Sensitizing effect of the phosphatidylinositol 3-kinase inhibitor wortmannin on thermal neutron irradiation with or without boron compound

Wortmannin, a phosphatidylinositol 3-kinase inhibitor, has been found to be an efficient radiosensitizer. We have investigated the radiosensitizing effect of wortmannin on cell killing against thermal neutrons produced by the Kyoto University Research (KUR) reactor. Wortmannin was added to cells 2 hours before irradiation and removed 16 hours after irradiation. Cells were irradiated by thermal neutrons with or without boron at 0, 10, and 20 ppm. The biological end point of cell survival was measured by colony formation assay. The D0 values of thermal neutrons in different boron concentrations, 0, 10, and 20 ppm were 1.2, 1.1, and 1.0 Gy, respectively. When cells were treated with wortmannin, the D0 values decreased to 0.5, 0.6, and 0.8 Gy at boron concentrations of 0, 10, and 20 ppm, respectively. Wortmannin enhanced cell death against thermal neutron irradiation especially in the absence of boron. Thus, our results suggest that wortmannin may be useful to combine with boron neutron capture therapy (BNCT) treatment when boron uptake by cells is limited.

The effects of boron neutron capture therapy on liver tumors and normal hepatocytes in mice

To explore the feasibility of employing boron neutron capture therapy (BNCT) to treat liver tumors, the effects of BNCT were investigated by using liver tumor models and normal hepatocytes in mice. Liver tumor models in C3H mice were developed by intrasplenic injection of SCCVII tumor cells. After borocaptate sodium (BSH) and boronophenylalanine (BPA) administration, (10)B concentrations were measured in tumors and liver and the liver was irradiated with thermal neutrons. The effects of BNCT on the tumor and normal hepatocytes were studied by using colony formation assay and micronucleus assay, respectively. To compare the effects of BSH-BNCT and BPA-BNCT, the compound biological effectiveness (CBE) factor was determined. The CBE factors for BSH on the tumor were 4.22 and 2.29 using D(10) and D(0) as endpoints, respectively. Those for BPA were 9.94 and 5.64. In the case of hepatocytes, the CBE factors for BSH and BPA were 0.94 and 4.25, respectively. Tumor-to-liver ratios of boron concentration following BSH and BPA administration were 0.3 and 2.8, respectively. Considering the accumulation ratios of (10)B, the therapeutic gain factors for BSH and BPA were 0.7 - 1.3 and 3.8 - 6.6, respectively. Therefore, it may be feasible to treat liver tumors with BPA-BNCT.

Molecular structural analysis of HPRT mutations induced by thermal and epithermal neutrons in Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells were exposed to thermal and epithermal neutrons, and the occurrence of mutations at the HPRT locus was investigated. The Kyoto University Research Reactor (KUR), which has been improved for use in neutron capture therapy, was the neutron source. Neutron energy spectra ranging from nearly pure thermal to epithermal can be chosen using the spectrum shifters and thermal neutron filters. To determine mutant frequency and cell survival, cells were irradiated with thermal and epithermal neutrons under three conditions: thermal neutron mode, mixed mode with thermal and epithermal neutrons, and epithermal neutron mode. The mutagenicity was different among the three irradiation modes, with the epithermal neutrons showing a mutation frequency about 5-fold that of the thermal neutrons and about 1.5-fold that of the mixed mode. In the thermal neutron and mixed mode, boron did not significantly increase the frequency of the mutants at the same dose. Therefore, the effect of boron as used in boron neutron capture therapy (BNCT) is quantitatively minimal in terms of mutation induction. Over 300 independent neutron-induced mutant clones were isolated from 12 experiments. The molecular structure of HPRT mutations was determined by analysis of all nine exons by multiplex polymerase chain reaction. In the thermal neutron and mixed modes, total and partial deletions were dominant and the fraction of total deletions was increased in the presence of boron. In the epithermal neutron mode, more than half of the mutations observed were total deletions. Our results suggest that there are clear differences between thermal and epithermal neutron beams in their mutagenicity and in the structural pattern of the mutants that they induce. Mapping of deletion breakpoints of 173 partial-deletion mutants showed that regions of introns 3-4, 7/8-9 and 9-0 are sensitive to the induction of mutants by neutron irradiation.

