Current State of Melanoma Therapy and Next Steps: Battling Therapeutic Resistance

Melanoma is the most aggressive and deadly form of skin cancer due to its high propensity to metastasize to distant organs. Significant progress has been made in the last few decades in melanoma therapeutics, most notably in targeted therapy and immunotherapy. These approaches have greatly improved treatment response outcomes; however, they remain limited in their abilities to hinder disease progression due, in part, to the onset of acquired resistance. In parallel, intrinsic resistance to therapy remains an issue to be resolved. In this review, we summarize currently available therapeutic options for melanoma treatment and focus on possible mechanisms that drive therapeutic resistance. A better understanding of therapy resistance will provide improved rational strategies to overcome these obstacles.

99mTc-Labeled Cyclic Peptide Targeting PD-L1 as a Novel Nuclear Imaging Probe

Recent cancer therapies have focused on reducing immune suppression in the tumor microenvironment to prevent cancer progression and metastasis. PD-1 is a checkpoint protein that stops the immune response and is expressed on immune T cells. Cancer cells express a PD-1 ligand (PD-L1) to bind to the T-cell surface and activate immunosuppressive pathways. This study aimed to design, synthesize, and evaluate a 99mTc-labeled PD-L1-targeting cyclic peptide inhibitor (99mTc-iPD-L1) as a novel SPECT radiopharmaceutical for PD-L1 expression imaging. AutoDock software (version 1.5) was used to perform molecular docking for affinity calculations. The chemical synthesis was based on the coupling reaction of 6-hydrazinylpyridine-3-carboxylic acid with a 14-amino-acid cyclic peptide. iPD-L1 was prepared for 99mTc labeling. Radio-HPLC was used to verify radiochemical purity. The stability of the radiopeptide in human serum was evaluated by HPLC. iPD-L1 specificity was assessed by SDS-PAGE. [99mTc]Tc-iPD-L1 cellular uptake in PD-L1-positive cancer cells (HCC827 and HCT116) and biodistribution in mice with induced tumors were also performed. One patient with advanced plantar malignant melanoma received [99mTc]Tc-iPD-L1. The iPD-L1 ligand (AutoDock affinity: -6.7 kcal/mol), characterized by UPLC mass, FT-IR, and UV-Vis spectroscopy, was obtained with a chemical purity of 97%. The [99mTc]Tc-iPD-L1 was prepared with a radiochemical purity of >90%. In vitro and in vivo analyses demonstrated [99mTc]Tc-iPD-L1 stability (>90% at 24 h) in human serum, specific recognition for PD-L1, high uptake by the tumor (6.98 ± 0.89% ID/g at 1 h), and rapid hepatobiliary and kidney elimination. [99mTc]Tc-iPD-L1 successfully detected PD-L1-positive lesions in a patient with plantar malignant melanoma. The results obtained in this study warrant further dosimetric and clinical studies to determine the sensitivity and specificity of [99mTc]Tc-iPD-L1/SPECT for PD-L1 expression imaging.

The Risk of Opportunistic Infections and the Role of Antibiotic Prophylaxis in Patients on Checkpoint Inhibitors Requiring Steroids

BACKGROUND

Immune-related adverse events (irAEs) often require treatment with high-dose systemic steroids (SS) and other immunosuppressive agents (ISAs). NCCN Guidelines recommend prophylactic antibiotics for Pneumocystis jirovecii pneumonia (PJP) for patients receiving prolonged SS/ISAs. However, there is a paucity of evidence regarding the incidence of opportunistic infections (OIs) and non-OIs and the role of prophylactic antibiotics in patients on SS/ISAs for irAEs.

METHODS

A retrospective analysis was conducted of patients treated using immune checkpoint inhibitor (ICI) therapy at 5 MedStar Health hospitals from January 2011 to April 2018. OIs were defined per the Infectious Diseases Society of America guidelines for the prevention and treatment of OIs in patients with HIV. The study cohort included patients who received ≥20 mg daily of a prednisone equivalent for ≥4 weeks to manage irAEs.

