Killing Of Hypoxic Cells Research Articles

Survival of Oxygenated and Hypoxic Tumor Cells in the Extended-Peak Regions of Heavy Charged-Particle Beams

The survival of oxygenated and hypoxic cells of the R-1 rat rhabdomyosarcoma tumor line in suspension culture has been measured at several positions in the plateau and the extended peak regions of carbon-, neon-, and argon-ion beams. Both the carbon and neon beams had 14- and 23-cm ranges in water; the argon beam has a 13-cm range. Peak regions extended to both 4 and 10 cm were studied for each ion species. In the 10-cm extended peak, OER values were close to 2.0 for the carbon-ion beam, 1.9-1.5 for the neon beam, and 1.4-1.2 for neutrons, while the argon OER in the extended peak is lower than that for neutrons. The RBE values increased through the carbon peak region, were large and relatively constant through the neon peak region, and decreased through the argon peak region, thus reflecting the changing effective LET that results from the changing energies and the different charges of the particles. An analysis of the effectiveness of the different ion beams for killing hypoxic cells in the peak relative to killing oxygenated cells in the plateau implies that, for single-port irradiations, carbon ions may be the most advantageous charged-particle species for the treatment of deep-seated hypoxicmore » tumors. However, for tumors at shallow depths, the present results indicate that carbon and neon ions are similar in their effectiveness. Argon ions may be superior for the treatment of poorly oxygenated tumors close to the body surface.« less

Evidence suggesting that the mechanism for aerobic and hypoxic cytotoxicity of nitroheterocycles is the same

The fluorescence of three nitroheterocycles (AF-2, trans-5-amino-3-(2-(5-nitro-2furyl) vinyl)- 1,2,4-oxadiazole and 4-NQO) was used to quantitate cellular uptake and binding using a fluorescence-activated cell sorter. Mean cellular fluorescence, proportional to the amount of bound drug, allowed accurate prediction of the amount of cell killing. At equitoxic concentrations, the same amount of drug was bound under either aerobic or hypoxic conditions. In addition, 5 mM glutathione was equally effective at inhibiting aerobic and hypoxic cell killing by AF-2. These results suggest that the mechanism for cell killing may be similar under aerobic and hypoxic conditions, and the presence of oxygen may influence the rate of drug uptake rather than the nature of the toxic species. The nitro anion radical, formed in the presence and absence of oxygen, seems a likely candidate for the “toxic species.”

In vivo interaction of anti-cancer drugs with misonidazole or metronidazole: cyclophosphamide and BCNU.

The addition of misonidazole (MISO) or metronidazole (METRO) to treatment with cyclophosphamide (CY) increased delay to regrowth of 2 experimental tumours. The effect was observed for large an small tumours, was present for doses of MISO that are ineffective for killing hypoxic cells, and required that it be given with, or shortly before CY. Mice receiving combined treatment had more weight loss and myelosuppression than those receiving CY alone, and the Therapeutic Index was lower. MISO caused a marked increase in growth delay when combined with BCNU to treat the KHT sarcoma. This effect was observed for small and large tumours, required simultaneous administration of drugs, and also led to increased host toxicity. There was no therapeutic advantage from combined treatment. Survival of aerobic or anoxic Chinese hamster ovary (CHO) cells was assessed after exposure in vitro to serum from mice that had received CY or BCNU alone. MISO alone, or combined treatment. Results of these experiments suggest that (1) MISO delays the excretion or breakdown of active metabolites of CY, and (2) at a dose that does not kill hypoxic cells, it may selectively "sensitize" hypoxic cells (but not aerobic cells) to the action of BCNU. The presence of other undetermined interactions of BCNU and MISO is inferred from the increased toxicity to (aerobic) normal tissue. Misonidazole or metronidazole should be used with caution in patients who are receiving BCNU or cyclophosphamide.

Combination studies with misonidazole and a cis-platinum complex: cytotoxicity and radiosensitization in vitro.

cis-Dichlorodiammineplatinum(II) (cis-Pt(II) can act as a radiosensitizer of hypoxic mammalian cells in vitro. Used in combination with misonidazole the level of sensitization achieved is greater than that seen with either drug alone, and it is suggested that these compounds sensitize by independent mechanisms. For cells held at 37 degrees C, cis-Pt(II) shows much greater toxicity to hypoxic cells than to aerobic cells. In combination with misonidazole, no additional cytotoxic effect is shown towards aerobic cells than that seen for cis-Pt(II) alone. However, there is additional killing of hypoxic cells when they are treated with both drugs.

Cytotoxicity of misonidazole in vivo under conditions of prolonged contact of drug with the tumour cells.

A single high dose of misonidazole (greater than or equal to 1 mg/g) given to BALB/c mice bearing EMT6 tumours kills approximately 90% of the tumour cells. No cytotoxicity, however, can be demonstrated at more clinically relevant dose levels (less than 0.3 mg/g). However, Stratford and Adams (1978) have shown that extensive killing of hypoxic cells occurs in vitro with low concentrations of misonidazole provided that the contact time is long, such as would occur in man in whom the plasma half-life of misonidazole is approximately 12 hours. We have attempted to simulate the human situation in the BALB/c mouse by performing bilateral kidney ligations prior to injection of misonidazole. This extends the apparent plasma half-life of misonidazole plus its O-demethylated metabolite after an injection of 0.1 mg/g of misonidazole from approximately one hour to seven hours. This provided a good fit over the first nine hours to the in vitro simulation of the human plasma clearance curve done by Stratford and Adams (1978). However, despite finding extensive killing of tumour cells at the high dose of misonidazole of 1.2 mg/g, no detectable cytotoxicity was observed in the low dose (0.1 mg/g) mice in which the plasma half-life had been extended to seven hours. This suggests that misonidazole will produce little, if any, cytoxocity to human tumours.