Change in oxygenation status in intratumour total and quiescent cells following gamma-ray irradiation, tirapazamine administration, cisplatin injection and bleomycin treatment

C3H/He mice bearing SCC VII tumours received 5-bromo-2'-deoxyuridine (BrdU) continuously for 5 days via implanted mini-osmotic pumps to label all proliferating (P) cells. The mice then received gamma-ray irradiation, or administration of tirapazamine (TPZ), cisplatin or bleomycin. At various time points after each treatment, tumour-bearing mice were irradiated with a series of test doses of gamma-rays, while alive or after being killed, to obtain hypoxic fractions (HFs) in the tumours. Immediately after gamma-ray test irradiation, the tumours were excised, minced and trypsinized. Tumour cell suspensions obtained were incubated with cytochalasin-B, a cytokinesis blocker, and the micronucleus (MN) frequency in cells without BrdU labelling (i.e. quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. MN frequency in the total (P + Q) tumour cells was determined from the tumours that were not pre-treated with BrdU. MN frequency of BrdU-unlabelled cells was then used to calculate the surviving fraction of the unlabelled cells from the regression line for the relationship between the MN frequency and the surviving fraction of total tumour cells. TPZ and cisplatin reduced the HF after treatment, especially in Q cells, and this tendency was particularly marked with TPZ. In contrast, bleomycin increased the HF after treatment. Both reoxygenation following gamma-ray irradiation or bleomycin treatment and a subsequent return to pre-treatment levels of HF following TPZ or cisplatin treatment (rehypoxiation) occurred more rapidly in total (P + Q) cells than in Q cells. Based on our previous report that total (P + Q) and Q cells within this tumour have large acutely and chronically HFs, respectively, we conclude that acute hypoxic cells play a major role in reoxygenation and rehypoxiation in SCC VII tumours.

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

10 B-Enriched borocaptate (BSH) was administered intraperitoneally to SCCVII tumor-bearing C3H / He mice. Electroporation (EP) was conducted by using a tweezers-type electrode. The (10) B contents in tumors were measured by prompt gamma-ray spectrometry. The colony formation assay was applied to investigate the antitumor effects of boron neutron capture therapy (BNCT) and thereby to estimate the intratumor localization of BSH. The (10) B concentrations 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 BSH injection delayed the clearance of BSH from tumors, and the (10) B level remained at 19.4(0.9) ppm at 3 h. The effect of BNCT increased with the (10) B concentration in tumors, and the combination with EP showed a remarkably 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 (10) B level (r = 0.982), and that of BSH-BNCT combined with EP lay close to the same correlation line. However, tumors subjected to EP after BSH injection did not show high radiosensitivity when irradiated after conversion to a single cell suspension by enzymatic digestion. This indicates that the increase of the BNCT effect by EP was a consequence of enclosure of BSH in the interstitial space of tumor tissue and not within tumor cells. This is different from a previous in vitro study. The combination 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 method is employed.

Changes in the sensitivity of intratumor cells during fractionated tirapazamine administration

Mice bearing solid tumors received 10 intraperitoneal administrations of 5-bromo-2'-deoxyuridine (BrdU) to label the proliferating (P) tumor cells. Then, as a priming treatment, tirapazamine (TPZ) was intraperitoneally administered. Further, 0 through 48 h later, the tumor-bearing mice received TPZ again at various doses. The tumor cells were isolated and incubated with a cytokinesis blocker. The micronucleus (MN) frequencies in cells with and without BrdU labeling, which were regarded as P and quiescent (Q) cells at the priming treatment, respectively, were determined using immunofluorescence staining for BrdU. The MN frequency in the total (P + Q) tumor cells was determined from the tumors that were not pretreated with BrdU. In addition, P cell ratios in the tumors at the second treatment were determined using immunofluorescence staining for P cell nuclear antigen. In each cell fraction, the longer the interval between the two treatments, the higher was the sensitivity to TPZ, except 1 h after the priming treatment. More than 24 h later, total and P cells, especially P cells, showed significantly higher sensitivity to TPZ than in the case of a single TPZ treatment. The longer the period between the two TPZ treatments, the lower was the P cell ratio at the second treatment. These findings were thought to indicate that the use of TPZ in the treatment of solid tumors causes a shift from the P to the Q state in vivo.

Combined effects of tirapazamine and mild hyperthermia on anti-angiogenic agent (TNP-470) treated tumors-reference to the effect on intratumor quiescent cells

PURPOSE

To evaluate the efficacy of the use of tirapazamine (TPZ), especially combined with mild hyperthermia (40 degrees C, 60 min), in the treatment of solid tumors following an anti-angiogenic treatment with TNP-470. In addition, we assessed the effect of TPZ and/or mild hyperthermia (MHT) combined with conventional radiotherapy or chemotherapy on TNP-470 treated tumors.

