Caveolin-1 and CDC42 mediated endocytosis of silica-coated iron oxide nanoparticles in HeLa cells.

Nanomedicine is a rapidly growing field in nanotechnology, which has great potential in the development of new therapies for numerous diseases. For example iron oxide nanoparticles are in clinical use already in the thermotherapy of brain cancer. Although it has been shown, that tumor cells take up these particles in vitro, little is known about the internalization routes. Understanding of the underlying uptake mechanisms would be very useful for faster and precise development of nanoparticles for clinical applications. This study aims at the identification of key proteins, which are crucial for the active uptake of iron oxide nanoparticles by HeLa cells (human cervical cancer) as a model cell line. Cells were transfected with specific siRNAs against Caveolin-1, Dynamin 2, Flotillin-1, Clathrin, PIP5Kα and CDC42. Knockdown of Caveolin-1 reduces endocytosis of superparamagnetic iron oxide nanoparticles (SPIONs) and silica-coated iron oxide nanoparticles (SCIONs) between 23 and 41%, depending on the surface characteristics of the nanoparticles and the experimental design. Knockdown of CDC42 showed a 46% decrease of the internalization of PEGylated SPIONs within 24 h incubation time. Knockdown of Dynamin 2, Flotillin-1, Clathrin and PIP5Kα caused no or only minor effects. Hence endocytosis in HeLa cells of iron oxide nanoparticles, used in this study, is mainly mediated by Caveolin-1 and CDC42. It is shown here for the first time, which proteins of the endocytotic pathway mediate the endocytosis of silica-coated iron oxide nanoparticles in HeLa cells in vitro. In future studies more experiments should be carried out with different cell lines and other well-defined nanoparticle species to elucidate possible general principles.

Efficacy and safety of intratumoral thermotherapy using magnetic iron-oxide nanoparticles combined with external beam radiotherapy on patients with recurrent glioblastoma multiforme.

Therapy options at the time of recurrence of glioblastoma multiforme are often limited. We investigated whether treatment with a new intratumoral thermotherapy procedure using magnetic nanoparticles improves survival outcome. In a single-arm study in two centers, 66 patients (59 with recurrent glioblastoma) received neuronavigationally controlled intratumoral instillation of an aqueous dispersion of iron-oxide (magnetite) nanoparticles and subsequent heating of the particles in an alternating magnetic field. Treatment was combined with fractionated stereotactic radiotherapy. A median dose of 30 Gy using a fractionation of 5 × 2 Gy/week was applied. The primary study endpoint was overall survival following diagnosis of first tumor recurrence (OS-2), while the secondary endpoint was overall survival after primary tumor diagnosis (OS-1). Survival times were calculated using the Kaplan-Meier method. Analyses were by intention to treat. The median overall survival from diagnosis of the first tumor recurrence among the 59 patients with recurrent glioblastoma was 13.4 months (95% CI: 10.6-16.2 months). Median OS-1 was 23.2 months while the median time interval between primary diagnosis and first tumor recurrence was 8.0 months. Only tumor volume at study entry was significantly correlated with ensuing survival (P < 0.01). No other variables predicting longer survival could be determined. The side effects of the new therapeutic approach were moderate, and no serious complications were observed. Thermotherapy using magnetic nanoparticles in conjunction with a reduced radiation dose is safe and effective and leads to longer OS-2 compared to conventional therapies in the treatment of recurrent glioblastoma.

Magnetic nanoparticle hyperthermia for prostate cancer.

Magnetic nanoparticles are increasingly used for clinical applications such as drug delivery, magnetic resonance imaging and magnetic fluid hyperthermia. A novel method of interstitial heating of tumours following direct injection of magnetic nanoparticles has been evaluated in humans in recent clinical trials. In prostate cancer this approach has been investigated in two separate phase I studies, employing magnetic nanoparticle thermotherapy alone and in combination with permanent seed brachytherapy. The feasibility and good tolerability was shown in both trials, using the first prototype of an alternating magnetic field applicator. As with any other heating technique, this novel approach requires specific tools for planning, quality control and thermal monitoring, based on appropriate imaging and modelling techniques. In these first clinical trials a newly developed method for planning and non-invasive calculations of the 3-dimensional temperature distribution based on computed tomography was validated. Limiting factors of the new approach at present are patient discomfort at high magnetic field strengths and irregular intratumoural heat distribution. Until these limitations are overcome and thermoablation can safely be applied as a monotherapy, this treatment modality is being evaluated in combination with irradiation in patients with localised prostate cancer.

