Tumor hypoxia imaging in orthotopic liver tumors and peritoneal metastasis: a comparative study featuring dynamic 18F-MISO and 124I-IAZG PET in the same study cohort

PURPOSE

The purpose of this paper is to compare the uptake of two clinically promising positron emission tomography (PET) hypoxia targeting agents, (124)I-iodoazomycin galactopyranoside ((124)I-IAZG) and (18)F-fluoromisonidazole ((18)F-FMISO), by dynamic microPET imaging, in the same rats bearing liver tumors and peritoneal metastasis.

METHODS

Morris hepatoma (RH7777) fragments were surgically implanted into the livers of four nude rats. Tumors formed in the liver and disseminated into the peritoneal cavity. Each rat had a total of two to three liver tumors and peritoneal metastasis measuring 10-15 mm in size. Animals were injected with (18)F-FMISO, followed on the next day (upon complete (18)F decay) by (124)I-IAZG. The animals were imaged in list mode on the microPET system from the time of injection of each tracer for 3 h and then again at 6 h and 24 h for the long-lived (124)I-IAZG tracer (4.2-day half-life). Micro computed tomography (CT) scans of each rat were performed for co-registration with the microPET scans acquired with a liver contrast agent, allowing tumor identification. Regions of interest (ROIs) were drawn over the heart, liver, muscle, and the hottest areas of the tumors. Time-activity curves (TACs) were drawn for each tissue ROI.

RESULTS

The (18)F-FMISO signal increased in tumors over the 3-h time course of observation. In contrast, after the initial injection, the (124)I-IAZG signal slowly and continuously declined in the tumors. Nevertheless, the tumor-to-normal-tissue ratios of (124)I-IAZG increased, but more slowly than those of (18)F-FMISO and as a result of the differentially faster clearance from the surrounding normal tissues. These pharmacokinetic patterns were seen in all 11 tumors of the four animals.

CONCLUSIONS

(18)F-FMISO localizes in the same intra-tumor regions as (124)I-IAZG. The contrast ratios (tumor/background) reach similar values for the two hypoxia tracers, but at later times for (124)I-IAZG than for (18)F-FMISO and, therefore, with poorer count statistics. As a consequence, the (18)F-FMISO images are of superior diagnostic image quality to the (124)I-IAZG images in the Morris hepatoma McA-R-7777 tumor model.

Evaluation of the radiosensitizing effects of RK28 intravenous, intraarterial, and intratumoral injections on the rabbit VX2 tumor system

PURPOSE

To evaluate the differences in the radiosensitizing effects of intravenous (i.v.) injection, intraarterial (i.a.) injection, and intratumoral (i.t.) injections of the hypoxic cell radiosensitizer RK28 ([1-(4'-hydroxy-2'-butenoxy)methyl-2-nitroimidazole], a 2-nitroimidazole with an acyclic sugar analogue substituted at the N-1 position of the imidazole ring) using an animal experimental system.

METHODS AND MATERIALS

Rabbit VX2 tumors, which were implanted in the muscle of left hind legs and grown to 3 cm in diameter, were treated with RK28 (80 mg/kg x b.wt.) before 15 Gy of local x-ray irradiation. The auricular vein and the left saphenous artery were used for systemic injection and regional injection, respectively. For i.t. injection, a 21-gauge needle with three lateral holes was positioned in the central area of the tumor. Tumor regression was precisely evaluated by computed tomograpy (CT), and survival time was also studied. Using high-performance liquid chromatography (HPLC), pharmacokinetic studies for RK28 and its seven major metabolites were performed in tumor and serum at 0, 10, 20, 30, and 60 min after drug injection was completed.

RESULTS

Radiosensitizing effects of RK28 were considered present after i.a. injection (p < 0.05) and i.t. injection (p < 0.05) after analyzing tumor volumes on day 21 after treatment. Increased survival was not observed in any group with RK28 injection compared with survival in the group treated by x-ray irradiation alone. Pharmacokinetic studies showed the average concentration of RK28 in the tumor during x-ray irradiation was 1.3 times higher after i.a. injection and 3.5 times higher after i.t. injection than that after i.v. injection. The time modifying factor50 (TMF50: ratio of time for tumor to decrease by 50%, radiation alone vs. radiation plus drug) was calculated to be 1.5 after i.v. injection, 1.7 after i.a. injection, and 2.3 after i.t. injection. The values of TMF50 correlated to the average concentrations of RK28 in the tumor. As to metabolites of RK28, beta-glucuronated compound and cysteine conjugate were highly detected. The concentrations of cysteine conjugate were higher in the tumor than in serum via i.v. injection.

CONCLUSIONS

Radiosensitizing effects of RK28 were observed on the rabbit VX-2 tumor system after i.a. or i.t. injection. Pharmacokinetic studies proved that radiosensitizing effects depended on the concentration in the tumor, though the administration routes were different. Combined forms with nonprotein thiols were detected. However, survival benefits were not obtained by RK28. For clinical applications of RK28, i.a. or i.t. injection could facilitate better local control of cancer.

Neurotoxicity of misonidazole in rats following intravenous administration

Misonidazole is a hypoxic cell radiosensitizer that induces a peripheral neuropathy in humans after exceeding a schedule-dependent cumulative threshold dose. Clinical studies of misonidazole have been conducted using oral administration, whereas most other radiosensitizers have been administered intravenously. Since route of exposure can potentially influence the toxicity of xenobiotics, the objective of this study was to assess the neurotoxicity of misonidazole in rats following intravenous dosing using a battery of routine clinical, neurofunctional, biochemical, and histopathologic screening methods. Male Sprague-Dawley rats were administered intravenous doses of misonidazole at 0 (vehicle control), 100, 200, 300, or 400 mg kg-1 once per day, 5 days per week, for 2 weeks. Animals were evaluated for neurofunctional and pathological changes following termination of treatment (Days 15-17) and at the end of a 4 week observation period (Days 43-45). During the dosing phase, hypoactivity, salivation, rhinorrhea, chromodacryorrhea, rough pelage and ataxia were observed at 400 mg kg-1, and body weight gain of the 300 and 400 mg kg-1 groups was significantly decreased relative to the vehicle controls by 24% and 49%, respectively. Corresponding reductions in food consumption were 8% and 23%, respectively. Although most 400 mg kg-1 animals appeared normal on Day 15 prior to the neurofunctional evaluations, rotorod testing precipitated a number of clinical signs including: ataxia, impaired righting reflex, excessive rearing, tremors, vocalization, circling, head jerking, excessive sniffing and hyperactivity. All of these animals recovered and appeared normal from Day 17 through study termination. There were no treatment-related effects on motor activity, acoustic startle response, rotorod performance, forelimb group strength, toe and tail pinch reflexes, tibial nerve beta-glucuronidase activity or tail nerve conduction velocity. Although hindlimb grip strength of the 400 mg kg-1 group was significantly decreased by 17% relative to the vehicle controls on Day 15, this finding appeared related to the reduced food consumption and body weight gain in these animals. No microscopic changes were detected in peripheral nerves. Necrosis and proliferation of fibrillary astrocytes (gliosis) were seen in the cerebellum and medulla of the 400 mg kg-1 animals on Day 16. Gliosis in these same brain regions was observed in the 300 and 400 mg kg-1 groups on Day 44. The results show that intravenous administration of misonidazole to rats causes dose-limiting central nervous system toxicity without effects on peripheral nervous tissue. The lack of peripheral neurotoxicity was most likely due to a combination of several interrelated factors including route of administration, duration and intensity of the dosing regimen, and total cumulative dose.

Adverse effects at adjuvant treatment of liver metastases in rat with RSU-1069 + microspheres, or liposomal MTP-PE

Rats were inoculated via the portal vein with a suspension of tumor cells from a transplantable dimethylhydrazine-induced adenocarcinoma of rat colon. In one set of experiments, the bioreductive drug RSU-1069 was injected once via the portal vein with or without degradable starch microspheres (DSM) 10 mins after tumour cell inoculation. In another set the immunostimulator liposomal-encapsulated muramyl tripeptide phosphatidyl-ethanolamine (MTP-PE) was injected via the portal vein or penile vein 1 day before tumour-cell inoculation and then twice a week. The experiments were finished after 2 to 3 weeks. Tumour take, numbers and volumes were measured.

