The Ability of the Nitric Oxide Synthases Inhibitor T1023 to Selectively Protect the Non-Malignant Tissues

Previously, we showed that a nitric oxide synthase (NOS) inhibitor, compound T1023, induces transient hypoxia and prevents acute radiation syndrome (ARS) in mice. Significant efficacy (according to various tests, dose modifying factor (DMF)-1.6-1.9 against H-ARS/G-ARS) and safety in radioprotective doses (1/5-1/4 LD10) became the reason for testing its ability to prevent complications of tumor radiation therapy (RT). Research methods included studying T1023 effects on skin acute radiation reactions (RSR) in rats and mice without tumors and in tumor-bearing animals. The effects were evaluated using clinical, morphological and histological techniques as well as RTOG classification. T1023 administration prior to irradiation significantly limited the severity of acute RSR. This was due to a decrease in radiation alteration of the skin and underlying tissues, and the preservation of the functional activity of cell populations that are critical in the pathogenesis of radiation burn. The DMF values for T1023 for skin protection were 1.4-1.7. Moreover, its radioprotective effect was fully selective to normal tissues in RT models of solid tumors-T1023 reduced the severity of acute RSR and did not modify the antitumor effects of γ-radiation. The results indicate that T1023 can selectively protect the non-malignant tissues against γ-radiation due to hypoxic mechanism of action and potentiate opportunities of NOS inhibitors in RT complications prevention.

Hyperthermal Effects in Phototherapy with Hematoporphyrin Derivative Sensitization

Although the photochemical reaction of hematoporphyrin derivative (HpD) appears to play a major role in cytotoxic activity, the hyperthermal contribution to tumor destruction has not yet been clarified. We investigated its role in the effectiveness of laser photoradiation therapy using MS-2 sarcoma transplanted into the hind pad of BALB/c mice as the experimental model. Mice received HpD i.V., 25 mg/kg - 24 h before exposure to light delivered from a dye laser or Nd-YAG laser, or before warming in a thermostated bath. Since our aim was not to cure the tumor, the treatment response was evaluated only as inhibition of tumor growth at different days after treatment. Our results support the view that in laser photochemotherapy the hyperthermia produced by irradiation and the photodynamic effect mediated by HpD could contribute to tumor destruction. Moreover, a synergistic interaction between the photodynamic effect and heat was observed in this experimental model.

Radiation Therapy Combined with Photofrin or 5-Ala: Effect on Lewis Sarcoma Tumor Lines Implanted in Mice. Preliminary Results

Aims and background

Ionizing irradiation is a well-established therapeutic modality for cancer. Photodynamic therapy (PDT), especially with 5-ALA and Photofrin, is highly effective in some tumor types. Chemical modifiers, so-called radiosensitizers, are used in order to increase the efficacy of radiotherapy. Most of the known and routinely used radiosensitizers are not tumor selective, so that the normal tissue reaction toxicity is also increased. In the present study we investigated whether a porphyrin derivative that is currently used as a tumor-photosensitizing agent in photodynamic therapy (PDT) may also act as a tumor-specific radiosensitizer.

Materials and methods

For our investigation we used Balb/c mice implanted with Lewis sarcoma and irradiated with 3 Gy combined with injection of 5-ALA or Photofrin at various concentrations before irradiation.

Results

5-ALA had no effect as a radiosensitizer at any of the concentrations examined. Photofrin at a concentration of 5 mg/kg proved to be a chemical modifier of ionizing radiation, delaying tumor growth and reducing the overall tumor volume by about 50% after six days.

Conclusion

Photofrin has marked efficacy as a radiosensitizer and can be used in the future as a selective tumor radiosensitizer.

Oxygen microbubbles improve radiotherapy tumor control in a rat fibrosarcoma model - A preliminary study

Cancer affects 39.6% of Americans at some point during their lifetime. Solid tumor microenvironments are characterized by a disorganized, leaky vasculature that promotes regions of low oxygenation (hypoxia). Tumor hypoxia is a key predictor of poor treatment outcome for all radiotherapy (RT), chemotherapy and surgery procedures, and is a hallmark of metastatic potential. In particular, the radiation therapy dose needed to achieve the same tumor control probability in hypoxic tissue as in normoxic tissue can be up to 3 times higher. Even very small tumors (<2-3 mm3) comprise 10-30% of hypoxic regions in the form of chronic and/or transient hypoxia fluctuating over the course of seconds to days. We investigate the potential of recently developed lipid-stabilized oxygen microbubbles (OMBs) to improve the therapeutic ratio of RT. OMBs, but not nitrogen microbubbles (NMBs), are shown to significantly increase dissolved oxygen content when added to water in vitro and increase tumor oxygen levels in vivo in a rat fibrosarcoma model. Tumor control is significantly improved with OMB but not NMB intra-tumoral injections immediately prior to RT treatment and effect size is shown to depend on initial tumor volume on RT treatment day, as expected.

Characterizing the Potency and Impact of Carbon Ion Therapy in a Primary Mouse Model of Soft Tissue Sarcoma

Carbon ion therapy (CIT) offers several potential advantages for treating cancers compared with X-ray and proton radiotherapy, including increased biological efficacy and more conformal dosimetry. However, CIT potency has not been characterized in primary tumor animal models. Here, we calculate the relative biological effectiveness (RBE) of carbon ions compared with X-rays in an autochthonous mouse model of soft tissue sarcoma. We used Cre/loxP technology to generate primary sarcomas in KrasLSL-G12D/+; p53fl/fl mice. Primary tumors were irradiated with a single fraction of carbon ions (10 Gy), X-rays (20 Gy, 25 Gy, or 30 Gy), or observed as controls. The RBE was calculated by determining the dose of X-rays that resulted in similar time to posttreatment tumor volume quintupling and exponential growth rate as 10 Gy carbon ions. The median tumor volume quintupling time and exponential growth rate of sarcomas treated with 10 Gy carbon ions and 30 Gy X-rays were similar: 27.3 and 28.1 days and 0.060 and 0.059 mm3/day, respectively. Tumors treated with lower doses of X-rays had faster regrowth. Thus, the RBE of carbon ions in this primary tumor model is 3. When isoeffective treatments of carbon ions and X-rays were compared, we observed significant differences in tumor growth kinetics, proliferative indices, and immune infiltrates. We found that carbon ions were three times as potent as X-rays in this aggressive tumor model and identified unanticipated differences in radiation response that may have clinical implications. Mol Cancer Ther; 17(4); 858-68. ©2018 AACR.

[Certain results of the investigations into the anti-tumour action of the magnetic field under experimental conditions]

This paper summarizes the results of the application of thr magnetic fields for the treatment of experimental tumours, such as sarcoma M-1, alveolar liver cancer PC-1, and Erlich's carcinoma. The evidence of the anti-tumour action of both strong (1200 mTI) and weak (5 to 100 mTI) magnetic fields has been obtained. The author describes the modulating effect of the magnetic fields on the anti-tumour potency of photodynamic therapy and chemotherapy. The data concerning the impact of ferromagnetic hyperthermal therapy on the tumour growth and the survival rate among the tumour-bearing animals are presented.

Radiation and ATM inhibition: the heart of the matter

Numerous in vitro studies have shown that human cell lines lacking functional ATM are extremely radiosensitive. In this issue, Moding et al. demonstrate using a murine model of sarcoma that deletion of the Atm gene has much less of a radiosensitizing effect on normal cardiac endothelia than on rapidly proliferating tumor endothelia. This work confounds our assumptions about the generality of the role of ATM in radiation sensitivity and the potential use of ATM inhibitors as radiosensitizers.

