Anemia: a problem or an opportunity in radiotherapy?

Protection of pig epidermis against radiation-induced damage by the infusion of BW12C

BW12C, which was developed as an agent for the treatment of sickle cell anaemia, increases the binding of oxygen to haemoglobin and hence reduces the availability of oxygen to tissues. Due to these changes in oxygen availability BW12C could act as a protector against radiation-induced injury to normal tissues. In this study the potential value of BW12C, as a radioprotector, was studied in the irradiated epidermis of the pig. The infusion of BW12C caused an instant left shift of the oxygen dissociation curve, an effect that lasted for approximately 1.5 h. This left shift in the oxygen dissociation curves increased with increasing dose of the drug. There appeared to be no long-term systemic effects produced by doses of 20-100 mg/kg of BW12C. In the first 90 min after the infusion of BW12C skin fields were irradiated with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint for assessing the severity of the radiation response. With animals breathing approximately 70% oxygen in the anaesthetic gas mixture, the ED50 values for moist desquamation were 30-31 Gy after a dose of 30 and 50 mg/kg, and 37-38 Gy for 75 and 100 mg/kg doses of BW12C. These ED50 values were significantly higher than the value of 27.3 Gy for radiation alone. This indicated dose modification factors (DMF) with mean values of approximately 1.13 and approximately 1.40 for irradiation following the infusion of low (30-50 mg/kg) and high (75-100 mg/kg) doses of the drug, respectively. With the animals breathing air (approximately 21% of oxygen) in the 2% halothane anaesthesia gas mixture, irradiation in the presence of 30 and 50 mg/kg of BW12C resulted in ED50 values of approximately 39 Gy for moist desquamation, which was significantly higher than the value of 31.2 Gy for radiation alone. Surprisingly, a higher dose of 75 mg/kg of BW12C resulted in a lower ED50 value for moist desquamation of 34.38 Gy. Irradiation in the presence of a dose of 100 mg/kg of BW12C produced an ED50 value which was not significantly different from that for radiation alone. In the situation where animals were breathing air (approximately 21% oxygen) during irradiation a DMF of 1.14 was obtained for irradiation alone, when the results were compared with those for irradiation alone with approximately 70% oxygen in the anaesthetic gas mixture.(ABSTRACT TRUNCATED AT 400 WORDS)

What is the importance of anaemia in radiotherapy? The value of animal studies

It has been recognised for many years that anaemic cancer patients have a particularly poor prognosis (see recent reviews [4,8]). New data is regularly appearing in the literature, extending our knowledge to include many tumor sites. The evidence is now overwhelming that for most of these, local tumor control by radiotherapy is compromised in patients who are anaemic before and during radiotherapy. The role of the radiobiologist must be to offer an explanation for the clinical observations and to suggest a means of compensating for the problem in those patients whose treatment is prejudiced by anaemia. This statement assumes a cause and effect relationship between anaemia and tumor curability, supposedly through an impairment of oxygen transport to the tumor cells. We must then consider the consequences of a reduction in circulating haemoglobin levels in model tumor systems in animals, combine that information with our knowledge of physiological mechanisms and attempt to reconcile our conclusions with the clinical findings. We should be aware of course, that a failure to achieve this could be the result of inadequacies of the mouse model or because anaemia is simply not the cause of clinical radioresistance but rather a consequence, along with radiosensitivity of particular tumor characteristics. What do the experimental animal data reveal? We will consider two clinically important questions: 1) Are tumors in mice with lower than normal haemoglobin levels more resistant to radiation and what is the temporal relationship between duration of anaemia and sensitivity? 2) Does the restoration of haemoglobin levels before radiotherapy change sensitivity?