RESULTS

RSU-1069 enhanced tumour growth when combined with DSM. Liposomal MTP-PE also increased tumour growth.

CONCLUSION

A bioreductive drug combined with microspheres, known to suppress the growth of an established tumour, may enhance its growth in the adjuvant setting. An accepted immunostimulator may enhance tumour take. Drugs used for the treatment of tumours must be carefully employed, if applied in an adjuvant setting. The effect on the normal immune system should be further studied.

The EORTC randomized trial on three fractions per day and misonidazole (trial no. 22811) in advanced head and neck cancer: long-term results and side effects

From 1981 to 1984, a randomized study was done by the EORTC Radiotherapy Group comparing a fractionation schedule with three fractions per day (multiple fractions per day, MFD), with or without misonidazole, to conventional fractionation. The aim of the study was to obtain improved local and regional control and survival by shortening of the treatment time in the first 2 weeks of irradiation. Three fractions of 1.6 Gy/day (4-h interval) were given during 10 irradiation days to a total of 48 Gy. After 3-4-weeks interval, a boost was given to 67.2 or 72 Gy also in three fractions per day. This schedule was compared to an identical arm with misonidazole 1 g/m2/day and a third arm with conventional fractionation (70 Gy in 35 fractions, 7 weeks or 75 Gy in 44 fractions, 9 weeks). A total number of 523 patients was included in the study. Acute mucositis was much heavier in patients treated with three fractions per day (Van den Bogaert et al. Int. J. Radiat. Oncol. Biol. Phys. 8: 1649-1655, 1982). Early results, communicated in 1986 (Van den Bogaert et al. Int. J. Radiat. Oncol. Biol. Phys. 12: 587-591, 1986) showed no differences in treatment outcome between the three treatment arms. Long-term results and data on late effects are now available. Survival at 5 years was 18% (SE 1.9%) and locoregional control was 27% (SE 2.9%). No statistically significant differences could be observed between the three treatment arms.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and evaluation of suppositories for RK-28 (a new radiosensitizer) using rabbits

The pharmacokinetics of RK-28 [1-(4-hydroxy-2-butenoxy)methyl-2-nitroimidazole], a new hypoxic cell radiosensitizer, was studied following intravenous, oral, and rectal administration to rabbits. After an oral administration of RK-28 solution, the plasma concentration of RK-28 was considerably lower than that after intravenous administration through all time periods, and the absolute bioavailability was a mere 4.2%. It was presumed that a specific acid-catalized decomposition of RK-28 progressed in the stomach, and also, the absorbed RK-28 suffered first-pass effects in the liver. In contrast, the absolute bioavailability following the rectal administration of a solidified RK-28 suppository preparation was significantly increased in comparison with that obtained by other administration routes. Also, RK-28 emulsion suppositories were prepared by emulsifying various amounts of the drug with 1-hexadecanol and hydrogenated castor oil (HCO 60) at 80 degrees C, and these were administered into the rabbit rectum. The resulting absolute bioavailability was 91% for the RK-28 emulsion suppository and 86.9% for an RK-28 emulsion suppository containing small amounts of Eudispert hv. These values were better than those in rats. The rectal administration of the RK-28 emulsion suppository containing small amounts of Eudispert hv showed a preferable plasma concentration-time pattern that reflects on radiation therapy.

Low concentrations of nitroimidazoles: effective radiosensitizers at low doses

PURPOSE

There have been various reports that nitroimidazole radiosensitizers are less effective modifiers of radiation response in the clinically relevant x-ray dose regions (0-4 Gy) than they are at doses used in classical in vitro experiments. Our studies at low concentrations of etanidazole led us to question this generalization, and our purpose was to further investigate low concentrations at low doses, using the microscopic location of cells to facilitate these experiments. The observations are compared with data on these drugs in the literature using other methods and systems.

METHODS AND MATERIALS

Survival of V79 cells after irradiation in hypoxia +/- drug at various concentrations was assessed using the Cell Analyser (DMIPS) for low doses, in comparison with the standard clonogenic assay (higher doses). Enhancement ratios (ERs) were calculated at 80% and 2% survival, respectively.

RESULTS

Etanidazole (SR-2508) consistently gave higher ERs at low doses (measured at 80% survival) than at high doses (survival 2%), when cells were exposed to drug concentrations below approximately 2 mM (e.g., at 1 mM, ER80% = 2.2, ER2% = 1.8 in CHO cells after 1 h preincubation at 37 degrees C). Preincubation of cells for 1 h or 15 min at 37 degrees C with etanidazole prior to irradiation increased the ERs at high and low doses but did not change the "cross-over" behavior (ER80% > ER2% at low concentrations, ER2% > ER80% above 2 mM, regardless of pretreatment at 37 degrees C or cell line, CHO and V79 cells), whereas the 5-nitroimidazole nimorazole consistently gave the same ERs whether determined at high or low radiation doses (e.g., at 1 mM, 1 h preincubation at 37 degrees C ER80% = ER2% = 1.3). This crossover behavior also occurred after irradiation/preincubation at 0 degrees C. The 2-nitroimidazole predecessor, misonidazole, shows the same cross-over behavior.

CONCLUSION

Two nitroimidazoles at low concentrations appear to be as effective sensitizers (or better) at low doses (80% S); at high doses (2% S).

Pharmacokinetics of RK-28 (a new radiosensitizer) and pharmaceutical design of a suppository form using rats

The pharmacokinetics of RK-28, a new hypoxic cell radiosensitizer, was studied in rats following its intravenous, intraportal, oral, and rectal administration. The pharmaceutical design of an RK-28 suppository form was also examined. After intravenous injection, RK-28 was rapidly removed from the plasma (biological half-life of 17 min) and its area under the curve (AUC) was proportional to the amount of RK-28 administered. The absolute bioavailability of RK-28 was 59.7% for intraportal administration and 36.9% for oral administration. Following oral administration of RK-28, it seems likely that specific acid-catalyzed decomposition of RK-28 takes place in the stomach and then the absorbed RK-28 undergoes first-pass metabolism in the liver. When "solidified RK-28 suppository," made by solidifying molten RK-28, was inserted into the rectum, hepatic first-pass metabolism could be avoided substantially. The resulting absolute bioavailability of RK-28 increased to 75%. Furthermore, "RK-28 emulsion suppository," prepared by emulsifying RK-28 with 1-hexadecanol and hydrogenated castor oil (HCO 60) at 80 degrees C, showed a plasma concentration-time curve very suitable for radiation therapy; the maximum plasma concentration was attained 30 min after rectal administration and then decreased within a short period. Administration of "RK-28 emulsion suppository," resulted in an absolute bioavailability of 76%.

Degradable starch microspheres in cytostatic treatment of a liver carcinoma; experimental studies in rats with 5-fluorouracil, tauromustine, carmustine, doxorubicin and RSU-1069

The degradable starch microspheres (DSM) used have a size of 45 microns and are dissolved by amylase in blood. After intraarterial administration of a mixture of DSM and cytostatic drugs the coinjected drugs remain for a longer time in the target tissue/tumor. A transient hypoxia occurs. Systemic exposure of drugs is decreased. Rats with a carcinoma implanted into the liver were given DSM and drugs via the hepatic artery. DSM did not significantly increase the incorporation of 5-fluorouracil (5-FU) into liver tumor RNA. The incorporation of 5-FU into intestinal and bone marrow RNA increased. DSM increased the antitumor effect of doxorubicin, tauromustine, carmustine and RSU-1069 (aziridine 2-nitroimidazole). Side effects, such as liver and gastric necroses and body weight loss, appeared in some rats. The toxic overspill to the stomach seemed to be reduced by giving the DSM in two parts, with all the cytotoxic drug in the first part. The effect on liver and tumor was not decreased by this procedure. DSM alone had no anti-tumor effect. DSM alone decreased liver UDP-glucuronic acid in tumor-free rats, given either by the hepatic artery or, in the double dose, by the portal vein. DSM alone did not increase liver NADPH-cytochrome c reductase activity or serum ASAT (aspartate-aminotransferase) or ALAT (alanine-aminotransferase), indicating that the DSM are inert to the liver, when infused into the tributary vessels.

