Durable Suppression of Acquired MEK Inhibitor Resistance in Cancer by Sequestering MEK from ERK and Promoting Antitumor T-cell Immunity

Comprehensive review of signaling pathways and therapeutic targets in gastrointestinal cancers

Targeted therapy, the milestone in the development of human medicine, originated in 2004 when the FDA approved the first targeted agent bevacizumab for colorectal cancer treatment. This new development has resulted from drug developers moving beyond traditional chemotherapy, and several trials have popped up in the last two decades with an unprecedented speed. Specifically, EGF/EGFR, VEGF/VEGFR, HGF/c-MET, and Claudin 18.2 therapeutic targets have been developed in recent years. Some targets previously thought to be undruggable are now being newly explored, such as the RAS site. However, the efficacy of targeted therapy is extremely variable, especially with the emergence of new drugs and the innovative use of traditional targets for other tumors in recent years. Accordingly, this review provides an overview of the major signaling pathway mechanisms and recent advances in targeted therapy for gastrointestinal cancers, as well as future perspectives.

Regorafenib Combined with BRAF/MEK Inhibitors for the Treatment of Refractory Melanoma Brain Metastases

BACKGROUND

There are no active treatment options for patients with progressive melanoma brain metastases (MBM) failing immune checkpoint blockade (ICB) and BRAF/MEK inhibitors (BRAF/MEKi). Regorafenib (REGO), an oral multi-kinase inhibitor (incl. RAF-dimer inhibition), can overcome adaptive resistance to BRAF/MEKi in preclinical models.

METHODS

This is a single-center retrospective case series of patients with refractory MBM treated with REGO plus BRAF/MEKi (compassionate use).

RESULTS

A total of 22 patients were identified (18 BRAF-mutant, 4 NRASQ61-mutant; 19 with progressive MBM; 11 on corticosteroids). Thirteen BRAFV600-mutant patients were progressing on BRAF/MEKi at the time of REGO association. BRAF-mutant patients received REGO (40-80 mg once daily) combined with BRAF/MEKi, NRAS-mutant patients were treated with REGO + MEKi (+low-dose BRAFi to mitigate skin-toxicity). Grade 3 TRAE included arterial hypertension (n = 4) and maculopapular rash (n = 3). There were no G4/5 TRAE. In BRAF-mutant patients, overall and intracranial objective response rates (overall ORR and IC-ORR) were 11 and 29%, and overall and intracranial disease control rates (overall DCR and IC-DCR) were 44 and 59%, respectively. In NRAS-mutant patients overall ORR and IC-ORR were 0 and 25% and overall DCR and IC-DCR were 25 and 50%, respectively. The median PFS and OS were, respectively, 7.1 and 16.4 weeks in BRAF-mutant and 8.6 and 10.1 weeks in NRAS-mutant patients.

CONCLUSIONS

In heavily pretreated patients with refractory MBM, REGO combined with BRAF/MEKi demonstrated promising anti-tumor activity with an acceptable safety profile. In BRAFV600-mutant melanoma patients, responses cannot solely be attributed to BRAF/MEKi rechallenge. Further investigation in a prospective trial is ongoing to increase understanding of the efficacy.

Targeted Therapy Innovations for Melanoma

Melanoma, a malignant tumor of melanocytes, poses a significant clinical challenge due to its aggressive nature and high potential for metastasis. The advent of targeted therapy has revolutionized the treatment landscape of melanoma, particularly for tumors harboring specific genetic alterations such as BRAF V600E mutations. Despite the initial success of targeted agents, resistance inevitably arises, underscoring the need for novel therapeutic strategies. This review explores the latest advances in targeted therapy for melanoma, focusing on new molecular targets, combination therapies, and strategies to overcome resistance.

Regorafenib in patients with pretreated advanced melanoma: a single-center case series

Melanoma patients failing all approved treatment options have a poor prognosis. The antimelanoma activity of regorafenib (REGO), a multitargeted kinase inhibitor, has not been investigated in this patient population. The objective response rate and safety of REGO treatment in advanced melanoma patients was investigated retrospectively. Twenty-seven patients received REGO treatment. All patients had progressed on anti-programmed cell death protein 1 (PD-1) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) checkpoint inhibition and BRAF/MEK inhibitors (in case of a BRAF V600 mutation). REGO was administered in continuous dosing and combined (upfront or sequentially) with nivolumab ( n  = 5), trametinib ( n  = 8), binimetinib ( n  = 2), encorafenib ( n  = 1), dabrafenib/trametinib ( n  = 9), or encorafenib/binimetinib ( n  = 7). The best overall response was partial response (PR) in five patients (18.5%) and stable disease in three patients (11.1%). Three of seven (42.8%) BRAF  V600mut patients treated with REGO in combination with BRAF/MEK inhibitors obtained a PR (including regression of brain metastases in all three patients). In addition, PR was documented in a BRAF V600mut patient treated with REGO plus anti-PD-1, and a NRASQ61mut patient treated with REGO plus a MEK inhibitor. Common grade 3-4 treatment-related adverse events included arterial hypertension ( n  = 7), elevated transaminase levels ( n  = 5), abdominal pain ( n  = 3), colitis ( n  = 2), anorexia ( n  = 1), diarrhea ( n  = 1), fever ( n  = 1), duodenal perforation ( n  = 1), and colonic bleeding ( n  = 1). Median progression-free survival was 11.0 weeks (95% confidence interval, 7.1-14.9); median overall survival was 23.1 weeks (95% confidence interval, 13.0-33.3). REGO has a manageable safety profile in advanced melanoma patients, in monotherapy as well as combined with BRAF/MEK inhibitors or PD-1 blocking monoclonal antibodies. The triplet combination of REGO with BRAF/MEK inhibitors appears most active, particularly in the BRAF V600mut patients.

