The effect of mild temperature hyperthermia on tumour hypoxia and blood perfusion: relevance for radiotherapy, vascular targeting and imaging

Quantitative analysis of radiosensitizing effect for magnetic hyperthermia-radiation combined therapy on prostate cancer cells

BACKGROUND

Magnetic hyperthermia (MHT) has emerged as a promising therapeutic approach in the field of radiation oncology due to its superior precision in controlling temperature and managing the heating area compared to conventional hyperthermia. Recent studies have proposed solutions to address clinical safety concerns associated with MHT, which arise from the use of highly concentrated magnetic nanoparticles and the strong magnetic field needed to induce hyperthermic effects. Despite these efforts, challenges remain in quantifying therapeutic outcomes and developing treatment plan systems for combining MHT with radiation therapy (RT).

PURPOSE

This study aims to quantitatively measure the therapeutic effect, including radiation dose enhancement (RDE) in the magnetic hyperthermia-radiation combined therapy (MHRT), using the equivalent radiation dose (EQD) estimation method.

METHODS

To conduct EQD estimation for MHRT, we compared the therapeutic effects between the conventional hyperthermia-radiation combined therapy (HTRT) and MHRT in human prostate cancer cell lines, PC3 and LNCaP. We adopted a clonogenic assay to validate RDE and the radiosensitizing effect induced by MHT. The data on survival fractions were analyzed using both the linear-quadradic model and Arrhenius model to estimate the biological parameters describing RDE and radiosensitizing effect of MHRT for both cell lines through maximum likelihood estimation. Based on these parameters, a new survival fraction model was suggested for EQD estimation of MHRT.

RESULTS

The newly designed model describing the MHRT effect, effectively captures the variations in thermal and radiation dose for both cell lines (R2 > 0.95), and its suitability was confirmed through the normality test of residuals. This model appropriately describes the survival fractions up to 10 Gy for PC3 cells and 8 Gy for LNCaP cells under RT-only conditions. Furthermore, using the newly defined parameter r, the RDE effect was calculated as 29% in PC3 cells and 23% in LNCaP cells. EQDMHRT calculated through this model was 9.47 Gy for PC3 and 4.71 Gy for LNCaP when given 2 Gy and MHT for 30 min. Compared to EQDHTRT, EQDMHRT showed a 26% increase for PC3 and a 20% increase for LNCaP.

CONCLUSIONS

The proposed model effectively describes the changes of the survival fraction induced by MHRT in both cell lines and adequately represents actual data values through residual analysis. Newly suggested parameter r for RDE effect shows potential for quantitative comparisons between HTRT and MHRT, and optimizing therapeutic outcomes in MHRT for prostate cancer.

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.

Research progress of hyperthermia in tumor therapy by influencing metabolic reprogramming of tumor cells

Cellular metabolic reprogramming is an important feature of malignant tumors. Metabolic reprogramming causes changes in the levels or types of specific metabolites inside and outside the cell, which affects tumorigenesis and progression by influencing gene expression, the cellular state, and the tumor microenvironment. During tumorigenesis, a series of changes in the glucose metabolism, fatty acid metabolism, amino acid metabolism, and cholesterol metabolism of tumor cells occur, which are involved in the process of cellular carcinogenesis and constitute part of the underlying mechanisms of tumor formation. Hyperthermia, as one of the main therapeutic tools for malignant tumors, has obvious effects on tumor cell metabolism. In this paper, we will combine the latest research progress in the field of cellular metabolic reprogramming and focus on the current experimental research and clinical treatment of hyperthermia in cellular metabolic reprogramming to discuss the feasibility of cellular metabolic reprogramming-related mechanisms guiding hyperthermia in malignant tumor treatment, so as to provide more ideas for hyperthermia to treat malignant tumors through the direction of cellular metabolic reprogramming.

From Localized Mild Hyperthermia to Improved Tumor Oxygenation: Physiological Mechanisms Critically Involved in Oncologic Thermo-Radio-Immunotherapy

(1) Background: Mild hyperthermia (mHT, 39-42 °C) is a potent cancer treatment modality when delivered in conjunction with radiotherapy. mHT triggers a series of therapeutically relevant biological mechanisms, e.g., it can act as a radiosensitizer by improving tumor oxygenation, the latter generally believed to be the commensurate result of increased blood flow, and it can positively modulate protective anticancer immune responses. However, the extent and kinetics of tumor blood flow (TBF) changes and tumor oxygenation are variable during and after the application of mHT. The interpretation of these spatiotemporal heterogeneities is currently not yet fully clarified. (2) Aim and methods: We have undertaken a systematic literature review and herein provide a comprehensive insight into the potential impact of mHT on the clinical benefits of therapeutic modalities such as radio- and immuno-therapy. (3) Results: mHT-induced increases in TBF are multifactorial and differ both spatially and with time. In the short term, changes are preferentially caused by vasodilation of co-opted vessels and of upstream normal tissue vessels as well as by improved hemorheology. Sustained TBF increases are thought to result from a drastic reduction of interstitial pressure, thus restoring adequate perfusion pressures and/or HIF-1α- and VEGF-mediated activation of angiogenesis. The enhanced oxygenation is not only the result of mHT-increased TBF and, thus, oxygen availability but also of heat-induced higher O₂ diffusivities, acidosis- and heat-related enhanced O₂ unloading from red blood cells. (4) Conclusions: Enhancement of tumor oxygenation achieved by mHT cannot be fully explained by TBF changes alone. Instead, a series of additional, complexly linked physiological mechanisms are crucial for enhancing tumor oxygenation, almost doubling the initial O₂ tensions in tumors.

Combined hyperthermia and radiotherapy for prostate cancer: a systematic review

Optimization of treatment strategies for prostate cancer patients treated with curative radiation therapy (RT) represents one of the major challenges for the radiation oncologist. Dose escalation or combination of RT with systemic therapies is used to improve tumor control in patients with unfavorable prostate cancer, at the risk of increasing rates and severity of treatment-related toxicities. Elevation of temperature to a supra-physiological level has been shown to both increase tumor oxygenation and reduce DNA repair capabilities. Thus, hyperthermia (HT) combined with RT represents a compelling treatment strategy to improve the therapeutic ratio in prostate cancer patients. The aim of the present systematic review is to report on preclinical and clinical evidence supporting the combination of HT and RT for prostate cancer, discussing future applications and developments of this combined treatment.

