The effects of whole body hyperthermia on the pharmacokinetics and toxicity of the basic 2-nitroimidazole radiosensitizer Ro 03-8799 in mice

Localized hypoxia within the subgranular zone determines the early survival of newborn hippocampal granule cells

The majority of adult hippocampal newborn cells die during early differentiation from intermediate progenitors (IPCs) to immature neurons. Neural stem cells in vivo are located in a relative hypoxic environment, and hypoxia enhances their survival, proliferation and stemness in vitro. Thus, we hypothesized that migration of IPCs away from hypoxic zones within the SGZ might result in oxidative damage, thus triggering cell death. Hypoxic niches were observed along the SGZ, composed of adult NSCs and early IPCs, and oxidative byproducts were present in adjacent late IPCs and neuroblasts. Stabilizing hypoxia inducible factor-1α with dimethyloxallyl glycine increased early survival, but not proliferation or differentiation, in neurospheres in vitro and in newly born SGZ cells in vivo. Rescue experiments in Bax(fl/fl) mutants supported these results. We propose that localized hypoxia within the SGZ contributes to the neurogenic microenvironment and determines the early, activity-independent survival of adult hippocampal newborn cells.

Effect of whole-body hyperthermia on the pharmacokinetics and toxicity of lonidamine in dogs

The pharmacokinetics and toxicity of intravenous lonidamine were investigated in dogs receiving four cycles of lonidamine (400 or 800 mg/m2) +/- whole-body hyperthermia (WBH). Clearance and volume of distribution in dogs receiving lonidamine during WBH increased 1.6-2.3 and 1.9-3.5-fold respectively, relative to dogs receiving lonidamine under euthermic conditions (p < 0.02). In dogs receiving lonidamine under euthermic conditions or 400 mg/m2 + WBH, the area under the lonidamine concentration versus time curve (AUC) measured during the fourth treatment was 21-58% lower than the first treatment AUC. However, in dogs receiving 800 mg/m2 + WBH, the fourth treatment AUC was four-fold higher than the first treatment AUC (p < 0.02). This suggests repeated exposure to 800 mg/m2 lonidamine and WBH impairs lonidamine metabolism. Weakness, hypoglycaemia, and elevations in amylase, alanine aminotransferase, alkaline phosphatase and bilirubin were more severe or occurred exclusively in dogs receiving 800 mg/m2 + WBH. Since these changes were attributable to marked AUC increases, which occurred secondary to repeated exposure to 800 mg/m2 lonidamine during WBH, 400 mg/m2 was identified as the maximum tolerable dose to be administered intravenously to dogs during WBH.

Relationship between the melanin content of a human melanoma cell line and its radiosensitivity and uptake of pimonidazole

The intra-cellular uptake of the weakly basic radiosensitiser pimonidazole (PIMO) was determined as a function of the pigmentation of Na11+ human melanotic melanoma cells in vitro. Two experimental conditions were considered: exponentially growing cells (Exp.) and plateau-phase cells (PI.). The melanin content of Na11+ cells ranged from 500 micrograms/g cell weight in exponentially growing cells to 6000 micrograms/g in heavily pigmented plateau-phase cells. Cells were exposed to PIMO (medium dose, 0.2 mmol/dm3; 58.2 micrograms/ml). The intra-cellular concentration ranged from 163 micrograms/g in Exp. to 900 micrograms/g in pigmented Pl.; the latter being equivalent to an intra- to extracellular concentration ratio (Ci/Ce) of 17. However, this increase in the cellular uptake of PIMO was not accompanied by an increase in radiosensitising efficiency. In comparison, the Ci/Ce for etanidazole (ETA), a radiosensitiser that is uncharged at physiological pH, remained approximately constant at 1 for all values of melanin contents. Treatment of Na11+ tumours in vivo with [3H]-PIMO resulted in a tumour:blood ratio of about 3 at 30-60 min after administration. However, at 24 h a grain count of label derived from [3H]-PIMO showed that picnotic areas of tumours contained levels that were some 40 times greater than the background value. This high level of label was coincident with areas of highest apparent melanin content. In conclusion, PIMO accumulates in very heavily pigmented melanoma cells present in necrotic zones with picnosis. As these cells are probably non-clonogenic, PIMO is not suitable for use in melanoma radiotherapy.

