Chemotherapy resistance in solid tumours overcome with CRISPR

CRISPR-based genome editing has been used to overcome chemotherapy resistance in lung tumours by disabling a tumour-specific mutation in the NRF2 gene.

NRF2 is a master regulator of cellular stress responses, helping cells survive oxidative and toxic insults. However, when mutations cause this gene to become overactive, it can help cells evade chemotherapy. In the study published in Molecular Therapy Oncology, researchers focused on one of these mutations – R34G – due to its prevalence in lung cancer. This mutation creates a unique CRISPR/Cas9 cleavage site, which they targeted to develop a CRISPR-based therapy to overcome this resistance.

'This work brings transformational change to how we think about treating resistant cancers. Instead of developing entirely new drugs, we are using gene editing to make existing ones effective again,' said Dr Eric Kmiec, senior author of the study and executive director and chief scientific officer at the ChristianaCare Gene Editing Institute in Delaware.

Using CRISPR/Cas9 genome editing, the researchers engineered a human lung cancer cell line with the R34G mutation and successfully knocked out NRF2. In addition, when the same genome editing was applied to cells without the mutation, no editing occurred, confirming the specificity of the approach.

Lipid nanoparticles, a method of high efficiency and low risk of off-target effects, were used to deliver the CRISPR/Cas9 therapy by injection to the tumour site in mice. The results showed that editing 20 to 40 percent of the tumour cell population was enough to resensitise tumours to chemotherapy drugs, such as carboplatin and paclitaxel. Furthermore, they observed tumour size reduction compared to mice receiving chemotherapy alone. Gene expression analysis from treated tumours showed decreased levels of NRF2 target genes, such as NQO1, indicating a disruption of NRF2-driven survival pathways.

'The surprising finding was that complete gene editing in the tumours wasn't necessary to see an effect with and without the combination of chemotherapy – suggesting a threshold level of NRF2 that needs to be knocked out for tumours to respond,' Dr Kelly Banas, first author of the study and associate director of research at the ChristianaCare Gene Editing Institute told Inside Precision Medicine.

NRF2 mutations that cause chemotherapy resistance are common in multiple solid tumours, such as liver, oesophageal and head and neck cancers. Thus, the authors hypothesise that this approach could be expanded to other groups of cancer patients and that the therapy could allow patients to be treated with lower doses of chemotherapy, without compromising on therapeutic efficacy, as well as reducing side effects and extending treatment duration.

'The team has completed proof-of-concept work and assembled all the components necessary for a pre-IND submission – delivery strategy, in vitro and in vivo validation, and off-target analysis,' said Dr Banas.