) Materials and methods: A total of 53 sets of experimental data obtained wit h 44 human cell lines were collected from the literature and the above rela tionships were studied. Results: Analysis showed a statistically significant correlation between al pha(s)/alpha(r) and SF2 (p=0.0023, 10 sets of data), and a statistically si gnificant inverse correlation between beta(RR) and SF2 (P=0.0005, 36 sets o f data, AT excluded). Furthermore, the analysis of the relationship between the challenge dose SF2 (after a clinical-sized priming dose) and that of t he single-dose SF2 (27 sets of data, AT excluded) showed a statistically si gnificant correlation (p<0.0001), which deviates from, and becomes higher t han, the one-to-one relationship for single-dose SF2 <0.30, suggesting that the final response to fractionated irradiation in radiosensitive cells mig ht not be predictable on the basis of simple reconstitution of survival fro m the single-dose treatment. Conclusion: The comparison between the two relationships: SF2/(alpha(s)/alp ha(r)) and SF2/beta(RR), suggests some parallelism indicating that these tw o phenomena may be inversely correlated and could be attributed to induced resistance mechanisms that might be triggered differently in sensitive and resistant cell lines.