RESULTS

The study cohort identified 112 (15%) of 758 total patients treated using ICIs. Baseline characteristics included the following: median age was 64 years, 74% (n=82) of patients were White, 89% (n=100) had an ECOG performance status ≤1, 61% (n=68) had melanoma, 19% (n=21) had non-small cell lung cancer, 45% (n=50) were treated using an anti-PD-(L)1 ICI, and 33% (n=37) were treated using an anti-PD-1/anti-CTLA-4 combination. The median starting SS dose was 100 mg of a prednisone equivalent, and 25% of patients required additional ISAs, with infliximab (n=15) and mycophenolate mofetil (n=9) being the most common. We found that 20% (n=22) of patients developed any infection, including 7% (n=8) with OIs (oral candidiasis [n=4], nondisseminated varicella zoster infection [n=2], PJP [n=1], and Listeria monocytogenes endophthalmitis [n=1]) and 13% (n=14) with non-OIs (most common: Clostridium difficile and pneumonia [n=5 each]). PJP prophylaxis with sulfamethoxazole/trimethoprim was given to 13% (n=14) patients, of whom 43% (n=6) developed OIs/non-OIs.

CONCLUSIONS

Our study highlights the fundamental issues for patients on ICI therapy who require SS/ISAs for irAEs: the degree of immunosuppression and the relative risk of OI. We noted a low incidence of OIs overall and breakthrough infections despite PJP prophylaxis. We question whether PJP prophylaxis is efficacious or necessary. Prospective trials are required to answer these questions.

Development of Radiotracers for Imaging of the PD-1/PD-L1 Axis

Immune checkpoint inhibitor (ICI) therapy has emerged as a major treatment option for a variety of cancers. Among the immune checkpoints addressed, the programmed death receptor 1 (PD-1) and its ligand PD-L1 are the key targets for an ICI. PD-L1 has especially been proven to be a reproducible biomarker allowing for therapy decisions and monitoring therapy success. However, the expression of PD-L1 is not only heterogeneous among and within tumor lesions, but the expression is very dynamic and changes over time. Immunohistochemistry, which is the standard diagnostic tool, can only inadequately address these challenges. On the other hand, molecular imaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) provide the advantage of a whole-body scan and therefore fully address the issue of the heterogeneous expression of checkpoints over time. Here, we provide an overview of existing PET, SPECT, and optical imaging (OI) (radio)tracers for the imaging of the upregulation levels of PD-1 and PD-L1. We summarize the preclinical and clinical data of the different molecule classes of radiotracers and discuss their respective advantages and disadvantages. At the end, we show possible future directions for developing new radiotracers for the imaging of PD-1/PD-L1 status in cancer patients.

PD-1/PD-L1 pathway: Basic biology and role in cancer immunotherapy

Over the course of past few years, cancer immunotherapy has been accompanied with promising results. However, preliminary investigations with respect to immunotherapy concentrated mostly on targeting the immune checkpoints, nowadays, emerge as the most efficient strategy to raise beneficial antitumor immune responses. Programmed cell death protein 1 (PD-1) plays an important role in subsiding immune responses and promoting self-tolerance through suppressing the activity of T cells and promoting differentiation of regulatory T cells. PD-1 is considered as an immune checkpoint and protects against autoimmune responses through both induction of apoptosis in antigen-specific T cells and inhibiting apoptosis in regulatory T cells. Several clinical trials exerting PD-1 monoclonal antibodies as well as other immune-checkpoint blockades have had prosperous outcomes and opened new horizons in tumor immunotherapy. Nonetheless, a bulk of patients have failed to respond to these newly emerging immune-based approach and the survival rate was not satisfying. Additional strategies, especially combination therapies, has been initiated and been further promising. Attempts to identify novel and well-suited predictive biomarkers are also sensed. In this review, the promotion of cancer immunotherapy targeting PD-1 immunoinhibitory pathway is discussed.