Modification of aminosilanized superparamagnetic nanoparticles: feasibility of multimodal detection using 3T MRI, small animal PET, and fluorescence imaging.

PURPOSE: The aim of our study was to modify an aminosilane-coated superparamagnetic nanoparticle for cell labeling and subsequent multimodal imaging using magnetic resonance imaging (MRI), positron emission tomography (PET), and fluorescent imaging in vivo. PROCEDURES: We covalently bound the transfection agent HIV-1 tat, the fluorescent dye fluorescein isothiocyanate, and the positron-emitting radionuclide gallium-68 to the particle and injected them intravenously into Wistar rats, followed by animal PET and MRI at 3.0 T. As a proof of principle hepatogenic HuH7 cells were labeled with the particles and observed for cell toxicity as well as detectability by MRI and biodistribution in vivo. RESULTS: PET imaging and MRI revealed increasing hepatic and splenic accumulation of the particles over 24 h. Adjacent in vitro studies in hepatogenic HuH7 cells showed a rapid intracellular accumulation of the particles with high labeling efficiency and without any signs of toxicity. In vivo dissemination of the labeled cells could be followed by dynamic biodistribution studies. CONCLUSIONS: We conclude that our modified superparamagnetic nanoparticles are stable under in vitro and in vivo conditions and are therefore applicable for efficient cell labeling and subsequent multimodal molecular imaging. Moreover, their multiple free amino groups suggest the possibility for further modifications and might provide interesting opportunities for various research fields.

Hyperthermia classic commentary: 'Inductive heating of ferrimagnetic particles and magnetic fluids: Physical evaluation of their potential for hyperthermia' by Andreas Jordan et al., International Journal of Hyperthermia, 1993;9:51-68.

In order to increase the specific power absorption (SAR) in deep seated tumors, the idea was born to use AC magnetic fields in combination with magnetic particles instead of conventional E-field dominant systems. It was found, that nanoscaled particles were superior to micron-sized, multi-domain particles in terms of SAR due to different mechanisms how the field energy is converted into heat. Crucial parameters were identified for the human application of the method, such as the AC magnetic field amplitude and frequency, the nanoparticle composition and size distribution. Based on these physical and chemical relationships, a new thermotherapy method has been developed to heat up deep regional tumors using aqueous dispersions of iron oxide nanoparticles (magnetic fluids). Several clinical studies were initiated using this new heating technology. The results of the most advanced efficacy study for recurrent glioblastoma multiforme patients in combination with conventional radiation therapy are expected at the end of this year, 16 years after publication of this fundamental paper.

A systematic proteomic study of irradiated DNA repair deficient Nbn-mice.

BACKGROUND: The NBN gene codes for the protein nibrin, which is involved in the detection and repair of DNA double strand breaks (DSBs). The NBN gene is essential in mammals. METHODOLOGY/PRINCIPAL FINDINGS: We have used a conditional null mutant mouse model in a proteomics approach to identify proteins with modified expression levels after 4 Gy ionizing irradiation in the absence of nibrin in vivo. Altogether, amongst approximately 8,000 resolved proteins, 209 were differentially expressed in homozygous null mutant mice in comparison to control animals. One group of proteins significantly altered in null mutant mice were those involved in oxidative stress and cellular redox homeostasis (p<0.0001). In substantiation of this finding, analysis of Nbn null mutant fibroblasts indicated an increased production of reactive oxygen species following induction of DSBs. CONCLUSIONS/SIGNIFICANCE: In humans, biallelic hypomorphic mutations in NBN lead to Nijmegen breakage syndrome (NBS), an autosomal recessive genetic disease characterised by extreme radiosensitivity coupled with growth retardation, immunoinsufficiency and a very high risk of malignancy. This particularly high cancer risk in NBS may be attributable to the compound effect of a DSB repair defect and oxidative stress.

