Controlled-Release Technology - American Chemical Society

Chapter 19

New Liposomal Delivery System for Controlled Drug Release Victoria M. Knepp, Robert S. Hinz, Francis C. Szoka, Jr., and Richard H. Guy

Downloaded by PURDUE UNIV on October 26, 2016 | http://pubs.acs.org Publication Date: September 4, 1987 | doi: 10.1021/bk-1987-0348.ch019

Departments of Pharmaceutical Chemistry and Pharmacy, University of California—San Francisco, San Francisco, CA 94143

The in vitro release characteristics of a liposomal drug delivery device have been studied. The system consists of a molded agarose matrix in which progesterone is dispersed either free or associated with a liposome formulation. Drug release rates from the devices into aqueous buffer were measured at 37°C. The free progesterone release rate decreased rapidly over 24 hr with > 90% delivered. The liposomal patch, on the other hand, imposed apparent zero-order kinetics, delivering its progesterone payload at about 1%/hr over 24 hr. Further, the liposomal patch significantly slowed transdermal drug delivery across excised hairless mouse skin. The results suggest that the liposomal-based reservoir system can modulate drug input via the skin, and that the zero-order release of progesterone from liposomes is determined by slow transport out of the bilayer. The g o a l o f the r e s e a r c h d e s c r i b e d here was t o c h a r a c t e r i z e a new l i p o s o m a l r e s e r v o i r system f o r c o n t r o l l e d drug r e l e a s e (_1_) and t o determine whether i t c o u l d meter drug d e l i v e r y t o the s k i n . While i t seems t h a t liposomes cannot c a r r y drugs a c r o s s the s k i n ( 2 , 3 ) ( d e s p i t e e a r l i e r c l a i m s (4,5) t o the c o n t r a r y ) , t h e i r a m p h i p a t h i c s t r u c t u r e p r o v i d e s an environment i n which h i g h c o n c e n t r a t i o n s o f d r u g s , of d i v e r s e p h y s i c o c h e m i c a l p r o p e r t i e s , can be s o l u b i l i z e d . A l s o , the b i l a y e r can be used t o modulate drug r e l e a s e through the c h o i c e of l i p i d f o r m u l a t i o n . P r e l i m i n a r y e x p l o r a t i o n o f these p o t e n t i a l a t t r i b u t e s a s s o c i a t e d w i t h drug d e l i v e r y from liposomes i s described. Methods The c o n t r o l l e d r e l e a s e d e v i c e c o n s i s t s of a t h i n drug f o r m u l a t i o n agarose g e l s u p p o r t e d on an impermeable b a c k i n g m a t e r i a l . A number