MATERIALS AND METHODS

C3H/He mice bearing SCC VII tumors subcutaneously received TNP-470 at two doses of 100 mg/kg after tumor cell inoculation. At the same time, the tumor-bearing mice received 5-bromo-2'-deoxyuridine (BrdU) continuously for 5 days via implanted mini-osmotic pumps to label all proliferating (P) cells. The mice then received TPZ administration combined with or without MHT, gamma-ray irradiation combined with or without TPZ and/or MHT, or cisplatin injection with or without TPZ and/or MHT. Another group of mice received a series of test doses of gamma-rays while alive or after being killed to obtain hypoxic fractions (HFs) in the tumors at various time points after the above-mentioned cytotoxic treatment point. After each treatment, the tumors were excised, minced, and trypsinized. The tumor cell suspensions thus obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the micronucleus (MN) frequency in cells without BrdU labeling (or quiescent [Q] cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total (P + Q) tumor cells was determined from the tumors that were not pretreated with BrdU. For the measurement of the HFs, the MN frequency of BrdU-unlabeled cells was then used to calculate the surviving fraction of the unlabeled cells from the regression line for the relationship between the MN frequency and the surviving fraction of total tumor cells.

RESULTS

TPZ administration combined with TNP-470 treatment and MHT increased the MN frequency more markedly than treatment with TPZ alone, and this tendency was more remarkable in Q cells than total cells. In both total and Q cells, combined treatment with TPZ and MHT produced significant increases in MN frequencies whether gamma-rays were delivered to TNP-470 treated tumors or cisplatin was injected into the TNP-470 administered mice. Although not significantly, the HFs of total and Q cell populations within solid tumors increased after TNP-470 treatment.

CONCLUSION

Combined treatment with TPZ and MHT, whether other cytotoxic treatments such as gamma-ray irradiation or chemotherapy using cisplatin were combined or not, was useful for sensitizing tumor cells in vivo including Q cells even after TNP-470 treatment.

Usefulness of tirapazamine as a combined agent in chemoradiation and thermo-chemoradiation therapy at mild temperatures: reference to the effect on intratumor quiescent cells

C3H / He mice bearing SCC VII tumors received 5-bromo-2'-deoxyuridine (BrdU) continuously for 5 days via implanted mini-osmotic pumps to label all proliferating (P) cells. The mice then received one of six different DNA-damaging agents with or without mild temperature hyperthermia (40 degrees C, 30 min, MTH). These agents were adriamycin (ADM), mitomycin C (MMC), cyclophosphamide (CPA), bleomycin (BLM), cisplatin (CDDP), and tirapazamine (TPZ). After the drug treatment, the tumor-bearing mice were irradiated with a series of doses of gamma-rays. Immediately after irradiation, the tumors were excised, minced and trypsinized. The tumor cell suspensions thus obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the micronucleus (MN) frequency in cells without BrdU labeling ( = quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total (P + Q) tumor cells was determined from the tumors that had not been pretreated with BrdU. MTH significantly increased the MN frequency of total cells in tumors irradiated with gamma-rays combined with CPA, BLM, CDDP or TPZ, and that of Q cells in tumors irradiated with gamma-rays combined with BLM or TPZ. The sensitivity difference in the MN frequency between total and Q tumor cells was significantly decreased by the combination with TPZ. TPZ combined with radiotherapy and TPZ combined with thermo-radiotherapy at mild temperatures appear to be promising modalities for sensitizing tumor cells in vivo, including Q tumor cells.

Endocardiac infectivity and binding to extracellular matrix proteins of oral Abiotrophia species

Microorganisms of the genus Abiotrophia, formerly known as nutritionally variant streptococci, are members of the oral flora and often isolated from patients with endocarditis, but pathogenicity of oral Abiotrophia species has not been examined yet. In this study, 17 strains isolated from healthy human oral cavities and 7 reference strains (all derived from patients with endocarditis) of Abiotrophia spp. were tested for their abilities to cause infections in damaged heart tissues in catheterized rats and to adhere to extracellular matrix proteins in vitro. The reference strains of A. defectiva and A. adiacens showed high infectivities in the rats. Four oral isolates of these two species showed similarly high infectivities and three had moderate infectivities. Most of 10 oral strains of A. para-adiacens and A. elegans were found to be generally less infective. The highly infective A. adiacens strains showed markedly high fibronectin-binding capacity, suggesting a possible relationship between the fibronectin-binding capacity and damaged heart tissue infectivity of the Abiotrophia species. A. defectiva strains which were also highly infective had moderate levels of binding to fibronectin and other extracellular matrix proteins. Most of A. para-adiacens and A. elegans strains showed low or negligible binding capacities to any extracellular matrix proteins tested.

Alteration of sensitivity of intratumor quiescent and total cells to gamma-rays following thermal neutron irradiation with or without 10B-compound

PURPOSE

Changes in the sensitivity of intratumor quiescent (Q) and total cells to gamma-rays following thermal neutron irradiation with or without 10B-compound were examined.

