A new animal model for human undifferentiated thyroid carcinoma

Optimization of boron neutron capture therapy for the treatment of undifferentiated thyroid cancer

PURPOSE

To analyze the possible increase in efficacy of boron neutron capture therapy (BNCT) for undifferentiated thyroid carcinoma (UTC) by using p-boronophenylalanine (BPA) plus 2,4-bis (alpha,beta-dihydroxyethyl)-deutero-porphyrin IX (BOPP) and BPA plus nicotinamide (NA) as a radiosensitizer of the BNCT reaction.

METHODS AND MATERIALS

Nude mice were transplanted with a human UTC cell line (ARO), and after 15 days they were treated as follows: (1) control, (2) NCT (neutrons alone), (3) NCT plus NA (100 mg/kg body weight [bw]/day for 3 days), (4) BPA (350 mg/kg bw) + neutrons, (5) BPA + NA + neutrons, and (6) BPA + BOPP (60 mg/kg bw) + neutrons. The flux of the mixed (thermal + epithermal) neutron beam was 2.8 x 10(8) n/cm(2)/sec for 83.4 min.

RESULTS

Neutrons alone or with NA caused some tumor growth delay, whereas in the BPA, BPA + NA, and BPA + BOPP groups a 100% halt of tumor growth was observed in all mice at 26 days after irradiation. When the initial tumor volume was 50 mm(3) or less, complete remission was found with BPA + NA (2 of 2 mice), BPA (1 of 4), and BPA + BOPP (7 of 7). After 90 days of complete regression, recurrence of the tumor was observed in BPA + NA (2 of 2) and BPA + BOPP (1 of 7). The determination of apoptosis in tumor samples by measurements of caspase-3 activity showed an increase in the BNCT (BPA + NA) group at 24 h (p < 0.05 vs. controls) and after the first week after irradiation in the three BNCT groups. Terminal transferase dUTP nick end labeling analysis confirmed these results.

CONCLUSIONS

Although NA combined with BPA showed an increase of apoptosis at early times, only the group irradiated after the combined administration of BPA and BOPP showed a significantly improved therapeutic response.

Boron neutron capture therapy in cancer: past, present and future

Undifferentiated thyroid cancer (UTC) is a very aggressive tumor with no effective treatment, since it lacks iodine uptake and does not respond to radio or chemotherapy. The prognosis of these patients is bad, due to the rapid growth of the tumor and the early development of metastasis. Boron neutron capture therapy (BNCT) is based on the selective uptake of certain boron non-radioactive compounds by a tumor, and the subsequent irradiation of the area with an appropriate neutron beam. 10B is then activated to 11B, which will immediately decay releasing alpha particles and 7Li, of high linear energy transfer (LET) and limited reach. Clinical trials are being performed in patients with glioblastoma multiforme and melanoma. We have explored its possible application to UTC. Our results demonstrated that a cell line of human UTC has a selective uptake of borophenylalanine (BPA) both in vitro and after transplantation to nude mice. Treatment of mice by BNCT led to a complete control of growth and cure of 100% of the animals. Moreover dogs with spontaneous UTC also have a selective uptake of BPA. At the present we are studying the biodistribution of BPA in patients with UTC before its application in humans.

Genetic alterations in thyroid cancer: the role of mouse models

Thyroid carcinomas are the most common endocrine neoplasms in humans, with a globally increasing incidence. Thyroid follicular cells and neuroendocrine (parafollicular) C cells are each susceptible to neoplastic transformation, resulting in thyroid cancers of differing phenotypes with unique associated genetic mutations and clinical outcomes. Over the past 15 years, several sophisticated genetically engineered mouse models of thyroid cancer have been created to further our understanding of the genetic events leading to thyroid carcinogenesis in vivo. The most significant mouse models of papillary, follicular, anaplastic, and medullary thyroid carcinoma are highlighted, with particular emphasis on the relationship between the relevant oncogenes in these models and genetic events in the naturally occurring human disease. Limitations of each model are presented, and the need for additional models to better recapitulate certain aspects of the human disease is discussed.

