Comparison of intracerebral delivery of carboplatin and photon irradiation with an optimized regimen for boron neutron capture therapy of the F98 rat glioma

Radiation therapy combined with intracerebral convection-enhanced delivery of cisplatin or carboplatin for treatment of the F98 rat glioma

BACKGROUND

The purpose of this review is to summarize our own experimental studies carried out over a 13-year period of time using the F98 rat glioma as model for high grade gliomas. We evaluated a binary chemo-radiotherapeutic modality that combines either cisplatin (CDDP) or carboplatin, administered intracerebrally (i.c.) by means of convection-enhanced delivery (CED) or osmotic pumps, in combination with either synchrotron or conventional X-irradiation.

METHODS

F98 glioma cells were implanted stereotactically into the brains of syngeneic Fischer rats. Approximately 14 days later, either CDDP or carboplatin was administered i.c. by CED, followed 24 h later by radiotherapy using either a synchrotron or, subsequently, megavoltage linear accelerators (LINAC).

RESULTS

CDDP was administered at a dose of 3 µg in 5 µL, followed 24 h later with an irradiation dose of 15 Gy or carboplatin at a dose of 20 µg in 10 µL, followed 24 h later with 3 fractions of 8 Gy each, at the source at the European Synchrotron Radiation Facility (ESRF). This resulted in a median survival time (MeST) > 180 days with 33% long term survivors (LTS) for CDDP and a MeST > 60 days with 8 to 22% LTS, for carboplatin. Subsequently it became apparent that comparable survival data could be obtained with megavoltage X-irradiation using a LINAC source. The best survival data were obtained with a dose of 72 µg of carboplatin administered by means of Alzet® osmotic pumps over 7 days. This resulted in a MeST of > 180 days, with 55% LTS. Histopathologic examination of all the brains of the surviving rats revealed no residual tumor cells or evidence of significant radiation related effects.

CONCLUSIONS

The results obtained using this combination therapy has, to the best of our knowledge, yielded the most promising survival data ever reported using the F98 glioma model.

Synthesis and Evaluation of Dodecaboranethiol Containing Kojic Acid (KA-BSH) as a Novel Agent for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a form of tumor-cell selective particle irradiation using low-energy neutron irradiation of boron-10 (¹⁰B) to produce high-linear energy transfer (LET) alpha particles and recoiling ⁷Li nuclei (¹⁰B [n, alpha] ⁷Li) in tumor cells. Therefore, it is important to achieve the selective delivery of large amounts of ¹⁰B to tumor cells, with only small amounts of ¹⁰B to normal tissues. To develop practical materials utilizing ¹⁰B carriers, we designed and synthesized novel dodecaboranethiol (BSH)-containing kojic acid (KA-BSH). In the present study, we evaluated the effects of this novel ¹⁰B carrier on cytotoxicity, ¹⁰B concentrations in F98 rat glioma cells, and micro-distribution of KA-BSH in vitro. Furthermore, biodistribution studies were performed in a rat brain tumor model. The tumor boron concentrations showed the highest concentrations at 1 h after the termination of administration. Based on these results, neutron irradiation was evaluated at the Kyoto University Research Reactor Institute (KURRI) with KA-BSH. Median survival times (MSTs) of untreated and irradiated control rats were 29.5 and 30.5 days, respectively, while animals that received KA-BSH, followed by neutron irradiation, had an MST of 36.0 days (p = 0.0027, 0.0053). Based on these findings, further studies are warranted in using KA-BSH as a new B compound for malignant glioma.

Convection-Enhanced Delivery in Malignant Gliomas: A Review of Toxicity and Efficacy

