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As we all know, drug discovery and development are a multifaceted process that includes target identification and validation, lead identification and optimization, preclinical and clinical studies, new drug application, and approval. This is an expensive process due to the high budgets of R&D and clinical trials, which may take almost an average $2.6 billion and 12-15 years to introduce a new drug to market for treating patients. On average, out of a million molecules screened, only one molecule may end up being explored in late-stage clinical trials and used in patients. Therefore, the process is a long and challenging task from initial discovery to a marketable medicine. There are multiple defined stages for this process.
Fig.1 Schematic representation of the drug discovery and development process (Robin, 2019)
The first step in the discovery of a drug is to identify targets involved in specific diseases. It is also important to know the biological origin of a disease. A target is usually a molecule such as the nucleic acid or protein that integral to gene regulation or intracellular signaling. An ideal target should be druggable, meet clinical and commercial requirements, and its activity can be modulated by an exogenous compound. After selecting a potential target, researchers must conduct careful and precise target validation experiments to demonstrate that it is associated with the progression of a given disease. Target validation can be broken down into two key steps, including the reproducibility to confirm that it can be successfully reproduced and that introduce variation to the ligand (drug)-target environment.
Lead identification aims to identify or create a compound that can interact with the target previously selected. The compound should be synthetically stable, feasible drug with acceptable specificity, affinity, and selectivity for the target receptor. Researchers can conduct screening experiments, test the mechanism of action and initial safety, as well as pharmacokinetics and pharmacodynamics of the drug. After the compounds have been identified, they need to be optimized for efficacy and safety. Lead identification is a process of designing drug candidates after an initial lead compound is identified. The process involves the design of synthetic molecules, characterization, the optimization of dosage and introduction route, and safety testing in animal models.
Once a lead compound is found, researchers began to determine the efficacy and safety of the drug. The content includes the absorption, distribution, disposition, metabolism, & excretion (ADME) information of the new drug on non-human subjects, Proof of Principle (PoP) study, in vivo, in vitro & ex vivo assays, in silico assays, the development of drug delivery methods, and the formulation optimization & improving bioavailability.
After completing preclinical studies, the researchers proceed to clinical drug development, which includes clinical trials and volunteer studies to fine-tune the drug for use in humans. Clinical trials follow a typical series from Phase 1 studies to Phase 3 studies. It moves on to the next phase if a treatment is successful in one phase. The clinical trial design must be safe and efficacious, and to achieve the desired goal as much as possible.
The pharmaceutical company can elect to move forward with a New Drug Application after the Phase 3 studies is concluded. At this time, the FDA reviews the study data and approves, or does not approve, the drug application. The new drug regulatory approval timeline may be up to a year or occur sooner depending on its applications and necessity for patients. Following drug approval and manufacturing, the FDA requires pharmaceutical companies to conduct the post-marketing surveillance trial o assure long-term safety and effectiveness of their drugs.
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