New strategies are currently being developed with regard to targeted (missile)
therapy for
cancer using
anticancer agent-labeled specific
antibodies. A range of problems prevent their clinical application, however, because each specific
cancer may not yet have a known unique
antigen. In turn, this serves to impede the development of specific
antibodies. Regarding
thyroid cancer, no reports of targeted
therapy have appeared since specific
antigens remain to be identified.
Monoclonal antibodies A2B5, HISL-19 and 4F2 bind to
neuroendocrine tumors (A2B5, HISL-19) and severe malignant
tumors (4F2) indicating rapid growth, enabling these
tumors to express common anti-genetic determinants to our
monoclonal antibodies. The immunohistochemical study for
thyroid cancers revealed that A2B5 and HISL-19 only react with
medullary carcinoma and that 4F2 only reacts with
anaplastic carcinoma. When 131I-labeled A2B5 was injected into the rat bearing
insulinoma, the
antigen of which is common to
medullary carcinoma of the thyroid, clear accumulation of radiolabeled antibody corresponding to the transplanted
tumor was observed by scintiscanning. Furthermore, the biochemical study undertaken to identify anti-genetic
protein using the Western blotting procedure demonstrated new HISL-19
antigen in
medullary carcinoma of the thyroid, which is not recognized in benign endocrine
tumor, and
4F2 antigen in
anaplastic carcinoma. Since these
antigens do not circulate in the blood stream, the administered antibody reaches the targeted lesion without decreasing antibody titer. Although many problems remain, such as the effect on normal cells and affinity to the targeted lesion, our current aim is to establish an efficient and effective
chemotherapy using
monoclonal antibodies in
medullary carcinoma and
anaplastic carcinoma arising in the thyroid.