Shinji Kawabata

Current status of boron neutron capture therapy of high grade gliomas and recurrent head and neck cancer

Boron neutron capture therapy (BNCT) is a biochemically targeted radiotherapy based on the nuclear capture and fission reactions that occur when non-radioactive boron-10, which is a constituent of natural elemental boron, is irradiated with low energy thermal neutrons to yield high linear energy transfer alpha particles and recoiling lithium-7 nuclei. Clinical interest in BNCT has focused primarily on the treatment of high grade gliomas, recurrent cancers of the head and neck region and either primary or metastatic melanoma. Neutron sources for BNCT currently have been limited to specially modified nuclear reactors, which are or until the recent Japanese natural disaster, were available in Japan, the United States, Finland and several other European countries, Argentina and Taiwan. Accelerators producing epithermal neutron beams also could be used for BNCT and these are being developed in several countries. It is anticipated that the first Japanese accelerator will be available for therapeutic use in 2013. The major hurdle for the design and synthesis of boron delivery agents has been the requirement for selective tumor targeting to achieve boron concentrations in the range of 20 μg/g. This would be sufficient to deliver therapeutic doses of radiation with minimal normal tissue toxicity. Two boron drugs have been used clinically, a dihydroxyboryl derivative of phenylalanine, referred to as boronophenylalanine or “BPA”, and sodium borocaptate or “BSH” (Na2B12H11SH). In this report we will provide an overview of other boron delivery agents that currently are under evaluation, neutron sources in use or under development for BNCT, clinical dosimetry, treatment planning, and finally a summary of previous and on-going clinical studies for high grade gliomas and recurrent tumors of the head and neck region. Promising results have been obtained with both groups of patients but these outcomes must be more rigorously evaluated in larger, possibly randomized clinical trials. Finally, we will summarize the critical issues that must be addressed if BNCT is to become a more widely established clinical modality for the treatment of those malignancies for which there currently are no good treatment options.

Targeted delivery of methotrexate to epidermal growth factor receptor–positive brain tumors by means of cetuximab (IMC-C225) dendrimer bioconjugates

We have constructed a drug delivery vehicle that targets the epidermal growth factor receptor (EGFR) and its mutant isoform EGFRvIII. The monoclonal antibody, cetuximab, previously known as C225, which binds to both EGFR and EGFRvIII, was covalently linked via its Fc region to a fifth-generation (G5) polyamidoamine dendrimer containing the cytotoxic drug methotrexate. As measured by mass spectrometry and UV/vis spectroscopy, the resulting bioconjugate, designated C225-G5-MTX, contained 12.6 molecules of methotrexate per unit of dendrimer. Specific binding and cytotoxicity of the bioconjugate was evaluated against the EGFR-expressing rat glioma cell line F98EGFR. Using a competitive binding assay, it was shown that the bioconjugate retained its affinity for F98EGFR cells, with a 0.8 log unit reduction in its EC50. Only cetuximab completely inhibited binding of the bioconjugate, which was unaffected by methotrexate or dendrimer. Cetuximab alone was not cytotoxic to F98EGFR cells at the concentration tested, whereas the IC50 of the bioconjugate was 220 nmol/L, which was a 2.7 log unit decrease in toxicity over that of free methotrexate. The biodistribution of C225-G5-MTX in rats bearing i.c. implants of either F98EGFR or F98WT gliomas was determined 24 hours following convection enhanced delivery of 125I-labeled bioconjugate. At this time, 62.9 ± 14.7% ID/g tumor was localized in rats bearing F98EGFR gliomas versus 11.3 ± 3.6% ID/g tumor in animals bearing F98WT gliomas, thereby showing specific molecular targeting of the tumor. The corresponding radioactivity of normal brain from the F98EGFR tumor-bearing right and non-tumor-bearing left cerebral hemisphere were 5.8 ± 3.4% and 0.8 ± 0.6% ID/g, respectively. Based on these results, therapy studies were initiated in F98EGFR glioma-bearing rats. Animals that received C225-G5-MTX, cetuximab, or free methotrexate had median survival times of 15, 17, and 19.5 days, respectively, which were not statistically different from each other or untreated control animals. Our results, which are both positive and negative, show that specific molecular targeting is but one of several requirements that must be fulfilled if an antibody-drug bioconjugate will be therapeutically useful. [Mol Cancer Ther 2006;5(1):52–9]

The distribution of vascular endothelial growth factor-producing cells in clinical radiation necrosis of the brain: pathological consideration of their potential roles.