Relationship between intracellular concentration and radiosensitizing effect of pimonidazole and etanidazole on two human melanoma cell lines

A study on the uptake and radiosensitizing properties of pimonidazole (PIMO) and etanidazole (ETA) was made in vitro with two melanoma cell lines: Na11+ and Na11-. The amelanotic Na11- was derived from the pigmented Na11+ cell line and was characterized by the complete absence of pigmentation in vitro. Plateau-phase cells were heavily pigmented for the Na11+ line whereas exponential cells showed a lower melanin content. Radiosensitivity was studied using an in vitro colony assay; intracellular drug concentration was determined by HPLC. For both cell lines the uptake of PIMO was always higher than the uptake of ETA, and slightly higher in hypoxia than in air. The uptake of PIMO was exceptionally high in plateau-phase cells of the pigmented Na11+ cell line. The radiosensitizing effect of ETA did not differ greatly as a function of the cell kinetics in both cell lines, whereas the radiosensitizing effect of PIMO was cell line-dependent. Sensitization of exponential cells by PIMO was similar in both cell lines but significantly less in plateau-phase cells, with the heavily pigmented Na11+ cell line being least affected, despite a three-fold increase in PIMO uptake observed in plateau cells relative to exponentially growing Na11+ cells. The uptake of PIMO may be related to the high melanin content of plateau-phase Na11+ cells and therefore this in vitro model may be useful for predicting the effects of agents such as PIMO towards melanotic melanomas in vivo.

Effects of local hyperthermia on the tissue levels and toxicity of three radiosensitizers in mice

The toxicity of the radiosensitizers misonidazole (MISO), demethylmisonidazole (DEMISO) and pimonidazole (PIM) in mice can be affected differently when combined with local hyperthermia at 43 degrees C for 30 min. At a dose of 1 mg/g, only MISO plus heat resulted in 50% lethality in animals over a period of 7 days post-treatment, whereas 100% survival was observed in the case of DEMISO and PIM. The enhanced lethality may be associated with the production of toxic intermediates of MISO. Heat did not affect the levels of DEMISO in the tissues studied (plasma, brain and tumour), whereas those of PIM were markedly lowered in tumour but not affected in brain for up to 4 h after combined treatment. MISO was found to be decreased in the tumour at all times but affected differently in brain after 1 and 2 h, initially decreasing and then increasing significantly. In all cases the treatment sequence, i.e. sensitizer plus heat or vice-versa, did not affect the rate of survival. At a dose of 2 mg/g, DEMISO plus heat was found to be more toxic when DEMISO was given first (25% survival) compared to 58% on reversal. However, the levels of DEMISO in the tissues were not affected by heat. Thus, it would appear that there is no correlation between parent drug levels measured in plasma, tumour or brain and hyperthermia-induced drug lethality.

Effects of elevated temperature on misonidazole O-demethylation by mouse liver microsomes: kinetic and stability studies of a model mixed-function oxidase reaction

We investigated the effects of a range of temperatures (33 degrees-44 degrees C) on the stability and kinetics of C3H mouse liver microsomal misonidazole (MISO) O-demethylase in vitro. Microsomal O-demethylase activity was stable for 60 min at 37 degrees C and for 30 min at 41 degrees C but was steadily inactivated with longer incubation times. Inactivation at 44 degrees and 47 degrees C was exponential, with half-lives of 41 and 11 min, respectively. MISO O-demethylation followed Michaelis-Menten kinetics from 33 degrees to 44 degrees C. The apparent Vmax for desmethylmisonidazole (Ro 05-9963) formation was decreased by 32% (from 2.14 to 1.47 nmol min-1 mg-1 protein) with a 4 degrees decrease from 37 degrees to 33 degrees C. An increase of 4 degrees from 37 degrees to 41 degrees C enhanced the Vmax by 47%, but there was only an additional 9% increase for a further 3 degrees rise to 44 degrees C. Apparent Km values were unaltered at about 1.6 mM. These results show that elevated temperatures in the clinically relevant hyperthermia range (41 degrees-44 degrees C) can enhance a model mixed-function oxidase reaction in vitro. Such effects may be important for the metabolism, activity and toxicity of anticancer drugs combined with hyperthermia in vivo.

Effects of localised tumour hyperthermia on pimonidazole (Ro 03-8799) pharmacokinetics in mice

