Optimization of the classical oral cancerization protocol in hamster to study oral cancer therapy.

OBJECTIVE(S): The hamster carcinogenesis model recapitulates oral oncogenesis. Dimethylbenz[a]anthracene (DMBA) cancerization induces early severe mucositis, affecting animal's welfare and causing tissue loss and pouch shortening. "Short" pouches cannot be everted for local irradiation for boron neutron capture therapy (BNCT). Our aim was to optimize the DMBA classical cancerization protocol to avoid severe mucositis, without affecting tumor development. We evaluated BNCT in animals cancerized with this novel protocol. MATERIALS AND METHODS: We studied: Classical cancerization protocol (24 applications) and Classical with two interruptions (completed at the end of the cancerization protocol). BNCT mediated by boronophenylalanine (BPA) was performed in both groups. RESULTS: The twice-interrupted group exhibited a significantly lower percentage of animals with severe mucositis versus the non-interrupted group (17% versus 71%) and a significantly higher incidence of long pouches (100% versus 53%). Tumor development and the histologic characteristics of tumor and precancerous tissue were not affected by the interruptions. For both groups, overall tumor response was more than 80%, with a similar incidence of BNCT-induced severe mucositis. CONCLUSION(S): The twice-interrupted protocol reduced severe mucositis during cancerization without affecting tumor development. This favored the animal's welfare and reduced the number of animals to be cancerized for our studies, without affecting BNCT response.

Different oral cancer scenarios to personalize targeted therapy: Boron Neutron Capture Therapy translational studies.

Boron neutron capture therapy (BNCT) is a targeted therapy, which consists of preferential accumulation of boron carriers in tumor followed by neutron irradiation. Each oral cancer patient has different risks of developing one or more carcinomas and/or oral mucositis induced after treatment. Our group proposed the hamster oral cancer model to study the efficacy of BNCT and associated mucositis. Translational studies are essential to the advancement of novel boron delivery agents and targeted strategies. Herein, we review our work in the hamster model in which we studied BNCT induced mucositis using three different cancerization protocols, mimicking three different clinical scenarios. The BNCT-induced mucositis increases with the aggressiveness of the carcinogenesis protocol employed, suggesting that the study of different oral cancer patient scenarios would help to develop personalized therapies.

Electroporation optimizes the uptake of boron-10 by tumor for boron neutron capture therapy (BNCT) mediated by GB-10: a boron biodistribution study in the hamster cheek pouch oral cancer model.

Boron neutron capture therapy (BNCT) is a promising cancer binary therapy modality that utilizes the nuclear capture reaction of thermal neutrons by boron-10 resulting in a localized release of high- and low-linear energy transfer (LET) radiation. Electrochemotherapy (ECT) is based on electroporation (EP) that induces opening of pores in cell membranes, allowing the entry of compounds. Because EP is applied locally to a tumor, the compound is incorporated preferentially by tumor cells. Based on the knowledge that the therapeutic success of BNCT depends centrally on the boron content in tumor and normal tissues and that EP has proven to be an excellent facilitator of tumor biodistribution of an anti-tumor agent, the aim of this study was to evaluate if EP can optimize the delivery of boronated compounds. We performed biodistribution studies and qualitative microdistribution analyses of boron employing the boron compound sodium decahydrodecaborate (GB-10) + EP in the hamster cheek pouch oral cancer model. Syrian hamsters with chemically induced exophytic squamous cell carcinomas were used. A typical EP treatment was applied to each tumor, varying the moment of application with respect to the administration of GB-10 (early or late). The results of this study showed a significant increase in the absolute and relative tumor boron concentration and optimization of the qualitative microdistribution of boron by the use of early EP + GB-10 versus GB-10 without EP. This strategy could be a tool to improve the therapeutic efficacy of BNCT/GB-10 in vivo.

Translational boron neutron capture therapy (BNCT) studies for the treatment of tumors in lung.