The in vivo radiation response of an experimental tumor: The effect of exposing tumor-bearing mice to a reduced oxygen environment prior to but not during irradiation

The effect of single or fractionated doses of radiaton on the transplantable KHT sarcoma has been studied in mice which were exposed to a reduced oxygen (O 2) environment prior to but not during irradiation. Tumor-bearing mice were kept in a 12% O 2 environment for a period of time; then their tumors were irradiated locally with a single dose of 2000 rad at a dose rate of 1140 rad/min while the mice breathed air, O 2 or carbogen (5% CO 2:95% O 2). Following irradiation, tumor cell survival was determined using an in vivo lung colony or an in vitro agar colony assay. The results indicate that overnight exposure of tumor-bearing mice (15 hr) to 12% O 2, prior to irradiation of their tumors under air-breathing conditions, leads to a reduction in tumor cell survival by a factor of 3–4 over that found for tumors of air-breathing mice not given a low O 2 pre-treatment. A similar reduction in tumor cell survival is observed for irradiation without prior exposure to the low O 2 environment when the mice are given O 2 or carbogen to breathe instead of air. If the tumors are irradiated while the animals breathe O 2 or carbogen after exposure to 12% O 2, tumor cell survival is reduced to a value ∼10 times lower than is obtained in tumors of air-breathing mice not given a low O 2 pre-treatment. During a course of fractionated radiation (seven 500 rad fractions at 24 hr intervals) delivered while the tumor-bearing mice breathed air or carbogen, a 12% O 2 exposure prior to alternate dose fractions was found to lead to significant enhancement of tumor cell killing above that observed when no pre-treatment with 12% O 2 was employed. The reduction in tumor cell survival almost certainly results from a decrease in the number of hypoxic cells in the tumors but the mechanism by which this reduction occurs is not known at present. The decrease may be because of direct killing of hypoxic cells by the low O 2 environment or because of physiological adaptation to the low O 2 environment which persists when the animals are returned to an air atmosphere, leading to an improved O 2 delivery to the tumor. A number of adaptation mechanisms were studied but these shpwed little correlation with the radiobiological effect. Consequently, no clear explanation of the results can be given at present. Regardless of the mechanism, the findings indicate an approach to increasing the effectiveness of radiation treatment of tumors.

Killing of Glucose-Deprived Hypoxic Cells with Moderate Hyperthermia

Investigations were carried out to determine the importance of glucose as a modifying factor for hyperthermic cellular damage. HeLa S-3 cells were heated under oxic and hypoxic conditions, in the presence and absence of D-glucose. Temperatures as low as 41?C selectively enhanced killing of the glucose deprived hypoxic cell. Glucose deprivation (37?C, 2 hr) or heat alone (41?C for 2 hr in regular medium with glucose) produced minimal cell kill under oxic or hypoxic conditions. No enhancement was seen with hyperthermia under oxic condition in the absence of glucose. The result suggests that the interplay between glucose concentration is important for hyper

Studies with bleomycin and misonidazole on aerated and hypoxic cells.

Bleomycin is a chemotherapuetic drug used primarily in the treatment of squamous-cell carcinoma, while misonidazole is an effective radiosensitizer and potent cytotoxic agent selectively affecting hypoxic cells. V79 Chinese hamster cells were used to investigate the cytotoxicity of bleomycin (BLM) under aerated and hypoxic conditions as a function of drug concentration. At a lowered temperature of 17.5 degrees C, or at an elevated temperature of 42.5 degrees C, hypoxic cells are more sensitive to killing by BLM than aerated cells. At either of these temperatures, progression through the cell cycle is inhibited. However, at 37.5 degrees C, mimicking a clinical situation, the sensitivies are reversed, and hypoxic cells are appreciably more resistant. Although many factors are involved, the major reason for this is that aerated cells are cycling while hypoxic cells are not. Aerated cells can progress into phases of the cell cycle where they are more sensitive to killing by BLM. Misoinidazole (=Ro-07-0582) was used in combination with BLM, since its mode of action has been shown to be psecific for killing hypoxic cells. It concomitant use with BLM could be of potential use in chemotherapy when confronted with the hypoxic cell component of solid tumours.

Metronidazole (Flagyl): characterization as a cytotoxic drug specific for hypoxic tumour cells.

The cytocidal properties of metronidazole against hypoxic mammalian cells are described. This chemotherapeutic action has been shown to be dependent on drug concentration and duration of exposure. The x-ray TCD50 for a murine anaplastic carcinoma was reduced from 6081 rad to 4643 rad when animals were given metronidazole orally for 36 h before radiation treatment. The effect is attributed to the direct killing of hypoxic tumour cells by a mechanism analogous to that proposed for the action of the drug on anaerobic micro-organisms. It is concluded that further work with metronidazole as a cytotoxin specific for hypoxic cells is warranted, particularly in view of the reported lack of toxicity associated with the preliminary clinical use of the drug as a radiosensitizer in man.

Letter: Enhanced killing of hypoxic tumour cells by hyperthemia.

There is abundant evidence that cancer cells grown in vivo or in vitro are sensitive to elevated temperature (Cavaliere, 1967; Overgaard and Overgaard, 1972). Clinically, Coley (1893), near the beginning of this century, achieved a considerable success in the regression of tumours by inducing high temperatures in cancer patients with bacterial toxins. Since then, the literature contains numerous cases of the arrest or total disappearance of cancer after prolonged fever (Cavaliere, 1967). Recently, renewed interest in the combined use of hyperthermia and radiotherapy or chemotherapy has been generated at both the laboratory and the clinical level (Suit and Shwayder, 1974).