The usefulness of mild temperature hyperthermia combined with continuous tirapazamine administration under reduced dose–rate irradiation with γ-rays

Figures & data

Table I.  Plating efficiencies and micronucleus frequencies at 0 Gy.

Treatment	Total cells	Quiescent cells
Plating efficiency (%)
No drug	70.7 (61.9–79.5)*	–
MTH**	72.8 (65.0–80.6)	–
TPZ#	27.0 (22.7–31.3)	–
TPZ + MTH	22.3 (20.2–24.4)	–
Micronucleus frequency
No drug	0.053 (0.047–0.059)	0.083 (0.075–0.094)
MTH	0.059 (0.052–0.066)	0.111 (0.101–0.121)
TPZ	0.144 (0.129–0.159)	0.177 (0.159–0.195)
TPZ + MTH	0.167 (0.147–0.187)	0.208 (0.187–0.229)

Notes: When the ranges of 95% confidence limits have no overlapping between any two values, the difference between the two values was considered significant (p < 0.05). *Numbers in parentheses are 95% confidence limits, determined using mean values, standard deviations, and the numbers of observations on which the means and standard deviations were based. **Mild temperature hyperthermia. #Tirapazamine (Continuous subcutaneous administration).

Figure 1. The clonogenic cell survival curves after γ-ray irradiation with conventional high dose-rate irradiation (HDRI) (left panel) or reduced dose-rate irradiation (RDRI) (right panel) in combination with tirapazamine (TPZ) and/or mild temperature hyperthermia (MTH) or without TPZ or MTH. TPZ was given by continuous subcutaneous administration. Bars represent 95% confidence limits.

Figure 2. The normalized micronucleus frequencies after γ-ray irradiation with conventional high dose-rate irradiation (HDRI) (left panel) or reduced dose-rate irradiation (RDRI) (right panel) in combination with tirapazamine (TPZ) and/or mild temperature hyperthermia (MTH) or without TPZ or MTH in the total tumour cell population. TPZ was given by continuous subcutaneous administration. Bars represent 95% confidence limits.

Figure 3. The normalized micronucleus frequencies after γ-ray irradiation with conventional high dose-rate irradiation (HDRI) (left panel) or reduced dose-rate irradiation (RDRI) (right panel) in combination with tirapazamine (TPZ) and/or mild temperature hyperthermia (MTH) or without TPZ or MTH in the quiescent tumour cell population. TPZ was given by continuous subcutaneous administration. Bars represent 95% confidence limits.

Table II.  The effect* of TPZ** and/or MTH*** on each end-point.

Treatment	Total cells	Quiescent cells
Surviving fraction = 0.02
HDRI#
MTH	1.05 (1.0–1.1)##	–
TPZ	1.25 (1.2–1.3)	–
TPZ + MTH	1.4 (1.3–1.5)	–
RDRI###
MTH	1.1 (1.05–1.15)	–
TPZ	1.35 (1.3–1.4)	–
TPZ + MTH	1.45(1.4–1.5)	–
Normalized micronucleus frequency = 0.4
HDRI
MTH	1.05 (1.0–1.1)	1.1 (1.05–1.15)
TPZ	1.3(1.25–1.35)	1.35 (1.3–1.4)
TPZ + MTH	1.4 (1.35–1.45)	1.45 (1.4–1.5)
RDRI
MTH	1.1 (1.05–1.15)	1.15(1.1–1.2)
TPZ	1.35 (1.3–1.4)	1.4 (1.35–1.45)
TPZ + MTH	1.5 (1.45–1.55)	1.55 (1.5–1.6)

Notes: When the ranges of 95% confidence limits have no overlapping between any two values, the difference between the two values was considered significant (p < 0.05). *The dose of radiation required to obtain each end-point without each treatment in relation to that required to obtain each end-point with each treatment. **Tirapazamine (Continuous subcutaneous administration). ***Mild temperature hyperthermia. #High dose-rate irradiation. ##Numbers in parentheses are 95% confidence limits, determined using mean values, standard deviations, and the numbers of observations on which the means and standard deviations were based. ###Reduced dose-rate irradiation.

Table III.  The effect* of TPZ** and/or MTH# on the repair from radiation-induced damage.

Treatment	Total cells	Quiescent cells
Surviving fraction = 0.02
γ-rays only	1.2 (1.15–1.25)##	–
+MTH	1.15 (1.1–1.2)	–
+TPZ	1.1 (1.05–1.15)	–
+TPZ + MTH	1.05 (1.0–1.1)	–
Normalized micronucleus frequency = 0.4
γ-rays only	1.5 (1.4–1.6)	1.6 (1.5–1.7)
+MTH	1.45 (1.4–1.5)	1.5 (1.45–1.55)
+TPZ	1.4 (1.35–1.45)	1.45 (1.4–1.5)
+TPZ + MTH	1.35 (1.3–1.4)	1.4 (1.35–1.45)

Notes: When the ranges of 95% confidence limits have no overlapping between any two values, the difference between the two values was considered significant (p < 0.05). *The dose of radiation required to obtain each end-point with reduced dose-rate irradiation (RDRI) in relation to that required to obtain each end-point with high dose-rate irradiation (HDRI). **Tirapazamine (Continuous subcutaneous administration). #Mild temperature hyperthermia. ##Numbers in parentheses are 95% confidence limits, determined using mean values, standard deviations, and the numbers of observations on which the means and standard deviations were based.

Table IV.  Dose ratios* for quiescent tumour cells relative to the total tumour cell population.

Treatment	HDRI**	RDRI***
Normalized micronucleus frequency = 0.4
γ-rays only	1.8 (1.7–1.9)#	1.9 (1.8–2.0)
+MTH##	1.75 (1.7–1.8)	1.85 (1.75–1.95)
+TPZ###	1.7 (1.65–1.75)	1.75 (1.7–1.8)
+TPZ + MTH	1.65 (1.6–1.7)	1.7 (1.65–1.75)

Notes: When the ranges of 95% confidence limits have no overlapping between any two values, the difference between the two values was considered significant (p < 0.05). *The dose of radiation required to obtain a normalized micronucleus frequency of 0.4 in quiescent tumour cells in relation to that required to obtain a normalized micronucleus frequency of 0.4 in total tumour cells. **High dose-rate irradiation. ***Reduced dose-rate irradiation. #Numbers in parentheses are 95% confidence limits, determined using mean values, standard deviations and the numbers of observations on which the means and standard deviations were based. ##Mild temperature hyperthermia. ###Tirapazamine (Continuous subcutaneous administration).