Elisa A. Rozeman

Identification of CMTM6 and CMTM4 as PD-L1 protein regulators

The clinical benefit for patients with diverse types of metastatic cancers that has been observed upon blockade of the interaction between PD-1 and PD-L1 has highlighted the importance of this inhibitory axis in the suppression of tumour-specific T-cell responses. Notwithstanding the key role of PD-L1 expression by cells within the tumour micro-environment, our understanding of the regulation of the PD-L1 protein is limited. Here we identify, using a haploid genetic screen, CMTM6, a type-3 transmembrane protein of previously unknown function, as a regulator of the PD-L1 protein. Interference with CMTM6 expression results in impaired PD-L1 protein expression in all human tumour cell types tested and in primary human dendritic cells. Furthermore, through both a haploid genetic modifier screen in CMTM6-deficient cells and genetic complementation experiments, we demonstrate that this function is shared by its closest family member, CMTM4, but not by any of the other CMTM members tested. Notably, CMTM6 increases the PD-L1 protein pool without affecting PD-L1 (also known as CD274) transcription levels. Rather, we demonstrate that CMTM6 is present at the cell surface, associates with the PD-L1 protein, reduces its ubiquitination and increases PD-L1 protein half-life. Consistent with its role in PD-L1 protein regulation, CMTM6 enhances the ability of PD-L1-expressing tumour cells to inhibit T cells. Collectively, our data reveal that PD-L1 relies on CMTM6/4 to efficiently carry out its inhibitory function, and suggest potential new avenues to block this pathway.

Cancer drug addiction is relayed by an ERK2-dependent phenotype switch

Observations from cultured cells, animal models and patients raise the possibility that the dependency of tumours on the therapeutic drugs to which they have acquired resistance represents a vulnerability with potential applications in cancer treatment. However, for this drug addiction trait to become of clinical interest, we must first define the mechanism that underlies it. We performed an unbiased CRISPR–Cas9 knockout screen on melanoma cells that were both resistant and addicted to inhibition of the serine/threonine-protein kinase BRAF, in order to functionally mine their genome for ‘addiction genes’. Here we describe a signalling pathway comprising ERK2 kinase and JUNB and FRA1 transcription factors, disruption of which allowed addicted tumour cells to survive on treatment discontinuation. This occurred in both cultured cells and mice and was irrespective of the acquired drug resistance mechanism. In melanoma and lung cancer cells, death induced by drug withdrawal was preceded by a specific ERK2-dependent phenotype switch, alongside transcriptional reprogramming reminiscent of the epithelial–mesenchymal transition. In melanoma cells, this reprogramming caused the shutdown of microphthalmia-associated transcription factor (MITF), a lineage survival oncoprotein; restoring this protein reversed phenotype switching and prevented the lethality associated with drug addiction. In patients with melanoma that had progressed during treatment with a BRAF inhibitor, treatment cessation was followed by increased expression of the receptor tyrosine kinase AXL, which is associated with the phenotype switch. Drug discontinuation synergized with the melanoma chemotherapeutic agent dacarbazine by further suppressing MITF and its prosurvival target, B-cell lymphoma 2 (BCL-2), and by inducing DNA damage in cancer cells. Our results uncover a pathway that underpins drug addiction in cancer cells, which may help to guide the use of alternating therapeutic strategies for enhanced clinical responses in drug-resistant cancers.

Cooperative targeting of melanoma heterogeneity with an AXL antibody-drug conjugate and BRAF/MEK inhibitors

