Insights into the therapeutic potential of histone deacetylase inhibitor/immunotherapy combination regimens in solid tumors

Solid tumors including skin, lung, breast, colon, and prostate cancers comprise the most diagnosed cancers worldwide. Treatment of such cancers is still challenging specially in the advanced/metastatic setting. The growing understanding of the tumor microenvironment has revolutionized the cancer therapy paradigms. Targeting programmed death-1 (PD-1)/PD-L1 immune checkpoint has been extensively studied over this decade as a new trend in the management of hard-to-treat cancers by harnessing the power of the immune system to eradicate the tumors. Yet, low response rate and resistance were observed when immunotherapies were tested as monotherapy. This urged the need to develop combinatorial regimens of immunotherapy with other immune modulatory agents to enhance its therapeutic potential and help in reverting the resistance. Epigenetic modifiers such as histone deacetylase inhibitors (HDACIs) showed favorable effects on modulating the tumor microenvironment along with the host immune cells. This qualified HDACIs as an attractive candidate class to be tested in combination with immunotherapy. In this review we cover the ongoing clinical trials that investigate the safety and/or the efficacy of HDACI/immunotherapy combinations in solid tumors including skin cancer, prostate cancer, breast cancer, colorectal cancer, lung cancer and recapitulates areas for future research.

Regulation of epigenetic homeostasis in uveal melanoma and retinoblastoma

Uveal melanoma (UM) and retinoblastoma (RB), which cause blindness and even death, are the most frequently observed primary intraocular malignancies in adults and children, respectively. Epigenetic studies have shown that changes in the epigenome contribute to the rapid progression of both UM and RB following classic genetic changes. The loss of epigenetic homeostasis plays an important role in oncogenesis by disrupting the normal patterns of gene expression. The targetable nature of epigenetic modifications provides a unique opportunity to optimize treatment paradigms and establish new therapeutic options for both UM and RB with these aberrant epigenetic modifications. We aimed to review the research findings regarding relevant epigenetic changes in UM and RB. Herein, we 1) summarize the literature, with an emphasis on epigenetic alterations, including DNA methylation, histone modifications, RNA modifications, noncoding RNAs and an abnormal chromosomal architecture; 2) elaborate on the regulatory role of epigenetic modifications in biological processes during tumorigenesis; and 3) propose promising therapeutic candidates for epigenetic targets and update the list of epigenetic drugs for the treatment of UM and RB. In summary, we endeavour to depict the epigenetic landscape of primary intraocular malignancy tumorigenesis and provide potential epigenetic targets in the treatment of these tumours.

Genetic Landscape and Emerging Therapies in Uveal Melanoma

Despite successful treatment of primary uveal melanoma, up to 50% of patients will develop systemic metastasis. Metastatic disease portends a poor outcome, and no adjuvant or metastatic therapy has been FDA approved. The genetic landscape of uveal melanoma is unique, providing prognostic and potentially therapeutic insight. In this review, we discuss our current understanding of the molecular and cytogenetic mutations in uveal melanoma, and the importance of obtaining such information. Most of our knowledge is based on primary uveal melanoma and a better understanding of the mutational landscape in metastatic uveal melanoma is needed. Clinical trials targeting certain mutations such as GNAQ/GNA11, BAP1, and SF3B1 are ongoing and promising. We also discuss the role of liquid biopsies in uveal melanoma in this review.

Deregulation of HLA-I in cancer and its central importance for immunotherapy

It is now well accepted that many tumors undergo a process of clonal selection which means that tumor antigens arising at various stages of tumor progression are likely to be represented in just a subset of tumor cells. This process is thought to be driven by constant immunosurveillance which applies selective pressure by eliminating tumor cells expressing antigens that are recognized by T cells. It is becoming increasingly clear that the same selective pressure may also select for tumor cells that evade immune detection by acquiring deficiencies in their human leucocyte antigen (HLA) presentation pathways, allowing important tumor antigens to persist within cells undetected by the immune system. Deficiencies in antigen presentation pathway can arise by a variety of mechanisms, including genetic and epigenetic changes, and functional antigen presentation is a hard phenomenon to assess using our standard analytical techniques. Nevertheless, it is likely to have profound clinical significance and could well define whether an individual patient will respond to a particular type of therapy or not. In this review we consider the mechanisms by which HLA function may be lost in clinical disease, we assess the implications for current immunotherapy approaches using checkpoint inhibitors and examine the prognostic impact of HLA loss demonstrated in clinical trials so far. Finally, we propose strategies that might be explored for possible patient stratification.

