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The HD Pipeline
Research and Drug Development for Huntington's Disease
Introduction
Have you ever wondered how new medicines are discovered? The process of going from an important discovery in a science laboratory to a successful drug available to the public is complex, costly, and time-consuming. This process is often referred to as Research and Development, or the R&D pipeline. It has many stages that interact and feedback into one another, takes many years, and costs millions of dollars.
In a way, R&D is like searching for two separate needles in two separate haystacks. The process begins with a thorough search and identification of all the different biological pathways that are involved in the disease process. The goal is to identify one or more pathways that contain possible biological targets for treating the disease. After finding one or more targets, the next step is to find potential drugs that block or change how the target causes or contributes to disease; this can be done by either designing a drug based on knowledge of the target's molecular structure and function, or by screening large libraries of chemicals and molecular compounds to find one.
A potential drug treatment may emerge from these extensive searches. However, this "candidate" drug is not yet available for treating patients. First, it must journey through more research, tests, and clinical trials before it is finally approved by the Federal government's Food and Drug Administration (FDA). Only then, many years later (and after spending a lot of money!), might a new medicine be available to help patients with debilitating diseases. For every attempt, the probability of success is less than 1%. But thousands of scientists around the world are working hard to beat those odds every day, discovering new biological pathways to target and new chemicals to try for all sorts of diseases.
Let's take a closer look at the steps of the R&D pipeline. Below is a brief overview of each stage, and you can click on the headings for any of the steps to get a more comprehensive look at that stage of the process and how it applies to HD research.
Basic Research:
Before scientists can even begin to think about finding treatments for a disease, they must have a good understanding of the biology and chemistry involved in the disease's molecular pathways. Basic research tries to understand how certain biological and chemical imbalances cause disease. Scientists must investigate everything, from the genes and proteins involved, to clinical symptoms and disease progression.
Target Identification and Validation:
While gaining a thorough understanding of a disease through basic research, scientists also attempt to identify biological targets- usually genes or proteins - that trigger or contribute to a disease. A biological target is a good place to start looking for a treatment. There are numerous genes and proteins involved in most diseases- so how can scientists know if they have picked the right one to target? Researchers generally perform experiments on animal models to assess whether the biological target they have identified is crucial to the disease pathway.
Drug Optimization:
The next step is to find one or more drugs that might make a useful treatment. One way to find candidates is to search through, or screen, thousands of chemical compounds to identify potential drugs. Alternatively, if enough is known about the shape and function of the biological target, scientists may be able to design new molecules or drugs that change the way the target behaves in living cells and patients. As opposed to screening, this approach is often called "rational drug design." A potential drug must interact with the chosen biological target, and modify it in a way that will cure the disease or decrease its effects.
Drug Development/ Pre-Clinical Animal Studies:
When a potential drug is discovered from a screen or rational drug design, it has much promise as a therapeutic drug. However, little is known about the safety and effectiveness of this so-called lead compound in animals or humans. All lead compounds must be thoroughly tested in at least two animal models to determine safe doses, understand side effects, and discover more about long-term toxicity.
Investigational New Drug (IND) Application:
After animal model studies have been completed, pharmaceutical companies must submit an IND application to the Food and Drug Administration (FDA) to continue drug development. If approved, it gives the pharmaceutical company permission to begin clinical trials which involve testing the potential drug in human participants. The IND application must include data from animal studies, information about the drug's production, and a detailed proposal for human clinical trials. Unless the FDA specifically objects, an IND application is automatically accepted after 30 days and clinical trials can begin.
Clinical Trials: Phase I Phase I clinical trials are also called "First-In-Man" studies. These studies are mostly concerned with safety, determining the maximum tolerated dose (MTD) of the drug in healthy volunteers that do not have the disease of interest. They also look for how the drug should be delivered (for example, by pill, injection, or IV fluid), how it is absorbed into different organs, how it is excreted from the body, and if it has any side effects. Approximately, 70% of potential drugs make it through this initial stage of testing.
Clinical Trials: Phase II
Once a safe dose of the potential drug has been found in healthy human participants, phase II clinical trials test it in participants with the disease of interest. Like phase I trials, these trials look for evidence of toxicity, and side effects, but they also look for evidence that the drug helps patients with the disease feel better in some way. These trials help to further refine the optimal dosage, in order to maximize beneficial effects and minimize harmful side effects.
Clinical Trials: Phase III Phase III clinical studies are the most expensive, time consuming, and complex trials to design and run. They use a very large participant group, all of whom have the relevant disease condition. These studies determine if the drug's benefits outweigh the risks (like side-effects and long term toxicity) in a larger patient group, and also compares the new potential drug with older, more commonly used treatments if any are already on the market.
New Drug Application (NDA): The FDA must review results at the end of each phase to approve the drug before it can move into the next phase of trials. Once phase I, II, and III trials have all been successfully completed, the pharmaceutical company submits a New Drug Application (NDA) to the FDA. The results of all of the trials are given, as well as the results of animal studies, manufacturing procedures, formulation details, and shelf life. In short, they include everything that would be used to label the drug. If the FDA approves a company's NDA, they can begin to mass produce and market the drug in the US. Pharmaceutical companies submit similar applications to authorities in Europe, Australia and elsewhere to market successful treatments there.
Clinical Trials: Phase IV: Phase IV trials are done after a drug has been approved, officially manufactured, and put on the market. They are done to determine the absolute optimal dosages in case it needs to be refined, to look at the very long term safety and efficacy of a drug, and to discover any rare side-effects. Phase IV trials are also used to identify the potential for new indication studies, meaning that the same drug may be able to treat diseases other than the one for which it was initially tested.
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