Fluorine-18-labeled boronophenylalanine positron emission tomography for oral cancers: Qualitative and quantitative analyses of malignant tumors and normal structures in oral and maxillofacial regions

Biocompatible Iron-Boron Nanoparticles Designed for Neutron Capture Therapy Guided by Magnetic Resonance Imaging

The combination of multiple functions in a single nanoparticle (NP) represents a key advantage of nanomedicine compared to traditional medical approaches. This is well represented by radiotherapy in which the dose of ionizing radiation should be calibrated on sensitizers biodistribution. Ideally, this is possible when the drug acts both as radiation enhancer and imaging contrast agent. Here, an easy, one-step, laser-assisted synthetic procedure is used to generate iron-boron (Fe-B) NPs featuring the set of functions required to assist neutron capture therapy (NCT) with magnetic resonance imaging. The Fe-B NPs exceed by three orders of magnitude the payload of boron isotopes contained in clinical sensitizers. The Fe-B NPs have magnetic properties of interest also for magnetophoretic accumulation in tissues and magnetic hyperthermia to assist drug permeation in tissues. Besides, Fe-B NPs are biocompatible and undergo slow degradation in the lysosomal environment that facilitates in vivo clearance through the liver-spleen-kidneys pathway. Overall, the Fe-B NPs represent a new promising tool for future exploitation in magnetic resonance imaging-guided boron NCT at higher levels of efficacy and tolerability.

The importance of optimal ROIs delineation for FBPA-PET before BNCT

One of the eligible criteria for patients to receive boron neutron capture therapy (BNCT) is based on the tumour-to-normal ratio (T/N) measured by FBPA-PET. However, there is no standard protocol for normal region-of-interested delineation. With comparison of contralateral cerebrum, our study revealed the consistency (p < 0.05) and high feasibility using the cerebellum as an alternative normal tissue baseline because of its homogeneous uptake. Following RECIST version 1.1, the standard-operating-procedure (SOP) for the BNCT fulfilled the expected tumour response and tumour shrinkage rate (p < 0.05). Our modified procedure can provide more precise information for BNCT within a reasonable time.

4-Borono-2-18F-fluoro-L-phenylalanine PET for boron neutron capture therapy-oriented diagnosis: overview of a quarter century of research

4-¹⁰B-Borono-2-¹⁸F-fluoro-L-phenylalanine (¹⁸F-FBPA) was developed for monitoring the pharmacokinetics of 4-¹⁰B-borono-L-phenylalanine (¹⁰B-BPA) used in boron neutron capture therapy (BNCT) with positron emission tomography (PET). The tumor-imaging potential of ¹⁸F-FBPA was demonstrated in various animal models. Accumulation of ¹⁸F-FBPA was higher in melanomas than in non-melanoma tumors in animal models and cell cultures. ¹⁸F-FBPA was incorporated into tumors mediated mainly by L-type amino acid transporters in in vitro and in vivo models. Tumoral distribution of ¹⁸F-FBPA was primarily related to the activity of DNA synthesis. ¹⁸F-FBPA is metabolically stable but is incorporated into melanogenesis non-enzymatically. These in vitro and in vivo characteristics of ¹⁸F-FBPA corresponded well to those of ¹⁰B-BPA. Nuclear magnetic resonance and other studies using non-radioactive ¹⁹F-^10/11B-FBPA also contributed to characterization. The validity and reliability of ^18/19F-FBPA as an in vivo probe of ¹⁰B-BPA were confirmed by comparison of the pharmacokinetics of ¹⁸F-FBPA and ¹⁰B-BPA and direct measurement of both ¹⁸F and ¹⁰B in tumors with various doses of both probes administered by different routes and methods. Clinically, based on the kinetic parameters of dynamic ¹⁸F-FBPA PET, the estimated ¹⁰B-concentrations in tumors with continuous ¹⁰B-BPA infusion were similar to those measured directly in surgical specimens. The significance of ¹⁸F-FBPA PET was verified for the estimation of ¹⁰B-concentration and planning of BNCT. Later ¹⁸F-FBPA PET has been involved in ¹⁰B-BPA BNCT of patients with intractable tumors such as malignant brain tumors, head and neck tumors, and melanoma. Usually a static PET scan is used for screening patients for BNCT, prediction of the distribution and accumulation of ¹⁰B-BPA, and evaluation of treatment after BNCT. In some clinical trials, a tumor-to-normal tissue ratio of ¹⁸F-FBPA > 2.5 was an inclusion criterion for BNCT. Apart from BNCT, ¹⁸F-FBPA was demonstrated to be a useful PET probe for tumor diagnosis in nuclear medicine: better tumor-to-normal brain contrast compared with ¹¹C-methionine, differentiation of recurrent and radiation necrosis after radiotherapy, and melanoma-preferential uptake. Further progress in ¹⁸F-FBPA studies is expected for more elaborate evaluation of ¹⁰B-concentrations in tumors and normal tissues for successful ¹⁰B-BPA BNCT and for radiosynthesis of ¹⁸F-FBPA to enable higher ¹⁸F-activity amounts and higher molar activities.