Mouse jejunal response to multifraction treatments with gamma radiation and chemicals

Jejunal response in adult BALB/c mice was studied after acute (15.0 Gy) and fractionated irradiation (2.5 Gy x 6, 5.0 Gy x 3 or 7.5 Gy x 2) with or without 30 min prior injection of fractionated doses of misonidazole (MISO) or bleomycin (BLM). The crypt survival, crypt and villous cellularity, mitotic index and cell death in the jejunal cross section on day 3 post treatment was evaluated. Acute irradiation produced extensive damage to the jejunal mucosa with almost complete loss of crypts and collapse of villi. Dose fractionation resulted in significant tissue sparing with restoration of near normal histology. MISO administered prior to irradiation significantly reduced the crypt survival and increased the mitotic activity and abnormal divisions. But the crypt and villous cellularity remained within the irradiated control range. BLM produced a higher enhancement of the radiation damage, significantly reducing both crypt survival and crypt and villous cell populations. The protective effect of radiation dose fractionation was counteracted by the drug pretreatment. The results warrant caution in the use of these drugs with radiation in the treatment of abdominal malignancies.

Intra-hepatic-arterial infusion of misonidazole--an experimental study of regional radiosensitisation by intraarterial embolisation

The purpose of this study was to generate a selective radiosensitising effect by the intra-hepatic-arterial infusion of misonidazole (MISO). MISO (10 mg) was infused after transcatheter hepatic-arterial embolisation into the livers of rabbits bearing VX2 liver cancer. This procedure was followed by 15 Gy electron irradiation. Evaluation of tumour volume and histological examination was carried out on the 7th day after treatment. The greatest tumour response was obtained in the group which received MISO followed by radiation and was characterised by extensive fibrosis around the tumour and nearly complete tumour necrosis. Liver cell regeneration was also noted in adjacent liver tissue. The advantages of regional infusion of MISO following hepatic-arterial embolisation are: (1) Selectivity increased radiosensitivity of liver cancer alongside very low drug concentration in the plasma. (2) Reduced or absent deleterious side effects of MISO with higher tumour/normal tissue ratios of drug concentration. (3) Reduced cost due to the lower dosage of MISO required for regional infusion.

[The experimental and clinical study of hyperthermia with thermosensitizer for gastric cancer patients with peritoneal seeding]

We examined experimentally and clinically the effect of misonidazole (MISO), a hypoxic cell radiosensitizer, in combination with hyperthermia. First, tissue blood flow and tumor growth of xenoplanted human gastric cancer in nude mice were measured after treatment with MISO 500 mg/kg ip plus hyperthermia at 40.5, 42.0 and 43.5 degrees C. Also clinically, 17 advanced gastric cancer patients with peritoneal seeding underwent intraperitoneal hyperthermic perfusion (IPHP). They were given MISO 1.45 g/m2 po twice (12 hours and 5 hours before IPHP). And plasma MISO levels were measured. MISO plus hyperthermia produced a more prolonged decrease of the tumor blood flow than hyperthermia alone. At 43.5 degrees C, TbF recovered 2 days after the treatment. MISO plus hyperthermia also made tumor growth delay more marked than hyperthermia alone. In gastric cancer patients treated with MISO plus IPHP, T 1/2 of serum MISO was 7.7 hours and the AUC was 1,087 micrograms.hr/ml. There were no side effects observed which were caused by MISO. Thus MISO can be an effective thermosensitizer when used in combination with hyperthermia.

The same chemicals induce different neurotoxicity when administered in high doses for short term or low doses for long term to rats and dogs

Dose- and term-dependent differences in the location and nature of brain lesions induced in rats and dogs by 2,5-hexanedione (2,5-HD), misonidazole, clioquinol, and acrylamide are reported. Subchronic neuropathies ("distal axonopathy") were induced by low-dose administration of these neurotoxicants and at high doses, lesions caused by acute or subacute neurotoxicity were found in the central nervous system (CNS). In rats, 2,5-HD induced extracellular edema, nerve cell degeneration, and axonal degeneration in the cerebellar and vestibular nuclei. Similar lesions were observed in misonidazole-treated dogs and clioquinol induced nerve cell degeneration in the hippocampus and malacia in the piriform lobes of these animals. In rats, acrylamide induced degeneration of Purkinje cells. Although the mechanism(s) underlying the differential neurotoxicity of high and low doses of these neurotoxicants remains unclear, we suggest certain biochemical mechanisms, cytotoxic edema and excitotoxicity, as factors in the production of such lesions after high-dose treatment.

Effect of administration schedules on the potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) by misonidazole in subcutaneous 9L tumors

Our previous studies demonstrated that metabolism of misonidazole (MISO) by hypoxic cells is required to potentiate the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in sc 9L tumors. To determine the influence of administration schedules on this chemosensitization, tumors were either clamped to produce a reversible hypoxia or left unclamped. MISO (2.5 mmoles kg-1) was administered to rats with unclamped tumors simultaneously with BCNU (9 or 12 mg kg-1), 20 min before BCNU, or 2.5 hr before BCNU, and the drug pharmacokinetics and BCNU cytotoxicity were measured. MISO administered 20 min or 2.5 hr before BCNU increased the plasma elimination half-time (t1/2) of BCNU, but MISO administered simultaneously with BCNU did not change the plasma elimination t1/2 of BCNU. In unclamped sc 9L tumors, all administration schedules decreased the peak BCNU concentration and increased the initial BCNU elimination t1/2; however, the BCNU exposure dose (AUC0-infinity) calculated from these data did not change significantly. In agreement with the AUC calculations, none of the administration schedules altered the BCNU cytotoxicity in unclamped tumors. If the tumors were clamped for 5-120 min after the peak MISO concentration was reached, BCNU-induced cell kill was increased by a constant factor of 3 over the first hour of the clamping period and by an additional factor of 7 over the second hour of the clamping period. If the tumors were clamped for 2 hr after the peak MISO concentration was reached and then BCNU administered 0-60 min after the clamp was released, this chemosensitization remained at a constant factor of approximately 20 for the first 10 min, and then decreased rapidly to a factor of approximately 3 by 20 min after the clamp was released. These data indicate that in sc 9L tumors, (1) at least two biochemical mechanisms are involved in this MISO-BCNU interaction, one of which depends on the duration and extent of the metabolism of MISO by hypoxic cells, and (2) reoxygenation does not immediately eliminate the potentiation of BCNU by MISO. These data also suggest that MISO should be given 2-4 hr before BCNU to achieve the maximum chemosensitization in clinical trials.

Modification of alkylating agent induced cell kill by 2-nitroimidazoles in unclamped and clamped SC 9L tumors

Enhanced cell kill has been observed when experimental tumors were treated with alkylating agents in combination with 2-nitroimidazoles (2-NI). In this study, modification of the cell kill induced by cyclophosphamide (CY) and an analog, ifosfamide (IFO), by two radiation sensitizers, misonidazole (MISO) and etanidazole (SR-2508), was measured. Three important parameters were determined: (a) the necessity for hypoxic reduction of the 2-NI to achieve an increase in tumor cell kill, (b) the optimal timing for administration of the alkylating agents and the 2-NI, and (c) the degree of enhancement of the CY- and IFO-induced cell kill. The subcutaneous (sc) 9L tumor model in male Fisher 344 rats was used in these experiments, and the endpoint measured was clonogenic cell survival 18-20 hr after treatment. Under hypoxic conditions, MISO potentiated both CY- and IFO-induced cell kill with a sensitizer enhancement ratio of approximately 1.3 and 1.5, respectively, at the 10(-3) survival level. This enhancement was seen when CY was administered simultaneously or 1.5 hr prior to MISO administration. A similar enhancement of CY-induced cell kill was measured under hypoxic conditions when SR-2508 was used. Enhanced IFO-induced cell kill was measured under hypoxic conditions only when the IFO was given 1 hr before MISO administration. No enhancement of the IFO-induced cell kill was observed when SR-2508 was used instead of MISO. Increased normal tissue damage (i.e., hemorrhagic cystitis) was observed when the MISO was administered along with CY or IFO. Four conclusions can be drawn from these data. Metabolism of the 2-NI by hypoxic cells is necessary for potentiation of CY- or IFO-induced cell kill. Only MISO can potentiate the cell kill induced by IFO. The timing of administration of the alkylating agents and the 2-NI is a critical determinant of the extent of the cell kill obtained. Cell kill induced by IFO appears to be enhanced by MISO to a greater extent than the cell kill induced by CY.

