Clinical Evidence for Thermometric Parameters to Guide Hyperthermia Treatment

Predicted SAR/temperature changes induced by phase-amplitude steering are minimally affected by uncertainties in tissue properties: a basis for robust on-line adaptive hyperthermia treatment planning

BACKGROUND

Reliability of absolute specific absorption rate (SAR)/temperature levels predicted by treatment planning is strongly affected by tissue parameter uncertainties. Therefore, regular re-optimization to suppress hot spots can accidentally induce new hot spots elsewhere. Adaptive planning methods to avoid this problem re-optimize with respect to the current predicted 3D-distribution. This strategy is robust if reliability of predicted SAR/temperature changes (i.e., increases/decreases) after phase-amplitude adjustments is minimally affected by parameter uncertainties; this work evaluated this robustness.

METHODS

We validated the basic concept in an inhomogeneous phantom, followed by a patient model. Uncertainties in electrical conductivity, permittivity and perfusion were mimicked by simulations using 100 random parameter samples from normal distributions. Reliability of predicted SAR/temperature increase/decrease after phase-amplitude adjustments was evaluated. Next, correlations between measured and simulated SAR and SAR changes were determined for phase settings evaluated at the treatment start for a treatment series. Finally, practical use in an adaptive workflow was illustrated.

RESULTS

Local SAR/temperature increases/decreases after phase-amplitude adjustments can be predicted accurately. For the phantom, the measured 28.5% SAR decrease was predicted accurately(28.5 ± 0.7%). In the patient model, predicted SAR/temperature changes were typically accurate within a few percent. For the treatment series, correlations between measured and simulated (relative) SAR changes were much better(R2=0.70-0.82) than for absolute SAR levels(R2=0.29). Predictions of steering effects during treatment corresponded qualitatively with measurements/observations.

CONCLUSION

Predictions of SAR/temperature increases/decreases induced by phase-amplitude steering are hardly affected by tissue parameter uncertainties. On-line adaptive planning based on predicted changes is thus robust to effectively support clinical steering strategies.

A translational review of hyperthermia biology

This review was written to be included in the Special Collection 'Therapy Ultrasound: Medicine's Swiss Army Knife?' The purpose of this review is to provide basic presentation and interpretation of the fundamentals of hyperthermia biology, as it pertains to uses of therapeutic ultrasound. The fundamentals are presented but in the setting of a translational interpretation and a view toward the future. Subjects that require future research and development are highlighted. The effects of hyperthermia are time and temperature dependent. Because intra-tumoral temperatures are non-uniform in tumors, one has to account for differential biologic effects in different parts of a tumor that occur simultaneously during and after hyperthermia.

Optimization of microwave hyperthermia system for focused breast cancer treatment: A study using realistic digital breast phantoms

BACKGROUND

Microwave breast hyperthermia is a noninvasive treatment method for breast cancer that utilizes microwave energy (ME) sources to raise tissue temperatures above 42∘ C $^{\circ }{\rm C}$ , inducing tumor cell necrosis. The efficiency of ME deposition depends on the electric field magnitude and tissue conductivity, with antenna phase and amplitude adjustments used to maximize the electric field magnitude within tumors. Achieving precise ME focusing in the complex and heterogeneous breast tissue is challenging and can lead to unwanted hot spots in normal tissue. This study presents a novel method for optimizing ME focusing on the center of target tumors, using a simplified calculation of antenna phases, heuristic optimization for antenna amplitudes, and realistic breast phantoms for performance evaluation.

PURPOSE

In this work, we propose an approach to optimize the microwave hyperthermia system, employing phase and amplitude modulation techniques to concentrate the electric field at the center of a malignant tumor within a breast medium. The approach uses line sources arranged in a circular pattern around realistic breast models. The method begins by determining the phase, followed by adjusting the amplitudes of each source in order to maximize the total electric field at the tumor's center. The goal is to maximize the electric field at the tumor center while minimizing the optimization cost and complexity.