Clinical Trials in Metastatic Uveal Melanoma: Immunotherapy

BACKGROUND

Uveal melanoma (UM) is a rare subtype of melanoma that generally has a poor prognosis once it has metastasized. Clinical trials evaluating immune checkpoint inhibitors (ICIs) in UM have demonstrated response rates lower than those seen in cutaneous melanoma. Despite lower efficacy demonstrated in initial ICI studies, there are a number of ongoing clinical trials investigating novel immunotherapy approaches in UM.

SUMMARY

This review aims to summarize important ongoing clinical trials investigating immunotherapeutic approaches in UM and previous trials that have evaluated a number of immunologic interventions. A thorough clinical trial investigation was conducted through clinicaltrials.gov using the disease search terms "uveal melanoma" and "ocular melanoma," excluding non-immunotherapy-related trials. Here, we report on ICI, vaccine, adoptive T cells, and combination immunotherapy trials in UM.

KEY MESSAGES

There is an increasing effort in the search for new, effective therapies for this difficult-to-treat disease, with immunotherapeutic approaches being of particular interest. Increasing knowledge of UM biology and development of new biomarkers will direct future drug development and trial design.

How to Make Immunotherapy an Effective Therapeutic Choice for Uveal Melanoma

Simple Summary

Despite improvements in the early identification and successful control of primary uveal melanoma, 50% of patients will develop metastatic disease with only marginal improvements in survival. This review focuses on the tumor microenvironment and the cross-talk between tumor and immune cells in a tumor characterized by low mutational load, the induction of immune-suppressive cells, and the expression of alternative immune checkpoint molecules. The choice of combining different strategies of immunotherapy remains a feasible and promising option on selected patients.

Abstract

Uveal melanoma (UM), though a rare form of melanoma, is the most common intraocular tumor in adults. Conventional therapies of primary tumors lead to an excellent local control, but 50% of patients develop metastases, in most cases with lethal outcome. Somatic driver mutations that act on the MAP-kinase pathway have been identified, yet targeted therapies show little efficacy in the clinics. No drugs are currently available for the G protein alpha subunitsGNAQ and GNA11, which are the most frequent driver mutations in UM. Drugs targeting the YAP–TAZ pathway that is also activated in UM, the tumor-suppressor gene BRCA1 Associated Protein 1 (BAP1) and the Splicing Factor 3b Subunit 1 gene (SF3B1) whose mutations are associated with metastatic risk, have not been developed yet. Immunotherapy is highly effective in cutaneous melanoma but yields only poor results in the treatment of UM: anti-PD-1 and anti-CTLA-4 blocking antibodies did not meet the expectations except for isolated cases. Here, we discuss how the improved knowledge of the tumor microenvironment and of the cross-talk between tumor and immune cells could help to reshape anti-tumor immune responses to overcome the intrinsic resistance to immune checkpoint blockers of UM. We critically review the dogma of low mutational load, the induction of immune-suppressive cells, and the expression of alternative immune checkpoint molecules. We argue that immunotherapy might still be an option for the treatment of UM.

Thinking Small: Small Molecules as Potential Synergistic Adjuncts to Checkpoint Inhibition in Melanoma

Metastatic melanoma remains the deadliest form of skin cancer. Immune checkpoint inhibition (ICI) immunotherapy has defined a new age in melanoma treatment, but responses remain inconsistent and some patients develop treatment resistance. The myriad of newly developed small molecular (SM) inhibitors of specific effector targets now affords a plethora of opportunities to increase therapeutic responses, even in resistant melanoma. In this review, we will discuss the multitude of SM classes currently under investigation, current and prospective clinical combinations of ICI and SM therapies, and their potential for synergism in melanoma eradication based on established mechanisms of immunotherapy resistance.

Novel Approaches to the Systemic Management of Uveal Melanoma

PURPOSE OF REVIEW

Uveal melanoma is a distinct subtype of melanoma characterized by a unique biology and divergent response to immune therapies. In this review, we will discuss our current understanding of the pathophysiology of uveal melanoma, systemic treatment options for advanced disease, and potential future therapeutic directions.

RECENT FINDINGS

Although treatment with single-agent checkpoint blockade has been generally disappointing, the results of combined checkpoint blockade are modestly more promising. Several alternative systemic therapeutic approaches have been or are currently being investigated, including two agents that have been taken into registration-intent clinical trials: tebentafusp, a T cell redirecting agent, and IDE196, an oral protein kinase C inhibitor. Treatment of advanced uveal melanoma remains challenging, however, encouraging results from novel agents offer hope for improvement in the near future.