Malignant gliomas are undifferentiated or anaplastic gliomas. They remain incurable with a multitude of modalities, including surgery, radiation, chemotherapy, and alternating electric field therapy. Convection-enhanced delivery (CED) is a local treatment that can bypass the blood-brain barrier and increase the tumor uptake of therapeutic agents, while decreasing exposure to healthy tissues. Considering the multiple choices of drugs with different antitumor mechanisms, the supra-additive effect of concomitant radiation and chemotherapy, CED appears as a promising modality for the treatment of brain tumors. In this review, the CED-related toxicities are summarized and classified into immediate, early, and late side effects based on the time of onset, and local and systemic toxicities based on the location of toxicity. The efficacies of CED of various therapeutic agents including targeted antitumor agents, chemotherapeutic agents, radioisotopes, and immunomodulators are covered. The phase III trial PRECISE compares CED of IL13-PE38QQR, an interleukin-13 conjugated to Pseudomonas aeruginosa exotoxin A, to Gliadel® Wafer, a polymer loaded with carmustine. However, in this case, CED had no significant median survival improvement (11.3 months vs. 10 months) in patients with recurrent glioblastomas. In phase II studies, CED of recombinant poliovirus (PVSRIPO) had an overall survival of 21% vs. 14% for the control group at 24 months, and 21% vs. 4% at 36 months. CED of Tf-diphtheria toxin had a response rate of 35% in recurrent malignant gliomas patients. On the other hand, the TGF-β2 inhibitor Trabedersen, HSV-1-tk ganciclovir, and radioisotope 131I-chTNT-1/B mAb had a limited response rate. With this treatment, patients who received CED of the chemotherapeutic agent paclitaxel and immunomodulator, oligodeoxynucleotides containing CpG motifs (CpG-ODN), experienced intolerable toxicity. Toward the end of this article, an ideal CED treatment procedure is proposed and the methods for quality assurance of the CED procedure are discussed.

Folate receptor-targeted novel boron compound for boron neutron capture therapy on F98 glioma-bearing rats

Folic acid (FA) has high affinity for the folate receptor (FR), which is limited expressed in normal human tissues, but over-expressed in several tumor cells, including glioblastoma cells. In the present work, a novel pteroyl-closo-dodecaborate conjugate (PBC) was developed, in which the pteroyl group interacts with FR, and the efficacy of boron neutron capture therapy (BNCT) using PBC was investigated. Thus, in vitro and in vivo studies were performed using F98 rat glioma cells and F98 glioma-bearing rats. For the in vivo study, boronophenylalanine (BPA) was intravenously administered, while PBC was administered by convection-enhanced delivery (CED)-a method for direct local drug infusion into the brain of rats. Furthermore, a combination of PBC administered by CED and BPA administered by intravenous (i.v.) injection was also investigated. In the biodistribution experiment, PBC administration at 6 h after CED termination showed the highest cellular boron concentrations (64.6 ± 29.6 µg B/g). Median survival time (MST) of untreated controls was 23.0 days (range 21-24 days). MST of rats administered PBC (CED) followed by neutron irradiation was 31 days (range 26-36 days), which was similar to that of rats administered i.v. BPA (30 days; range 25-37 days). Moreover, the combination group [PBC (CED) and i.v. BPA] showed the longest MST (38 days; range 28-40 days). It is concluded that a significant MST increase was noted in the survival time of the combination group of PBC (CED) and i.v. BPA compared to that in the single-boron agent groups. These findings suggest that the combination use of PBC (CED) has additional effects.

Evaluation of a novel sodium borocaptate-containing unnatural amino acid as a boron delivery agent for neutron capture therapy of the F98 rat glioma

BACKGROUND

Boron neutron capture therapy (BNCT) is a unique particle radiation therapy based on the nuclear capture reactions in boron-10. We developed a novel boron-10 containing sodium borocaptate (BSH) derivative, 1-amino-3-fluorocyclobutane-1-carboxylic acid (ACBC)-BSH. ACBC is a tumor selective synthetic amino acid. The purpose of this study was to assess the biodistribution of ACBC-BSH and its therapeutic efficacy following Boron Neutron Capture Therapy (BNCT) of the F98 rat glioma.

METHODS

We evaluated the biodistribution of three boron-10 compounds, ACBC-BSH, BSH and boronophenylalanine (BPA), in vitro and in vivo, following intravenous (i.v.) administration and intratumoral (i.t.) convection-enhanced delivery (CED) in F98 rat glioma bearing rats. For BNCT studies, rats were stratified into five groups: untreated controls, neutron-irradiation controls, BNCT with BPA/i.v., BNCT with ACBC-BSH/CED, and BNCT concomitantly using BPA/i.v. and ACBC-BSH/CED.