METHODS

Simulations are performed at 4 GHz frequency using two different types of digital breast phantoms (fatty and dense breasts) as test beds. The algorithm is tested by using three quantities; that is, the electric field distribution, the power density distribution, and the temperature distribution inside the whole breast region. The electric field and power density are calculated using an in-house method of moments (MoM) algorithm, while the temperature distributions are obtained with computer simulation technology (CST) software. To further evaluate the method with quantitative measures of success, thermal indices are calculated for each phantom and method.

RESULTS

The specific absorbtion rate (SAR) results and corresponding temperature distributions for each breast type and optimization demonstrate that effective focusing is achieved in both cases. However, the combined phase-amplitude optimization provides more precise focusing by eliminating hot spots. Among thermal indices, the TC75 and T90 values obtained from the phase-amplitude combined optimization for both breast types outperform the results found in the literature. The T50 values obtained using the combined optimization are above 42C ∘ ${\rm C}^\circ$ .

CONCLUSIONS

This study presents an optimization method for focusing ME within breast tissue, performed in two steps: first phase optimization, followed by amplitude optimization. The electric field calculations are performed using both the MoM and Finite Difference Time Domain methods. The technique is numerically tested on two realistic breast models, with thermal indices calculated for each phantom and optimization process. Results show T90 values exceeding 40∘ C $^\circ{\rm C}$ and T50 values above 42∘ C $^\circ{\rm C}$ . While the study employs a 2D applicator, it provides a strong foundation for future development in 3D applications.

Superparamagnetic Superparticles for Magnetic Hyperthermia Therapy: Overcoming the Particle Size Limit

Iron oxide (e.g., Fe3O4 or γ-Fe2O3) nanoparticles are promising candidates for a variety of biomedical applications ranging from magnetic hyperthermia therapy to drug delivery and biodetection due to their superparamagnetism, nontoxicity, and biodegradability. While particles of small size (below a critical size, ∼20 nm) display superparamagnetic behavior at room temperature, these particles tend to penetrate highly sensitive areas of the body such as the blood-brain barrier, leading to undesired effects. In addition, these particles possess a high probability of retention, which can lead to genotoxicity and biochemical toxicity. Increasing particle size is a means for addressing these problems but also suppresses the superparamagnetism. We have overcome this particle size limit by synthesizing unique polycrystalline iron oxide nanoparticles composed of multiple nanocrystals of 10 to 15 nm size while tuning particle size from 160 to 400 nm. These so-called superparticles preserve superparamagnetic characteristics and exhibit excellent hyperthermia responses. The specific absorption rates exceed 250 W/g (HAC = 800 Oe, f = 310 kHz) at a low concentration of 0.5 mg/mL, indicating their capability in cancer treatment with minimum dose. Our study underscores the potential of size-tunable polycrystalline iron oxide superparticles with superparamagnetic properties for advanced biomedical applications and sensing technologies.

Radiosensitization Induced by Magnetic Hyperthermia of PEGylated Nickel Ferrite Nanoparticles on Breast Cancer Cells

Magnetic hyperthermia can complement traditional cancer treatments by exploiting the greater heat sensitivity of tumor cells. This approach allows for localized action, increasing its therapeutic effectiveness. In this study, MCF-7 breast cancer cell radiosensitization, induced by the magnetic hyperthermia of PEGylated nickel ferrite magnetic nanoparticles (PEG-NiF MNPs), was evaluated by exposing the cells in the presence of MNPs to an alternating magnetic field followed by 60Co gamma irradiation. Superparamagnetic PEG-NiF MNPs (25.6 ± 0.5 nm) synthesized via the hydrothermal method exhibited a hydrodynamic size below 150 nm, a saturation magnetization of 53 emu·g-1, biocompatibility of up to 100 µg·mL-1, selectivity for breast cancer cells, and an up-to-fivefold increase in therapeutic efficacy of radiation. When combined with magnetic hyperthermia, this increase reached up-to-sevenfold. These results indicate that PEG-NiF MNPs are suitable thermal radiosensitization agents for breast cancer cells.

