Macromolecules in drug delivery

Transcription

1 Macromolecules in drug delivery Macromolecular targeting agents, carriers, and drugs 1

2 Why macromolecules in drug delivery? WHY? Increase therapeutic index Reduced side effects Prolonged effects HOW? Targeting A carrier for small drugs A release mechanism (if necessary) Protection of drug cargo Classic chemotherapy Drug delivery using macromolecular system 2

3 How? Overcome obstacles Capitalize on opportunities Classic chemotherapy Drug delivery using macromolecular system 3

4 Blood flow through the body Bertrand and Leroux. J Controlled Release (2012)

5 Physical obstacles to drug delivery Pulmonary capillaries (2 13 µm) Pore size 4.2 nm Bertrand and Leroux. J Controlled Release (2012)

6 Chemical obstacles to drug delivery Spleen or Liver Marasco and Sui. Nature Biotechnology (2007) 25,

7 Passive targeting the EPR effect Enhanced Permeation and Retention Kratz et al. ChemMedChem 3 (2008) Khandare and Minko. Prog Polym Sci 31 (2006)

8 Active targeting Peer, Karp, Hong, Farokhzad, Margalit, Langer. Nature Nanotechnology (2007) 2,

9 Outline 1. Macromolecular targeting agents + carriers * Release of drug via a linker Drug 2. Macromolecular carriers * Small molecule targeting ligands 3. Macromolecular drugs 9

10 SECTION 1 Antibody drug conjugates Antibodies are examples of carriers which are simultaneously targeting ligands Anticancer drugs are given at sub optimal doses because of toxicity to healthy tissue. Adding a targeting moiety increases the dose of drug to the target tissue. Important issues: Choice of targeting ligand Choice of drug Choice of linker 10 Zolot, Basu, Million, Nature Reviews Drug Discovery (2013) 12,

11 Choice of target Receptor expression: High density on surface of target For example, a receptor density of 10 5 ERBB2 receptors per cell was required for an improved therapeutic effect of anti ERBB2 targeted liposomal doxorubicin over non targeted liposomal doxorubicin in a metastatic breast cancer model High degree of homogeneity Must not be shed by cells Circulating shed antigen will compete with the target cells for binding of the targeted therapeutics, and any complexes that form would be rapidly cleared from the circulation Allen. Nature Rev Cancer 2 (2002)

12 Consequence of ligand receptor binding Binding of antibodies to their receptors can cause internalization, but not always. Allen. Nature Rev Cancer 2 (2002)

13 A variety of targets expressed by tumors Schrama et al. Nature Rev Drug Disc (2006) 5,

14 Issues for targeting Binding affinity (high or low)? Tumor (relatively low binding) In circulation (relatively high binding) EPR effect helps concentrate antibodies in tumors Distribution to target location (linker must be stable) Allen. Nature Rev Cancer (2002) 2,

15 Choice of drug Antibodies have low drug loadings Large amounts of antibodies can saturate the binding site Expensive Increased chance of immunological reactions The drug must be very potent e.g., calicheamicin, the maytansine derivative DM1, or monomethyl auristatin E Drug loading must be low to permit FcRn recycling 15

16 FcRn recycling Roopenian, Akilesh. Nature Reviews Immunology (2007) 7,

17 Immune response to antibodies 17

18 How to attach drugs to antibodies Garnett. Adv Drug Del Rev 53 (2001)

19 Drug release Linker chemistry Extracellular enzymes Redox Enzymes, ph, redox Allen. Nature Rev Cancer 2 (2002)

20 Linker considerations Permanent bonds Useful if the carrier is (bio)degradable Risk of drug inactivation Labile bonds Risk of pre-mature release Used to trigger drug release upon internalization The choice of linker is crucial for the success of the drug delivery system. Macromolecule Labile bonds Linker Drug Permanent bond 20

21 Common permanent linker chemistry A + B = Amide Amine Carboxylic acid Amine Amine (via Schiff base) Thioethers Thiol R: Drug ; Prot: Macromolecule Gauthier and Klok. Chem Commun (2008)

22 Labile linker chemistry Type Structure Use/ Comments Redox-sensitive R SS R (disulfides) Reduction in the cytoplasm releases the drug ph-sensitive N=N C (hydrazones ) Orthoesters Acetals, etc. Relatively unstable in the blood Designed to cleave in the acidic endosomal/lysosomal compartments Enzyme sensitive 22 22

23 Enzyme-cleavable linkers These are all short peptides easily prepared synthetically Kratz et al. ChemMedChem 3 (2008)

24 Some considerations Location of cleavage is not as well established as for redox- or ph-sensitive linkers Kratz et al. ChemMedChem 3 (2008)

25 Example : Mylotarg Mylotarg, a conjugate of the cytotoxic antibiotic calicheamicin and an anti- CD33 humanized antibody, is the only antibody prodrug that has received market approval but Kratz et al. ChemMedChem 3 (2008)