A comprehensive overview of the molecular features and therapeutic targets in BRAFV600E-mutant colorectal cancer

As one of the most prevalent digestive system tumours, colorectal cancer (CRC) poses a significant threat to global human health. With the emergence of immunotherapy and target therapy, the prognosis for the majority of CRC patients has notably improved. However, the subset of patients with BRAF exon 15 p.V600E mutation (BRAFV600E) has not experienced remarkable benefits from these therapeutic advancements. Hence, researchers have undertaken foundational investigations into the molecular pathology of this specific subtype and clinical effectiveness of diverse therapeutic drug combinations. This review comprehensively summarised the distinctive molecular features and recent clinical research advancements in BRAF-mutant CRC. To explore potential therapeutic targets, this article conducted a systematic review of ongoing clinical trials involving patients with BRAFV600E-mutant CRC.

MEK inhibitors: a promising targeted therapy for cardiovascular disease

Cardiovascular disease (CVD) represents the leading cause of mortality and disability all over the world. Identifying new targeted therapeutic approaches has become a priority of biomedical research to improve patient outcomes and quality of life. The RAS-RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase) pathway is gaining growing interest as a potential signaling cascade implicated in the pathogenesis of CVD. This pathway is pivotal in regulating cellular processes like proliferation, growth, migration, differentiation, and survival, which are vital in maintaining cardiovascular homeostasis. In addition, ERK signaling is involved in controlling angiogenesis, vascular tone, myocardial contractility, and oxidative stress. Dysregulation of this signaling cascade has been linked to cell dysfunction and vascular and cardiac pathological remodeling, which contribute to the onset and progression of CVD. Recent and ongoing research has provided insights into potential therapeutic interventions targeting the RAS-RAF-MEK-ERK pathway to improve cardiovascular pathologies. Preclinical studies have demonstrated the efficacy of targeted therapy with MEK inhibitors (MEKI) in attenuating ERK activation and mitigating CVD progression in animal models. In this article, we first describe how ERK signaling contributes to preserving cardiovascular health. We then summarize current knowledge of the roles played by ERK in the development and progression of cardiac and vascular disorders, including atherosclerosis, myocardial infarction, cardiac hypertrophy, heart failure, and aortic aneurysm. We finally report novel therapeutic strategies for these CVDs encompassing MEKI and discuss advantages, challenges, and future developments for MEKI therapeutics.

Novel RAF-directed approaches to overcome current clinical limits and block the RAS/RAF node

Mutations in the RAS-RAF-MEK-ERK pathway are frequent alterations in cancer and RASopathies, and while RAS oncogene activation alone affects 19% of all patients and accounts for approximately 3.4 million new cases every year, less frequent alterations in the cascade's downstream effectors are also involved in cancer etiology. RAS proteins initiate the signaling cascade by promoting the dimerization of RAF kinases, which can act as oncoproteins as well: BRAFV600E is the most common oncogenic driver, mutated in the 8% of all malignancies. Research in this field led to the development of drugs that target the BRAFV600-like mutations (Class I), which are now utilized in clinics, but cause paradoxical activation of the pathway and resistance development. Furthermore, they are ineffective against non-BRAFV600E malignancies that dimerize and could be either RTK/RAS independent or dependent (Class II and III, respectively), which are still lacking an effective treatment. This review discusses the recent advances in anti-RAF therapies, including paradox breakers, dimer-inhibitors, immunotherapies, and other novel approaches, critically evaluating their efficacy in overcoming the therapeutic limitations, and their putative role in blocking the RAS pathway.

Targeting RAF dimers in RAS mutant tumors: From biology to clinic

RAS mutations occur in approximately 30% of tumors worldwide and have a poor prognosis due to limited therapies. Covalent targeting of KRAS G12C has achieved significant success in recent years, but there is still a lack of efficient therapeutic approaches for tumors with non-G12C KRAS mutations. A highly promising approach is to target the MAPK pathway downstream of RAS, with a particular focus on RAF kinases. First-generation RAF inhibitors have been authorized to treat BRAF mutant tumors for over a decade. However, their use in RAS-mutated tumors is not recommended due to the paradoxical ERK activation mainly caused by RAF dimerization. To address the issue of RAF dimerization, type II RAF inhibitors have emerged as leading candidates. Recent clinical studies have shown the initial effectiveness of these agents against RAS mutant tumors. Promisingly, type II RAF inhibitors in combination with MEK or ERK inhibitors have demonstrated impressive efficacy in RAS mutant tumors. This review aims to clarify the importance of RAF dimerization in cellular signaling and resistance to treatment in tumors with RAS mutations, as well as recent progress in therapeutic approaches to address the problem of RAF dimerization in RAS mutant tumors.