Clinical applications of magnetic nanoparticles for hyperthermia.

Magnetic fluids are increasingly used for clinical applications such as drug delivery, magnetic resonance imaging and magnetic fluid hyperthermia. The latter technique that has been developed as a cancer treatment for several decades comprises the injection of magnetic nanoparticles into tumors and their subsequent heating in an alternating magnetic field. Depending on the applied temperature and the duration of heating this treatment either results in direct tumor cell killing or makes the cells more susceptible to concomitant radio- or chemotherapy. Numerous groups are working in this field worldwide, but only one approach has been tested in clinical trials so far. Here, we summarize the clinical data gained in these studies on magnetic fluid induced hyperthermia.

[Thermal therapy of prostate cancer using magnetic nanoparticles]. / Termoterapia en cáncer de próstata mediante el uso de nanopartículas magnéticas.

A novel method of interstitial heating using magnetic nanoparticles and a direct injection technique has been evaluated in human cancers in recent clinical trials. In prostate cancer, this approach was investigated in two separate phase-I-studies, employing magnetic nanoparticle thermotherapy alone and in combination with permanent seed brachytherapy. The feasibility and good tolerability was shown in both trials, using the first prototype of a magnetic field applicator. As with any other heating technique, this novel approach requires specific tools for planning, quality control and thermal monitoring, based on appropriate imaging and modelling techniques. In these first clinical trials, a newly developed method for planning and non-invasive calculations of the 3-dimensional temperature distribution based on computed tomography could be validated. Limiting factors of this approach at present are patient discomfort at high magnetic field strengths and suboptimal intratumoral distribution of nanoparticles. Until these limitations will be overcome and thermal ablation can safely be applied as a monotherapy, this treatment modality is being evaluated in combination with irradiation in patients with localized prostate cancer.

Intracranial thermotherapy using magnetic nanoparticles combined with external beam radiotherapy: results of a feasibility study on patients with glioblastoma multiforme.

We aimed to evaluate the feasibility and tolerability of the newly developed thermotherapy using magnetic nanoparticles on recurrent glioblastoma multiforme. Fourteen patients received 3-dimensional image guided intratumoral injection of aminosilane coated iron oxide nanoparticles. The patients were then exposed to an alternating magnetic field to induce particle heating. The amount of fluid and the spatial distribution of the depots were planned in advance by means of a specially developed treatment planning software following magnetic resonance imaging (MRI). The actually achieved magnetic fluid distribution was measured by computed tomography (CT), which after matching to pre-operative MRI data enables the calculation of the expected heat distribution within the tumor in dependence of the magnetic field strength. Patients received 4-10 (median: 6) thermotherapy treatments following instillation of 0.1-0.7 ml (median: 0.2) of magnetic fluid per ml tumor volume and single fractions (2 Gy) of a radiotherapy series of 16-70 Gy (median: 30). Thermotherapy using magnetic nanoparticles was tolerated well by all patients with minor or no side effects. Median maximum intratumoral temperatures of 44.6 degrees C (42.4-49.5 degrees C) were measured and signs of local tumor control were observed. In conclusion, deep cranial thermotherapy using magnetic nanoparticles can be safely applied on glioblastoma multiforme patients.

Thermotherapy of prostate cancer using magnetic nanoparticles: feasibility, imaging, and three-dimensional temperature distribution.

