VERSATILITY OF DRUGS DELIVERED USING LIPOSOMES
3. VERSATILITY OF DRUGS DELIVERED USING LIPOSOMES
Since their discovery in the mid-1960s, liposomes have been extensively studied as parenteral delivery systems for a wide range of pharmaceutical therapeutic drug candidates that include traditional low molecular weight compounds, biotechnology-derived proteins and peptides as well as
252 Patil and Burgess
DNA-based therapeutics. Liposomal delivery for low molecular weight drugs is one of the earliest and conse- quently one of the most clinically advanced amongst all other therapeutics.
3.1. Low Molecular Weight Drugs Low molecular weight pharmaceutical compounds that have
been investigated for parenteral delivery in liposome systems include antifungals (10,11), antibiotics (12,13), and anti cancer drugs (14). Liposomal delivery of these drugs can be used to alter drug pharmacokinetics, to assure adequate levels in tissues of interest and to reduce =avoid toxic side effects (for details, refer Sec. 4 ). Some of the approved low molecular weight liquid parenteral liposomal formulations include: AmBisome Õ , which contains amphotericin B and is indicated for systemic fungal infections (11) and visceral
leishmaniasis; Amphotec Õ (branded as Amphocil outside United States) and Abelcet Õ which also contain amphotericin
B (15–17) and are indicated for systemic fungal infections (18); DaunoXome Õ , which contains duanorubicin and is indi-
cated for first-line treatment of advanced Kaposi’s sarcoma; DepoDur Õ , which contains morphine and is indicated for pain
management following major surgery; DepoCyt Õ , which con- tains cytarabine and is indicated for lymphomatous meningi-
tis; Doxil Õ (branded as Caelyx outside United States), and
Myocet Õ (formerly known as Evacet ), both of which contain doxorubicin and, whereas, Doxil is indicated for metastatic
ovarian cancer and Kaposi’s sarcoma, Myocet is being used for treating breast cancer; MiKasome Õ , which contains the
aminoglycoside antibiotic amikacin and is indicated for severe infections; and Visudyne Õ , which contains the photosensitizer
dye verteporfin and is indicated for age-related macular degeneration (19). The reader is referred to the case studies in this book on the development of Doxil by Martin and on the development of AmBisome by Adler-Moore. Currently, sev- eral liposome formulations containing low molecular weight drugs are in clinical trials for a range of pharmacologic effects (such as antibacterial, anticancer, antifungal, and anti-HIV activities) (20,21). See Table 1 for additional information on
Liposomes:
Table 1 Marketed Liposomal Products Design
Marketed formulation—Company
Liposome composition
Indication and
AmBisome—Gilead-Fujisawa
Systemic fungal Manufacturing Healthcare
Amphotericin B
HSPC, cholesterol,
and DSPG
infections and visceral leishmaniasis
Amphotec =Amphocil a,b —InterMune
Cholesteryl sulfate a Aspergillosis Abelcet—Elan
Amphotericin B
Fungal infections DaunoXome—NeXstar Pharmaceuticals
Amphotericin B
DMPC and DMPG
Daunorubicin
Cholesterol and DSPC
Kaposi’s sarcoma
citrate
Doxil =Caelyx b,c —Ortho Biotech
Doxorubicin
MPEG-DSPE, HSPC,
Metastatic ovarian
hydrochloride
and Cholesterol
cancer and Kaposi’s sarcoma
DepoDur—SkyePharma—Endo
Morphine sulfate
Cholesterol, DOPC,
Pain following major
surgery DepoCyt—SkyePharma—Enzon
and DPPG
Cytarabine
Cholesterol, DOPC,
Lymphomatous
meningitis Myocet (formerly known and
and DPPG
Breast cancer Evacet)—Elan
Doxorubicin
Egg PC and cholesterol
hydrochloride
MiKasome—NeXstar
Amikacin
HSPC, cholesterol,
Bacterial infections
and DSPG
253 (Continued)
© 2005 by Taylor & Francis Group, LLC
Table 1 254 Marketed Liposomal Products (Continued ) Marketed formulation—Company
Pharmaceutical
name
Indication Visudyne—Novartis
drug
Liposome composition
Age-related macular degeneration Epaxal d —Berna Biotech
Verteporfin
Egg PG and DMPC
Hepatitis A
Hemagglutinin,
Hepatitis A
antigen
neuraminidase, and lecithin
Inflexal V d —Berna Biotech
Influenza Pevaryl Lipogel e —Cilag
Dermatomycosis and gynecological mycosis
Topical anesthetic as ELA-Max)—
L.M.X.4 e (formerly known
Lidocaine
Cholesterol
and hydrogenated
Ferndale Laboratories
lecithin
MPEG-DSPE, N-(carbonyl-methoxypolyethylene glycol 2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine sodium salt; HSPC, hydrogenated soy phosphatidylcholine; DSPG, distearoyl phosphatidylglycerol; DMPC, dimyristoyl phosphatidylcholine; DMPG, dimyr- istoyl phosphatidylglycerol; DOPC, dioleoyl phosphatidylcholine; DPPG, dipalmitoyl phosphatidylglycerol; DSPC, distearoyl phosphati- dylcholine; Egg PC, egg phosphatidylcholine; Egg PG, egg phosphatidylglycerol.