Atm deletion with dual recombinase technology preferentially radiosensitizes tumor endothelium

Cells isolated from patients with ataxia telangiectasia are exquisitely sensitive to ionizing radiation. Kinase inhibitors of ATM, the gene mutated in ataxia telangiectasia, can sensitize tumor cells to radiation therapy, but concern that inhibiting ATM in normal tissues will also increase normal tissue toxicity from radiation has limited their clinical application. Endothelial cell damage can contribute to the development of long-term side effects after radiation therapy, but the role of endothelial cell death in tumor response to radiation therapy remains controversial. Here, we developed dual recombinase technology using both FlpO and Cre recombinases to generate primary sarcomas in mice with endothelial cell-specific deletion of Atm to determine whether loss of Atm in endothelial cells sensitizes tumors and normal tissues to radiation. Although deletion of Atm in proliferating tumor endothelial cells enhanced the response of sarcomas to radiation, Atm deletion in quiescent endothelial cells of the heart did not sensitize mice to radiation-induced myocardial necrosis. Blocking cell cycle progression reversed the effect of Atm loss on tumor endothelial cell radiosensitivity. These results indicate that endothelial cells must progress through the cell cycle in order to be radiosensitized by Atm deletion.

Synergistic combination of hyperoxygenation and radiotherapy by repeated assessments of tumor pO2 with EPR oximetry

The effect of hyperoxygenation with carbogen (95% O(2) + 5% CO(2)) inhalation on RIF-1 tumor pO(2 )and its consequence on growth inhibition with fractionated radiotherapy is reported. The temporal changes in the tumor pO(2) were assessed by in vivo Electron Paramagnetic Resonance (EPR) oximetry in mice breathing 30% O(2) or carbogen and the tumors were irradiated with 4 Gy/day for 5 consecutive days; a protocol that emulates the clinical application of carbogen. The RIF-1 tumors were hypoxic with a tissue pO(2) of 5-9 mmHg. Carbogen (CB) breathing significantly increased tumor pO(2), with a maximum increase at 22.9-31.2 min on days 1-5, however, the magnitude of increase in pO(2) declined on day 5. Radiotherapy during carbogen inhalation (CB/RT) resulted in a significant tumor growth inhibition from day 3 to day 6 as compared to 30%O(2)/RT and carbogen (CB/Sham RT) groups. The results provide unambiguous quantitative information on the effect of carbogen inhalation on tumor pO(2) over the course of 5 days. Tumor growth inhibition in the CB/RT group confirms that the tumor oxygenation with carbogen was radiobiologically significant. Repeated tumor pO(2) measurements by EPR oximetry can provide temporal information that could be used to improve therapeutic outcomes by scheduling doses at times of improved tumor oxygenation.

Time benefit in the assessment of recurrences following fractionated radiotherapy in an experimental tumour system using positron‐emission tomography with18F‐fluorodeoxyglucose

PURPOSE

To determine the sensitivity and specificity of 18F-fluorodeoxyglucose-positron-emission tomography (FDG-PET) in the diagnosis of R1H tumours after fractionated radiotherapy, and the dependency of sensitivity and specificity on time after therapy. In addition, the time benefit of FDG-PET concerning early recognition of recurrences after fractionated radiotherapy was assessed.

MATERIAL AND METHODS

Subcutaneously growing rat rhabdomyosarcoma R1H tumours were irradiated by applying total doses of 80 or 85 Gy after reaching a start volume of 0.8 cm3. Twenty animals were treated. Tumour volume was determined twice a week. FDG-PET was performed weekly before, during and for 6 months after therapy using a conventional full-ring whole-body PET scanner. In total, 600 PET results were evaluated qualitatively using a six-scale score. PET results and actual tumour volumes were compared. The sensitivity and specificity of tumour detection by PET was calculated for different times after the onset of therapy. The optimal score for tumour detection and the influence of time after therapy on the quality of PET (time benefit) was evaluated using receiver-operating characteristics.

RESULTS

After irradiation, 8/20 tumours (40%) were locally controlled, while 12/20 recurred. In this tumour model, evidence of relapse is assured when a volume of 0.1 cm3 is reached. Sensitivity of tumour diagnosis by PET increases with time, i.e. with the volume of recurrent tumours after the onset of therapy, mounting to > 0.95 after 100 days. Specificities of 0.95-1.0 were determined after therapy, showing no increase with time. Tumour diagnosis by PET is highly accurate when performed 80 days after the start of treatment. On average, tumours were recognized by PET on 31, 62, 74 and 81 days (median) before approaching volumes of 0.2, 0.5, 0.8 or 1.0 cm3, respectively.

CONCLUSION

An experimental system was implemented that allows reproducible detection of recurrent R1H tumours after radiotherapy using FDG-PET. The usefulness of PET as a diagnostic test for R1H tumours is very good and a reliable resolution for PET is demonstrated for volumes < 1 cm3. The results indicate that FDG-PET enables early recognition of recurrences after fractionated radiotherapy.

[Biological effects of Lamipharen photodynamic therapy]

Biological effects of Lamipharen treatment of sarcoma M-1 was studied in newborn rats and photodynamic therapy in combination with radiation was evaluated.

Tirapazamine plus cisplatin and irradiation in a mouse model: improved tumor control at the cost of increased toxicity

PURPOSE

Tirapazamine (TPZ) reportedly enhances the tumor cell killing effect of cisplatin up to fivefold and it is an attractive drug for combination with radiotherapy. We evaluated the toxicity of a fractionated combined treatment.

METHODS

Murine RIF-1 fibrosarcomas growing on the right hind foot of C3-H mice were used. Within 2 weeks, animals were treated with six i.p. injections of TPZ (43.2-172.8 mg/kg total), and/or cisplatin (24 mg/kg total) and ten fractions of 2 Gy to the tumor. All treatments were carried out under anesthesia. Maximum follow-up was 35 days. The local tumor control was determined by calculating the tumor doubling time t (2vo). In addition to standard toxicity assessment, the major inner organs were examined histologically.

RESULTS

The administration of low TPZ doses to the cisplatin/radiotherapy treatment caused only little changes in tumor doubling time (t (2vo)) and led to a lethality rate of 15-30%. Higher TPZ doses caused an increase in t (2vo), but also a further increase in lethality and toxicity in particular to the heart, liver, kidney and stomach. Cisplatin/radiotherapy treatment without TPZ produced no severe toxicity.

CONCLUSIONS

This is a detailed study of both the acute and delayed toxicities of combined TPZ treatment in a mouse model. In our study the addition of TPZ to the cisplatin/radiotherapy treatment caused a significant increase in toxicity with only moderate effect on the tumor.

The effect of electromagnetic field and local inductive hyperthermia on nonlinear dynamics of the growth of transplanted animal tumors

AIM

To examine the effects of electromagnetic field with amplified magnetic component and local inductive hyperthermia (IH) on nonlinear dynamics of the growth of animal tumors.

MATERIALS AND METHODS

Guerin carcinoma, Lewis lung carcinoma, sarcoma 45, Walker 256 carcinosarcoma and Pliss lymphosarcoma were studied. The animal tumors were exposed inside of loop aerial, 3 cm in diameter locally for 30 min. Parameters of electromagnetic irradiation (EI): frequency 40 MHz, magnetic intensity 72 A/m, electric intensity 200 V/m and the output power 50 W. The temperature measured by immersion of thermocouple inside the center of the tumor didn't exceed 38.5-39.5 degrees C. Nonlinear dynamics of the growth of animal tumors was analyzed by autocatalytic equation. The heterogeneity of ultrasonic image of the tumor was analyzed by Moran spatial autocorrelation.

RESULTS

The strongest inhibition effect under the influence of EI was in Pliss lymphosarcoma and sarcoma 45. The growth stimulation of animal tumors after EI was recorded in Walker 256 carcinosarcoma. The use of mild IH increased the blood flow in the tumor of Guerin carcinoma.

CONCLUSION

These results are important for clinical application because they testify the necessity of optimization of schemes for local EI during anticancer neoadjuvant therapy with the use of drugs or magnetic nanoparticles. The use of mild IH as a basis for the monotherapy of malignant tumors is not expedient.

Production and tumour uptake of [64Cu]Pyruvaldehyde-bis (N4-methylthiosemicarbazone) for PET and/or therapeutic purposes

BACKGROUND

Copper-64 (T(1/2)=12.7 degrees h) is an important radionuclide used both in PET imaging and therapy. [(64)Cu]-pyruvaldehyde- bis(N(4)-methylthiosemicarbazone) ([64Cu]-PTSM) has already been used in the detection of cerebral and myocardial blood flow. In this study, a simple production method and tumor accumulation of [(64)Cu]-PTSM in fibrosarcoma-bearing mice were reported.

