Realistic biological approaches for improving thermoradiotherapy

Treatment of Pelvic and Spinal Bone Metastases: Radiotherapy and Hyperthermia Alone vs. in Combination

Painful pelvic and spinal bone metastases are a considerable challenge for doctors and patients. Conventional therapies include morphine-equivalent medication (MeM) and local radiotherapy (RT), but these interventions are not always successful. More recently, hyperthermia (HT) has been applied to complement RT and MeM, and this complex approach has shown promising synergistic results. The objective of our study was to present the results of RT combined with a special kind of HT (modulated electrohyperthermia, mEHT), in which some of the thermal effect is contributed by equivalent nonthermal components, drastically reducing the necessary power and energy. This retrospective study included 61 patients divided into three groups with pelvic and spinal bone metastases to compare the effects of RT and mEHT alone and in combination (RT + mEHT). A detailed evaluation of pain intensity, measured by the brief pain inventory score, MeM use, and breakthrough pain episodes, revealed no significant differences between RT and mEHT alone; thus, these individual methods were considered equivalent. However, RT + mEHT yielded significantly better results in terms of the above parameters. Clinically, mEHT has a lower risk of adverse thermal effects, and due to its efficacy, mEHT can be used to treat RT-resistant lesions.

Extirpating the cancer stem cell hydra: Differentiation therapy and Hyperthermia therapy for targeting the cancer stem cell hierarchy

Ever since the discovery of cancer stem cells (CSCs), they have progressively attracted more attention as a therapeutic target. Like the mythical hydra, this subpopulation of cells seems to contribute to cancer immortality, spawning more cells each time that some components of the cancer cell hierarchy are destroyed. Traditional modalities focusing on cancer treatment have emphasized apoptosis as a route to eliminate the tumor burden. A major problem is that cancer cells are often in varying degrees of dedifferentiation contributing to what is known as the CSCs hierarchy and cells which are known to be resistant to conventional therapy. Differentiation therapy is an experimental therapeutic modality aimed at the conversion of malignant phenotype to a more benign one. Hyperthermia therapy (HT) is a modality exploiting the changes induced in cells by the application of heat produced to aid in cancer therapy. While differentiation therapy has been successfully employed in the treatment of acute myeloid leukemia, it has not been hugely successful for other cancer types. Mounting evidence suggests that hyperthermia therapy may greatly augment the effects of differentiation therapy while simultaneously overcoming many of the hard-to-treat facets of recurrent tumors. This review summarizes the progress made so far in integrating hyperthermia therapy with existing modules of differentiation therapy. The focus is on studies related to the successful application of both hyperthermia and differentiation therapy when used alone or in conjunction for hard-to-treat cancer cell niche with emphasis on combined approaches to target the CSCs hierarchy.

Does the combination of hyperthermia with low LET (linear energy transfer) radiation induce anti-tumor effects equivalent to those seen with high LET radiation alone?

INTRODUCTION

The combination of hyperthermia with low LET (linear energy transfer) radiation may have similar anti-tumor effects as high LET radiation alone. This pre-clinical study determined the optimal heating temperature and time interval between radiation and heat to achieve this equivalent effect.

METHODS

C3H mammary carcinomas (200 mm³ in size) growing in the right rear foot of CDF1 mice was used in all experiments. Tumors were locally irradiated with graded doses of either 240 kV ortho- or 6 MV mega-voltage X-rays to produce full dose-response curves. Heating (41.0-43.5 °C; 60 min) was achieved by immersing the tumor bearing foot in a water-bath applied at the same time, or up to 4-hours after, irradiating. The endpoint was the percentage of mice showing local tumor control at 90 days, with enhancements calculated from the ratios of the radiation doses causing 50% tumor control (± 95% confidence intervals).

RESULTS

Previous published results in this tumor model reported that carbon ions were 1.3-1.7 times more effective than low LET radiation at inducing tumor control. Similar enhancements occurred with a temperature of only 41.0 °C with a simultaneous heat and radiation treatment. However, higher temperatures were needed with the introduction of any interval; at 42.5 °C, the enhancement was 2.5 with a simultaneous treatment, decreasing to a value within the carbon ion range with a 4-hour interval.

CONCLUSIONS

Combining hyperthermia with low LET radiation can be as effective as high LET at inducing tumor control, but the temperature needed depended on the time interval between the two modalities.