PURPOSE: Boron neutron capture therapy (BNCT) combines selective accumulation of 10B carriers in tumor tissue with subsequent neutron irradiation. BNCT has been proposed for the treatment of multiple, non-resectable, diffuse tumors in lung. The aim of the present study was to evaluate the therapeutic efficacy and toxicity of BNCT in an experimental model of lung metastases of colon carcinoma in BDIX rats and perform complementary survival studies. MATERIALS AND METHODS: We evaluated tumor control and toxicity in lung 2 weeks post-BNCT at 2 dose levels, including 5 experimental groups per dose level: T0 (euthanized pre-treatment), Boronophenylalanine-BNCT (BPA-BNCT), BPA + Sodium decahydrodecaborate-BNCT ((BPA + GB-10)-BNCT), Beam only (BO) and Sham (no treatment, same manipulation). Tumor response was assessed employing macroscopic and microscopic end-points. An additional experiment was performed to evaluate survival and oxygen saturation in blood. RESULTS AND CONCLUSIONS: No dose-limiting signs of short/medium-term toxicity were observed in lung. All end-points revealed statistically significant BNCT-induced tumor control vs Sham at both dose levels. The survival experiment showed a statistically significant 45% increase in post-treatment survival time in the BNCT group (48 days) versus Sham (33 days). These data consistently revealed growth suppression of lung metastases by BNCT with no manifest lung toxicity. Highlights Boron Neutron Capture Therapy suppresses growth of experimental lung metastases No BNCT-induced short/medium-term toxicity in lung is associated with tumor control Boron Neutron Capture Therapy increased post-treatment survival time by 45.

Boron neutron capture therapy (BNCT) translational studies in the hamster cheek pouch model of oral cancer at the new "B2" configuration of the RA-6 nuclear reactor.

Boron neutron capture therapy (BNCT) is based on selective accumulation of B-10 carriers in tumor followed by neutron irradiation. We demonstrated, in 2001, the therapeutic effect of BNCT mediated by BPA (boronophenylalanine) in the hamster cheek pouch model of oral cancer, at the RA-6 nuclear reactor. Between 2007 and 2011, the RA-6 was upgraded, leading to an improvement in the performance of the BNCT beam (B2 configuration). Our aim was to evaluate BPA-BNCT radiotoxicity and tumor control in the hamster cheek pouch model of oral cancer at the new "B2" configuration. We also evaluated, for the first time in the oral cancer model, the radioprotective effect of histamine against mucositis in precancerous tissue as the dose-limiting tissue. Cancerized pouches were exposed to: BPA-BNCT; BPA-BNCT + histamine; BO: Beam only; BO + histamine; CONTROL: cancerized, no-treatment. BNCT induced severe mucositis, with an incidence that was slightly higher than in "B1" experiments (86 vs 67%, respectively). BO induced low/moderate mucositis. Histamine slightly reduced the incidence of severe mucositis induced by BPA-BNCT (75 vs 86%) and prevented mucositis altogether in BO animals. Tumor overall response was significantly higher in BNCT (94-96%) than in control (16%) and BO groups (9-38%), and did not differ significantly from the "B1" results (91%). Histamine did not compromise BNCT therapeutic efficacy. BNCT radiotoxicity and therapeutic effect at the B1 and B2 configurations of RA-6 were consistent. Histamine slightly reduced mucositis in precancerous tissue even in this overly aggressive oral cancer model, without compromising tumor control.

Validation and Comparison of the Therapeutic Efficacy of Boron Neutron Capture Therapy Mediated By Boron-Rich Liposomes in Multiple Murine Tumor Models.

