PHA111 Peptide and Peptidomimetic Drugs.pptx

MPharm Programme Peptide & Peptidomimetic Drugs Dr. Mark Gray Slide 1 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Problems with Peptides & Proteins as Drugs Oral Administration: Enzymatic hydrolysis of peptide bonds in gastrointestinal tract, as well as in kidney and liver. Other Routes: Meta...

MPharm Programme Peptide & Peptidomimetic Drugs Dr. Mark Gray Slide 1 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Problems with Peptides & Proteins as Drugs Oral Administration: Enzymatic hydrolysis of peptide bonds in gastrointestinal tract, as well as in kidney and liver. Other Routes: Metabolism also occurs in lung, nasal mucosa and in the blood. Compact globular nature of many full sized proteins makes these generally more resistant than small proteins and polypeptides. Key metabolic enzymes include carboxypeptidases (Cterminal residue cleavage), dipeptidyl carboxypeptidases, aminopeptidases (N-terminal cleavage) and amidases (internal cleavage). Many peptides / proteins are significantly hydrophilic and display poor passage through lipid membranes. Slide 2 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Peptidases in the GI Tract Stomach, pH~2. Gastric mucosa secretes Pepsin. Pepsin is an endopepsidase that cleaves at the carbonyl side of aromatic (Phe, Tyr & Trp) and acidic (Glu, Asp) residues. Small intestine, pH~7. Encounter trypsin, chymotrypsin and elastase, all secreted by the pancreas. Trypsin: cleaves at carbonyl side of basic (Lys & Arg) residue. Chymotrypsin: cleaves at aromatic (Tyr, Phe, Trp) residues. Elastase: cleaves at small, sterically unhindered residues (Ala, Gly & Ser). Small units from first wave of digestion attacked further by carboxy- and aminopeptidases. Slide 3 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Decreasing Proteolysis Replace selected L-amino acids with their Dcounterparts. This may increase resistance to proteolysis while retaining intended activity. Change primary amide to secondary amides at key cleavage sites. Most commonly through Nmethylation or replacement of natural residue (wt) with proline. Other strategies include reversing the peptide bond, or use of pseudo peptides. Co-administration of protease inhibitors and permeation enhancers aids in nasal delivery. Slide 4 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs A comparison of routes of administration as % Dose Absorbed Route Insulin Leuprolide Oral 0.05 0.05 Nasal 30 2-3 Buccal 0.5 n/a Rectal 2.5 8 Vaginal 18 38 Subcutaneous 80 65 Leuprolide is an analogue of gonadotropin releasing hormone Slide 5 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs How can we get around the problems that peptides pose as drug candidates? Peptidomimetics mimic the structures of particular peptides. This mimicry can fool a receptor into thinking it is binding the actual peptide and induce the same biological effect. For enzymes, a non-hydrolysable peptide mimic that binds to the active site would be expected to act as a competitive inhibitor of the hydrolysis of the real substrate. In addition, replacement of non-pharmacophoric polar sections of the natural molecule with lipophillic moieties will increase membrane permeation and often increase bioavailability. Usually most of the peptide backbone can be replaced with alternate atoms / groups. Slide 6 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Use of unnatural amino acids The phenylalanine analogues above display different conformational restriction profiles and differ in lipophilicity. Structural extension can result in reinforcing interactions with portions of the target binding site not reached by the natural substrate, resulting in higher affinity. Slide 7 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Conformational restriction along the peptide backbone Slide 8 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Mimicry of secondary structure Slide 9 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs RGD Scaffold Mimics RGD is the one letter code for the sequence arginineglycine-aspartic acid. This motif is known to block the binding of fibrinogen to its receptor, glycoprotein IIb/IIIa. By blocking this binding platelet aggregation is prevented, which is valuable in the treatment of stroke and heart attacks. Slide 10 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs A peptidomimetic analogue of a somatostatin agonist Somatostatin (Growth Hormone Inhibiting Hormone) is a 14-residue peptide macrocyclised through a Cys-Cys disulphide bridge. Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys Glucose scaffold analogue of a small cyclic peptide agonist displays effective GH inhibition in cultured rat anterior pituitary cells. Slide 11 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs A peptidomimetic of thyrotropinreleasing hormone These compounds and their derivatives are leads for the treatment of Alzheimer’s disease and other cognitive disorders Slide 12 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Other common ways to change a peptide backbone: pseudopeptides Slide 13 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Azapeptides, azatides & peptoids Slide 14 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Summary Some peptides and proteins are administered unchanged as drugs. However, for most peptides which display significant biological activity adverse ADME profiles prohibit their use. Peptidomimetics provide a way to get around this. These analogues of active peptides retain activity through appropriate display of the binding subunits in 3-dimensional space (pharmacophore). The replacement strategy employed maximises hydrolytic stability and may be used to improve passage of the drug through biological membranes through fine tuning lipophilicity. Slide 15 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Selected Drug Discovery Approaches Combinatorial – Produce 100’s → 1000’s new compounds using Solid Phase Organic Synthesis (SPOS). – Use High Throughput Screening Assays to test for level of activity against multiple targets. Rational – Design drugs to fit receptor / active site (10 → 100 molecules). – Test against selected target(s). Slide 16 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Example: HIV Protease Inhibitors Active site Crucial for formation of mature infectious virions Cleaves viral polyproteins → functional viral proteins Slide 17 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Natural Target: Lead for Inhibitor Design S3 Protease Cleavage S1 S2' O H N Viral Polypeptide O H2N O NH2 O N H O N N H O H N O S1' S2 O N H Viral Polypeptide S3' Proteases cleave amide bonds in other peptides. HIV protease selective for this peptide sequence. Design mimic with no cleavable peptide. Slide 18 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Protease Mechanism N H O O Asp-25 O H O O H H O H OH N H O O Asp-25' O O Asp-25 N O H O O Asp-25' H O O O Asp-25 Reaction uses a bound water molecule present in the active site. Proceeds via a key diol intermediate. Slide 19 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs O Asp-25' Transition State Analogues O Z-Leu-Asn N H N H COIleNHtBu Z N IC50 = 750 nM OH H O H N O H H N H OH CONH2 H CO2tBu Z N IC50 = 23 nM H O H N H N H H N IC50 = 6500 nM OH H H N N H OH CONH2 Slide 20 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs CO2tBu CO2tBu IC50 = 140 nM Saquinavir S1 HBA S3 S2' O N H O H N O IC50 < 0.4 nM S2 H N H OH NH2 H N N H H H O S1' Asp-25 + Asp25' Slide 21 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs Summary  Solid Phase Organic Synthesis is used widely in Combinatorial Chemistry.  Combinatorial Chemistry and Rational Drug Design are two major methods of drug discovery.  Clinical drugs can be developed from a detailed knowledge of the chemistry of a protein target. Slide 24 of 22 MPharm PHA111 Peptide & Peptidomimetic Drugs