2-Nitroimidazole potentiation of nitrosourea induced cytotoxicity in subcutaneous implants of rat 9L brain tumor cells

To determine if the 2-nitroimidazole (2-NI) and the nitrosourea (NU) in a brain tumor chemopotentiation trial should be selected on the basis of known structure-activity relationships (electron affinity, lipophilicity, alkylating activity, carbamoylating activity), s.c. implants of rat 9L brain tumor cells were treated with combinations of misonidazole (MISO) or etanidazole (SR-2508) administered under oxic and hypoxic conditions, and BCNU, CCNU or chlorozotocin (CLZ) administered under oxic conditions. Cell kill was assessed by an in vivo to in vitro colony formation assay. To mimic the 'preincubation effect', the 2-NI was injected i.p., and 30 min later the tumor was clamped. After 2 hr, the clamp was released, and the NU administered immediately. MISO (2.5 mmole/kg) and SR-2508 (3.75 mmole/kg) reached the same peak tumor concentration in 30 min. Both 2-NIs were metabolized at the same rate in the clamped tumors; however, metabolism of the 2-NIs by hypoxic cells over the 2 hr clamping period did not produce any measurable s.c. 9L cell kill. The relative effectiveness of the NUs for killing oxic s.c. 9L tumor cells was: BCNU greater than CCNU greater than CLZ. Clamping the tumor prior to NU administration did not change the NU cytotoxicity. No potentiation of the NU cytotoxicity by the 2-NIs was observed in oxic tumors. Although metabolism of MISO by hypoxic cells did not result in potentiation of CLZ cytotoxicity at any dose, it resulted in potentiation of BCNU cytotoxicity at all doses and CCNU cytotoxicity at high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement in therapeutic ratio of radiotherapy for a murine sarcoma by indomethacin plus misonidazole

In this study we asked whether the improvement in the therapeutic ratio of radiotherapy by indomethacin (INDO), which potentiates tumor radioresponse through stimulation of the immune system, could be further improved by combining it with the hypoxic cell radiosensitizer misonidazole (MISO). Mice bearing the syngeneic sarcoma fibrosarcoma (8 mm) in the leg were treated with single graded doses of gamma-rays to the tumor or with irradiation combined with INDO, MISO, or both drugs. Local tumor control was the end point of tumor radioresponse. In addition, the effect of these drugs on radiation-caused hair loss and leg contractures was assessed. INDO increased tumor radioresponse by a factor of 1.31, but it did not affect either hair loss or leg contractures. MISO increased tumor radioresponse by a factor of 1.86, hair loss by a factor of 1.69, and leg contractures by a factor of 1.54, thus providing only a small therapeutic gain. The combined INDO plus MISO treatment increased tumor radioresponse by a factor of 2.72, which was more than the additive effect of the individual drugs. On the other hand, the combined treatment caused no additional hair loss compared to that caused by MISO only. Overall, our results show that INDO plus MISO treatment increased tumor radioresponse more than INDO or MISO alone and provided a significant therapeutic gain. Furthermore, they illustrate that combinations of two radiopotentiating agents with different mechanisms of action may improve the radiotherapeutic effect.

Oral (po) dosing with RSU 1069 or RB 6145 maintains their potency as hypoxic cell radiosensitizers and cytotoxins but reduces systemic toxicity compared with parenteral (ip) administration in mice

RB 6145 is a pro-drug of the hypoxic cell radiosensitizer RSU 1069 with reduced systemic toxicity. The maximum tolerated dose (MTD) of RSU 1069 for C3H/He mice was 80 mg/kg (0.38 mmol/kg) ip but 320 mg/kg (1.5 mmol/kg) following po administration. The MTD values of RB 6145 were 350 mg/kg (0.94 mmol/kg) ip and 1 g/kg (2.67 mmol/kg) po. Toxicity of RSU 1069 toward bone marrow stem cells was also less after po administration than after ip administration; 0.1 mmol/kg ip RSU 1069 and 0.38 mmol/kg po RSU 1069 both reduced the surviving fraction of clonogenic CFU-A cells by 50%. Oral administration of RSU 1069 resulted in lower spermatogenic toxicity. No loss of intestinal crypts was detected after ip or po administration of RSU 1069. Some nephrotoxicity was observed in half of the mice given the highest po dose of 1.5 mmol/kg of RSU 1069; this was not observed following the highest ip dose of drug. For RSU 1069 and RB 6145, administered by either route, the maximum hypoxic cell radiosensitization in murine KHT sarcomas, occurred when the drugs were given 45-60 min before 10 Gy of X rays. The degree of radiosensitization produced by a particular dose of either compound was largely independent of the route of administration. Preliminary pharmacokinetic studies, using 3H-RSU 1069, suggested that anti-tumor efficacy correlated with peak blood level of label and concentration in the tumor at the time of irradiation, which were not reduced by po compared with ip administration. Normal tissue toxicity tended to correlate with total exposure over time, which was reduced approximately two-fold by po administration. Oral administration of RSU 1069 or RB 6145, as well as being convenient, may give therapeutic benefit since dose-limiting toxicity in mice was reduced compared with parenteral administration, whereas radiosensitizing activity was less affected.

[Intraarterial infusion of hypoxic radiosensitizer RK28 in rabbit VX2 tumor system]

The effect of regional intra-arterial infusion of a hypoxic cell radiosensitizer RK28 (2-nitro-imidazole nucleoside analogue) on rabbit VX2 tumor was evaluated. Rabbits each weighing 2.5-3 kg were implanted with VX2 tumor in the left hind legs. Solid tumors grown up to 3 cm in diameter were treated with X-ray irradiation. Tumor volumes were assayed weekly by computed tomography (CT). Six rabbits were treated with 15 Gy of X-ray irradiation alone, and the other six rabbits were treated with intra-arterial infusion of RK28 (80 mg/kg) two minutes before 15 Gy of irradiation. The latter tumors regressed more rapidly than the former (p less than 0.01), and the latter rabbits seemed to survive longer than the former. The pharmacokinetics of RK28 and its metabolites in tumor tissue and serum were measured by high performance liquid chromatography (HPLC) using six rabbits. During irradiation, a high concentration of the agent was achieved in tumor tissue. It is suggested that a successful radiosensitizing effect will be obtained when regional intra-arterial infusion of RK28 is clinically combined with intraoperative radiation therapy and brachytherapy.

Misonidazole conjugates of the colorectal tumor associated monoclonal antibody 17-1A

The radiation sensitizer misonidazole has been linked to the monoclonal antibody 17-1A which recognizes a nonshed antigen of a human gastrointestinal tumor. Linkage was accomplished through a hemisuccinate of misonidazole attached by a mixed anhydride coupling and gave a conjugate whose plasma half-life (for drug cleavage) was ca. 70 h. The degree of substitution on the antibody could be precisely regulated by varying the reactant ratios. The binding avidities of the resulting conjugates to the SW1116 colorectal tumor cells decrease logarithmically with increasing drug load. Four to six misonidazoles per antibody represented the optimum drug loading on this system. Enzymatic cleavage of the conjugate-drug union took place at both the ester and the amide linkages with the former scission predominating.

