The in vivo interaction between flavone acetic acid and hyperthermia

Molecular and biological rationale of hyperthermia as radio- and chemosensitizer

Mild hyperthermia, local heating of the tumour up to temperatures <43 °C, has been clinically applied for almost four decades and has been proven to substantially enhance the effectiveness of both radiotherapy and chemotherapy in treatment of primary and recurrent tumours. Clinical results and mechanisms of action are discussed in this review, including the molecular and biological rationale of hyperthermia as radio- and chemosensitizer as established in in vitro and in vivo experiments. Proven mechanisms include inhibition of different DNA repair processes, (in)direct reduction of the hypoxic tumour cell fraction, enhanced drug uptake, increased perfusion and oxygen levels. All mechanisms show different dose effect relationships and different optimal scheduling with radiotherapy and chemotherapy. Therefore, obtaining the ideal multi-modality treatment still requires elucidation of more detailed data on dose, sequence, duration, and possible synergisms between modalities. A multidisciplinary approach with different modalities including hyperthermia might further increase anti-tumour effects and diminish normal tissue damage.

Induction of hypoxia by vascular disrupting agents and the significance for their combination with radiation therapy

PURPOSE

This pre-clinical study was designed to investigate the effect of various vascular disrupting agents (VDAs) that have undergone or are in clinical evaluation, had on the oxygenation status of tumours and what effects that could have on the combination with radiation.

MATERIAL AND METHODS

The tumour model was a C3H mammary carcinoma grown in the right rear foot of female CDF1 mice and treated when at 200 mm(3) in size. The VDAs were the flavenoid compounds flavone acetic acid (FAA) and its more recent derivative 5,6-dimethylxanthenone-4-acetic acid (DMXAA), and the leading tubulin binding agent combretastatin A-4 phosphate (CA4P) and the A-1 analogue OXi4503. Oxygenation status was estimated using the Eppendorf oxygen electrode three hours after drug injection. Radiation response was determined following single or fractionated (10 fractions in 12 days) irradiations with a 240 kV x-ray machine using either a tumour re-growth or local tumour control assay.

RESULTS

All VDAs significantly reduced the oxygenation status of the tumours. They also influenced radiation response, but the affect was time and sequence dependent using single radiation schedules; an enhanced effect when the VDAs were injected at the same time or after irradiating, but no or even a reduced effect when given prior to irradiation. Only OXi4503 showed an increased response when given before the radiation. CA4P and OXi4503 also enhanced a fractionated radiation treatment if the drugs were administered after fractions 5 and 10.

CONCLUSIONS

VDAs clearly induced tumour hypoxia. This had the potential to decrease the efficacy of radiation. However, if the appropriate timing and scheduling were used an enhanced effect was observed using both single and fractionated radiation treatments.

The new vascular disrupting agent combretastatin-A1-disodium-phosphate (OXi4503) enhances tumour response to mild hyperthermia and thermoradiosensitization

PURPOSE

The aim of this study was to investigate the anti-cancer effect of the novel vascular disrupting agent (VDA), combretastatin-A1-disodium-phosphate (OXi4503), when combined with mild hyperthermia and/or radiation.

MATERIALS AND METHODS

A C3H mammary carcinoma was grown subcutaneously in the rear right foot of female CDF1 mice, and treated when a volume of 200 mm(3) was reached. OXi4503 was administered intra-peritoneally at variable doses. Hyperthermia was administered locally to the tumour-bearing foot using a thermostat-controlled water bath. Radiation treatment was performed locally using a conventional X-ray machine. Tumour response was assessed with either a tumour growth time or a tumour control assay.

