New Drug Development-screening

Drug screening Drug screening Sequence of experimentation and characterisation. Objectives Identify hits Lead identification Lead optimisation Define the pharmacological and pharmacokinetic profile of the drug, Methods 1. Non biological methods 2. Computational methods: Virtual screening, NMR 3. Biological methods In vitro assays Molecular assays Cellular/Tissue/Organ assays In-vivo assays Systems or disease models Non biological method Virtual screening: SAR based NMR spectroscopy Use computational models to arrive at promising molecules for biological screening. Promising molecules are picked up on the basis of the intensity with which the drug molecules combine with the receptor. 10,000 molecules may be subjected to arrive at 1000 promising molecules Biological methods In- vitro assays Molecular assays Cellular/Tissue/Organ assays In-vivo assays Systems or disease models Assays

using biological tissues Cell membranes,isolated whole cells,isolated tissues,isolated organs and whole animals are used. Helps in identifying the Hits,Lead,and the Candidate drugs for further evaluation 1. Molecular assays In-vitro assays Detect the affinity and selectivity of the drug at the level of receptors. May or may not detect the efficacy or the functional changes

Identification

of the hit molecules(should beeffective at 50 mm conc).

E.g. Cell

membrane fractions from organs or cultured cells---source of receptors ----for affinity and selectivity E.g.Alpha adrenoceptors to evaluate binding of alpha agonists Enzymes e.g.Tyrosine hydroxylase from sympathetic nerve endings---enzyme inhibition by –Inhibitors Patch

clamp techniques ---for ion channels, conductance of sodium ions

local anesthetics Advantages Large

number of molecules can be screened as high throughput screening

Limitations Functional

aspect cannot be evaluated Other aspects like PK safety cannot be evaluated 2. Cellular assays In vitro assays Detect the cellular function-Affinity, selectivity and potency of the drug. Effect on post-receptor mechanisms Pharmacokinetics e.g.absorption across CaCo-2 cell lines In-vitro metabolism Hep-G2 CELL lines Hepatocytocytes and Kidney cell line-- toxicity Drug- interaction studies Lead identification E.g.Islet cell culture—Beta cells for release of Insulin. Hepatocyte culture for hepatotoxic effect Advantages More

realistic models than the molecular assays. Post target activation/or inhibition can be studied Limitations Cannot assessDose determination Effect on other organ systems Tolerability

High throughput screening Large libraries of chemicals are tested for their ability to modify the target Most common target is the GPCR Can screen upto 10,000 molecules per day Ultra high throughput screening 1,00,000 Detects the agonists and antagonists Also detects the selectivity of the drug using cross screening techniques. Functional benefits Automated sample generation and Preperation Target finding and validation Genomics Proteomics Parallel synthesis stations.etc. HTS Advantages Time saving Large number can be screened Techniques Radioligand binding assays Fluorescent assays System or disease models In vivo assays Detect the in- vivo efficacy in the disease conditions Help in lead optimisation based on the pharmacodynamic and pharmacokinetic characteristics More information on route of drug administration,duration of action Adverse effects may be identified May detect the unidentified additional therapeutic benefit Pharmacokinetic data can be generated-absorption,bioavailability and metabolism Drug interactions can be studied E.g. Mouse or Rat models of anxiety for Benzodiazepine like drugs. Anesthetised

dogs for anti-hypertensive drug evaluation