The effect of thermal dose on hyperthermia-mediated inhibition of DNA repair through homologous recombination

Hyperthermia has a number of biological effects that sensitize tumors to radiotherapy in the range between 40-44 °C. One of these effects is heat-induced degradation of BRCA2 that in turn causes reduced RAD51 focus formation, which results in an attenuation of DNA repair through homologous recombination. Prompted by this molecular insight into how hyperthermia attenuates homologous recombination, we now quantitatively explore time and temperature dynamics of hyperthermia on BRCA2 levels and RAD51 focus formation in cell culture models, and link this to their clonogenic survival capacity after irradiation (0-6 Gy). For treatment temperatures above 41 °C, we found a decrease in cell survival, an increase in sensitization towards irradiation, a decrease of BRCA2 protein levels, and altered RAD51 focus formation. When the temperatures exceeded 43 °C, we found that hyperthermia alone killed more cells directly, and that processes other than homologous recombination were affected by the heat. This study demonstrates that optimal inhibition of HR is achieved by subjecting cells to hyperthermia at 41-43 °C for 30 to 60 minutes. Our data provides a guideline for the clinical application of novel combination treatments that could exploit hyperthermia's attenuation of homologous recombination, such as the combination of hyperthermia with PARP-inhibitors for non-BRCA mutations carriers.

Commentary on the clinical and preclinical dosage limits of interstitially administered magnetic fluids for therapeutic hyperthermia based on current practice and efficacy models

We offer a critique of what constitutes a suitable dosage limit, in both clinical and preclinical studies, for interstitially administered magnetic nanoparticles in order to enable therapeutic hyperthermia under the action of an externally applied alternating magnetic field. We approach this first from the perspective of the currently approved clinical dosages of magnetic nanoparticles in the fields of MRI contrast enhancement, sentinel node detection, iron replacement therapy and magnetic thermoablation. We compare this to a simple analytical model of the achievable hyperthermia temperature rise in both humans and animals based on the interstitially administered dose, the heating and dispersion characteristics of the injected fluid, and the strength and frequency of the applied magnetic field. We show that under appropriately chosen conditions a therapeutic temperature rise is achievable in clinically relevant situations. We also show that in such cases it may paradoxically be harder to achieve the same therapeutic temperature rise in a preclinical model. We comment on the implications for the evidence-based translation of hyperthermia based interventions from the laboratory to the clinic.

Enhancing radiosensitisation of BRCA2-proficient and BRCA2-deficient cell lines with hyperthermia and PARP1-i

Poly(ADP-ribose)polymerase1 (PARP1) is an important enzyme in regulating DNA replication. Inhibition of PARP1 can lead to collapsed DNA forks which subsequently causes genomic instability, making DNA more susceptible in developing fatal DNA double strand breaks. PARP1-induced DNA damage is generally repaired by homologous recombination (HR), in which BRCA2 proteins are essential. Therefore, BRCA2-deficient tumour cells are susceptible to treatment with PARP1-inhibitors (PARP1-i). Recently, BRCA2 was shown to be down-regulated by hyperthermia (HT) temporarily, and this consequently inactivated HR for several hours. In this study, we investigated whether HT exclusively interferes with HR by analysing thermal radiosensitisation of BRCA2-proficient and deficient cells. After elucidating the equitoxicity of PARP1-i on BRCA2-proficient and deficient cells, we studied the cell survival, apoptosis, DNA damage (γ-H2AX foci and comet assay) and cell cycle distribution after different treatments. PARP1-i sensitivity strongly depends on the BRCA2 status. BRCA2-proficient and deficient cells are radiosensitised by HT, indicating that HT does not exclusively act by inhibition of HR. In all cell lines, the addition of HT to radiotherapy and PARP1-i resulted in the lowest cell survival, the highest levels of DNA damage and apoptotic levels compared to duo-modality treatments. Concluding, HT not only inhibits HR, but also has the capability of radiosensitising BRCA2-deficient cells. Thus, in case of BRCA2-mutation carriers, combining HT with PARP1-i may boost the treatment efficacy. This combination therapy would be effective for all patients with PARP1-i regardless of their BRCA status.