Diffuse Optical Spectroscopy Monitoring of Experimental Tumor Oxygenation after Red and Blue Light Photodynamic Therapy

Photodynamic therapy (PDT) is an effective technique for cancer treatment based on photoactivation of photosensitizer accumulated in pathological tissues resulting in singlet oxygen production. Employment of red (660 nm) or blue (405 nm) light differing in typical penetration depth within the tissue for PDT performance provides wide opportunities for improving PDT protocols. Oxygenation dynamics in the treated area can be monitored using diffuse optical spectroscopy (DOS) which allows evaluating tumor response to treatment. In this study, we report on monitoring oxygenation dynamics in experimental tumors after PDT treatment with chlorin-based photosensitizers using red or blue light. The untreated and red light PDT groups demonstrate a gradual decrease in tumor oxygen saturation during the 7-day observation period, however, the reason is different: in the untreated group, the effect is explained by the excessive tumor growth, while in the PDT group, the effect is caused by the blood flow arrest preventing delivery of oxygenated blood to the tumor. The blue light PDT procedure, on the contrary, demonstrates the preservation of the blood oxygen saturation in the tumor during the entire observation period due to superficial action of the blue-light PDT and weaker tumor growth inhibition. Irradiation-only regimes show a primarily insignificant decrease in tumor oxygen saturation owing to partial inhibition of tumor growth. The DOS observations are interpreted based on histology analysis.

Theoretical Evaluation of the Impact of Hyperthermia in Combination with Radiation Therapy in an Artificial Immune-Tumor-Ecosystem

Simple Summary

Radio-sensitizing effects of moderate or mild hyperthermia (heating up tumor cells up to 41–43 °C) in combination with radiotherapy (thermoradiotherapy) have been evaluated for decades. However, how this combination might modulate an anti-tumor immune response is not well known. To investigate the dynamic behavior of immune–tumor ecosystems in different scenarios, a model representing an artificial adaptive immune system in silico is used. Such a model may be far removed from the real situation in the patient, but it could serve as a laboratory to investigate fundamental principles of dynamics in such systems under well-controlled conditions and it could be used to generate and refine hypothesis supporting the design of clinical trials. Regarding the results of the presented computer simulations, the main effect is governed by the cellular radio-sensitization. In addition, the application of hyperthermia during the first radiotherapy fractions seems to be more effective.

Abstract

There is some evidence that radiotherapy (RT) can trigger anti-tumor immune responses. In addition, hyperthermia (HT) is known to be a tumor cell radio-sensitizer. How HT could enhance the anti-tumor immune response produced by RT is still an open question. The aim of this study is the evaluation of potential dynamic effects regarding the adaptive immune response induced by different combinations of RT fractions with HT. The adaptive immune system is considered as a trainable unit (perceptron) which compares danger signals released by necrotic or apoptotic cell death with the presence of tumor- and host tissue cell population-specific molecular patterns (antigens). To mimic the changes produced by HT such as cell radio-sensitization or increase of the blood perfusion after hyperthermia, simplistic biophysical models were included. To study the effectiveness of the different RT+HT treatments, the Tumor Control Probability (TCP) was calculated. In the considered scenarios, the major effect of HT is related to the enhancement of the cell radio-sensitivity while perfusion or heat-based effects on the immune system seem to contribute less. Moreover, no tumor vaccination effect has been observed. In the presented scenarios, HT boosts the RT cell killing but it does not fundamentally change the anti-tumor immune response.

Stimuli-responsive graphene oxide and methotrexate-loaded magnetic nanoparticles for breast cancer-targeted therapy

Aim: Nanocomposites of graphene oxide (GO) loaded with PEGylated superparamagnetic iron oxide nanoparticles and grafted with methotrexate and stimuli-responsive linkers (GO-SPION-MTX) were developed for photothermal and chemotherapy of breast cancer. Methods: PEGylated SPIONs were synthesized and conjugated with chemotherapeutic targeting agent MTX, which were then loaded on GO to prepare GO-SPION-MTX nanocomposites. To evaluate the photothermal effect of the nanocomposites, they were examined in breast cancer cell lines with low doses of near-infrared (NIR) laser radiation with/without acetazolamide. Results: The GO-SPION-MTX nanocomposites were found to be internalized by the folate-receptor-positive cancer cells and induce high cytotoxicity on exposure to NIR laser rays. Conclusion: Our findings suggest that the GO-SPION-MTX nanocomposite can potentially be used as a multimodal nanomedicine/theranostic against breast cancer.

Magnetism-mediated targeting hyperthermia-immunotherapy in "cold" tumor with CSF1R inhibitor

Background: Immunotherapy has profoundly changed the landscape of cancer management and represented the most significant breakthrough. Yet, it is a formidable challenge that the majority of cancers - the so-called “cold” tumors - poorly respond to immunotherapy. To find a general immunoregulatory modality that can be applied to a broad spectrum of cancers is an urgent need.

Methods: Magnetic hyperthermia (MHT) possesses promise in cancer therapy. We develop a safe and effective therapeutic strategy by using magnetism-mediated targeting MHT-immunotherapy in “cold” colon cancer. A magnetic liposomal system modified with cell-penetrating TAT peptide was developed for targeted delivery of a CSF1R inhibitor (BLZ945), which can block the CSF1-CSF1R pathway and reduce M2 macrophages. The targeted delivery strategy is characterized by its magnetic navigation and TAT-promoting intratumoral penetration.

Results: The liposomes (termed TAT-BLZmlips) can induce ICD and cause excessive CRT exposure on the cell surface, which transmits an “eat-me” signal to DCs to elicit immunity. The combination of MHT and BLZ945 can repolarize M2 macrophages in the tumor microenvironment to relieve immunosuppression, normalize the tumor blood vessels, and promote T-lymphocyte infiltration. The antitumor effector CD8⁺ T cells were increased after treatment.

Conclusion: This work demonstrated that TAT-BLZmlips with magnetic navigation and MHT can remodel tumor microenvironment and activate immune responses and memory, thus inhibiting tumor growth and recurrence.