METHODS AND MATERIALS

5-Bromo-2'-deoxyuridine (BrdU) was injected to SCC VII tumor-bearing mice intraperitoneally 10 times to label all the proliferating (P) tumor cells. As priming irradiation, thermal neutrons alone or thermal neutrons with 10B-labeled sodium borocaptate (BSH) or dl-p-boronophenylalanine (BPA) were administered. The tumor-bearing mice then received a series of gamma-ray radiation doses, 0 through 24 h after the priming irradiation. During this period, no BrdU was administered. Immediately after the second irradiation, the tumors were excised, minced, and trypsinized. Following incubation of tumor cells with cytokinesis blocker, the micronucleus (MN) frequency in cells without BrdU labeling (= Q cells at the time of priming irradiation) was determined using immunofluorescence staining for BrdU. The MN frequency in the total (P + Q) tumor cells was determined from the tumors that were not pretreated with BrdU before the priming irradiation. To determine the BrdU-labeled cell ratios in the tumors at the time of the second irradiation, each group also included mice that were continuously administered BrdU until just before the second irradiation using mini-osmotic pumps which had been implanted subcutaneously 5 days before the priming irradiation.

RESULTS

In total cells, during the interval between the two irradiations, the tumor sensitivity to gamma-rays relative to that immediately after priming irradiation decreased with the priming irradiation ranking in the following order: thermal neutrons only > thermal neutrons with BSH > thermal neutrons with BPA. In contrast, in Q cells, during that time the sensitivity increased in the following order: thermal neutrons only < thermal neutrons with BSH < thermal neutrons with BPA. The longer the interval between the two irradiations, the higher was the BrdU-labeled cell ratio at the second irradiation. The labeled cell ratio at the same time point after each priming irradiation increased in the following order: thermal neutrons only < thermal neutrons with BSH < thermal neutrons with BPA.

CONCLUSION

These findings indicated that the use of 10B-compound, especially BPA, in thermal neutron irradiation causes the recruitment from the Q to P population.

Repair of potentially lethal damage by total and quiescent cells in solid tumors following a neutron capture reaction

PURPOSE

We analyzed the time-course of changes in the sensitivity of total (proliferating + quiescent and quiescent (Q) cell populations within solid tumors in situ following a neutron capture reaction and compared it with that after gamma-ray irradiation.

METHODS

After continuous labeling of proliferating cells with BrdU for 5 days, mice bearing SCC VII tumors received thermal neutron irradiation with or without a (10)B-labeled compound (sodium [(10)B]borocaptate, BSH, or DL-p-[(10)B]boronophenylalanine, BPA), or gamma-ray irradiation. From 5 min to 72 h after treatment, tumors were excised, minced, and trypsinized. Cell suspensions were incubated for 48 h with the cytokinesis blocker cytochalasin-B. The micronucleus frequency for BrdU-unlabeled cells, Q cells at treatment, was then determined by immunofluorescence staining for BrdU. The micronucleus frequency for total cells was obtained from tumors that had not been pretreated with BrdU labeling. The sensitivity was evaluated in terms of the frequency of induced micronuclei in binuclear tumor cells (micronucleus frequency).

RESULTS

Overall, Q cells showed greater repair capacities than total cells. gamma-Ray irradiation and neutron irradiation with BPA induced larger repair capacities in each cell population. In contrast, thermal neutron irradiation without a (10)B-labeled compound induced the smallest repair capacity in both cell populations. The use of a (10)B-labeled compound, especially BPA, widened the difference in sensitivity between total and Q cells, resulted in an increase in repair capacity in both cell populations, and made the repair patterns of the two cell populations look like those induced by gamma-ray irradiation.

CONCLUSION

Differences in sensitivity and repair patterns following the neutron capture reaction were thought to depend on differences in the distribution of the (10)B-labeled compound between the proliferating and Q cell populations.

The effect of graft perfusion with warm blood cardioplegia for cadaver heart transplantation

This study was designed to verify the effect of reperfusion of donor hearts in a perfusion apparatus after 60 min of global ischemia prior to heart transplantation. Thirteen dogs were exsanguinated from the femoral artery and cardiac arrest was achieved. The hearts were left in situ at room temperature (25 degrees C) for 60 min. In group A (n = 7), the hearts were excised and reperfused 60 min after cardiac arrest in the perfusion apparatus with substrate-enriched warm blood cardioplegia (WBCP) containing a hydroxyl radical scavenger, EPC, followed by 45 min of blood perfusion. Next, the hearts were preserved in cold (4 degrees C) University of Wisconsin (UW) solution. In group B (n = 6), the hearts were perfused with cold (4 degrees C) St. Thomas' solution 60 min after cardiac arrest and preserved in cold UW solution. Thereafter, all hearts in both groups were transplanted orthotopically to recipient dogs. In group A, 6 of 7 dogs were weaned from cardiopulmonary bypass (CPB). In group B, only 2 of 6 dogs were weaned from CPB. Moreover, 3 of the 6 hearts in group B did not start beating after transplantation (stone heart). This study suggested reperfusion of the donor heart in the perfusion apparatus with WBCP to be a beneficial preconditioning method when utilizing 60-min arrested hearts for transplantation.

