Thanks to the abundance of primary cells in the market now, we can speak specifically about primary cell screens which are truly valuable for the information they can reveal.
So let’s break it down. What is a primary cell screen and what is High-Throughput Screening (HTS)? As I’ll explain shortly, a primary cell screen is just a high-throughput screen using primary cells. HTS is a method used in drug discovery and the development of therapeutic agents which involves the use of automated equipment to rapidly test thousands of samples using your target organism or cellular pathway. The substances used in these screens can be chemicals, drugs, antibodies and most notably today, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) substrates. Ultimately, HTS is a combination of technologies including robotics, advanced data analysis, and potentially even AI (Artificial Intelligence). The exact set-up can vary based on the size of the screen, resources available, and the individual lab doing the screen.
Think of it as a huge jump start in the entire discovery process.
Those involved in screening applications want to see what affect, if any, these compounds, will have on the cells or their pathway.
Today, there are two main types of high-throughput screens that are important in the drug discovery process. One is gain-of-function and the other is loss-of-function. Both of these fall under the broader term “Functional Screens”. In a gain-of function screen, gene expression is driven so that more mRNA and protein are made. With loss-of function, the goal is to stop the mRNA and protein production that is associated with your gene(s) of interest.
With either method, you will see phenotypic changes and this indicates the involvement of a gene in your pathway or disease of interest.
In the realm of drug discovery, loss-of function screens are the predominate choice in identifying new drugs.
Ok, great! But what steps are involved? Here are the five main steps involved with screening:
- Target Identification and Validation
- Compound Screening
- Hit Validation
- Lead Identification and Optimization
- Clinical Trials and FDA Approvals
Let’s define each step a little more. Target Identification is where you will identify the gene(s) that are associated with the disease you want to study. For example, a large primary cell screen can be used to test compounds to disrupt various genes. Let’s say as a result of some of your Compound Screening, you induce a disease phenotype in a healthy cell. This would tell you that the gene you are studying is very likely involved with that disease.
Now you have identified your target and next you need to validate it. This means, in very basic terms, running many iterations of your screen so you can confirm that the gene you have identified is directly linked to the phenotypic effect you saw.
Next, if that target validation goes well, you will proceed with Hit Validation. This usually consists of running many assays to confirm the “hit” and on-target activity with the expected target. It also can establish an initial ranking of compounds by activity.
Next up is Lead Identification and Optimization. This is a major critical step in the process where the identification of your preclinical candidate takes place. Essentially the most promising hits are identified as leads and then further optimized.
Finally, we have Clinical Trials and FDA Approvals. For more information about that topic, please see our previous article about the basics of clinical trials.
A Quick Word About CRISPR Screens
CRISPR screens are very much a cornerstone within the world of functional genomics these days. Functional genomics aims to elucidate how genes and different regions of the genome function and interact. This can include studying how genes are switched on or off (epigenetics), transcription, and translation. Given the powerful ability of CRISPR to target specific areas within a genome, you can see how this approach has become so popular. The steps used with a CRISPR screen will still follow the same guidelines outlined above.
This leads us to a very nice tie-in with how Lonza fits into the world of screening and CRISPR screens in particular.
Lonza’s Nucleofector® Technology, namely our 384-well Nucleofector® System, is your go-to solution for your screening needs in 384-well format. The 384-well Nucleofector® System is designed to integrate with LHS Systems, including Tecan, Beckman and Hamilton. This may help to reduce your handling time and speed up the discovery process.
You can read and learn much more about Lonza’s tools for screening and drug discovery on our CRISPR screening page.
I hope I have provided you with a foundational basis for understanding screening and its purpose as well as the steps involved. Please remember that there are numerous options when it comes to choosing your screening method and I have only scratched the surface of what is possible. Please take the time to fully investigate what you need to accomplish and the best approach to take. With the right tools, you will be well on your way to the next discovery!
Written by
Sean
Group Leader, US Scientific Support
