A tumor in the liver of a mouse formed by human colorectal cancer cells. Image credit: Alexander Nguyen (CC BY 4.0)
Colorectal cancer, also known as bowel cancer, is the second most deadly cancer in the United States, where it affects over 140,000 people each year. This cancer often spreads to the liver, in a process known as metastasis. To do this, the colorectal cancer cells must survive the low oxygen levels found in the blood that carries them from the gut to the liver, and in the liver itself. The majority of colorectal cancer cells that arrive in the liver die, but some survive leading to secondary tumors.
To investigate how the colorectal cancer cells that survive and metastasize to the liver accomplish this feat, Yamaguchi, Weinberg, Nguyen et al. took colorectal tumors from patients and introduced them into mice. This showed that tumors from patients with the worst outcomes tended to metastasize more efficiently in mice.
Next, Yamaguchi et al. looked to see which genes were active in the colorectal cancer cells that were able to metastasize and compared them to those that were active in the cells that could not. This analysis revealed that the gene coding for a protein called PCK1 was more active in the cells that could metastasize. In healthy cells, PCK1 promotes the generation of the sugar glucose, and Yamaguchi et al. observed that, in a low oxygen environment, higher levels of PCK1 allowed colorectal cancer cells to proliferate faster. Unexpectedly, this was due to PCK1 increasing the production of a molecule needed to make nucleotides, which are the building blocks for DNA and RNA. Consistent with this, metastasizing colorectal cancer cells generated more nucleotide precursors, and inhibiting the enzyme involved in nucleotide synthesis (DHODH) with an arthritis drug called leflunomide stopped colorectal cancer cells from spreading.
Metastasizing colorectal cancer cells depend on PCK1 and the nucleotide-synthesizing enzyme to grow, so therapies that target these proteins may help more patients to survive this kind of cancer. The findings also suggest that the arthritis drug leflunomide should be explored further as a potential drug for the treatment of colorectal cancer.