Insight on ecDNA-mediated tumorigenesis and drug resistance

Extrachromosomal DNAs (ecDNAs) are a pervasive feature found in cancer and contain oncogenes and their corresponding regulatory elements. Their unique structural properties allow a rapid amplification of oncogenes and alter chromatin accessibility, leading to tumorigenesis and malignant development. The uneven segregation of ecDNA during cell division enhances intercellular genetic heterogeneity, which contributes to tumor evolution that might trigger drug resistance and chemotherapy tolerance. In addition, ecDNA has the ability to integrate into or detach from chromosomal DNA, such progress results into structural alterations and genomic rearrangements within cancer cells. Recent advances in multi-omics analysis revealing the genomic and epigenetic characteristics of ecDNA are anticipated to make valuable contributions to the development of precision cancer therapy. Herein, we conclud the mechanisms of ecDNA generation and the homeostasis of its dynamic structure. In addition to the latest techniques in ecDNA research including multi-omics analysis and biochemical validation methods, we also discuss the role of ecDNA in tumor development and treatment, especially in drug resistance, and future challenges of ecDNA in cancer therapy.

Investigational Approaches for Treatment of Melanoma Patients Progressing After Standard of Care

ABSTRACT

The advent of effective immunotherapy, specifically cytotoxic T-lymphocyte associated protein 4 and programmed cell death 1 inhibitors, as well as targeted therapy including BRAF/MEK inhibitors, has dramatically changed the prognosis for metastatic melanoma patients. Up to 50% of patients may experience long-term survival currently. Despite these advances in melanoma treatment, many patients still progress and die of their disease. As such, there are many studies aimed at providing new treatment options for this population. Therapies currently under investigation include, but are not limited to, novel immunotherapies, targeted therapies, tumor-infiltrating lymphocytes and other cellular therapies, oncolytic viral therapy and other injectables, and fecal microbiota transplant. In this review, we discuss the emerging treatment options for metastatic melanoma patients who have progressed on standard of care treatments.

BRAF - a tumour-agnostic drug target with lineage-specific dependencies

In June 2022, the FDA granted Accelerated Approval to the BRAF inhibitor dabrafenib in combination with the MEK inhibitor trametinib for the treatment of adult and paediatric patients (≥6 years of age) with unresectable or metastatic BRAFV600E-mutant solid tumours, except for BRAFV600E-mutant colorectal cancers. The histology-agnostic approval of dabrafenib plus trametinib marks the culmination of two decades of research into the landscape of BRAF mutations in human cancers, the biochemical mechanisms underlying BRAF-mediated tumorigenesis, and the clinical development of selective RAF and MEK inhibitors. Although the majority of patients with BRAFV600E-mutant tumours derive clinical benefit from BRAF inhibitor-based combinations, resistance to treatment develops in most. In this Review, we describe the biochemical basis for oncogenic BRAF-induced activation of MAPK signalling and pan-cancer and lineage-specific mechanisms of intrinsic, adaptive and acquired resistance to BRAF inhibitors. We also discuss novel RAF inhibitors and drug combinations designed to delay the emergence of treatment resistance and/or expand the population of patients with BRAF-mutant cancers who benefit from molecularly targeted therapies.

The role of CRAF in cancer progression: from molecular mechanisms to precision therapies

The RAF family of kinases includes key activators of the pro-tumourigenic mitogen-activated protein kinase pathway. Hyperactivation of RAF proteins, particularly BRAF and CRAF, drives tumour progression and drug resistance in many types of cancer. Although BRAF is the most studied RAF protein, partially owing to its high mutation incidence in melanoma, the role of CRAF in tumourigenesis and drug resistance is becoming increasingly clinically relevant. Here, we summarize the main known regulatory mechanisms and gene alterations that contribute to CRAF activity, highlighting the different oncogenic roles of CRAF, and categorize RAF1 (CRAF) mutations according to the effect on kinase activity. Additionally, we emphasize the effect that CRAF alterations may have on drug resistance and how precision therapies could effectively target CRAF-dependent tumours. Here, we discuss preclinical and clinical findings that may lead to improved treatments for all types of oncogenic RAF1 alterations in cancer.

Comparative Genomic Analysis and Clinical Outcomes of BRAF-mutated Advanced Biliary Tract Cancers

PURPOSE

BRAF mutations are rare in biliary tract cancers (BTC), but are of interest given the recent developments in targeted therapy for BTC. We investigated the clinical outcomes in a cohort of BRAF-mutant advanced BTC treated with first-line chemotherapy. Furthermore, we investigated the genomic landscape of BRAF class I, II, and III mutations in the intrahepatic cholangiocarcinoma (iCCA) subgroup of BTC.

EXPERIMENTAL DESIGN

We analyzed two nonoverlapping cohorts. We examined the genomic landscape of BRAF-mutated iCCA in a "genomic cohort" [187 class I, 82 class II, 113 class III BRAF mutants and 8,026 wildtype (WT)]. We also analyzed median progression-free survival (PFS) and overall survival (OS) on first-line chemotherapy in a separate multi-institutional "clinical cohort" of patients with BTC (including iCCA and extrahepatic cholangiocarcinoma (eCCA) and gallbladder cancer; 41 class I, 32 class II+III BRAF mutants and 1,042 WT).