MATERIAL AND METHODS

Cu-64 was produced via the 68Zn(p, alpha n)(64)Cu nuclear reaction. [(64)Cu]-PTSM was prepared using in-house made PTSM ligand and [(64)Cu]cuprous acetate and injected to fibrosarcoma-bearing mice.

RESULTS

Copper-64 was prepared in chloride form ( approximately 200 mCi, > 95% chemical yield at 180 degrees microA for 1.1 h irradiation, radionuclidic purity > 96%, copper-67 as impurity). The solution of (64)Cu- PTSM was prepared in > 80% radiochemical yield and more than 98% radiochemical purity. A significant tumor uptake was observed 2 hours post injection in tumor-bearing mice (tumor/muscle: 9, tumor/blood: 6).

CONCLUSION

[(64)Cu]-PTSM was prepared on a radiopharmaceutical scale using readily available zinc-68, with high quality and was shown to possess application in the therapy and/or imaging of fibrosarcoma.

Untersuchungen zur Toxizität von Tirapazamine plus Cisplatin in einem Maus-Tumormodell

BACKGROUND AND PURPOSE

Tirapazamine (TPZ) is an anticancer drug that is selectively activated by the low oxygen environment in solid tumors. Furthermore, TPZ also enhances the tumor cell-killing effect of cisplatin. So far, detailed information on the toxicity of combined treatment is rare. The authors evaluated the toxicity of TPZ in combination with cisplatin in a mouse tumor model. For this purpose, general toxicity was monitored and all inner organs were examined histologically.

MATERIAL AND METHODS

RIF-1 fibrosarcomas of murine origin growing in the right hindfoot dorsum of C3H mice were used. The animals were treated with 10 x 2 Gy irradiation plus six i.p. injections of 4 mg/kg cisplatin (total dose 24 mg/kg) together with varying doses of TPZ (0-28 mg/kg per injection; total dose 0, 43.2, 86.4, 129.6, 151.2, 172.8 mg/kg). Treatment was applied within 2 weeks (Figure 1). Total observation period was up to 35 days.

RESULTS

Combined treatment with TPZ led to a dose-dependent, significant decrease in motor activity (Table 1) and body weight and an increase in mortality (Figures 2 and 3, Tables 2 and 3). Histological analyses showed areas of necrosis in the heart, liver and kidney and gastric ulcers (Table 4). Cisplatin alone produced no severe toxicity. Tumor doubling times were TPZ dose-dependent and comparable with data from the literature (Figures 4 and 5, Table 3).

CONCLUSION

Unlike most data from the literature a dose-dependent increase in toxicity was seen when adding TPZ to a standard treatment of cisplatin plus irradiation. To the authors' knowledge this is the first study histologically examining in detail the organ toxicity of TPZ in a mouse model. Furthermore, they expand the rare data on long-term toxicity after TPZ plus cisplatin in a fractionated therapy regimen. The results question the usefulness of frequently performed therapeutic studies where only short-term treatment and observation endpoints are used, since essential toxicities are likely to be overlooked.

Electroporation Enhances Radiation and Doxorubicin-Induced Toxicity in Solid Tumor In Vivo

Treatment of cancer patients is subject to limitations in radiotherapy and chemotherapy. This necessitates development of new protocols, and the present work reports on the effects of a combination of local electroporation with ionizing radiation and/or anticancer drug doxorubicin hydrochloride (DOX) on subcutaneous solid tumor murine fibrosarcoma. Localized treatment of fibrosarcoma tumor, grown in right hind leg of Swiss mice, has been carried out using DOX (0.6 mg/kg body weight), radiation (Co 60 gamma-rays, dose rate 0.37 Gy/min) and electroporation (1 kV/cm, 200 micros, 8 pulses per burst, 10 bursts) individually or in combinations. Measurements of the tumor growth kinetics after treatment with combinations have revealed significant growth delay. The treatment groups, (i) radiation and electroporation, (ii) DOX and electroporation, and (iii) radiation, DOX and electroporation, have yielded tumor growth delays (TGDs) of 1.22, 1.5, and 1.73 days, respectively, compared to control with the tumor volumes being 53%, 57%, and 49% that of control on the final day of observation. These results suggest that the antitumor effects of a moderate dose of gamma radiation and low concentration of DOX can be significantly enhanced by combination with electroporation.

Preclinical studies of the novel vascular disrupting agent MN-029

BACKGROUND

Vascular disrupting agents (VDAs) are designed to cause a rapid and selective shutdown of the established tumor vasculature, which leads to secondary ischemic tumor cell death.

MATERIALS AND METHODS

We examined the efficacy of a novel VDA, MN-029, in the rodent KHT sarcoma model.

RESULTS

A significant reduction in the functional vessel number was observed after intraperitoneal injection of MN-029 at a dose of 100 mg/kg. Histological evaluation showed extensive necrosis (approximately 90%) by 24 h. MN-029 treatment to the tumor-bearing mice also resulted in a dose-dependent tumor cell killing. When used in combination with radiation or cisplatin chemotherapy, a 100 mg/kg dose of MN-029 significantly enhanced tumor killing compared to that seen with radiation or cisplatin alone.

CONCLUSION

The results demonstrated that MN-029 could cause rapid vascular shutdown in solid tumors, dose-dependent secondary tumor cell killing, and effective enhancement of the antitumor effects of radiation and cisplatin chemotherapy.

Tirapazamine Administered as a Neoadjuvant to Radiotherapy Reduces Metastatic Dissemination

PURPOSE

The level of hypoxia in primary tumors has been linked both clinically and experimentally to the incidence of metastases. This study was designed to address the effect of selectively targeting hypoxic cells in primary tumors on subsequent presentation of metastasis.

EXPERIMENTAL DESIGN

The murine KHT model was used as a reproducible temporal and spatial onset of metastases is revealed following treatment of primary ( approximately 400 mm(3)) s.c. tumors with a 25 Gy radiation dose. The bioreductive drugs tirapazamine and RB6145 were administered in multiple doses before radiotherapy.

RESULTS

Fractionated treatment with both tirapazamine and RB6145 significantly reduced the hypoxic fraction of the primary tumor, as assessed by pimonidazole binding, and had no effect on the overall growth rate of the primary tumor. Excision assays showed an increased level of cell kill in tirapazamine-treated versus RB6145-treated tumors consistent with tirapazamine targeting hypoxic cells at a broader range of oxygen tensions than RB6145. Tirapazamine treatment significantly reduced the presentation of metastases following radiotherapy (P = 0.003 versus saline controls) whereas RB6145 had no effect. Local control rates increased from 20% to 32% and 50% when radiation was combined with RB6145 and tirapazamine, respectively.

CONCLUSIONS

These data provide direct evidence that selective targeting of hypoxic cells in primary tumors is a viable approach in the control of metastatic disease. The enhanced efficacy of tirapazamine versus RB6145 suggests that the radioresistant cells at intermediate oxygen tensions, conducive to targeting with tirapazamine but not with the more stringent bioreductive RB6145, predominate in terms of linking primary tumor hypoxia and metastases.

CpG oligodeoxynucleotide enhances tumor response to radiation

CpG oligodeoxynucleotides (ODNs) are synthetic DNA sequences containing unmethylated cytosine-guanine motifs with potent immunomodulatory effects. Via Toll-like receptor 9 agonism of dendritic cells and B cells, CpG ODNs induce cytokines, activate natural killer cells, and elicit vigorous T-cell responses that lead to significant antitumor effects, including improved efficacy of chemotherapeutic agents. On the basis of these properties of CpG ODNs, we tested whether they also could enhance tumor response to radiotherapy. Using an immunogenic mouse tumor, designated FSa, the response to radiotherapy was assayed by tumor growth delay and tumor cure rate (TCD(50), radiation dose yielding 50% tumor cure rate). Treatments were initiated when established tumors were either 6 or 8 mm in diameter. CpG ODN as a single agent given s.c. peritumorally had little effect on tumor growth; however, it dramatically enhanced tumor growth delay in response to single-dose radiation by a factor of 2.58-2.65. CpG ODN also dramatically improved tumor radiocurability, reducing the TCD(50) by a factor of 1.93, from 39.6 (36.1-43.1) Gy to 20.5 (14.3-25.7) Gy. The CpG ODN-induced enhancement of tumor radioresponse was diminished in tumor-bearing mice immunocompromised by sublethal whole-body radiation. Tumors treated with CpG ODN and radiation showed histologic changes characterized by increased necrosis, heavy infiltration by host inflammatory cells (lymphocytes and granulocytes), and reduced tumor cell density. These results show that CpG ODNs are potent enhancers of tumor radioresponse and as such have potential to improve clinical radiotherapy.