Addition of 2-nitroimidazole radiosensitizers to cis-diamminedichloroplatinum(II) with radiation and with or without hyperthermia in the murine FSaIIC fibrosarcoma

We have examined the ability of misonidazole (MISO) or etanidazole (ETA) to improve the antitumor efficacy of cisplatin (CDDP), hyperthermia, and radiation in the FSaIIC murine fibrosarcoma. A growth delay of about 25 days was produced with CDDP (5 mg/kg) and hyperthermia (43 degrees C, 30 min) prior to radiation (3 Gy daily for 5 days) on day 1. The addition of MISO (1 g/kg) on day 1 resulted in a tumor growth delay of about 28 days. The addition of ETA at 0.5 g/kg or 1 g/kg resulted in tumor growth delays of about 33 and 43 days, respectively. Tumor cell survival assay showed that MISO was additive with CDDP either at 37 degrees C or with hyperthermia (43 degrees C, 30 min). In contrast, ETA at both 0.5 g/kg and 1 g/kg was dose modifying over the CDDP dosage range at 37 degrees C or 43 degrees C. Analysis of tumor cell killing in Hoechst 33342 selected bright (presumably oxic) and dim (presumably hypoxic) tumor cell subpopulations demonstrated that the addition of MISO to the CDDP trimodality regimen increased killing in the dim cell subpopulation, while the addition of ETA increased tumor cell killing in both subpopulations, although the greater effect was in the dim cell subpopulation. These results indicate that ETA may add to the efficacy of the CDDP trimodality in the clinic and may be of value as a chemosensitizer with CDDP.

Anal submucosal injection: a new route for drug administration in pelvic malignancies. III. Misonidazole distribution in serum, uterus and vagina: an experimental study

The anal and oral administration routes were compared in 40 rats to study the distribution of misonidazole (MIS), a radiation sensitizer, in the serum, uterus and vagina. 14C-labelled MIS was administered in a dose of 0.2 ml water/100 g body weight containing 1 microCi MIS. The dose was given orally in 20 rats and was injected in the anal submucosa in another 20 rats. Animals were then sacrificed after 15, 30, 60 or 120 min or after 24 h. Serum samples was taken at the time of sacrifice; organs were dissected and radioactivity was determined in each by the internal standard method. The study has shown that the highest drug concentration in uterus and vagina relative to serum was achieved by the anal submucosal route. They showed a drug concentration of 10 and 8 times, respectively, of the serum level after 15 min in contrast to oral administration, which in the same period of time produced a drug concentration of 1/5 and 1/4 the serum level. The anal route thus offers an adequate channel for MIS administration to promote radiation responsiveness in cancer of uterus and vagina.

The in vivo response of a C3H mammary carcinoma to treatment with misonidazole, cyclophosphamide and radiation

The potential chemosensitizing effect of the nitroaromatic radiosensitizer misonidazole (MISO) on the alkylating agent cyclophosphamide (CTX), and the interactions of these agents with radiation, have been investigated in a C3H mammary carcinoma in CDF1 mice. MISO at 1,000 mg/kg caused a small increase in tumour growth time (TGT; time to reach 3 times treatment volume) from 3.6 days to 4.5 days. CTX (100 mg/kg) increased the TGT to 15.7 days. The combined treatment of MISO and CTX given with intervals of either 15 min or 4 h increased the TGT to 23.3 and 23.8 days respectively. The radiation enhancement ratio (ER) was found to be 2.13 and 1.10 for MISO administered before or after x-rays respectively. The corresponding ERs for CTX were 1.16 and 1.22. The two drugs given in combination resulted in significant radiation ERs of 2.68 (both drugs given within 30 min before x-rays), 3.00 (MISO 30 min before and CTX 3 1/2 h after x-rays) and 1.40 (both drugs given after x-rays). In contrast to what has previously been reported, and in contrast to the tumour regrowth delay data, the results of the tumour control experiments were found to reflect no more than an additive action of the two drugs when used together with radiation in vivo.

Cytotoxic effect of misonidazole and cyclophosphamide on aerobic and hypoxic cells in a C3H mammary carcinoma in vivo

The chemosensitising effect of the nitroaromatic radiosensitiser misonidazole (MISO) on the alkylating agent cyclophosphamide (CTX) has been investigated in a C3H mammary carcinoma in CDF1 mice. The selective cytotoxicity against aerobic and hypoxic cells was measured indirectly, using a local tumour control (TCD50) assay. The hypoxic fraction was calculated from the dose difference between the TCD50S for tumours irradiated either in air or under clamped conditions. The relative survival of tumour cells after drug therapy was expressed as a surviving fraction (SF). CTX (100 mg kg-1) was found to be considerably more toxic towards hypoxic than aerobic cells (SF 4% versus 52%). MISO (1000 mg kg-1) was almost exclusively toxic to hypoxic cells (SF 22%). When MISO and CTX were administered simultaneously a decrease in the surviving fraction was observed. The effect on aerated cells was found to be 10-fold more than expected from addition of toxicities, suggesting a chemosensitising effect on these cells by MISO when used in combination with CTX. No synergistic effect was found on radiobiologically hypoxic cells. The exact role of hypoxia for the development of chemosensitisation seems to be complex and requires additional research in the future.

Manipulation of oxygenation in a human tumour xenograft with BW12C or hydralazine: effects on responses to radiation and to the bioreductive cytotoxicity of misonidazole or RSU-1069

The influence of altered tumour oxygenation on the responses to radiation and/or bioreductive 2-nitroimidazole compounds was studied in a well differentiated, human, colon adenocarcinoma (MAWI), grown as a subcutaneous xenograft in nude mice. Tumour growth delays were measured after local, single 5-18 Gy doses of X-rays. BW12C, which inhibits dissociation of oxyhaemoglobin, produced radioprotection similar to that resulting from clamping off the tumour blood supply during irradiation. Hydralazine, a vasoactive agent, also appeared to give radioprotection. BW12C or misonidazole (MISO) alone had no measurable inhibitory effect on xenograft growth. Hydralazine or RSU-1069 slightly increased the time for tumours to reach 6 times their original volumes. When hydralazine was given 40 min after a dose of 800 mg/kg of MISO, without X-rays, growth delays in excess of 5 tumour volume doubling times resulted and fewer tumour cells were present in histological sections. Lower doses of MISO combined with hydralazine were ineffective. Other combinations of bioreductive cytotoxic agents and methods of manipulation of tumour blood flow/oxygenation induced slight and inconsistent growth delays. Hydralazine was injected after irradiation of tumours in mice previously treated with various doses of MISO in an attempt to exploit the bioreductive cytotoxic potential of MISO in conjunction with its radiosensitizing properties; however, tumour growth delays were similar with or without hydralazine after irradiation. Thus, post-irradiation restriction of tumour blood flow appears to be an ineffective therapeutic strategy in this human xenograft tumour model.

Pharmacokinetic analysis in intraperitoneal hyperthermic chemotherapy of far-advanced gastric cancer patients

The pharmacokinetics of mitomycin C (MMC) has been evaluated in 10 far-advanced gastric cancer patients by means of an intraperitoneal hyperthermic perfusion (IPHP) using MMC to prevent and/or treat peritoneal dissemination. Further, misonidazole (MIS), which was used as a thermosensitizer, also was evaluated. The IPHP was performed for 120 min right after surgical procedure, using a closed-circuit with an inflow perfusate temperature from 46.3 approximately 47.5 degrees C and an outflow temperature of 44.0 approximately 46.0 degrees C. The MMC level in the perfusate was 10 micrograms/ml at the onset of IPHP and thereafter decreased to 1.7 +/- 0.4 micrograms/ml minutes later. The average AUC (area under the curve) in the perfusate was 3.3 micrograms/ml during the IPHP. The MMC level in the peripheral blood was 0.15 +/- 0.04 micrograms/ml 30 min after start of the IPHP and increased to 0.18 +/- 0.05 micrograms/ml at the end of IPHP. Additionally, the MIS level in the peripheral blood was 64.7 +/- 10.3 micrograms/ml 60 min after the IPHP, 60.6 +/- 9.2 micrograms/ml at 120 min, and then decreased to 32.8 +/- 10.3 micrograms/ml at 12 hours after IPHP. The AUC was calculated as being 975 micrograms.hr/ml. Again, the level in the portal vein blood was calculated from the peritoneal permeability and the peripheral blood level of the drug. From data, it was concluded that the perfusate and portal vein blood level of MMC, the peripheral blood level of MIS, as well as the perfusate temperature, are important in providing a favorable, safe, antitumoral treatment.