RESULTS

The optimal delay between administration of 50 mg/kg of OXi4503 and hyperthermia was found to be 3 hours. The linear relationship between tumour growth time (TGT) and heating time at a specific temperature resulted in slope values between -0.003 days/min and 0.09 days/min at temperatures between 40 degrees C and 42.5 degrees C. When combined with OXi4503 this was significantly increased to 0.008 days/min and 0.03 days/min at temperatures between 39.5 degrees C and 41 degrees C, respectively. Above 41 degrees C, combined treatment did not result in significantly greater slope values. The radiation dose required to control 50% of the tumours (TCD50) was 52 Gy. Combining radiation with either heat treatment at 41.5 degrees C for 1 hour or OXi4503 reduced the TCD50 to 47 Gy and 41 Gy, respectively. Combining radiation with heat and OXi4503 further reduced the TCD50 to 37 Gy.

CONCLUSIONS

OXi4503 is a highly potent VDA, which is capable of significantly enhancing the anti-cancer effect of mild hyperthermia. Mild temperature thermoradiosensitization was also enhanced.

Pathophysiologic Effects of Vascular-Targeting Agents and the Implications for Combination with Conventional Therapies

A functional vascular supply is critical for the continued growth and development of solid tumors. It also plays a major role in metastatic spread of tumor cells. This importance has led to the concept of targeting the vasculature of the tumor as a form of cancer therapy. Two major types of vascular-targeting agent (VTA) have now emerged: those that prevent the angiogenic development of the neovasculature of the tumor and those that specifically damage the already established tumor vascular supply. When used alone neither approach readily leads to tumor control, and so, for VTAs to be most successful in the clinic they will need to be combined with more conventional therapies. However, by affecting the tumor vascular supply, these VTAs should induce pathophysiologic changes in variables, such as blood flow, pH, and oxygenation. Such changes could have negative or positive influences on the tumor response to more conventional therapies. This review aims to discuss the pathophysiologic changes induced by VTAs and the implications of these effects on the potential use of VTAs in combined modality therapy.

The effects of the vascular disrupting agents combretastatin A-4 disodium phosphate, 5,6-dimethylxanthenone-4-acetic acid and ZD6126 in a murine tumour: a comparative assessment using MRI and MRS

The aim of this study was to use magnetic resonance (MR) techniques to non-invasively compare the effects of the three leading vascular disrupting agents, namely combretastatin A-4 disodium phosphate (CA4DP), 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and ZD6126. A C3H mouse mammary carcinoma grown in the right rear foot of female CDF1 mice was used and treatments performed when tumours had reached 200 mm3 in volume. Drugs were prepared fresh before each experiment and intraperitoneally injected into restrained non-anaesthetised mice. Tumour response was evaluated using 31P-MR spectroscopy and T1- and T2- weighted imaging with a 7-Tesla, horizontal bore magnet, before and up to 24 hours after treatment. All three drugs significantly decreased bioenergetic status and pH, and did so in a time and dose dependent fashion, but there were differences; the decrease by CA4DP occurred more rapidly than for DMXAA or ZD6126, while DMXAA had a narrow window of activity compared to CA4DP and ZD6126. Changes in T1 weighted images for all three agents suggested a dose dependent increase in tumour oedema within three hours after treatment, consistent with an increase in vessel permeability. Using T2 weighted images there was some evidence of haemorrhagic necrosis by DMXAA, but such necrosis was limited following treatment with CA4DP or ZD6126.

Tissue physiology and the response to heat

The most important physiological parameter influencing tissue response to heat is blood flow. At mild hyperthermia temperatures blood perfusion increases in many tumours and this effect is heating time-, temperature- and tumour-dependent. These flow increases can improve tumour oxygenation. When heating is terminated, perfusion and oxygenation commonly recover, although how quickly this occurs appears to be tumour-specific. While these effects are unlikely to have any anti-tumour activity they can be exploited to improve the combination of heat with other therapies. However, since similar physiological effects should occur in normal tissues, such combination therapies must be carefully applied. Heating tumours to higher temperatures typically causes a transient increase in perfusion during heating, followed by vascular collapse which if sufficient will increase tumour necrosis. The speed and degree of vascular collapse is dependent on heating time, temperature and tumour model used. Such vascular collapse generally occurs at temperatures that cause a substantial blood flow increase in certain normal tissues, thus preferential anti-tumour effects can be achieved. The tumour vascular supply can also be exploited to improve the response to heat. Decreasing blood flow, using transient physiological modifiers or longer acting vascular disrupting agents prior to the initiation of heating, can both increase the accumulation of physical heat in the tumour, as well as increase heat sensitivity by changing the tumour micro-environmental parameters, primarily an increase in tumour acidity. Such changes are generally not seen in normal tissues, thus resulting in a therapeutic benefit.

