The potential of using hyperthermia to eliminate radioresistant hypoxic cells

Temperature-sensitive polymers to promote heat-triggered drug release from liposomes: Towards bypassing EPR

Heat-triggered drug release from temperature-sensitive nanocarriers upon the application of mild hyperthermia is a promising approach to achieve site-specific delivery of drugs. The combination of mild hyperthermia (41-42 °C) and temperature-sensitive liposomes (TSL) that undergo lipid phase-transition and drug release has been studied extensively and has shown promising therapeutic outcome in a variety of animal tumor models as well as initial indications of success in humans. Sensitization of liposomes to mild hyperthermia by means of exploiting the thermal behavior of temperature-sensitive polymers (TSP) provides novel opportunities. Recently, TSP-modified liposomes (TSPL) have shown potential for enhancing tumor-directed drug delivery, either by triggered drug release or by triggered cell interactions in response to heat. In this review, we describe different classes of TSPL, and analyze and discuss the mechanisms and kinetics of content release from TSPL in response to local heating. In addition, the impact of lipid composition, polymer and copolymer characteristics, serum components and PEGylation on the mechanism of content release and TSPL performance is addressed. This is done from the perspective of rationally designing TSPL, with the overall goal of conceiving efficient strategies to increase the efficacy of TSPL plus hyperthermia to improve the outcome of targeted anticancer therapy.

The Effect of Hyperthermia and Radiotherapy Sequence on Cancer Cell Death and the Immune Phenotype of Breast Cancer Cells

Simple Summary

Hyperthermia (HT) is a cancer treatment which locally heats the tumor to supraphysiological temperature, and it is an effective sensitizer for radiotherapy (RT) and chemotherapy. HT is further capable of modulating the immune system. Thus, a better understanding of its effect on the immune phenotype of tumor cells, and particularly when combined with RT, would help to optimize combined anti-cancer treatments. Since in clinics, no standards about the sequence of RT and HT exist, we analyzed whether this differently affects the cell death and immunological phenotype of human breast cancer cells. We revealed that the sequence of HT and RT does not strongly matter from the immunological point of view, however, when HT is combined with RT, it changes the immunophenotype of breast cancer cells and also upregulates immune suppressive immune checkpoint molecules. Thus, the additional application of immune checkpoint inhibitors with RT and HT should be beneficial in clinics.

Abstract

Hyperthermia (HT) is an accepted treatment for recurrent breast cancer which locally heats the tumor to 39–44 °C, and it is a very potent sensitizer for radiotherapy (RT) and chemotherapy. However, currently little is known about how HT with a distinct temperature, and particularly, how the sequence of HT and RT changes the immune phenotype of breast cancer cells. Therefore, human MDA-MB-231 and MCF-7 breast cancer cells were treated with HT of different temperatures (39, 41 and 44 °C), alone and in combination with RT (2 × 5 Gy) in different sequences, with either RT or HT first, followed by the other. Tumor cell death forms and the expression of immune checkpoint molecules (ICMs) were analyzed by multicolor flow cytometry. Human monocyte-derived dendritic cells (moDCs) were differentiated and co-cultured with the treated cancer cells. In both cell lines, RT was the main stressor for cell death induction, with apoptosis being the prominent cell death form in MCF-7 cells and both apoptosis and necrosis in MDA-MB-231 cells. Here, the sequence of the combined treatments, either RT or HT, did not have a significant impact on the final outcome. The expression of all of the three examined immune suppressive ICMs, namely PD-L1, PD-L2 and HVEM, was significantly increased on MCF-7 cells 120 h after the treatment of RT with HT of any temperature. Of special interest for MDA-MB-231 cells is that only combinations of RT with HT of both 41 and 44 °C induced a significantly increased expression of PD-L2 at all examined time points (24, 48, 72, and 120 h). Generally, high dynamics of ICM expression can be observed after combined RT and HT treatments. There was no significant difference between the different sequences of treatments (either HT + RT or RT + HT) in case of the upregulation of ICMs. Furthermore, the co-culture of moDCs with tumor cells of any treatment had no impact on the expression of activation markers. We conclude that the sequence of HT and RT does not strongly affect the immune phenotype of breast cancer cells. However, when HT is combined with RT, it results in an increased expression of distinct immune suppressive ICMs that should be considered by including immune checkpoint inhibitors in multimodal tumor treatments with RT and HT. Further, combined RT and HT affects the immune system in the effector phase rather than in the priming phase.

