The COVID-19 pandemic taught us about the dangers of viral mutations. According to the WHO, by 2023, at least nine prominent variants of the Coronavirus were in circulation around the world.
Mutations in pathogens are bad news because they can make organisms more resistant to vaccines and drugs over time. The same is also true of cancer cells. Genetic mutations can confer treatment resistance in many types of cancer.
The most common examples include non-small cell lung cancer, melanoma, HER2-positive breast cancers, colorectal cancers, leukemia, and multiple myeloma. In these cancers, multiple mutations often co-exist and compete for supremacy inside the tumors.
While some cell populations may be vulnerable to a popular drug, others may resist it through mutations. Knowing which mutation is dominant is crucial for successful treatment using the appropriate mix of drugs.
This is where a technique called “Clonal Competition Assays” (CCA) has major implications. Developed over several decades of technological advances in molecular biology and gene sequencing, the technique started gaining credence only in the 2010s in cancer research.
In 2024, a team of researchers at the H12O – CNIO Hematological Malignancies Clinical Research Unit in Madrid, Spain used the technique to study competing cancer cell populations in multiple myeloma and uncover new insights into drug-resistant mutations.
The Science and Theory Behind Clonal Competition Assays
The foundation of CCA can be traced back to the basics of evolutionary theory in biology. Concepts like natural selection, adaptation, and selection pressure explain how organisms survive, reproduce, and evolve in an ecosystem.
A cancerous tumor is also like an ecosystem, where various populations of cells (called clones) compete with each other. External factors like the body’s immune cells and cancer drugs act as predators, exerting selection pressure on the clonal populations.
Cells that lack the traits to resist these pressures will die off, while cells with mutations that help them evade the predators will succeed and thrive. CCA allows researchers to study the competition between different various clonal populations using a combination of tools:
- Fluorescent Assays: these are special dyes, proteins, or nanoparticles that can bind to specific cell populations and mark them in specific colors for visual identification
- Genetic Barcoding: tagging the cells with unique DNA sequences for easier tracking of their lineages over time
- Live Imaging: using specialized microscopes to observe the competition between different tagged clonal populations in real-time
- Gene Editing: modern tools like CRISPR allow scientists to modify or introduce new mutations inside the clones for further research
In relatively simple terms, CCA involves taking a tissue sample containing several competing cancer cell populations and marking them with different colors. The researchers can then observe how the different populations react to environmental changes.
They can starve the cancer cells by depriving them of access to essential nutrients, adding specific drugs, or even editing the mutations to see how they impact the overall ecosystem. CCA allows researchers to map out how different cell populations react to these changes.
Why is Clonal Competition Assay Relevant for Multiple Myeloma?
The CCA study conducted at the Madrid Institute focused on multiple myeloma (MM), a type of blood cancer that affects plasma cells. An estimated 35,000 new cases of myeloma are reported each year in the US alone, according to this highly informative video by the Mayo Clinic.
Although the root cause of the disease is unknown, obesity, radiation, and long-term exposure to certain aromatic hydrocarbons are all known risk factors. Myeloma is more common in men than women and is very rare in people under the age of 40.
Blood cells in the bone marrow work overtime to produce new cells for the immune system. Since these cells have a much higher rate of cell division when compared to the rest of the body, cancers like myeloma that affect the blood cells are more likely to mutate.
A higher rate of mutations can give rise to multiple competing clonal populations within the cancer ecosystem. As already noted, increased genetic diversity can make such cancers harder to treat.
Myeloma has no known cure and the objective of current treatments is to slow down the progression, and in the best-case scenario, put the cancer into remission. Dr. Cesar Valdes, Clinical Director of MM at Mount Sinai, considers it more as a “chronic disease, almost like diabetes” that may require on-and-off therapy to keep it under control.
However, in many patients, MM has a habit of relapsing after showing initial signs of remission, even after a marrow transplant. This usually happens when the cancer cells acquire mutations that make them more resistant to previously used drugs.
Key Findings from the CCA Study
KRAS is a very important gene in the body responsible for handling cell growth and division. Thanks to its highly strategic position, mutations in the KRAS gene are a key ingredient in the evolution of many cancers.
At least 20% of all patients with MM show some mutations in their KRAS gene. Using the CCA technique allowed the researchers to identify two KRAS mutations that helped cancer cells multiply at a much faster rate than normal plasma cells.
Perhaps more significant was the discovery of several other genetic mutations that increased drug resistance. When popular myeloma drugs were applied, all the “weaker” cells died, allowing the survivors with the mutations to take their place.
The net result was a stronger, more resilient cancer with the ability to bounce back after an initial remission. Knowledge about these specific mutations could prove invaluable in helping us design more effective treatment plans.
It also raises the possibility of screening tests that look for these mutations. If the tests are positive, doctors can make more informed decisions about switching to other drugs. The study also explains how aggressive treatment can actually strengthen these cancers.
When there are competing clonal populations, wiping out the non-resistant cells gives the mutated cells more room to grow. According to the authors of the study, taking breaks between drug treatments may help reduce the risk of tumors becoming resistant.
It is fascinating how our very attempt to kill the disease can paradoxically make it stronger in the long run by contributing to the evolutionary cycle of natural selection within the cancer ecosystem. With critical insights like these, the CCA technique is proving to be a major asset in our fight against cancer.