Tumor-Selective Immune-Active Mild Hyperthermia Associated with Chemotherapy in Colon Peritoneal Metastasis by Photoactivation of Fluorouracil-Gold Nanoparticle Complexes

Peritoneal metastasis (PM) is considered as the terminal stage of metastatic colon cancer, with still poor median survival rate even with the best recent chemotherapy treatment. The current PM treatment combines cytoreductive surgery, which consists of resecting all macroscopic tumors, with hyperthermic intraperitoneal chemotherapy (HIPEC), which uses mild hyperthermia to boost the diffusion and cytotoxic effect of chemotherapeutic drugs. As HIPEC is performed via a closed circulation of a hot liquid containing chemotherapy, it induces uncontrolled heating and drug distribution in the whole peritoneal cavity with important off-site toxicity and a high level of morbidity. Here, we propose a safer precision strategy using near-infrared (NIR) photoactivated gold nanoparticles (AuNPs) coupled to the chemotherapeutic drug 5-fluorouracil (5-FU) to enable a spatial and temporal control of mild chemo-hyperthermia targeted to the tumor nodules within the peritoneal cavity. Both the 16 nm AuNPs and the corresponding complex with 5-FU (AuNP-5-FU) were shown as efficient NIR photothermal agents in the microenvironment of subcutaneous colon tumors as well as PM in syngeneic mice. Noteworthy, NIR photothermia provided additional antitumor effects to 5-FU treatment. A single intraperitoneal administration of AuNP-5-FU resulted in their preferential accumulation in tumor nodules and peritoneal macrophages, allowing light-induced selective hyperthermia, extended tumor necrosis, and activation of a pro-inflammatory immune response while leaving healthy tissues without any damage. From a translational standpoint, the combined and tumor-targeted photothermal and chemotherapy mediated by the AuNP-drug complex has the potential to overcome the current off-target toxicity of HIPEC in clinical practice.

Hyperthermic intraperitoneal chemotherapy (HIPEC): Should we look closer at the microenvironment?

The age of cancer as an isolated single-cell concept is now behind us. It is now established that epithelial ovarian cancer, like other cancers, interacts with the healthy bystander cells to influence them and takes advantage of their nutritional, immunological, disseminating and other capacities. This interaction has become a therapeutic target, as shown by the numerous studies on this subject. Intraperitoneal chemo-hyperthermia has been part of the therapeutic armamentarium for some time yet its efficiency in ovarian cancer has only been recently proven in a randomized controlled trial. However, its therapeutic performance is not revolutionary and epithelial ovarian cancer maintains a high mortality. In this review, we studied the impact of HIPEC on the microenvironment and vice versa to determine whether it could be the key to this lukewarm efficacy. We began by exploring the modalities of HIPEC and establishing the reasons that make this treatment topical. Then, we examined its impact on each element of the tumor environment to obtain a global view of the resistance mechanisms at work in HIPEC.

Cancer Stem Cells and Combination Therapies to Eradicate Them

Cancer stem cells (CSCs) show self-renewal ability and multipotential differentiation, like normal stem or progenitor cells, and which proliferate uncontrollably and can escape the effects of drugs and phagocytosis by immune cells. Traditional monotherapies, such as surgical resection, radiotherapy and chemotherapy, cannot eradicate CSCs, however, combination therapy may be more effective at eliminating CSCs. The present review summarizes the characteristics of CSCs and several promising combination therapies to eradicate them.

Hyperthermia with photon radiotherapy is thermoradiobiologically analogous to neutrons for tumors without enhanced normal tissue toxicity

The depth dose profiles of photons mirror those of fast neutrons. However, in contrast to the high linear energy transfer (LET) characteristics of neutrons; photons exhibit low LET features. Hyperthermia (HT) inhibits the repair of radiation-induced DNA damage and is cytotoxic to the radioresistant hypoxic tumor cells. Thus, thermoradiobiologically, HT simulates high LET radiation with photons. At temperatures of 39-45 °C, the physiological vasodilation allows rapid heat dissipation from normal tissues. On the contrary, the chaotic and relatively rigid tumor vasculature results in heat retention leading to higher intratumoural temperatures. Consequently, the high LET attributes of HT with photon radiations are mostly limited to the confines of the heated tumor while the normothermic normal tissues would be irradiated with low LET photons. HT thereby augments photon therapy by conferring therapeutic advantages of high LET radiations to the tumors akin to neutrons, while the 'heat-sink' effect spares the normal tissues from thermal radiosensitization. Thus, photon thermoradiotherapy imparts radiobiological advantages selectively to tumors analogous to neutrons without exaggerating normal tissue morbidities. The later has been the major concern with clinical fast neutron beam therapy. Outcomes reported from several clinical trials in diverse tumor sites add testimony to the enhanced therapeutic efficacy of photon thermoradiotherapy.

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.

Janus Nanobullets Combine Photodynamic Therapy and Magnetic Hyperthermia to Potentiate Synergetic Anti-Metastatic Immunotherapy

Photodynamic therapy (PDT) is clinically promising in destructing primary tumors but ineffective against distant metastases. This study reports the use of immunogenic nanoparticles mediated combination of PDT and magnetic hyperthermia to synergistically augment the anti-metastatic efficacy of immunotherapy. Janus nanobullets integrating chlorine e6 (Ce6) loaded, disulfide-bridged mesoporous organosilica bodies with magnetic heads (M-MONs@Ce6) are tailored for redox/pH-triggered photosensitizer release accompanying their matrix degradation. Cancer cell membrane cloaking enables favorable tumor-targeted accumulation and prolonged blood circulation time of M-MONs@Ce6. The combination of PDT and magnetic hyperthermia has a strong synergy anticancer activity and simultaneously elicits a sequence of immunogenic cell death, resulting in synergistically tumor-specific immune responses. When combined with anti-CTLA-4 antibody, the biomimetic and biodegradable nanoparticle enables the notable eradication of primary and deeply metastatic tumors with low systematic toxicity, thus potentially advancing the development of combined hyperthermia, PDT, and checkpoint blockade immunotherapy to combat cancer metastasis.

