Effect of hyperthermia on hypoxic cell fraction in tumor

Effects of Nanobubbles on Photochemical Processes of Levofloxacin Photosensitizer

Photodynamic therapy (PDT) stands as an efficacious modality for the treatment of cancer and various diseases, in which optimization of the electron transfer and augmentation of the production of lethal reactive oxygen species (ROS) represent pivotal challenges to enhance its therapeutic efficacy. Empirical investigations have established that the spontaneous initiation of redox reactions associated with electron transfer is feasible and is located in the gas-liquid interfaces. Meanwhile, nanobubbles (NBs) are emerging as entities capable of furnishing a plethora of such interfaces, attributed to their stability and large surface/volume ratio in bulk water. Thus, NBs provide a chance to expedite the electron-transfer kinetics within the context of PDT in an ambient environment. In this paper, we present a pioneering exploration into the impact of nitrogen nanobubbles (N2-NBs) on the electron transfer of the photosensitizer levofloxacin (LEV). Transient absorption spectra and time-resolved decay spectra, as determined through laser flash photolysis, unequivocally reveal that N2-NBs exhibit a mitigating effect on the decay of the LEV excitation triplet state, thereby facilitating subsequent processes. Of paramount significance is the observation that the presence of N2-NBs markedly accelerates the electron transfer of LEV, albeit with a marginal inhibitory influence on its energy-transfer reaction. This observation is corroborated through absorbance measurements and offers compelling evidence substantiating the role of NBs in expediting electron transfer within the ambit of PDT. The mechanism elucidated herein sheds light on how N2-NBs intricately influence both electron-transfer and energy-transfer reactions in the photosensitizer LEV. These findings not only contribute to a nuanced understanding of the underlying processes but also furnish novel insights that may inform the application of NBs in the realm of photodynamic therapy.

Recent advances in in situ oxygen-generating and oxygen-replenishing strategies for hypoxic-enhanced photodynamic therapy

Cancer is a leading cause of death worldwide, accounting for an estimated 10 million deaths by 2020. Over the decades, various strategies for tumor therapy have been developed and evaluated. Photodynamic therapy (PDT) has attracted increasing attention due to its unique characteristics, including low systemic toxicity and minimally invasive nature. Despite the excellent clinical promise of PDT, hypoxia is still the Achilles' heel associated with its oxygen-dependent nature related to increased tumor proliferation, angiogenesis, and distant metastases. Moreover, PDT-mediated oxygen consumption further exacerbates the hypoxia condition, which will eventually lead to the poor effect of drug treatment and resistance and irreversible tumor metastasis, even limiting its effective application in the treatment of hypoxic tumors. Hypoxia, with increased oxygen consumption, may occur in acute and chronic hypoxia conditions in developing tumors. Tumor cells farther away from the capillaries have much lower oxygen levels than cells in adjacent areas. However, it is difficult to change the tumor's deep hypoxia state through different ways to reduce the tumor tissue's oxygen consumption. Therefore, it will become more difficult to cure malignant tumors completely. In recent years, numerous investigations have focused on improving PDT therapy's efficacy by providing molecular oxygen directly or indirectly to tumor tissues. In this review, different molecular oxygen supplementation methods are summarized to alleviate tumor hypoxia from the innovative perspective of using supplemental oxygen. Besides, the existing problems, future prospects and potential challenges of this strategy are also discussed.

Nanomedicine-Based Strategies Assisting Photodynamic Therapy for Hypoxic Tumors: State-of-the-Art Approaches and Emerging Trends

Since the first clinical cancer treatment in 1978, photodynamic therapy (PDT) technologies have been largely improved and approved for clinical usage in various cancers. Due to the oxygen-dependent nature, the application of PDT is still limited by hypoxia in tumor tissues. Thus, the development of effective strategies for manipulating hypoxia and improving the effectiveness of PDT is one of the most important area in PDT field. Recently, emerging nanotechnology has benefitted progress in many areas, including PDT. In this review, after briefly introducing the mechanisms of PDT and hypoxia, as well as basic knowledge about nanomedicines, we will discuss the state of the art of nanomedicine-based approaches for assisting PDT for treating hypoxic tumors, mainly based on oxygen replenishing strategies and the oxygen dependency diminishing strategies. Among these strategies, we will emphasize emerging trends about the use of nanoscale metal-organic framework (nMOF) materials and the combination of PDT with immunotherapy. We further discuss future perspectives and challenges associated with these trends in both the aspects of mechanism and clinical translation.

