Understanding The Cell Diversity in Drug Research and Discovery

We all are well aware of cells, but we say there are so many things that are hidden from you about cells. Yes, we are talking about the broad application of cells in drug research. Now, you may be assuming “What is the role of cells in drug research” Don’t hold up your curiosity let’s delve together to understand the dynamic role of cells.

There are numerous cells present in our body, millions to billions, and several cell types. Each cell is specialized in its functions and performs various tasks that are essential for the physiology of the body. 

Among all these cells researchers often face challenges in selecting the most appropriate cells for their studies and determining the optimal timing for their use. Cell lines, dissociated tumor cells, and primary culture cells each serve unique roles in research, though there is some overlap in their applications.

Cell Types and Derivation

Immortalized Cell Lines: These have been fundamental in research for over fifty years. They can be propagated indefinitely in culture, providing a consistent resource for various assays. Immortalized cell lines are often genetically modified and may not accurately represent in vivo conditions.

Dissociated Tumor Cells (DTCs): These originate from fresh tumor tissue, which is dissociated into single-cell suspensions and cryopreserved without additional modification. DTCs offer a diverse mixture of cells found in the tumor, including potential tumor-infiltrating lymphocytes (TILs).

Primary Culture Cells: Derived from tissue dissociation and cultured without cryopreservation, primary culture cells include epithelial cells or fibroblasts. They closely resemble the original tissue but may undergo phenotypic drift over time in culture.

Immune Cells: These cells are isolated from various tissues, such as bone marrow, spleen, or peripheral blood, immune cells play crucial roles in disease research. Techniques like density gradient centrifugation are used for isolation, producing populations of mononuclear cells from which T, B, NK cells, and monocytes can be obtained.

Each type of cell offers unique advantages and is suited to specific research applications, contributing to the advancement of various fields within biomedical research.

Understanding the differences between these cell types and knowing when to utilize them is crucial for researchers. Here, we explore the main categories of cells used in research, their derivation methods, and their applications in various fields of study.

Applications of Different Cell Types

Biomarker Discovery: DTCs and primary cells are preferred for biomarker studies as they closely mimic in vivo conditions, providing valuable insights into disease mechanisms and potential therapeutic targets.

Drug Discovery: A diverse inventory of diseased cell products is essential for accurately screening candidate compounds. Immortalized cell lines, primary cells, and DTCs offer valuable tools for assessing drug efficacy and toxicity.

Cell Therapy: DTCs, primary cells, and immune cells serve as crucial targets for cell therapy research. Their direct derivation from human donors without alteration makes them valuable for validating gene editing techniques and assessing therapeutic interventions.

Diagnostic Development: Cells derived from diseased tissue are critical for developing diagnostic techniques across various disease types. DTCs and primary cells provide essential tools for identifying disease biomarkers and developing diagnostic assays.

Immunotoxicity Evaluation: A diverse range of immune cells from different disease indications is necessary for evaluating the immunotoxicity of medical devices. Immune cells isolated from various tissues provide valuable insights into the immune response to medical interventions.

Culture Models: Cell lines, primary cells, and certain DTCs can be integrated into 2D and 3D culture models to create clinically relevant environments for drug screening and testing. These models offer a more accurate representation of in vivo conditions, facilitating the development of novel therapeutic strategies.

Personalized Medicine: Patient-derived cells, particularly DTCs, offer valuable insights into how specific disease cohorts respond to different drug therapies. By utilizing patient-derived cells, researchers can tailor treatment strategies to individual patients, advancing the field of personalized medicine.

The drug development process is incomplete without efficient screening of drugs. For this purpose, over the decade high-throughput techniques have come to light in drug design and discovery research. These techniques somehow reduce the workload on the shoulders of researchers and also save the cost of drug research. 

Cell-based assays in high throughput screening drug discovery

Cell-based assays are extensively utilized in compound screening programs within the biopharmaceutical industry.  These assays can distinguish between agonists and antagonists, identify allosteric modulators, and offer insights into compound characteristics like permeability and cytotoxicity. They provide a more biologically relevant microenvironment, bridging the gap between whole organisms and in vitro biochemical systems. Used throughout early drug discovery, from target identification to safety screening, cell-based assays yield tissue-specific responses and assist in identifying high-quality leads. The main components of a cell-based High-throughput drug discovery include cells, culture devices, and detection systems.