Preclinical Development of Magnetic Nanoparticles for Hyperthermia Treatment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a very challenging disease with a very poor prognosis. It is characterized by a dense desmoplastic stroma that hampers drug penetration and limits the effectiveness of conventional chemotherapy (CT). As an alternative, the combination of CT with hyperthermia (HT) has been proposed as an innovative treatment modality for PDAC. In previous works, we reported on the development of iron oxide magnetic nanoparticles (MNPs) that, when exposed to time-varying magnetic fields, exhibit strong HT responses that inhibited the growth of pancreatic cancers. We report here on advances toward the clinical use of these MNPs as an intratumorally administered sterile magnetic fluid (the "NoCanTher ThermoTherapy" or "NTT" Agent) alongside intravenous standard-of-care drugs (gemcitabine and nab-paclitaxel) for the treatment of PDAC. In vitro cell viability assays show that the combination of low doses of CT and HT is highly synergistic, particularly in the BxPC-3 cell line. In vivo, biodistribution assays showed that the NTT Agent MNPs remained mainly within the tumor, concentrated around areas with a high stromal component. Moreover, the combined CT/HT treatment shows clear advantages over CT alone in terms of drug penetration and reduction of the tumor volume, suggesting a potential direct effect of HT in the disruption of the interstitial stroma to facilitate the access of the drugs to malignant cells. These studies have led to the approval and commencement of a clinical investigational study at the Vall d'Hebron University Hospital (Barcelona, Spain) of the NTT Agent alongside CT in patients with locally advanced PDAC.

Hyperthermia and radiotherapy: physiological basis for a synergistic effect

In cancer treatment, mild hyperthermia (HT) represents an old, but recently revived opportunity to increase the efficacy of radiotherapy (RT) without increasing side effects, thereby widening the therapeutic window. HT disrupts cellular homeostasis by acting on multiple targets, and its combination with RT produces synergistic antitumoral effects on specific pathophysiological mechanisms, associated to DNA damage and repair, hypoxia, stemness and immunostimulation. HT is furthermore associated to direct tumor cell kill, particularly in higher temperature levels. A phenomenon of temporary resistance to heat, known as thermotolerance, follows each HT session. Cancer treatment requires innovative concepts and combinations to be tested but, for a meaningful development of clinical trials, the understanding of the underlying mechanisms of the tested modalities is essential. In this mini-review, we aimed to describe the synergistic effects of the combination of HT with RT as well as the phenomena of thermal shock and thermotolerance, in order to stimulate clinicians in new, clinically relevant concepts and combinations, which become particularly relevant in the era of technological advents in both modalities but also cancer immunotherapy.

Theoretical evaluation of the impact of diverse treatment conditions by calculation of the tumor control probability (TCP) of simulated cervical cancer Hyperthermia-Radiotherapy (HT-RT) treatments in-silico

INTRODUCTION

Hyperthermia (HT) induces various cellular biological processes, such as repair impairment and direct HT cell killing. In this context, in-silico biophysical models that translate deviations in the treatment conditions into clinical outcome variations may be used to study the extent of such processes and their influence on combined hyperthermia plus radiotherapy (HT + RT) treatments under varying conditions.

METHODS

An extended linear-quadratic model calibrated for SiHa and HeLa cell lines (cervical cancer) was used to theoretically study the impact of varying HT treatment conditions on radiosensitization and direct HT cell killing effect. Simulated patients were generated to compute the Tumor Control Probability (TCP) under different HT conditions (number of HT sessions, temperature and time interval), which were randomly selected within margins based on reported patient data.

RESULTS

Under the studied conditions, model-based simulations suggested a treatment improvement with a total CEM43 thermal dose of approximately 10 min. Additionally, for a given thermal dose, TCP increased with the number of HT sessions. Furthermore, in the simulations, we showed that the TCP dependence on the temperature/time interval is more correlated with the mean value than with the minimum/maximum value and that comparing the treatment outcome with the mean temperature can be an excellent strategy for studying the time interval effect.

CONCLUSION

The use of thermoradiobiological models allows us to theoretically study the impact of varying thermal conditions on HT + RT treatment outcomes. This approach can be used to optimize HT treatments, design clinical trials, and interpret patient data.