Intratumor heterogeneity is a key factor contributing to therapeutic failure and, hence, cancer lethality. Heterogeneous tumors show partial therapy responses, allowing for the emergence of drug-resistant clones that often express high levels of the receptor tyrosine kinase AXL. In melanoma, AXL-high cells are resistant to MAPK pathway inhibitors, whereas AXL-low cells are sensitive to these inhibitors, rationalizing a differential therapeutic approach. We developed an antibody-drug conjugate, AXL-107-MMAE, comprising a human AXL antibody linked to the microtubule-disrupting agent monomethyl auristatin E. We found that AXL-107-MMAE, as a single agent, displayed potent in vivo anti-tumor activity in patient-derived xenografts, including melanoma, lung, pancreas and cervical cancer. By eliminating distinct populations in heterogeneous melanoma cell pools, AXL-107-MMAE and MAPK pathway inhibitors cooperatively inhibited tumor growth. Furthermore, by inducing AXL transcription, BRAF/MEK inhibitors potentiated the efficacy of AXL-107-MMAE. These findings provide proof of concept for the premise that rationalized combinatorial targeting of distinct populations in heterogeneous tumors may improve therapeutic effect, and merit clinical validation of AXL-107-MMAE in both treatment-naive and drug-resistant cancers in mono- or combination therapy.

Immune checkpoint inhibition-related colitis: symptoms, endoscopic features, histology and response to management

Background Immune checkpoint inhibitors are successfully introduced as anticancer treatment. However, they may induce severe immune-related adverse events (irAEs). One of the most frequent irAEs is diarrhoea. The main objective of this study was to analyse symptoms (ie, grade of diarrhoea), endoscopic and histological features and response to management in immune checkpoint inhibition-related colitis (IRC). Patients and methods We retrospectively analysed patients who developed diarrhoea on checkpoint inhibition and therefore underwent an endoscopy and/or were treated with corticosteroids. Patients were treated between August 2010 and March 2016 for metastatic melanoma or non-small cell lung cancer. Severity of IRC was scored using the endoscopic Mayo score and the van der Heide score. Results Out of a cohort of 781 patients, 92 patients were identified who developed diarrhoea and therefore underwent an endoscopy and/or were treated with corticosteroids. Patients were treated with monotherapy anticytotoxic T-lymphocyte antigen-4, antiprogrammed death receptor-1 or a combination of both. All patients had symptoms of diarrhoea (grade 1: 16%; grade 2: 39% and grade 3: 44%). A complete colonoscopy was performed in 62 (67%) patients, of whom 42 (68%) had a pancolitis (≥3 affected segments). Ulcers were seen in 32% of endoscopies. There was no significant correlation between the grade of diarrhoea at presentation and endoscopic severity scores, the presence of ulcers or histological features. In 54 episodes of diarrhoea (56%), patients received one or more cycles infliximab for steroid-refractory colitis. Patients with higher endoscopic severity scores, ulcers and/or a pancolitis needed infliximab more often. Conclusions The correlation between grade of diarrhoea and endoscopic or histological features for severity of colitis is poor. Patients with higher endoscopic severity scores, ulcers or a pancolitis needed the addition of infliximab more often. Therefore, endoscopy may have value in the evaluation of the severity of IRC and may help in decision making for optimal management.

Advanced Melanoma: Current Treatment Options, Biomarkers, and Future Perspectives

Malignant melanoma accounts for the highest number of deaths from skin cancer, and the prognosis of patients with stage IV disease has historically been poor. Novel insights into both mutations driving tumorigenesis and immune escape mechanisms of these tumors have led to effective treatment options that have revolutionized the treatment of this disease. Targeting the MAPK kinase pathway (with BRAF and MEK inhibitors), as well as targeting checkpoints, such as cytotoxic T-lymphocyte associated protein 4 (CTLA-4) or programmed death 1 (PD-1), have improved overall survival in patients with late-stage melanoma, and biomarker research for personalized therapy is ongoing for each of these treatment modalities. In this review, we will discuss current first-line treatment options, discuss biomarkers supporting treatment decisions, and give an outlook on (combination) therapies we expect to become relevant in the near future.