Potentially lethal damage repair by total and quiescent tumor cells following various DNA-damaging treatments

After continuous labeling of proliferating (P) cells with 5-bromo-2'-deoxyuridine (BrdU) for 5 days, SCC VII tumor-bearing mice received various kinds of DNA-damaging treatments: gamma-ray irradiation, tirapazamine (TPZ, hypoxia-specific cytotoxin) administration, or cisplatin injection. From 0.5 to 72 hr after treatment, tumors were excised, minced, and trypsinized. Single tumor cell suspensions were incubated for 48 hr with a cytokinesis-blocker, cytochalasin-B. Then, the micronucleus (MN) frequency for BrdU-unlabeled cells, quiescent (Q) cells at treatment, was determined using immunofluorescence staining for BrdU. The MN frequency for total (P+Q) cells was obtained from tumors that were not pretreated with BrdU labeling. The sensitivity to each DNA-damaging treatment was evaluated in terms of the frequency of induced micronuclei in binuclear tumor cells (MN frequency). Treatment with gamma-rays or cisplatin resulted in a larger MN frequency in total cells than in Q cells. In contrast, TPZ treatment produced a smaller MN frequency in total cells than in Q cells. Regardless of the treatment used, Q cells showed greater repair capacities than total cells. However, TPZ caused much smaller repair capacity in both total and Q cells, compared with gamma-rays or cisplatin. Gamma-rays and cisplatin produced similar repair patterns. Differences in sensitivity between total and Q cells and repair patterns of the two cell populations were thought to depend on differences between the two cell populations in the toxicity of the DNA-damaging treatment and distribution pattern of the anticancer agent.

Reoxygenation in quiescent and total intratumor cells following thermal neutron irradiation with or without (10)B-compound-compared with that after gamma-ray irradiation

PURPOSE

Reoxygenation in quiescent (Q) and total tumor cells within solid tumors after thermal neutron irradiation with or without (10)B-compound was examined, comparing with that following gamma-ray irradiation.

METHODS AND MATERIALS

C3H/He mice bearing SCC VII tumors received 5-bromo-2'-deoxyuridine (BrdU) continuously for 5 days via implanted mini-osmotic pumps to label all proliferating (P) cells. Thirty minutes after intraperitoneal injection of sodium borocaptate-(10)B (BSH), or 3 h after oral administration of dl-p-boronophenylalanine-(10)B (BPA), the tumors were irradiated with thermal neutrons, or those without (10)B-compounds were irradiated with thermal neutrons alone or gamma-rays. At various time points after each treatment, a series of test doses of gamma-rays were given to tumor-bearing mice while alive or after being killed to obtain hypoxic fractions in the tumors. Immediately after irradiation, the tumors were excised, minced, and trypsinized. Following incubation of tumor cells with cytokinesis blocker, the micronucleus (MN) frequency in cells without BrdU labeling ( = Q cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total (P + Q) tumor cells was determined from the tumors that were not pretreated with BrdU. The MN frequency of BrdU-unlabeled cells was then used to calculate the surviving fraction of the unlabeled cells from the regression line for the relationship between the MN frequency and the surviving fraction of total tumor cells.

RESULTS

In both total and Q tumor cells, the hypoxic fractions immediately after each treatment went up suddenly. Reoxygenation after each treatment occurred more rapidly in total cells than in Q cells. In both cell populations, reoxygenation appeared to be rapidly induced in the following order: neutron irradiation without (10) gamma-ray irradiation.

CONCLUSION

Based on our previous report that total and Q cell fractions within these tumors have larger acutely and chronically hypoxic fractions, respectively, acute hypoxic cells appeared to play a larger role in reoxygenation. BSH was thought to have a potential to distribute more homogeneously in solid tumors than BPA, because BSH induced the nearer reoxygenation pattern to that following neutron irradiation alone than BPA.

The combined effect of boronophenylalanine and borocaptate in boron neutron capture therapy for SCCVII tumors in mice

PURPOSE

To increase the effect of boron neutron capture therapy (BNCT) on tumors in vivo, the combined effects of para-boronophenylalanine (BPA) and borocaptate sodium (BSH) were investigated.

METHODS AND MATERIALS

10B-enriched BPA and BSH were administered to C3H/He mice bearing SCCVII tumors by intragastric and intravenous injections, respectively. The colony formation and tumor control assays were employed for investigating antitumor effects of BNCT. The extent of homogeneity of tumor cell killing effect was examined by the distribution of frequencies of binuclear cells (BNC) producing a certain number of micronuclei (0,1,2,--,> or =5) to total number of BNC and by the comparison between surviving cell fraction (SF) in colony formation assay and the normal nuclear division fraction (NNDF) at first mitosis following BNCT.