The cell type and localization of vascular endothelial growth factor (VEGF)-producing cells in human radiation necrosis (RN) are investigated from a histopathological and immunohistochemical standpoint using clinical specimens. Eighteen surgical specimens of symptomatic RN in the brain were retrospectively reviewed. These cases included different original histological tumor types and were treated with different radiation modalities. Histological analyses were performed using hematoxylin and eosin (H&E) staining, and anti-VEGF and anti-hypoxia-inducible factor (HIF)-1α immunohistochemistry. H&E staining showed marked angiogenesis and reactive astrocytosis at the perinecrotic area. The most prominent vasculature in this area was identified as telangiectasis. Immunohistochemistry indicated that HIF-1α was expressed predominantly in the perinecrotic area and that a large majority of VEGF-expressing cells were reactive astrocytes intensively distributed in this area. VEGF produced by the reactive astrocytes localized mainly in the perinecrotic area might be a major cause of both angiogenesis and the subsequent perilesional edema typically found in RN of the brain. The benefits of anti-VEGF antibody (bevacizumab) treatment in RN may be that VEGF secretion from the perinecrotic tissue is inhibited and that surgery would remove this tissue; both of these benefits result in effective reduction of edema associated with RN.

Boron neutron capture therapy for malignant tumors related to meningiomas.

OBJECTIVE Malignant meningiomas, similar to glioblastomas, are difficult tumors to control. We tried to control malignant tumors related to meningiomas by boron neutron capture therapy (BNCT). METHODS Since June 2005, we applied BNCT with 13 rounds of neutron irradiation to seven cases of malignant tumors related to meningiomas. Three were anaplastic meningiomas, two were papillary meningiomas, one was an atypical meningioma, and one was a sarcoma transformed from a meningioma with cervical lymph node metastasis. All patients had previously undergone repetitive surgeries and radiotherapy. Follow-up images were available for six patients with an observation period between 7 and 13 months. We applied 18F-boronophenylalanine (BPA)-positron emission tomography (PET) before BNCT in six of the seven patients. One patient underwent methionine-PET instead of 18F-BPA-PET. RESULTS Five of the six patients who underwent BPA-PET analysis showed good BPA uptake, with a greater than 2.7 tumor-to-healthy brain ratio. The atypical meningioma case showed a tumor-to-healthy brain ratio of 2.0. The original tumor sizes were between 13.6 and 109 ml. Two of the three anaplastic meningiomas showed a complete response, and all six patients available for follow-up imaging showed radiographic improvements. Clinical symptoms before BNCT, such as hemiparesis and facial pain, were improved after BNCT in all but one patient. In this patient, a huge atypical meningioma arose from the falcotentorial junction and extended to the bilateral occipital lobes and brainstem; visual problems worsened after repetitive BNCT, with an increase in peritumoral edema. CONCLUSION Malignant meningiomas seem to be good candidates for BNCT.

The Early Successful Treatment of Glioblastoma Patients with Modified boron Neutron Capture Therapy