We have investigated the effects of localised tumour hyperthermia (LTH; 43.5 degrees C x 30 min) on the acute toxicity and pharmacokinetics of the hypoxic cell sensitizer pimonidazole (Ro 03-8799) in mice. There were three treatment groups: unrestrained controls, sham-treated and LTH treated mice. LTH had minimal effects on the acute toxicity (LD50/7d) of pimonidazole with no significant difference between the three treatment groups. Pharmacokinetic studies were carried out at the maximum tolerated dose (MTD; approximately 60% LD50) of 437 micrograms g-1 i.v. in plasma, brain and tumour. Sham tumour treatment consistently increased plasma drug concentrations compared to unrestrained controls but had minimal effects on the elimination t1/2. The AUC0-infinitive was increased by 35% and the plasma clearance decreased by 26%. By contrast, LTH had minimal effects on these parameters compared to sham treatment. Brain pimonidazole concentrations were increased in restrained mice (sham and LTH treatments) compared to unrestrained controls, but average brain/plasma ratios were similar in all three groups at between 400 and 500%. Sham tumour treatment markedly reduced peak tumour pimonidazole concentrations compared to unrestrained controls giving a 29% lower AUC0-180min. Average tumour/plasma ratios were reduced from 236 to 129%. The most important finding was that LTH further reduced pimonidazole tumour concentrations, giving a 31% lower AUC0-180 min compared to sham treated tumours. Tumour/plasma ratios for pimonidazole were reduced by 41%. Plasma exposure to the pimonidazole N-oxide metabolite, Ro 31-0313, was unaltered by LTH. The markedly reduced drug concentrations in heated tumours may be a result of hyperthermia-stimulated bioreductive drug activation.

Ro 03-8799: preferential relative uptake in human tumor xenografts compared to a murine tumor: comparison with SR-2508

The pharmacokinetics of Ro 03-8799 and SR-2508 were studied in 6 tumor cell lines (5 human, 1 murine) transplanted into athymic nude mice. The human tumors were rectocolic adenocarcinomas (HRT18, HT29) and melanomas (Be11, Na11+, Na11-), the rodent tumor was a mammary tumor (EMT6). The concentrations of drugs in tumor, blood, plasma, and red cells were measured by HPLC 15, 30, and 45 minutes after the simultaneous i.v. injection of 0.1 mg/g of each compound. Little or no difference was found between the concentrations in the plasma, blood, and red cells for either drug; SR-2508 concentration was higher than that of Ro 03-8799. Both compounds were concentrated in all the tumors, the concentration increases or decreases as a function of the time, depending on the cell line; there was more Ro 03-8799 in the pigmented melanomas than in the other tumors. The relative uptake of Ro 03-8799 and SR-2508 in the tumor was evaluated by the ratio of drug concentrations in the tumor and in the blood. The results suggest that Ro 03-8799 and SR-2508 accumulated in all the tumors, the relative uptake of Ro 03-8799 was higher than that of SR-2508. For human tumors, the ratios increased between 15 and 45 minutes. They ranged from 1.2 to 3.6 for SR-2508 and from 3.1 to 14.6 for Ro 03-8799. For Ro 03-8799, the highest ratios were found for the melanomas; the uptake was higher in the pigmented Na11+ tumors than in the non-pigmented Na11-. The ratios for EMT6 were about 2.3 for SR-2508 and 4.7 for Ro 03-8799; these ratios varied slightly between 15 and 45 minutes.

Hypoxic cell radiosensitizers in the treatment of high grade gliomas: a new direction using combined Ro 03-8799 (pimonidazole) and SR 2508 (etanidazole)

The hypoxic cell radiosensitizers Ro 03-8799 (pimonidazole) and SR 2508 (etanidazole) have been evaluated for their simultaneous penetration into human brain tumors and surrounding normal tissue. Thirteen patients received a dose of 1 g of each agent, infused over a 10 minute period during neurosurgery. Samples of glioma (20), brain (10) and cerebrospinal fluid (1) were obtained at a mean time (+/- SD) of 31 +/- 18 min from the end of infusion. A 24 hr plasma time course was measured in six patients. Nitroimidazole concentrations were determined by HPLC. For a mean dose of 0.55 g/m2 of each agent, the mean tumor concentrations (+/- SD) were 17.0 +/- 12.0 micrograms/g for Ro 03-8799 and 13.5 +/- 10.9 micrograms/g for SR 2508. The tumor/plasma ratios were 279 +/- 230% and 47 +/- 34% respectively. For adjacent 'normal' brain tissue, the radiosensitizer concentrations were 29.9 +/- 13.1 micrograms/g for Ro 03-8799, and 4.0 +/- 1.7 micrograms/g for SR 2508, and the brain/plasma ratios were 430 +/- 29% and 14 +/- 8% respectively. There was a significant trend towards increasing accumulation of both agents with time, in both tumor and normal brain. Concentrations in cerebrospinal fluid were very low. Plasma pharmacokinetics for Ro 03-8799 were similar to previous experience, but for SR 2508 the terminal half-life was greater in this series by a factor of 1.3. The results confirm that Ro 03-8799 is distributed widely in the central nervous system, and demonstrate that SR 2508 can achieve high tumor concentrations when the blood-brain barrier is compromised. The concentrations achieved with the combination are indicative of a significant advantage over metronidazole, misonidazole, or either agent alone, and normalized to the therapeutic dose of 0.75 g/m2 plus 2.0 g/m2 SR 2508 are consistent with those giving additive sensitization in an in vivo mouse tumor model.