Hyperthermia and Temperature-Sensitive Nanomaterials for Spatiotemporal Drug Delivery to Solid Tumors

Nanotechnology has great capability in formulation, reduction of side effects, and enhancing pharmacokinetics of chemotherapeutics by designing stable or long circulating nano-carriers. However, effective drug delivery at the cellular level by means of such carriers is still unsatisfactory. One promising approach is using spatiotemporal drug release by means of nanoparticles with the capacity for content release triggered by internal or external stimuli. Among different stimuli, interests for application of external heat, hyperthermia, is growing. Advanced technology, ease of application and most importantly high level of control over applied heat, and as a result triggered release, and the adjuvant effect of hyperthermia in enhancing therapeutic response of chemotherapeutics, i.e., thermochemotherapy, make hyperthermia a great stimulus for triggered drug release. Therefore, a variety of temperature sensitive nano-carriers, lipid or/and polymeric based, have been fabricated and studied. Importantly, in order to achieve an efficient therapeutic outcome, and taking the advantages of thermochemotherapy into consideration, release characteristics from nano-carriers should fit with applicable clinical thermal setting. Here we introduce and discuss the application of the three most studied temperature sensitive nanoparticles with emphasis on release behavior and its importance regarding applicability and therapeutic potentials.

A moderate thermal dose is sufficient for effective free and TSL based thermochemotherapy

Hyperthermia, i.e. heating the tumor to a temperature of 40-43 °C is considered by many a valuable treatment to sensitize tumor cells to radiotherapy and chemotherapy. In recent randomized trials the great potential of adding hyperthermia to chemotherapy was demonstrated for treatment of high risk soft tissue sarcoma: +11.4% 5 yrs. overall survival (OS) and for ovarian cancer with peritoneal involvement nearly +12 months OS gain. As a result interest in combining chemotherapy with hyperthermia, i.e. thermochemotherapy, is growing. Extensive biological research has revealed that hyperthermia causes multiple effects, from direct cell kill to improved oxygenation, whereby each effect has a specific temperature range. Thermal sensitization of the tumor cell for chemotherapy occurs for many drugs at temperatures ranging from 40 to 42 °C with little additional increase of sensitization at higher temperatures. Increasing perfusion/oxygenation and increased extravasation are two other important hyperthermia induced mechanisms. The combination of free drug and hyperthermia has not been found to increase tumor drug concentration. Hence, enhanced effectiveness of free drug will depend on the thermal sensitization of the tumor cells for the applied drug. In contrast to free drugs, experimental animal studies combining hyperthermia and thermo-sensitive liposomal (TSL) drugs delivery have demonstrated to result in a substantial increase of the drug concentration in the tumor. For TSL based chemotherapy, hyperthermia is critical to both increase perfusion and extravasation as well as to trigger TSL drug release, whereby the temperature controlled induction of a local high drug concentration in a highly permeable vessel is driving the enhanced drug uptake in the tumor. Increased drug concentrations up to 26 times have been reported in rodents. Good control of the tissue temperature is required to keep temperatures below 43 °C to prevent vascular stasis. Further, careful timing of the drug application relative to the start of heating is required to benefit optimal from the combined treatment. From the available experimental data it follows that irrespective whether chemotherapy is applied as free drug or using a thermal sensitive liposomal carrier, the optimal thermal dose for thermochemotherapy should be 40-42 °C for 30-60 min, i.e. equivalent to a CEM43 of 1-15 min. Timing is critical: most free drug should be applied simultaneous with heating, whereas TSL drugs should be applied 20-30 min after the start of hyperthermia.

Hyperthermia can alter tumor physiology and improve chemo- and radio-therapy efficacy

Hyperthermia has demonstrated clinical success in improving the efficacy of both chemo- and radio-therapy in solid tumors. Pre-clinical and clinical research studies have demonstrated that targeted hyperthermia can increase tumor blood flow and increase the perfused fraction of the tumor in a temperature and time dependent manner. Changes in tumor blood circulation can produce significant physiological changes including enhanced vascular permeability, increased oxygenation, decreased interstitial fluid pressure, and reestablishment of normal physiological pH conditions. These alterations in tumor physiology can positively impact both small molecule and nanomedicine chemotherapy accumulation and distribution within the tumor, as well as the fraction of the tumor susceptible to radiation therapy. Hyperthermia can trigger drug release from thermosensitive formulations and further improve the accumulation, distribution, and efficacy of chemotherapy.

Integrating Hyperthermia into Modern Radiation Oncology: What Evidence Is Necessary?