Chemosensitization at reduced nitroimidazole concentrations by mixed-function compounds combining 2-nitroimidazole and chloroethylnitrosourea

A mixed-function compound (I-278) combining 2-nitroimidazole and chloroethylnitrosourea has been shown to be greater than 2-fold more toxic to hypoxic HeLa-MR cells than to cells similarly exposed under aerobic conditions, consistent with chemosensitization of nitrosourea toxicity by the 2-nitroimidazole Misonidazole (MISO). However, in the case of I-278, the enhancement resulted from micromolar concentrations of 2-nitroimidazole as opposed to the millimolar quantities required for a similar enhancement by MISO. These experiments provide evidence (1) that the enhanced hypoxic toxicity of I-278 is not attributable to additional, independent hypoxic cell killing by the nitroimidazole group and (2) that the interaction between the two functions under hypoxic conditions results in increased crosslink formation typical of chemosensitization. The data strongly suggest that the chemosensitizing efficiency of nitroimidazoles can be dramatically improved by covalent linkage to a chloroethylating species.

Combined radiation-protective and radiation-sensitizing agents. IV: Measurement of intracellular protector concentrations

Radiosensitization of hypoxic V79 Chinese hamster cells by 0.5 mM misonidazole at approximately 0-4 degrees C is substantially enhanced by pretreating the cells overnight with 0.1 mM buthionine sulfoximine, which lowers the cellular glutathione content to 5% of control values (from 4 mM to approximately 0.2 mM). The enhanced sensitization is reversed by concentrations of exogenous cysteine that are much lower (0.02 mM) than the original glutathione content. Reduced Co-enzyme A affords reversal of the enhancing effect at concentrations of about 1 mM. Sodium ascorbate gives no protection at all even at concentrations of 2 mM. The intracellular concentration of the reducing agents was measured using a spin-through oil technique. There was no diffusion of Co-A (MW greater than 750) or ascorbate (excluded by charge) into the cells. In contrast, cysteine was rapidly concentrated by factors of 4-10, even at the low temperatures used. Extracellular ascorbate's inability to radioprotect argues against electron transfer across the cell membrane as a mechanism for radioprotection. This mechanism could have explained the ability of exogenous thiols to radioprotect in former studies using glutathione, and in the present studies using Co-A. The potential of cysteine to be concentrated by cells poses a problem in the interpretation of "exogenous protection" by non-diffusing thiols, since trace contamination by cysteine could lead to the actual protection observed. Cysteine could also be formed by exchange reactions of exogenous thiols with the disulfide of cysteine, present in all media formulations.

High-dose melphalan, misonidazole, and autologous bone marrow transplantation for the treatment of metastatic colorectal carcinoma. A phase I study

To augment the antitumor effect of high-dose melphalan and determine pharmacokinetics we conducted a phase I trial of escalating doses of high-dose IV melphalan with the chemosensitizer misonidazole for patients with advanced colorectal carcinoma. Fourteen patients with modified Dukes D adenocarcinoma of the colorectum were treated with a single course of melphalan (40-60 mg/m2 i.v. bolus q.d. X 3 days) and misonidazole (1-3 g/m2 p.o. q.d. X 3 days) followed by autologous bone marrow transplantation. Toxicity consisted of severe myelosuppression, moderate nausea and vomiting, and mild mucositis and diarrhea. One patient developed unexplained renal tubular acidosis, and a diffuse encephalopathy occurred in another patient. Three patients died within the first 30 days after the start of treatment, two due to tumor progression and one due to sepsis and disseminated intravascular coagulation-induced intracerebral hemorrhage. Six of 14 patients achieved a partial response, and the median response duration was 4 months (range 3-10 months). Analysis of misonidazole serum concentrations showed similar pharmacokinetics to those previously reported, suggesting no significant drug interaction with intravenous melphalan. Mean peak serum concentrations ranged from 81.8 micrograms/ml to 115.2 micrograms/ml at the second and third misonidazole dose levels, which approximate those known to provide effective chemosensitization with melphalan in animal models. In this phase I study, we showed that maximally tolerated doses of intravenous melphalan can safely be combined with oral misonidazole. In view of the large volumes of oral misonidazole required at the highest dose level, subsequent studies to determine the maximally tolerated dose of misonidazole should employ the intravenous form.

Induction of tumour hypoxia post-irradiation: a method for increasing the sensitizing efficiency of misonidazole and RSU 1069 in vivo

It is known that hydralazine can decrease blood flow to experimental murine tumours. A consequence of this, in the KHT sarcoma, is the induction of close to 100 per cent radiobiological hypoxia, which lasts for nearly 2 h following i.v. injection of 5 mg/kg hydralazine to the mouse. This phenomenon is exploitable in order to increase the apparent sensitizing efficiency of the nitroheterocyclic radiosensitizers, misonidazole and RSU 1069, and is demonstrated using the treatment schedule: sensitizer----60 min----X-rays----1 min----hydralazine. Such a strategy will first take advantage of the radiosensitizing properties of the nitroimidazole, then after irradiation the hydralazine should allow expression of the differential toxicity towards hypoxic cells known to occur with misonidazole and RSU 1069. Misonidazole gives an enhancement ratio (ER) of 1.3 at 100 mg/kg, rising to 2.0 at 1000 mg/kg. Where hydralazine is given after irradiation, no additional cell kill is observed with 1000 mg/kg. In contrast, at lower doses of misonidazole, hydralazine induces a substantial increase in cell killing such that the ER obtained with 100 mg/kg is the same as that achieved with 1000 mg/kg misonidazole when used alone with radiation. Similarly, 20 mg/kg RSU 1069 with radiation followed by hydralazine is equivalent to the radiosensitizing effect of 80 mg/kg RSU 1069 without hydralazine. In addition, doses of RSU 1069 that normally give no radiosensitization (5 or 10 mg/kg) produce substantial increases in cell killing when combined with hydralazine.

[Extended treatment for gastric cancer patients with peritoneal seeding]

Fourteen patients with far-advanced gastric cancer were treated surgically followed by intraperitoneal hyperthermic perfusion (IPHP) with mitomycin C (MMC) and misonidazole (MIS), a thermosensitizing drug. Immediately after extensive resection of the abdominal tumors, a 2-hour IPHP was performed at the inflow temperature 47.4 +/- 0.5 degrees C and at the outflow temperature 45.3 +/- 0.5 degrees C, using equipment designed for treatment of cancerous peritoneal seeding, as a closed circuit, and under hypothermic general anesthesia at 31.2 +/- 0.5 degrees C. In 6 of the 14 patients, cancerous ascites was absent after IPHP. Repeated cytologic examination of the lavage from pelvic cul-de-sac were negative, in all cases. The postoperative courses were uneventful except for 2 patients, in whom slight leakage occurred. All patients were discharged, and 4 in the 14 patients died of recurrence in the liver, abdominal and/or pleural cavities 8.8 +/- 2.1 months after IPHP. The remaining 10 are in good health 12.1 +/- 3.1 months after IPHP. Transient hepatic dysfunction and hypoproteinemia occurred after hyperthermia in all cases. This extensive surgery combined with IPHP using MMC and MIS was well tolerated and is a safe anti-tumor treatment for gastric cancer with peritoneal dissemination. Neurotoxicity due to MIS was nil.

Postirradiation modification of tumor blood flow: a method to increase the effectiveness of chemical radiosensitizers

The effect of postirradiation hypoxia induced by administration of the vasodilator hydralazine on the efficacy of misonidazole and RSU-1069 used in combination with radiation has been evaluated. Studies with the Lewis lung carcinoma indicate that hydralazine at a dose of 5 mg/kg reduces tumor blood flow and consequently increases the amount of hypoxia in the tumor tissue. Administration of hydralazine immediately after radiation treatment increased the amount of cell kill. However, the increase in cell kill was more pronounced when hydralazine was used in treatment regimes in which misonidazole (0.2 mg/g) or RSU-1069 (0.02 mg/g) was administered pre- or postirradiation. The finding that similar effects are observed if the nitroimidazoles were administered either before or after radiation in the regimes involving hydralazine suggests that the enhanced cell killing observed is due to hypoxic cell cytotoxicity. In contrast to the effects of hydralazine on the response of tumors to radiation plus misonidazole or RSU-1069, it has no effect on the response of mouse intestine to such treatment regimes. Thus therapeutic gain may accrue from the use of hydralazine in radiation treatments which incorporate the nitroimidazole radiosensitizers misonidazole and RSU-1069.

