BACKGROUND:BNCT (Boron Neutron Capture Therapy) is a tumor-selective particle radiotherapy that combines preferential boron accumulation in tumors and neutron irradiation. Although p-boronophenylalanine (BPA) has been clinically used, new boron compounds are needed for the advancement of BNCT. Based on previous studies in colon tumor-bearing mice, in this study, we evaluated MID:BSA (maleimide-functionalized closo-dodecaborate conjugated to bovine serum albumin) biodistribution and MID:BSA/BNCT therapeutic effect on tumors and associated radiotoxicity in the hamster cheek pouch oral cancer model.METHODS:Biodistribution studies were performed at 30 mg B/kg and 15 mg B/kg (12 h and 19 h post-administration). MID:BSA/BNCT (15 mg B/kg, 19 h) was performed at three different absorbed doses to precancerous tissue.RESULTS:MID:BSA 30 mg B/kg protocol induced high BSA toxicity. MID:BSA 15 mg B/kg injected at a slow rate was well-tolerated and reached therapeutically useful boron concentration values in the tumor and tumor/normal tissue ratios. The 19 h protocol exhibited significantly lower boron concentration values in blood. MID:BSA/BNCT exhibited a significant tumor response vs. the control group with no significant radiotoxicity.CONCLUSIONS:MID:BSA/BNCT would be therapeutically useful to treat oral cancer. BSA toxicity is a consideration when injecting a compound conjugated to BSA and depends on the animal model studied.

The aim of the present study was to analyze the histopathological features of Paget's disease of the jaws observed in a series comprising 31 cases. The study comprised all cases of Paget's disease of the jaws filed in the archives of the Surgical Pathology Laboratory of the Oral Pathology Department, School of Dentistry, University of Buenos Aires, between 1960 and 2018. Their microscopic features were evaluated, and available clinical data and radiographic studies were analyzed. Paget's disease of the jaws accounted for 0.05% of retrieved oral-maxillofacial pathologies. Microscopically, all cases showed lamellar bone trabeculae with the characteristic mosaic pattern. Twenty cases (64%) showed osteoblastic-osteoclastic activity, and all showed areas of necrosis. Cemento-osseous trabeculae were observed in 15 cases (48%), and cementicles were observed in 13 (42%). Osteomyelitis was seen in 11 cases (35%), all of which showed cemento-osseous trabeculae with a mosaic structure, sclerosis and necrosis, and chronic inflammation with abscess formation. Mean age was 61 years (44-85 years); 19 cases were women. Localization was the maxilla in 13 cases (42%), and the disease involved other skeletal bones in five cases. To our knowledge, this is the largest series of Paget's disease of the jaws reported to date. Paget's disease is infrequent in the jaws and has distinct histopathological features that not only differ from those observed at other skeletal sites but also require differential diagnosis from other pathologies affecting the jaws exclusively.

OBJECTIVE The aim of the present study was to evaluate the local and regional therapeutic efficacy and abscopal effect of BNCT mediated by boronophenyl-alanine, combined with Bacillus Calmette-Guerin (BCG) as an immunotherapy agent in this model. METHODS The local effect of treatment was evaluated in terms of tumor response in the irradiated tumor-bearing right hind flank. Metastatic spread to tumor-draining lymph nodes was analyzed as an indicator of regional effect. The abscopal effect of treatment was assessed as tumor growth inhibition in the contralateral (non-irradiated) left hind flank inoculated with tumor cells 2 weeks post-irradiation. The experimental groups BNCT, BNCT + BCG, BCG, Beam only (BO), BO +BCG, SHAM (tumor-bearing, no treatment, same manipulation) were studied. RESULTS BNCT and BNCT + BCG induced a highly significant local anti-tumor response, whereas BCG alone induced a weak local effect. BCG and BNCT + BCG induced a significant abscopal effect in the contralateral non-irradiated leg. The BNCT + BCG group showed significantly less metastatic spread to tumor-draining lymph nodes vs SHAM and vs BO. CONCLUSION This study suggests that BNCT + BCG-immunotherapy would induce local, regional and abscopal effects in tumor-bearing animals. BNCT would be the main effector of the local anti-tumor effect whereas BCG would be the main effector of the abscopal effect. ADVANCES IN KNOWLEDGE Although the local effect of BNCT has been widely evidenced, this is the first study to show the local, regional and abscopal effects of BNCT combined with immunotherapy, contributing to comprehensive cancer treatment with combined therapies.

