the present invention provides a method for facilitating drug entry into cells and for delivering drugs selectively to intracellular organelles . this is achieved by conjugating the desired therapeutic agent to a lipid carrier and administering this conjugate by standard techniques , including topical application . the activity of these conjugates can be further refined by attaching the lipid carrier to a therapeutic agent through a spacer group having a first and a second end . specifically , this is achieved through first linking the lipid to the first end of the spacer group through a linker functional group . in such a case , the therapeutic agent is then bound to a second end of the spacer group through a second linker functional group . this lipid / spacer / drug conjugate will provide enhanced flexibility and versatility in targeting drug delivery and in facilitating drug release upon reaching the target site . experimentally , it was found that the distribution of fluorescent ceramide is markedly different in neoplastic and virally infected cell lines as compared to &# 34 ; normal &# 34 ; cells . the marked difference in the distribution of fluorescent ceramide suggests that the neoplastic and virally infected cells have compromised golgi . cells with compromised golgi could be made more susceptible to inactivation by treating them with ceramide linked to therapeutic agents which would direct them within the cell to the golgi . a drug , as used herein , will be defined as including , but not necessarily limited to any anti - viral , antineoplastic drug . for the purposes of this application , compound 8 , as referred to herein , is defined as the hiv1 protease inhibitor identified as compound 8 in dreyer , g . b ., et . al ., inhibition of human immunodeficiency virus 1 protease inhibitor in vitro . rational design of substrate analog inhibitors pnas vol . 86 , pp . 9752 - 56 , dec . 1986 . a lipid carrier , as defined herein will be taken to mean any lipid having an affinity for , or capable of crossing , a biological membrane , including but not limited to ceramide , phophotidyl choline , phosphatidic acid , estrogen , ether lipids , sphingomyelin or other sphingolipids . a linker functional group is defined as any functional group for covalently binding the lipid carrier or therapeutic agent to the spacer group . these groups can be designated either &# 34 ; weak &# 34 ; or &# 34 ; strong &# 34 ; based on the stability of the covalent bond which the linker functional group will form between the spacer and either the lipid carrier or the drug . the weak functionalities include , but are not limited to phosphoramide , phosphoester , carbonate , amide , carboxyl - phosphoryl anhydride , ester and thioester . the strong functionalities include , but are not limited to ether , thioether , amine , amide and ester . the use of a strong linker functional group between the spacer group and the drug will decrease the rate at which the drug will be released at the target site , whereas the use of a weak linker functional group between the spacer group and the drug may act to facilitate release of the drug at the target site . enzymatic release is another possibility , however , the rate of release of the drug would not necessarily be correlated with bond strength . a spacer group may be broadly defined as any chemical group designed to facilitate the attachment of the drug / lipid conjugates to a target cell and / or the release of the drug at the desired target site . such spacers may , facilitate enzymatic release at certain intracellular sites . some spacers may simply present an &# 34 ; unhindered inhibitor ,&# 34 ; still linked to the carrier - spacer conjugate , to a target enzyme . spacer groups , as described herein , include , but are not limited to aminohexanoic acid , polyglycine , polyamides , polyethylenes , and short functionalized polymers having a carbon backbone which is one to about twelve carbon molecules in length . throughout the description of the examples , it will be assumed that all intermediate compounds will be isolated using standard methods . an antiviral compound consisting of sphingosine conjugated to compound 8 . sphingosine is reacted with 1 , 3 bis ( trimethylsilyl ) urea as described in w . verbloom et al ., 1981 , synthesis 807 to give a trimethyl silyl derivative of sphingosine . the sphingosine derivative is then conjugated with compound 8 in which the terminal amine is covered by a tboc protecting group in the presence of diethyl azodicarboxylate ( dead ) and triphenyl phosphine as described in y . kishimoto , ( 1975 ), chemistry and physics of lipids , 15 : 33 - 36 . the sphingosine / compound 8 conjugate is then reacted in the presence of pyridine hydrofluoride as described in matsuura , s . et al ., ( 1976 ): j . chem . soc .- chem . communications , pg . 