Thermotherapy in the management of choroidal melanoma

During the past 20 years of enucleation, which was the standard treatment for choroidal melanoma over more than a century, has largely been replaced by eye salvaging therapies such as radiotherapy or local resection. In 1995 transpupillary thermotherapy (TTT) using an infrared diode laser was introduced as a new conservative therapy for patients with choroidal melanoma. TTT can be defined as a heat treatment modality, which is delivered through a dilated pupil to the tumour surface. The technique uses a wide diode laser beam diameter with a low irradiance and a long exposure time. TTT induces tumour necrosis at sub-photocoagulation levels by a direct cell destructive effect with only a few ocular complications. TTT can be performed as sole therapy or combined with plaque radiotherapy, thus permitting a lower radiation dose. For amelanotic tumours dye-enhanced TTT with indocyanine green can be used. In this paper we review the role of sole or combined TTT, related to the current other treatment modalities for choroidal melanoma.

Improvement of tumor oxygenation by mild hyperthermia

There is now abundant evidence that oxygenation in rodent, canine and human tumors is improved during and for up to 1-2 days after heating at mild temperatures. An increase in tumor blood perfusion along with a decline in the oxygen consumption rate appears to account for the improvement of tumor oxygenation by mild hyperthermia. The magnitude of the increase in tumor pO(2), determined with oxygen-sensitive microelectrodes, caused by mild hyperthermia is less than that caused by carbogen breathing. However, mild hyperthermia is far more effective than carbogen breathing in increasing the radiation response of experimental tumors, probably because mild hyperthermia oxygenates both (diffusion-limited) chronically hypoxic and (perfusion-limited) acutely hypoxic cells, whereas carbogen breathing oxygenates only the chronically hypoxic cells. Mild hyperthermia is also more effective than nicotinamide, which is known to oxygenate acutely hypoxic cells, in enhancing the radiation response of experimental tumors. The combination of mild hyperthermia with carbogen or nicotinamide is highly effective in reducing the hypoxic cell fraction in tumors and increasing the radiation response of experimental tumors. A primary rationale for the use of hyperthermia in combination with radiotherapy has been that hyperthermia is equally cytotoxic toward fully oxygenated and hypoxic cells and that it directly sensitizes both fully oxygenated and hypoxic cells to radiation. Such cytotoxicity and such a radiosensitizing effect may be expected to be significant when the tumor temperature is elevated to at least 42-43 degrees C. Unfortunately, it is often impossible to uniformly raise the temperature of human tumors to this level using the hyperthermia devices currently available. However, it is relatively easy to raise the temperature of human tumors into the range of 39-42 degrees C, which is a temperature that can improve tumor oxygenation for up to 1-2 days. The potential usefulness of mild hyperthermia to enhance the response of human tumors to radiotherapy by improving tumor oxygenation merits continued investigation.

Comparison of tumour blood flow changes induced by step-up and step-down heating

The changes in the blood flow in SCC-VII tumours after step-down and step-up heating (SDH and SUH) were compared. SDH was carried out by initial treatment of tumours in a water bath at 44.5 degrees C for 10 min, immediately followed by heating at 41.5 degrees C for 60 min. For SUH, the sequence of these high- and low-temperature treatments was reversed. Tumour perfusion was evaluated by laser Doppler flowmetry (LDF) at 1, 2, and 24h after finishing the hyperthermia. It was shown that the decrease in the blood flow in tumours was more substantial after SDH than after SUH; in the former case, the drop in LDF values was both faster and larger than in the latter. It is concluded that such a "physiological' component may be involved in the difference in the antitumour effect between SDH and SUH.