Intraperitoneal hyperthermic perfusion combined with surgery effective for gastric cancer patients with peritoneal seeding

Fifteen patients with far-advanced gastric cancer were given surgical treatment followed by intraperitoneal hyperthermic perfusion (IPHP) with mitomycin C (MMC) and misonidazole (MIS), a thermosensitizing drug. Immediately after extensive resection of the abdominal tumors, a 2-hour IPHP was performed at the inflow temperature of 44.7 to 48.7 C, using equipment designed for treatment of cancerous peritoneal seeding as a closed circuit, and under hypothermic general anesthesia at 30 to 31 C. In nine of the 15 patients with peritoneal seeding and/or ascites, cancerous ascites was absent after this treatment. In all cases, repeated cytologic examinations of the lavage from Douglas's pouch were negative. The postoperative courses were uneventful except for Patients 1 and 10, in whom slight leakage occurred. All patients were discharged and are in good health at the time of this writing, 7.2 +/- 4.6 months after the treatment. The Case 4 Patient recently died in a traffic accident. In all patients, transient hepatic dysfunction and hypoproteinemia occurred after the operation. This extensive surgery combined with IPHP using MMC and MIS was well tolerated and is a safe antitumor treatment for gastric cancer with peritoneal dissemination. Neurotoxicity due to MIS was nil.

Potentiation of combination chemotherapy by nitroheterocyclics

The effect of including a nitroimidazole in a treatment regimen combining two alkylating chemotherapeutic agents was evaluated in a mouse tumor model. KHT sarcoma-bearing female C3H/HeJ mice were treated with a single dose of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) either alone or in combination with the radiosensitizer misonidazole (MISO) prior to a range of cyclophosphamide (CY) doses. CCNU (5 mg/kg) preceded CY treatment by 3 hr. MISO (1 mmol/kg) was given 1 hr after CCNU (2 hr prior to CY). Tumor response was assessed using either an in vitro to in vivo clonogenic cell survival assay 22-24 hr after treatment or an in situ delay of tumor regrowth assay. The results demonstrated that the inclusion of MISO at a dose of 1.0 mmol/kg increased tumor cell kill resulting from the combination of CCNU-CY by a factor of 1.4-1.5 compared to that seen in the absence of the nitroimidazole. Normal tissue toxicity resulting from the CCNU-CY or CCNU-MISO-CY combinations was determined by measuring bone marrow stem cell (CFU-S or CFU-GM) toxicity. Compared to CCNU-CY alone, the addition of MISO did not enhance this normal tissue toxicity. These findings indicate that the inclusion of MISO in a combination chemotherapy protocol may yield a significant therapeutic benefit.

Enhancement of hyperthermochemotherapy for human gastric cancer in nude mice by thermosensitization with nitroimidazoles

Hyperthermia for human gastric cancer xenotransplanted into the hindlegs of nude mice was performed to determine whether misonidazole (MISO) or metronidazole (MTR), derivatives of nitroimidazole, would intensify the antitumour effects of hyperthermia only, or combined with mitomycin C (MMC). MISO, MTR and MMC were given i.p. at doses of 500 mg kg-1, 500 mg kg-1 and 2.0 mg kg-1 respectively, and MISO or MTR was administered 45 min before MMC. Hyperthermia was applied twice at 48 h intervals, by means of a water bath at 43.5 +/- 0.1 degrees C for 23 min. Tumour tripling times following heat alone, MTR plus heat, and MISO plus heat were about 6.7, 8.0 and 7.9 days respectively, compared with 4.6 days for the control, but tumour regression occurred in the heat plus MISO group only. Tumour tripling times for MMC plus heat, MMC plus MTR plus heat, and MMC plus MISO plus heat were 9.6, 11.6 and 17.1 days respectively, compared to 4.6 days for the control and 6.7 days for heat alone. These data suggest that the antitumour activity of MMC plus MISO plus heat is an additive phenomenon.

Enhancement of the clinical activity of melphalan by the hypoxic cell sensitizer misonidazole

One hundred patients with non-small cell lung cancer were entered by members of the Northern California Oncology Group into a randomized Phase II trial of i.v. melphalan versus i.v. melphalan with concomitant oral misonidazole. The patients had not received prior chemotherapy. Eighty-five patients were evaluable for assessment of response and 89 were evaluable for toxicity analysis. The melphalan/misonidazole group had a superior response rate (two complete and four partial responses among 42 patients or 14%) compared to the melphalan group in which there were no responses among 43 patients (p = 0.024, two-sided Fisher exact test). Since hematological toxicity was equivalent in the two groups, there was an improvement in therapeutic index. Data from 12 patients undergoing pharmacological studies demonstrated that the plasma concentration of melphalan was 25% higher in the misonidazole group, a difference that is not statistically significant. Although the mechanism of interaction has not been fully established, this randomized trial demonstrates that a chemosensitizer can enhance the clinical antitumor activity of an alkylating agent and suggests that chemosensitizers in combination with alkylating agents should be investigated in further clinical trials.

Interstitial misonidazole: clinical experience in advanced mouth cancer

In an attempt to obtain full radiosensitisation and avoid dose-limiting neurotoxicity, a needle has been specially developed for the injection of misonidazole pellets into tumours. The methods of production and insertion of the pellets are described. Thirteen advanced, untreated squamous carcinomas of the mouth were injected and then irradiated to tolerance. Twelve out of 13 implanted lesions had completely regressed at the end of treatment but only six remained healed after 1 year.

Effect of anemia on tumor radiosensitivity under normo and hyperbaric conditions

The effect of chronic anemia on tumor radiosensitivity in a murine tumor has been investigated. Anemia was induced by bilateral kidney irradiation given several months before tumor implantation. Anemic, anemic transfused, and normal non-anemic age-matched tumor bearing animals were irradiated with X rays (2 F/24 hr) either in air, air plus misonidazole, or under hyperbaric oxygen. The most resistant response was that of tumors grown in normal mice treated in air. Anemia produced an increase in radiosensitivity which was further enhanced by red blood cell replacement. The most sensitive overall response was seen in the anemic-transfused group treated with HBO.

Enhancement of radiation-induced normal tissue damage by a fibrosarcoma

Normal tissue damage in the legs of mice was enhanced by the presence of a fibrosarcoma (FSa I) in the leg at the time of treatment with single doses of 30 to 70 Gy. Damage was assessed by measuring leg contracture 23 to 365 days after irradiation of 8 mm diameter tumors. Animals with and without tumors were treated with 1.0 mg misonidazole/g body weight 30 min before irradiation to ensure that the tumors did not recur and interfere with the assessment of contracture. The data suggest that in some cases, late damage may be enhanced by destructive effects of the tumor on the tumor bed.

The treatment of advanced stage ovarian carcinoma with a combination of chemotherapy, radiotherapy, and radiosensitizer: report of a pilot study from the National Cancer Institute

Twenty-eight patients with Stage III or IV ovarian carcinoma were treated with combined chemotherapy-radiotherapy employing a unique protocol. Four cycles of cyclophosphamide and hexamethylmelamine alternated with four cycles of concurrent cisplatin, whole abdominal radiotherapy, and intraperitoneal misonidazole. The entire treatment program lasted six months. Clinical complete responses were seen in 50% of the patients with an overall response rate of 61%. Pathologic complete response (PCR) confirmed at second look surgery occurred in 18% of the group (5 patients). Median survival of the entire group was 15.2 months with all PCR's alive NED. This outcome was no different than our previous experience with combination chemotherapy alone. Toxicities seen included leukopenia, thrombocytopenia, nausea, vomiting, and weight loss. However, these side effects were manageable. Two non-tumor deaths occurred. This study demonstrates the feasibility of combining drug and radiation therapy concurrently in the treatment of ovarian cancer; further research is needed to explore different sequencing and dose levels that could improve the outcome.

