Differential cytotoxic effects of metronidazole and other nitro-heterocyclic drugs against hypoxic tumour cells

The energy metabolism of RIF-1 tumours following hydralazine

Phosphorus-31 Magnetic Resonance Spectroscopy (MRS) was used to observe the effect of two doses of the vasodilator hydralazine on the energy status of RIF-1 tumours. An intravenous dose of 5 mg/kg hydralazine reduced the high energy phosphate metabolites PCr and ATP, lowered pHMRS and raised the levels of inorganic phosphate of tumours within 20 min of administering the drug. The levels of high energy metabolites continued to decrease for at least 24 h. Normal muscle spectra obtained up to 1 h after drug administration remained unchanged. An intravenous dose of 0.5 mg/kg hydralazine also reduced NTP/Pi and PCr/Pi levels of tumours up to at least 5 h after drug administration, but the effect was smaller than for the higher dose. Blood flow measurements and measurements of systemic blood pressure demonstrated that 5 mg/kg of hydralazine produced a reduction in both systemic blood pressure and tumour blood flow relative to most normal tissues investigated. It is concluded that the changes in the P-31 MRS spectra of tumours were due to a reduction in tumour vascular perfusion following administration of hydralazine.

Palliation of advanced pelvic malignant disease with large fraction pelvic radiation and misonidazole: final report of RTOG phase I/II study

Between October 1979 and June 1982 forty-six patients were entered on a non-randomized Phase I-II protocol for the evaluation of Misonidazole combined with high dose per fraction radiation for the treatment of advanced pelvic malignancies. Pelvic radiation consisted of 1000 cGy in one fraction repeated at 4-week intervals for a total of three treatments. Oral Misonidazole at a dose of 4 gm/m2 was administered 4-6 hr prior to radiation (total dose 12 g/m2). The distribution of histology consisted of 20 gynecologic, 24 bowel, and 2 prostate malignancies. Of the thirty-seven patients completing the three treatments; there were 6 complete responses (14% CR), 10 partial responses (27% PR) 19 minimal or no response (32% NR), and 4 unevaluable. One patient remains NED 5.5 years following radiation. Toxicity directly related to Misonidazole was minimal and consisted primarily of transcient Grade 1, 2 peripheral neuropathy (20% Grade 1, 4% Grade 2) and Grade 2 ototoxicity (4%). Radiation toxicity was significant for late bowel damage. There were 4 (11%) Grade 3 and 7 (19%) Grade 4 gastro-intestinal (GI) toxicities. Kaplan-Meier plot of GI toxicity showed a progressive increase in incidence with time for projected rate of 49% Grade 3, 4 by 12-month. GI toxicity (Grade 3, 4) was also related to tumor response. The complication rate was 80% (4/6) for CR, 30% (3/10) for PR and 26% (5/19) for NR or progression. Because of the GI complication rate, this protocol for palliation of advanced pelvic malignancies has been replaced by a protocol that uses 4 fractions over 2 days (b.i.d.) of 370 cGy per fraction repeated at 3-week intervals for a total of 3 courses.

Non-nitro radiation sensitizers

A review of the literature on radiosensitization reveals that at least some of the non-nitro compounds, such as metabolic inhibitors and membrane-active drugs, could be considered as potentially valuable radiosensitizers for possible use in future cancer radiotherapy.

Hypoxic fractions of solid tumors: experimental techniques, methods of analysis, and a survey of existing data

Hypoxic fractions are measured by indirect techniques, which compare the response of tumors to large single doses of radiation given under normal aeration and artificial hypoxia. This paper reviews hypoxic fraction measurements and measurement techniques, giving particular attention to the biological, technical, and statistical aspects of the assays; the implicit assumptions underlying the analyses; and the dependence of the determinations on the assay conditions and the tumor and host characteristics. The three major hypoxic fraction assay techniques (paired survival curve, clamped tumor control, and clamped growth delay) share common biological assumptions. They require that the survival curves of naturally and artificially hypoxic cells have the same slope and intercept. They assume that the majority of the cells are either fully oxic or fully hypoxic. They assume that the methods used to induce artificial hypoxia leave no oxygenated regions and that tumor cells rendered artificially hypoxic are no less viable than cells in normally-aerated tumors. The universal validity of these assumptions is questionable. Each technique uses additional special assumptions and each may measure a different population of hypoxic cells. This paper reviews 92 hypoxic fraction determinations in 42 tumor systems. Radiobiologically hypoxic cells appear to be present in the majority of macroscopic solid rodent tumors. The hypoxic fraction was found to increase as the tumor size increased from microscopic to macroscopic; the dependence of hypoxic fraction on tumor size at macroscopic sizes was less clear. The site of tumor implantation, the use of anesthesia, and certain host characteristics may influence the hypoxic fraction. The hypoxic fraction generally did not depend on the tumor growth rate, transplantation history, or histology. These findings indicate that hypoxic cells are a common feature of solid tumors in rodents and provide no evidence that hypoxic cells should not be present in human tumors.

