New in vitro research: Elderberry agglutinin binds to sialic acid structures on ovarian cancer cells reducing their growth
A protein from elderberries called Sambucus nigra agglutinin (SNA) has been shown in a recent study to, selectively bind to, and cause the death of ovarian cancer cells.
SNA, which we will also refer to as elderberry agglutinin, is a lectin, which means that it binds to certain sugars on cells and causes agglutination or clumping together of the cells. SNA binds selectively to the sialic acids which are sugars found on the surfaces of all cells. Metastatic cancer cells however, have much higher amounts of these sialic acid structures on their surfaces compared to normal cells.
Why did the researchers choose elderberry agglutinin instead of the many other lectins?
Before the study started, the researchers had a theory that sialic acids play a role in the spread of ovarian tumours, since they are present on the surface of these cells in large numbers compared to normal cells.
So researchers were looking for the right lectin to test against the cancer cells, since they bind to sialic acid structures. They decided to go with elderberry agglutinins, because they selectively bind to α-2, 6-linked sialic acids, a specific kind of bond. This particular type of sialic-linked structures were highly represented on the ovarian cancer cells which the researchers used.
After treating cancer versus normal cells with the elderberry agglutinins, the normal cells showed hardly any change. But the cancer cells stopped growing. The elderberry agglutinins activated a cascade of reactions after binding to the sialic acids on the cancer cells, which culminated in the death of mitochondria (which produce energy in cells). As a result, the cancer cells died, while the normal cells did not. The dosage added to the cells in vitro was, 12 μg/ml. A dose of 6 μg/ml was sufficient to cause 50% growth inhibition.
Additionally, the elderberry agglutinin may prevent the cancer cells from migrating, by binding the sialic acids on their surfaces. Metastatic cancer cells use their salic acid structures to bind to molecules called selectin (also a type of lectin) on blood vessel cells, and can hence move around like white blood cells do.
This research was the first of its kind and may help develope alternative cancer treatments with less side-effects. The importance of the findings is not to be underestimated.
It is worth noting that Elderberry agglutinins may also play a role in helping to fight off viral infections, by binding to the available sialic acid structures on the human cells, thereby reducing the possibility of viruses to enter the cell. Many viruses such as some adenoviruses, rotaviruses and influenza viruses can use sialic acid structures on human cells to bind to the cells before entering.