Targeting therapy-resistant cancer stem cells by hyperthermia

Eradication of all malignant cells is the ultimate but challenging goal of anti-cancer treatment; most traditional clinically-available approaches fail because there are cells in a tumour that either escape therapy or become therapy-resistant. A subpopulation of cancer cells, the cancer stem cells (CSCs), is considered to be of particular significance for tumour initiation, progression and metastasis. CSCs are considered in particular to be therapy-resistant and may drive disease recurrence, which positions CSCs in the focus of anti-cancer research, but successful CSC-targeting therapies are limited. Here, we argue that hyperthermia - a therapeutic approach based on local heating of a tumour - is potentially beneficial for targeting CSCs in solid tumours. First, hyperthermia has been described to target cells in hypoxic and nutrient-deprived tumour areas where CSCs reside and ionising radiation and chemotherapy are least effective. Second, hyperthermia can modify factors that are essential for tumour survival and growth, such as the microenvironment, immune responses, vascularisation and oxygen supply. Third, hyperthermia targets multiple DNA repair pathways, which are generally upregulated in CSCs and protect them from DNA-damaging agents. Addition of hyperthermia to the therapeutic armamentarium of oncologists may thus be a promising strategy to eliminate therapy-escaping and -resistant CSCs.

Homologous recombination preferentially repairs heat-induced DNA double-strand breaks in mammalian cells

PURPOSE

Heat shock induces DNA double-strand breaks (DSBs), but the precise mechanism of repairing heat-induced damage is unclear. Here, we investigated the DNA repair pathways involved in cell death induced by heat shock.

MATERIALS AND METHODS

B02, a specific inhibitor of human RAD51 (homologous recombination; HR), and NU7026, a specific inhibitor of DNA-PK (non-homologous end-joining; NHEJ), were used for survival assays of human cancer cell lines with different p53-gene status. Mouse embryonic fibroblasts (MEFs) lacking Lig4 (NHEJ) and/or Rad54 (HR) were used for survival assays and a phosphorylated histone H2AX at Ser139 (γH2AX) assay. MEFs lacking Rad51d (HR) were used for survival assays. SPD8 cells were used to measure HR frequency after heat shock.

RESULTS

Human cancer cells were more sensitive to heat shock in the presence of B02 despite their p53-gene status, and the effect of B02 on heat sensitivity was specific to the G₂ phase. Rad54-deficient MEFs were sensitive to heat shock and showed prolonged γH2AX signals following heat shock. Rad51d-deficient MEFs were also sensitive to heat shock. Moreover, heat shock-stimulated cells had increased HR.

CONCLUSIONS

The HR pathway plays an important role in the survival of mammalian cells against death induced by heat shock via the repair of heat-induced DNA DSBs.

Photoinduced Mild Hyperthermia and Synergistic Chemotherapy by One-Pot-Synthesized Docetaxel-Loaded Poly(lactic-co-glycolic acid)/Polypyrrole Nanocomposites

Mild hyperthermia has shown great advantages when combined with chemotherapy. The development of a multifunctional platform for the integration of mild hyperthermia capability into a drug-loading system is a key issue for cancer multimodality treatment application. Herein, a facile one-pot in situ fabrication protocol of docetaxel (DTX)-loaded poly(lactic-co-glycolic acid) (PLGA)/polypyrrole (PPy) nanocomposites was developed. While the PLGA nanoparticles (NPs) allow efficient drug loading, the PPy nanobulges embedded within the surface of the PLGA NPs, formed by in situ pyrrole polymerization without the introduction of other template agents, can act as ideal mediators for photoinduced mild hyperthermia. Physiochemical characterizations of the as-prepared nanocomposites, including structure, morphology, photothermal effects, and an in vitro drug release profile, were systematically investigated. Further, 2-deoxyglucose-terminated poly(ethylene glycol) (PEG) was anchored onto the surface of the nanocomposites to endow the nanoplatform with targeting ability to tumor cells, which resulted in a 17-fold increase of NP internalization within human breast cancer cells (MCF-7) as competed with PEG-modified nanocomposites. Mild hyperthermia can be successfully mediated by the nanoplatform, and the temperature can be conveniently controlled by careful modulation of the PPy contents within the nanocomposites or the laser power density. Importantly, we have demonstrated that MCF-7 cells, which are markedly resistant to heat treatment of traditional water-bath hyperthermia, became sensitive to the PLGA/PPy nanocomposite-mediated photothermal therapy under the same mild-temperature hyperthermia. Moreover, DTX-loaded PLGA/PPy-nanocomposite-induced mild hyperthermia can strongly enhance drug cytotoxicity to MCF-7 cells. Under the same thermal dose, photoinduced hyperthermia can convert the interaction between hyperthermia and drug treatment from interference to synergism. This is the first report on the one-pot synthesis of PLGA/PPy nanocomposites by in situ pyrrole polymerization, and such a multifunctional nanoplatform is demonstrated as a high-potential agent for photoinduced mild hyperthermia and enhanced chemotherapy.