Radiation and chemotherapy sensitizers and protectors

Radiosensitizers and radioprotectors are part of the chemical modifier approach to cancer therapy whereby the state of the tumor cells and/or normal tissues are modified such that a therapeutic gain is achieved using conventional radiation or chemotherapy. Radiosensitization can be achieved by the use of oxygen-mimetic compounds, agents that alter DNA sensitivity to irradiation, maneuvers that alter DNA repair processes, and manipulation of tissue oxygenation. Standard chemotherapeutic agents such as cisplatin can be utilized in a manner that optimizes the radiosensitization properties. Protection and sensitization can occur by altering the thiol status of the cell. The chemical modifiers field is both developing novel approaches to cancer treatment and increasing the understanding of basic cancer biology.

Prognostic importance of anemia related parameters in patients with carcinoma of the cervix uteri

The authors investigated the pretreatment values of hemoglobin, hematocrit, plasma iron and other laboratory parameters in 121 patients with cervical cancer treated by combined intracavitary and external irradiation. A pronounced correlation was found between plasma iron values and the length of disease-free survival. The correlation between hematocrit values and disease-free survival was less pronounced and the correlation between hemoglobin values and disease-free survival did not reach statistical significance. It is suggested that anemia-related parameters may reflect the aggressiveness of the disease or its spread.

The role of hemoglobin concentration in the outcome of misonidazole-sensitized radiotherapy of head and neck cancers: based on RTOG trial #79-15

Recent data from the DAHANCA (Danish Head and Neck Cancer) 2 study implies a positive effect of high hemoglobin concentration in concert with misonidazole for the treatment of head and neck cancers by radiotherapy. We have therefore reviewed and updated our analysis of RTOG protocol 79-15, which included the effect of misonidazole plus radiotherapy in a presumably similar population. Despite additional follow-up and more sophisticated analysis, our analysis does not demonstrate an influence of hemoglobin concentration on any of the outcome measures we examined. Possible explanations for the difference in findings of RTOG 79-15 and DAHANCA 2 are discussed. Radiation therapy of head and neck squamous cancers, Hypoxia and hemoglobin conc. in head and neck cancers, Oral cavity cancer, Effect of radiation therapy, Oropharynx cancer, Hemoglobin and radiotherapy, Hemoglobin concentration, Effect upon radiotherapy, Irradiation of oropharynx cancer, Hgb effect.

Sensitization of hypoxic tumour cells--clinical experience

There is substantial evidence for the presence of hypoxia in human tumours. This is documented by histopathological demonstration of vascular insufficiency, direct oxygen measurements in tumours, as well as by physiological imaging and mapping of hypoxic areas. As a consequence, clinical trials have focused on the hypoxia problem for more than 30 years. This includes the use of hyperbaric oxygen, hypoxic cell radiosensitizers, and, more recently, modification of the oxygen-unloading capacity of haemoglobin. Agents directed towards destruction of hypoxic cells have also been applied, such as hyperthermia and bio-reductive drugs. Despite decades of clinical trials, the results are still inconclusive, and although some trials have shown significant benefit, it has become apparent that hypoxia is a complex problem. Hypoxia appears to be especially a problem in certain tumour types (e.g. squamous cell carcinoma), but even within tumours of the same type, site, and stage, hypoxia does not occur to the same extent. Furthermore, there are increasing suggestions that hypoxia may occur in two principally different ways, namely acutely and chronically, yielding varying responses to modifying agents. Although improvement in hypoxic cell radiosensitizers and other agents is under way, a definitive solution to the hypoxia problem will not be found until the tumours in which hypoxia occurs can be identified. This will require detailed analysis of individual tumours and patients' parameters, and better knowledge of the mechanisms of reoxygenation in clonogenic tumour cells.

Chemical manipulations of tissue oxygenation for therapeutic benefit

Many new approaches are currently being explored to improve cancer treatment through hypoxic cell radiosensitization. Oxygen carriers, calcium antagonists, some drugs which shift the oxygen hemoglobin curve to the right improve the oxygen availability in the tumors. An alternative way to improve radiotherapy or chemotherapy is to increase tumor hypoxia either by shifting the hemoglobin oxygen dissociation curve to the left or by using vasodilators. This paper summarizes main results obtained in that field. The relevance of data obtained from animal experiments to clinical practice will be discussed.