The Central Role of Inflammation Associated with Checkpoint Inhibitor Treatments

An important function of the immune system is its ability to differentiate between healthy cells in the organism and "foreign" cells, allowing the latest to be attacked and the first ones to be conserved. The most important molecules in this process are considered to be checkpoint inhibitors. This review is focused on the association between cancer and inflammation, underlying the mechanisms of action of monoclonal antibodies that are targeting checkpoint inhibitors: ipilimumab against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and pembrolizumab and nivolumab against programmed cell death protein 1 (PD-1), their indications for treatment, and side effects. Presence of antibodies against checkpoint inhibitors shows promising results in the clinical trials in patients with types of cancer difficult to treat until now such as melanoma, non-small-cell lung cancer (NSCLC), and renal cell carcinoma, offering an increase in the overall survival rate, response rate, and progression-free rate. Resistance is now observed to emerge in patients treated with this therapy, showing the need for more studies in order to design a biomarker that will predict the type of response to immunotherapy.

The use of immunotherapy in the treatment of melanoma

Patients with advanced melanoma have a compromised anti-tumor immune response leading to tumor immune tolerance and a tumor microenvironment conducive to disease progression. Immunotherapy that successfully overcomes this tumor-mediated immune suppression has made the greatest impact in the management of this disease over the past few years. This progress through immunotherapy builds upon earlier successes that interferon-α had in the treatment of melanoma in the adjuvant setting, as well as that of high-dose interleukin-2 in advanced melanoma. The development of immune checkpoint inhibitors has led to dramatic clinical activity in advanced melanoma. In particular, anti-CTLA4 and anti-PD1 monoclonal antibodies have taken us forward into the realm of longer survival and durable responses with the possibility of cure in a continuously increasing proportion of patients. Combination immunotherapeutic strategies and novel immunotherapeutic agents are being tested at an accelerated pace where the outlook for long-term survival benefits for the majority of patients appears brighter than ever.

Advances in the Immunobiological Therapies for Advanced Melanoma

Metastatic or locally advanced unresectable melanoma carries a high morbidity and mortality. However, notable advances have been made in recent years in the systemic treatment of this disease, with the appearance of targeted therapy using tyrosine kinase inhibitors that block the mitogen activated protein kinase pathway, and of modern immunotherapy with immune-modulating monoclonal antibodies. In this paper, we provide an update of available data on new immune therapies and we review the clinical development that led to their approval for use in routine clinical practice.

Radiosurgery/stereotactic radiotherapy in combination with immunotherapy and targeted agents for melanoma brain metastases

INTRODUCTION

The clinical landscape of advanced melanoma drastically changed after the introduction of both targeted therapies and immunotherapy. This rapid development in systemic therapies led to a change in the management of patients with brain metastases, with the subsequent need to re-assess the role of local therapies, in particular stereotactic radiosurgery (SRS). Areas covered: In this non-systematic review, we report on the current knowledge on the use of SRS in combination with immunotherapy and BRAF/MEK inhibitors for patients with melanoma brain metastases, as well as ongoing trials in this field. Expert commentary: It is now more common to observe patients with melanoma brain metastases with better performance status and prolonged life expectancy. A combination of targeted therapy and immunotherapy, in different sequences, has been shown to be feasible and well tolerable, on the basis of retrospective reports. Additional data from ongoing prospective trials are however needed to confirm or not these findings and better explore the efficacy of the combination.