OBJECTIVES: To investigate the feasibility of thermotherapy using biocompatible superparamagnetic nanoparticles in patients with locally recurrent prostate cancer and to evaluate an imaging-based approach for noninvasive calculations of the three-dimensional temperature distribution. METHODS: Ten patients with locally recurrent prostate cancer following primary therapy with curative intent were entered into a prospective phase 1 trial. The magnetic fluid was injected transperineally into the prostates according to a preplan. Patients received six thermal therapies of 60-min duration at weekly intervals using an alternating magnetic field applicator. A method of three-dimensional thermal analysis based on computed tomography (CT) of the prostates was developed and correlated with invasive and intraluminal temperature measurements. The sensitivity of nanoparticle detection by means of CT was investigated in phantoms. RESULTS: The median detection rate of iron oxide nanoparticles in tissue specimens using CT was 89.5% (range: 70-98%). Maximum temperatures up to 55 degrees C were achieved in the prostates. Median temperatures in 20%, 50%, and 90% of the prostates were 41.1 degrees C (range: 40.0-47.4 degrees C), 40.8 degrees C (range: 39.5-45.4 degrees C), and 40.1 degrees C (range: 38.8-43.4 degrees C), respectively. Median urethral and rectal temperatures were 40.5 degrees C (range: 38.4-43.6 degrees C) and 39.8 degrees C (range: 38.2-43.4 degrees C). The median thermal dose was 7.8 (range: 3.5-136.4) cumulative equivalent minutes at 43 degrees C in 90% of the prostates. CONCLUSION: The heating technique using magnetic nanoparticles was feasible. Hyperthermic to thermoablative temperatures were achieved in the prostates at 25% of the available magnetic field strength, indicating a significant potential for higher temperatures. A noninvasive thermometry method specific for this approach could be developed, which may be used for thermal dosimetry in future studies.

Magnetic nanoparticles for intracranial thermotherapy.

Thermotherapy using magnetic nanoparticles, also termed nanotherapy, is a new therapeutic concept in which tumor cells are damaged via local heat application. The principle of this method is direct injection of a magnetic fluid into a tumor and its subsequent heating in an alternating magnetic field. The heat created this way (thermotherapy) causes either direct damage to the tumor cells (depending on temperature and reaction time) or make cells more susceptible to accompanying radio- or chemotherapy. The results of a feasibility trial (phase I) on the treatment of brain tumors (glioblastoma multiforme) are presented.

18F-FET PET for planning of thermotherapy using magnetic nanoparticles in recurrent glioblastoma.

PURPOSE: Thermotherapy using magnetic nanoparticles (nano cancer therapy) is a new concept of local tumour therapy, which is based on controlled heating of intra-tumoural injected magnetic nanoparticles. The aim of this study was to evaluate the usefulness of PET with a recently introduced amino acid tracer O-(2-[18F]fluoroethyl)-]L-tyrosine (FET) for targeting the nanoparticles implantation. MATERIALS AND METHODS: Eleven patients with glioblastoma recurrences underwent MR and FET-PET imaging for planning of the nano cancer therapy. Thereafter, the gross tumour volumes (GTV) were defined, taking into consideration the results of both imaging tools. RESULTS: The MRI-based mean GTV was 24.3 cm3 (range 2.5-59.7) and the PET-based mean GTV 31.9 cm3 (range 5.2-77.9). On the average the MRI identified an additional 8.9 +/- 4.7 cm3 and the FET-PET scan-an additional 16.5 +/- 15.2 cm3 outside of the common GTV (15.4 +/- 11.0 cm3). The mean final GTV accounted to 33.8 cm3 (range, 5.2-77.9). The additional information of FET-PET led to an increase in GTV by 22-286% in eight patients and to a decrease of 23% and 26%, respectively, in two patients. In one patient, the final GTV was defined on the basis of MRI data only. CONCLUSIONS: FET-PET adds important information on the actual tumour volume in recurrent glioblastomas and is highly valuable for defining the target volume for the nano cancer therapy.

Local arterial infusion of superparamagnetic iron oxide particles in hepatocellular carcinoma: A feasibility and 3.0 T MRI study.