RESULTS

In the entire BTC clinical cohort, the median PFS was shorter for class I [HR, 2.11 (P < 0.001)] and class II+III [HR, 1.72 (P = 0.007)] as compared with BRAF WT. OS was also shorter in class I [HR, 2.04 (P = 0.011)] and class II+III [HR, 1.86 (P = 0.002)] as compared with BRAF WT. In the iCCA subgroup, class I alterations were mutually exclusive with FGFR2, IDH1/2, ERBB2, and KRAS mutations. Class II+III mutations appear to be mutually exclusive with FGFR2 and KRAS.

CONCLUSIONS

In BTC, all classes of BRAF mutations are associated with a worse prognosis. BRAF mutations occur in 5% of iCCA subgroup and may be mutually exclusive with other targetable mutations.

SOS1 and KSR1 modulate MEK inhibitor responsiveness to target resistant cell populations based on PI3K and KRAS mutation status

KRAS is the most commonly mutated oncogene. Targeted therapies have been developed against mediators of key downstream signaling pathways, predominantly components of the RAF/MEK/ERK kinase cascade. Unfortunately, single-agent efficacy of these agents is limited both by intrinsic and acquired resistance. Survival of drug-tolerant persister cells within the heterogeneous tumor population and/or acquired mutations that reactivate receptor tyrosine kinase (RTK)/RAS signaling can lead to outgrowth of tumor-initiating cells (TICs) and drive therapeutic resistance. Here, we show that targeting the key RTK/RAS pathway signaling intermediates SOS1 (Son of Sevenless 1) or KSR1 (Kinase Suppressor of RAS 1) both enhances the efficacy of, and prevents resistance to, the MEK inhibitor trametinib in KRAS-mutated lung (LUAD) and colorectal (COAD) adenocarcinoma cell lines depending on the specific mutational landscape. The SOS1 inhibitor BI-3406 enhanced the efficacy of trametinib and prevented trametinib resistance by targeting spheroid-initiating cells in KRASG12/G13-mutated LUAD and COAD cell lines that lacked PIK3CA comutations. Cell lines with KRASQ61 and/or PIK3CA mutations were insensitive to trametinib and BI-3406 combination therapy. In contrast, deletion of the RAF/MEK/ERK scaffold protein KSR1 prevented drug-induced SIC upregulation and restored trametinib sensitivity across all tested KRAS mutant cell lines in both PIK3CA-mutated and PIK3CA wild-type cancers. Our findings demonstrate that vertical inhibition of RTK/RAS signaling is an effective strategy to prevent therapeutic resistance in KRAS-mutated cancers, but therapeutic efficacy is dependent on both the specific KRAS mutant and underlying comutations. Thus, selection of optimal therapeutic combinations in KRAS-mutated cancers will require a detailed understanding of functional dependencies imposed by allele-specific KRAS mutations.

Tumor Cell Resistance to the Inhibition of BRAF and MEK1/2

BRAF is one of the most frequently mutated oncogenes, with an overall frequency of about 50%. Targeting BRAF and its effector mitogen-activated protein kinase kinase 1/2 (MEK1/2) is now a key therapeutic strategy for BRAF-mutant tumors, and therapies based on dual BRAF/MEK inhibition showed significant efficacy in a broad spectrum of BRAF tumors. Nonetheless, BRAF/MEK inhibition therapy is not always effective for BRAF tumor suppression, and significant challenges remain to improve its clinical outcomes. First, certain BRAF tumors have an intrinsic ability to rapidly adapt to the presence of BRAF and MEK1/2 inhibitors by bypassing drug effects via rewired signaling, metabolic, and regulatory networks. Second, almost all tumors initially responsive to BRAF and MEK1/2 inhibitors eventually acquire therapy resistance via an additional genetic or epigenetic alteration(s). Overcoming these challenges requires identifying the molecular mechanism underlying tumor cell resistance to BRAF and MEK inhibitors and analyzing their specificity in different BRAF tumors. This review aims to update this information.

Pro-Apoptotic Activity of MCL-1 Inhibitor in Trametinib-Resistant Melanoma Cells Depends on Their Phenotypes and Is Modulated by Reversible Alterations Induced by Trametinib Withdrawal

BACKGROUND

Although BRAFV600/MEK inhibitors improved the treatment of melanoma patients, resistance is acquired almost inevitably.

METHODS

Trametinib withdrawal/rechallenge and MCL-1 inhibition in trametinib-resistance models displaying distinct p-ERK1/2 levels were investigated.

RESULTS

Trametinib withdrawal/rechallenge caused reversible changes in ERK1/2 activity impacting the balance between pro-survival and pro-apoptotic proteins. Reversible alterations were found in MCL-1 levels and MCL-1 inhibitors, BIM and NOXA. Taking advantage of melanoma cell dependency on MCL-1 for survival, we used S63845. While it was designed to inhibit MCL-1 activity, we showed that it also significantly reduced NOXA levels. S63845-induced apoptosis was detected as the enhancement of Annexin V-positivity, caspase-3/7 activation and histone H2AX phosphorylation. Percentages of Annexin V-positive cells were increased most efficiently in trametinib-resistant melanoma cells displaying the p-ERK1/2low/MCL-1low/BIMhigh/NOXAlow phenotype with EC50 values at concentrations as low as 0.1 μM. Higher ERK1/2 activity associated with increased MCL-1 level and reduced BIM level limited pro-apoptotic activity of S63845 further influenced by a NOXA level.