RESULTS

The relationships between SF and radiation dose in Gy (D) at around 10 ppm of 10B in tumors were as follow: -InSF = -0.101 + 0.648 Gy(-1) x D, 0.0606+0.435 Gy(-1) x D, and -0.0155 + 0.342 Gy(-1) x D for BPA, BPA + BSH, and BSH, respectively. In tumor control assay, BPA was also more effective than BSH, but the difference of effectiveness significantly decreased: 1.9 times more effective in colony assay vs. 1.2 times in tumor control assay. The most effective treatment to achieve tumor cure was BNCT using BPA + BSH, and it was 1.9 times more effective than BSH-BNCT. In BSH-BNCT, NNDF decreased exponentially with radiation dose and was equal to SF. However, NNDF following BPA-BNCT showed a biphasic decrease with radiation dose, and SF was much lower than NNDF. In the combination of BPA and BSH, the discrepancy between NNDF and SF decreased in comparison with BPA-BNCT. The distribution of frequency of BNC with a certain number of micronuclei to total BNC was very close to Poisson distribution in BSH-BNCT tumors; however, it deviated from the Poisson in BPA-BNCT tumors. In combination with BPA and BSH, the distribution showed an intermediate pattern. These findings indicate that BSH distributes homogeneously with a heterogeneous distribution of BPA in tumors, and the heterogeneous effect of BPA-BNCT was improved by the combination of two boron compounds.

CONCLUSION

The heterogeneous cell killing effect of BPA-BNCT was improved by the combination of BSH, and increased tumor control rates. Therefore, this combination may improve clinical outcome of BNCT although the effects on normal tissues have to be examined before clinical application.

Modification of tirapazamine-induced cytotoxicity in combination with mild hyperthermia and/or nicotinamide: reference to effect on quiescent tumour cells

C3H/He and Balb/c mice bearing SCC VII or EMT6/KU tumours received continuous administration of 5-bromo-2'-deoxyuridine (BrdU) for 5 days to label all proliferating (P) cells. The tumours were locally heated at 40 degrees C for 60 min and/or the tumour-bearing mice received intraperitoneal injection of nicotinamide, and then tirapazamine (TPZ) was injected intraperitoneally. Sixty minutes after TPZ injection, the tumours were excised, minced and trypsinized. The tumour cell suspensions were incubated with cytochalasin-B (a cytokinesis-blocker), and the micronucleus (MN) frequency in cells without BrdU labelling (quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. The MN frequency in total (P+Q) tumour cells was determined from the tumours that were not pretreated with BrdU. The cytotoxicity of TPZ was evaluated in terms of the frequency of induced micronuclei in binuclear tumour cells (= MN frequency). In both tumour systems, the MN frequencies of Q cells were greater than those of total tumour cell populations. Mild heat treatment elevated the MN frequency in total and Q cells in both tumour systems, but the effect was more marked in Q cells. In total cells, mild heat treatment increased the MN frequency in EMT6/KU tumour cells more markedly than in SCC VII tumour cells. In contrast, in both tumour systems, nicotinamide decreased the MN frequency in both cell populations, with a greater influence on the total cells. The combination of TPZ and mild heat treatment may be useful for sensitizing tumour cells in vivo, including Q cells.

The role of valence on the high-affinity binding of Griffonia simplicifolia isolectins to type A human erythrocytes

The Griffonia simplicifolia-I (GS-I) isolectins have been used to probe the effect of lectin valence on their high-affinity binding to human erythrocytes. These tetrameric lectins are composed of A and B subunits and constitute a series of five isolectins (A4, A3B, A2B2, AB3, B4). The A subunit is specific for alpha-D-GalNAc end groups and binds to the blood type A determinant GalNAcalpha1, as well as to terminal alpha-D-Gal groups found on type B cells. The B subunit is specific for alpha-D-Gal end groups, and binds very specifically to type B erythrocytes. This series of isolectins is tetravalent (A4), trivalent (A3B), divalent (A2B2), and monovalent (AB3) for type A erythrocytes; thus, this system provides the opportunity to examine the effect of lectin valency on the association constants of these GS-I isolectins binding to cells. Cell binding experiments carried out using 125I-labeled GS-I isolectins and type A human erythrocytes allowed us to demonstrate that (1) the association constant of the isolectin monovalent for alpha-D-GalNAc (AB3) is virtually identical to its association constant for the haptenic sugar methyl-N-acetyl-alpha-D-galactosaminide, reported previously, and (2) the association constant of the GS-I isolectins for human type A erythrocytes increases with increasing valency of the isolectin. These results indicate that the increased affinity displayed by the GS-I isolectins for human type A erythrocytes is dependent on their multivalency, and not on an extended binding site nor on nonspecific, or noncarbohydrate, interactions of the lectin with the cell surface. These findings should be of general relevance to understanding the high-affinity interactions observed between other multivalent proteins and multivalent ligands (e.g., cell surfaces).