The effect of hyperthermia on reoxygenation during the fractionated radiotherapy of two murine tumors, FSa-II and MCa

PURPOSE

To investigate the effect of hyperthermia on the tumor reoxygenation during fractionated irradiations. It has been shown that hyperthermia increases the size of hypoxic cell fraction in some murine tumors and reoxygenation is critical for successful radiotherapy.

METHODS AND MATERIALS

Tumors were early generation isotransplants of spontaneous murine fibrosarcoma (FSa-II) and mammary carcinoma (MCa) in C3Hf/Sed mice. Treatments were initiated when they reached an average diameter of 4 mm. A local heat treatment at 43.5 degrees C for 45 min was given in a constant temperature water bath 24 h before irradiation(s). This interval was selected to avoid heat-radiation interaction and to simply investigate the heat effect on the reoxygenation process. Tumors were irradiated under hypoxic conditions or in air and observed for recurrences for 120 days. The foot reaction of animals with controlled-tumors was scored on the last day of experiments. The TCD50 (50% tumor control dose) and RD50 (dose to induce partial foot atrophy in 50% of treated animals) were calculated.

RESULTS

The TCD50s following a various number of fractions were obtained for FSa-II and MCa with or without hyperthermia. The difference between the TCD50 (hypoxia) and TCD50 (in air) without hyperthermia increased with an increasing number of fractions, suggesting that significant reoxygenation occurred during the fractionated irradiation. The TCD50s (with heat, in air) were smaller than the TCD50s (radiation alone, in air) following fractionated irradiations, indicating that hyperthermia did not affect tumor reoxygenation. The difference between these TCD50 values was greater for heat-sensitive MCa than for heat-resistant FSa-II, suggesting that this difference was due to additive heat cytotoxicity. An unexpected observation was that heat significantly enhanced the foot reaction with no resultant therapeutic gain for both MCa and FSa-II tumors.

CONCLUSION

Hyperthermia given independently prior to fractionated irradiation did not affect tumor reoxygenation, nor was there a therapeutic gain for the two murine tumors. These results suggest that selective tumor heating is essential in clinical thermoradiotherapy.

Timing and sequence of hyperthermia in fractionated radiotherapy of a murine fibrosarcoma

PURPOSE

This study investigated the effect of timing and sequence of hyperthermia on fractionated radiotherapy, since it has been shown that the heat increases the size of hypoxic cell fraction which could affect the effect of subsequent radiation doses.

METHODS AND MATERIALS

Animal-tumors were early generation isotransplants of a spontaneous fibrosarcoma, FSa-II, in C3Hf/Sed mice. Tumor response was studied by tumor growth time and TCD50 (50% tumor control dose) assays. The tumor growth time is the time required for one-half of the treated tumors to reach 500 mm3 from the first treatment day. The TCD50 is a radiation dose to control one-half of the treated tumors for 120 days following treatments. One heat treatment at 43.5 degrees C for 45 min was given in a water bath in combination with fractionated doses independently (24 hr interval) or simultaneously (2 min interval). For the normal tissue study, the mouse foot was treated, and the acute foot reaction was scored daily and averaged. The late foot reaction was scored in animals used in the TCD50 assay that developed no recurrence for 120 days. The RD50(2.0) and RD50(5.0), or total radiation doses to induce an average score of 2.0 (complete epilation) and 5.0 (partial foot atrophy) in 50% of treated animals, were calculated.

RESULTS

Thermal radiosensitization was most prominent when heat was combined simultaneously with the first or last radiation dose in both the tumor growth time and TCD50 assays. However, the thermal enhancement was greatest when heat was given either with the first or last radiation dose in the TCD50 assay; whereas it was greatest when heat was administered with the last radiation dose in the tumor growth time assay. Both acute and late skin reactions were significantly potentiated by heat administered 24 hr before the first radiation dose.