Boron neutron capture therapy (BNCT) was performed at the University of Missouri Research Reactor in mice bearing CT26 colon carcinoma flank tumors and the results were compared with previously performed studies with mice bearing EMT6 breast cancer flank tumors. Mice were implanted with CT26 tumors subcutaneously in the caudal flank and were given two separate tail vein injections of unilamellar liposomes composed of cholesterol, 1,2-distearoyl-sn-glycer-3-phosphocholine, and K[nido-7-CH3(CH2)15-7,8-C2B9H11] in the lipid bilayer and encapsulated Na3[1-(2`-B10H9)-2-NH3B10H8] within the liposomal core. Mice were irradiated 30 hours after the second injection in a thermal neutron beam for various lengths of time. The tumor size was monitored daily for 72 days. Despite relatively lower tumor boron concentrations, as compared to EMT6 tumors, a 45 minute neutron irradiation BNCT resulted in complete resolution of the tumors in 50% of treated mice, 50% of which never recurred. Median time to tumor volume tripling was 38 days in BNCT treated mice, 17 days in neutron-irradiated mice given no boron compounds, and 4 days in untreated controls. Tumor response in mice with CT26 colon carcinoma was markedly more pronounced than in previous reports of mice with EMT6 tumors, a difference which increased with dose. The slope of the dose response curve of CT26 colon carcinoma tumors is 1.05 times tumor growth delay per Gy compared to 0.09 times tumor growth delay per Gy for EMT6 tumors, indicating that inherent radiosensitivity of tumors plays a role in boron neutron capture therapy and should be considered in the development of clinical applications of BNCT in animals and man.

Therapeutic efficacy of boron neutron capture therapy mediated by boron-rich liposomes for oral cancer in the hamster cheek pouch model.

The application of boron neutron capture therapy (BNCT) mediated by liposomes containing (10)B-enriched polyhedral borane and carborane derivatives for the treatment of head and neck cancer in the hamster cheek pouch oral cancer model is presented. These liposomes are composed of an equimolar ratio of cholesterol and 1,2-distearoyl-sn-glycero-3-phosphocholine, incorporating K[nido-7-CH3(CH2)15-7,8-C2B9H11] (MAC) in the bilayer membrane while encapsulating the hydrophilic species Na3[ae-B20H17NH3] (TAC) in the aqueous core. Unilamellar liposomes with a mean diameter of 83 nm were administered i.v. in hamsters. After 48 h, the boron concentration in tumors was 67 ± 16 ppm whereas the precancerous tissue contained 11 ± 6 ppm, and the tumor/normal pouch tissue boron concentration ratio was 10:1. Neutron irradiation giving a 5-Gy dose to precancerous tissue (corresponding to 21 Gy in tumor) resulted in an overall tumor response (OR) of 70% after a 4-wk posttreatment period. In contrast, the beam-only protocol gave an OR rate of only 28%. Once-repeated BNCT treatment with readministration of liposomes at an interval of 4, 6, or 8 wk resulted in OR rates of 70-88%, of which the complete response ranged from 37% to 52%. Because of the good therapeutic outcome, it was possible to extend the follow-up of BNCT treatment groups to 16 wk after the first treatment. No radiotoxicity to normal tissue was observed. A salient advantage of these liposomes was that only mild mucositis was observed in dose-limiting precancerous tissue with a sustained tumor response of 70-88%.

Boron biodistribution for BNCT in the hamster cheek pouch oral cancer model: combined administration of BSH and BPA.

Sodium mercaptoundecahydro-closo-dodecaborate (BSH) is being investigated clinically for BNCT. We examined the biodistribution of BSH and BPA administered jointly in different proportions in the hamster cheek pouch oral cancer model. The 3 assayed protocols were non-toxic, and showed preferential tumor boron uptake versus precancerous and normal tissue and therapeutic tumor boron concentration values (70-85ppm). All 3 protocols warrant assessment in BNCT studies to contribute to the knowledge of (BSH+BPA)-BNCT radiobiology for head and neck cancer and optimize therapeutic efficacy.

Boron neutron capture therapy (BNCT) for liver metastasis in an experimental model: dose­response at five-week follow-up based on retrospective dose assessment in individual rats.

