Melanoma drugs potentially harmful to some patients

It is well known within the scientific community that the BRAF gene is faulty in approximately half of malignant melanomas and many other cancers, making it a suitable drug target. Drugs that block BRAF function in cells are already showing positive results in early clinical trials in melanoma. While the long-term effects of these drugs are not yet known, two new reports have suggested that these drugs may have unintended consequences in patients whose tumours lack mutations in the BRAF gene.

In separate studies, conducted by researchers in the US, from the Memorial Sloan-Kettering Cancer Center, and the UK, by the Institute of Cancer Research (ICR), scientists tested the drugs to better understand how they behave in cells, and found that they spurred the growth of some tumours. These preliminary findings raise the possibility that certain patients should not receive BRAF inhibitors, as they could make their cancers worse.

Based on these studies, it is thought that giving these drugs to patients whose tumours have normal copies of the BRAF gene could accelerate tumour growth. The findings suggest that physicians need to avoid treating patients who do not have certain genetic mutations, as they could potentially cause harm. The drugs primarily target a mutation in the BRAF gene, called V600E. Many, but not all of the patients enrolled in clinical trials of BRAF inhibitors have had this mutation in their tumours. The alteration is present in approximately half of all melanomas and it activates growth-promoting messages from the MAPK signalling pathway.

The new studies focused on tumours that had mutations elsewhere in the pathway. Both groups found that BRAF inhibitors can promote tumour growth in melanoma cells that lack the V600E mutation by activating other elements of the pathway. The researchers proposed several models that could potentially explain how a drug designed to inhibit the pathway could lead to its activation. The US study's first author, Dr Georgia Hatzivassiliou, of Genentech (Roche), noted that the new results, which were published in the 3rd February online edition of Nature (10.1038/nature08833), clearly indicate that the effects of BRAF inhibitors depend on the cellular context of a tumour cell. For instance, both research teams found that the drugs could activate BRAF signalling in melanoma tumours with mutations in the RAS gene, which is part of the BRAF pathway.

As reported by the ICR in the 22nd January issue of Cell (2010;140:209-221), the drugs fuelled rather than blocked the growth of melanoma cells with RAS mutations. Both studies concluded that a central player in the activation of the BRAF pathway was a protein, called CRAF, which is a close relative of BRAF. These findings provide a framework for understanding possible mechanisms of resistance to BRAF inhibitors and give researchers information about where to look in the signalling pathway.

This work has large implications, with every tumour being different; understanding more surrounding the biology of these tumours may allow scientists to develop better treatment options. Further, the impact of this research will enable physicians to target treatments more precisely to patients who will definitely benefit, and avoid treating those who will not. The financial impact of these findings is at present unknown, however, there are BRAF inhibitors currently in clinical development. Plexxikon's PLX4032 (also known as RG7204), which is in-licensed by Roche, is currently in an open-label, single-arm, Phase II trial, called BRIM2 (B-Raf Inhibitor in Melanoma), in previously-treated metastatic melanoma patients, and recently entered a pivotal Phase III trial, BRIM3, for the same indication.

Alice Rossiter
Editor, Cancer Drug News

Progress made in identifying genetic causes of melanoma

Researchers have identified various genes that cause melanoma and also novel epigenetic markers of the disease that may herald new treatments for patients.

Two studies, published online in Nature Genetics (10.1038/ng.410 and 10.1038/ng.411), and conducted by investigators at Queensland Institute of Medical Research in Australia, King's College London and the University of Leeds, have revealed novel genes implicated in the development of melanoma. One study found that specific changes in two genes, MTAP and PLA2G6, were found to make people more susceptible to developing nevi. In a further 4,000 people, the researchers went on to show that these genes increased the risk of developing melanoma; specifically, those who carry one of the two SNPs have a 25 per cent increased chance of developing melanoma, while for individuals carrying both variants, the risk is doubled.

The second study identified five loci with genotyped or imputed SNPs reaching very high significance. The analysis showed that the genes, MC1R and TYR, are associated with pigmentation, freckling and cutaneous sun sensitivity.

Separately, researchers from Yale University have mapped chemical modifications of DNA in the melanoma genome, finding new markers that will help to develop more effective treatment strategies to fight this disease. In this work, published online in Genome Research (10.1101/gr.091447.109), scientists found 76 promoters with altered methylation patterns in melanomas, most of these showing increased methylation compared to normal. The team focused on five genes in particular, three of which had not been implicated in melanoma until now. The scientists are hopeful that these epigenetic markers may provide a better method for determining the aggressiveness of the disease and for setting a course of treatment.

The incidence of melanoma has been increasing over the past decades. Currently, approximately 132,000 melanoma skin cancers occur globally each year and around 48,000 people worldwide die of melanoma annually. One in every three cancers diagnosed is a skin cancer and, according to Skin Cancer Foundation Statistics, one in every five Americans will develop skin cancer in their lifetime. Melanoma is diagnosed in more than 50,000 new patients in the US annually.

While the rate of incidences continues to rise, survival rate has not improved and the race is on to find the genetic and cellular changes driving melanoma and to devise new means of detection and treatment.

Alice Rossiter - Cancer Drug News Editor