CONCLUSION

A significant observation in this study was that, in both the tumor growth time and TCD50 assays, heat given independently or simultaneously did not result in any therapeutic gain compared to the radiation alone treatment.

Comparative study of thermoradiosensitization by misonidazole and metronidazole in vivo: antitumour effect and pharmacokinetics

Tumour control by local hyperthermia (43.5 degrees C, 30 min) and radiation (20 Gy) given in combination with misonidazole (MISO) or metronidazole (METRO) was studied using FSa-II murine fibrosarcoma. When MISO or METRO (5 mmol/kg) was given 30 min before heat and subsequently treated with radiation, tumour regression was observed for both agents. Radiation dose-response curves for MISO and METRO with heating at 43.5 degrees C for 30 min were identical. Mouse foot reaction was used to evaluate local toxicity following combined heat, a nitroimidazole and radiation treatment. MISO enhanced the magnitude of foot reaction and prolonged the recovery time compared with heat plus radiation controls. There were no observable differences of foot reaction between animals treated with heat plus radiation and those animals treated with heat, radiation and METRO. Pharmacokinetics of the nitroimidazoles heated at 43.5 degrees C for 30 min in FSa-II tumours were investigated as a possible mechanism of thermal sensitization. Local hyperthermia did not alter the pharmacokinetics of METRO. Tumour concentration and tumour/plasma ratio of MISO were slightly decreased during heating. Since the hypoxic metabolism of the nitroimidazoles did not increase significantly during the heat treatment, the thermal enhancement of MISO or METRO radiosensitization cannot be explained by the increase in hypoxic cytotoxicity of the nitroimidazoles at elevated temperature alone. The two nitroimidazoles also were not accumulated in the tumour after heating. Therefore, alternation of pharmacokinetics is not the major mechanism for the thermal enhancement of nitroimidazole radiosensitization. The METRO radiosensitization effect became identical to that of MISO at elevated temperatures is of particular importance in clinical radiosensitization. The very low local and systemic toxicity together with the high efficacy of METRO at elevated temperatures will make it an attractive candidate as a future clinical radiosensitizer.

Enhancement of misonidazole chemosensitization effect by mild local hyperthermia

In an attempt to increase the chemosensitization effect of the alkylating agents 1,3 bis(2-chloroethyl)-1-nitrosourea (BCNU) and cyclophosphamide (CY), by misonidazole (MISO) at the tumor site, mild hyperthermic treatment (41.5 degrees C, 1 hr) was applied at various administration sequences. C3Hf/Sed mice bearing subcutaneous FSa-II tumors in the foot were used for a tumor growth time assay. Local hyperthermic treatment increased the antitumor activities of BCNU and CY by 1.4 and 2.4 fold, respectively. MISO at 2.5 mmole/kg potentiated the antitumor activities of BCNU, but not CY, at normal body temperature. There were no significant improvement of MISO chemosensitization when heat was given before the administration of BCNU and CY. However, a significant enhancement of chemosensitization was observed when heat was given after the administration of MISO and the alkylating agents. Enhancement ratios of about 2.4 and 4.7 were observed with BCNU and CY, respectively. There may be two mechanisms responsible for this thermal enhancement. First, the MISO pre-incubation time that was required for the expression of chemosensitization effect decreased substantially at elevated temperatures. This hypothesis was supported by the pharmacokinetic studies that MISO was rapidly eliminated from tumors in the first 10 min during the local heat treatment and remained at a plateau with a concentration of about 5-fold less than the peak MISO concentration in the control tumors. This rapid elimination might result from the increase in the rate of hypoxic metabolism of MISO in heated tumors. Second, heat may increase the MISO-alkylating agent interactions, which are independent of pre-incubation time. This effect was especially pronounced in CY because pre-incubation-induced chemosensitization of CY in unheated tumor was insignificant in this study. The significant improvement of MISO chemosensitization at moderately elevated temperatures can be useful clinically in combined hyperthermia and chemotherapy treatment.