Hyperthermia (HT) is one of the hot topics that have been discussed over decades. However, it never made its way into primetime. The basic biological rationale of heat to enhance the effect of radiation, chemotherapeutic agents, and immunotherapy is evident. Preclinical work has confirmed this effect. HT may trigger changes in perfusion and oxygenation as well as inhibition of DNA repair mechanisms. Moreover, there is evidence for immune stimulation and the induction of systemic immune responses. Despite the increasing number of solid clinical studies, only few centers have included this adjuvant treatment into their repertoire. Over the years, abundant prospective and randomized clinical data have emerged demonstrating a clear benefit of combined HT and radiotherapy for multiple entities such as superficial breast cancer recurrences, cervix carcinoma, or cancers of the head and neck. Regarding less investigated indications, the existing data are promising and more clinical trials are currently recruiting patients. How do we proceed from here? Preclinical evidence is present. Multiple indications benefit from additional HT in the clinical setting. This article summarizes the present evidence and develops ideas for future research.

The chemopotentiation of cisplatin by the novel bioreductive drug AQ4N

AQ4N is a bioreductive drug that can significantly enhance the anti-tumour effect of radiation and cyclophosphamide. The aim of this study was to examine the ability of AQ4N to potentiate the anti-tumour effect of cisplatin and to compare it to the chemopotentiation effect of tirapazamine. In the T50/80 murine tumour model, AQ4N (50-100 mg/kg) was administered 30 min, 2.5 or 6 h prior to cisplatin (4 mg/kg or 8 mg/kg); this produced an anti-tumour effect that was approximately 1.5 to 2 times greater than that achieved by a single 4 or 8 mg/kg dose of cisplatin. Tirapazamine (25 mg/kg) administered 2.5 h prior to cisplatin (4 mg/kg) resulted in a small increase in anti-tumour efficacy. AQ4N was also successful in enhancing the anti-tumour effect of cisplatin in the SCCVII and RIF-1 murine tumour models. This resulted in an increased cell kill of greater than 3 logs in both models; this was a greater cell kill than that observed for tirapazamine with cisplatin. Combination of cisplatin with AQ4N or tirapazamine resulted in no additional bone marrow toxicity compared to cisplatin administered alone. In conclusion, AQ4N has the potential to improve the clinical efficacy of cisplatin.

The use of a hypoxic cell radiosensitizer AK-2123 gave no improvement in thermoradiotherapy combined with hydralazine

An electron-affinic compound, AK-2123, and the anti-hypertensive agent, hydralazine, were combined with radiation and hyperthermia for treatment of murine SCC-VII tumours. Hydralazine markedly decreased tumour perfusion while AK-2123 had no influence on it. Hydralazine enhanced the tumouricidal effects of hyperthermia alone and in combination with radiation. AK-2123 provided a radiosensitization which was significant only in tumours irradiated without supplementary hyperthermia. The greatest tumour response was achieved when thermoradiotherapy was combined with hydralazine alone; the additional use of AK-2123 with this treatment combination did not further increase the effect. It is concluded that hydralazine plus heat virtually eliminated a hypoxia-related radioresistance in tumours, thus removing the requirement for AK-2123 administration.

Winner of the Lund Science Award 1992. Thermosensitization induced by step-down heating. A review on heat-induced sensitization to hyperthermia alone or hyperthermia combined with radiation

A few minute's exposure to a high temperature (sensitizing treatment, ST) may substantially increase the cytotoxic and the radiosensitizing effect of a subsequent heating at a lower temperature (test treatment, TT). This phenomenon, which is known as step-down heating (SDH) or thermosensitization, has been observed both in cultured cells in vitro and in tumours and normal tissues in vivo. The effect of SDH increases with a lowering of TT temperature, but it is rapidly lost at temperatures very close to 37 degrees C. SDH-induced thermosensitization decays within a few hours, when an interval is inserted between ST and TT. In vitro results suggest an exponential decay of the SDH effect with half times ranging from 1.5- to 3.1 h. The effect of SDH increases with increasing ST time or temperature. For single heating, the Arrhenius plot is biphasic with activation energies of 500-800 and 1200-1700 kJ/mol above and below a break point temperature in the region 42.5-43.0 degrees C, respectively. For SDH, the Arrhenius plot gradually becomes monophasic with increasing severity of ST and it approaches asymptotically to an activation energy of about 400 kJ/mol. The reduction of the activation energy depends on cell survival after the priming ST and not on the specific ST heating time or temperature. SDH strongly enhances hyperthermic radiosensitization with a 5-6-fold reduction of the radiation dose required to achieve tumour control. The thermosensitizing and the radiosensitizing effects of SDH have several features in common. Both effects become more prominent when the TT temperature is decreased and when the ST heating time or temperature increases. In addition, the decay kinetics for both effects are comparable. For heat alone, the effect of SDH in tumour and normal tissue seems to be quantitatively similar. However, the therapeutic ratio may be increased by combining SDH with radiation. Biologically, the critical subcellular targets involved in the SDH effect have not been revealed. However, the ability of SDH to inhibit the clearance of heat-induced aggregation of proteins in the nucleus is interesting. Blockage of the nuclear function by proteins is a central theory in the present molecular biological models for both cell kill by heat and heat radiosensitization. Clinically, SDH may be an advantage since even a short exposure to high temperature increases the effect of an otherwise inadequate heat treatment. The disadvantages are that SDH complicates thermal dose calculations, and may cause unacceptable damage to normal tissue.