OBJECTIVES: We sought to prove feasibility of selective arterial infusion of superparamagnetic iron oxide (SPIO) particles in patients with hepatocellular carcinoma (HCC). MATERIALS AND METHODS: We studied 13 patients with HCC who underwent modified transarterial chemoembolization (TACE). Six patients received concurrent infusion of Ferucarbotran (Resovist, Schering, Berlin, Germany) in tumor-feeding arteries, and another 6 received MFL AS (MagForce, Nanotechnologies, Berlin, Germany). The iron content of both dispersions was 3.92 mg. One patient served as a control. All patients underwent magnetic resonance imaging (MRI) as baseline and immediate follow-up investigation. RESULTS: Selective arterial infusion of both SPIO particles resulted in significant intratumoral signal intensity decrease on T1-weighted sequences (P < 0.0001), which was greater after MagForce infusion compared with Resovist (P = 0.002). Only minimal amounts of dispersed particles were found in adjacent normal liver parenchyma. No change in intratumoral signal intensity was noted when ferromagnetic particles were omitted. CONCLUSIONS: Modified TACE with selective arterial infusion of SPIO particles can be used for precise tumor targeting in patients with HCC, for which MagForce appeared superior to Resovist.

The effect of thermotherapy using magnetic nanoparticles on rat malignant glioma.

Thermotherapy using magnetic nanoparticles is a new technique for interstitial hyperthermia and thermoablation based on magnetic field-induced excitation of biocompatible superparamagnetic nanoparticles. To evaluate the potential of this technique for minimally invasive treatment, we carried out a systematic analysis of its effects on experimental glioblastoma multiforme in a rat tumor model. Tumors were induced by implantation of RG-2-cells into the brains of 120 male Fisher rats. Animals were randomly allocated to 10 groups of 12 rats each, including controls. Animals received two thermotherapy treatments following a single intratumoral injection of two different magnetic fluids (dextran- or aminosilane-coated iron-oxide nanoparticles). Treatment was carried out on days four and six after tumor induction using an alternating magnetic field applicator system operating at a frequency of 100 kHz and variable field strength of 0-18 kA/m. The effectiveness of treatment was determined by the survival time of the animals and histopathological examinations of the brain and the tumor.Thermotherapy with aminosilane-coated nanoparticles led up to 4.5-fold prolongation of survival over controls, while the dextran-coated particles did not indicate any advantage. Intratumoral deposition of the aminosilane-coated particles was found to be stable, allowing for serial thermotherapy treatments without repeated injection. Histological and immunohistochemical examinations after treatment revealed large necrotic areas close to particle deposits, a decreased proliferation rate and a reactive astrogliosis adjacent to the tumor.Thus, localized interstitial thermotherapy with magnetic nanoparticles has an antitumoral effect on malignant brain tumors. This method is suitable for clinical use and may be a novel strategy for treating malignant glioma, which cannot be treated successfully today. The optimal treatment schedules and potential combinations with other therapies need to be defined in further studies.

Magnetic nanoparticles for interstitial thermotherapy--feasibility, tolerance and achieved temperatures.

BACKGROUND: The concept of magnetic fluid hyperthermia is clinically evaluated after development of the whole body magnetic field applicator MFH 300F and the magnetofluid MFL 082AS. This new system for localized thermotherapy is suitable either for hyperthermia or thermoablation. The magnetic fluid, composed of iron oxide nanoparticles dispersed in water, must be distributed in the tumour and is subsequently heated by exposing to an alternating magnetic field in the applicator. We performed a feasibility study with 22 patients suffering from heavily pretreated recurrences of different tumour entities, where hyperthermia in conjunction with irradiation and/or chemotherapy was an option. The potential to estimate (by post-implantation analyses) and to achieve (by improving the technique) a satisfactory temperature distribution was evaluated in dependency on the implantation technique. MATERIAL AND METHODS: Three implantation methods were established: Infiltration under CT fluoroscopy (group A), TRUS (transrectal ultrasound)--guided implantation with X-fluoroscopy (group B) and intra-operative infiltration under visual control (group C). In group A and B the distribution of the nanoparticles can be planned prior to implantation on the basis of three-dimensional image datasets. The specific absorption rates (SAR in W/kg) can be derived from the particle distribution imaged via CT together with the actual H-field strength (in kA/m). The temperature distribution in the tumour region is calculated using the bioheat-transfer equation assessing a mean perfusion value, which is determined by matching calculated temperatures to direct (invasive or endoluminal) temperature measurements in reference points in or near the target region. RESULTS: Instillation of the magnetic fluid and the thermotherapy treatments were tolerated without or with only moderate side effects, respectively. Using tolerable H-field-strengths of 3.0-6.0 kA/m in the pelvis, up to 7.5 kA/m in the thoracic and neck region and >10.0 kA/m for the head, we achieved SAR of 60-380 W/kg in the target leading to a 40 degrees C heat-coverage of 86%. However, the coverage with > or =42 degrees C is unsatisfactory at present (30% of the target volume in group A and only 0.2% in group B). CONCLUSION: Further improvement of the temperature distribution is required by refining the implantation techniques or simply by increasing the amount of nanofluid or elevation of the magnetic field strength. From the actual nanoparticle distribution and derived temperatures we can extrapolate, that already a moderate increase of the H-field by only 2 kA/m would significantly improve the 42 degrees C coverage towards 100% (98%). This illustrates the great potential of the nanofluid-based heating technology.