Reliable radiosynthesis of 4-[10B]borono-2-[18F]fluoro-L-phenylalanine with quality assurance for boron neutron capture therapy-oriented diagnosis

Objective

The aim of this study was to establish a reliable and routine method for the preparation of 4-[¹⁰B]borono-2-[¹⁸F]fluoro-l-phenylalanine (l-[¹⁸F]FBPA) for boron neutron capture therapy-oriented diagnosis using positron emission tomography.

Methods

To produce l-[¹⁸F]FBPA by electrophilic fluorination of 4-[¹⁰B]borono-l-phenylalanine (l-BPA) with [¹⁸F]acetylhypofluorite ([¹⁸F]AcOF) via [¹⁸F]F₂ derived from the ²⁰Ne(d,α)¹⁸F nuclear reaction, several preparation parameters and characteristics of l-[¹⁸F]FBPA were investigated, including: pre-irradiation for [¹⁸F]F₂ production, the carrier F₂ content in the Ne target, l-BPA-to-F₂ ratios, separation with high-performance liquid chromatography (HPLC) using 10 different eluents, enantiomeric purity, and residual trifluoroacetic acid used as the reaction solvent by gas chromatography-mass spectrometry.

Results

The activity yields and molar activities of l-[¹⁸F]FBPA (n = 38) were 1200 ± 160 MBq and 46–113 GBq/mmol, respectively, after deuteron-irradiation for 2 h. Two 5 min pre-irradiations prior to [¹⁸F]F₂ production for ¹⁸F-labeling were preferable. For l-[¹⁸F]FBPA synthesis, 0.15–0.2% of carrier F₂ in Ne and l-BPA-to-F₂ ratios > 2 were preferable. HPLC separations with five of the 10 eluents provided injectable l-[¹⁸F]FBPA without any further formulation processing, which resulted in a synthesis time of 32 min. Among the five eluents, 1 mM phosphate-buffered saline was the eluent of choice. The l-[¹⁸F]FBPA injection was sterile and pyrogen-free, and contained very small amounts of D-enantiomer (< 0.1% of l-[¹⁸F]FBPA), l-BPA (< 1% of l-FBPA), and trifluoroacetic acid (< 0.5 ppm).

Conclusions

l-[¹⁸F]FBPA injection was reliably prepared by the electrophilic fluorination of l-BPA with [¹⁸F]AcOF followed by HPLC separation with 1 mM phosphate-buffered saline.

Dynamic changes in 18F-borono-L-phenylalanine uptake in unresectable, advanced, or recurrent squamous cell carcinoma of the head and neck and malignant melanoma during boron neutron capture therapy patient selection

Background

We evaluated dynamic changes in ¹⁸F–borono-L-phenylalanine (¹⁸F–BPA) uptake in unresectable, advanced, or recurrent squamous cell carcinoma of the head and neck (SCC) and malignant melanoma (MM) during boron neutron capture therapy (BNCT) patient selection.

Methods

Dynamic changes in the maximum standardized uptake value (SUVmax), tumor-to-normal tissue ratio (TNR), and tumor-to-blood pool ratio (TBR) for ¹⁸F–BPA were evaluated in 20 patients with SCC and 8 patients with MM.