Radiosensitization by Hyperthermia Critically Depends on the Time Interval

PURPOSE

Hyperthermia is a potent sensitizer of radiation therapy that improves both tumor control and survival in women with locally advanced cervical cancer (LACC). The optimal sequence and interval between hyperthermia and radiation therapy are still under debate.

METHODS AND MATERIALS

We investigated the interval and sequence in vitro in cervical cancer cell lines, patient-derived organoids, and SiHa cervical cancer hind leg xenografts in athymic nude mice and compared the results with retrospective results from 58 women with LACC treated with thermoradiotherapy.

RESULTS

All 3 approaches confirmed that shortening the interval between hyperthermia and radiation therapy enhanced hyperthermic radiosensitization by 2 to 8 times more DNA double-strand breaks and apoptosis and 10 to 100 times lower cell survival, delayed tumor growth in mice, and increased the 5-year survival rate of women with LACC from 22% (interval ≥80 minutes) to 54% (interval <80 minutes). In vitro and in vivo results showed that the sequence of hyperthermia and radiation therapy did not affect the outcome.

CONCLUSIONS

Shortening the interval between hyperthermia and radiation therapy significantly improves treatment outcomes. The sequence of hyperthermia and radiation therapy (before or after) does not seem to matter.

Mild photothermal therapy assist in promoting bone repair: Related mechanism and materials

Achieving precision treatment in bone tissue engineering (BTE) remains a challenge. Photothermal therapy (PTT), as a form of precision therapy, has been extensively investigated for its safety and efficacy. It has demonstrated significant potential in the treatment of orthopedic diseases such as bone tumors, postoperative infections and osteoarthritis. However, the high temperatures associated with PTT can lead to certain limitations and drawbacks. In recent years, researchers have explored the use of biomaterials for mild photothermal therapy (MPT), which offers a promising approach for addressing these limitations. This review provides a comprehensive overview of the mechanisms underlying MPT and presents a compilation of photothermal agents and their utilization strategies for bone tissue repair. Additionally, the paper discusses the future prospects of MPT-assisted bone tissue regeneration, aiming to provide insights and recommendations for optimizing material design in this field.

Radiotherapy combined with deep regional hyperthermia in elderly and frail patients with muscle-invasive bladder cancer: quality analysis of hyperthermia and impact on clinical results

Purpose: Radiotherapy (RT) in combination with deep regional hyperthermia (HT) after transurethral removal of bladder tumor (TURBT) can be offered to elderly and frail patients with muscle-invasive bladder cancer (MIBC).Methods: In total, 21 patients (mean age 84 years) with unifocal or multifocal MIBC received radiation to a dose of 48-50 Gy/16-20 fractions with weekly HT. The primary endpoint was the variation in temperature metrics, thermal dose expressed as cumulative equivalent minutes at 43 °C when the measured temperature is T90 (CEM43T90) and net power applied in target volume per each HT session. Secondary endpoints were three-year overall survival (OS), disease-free survival (DFS), local progression-free survival (LPFS) and toxicity.Results: The temperature metrics, CEM43T90, mean and maximum net power applied did not differ significantly among the HT sessions of the 21 patients. With a median follow-up of 65 months, 52% (95% CI 32-72%) of patients had died 3 years after treatment. The three-year DFS and LPFS rates were 62% (95%CI 41-79%) and 81% (95%CI 60-92%), respectively. The three-year bladder preservation rate was 100%. Three out of four patients with local failure received a thermal dose CEM43T90 below a median of 2.4 min. The rates of acute and late grade-3 toxicities were 10% and 14%, respectively.Conclusion: The reproducibility of HT parameters between sessions was high. A moderately high CEM43T90 (> 2.4 min) for each HT session seems to be preferable for local control. RT combined with HT is a promising organ-preservation therapy for elderly and frail MIBC patients.

Development of a Treatment Planning Framework for Laser Interstitial Thermal Therapy (LITT)

PURPOSE

Develop a treatment planning framework for neurosurgeons treating high-grade gliomas with LITT to minimize the learning curve and improve tumor thermal dose coverage.