Significance of additive heat effect in the therapeutic gain factor in combined hyperthermia and radiotherapy: murine tumor response and foot reaction

The thermal enhancement ratio (TER) and therapeutic gain factor (TGF) were evaluated for combined hyperthermia and radiation treatments of a murine fibrosarcoma, FSa-II. The TER is the ratio of the radiation dose that induces a given reaction without hyperthermia to that with hyperthermia. The TGF is defined as the ratio of TER for tumor response to TER for normal tissue response. Tumors in the subcutaneous tissue of the right foot were irradiated with graded radiation doses when they reached an average diameter of 6 mm (110 mm3). Hyperthermia was given by immersing animal feet in a constant temperature water bath 10 min before or after irradiation. The tumor growth time to reach 500 mm3 was obtained for each tumor and the median tumor growth time was calculated for each treatment group. For the normal tissue study, the non-tumor bearing murine foot was treated, as was the tumor, and the foot reaction was scored after treatment, according to our numerical score system for radiation damage, until the 35th post-treatment day and averaged. Using the fraction of animals showing a given average foot reaction score in a treatment group, the RD50, or the radiation dose to induce the given foot reaction or greater, was calculated. A single heating at 45.5 degrees C for 10 min and a step-down heating (first heat at 45.5 degrees C for 10 min immediately followed by the second heat at 41.5 degrees C for 60 min) prolonged the tumor growth time, indicating that hyperthermia per se resulted in some cell killing. The prolongation was greater following step-down heating than following single heating. These heat treatments alone induced no noticeable heat damage on the foot, but decreased the threshold dose observed on the radiation dose response curves for the foot reaction. Accordingly, TER and TGF were evaluated with or without normalizing this thermal effect. TER's for both tumor and foot responses without normalization were greater than the TER's after normalization and decreased with increasing radiation dose (between 1.9 and 7.1 or greater for tumor and between 1.3 and 4.3 or greater for foot reaction), whereas the normalized TER's were relatively constant (between 1.6 and 1.7 for tumor and between 0.7 and 1.5 for foot reaction). TGF's without normalization were greater than those obtained after normalization. The former was large at small doses and decreased with increasing radiation dose (between 1.5 and 4.0 or greater), whereas the latter was within 0.8 and 1.3 and relatively independent of radiation dose.(ABSTRACT TRUNCATED AT 400 WORDS)

Tumour microcirculation as a target for hyperthermia

A great number of investigators have, independently, shown that tumour blood flow is affected by a hyperthermic treatment to a larger extent than normal tissue blood flow. While the majority of the studies on experimental tumours show a decrease and even a lapse in blood flow within the microcirculation during or after hyperthermia, the data on human tumours are less conclusive. Some of the investigators do not find a decrease in circulation, while others do. Obviously, this is an important field of investigation in the clinical application of hyperthermia because a shut down of the circulation would not only facilitate tumour heating (by reducing venous outflow, this reducing the 'heat clearance' from the tumour), but would also facilitate tumour cell destruction. The same holds for alterations that occur subsequently to the circulatory changes, like a heat-induced decrease of tissue pO2 and pH. If the frequently reported circulatory collapse of the tumour circulation could selectively be stimulated by, e.g. acidification or by vasoactive agents, hyperthermic treatment of patients would possibly be greatly facilitated and intensified. In hyperthermic tumour therapy a number of complex processes and interactions takes place, especially when the treatment is performed in combination with radiation therapy. One of them represents the group of processes related to the random probability of cell sterilization of individual tumour cells resulting in exponential survival curves which are typically evaluated with e.g. cell survival assays. This aspect has not been the issue of this paper. The other group of processes deals with the heat-induced changes in the micro-physiology of tumours and normal tissues which, as discussed before, may not only enhance the exponential cell kill, but which may also culminate in vascular collapse with the ensuing necrosis of the tumour tissue in the areas affected. If this takes place, a process of bulk killing of tumour cells results, rather than the random type of cell sterilization. At present it is not clear to what extent the various separate mechanisms contribute to the total effect of tumour control. With all these considerations in mind, one should be aware of the fact that effects, secondary to heat-induced vascular stasis alone will never be efficient enough to eliminate all tumour cells, even though a heat reservoir is created. This is so because some malignant cells will inevitably have already infiltrated normal, surrounding structures and will therefore not be affected by changes in the tumour vascular bed.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of sequencing of the total course of combined hyperthermia and radiation on the RIF-1 murine tumor