a Amphotec b Brand name of the product marketed outside United States. =Amphocil is a amphotericin B cholesteryl sulfate complex for injection. Patil
c Sterically stabilized (Stealth) liposomes. d Immunopotentiating reconstituted influenza virosomes.
and e Formulation for transdermal application. Burgess
© 2005 by Taylor & Francis Group, LLC © 2005 by Taylor & Francis Group, LLC
3.2. Protein Therapeutics Liposomes have been used as vaccine adjuvants for recombi-
nant protein-based vaccines. Epaxal and Inflexal V are licensed liposomal protein vaccines that were globally approved in the mid-1990s for hepatitis A and influenza, respectively. Epaxal and Inflexal are immunopotentiating unilamellar vesicles known as virosomes since they contain phospholipids and pro- teins derived from the influenza virus (22,23). Virosome formu- lations are comprised of vaccine-specific antigens of interest embedded in the liposomal bilayer composed of the following two components: (i) natural and synthetic phospholipids (lecithin, cephalin, and envelope phospholipids from the influ- enza virus); and (ii) influenza surface glycoproteins: hemagglu- tinin and neuraminidase. For the Epaxal formulation (24), the antigen of interest is the hepatitis A virion, whereas, the Inflexal V (25) formulation contains a combination of surface antigens of three currently circulating strains of the influenza
mal products for the delivery of proteins.
3.3. DNA-Based Therapeutics In addition to the commercial licensing of a range of liposomal
formulations, recent years have witnessed significant research efforts directed toward the development of liposomes as delivery vectors for DNA-based therapeutics (26–29). In vivo delivery of DNA-based therapeutics such as plasmids for gene expression, antisense oligonucleotides, siRNAs, ribozymes, etc., typically requires assistance of delivery vectors (29). Currently used gene delivery vectors are attenuated replica- tion-defective viruses such as adenoviruses, adeno-associated viruses, polyomavirus, and retroviruses (26,30–33). Due to their natural mechanism of targeted introduction of DNA into cells, these vectors have high efficiency in DNA transfer (30). However, a number of potential problems are associated with viral vectors, including deletion of sequences during replication, recombination with endogenous sequences to pro-
Liposomes: Design and Manufacturing 255
virus. See Table 1 for additional information on approved liposo-
256 Patil and Burgess
duce infectious recombinant viruses, activation of cellular oncogenes, introduction of viral oncogenes, inactivation of host genes, development of toxic immune responses and inflamma- tion that has been demonstrated to be lethal (26,34–36). Phar- maceutical formulations of viruses are expensive and difficult to manufacture, have a very low shelf life, and can lose potency upon storage (37,38). Thus, despite their superlative efficiency, many of these vectors are unsuitable for clinical use. As a con- sequence of the problems associated with viral gene delivery vectors, several alternative non-viral gene delivery systems are under development (29,39–41). Liposomal delivery vectors are emerging to be the most popular non-viral alternative to viral vectors for gene delivery (26,40,41). Liposomal formula- tions of DNA-based therapeutics protect these molecules from enzymatic inactivation in the plasma by degradative endo- and exo-nucleases, facilitate the entry of DNA into the cell cyto- plasm, are relatively easy and inexpensive to manufacture, and are non-immunogenic (26). Both anionic and cationic lipo- somes have been utilized for gene delivery (26,42,43). DNA typically is entrapped inside anionic liposomes and is sur- face-complexed with cationic liposomes. These liposomal for- mulations have achieved tremendous success in introducing DNA-based gene therapeutics into a wide range of tissues and cells in animal as well as cell culture models. The first clin- ical trial for gene therapy for melanoma using cationic lipo- somes was conducted in 1992 by Nabel et al. (44,45). Currently, although several cationic liposomes are in advanced clinical trials for gene therapy of cystic fibrosis, and cancer, there is no commercially licensed formulation (45). In addition to their use in protein delivery, as described in detail in Sec. 3.2, virosomes have also been employed for gene transfer (46,47).