0097-6156/87/0348-0267$06.00/0 © 1987 American Chemical Society

Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

CONTROLLED-RELEASE TECHNOLOGY

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of drug f o r m u l a t i o n s have been c o n s i d e r e d , two of which are d i s c u s s e d here: (a) p r o g e s t e r o n e (PG) a l o n e , (b) PG a s s o c i a t e d w i t h m u l t i l a m e l l a r egg p h o s p h a t i d y l c h o l i n e (EPC) liposomes, PG was purchased from Sigma C h e m i c a l Co. ( S t . L o u i s , MO); f o r a n a l y s i s of drug i n the r e l e a s e e x p e r i m e n t s , a s m a l l amount of Cl a b e l e d PG (R.P.I. Corp., Mount P l e a s a n t o n , IL; 50 yCi/ymole) was i n c o r p o r a t e d i n t o the f o r m u l a t i o n s d u r i n g p r e p a r a t i o n . L i p i d s were o b t a i n e d from Sigma C h e m i c a l Co. ( S t . L o u i s , MO) and were checked f o r p u r i t y by t h i n l a y e r chromatography. Agarose used i n the d e l i v e r y systems was Seaplaque® (FMC Corp., R o c k l a n d , ME) and the d e v i c e s were c a s t on Gelbond (FMC Corp., Marine C o l l o i d s D i v i s i o n , R o c k l a n d , ME). M u l t i l a m e l l a r liposomes were p r e p a r e d by s t a n d a r d methods ( 6 ) , and p r i o r to i n c o r p o r a t i o n i n t o the d e l i v e r y systems, were passed t h r o u g h a 0.8 μιη f i l t e r ( N u c l e o p o r e , P l e a s a n t o n , CA) to remove v e r y l a r g e s t r u c t u r e s and/or a g g r e g a t e s . D e v i c e s were prepared as f o l l o w s : - 0.5 ml of PG f o r m u l a t i o n ( e i t h e r f r e e drug, or drug a s s o c i a t e d w i t h EPC l i p o s o m e s , i n NaCl (0.1 M) - Na c i t r a t e (0.03 mM) pH 4.5 b u f f e r ) and 0.5 ml agarose were warmed to 65-70°C and were then mixed t h o r o u g h l y . The m i x t u r e was poured i n t o a mold (a 2.0 cm d i a m e t e r T e f l o n 0 - r i n g ) s e t up on the Gelbond b a c k i n g . The d e v i c e s produced were a p p r o x i m a t e l y 0.3 cm thick. The 0 - r i n g was removed once the d e v i c e had s o l i d i f i e d on cooling. Systems were s t o r e d f o r no l o n g e r than 24 hr at 4°C p r i o r to t e s t i n g . PG r e l e a s e from the two d e l i v e r y systems was monitored u s i n g an automated, i n v i t r o d i f f u s i o n c e l l system. The d e v i c e s were clamped i n v e r t i c a l g l a s s d i f f u s i o n c e l l s w i t h the r e l e a s i n g s u r f a c e of the system f a c i n g i n t o the r e c e p t o r chamber. The l a t t e r c o n t a i n e d N a C l Na c i t r a t e b u f f e r and was c o n t i n u o u s l y p e r f u s e d at 10 ml/hr. P e r f u s a t e was c o l l e c t e d h o u r l y f o r up to 48 h o u r s . The r e c e p t o r phase of the d i f f u s i o n c e l l was m a g n e t i c a l l y s t i r r e d and was kept at 37°C. Samples were a n a l y z e d by l i q u i d s c i n t i l l a t i o n c o u n t i n g . For each d e l i v e r y system, 6 r e p l i c a t e s were run and the d a t a p r o v i d e d both c u m u l a t i v e PG r e l e a s e d and PG r e l e a s e r a t e per u n i t t i m e . T r a n s d e r m a l t r a n s p o r t of PG was f o l l o w e d ±n_ v i t r o . Fullt h i c k n e s s s k i n , e x c i s e d from h a i r l e s s mice (SKH:HR-1, S k i n Cancer H o s p i t a l , P h i l a d e l p h i a , PA) and used immediately, was i n t e r p o s e d between d e l i v e r y system and r e c e p t o r chamber. S e r i a l samples of r e c e p t o r f l u i d were c o l l e c t e d and a n a l y z e d as b e f o r e . Experiments were performed i n q u a d r u p l i c a t e . Results PG r e l e a s e curves i n t o b u f f e r from f o r m u l a t i o n s (a) and (b) are i n F i g u r e s 1 and 2, r e s p e c t i v e l y . The F i g u r e s show mean (± S.D.) r e l e a s e r a t e of drug as a f u n c t i o n of time and a r e p r e s e n t a t i v e p l o t of the c u m u l a t i v e PG l i b e r a t e d from the d e l i v e r y system d u r i n g the experiment. The ' f r e e ' PG system [ ( a ) ] r e l e a s e d 90.4% (±5.5%) of the dose i n 24 hours compared to the EPC d e v i c e [ ( b ) ] from w h i c h 24.8% (±3.8%) was l i b e r a t e d d u r i n g the same p e r i o d . The v a l u e s are s i g n i f i c a n t l y d i f f e r e n t at ρ < 0.01.



19.

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PG f l u x e s i n t o the r e c e p t o r chamber f o l l o w i n g d e l i v e r y a c r o s s h a i r l e s s mouse s k i n from f o r m u l a t i o n s (a) and (b) are shown i n F i g u r e s 3 and 4, r e s p e c t i v e l y . PG a s s o c i a t i o n w i t h EPC liposomes [ ( b ) ] lowers by o n e - h a l f the t r a n s d e r m a l d e l i v e r y of the drug when compared to the ' f r e e p a t c h [ ( a ) ] . 1


Discussion The PG r e l e a s e d a t a i n t o b u f f e r ( F i g u r e s 1 and 2) show that the EPC liposome f o r m u l a t i o n can r e p r o d u c i b l y change the drug d e l i v e r y kinetics. The z e r o - o r d e r b e h a v i o r o b s e r v e d s u g g e s t s t h a t PG i s not r e l e a s e d from system (b) by a s i m p l e d i f f u s i o n mechanism. Such a p r o c e s s would e x h i b i t a c l a s s i c " b u r s t e f f e c t " (7_) and the c u m u l a t i v e PG r e l e a s e d would be l i n e a r w i t h the square r o o t of time; i n s t e a d , c o n s t a n t r e l e a s e r a t e w i t h time i s seen. A p o s s i b l e mechanism i n v o k e s slow t r a n s p o r t of PG out of the l i p o s o m a l b i l a y e r as the r a t e - d e t e r m i n i n g s t e p . The o c t a n o l - w a t e r p a r t i t i o n c o e f f i c i e n t of PG i s almost 1 0 (8) and n e a r l y a l l the PG i n f o r m u l a t i o n (b) i s a s s o c i a t e d w i t h the l i p i d b i l a y e r , t h e r e f o r e . If the i n t e r f a c i a l t r a n s f e r of drug from b i l a y e r to s u r r o u n d i n g aqueous medium i s slow compared to i t s subsequent d i f f u s i o n through the aqueous spaces of the agarose g e l , then the PG e f f l u x r a t e w i l l be p r o p o r t i o n a l to k.c, where k i s the t r a n s f e r r a t e c o n s t a n t and c i s the PG c o n c e n t r a t i o n i n the b i l a y e r . T h i s f o r m a l i s m i s r e a s o n a b l e p r o v i d e d t h a t the b i l a y e r - a s s o c i a t e d PG i s not s i g n i f i c a n t l y depleted. F o r the f i r s t 24 hours of PG r e l e a s e from system ( b ) , a t l e a s t , the r e s u l t s are s u p p o r t i v e of the above h y p o t h e s i s . Further work i s r e q u i r e d to v a l i d a t e f u l l y the mechanism p r o p o s e d . 4