Tumor Reoxygenation and Blood Perfusion Enhanced Photodynamic Therapy using Ultrathin Graphdiyne Oxide Nanosheets

Both diffusion-limited and perfusion-limited hypoxia are associated with tumor progression, metastasis, and the resistance to therapeutic modalities. A strategy that can efficiently overcome both types of hypoxia to enhance the efficacy of cancer treatment has not been reported yet. Here, it is shown that by using biomimetic ultrathin graphdiyne oxide (GDYO) nanosheets, both types of hypoxia can be simultaneously addressed toward an ideal photodynamic therapy (PDT). The GDYO nanosheets, which are oxidized and exfoliated from graphdiyne (GDY), are able to efficiently catalyze water oxidation to release O₂ and generate singlet oxygen (¹O₂) using near-infrared irradiation. Meanwhile, GDYO nanosheets also exhibit excellent light-to-heat conversion performance with a photothermal conversion efficiency of 60.8%. Thus, after the GDYO nanosheets are coated with iRGD peptide-modified red blood membrane (i-RBM) to achieve tumor targeting, the biomimetic GDYO@i-RBM nanosheets can simultaneously enhance tumor reoxygenation and blood perfusion for PDT. This study provides new insights into utilizing novel water-splitting materials to relieve both diffusion- and perfusion-limited hypoxia for the development of a novel therapeutic platform.

Multimodal cancer cell therapy using Au@Fe2O3 core-shell nanoparticles in combination with photo-thermo-radiotherapy

In this study, gold coated iron oxide nanoparticle (Au@Fe₂O₃ NP) was synthesized in a core-shell structure. Photothermal and radiosensitization effects of Au@Fe₂O₃ NPs were investigated on KB human mouth epidermal carcinoma cell line. Cell death and apoptosis were measured to study the effects of nanoparticles in combination with both radiotherapy (RT) and photothermal therapy (PTT). The KB cells were treated with Au@Fe₂O₃ NPs (20 μg/ml; 4 h) and then received different treatment regimens of PTT and/or RT using laser (808 nm, 6 W/cm², 10 min) and/or 6 MV X-ray (single dose of 2 Gy). Following the various treatments, MTT assay was performed to evaluate the cell survival rate. Also, the mode of cell death was determined by flow cytometry using an annexinV-fluorescein isothiocyanate/propidium iodide apoptosis detection kit. No significant cell death was observed due to laser irradiation. The viability of the cells firstly incubated with NPs and then exposed to the laser was significantly decreased. Additionally, our results demonstrated that Au@Fe₂O₃ NP is a good radiosensitizer at megavoltage energies of X-ray. When nanoparticles loaded KB cells were received both laser and X-ray, the cell viability substantially decreased. Following such a combinatorial treatment, flow cytometry determined that the majority of cell death relates to apoptosis. In conclusion, Au@Fe₂O₃ NP has a great potential to be applied as a photo-thermo-radiotherapy sensitizer for treatment of head and neck tumors.

The effect of time interval between radiotherapy and hyperthermia on planned equivalent radiation dose

PURPOSE

Thermoradiotherapy is an effective treatment for locally advanced cervical cancer. However, the optimal time interval between radiotherapy and hyperthermia, resulting in the highest therapeutic gain, remains unclear. This study aims to evaluate the effect of time interval on the therapeutic gain using biological treatment planning.

METHODS

Radiotherapy and hyperthermia treatment plans were created for 15 cervical cancer patients. Biological modeling was used to calculate the equivalent radiation dose, that is, the radiation dose that results in the same biological effect as the thermoradiotherapy treatment, for different time intervals ranging from 0-4 h. Subsequently, the thermal enhancement ratio (TER, i.e. the ratio of the dose for the thermoradiotherapy and the radiotherapy-only plan) was calculated for the gross tumor volume (GTV) and the organs at risk (OARs: bladder, rectum, bowel), for each time interval. Finally, the therapeutic gain factor (TGF, i.e. TER_GTV/TER_OAR) was calculated for each OAR.

RESULTS

The median TER_GTV ranged from 1.05 to 1.16 for 4 h and 0 h time interval, respectively. Similarly, for bladder, rectum and bowel, TER_OARs ranged from 1-1.03, 1-1.04 and 1-1.03, respectively. Radiosensitization in the OARs was much less than in the GTV, because temperatures were lower, fractionation sensitivity was higher (lower α/β) and direct cytotoxicity was assumed negligible in normal tissue. TGFs for the three OARs were similar, and were highest (around 1.12) at 0 h time interval.

CONCLUSION

This planning study indicates that the largest therapeutic gain for thermoradiotherapy in cervical cancer patients can be obtained when hyperthermia is delivered immediately before or after radiotherapy.

Re-irradiation and Hyperthermia in Breast Cancer

Half of locoregional recurrences after breast cancer treatment are isolated events. Restaging should be carried out to select patients for curative salvage treatment. The approach depends on the characteristics of the primary and recurrent cancer, previous locoregional and systemic treatments, site of recurrence, comorbidities and the patient's wishes. A multidisciplinary discussion should be associated with the shared decision-making process. In view of the potential long-term disease-free survival, meticulous target volume delineation and selection of the most appropriate techniques should be used to decrease the risk of toxicity. This overview aims to provide clinicians with tools to manage the different scenarios of breast cancer patients with locoregional recurrences in the context of re-irradiation.

Effect of Tirapazamine, Metformin or Mild Hyperthermia on Recovery From Radiation-Induced Damage in Pimonidazole-Unlabeled Quiescent Tumor Cells

Background

The aim of the study was to examine the effect of tirapazamine (TPZ) on recovery from radiation-induced damage in pimonidazole-unlabeled quiescent (Q) tumor cells compared with that of metformin (Met) or mild temperature hyperthermia (MTH).

Methods

Proliferating (P) cells in EL4 tumors were labeled by continuous 5-bromo-2'-deoxyuridine (BrdU) administration. Tumors received γ-rays at 1 h after pimonidazole administration followed by Met or TPZ treatment or MTH. Twenty-four hours later, the responses of Q and total (P + Q) cells and those of the pimonidazole-unlabeled cells were assessed with micronucleation and apoptosis frequencies using immunofluorescence staining for BrdU and apoptosis frequency using immunofluorescence staining for pimonidazole, respectively.