METHODS

Deidentified patient images were segmented using the image segmentation software Materialize MIMICS©. Segmented images were imported into the commercial finite element analysis (FEA) software COMSOL Multiphysics© to perform bioheat transfer simulations. The laser probe was modeled as a cylindrical object with radius 0.7 mm and length 100 mm, with a constant beam diameter. A modeled laser probe was placed in the tumor in accordance with patient specific patient magnetic resonance temperature imaging (MRTi) data. The laser energy was modeled as a deposited beam heat source in the FEA software. Penne's bioheat equation was used to model heat transfer in brain tissue. The cerebrospinal fluid (CSF) was modeled as a solid with convectively enhanced conductivity to capture heat sink effects. In this study, thermal damage-dependent blood perfusion was assessed. Pulsed laser heating was modeled based on patient treatment logs. The stationary heat source and pullback heat source techniques were modeled to compare the calculated tissue damage. The developed bioheat transfer model was compared to MRTi data obtained from a laser log during LITT procedures. The application builder module in COMSOL Multiphysics© was utilized to create a Graphical User Interface (GUI) for the treatment planning framework.

RESULTS

Simulations predicted increased thermal damage (10-15%) in the tumor for the pullback heat source approach compared with the stationary heat source. The model-predicted temperature profiles followed trends similar to those of the MRTi data. Simulations predicted partial tissue ablation in tumors proximal to the CSF ventricle.

CONCLUSION

A mobile platform-based GUI for bioheat transfer simulation was developed to aid neurosurgeons in conveniently varying the simulation parameters according to a patient-specific treatment plan. The convective effects of the CSF should be modeled with heat sink effects for accurate LITT treatment planning.

Optimal heat transport induced by magnetic nanoparticle delivery in vascularised tumours

We describe a novel mathematical model for blood flow, delivery of nanoparticles, and heat transport in vascularised tumour tissue. The model, which is derived via the asymptotic homogenisation technique, provides a link between the macroscale behaviour of the system and its underlying, tortuous micro-structure, as parametrised in Penta and Ambrosi (2015). It consists of a double Darcy's law, coupled with a double advection-diffusion-reaction system describing heat transport, and an advection-diffusion-reaction equation for transport and adhesion of particles. Particles are assumed sufficiently large and do not extravasate to the tumour interstitial space but blood and heat can be exchanged between the two compartments. Numerical simulations of the model are performed using a finite element method to investigate cancer hyperthermia induced by the application of magnetic field applied to injected iron oxide nanoparticles. Since tumour microvasculature is more tortuous than that of healthy tissue and thus suboptimal in terms of fluid and drug transport, we study the influence of the vessels' geometry on tumour temperature. Effective and safe hyperthermia treatment requires tumour temperature within certain target range, generally estimated between 42 °C and 46 °C, for a certain target duration, typically 0.5h to 2h. As temperature is difficult to measure in situ, we use our model to determine the ranges of tortuosity of the microvessels, magnetic intensity, injection time, wall shear stress rate, and concentration of nanoparticles required to achieve given target conditions.

Quantitative Ultrasound for Evaluation of Tumour Response to Ultrasound-Microbubbles and Hyperthermia

Objectives: Prior study has demonstrated the implementation of quantitative ultrasound (QUS) for determining the therapy response in breast tumour patients. Several QUS parameters quantified from the tumour region showed a significant correlation with the patient's clinical and pathological response. In this study, we aim to identify if there exists such a link between QUS parameters and changes in tumour morphology due to combined ultrasound-stimulated microbubbles (USMB) and hyperthermia (HT) using the breast xenograft model (MDA-MB-231). Method: Tumours grown in the hind leg of severe combined immuno-deficient mice were treated with permutations of USMB and HT. Ultrasound radiofrequency data were collected using a 25 MHz array transducer, from breast tumour-bearing mice prior and post-24-hour treatment. Result: Our result demonstrated an increase in the QUS parameters the mid-band fit and spectral 0-MHz intercept with an increase in HT duration combined with USMB which was found to be reflective of tissue structural changes and cell death detected using haematoxylin and eosin and terminal deoxynucleotidyl transferase dUTP nick end labelling stain. A significant decrease in QUS spectral parameters was observed at an HT duration of 60 minutes, which is possibly due to loss of nuclei by the majority of cells as confirmed using histology analysis. Morphological alterations within the tumour might have contributed to the decrease in backscatter parameters. Conclusion: The work here uses the QUS technique to assess the efficacy of cancer therapy and demonstrates that the changes in ultrasound backscatters mirrored changes in tissue morphology.