Results

SUVmax in SCC tumors decreased significantly from 30 to 120 min. There was a non-statistically significant decrease in SUVmax for SCC tumors from 30 to 60 min and from 60 to 120 min. Patients with MM had nonsignificant SUVmax changes in ¹⁸F–BPA uptake on delayed imaging. Nonsignificant ¹⁸F–BPA TNR and TBR changes were seen in patients with SCC and MM.

Conclusions

Dynamic changes in SUVmax for ¹⁸F–BPA uptake had a washout pattern in SCC and a persistent pattern in MM. Dynamic ¹⁸F–BPA -PET studies should be performed to investigate the pharmacokinetics of ¹⁸F–BPA in humans and select appropriate candidates who may benefit from BNCT.

Comparison of the image-derived radioactivity and blood-sample radioactivity for estimating the clinical indicators of the efficacy of boron neutron capture therapy (BNCT): 4-borono-2-18F-fluoro-phenylalanine (FBPA) PET study

Background

In boron neutron capture therapy (BNCT), positron emission tomography (PET) with 4-borono-2-¹⁸F-fluoro-phenylalanine (FBPA) is the only method to estimate an accumulation of ¹⁰B to target tumor and surrounding normal tissue after administering ¹⁰B carrier of L-paraboronophenylalanine and to search the indication of BNCT for individual patient. Absolute concentration of ¹⁰B in tumor has been estimated by multiplying ¹⁰B concentration in blood during BNCT by tumor to blood radioactivity (T/B) ratio derived from FBPA PET. However, the method to measure blood radioactivity either by blood sampling or image data has not been standardized. We compared image-derived blood radioactivity of FBPA with blood sampling data and studied appropriate timing and location for measuring image-derived blood counts.

Methods

We obtained 7 repeated whole-body PET scans in five healthy subjects. Arterialized venous blood samples were obtained from the antecubital vein, heated in a heating blanket. Time-activity curves (TACs) of image-derived blood radioactivity were obtained using volumes of interest (VOIs) over ascending aorta, aortic arch, pulmonary artery, left and right ventricles, inferior vena cava, and abdominal aorta. Image-derived blood radioactivity was compared with those measured by blood sampling data in each location.

Results

Both the TACs of blood sampling radioactivity in each subject, and the TACs of image-derived blood radioactivity showed a peak within 5 min after the tracer injection, and promptly decreased soon thereafter. Linear relationship was found between blood sampling radioactivity and image-derived blood radioactivity in all the VOIs at any timing of data sampling (p < 0.001). Image-derived radioactivity measured in the left and right ventricles 30 min after injection showed high correlation with blood radioactivity. Image-derived blood radioactivity was lower than blood sampling radioactivity data by 20 %. Reduction of blood radioactivity of FBPA in left ventricle after 30 min of FBPA injection was minimal.

Conclusion

We conclude that the image-derived T/B ratio can be reliably used by setting the VOI on the left ventricle at 30 min after FBPA administration and correcting for underestimation due to partial volume effect and reduction of FBPA blood radioactivity.

Boron Neutron Capture Therapy in the Treatment of Recurrent Laryngeal Cancer

PURPOSE

To investigate the safety and efficacy of boron neutron capture therapy (BNCT) as a larynx-preserving treatment option for patients with recurrent laryngeal cancer.

METHODS AND MATERIALS

Six patients with locally recurrent squamous cell laryngeal carcinoma and 3 patients with persistent laryngeal cancer after prior treatment were treated with BNCT at the FiR1 facility (Espoo, Finland) in 2006 to 2012. The patients had received prior radiation therapy with or without concomitant chemotherapy to a cumulative median dose of 66 Gy. The median tumor diameter was 2.9 cm (range, 1.4-10.9 cm) before BNCT. Boron neutron capture therapy was offered on a compassionate basis to patients who either refused laryngectomy (n=7) or had an inoperable tumor (n=2). Boronophenylalanine-fructose (400 mg/kg) was used as the boron carrier and was infused over 2 hours intravenously before neutron irradiation.

RESULTS

Six patients received BNCT once and 3 twice. The estimated average gross tumor volume dose ranged from 22 to 38 Gy (W) (mean; 29 Gy [W]). Six of the 8 evaluable patients responded to BNCT; 2 achieved complete and 4 partial response. One patient died early and was not evaluable for response. Most common side effects were stomatitis, fatigue, and oral pain. No life-threatening or grade 4 toxicity was observed. The median time to progression within the target volume was 6.6 months, and the median overall survival time 13.3 months after BNCT. One patient with complete response is alive and disease-free with a functioning larynx 60 months after BNCT.