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.

Purpose: Boron neutron capture therapy (BNCT) combines selective accumulation of B-10 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.

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.

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.

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.

External carcinogens, such as tobacco and alcohol, induce molecular changes in large areas of oral mucosa, which increase the risk of malignant transformation. This condition, known as field cancerization', can be detected in biopsy specimens using histochemical techniques, even before histological alterations are identified. The efficacy of these histochemical techniques as biomarkers of early cancerization must be demonstrated in appropriate models. The hamster cheek pouch oral cancer model, universally employed in biological studies and in studies for the prevention and treatment of oral cancer, is also an excellent model of field cancerization. The carcinogen is applied in solution to the surface of the mucosa and induces alterations that recapitulate the stages of cancerization in human oral mucosa. We have demonstrated that the following can be used for the early detection of cancerized tissue: silver staining of nucleolar organizer regions; the Feulgen reaction to stain DNA followed by ploidy analysis; immunohistochemical analysis of fibroblast growth factor-2, immunohistochemical labeling of proliferating cells to demonstrate an increase of epithelial cell proliferation in the absence of inflammation; and changes in markers of angiogenesis (i.e. those indicating vascular endothelial growth factor activity, endothelial cell proliferation and vascular density). The hamster cheek pouch model of oral cancer was also proposed and validated by our group for boron neutron capture therapy studies for the treatment of oral cancer. Clinical trials of this novel treatment modality have been performed and are underway for certain tumor types and localizations. Having demonstrated the efficacy of boron neutron capture therapy to control tumors in the hamster cheek pouch oral cancer model, we adapted the model for the long-term study of field cancerized tissue. We demonstrated the inhibitory effect of boron neutron capture therapy on tumor development in field cancerized tissue with acceptable levels of mucositis, a dose-limiting side-effect.

Background. We previously demonstrated the therapeutic success of sequential boron neutron capture therapy (Seq-BNCT) in the hamster cheek pouch oral cancer model. It consists of BPA-BNCT followed by GB-10-BNCT 24 or 48 hours later. Additionally, we proved that tumor blood vessel normalization with thalidomide prior to BPA-BNCT improves tumor control. The aim of the present study was to evaluate the therapeutic efficacy and explore potential boron microdistribution changes in Seq-BNCT preceded by tumor blood vessel normalization.Material and Methods. Tumor bearing animals were treated with thalidomide for tumor blood vessel normalization, followed by Seq-BNCT (Th + Seq-BNCT) or Seq-Beam Only (Th + Seq-BO) in the window of normalization. Boron microdistribution was assessed by neutron autoradiography.Results. Th + Seq-BNCT induced overall tumor response of 100%, with 87 (4)% complete tumor response. No cases of severe mucositis in dose-limiting precancerous tissue were observed. Differences in boron homogeneity between tumors pre-treated and not pre-treated with thalidomide were observed.Conclusion. Th + Seq-BNCT achieved, for the first time, response in all treated tumors. Increased homogeneity in tumor boron microdistribution is associated to an improvement in tumor control.

AIM:To evaluate vascular morphology and density, angiogenic switch activation, vascular endothelial growth factor (VEGF) expression, and endothelial cell (EC) proliferation in the hamster cheek pouch (HCP) model of oral cancer.MATERIALS AND METHODS:Immunohistochemical detection of factor VIII, 5'-Bromo-2'-Deoxyuridine (BrdU) and VEGF was performed in pre-malignant and tumoral tissues.RESULTS:Activation of angiogenesis was detected adjacent to epithelial dysplasia. Vascularized area and perimeter (p<0.001) increased in dysplasias and tumors. Tumor blood vessels exhibited an enhanced vascular compression (p<0.001) and structural alterations. EC proliferation was similar in dysplasias and carcinomas. An increase in vascular density, EC proliferation and VEGF expression was found in potentially malignant tissues but not in carcinomas.CONCLUSION:The angiogenic switch occurs in the dysplastic stage preceding tumor development in the HCP model of oral cancer. In potentially malignant tissues, increased VEGF expression favors EC proliferation and an increase in vascular density. Conversely, in tumors, VEGF is no longer of pivotal importance.

Boron neutron capture therapy (BNCT) is based on selective accumulation of 10B 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 10B/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 (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 dose–response 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: 4.5–8.9 Gy and BPA-BNCT II: 9.2–16 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.

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.

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.

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.

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.

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 10B 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 B10H10), 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.

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.