Drug Discovery, Hit to Lead
Drug Discovery, Hit to Lead
Twelve Principles for Drug Optimization
|1. Increasing Potency
In the analogue class of the histamine H2-receptor antagonists (cimetidine, nizatidine, ranitidine, roxatidine, and famotidine), an increasing potency of the drug analogues can be observed. Famotidine is the most potent member of this class.2. Improving the Ratio of the Main Activity to Adverse Affects
The pioneer drug of the adrenergic β-blockers is propranolol, which blocked both β1– and β2-receptors. However, blocking β2-receptors in asthma is harmful. Several selective blockers were developed and used in cardiology, such as atenolol, metoprolol, etc.
3. Improving the Physicochemical Properties with the Help of Analogues
4. Decreasing Resistance to Anti-Infective Drugs
5 .Decreasing Resistance to Anticancer Agents
6. Improving Oral Bioavailability
|based drug research afforded the lysylproline analogue, lisinopril, which has an acceptable bioavailability and it does not require metabolic activation.
7. Long-Acting Drugs for Chronic Diseases
8. Ultrashort-Acting Drugs in Emergency Cases
9. Decreasing Interindividual Pharmacokinetic Differences
10. Decreasing Systemic Activities
11. Decreasing Drug Interactions with the Help of Analogues
12. Synergistic Interactions between Analogues
We analyzed the Top 100 most frequently used drugs and nine standalone drugs were identified, that is, pioneer drugs for which there are no effective analogues. These are the following drugs: acetaminophen, acetylsalicylic acid, aripiprazole, bupropion, ezetimibe, lamotrigine, metformin, topiramate, and valproate semisodium.
Acetaminophen is one of the oldest drugs, which even nowadays has a broad application as an analgesic and antipyretic agent. However, acute overdose can cause severe hepatic damage.
Acetylsalicylic acid (aspirin) is also one of the oldest drugs and, contrary to acetaminophen, its mechanism of action is partly known: it irreversibly inhibits the cyclooxygenase-1 enzyme. A more potent derivative with a better adverse effect profile would be advantageous.
Aripiprazole is a relatively new antipsychotic drug which acts as a dopamine partial agonist for the treatment of schizophrenia. A more effective drug is needed for the treatment of refractory patients, to improve treatment of negative symptoms and cognitive dysfunction.
Bupropion is a unique antidepressant drug. It is the first non-nicotine medication for the treatment of smoking cessation.
Ezetimibe is a relatively new cholesterol absorption inhibitor. Its mechanism of action was discovered only recently (2005). Analogue-based drug research is underway.
Lamotrigine, topiramate, and valproate are widely used anticonvulsant drugs, whose mechanism of action is not known. Several efforts have been made to find better analogues, so far without positive results.
Metformin is already an old standalone drug for the treatment of type 2 diabetes. It is used alone or in combination with new antidiabetic agents. Its mechanism of action is not known which makes it difficult to conduct an analogue-based drug research.
DESIGNING A BETTER DRUG: The combination of chemical groups from three different fragments that bind weakly to an enzyme produce a potent new enzyme inhibitor (center) that binds in the nM range.COURTESY OF RODERICK HUBBARD
In search of better drugs and therapies, researchers are constantly looking for new ways to identify compounds that selectively block disease pathways. Industrial labs have relied on high-throughput screening to finger promising new molecules, but most academic labs lack the equipment and resources to scan many thousands, even millions, of compounds. For a long while this shut academic labs out of such searches, but a related technique, fragment-based drug discovery (also called fragment-based lead discovery), offers another way to develop small-molecule drugs and chemical probes for investigating biological processes. And this approach relies on instruments and expertise available at many academic institutions.
A guide to fragment-based drug discovery
In the pursuit of new pharmaceuticals, many medicinal chemists want to start their leg of the drug discovery race with a drug-sized molecule that binds with a tenacious grip—we’re talking nanomolar potency—to its biological target. After all, there are so many molecular traits to optimize, such as reducing a drug lead’s toxicity and increasing its solubility in the body, that beginning with high-binding affinity seems like starting on the right foot. That’s why high-affinity hits are the primary aim of high-throughput screening (HTS), a bread-and-butter starting point for drug lead discovery.
But a growing number of medicinal chemists are leaving the high-affinity paradigm behind. These researchers are sidestepping some of the cherished tenets of HTS in favor of an emerging drug discovery strategy called fragment-based lead discovery (FBLD).