Thermotherapy using magnetic nanoparticles combined with external radiation in an orthotopic rat model of prostate cancer.

BACKGROUND: We evaluated the effects of thermotherapy using magnetic nanoparticles, also referred to as magnetic fluid hyperthermia (MFH), combined with external radiation, in the Dunning model of prostate cancer. METHODS: Orthotopic tumors were induced in 96 male Copenhagen rats. Animals were randomly allocated to eight groups, including controls and groups for dose-finding studies of external radiation. Treatment groups received two serial thermotherapy treatments following a single intratumoral injection of magnetic fluid or thermotherapy followed by external radiation (10 Gy). On day 20, after tumor induction, tumor weights in the treatment and control groups were compared and iron measurements in selected organs were carried out. RESULTS: Mean maximal and minimal intratumoral temperatures obtained were 58.7 degrees C (centrally) and 42.7 degrees C (peripherally) during the first thermotherapy and 55.4 degrees C and 42.3 degrees C, respectively, during the second of two treatment sessions. Combined thermotherapy and radiation with 20 Gy was significantly more effective than radiation with 20 Gy alone and reduced tumor growth by 87.5-89.2% versus controls. Mean iron content in the prostates on day 20 was 87.5% of the injected dose of ferrites, whereas only 2.5% was found in the liver. CONCLUSIONS: An additive effect was demonstrated for the combined treatment at a radiation dose of 20 Gy, which was equally effective in inhibiting tumor growth as radiation alone with 60 Gy. Serial heat treatments were possible without repeated injection of magnetic fluid. The optimal treatment schedules of this combination regarding temperatures, radiation dose, and fractionation need to be defined in further experimental studies.

Iodinated nitroimidazoles as radiosensitizers.

Four different nitroimidazole derivatives, with up to two iodine atoms on the imidazole ring, were investigated for their radiosensitizing potency under hypoxic conditions, in order to test whether the introduction of iodine atoms increases the radiosensitizing potency of nitroimidazoles. Misonidazole and metronidazole were used as controls. Human colonic adenocarcinoma cells were incubated with the drugs at different concentrations and for different time-periods. Photon energies of 50 kV, 60 kV and 20 MV and total radiation doses of up to 20 Gy were used. The introduction of additional iodine atoms into the nitroimidazole derivatives resulted in a strong increase in cytotoxicity of the compounds. In parallel, there were indications that the radiosensitizing potency was also increased.

Imaging of single human carcinoma cells in vitro using a clinical whole-body magnetic resonance scanner at 3.0 T.

The purpose of the present study was to examine whether single human carcinoma cells labeled with iron oxide nanoparticles could be detected by magnetic resonance (MR) imaging on a clinical 3-T scanner using a surface coil only. WiDr human colon carcinoma cells were loaded with two kinds of iron oxide nanoparticles differing by coating and size: aminosilan-coated (MagForce) and carboxy-dextran-coated particles (Resovist). The latter were preferred by the colon carcinoma cell line used here and taken up much faster (12 h) than the smaller carboxydextran-coated Resovist (48 h). Labeled single carcinoma cells, distributed in an agarose gel in a monodisperse layer as controlled by light microscopy, became detectable as punctuate signal extinctions when using a small circularly polarized surface coil in conjunction with a T(2)*-weighted GE sequence at 3 T. The threshold for the detectability of labeled colon carcinoma cells ranged at a load of 4-5 mug iron/10(6) cells. Obviating the need for special hardware additions, this study opens a new lane for single-cell tracking on clinical 3-T MR scanners amenable to patient studies.