Boron neutron capture therapy (BNCT) was proposed for untreatable colorectal liver metastases. Employing an experimental model of liver metastases in rats, we recently demonstrated that BNCT mediated by boronophenylalanine (BPA-BNCT) at 13 Gy prescribed to tumor is therapeutically useful at 3-week follow-up. The aim of the present study was to evaluate dose­response at 5-week follow-up, based on retrospective dose assessment in individual rats. BDIX rats were inoculated with syngeneic colon cancer cells DHD/K12/TRb. Tumor-bearing animals were divided into three groups: BPA-BNCT (n = 19), Beam only (n = 8) and Sham (n = 7) (matched manipulation, no treatment). For each rat, neutron flux was measured in situ and boron content was measured in a pre-irradiation blood sample for retrospective individual dose assessment. For statistical analysis (ANOVA), individual data for the BPA-BNCT group were pooled according to absorbed tumor dose, BPA-BNCT I: 4.5­8.9 Gy and BPA-BNCT II: 9.2­16 Gy. At 5 weeks post-irradiation, the tumor surface area post-treatment/pre-treatment ratio was 12.2 ± 6.6 for Sham, 7.8 ± 4.1 for Beam only, 4.4 ± 5.6 for BPA-BNCT I and 0.45 ± 0.20 for BPA-BNCT II; tumor nodule weight was 750 ± 480 mg for Sham, 960 ± 620 mg for Beam only, 380 ± 720 mg for BPA-BNCT I and 7.3 ± 5.9 mg for BPA-BNCT II. The BPA-BNCT II group exhibited statistically significant tumor control with no contributory liver toxicity. Potential threshold doses for tumor response and significant tumor control were established at 6.1 and 9.2 Gy, respectively.

Biodistribution of sodium borocaptate (BSH) for boron neutron capture therapy (BNCT) in an oral cancer model.

Boron neutron capture therapy (BNCT) is based on selective accumulation of ¹°B carriers in tumor followed by neutron irradiation. We previously proved the therapeutic success of BNCT mediated by the boron compounds boronophenylalanine and sodium decahydrodecaborate (GB-10) in the hamster cheek pouch oral cancer model. Based on the clinical relevance of the boron carrier sodium borocaptate (BSH) and the knowledge that the most effective way to optimize BNCT is to improve tumor boron targeting, the specific aim of this study was to perform biodistribution studies of BSH in the hamster cheek pouch oral cancer model and evaluate the feasibility of BNCT mediated by BSH at nuclear reactor RA-3. The general aim of these studies is to contribute to the knowledge of BNCT radiobiology and optimize BNCT for head and neck cancer. Sodium borocaptate (50 mg ¹°B/kg) was administered to tumor-bearing hamsters. Groups of 3-5 animals were killed humanely at nine time-points, 3-12 h post-administration. Samples of blood, tumor, precancerous pouch tissue, normal pouch tissue and other clinically relevant normal tissues were processed for boron measurement by optic emission spectroscopy. Tumor boron concentration peaked to therapeutically useful boron concentration values of 24-35 ppm. The boron concentration ratio tumor/normal pouch tissue ranged from 1.1 to 1.8. Pharmacokinetic curves showed that the optimum interval between BSH administration and neutron irradiation was 7-11 h. It is concluded that BNCT mediated by BSH at nuclear reactor RA-3 would be feasible.

Boron neutron capture therapy demonstrated in mice bearing EMT6 tumors following selective delivery of boron by rationally designed liposomes.

The application of boron neutron capture therapy (BNCT) following liposomal delivery of a (10)B-enriched polyhedral borane and a carborane against mouse mammary adenocarcinoma solid tumors was investigated. Unilamellar liposomes with a mean diameter of 134 nm or less, composed of an equimolar mixture of cholesterol and 1,2-distearoyl-sn-glycero-3-phosphocholine and incorporating Na3[1-(2'-B10H9)-2-NH3B10H8] in the aqueous interior and K[nido-7-CH3(CH2)15-7,8-C2B9H11] in the bilayer, were injected into the tail veins of female BALB/c mice bearing right flank EMT6 tumors. Biodistribution studies indicated that two identical injections given 24 h apart resulted in tumor boron levels exceeding 67 µg/g tumor at 54 h--with tumor/blood boron ratios being greatest at 96 h (5.68:1; 43 µg boron/g tumor)--following the initial injection. For BNCT experiments, tumor-bearing mice were irradiated 54 h after the initial injection for 30 min with thermal neutrons, resulting in a total fluence of 1.6 × 10(12) neutrons per cm(2) (±7%). Significant suppression of tumor growth was observed in mice given BNCT vs. control mice (only 424% increase in tumor volume at 14 d post irradiation vs. 1551% in untreated controls). In a separate experiment in which mice were given a second injection/irradiation treatment 7 d after the first, the tumor growth was vastly diminished (186% tumor volume increase at 14 d). A similar response was obtained for mice irradiated for 60 min (169% increase at 14 d), suggesting that neutron fluence was the limiting factor controlling BNCT efficacy in this study.