[Angioroentgenologic response of rat M-1 sarcoma to low-energy infrared laser irradiation at varying frequency]

After rats with sarcoma M-1 inoculated in the femur area were exposed to low-energy (0.54 mT1) infra-red laser irradiation, 100Hz, for 10 min, the number of contrast-enhanced vessels of tumor fell sharply as compared with controls. That effect lasted for almost 24 hrs. At 1kHz, the total-sum of diameters of such vessels still increased 24 hrs after the exposure. When at 10kHz, that index decreased, and by day 3 vascular pattern and diameter came back to normal in all experiments.

Electroporation of LPB sarcoma cells in vitro and tumors in vivo increases the radiosensitizing effect of cisplatin

BACKGROUND

Cisplatin is a cytotoxic drug with radiosensitizing effect. In this study a physical drug delivery system, electroporation, was used to facilitate cisplatin delivery into the cells and tumors with the aim of increasing radiation response.

MATERIALS AND METHODS

LPB murine sarcoma cells and tumors were treated either by cisplatin, electroporation or ionizing radiation, and combinations of these. In vitro radiation response was determined by colony forming assay while in vivo treatment effectiveness was determined by local tumor control (TCD50). Platinum accumulation in tumors by atomic absorption spectrometry and tumor perfusion changes by Patent blue staining were determined to elucidate some underlying antitumor mechanisms.

RESULTS

Exposure of cells in vitro to a combination of cisplatin and electroporation followed by irradiation increased the radiosensitizing effect of cisplatin. Also, the tumor radiocurability of this combined treatment was significantly enhanced, compared to irradiated tumors (enhancement factor; EF = 1.6) and to tumors treated with cisplatin and irradiation (EF = 1.4). Application of electric pulses to the tumors resulted in increased and prolonged accumulation of cisplatin and reduced tumor perfusion.

CONCLUSION

This study demonstrated that electroporation of cells and tumors increases the radiosensitizing effect of cisplatin, and that the predominant underlying mechanism is increased platinum delivery into the tumors due to the electroporation.

Sensitization of a tumor, but not normal tissue, to the cytotoxic effect of ionizing radiation using Panax notoginseng extract

The aim of the present study was to investigate any sensitization effect of the Panax notoginseng extract (PNE) and the purified Saponin (Rb1) on the radiation response of an experimental tumor (KHT sarcoma) in mice, in comparison with any effects on a normal tissue (bone marrow). PNE at a concentration of 0.1-100 mg/kg produced an increase in tumor radiosensitivity. The sensitization effect was maximal at 10 mg/kg and at 30 minutes after injection. Higher doses were toxic to the bone marrow stem cells. Similarly Rb1 at a concentration 0.001 to 1 mg/kg also produced an increase in tumor radiosensitivity, with maximum effect at 1 mg/kg. Higher doses were not toxic to the bone marrow stem cells in this case. Radiosensitization factors were calculated as ratios of D0 (the radiosensitivity parameter), and these were highly significant for the tumor and very similar for both compounds at the doses used, namely 1.18-1.19. There was no significant effect for bone marrow stem cells (sensitization factors of 0.99 +/- 0.01 for both compounds). The differential effect on tumor, and the magnitude of the radiosensitization, suggest that further purified or synthetic versions of this extract may be useful not only in vascular-related diseases but also in cancer therapy.

Effects of hyperglycemia on oxygenation, radiosensitivity and bioenergetic status of subcutaneous RIF-1 tumors

Since tissue oxygen tension is a balance between delivery and consumption of oxygen, considerable effort has been directed at increasing the former and/or decreasing the latter. Techniques to decrease the rate of cellular oxygen consumption (increasing the distance oxygen can diffuse into tissues) include increasing glycolysis by administering supra-physiologic levels of glucose. We have examined the effect of hyperglycemia produced by intravenous glucose infusion on the tissue oxygenation and radiation response of subcutaneously implanted murine radiation induced fibrosarcomas (RIF-1). A 0.3 M glucose solution was delivered via tail vein injection according to a protocol that maintained glucose at a plasma concentration of 17+/-1 mM. The effect of this treatment on radiation response (clonogenic and growth delay studies), tumor oxygenation (needle electrode pO2 and 2-[2-nitro-1H-imidazol-1-yl]-N-(2,2,3,3,3-pentafluoropropyl) acetamide (EF5) binding), and tumor bioenergetics and pH (31P NMR spectroscopy) was examined. Systemic measurements included hematocrit and blood glucose and lactate concentrations. The results of these studies suggest that these subcutaneously implanted RIF-1 tumors are both radiobiologically and metabolically hypoxic and that intravenous glucose infusion is not an effective method of modifying this metabolic state.

Preclinical evaluations of therapies combining the vascular targeting agent combretastatin A-4 disodium phosphate and conventional anticancer therapies in the treatment of Kaposi's sarcoma

The antitumor efficacy of the vascular targeting agent combretastatin A-4 disodium phosphate (CA4DP) was evaluated in a xenograft model of Kaposi's sarcoma (KS) grown in athymic mice. Response to CA4DP alone or in combination with localized radiation treatment or systemic chemotherapy (cisplatin or vinblastine) was assessed using a clonogenic cell survival or tumor growth delay assay. Administering increasing doses of CA4DP to tumor-bearing mice resulted in a dose-dependent increase in tumor cell kill. CA4DP also enhanced the antitumor effects of radiation and chemotherapy approximately 10-100-fold. Although single doses of CA4DP as large as 300 mg/kg failed to alter tumor growth, the same total dose, administered as 3 fractions in 5 or 9 days, resulted in significant growth delay. Such repeated CA4DP exposures also significantly increased the response of KS xenografts to cisplatin. These findings suggest that CA4DP ought to be considered as a candidate agent for therapeutic evaluation in AIDS-KS patients.

Enhancement of radiation therapy by the novel vascular targeting agent ZD6126

PURPOSE

The aim of this study was to evaluate the antitumor efficacy of the novel vascular targeting agent ZD6126 (N-acetylcochinol-O-phosphate) in the rodent KHT sarcoma model, either alone or in combination with single- or fractionated-dose radiation therapy.

METHODS

C3H/HeJ mice bearing i.m. KHT tumors were injected i.p. with ZD6126 doses ranging from 10 to 150 mg/kg. Tumors were irradiated locally in unanesthetized mice using a linear accelerator. Tumor response to ZD6126 administered alone or in combination with radiation was assessed by clonogenic cell survival assay or tumor growth delay.

RESULTS

Treatment with ZD6126 led to a rapid tumor vascular shutdown as determined by Hoechst 33342 diffusion. Histologic evaluation showed morphologic damage of tumor cells within a few hours after drug exposure, followed by extensive central tumor necrosis and neoplastic cell death as a result of prolonged ischemia. When combined with radiation, a 150 mg/kg dose of ZD6126 reduced tumor cell survival 10-500-fold compared with radiation alone. These enhancements in tumor cell killing could be achieved for ZD6126 given both before and after radiation exposure. Further, the shape of the cell survival curve observed after the combination therapy suggested that including ZD6126 in the treatment had a major effect on the radiation-resistant hypoxic cell subpopulation associated with this tumor. Finally, when given on a once-weekly basis in conjunction with fractionated radiotherapy, ZD6126 treatment was found to significantly increase the tumor response to daily 2.5 Gy fractions.

