CRISPR-Cas9 used to systematically inactivate genes in colorectal cancer

A team of researchers have used CRISPR-Cas9 to systematically inactivate genes in two human colorectal cancer cell lines — one with normal KRAS gene and one with a mutant KRAS. They then tested the ability of each of these cell lines to grow as tumours in mice and found that inactivating two metabolic enzymes, NADK and KHK, reduced the growth of KRAS-mutant tumours by approximately 50 percent, but had no effect on normal KRAS tumours. 

The researchers at the University of California San Diego School of Medicine also blocked these same enzymes with commercially available small molecule inhibitors and saw a significant reduction in tumour growth in mice only in tumour cells with mutant KRAS, they then tested the ability of each of these cell lines to grow as tumours in mice.

It was found that inactivating two metabolic enzymes, NADK and KHK, reduced the growth of KRAS-mutant tumours by approximately 50 percent, but had no effect on normal KRAS tumours. They also blocked these same enzymes with commercially available small molecule inhibitors and saw a significant reduction in tumour growth in mice only in tumour cells with mutant KRAS.

Dr Tariq Rana, Professor of Pediatrics at UC San Diego School of Medicine and Moores Cancer Center and his team also identified several new genes that, when inactivated, had the opposite effect — they increased KRAS-mutant tumour growth, but not the growth of normal KRAS tumours.

These types of genes are known as “tumour suppressors” because they normally keep cancer cell growth in check.

One of these new tumour suppressor genes encodes INO80C, a large multi-subunit protein that, among other things, stabilizes the genome. Dr Rana, Dr Yau and their colleagues are now taking steps to carry their findings forward, with the ultimate goal of better understanding how KRAS-mutant cancers develop and translating these insights into developing new therapies to stop them.

“We did not get these same results with cancer cells grown in the lab — the growth inhibition we saw when the NADK and KHK genes were inactivated only occurs in tumors in a mammalian system, in a more realistic microenvironment where the tumor has to survive,” said  Dr Rana,  “That suggests that the metabolic dependencies of tumour cells growing in a laboratory dish may differ dramatically compared to the same cells growing in a living system, underscoring potential limitations of standard laboratory-based cancer cell growth tests.”

Approximately 20 to 30 percent of all human cancers have mutations in the KRAS gene. KRAS mutations occur in many of the most lethal and most difficult to treat cancers, including lung, pancreatic and colorectal cancer. KRAS mutant cancer cells are able to rewire their metabolism in a way that gives them a growth advantage compared to normal cells.