The Role of Anti-PD-1/PD-L1 Agents in Melanoma: Progress to Date

The discovery of immune inhibitory checkpoints has revolutionized the approach to the systemic treatment of cancer. The programmed death 1 (PD-1) inhibitory checkpoint, in particular, has played a key role in understanding how certain cancers can evade immune surveillance. Blocking the interaction between the PD-1 receptor and its primary ligand (PD-L1) has demonstrated remarkable anti-cancer activity, and has led to the recent accelerated approval of two anti-PD-1 drugs for use in unresectable and metastatic melanoma in the USA. Results of these therapeutic advances have solidified the role of immunotherapy in the treatment of melanoma, results that may be applicable to the treatment of other cancers. In this review, we discuss the role of the PD-1 pathway in the immune system and the anti-cancer mechanism of action of inhibiting the PD-1/PD-L1 interaction. We also review the efficacy and safety data of currently approved and in-development anti-PD-1 agents, and explore the next steps to further improve patient outcomes.

Immune based therapy for melanoma

A few years ago therapeutic options in advanced melanoma were very limited and the prognosis was somber. Although recent progresses are far from providing a cure for advanced melanoma, yet these have kindled new hopes and searching for a cure does not seem unreasonable. Seven new medicines have been authorized in various regions of the world in the recent past in the therapy of advanced melanoma, over half of them acting by mechanisms involving the immune system of the host. The anti-CTLA-4 (cytotoxic T lymphocyte associated protein-4) ipilimumab has been followed by anti-PD1 (programmed death1) inhibitors, more effective and safer. Very recently, the first oncolytic immunotherapy, talimogene laherparepvec (T-VEC) has been authorized for placing on the market and a variety of combinations of the new therapies are currently being evaluated or considered. Besides, a plethora of other molecules and approaches, especially monoclonal antibodies, are in the preliminary phases of clinical investigation and are likely to bring new benefits for the treatment of this potentially fatal form of cancer.

Checkpoint Blockade for the Treatment of Advanced Melanoma

Immunotherapy with immune checkpoint inhibition has been improving the outcomes of patients with many different types of malignancies. Immune checkpoint inhibition has been most extensively studied in patients with advanced melanoma and there are three FDA approved antibodies already widely used in clinical practice (ipilimumab, nivolumab, and pembrolizumab). In this chapter, we review the mechanistic basis behind the development of immune checkpoint blocking antibodies. We then discuss specifics regarding each agent, unique clinical considerations in treating patients with this approach, and future directions, including combination strategies. This chapter is focused on melanoma, but the principles related to this immunotherapy approach are applicable to patients with many types of malignancies.

Tumor associated PD-L1 expression pattern in microscopically tumor positive sentinel lymph nodes in patients with melanoma

BACKGROUND

Characterization of PD-L1 expression within clinically/radiologically negative but microscopically tumor positive sentinel lymph nodes (SLN) is important to our understanding of the relevance of this immune checkpoint pathway for adjuvant therapy.

METHODS

Patients included had primary cutaneous melanoma, Breslow thickness of 2.01-4.0 or >4 mm with or without tumor ulceration (T3a, T3b, T4a, T4b). All patients had microscopically tumor positive SLN. Hematoxylin and eosin (H&E) staining was performed, followed by PD-L1 immunohistochemical (IHC) staining using a preliminary IHC assay with anti-PD-L1 antibody clone 22C3. The slides were separately evaluated by two pathologists (JY and CG). Samples containing metastatic melanoma lesions were scored separately for PD-L1 expression in intratumoral and peritumoral locations, by utilizing two scoring methods.

RESULTS

Twenty-four patients where metastatic melanoma presence in the SLN was confirmed by H&E review of the cut sections were included in the final analysis of PD-L1 expression. SLN tumor size ranged from 1 to 2 mm. For three patients, the melanin content was too high to confidently assign a PD-L1 score. For the remaining 21 patients, all had some evidence of either intratumoral or peritumoral PD-L1 expression. The frequency of intratumoral tumor-associated PD-L1 expression was: 0 % of tumor cells (3 pts, 14 %); <1 % (5 pts, 24 %); 1-10 % (6 pts, 29 %) and >10 % (7 pts, 33 %).