Results

With γ-rays only, the pimonidazole-unlabeled cell fraction showed significantly enhanced radio-sensitivity compared with the whole cell fraction more remarkably in Q than total cells. However, a significantly greater decrease in radio-sensitivity in the pimonidazole-unlabeled than the whole cell fraction, evaluated using a delayed assay, was more clearly observed in Q than total cells. Post-irradiation MTH or Met treatment more clearly repressed the decrease in radio-sensitivity in the Q than total cells. Post-irradiation TPZ administration produced a large radio-sensitizing effect on both total and Q cells, especially on Q cells. In pimonidazole-unlabeled cell fractions in both total and Q cells, TPZ suppressed the reduction in sensitivity much more efficiently than MTH or Met without any radio-sensitizing effect.

Conclusion

Post-irradiation TPZ administration has the potential to both suppress recovery from radiation-induced damage and enhance the radio-sensitivity both in total and Q tumor cells. Post-irradiation TPZ administration may be useful for controlling tumors.

Measurement and analysis of the impact of time-interval, temperature and radiation dose on tumour cell survival and its application in thermoradiotherapy plan evaluation

PURPOSE

Biological modelling of thermoradiotherapy may further improve patient selection and treatment plan optimisation, but requires a model that describes the biological effect as a function of variables that affect treatment outcome (e.g. temperature, radiation dose). This study aimed to establish such a model and its parameters. Additionally, a clinical example was presented to illustrate the application.

METHODS

Cell survival assays were performed at various combinations of radiation dose (0-8 Gy), temperature (37-42 °C), time interval (0-4 h) and treatment sequence (radiotherapy before/after hyperthermia) for two cervical cancer cell lines (SiHa and HeLa). An extended linear-quadratic model was fitted to the data using maximum likelihood estimation. As an example application, a thermoradiotherapy plan (23 × 2 Gy + weekly hyperthermia) was compared with a radiotherapy-only plan (23 × 2 Gy) for a cervical cancer patient. The equivalent uniform radiation dose (EUD) in the tumour, including confidence intervals, was estimated using the SiHa parameters. Additionally, the difference in tumour control probability (TCP) was estimated.

RESULTS

Our model described the dependency of cell survival on dose, temperature and time interval well for both SiHa and HeLa data (R²=0.90 and R²=0.91, respectively), making it suitable for biological modelling. In the patient example, the thermoradiotherapy plan showed an increase in EUD of 9.8 Gy that was robust (95% CI: 7.7-14.3 Gy) against propagation of the uncertainty in radiobiological parameters. This corresponded to a 20% (95% CI: 15-29%) increase in TCP.

CONCLUSIONS

This study presents a model that describes the cell survival as a function of radiation dose, temperature and time interval, which is essential for biological modelling of thermoradiotherapy treatments.

A short time interval between radiotherapy and hyperthermia reduces in-field recurrence and mortality in women with advanced cervical cancer

Background

Combined radiotherapy and hyperthermia is a well-established alternative to chemoradiotherapy for advanced stage cervical cancer patients with a contraindication for chemotherapy. Pre-clinical evidence suggests that the radiosensitizing effect of hyperthermia decreases substantially for time intervals between radiotherapy and hyperthermia as short as 1–2 h, but clinical evidence is limited. The purpose of this study is to determine the effect of the time interval between external beam radiotherapy (EBRT) and same-day hyperthermia on in-field recurrence rate, overall survival and late toxicity in women with advanced stage cervical cancer.

Methods

Patients with advanced stage cervical cancer who underwent a full-course of curative daily EBRT and (4–5) weekly hyperthermia sessions between 1999 and 2014 were included for retrospective analysis. The mean time interval between EBRT fractions and same-day hyperthermia was calculated for each patient; the median thereof was used to divide the cohort in a ‘short’ and ‘long’ time-interval group. Kaplan-Meier analysis and stepwise Cox regression were used to compare the in-field recurrence and overall survival. Finally, high-grade (≥3) late toxicity was compared across time-interval groups. DNA repair suppression is an important hyperthermia mechanism, DNA damage repair kinetics were therefore studied in patient biopsies to support clinical findings.

Results

Included were 58 patients. The 3-year in field recurrence rate was 18% and 53% in the short (≤79.2 min) and long (>79.2 min) time-interval group, respectively (p = 0.021); the 5-year overall survival was 52% and 17% respectively (p = 0.015). Differences between time-interval groups remained significant for both in-field recurrence (HR = 7.7, p = 0.007) and overall survival (HR = 2.3, p = 0.012) in multivariable Cox regression. No difference in toxicity was observed (p = 1.00), with only 6 and 5 events in the short and long group, respectively. The majority of DNA damage was repaired within 2 h, potentially explaining a reduced effectiveness of hyperthermia for long time intervals.

Conclusions

A short time interval between EBRT and hyperthermia is associated with a lower risk of in-field recurrence and a better overall survival. There was no evidence for difference in late toxicity.

Exploiting the cancer niche: Tumor-associated macrophages and hypoxia as promising synergistic targets for nano-based therapy

The tumor microenvironment has been widely exploited as an active participant in tumor progression. Extensive reports have defined the dual role of tumor-associated macrophages (TAMs) in tumor development. The protumoral effect exerted by the M2 phenotype has been correlated with a negative outcome in most solid tumors. The high infiltration of immune cells in the hypoxic cores of advanced solid tumors leads to a chain reaction of stimuli that enhances the expression of protumoral genes, thrives tumor malignancy, and leads to the emergence of drug resistance. Many studies have shown therapeutic targeting systems, solely to TAMs or tumor hypoxia, however, novel therapeutics that target both features are still warranted. In the present review, we discuss the role of hypoxia in tumor development and the clinical outcome of hypoxia-targeted therapeutics, such as hypoxia-inducible factor (HIF-1) inhibitors and hypoxia-activated prodrugs. Furthermore, we review the state-of-the-art of macrophage-based cancer therapy. We thoroughly discuss the development of novel therapeutics that simultaneously target TAMs and tumor hypoxia. Nano-based systems have been highlighted as interesting strategies for dual modality treatments, with somewhat improved tissue extravasation. Such approach could be seen as a promising strategy to overcome drug resistance and enhance the efficacy of chemotherapy in advanced solid and metastatic tumors, especially when exploiting cell-based nanotherapies. Finally, we provide an in-depth opinion on the importance of exploiting the tumor microenvironment in cancer therapy, and how this could be translated to clinical practice.