Altered radiosensitivity in a mouse carcinoma after administration of clofibrate and bezafibrate

We have investigated the ability of the antilipidaemia drugs clofibrate and bezafibrate, to reduce the binding affinity of haemoglobin for oxygen and to sensitize an experimental tumour (the SCCVII/St carcinoma) in the mouse to radiation. Clofibrate at a high dose (4.1 mmol/kg, p.o.) increased the P50 of the blood by about 10 mm Hg. Its effect on tumour radiosensitivity was dependent on tumour size. Highly significant sensitization, equivalent to a 40-fold reduction in the number of hypoxic cells, was seen in small tumours; but in large tumours there was much less effect. At a low dose, which is close to that currently used clinically (0.3 mmol/kg), clofibrate produced a small and barely significant increase in P50. The effect of low dose clofibrate on tumour radiosensitivity also depended on tumour size, small tumours (200 mg) being significantly sensitized, while no significant effect was seen in large tumours. Bezafibrate, at the low dose of 0.3 mmol/kg, gave a significant increase in P50 (by approximately equal to 8 mm Hg), but sensitization to radiation in small tumours was not impressive and not statistically significant. We must gain a better understanding of the mechanisms involved in these effects before applying this approach to clinical radiotherapy.

Chlorophenoxy acetic acid derivatives as hemoglobin modifiers and tumor radiosensitizers

We have studied the influence of the antilipidemia drug, clofibrate, and several structurally related analogs on the binding affinity of hemoglobin for oxygen and the radiation sensitivity of the SCCVII/St carcinoma in the mouse. Several compounds in this class reduced hemoglobin affinity in vivo; and two of these, ML1024 (etophyline clofibrate) and ML1037, were at least as effective as clofibrate at reducing hemoglobin affinity and much less toxic. When given orally at a dose of 4.1 m mole/Kg, 1/2-2 hrs before 20 Gy X rays, clofibrate gave radiosensitization in the SCCVII/St tumor equivalent to a 40-fold reduction in hypoxic fraction. ML1024 and ML1037 at a dose (3.0 m mole/Kg), which had a similar effect on hemoglobin, gave much less sensitization of the tumor. Only ML1024 produced a statistically significant effect, equivalent to a four-fold reduction in hypoxic fraction. We conclude that there are several clofibrate analogs which in relation to their toxicity are much better hemoglobin modifiers than the parent compound. They do not, however, show the same radiosensitizing effects, leading us to believe that mechanisms other than changes in hemoglobin/oxygen binding must also be involved.

The influence of initial hemoglobin and blood pressure levels on results of radiation therapy for carcinoma of the prostate

A group of 914 patients with carcinoma of the prostate treated by definitive radiotherapy at Stanford between 1956 and 1985 was studied. Of these, the initial hemoglobin level was recorded in 656 cases and the initial blood pressure in 760 cases. End-points studied in actuarial analyses were survival, disease-specific survival, local control, freedom from distant relapse, and occurrence of late intestinal complications. Although the anemic group (Hb less than 13.5 g/dl) was correlated negatively with survival (p = 0.02), there was no correlation with disease-specific survival or local control. The conclusion was that anemia per se did not affect the outcome of radiation therapy. A pulse pressure greater than or equal to 60 mm Hg was significantly correlated with worse survival (p = 0.01) and local control (p = 0.04), but no correlation was found between systolic and diastolic blood pressure and the end-points measured. Neither anemia nor hypertension were significantly correlated with late intestinal complications.

Manipulations in the oxygen transport capacity of blood as a means of sensitizing tumors to radiation therapy