CONCLUSIONS

Our study supports the notion that the efficiency of an agent designed to target a single protein can largely depend on the phenotype of cancer cells. Thus, it is important to define appropriate phenotype determinants to stratify the patients for the novel therapy.

NF1 alterations in cancers: therapeutic implications in precision medicine

INTRODUCTION

NF1 is a tumor suppressor gene encoding neurofibromin, an inhibitor of the RAS/MAPK and PI3K-AKT-mTOR signaling pathways. NF1 germline pathogenic variants cause the tumor predisposition syndrome neurofibromatosis type 1. Targeted therapies (MEK inhibitors) have been approved for benign nerve sheath tumors in neurofibromatosis type 1 patients. NF1 somatic alterations are present in ~5% of all human sporadic cancers. In melanomas, acute myeloid leukemias and lung adenocarcinomas, the NF1 somatic alteration frequency is higher (~15%). However, to date, the therapeutic impact of NF1 somatic alterations is poorly investigated.

AREAS COVERED

This review presents a comprehensive overview of targeted therapies and immunotherapies currently developed and evaluated in vitro and in vivo for NF1-altered cancer treatment. A PubMed database literature review was performed to select relevant original articles. Active clinical trials were researched in ClinicalTrials.gov database in August 2022. TCGA and HGMD® databases were consulted.

EXPERT OPINION

This review highlights the need to better understand the molecular mechanisms of NF1-altered tumors and the development of innovative strategies to effectively target NF1-loss in human cancers. One of the current major challenges in cancer management is the targeting of tumor suppressor genes such as NF1 gene. Currently, most studies are focusing on inhibitors of the RAS/MAPK and PI3K-AKT-mTOR pathways and immunotherapies.

Antigen presentation by clonally diverse CXCR5+ B cells to CD4 and CD8 T cells is associated with durable response to immune checkpoint inhibitors

Introduction

Increased T cell infiltration and interferon gamma (IFNγ) pathway activation are seen in tumors of melanoma patients who respond to ICI (immune checkpoint inhibitor) or MAPK pathway inhibitor (MAPKi) therapies. Yet, the rate of durable tumor control after ICI is almost twice that of MAPKi, suggesting that additional mechanisms may be present in patients responding to ICI therapy that are beneficial for anti-tumor immunity.

Methods

We used transcriptional analysis and clinical outcomes from patients treated with ICI or MAPKi therapies to delineate immune mechanisms driving tumor response.

Results

We discovered response to ICI is associated with CXCL13-driven recruitment of CXCR5+ B cells with significantly higher clonal diversity than MAPKi. Our in vitro data indicate that CXCL13 production was increased in human peripheral blood mononuclear cells by anti-PD1, but not MAPKi, treatment. Higher B cell infiltration and B cell receptor (BCR) diversity allows presentation of diverse tumor antigens by B cells, resulting in activation of follicular helper CD4 T cells (Tfh) and tumor reactive CD8 T cells after ICI therapy. Higher BCR diversity and IFNγ pathway score post-ICI are associated with significantly longer patient survival compared to those with either one or none.

Conclusions

Response to ICI, but not to MAPKi, depends on the recruitment of CXCR5+ B cells into the tumor microenvironment and their productive tumor antigen presentation to follicular helper and cytotoxic, tumor reactive T cells. Our study highlights the potential of CXCL13 and B cell based strategies to enhance the rate of durable response in melanoma patients treated with ICI.

New Approaches to Targeted Therapy in Melanoma

It was just slightly more than a decade ago when metastatic melanoma carried a dismal prognosis with few, if any, effective therapies. Since then, the evolution of cancer immunotherapy has led to new and effective treatment approaches for melanoma. However, despite these advances, a sizable portion of patients with advanced melanoma have de novo or acquired resistance to immune checkpoint inhibitors. At the same time, therapies (BRAF plus MEK inhibitors) targeting the BRAFV600 mutations found in 40-50% of cutaneous melanomas have also been critical for optimizing management and improving patient outcomes. Even though immunotherapy has been established as the initial therapy in most patients with cutaneous melanoma, subsequent effective therapy is limited to BRAFV600 melanoma. For all other melanoma patients, driver mutations have not been effectively targeted. Numerous efforts are underway to target melanomas with NRAS mutations, NF-1 LOF mutations, and other genetic alterations leading to activation of the MAP kinase pathway. In this era of personalized medicine, we will review the current genetic landscape, molecular classifications, emerging drug targets, and the potential for combination therapies for non-BRAFV600 melanoma.

Combination of immune-checkpoint inhibitors and targeted therapies for melanoma therapy: The more, the better?

