Immunotherapy for Advanced Melanoma

Abstract

Over the past decade, outcomes for patients with advanced melanoma have been transformed with the introduction of immune checkpoint inhibitors and molecular targeted therapies directed against the MAPK pathway. Prior to the introduction of these treatments, the median overall survival (OS) of patients with melanoma was 9-12 months. In contrast, patients treated with combination anti-CTLA-4 and anti-PD1 immune checkpoint inhibitors (ipilimumab-nivolumab) now exhibit OS rates at the 5-year landmark that exceed 50%. This stunning revolution in systemic therapeutics for melanoma has paved the way for the use of anti-PD1 immunotherapy in various other solid cancer types.

The central aim of this thesis is to provide additional knowledge that may improve outcomes for patients with advanced melanoma through the refinement and development of new approaches to the use of immunotherapy. The first chapter addresses the sequencing of systemic treatment in patients with melanoma brain metastases where previously outcomes were dismal with a median OS of 6 months or less. Phase II studies show that the first line combination dabrafenib-trametinib (BRAF-MEKi) or ipilimumab-nivolumab both display intracranial response rates of 50-55%. Notably responses to targeted therapy are relatively shortly lived at approximately 6 months whereas immunotherapy displays potentially durable intracranial activity. Critically, the real-world outcomes and the sequencing of targeted therapy and immunotherapy is currently unknown. This thesis shows that ipilimumab-nivolumab given after progression of BRAF-MEKi has modest intracranial activity with objective response rates of less than 5%. Given this unexpected result, whole transcriptome sequencing of BRAF V600 melanoma brain metastases naive to systemic treatment and those excised after progression of BRAF-MEKi treatment was performed to identify potential mechanisms of resistance to both targeted and immunotherapy. Gene set testing of this cohort showed enrichment of the Innate PD-1 Resistance Signature (IPRES) with upregulation of endothelial and myeloid cell activation genes. Furthermore, macrophage infiltration of the BRAF-MEKi resistant brain metastases was higher than lesions naive to treatment which suggests that this cell type is involved with resistance to immunotherapy particularly in the central nervous system (CNS).

The second chapter of this thesis investigates whether the addition of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) can augment adoptive cell transfer (ACT) immunotherapy in combination with BRAF-MEKi. Other laboratories have shown that the addition of BRAF-MEKi with pmel-1 ACT can augment anti-tumour activity against the murine melanoma cell line SM1 in vivo. The addition of BRAF-MEKi not only enhanced anti-tumour activity by blockade of the MAPK pathway, but also exerted immunomodulatory effects including upregulation of melanoma differentiation antigens and antigen presentation pathways. The addition of CDK4/6i might enhance anti-tumour activity of combination BRAF-MEKi with ACT as melanoma exhibits a high rate of molecular aberrations that impact upon the cell cycle pathways and are an emerging therapeutic target. CDK4/6i such as palbociclib might further enhance ACT by inducing cell cycle arrest; moreover, several papers also show immunomodulatory effects such as increased tumour expression of major histocompatibility complex (MHC) class I and inhibition of T regulatory cells in the tumour microenvironment. The data contained herein shows that the CDK4/6 inhibitor, palbociclib did not further enhance expression of MHC Class I on SM1 or YOVAL1.1 melanoma cell lines by itself or in combination with BRAF-MEKi. However, combination BRAF-MEK-CDK4/6 inhibitor with OT-1 adoptive cell transfer leads to robust anti-tumour activity in vivo against YOVAL1.1.

The third chapter of the thesis explores whether the addition of denosumab to standard immune checkpoint inhibitor regimens improves outcomes for patients with advanced melanoma. Denosumab is an anti-RANKL antibody and is an approved agent for osteoporosis, prevention of bone metastases and giant cell carcinoma. Recent pre-clinical studies show denosumab can enhance in vivo antitumour activity in pre-clinical models of melanoma, renal cell and prostate carcinoma. Given there are no known overlapping toxicities of denosumab with nivolumab or with the combination ipilimumab-nivolumab, we developed a Phase Ib/II trial of Ipilimumab-Nivolumab-Denosumab or Nivolumab-Denosumab for Unresectable or Metastatic Melanoma (NCT03161756). This multi-centre, investigator-initiated study was opened in December 2017. Available data of the combination of nivolumab-denosumab shows no concerning safety signals.

Overall, this thesis sought to identify optimal treatment sequencing strategies for brain metastases, the development of novel immunotherapy strategies involving CDK4/6i with adoptive cell transfer and the safety of combining denosumab with nivolumab and ipilimumab-nivolumab.