Patrick: An Introduction to Medicinal Chemistry 5e ANTICANCER AGENTS Chapter 21 ANTICANCER AGENTS MATRIX METALLOPROTEINASE INHIBITORS modfied

1. Matrix metalloproteinases Notes Zinc-dependent enzymes Play an important role in metastasis Destructive enzymes Play a role in the breakdown, normal turnover and remodelling of the extracellular matrix Play a role in releasing VEGF from storage depots in extracellular matrix Four types - collagenases, gelatinases, stromelysins and membrane type

1. Matrix metalloproteinases Reaction catalysed by collagenases Wiggly lines removed Notes Proteins are substrates for these enzymes Enzyme hydrolyses the peptide bond between glycine and isoleucine

1. Matrix metalloproteinases Binding interactions Wiggly lines removed Notes Zinc ion interacts with the susceptible carbonyl oxygen Activates the peptide bond for hydrolysis NH of the susceptible peptide forms a hydrogen bond to alanine Bridging water molecule present between zinc cofactor and glutamate residue Bridging water acts as a nucleophile for hydrolysis Bridging water is activated by glutamate and zinc

2. Matrix metalloproteinase inhibiters Notes Potential agents for inhibiting angiogenesis and metastasis First-generation inhibitors are based on the structure of the substrate Susceptible peptide bond is replaced with a stable transition-state isostere Hydrophobic substituents are present to fit the enzyme subsites Substituents mimicking P1’ or P2’ (right-hand side inhibitors) are better than substituents mimicking P1 or P2 (left-hand-side inhibitors) Functional group(s) are included to form H-bonds with the enzyme backbone A group is included to form a strong interaction with the zinc ion cofactor Zinc ligands commonly used - thiol, carboxylate or hydroxamic acid First-generation

2. Matrix metalloproteinase inhibiters Marimastat Transition-state isostere t-Butyl group Hydroxamic acid Notes Orally active synthetic compound Undergoing phase III clinical trials for breast and prostrate cancer Hydroxamic acid acts as the zinc ligand Hydroxymethylene group acts as the transition-state isostere Isostere replaces the NH of the previously susceptible peptide bond Hydroxyl group of the isostere is good for aqueous solubility

2. Matrix metalloproteinase inhibiters Marimastat Transition-state isostere t-Butyl group Hydroxamic acid Notes t-Butyl group acts as a steric shield to protect N-terminal amide from hydrolysis t-Butyl group desolvates peptide bonds No desolvation penalty for binding

2. Matrix metalloproteinase inhibiters Marimastat - binding interactions P1’ P2’ P3’ HBD Notes Three hydrophobic substituents fit enzyme sub pockets Substituents bind using van der Waals interactions Hydroxamic acid acts as a bidentate ligand for zinc Hydroxamic acid NH acts as a hydrogen bond donor The alcohol group is good for activity and solubility The alcohol group is directed away from the protein surface and forms a hydrogen bond to water

2. Matrix metalloproteinase inhibiters BMS 275291 Thiol Hydantoin ring Right-hand Sub pockets Notes Thiol group acts as a zinc ligand Substituents (P1-P3’) fit four enzyme sub pockets Right-hand half is identical to marimastat

2. Matrix metalloproteinase inhibiters Design aims for second-generation inhibitors Reduce or eliminate peptide character Increase selectivity Decrease side effects Increase aqueous solubility Increase resistance to peptidases in gastrointestinal tract

2. Matrix metalloproteinase inhibiters Second-generation inhibitors CGS 27023A Steric shield Notes Hydroxamic acid acts as a zinc ligand Two substituents fit enzyme sub pockets Decreased peptide character Lack of selectivity Isopropyl group acts as a steric shield Thought to protect hydroxamic acid from metabolism

2. Matrix metalloproteinase inhibiters Second-generation inhibitors Pyridine CGS 27023A Prinomastat Rigidification Prinomastat Steric shield Notes on prinomastat Isopropyl substituent is incorporated into a ring - rigidification Less conformations are available Results in increased activity Pyridine ring allows extra binding interactions - extension strategy

2. Matrix metalloproteinase inhibiters Second-generation inhibitors Zinc ligand BAY 12 9655 Notes The carboxylate group acts as the ligand for the zinc ion Entered clinical trials