MOLECULAR MANIPULATION AND PHARMACOKINETICS 

The Quarterly Journal of Nuclear Medicine 1998 December;42(4):271-9

Copyright © 2000 EDIZIONI MINERVA MEDICA

language: English

Liposomes for scintigraphic imaging: optimization of in vivo behavior

Boerman O. C., Oyen W. J. G., Corstens F. H. M., Storm G.*

From the Department of Nuclear Medicine University Hospital Nijmegen, The Netherlands * Department of Pharmaceutics Utrecht Institute for Pharmaceutical Sciences (UIPS) Utrecht University, The Netherlands

Liposomes, micro­scop­ic lip­id ves­i­cles con­sist­ing of con­cen­tric phos­pho­lip­id bilay­ers enclos­ing dis­crete aque­ous spac­es, ­have ­been inves­ti­gat­ed exten­sive­ly as car­riers for ­drugs in ­attempts to ­achieve selec­tive dep­o­si­tion and/or ­reduced tox­ic­ity. Liposomes radio­lab­eled ­with gam­ma emit­ters (67Ga, 111In and 99mTc) ­have ­been ­used for imag­ing pur­pos­es. Liposomes as for­mu­lat­ed in the ­past, are rap­id­ly tak­en up by ­cells of the mono­nu­cle­ar phag­o­cyte ­system, pri­mar­i­ly ­those locat­ed in liv­er and ­spleen. However, it has ­been ­shown dur­ing the ­last two ­decades ­that the in ­vivo behav­ior of lipo­somes can be mod­ulat­ed by mod­i­fy­ing ­their for­mu­la­tion. The ­size and the lip­id com­po­si­tion ­have a ­major influ­ence on the ­blood clear­ance ­rate, hepat­ic ­uptake and splen­ic ­uptake of lipo­somes. The devel­op­ment of ­long cir­cu­lat­ing lipo­somes, in par­tic­u­lar coat­ing of the bilay­er ­with poly­ethy­le­neg­ly­col (PEG) result­ed in lipo­somes ­that ­oppose rec­og­ni­tion by the MPS, ­thus dis­play­ing ­even long­er cir­cu­la­to­ry ­half-­lives. By care­ful­ly adjust­ing the lip­o­so­mal for­mu­la­tion, the in ­vivo char­ac­ter­is­tics of lipo­somes can be tail­ored ­such ­that ­they ­become suit­able vehi­cles for imag­ing var­i­ous path­o­log­i­cal pro­cess­es in ­vivo. Liposomes ­have ­been pro­posed for ­tumor imag­ing, for infec­tion imag­ing and as ­blood ­pool mark­ers. Here, the fac­tors ­that deter­mine the in ­vivo behav­ior of lipo­somes and the cur­rent stat­us of lipo­some-­based radio­phar­ma­ceu­ti­cals are ­reviewed.