26 Some concluding remarks Low drug loading (3 10 molecules per antibody) Pre-clinical studies often show: Better accumulation in tumors versus non-targeted antibodies Better efficacy versus free drug Reduced toxicity versus free drug This approach is well-suited to very cytotoxic drugs Immunogenicity: requires chimeric or humanized abs. 26

27 Outlook 27

28 SECTION 2 Macromolecular carriers Polymer therapeutic are examples of inert carriers with pendant targeting units and drugs Small drugs distribute randomly through the body. This often leads to side effects. The attachment to a polymeric carrier can: Prolong circulation lifetime to promote passive tumor uptake. Promote targeting and receptor-mediated uptake through a targeting ligand. Duncan Nature Rev Cancer 6 (2006) Ringsdorf. J Pharm Sci Polym Sci 51 (1975)

29 Targeting polymer therapeutics Passive targeting via EPR effect Active targeting via a targeting ligand Kratz et al. ChemMedChem 3 (2008) Khandare and Minko. Prog Polym Sci 31 (2006)

30 Basic requirements for the carrier The polymer must be non-toxic and non-immunogenic Polymer MW should be high enough to ensure long circulation, but nonbiodegradable polymers must be less than 40,000 g.mol -1 to enable renal elimination. Usually MW is between 30, ,000 g.mol -1 The polymer must be able to carry an adequate payload The polymer must be stable during transport, but release the drug upon arrival at target location Duncan Nature Rev Cancer 6 (2006)

31 Types of carriers Carrier Proteins Polysaccharides Synthetic polymers Example Antibody, antibody fragment Albumin Lectins Hormones (peptides), etc. Dextran Hyaluronic acid Heparin sulfate Poly(L-lysine), poly(l-lysine citramide) Poly(L-glutamic acid) Poly(α,β-(N-hydroxyethyl)-D,L-aspartamide) Poly(N-(2-hydroxyethyl)-L-glutamine) Poly(L-aspartic acid) Poly(N-(2-hydroxypropyl)methacrylamide) Poly(ethylene glycol) Poly(styrene-co-maleic acid) (SMA) Dendrimers, hyperbranched polymers, etc. Uni-molecular Can also be used as targeting ligands Natural biopolymers Variable structure Polydisperse Flexibility of design Cheap and easy to prepare 31

32 Most commonly used synthetic polymers 32

33 PEGylation of small-molecule drugs 7 Enhances water solubility and decreases immunogenicity Limited conjugation capacity (only two terminal functional groups exist at the end of the polymer chain) This limitation can be overcome by use of a multi-functional linker (but can lead to steric hindrance problems) Loss of activity (mmeg 5000 pactilaxel-7-carbamates 10 3 times less active than native drug) Large PEG blocks the activity at the target cell Drug does not reach target cells in sufficient concentration (low loading) Greenwald et al. Adv Drug Del Rev 55 (2003)

34 Poly(glutamic acid) (PGA) Random-coil at ph 7 High drug loading Biodegradable (cathepsin B, found in mice not expressing this enzyme) Slow release of drugs by hydrolysis and fast release by enzymatic degradation 34

35 PGA conjugates PGA paclitaxel conjugate (CT-2103; Xyotax) In phase I/II clinical trials, PGA paclitaxel (CT-2103) showed a significant number of partial responses or stable disease (patients with mesothelioma, renal cell carcinoma, non-small cell lung carcinoma (NSCLC)) ovarian cancer. In one recent randomized phase III clinical trial, PGA paclitaxel was compared with gemcitabine or vinorelbine as a first-line treatment for poor performance status (PS2) NSCLC patients. The conjugate showed significantly reduced severe side effects when compared with control patients, most of whom received gemcitabine. A PGA conjugate (CT-2106) of M w 50,000 g mol -1 and containing a Gly linker to camptothecin (33 35 wt%) has also entered phase I/II trials. Duncan Nature Rev Cancer 6 (2006)

36 Poly(2-hydroxypropyl methacrylamide) (phpma) Since 1973, PHPMA is the most investigated and advanced polymer used in therapeutics due to its versatility as a vehicle. Can be modified along its side chain PHPMA being hydrophilic, increases water solubility of the drugs and has proven to be non-toxic in rats. 36

37 Synthesis of phpma Two possible routes for preparing HPMA-drug conjugates 37

38 Bottom-up synthesis Lu et al. J Controlled Release 78 (2002)

39 Post-polymerization modification approach Active ester group for post-polymerization modification with a targeting moiety 39

40 Example of a phpma conjugate A PHPMA copolymer with adriamycin conjugated with the peptidyl linker Gly-Phe-Leu-Gly (PK1), has been developed. These conjugates are less toxic than the free drug and can accumulate inside solid tumor models. An HPMA copolymer Gly-Phe-Leu-Gly-doxorubicin conjugate that also contained galactosamine (PK2; FCE28069) was designed to promote multivalent targeting of the hepatocyte asialoglycoprotein receptor (ASGR) to treat primary liver cancer. Duncan Nature Rev Cancer 6 (2006)