It's Getting Hot in Here: Targeting Cancer Stem-like Cells with Hyperthermia

Cancer stem-like cells (CSCs) are a subset of cancer cells that are resistant to conventional radiotherapy and chemotherapy. As such, CSCs have been recognized as playing a large role in tumor initiation and recurrence. Although hyperthermia is broadly used in cancer treatment either alone or in combination with radio- or chemo-therapy, its potential to target CSCs is not well understood. In this review, we discuss different types of hyperthermia and potential mechanisms of action in cancer treatment, particularly in regards to killing CSCs.

Tumor hypoxia and reoxygenation: the yin and yang for radiotherapy

Tumor hypoxia, a common feature occurring in nearly all human solid tumors is a major contributing factor for failures of anticancer therapies. Because ionizing radiation depends heavily on the presence of molecular oxygen to produce cytotoxic effect, the negative impact of tumor hypoxia had long been recognized. In this review, we will highlight some of the past attempts to overcome tumor hypoxia including hypoxic radiosensitizers and hypoxia-selective cytotoxin. Although they were (still are) a very clever idea, they lacked clinical efficacy largely because of ‘reoxygenation’ phenomenon occurring in the conventional low dose hyperfractionation radiotherapy prevented proper activation of these compounds. Recent meta-analysis and imaging studies do however indicate that there may be a significant clinical benefit in lowering the locoregional failures by using these compounds. Latest technological advancement in radiotherapy has allowed to deliver high doses of radiation conformally to the tumor volume. Although this technology has brought superb clinical responses for many types of cancer, recent modeling studies have predicted that tumor hypoxia is even more serious because ‘reoxygenation’ is low thereby leaving a large portion of hypoxic tumor cells behind. Wouldn’t it be then reasonable to combine hypoxic radiosensitizers and/or hypoxia-selective cytotoxin with the latest radiotherapy? We will provide some preclinical and clinical evidence to support this idea hoping to revamp an enthusiasm for hypoxic radiosensitizers or hypoxia-selective cytotoxins as an adjunct therapy for radiotherapy.

Fast and high temperature hyperthermia coupled with radiotherapy as a possible new treatment for glioblastoma

Background

A new transcranial focused ultrasound device has been developed that can induce hyperthermia in a large tissue volume. The purpose of this work is to investigate theoretically how glioblastoma multiforme (GBM) can be effectively treated by combining the fast hyperthermia generated by this focused ultrasound device with external beam radiotherapy.

Methods/Design

To investigate the effect of tumor growth, we have developed a mathematical description of GBM proliferation and diffusion in the context of reaction–diffusion theory. In addition, we have formulated equations describing the impact of radiotherapy and heat on GBM in the reaction–diffusion equation, including tumor regrowth by stem cells. This formulation has been used to predict the effectiveness of the combination treatment for a realistic focused ultrasound heating scenario.

Our results show that patient survival could be significantly improved by this combined treatment modality.

Discussion

High priority should be given to experiments to validate the therapeutic benefit predicted by our model.

Electronic supplementary material

The online version of this article (doi:10.1186/s40349-016-0078-3) contains supplementary material, which is available to authorized users.

3D radiobiological evaluation of combined radiotherapy and hyperthermia treatments

PURPOSE

Currently, clinical decisions regarding thermoradiotherapy treatments are based on clinical experience. Quantification of the radiosensitising effect of hyperthermia allows comparison of different treatment strategies, and can support clinical decision-making regarding the optimal treatment. The software presented here enables biological evaluation of thermoradiotherapy plans through calculation of equivalent 3D dose distributions.

METHODS

Our in-house developed software (X-Term) uses an extended version of the linear-quadratic model to calculate equivalent radiation dose, i.e. the radiation dose yielding the same effect as the thermoradiotherapy treatment. Separate sets of model parameters can be assigned to each delineated structure, allowing tissue specific modelling of hyperthermic radiosensitisation. After calculation, the equivalent radiation dose can be evaluated according to conventional radiotherapy planning criteria. The procedure is illustrated using two realistic examples. First, for a previously irradiated patient, normal tissue dose for a radiotherapy and thermoradiotherapy plan (with equal predicted tumour control) is compared. Second, tumour control probability (TCP) is assessed for two (otherwise identical) thermoradiotherapy schedules with different time intervals between radiotherapy and hyperthermia.

RESULTS

The examples demonstrate that our software can be used for individualised treatment decisions (first example) and treatment optimisation (second example) in thermoradiotherapy. In the first example, clinically acceptable doses to the bowel were exceeded for the conventional plan, and a substantial reduction of this excess was predicted for the thermoradiotherapy plan. In the second example, the thermoradiotherapy schedule with long time interval was shown to result in a substantially lower TCP.

CONCLUSIONS

Using biological modelling, our software can facilitate the evaluation of thermoradiotherapy plans and support individualised treatment decisions.

Thermoradiotherapy planning: Integration in routine clinical practice

Planning of combined radiotherapy and hyperthermia treatments should be performed taking the synergistic action between the two modalities into account. This work evaluates the available experimental data on cytotoxicity of combined radiotherapy and hyperthermia treatment and the requirements for integration of hyperthermia and radiotherapy treatment planning into a single planning platform. The underlying synergistic mechanisms of hyperthermia include inhibiting DNA repair, selective killing of radioresistant hypoxic tumour tissue and increased radiosensitivity by enhanced tissue perfusion. Each of these mechanisms displays different dose-effect relations, different optimal time intervals and different optimal sequences between radiotherapy and hyperthermia. Radiosensitisation can be modelled using the linear-quadratic (LQ) model to account for DNA repair inhibition by hyperthermia. In a recent study, an LQ model-based thermoradiotherapy planning (TRTP) system was used to demonstrate that dose escalation by hyperthermia is equivalent to ∼10 Gy for prostate cancer patients treated with radiotherapy. The first step for more reliable TRTP is further expansion of the data set of LQ parameters for normally oxygenated normal and tumour tissue valid over the temperature range used clinically and for the relevant time intervals between radiotherapy and hyperthermia. The next step is to model the effect of hyperthermia in hypoxic tumour cells including the physiological response to hyperthermia and the resulting reoxygenation. Thermoradiotherapy planning is feasible and a necessity for an optimal clinical application of hyperthermia combined with radiotherapy in individual patients.