RESULTS

In vitro, ACBC-BSH attained higher cellular uptake F98 rat glioma cells compared with BSH. In vivo biodistribution studies following i.v. administration and i.t. CED of ACBC-BSH attained significantly higher boron concentrations than that of BSH, but much lower than that of BPA. However, following convection enhanced delivery (CED), ACBC-BSH attained significantly higher tumor concentrations than BPA. The i.t. boron-10 concentrations were almost equal between the ACBC-BSH/CED group and BPA/i.v. group of rats. The tumor/brain boron-10 concentration ratio was higher with ACBC-BSH/CED than that of BPA/i.v. group. Based on these data, BNCT studies were carried out in F98 glioma bearing rats using BPA/i.v. and ACBC-BSH/CED as the delivery agents. The corresponding mean survival times were 37.4 ± 2.6d and 44.3 ± 8.0d, respectively, and although modest, these differences were statistically significant.

CONCLUSIONS

Our findings suggest that further studies are warranted to evaluate ACBC-BSH/CED as a boron delivery agent.

Convection-enhancement delivery of platinum-based drugs and Lipoplatin(TM) to optimize the concomitant effect with radiotherapy in F98 glioma rat model

The prognosis for patients with glioblastoma remains poor with current treatments. Although platinum-based drugs are sometimes offered at relapse, their efficacy in this setting is still disputed. In this study, we use convection-enhanced delivery (CED) to deliver the platinum-based drugs (cisplatin, carboplatin, and Lipoplatin(TM) - liposomal formulation of cisplatin) directly into the tumor of F98 glioma-bearing rats that were subsequently treated with γ radiation (15 Gy). CED increased by factors varying between 17 and 111, the concentration of these platinum-based drugs in the brain tumor compared to intra-venous (i.v.) administration, and by 9- to 34-fold, when compared to intra-arterial (i.a.) administration. Furthermore, CED resulted in a better systemic tolerance to platinum drugs compared to their i.a. injection. Among the drugs tested, carboplatin showed the highest maximum tolerated dose (MTD). Treatment with carboplatin resulted in the best median survival time (MeST) (38.5 days), which was further increased by the addition of radiotherapy (54.0 days). Although the DNA-bound platinum adduct were higher at 4 h after CED than 24 h for carboplatin group, combination with radiotherapy led to similar improvement of median survival time. However, less toxicity was observed in animals irradiated 24 h after CED-based chemotherapy. In conclusion, CED increased the accumulation of platinum drugs in tumor, reduced the toxicity, and resulted in a higher median survival time. The best treatment was obtained in animals treated with carboplatin and irradiated 24 h later.

Pharmacokinetic analysis and uptake of 18F-FBPA-Fr after ultrasound-induced blood-brain barrier disruption for potential enhancement of boron delivery for neutron capture therapy

Boronophenylalanine has been applied in clinical boron neutron capture therapy for the treatment of high-grade gliomas. The purpose of this study was to evaluate the pharmacokinetics of 4-borono-2-(18)F-fluoro-L-phenylalanine-fructose ((18)F-FBPA-Fr) in F98 glioma-bearing Fischer 344 rats by means of intravenous injection of (18)F-FBPA-Fr both with and without blood-brain barrier disruption (BBB-D) induced by focused ultrasound (FUS).

METHODS

Dynamic PET imaging of (18)F-FBPA-Fr was performed on the ninth day after tumor implantation. Blood samples were collected to obtain an arterial input function for tracer kinetic modeling. Ten animals were scanned for approximately 3 h to estimate the uptake of (18)F radioactivity with respect to time for the pharmacokinetic analysis. Rate constants were calculated by use of a 3-compartment model.

RESULTS

The accumulation of (18)F-FBPA-Fr in brain tumors and the tumor-to-contralateral brain ratio were significantly elevated after intravenous injection of (18)F-FBPA-Fr with BBB-D. (18)F-FBPA-Fr administration after sonication showed that the tumor-to-contralateral brain ratio for the sonicated tumors (3.5) was approximately 1.75-fold higher than that for the control tumors (2.0). Furthermore, the K1/k2 pharmacokinetic ratio after intravenous injection of (18)F-FBPA-Fr with BBB-D was significantly higher than that after intravenous injection without BBB-D.

CONCLUSION

This study demonstrated that radioactivity in tumors and the tumor-to-normal brain ratio after intravenous injection of (18)F-FBPA-Fr with sonication were significantly higher than those in tumors without sonication. The K1/k2 ratio may be useful for indicating the degree of BBB-D induced by FUS. Further studies are needed to determine whether FUS may be useful for enhancing the delivery of boronophenylalanine in patients with high-grade gliomas.