Chemical manipulations of tissue oxygenation for therapeutic benefit

Nicotinamide and carbogen: major effect on the radiosensitivity of EMT6 and HRT18 tumours

The effect of nicotinamide and/or carbogen breathing on the response of EMT6 and HRT18 tumours, irradiated in vivo, was evaluated using an in vitro colony assay. In the single dose schedules, the most efficient treatment was carbogen plus nicotinamide compared to air breathing mice. In a fractionated regime carbogen plus nicotinamide increased also response to radiation.

Radiosensitivity, blood perfusion and tumour oxygenation after perflubron emulsion injection

The effect of 90% and/or 100% w/v perflubron (perfluorooctyl bromide (PFOB); Alliance Pharmaceutical Corp.) emulsions on radiosensitivity, tumour relative perfusion and oxygenation was studied using EMT6 tumours in nude mice. Perflubron (2-15 ml/kg) emulsion was injected. The mice inhaled carbogen for 30 min and 60 min prior to irradiation. The radiosensitizing effect of the 90% w/v emulsion was maximal at 4 ml/kg. The tumour relative perfusion diminished after injection of both 100% and 90% w/v emulsions in carbogen-breathing mice at a dose of 15 ml/kg. This drop could explain the lack of efficiency of these treatments at this high concentration. Lastly, tumour oxygenation was increased after administration of perflubron emulsion plus carbogen.

Chemical radiosensitizers in cancer therapy

The development of effective low-LET radiation therapy for cancer has been hindered by the lack of consistent differential responses to radiation between tumor and normal tissues. One major difference between many solid tumors and the surrounding normal stroma is the presence of hypoxic foci in solid tumors due to the inadequate supply of nutritional needs as a result of the breakdown of microvasculature. Consequently, failure of conventional radiotherapy and local recurrences are in part attributed to the radioresistant hypoxic cell populations, present in the tumor. Local cure/control rates of a tumor can be increased only by an effective increase in the radiation dose. At the same time, an increase in such a dose would damage the oxic normal stroma, more than the hypoxic tumor cells. Hence, specific modification of tumor radiosensitivity by the use of chemical radiosensitizers, in combination with conventional radiotherapy, is an attractive alternative. Many clinicians and radiotherapists are skeptical about the outcome of using radiosensitizers in patients. Nevertheless, a vast amount of information is currently available regarding the first- and second-generation radiosensitizers both in murine and in human tumors. As a result, it is hoped that eventually a radiosensitizing drug would be discovered/synthesized that will overcome the drawbacks so far encountered in their use in the clinic. In this article, the development of chemical radiosensitizers since the early sixties, the basis for their selection, their mechanism(s) of action, and the results obtained with the various groups of radiosensitizers are reviewed.

Effects of clonidine-induced hypotension and dopamine-induced hypertension on blood flows in prostatic adenocarcinoma (Dunning R3327) and normal tissues

In the present study it was investigated whether hypertension induced by dopamine or hypotension induced by clonidine could influence the relative blood distribution in a s.c. transplanted prostatic adenocarcinoma in relation to blood flow in normal tissues in rats. The blood flow was measured by using a radioactive microspheres technique. A bolus injection of 5 micrograms clonidine caused a decrease in the systemic blood pressure with 15-45 mm Hg, and blood flow to the central parts of the tumor, decreased with more than 50%. In the prostate, testes and ileo-psoas muscle a similar reaction was seen. During an infusion of 95-120 micrograms/kg/min dopamine, the blood pressure increased with 15-30 mm Hg, but the blood flow to the tumor was unchanged. However, in the testes and kidneys a decreased blood flow was observed. Moreover, mean blood flow to the central parts of the tumor decreased with increase in tumor size. The results further indicated that hyper- or hypotension or concomitantly given vasoactive drugs with the specific cancer treatment can have unwarranted effects on the distribution of cytotoxic drugs and oxygenation of the tumor.

Tumor hypoxia, reoxygenation and oxygenation strategies: possible role in photodynamic therapy

The concept of hypoxia and its role in tumor therapy are currently under re-evaluation. Poor oxygenation is no longer visualized as an independent feature promoting necrosis and resistance to treatments, but rather as one of the several interdependent microenvironmental parameters associated with impaired blood perfusion. Tumor cells display several survival strategies and remain clonogenic for long periods in nutrient-deprived situations. Reoxygenation may cause lethal damage, improve the response to therapy, or else allow the cell variants adapted to hypoxia to resume proliferation with enhanced aggressiveness and resistance to treatment. The blood supply parameters, oxygenation status and metabolism of malignant cells are discussed here from the standpoint of tumor photodynamic therapy. The role of the tumor interstitial fluid as oxygen- and sensitizer-carrier is discussed. Techniques for assessing tumor oxygenation and for mapping hypoxic territories are described. Strategies for locally improving the oxygenation levels or for selectively destroying the hypoxic populations are outlined.