Blood vessel normalization in the hamster oral cancer model for experimental cancer therapy studies.

BACKGROUND: Normalization of tumor blood vessels improves drug and oxygen delivery to cancer cells. The aim of this study was to develop a technique to normalize blood vessels in the hamster cheek pouch model of oral cancer. MATERIALS AND METHODS: Tumor-bearing hamsters were treated with thalidomide and were compared with controls. RESULTS: Twenty eight hours after treatment with thalidomide, the blood vessels of premalignant tissue observable in vivo became narrower and less tortuous than those of controls; Evans Blue Dye extravasation in tumor was significantly reduced (indicating a reduction in aberrant tumor vascular hyperpermeability that compromises blood flow), and tumor blood vessel morphology in histological sections, labeled for Factor VIII, revealed a significant reduction in compressive forces. These findings indicated blood vessel normalization with a window of 48 h. CONCLUSION: The technique developed herein has rendered the hamster oral cancer model amenable to research, with the potential benefit of vascular normalization in head and neck cancer therapy.

Boron neutron capture therapy (BNCT) for liver metastasis: therapeutic efficacy in an experimental model.

Boron neutron capture therapy (BNCT) was proposed for untreatable colorectal liver metastases. The present study evaluates tumor control and potential radiotoxicity of BNCT in an experimental model of liver metastasis. BDIX rats were inoculated with syngeneic colon cancer cells DHD/K12/TRb. Tumor-bearing animals were divided into three groups: BPA-BNCT, boronophenylalanine (BPA) + neutron irradiation; Beam only, neutron irradiation; Sham, matched manipulation. The total absorbed dose administered with BPA-BNCT was 13 ± 3 Gy in tumor and 9 ± 2 Gy in healthy liver. Three weeks post-treatment, the tumor surface area post-treatment/pre-treatment ratio was 0.46 ± 0.20 for BPA-BNCT, 2.7 ± 1.8 for Beam only and 4.5 ± 3.1 for Sham. The pre-treatment tumor nodule mass of 48 ± 19 mg fell significantly to 19 ± 16 mg for BPA-BNCT, but rose significantly to 140 ± 106 mg for Beam only and to 346 ± 302 mg for Sham. For both end points, the differences between the BPA-BNCT group and each of the other groups were statistically significant (ANOVA). No clinical, macroscopic or histological normal liver radiotoxicity was observed. It is concluded that BPA-BNCT induced a significant remission of experimental colorectal tumor nodules in liver with no contributory liver toxicity.

Boron delivery with liposomes for boron neutron capture therapy (BNCT): biodistribution studies in an experimental model of oral cancer demonstrating therapeutic potential.