Tumour-specific enhancement of thermoradiotherapy at mild temperatures by the vascular targeting agent 5,6-dimethylxanthenone-4-acetic acid

The effect of combining the vascular targeting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) with both radiation and hyperthermia treatments was investigated in a transplanted C3H mouse mammary carcinoma and a normal mouse tissue. Tumours were grown on the right rear foot of female CDF1 mice and treated when sized 200 mm3. The foot skin of non-tumour-bearing CDF1 mice was used to assess normal tissue damage. Radiation and hyperthermia were given locally to the tumour/skin of restrained non-anaesthetized animals. DMXAA (20 mg/kg) was dissolved in saline and injected intraperitoneally 1 h after irradiating and then heating started 3 h later. The endpoints were local tumour control within 90 days or the development of moist desquamation in skin between 11 and 23 days after treatment. The radiation dose (+/- 95% confidence intervals) producing local tumour control in 50% of treated animals was 53 (51-55) Gy for radiation alone. This value was significantly (Chi-squared test; p < 0.05) decreased to 47 (42-52) Gy by DMXAA and to 47 (44-51) Gy by heating (41.5 degrees C/60 min) 4 h after irradiation. Combining both DMXAA and heating further reduced this to 30 (26-35) Gy. When the heating temperature was decreased to 40.5 degrees C, the effect of the triple combination was decreased but was still significant compared with radiation + DMXAA or radiation + hyperthermia. However, this enhancement disappeared at 39.5 degrees C. Radiation damage of normal foot skin was not enhanced by combining DMXAA and hyperthermia at 41.5 degrees C. In conclusion, adding DMXAA to thermoradiotherapy at 40.5-41.5 degrees C significantly improved local tumour control without enhancing normal tissue damage. Thus, including a vascular targeting agent in a mild thermoradiotherapy treatment regimen is a useful approach that may lead to a re-evaluation of the use of hyperthermia in cancer treatment.

Combination of vascular targeting agents with thermal or radiation therapy

PURPOSE

The most likely clinical application of vascular targeting agents (VTAs) is in combination with more conventional therapies. In this study, we report on preclinical studies in which VTAs were combined with hyperthermia and/or radiation.

METHODS AND MATERIALS

A C3H mammary carcinoma grown in the right rear foot of female CDF1 mice was treated when at 200 mm3 in size. The VTAs were combretastatin A-4 disodium phosphate (CA4DP, 25 mg/kg), flavone acetic acid (FAA, 150 mg/kg), and 5,6-dimethylxanthenone-4-acetic acid (DMXAA, 20 mg/kg), and were all injected i.p. Hyperthermia and radiation were locally administered to tumors of restrained, nonanesthetized mice, and response was assessed using either a tumor growth or tumor control assay.

RESULTS

Heating tumors at 41.5 degrees C gave rise to a linear relationship between the heating time and tumor growth with a slope of 0.02. This slope was increased to 0.06, 0.09, and 0.08, respectively, by injecting the VTAs either 30 min (CA4DP), 3 h (FAA), or 6 h (DMXAA) before heating. The radiation dose (+/-95% confidence interval) that controls 50% of treated tumors (the TCD(50) value) was estimated to be 53 Gy (51-55 Gy) for radiation alone. This was decreased to 48 Gy (46-51 Gy), 45 Gy (41-49 Gy), and 42 Gy (39-45 Gy), respectively, by injecting CA4DP, DMXAA, or FAA 30-60 min after irradiating. These values were further decreased to around 28-33 Gy if the tumors of VTA-treated mice were also heated to 41.5 degrees C for 1 h, starting 4 h after irradiation, and this effect was much larger than the enhancement seen with either 41.5 degrees C or even 43 degrees C alone.

