Hyperthermia for the treatment of brain tumors

Modulated Electrohyperthermia in Integrative Cancer Treatment for Relapsed Malignant Glioblastoma and Astrocytoma: Retrospective Multicenter Controlled Study

BACKGROUND

There are interesting studies on glioma therapy with modulated electrohyperthermia (mEHT), which combines heat therapy with an electric field. Clinical researchers not only found the mEHT method feasible for palliation but also reported evidence of therapeutic response.

PURPOSE

To study the efficacy and safety of mEHT for the treatment of relapsed malignant glioma and astrocytoma versus best supportive care (BSC).

METHODS

We collected data retrospectively on 149 patients affected by malignant glioma and astrocytoma. Inclusion criteria were informed consent signed; >18 years old; histological diagnosis of malignant glioma or astrocytoma; relapsed after surgery, adjuvant temozolomide-based chemotherapy, and radiotherapy; and indication for treatment with mEHT in palliative setting. mEHT was performed with capacitive coupling technique keeping the skin surface at 26°C and the tumor temperature at 40°C to 42.5°C for > 90% of treatment duration (20-60 minutes). The applied power was 40 to 150 W using a step-up heating protocol. Results from patients treated with mEHT were compared with those treated with BSC.

RESULTS

A total of 149 consecutive patients were enrolled in the study, 111 (74%) had glioblastoma multiforme (GBM), and 38 (26%) had astrocytoma (AST). mEHT was performed for 28 (25%) of GBM and 24 (63%) of AST patients. Tumor response at the 3-month follow-up was observed in 29% and 48% of GBM and AST patients after mEHT, and in 4% and 10% of GBM and AST patients after BSC, respectively. The survival rate at first and second year in the mEHT group was 77.3% and 40.9% for AST, and 61% and 29% for GBM, respectively. The 5-year overall survival of AST was 83% after mEHT versus 25% after BSC and 3.5% after mEHT versus 1.2% after BSC for GBM. The median overall survival of mEHT was 14 months (range 2-108 months) for GBM and 16.5 months (range 3-156 months) for the AST group. We observed 4 long-term survivors in the AST and 2 in the GBM group. Two of the long survivors in AST and 1 in GBM group were treated by mEHT.

CONCLUSIONS

mEHT in integrative therapy may have a promising role in the treatment and palliation of relapsed GBM and AST.

Mild heat shock induces autophagic growth arrest, but not apoptosis in U251-MG and U87-MG human malignant glioma cells

Although hyperthermia has been used as a treatment of malignant brain tumors, it is not yet clear what is the mechanism of the cell growth inhibition by heat shock, especially by the temperature which has clinically been applied to tumor-brain border-zone, 42-43 degrees C. Therefore, we evaluated the change of U251-MG and U87-MG human malignant glioma cells after 43 degrees C-heat shock comparing with that of 45 degrees C. First, we observed that cell growth was transiently inhibited after 43 degrees C-heat shock for 3 or 5 days, in U251-MG or U87-MG cells, respectively, which was followed by regrowth. During the period of transient growth inhibition, mild G2/M arrest was observed. However, apoptosis was observed in only 2.7% or 1.5%, of 43 degrees C-heated cells, in U251-MG or U87-MG cells, respectively. Instead, transmission electron micrography showed the formation of vacuoles, degeneration of mitochondria, and autophagosomes. Moreover, in the both cell lines, flow-cytometric analysis with acridine orange revealed the induction of acidic vesicle organelles, which was blocked by 3-methyladenine (3-MA), suggesting the involvement of autophagy. Furthermore, while 3-MA did not increase the anti-tumor effect of 43 degrees C-heat shock, bafilomycin A1, another autophagy inhibitor, did significantly enhance the effect in U251-MG cells. Taken together, mild heat shock (43 degrees C for 2 h) causes autophagy and mild G2/M arrest, but does not induce apparent apoptosis in U251-MG and U87-MG glioma cells. Inhibition of autophagy with bafilomycin A1 may increase the anti-tumor efficacy of mild heat shock against some malignant glioma cells.

Induced hyperthermia in brain tissue in vivo

Concerning hypothermia treatment, knowledge of time-temperature and of temperature distributions within tumor volumes is essential in order to obtain the maximal therapeutic effect. New techniques are being developed to overcome these difficulties. Two different heat sources, a contact Nd:YAG laser system and an automatically controlled high-frequency current system were investigated on 15 rabbits. Changes of the intracerebral temperature were registered at 4 different distances from the energy source. The intracerebral temperature was increased to 42.5 degrees C at a distance of 5 mm to the heat source and maintained at this level for a period of 60 min. The contact Nd:YAG laser system reached 42.5 degrees C at 3 W of output power. Using higher laser output power, brain tissue herniation (brain edema) through the burrhole was observed. The automatically controlled high-frequency current system reached 42.5 degrees C at 18.75 W of output current. A very small herniation of brain tissue could be observed using higher output current. Both heat sources presented an exponential decrease of the temperature profile depending on the distance. The tissue heat clearance was compensated for by intermittent laser or high-frequency current application. Both systems proved efficient for inducing hyperthermia as needed for antitumoral therapy.