Effect of misonidazole on the radiosensitivity and repair of potentially lethal damage of L5178Y ascites tumor cells

The radiosensitizing effect of low concentrations of misonidazole was investigated by using L5178Y cells growing as an ascites tumor in DBA-2 mice. The cells were irradiated in vivo with graded doses of X-rays in the presence or absence of 0.1-0.5 mg/g body weight of misonidazole. Then cell survival was assayed in vitro by plating cells in soft agar medium. By analyzing the X-ray survival curves with or without misonidazole, the dose-modifying effects were determined. The results indicated that the slope and shoulder of the survival curves were greatly modified by the treatment with misonidazole. The dose-modifying factor in terms of the D0 ratio between the drug-treated and untreated control cells was increased as the drug concentration was increased. Further, it was revealed that the isoeffect dose ratios, estimated by the linear quadratic equation of Chadwick and Leenhouts, were higher at a low-radiation dose range. This is due to the suppression of the shoulder region of survival curves for the drug-treated cells. The inhibition of the X-ray-induced repair of potentially lethal damage was apparent with 0.1 mg/g body weight of misonidazole. The inhibition became more effective as the drug concentration increased.

Effect of hyperthermia and misonidazole on the radiosensitivity of a transplantable murine tumor: influence of factors modifying the fraction of hypoxic cells

Hypoxia has been demonstrated to play an important role in the effect of hyperthermia on tumors. We have studied the influence of different factors modifying the oxygenation status of a transplantable murine mammary adenocarcinoma (tumor volume and pentobarbital sodium anesthesia). The effect of hyperthermia alone on the tumor is not significantly influenced by the change in oxygenation status during the growth of the tumor. Also, the large increase of the acutely hypoxic cell fraction, as a result of anesthesia, does not change the effect of hyperthermia alone. In the combined irradiation-heat treatment there is a clear influence of the chronically hypoxic cell fraction on the response to hyperthermia: an increase in tumor size, resulting in a larger hypoxic cell fraction, leads to an increase in thermal enhancement ratio. However, the increased acutely hypoxic cell fraction, resulting from anesthesia, did not lead to an increase in thermal enhancement ratio; in fact the enhancement ratio apparently decreased. In spite of the fact that hyperthermia was applied immediately after irradiation no potentiation of radiation effects was found. The thermal enhancement of the radiation response was never larger than the enhancement as a result of misonidazole. All thermal enhancement could be explained by effects of heat on the chronically hypoxic cell fraction. Misonidazole had no effect on the response of tumors to heat alone, but greatly enhanced the effect of heat combined with irradiation. Anesthesia of the animals did not influence these effects of misonidazole.

Effect of misonidazole and hyperthermia on the radiosensitivity of a C3H mouse mammary carcinoma and its surrounding normal tissue

Both misonidazole (MISO) and hyperthermia are known to enhance the radiation response of hypoxic cells, and to be selectively cytotoxic against cells in a hypoxic and acidic environment. The ability of these conditions to modify the effect of irradiation and their individual relationship was studied in a C3H mammary carcinoma and its surrounding skin. Simultaneous treatment with MISO, hyperthermia and radiation increased the radiation effect, with enhancement ratios (ER) of up to about 15 (1 mg/g MISO and 43.5 degrees C for 60 min.). However, such treatment also caused a smaller hyperthermic radiosensitization of the normal tissue, so that the therapeutic ratio was only increased by a factor of about 3 compared to radiation alone. Simultaneous MISO and radiation followed by hyperthermia 4 h later gave a moderate enhancement, with ER up to 3 in the tumour, but with no enhancement of the normal tissue, so that there is a similar 3-fold increase in therapeutic gain. The mechanism by which MISO and hyperthermia enhanced the radiation response may be explained as an independent action of the hypoxic radiosensitization of MISO and the selective hyperthermic cytotoxicity against acidic and chronic hypoxic cells; simultaneous hyperthermia added a further heat-induced general radiosensitization. Surprisingly, no MISO cytotoxicity could be detected in this tumour system, with or without simultaneous hyperthermia. The results indicate that in the proper treatment schedule, MISO may be a valuable addition to a combined hyperthermia and radiation treatment.