CONCLUSIONS

Our preclinical studies and those of others clearly demonstrate that VTAs can enhance tumor response to hyperthermia and/or radiation and support the concept that such combination studies should be undertaken clinically for the full potential of VTAs to be realized.

Acute effects of vascular modifying agents in solid tumors assessed by noninvasive laser Doppler flowmetry and near infrared spectroscopy

The potential of noninvasive laser Doppler flowmetry (LDF) and near infrared spectroscopy (NIRS) to detect acute effects of different vascular-modifying agents on perfusion and blood volume in tumors was evaluated. C3H mouse mammary carcinomas (approximately 200 mm(3)) in the rear foot of CDF1 mice were treated with flavone acetic acid (FAA, 150 mg/kg), 5,6-dimethylxanthenone-4-acetic acid (DMXAA, 20 mg/kg), combretastatin A-4 disodium phosphate (CA4DP, 250 mg/kg), hydralazine (HDZ, 5 mg/kg), or nicotinamide (NTA, 500 mg/kg). Tumor perfusion before and after treatment was evaluated by noninvasive LDF, using a 41 degrees C heated custom-built LDF probe with four integrated laser/receiver units, and tumor blood volume was estimated by NIRS, using light guide coupled reflectance measurements at 800+/-10 nm. FAA, DMXAA, CA4DP, and HDZ significantly decreased tumor perfusion by 50%, 47%, 73%, and 78%, respectively. In addition, FAA, DMXAA, and HDZ significantly reduced the blood volume within the tumor, indicating that these compounds to some degree shunted blood from the tumor to adjacent tissue, HDZ being most potent. CA4DP caused no change in the tumor blood volume, indicating that the mechanism of action of CA4DP was vascular shut down with the blood pool trapped in the tumor. NTA caused no change in either tumor perfusion or tumor blood volume. We conclude that noninvasive LDF and NIRS can determine acute effects of vascular modifying agents on tumor perfusion and blood volume.

Combretastatin A-4 disodium phosphate: a vascular targeting agent that improves that improves the anti-tumor effects of hyperthermia, radiation, and mild thermoradiotherapy

PURPOSE

To investigate the effect of combining the vascular targeting drug combretastatin A-4 disodium phosphate (CA4DP) with hyperthermia, radiation, or mild thermoradiotherapy in a transplanted C3H mouse mammary carcinoma.

METHODS AND MATERIALS

The C3H mammary carcinoma was grown on the rear foot of female CDF1 mice and treated when at 200 mm(3) in size. CA4DP was dissolved in saline and injected i.p. Hyperthermia and/or radiation were locally given to tumors in restrained nonanesthetized mice. Tumor response was assessed using either a tumor growth or a tumor control assay. Mouse foot skin was used to assess normal tissue damage.

RESULTS

CA4DP significantly enhanced thermal damage in this tumor model. This effect was independent of drug doses between 25-400 mg/kg, but was strongly dependent on the time interval between drug injection and heating, with the greatest improvement seen when CA4DP preceded the heating by 1 h or less. There was also a suggestion of a temperature dependency with a 1.9-fold increase in heat damage at 42.5 degrees C and a 2.6-fold increase at 41.5 and 40.5 degrees C. Heat-induced normal tissue damage was also enhanced by combining CA4DP with heat, but the degree of enhancement was less than that seen in tumors. CA4DP (25 mg/kg) significantly increased radiation-induced local tumor control and this was further enhanced by combining CA4DP with mild temperature (41.5 degrees C, 60 min) heating.