41 Dextran Dextran is poly(glucose) with α-1,6 linkages. Multiple groups for drug conjugation. Conjugation can also be achieved by prior periodate oxidation of the polymer After oral administration, the polymer is not significantly absorbed. Effective applications of dextran as polymeric carriers are through injections. Garnett. Adv Drug Del Rev (2001)

42 Example of dextran drug conjugate K 1, K 2 : slow hydrolysis K 3 : enzymatic hydrolysis 42 42

43 Prolonged circulation 43

44 Example of targeted dextran doxorubicin 44

45 Importance (effect) of drug loading Too high loading can lead to a significant change in the properties of the drug delivery system! 45

46 Antibody vs. non-antibody targeting agents Readily available, inexpensive, and easy to handle, some selectivity Very specific, expensive, timeconsuming to produce, immunogenicity, etc. Allen. Nature Rev Cancer (2002) 2,

47 Targeting ligands Folate receptor over-expressed in many human cancers. Large amounts of folic acid in food competitively reduces the efficiency of this ligand 47

48 Cell penetrating peptides Short peptides of less than 30 amino acids that are able to penetrate cell membranes They translocate different cargoes into cells. They are amphipathic and net positively charged. The mechanism of cell translocation is not known but it is apparently receptor and energy independent although, in certain cases, translocation can be partially mediated by endocytosis. Cargoes that are successfully internalized by CPPs range from small molecules to proteins and supramolecular particles. Most CPPs are inert or have very limited side effects. Zorko and Langel. Adv Drug Del Rev 57 (2005)

49 Examples Zorko and Langel. Adv Drug Del Rev 57 (2005)

50 In clinical trials Kratz et al. ChemMedChem 3 (2008)

51 Some conclusions Natural or synthetic macromolecular carriers offer a large amount of flexibility for conjugate design. They constitute excellent means for altering the biological properties of small-molecule therapeutics. High drug loading (beware steric hindrance and spacer length) Possibility of adding targeting ligands Interesting for combination therapy (more than one type of drug attached to the polymer 51

52 SECTION 3 Macromolecular drugs Therapeutic proteins are examples of carriers which are simultaneously drugs Proteins that are engineered in the laboratory for pharmaceutical use are known as therapeutic proteins. The majority of biopharmaceuticals marketed to date are recombinant therapeutic protein drugs. Today therapeutic proteins are used to relieve patients suffering from many conditions, including: Various cancers (Monoclonal antibodies, Interferons), Heart attacks, strokes, cystic fibrosis, Gaucher's disease (Enzymes, Blood factors), Diabetes (Insulin), Anaemia (Erythropoietin), Haemophilia (Blood clotting factors) 52

53 Obstacles to protein delivery Frokjaer and Otzen. Nature Rev Drug Disc 4 (2005)

54 Aggregation Other obstacles 54

55 Other obstacles Immunogenicity Must produce highly pure proteins that are (nearly) identical to human proteins to avoid T and B lymphocytes 55

56 Protein engineering approach Example of insulin Mutation of amino acid sequence to promote monomer formation (fast release) Chemical attachment of fatty acids to the protein surface can increase affinity to serum albumin. This can increase its circulation time in the blood (slow release) Frokjaer and Otzen. Nature Rev Drug Disc 4 (2005)

57 Chemical engineering approach PEGylation Why PEG? Non-toxic and non-immunogenic Flexible, highly water soluble, has a hydrodynamic radius which is ca 5-10 times greater than that of an equivalent globular protein Can be prepared with very specific ligation chemistry Veronese and Pasut. Drug Delivery Today 10 (2005)

58 Some approaches for PEGylation Veronese and Pasut. Drug Delivery Today 10 (2005) Gauthier and Klok. Chem Commun (2008)

59 Example L-asparaginase Gauthier and Klok Polym Chem (2010) /c0py90001j 59

60 Effect of PEG MW on renal clearance Luxon et al. Clin Ther 24 (2002)

61 Circulation half-life Luxon et al. Clin Ther 24 (2002)

62 Maintaining protein structure PEG Permanent bond between PEG and INF! Loss of ~93 % of antiviral activity of IFN In this case, activity not related to PEG MW. Interferon α-2b This can contrast to when PEG is added to amino groups on this protein Shaunak et al. Nature Chem Biol 2 (2006)

63 Some conclusions PEGylation is an effective means of improving the properties of therapeutic proteins (circulation time, immunogenicity, etc.) Limitations: PEG is not unimolecular (potentially different biological properties) This leads to a population of drug conjugates, which might have different biological properties, mainly in body-residence time and immunogenicity. This is important for low MW proteins the polydispersity problem must be taken into consideration when dealing with low molecular-weight drugs, either peptide or non-peptide drugs, where the mass of linked PEG is more relevant for conveying the conjugate's characteristics (size). Large MW PEG is not excreted As for other polymers, PEGs are usually excreted in urine or feces but at high molecular weights they can accumulate in the liver, leading to macromolecular syndrome. 63

64 Accepted by US FDA 64