Boron neutron capture therapy (BNCT) combines selective accumulation of (10)B carriers in tumor tissue with subsequent neutron irradiation. We previously demonstrated the therapeutic efficacy of BNCT in the hamster cheek pouch oral cancer model. Optimization of BNCT depends largely on improving boron targeting to tumor cells. Seeking to maximize the potential of BNCT for the treatment for head and neck cancer, the aim of the present study was to perform boron biodistribution studies in the oral cancer model employing two different liposome formulations that were previously tested for a different pathology, i.e., in experimental mammary carcinoma in BALB/c mice: (1) MAC: liposomes incorporating K[nido-7-CH(3)(CH(2))(15)-7,8-C(2)B(9)H(11)] in the bilayer membrane and encapsulating a hypertonic buffer, administered intravenously at 6 mg B per kg body weight, and (2) MAC-TAC: liposomes incorporating K[nido-7-CH(3)(CH(2))(15)-7,8-C(2)B(9)H(11)] in the bilayer membrane and encapsulating a concentrated aqueous solution of the hydrophilic species Na(3) [ae-B(20)H(17)NH(3)], administered intravenously at 18 mg B per kg body weight. Samples of tumor, precancerous and normal pouch tissue, spleen, liver, kidney, and blood were taken at different times post-administration and processed to measure boron content by inductively coupled plasma mass spectrometry. No ostensible clinical toxic effects were observed with the selected formulations. Both MAC and MAC-TAC delivered boron selectively to tumor tissue. Absolute tumor values for MAC-TAC peaked to 66.6 ± 16.1 ppm at 48 h and to 43.9 ± 17.6 ppm at 54 h with very favorable ratios of tumor boron relative to precancerous and normal tissue, making these protocols particularly worthy of radiobiological assessment. Boron concentration values obtained would result in therapeutic BNCT doses in tumor without exceeding radiotolerance in precancerous/normal tissue at the thermal neutron facility at RA-3.

Tumor blood vessel "normalization" improves the therapeutic efficacy of boron neutron capture therapy (BNCT) in experimental oral cancer.

We previously demonstrated the efficacy of BNCT mediated by boronophenylalanine (BPA) to treat tumors in a hamster cheek pouch model of oral cancer with no normal tissue radiotoxicity and moderate, albeit reversible, mucositis in precancerous tissue around treated tumors. It is known that boron targeting of the largest possible proportion of tumor cells contributes to the success of BNCT and that tumor blood vessel normalization improves drug delivery to the tumor. Within this context, the aim of the present study was to evaluate the effect of blood vessel normalization on the therapeutic efficacy and potential radiotoxicity of BNCT in the hamster cheek pouch model of oral cancer. Blood vessel normalization was induced by two doses of thalidomide in tumor-bearing hamsters on 2 consecutive days. All studies in thalidomide-treated animals were performed 48 h after the first dose of thalidomide, previously established as the window of normalization. Biodistribution studies were performed with BPA at a dose of 15.5 mg (10)B/kg in thalidomide-treated (Th+) and untreated (Th-) tumor-bearing hamsters. The effect of blood vessel normalization prior to BPA administration on the efficacy of BNCT was assessed in in vivo BNCT studies at the RA-3 Nuclear Reactor in tumor-bearing hamsters. Group I was treated with BPA-BNCT after treatment with thalidomide (Th+ BPA-BNCT). Group II was treated with BPA-BNCT alone (Th- BPA-BNCT). Group III was treated with the beam only after treatment with thalidomide (Th+ BO), and Group IV was treated with the beam only (Th- BO). Groups I and II were given the same dose of BPA (15.5 mg (10)B/kg), and all groups (I-IV) were exposed to the same neutron fluence. Two additional groups were treated with the beam only at a higher dose to exacerbate mucositis in precancerous tissue and to explore the potential direct protective effect of thalidomide on radiation-induced mucositis in a scenario of more severe toxicity, i.e. Group V (Th+ hdBO) and Group VI (Th- hdBO). The animals were followed for 28 days. Biodistribution studies revealed no statistically significant differences in gross boron content between Th+ and Th- animals. Overall tumor control (complete response + partial response) at 28 days post-treatment was significantly higher for Group I (Th+ BPA-BNCT) than for Group II (Th- BPA-BNCT): 84 ± 3% compared to 67 ± 5%. Pretreatment with thalidomide did not induce statistically significant changes in overall tumor control induced by the beam only, i.e. 15 ± 5% in Group III (Th+ BO) and 18 ± 5% in Group IV (Th- BO), or in overall tumor control induced by the high-dose beam only, i.e. 60 ± 7% in Group V (Th+ hdBO) and 47 ± 10% in Group VI (Th- hdBO). BPA-BNCT alone (Group II) induced mucositis in precancerous tissue that reached Grades 3-4 in 80% of the animals, whereas pretreatment with thalidomide (Group I) prevented mucositis Grades 3 and 4 completely. Beam-only Group III (Th+ BO) exhibited only Grade 1 mucositis in precancerous tissue, whereas 17% of the animals in beam-only Group IV (Th- BO) reached Grade 2 mucositis. High-dose beam-only group V (Th+ hdBO) exhibited only Grade 2 mucositis, whereas high-dose beam-only group VI (Th- hdBO) reached Grade 3 mucositis in 83% of the animals. In all cases mucositis in precancerous tissue was reversible. No normal tissue radiotoxicity was observed with any of the protocols. Pretreatment with thalidomide enhanced the therapeutic efficacy of BNCT and reduced precancerous tissue toxicity.

