Drug discovery is a process of identification, screening and analysis of potential compounds for their role in therapeutics. Assessment of these compounds is a time consuming and sophisticated approach, involving high degree of uncertainty whether it will actually succeed as a drug or not. In order to remove these barriers, new technologies like CRISPR can be essential for the development of drug discovery process.
CRISPR-Cas9 and Genome editing
The “Clustered Regularly Interspaced Short Palindromic Repeats” or CRISPR, are the major component of a bacterial defense mechanism representing a novel genome editing technology also known as CRISPR-Cas9.CRISPR “spacer” sequences are transcribed into short RNA sequences i.e., “CRISPR RNAs” or “crRNAs” which can guide the system to corresponding sequences of DNA. Following identification, Cas9 associates with the target and shuts the targeted gene. With recent advancements, researchers can activate gene expression instead of denaturing the DNA by using modified versions of this system (Cas9).
Drug discovery workflow in CRISPR: editing
Drug discovery depends on the potential to alter genomes at the preclinical stage. Manipulation in the genetic sequence or expression may form a sequence of assays to determine the disease targets and evaluate therapeutic ability. But, performing such in a rapid, precise, and economic manner includes various limitations.
The zinc finger nucleases and transcription activator-like effector nucleases are the 1stgen gene-editing tools which are designed for complete knockouts. However, these tools are lengthy as well as expensive due to their complicated designs. On the other hand, CRISPR system comprises of only a single nuclease i.e., Cas9 and a guide RNA (gRNA)which makes it an easy to develop tool with wider range of functions.With the help of this tool, the researchers can design a short guide sequence which has the potential to target almost any gene or genetic locus for Cas9 to induce a double-strand cleavage.
Modified CRISPRs can be designed with a higher ability of activation and inhibition of gene expression. Moreover, the simplicity and dynamics of CRISPR allows it to overcome various technical challenges of drug discovery.
Drug discovery workflow
Target identification and validation
Potential drug targets (DNA, RNA or Protein) associated with a disease are identified and validated. CRISPR-based basic science research and loss/gain-of-function screens identify gene functions. Knockout and knock-in cell lines are used to ensure the association of target with the disease of interest.
High-throughput screens are used to rapidly assess millions of compounds, resulting in the identification of hundreds of drug candidates (hits). CRISPR-can facilitates the generation of cells with disease-specific mutations for screening.
Cell-based assays are developed to more specifically test the therapeutic potential of the hits, narrowing the candidates to leads. CRISPR is used to generate isogenic cell lines and disease models using the most relevant cell types (primary cells and iPSCs).
Lead identification and optimization
Leads are optimized for efficiency and tested for safety. CRISPR provides better safety models for toxicology studies. It can ultimately generate accurate in vivo disease models rapidly.
Clinical trials and FDA approval
The qualified leads (less than 10) then progress to clinical trials. They undergo testing phase for therapeutic effects in human subjects. The potential leads then get approval from FDA and become drugs.