Effect of etoposide, carmustine, vincristine, 5-fluorouracil, or methotrexate on radiobiologically oxic and hypoxic cells in a C3H mouse mammary carcinoma in situ

The effect of etoposide (VP16), carmustine (BCNU), vincristine (VCR), methotrexate (MTX), and 5-fluorouracil (5-FU) on the oxic and hypoxic cells in a C3H mammary carcinoma in CDF1 mice was investigated using an in situ local-tumor-control (TCD50) assay. The surviving fraction (SF) was calculated from the size of the radiation dose needed to inactivate the surviving tumor cells in drug-treated tumors relative to untreated controls. Preferential drug cytotoxicity towards oxic and hypoxic cells was evaluated from the difference in the response to irradiation under ambient and clamped conditions, respectively. Three drugs caused a significant (P less than 0.05) reduction in the survival of hypoxic cells, the SFs being 0.31 (VP-16), 0.13 (BCNU) and 0.16 (VCR). VCR was also toxic towards oxic cells (SF, 0.17), whereas VP16 and BCNU had no significant effect on these cells (SF, 0.5 and 0.76, respectively). Two drugs produced significant killing of cells in the oxic compartment: 5-FU (SF, 0.10) and MTX (SF, 0.22); these two drugs had no effect on hypoxic cells (SF, 0.78 and 1.11, respectively).

Interaction of misonidazole, hyperthermia, and irradiation in a C3H mammary carcinoma and its surrounding skin in vivo

The interaction of irradiation, Misonidazole (MISO), and hyperthermia was studied in a C3H mouse mammary carcinoma and its surrounding skin in vivo. MISO (0.5-1.0 mg/g) was injected 30 min before irradiation. Hyperthermia (41.5 degrees-43.5 degrees C for 60 min) was given either simultaneously, 0.5 hr, or 4 hr after X rays. The results were evaluated as the radiation dose to achieve tumor control (TCD50) or moist desquamation of the skin (DD50) in half of the treated animals. A therapeutic gain was found when the enhancement in tumors were greater than that found in skin. The combination of simultaneous heat and irradiation caused great enhancement in radiation response, but with no therapeutic gain. A slightly lower enhancement of the damage in both tissues was found with a 30 min interval between irradiation and hyperthermia, whereas heat 4 hr after X rays gave a small, but significant therapeutic gain. MISO significantly enhanced the response in tumors but not in skin. Combined trimodality treatment with MISO, irradiation, and hyperthermia resulted in enhancement ratios up to 15, dependent on temperature, radiation-heat interval, and to a lesser extent the MISO dose. The enhancement was for all schedules most pronounced in the tumors, resulting in an improved therapeutic effect. The combination of MISO and hyperthermia may be a valuable addition to radiotherapy, especially if heat and irradiation can be applied with close interval and with one of the modalities given selectively to the tumor.

Effect of step-down heating on the interaction between heat and radiation in a C3H mammary carcinoma in vivo

The effect of step-down heating (SDH) on the interaction between heat and radiation was investigated in a C3H mammary carcinoma in vivo. SDH consisted of an initial sensitizing treatment (ST) performed at 44.5 degrees C or 43.5 degrees C followed by a lower temperature test treatment (TT) in the range 41.0-43.0 degrees C. Step-up heating (SUH), i.e. TT followed by ST, and single heating were used as controls. The end-point was the radiation dose needed to control 50% of the tumours (TCD50). The results were evaluated by calculating the thermal enhancement ratio (TER) defined as TER = TCD50 (radiation alone)/TCD50 (radiation and heat). For a simultaneous application of TT and radiation a significant enhancement of direct heat radiosensitization was observed with increasing ST time or ST temperature using SDH. In contrast, only a minor increase was seen with SUH. A comparison between TCD50 values for the corresponding SUH and SDH schedules revealed that the SDH effect was largest at 41.0-42.0 degrees C and decreased with increasing TT temperature. The radiosensitizing effect of SDH also decreased if an interval was allowed between ST and TT or between TT and radiation. However, as a result of an increased cytotoxicity towards hypoxic tumour cells, the TCD50 value for SDH remained significantly smaller than for SUH, even with a sequential combination of radiation and heat.

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

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