Tumor response to radiation is dependent not only on the quantity of hemoglobin (Hb) available for oxygen (O2) transport but also on the position of the Hb-O2 dissociation curve (Hb affinity). Previous studies have shown that administering agents which shift the Hb-O2 dissociation curve to the right (decrease Hb affinity) sensitize tumors to radiation by reducing the fraction of radiobiologically hypoxic cells. However, there may be toxicity limitations when agents aimed at altering Hb affinity are administered directly to the host. The present studies evaluated the therapeutic benefit of shifting the Hb-O2 dissociation curve in vitro prior to the transfusion of the biochemically modified RBCs into recipient hosts. Mice were given a hemolysis agent (phenylhydrazine hydrochloride, PH) prior to transfusing RBCs with normal or altered Hb affinity. A 100 mg/kg dose of PH reduced the hematocrit to approximately 60% of control 24 hr after treatment. Tumors irradiated at this time demonstrated an increased fraction of hypoxic cells. If the hematocrit was returned to normal by transfusing mice prior to irradiation, a significant but transient reduction in the hypoxic fraction was seen. Tumor response was reduced if RBCs with elevated Hb affinity, obtained by storing the erythrocytes at 4 degrees C, were used. Alternatively, tumor sensitization was noted when animals were transfused with RBCs having decreased Hb affinities. The latter was achieved by incubating the RBCs in the presence of either clofibrate or the precursors of 2,3 diphosphoglycerate (2,3 DPG). These findings further support the notion that the Hb affinity is an important parameter in determining tumor response to radiation and suggest that this factor ought to be considered when RBCs are used to transfuse anemic patients undergoing radiotherapy.

Modification of the radiation response of pig skin by manipulation of tissue oxygen tension using anesthetics and administration of BW12C

The importance of tissue oxygen tension on radiosensitivity was studied by examining modifications in the incidence of moist desquamation in pig skin after irradiation with strontium-90 plaques. The effects were analyzed using quantal dose-response data and comparisons were made using ED50 values for moist desquamation. Under standard anesthetic conditions of 2% halothane, approximately 70% oxygen, and approximately 30% nitrous oxide, the ED50 value (+/- SE) for moist desquamation was 27.32 +/- 0.52 Gy with no significant variation in radiosensitivity between dorsal, lateral, and ventral skin sites on the flank. Irradiation with 2% halothane and air increased the ED50 to 31.25 +/- 0.94 Gy, primarily due to an increased radioresistance of the dorsal sites. When combined with BW12C, a drug which binds oxygen selectively to hemoglobin and hence reduced the oxygen availability to tissues, a further increase in the ED50 values was observed. This was approximately 39 Gy with BW12C concentrations of 30 mg/kg and 50 mg/kg b.w. of BW12C, indicating a dose modification factor (DMF) of approximately 1.26. However, when animals were breathing the standard gas mixture, this DMF was reduced to 1.15 for 30 mg/kg of BW12C, indicating that a higher level of oxygen partly counteracted the effects of the drug in these studies with BW12C. The greatest variability in radiosensitivity was seen in the dorsal fields. This suggested complex physiological adaptation, a phenomenon that might also explain the absence of any modification of the radiation response when 100 mg/kg of BW12C was used.

Prognostic value of hemoglobin concentrations and blood transfusions in advanced carcinoma of the cervix treated by radiation therapy: results of a retrospective study of 386 patients

A retrospective study was carried out on 386 patients with advanced cervical carcinomas treated with radiation therapy between 1973 and 1983. The influence of hemoglobin concentrations and blood transfusions before and/or during treatment on the occurrence of distant and/or local regional failures were examined in a univariate and multivariate analyses. In the multivariate analysis hemoglobin concentrations were prognostic only during treatment and patients with at least one value below the threshold of 10 gm% had a significantly higher risk of local regional failure than the patients with all their values above the threshold. Moreover 70% of these high risk patients had less than half of their values below the threshold. It is possible that blood transfusions might be beneficial when given before treatment. However, although it was not significant, blood transfusions given during treatment tended to be an adverse prognostic factor suggesting that blood transfusions might not have completely offset acute anemia prior to transfusion. Our study suggests that anemia during treatment, even of short duration might be detrimental to patients.