The reporter gene techniques involve the expression of reporter gene products, such as enzymes or green fluorescent proteins, to measure gene activation or cellular responses. Recent advancements include 3D cell-based fluorescent assays and microfluidic systems for HTS. 

Why utilize cell-based assays over biochemical assays in high throughput screening drug discovery?

Biochemical assays, like enzyme inhibition and receptor-ligand binding assays, have been widely used but have limitations in representing tissue-specific responses. Cell-based assays, including second messenger, reporter gene, and cell proliferation assays, are gaining popularity due to their ability to provide early indications of drug toxicity and better represent tissue-specific responses. Biochemical assays allow for miniaturization and homogeneous reactions but may not accurately reflect cellular contexts. In vitro cell-based assays are increasingly preferred for toxicity testing, offering insights into the toxicity characteristics of drug candidates.

Cells involved in efficient drug delivery 

The efficient delivery of drugs is a crucial step in drug research. To fulfill this purpose cells, play a very sensitive role. Let’s try to understand the science behind the drug delivery via cells. 

Red blood cells (RBCs): Recent advancements have expanded the utility of RBCs for in vivo applications by developing methods to couple molecules using a range of covalent and non-covalent crosslinkers.

One approach involves utilizing receptor-specific ligands and binding agents, such as the bio-bridge method, to attach therapeutic agents to the surface of RBCs. This method has successfully attached various proteins, RNA, and DNA-based therapeutics to RBC surfaces, achieving high yields without compromising the cells’ 24-hour survival in circulation.

In addition to specific bridging methods, nonspecific forces such as van der Waals forces, electrostatic interactions, hydrogen bonds, and hydrophobic forces can also be employed to attach therapeutic agents to RBC surfaces. (PMID: 31669698)

RBCs possess advantageous circulatory properties that enable them to reach blood clots in vascular endothelial structures without infiltrating tissues, making them ideal carriers for targeted therapies.(PMID: 33096949)

Platelets have storage capacity: Platelets, derived from megakaryocytes in the bone marrow, are crucial components of blood, playing a vital role in hemostasis. They are small, anucleate, discoid-shaped cells containing cytoplasmic granules packed with biologically active proteins essential for their function.

In drug delivery applications, platelets can be loaded with therapeutic proteins to act as circulating reservoirs. Studies have demonstrated various strategies for utilizing platelets in drug delivery. For instance, platelets can deliver coagulation factors directly to sites of vascular injury, enhancing thrombogenesis and facilitating localized drug release.(PMID: 33096949)

Leukocytes: Leukocytes, compared to other blood cells, exhibit unique characteristics that make them promising candidates for drug delivery. Utilizing leukocytes as carriers for drug delivery capitalizes on their biocompatibility and biological functions to prolong the drugs’ lifespan in vivo and target inflammatory tissues for site-specific delivery. Both small molecule and macromolecular therapeutics can be encapsulated within leukocytes via passive diffusion. (PMID: 33096949)

Neutrophils: Neutrophils exhibit several novel properties that make them promising carriers for delivering nanotherapeutics:

1. Neutrophils are the first responders at sites of infection or inflammation, producing cytokines to recruit other immune cells before being cleared within a few days.
2. Despite their short lifespan in circulation, neutrophils are the most abundant cells during acute inflammation compared to monocytes/macrophages, facilitating rapid drug delivery.
3. In response to inflammation, neutrophil numbers can increase by a hundredfold or more in a short period, making them attractive targets for enhancing therapeutic efficacy.

Neutrophils’ capability to traverse the vascular barrier into tissues makes them excellent vectors for transporting nanoparticles. proposed a method for delivering nanotherapeutic drugs to deep tissues through the neutrophil transmigration pathway. (PMID: 33096949)

Conclusion 

Immortalized cell lines provide a continuous resource for repeated assays, while DTCs and primary cells closely mimic in vivo conditions, making them valuable for biomarker discovery and drug screening. Immune cells play crucial roles in disease research and immunotoxicity evaluation, while culture models offer a more accurate representation of clinical environments. By understanding the characteristics and applications of different cell types, researchers can effectively utilize these tools to advance drug research and develop innovative therapeutic strategies.