Boron Neutron Capture Therapy (BNCT) in an oral precancer model: therapeutic benefits and potential toxicity of a double application of BNCT with a six-week interval.

Given the clinical relevance of locoregional recurrences in head and neck cancer, we developed a novel experimental model of premalignant tissue in the hamster cheek pouch for long-term studies and demonstrated the partial inhibitory effect of a single application of Boron Neutron Capture Therapy (BNCT) on tumor development from premalignant tissue. The aim of the present study was to evaluate the effect of a double application of BNCT with a 6 week interval in terms of inhibitory effect on tumor development, toxicity and DNA synthesis. We performed a double application, 6 weeks apart, of (1) BNCT mediated by boronophenylalanine (BPA-BNCT); (2) BNCT mediated by the combined application of decahydrodecaborate (GB-10) and BPA [(GB-10+BPA)-BNCT] or (3) beam-only, at RA-3 nuclear reactor and followed the animals for 8 months. The control group was cancerized and sham-irradiated. BPA-BNCT, (GB-10+BPA)-BNCT and beam-only induced a reduction in tumor development from premalignant tissue that persisted until 8, 3, and 2 months respectively. An early maximum inhibition of 100% was observed for all 3 protocols. No normal tissue radiotoxicity was detected. Reversible mucositis was observed in premalignant tissue, peaking at 1 week and resolving by the third week after each irradiation. Mucositis after the second application was not exacerbated by the first application. DNA synthesis was significantly reduced in premalignant tissue 8 months post-BNCT. A double application of BPA-BNCT and (GB-10+BPA)-BNCT, 6 weeks apart, could be used therapeutically at no additional cost in terms of radiotoxicity in normal and dose-limiting tissues.

"Sequential" boron neutron capture therapy (BNCT): a novel approach to BNCT for the treatment of oral cancer in the hamster cheek pouch model.

In the present study the therapeutic effect and potential toxicity of the novel "Sequential" boron neutron capture therapy (Seq-BNCT) for the treatment of oral cancer was evaluated in the hamster cheek pouch model at the RA-3 Nuclear Reactor. Two groups of animals were treated with "Sequential" BNCT, i.e., BNCT mediated by boronophenylalanine (BPA) followed by BNCT mediated by sodium decahydrodecaborate (GB-10) either 24 h (Seq-24h-BNCT) or 48 h (Seq-48h-BNCT) later. In an additional group of animals, BPA and GB-10 were administered concomitantly [(BPA + GB-10)-BNCT]. The single-application BNCT was to the same total physical tumor dose as the "Sequential" BNCT treatments. At 28 days post-treatment, Seq-24h-BNCT and Seq-48h-BNCT induced, respectively, overall tumor responses of 95 ± 2% and 91 ± 3%, with no statistically significant differences between protocols. Overall response for the single treatment with (BPA + GB-10)-BNCT was 75 ± 5%, significantly lower than for Seq-BNCT. Both Seq-BNCT protocols and (BPA + GB-10)-BNCT induced reversible mucositis in the dose-limiting precancerous tissue around treated tumors, reaching Grade 3/4 mucositis in 47 ± 12% and 60 ± 22% of the animals, respectively. No normal tissue toxicity was associated with tumor response for any of the protocols. "Sequential" BNCT enhanced tumor response without an increase in mucositis in dose-limiting precancerous tissue.