The effect of artificially induced hyperglycemia on the radiation response of the Lewis lung and EMT6 tumor models

The effect of hyperglycemia, induced by administration of glucose, on the radiation response of the Lewis lung and EMT6 tumor models has been evaluated. Neither acute (single i.p. injection of 8 mg/glucose) nor chronic (multiple i.p. injections of 6 mg/g glucose plus glucose in the water bottles) administrations of glucose increased the radiation response of either tumor. A combination of a single i.p. injection of glucose and a reduction of the O2 content of the inspired gas to 10 per cent did by itself reduce cell survival by 55-75 per cent in the EMT6 and 80-90 per cent in the Lewis lung carcinoma. However, this treatment had little effect on the shape of the radiation dose-response curve, and simply gave rise to a parallel shift of the survival curve, indicating that this treatment had little or no specificity for hypoxic cells.

Perioperative blood transfusion and solid tumour recurrence

Evidence regarding the association of blood transfusions with recurrence of solid tumours is largely conflicting. This is perhaps unsurprising given the retrospective nature of the studies performed to date, the complexity of the disease and its treatment, and variations in local transfusion practices. Nonetheless, new data demonstrating that transfusions of whole blood, as opposed to red cell concentrates, are associated with earlier cancer recurrence are most readily explained by a cause and effect relationship. There is a growing literature documenting previously unforeseen immunologic consequences of homologous blood transfusion. These possible clinical consequences include earlier cancer recurrence and increased susceptibility to infection with bacteria and viruses. The questions raised in this review can be answered conclusively only by controlled prospective studies. For the present the prudent clinician will select red blood cells rather than whole blood for transfusion, employ autologous transfusions whenever feasible, and recognize that blood transfusion is a therapy with considerable benefits, but also considerable risks.

The influence of haemoglobin affinity for oxygen on tumour radiosensitivity

Appropriate control of the affinity of haemoglobin for oxygen is fundamental to the efficient oxygenation of our tissues. Important modifiers of this relationship are pH, CO2 concentration and the intraerythrocytic level of 2,3-diphosphoglycerate (2,3-DPG). We have studied the influence of haemoglobin affinity on the radiosensitivity of the RIF-1 sarcoma in the mouse. Changes in haemoglobin affinity were induced by exposing donor mice to either 10% oxygen, normal air, or 100% oxygen for 48 h. Blood was drawn from these animals and exchanged transfused into tumour-bearing mice immediately before irradiation. Transfusion of blood from mice breathing 10% oxygen carried a lowered haemoglobin affinity and produced marked radiosensitization of the tumours in the recipients; transfusion with normal blood had no significant effect and transfusions from mice breathing 100% oxygen caused a small increase in radioresistance. Measurements of the level of 2,3-DPG in the blood of these groups showed higher concentrations in the oxygen-deprived animals than in controls but no significant change in animals exposed to 100% oxygen. These results demonstrate that alterations in haemoglobin affinity, probably resulting from changes in 2,3-DPG levels, can have a powerful influence on tumour radiosensitivity. We feel that this mechanism could have considerable clinical importance.

The adaptive response of mouse tumours to anaemia and retransfusion

We have developed exchange transfusion methods to alter the hematocrit of tumour-bearing mice. The effects of anaemia and its correction by blood transfusion on the radiosensitivity of two mouse tumours (SCCVII/St and RIF-1) were studied using excision, in vivo/in vitro assay. An acute reduction in haematocrit caused a high degree of radioresistance equivalent to an increase in the hypoxic fractions by factors of 10 (SCCVII/St) and 30 (RIF-1). As the duration of the anaemia was prolonged, radioresistance was lost until within about 6 h normal radiosensitivity was observed even though the anaemia persisted. The restoration of the normal haematocrit by red blood cell transfusion after 24 h of anaemia caused increased radiosensitivity equivalent to a reduction in the hypoxic fraction by factors of 5 (SCCVII/St) and 10 (RIF-1), but again the effect was transient and normal radiosensitivity was re-established within 24-48 h of retransfusion. Measurements of 14C misonidazole (MISO) binding to RIF-1 tumours after these procedures indicated changes in the number of hypoxic cells which were qualitatively almost identical to those using the cell survival endpoint, leading us to believe that changes in oxygenation were responsible for the altered radiosensitivity. We feel that transfusion procedures could be used to advantage in the radiotherapy of some cancers.