CONCLUSION

The present results demonstrated that in the KHT sarcoma, ZD6126 caused rapid tumor vascular shutdown, induction of central tumor necrosis, tumor cell death secondary to ischemia, and enhancement of the antitumor effects of radiation therapy.

[Growth kinetics and functional morphology of M-1 sarcoma in rats before and after gamma-irradiation]

The study was concerned with growth of sarcoma M-1 and basic morphological characteristics of proliferative activity of cells of this strain as well as apoptosis of cells at different stages of tumor progression in rats before and after a single gamma irradiation at 30 Gy. At the parenchymal periphery which determines tumor growth, the PCNA index of proliferating cells was 76.5%; spontaneous cell death--0.28%. During post-irradiation period, the sarcoma PCNA index fell to 62.3% while the apoptotic index rose five-fold. These findings support the concept of radiation-induced apoptosis being a major pathogenetic factor responsible for effectiveness of radiotherapy of tumors. Indirect evidence on PCNA immunostaining suggested that synthesis of this cyclin is sensitive to the level of oxygen input in the cell, yet it offers sufficient resistance to gamma-radiation.

Evaluation of apoptosis and micronucleation induced by reactor neutron beams with two different cadmium ratios in total and quiescent cell populations within solid tumors

PURPOSE

Response of quiescent (Q) and total tumor cells in solid tumors to reactor neutron beam irradiation with two different cadmium (Cd) ratios was examined in terms of micronucleus (MN) frequency and apoptosis frequency, using four different tumor cell lines.

METHODS AND MATERIALS

C57BL mice bearing EL4 tumors, C3H/He mice bearing SCC VII or FM3A tumors, and Balb/c mice bearing EMT6/KU tumors received 5-bromo-2'-deoxyuridine (BrdU) continuously for 5 days via implanted mini-osmotic pumps to label all proliferating (P) cells. Thirty min after i.p. injection of sodium borocaptate-10B (BSH), or 3 h after oral administration of p-boronophenylalanine-10B (BPA), the tumors were irradiated with neutron beams. The tumors without 10B-compound administration were irradiated with neutron beams or gamma-rays. This neutron beam irradiation was performed using neutrons with two different Cd ratios. The tumors were then excised, minced, and trypsinized. The tumor cell suspensions thus obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the MN frequency in cells without BrdU labeling (=Q cells) was determined using immunofluorescence staining for BrdU. Meanwhile, for apoptosis assay, 6 h after irradiation, tumor cell suspensions obtained in the same manner were fixed, and the apoptosis frequency in Q cells was also determined with immunofluorescence staining for BrdU. The MN and apoptosis frequencies in total (P + Q) tumor cells were determined from the tumors that were not pretreated with BrdU.

RESULTS

Without 10B-compounds, the sensitivity difference between total and Q cells was reduced by neutron beam irradiation. Under our particular neutron beam irradiation condition, relative biological effectiveness (RBE) of neutrons was larger in Q cells than in total cells, and the RBE values were larger for low Cd-ratio than high Cd-ratio neutrons. With 10B-compounds, both frequencies were increased for each cell population, especially for total cells. BPA increased both frequencies for total cells more than BSH did. Nevertheless, the sensitivity of Q cells treated with BPA was lower than that of Q cells treated with BSH. Whether based on the MN frequency or the apoptosis frequency, similar results concerning the sensitivity difference between total and Q cells, the values of RBE, and the enhancement effect by the use of 10B-compound were obtained.

CONCLUSION

Apoptosis frequency, as well as the MN frequency, can be applied to our method for measuring the Q cell response to reactor neutron beam irradiation within solid tumor in which the ratio of apoptosis to total cell death is relatively high, as in EL4 tumor. The absolute radiation dose required to achieve the same endpoint for Q cells is much higher than that for total cells when combined with 10B-compound, especially with BPA.

Interaction between combretastatin A-4 disodium phosphate and radiation in murine tumors

BACKGROUND AND PURPOSE

The ability of combretastatin A-4 disodium phosphate (CA4DP) to induce vascular damage and enhance the radiation response of murine tumors was investigated.

MATERIALS AND METHODS

A C3H mouse mammary carcinoma transplanted in the foot of CDF1 mice and the KHT mouse sarcoma growing in the leg muscle of C3H/HeJ mice were used. CA4DP was dissolved in saline and injected intraperitoneally. Tumor blood perfusion was estimated using 86RbCl extraction and Hoechst 33342 fluorescent labelling. Necrotic fraction was determined from histological sections. Tumors were locally irradiated in non-anaesthetised mice and response assessed by local tumor control for the C3H mammary carcinoma and in vivo/in vitro clonogenic cell survival for the KHT sarcoma.

RESULTS

CA4DP decreased tumor blood perfusion and increased necrosis in a dose-dependent fashion in the C3H mammary carcinoma, which was maximal at 250 mg/kg. The decrease in perfusion and induction of necrosis by CA4DP was more extensive in the KHT sarcoma. CA4DP enhanced radiation damage in both tumor types. In the KHT sarcoma this enhancement was independent of whether the drug was given before or after irradiating, whereas for C3H mammary carcinoma the enhancement was only significant when administered at the same time or after the radiation, with no enhancement seen if CA4DP was given before. These effects were drug-dose dependent. CA4DP did not enhance radiation damage in normal skin.

CONCLUSIONS

CA4DP enhanced radiation damage in the two tumor models without enhancing normal tissue damage. These radiation effects were clearly consistent with the anti-vascular action of CA4DP.

T cell-mediated tumor rejection displays diverse dependence upon perforin and IFN-gamma mechanisms that cannot be predicted from in vitro T cell characteristics

Experimental pulmonary metastases have been successfully treated by adoptive transfer of tumor-sensitized T cells from perforin knockout (KO) or Fas/APO-1 ligand(KO) mice, suggesting a prominent role for secretion of cytokines such as IFN-gamma. In the present study we confirmed that rejection of established methylcholanthrene-205 (MCA-205) pulmonary metastases displayed a requirement for T cell IFN-gamma expression. However, this requirement could be obviated by transferring larger numbers of tumor-sensitized IFN-gamma (KO) T cells or by immunosensitizing sublethal irradiation (500 rad) of the host before adoptive therapy. Extrapulmonary tumors (MCA-205 s.c. and intracranial) that required adjunct sublethal irradiation for treatment efficacy also displayed no requirement for host or T cell expression of IFN-gamma. Nonetheless, rejection of MCA-205 s.c. tumors and i.p. EL-4 tumors, but not MCA-205 pulmonary or intracranial tumors, displayed a significant requirement for T cell perforin expression (i.e., CTL participation). The capacity of T cells to lyse tumor targets and secrete IFN-gamma in vitro before adoptive transfer was nonpredictive of the roles of these activities in subsequent tumor rejection. Adoptive therapy studies employing KO mice are therefore indispensable for revealing a diversity of tumor rejection mechanisms that may lack in vitro correlation due to delays in their induction. Seemingly contradictory KO data from different studies are reconciled by the capacity of anti-tumor T cells to rely on alternative mechanisms when treated in larger numbers, the variable participation of CTL at different anatomic locations of tumor, and the apparent capacity of sublethal irradiation to provide a therapeutic alternative to host or T cell IFN-gamma production.

The effect of evening primrose oil on the radiation response and blood flow of mouse normal and tumour tissue

PURPOSE

To investigate the effect of the oral administration of evening primrose oil on the radiation response and the blood flow of normal tissue and a tumour in BALB/c mice.

METHODS AND MATERIALS

Aliquots of evening primrose oil were fed to BALB/c mice daily and the radiation response of the skin was assessed by the determination of ED50 values for the incidence of moist desquamation, using probit analysis. Tumour radiosensitivity was investigated by determining the growth delay caused by irradiation of a transplantable rhabdomyosarcoma. The 86RbCl uptake technique was used to determine the blood flow in normal foot and tumour tissue. The fatty-acid content of red blood cells, plasma and tumour tissue was measured using gas chromatography.