The approval of immune-checkpoint inhibitors (CPI) and mitogen activated protein kinase inhibitors (MAPKi) in recent years significantly improved the treatment management and survival of patients with advanced malignant melanoma. CPI aim to counter-act receptor-mediated inhibitory effects of tumor cells and immunomodulatory cell types on effector T cells, whereas MAPKi are intended to inhibit tumor cell survival. In agreement with these complementary modes of action preclinical data indicated that the combined application of CPI and MAPKi or their optimal sequencing might provide additional clinical benefit. In this review the rationale and preclinical evidence that support the combined application of MAPKi and CPI either in concurrent or consecutive regimens are presented. Further, we will discuss the results from clinical trials investigating the sequential or combined application of MAPKi and CPI for advanced melanoma patients and their implications for clinical practice. Finally, we outline mechanisms of MAPKi and CPI cross-resistance which limit the efficacy of currently available treatments, as well as combination regimens.

Ongoing complete response after treatment cessation with dabrafenib, trametinib, and cetuximab as third-line treatment in a patient with advanced BRAFV600E mutated, microsatellite-stable colon cancer: A case report and literature review

Metastatic BRAFV600E mutated colorectal cancer is associated with poor overall survival and modest effectiveness to standard therapies. Furthermore, survival is influenced by the microsatellite status. Patients with microsatellite-stable and BRAFV600E mutated colorectal cancer have the worst prognosis under the wide range of genetic subgroups in colorectal cancer. Herein, we present a patient case of an impressive therapeutic efficacy of dabrafenib, trametinib, and cetuximab as later-line therapy in a 52-year-old woman with advanced BRAFV600E mutated, microsatellite-stable colon cancer. This patient achieved a complete response after 1 year of triple therapy. Due to skin toxicity grade 3 and recurrent urinary tract infections due to mucosal toxicity, a therapy de-escalation to dabrafenib and trametinib was performed, and the double therapy was administered for further 41 months with ongoing complete response. For 1 year, the patient was off therapy and is still in complete remission.

Multi-organ landscape of therapy-resistant melanoma

Metastasis and failure of present-day therapies represent the most common causes of mortality in patients with cutaneous melanoma. To identify the underlying genetic and transcriptomic landscapes, in this study we analyzed multi-organ metastases and tumor-adjacent tissues from 11 rapid autopsies after treatment with MAPK inhibitor (MAPKi) and/or immune checkpoint blockade (ICB) and death due to acquired resistance. Either treatment elicits shared genetic alterations that suggest immune-evasive, cross-therapy resistance mechanisms. Large, non-clustered deletions, inversions and inter-chromosomal translocations dominate rearrangements. Analyzing data from separate melanoma cohorts including 345 therapy-naive patients and 35 patients with patient-matched pre-treatment and post-acquired resistance tumor samples, we performed cross-cohort analyses to identify MAPKi and ICB as respective contributors to gene amplifications and deletions enriched in autopsy versus therapy-naive tumors. In the autopsy cohort, private/late mutations and structural variants display shifted mutational and rearrangement signatures, with MAPKi specifically selecting for signatures of defective homologous-recombination, mismatch and base-excision repair. Transcriptomic signatures and crosstalks with tumor-adjacent macroenvironments nominated organ-specific adaptive pathways. An immune-desert, CD8+-macrophage-biased archetype, T-cell exhaustion and type-2 immunity characterized the immune contexture. This multi-organ analysis of therapy-resistant melanoma presents preliminary insights with potential to improve therapeutic strategies.

Blocking Genomic Instability Prevents Acquired Resistance to MAPK Inhibitor Therapy in Melanoma

Blocking cancer genomic instability may prevent tumor diversification and escape from therapies. We show that, after MAPK inhibitor (MAPKi) therapy in patients and mice bearing patient-derived xenografts (PDX), acquired resistant genomes of metastatic cutaneous melanoma specifically amplify resistance-driver, nonhomologous end-joining (NHEJ), and homologous recombination repair (HRR) genes via complex genomic rearrangements (CGR) and extrachromosomal DNAs (ecDNA). Almost all sensitive and acquired-resistant genomes harbor pervasive chromothriptic regions with disproportionately high mutational burdens and significant overlaps with ecDNA and CGR spans. Recurrently, somatic mutations within ecDNA and CGR amplicons enrich for HRR signatures, particularly within acquired resistant tumors. Regardless of sensitivity or resistance, breakpoint-junctional sequence analysis suggests NHEJ as critical to double-stranded DNA break repair underlying CGR and ecDNA formation. In human melanoma cell lines and PDXs, NHEJ targeting by a DNA-PKCS inhibitor prevents/delays acquired MAPKi resistance by reducing the size of ecDNAs and CGRs early on combination treatment. Thus, targeting the causes of genomic instability prevents acquired resistance.

SIGNIFICANCE

Acquired resistance often results in heterogeneous, redundant survival mechanisms, which challenge strategies aimed at reversing resistance. Acquired-resistant melanomas recurrently evolve resistance-driving and resistance-specific amplicons via ecDNAs and CGRs, thereby nominating chromothripsis-ecDNA-CGR biogenesis as a resistance-preventive target. Specifically, targeting DNA-PKCS/NHEJ prevents resistance by suppressing ecDNA/CGR rearrangements in MAPKi-treated melanomas. This article is highlighted in the In This Issue feature, p. 799.