CONCLUSIONS

CA4DP improved the anti-tumor effect of hyperthermia, especially at mild temperatures. More importantly, it also increased the tumor response to mild hyperthermia and radiation, which suggests that CA4DP may ultimately have an important application in clinical thermoradiotherapy.

Improved tumor response by combining radiation and the vascular-damaging drug 5,6-dimethylxanthenone-4-acetic acid

The interaction between 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and radiation was investigated in two different mouse tumor models and a normal mouse tissue. C3H mouse mammary carcinomas transplanted in the feet of CDF1 mice and KHT mouse sarcomas growing in the leg muscles of C3H/HeJ mice were used. DMXAA was dissolved in saline and injected intraperitoneally. Tumors were irradiated locally in nonanesthetized mice, and response was assessed using tumor growth for the C3H mammary carcinoma and in vivo/in vitro clonogenic cell survival for the KHT sarcoma. DMXAA alone had an antitumor effect in both tumor types, but only at doses above 15 mg/kg. DMXAA also enhanced radiation damage, and again there was a threshold dose. No enhancement was seen in the C3H mammary carcinoma at 10 mg/kg and below, while in the KHT sarcoma, doses above 15 mg/kg were necessary. This enhancement of radiation damage was also dependent on the sequence of and interval between the treatments with DMXAA and radiation. Combining radiation with DMXAA at the maximum tolerated dose (i.e., the highest dose that could be injected without causing any lethality) of either 20 mg/kg (CDF1 mice) or 17.5 mg/kg (C3H/HeJ mice) gave an additive response when the two agents were administered simultaneously. Even greater antitumor effects were achieved when DMXAA was administered 1-3 h after irradiation. However, when administration of DMXAA preceded irradiation, the effect was similar to that seen for radiation alone, suggesting that appropriate timing is essential to maximize the utility of this agent. When such conditions were met, DMXAA was found to increase the tumor response significantly in the absence of an enhancement of radiation damage in normal skin, thus giving rise to therapeutic gain.

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.

The effect of combretastatin A-4 disodium phosphate in a C3H mouse mammary carcinoma and a variety of murine spontaneous tumors

PURPOSE

To investigate the activity of combretastatin A-4 disodium phosphate in a transplanted C3H mouse mammary carcinoma and several murine spontaneous tumors.

METHODS AND MATERIALS

The C3H mammary carcinoma was grown in the right rear foot of female CDF1 mice and treated when 200 mm3 in size. Spontaneous tumors (341-1437 mm3 in size) arose at different sites in female CDF1 mice that, 19-21 months earlier, had been irradiated. Oxygen partial pressure (pO2) distributions in the C3H tumors were measured with an Eppendorf oxygen electrode at various times after injecting combretastatin (100 mg/kg, i.p.) in restrained, nonanesthetized mice. Immediately after measurement, tumors were excised and necrotic fraction determined from histological sections. In the spontaneous tumors, pO2 was measured before and 3 h after giving combretastatin. The location of these spontaneous tumors required that measurements be made in anesthetised animals, achieved by injecting a mixture of hypnorm and diazepam.

RESULTS

In untreated C3H tumors, the mean (+/- 1 SE) percentage of pO2 values < or = 2.5 mmHg was 32% (+/- 11). This was significantly (Student's t-test; p < 0.05) increased to 74% (+/- 4) within 1 h after injecting combretastatin, and remained at this level for at least 6 h, although some recovery was seen at 12 and 24 h. The necrotic fraction in control tumors was 1.9% (+/- 0.4) and this was significantly increased to 16.1% (+/- 3.7) 24 h after drug administration. In spontaneous tumors, the pO2 measurements indicated that 5 of 6 showed some response to combretastatin, although the degree of change was variable.

CONCLUSIONS

Combretastatin increased tumor hypoxia and necrosis in the C3H mammary carcinoma, consistent with the induction of vascular damage. Drug-induced changes in pO2 were also found in spontaneous tumors, suggesting that the activity of this drug is not restricted to transplanted tumors alone.