Short-term CTLA-4 blockade directly followed by PD-1 blockade in advanced melanoma patients: a single-center experience

Background Combination of T cell checkpoint blockade by CTLA-4- and PD-1-blockade is one of the most promising therapies in patients with advanced melanoma. It induces superior response rates when compared with single-agent therapy, but at the cost of a high percentage of grade 3 and 4 adverse events (AEs). This combination therapy was until July 2016 not available in the Netherlands, which prompted several physicians to treat patients with less than standard numbers of courses of ipilimumab followed directly by nivolumab or pembrolizumab. Patients and methods In this retrospective analysis, patients were included who were treated with two courses (day 0 and 21) anti-CTLA-4 (ipilimumab 3 mg/kg q3wk), directly followed by anti-PD-1 (starting at day 22 with nivolumab 3mg/kg q2wk or pembrolizumab 2 mg/kg q3wk). Data on treatment-related AEs were collected from electronic patient records and scored according to CTCAE 4.03 criteria. Overall response was evaluated using RECIST 1.1 for CT-scans and EORTC criteria for PET-scans. Results Forty advanced melanoma patients could be included (29/40 pembrolizumab, 11/40 nivolumab). Median follow-up (FU) was 51 weeks (range: 4–63 weeks) with a minimum FU of 26 weeks. Treatment-related AEs of grade 3 and 4 occurred in 38% of the patients. The best overall response rate (BORR) was 55% (95% CI 39–70) and disease control rate was 75% (95% CI 59–87). Ongoing responses were observed in 82% of responding patients. Conclusion Treatment with short-term CTLA-4 blockade directly followed by PD-1 blockade may have similar efficacy but potentially lower toxicity when compared with concurrent therapy with anti-CTLA-4 and anti-PD-1. These results warrant further investigation in a prospective randomized controlled clinical trial.

PO-512 Gene expression signature comprising distinct stromal and tumor-intrinsic signals predicts response to combined anti-PD1 and anti-CTLA4 checkpoint inhibition

Introduction Innovations in both targeted and immunotherapy (IT) of metastatic melanoma have led to improved responses in a considerable number of patients. For both types of therapies, resistance remains a formidable challenge. For IT, knowledge on the mechanisms behind resistance is an urgent and unmet need for better patient stratification. Gene expression signatures to predict response in baseline samples could help to better stratify patients. It is expected that both tumour cell intrinsic signals and stromal signals play a role. However, gene expression signatures are typically derived from RNA-sequencing data from patients’ tumours, where the distinction between stromal and tumour signals cannot be made. Here, we take advantage of our melanoma PDX platform [Kemper et al. Cell Reports 2016] to dissect the stromal and tumour cell intrinsic signals and relate these to the response to immune checkpoint blockade. Material and methods RNA sequencing was performed on 95 PDX tumours derived from metastatic melanoma [Kemper et al. Cell Reports 2016]. Gene expression data and clinical information of patients treated with anti-PD1 and anti-CTLA4 were downloaded [Hugo et al. 2016 & Van Allen, 2015]. Additionally, we performed RNA sequencing on samples of patients treated with the combination of anti-CTLA4 and anti-PD1 [Blank et al. submitted]. Results and discussions We found that tumour cell-intrinsic and stromal gene expression signatures differentially predicted response to anti-PD1 and anti-CTLA4 immune checkpoint inhibition. Furthermore, a combination of signatures predicts response in patients treated with the combination of anti-PD1 and anti-CTLA4. Conclusion Our PDX platform provided the possibility to computationally dissect the gene expression signals from tumour cells and stromal tissue. These stromal and tumour intrinsic gene expression signatures differentially predict response to anti-PD1 and anti-CTLA4 in baseline samples which can be used for better patient stratification.

Targeting tumor-associated acidity in cancer immunotherapy

Checkpoint inhibitors, such as cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) and programmed cell death-1 (PD-1) monoclonal antibodies have changed profoundly the treatment of melanoma, renal cell carcinoma, non-small cell lung cancer, Hodgkin lymphoma, and bladder cancer. Currently, they are tested in various tumor entities as monotherapy or in combination with chemotherapies or targeted therapies. However, only a subgroup of patients benefit from checkpoint blockade (combinations). This raises the question, which all mechanisms inhibit T cell function in the tumor environment, restricting the efficacy of these immunotherapeutic approaches. Serum activity of lactate dehydrogenase, likely reflecting the glycolytic activity of the tumor cells and thus acidity within the tumor microenvironment, turned out to be one of the strongest markers predicting response to checkpoint inhibition. In this review, we discuss the impact of tumor-associated acidity on the efficacy of T cell-mediated cancer immunotherapy and possible approaches to break this barrier.