The optimal sequence for clinical utilization of combined radiotherapy and hyperthermia is not known. The clinical trials have resulted in similar responses whether hyperthermia is given before or after radiation. Moreover, studies addressing the best sequence for an entire course of multifractionated hyperthermia and radiation are lacking. In these experiments, the importance of sequencing of heat and irradiation in a multifractionated treatment regimen in RIF-1 murine tumors was studied. It was observed that a close sequence of heat and irradiation is more beneficial than separate cytotoxic action. When heat and irradiation were given simultaneously, (within 1 hour) 67% to 75% of the tumors were cured. Heat and irradiation given sequentially (the entire course of one following the entire course of the other, each separated by 72 hours) cured 20% of the tumors. No tumors were cured when treated with heat or irradiation alone. The tumor regrowth time (mean tumor doubling time) is much longer in simultaneous treatment than in sequential treatment. It appears that heating first decreases the effectiveness of subsequent irradiation, causing a shorter growth delay than the opposite sequence. Heat alone does not alter the tumor bed permanently, but irradiation seems to do so, resulting in a slower rate of growth upon recurrence.

Physiological mechanisms in hyperthermia: a review

In experimental animal systems, hyperthermia at therapeutic temperature (43-45 degrees C) causes a profound increase in blood flow in normal tissues while it induces only meager and temporal increases in blood flow in tumors. A severe vascular occlusion and hemorrhage usually follows the increase in blood flow in the tumors at the above temperatures. Another pronounced physiological change in tumors by heat is a prompt decrease in intratumor pH. The decrease in intratumor pH would accentuate the thermokilling of tumor cells and also possibly inhibit repair of thermodamage and development of thermotolerance in tumors. The temperature in tumors may rise higher than that in normal tissues during heating because of inefficient heat dissipation from the tumor as a result of decrease blood flow or vascular occlusion. Thus, the differential effects of heat on vascular function and pH in tumors and normal tissues may result in a greater damage in tumors than in surrounding normal tissues. Further investigation is urgently needed to find out whether similar physiological changes occur in human tumors and normal tissues by hyperthermia.

Micronucleus formation in human melanoma xenografts following exposure to hyperthermia

The formation of micronuclei in two human melanoma xenografts (E. E. and V. N.) following hyperthermic treatment (42.5 degrees C for 60 min) was studied and compared to that following single dose irradiation. The melanomas were grown in the hind leg of athymic mice and heated by immersing the tumour-bearing leg into a water-bath. Histological sections were prepared from tumours removed from the mice at predetermined times after treatment and the fraction of abnormal mitotic figures and the number of micronuclei per nucleus were scored. During the first 24 h after treatment, the fraction of abnormal mitotic figures increased abruptly to 90%-100% followed by a rapid decrease to 40%-50%. It then decreased slowly towards about twice the level in untreated tumours. The number of micronuclei started to increase at about the same time as the fraction of abnormal mitotic figures was highest, reached a maximum at about 2-3 days after treatment, and then decreased slowly. The number of micronuclei seen after the hyperthermic treatment was lower than that seen after radiation treatments causing similar tumour regrowth delays. The same hyperthermic treatment resulted in more micronuclei and larger regrowth delays for E. E. than for V. N. melanoma. The present results indicate that DNA damage is involved in heat-induced cell death in tumours treated in vivo.