Platinum-DNA adducts in leukocyte DNA correlate with disease response in ovarian cancer patients receiving platinum-based chemotherapy

Fifty-five ovarian cancer patients receiving platinum drug-based chemotherapy have been studied prospectively to determine the extent of formation of the bidentate intrastrand adducts of diammineplatinum covalently attached to the N7 positions of adenosine and/or guanosine in leukocyte DNA. Data for clinical response, obtained from medical records, were then correlated with the adduct values. Patients were treated with platinum-based single-agent or combination chemotherapy containing cis-diamminedichloroplatinum (II) or diamminecyclobutane-dicarboxylatoplatinum on approved experimental protocols. Adduct measurements were performed by ELISA, and disease response to therapy was assessed by standard oncologic criteria. This study comprises a total of 101 blood samples obtained after intravenous cis-diamminedichloroplatinum (II) or diamminecyclobutane-dicarboxylatoplatinum infusion from 55 individuals, and in each case the highest (or "peak") adduct level for each patient was chosen for statistical analysis. Values for median adduct levels in patients grouped by complete response, partial response, and no response were 212, 193, and 62 amol of adduct per microgram of DNA, respectively. Analysis of these data by Jonckheere's test (an extension of the Mann-Whitney test) shows that higher levels of adduct formation correlates with disease response with a two-sided P value of 0.030. Of eight patients on single-agent therapy whose buffy-coat samples did not have measurable adduct levels, none responded to therapy. Analysis of these data using the exact test for trend shows that the formation of adduct at a level of 160 amol/micrograms of DNA or greater correlates with disease response with a two-sided P value of 0.032. Thus in ovarian cancer patients, the formation of the intrastrand diammineplatinum adducts in leukocyte DNA is associated with favorable disease response to cis-diamminedichloroplatinum (II) or diamminecyclobutane-dicarboxylatoplatinum chemotherapy.

Radical radiation and oral and intra-vesical misonidazole for bladder cancer

Patients with T2 grade 3 and T3 bladder cancer were entered into studies to evaluate the efficacy of 40 Gy in 2 Gy fractions (5/week) to the whole pelvis followed by 12 Gy in 6 Gy fractions (1/week) to a coned down volume plus oral and intravesical misonidazole (MISO). In a pilot study of 22 patients the complete response rate at cystoscopy at 6 months was 73% and the 5-year survival rate (life-table) with and without bladder preservation was 48% and 54% respectively. The 5-year bowel major complication rate (life-table method) was 8%. These results are statistically significantly improved over that seen in a series of historical controls. A prospective randomized trial has been completed comparing the above regimen with 40 Gy to the whole pelvis followed by 20 Gy to the coned down volume in 2 Gy fractions (5/week). Fifty-eight patients were entered and 53 are evaluable. The complete response rate at cystoscopy at 6 months is 69% (18/26) in the patients treated with MISO and 63% (17/27) in those treated without MISO. As this is an important prognostic indicator, it is unlikely that there will be an advantage in either group and this is supported by the initial follow-up data. The complete response rate at cystoscopy at 6 months is higher in both arms of this study than in the historical series.

Evaluation of CCNU and misonidazole in the treatment of advanced colorectal cancer

Eighteen adult colorectal cancer patients, previously untreated with systemic chemotherapy, were given CCNU and MISO. One patient had an excellent partial response of pulmonary metastases, but the overall response rate was only 6%. Gastrointestinal toxicity was modest, hematologic toxicity was similar to what would have been predicted for CCNU alone, and there was no neurotoxicity detected. This Phase II study demonstrates that these two agents can be administered safely, but have no advantage over CCNU alone.

Clinical experience with intravenous radiosensitizers in unresectable sarcomas

Traditionally, adult bone and soft tissue sarcomas have been considered to be "radioresistant." Because of this philosophy, patients who present with locally advanced, unresectable sarcomas often are treated in a palliative fashion, usually with low-dose radiotherapy. Over the last 6 years, 29 patients with unresectable primary or metastatic sarcomas were treated using a combination of intravenous chemical radiosensitizers and high-dose irradiation. Twenty-two of 29 patients achieved clinical local control, with six patients having a complete clinical response. The time to tumor response is often several months or longer, which is in contrast to other tumor histologies (carcinomas, lymphomas), where tumor response usually occurs over several weeks. Several large tumors have shown only a minimal tumor response, yet were found to be sterilized in posttreatment biopsy or autopsy examination. Of 15 patients with primary sarcomas without metastases, 11 patients (73%) remain free of local tumor progression from 12 to 83 months. Adult high-grade sarcomas can be controlled with high-dose radiotherapy and intravenous radiosensitizers, although the precise role of these agents is unclear.

Misonidazole and CCNU chemotherapy for recurrent primary brain tumor

CCNU chemotherapy prolongs survival of patients with primary brain tumor when given at the time of tumor progression following radiation therapy. Used as single agent, response rates of 30 to 80 per cent have been reported with median response durations of five to six months. Experimentally, tumor cytotoxicity is enhanced using the combination of misonidazole and CCNU, without increasing myelotoxicity. In this phase I/II study, 23 patients with primary brain tumor which progressed following radiation therapy were treated with combined CCNU and misonidazole. In all patients either the diagnosis of high grade glioma was made at the time of initial diagnosis prior to radiation therapy or the tumor transformed from low grade to high grade glioma at the time of progression following radiation therapy. CCNU 120 mg/M2 was given four hours following misonidazole 3.5 g/M2 every six weeks, with dosage adjustments for myelotoxicity. Treatment was continued for one year or until tumor progression. Of the 17 patients in the study for one year or more, 11 (65 per cent) survived for one year, and six (35 per cent) remained free of tumor progression for one year. Median time to tumor progression from start of CCNU plus misonidazole chemotherapy was 27 weeks and median survival was 80 weeks. No severe complications resulted from myelotoxicity. One patient developed mild peripheral neuropathy which disappeared following discontinuation of misonidazole.

Potentiation of CCNU activity by misonidazole in metastases

The KHT sarcoma is a model system in which metastases can be studied in multiple organs without prior clonal selection. The present series of experiments were designed to evaluate and compare the extent of potentiation of chemotherapeutic agent activity by radiosensitizers when KHT sarcoma cells were grown in different anatomical sites. In these studies the effect of combining misonidazole (MISO) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) on KHT lung nodules and ovarian metastases was determined. Ovarian metastases were a consequence of the direct spread of tumor cells growing as lung nodules. Once established, KHT cells in the lungs and ovaries grew with a similar doubling time (1-2 days). Response of tumors at either site to chemotherapy in the presence or absence of a sensitizer was assessed using an in vivo to in vitro excision assay. MISO (1.0 mmol/kg) was administered simultaneously with a range of CCNU doses and survival of clonogenic tumor cells was measured 24 h after treatment. The results demonstrate that the addition of MISO to CCNU treatment potentiated the action of this chemotherapeutic agent at both tumor sites although greater cell kill enhancement occurred in the ovarian metastases. In the lung nodules, when combined with CCNU, a 1.0 mmol/kg dose of MISO was found to yield a dose modifying factor (DMF) of approximately 1.3. The same combination resulted in a DMF of approximately 1.8 in the ovarian metastases. This difference in DMF was not a result of an intrinsic difference in sensitivity to CCNU since cells grown at either site gave rise to the same dose response curve. Rather the difference in dose modification by MISO appears to be a consequence of the larger fraction of radiobiologically hypoxic cells in the ovarian tumors (approximately 50 per cent) than in the lung nodules (approximately 5 per cent) at the time of treatment. These findings suggest the use of drug-sensitizer combinations to treat disseminated disease and provide further evidence for the requirement of hypoxia in chemopotentiation by radiosensitizers.

Palliative topical and systemic misonidazole with low-dose irradiation for recurrent carcinoma of the cervix uteri

This report concerns a determinate series of 11 patients with progressive recurrent cancer of the cervix uteri, who were treated with misonidazole (1 g) applied locally for 24 hours and an oral dose of 2.9 g/m2 four hours before a single mid-plane dose of 5.00 Gy. Four of 11 (36%) remained free of disease at one year. It is suggested that this is largely a hypoxic cell cytotoxic effect and is a useful method of palliation.