Liposomal delivery of boron for BNCT

The development of effective targeting strategies for the selective transport of boron to cancer cells has been the single most urgent problem in the area of BNCT. Successful therapy requires the site-specific delivery of relatively large amounts of boron to tumors. Strategies employed have included the use of boron compounds with some natural affinity for tumors such as 4-(dihydroxyboryl)phenylalanine (BPA) or B12H11SH2-, the attachment of boron species to other molecules such as porphyrins, and the conjunction of boron compounds with tumor-specific monoclonal antibodies. In any targeting strategy, the primary difficulties are delivering therapeutic quantities of boron, lack of specificity, and loss of specificity after incorporating useful amounts of boron in the targeting agent. Liposomes represent a new approach to these problems. While liposomes, in general, do not concentrate specifically in tumors, Vestar, Inc. has shown that certain liposomes can be made to accumulate in tumors in high concentration relative to normal tissue, including blood. Further, liposomes can encapsulate a wide variety of water soluble species in significant amounts. The authors have been investigating these liposomes as specific carriers of boron compounds to cancerous cells