Targeting the ERK Signaling Pathway in Melanoma

The discovery of the role of the RAS/RAF/MEK/ERK pathway in melanomagenesis and its progression have opened a new era in the treatment of this tumor. Vemurafenib was the first specific kinase inhibitor approved for therapy of advanced melanomas harboring BRAF-activating mutations, followed by dabrafenib and encorafenib. However, despite the excellent results of first-generation kinase inhibitors in terms of response rate, the average duration of the response was short, due to the onset of genetic and epigenetic resistance mechanisms. The combination therapy with MEK inhibitors is an excellent strategy to circumvent drug resistance, with the additional advantage of reducing side effects due to the paradoxical reactivation of the MAPK pathway. The recent development of RAS and extracellular signal-related kinases (ERK) inhibitors promises to add new players for the ultimate suppression of this signaling pathway and the control of pathway-related drug resistance. In this review, we analyze the pharmacological, preclinical, and clinical trial data of the various MAPK pathway inhibitors, with a keen interest for their clinical applicability in the management of advanced melanoma.

Combination Treatment of Patients with BRAF-Mutant Melanoma: A New Standard of Care

Raf-mitogen-activated protein kinase (Raf-MAPK) pathway inhibition with the BRAF inhibitors vemurafenib and dabrafenib, alone or in combination with a MEK inhibitor, has become a standard therapeutic approach in patients with BRAF-mutated metastatic melanoma. Both vemurafenib and dabrafenib have shown good safety and efficacy as monotherapy compared with chemotherapy. However, the duration of response is limited in the majority of patients treated with BRAF inhibitor monotherapy because of the development of acquired resistance. The addition of a MEK inhibitor can improve blockade of the MAPK pathway and may help to overcome resistance and thereby prolong efficacy, as well as reduce cutaneous toxicity. Combinations of BRAF inhibitors and MEK inhibitors (dabrafenib plus trametinib and vemurafenib plus cobimetinib) have been approved for the treatment of BRAF-mutant metastatic melanoma and may become a new standard of care. However, acquired resistance is still a significant concern with BRAF and MEK inhibitor combination therapy, and other strategies are being investigated, including the use of sequential and intermittent schedules. The combination of BRAF or MEK inhibitors with immunotherapy has been shown to hold considerable promise, with several combinations being evaluated in clinical trials. Preliminary results from clinical trials involving triple combination therapy with BRAF-MEK inhibitors and anti-PD-L1 antibodies appear promising and may indicate a new strategy to treat patients with BRAF-mutated metastatic melanoma. Biomarkers are needed to help identify patients with BRAFV600 mutations most likely to benefit from first-line BRAF/MEK inhibitor therapy rather than immunotherapy and vice versa.

Systemic therapy of metastatic melanoma

For patients with metastatic melanoma, there are currently several effective therapeutic options. The BRAF inhibitors vemurafenib and dabrafenib are characterized by rapid tumor control and high response rates. In combination with one of the two MEK inhibitors trametinib and cobimetinib, they achieve response rates (CR + PR, complete plus partial remissions) of 70%, while delaying the development of treatment resistance, as well as a median overall survival of > 2 years with tolerable side effects. Showing long-term survival rates of approximately 20%, the anti-CTLA-4 antibody ipilimumab is the first substance that has led to a significant prolongation of overall survival in patients with metastatic melanoma. However, delayed treatment response and severe immune-mediated side effects may pose limitations to its therapeutic benefit. Usually well tolerated, anti-PD-1 antibody monotherapy using nivolumab and pembrolizumab has yielded response rates (CR + PR) of up to 45% and one-year survival rates of > 70%. The combination of ipilimumab and nivolumab has shown response rates of up to 58% and a median progression-free survival of > 11 months. While this combination is expected to result in a rapid and long-lasting response, this potential benefit comes at the expense of a high level of toxicity. Strategies for treatment sequencing and treatment combinations are currently being investigated in clinical studies. Overall, the prognosis for patients with metastatic melanoma has significantly improved. With long-term survival a possibility, not only acute but also long-term therapeutic side effects must be taken into account.

Novel melanoma therapy

With the rapid succession of new effective agents for melanoma in the recent years, the paradigm for treatment of metastatic melanoma is changing. The success of combining multiple effective agents compared with outcomes of monotherapy also brings increasing complexity in the treatment algorithm for various subsets of metastatic melanoma patients. We reviewed the recent reports on novel melanoma therapy to shed light on rational decision-making in treating these patients.

Combination therapy with BRAF and MEK inhibitors for melanoma: latest evidence and place in therapy

Treatment with BRAF inhibitors such as vemurafenib or dabrafenib in patients with advanced BRAFV600 mutated melanoma has shown objective tumor responses in approximately half of the patients. However, the duration of responses is limited in a majority of these patients, with progression-free survival rates around 6 months due to tumor progression from development of acquired resistance. Preclinical studies have suggested that concurrent inhibition of the BRAF kinases and MEK of the mitogen-activated protein kinase (MAPK) pathway could decrease MAPK-driven acquired resistance, resulting in longer duration of responses, higher rate of tumor responses, and a decrease in the cutaneous toxicities observed from paradoxical MAPK pathway activation with BRAF inhibitor monotherapy. This review provides an overview of the currently available clinical trial data on BRAF and MEK inhibitors together and in combinations with other therapeutic agents.

Cobimetinib: First Global Approval

Genentech (a subsidiary of Roche) and Exelixis are developing cobimetinib, an orally available small molecule, for the treatment of various cancers, including malignant melanoma and breast cancer. Cobimetinib inhibits the MEK (mitogen-activated protein kinase) component of the MAPK/ERK signalling pathway, which is frequently over-activated in human tumours. The product has been approved in Switzerland in combination with vemurafenib for the treatment of patients with unresectable or metastatic BRAF V600 mutation-positive melanoma, and is under regulatory review for the same indication in several countries, including the USA and the EU. This article summarizes the milestones in the development of cobimetinib leading to this first approval for unresectable or metastatic BRAF V600 mutation-positive melanoma melanoma.