Single agent nanoparticle for radiotherapy and radio-photothermal therapy in anaplastic thyroid cancer

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive human malignancies. The aggressive behavior of ATC and its resistance to traditional treatment limit the efficacy of radiotherapy, chemotherapy, and surgery. The purpose of this study is aimed at enhancing the therapeutic efficacy of radiotherapy (RT) combined with photothermal therapy (PTT) in murine orthotopic model of ATC, based on our developed single radioactive copper sulfide (CuS) nanoparticle platform. We prepare a new dual-modality therapy for ATC consisting of a single-compartment nanoplatform, polyethylene glycol-coated [(64)Cu]CuS NPs, in which the radiotherapeutic property of (64)Cu is combined with the plasmonic properties of CuS NPs. Mice with Hth83 ATC were treated with PEG-[(64)Cu]CuS NPs and/or near infrared laser. Antitumor effects were assessed by tumor growth and animal survival. We found that in mice bearing orthotopic human Hth83 ATC tumors, micro-PET/CT imaging and biodistribution studies showed that about 50% of the injected dose of PEG-[(64)Cu]CuS NPs was retained in tumor 48 h after intratumoral injection. Human absorbed doses were calculated from biodistribution data. In antitumor experiments, tumor growth was delayed by PEG-[(64)Cu]CuS NP-mediated RT, PTT, and combined RT/PTT, with combined RT/PTT being most effective. In addition, combined RT/PTT significantly prolonged the survival of Hth83 tumor-bearing mice compared to no treatment, laser treatment alone, or NP treatment alone without producing acute toxic effects. These findings indicate that this single-compartment multifunctional NPs platform merits further development as a novel therapeutic agent for ATC.

Thermoresponsive fluorinated small-molecule drugs: a new concept for efficient localized chemotherapy

We review the drugs used in combination with hyperthermia for cancer therapy and recent advances on small thermoresponsive molecules.

The intratumoral administration of ferucarbotran conjugated with doxorubicin improved therapeutic effect by magnetic hyperthermia combined with pharmacotherapy in a hepatocellular carcinoma model

Background

Local hyperthermia of tumor in conjunction with chemotherapy is a promising strategy for cancer treatment. The aim of this study was to evaluate the efficacy of intratumoral delivery of clinically approved magnetic nanoparticles (MNPs) conjugated with doxorubicin to simultaneously induce magnetic hyperthermia and drug delivery in a hepatocellular carcinoma (HCC) model.

Materials and methods

HCC cells expressing luciferase were implanted into the flank of BALB/c-nu mice (n = 19). When the tumor diameter reached 7–8 mm, the animals were divided into four groups according to the injected agents: group A (normal saline, n = 4), group B (doxorubicin, n = 5), group C (MNP, n = 5), and group D (MNP/doxorubicin complex, n = 5). Animals were exposed to an alternating magnetic field (AMF) to receive magnetic hyperthermia, and intratumoral temperature changes were measured.

Bioluminescence imagings (BLIs) were performed before treatment and at 3, 7, and 14 days after treatment to measure the tumoral activities. The relative signal intensity (RSI) of each tumor was calculated by dividing the BLI signal at each time point by the value measured before treatment. At day 14 post-treatment, all tumor tissues were harvested to assess the apoptosis rates by pathological examination.

Results

The rise in temperature of the tumors was 1.88 ± 0.21°C in group A, 0.96 ± 1.05°C in B, 7.93 ± 1.99°C in C, and 8.95 ± 1.31°C in D. The RSI of the tumors at day 14 post-treatment was significantly lower in group D (0.31 ± 0.20) than in group A (2.23 ± 1.14), B (0.94 ± 0.47), and C (1.02 ± 0.21). The apoptosis rates of the tumors were 11.52 ± 3.10% in group A, 23.0 ± 7.68% in B, 25.4 ± 3.36% in C, and 39.0 ± 13.2% in D, respectively.

Conclusions

The intratumoral injection of ferucarbotran conjugated with doxorubicin shows an improved therapeutic effect compared with doxorubicin or ferucarbotran alone when the complex is injected into HCC tissues exposed to AMF for magnetic hyperthermia. This strategy of combining doxorubicin and MNP-induced magnetic hyperthermia exhibits a synergic effect on inhibiting tumor growth in an HCC model.

Gold nanoparticle hyperthermia reduces radiotherapy dose

Gold nanoparticles can absorb near infrared light, resulting in heating and ablation of tumors. Gold nanoparticles have also been used for enhancing the X-ray dose to tumors. The combination of hyperthermia and radiotherapy is synergistic, importantly allowing a reduction in X-ray dose with improved therapeutic results. Here we intratumorally infused small 15 nm gold nanoparticles engineered to be transformed from infrared-transparent to infrared-absorptive by the tumor, then heated by infrared followed by X-ray treatment. Synergy was studied using a very radioresistant subcutaneous squamous cell carcinoma (SCCVII) in mice. It was found that the dose required to control 50% of the tumors, normally 55 Gy, could be reduced to <15 Gy (a factor of >3.7). Gold nanoparticles therefore provide a method to combine hyperthermia and radiotherapy to drastically reduce the X-ray radiation needed, thus sparing normal tissue, reducing side effects, and making radiotherapy more effective.

FROM THE CLINICAL EDITOR

Gold nanoparticles are known to enhance the efficacy of X-ray in tumor irradiation resulting in tumor heating and ablation. They also absorb near infrared light. This dual property was studied using a very radioresistant subcutaneous squamous cell carcinoma in mice, demonstrating that the dose required to control 50% of the tumors could be reduced by a factor of > 3.7, paving the way to potential future clinical applications.

