Emerging PD-1/PD-L1 antagonists for the treatment of malignant melanoma

INTRODUCTION

Increased understanding of the interactive mechanisms between tumors and the immune system led to the development of immune checkpoint inhibitors, which have revolutioned the treatment of metastatic melanoma and subsequently many other tumors. In 2014, nivolumab and pembrolizumab, two checkpoint inhibitors binding to PD-1, were approved for the treatment of metastatic melanoma. Since then, a plethora of new molecules have enriched the armamentarium against melanoma.

AREAS COVERED

This review summarizes the last updates about treatment with nivolumab and pembrolizumab, data on other PD-1/PDL-1 agents such as spartalizumab and atezolizumab and emerging compounds, new combinations with NKTR-214, anti LAG-3, anti IDO-1 and TVEC, new checkpoint inhibitors (e.g. TIM-3 or TIGIT) and other new molecules for the treatment of metastatic melanoma.

EXPERT OPINION

Currently, several ongoing clinical trials are investigating novel molecules, or immunotherapy combinations, in order to achieve even better survival outcomes for patients, overcoming resistance mechanisms and improving toxicity profiles. The challenge in the near future will be to select the most appropriate treatments according to the specific characteristics of the patients.

Chemotherapeutic and targeted agents can modulate the tumor microenvironment and increase the efficacy of immune checkpoint blockades

The development of immune checkpoint blockade (ICB)-based immunotherapy has dramatically changed methods of cancer treatment. This approach triggers a durable treatment response and prolongs patients' survival; however, not all patients can benefit. Accumulating evidence demonstrated that the efficacy of ICB is dependent on a robust antitumor immune response that is usually damaged in most tumors. Conventional chemotherapy and targeted therapy promote the antitumor immune response by increasing the immunogenicity of tumor cells, improving CD8+ T cell infiltration, or inhibiting immunosuppressive cells in the tumor microenvironment. Such immunomodulation provides a convincing rationale for the combination therapy of chemotherapeutics and ICBs, and both preclinical and clinical investigations have shown encouraging results. However, the optimal drug combinations, doses, timing, and sequence of administration, all of which affect the immunomodulatory effect of chemotherapeutics, as well as the benefit of combination therapy, are not yet determined. Future studies should focus on these issues and help to develop the optimal combination regimen for each cancer.

Metastatic melanoma: therapeutic agents in preclinical and early clinical development

Introduction: Advanced melanoma historically had a very poor outcome but targeted therapies and immune checkpoint inhibitors (IC) have changed the course of the disease and made durable responses possible. However, most patients will develop progressive disease, so further strategies to overcome treatment resistance are needed. Areas covered: Current treatment strategies and landmark trials are discussed. Novel targeted agents, immune checkpoint inhibitors, and further immune-modulatory drugs, cancer vaccines and tumor infiltrating lymphocytes and their potential role in the treatment of melanoma are described. Current trials investigating these emerging agents and treatment strategies were searched for on ClinicalTrials.gov and are presented on the background of the current literature explaining the rationale for employing these new agents and strategies. Combinations of tumor-directed agents with those causing immune augmentation as well as a new adjuvant and neoadjuvant strategies are discussed. Expert opinion: Questions regarding treatment combination, personalization, and sequence of treatment will become increasingly important and will be guided by new biomarkers. New treatment settings will broaden the patient selection and will highlight the need for further discussions regarding toxicity in long-term survivorship.

Dabrafenib, trametinib and pembrolizumab or placebo in BRAF-mutant melanoma

Blocking programmed death 1 (PD-1) may enhance the durability of anti-tumor responses that are induced by the combined inhibition of BRAF and MEK¹. Here we performed a randomized phase 2 trial ( NCT02130466 ), in which patients with treatment-naive BRAF^V600E/K-mutant, advanced melanoma received the BRAF inhibitor dabrafenib and the MEK inhibitor trametinib together with the PD-1-blocking antibody pembrolizumab (triplet; n = 60) or placebo (doublet; n = 60). The primary end point of progression-free survival was numerically improved in the triplet group-16.0 months-compared with 10.3 months in the doublet group (hazard ratio, 0.66; P = 0.043); however, the trial did not reach the planned benefit for a statistically significant improvement. Median duration of response was 18.7 months (95% confidence interval, 10.1-22.1) and 12.5 months (95% confidence interval, 6.0-14.1); 59.8 and 27.8% of responses were estimated to have lasted for more than 18 months for triplet and doublet treatment, respectively. Grade 3-5 treatment-related adverse events occurred in 58.3 and 26.7% of patients treated with triplet and doublet therapies, respectively, which were most commonly fever, increased transaminase levels and rash. One patient who received triplet therapy died of pneumonitis. In summary, triplet therapy with dabrafenib, trametinib and pembrolizumab conferred numerically longer progression-free survival and duration of response with a higher rate of grade 3/4 adverse events compared with the doublet therapy of dabrafenib, trametinib and placebo.