We very effectively treated two patients with recurrent glioblastoma with modified boron neutron capture therapy (BNCT). In this paper, we describe the effectiveness of this treatment, and discuss the ways in which we modified the treatment. A 61-year-old man had a first operation for a right temporal glioblastoma, followed by full-dose chemo-radiotherapy. One year after the operation a partial removal was performed for the recurrent tumor at the same site. Fifty days after the second surgery, the patient received BNCT. We used an epithermal neutron beam as the neutron source, and used both sodium borocapate and boronophenylalanine as boron compounds with the craniotomy. Forty-eight hours after the BNCT, the follow-up MRI was applied to estimate the early effect of this treatment, which showed a 70% reduction in the contrast enhanced lesion, compared with the pretreatment MRI. In addition, the lesion/normal brain ratio of thallium-SPECT had improved markedly. No serial sequelae appeared after this treatment, and the patient remains healthy 6 months after the treatment.A 29-year-old young lady had a right temporal brain tumor, which was partially resected and followed by stereotactic radiosurgery for the residual mass. Seven months after the radiosurgery, a second operation was performed, which revealed the glioblastoma as diagnosis. We applied BNCT uneventfully for this patient with epithermal beam and two kinds of boron compounds as described above. For the treatment of the patient irradiation was applied without craniotomy with marked reduction of tumor volume immediately after the treatment.

Pseudoprogression in boron neutron capture therapy for malignant gliomas and meningiomas

Pseudoprogression has been recognized and widely accepted in the treatment of malignant gliomas, as transient increases in the volume of the enhanced area just after chemoradiotherapy, especially using temozolomide. We experienced a similar phenomenon in the treatment of malignant gliomas and meningiomas using boron neutron capture therapy (BNCT), a cell-selective form of particle radiation. Here, we introduce representative cases and analyze the pathogenesis. Fifty-two cases of malignant glioma and 13 cases of malignant meningioma who were treated by BNCT were reviewed retrospectively mainly via MR images. Eleven of 52 malignant gliomas and 3 of 13 malignant meningiomas showed transient increases of enhanced volume in MR images within 3 months after BNCT. Among these cases, five patients with glioma underwent surgery because of suspicion of relapse. In histology, most of the specimens showed necrosis with small amounts of residual tumor cells. Ki-67 labeling showed decreased positivity compared with previous samples from the individuals. Fluoride-labeled boronophenylalanine PET was applied in four and two cases of malignant gliomas and meningiomas, respectively, at the time of transient increase of lesions. These PET scans showed decreased lesion:normal brain ratios in all cases compared with scans obtained prior to BNCT. With or without surgery, all lesions were decreased or stable in size during observation. Transient increases in enhanced volume in malignant gliomas and meningiomas immediately after BNCT seemed to be pseudoprogression. This pathogenesis was considered as treatment-related intratumoral necrosis in the subacute phase after BNCT.

Evaluation of fluoride-labeled boronophenylalanine-PET imaging for the study of radiation effects in patients with glioblastomas

Here we demonstrate that differentiation between glioblastoma (GB) tumor progression (TP) and radiation necrosis (RN) can be achieved with fluoride-labeled boronoalanine positron emission tomography (F-BPA-PET). F-BPA-PET images were obtained from histologically verified 38 GB, 8 complete RN, and 5 RN cases with partial residual tumors. The lesion/normal (L/N) ratios for these groups were 4.2 ± 1.4, 1.5 ± 0.3, and 2.0 ± 0.3, respectively. Ten GB patients underwent F-BPA-PET twice (once before and once after radiation treatment) due to enlargement of the original lesion or the development of new lesions post radiation. The L/N ratios of ten original site lesions had decreased by the second PET, and these lesions were revealed to be RN. In contrast, the L/N ratios of two lesions distant from the original site increased, and these lesions were revealed as cases of TP. Repeat PET imaging was found to be useful for evaluating changes in GB-associated tumor activity with respect to the treatment received.

Survival benefit from boron neutron capture therapy for the newly diagnosed glioblastoma patients.