Selection and characterization of heat-resistant variants of multidrug-resistant human gastric carcinoma cell lines.

AIM: To generate heat resistant variants selected from established human gastric carcinoma cell lines exhibiting different types of multidrug resistance (MDR) phenotype, i.e. EPG85-257P, the drug sensitive parental cell-line, EPG85-257RDB, a classical MDR subline and EPG85-257RNOV, which is an atypical multidrug resistant subline. METHODS: Thermoresistance was induced by stepwise increase of the growth temperature from 37.0 to 39.4 degrees C. Thermoresistance was determined by change of population doubling time (PDT) and clonogenic survival after acute hyperthermia at 42, 43, 44 and 45 degrees C. RESULTS: Most of the cells exhibited necrosis at elevated culture temperature. The PDT of the surviving thermoresistant variants were increased two-fold (EPG85-257P-TR) and 1.2-fold (EPG85-257RNOV-TR), respectively. No PDT change was observed with the lowest thermoresistant subline EPG85-257RDB-TR. Dose response curves after acute hyperthermia indicated a stable increase of thermotolerance of the parental cell line and the atypical MDR subline (50-90-fold at 45 degrees C), but not of the classical MDR subline, which was only increased at 43 degrees C (3-4-fold). Acquired thermoresistance did not change after freezing/thawing procedures. CONCLUSION: All cell lines achieved chronically induced thermoresistance. Thermotolerance after acute hyperthermia was present in the drug sensitive parental cell line and the atypical MDR subline, but not in cells exhibiting a classical MDR phenotype.

Magnetic fluid hyperthermia (MFH)reduces prostate cancer growth in the orthotopic Dunning R3327 rat model.

BACKGROUND: Magnetic fluid hyperthermia (MFH) is a new technique for interstitial hyperthermia or thermoablation based on AC magnetic field-induced excitation of biocompatible superparamagnetic nanoparticles. Preliminary studies in the Dunning tumor model of prostate cancer have demonstrated the feasibility of MFH in vivo. To confirm these results and evaluate the potential of MFH as a minimally invasive treatment of prostate cancer we carried out a systematic analysis of the effects of MFH in the orthotopic Dunning R3327 tumor model of the rat. METHODS: Orthotopic tumors were induced by implantation of MatLyLu-cells into the prostates of 48 male Copenhagen rats. Animals were randomly allocated to 4 groups of 12 rats each, including controls. Treatment animals received two MFH treatments following a single intratumoral injection of a magnetic fluid. Treatments were carried out on days 10 and 12 after tumor induction using an AC magnetic field applicator system operating at a frequency of 100 kHz and a variable field strength (0--18 kA/m). On day 20, animals were sacrificed and tumor weights in the treatment and control groups were compared. In addition, tumor growth curves were generated and histological examinations and iron measurements in selected organs were carried out. RESULTS: Maximum intratumoral temperatures of over 70 degrees C could be obtained with MFH at an AC magnetic field strength of 18 kA/m. At a constant field strength of 12.6 kA/m, mean maximal and minimal intratumoral temperatures recorded were 54.8 degrees C (centrally) and 41.2 degrees C (peripherally). MFH led to an inhibition of tumor growth of 44%-51% over controls. Mean iron content in the prostates of treated and untreated (injection of magnetic fluids but no AC magnetic field exposure) animals was 82.5%, whereas only 5.3% of the injected dose was found in the liver, 1.0% in the lung, and 0.5% in the spleen. CONCLUSIONS: MFH led to a significant growth inhibition in this orthotopic model of the aggressive MatLyLu tumor variant. Intratumoral deposition of magnetic fluids was found to be stable, allowing for serial MFH treatments without repeated injection. The optimal treatment schedules and temperatures for MFH need to be defined in further studies.