Boron neutron capture therapy for undifferentiated thyroid carcinoma: preliminary results with the combined use of BPA and BOPP

We have shown the selective uptake of borophenylalanine (BPA) by undifferentiated human thyroid cancer (UTC) ARO cells both in vitro and in vivo. Moreover, a 50% histologic cure of mice bearing the tumor was observed when the complete boron neutron capture therapy was applied. More recently we have analyzed the biodistribution of BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha,beta-dihydroxyethyl)-deutero-porphyrin IX) and showed that when BOPP was injected 5 days before BPA, and the animals were sacrificed 60 min after the i.p. injection of BPA, a significant increase in boron uptake by the tumor was found (38-45 ppm with both compounds vs. 20 ppm with BPA alone). Five days post the i.p BOPP injection and 1h after BPA the ratios were: tumor/blood 3.75; tumor/distal skin 2. Other important ratios were tumor/thyroid 6.65 and tumor/lung 3.8. The present studies were performed in mice transplanted with ARO cells and injected with BOPP and BPA. Only in mice treated with the neutron beam and injected with the boronated compounds we observed a 100% control of tumor growth. Two groups of mice received different total absorbed doses: 3.00 and 6.01 Gy, but no further improvement in the outcome was found compared to the previous results using BPA alone (4.3 Gy).

Biodistribution of Boron Compounds in an Animal Model of Human Undifferentiated Thyroid Cancer for Boron Neutron Capture Therapy

Undifferentiated thyroid carcinoma (UTC) is a rapidly growing, highly invasive malignant tumor that currently lacks any effective treatment. Boron neutron capture therapy (BNCT) has been investigated recently for some types of tumors including glioblastoma multiforme and malignant melanoma. In previous studies we have shown the selective uptake of p-boronophenylalanine (BPA) by undifferentiated thyroid cancer cells in vitro and in vivo, as well as the histologic cure of 50% of the nude mice transplanted with human UTC cells when treated with BPA and an appropriate neutron beam. The present studies were performed to further optimize this treatment through the investigation of a boronated porphyrin, both alone and in combination with BPA. In vitro studies with cells in culture showed that BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha,beta-dihydroxyethyl)-deutero-porphyrin IX) is localized intracellularly, with a highest concentration in the 11500g (mitochondrial-enriched pellet) fraction. When BOPP was administered alone to NIH nude mice transplanted with UTC human cells, no significant tumor uptake or selectivity in our in vivo model was observed. In contrast, when BOPP was injected 5-7 days before BPA and the animals were sacrificed 60 min after administration of BPA, a significant increase in boron uptake by the tumor was found (38-45 ppm with both compounds vs 20 ppm with BPA alone). On day 5 the tissue boron selectivity ratios were tumor/blood approximately 3.8 and tumor/distal skin approximately 1.8. Other important ratios were tumor/thyroid approximately 6.6 and tumor/lung approximately 2.9. These results open the possibility of improving the efficacy of BNCT for the treatment of this so far "orphan" tumor.

Biodistribution of p-borophenylalanine (BPA) in dogs with spontaneous undifferentiated thyroid carcinoma (UTC)

Human undifferentiated thyroid carcinoma (UTC) is a very aggressive tumor which lacks an adequate treatment. The UTC human cell line ARO has a selective uptake of BPA in vitro and after transplanting into nude mice. Applications of boron neutron capture therapy (BNCT) to mice showed a 100% control of growth and a 50% histological cure of tumors with an initial volume of 50 mm(3) or less. As a further step towards the potential application in humans we have performed the present studies. Four dogs with diagnosis of spontaneous UTC were studied. A BPA-fructose solution was infused during 60 min and dogs were submitted to thyroidectomy. Samples of blood and from different areas of the tumors (and in one dog from normal thyroid) were obtained and the boron was determined by ICP-OES. Selective BPA uptake by the tumor was found in all animals, the tumor/blood ratios ranged between 2.02 and 3.76, while the tumor/normal thyroid ratio was 6.78. Individual samples had tumor/blood ratios between 8.36 and 0.33. These ratios were related to the two histological patterns observed: homogeneous and heterogeneous tumors. We confirm the selective uptake of BPA by spontaneous UTC in dogs and plan to apply BNCT in the future.