Researchers silence leading cancer-causing gene

Using bioluminescence, researchers showed that the novel molecule “KRAS silencing RNA” or "KRAS siRNA” (right) reduced the size of a tumor in mice. Researchers used a “non-KRAS silencing” molecule as the control (left) as a comparison. Credit: Image courtesy of University of North Carolina Health Care

Researchers from the UNC School of Medicine and colleagues at The University of Texas MD Anderson Cancer Center have developed a new approach to block the KRAS oncogene, one of the most frequently mutated genes in human cancer. The approach, led by Chad Pecot, MD, an assistant professor of medicine at UNC, offers another route to attack KRAS, which has proven to be an elusive and frustrating target for drug developers.

The new method relies upon a specifically sequenced type of small interfering RNA -- or siRNA. The findings, published in the journal Molecular Cancer Therapeutics, show that using a form of siRNA to halt KRAS not only dramatically stunted the growth of lung and colon cancers in cultured cells and mice but also stopped metastasis -- the main cause of cancer deaths.

"KRAS has been widely regarded as an undruggable protein, but we show that that's simply not the case," said Pecot, the study lead author and member of the UNC Lineberger Comprehensive Cancer Center.

KRAS is a signaling molecule -- a protein switch that triggers a cascade of molecular events that tell cells to grow and survive. Mutations in the KRAS gene create a switch that is perpetually "on," causing cells to divide uncontrollably. KRAS mutations are present in roughly 30 percent of human cancers, particularly lung, colon, pancreatic, and thyroid.

"It is the elephant in the room," Pecot said. "KRAS was one of the first cancer-causing genes ever discovered, and it was the obvious target to go after. People have been trying for decades to hit it, but they haven't had much luck."

Inhibiting KRAS signaling has been tricky because it lacks good pockets or crevices for small molecules and drugs to bind to. Some researchers have tried instead to target the proteins downstream in the KRAS signaling cascade, but those attempts have also had limited success.

Rather than try another conventional approach, Pecot decided to use a new genetic tool known as RNA interference -- or RNAi -- to destroy the KRAS protein before it fully forms. RNAi uses bits of synthetically engineered RNA -- the single-stranded molecule transcribed from DNA -- to silence specific genes. These bits of RNA bind to specific genetic messages called mRNA in the cell and direct enzymes to recognize the messages as enemies. In this context, the enzymes destroyed the genetic messages of KRAS mRNA so that KRAS can't be made. As a result, the cells don't grow, replicate, or move nearly as well.

RNAi has shown great promise in the treatment of liver diseases, viral infections, and cancers. To see if this approach could thwart the KRAS oncogene, Pecot and his colleagues first had to test different sequences of RNA to determine which one most effectively tagged KRAS for destruction. Of five RNA sequences, the researchers identified two candidates worthy to take into cancer models.

When they delivered these sequences into tissue culture cells, they found that the siRNAs destroyed more than 90 percent of the KRAS gene messages, significantly impairing the growth of cancer cell lines. The technique also led to marked reduction of two signaling molecules called pERK and pMEK, which lie downstream of KRAS and have been implicated in cancer cell proliferation and tumor growth.

Next, Pecot and his colleagues tested the siRNAs in mouse models of lung and colon cancer. They wrapped the sequences in protective lipid nanoparticles and delivered the siRNA solution into the mice. The researchers found that this treatment significantly slowed the growth of primary tumors. For example, tumors from colon cancer models that had been treated with the KRAS siRNAs were 69 percent smaller than tumors treated with control RNA sequences.

In addition, the researchers discovered that silencing KRAS stemmed the spread of cancer cells to other organs. The siRNA treatment reduced the number of these secondary malignant growths by about 80 percent in mice with lung cancer and to a similar degree in colon cancer models.

Pecot's findings come on the heels of two other papers using siRNAs to target KRAS, one from Frank McCormick's laboratory at the University of California at San Francisco and the other from Tyler Jacks' laboratory at the Massachusetts Institute of Technology. What sets the UNC study apart is that it demonstrates that this approach can be used to control the development of metastatic disease.

"Having all three papers come out at about the same time is encouraging because it means that KRAS is druggable if you use outside-the-box methods," Pecot said. "Now, we essentially have three platforms for targeting KRAS with siRNAs that may get to the clinic."

Pecot said the results, while promising, are just a first step in combating this cancer-causing gene. Ultimately, the siRNA sequences will have to be designed to specifically target the mutant form of KRAS without disrupting the normal form of the gene, which is necessary for maintaining normal growth in healthy cells.

Source: University of North Carolina Health Care

‘Smart’ drugs won’t make smart people smarter, research concludes

Dr. Ahmed Dahir Mohamed is in the School of Psychology at The University of Nottingham Malaysia Campus. Credit: The University of Nottingham

The study carried out by Dr Ahmed Dahir Mohamed, in the School of Psychology at The University of Nottingham Malaysia Campus, and published in the open access journal PLOS ONE, showed the drug had negative effects in healthy people.

Dr Mohamed said: "We looked at how the drug acted when you are required to respond accurately and in a timely manner. Our findings were completely opposite to the results we expected."

In a randomised double blind study, 'Modafinil increases the latency of response in the Hayling Sentence Completion Test in Healthy Volunteers: A Randomised Controlled Trial', they administered 32 participants with the drug and 32 with a placebo. All the participants were given a famous neuropsychological task known as the Hayling Sentence Completion Test in which they were asked to respond both quickly and accurately. Dr Mohamed found the drug slowed down reaction times, impaired their ability to respond in a timely manner and failed to improve their performance of the task.

Dr Mohamed said: "It has been argued that Modafinil might improve your performance by delaying your ability to respond. It has been suggested this 'delay dependent improvement' might improve cognitive performance by making people less impulsive. We found no evidence to support those claims.

"Our research showed that when a task required instant reactions the drug just increased reaction times with no improvement to cognitive performance."

This backs up the findings of a previous study carried out by Dr Mohamed and published in September 2014 in The Journal of Creative Behaviour. The study: The Effects of Modafinil on Convergent and Divergent Thinking of Creativity: A Randomised Controlled Trial showed that the so called 'smart' drug impaired the participant's ability to respond in a creative way particularly when they were asked to respond laterally -- outside the box.

Does Modafinil benefit anyone?

When Dr Mohamed looked at participant's ability to problem solve in a creative manner he found that those who weren't particularly creative to start with were improved by the drug while those who were creative were impaired by the drug. He said: "Our study backs up previous research that suggests psychostimulants improve people at the lower end of the spectrum in cognition whereas they impair people who are at the optimum level of cognitive function -- healthy people for example. It looks like Modafinil is not helpful for healthy individuals and it might even impair their ability to respond and might stifle their lateral thinking, while people who have some sort of deficiency in creativity are helped by the drug."

What can make us smarter?

Ahmed Mohamed's research was carried out while he was at Cambridge University. He has since moved to The University of Nottingham Malaysia Campus where he will be looking at the effects of non-pharmacological interventions, such as meditation, exercise and diet on the healthy brain. He is also currently using Electroencephalography (EEG) to study how mindfulness can affect the healthy adolescent brain.

Dr Mohamed said: "What I have found in my doctoral studies is that if you are already a healthy person and functioning at an optimum level, it is really difficult to improve your cognition. But the brain of the adolescent is still in development and you might be able to improve cognition at this stage of our development through positive interaction, healthy diet or mindfulness."

Source: University of Nottingham