CONCLUSIONS

Tumor-associated PD-L1 expression is readily detectable within melanoma micrometastases in the SLN of the majority of patients. These results support the testing of a therapeutic role for PD1/PD-L1 inhibition in the adjuvant setting, targeting melanoma micrometastases.

Risk of cutaneous toxicities in patients with solid tumors treated with immune checkpoint inhibitors: a meta-analysis

BACKGROUND

We performed a meta-analysis of the risk of cutaneous toxicities associated with immune checkpoint inhibitors.

METHODS

Eligible studies included randomized trials of patients with solid tumors on immune checkpoint inhibitors (ipilimumab, nivolumab, tremelimumab, pidlizumab and pembrolizumab); describing events of rash, vitiligo and pruritus.

RESULTS

A total of nine clinical trials were considered eligible for the meta-analysis. The relative risk of all-grade rash, vitiligo and pruritus was 4.06 (95% CI: 3.35-4.91; p < 0.0001), 16.3 (95% CI: 3.21-82.8; p = 0.0008) and 3.4 (95% CI: 2.24-5.16; p < 0.00001), respectively.

CONCLUSION

Our meta-analysis demonstrates that immune checkpoint inhibitors are associated with an increased risk of all grade skin rash, vitiligo and pruritus. Clinicians should perform regular clinical cutaneous monitoring.

Immune checkpoint inhibitors in melanoma

The potential to harness the power of the immune system and effectively treat patients with metastatic melanoma is finally being realized with the advent of immune checkpoint inhibitors. These new therapies herald a new era in the treatment of melanoma with the potential to produce very durable responses and possible cure for a subset of patients, though bring with them challenges including novel toxicities and nonconventional response patterns. This article reviews the currently available immune checkpoint inhibitors, potential biomarkers to predict response and promising investigational approaches including combination therapies.

Checkpoint blockade for cancer therapy: revitalizing a suppressed immune system

Immune checkpoint receptors are crucial molecules for fine-tuning immune responses. Checkpoint signaling dampens T cell activation to avoid autoimmunity and the destructive effects of an excessive inflammatory response. It is well established that tumors use several mechanisms to avoid elimination by the immune system, and one involves hijacking these checkpoint pathways. Checkpoint blockade therapy utilizes monoclonal antibodies to release the brakes from suppressed T cells, allowing them to be activated and recover their antitumor activity. This therapeutic approach has revolutionized cancer immunotherapy, and extraordinary increases in overall survival were noted, first with anti-CTLA-4 (cytotoxic T lymphocyte-associated protein 4) and subsequently with anti-PD-1 (programmed cell death receptor-1) in melanoma and other malignancies.

US FDA oncology drug approvals in 2014

Cancer is a close second to heart disease for cause of death in the USA, and could soon surpass heart disease as the population ages and the incidence of cancer continues to increase. While heart disease can be addressed through behavior modification and education (e.g., smoking cessation, dietary changes, exercises that promote cardiovascular fitness), pharmacology and improved surgical devices and methods, cancer ultimately requires improved and novel drug treatments to bring mortality rates down. In 2014, the US FDA approved 17 drugs and/or drug combinations in 12 disease sites for a total of 19 indications in melanoma, hematologic malignancies, gastrointestinal carcinoma, non-small-cell lung cancer, gynecologic malignancies and lymphoma/lymphoproliferative disorders.

Anti-programmed cell death protein-1/ligand-1 therapy in different cancers

Immunologic checkpoint blockade with antibodies against the programmed cell death protein-1 (PD-1) or its ligand (PD-L1) is an effective method for reversing cancer immunosuppression and thereby promoting immune responses against several cancer types. Anti-PD-1 and anti-PD-L1 antibodies have resulted in long-term responses with minimal side effects in significant numbers of patients with melanoma, lung, kidney, bladder and triple-negative breast cancer, as well as in chemotherapy-refractory Hodgkin disease. There is already evidence from at least one randomised trial that anti-PD-1 therapy is superior to chemotherapy in the treatment of patients with metastatic melanoma, and two anti-PD-1 antibodies, pembrolizumab and nivolumab, have been approved by the US Food and Drug Administration for the treatment of patients previously treated for metastatic melanoma. It is anticipated that approvals by drug regulatory bodies will be forthcoming in several cancers in the next months.