Combined PD-1, BRAF and MEK inhibition in BRAFV600E colorectal cancer: a phase 2 trial

While BRAF inhibitor combinations with EGFR and/or MEK inhibitors have improved clinical efficacy in BRAFV600E colorectal cancer (CRC), response rates remain low and lack durability. Preclinical data suggest that BRAF/MAPK pathway inhibition may augment the tumor immune response. We performed a proof-of-concept single-arm phase 2 clinical trial of combined PD-1, BRAF and MEK inhibition with sparatlizumab (PDR001), dabrafenib and trametinib in 37 patients with BRAFV600E CRC. The primary end point was overall response rate, and the secondary end points were progression-free survival, disease control rate, duration of response and overall survival. The study met its primary end point with a confirmed response rate (24.3% in all patients; 25% in microsatellite stable patients) and durability that were favorable relative to historical controls of BRAF-targeted combinations alone. Single-cell RNA sequencing of 23 paired pretreatment and day 15 on-treatment tumor biopsies revealed greater induction of tumor cell-intrinsic immune programs and more complete MAPK inhibition in patients with better clinical outcome. Immune program induction in matched patient-derived organoids correlated with the degree of MAPK inhibition. These data suggest a potential tumor cell-intrinsic mechanism of cooperativity between MAPK inhibition and immune response, warranting further clinical evaluation of optimized targeted and immune combinations in CRC. ClinicalTrials.gov registration: NCT03668431.

Inhibition of autophagy and MEK promotes ferroptosis in Lkb1-deficient Kras-driven lung tumors

LKB1 and KRAS are the third most frequent co-mutations detected in non-small cell lung cancer (NSCLC) and cause aggressive tumor growth. Unfortunately, treatment with RAS-RAF-MEK-ERK pathway inhibitors has minimal therapeutic efficacy in LKB1-mutant KRAS-driven NSCLC. Autophagy, an intracellular nutrient scavenging pathway, compensates for Lkb1 loss to support Kras-driven lung tumor growth. Here we preclinically evaluate the possibility of autophagy inhibition together with MEK inhibition as a treatment for Kras-driven lung tumors. We found that the combination of the autophagy inhibitor hydroxychloroquine (HCQ) and the MEK inhibitor Trametinib displays synergistic anti-proliferative activity in KrasG12D/+;Lkb1-/- (KL) lung cancer cells, but not in KrasG12D/+;p53-/- (KP) lung cancer cells. In vivo studies using tumor allografts, genetically engineered mouse models (GEMMs) and patient-derived xenografts (PDXs) showed anti-tumor activity of the combination of HCQ and Trametinib on KL but not KP tumors. We further found that the combination treatment significantly reduced mitochondrial membrane potential, basal respiration, and ATP production, while also increasing lipid peroxidation, indicative of ferroptosis, in KL tumor-derived cell lines (TDCLs) and KL tumors compared to treatment with single agents. Moreover, the reduced tumor growth by the combination treatment was rescued by ferroptosis inhibitor. Taken together, we demonstrate that autophagy upregulation in KL tumors causes resistance to Trametinib by inhibiting ferroptosis. Therefore, a combination of autophagy and MEK inhibition could be a novel therapeutic strategy to specifically treat NSCLC bearing co-mutations of LKB1 and KRAS.

Research progress of therapeutic effects and drug resistance of immunotherapy based on PD-1/PD-L1 blockade

The binding of programmed death-1 (PD-1) on the surface of T cells and PD-1 ligand 1 (PD-L1) on tumor cells can prevent the immune-killing effect of T cells on tumor cells and promote the immune escape of tumor cells. Therefore, immune checkpoint blockade targeting PD-1/PD-L1 is a reliable tumor therapy with remarkable efficacy. However, the main challenges of this therapy are low response rate and acquired resistance, so that the outcomes of this therapy are usually unsatisfactory. This review begins with the description of biological structure of the PD-1/PD-L1 immune checkpoint and its role in a variety of cells. Subsequently, the therapeutic effects of immune checkpoint blockers (PD-1 / PD-L1 inhibitors) in various tumors were introduced and analyzed, and the reasons affecting the function of PD-1/PD-L1 were systematically analyzed. Then, we focused on analyzing, sorting out and introducing the possible underlying mechanisms of primary and acquired resistance to PD-1/PD-L1 blockade including abnormal expression of PD-1/PD-L1 and some factors, immune-related pathways, tumor immune microenvironment, and T cell dysfunction and others. Finally, promising therapeutic strategies to sensitize the resistant patients with PD-1/PD-L1 blockade treatment were described. This review is aimed at providing guidance for the treatment of various tumors, and highlighting the drug resistance mechanisms to offer directions for future tumor treatment and improvement of patient prognosis.