RESULTS

Daily evening primrose oil dietary supplementation reduced the sensitivity of skin to radiation-induced moist desquamation and prevented the radiation-associated increase in blood flow that was observed in this tissue. No modification of tumour blood flow or of tumour sensitivity to radiation resulted from evening primrose oil supplementation of mice. Evening primrose oil supplementation resulted in changes in plasma levels of linoleic acid (LA), gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA). These changes were contingent on whether the mice had been irradiated or not. In red blood cells evening primrose oil supplementation increased the GLA level of unirradiated mice and the LA level at 20 days after irradiation. There were no changes in tumour fatty-acid levels as a result of evening primrose oil treatment.

CONCLUSIONS

Daily evening primrose oil supplementation reduced the sensitivity of skin to radiation-induced moist desquamation but did not alter tumour sensitivity to radiation.

Preferential enhancement of tumor radioresponse by a cyclooxygenase-2 inhibitor

Cyclooxygenase-2 (COX-2), an inducible isoform of cyclooxygenase, is overexpressed in many types of malignant tumors, where it mediates production of prostaglandins (PGs), which in turn may stimulate tumor growth and protect against damage by cytotoxic agents. This study investigated whether SC-'236, a selective inhibitor of COX-2, potentiates antitumor efficacy of radiation without increasing radiation injury to normal tissue. Mice bearing the sarcoma FSA in the hind legs were treated daily for 10 days with SC-'236 (6 mg/kg given in the drinking water) when tumors were 6 mm in diameter. When tumors reached 8 mm in diameter, the mice were given 11- to 50-Gy single-dose local tumor irradiation with or without SC-'236. SC-'236 inhibited tumor growth on its own, and it greatly enhanced the effect of tumor irradiation. The growth delay was increased from 14.8 days after 25-Gy single dose to 28.4 days after the combined treatment (P = 0.01). SC-'236 reduced TCD50 (radiation dose yielding 50% tumor cure) from 39.2 Gy to 20.9 Gy (enhancement factor = 1.87). SC-'236 did not appreciably alter radiation damage to jejunal crypt cells and tissue involved in the development of radiation-induced leg contractures. The SC-'236-induced enhancement of tumor radioresponse was associated with a decrease in PGE2 levels in FSA tumors. The drug had no effect on radiation-induced apoptosis. Neoangiogenesis was inhibited by SC-'236, which could account for some of the increase in tumor radioresponse. Overall, our findings demonstrated that treatment with a selective inhibitor of COX-2 greatly enhanced tumor radioresponse without markedly affecting normal tissue radioresponse. Thus, COX-2 inhibitors have a high potential for increasing the therapeutic ratio of radiotherapy.

Temperature-dependent changes in physiologic parameters of spontaneous canine soft tissue sarcomas after combined radiotherapy and hyperthermia treatment

PURPOSE

The objectives of this study were to evaluate effects of hyperthermia on tumor oxygenation, extracellular pH (pHe), and blood flow in 13 dogs with spontaneous soft tissue sarcomas prior to and after local hyperthermia.

METHODS AND MATERIALS

Tumor pO2 was measured using an Eppendorf polarographic device, pHe using interstitial electrodes, and blood flow using contrast-enhanced magnetic resonance imaging (MRI).

RESULTS

There was an overall improvement in tumor oxygenation observed as an increase in median pO2 and decrease in hypoxic fraction (% of pO2 measurements <5 mm Hg) at 24-h post hyperthermia. These changes were most pronounced when the median temperature (T50) during hyperthermia treatment was less than 44 degrees C. Tumors with T50 > 44 degrees C were characterized by a decrease in median PO2 and an increase in hypoxic fraction. Similar thermal dose-related changes were observed in tumor perfusion. Perfusion was significantly higher after hyperthermia. Increases in perfusion were most evident in tumors with T50 < 44 degrees C. With T50 > 44 degrees C, there was no change in perfusion after hyperthermia. On average, pHe values declined in all animals after hyperthermia, with the greatest reduction seen for larger T50 values.

CONCLUSION

This study suggests that hyperthermia has biphasic effects on tumor physiologic parameters. Lower temperatures tend to favor improved perfusion and oxygenation, whereas higher temperatures are more likely to cause vascular damage, thus leading to greater hypoxia. While it has long been recognized that such effects occur in rodent tumors, this is the first report to tie such changes to temperatures achieved during hyperthermia in the clinical setting. Furthermore, it suggests that the thermal threshold for vascular damage is higher in spontaneous tumors than in more rapidly growing rodent tumors.

[Assessment of antineoplastic action of dehydrogenases in peripheral blood lymphocytes in S-45 tumor-bearing rats exposed to weak ultra-low-frequency irradiation]

The aim of the investigation was to study the antitumor action of weak ultra low-frequency magnetic field (ULFMF) and application of a spectrum of dehydrogenases of peripheral blood lymphocytes as a sensitive indicator of such action in tumor S45-bearing rats. It was shown that application of weak ULFMF improves antitumor defenses and dehydrogenase activity tends to stay normal. The dehydrogenase activity of peripheral blood lymphocytes can be used to assess immune system tension and synchronization of resistance processes.

[The effect of low-intensity laser radiation on luminescence parameters of lymphocytes in experimental animals]

A luminescence microspectral examination of lymphocytes in peripheral blood sampled from experimental animals has revealed that spectral pattern and particularly, parameter a (one/two-spiral nucleic acid ratio in cells) may be instrumental in assessing their condition. Low-power laser radiation caused the synthetic potential of lymphocytes to activate which was evidenced by a well-defined peak (640 nm) of luminescence and high values of parameter alpha.

Maximizing therapeutic gain with gemcitabine and fractionated radiation

PURPOSE/OBJECTIVE

The nucleoside analogue gemcitabine inhibits cellular repair and repopulation, induces apoptosis, causes tumor growth delay, and enhances radiation-induced growth delay. After single doses of drug and radiation, maximum enhancement of tumor response was obtained when gemcitabine preceded radiation by at least 24 h. Conversely, the cellular radioresponse of the normal gastrointestinal epithelium was slightly protected when gemcitabine and radiation were separated by 24 h. This differential response created a time frame within which therapeutic gain could be maximized. In our present investigation, we sought to define the most therapeutically beneficial scheme of gemcitabine administration when combined with fractionated radiotherapy.

METHODS AND MATERIALS

C3Hf/Kam mice were given identical drug and radiation schedules of administration, and both normal tissue (jejunal mucosa) and tumor (Sa-NH) responses were measured. Irradiation was given once per day for 5 days in normal tissue and tumor growth delay studies and twice per day for the tumor cure endpoint. A total dose of 25 mg/kg gemcitabine was given i.p. in 1 of 3 schedules: a single dose of 25 mg/kg 24 h before the start of fractionated irradiation, 12.5 mg/kg 24 h before the first and third radiation doses, or 24 h before each of 5 radiation doses. Groups of mice bearing 7- or 8-mm diameter tumors were treated with gemcitabine alone or in combination with fractionated irradiation under ambient or hypoxic conditions. The survival response of the jejunal mucosa was quantified by the microcolony assay and histologically by quantifying apoptosis, mitosis, S-phase fraction, and crypt cellularity.

RESULTS

For tumor growth delay, dose-modifying factors (DMFs) were similar (1.34-1.46) for all 3 schedules of drug administration. In contrast, the response of the jejunum was strongly dependent on the schedule of gemcitabine administration. A single dose of gemcitabine before the start of fractionated radiotherapy resulted in slight radioprotection (DMF 0.96). Two doses and 5 daily doses of gemcitabine enhanced radiation response by factors of 1.09 and 1.23, respectively. Major factors affecting the response of the jejunal mucosa were apoptotic death of S-phase cells exposed to gemcitabine and cell cycle synchrony of surviving cells. Tumor reoxygenation was found to be a major mechanism for tumor radioenhancement, in addition to those reported earlier.

CONCLUSION

All 3 schedules of drug administration produced therapeutic gain; however, when gemcitabine was given more than once in a 5-fraction radiation treatment schedule, normal tissue toxicity increased. The highest therapeutic gain (1.4) was achieved by giving a single dose of gemcitabine (25 mg/kg) 24 h before the start of fractionated radiotherapy.

