Cell cycle dependence of boron uptake from two boron compounds used for clinical neutron capture therapy

doi:10.1016/S0304-3835(02)00380-4

Cancer Letters

Volume 187, Issues 1–2, 10 December 2002, Pages 135-141

https://doi.org/10.1016/S0304-3835(02)00380-4 Get rights and content

Abstract

In neutron capture therapy, it is important that the boron is selectively uptaken by tumor cells. In the present study, we used flow cytometry to sort the cells in the G0/G1 phase and those in the G2/M phase, and the boron concentration in each fraction was measured with inductively coupled plasma atomic emission spectroscopy. The results revealed that sodium borocaptate and boronophenylalanine (BPA), were associated with higher rates of boron uptake in the G2/M than in the G0/G1 phase. However, the difference was more prominent in the case of BPA. The G2/M:G0/G1 ratio decreased as a function of exposure time in BPA containing culture medium, thereby indicating the cell cycle dependency of BPA uptake. Such heterogeneity of boron uptake by tumor cells should be considered for microdosimetry.

Introduction

Tumor cells in host tissues have a high mitotic index. However, tumor cells are not always in the growth phase. Many cells enter into a quiescence phase because of hypoxia, under nutrition due to poor vascularization, or other reasons [1].

In boron neutron capture therapy (BNCT), due to the short range of alpha particles (about 10 mm), only the cells that incorporate the boron compound are selectively injured. Accordingly, it is desirable for boron to be taken up by all neoplastic cells. In previous investigations, the main issue was the difference in boron uptake between normal and neoplastic cells. Recently, the attention has focused on the differences in uptake by tumor cells in different phases of the cell cycle.

Masunaga et al. [2], [3] showed, based on indirect measurements, that the differences in the radiobiological effects of quiescent cells and growth-phase cells were particularly large between boronophenylalanine (BPA) and sodium borocaptate (BSH).

In this study, we directly measured the boron concentration in cells in different phase of the cell cycle.

Section snippets

Cell lines

V79 is a cell line of Chinese hamster lung origin. SCCVII is a mouse squamous cell carcinoma, and C6 is a rat glioma cell line. Each cell line was cultured with Earl's minimum essential medium (MEM) (SIGMA-Aldrich Japan, Tokyo, Japan) supplemented with 10% fetal bovine serum. The cell lines were maintained at 37°C in an atmosphere of 5% CO₂ in air.

Measurement of doubling time

A total of 2.5×10⁵ cells of each cell line were seeded on a 6-cm-diameter petri dish containing 5 ml MEM, and incubated for 0–80 h at 37°C.

Boron compounds

BSH (Boron

Cell growth and doubling time

Fig. 1 shows the growth curve of each cell line. The doubling time was 12.5 h for C6 and V79, and 17.7 h for SCCVII. As shown in Fig. 1, the cell started to multiply 24 h after they were seeded.

Boron uptake

The boron uptake from BSH and BPA as a function of time is shown in Fig. 2. The uptake of boron from BSH did not change much, but in the case of BPA the concentration of boron increased as a function of time. The level of boron uptake in the BPA group was three or four times higher than in the BSH group

Discussion

In BNCT, two boron compounds, BSH and BPA, have been used. BSH is known to accumulate in tumor cells only and is scarcely measurable in the normal brain, but the blood boron concentration to tumor blood concentration ratio is reported to be around 1 depending on the tumor sample [5], [6]. On the other hand, BPA accumulates in tumor cells and also in the normal brain with an uptake ratio of about 3:1. Considering the treatment of malignant gliomas with BNCT, in the case of BSH, the boron in the

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Cell cycle dependence of boron uptake from two boron compounds used for clinical neutron capture therapy

Abstract

Introduction

Section snippets

Cell lines

Measurement of doubling time

Boron compounds

Cell growth and doubling time

Boron uptake

Discussion

Int. J. Radiat. Oncol. Biol. Phys

J. Biol. Chem.

Int. J. Radiat. Oncol. Biol. Phys.

Int. J. Oncol. Biol. Phys.

Int. J. Radiat. Oncol. Biol. Phys.

The problem of the quiescent cancer cell

Adv. Enzyme Regul.

Evaluation of response to thermal neutron irradiation in quiescent cell populations within murine solid tumors using micronucleus assay

Annu. Rep. Res. Reactor Inst. Kyoto Univ.