In vitro determination of toxicity, binding, retention, subcellular distribution and biological efficacy of the boron neutron capture agent DAC-1

Comparative study of the radiobiological effects induced on adherent vs suspended cells by BNCT, neutrons and gamma rays treatments

The present work is part of a preclinical in vitro study to assess the efficacy of BNCT applied to liver or lung coloncarcinoma metastases and to limb osteosarcoma. Adherent growing cell lines can be irradiated as adherent to the culture flasks or as cell suspensions, differences in radio-sensitivity of the two modalities of radiation exposure have been investigated. Dose related cell survival and cell cycle perturbation results evidenced that the radiosensitivity of adherent cells is higher than that of the suspended ones.

Boric acid increases the expression levels of human anion exchanger genes SLC4A2 and SLC4A3

Boron is an important micronutrient in plants and animals. The role of boron in living systems includes coordinated regulation of gene expression, growth and proliferation of higher plants and animals. There are several well-defined genes associated with boron transportation and tolerance in plants and these genes show close homology with human anion exchanger genes. Mutation of these genes also characterizes some genetic disorders. We investigated the toxic effects of boric acid on HEK293 cells and mRNA expression of anion exchanger (SLC4A1, SLC4A2 and SLC4A3) genes. Cytotoxicity of boric acid at different concentrations was tested by using the methylthiazolyldiphenyl-tetrazolium bromide assay. Gene expression profiles were examined using quantitative real-time PCR. In the HEK293 cells, the nontoxic upper concentration of boric acid was 250 μM; more than 500 μM caused cytotoxicity. The 250 μM boric acid concentration increased gene expression level of SLC4A2 up to 8.6-fold and SLC4A3 up to 2.6-fold, after 36-h incubation. There was no significant effect of boric acid on SLC4A1 mRNA expression levels.

EGF-receptor targeted liposomes with boronated acridine: growth inhibition of cultured glioma cells after neutron irradiation

PURPOSE

To study survival of cultured U-343MGaCl 2:6 glioma cells after incubation with boron-containing liposomes targeting the epidermal growth factor receptor following neutron irradiation.

MATERIALS AND METHODS

Epidermal growth factor-tagged liposomes were loaded with water-soluble boronated acridine developed for boron neutron capture therapy, (BNCT). Cellular uptake and distribution were studied. Further, cells were placed at 3 cm depth in a phantom and exposed to an epithermal neutron beam to study clonogenic cell survival.

RESULTS

The cellular uptake of boron reached 90 ppm and it was determined by subcellular fractionation that most of the cell-associated boron was located outside of the nucleus. For clonogenic survival, the cells were incubated with epidermal growth factor receptor-targeted liposomes for 4 hours resulting in a cellular concentration of 55 ppm boron (11 ppm 10B). At a fluence of 3 x 10(12) neutrons/cm2 the cell killing effect of the boron-containing epidermal growth factor-liposomes was about ten times higher than for neutrons only. Furthermore, theoretical calculation of the survival by enriched compound (55 ppm 10B), using the parameters from non-enriched compound (11 ppm 10B), shows that the killing effect in this case would be approximately five orders of magnitude higher than for neutrons only.

CONCLUSION

The results in this study show that epidermal growth factor-receptor targeted liposomes are suitable as tumor-cell delivery agents of boron for BNCT and support further studies to demonstrate their effectiveness in vivo.

Chemistry and biology of some low molecular weight boron compounds for boron neutron capture therapy

Boronated DNA targeting agents are especially attractive candidates for BNCT because they may deliver boron-10 to the nuclei of tumor cells. Numerous boron-containing analogs have been synthesized and some have shown promising results in initial biological tests. One of the most challenging tasks in this special field of research remains the finding of suitable targeting strategies for the selective delivery of boron rich DNA-intercalator/alkylator to tumor cells. Synthetic and biological studies of boron compounds suitable for DNA-binding are reviewed. The amino acid p-boronophenylalanine (BPA) is presently of considerable clinical interest. Other boronated amino acids might also be candidates for BNCT either per se, as part of part of tumor-seeking peptides or conjugated to targeting macromolecules. A large number of boronated L- and D-amino acids with varying liphophicility and sterical requirements are now available for evaluation. Recent synthetic and biological studies of aromatic boronoamino acids, carboranylamino acids and carboranyl amines are also reviewed.