Radiofrequency Electromagnetic Fields Cause Non-Temperature-Induced Physical and Biological Effects in Cancer Cells

Simple Summary

Radiofrequency electromagnetic fields are used for tumor heating as adjunct therapy, but it appears that sufficient temperatures can sometimes not be reached. We therefore aimed to study potential non-temperature-induced anticancer effects when adding amplitude modulation to the radiofrequency waves. We could demonstrate in a colorectal cancer model that radiofrequency electromagnetic fields do have anticancer effects when not being induced by increased temperature that can be further increased by amplitude modulation. Therefore, this treatment could potentially serve as a more effective tumor therapy.

Abstract

Non-temperature-induced effects of radiofrequency electromagnetic fields (RF) have been controversial for decades. Here, we established measurement techniques to prove their existence by investigating energy deposition in tumor cells under RF exposure and upon adding amplitude modulation (AM) (AMRF). Using a preclinical device LabEHY-200 with a novel in vitro applicator, we analyzed the power deposition and system parameters for five human colorectal cancer cell lines and measured the apoptosis rates in vitro and tumor growth inhibition in vivo in comparison to water bath heating. We showed enhanced anticancer effects of RF and AMRF in vitro and in vivo and verified the non-temperature-induced origin of the effects. Furthermore, apoptotic enhancement by AM was correlated with cell membrane stiffness. Our findings not only provide a strategy to significantly enhance non-temperature-induced anticancer cell effects in vitro and in vivo but also provide a perspective for a potentially more effective tumor therapy.

Evaluation of the Heat Shock Protein 90 Inhibitor Ganetespib as a Sensitizer to Hyperthermia-Based Cancer Treatments

Simple Summary

Hyperthermia boosts the effects of radio- and chemotherapy regimens, but its clinical potential is hindered by the ability of (cancer) cells to activate a protective mechanism known as the heat stress response. Strategies that inhibit its activation or functions have the potential, therefore, to improve the overall efficacy of hyperthermia-based treatments. In this study, we evaluated the efficacy of the HSP90 inhibitor ganetespib in promoting the effects of radiotherapy or cisplatin combined with hyperthermia in vitro and in a cervix cancer mouse model.

Abstract

Hyperthermia is being used as a radio- and chemotherapy sensitizer for a growing range of tumor subtypes in the clinic. Its potential is limited, however, by the ability of cancer cells to activate a protective mechanism known as the heat stress response (HSR). The HSR is marked by the rapid overexpression of molecular chaperones, and recent advances in drug development make their inhibition an attractive option to improve the efficacy of hyperthermia-based therapies. Our previous in vitro work showed that a single, short co-treatment with a HSR (HSP90) inhibitor ganetespib prolongs and potentiates the effects of hyperthermia on DNA repair, enhances hyperthermic sensitization to radio- and chemotherapeutic agents, and reduces thermotolerance. In the current study, we first validated these results using an extended panel of cell lines and more robust methodology. Next, we examined the effects of hyperthermia and ganetespib on global proteome changes. Finally, we evaluated the potential of ganetespib to boost the efficacy of thermo-chemotherapy and thermo-radiotherapy in a xenograft murine model of cervix cancer. Our results revealed new insights into the effects of HSR inhibition on cellular responses to heat and show that ganetespib could be employed to increase the efficacy of hyperthermia when combined with radiation.