Effect of electroporation on cell killing by boron neutron capture therapy using borocaptate sodium (10B-BSH)

The cell membrane permeability of 10B-enriched borocaptate sodium (BSH) and the extent to which BSH is accumulated in cells are controversial. To elucidate these points and to enhance the accumulation of BSH in cells, the effect of electroporation on boron neutron capture therapy (BNCT) using BSH was investigated. The first group of SCCVII tumor cells was incubated in culture medium with 10B-BSH or 10B-enriched boric acid, and exposed to neutrons from the heavy water facility of the Kyoto University Reactor. More than 99% of neutrons were thermal neutrons at flux base. The second group was pretreated with electroporation in combination with 10B-BSH, and thereafter the cells were irradiated with neutrons. The cell-killing effect of BNCT was measured by colony formation assay. The surviving cell fraction decreased exponentially with neutron fluence, and addition of BSH significantly enhanced the cell-killing effect of NCT depending on 10B concentration and the preincubation time of cells in the BSH-containing culture medium. The electroporation of cells with BSH markedly enhanced the BNCT effect in comparison with that obtained with preincubation alone. The effect of BSH-BNCT with electroporation was almost equal to that of BNCT using 10B-boric acid at the same 10B concentration. The effect of BNCT on cells pretreated with BSH and electroporation was not reduced by repeated washing of the cells before neutron irradiation. Decrease of the effect of BSH-BNCT plus electroporation with increase in the waiting time between the electroporation and the neutron irradiation could be explained in terms of the extent of cell growth during that time. These data suggest that BSH penetrates the cells slowly and remains after washing. Electroporation can introduce BSH into the cells very efficiently, and BSH thus introduced stays in the cells and is not lost in spite of the intensive washing of the cells. Therefore, if electroporation is applied to tumors after BSH injection, 10B would remain in the tumors but be cleared from normal tissues, and selective accumulation of 10B in tumors will be achieved after an appropriate waiting time.

Electroporation increases the effect of borocaptate (10B-BSH) in neutron capture therapy

PURPOSE

The cell membrane permeability of borocaptate (10B-BSH) and its extent of accumulation in cells are controversial. This study was performed to elucidate these points.

METHODS AND MATERIALS

Two different treatments were applied to SCCVII tumor cells. The first group of tumor cells was incubated in culture medium with 10B-BSH or 10B-enriched boric acid, and was exposed to neutrons from the heavy water facility of the Kyoto University Reactor (KUR). More than 99% of neutrons were thermal neutrons at flux base. The second group was pretreated by electroporation in combination with 10B-BSH, and thereafter the cells were irradiated with neutrons. The cell killing effects of boron neutron capture therapy (BNCT) using BSH were investigated by colony formation assay.

RESULTS

Surviving cell fraction decreased exponentially with neutron fluence, and addition of BSH significantly enhanced the cell killing effect of neutron capture therapy (NCT) depending on 10B concentration. The effect of BSH-BNCT also increased with preincubation time of cells in the medium containing BSH. The electroporation of cells with BSH at 10 ppm 10B markedly enhanced BSH-BNCT effects in comparison with that of preincubation alone. The effect of BSH-BNCT with electroporation was equal to that of BNCT using 10B-boric acid at a same 10B concentration (10 ppm).

CONCLUSIONS

BSH is suggested to penetrate the cells slowly and remained after washing. Electroporation can introduce BSH into the cells very efficiently, and BSH stays in the cells and is not lost by washing. Therefore, if electroporation is applied to tumors after BSH injection, 10B remains in tumors but is cleared from normal tissues, and selective accumulation of 10B in tumors will be achieved after an adequate waiting time.

Positron emission tomography-based boron neutron capture therapy using boronophenylalanine for high-grade gliomas: part I

Determination of tumor boron-10 (10B) levels is required for accurate neutron dosimetry during boron neutron capture therapy. We assessed a new method for quantitative measurement of boronated drug uptake in high-grade gliomas. This method uses positron emission tomography (PET) with fluorine-18-labeled L-fluoroborono-phenylalanine (L-18F-10B-FBPA), which was synthesized as an analogue of L-boronophenylalanine. We studied the accumulation of L-18F-10B-FBPA by PET in patients with high-grade gliomas. Dynamic PET studies of brain tumors revealed that L-18F-10B-FBPA accumulated gradually after bolus injection, and the value of PET activity divided by the integrated plasma activity reached a constant level 42 min after injection, which was defined as the incorporation constant (Ic*). This constant reflected the appropriate L-18F-10B-FBPA accumulation in tumor tissue. Based on the Ic* constant, the methods for estimating tumor 10B concentration were devised. With this method, the estimated values of 10B concentration in gliomas were very close to the 10B levels in surgical specimens. This method was based solely on PET and can potentially provide data that would assist in the selection of patients for future treatment with boron neutron capture therapy after surgical resection of their brain tumors.

