The researchers stress that their findings need to be confirmed in studies that follow large groups of people over time.
Nevertheless, they urge oncologists and people at higher risk for melanoma to be aware of the potential risks of taking dietary supplements.
"There is not a lot of hard data on dietary supplement use," says senior study author Jing Chen, a professor of hematology and medical oncology at the Winship Cancer Institute of Emory University in Atlanta, GA.
"We found that we had to add a line to the forms melanoma patients fill out about their histories," he explains, "since we weren't asking before."
Chondroitin sulfate is an essential natural component of cartilage, the loss of which occurs in the joint disease osteoarthritis.
Supplements of chondroitin sulfate — combined with another natural component of cartilage called glucosamine — are often recommended for osteoarthritis.
The authors report their findings in a paper that is now published in the journal Molecular Cell.
Melanoma skin cancer
Melanoma is a cancer that starts in melanocytes, which are the cells that make the skin-coloring pigment melanin.
Although much less common than other types of skin cancer, melanoma is the most dangerous because it spreads more readily to other parts of the body if not found and treated early.
The cancer can develop on any part of the skin, but the most common sites are on the neck and face, on the legs in women, and on the chest and back in men. Other body parts — such as the mouth, eyes, genitals, and anus — can also develop melanoma.
The American Cancer Society (ACS) suggest that in the United States in 2018, there will be around 91,270 new cases of melanoma and 9,320 deaths to the cancer.
Chondroitin sulfate and V600E melanoma
Around half of skin melanomas are associated with a mutation in the BRAF gene known as V600E.
The drug vemurafenib can reduce the growth of melanoma cells by blocking a signaling pathway associated with this mutation. However, although the drug may show progress initially, V600E tumors eventually become resistant to vemurafenib, perhaps through the activation of an alternative pathway.
This new study has demonstrated that chondroitin sulfate "selectively promotes" the growth of patient-derived human melanoma cells that express the BRAF V600E mutation, but not of cells that do not express it.
The researchers found the same result when they gave chondroitin sulfate to mice implanted with V600E tumors.
In addition, they found that V600E tumors in mice that had been fed the supplement were more resistant to vemurafenib.
Higher risk of relapse
Commenting on the findings, Prof. Chen suggests that it might be possible that taking chondroitin sulfate if you have precancerous growths containing the BRAF V600E mutation could speed up growth of those cells.
He also mentions the possibility that chondroitin sulfate supplementation could raise the risk of relapse in people whose cancer is V600E-positive.
The researchers located chondroitin sulfate while studying a group of metabolic enzymes to see whether they could be drivers of cell growth in melanomas with BRAF mutations.
They were surprised to find that an enzyme associated with making a chained form of chondroitin sulfate came up. Prof. Chen explains that they had to "dig back in the literature to confirm that chondroitin sulfate does get taken up by cells."
The researchers believe that their evidence about chondroitin sulfate driving growth of melanoma cells points to the possibility that the compound is involved in cell signaling — something that scientists have not come across before.
"We want to be cautious about these results, and they should be followed up."
Prof. Jing Chen