The combined effect of electroporation and borocaptate in boron neutron capture therapy for murine solid tumors

B-10-Enriched borocaptate (BS11) was administered intraperitoneally to SCCV II tumor-bearing C3H/He mice, Electroporation (EP) was conducted by using a tweezers-type electrode, The B-10 contents in tumors were measured by prom pt gamma-ray spectrometry, The colony formation assay was applied to invest igate the antitumor effects of boron neutron capture therapy (BNCT) and the reby to estimate the intratumor localization of BS11, The B-10 concentratio ns in tumors decreased with time following BSH administration, falling to 5 .4(+/-0.1) ppm at 3 h, whereas EP treatment (3 repetitions) 15 min after BS H injection delayed the clearance of BSH from tumors, and the B-10 level re mained at. 19.4(+/-0.9) ppm at 3 h, The effect of BNCT increased with the B -10 concentration in tumors, and the combination with EP showed a remarkabl y large cell killing effect even at 3 h after BSH injection. The effect of BNCT, i.e., slope coefficient of the cell survival curve of tumors, without EP was proportional to tumor B-10 level (r=0.982), and that of BSH-BNCT co mbined with EP lay close to the same correlation line. However, tumors subj ected to EP after BSH injection did not show high radiosensitivity when irr adiated after conversion to a single cell suspension by enzymatic digestion . This indicates that the increase of the BNCT effect by EP was a consequen ce of enclosure of BSH in the interstitial space of tumor tissue and not wi thin tumor cells. This is different from a previous ill vitro study, The co mbination of EP and BNCT may be clinically useful, if a procedure to limit EP to the tumor region becomes available or if an alternative similar metho d is employed.