CONCLUSIONS

Boron neutron capture therapy given after prior external beam radiation therapy is well tolerated. Most patients responded to BNCT, but long-term survival with larynx preservation was infrequent owing to cancer progression. Selected patients with recurrent laryngeal cancer may benefit from BNCT.

Tumor-specific delivery of BSH-3R for boron neutron capture therapy and positron emission tomography imaging in a mouse brain tumor model

Glioblastoma, a malignant brain tumor with poor disease outcomes, is managed in modern medicine by multimodality therapy. Boron neutron capture therapy (BNCT) is an encouraging treatment under clinical investigation. In malignant cells, BNCT consists of two major factors: neutron radiation and boron uptake. To increase boron uptake in cells, we created a mercapto-closo-undecahydrododecaborate ([B12HnSH](2-)2Na(+), BSH) fused with a short arginine peptide (1R, 2R, 3R) and checked cellular uptake in vitro and in vivo. In a mouse brain tumor model, only BSH with at least three arginine domains could penetrate cell membranes of glioma cells in vitro and in vivo. Furthermore, to monitor the pharmacokinetic properties of these agents in vivo, we fused BSH and BSH-3R with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA); DOTA is a metal chelating agent for labeling positron emission tomography (PET) probe with (64)Cu. We administered BSH-DOTA-(64)Cu and BSH-3R-DOTA-(64)Cu to the tumor model through a mouse tail vein and determined the drugs' pharmacokinetics by PET imaging. BSH-3R showed a high uptake in the tumor area on PET imaging. We concluded that BSH-3R is the ideal boron compound for clinical use during BNCT and that in developing this compound for clinical use, the BSH-3R PET probe is essential for pharmacokinetic imaging.

FBPA PET in boron neutron capture therapy for cancer: prediction of (10)B concentration in the tumor and normal tissue in a rat xenograft model

Background

Boron neutron capture therapy (BNCT) is a molecular radiation treatment based on the ¹⁰B (n, α) ⁷Li nuclear reaction in cancer cells, in which delivery of ¹⁰B by 4-borono-phenylalanine conjugated with fructose (BPA-fr) to the cancer cells is of critical importance. The PET tracer 4-borono-2-¹⁸ F-fluoro-phenylalanine (FBPA) has been used to predict the accumulation of BPA-fr before BNCT. However, because of the difference in chemical structure between BPA-fr and FBPA and the difference in the dose administered between BPA-fr (therapeutic dose) and FBPA (tracer dose), the predictive value of FBPA PET for BPA-fr accumulation in the tumor and normal tissues is not yet clearly proven. We conducted this study to validate FBPA PET as a useful test to predict the accumulation of BPA-fr in the tumor and normal tissues before BNCT.

Methods

RGC-6 rat glioma cells (1.9 × 10⁷) were implanted subcutaneously in seven male F344 rats. On day 20 after the tumor implantation, dynamic PET scan was performed on four rats after injection of FBPA for 1 h. Whole-body PET/CT was performed 1 h after intravenous injection of the FBPA solution (30.5 ± 0.7 MBq, 1.69 ± 1.21 mg/kg). PET accumulation of FBPA in the tumor tissue and various normal tissues was estimated as a percentage of the injected dose per gram (%ID/g). One hour after the PET/CT scan, BPA-fructose (167.32 ± 18.65 mg/kg) was injected intravenously, and the rats were dissected 1 h after the BPA-fr injection. The absolute concentration of ¹⁰B in the autopsied tissues and blood was measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

Results

The highest absolute concentration of ¹⁰B determined by ICP-OES was found in the kidney (4.34 ± 0.84 %ID/g), followed by the pancreas (2.73 ± 0.63 %ID/g), and the tumor (1.44 ± 0.44 %ID/g). A significant positive correlation was found between the accumulation levels of BPA-fr and FBPA (r = 0.91, p < 0.05).

Conclusions

FBPA PET can reliably predict accumulation of BPA-fr in the tumor as well as normal tissues.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-014-0070-2) contains supplementary material, which is available to authorized users.