Autoradiography of boron-porphyrin derivatives and other boron compounds for neutron capture therapy

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1) Mercaptoundecahydrododecaborate has proved over the past 24 years to be effective as a neutron capturing nuclide for boron-neutron capture therapy of brain tumors. The search for more efficient compounds or compounds applicable to cancers other than brain tumors has been continuing. Boronotetraphenylporphyrin (BTPP) developed by Stephen Kahl of California University (Barkeley) is suggested to be promising for tumor treatments. As the first step to study the efficacy of this substance, neutron-induced alpha-autoradiographic study of a few boron compounds including BTPP was proposed. In spite of Kahl's pledge, BTPP was actually delivered only in the latter half of 1989.BTPP was administered by a systemic route (hypodermal injection) into the nude mice carrying transplanted canine osteosarcoma. After 6, 24, 48 and 72 hours the animals were sacrificed, and the whole body was frozen and was sliced. The slices were covered with cellulose nitrate film and they were exposed to neutrons which were captured by boron and produced lithium and alpha particles. By the analyses of these tracks registered on the film, it was concluded that this BTPP gradually builds up in the tumor, different from other compounds. The normal tissue surrounding the tumor did not appear to have any significant amount of boron. Consequently BTPP was considered to be suited to BNCT.Toxicological and kinectic studies will be required for actual therapeutic purpose.2) Kinectic studies on mercaptoundecahydrododecaborate which has been used are continued with human patients.