Combination Shows Early Promise in Melanoma

A recent study found that the combination of Tasigna (nilotinib) and Mekinist (trametinib) is synergistic for patients with BRAF/NRAS wild-type melanoma.

The combination offers a potential new therapeutic option in a subtype where few targeted therapies are available. In the study — which was presented by Marco Ranzani, Ph.D., postdoctoral fellow in experimental genetics, Sanger Institute — investigators screened 180 combinations of clinically relevant drugs for sensitivity in a collection of 20 BRAF/NRAS wild-type melanoma cell lines. Few were determined to be synergistic, said Ranzani.

“Synergy is pretty rare,” he said. “It only occurred in about 1 percent of all our results.” However, Tasigna plus three different MEK inhibitors did prove to be synergistic. The combination was evaluated using two independent experimental approaches. Overall, 24 percent (5 patients) of cell lines displayed synergy for Tasigna plus MEK inhibitors (delta AUC>0.1 for both MEK inhibitors).

The combination of Tasigna and the MEK inhibitor Mekinist was then investigated.

The synergy of the two drugs was first confirmed using an independent collection of BRAF/NRAS wild-type melanoma cell lines (seven patients), then a collection of BRAF/NRAS wild-type patient derived xenotransplant cultures (three patients), and finally a collection of BRAF V600E melanoma cell lines (nine patients)

“In all the collections that we analyzed, about one-fourth of all the cells lines that we tested are synergistic for this drug combination,” said Ranzani.

Investigators then generated a gene expression signature of synergistic cell lines for the Tasigna/Mekinist combination, and used it to classify human melanomas from two cohorts. In the first, which looked at 171 tumors samples, nearly 28 percent of tumors were classified as synergistic. In the second, which looked at 470 tumor samples, nearly 37 percent of tumors were classified as synergistic. The combination was also associated with a decreased overall and recurrence free survival, suggesting that it may be effective in a relevant fraction of aggressive tumors, according to study investigators.

Researchers also attempted to identify biomarkers that would predict synergy of the combination, but nothing was deemed to be statically significant, said Ranzani.

A further evaluation of potential mechanisms of resistance to the combination of Tasigna/Mekinist was then investigated. “In order to try and get inside the mechanism of the synergy, we performed a genetic screening to try and identify mechanisms of resistance to the combination,” said Ranzani.

Using CRISPR/Cas9 screening, investigator’s identified TSC2, TSC1, CDKN18 as genes that may cause resistance. All three genes are part of the tuberous sclerosis complex, suggesting that a loss of tuberous sclerosis complex, which is present in about 10 percent of melanomas, can confer resistance to Tasigna/Mekinist.

Investigators then looked at six representative synergistic cell lines and three representative non-synergistic cells lines treated with the single-agent Mekinist or the combination, to further understand the mechanism of synergy.

They found that Mekinist reduced P-ERK antibody in most of the cell lines. This was expected, said Ranzani. What was less expected was that Tasigna induced P-ERK, regardless of synergy in some of the cells lines, “It likely induces RAF paradoxical activation by being a suboptimal BRAF/CRAF inhibitor,” said Ranzani.

The combination was the most effective, further inhibiting P-ERK compared with single-agent cell lines and non-synergistic cell lines. As a final assessment of synergy, the combination of Tasigna/Mekinist was tested in a patient derived xenotransplant mouse model using five mice and 10 tumors per each of the four experimental groups.

The model showed that the combination is well tolerated and significantly more effective than the 2 drugs alone. These data suggest a strong clinical translation potential for the combination, according to study investigators.

“The results were pretty clear,” said Ranzani. “The tumors which were untreated grew pretty fast. The one treated with nilotinib displayed a minor reduction of the cell growth, the one treated with trametinib displayed a significant reduction of the cell growth but still it grew, but the combination induced partial shrinkage of the tumor, up to 6 weeks after treatment.”

The key takeaway from the study was that Tasigna/Mekinist has significant potential in BRAF/NRAS wild-type melanoma, said Ranzani.

“The combination of nilotinib/trametinib is synergistic in a fraction of melanoma models in vitro and in vivo,” he said. “We are further studying the mechanism of this synergy.”