Targeting the tumor vasculature with combretastatin A-4 disodium phosphate: effects on radiation therapy

PURPOSE

The aim of this study was to evaluate the antitumor efficacy of combretastatin A-4 disodium phosphate (combretastatin prodrug) in the rodent KHT sarcoma model either alone or in combination with radiation therapy.

METHODS

KHT tumors were grown in C3H/HeJ mice. Combretastatin A-4 prodrug was injected intraperitoneally at doses ranging from 10 to 100 mg/kg. Tumors were irradiated in unanesthetized mice using a 137Cs source. Tumor response to combretastatin A-4 prodrug was assessed by histological evaluations as well as an in vivo to in vitro cell survival assay.

RESULTS

Histological evaluation showed morphological damage of tumor cells within a few hours after drug treatment, followed by extensive central necrosis. Administering increasing doses of combretastatin A-4 prodrug to tumor-bearing mice resulted in a dose-dependent increase in cell killing irrespective of whether the tumors were irradiated or not. When combined with radiation, a 100 mg/kg dose of combretastatin A-4 prodrug reduced tumor cell survival 10-500-fold lower than that seen with radiation alone. Further, the shape of the cell survival curve observed following the combination therapy suggested that including combretastatin in the treatment had a major effect on the radiation-resistant hypoxic cell subpopulation associated with this tumor.

CONCLUSION

The present results demonstrated that in the KHT sarcoma, combretastatin A-4 prodrug caused rapid vascular shutdown, a concentration-dependent direct cell killing, and effective enhancement of the antitumor effects of radiation therapy.

Enhanced radiosensitivity in experimental tumours following erythropoietin treatment of chemotherapy-induced anaemia

The radiosensitivity of solid tumours in anaemic rats treated with recombinant human erythropoietin (rhEPO, epoetin beta) was studied. Anaemia was induced by a single dose of carboplatin (45 mg kg(-1) i.v.), resulting in a reduction in the haemoglobin concentration by 30%. In a second group, the development of anaemia was prevented by rhEPO (1000 IU kg(-1)) administered s.c. three times per week starting 6 days before the carboplatin application. Three days after carboplatin treatment, DS-sarcomas were implanted subcutaneously onto the hind foot dorsum. Neither carboplatin nor rhEPO treatment influenced tumour growth rate. Five days after implantation, tumours were irradiated with a single non-curative dose (10 Gy), resulting in a growth delay with a subsequent regrowth of the tumours. In the rhEPO-treated group, the growth delay lasted significantly longer (9.5 days vs. 4.5 days) and the regrowth was slower (6.0 days vs. 4.1 days) compared with the anaemic group. These data suggest that the correction of chemotherapy-induced anaemia by rhEPO (epoetin beta) treatment increases tumour radiosensitivity, presumably as a result of an improved oxygen supply to tumour tissue.

The effect of combined nicotinamide and carbogen treatments in human tumour xenografts: oxygenation and tumour control studies

BACKGROUND AND PURPOSE

This was an investigation to study the effect of giving carbogen and nicotinamide (CON) on pO2 and the radiation response of human xenografted tumours.

MATERIALS AND METHODS

The human xenografts were two sarcomas (ENE2 and ES3) and a glioblastoma (HTZ17). Nicotinamide (500 mg/ kg, i.p.) was administered 60 min before PO2 measurements and irradiation, while carbogen was given for 5 min before and during these treatments. Tumour pO2 was measured with an Eppendorf electrode and radiation response was assessed by local tumour control following irradiation with 10 daily fractions.

RESULTS

All three xenografts were found to be poorly oxygenated (about 80% of all pO2 values were < or =2.5 mmHg). CON treatment improved the oxygenation status in all three tumours such that 65, 52 and 71% of the pO2 values were < or =2.5 mmHg in ENE2, ES3 and HTZ17, respectively. However, only in ES3 was this decrease significant. The TCD50 doses for all tumours were around 52-54 Gy. No significant improvement was seen with CON in ENE2 (TCD50 = 48 Gy) and HTZ17 (TCD50 = 56 Gy), but for the ES3 xenograft a significant decrease to 42 Gy was found.

CONCLUSIONS

The three tumours used in this study appeared to show the same level of hypoxia as measured both by pO2 and radiation response. However, only one tumour showed a significant improvement after CON treatment, suggesting that not all hypoxic human tumours might benefit from this type of therapy.

Radiobiological hypoxia in the KHT sarcoma: predictions using the Eppendorf histograph

PURPOSE

To investigate whether electrode measurements of tumor oxygenation obtained under a range of different treatment conditions designed to alter the degree of tumor hypoxia could be correlated with estimates of radiobiological hypoxia measured under the same conditions.

METHODS AND MATERIALS

Experiments were performed in restrained, nonanesthetized, female C3H/He mice, which had approximately 0.5 g KHT sarcomas growing intramuscularly in the hind limbs. The treatments used to modify tumor oxygenation status included breathing gas mixtures of varying oxygen content, altering tumor blood flow, and shifting the hemoglobin oxygen dissociation curve. Radiobiological hypoxic fraction was estimated using the paired survival curve assay, while electrode measurements of tumor oxygenation were obtained with an Eppendorf histograph.

RESULTS

With the selected manipulations it was possible to vary the radiobiological hypoxic fraction in the tumors from approximately 1 to approximately 100% of the total viable cell population. Furthermore, these changes in radiation response were directly reflected in the changes in tumor oxygenation measurements made with the Eppendorf histograph.

CONCLUSION

These findings suggest that in the KHT tumor model the Eppendorf electrode measurements could predict the response of the tumors to radiation as determined by the proportion of hypoxic cells.

Tumour radiosensitization by high-oxygen-content gases: influence of the carbon dioxide content of the inspired gas on PO2, microcirculatory function and radiosensitivity

PURPOSE

To measure the effects of breathing high-oxygen-content gases, with a CO2 fraction of between 0 and 10%, on tumour radiosensitivity, blood flow and oxygenation.

METHODS AND MATERIALS

The murine sarcoma F was used, implanted subcutaneously (s.c.) in syngeneic CBA mice. We assessed the induced changes in tumour microregional blood flow and oxygenation using laser Doppler flowmetry, and pO2 histography, respectively. Radiation response was determined using an in vivo-in vitro clonogenic assay 18-20 h post treatment.

RESULTS

The results show that the level of radiosensitization achieved is dependent on both the CO2 content of the inspired gas and the duration of gas breathing. No radiosensitization was evident following inhalation of 90% O2 + 10% CO2. All other gases elicited radiosensitization; however, that achieved with 100% O2 disappeared at the extended preirradiation breathing time of 45 min. At this time, radiosensitization was maintained for gases containing 1%, 2.5%, or 5% CO2. Changes in oxygenation, as measured by PO2 electrodes, did indicate improved oxygenation status during inhalation of the gases. However, the time-course and extent of the changes did not mirror accurately the changes in radiosensitization. All the gases with a CO2 content of 2.5% or greater induced a 10-20% reduction in microregional blood flow, with no change evident following inhalation of 100% O2 or 99% O2 + 1% CO2.

CONCLUSIONS

The data imply that the decreased radiosensitization seen at extended breathing times of oxygen is unrelated to blood flow changes. The fact that radiosensitization is seen with extended breathing times of gases containing 2.5% and 5% CO2, despite blood flow decreases, is indicative of other overriding physiological changes, perhaps related to oxygen utilisation. The studies overall indicate that, at least in the tumour investigated, radiosensitization is not affected if the CO2 content of the inspired gas is reduced from 5% to 2.5%, or even 1%. Further evaluation of the radiosensitizing effects of such gas mixtures is now warranted. In addition, comparison with recent studies of other tumour types, where carbogen has been shown to improve tumour blood flow, suggests that this may be a tumour-specific phenomenon. Based on these data, further effort is required to elucidate the physiological mechanisms that determine these blood flow changes.