T r a n s d e r m a l PG d e l i v e r y a c r o s s h a i r l e s s mouse s k i n J j i v i t r o demonstrates t h a t the l i p o s o m a l p a t c h can modify percutaneous drug absorption. Comparison of F i g u r e s 1 and 3 shows t h a t PG appearance i n the r e c e p t o r chamber, f o l l o w i n g a d m i n i s t r a t i o n to the s k i n i n the free PG p a t c h [ ( a ) ] , i s s k i n - c o n t r o l l e d . In t h i s c a s e , the s k i n i s a r a t e - l i m i t i n g membrane and the d e l i v e r y system a c t s as a r e s e r v o i r of PG. T r a n s p o r t f o l l o w s F i c k ' s 1st Law of D i f f u s i o n and a s t e a d y - s t a t e f l u x of 0.45% per hour i s o b s e r v e d . PG a s s o c i a t e d w i t h EPC liposomes ( d e v i c e ( b ) , F i g u r e 4 ) , slows t r a n s d e r m a l throughput to one h a l f t h a t o b t a i n e d w i t h d e v i c e ( a ) . A l t h o u g h PG i s r e l e a s e d from system (b) f a s t e r than i t p e n e t r a t e s the s k i n , the d e v i c e does modify the percutaneous k i n e t i c s . I t seems r e a s o n a b l e t o suggest t h a t a p p r o p r i a t e a l t e r a t i o n of the l i p i d c o m p o s i t i o n of the b i l a y e r can slow f u r t h e r the PG r e l e a s e r a t e such t h a t g r e a t e r c o n t r o l of t r a n s d e r m a l d e l i v e r y r e s i d e s w i t h the p a t c h . f

f

Summary A. B. C.

A l i p o s o m a l drug d e l i v e r y system has been p r e p a r e d and characterized. The system has been t e s t e d i n v i t r o and i s c a p a b l e of m o d i f y i n g PG d e l i v e r y a c r o s s h a i r l e s s mouse s k i n . The mechanism of PG r e l e a s e from the l i p o s o m a l system may i n v o l v e slow p a r t i t i o n i n g of drug at the b i l a y e r - a q u e o u s phase interface.


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Acknowledgments P r i n c i p a l f u n d i n g was p r o v i d e d by Liposome Technology I n c . , Menlo Park, CA. A d d i t i o n a l s u p p o r t was r e c e i v e d from the Donors of the P e t r o l e u m R e s e a r c h Fund, a d m i n i s t e r e d by the American C h e m i c a l S o c i e t y (PRF //17438-AC7). We thank Dr. R.A. S i e g e l f o r h e l p f u l i n s i g h t and Andrea Mazel f o r p r e p a r i n g the m a n u s c r i p t .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. RECEIVED

Wester, R.C.; Szoka, F.C.; Bucks, D.A.W.; Maibach, H.I.; "Abstracts", American Pharmaceutical Association, Academy of Pharmaceutical Sciences, 37th National Meeting, 1984, 14, 229. Ganesan, M.G.; Weiner, N.D.; Flynn, G.L.; Ho, N.F.H. Int. J. Pharm., 1984, 20, 139-154. Ho, N.F.H.; Ganesan, M.G.; Weiner, N.D.; Flynn, G.L. J. Control. Rel., 1985, 2, 61-65. Mezei, M.; Gulasekharam, V. Life Sci., 1980, 26, 1473-1477. Mezei, M.; Gulasekharam, V. J. Pharm. Pharmacol., 1982, 34, 473-477. Szoka, F.C.; Papahadjopoulos, D. Ann. Rev. Biophys. Bioeng., 1980, 9, 467-508. Crank, J. "The Mathematics of Diffusion"; Oxford University Press: New York, 1975, 37. Leo, Α.; Hansch, C.; Elkins, D. Chem. Rev., 1971, 71, 525-616. October 10, 1986


Controlled-Release Technology - American Chemical Society

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