Positron emission tomography-based boron neutron capture therapy using boronophenylalanine for high-grade gliomas: part II

Based on pharmacokinetic findings of fluorine-18-labeled L-fluoroboronophenylalanine by positron emission tomography (PET), methods for estimating tumor 10B concentration were devised. In clinical practice of boron neutron capture therapy (BNCT) for high-grade gliomas, a large amount of L-boronophenylalanine (L-10B-BPA)-fructose solution is used. Under these conditions, a slow i.v. infusion of L-10B-BPA-fructose solution should be performed for BNCT; therefore, the changes over time in 10B concentration in the target tissue were estimated by convoluting the actual time course of changes in plasma 10B concentration with a PET-based weight function including the proper rate constants [K1 (ml/g/min), k2 (min(-1)), k3 (min(-1)), and k4 (min(-1))]. With this method, the estimated values of 10B concentration in gliomas were very close to the 10B levels in surgical specimens. This demonstrated the similarity in pharmacokinetics between fluorine-18-labeled L-fluoroboronophenylalanine and L-10B-BPA. This method, using the appropriate rate constant, permits the determination of tumor 10B concentration and is widely suitable for clinical BNCT, because the averaged PET data are enough to use in future patients without individual PET study.

Response of quiescent and total tumor cells in solid tumors to neutrons with various cadmium ratios

PURPOSE

Response of quiescent (Q) and total tumor cells in solid tumors to neutron irradiation with three different cadmium (Cd) ratios was examined. The role of Q cells in tumor control was also discussed.

METHODS AND MATERIALS

C3H/He mice bearing SCC VII tumors received continuous administration of 5-bromo-2'-deoxyuridine (BrdU) for 5 days using implanted mini-osmotic pumps to label all proliferating (P) cells. Thirty minutes after intraperitoneal injection of sodium borocaptate-10B (BSH), or 3 h after oral administration of dl-p-boronophenylalanine-10B (BPA), the tumors were irradiated with neutrons, or those without 10B-compounds were irradiated with gamma rays. This neutron irradiation was performed using neutrons with three different cadmium (Cd) ratios. The tumors were then excised, minced, and trypsinized. The tumor cell suspensions were incubated with cytochalasin-B (a cytokinesis-blocker), and the micronucleus (MN) frequency in cells without BrdU labeling (Q cells) was determined using immunofluorescence staining for BrdU. The MN frequency in total (P + Q) tumor cells was determined from tumors that were not pretreated with BrdU. The sensitivity to neutrons was evaluated in terms of the frequency of induced micronuclei in binuclear tumor cells (MN frequency).

RESULTS

Without 10B-compounds, the MN frequency in Q cells was lower than that in the total cell population. The sensitivity difference between total and Q cells was reduced by neutron irradiation. Relative biological effectiveness (RBE) of neutrons compared with gamma rays was larger in Q cells than in total cells, and the RBE values for low-Cd-ratio neutrons tended to be larger than those for high-Cd-ratio neutrons. With 10B-compounds, MN frequency for each cell population was increased, especially for total cells. This increase in MN frequency was marked when high-Cd-ratio neutrons were used. BPA increased the MN frequency for total tumor cells more than BSH. Nevertheless, the sensitivity of Q cells treated with BPA was lower than that in BSH-treated Q cells. This tendency was clearly observed in high-Cd-ratio neutrons.

CONCLUSION

From the viewpoint of enhancing the Q-cell sensitivity, tumors should be irradiated with high-Cd-ratio neutrons after BSH administration. However, normal tissue reaction remains to be examined because of its low tumor-to-normal tissue and tumor-to-blood biodistribution ratios.

Applicability of combination with tirapazamine in boron neutron capture therapy

SCC VII tumor-bearing mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating cells. After injection of tirapazamine (TPZ), a bioreductive agent, combined with sodium borocaptate-10B (BSH) or dl-p-boronophenylalanine-10B (BPA) administration, the tumors were irradiated with thermal neutrons, and then isolated and incubated with cytochalasin-B (a cytokinesis blocker). The micronucleus (MN) frequency in cells without BrdU labeling (quiescent (Q) cells) was determined by means of immunofluorescence staining for BrdU, and that for total cells was obtained from tumors not pretreated with BrdU. Even when no 10B-compound was administered, TPZ increased the MN frequency of tumor cells including Q cells, resulting in reduction of the difference in MN frequency between total and Q cells, mainly by increasing the MN frequency of Q cells. TPZ increased the MN frequency of Q cells when combined with BPA administration, but TPZ showed no apparent effect on each cell population when combined with BSH. Namely, TPZ reduced the difference in MN frequency between total and Q cells caused by 10B-compound administration, especially when BPA was administered. From the viewpoint of the overall cell killing effect in boron neutron capture therapy (BNCT), combination with TPZ appeared to be useful in BPA-BNCT, but not in BSH-BNCT.