451 ., to remove the tboc protecting group , to give compound 8 covalently bound to sphingosine through an amide bond . an antiviral compound consisting of ceramide conjugated to a first end of a polyglycine spacer through an ester linker functional group , wherein enzyme inhibitor compound 8 is conjugated through an amide linker functional group to a second end of the polyglycine spacer . polyglycine , as used in this example , has both a carboxy terminus and an amino terminus , the amino terminus being protected by a t - boc group . polyglycine is conjugated through its carboxy terminus to ceramide forming an ester linkage , as described in anderson et al ., 1963 , j . chem . soc .- chem . communications , 85 : 3039 . the resulting compound is further conjugated through the amino terminus of the polyglycine residue . compound 8 has a carboxy terminus and an amino terminus . in this example the amino terminus is protected by a t - boc protecting group . the conjugation takes place between the amino terminus of the polyglycine and the carboxy terminus of the hiv - 1 protease inhibitor . this reaction is carried out in the presence of dead and triphenyl phosphine according to the method of y . kishimoto , ( 1975 ), chemistry and physics of lipids , 15 : 33 - 36 . the amino terminus of the hiv - 1 protease inhibitor residue is deprotected according to the method of matsuura , s . et al , 1976 , j . chem . soc .- chem . communications , pg . 451 . an antiviral compound consisting of ceramide conjugated to azt - monophosphate . ceramide is reacted with azt - monophosphate in the presence of dicyclohexylcarbodiimide as described in smith , m . and khorana , g . ( 1958 ), j . a . c . s . 80 : 1141 to yield ceramide conjugated through a phosphodiester bond to azt - monophosphate . an antineoplastic compound wherein sphingosine is conjugated through a phosphodiester bond to 5 - fluorodeoxyuridine . sphingosine is reacted with 5 - fluorodeoxyuridine in the presence of dichlorophenyl phosphate according to the method of baer 1955 , can . j . biochem . phys . 34 : 288 , to yield sphingosine conjugated to 5 - fluorodeoxyuridine through a phosphodiester bond . an antiviral compound wherein ceramide is first conjugated to a first end of an oligomer 3 hydroxy propanoic acid spacer through an ester functional group , and wherein azt is conjugated to a second end of said polyester spacer through a phosphodiester bond . first a polyester spacer is obtained , having a carboxyl at a first end and a triphenylmethyl group esterified to a second end . this spacer is conjugated to ceramide at its first end through an ester functional linker group according to the method of anderson et al ., 1963 , j . a . c . s ., 85 : 3039 . this compound is then conjugated through the second end of the spacer compound to azt monophosphate by means of a phosphodiester bond according to the method of baer 1955 , can . j . biochem . phys . 34 : 288 . in this antiviral compound , the bond breakage between the spacer and the drug would be slow in the absence of a phosphohydrolase . an antiviral compound wherein phosphatidic acid , phosphatidyl choline , phophatidyl glycerol or phosphatidyl ethanolamine is linked through a phosphoester linker functional group to azt . phosphatidic acid , phosphatidyl choline , phophatidyl glycerol or phosphatidyl ethanolamine is conjugated to azido deoxythymidine according to the method of baer et al ., 1955 . an antiviral compound wherein ceramide is conjugated through an ester functional group to a first end of a polyglycine spacer , and wherein azt is conjugated through a phosphoester functional group to a second end of the polyglycine spacer . ceramide is first conjugated through an ester functional group to a first end of a polyglycine spacer ( as described in example 2 ). the ceramide - polyglycine compound is then conjugated through a phosphoester bond to a second end of the polyglycine spacer to azt monophosphate according to the method of paul , r ., and anderson , g . w ., 1960 , j . a . c . s . 82 : 4596 . an antiviral compound wherein aminohexanoyl sphingosine is conjugated to azt . aminohexanoyl sphingosine is conjugated with azt monophophoimidazole according to the method of paul , r ., and anderson , g . w ., 1960 , j . a . c . s . 82 : 4596 to yield aminohexanoyl sphingosine conjugated to azt through a phophoramide bond .
this invention relates to a novel method of drug targeting which comprises covalently binding a drug to a lipid carrier . this composition has the unique ability to both enhance the rate at which an antineoplastic or antiviral drug crosses the plasma membrane , and to direct the drug within the cell to specific organelles . the versatility of these conjugates may be further enhanced by including a spacer group between the drug and the lipid which may act to modulate drug release at the target site .