Clinical deployment of antibodies for treatment of melanoma

The concept of using immunotherapy to treat melanoma has existed for decades. The rationale comes from the knowledge that many patients with melanoma have endogenous immune responses against their tumor cells and clinically meaningful tumor regression can be achieved in a minority of patients using cytokines such as interleukin-2 and adoptive cellular therapy. In the last 5 years there has been a revolution in the clinical management of melanoma in large measure based on the development of antibodies that influence T cell regulatory pathways by overcoming checkpoint inhibition and providing co-stimulation, either of which results in significantly more effective immune-mediated tumor destruction. This review will describe the pre-clinical and clinical application of antagonistic antibodies targeting the T-cell checkpoints cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed death 1 (PD-1), and agonistic antibodies targeting the costimulatory pathways OX40 and 4-1BB. Recent progress and opportunities for future investigation of combination antibody therapy will be described.

Immunotherapies and novel combinations: the focus of advances in the treatment of melanoma

Since 2011, the approval of four different classes of novel drugs (the anti-CTLA-4 agent, ipilimumab; BRAF inhibitors [BRAFi]; MEK inhibitors [MEKi]; and the anti-PD-1 drug, pembrolizumab) has revolutionized the care of advanced melanoma, with the disease becoming a model for the development of new treatments for other types of cancer. Further advances in the treatment of melanoma represented some of the key highlights of the European Society of Medical Oncology (ESMO) 2014 congress. The first phase III trial of an anti-PD-1 agent to report the CA209-037 study included 405 patients with metastatic melanoma previously treated with ipilimumab who were randomized 2:1 to receive nivolumab 3 mg/kg every 2 weeks or investigator's choice chemotherapy. Nivolumab was associated with a higher response rate than chemotherapy and was well tolerated, with adverse events mostly low grade and manageable using recommended treatment algorithms. New data on other immunotherapies, namely ipilimumab and pembrolizumab, were also reported. In addition, outside of immunotherapy, combination approaches involving targeted agents were also a major focus of ESMO this year, with two major phase III studies of combined BRAF inhibition and MEK inhibition being reported. Overall, new clinical trial findings reported at ESMO further endorse the view that melanoma, given the continued development of novel, effective compounds, can accurately be described as the most "dynamic" field of oncology at present.

Combination approaches and anti-PD1 therapies: the focus of new research at ESMO and SMR

Research into the treatment of melanoma is continuing to progress, and both the European Society of Medical Oncology (26-30 September, Madrid, Spain) and the Society of Melanoma Research (13-16 November, Zurich, Switzerland) 2014 annual meetings provided important updates in this field. Areas of particular focus included combinations of a BRAF inhibitor with a MEK inhibitor (COMBI-v and CoBRIM trials) and new data on anti-PD1 therapies (nivolumab and pembrolizumab). Overall, the data reported at these two meetings again suggest that melanoma is perhaps the most dynamic field of oncology, with continuing advances in management of the disease that may improve outcomes for patients in clinical practice.

The role of chemotherapy in the modern management of melanoma

The last 4 years have seen dramatic changes in the treatment of advanced melanoma, largely based on advances in targeted therapy and immunotherapy. This article examines the role of chemotherapy in the modern management of melanoma. We examine the evidence for promising new agents and discuss their position in the sequencing of treatment options for patients with advanced disease. In addition, we discuss the combination of chemotherapy with targeted treatments and immune therapies. Finally, we discuss future areas of research for ensuring that we maximize the potential of all agents available to us and identify new, effective treatments.