Could CRISPR reverse drug resistance in lung cancer?

Using CRISPR/Cas9 gene editing combined with traditional chemotherapy, researchers “knocked out” (ie, removed) the nuclear factor erythroid 2-related factor (NRF2) gene to stop lung tumor growth and dramatically decrease tumor volume, according to researchers in a recently published article in Molecular Therapy Oncolytics.

“Cells with this gene knockout should then be more sensitive to chemotherapeutic agents, such as cisplatin, carboplatin, and vinorelbine, as the genes responsible for efflux of anticancer drugs would not be activated, even under the most environmentally stressful conditions,” wrote authors from the Gene Editing Institute, Helen F. Graham Cancer Center & Research Institute, Christiana Care Health System, Newark, DE.

Previous studies have shown that the NRF2 gene regulates the cell functions in non-small cell lung cancer tumors that help them resist the effect of chemotherapies that might otherwise weaken or destroy the tumor cells entirely.

“Our goal is to see if CRISPR can be used with chemotherapy to provide a safe, affordable way to give patients who are not responding to treatment at least a fighting chance against this very challenging cancer,” said principal author Eric Kmiec, PhD, director of the Gene Editing Institute. 

Targeting the master regulator

Emerging research indicates that drug resistance in lung cancer may be mediated in part by the upregulation of different genes involved in controlling efflux or drug inactivation. Among such genes, experts hypothesize that NEF2 is the master regulator of between 100 and 200 target genes yielding cellular responses to oxidative and/or electrophilic stress.

Chemotherapy and other cellular stressors trigger transcriptional activity of the NRF2 target genes, leading to a cytoprotective response such as enhanced resistance to chemotherapeutic agents. Other recent research findings have indicated that inhibitors of NRF2, such as luteolin and brusatol, boosted the efficacy of chemotherapeutic drugs in a gamut of cancer cell types and xenografts, including A549 lung cancer cells.

The team extended the concept of using NRF2 inhibition as a supplemental approach to treat cancer by combining CRISPR-directed gene editing with traditional chemotherapy. They hypothesized that cells exhibiting the NRF2 gene knockout would be more susceptible to chemotherapeutic drugs, including cisplatin, carboplatin, and vinorelbine, because the genes responsible for the inactivation of these drugs would be removed.

A potential synergy

The team found that cell lines demonstrated a higher sensitivity in response to increasing concentrations of cisplatin and, to a smaller degree, to increasing concentrations of carboplatin. Moreover, when cisplatin was administered with vinorelbine, higher sensitivity was noted.

Next, they used a xenograft mouse model in which A549 lung cancer cells were implanted in the mice and permitted to grow for more than 2 weeks. After the tumors grew to 100 mm³, the researchers treated the mice with cisplatin, carboplatin, or cisplatin/vinorelbine at various time points.

They found that tumor growth stopped during the 16-day treatment period, with a dramatic decrease in tumor volume in samples that received both CRISPR-directed gene editing and chemotherapy—suggesting a possible synergistic effect with this treatment combination.

“It is becoming increasingly apparent that CRISPR-directed gene editing will have a significant impact on the development of new therapeutic approaches to cancer and inherited diseases,” the authors predicted. “These genetic tools can identify and execute DNA cleavage, at specific sites within the chromosome, at a surprisingly high efficiency and with an improved precision.”