Increased tissue oxygenation and enhanced radiation sensitivity of solid tumors in rodents following polyethylene glycol conjugated bovine hemoglobin administration

BACKGROUND

Hypoxic tumors are frequently resistant to radiation therapy. Polyethylene glycol conjugated bovine hemoglobin (PEG-Hb) was tested for its ability to increase oxygen tension in the hypoxic rat osteogenic sarcoma UMR-106, murine Lewis lung carcinoma LL2 and rat gliosarcoma 9L. In addition, PEG-Hb was tested as an adjunct for radiotherapy in UMR-106 and human prostate carcinoma PC-3 solid tumors.

MATERIAL AND METHODS

Rodents bearing established subcutaneous tumors were intravenously administered PEG-Hb. Tumor surface tissue oxygen tension was measured by both OxySpot and OxyMap systems, which utilize the same phosphorescence quenching method.

RESULTS

A time-dependent rise in oxygen tension was noted, and the maximum tissue oxygen tensions were observed two hours post PEG-Hb administration, and sustained for at least 2 hours. Following a single dose radiation of 4 Gray, osteogenic sarcoma tumors in the PEG-Hb treated group showed dramatic regression (complete remission occurred in 100% of the high dose PEG-Hb treated rats), as compared to control (Ringer's lactate) group tumors that showed continued aggressive growth. All PEG-Hb plus radiation treated animals bearing human prostate carcinoma (PC-3) showed significant tumor growth delay compared to both control (Ringer's lactate) and irradiation only treated animals.

CONCLUSION

PEG-Hb increased tumor oxygen content and improved the effectiveness of radiotherapy in these rodent models.

Hypoxyradiotherapy: lack of experimental evidence for a preferential radioprotective effect on normal versus tumor tissue as shown by direct oxygenation measurements in experimental sarcomas

AIM

In order to investigate possible pathophysiological mechanisms underlying the postulated preferential protective effect of hypoxia on normal tissue during radiotherapy, the impact of acute respiratory hypoxia (8.2% O2 + 91.8% N2) on tissue oxygenation was assessed.

METHODS

Tumor and normal tissue oxygenation was directly determined using O2-sensitive electrodes in two experimental rat tumors (DS and Yoshida sarcomas) and in the normal subcutis of the hind foot dorsum.

RESULTS

During respiratory hypoxia, arterial blood O2 tension (pO2), oxyhemoglobin saturation and mean arterial blood pressure decreased. Changes in the arterial blood gas status were accompanied by a reflex hyperventilation leading to hypocapnia and respiratory alkalosis. In the subcutis, tissue oxygenation worsened during acute hypoxia, with decreases in the mean and median pO2. Significant increases in the hypoxic fractions were, however, not seen. In tumor tissues, oxygenation also worsened upon hypoxic hypoxia with significant decreases in the mean and median pO2 and increases in the size of the hypoxic fractions for both sarcomas.

CONCLUSION

These results suggest that during respiratory hypoxia, radiobiologically relevant reductions in the oxygenation (and a subsequent selective radioprotection) of normal tissue may not be achieved. In addition, in the tumor models studied, a worsening of tumor oxygenation was seen which could result in an increased radioresistance.

Effects of IL-3 gene expression on tumor response to irradiation in vitro and in vivo

Expression of a murine interleukin 3 gene in murine fibrosarcoma cells (FSA-JmIL-3) did not alter their survival after in vitro irradiation. However, FSA-JmIL-3 tumors established in vivo were much more sensitive to irradiation than was the parental tumor. Following 25 Gy of irradiation, parental fibrosarcoma tumors regrew after a growth delay of 10 days, but FSA-JmIL-3 tumors continued to regress. Examination of the cellular composition of tumors following irradiation revealed that, instead of tumor cell repopulation, the FSA-JmIL-3 tumors became heavily infiltrated with lymphocytes, indicating that the effect of irradiation was to allow the IL-3-elicited cellular immune response to infiltrate the tumors and mediate rejection. This study indicates that combining gene immunotherapy approaches with radiotherapy might increase the effectiveness of both, and it seems logical to pursue such treatment options.

Effects of carbogen plus fractionated irradiation on KHT tumor oxygenation

BACKGROUND AND PURPOSE

Numerous studies have demonstrated improvements in the oxygenation of tumor cells following both irradiation and carbogen breathing. The current studies were initiated to measure the combined effects of carbogen inhalation plus single and multi-dose irradiation on tumor oxygen availability, to better define the underlying physiological relationships.

MATERIALS AND METHODS

Using KHT murine sarcomas, radiation was delivered to the tumor-bearing legs of non-anesthetized mice. Tumors were quick-frozen prior to or following single or multifraction irradiation and carbogen breathing, and intravascular HbO2 saturation profiles were determined cryospectrophotometrically.

RESULTS

HbO2 levels for blood vessels located near the tumor surface initially decreased following 10 Gy irradiation, then increased and remained elevated. Interior HbO2 levels remained unchanged. Following 2.5 Gy, HbO2 changes were minimal. At 24 h following 10 Gy, HbO2 levels were significantly increased compared to non-irradiated controls, and carbogen breathing produced no additional benefit. At 24 h following five fractions of 2 Gy, HbO2 levels throughout the tumor volume were significantly higher in carbogen breathing animals than in air breathing controls.

CONCLUSIONS

Although peripheral blood vessels demonstrated substantial improvements in oxygenation following irradiation, oxygen availability nearer the tumor center remained at very low levels. The utility of carbogen in enhancing tumor oxygen availability was maintained following five clinically relevant fractions. At higher doses, radiation-induced enhancements in HbO2 levels overshadowed the carbogen effect. For either air or carbogen breathing, a decrease in the percentage of vessels with very low oxygen content did not appear to be a major factor in the reoxygenation of the KHT tumor.

Continuous, pulsed or single acute irradiation of a transplanted rodent tumour model

BACKGROUND

Recent advances in remote afterloading pulsed mode brachytherapy have provided a much needed tool for the radiation oncologist. It has the versatility of optimised physical dose distribution along with improved staff radiation protection and patient nursing.

PURPOSE

This preliminary study was designed to explore the radiobiological equivalence between conventional continuous low dose rate tumour irradiation (CLDR) and the new technique of pulsed dose irradiation (PDR).

MATERIALS AND METHODS

Subcutaneous isogenic sarcomas transplanted in female John's Strain Wistar rats were irradiated locally with acute, pulsed or continuous interstitial low dose-rate exposures at 9-11 mm mean diameter.

RESULTS

As expected, single acute doses (5-40 Gy) were more effective (P < 0.01) in achieving tumour growth delay (1.4 days/Gy) than CLDR exposure (4-51 Gy) over 24-48 h (0.93 days/Gy). However, PDR treatment (8 hourly fractions/day) at high dose-rate (8-48Gy) over 8-72 h was significantly (P = 0.01) more effective (1.66 days/Gy) than CLDR but not acute exposures.

CONCLUSIONS

These data suggest that, clinically a significantly improved therapeutic ratio may also be achievable with pulsed high dose rate brachytherapy, and that further radiobiological studies with in-vivo tumour models are needed.

Measurement of tumor oxygenation: a comparison between polarographic needle electrodes and a time-resolved luminescence-based optical sensor

A novel oxygen sensor which does not rely on electrochemical reduction has been used to measure the oxygenation of the murine sarcoma F in a comparative study with an existing polarographic electrode that is available commercially. The prototype luminescence sensor yielded an oxygen distribution comparable with readings made using a pO2 histograph. The percentage of regions detected that had a pO2 less than 5 mm Hg was 79 and 75 using the Eppendorf pO2 histograph and the luminescence fiber optic sensor, respectively. These values were compatible with a measured radiobiologically hypoxic fraction of 67% in this tumor. The polarographic method detected more regions with a pO2 of 2.5 mm Hg or less (69%) compared with the optical sensor (50%) (P < 0.05). This could reflect differences in the oxygen use of the sensing devices. This initial assessment indicates the potential of a fiber-optic-based oxygen-monitoring system. Such a system should have several advantages including monitoring temporal oxygen changes in a given microregion and use with NMR procedures.