The effect of hydralazine on blood flow and misonidazole toxicity in human tumour xenografts

The effect of post-irradiation hypoxia induced by 5 or 30 mg/kg hydralazine has been studied in three human tumour xenografts (two rectocolic adenocarcinomas and one melanoma) treated with two doses of misonidazole similar to those used in patients (0.1 and 0.2 mg/g). Only a small sensitization was detected using an in vitro colony assay. These results are in marked contrast to the results obtained with rodent tumours. This difference between human tumour xenografts and rodent tumours might be explained by differences in the reduction of tumour blood flow after hydralazine administration (5 and/or 10 mg/kg). Using the laser Doppler technique, the tumour blood flow reduction was 33% and 25% of the control for NA11 and HRT18 tumours, respectively. In contrast, hydralazine induced a 60-70% reduction in blood flow in the murine SCCVII tumour. Using the fluorescent marker Hoechst 33342, the reduction in perfusion was again more pronounced in the murine tumour as compared to the Na11 and HRT18 xenografts. The differences between human tumour xenografts and rodent tumours are not linked to the mouse strain used (nude versus C3H) nor to a tumour bed effect.

Nicotinamide, Fluosol DA and Carbogen: a strategy to reoxygenate acutely and chronically hypoxic cells in vivo

The effect of Nicotinamide and/or treatment with Fluosol DA and Carbogen breathing on the radiation response of 500-750 mg SCCVII and KHT tumours has been evaluated. Pretreatment with Fluosol DA/Carbogen or Nicotinamide resulted in relatively modest enhancements of radiation damage with enhancement factors of 1.1 and 1.3 being observed using an in vivo/in vitro clonogenic end-point. A combination of Nicotinamide and Fluosol DA/Carbogen resulted in a larger enhancement factor of 1.6 over the radiation dose ranges studied. These modification factors reflect a value close to that expected for a fully aerobic response in this survival range. Growth delay studies in the SCCVII tumour provided similar results. Using a recently developed fluorescence activated cell sorting technique, which utilizes the in vivo pharmacokinetic and DNA binding properties of the bisbenzamide stain Hoechst 33342, the effect of Nicotinamide and/or Fluosol DA/Carbogen schedules on the occurrence of acute hypoxia was assessed. The results clearly show that Nicotinamide significantly reduces the amount of 'acute hypoxia', but has a lesser effect on 'chronic' hypoxic cells. However, combinations of Nicotinamide and Fluosol DA/Carbogen significantly increase the response of both 'acutely' and 'chronically hypoxic' cells. The results provide evidence that a combination of Nicotinamide and Fluosol DA/Carbogen can provide an effective way of reoxygenating both acutely and chronically hypoxic cells.

The use of fluorocarbon emulsions in cancer radiotherapy

The chemical and physical properties of perfluorochemical emulsions which highlight their advantages and disadvantages for use in cancer radiotherapy are summarized. The radiobiological properties of two emulsions are reviewed: we have chosen the Fluosol-DA 20% and the PFOB emulsion 100 v/w% which is one of the most promising second generation fluorocarbon emulsions. The radiosensitization obtained in a human tumor xenograft with PFOB emulsion is compared to that obtained with other modalities used to overcome the radioresistance of tumour cells linked to hypoxia.

Intraductal breast carcinoma: initial results of a morphometric study using computerized digital image analysis

Extensive ductal carcinoma in situ (DCIS) and necrosis in breast carcinoma have been correlated with a higher incidence of local recurrence in patients treated with breast-conserving surgery and radiotherapy. In an attempt quantitatively to assess duct size distribution and necrosis in DCIS, the authors devised a method utilizing computerized digital image analysis. The method and results of a pilot study comparing 21 patients with DCIS, and 21 normal breast specimens are presented. Normal breast tissue from autopsy material revealed a mean duct diameter of 90 microns, whereas the mean diameter of ducts in patients with DCIS was 359 microns (P less than 0.001). The presence of necrosis in DCIS correlated strongly with average duct size. Of the ducts larger than 360 microns in diameter 94% exhibited intraductal necrosis, whereas ducts less than 360 microns showed necrosis in only 30% of the measurements. Ducts with necrosis revealed a mean diameter of 498 microns versus 198 microns in ducts without necrosis (P less than 0.001). The authors suggest that necrosis develops in response to tumour cell hypoxia associated with cross-sectional duct expansion in DCIS. This growth pattern predisposing to tumour cell hypoxia could be a factor contributing to radioresistance and increased local recurrence.