OBJECTIVE Since 2002-2007, we applied boron neutron capture therapy (BNCT) to >50 cases of malignant gliomas (MGs) with epithermal neutron irradiations. Recently, we showed the early radiographical improvement of malignant glioma patients by our modified BNCT, with simultaneous use of BPA (borono-phenylalanine) and BSH (sodium borocaptate). In this time, we focused on the survival benefit from BNCT for the newly diagnosed glioblastoma patients. METHODS BNCT group including 21 newly histological confirmed glioblastoma patients treated with surgical removal followed by BNCT in Osaka Medical College during 2002-2006 period. Ten patients were treated with BNCT only, and in the other 11 patients, 20-30 Gy fractionated external beam X-ray irradiation therapy (XRT) was performed after BNCT. No chemotherapy was administered until tumor progression was observed. RESULTS Treatments were well tolerated. Any kind of acute systemic or local severe toxicity were not demonstrated. Mean over all survival of the patients treated by BNCT was 20.7 and the median was 15.6 months with 2-years survival of 25%. Stratification by RPA criteria showed 6, 6, 8 and 1 patients, respectively, in classes III-VI. Three patients out of six in class III and one out of eight in class V are alive at the end point of this study. All the patients in classes IV and VI died. Median survival time for the BNCT group compared to the RTOG database was as follows: 20.6 months vs. 17.9 months for class III; 16.9 months vs. 11.1 months for class IV; 13.2 months vs. 8.9 months for class V. CONCLUSION The RTOG RPA prognostic criteria were helpful in establishing which class of glioma patients could potentially benefit from BNCT. BNCT showed a survival benefit in all of the RPA classes of the RTOG database not only for the good prognosis group.

Phase II clinical study of boron neutron capture therapy combined with X-ray radiotherapy/temozolomide in patients with newly diagnosed glioblastoma multiforme--study design and current status report.

Recently, we reported our clinical experiences of boron neutron capture therapy (BNCT) for the newly diagnosed glioblastoma. The major differences of our protocol from the other past studies were simultaneous use of both sodium borocapate and boronophenylalanine, and combination with fractionated X-ray irradiation. These results showed the efficacy of combination therapy with external beam X-ray irradiation and BNCT. For our future study, we planned the multi-centric phase II clinical study for newly diagnosed glioblastoma patients in Japan (OSAKA-TRIBRAIN0902, NCT00974987).

Computed Tomography Imaging of Transferrin Targeting Liposomes Encapsulating Both Boron and Iodine Contrast Agents by Convection-Enhanced Delivery to F98 Rat Glioma for Boron Neutron Capture Therapy

BACKGROUND:To achieve potent tumor-selective antitumor efficacy by boron neutron capture therapy (BNCT), it is important to have a significant differential uptake of 10B between tumor cells and normal cells. This should enable BNCT to reduce damage to normal tissues compared with other radiation therapies. OBJECTIVE:To augment the therapeutic efficacy of BNCT, we used transferrin-conjugated polyethylene glycol (PEG) (TF-PEG) liposome encapsulating sodium borocaptate and Iomeprol, an iodine contrast agent, with intratumoral convection-enhanced delivery (CED) in a rat glioma tumor model. METHODS:The in vitro 10B concentration of F98 rat glioma cells was determined by inductively coupled plasma atomic emission spectrometry after incubation with either TF-PEG or PEG liposomes. For in vivo biodistribution studies, 10B concentrations within blood, normal brain tissue, and intracerebrally transplanted F98 cells were measured with inductively coupled plasma-atomic emission spectrometry after CED of the compounds, and computed tomography was performed at selected time intervals. RESULTS:10B concentrations of F98 cultured glioma cells in vitro 6 hours after exposure to PEG and TF-PEG liposome were 16.1 and 51.9 ng10B/106 cells, respectively. 10B concentrations in F98 glioma tissue 24 hours after CED were 22.5 and 82.2 μg/g, by PEG and TF-PEG liposome, respectively, with lower 10B concentrations in blood and normal brain. Iomeprol provided vivid and stable enhanced computed tomography imaging of the transplanted tumor even 72 hours after CED by TF-PEG liposome. Conversely, tissue enhancement had already washed out at 24 hours after CED of the PEG liposomes. CONCLUSION:The combination of TF-PEG liposome encapsulating sodium borocaptate and Iomeprol and intratumoral CED enables not only a precise and potent targeting of boron delivery to the tumor tissue, but also the ability to follow the trace of boron delivery administered intratumorally by real-time computed tomography.