Intercalibration of physical neutron dosimetry for the RA-3 and MURR thermal neutron sources for BNCT small-animal research.

New thermal neutron irradiation facilities to perform cell and small-animal irradiations for Boron Neutron Capture Therapy research have been installed at the Missouri University Research Reactor and at the RA-3 research reactor facility in Buenos Aires, Argentina. Recognizing the importance of accurate and reproducible physical beam dosimetry as an essential tool for combination and intercomparisons of preclinical and clinical results from the different facilities, we have conducted an experimental intercalibration of the neutronic performance of the RA-3 and MURR thermal neutron sources.

Boron neutron capture therapy (BNCT) for the treatment of liver metastases: biodistribution studies of boron compounds in an experimental model.

We previously demonstrated the therapeutic efficacy of different boron neutron capture therapy (BNCT) protocols in an experimental model of oral cancer. BNCT is based on the selective accumulation of (10)B carriers in a tumor followed by neutron irradiation. Within the context of exploring the potential therapeutic efficacy of BNCT for the treatment of liver metastases, the aim of the present study was to perform boron biodistribution studies in an experimental model of liver metastases in rats. Different boron compounds and administration conditions were assayed to determine which administration protocols would potentially be therapeutically useful in in vivo BNCT studies at the RA-3 nuclear reactor. A total of 70 BDIX rats were inoculated in the liver with syngeneic colon cancer cells DHD/K12/TRb to induce the development of subcapsular tumor nodules. Fourteen days post-inoculation, the animals were used for biodistribution studies. We evaluated a total of 11 administration protocols for the boron compounds boronophenylalanine (BPA) and GB-10 (Na(2)(10)B(10)H(10)), alone or combined at different dose levels and employing different administration routes. Tumor, normal tissue, and blood samples were processed for boron measurement by atomic emission spectroscopy. Six protocols proved potentially useful for BNCT studies in terms of absolute boron concentration in tumor and preferential uptake of boron by tumor tissue. Boron concentration values in tumor and normal tissues in the liver metastases model show it would be feasible to reach therapeutic BNCT doses in tumor without exceeding radiotolerance in normal tissue at the thermal neutron facility at RA-3.

Development of a model of tissue with potentially malignant disorders (PMD) in the hamster cheek pouch to explore the long-term potential therapeutic and/or toxic effects of different therapeutic modalities.

OBJECTIVE: Given that locoregional recurrences developing from a tissue with potentially malignant disorders (PMD) in oral mucosa are a frequent cause of therapeutic failure, and that tissue with PMD is dose-limiting, the aim of the present study was to develop a model of tissue with PMD to evaluate the long-term therapeutic/toxic effects of different therapeutic modalities. MATERIALS AND METHODS: We evaluated 5 carcinogenesis protocols based on topical application of the carcinogen dimethyl-1,2-benzanthracene in the hamster cheek pouch, twice a week for 4, 6, 7, and 8 weeks and the classical 3 times a week for 12 weeks. RESULTS: Long-term follow-up (8 months after protocol completion) was only possible with the 4- and 6-week carcinogenesis protocols. Tumour development increased progressively with time and aggressiveness of the carcinogenesis protocols. The time at which tumours developed in > or =90% of the animals was at protocol completion (T0) for the 12-week protocol, 1 month post-T0 for the 8-week protocol, 3 months post-T0 for the 7-week protocol and 4 months post-T0 for the 6-week protocol. <40% of the animals in the 4-week protocol developed tumours within the 8 months follow-up period. DNA synthesis rose as a function of time and protocol aggressiveness. CONCLUSIONS: The 6-week carcinogenesis protocol was selected for long-term studies of different therapeutic modalities in tissue with PMD because it permitted long-term follow-up and guaranteed tumour development in > or =90% of the animals.