Radiopharmaceuticals for Theranosis

조회수 : 15 등록일 : 2017.11.29 15:36

일시 : 2017.11.22 17:00
소속 : 서울대학교 의과대학 핵의학과
발표자 : 정재민
장소 : RA204

   Theranosis means combination of therapy and diagnosis. Radiopharmaceuticals can be used both for therapy and diagnosis of cancers. Radiopharmaceuticals emitting gamma ray or positron are used for diagnosis, and beta and alpha emitters are used for therapy. Thus a peptide targeting a special cancer is labeled with gamma or positron emitter for diagnosis and the same peptide is labeled with beta or alpha emitters for therapy. The first peptide used for theranosis is octreotide derivatives. For example, 68Ga-DOTA-TOC is positron emitter and is used for diagnosis of neuroendocrine tumors by imaging with positron emission tomography (PET). After confirmation of the uptake, DOTA-TOC is labeled with beta emitters such as 177Lu or 90Y and administered to the patient for therapy. Then, therapeutic efficacy can be predicted by internal dosimetry and unnecessary administration of the radiopharmaceutical can be avoided. Actually, the origin of theranosis is radioiodine therapy of thyroid cancer. Thyroid cancer can be imaged by gamma emitters such as 99mTc and 123I and then 131I is administered for therapy, which has been used for more than 50 years. However, the development of new theranostic agent was delayed, and octreotide derivatives such as DOTA-TOC, DOTA-TATE and DOTA-NOC were breakthrough. However, the incidence of neuroendocrine tumor is very low and this method was not widely used. Several derivatives for targeting prostate specific membrane antigen (PSMA) were developed and labeled with 68Ga. These 68Ga-PSMA agents showed excellent images. And then 177Lu-PSMA agents were developed and showed excellent efficiency. Prostate cancer patients have high incidences and increasing very rapidly. Thus, theranosis of prostate cancer became very important part of cancer therapy and radiopharmaceuticals became more important. For imaging cancers, small peptides which can be cleared rapidly from body is adequate. However, they are not adequate for therapy due to rapid clearance. Slow clearance is better for delivery of enough radioactivity to cancer tissues. To decrease the clearance rate, increasing the molecular size is necessary. Thus, nanoparticles are used for increase the molecular size. Peptides and chelating agents are conjugated with adequate size of nanoparticles and then labeled with adequate radionuclides. Then they can be used for efficient theranostic agents. The application of nanotechnology might be useful for theranostic use of radiopharmaceuticals.

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