Hyperthermia as adjunct to intravesical chemotherapy for bladder cancer

Nonmuscle invasive bladder cancer remains a very costly cancer to manage because of high recurrence rates requiring long-term surveillance and treatment. Emerging evidence suggests that adjunct and concurrent use of hyperthermia with intravesical chemotherapy after transurethral resection of bladder tumor further reduces recurrence risk and progression to advanced disease. Hyperthermia has both direct and immune-mediated cytotoxic effect on tumor cells including tumor growth arrest and activation of antitumor immune system cells and pathways. Concurrent heat application also acts as a sensitizer to intravesical chemotherapy agents. As such the ability to deliver hyperthermia to the focus of tumor while minimizing damage to surrounding benign tissue is of utmost importance to optimize the benefit of hyperthermia treatment. Existing chemohyperthermia devices that allow for more localized heat delivery continue to pave the way in this effort. Current investigational methods involving heat-activated drug delivery selectively to tumor cells using temperature-sensitive liposomes also offer promising ways to improve chemohyperthermia efficacy in bladder cancer while minimizing toxicity to benign tissue. This will hopefully allow more widespread use of chemohyperthermia to all bladder cancer patients, including metastatic bladder cancer.

Conductive thermal ablation of 4T1 murine breast carcinoma reduces severe hypoxia in surviving tumour

PURPOSE

The purpose of this study was to quantify hypoxia changes in viable tumour volumes after thermal ablation of a murine breast carcinoma.

METHODS

Murine breast 4T1 tumours were grown in the rear leg of BALB/c mice to an average diameter of 10-12 mm. Tumours were treated with conductive interstitial thermal therapy (CITT) at a peak temperature of 80-90°C for 10 min. The animals were euthanised 72 h later, and the tumours were removed for immunohistochemical staining with pimonidazole - a marker of partial pressure of oxygen. The levels of pimonidazole staining intensity were used to quantify changes in hypoxia gradients in terms of strong, medium and weak positive pixel fractions.

RESULTS

The pimonidazole staining ratio of viable control tumour tissue to viable tissue in tumours that were ablated was 0.7 for weak staining, 2.7 for medium staining and 8.0 (p < 0.03) for strong pimonidazole staining.

CONCLUSION

This shift of pimonidazole staining toward lower intensity pixels in the remaining tumour indicates that tumour ablation with CITT may increase radiosensitivity of the remaining tumour tissue and presents a rationale for combination therapy.

Endocervical ultrasound applicator for integrated hyperthermia and HDR brachytherapy in the treatment of locally advanced cervical carcinoma

PURPOSE

The clinical success of hyperthermia adjunct to radiotherapy depends on adequate temperature elevation in the tumor with minimal temperature rise in organs at risk. Existing technologies for thermal treatment of the cervix have limited spatial control or rapid energy falloff. The objective of this work is to develop an endocervical applicator using a linear array of multisectored tubular ultrasound transducers to provide 3-D conformal, locally targeted hyperthermia concomitant to radiotherapy in the uterine cervix. The catheter-based device is integrated within a HDR brachytherapy applicator to facilitate sequential and potentially simultaneous heat and radiation delivery.

METHODS

Treatment planning images from 35 patients who underwent HDR brachytherapy for locally advanced cervical cancer were inspected to assess the dimensions of radiation clinical target volumes (CTVs) and gross tumor volumes (GTVs) surrounding the cervix and the proximity of organs at risk. Biothermal simulation was used to identify applicator and catheter material parameters to adequately heat the cervix with minimal thermal dose accumulation in nontargeted structures. A family of ultrasound applicators was fabricated with two to three tubular transducers operating at 6.6-7.4 MHz that are unsectored (360 degrees), bisectored (2 x 180 degrees), or trisectored (3 x 120 degrees) for control of energy deposition in angle and along the device length in order to satisfy anatomical constraints. The device is housed in a 6 mm diameter PET catheter with cooling water flow for endocervical implantation. Devices were characterized by measuring acoustic efficiencies, rotational acoustic intensity distributions, and rotational temperature distributions in phantom.

RESULTS

The CTV in HDR brachytherapy plans extends 20.5 +/- 5.0 mm from the endocervical tandem with the rectum and bladder typically <8 mm from the target boundary. The GTV extends 19.4 +/- 7.3 mm from the tandem. Simulations indicate that for 60 min treatments the applicator can heat to 41 degrees C and deliver > 5EM(43 degrees C) over 4-5 cm diameter with Tmax < 45 degrees C and 1 kg m(-3) s(-1) blood perfusion. The 41 degrees C contour diameter is reduced to 3-4 cm at 3 kg m(-3) s(-1) perfusion. Differential power control to transducer elements and sectors demonstrates tailoring of heating along the device length and in angle. Sector cuts are associated with a 14-47 degrees acoustic dead zone, depending on cut width, resulting in a approximately 2-4 degrees C temperature reduction within the dead zone below Tmax. Dead zones can be oriented for thermal protection of the rectum and bladder. Fabricated devices have acoustic efficiencies of 33.4%-51.8% with acoustic output that is well collimated in length, reflects the sectoring strategy, and is strongly correlated with temperature distributions.

CONCLUSIONS

A catheter-based ultrasound applicator was developed for endocervical implantation with locally targeted, 3-D conformal thermal delivery to the uterine cervix. Feasibility of heating clinically relevant target volumes was demonstrated with power control along the device length and in angle to treat the cervix with minimal thermal dose delivery to the rectum and bladder.

Enhanced reduction in cell viability by hyperthermia induced by magnetic nanoparticles

Colloidal suspensions of iron oxide magnetic nanoparticles are known to dissipate energy when exposed to an oscillating magnetic field. Such energy dissipation can be employed to locally raise temperature inside a tumor between 41°C and 45°C (hyperthermia) to promote cell death, a treatment known as magnetic fluid hyperthermia (MFH). This work seeks to quantify differences between MFH and hot-water hyperthermia (HWH) in terms of reduction in cell viability using two cancer cell culture models, Caco-2 (human epithelial colorectal adenocarcinoma) and MCF-7 (human breast cancer). Magnetite nanoparticles were synthesized via the co-precipitation method and functionalized with adsorbed carboxymethyl dextran. Cytotoxicity studies indicated that in the absence of an oscillating magnetic field, cell viability was not affected at concentrations of up to 0.6 mg iron oxide/mL. MFH resulted in a significant decrease in cell viability when exposed to a magnetic field for 120 minutes and allowed to rest for 48 hours, compared with similar field applications, but with shorter resting time. The results presented here suggest that MFH most likely induces apoptosis in both cell types. When compared with HWH, MFH produced a significant reduction in cell viability, and these effects appear to be cell-type related.