Avoiding Pitfalls in Thermal Dose Effect Relationship Studies: A Review and Guide Forward

The challenge to explain the diffuse and unconclusive message reported by hyperthermia studies investigating the thermal dose parameter is still to be unravelled. In the present review, we investigated a wide range of technical and clinical parameters characterising hyperthermia treatment to better understand and improve the probability of detecting a thermal dose effect relationship in clinical studies. We performed a systematic literature review to obtain hyperthermia clinical studies investigating the associations of temperature and thermal dose parameters with treatment outcome or acute toxicity. Different hyperthermia characteristics were retrieved, and their influence on temperature and thermal dose parameters was assessed. In the literature, we found forty-eight articles investigating thermal dose effect relationships. These comprised a total of 4107 patients with different tumour pathologies. The association between thermal dose and treatment outcome was the investigated endpoint in 90% of the articles, while the correlation between thermal dose and toxicity was investigated in 50% of the articles. Significant associations between temperature-related parameters and treatment outcome were reported in 63% of the studies, while those between temperature-related parameters and toxicity were reported in 15% of the studies. One clear difficulty for advancement is that studies often omitted fundamental information regarding the clinical treatment, and among the different characteristics investigated, thermometry details were seldom and divergently reported. To overcome this, we propose a clear definition of the terms and characteristics that should be reported in clinical hyperthermia treatments. A consistent report of data will allow their use to further continue the quest for thermal dose effect relationships.

Oncologic Thermoradiotherapy: Need for Evidence, Harmonisation, and Innovation

The road of acceptance of oncologic thermotherapy/hyperthermia as a synergistic modality in combination with standard oncologic therapies is still bumpy [...]

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.

Accurate Three-Dimensional Thermal Dosimetry and Assessment of Physiologic Response Are Essential for Optimizing Thermoradiotherapy

Numerous randomized trials have revealed that hyperthermia (HT) + radiotherapy or chemotherapy improves local tumor control, progression free and overall survival vs. radiotherapy or chemotherapy alone. Despite these successes, however, some individuals fail combination therapy; not every patient will obtain maximal benefit from HT. There are many potential reasons for failure. In this paper, we focus on how HT influences tumor hypoxia, since hypoxia negatively influences radiotherapy and chemotherapy response as well as immune surveillance. Pre-clinically, it is well established that reoxygenation of tumors in response to HT is related to the time and temperature of exposure. In most pre-clinical studies, reoxygenation occurs only during or shortly after a HT treatment. If this were the case clinically, then it would be challenging to take advantage of HT induced reoxygenation. An important question, therefore, is whether HT induced reoxygenation occurs in the clinic that is of radiobiological significance. In this review, we will discuss the influence of thermal history on reoxygenation in both human and canine cancers treated with thermoradiotherapy. Results of several clinical series show that reoxygenation is observed and persists for 24-48 h after HT. Further, reoxygenation is associated with treatment outcome in thermoradiotherapy trials as assessed by: (1) a doubling of pathologic complete response (pCR) in human soft tissue sarcomas, (2) a 14 mmHg increase in pO2 of locally advanced breast cancers achieving a clinical response vs. a 9 mmHg decrease in pO2 of locally advanced breast cancers that did not respond and (3) a significant correlation between extent of reoxygenation (as assessed by pO2 probes and hypoxia marker drug immunohistochemistry) and duration of local tumor control in canine soft tissue sarcomas. The persistence of reoxygenation out to 24-48 h post HT is distinctly different from most reported rodent studies. In these clinical series, comparison of thermal data with physiologic response shows that within the same tumor, temperatures at the higher end of the temperature distribution likely kill cells, resulting in reduced oxygen consumption rate, while lower temperatures in the same tumor improve perfusion. However, reoxygenation does not occur in all subjects, leading to significant uncertainty about the thermal-physiologic relationship. This uncertainty stems from limited knowledge about the spatiotemporal characteristics of temperature and physiologic response. We conclude with recommendations for future research with emphasis on retrieving co-registered thermal and physiologic data before and after HT in order to begin to unravel complex thermophysiologic interactions that appear to occur with thermoradiotherapy.