CRISPR gene editing: Can we make cancer cells easier to kill?

Lung cancer accounts for approximately one in five cancer deaths globally. The high death toll makes the development of new treatments and improvement of old ones a top priority. One of the challenges with traditional chemotherapy is that tumours can develop resistance to treatment. For several years, Eric B Kmiec, PhD, at the Gene Editing Institute of ChristianaCare, USA and colleagues have worked on clustered regularly interspaced short palindromic repeats (CRISPR). Using this technology, the researchers aim to develop new methods to make cancer cells more susceptible to chemotherapy. With their latest discovery, they hope to significantly improve the quality of life for cancer patients undergoing prolonged treatment.

Lung cancer is one of the leading causes of cancer-related deaths around the world for both men and women. The high death toll has a devastating impact on society and healthcare systems globally, making lung cancer prevention, early detection, and treatment a top priority for the research community worldwide. Early detection and appropriate treatment play a key role in preventing lung cancer from advancing and spreading to other parts of the body. This fact has led to an increased interest in developing new targeted treatments for various forms of lung cancer, called immunotherapy treatments.

Immunotherapy medication treats cancer by using the body’s defence (immune) system, specifically by activating or blocking the immune system depending on the disease. This form of treating tumours has recently become a crucial part of many standard cancer treatment plans, complementing the traditional chemotherapy agents which act mainly as poisons that kill cancer cells by blocking their division process (mitosis) or by damaging their DNA.

What is chemoresistance?

Despite the advances in research and the emergence of more specialised drugs, such as immunotherapy, chemotherapy remains a basic treatment option for cancer patients, including lung cancer patients. Thus, there is a great need for researchers to resolve any efficacy and toxicity issues that often appear when these agents are given to patients for a long period of time. At the Gene Editing Institute of ChristianaCare, USA, Eric B Kmiec, PhD, and his team have conducted extensive research to not only improve the efficiency of current standard cancer treatments, but also to revolutionise current cancer therapies by emphasising a patient-first approach.

Extended treatments not only have side effects that can be life threatening or could severely affect patient quality of life, but after a while, they can also make the tumour under treatment resistant to the chemotherapy drugs. This phenomenon is called chemoresistance. Chemoresistance occurs when any new mutated cancer cells or cancer cells adapted to protect themselves are able to take over and replace the initial sensitive cells that chemotherapy has efficiently killed. Such mutations or adaptations can present in a number of genes that are responsible for the cancer cell’s response to chemotherapy – the target genes.

Can we edit genes?

Clustered regularly interspaced short palindromic repeats, commonly known by the acronym CRISPR, is a technology that scientists use to find a specific segment of DNA inside a cell and modify it using a process called ‘gene editing’, making it possible to correct genetic defects in cells and living organisms. This revolutionary method is based on the bacterial immune mechanisms against invading viruses which involve using an enzyme, called CRISPR associated protein 9 or Cas9, to cut out and replace viral DNA.

Cas9 is easy for scientists to programme accordingly each time in order to modify the required DNA segment or gene. It also allows researchers to turn genes on or off without altering their DNA sequence. This groundbreaking method of genetic modification has already started to revolutionise the fields of medical research, biotechnology, and agriculture. Different CRISPR-based therapies (CRISPR therapeutics) are currently being explored in clinical trials for the treatment of human diseases, including hereditary diseases and different types of cancer.

Editing lung cancer DNA

With decades of experience in gene editing research, Kmiec and his team decided to use this technology to develop solutions and treatment options that address unmet medical needs. They began investigating the feasibility of using CRISPR gene editing to modify lung cancer cell DNA. The plan was to target the cancer cell DNA genes responsible for resistance to chemotherapy and make tumours more receptive to treatments. Combining cancer gene editing and chemotherapy in patients with solid tumours, such as lung cancer, could help shrink the tumours, contain the disease, and improve the treatment outcomes.

Focusing their efforts on this idea, the team developed a CRISPR gene editing tool that disables a gene called Nuclear Factor Erythroid 2-Related Factor-Like (NRF2) gene. The NRF2 gene plays a key role in boosting cellular response to perceived danger. Unfortunately, it behaves similarly in response to chemotherapy. The researchers conducted studies involving lung cancer cell lines and tissues which had been edited to have their NRF2 genes disabled to silence the cell protective behaviour of the target genes. The results of these studies revealed that the cancer cells with this gene disabled were more sensitive and susceptible to chemotherapy agents, such as cisplatin, carboplatin, and vinorelbine compared to the cancer cells without the CRISPR-directed editing which were found to be more resistant.

Experimental evidence – does the tool work on living cells?

Highly encouraged by the promising results in cancer cell lines and tissues, the team decided to evaluate their method on living organisms. To achieve this, they designed an experiment using a xenograft mouse model, an experimental model of cancer where the tissue or cells from a patient’s tumour are implanted into mice with a compromised immune system. For this experiment, the team used a lung cancer cell line called A549.

Half the experimental mice had the cancer cell line implanted in them without any modifications (control group). The other half had the same type of cancer cell line implanted, only this time the cells had their DNA CRISPR-edited to disable the NRF2 gene (knockout A549 mice). Both groups then developed tumours which were left to become approximately 100 mm3. The mice were then given a chemotherapy drug, called cisplatin. In the subsequent days, the researchers monitored the tumour volume and the cancer cell proliferation rate.

The results of this experiment demonstrated that the tumours of the mice in the control group did not respond well to cisplatin and continued growing, whereas the tumour cells of the knockout A549 mice stopped proliferating, leading to a stabilisation of their tumour sizes throughout the course of the experiment. Similar results were achieved when the researchers used other chemotherapeutic agents, such as vinorelbine and carboplatin, or a combination of more than one of these chemotherapy drugs.

Knockout NRF2 knocks out cancer

The experiment confirmed the team’s previous findings that CRISPR-induced knockout of the NRF2 gene causes lung cancer cells to be more receptive to chemotherapy. This finding is very important since it suggests that the combination of these treatments, when given to actual lung cancer patients, could not only better control the disease and increase their lifespan, but also help improve patient quality of life by minimising any toxicities related to chemotherapy, as patients would now receive lower doses of this powerful medication.

Besides improving the treatment outcomes for lung cancer patients, the team believes that their findings open a window of opportunity for similar clinical applications of CRISPR-directed NRF2 knockout to be developed, both for treating different types of cancers and other diseases. According to them, their research on NRF2 editing could also be used for treating head, neck, and oesophageal cancers, and potentially other cancers, including liver cancer, melanoma, and brain cancer.

The researchers also believe that this new method of editing cancer cell DNA could soon play an important role in ‘precision medicine’, a new approach for disease treatment and prevention that takes into account the individual’s genes, environment, and lifestyle. This method would allow future clinicians to offer personalised targeted treatment options to patients with different types of cancer gene mutations which will help them better control the disease and manage their health in the long term to not only achieve the best outcomes, but also to improve their quality of life and well-being.