BCL6 is regulated by the MAPK/ELK1 axis and promotes KRAS-driven lung cancer

Mutational activation of KRAS is a common oncogenic event in lung cancer, yet effective therapies are still lacking. Here, we identify B cell lymphoma 6 (BCL6) as a lynchpin in KRAS-driven lung cancer. BCL6 expression was increased upon KRAS activation in lung tumor tissue in mice and was positively correlated with the expression of KRAS-GTP, the active form of KRAS, in various human cancer cell lines. Moreover, BCL6 was highly expressed in human KRAS-mutant lung adenocarcinomas and was associated with poor patient survival. Mechanistically, the MAPK/ERK/ELK1 signaling axis downstream of mutant KRAS directly regulated BCL6 expression. BCL6 maintained the global expression of prereplication complex components; therefore, BCL6 inhibition induced stalling of the replication fork, leading to DNA damage and growth arrest in KRAS-mutant lung cancer cells. Importantly, BCL6-specific knockout in lungs significantly reduced the tumor burden and mortality in the LSL-Kras^G12D/+ lung cancer mouse model. Likewise, pharmacological inhibition of BCL6 significantly impeded the growth of KRAS-mutant lung cancer cells both in vitro and in vivo. In summary, our findings reveal a crucial role of BCL6 in promoting KRAS-addicted lung cancer and suggest BCL6 as a therapeutic target for the treatment of this intractable disease.

The future of targeted kinase inhibitors in melanoma

Melanoma is a cancer of the pigment-producing cells of the body and its incidence is rising. Targeted inhibitors that act against kinases in the MAPK pathway are approved for BRAF-mutant metastatic cutaneous melanoma and increase patients' survival. Response to these therapies is limited by drug resistance and is less durable than with immune checkpoint inhibition. Conversely, rare melanoma subtypes have few therapeutic options for advanced disease and MAPK pathway targeting agents show minimal anti-tumor effects. Nevertheless, there is a future for targeted kinase inhibitors in melanoma: in new applications such as adjuvant or neoadjuvant therapy and in novel combinations with immunotherapies or other targeted therapies. Pre-clinical studies continue to identify tumor dependencies and their corresponding actionable drug targets, paving the way for rational targeted kinase inhibitor combinations as a personalized medicine approach for melanoma.

Lipids for CD8+ TILs: Beneficial or harmful?

Lipids and lipid metabolism play crucial roles in regulating T cell function and are tightly related to the establishment of immune memory. It is reported that tumor-infiltrating CD8+T lymphocytes (CD8+TILs) burn fats to restore their impaired effector function due to the lack of glucose. Conversely, fatty acids (FAs) and cholesterol in the tumor microenvironment (TME) drive the CD8+ TILs dysfunction. The origin of dysfunctional CD8+ TILs shares important features with memory T cell’s precursor, but whether lipids and/or lipid metabolism reprogramming directly influence the memory plasticity of dysfunctional CD8+ TILs remains elusive. It is necessary to understand the interplay between cellular lipid metabolism and dysfunction of CD8+ TILs in the case of targeting T cell’s metabolism to synergize cancer immunotherapy. Therefore, in this review, we summarize the latest research on CD8+ TILs lipid metabolism, evaluate the impacts of lipids in the TME to CD8+ TILs, and highlight the significance of promoting memory phenotype cell formation by targeting CD8+ T cells lipid metabolism to provide longer duration of cancer immunotherapy efficacy.

Targeting metabolic vulnerability in mitochondria conquers MEK inhibitor resistance in KRAS-mutant lung cancer

MEK is a canonical effector of mutant KRAS; however, MEK inhibitors fail to yield satisfactory clinical outcomes in KRAS-mutant cancers. Here, we identified mitochondrial oxidative phosphorylation (OXPHOS) induction as a profound metabolic alteration to confer KRAS-mutant non-small cell lung cancer (NSCLC) resistance to the clinical MEK inhibitor trametinib. Metabolic flux analysis demonstrated that pyruvate metabolism and fatty acid oxidation were markedly enhanced and coordinately powered the OXPHOS system in resistant cells after trametinib treatment, satisfying their energy demand and protecting them from apoptosis. As molecular events in this process, the pyruvate dehydrogenase complex (PDHc) and carnitine palmitoyl transferase IA (CPTIA), two rate-limiting enzymes that control the metabolic flux of pyruvate and palmitic acid to mitochondrial respiration were activated through phosphorylation and transcriptional regulation. Importantly, the co-administration of trametinib and IACS-010759, a clinical mitochondrial complex I inhibitor that blocks OXPHOS, significantly impeded tumor growth and prolonged mouse survival. Overall, our findings reveal that MEK inhibitor therapy creates a metabolic vulnerability in the mitochondria and further develop an effective combinatorial strategy to circumvent MEK inhibitors resistance in KRAS-driven NSCLC.

Perspectives in Melanoma: meeting report from the Melanoma Bridge (December 2nd - 4th, 2021, Italy)

Advances in immune checkpoint and combination therapy have led to improvement in overall survival for patients with advanced melanoma. Improved understanding of the tumor, tumor microenvironment and tumor immune-evasion mechanisms has resulted in new approaches to targeting and harnessing the host immune response. Combination modalities with other immunotherapy agents, chemotherapy, radiotherapy, electrochemotherapy are also being explored to overcome resistance and to potentiate the immune response. In addition, novel approaches such as adoptive cell therapy, oncogenic viruses, vaccines and different strategies of drug administration including sequential, or combination treatment are being tested. Despite the progress in diagnosis of melanocytic lesions, correct classification of patients, selection of appropriate adjuvant and systemic theràapies, and prediction of response to therapy remain real challenges in melanoma. Improved understanding of the tumor microenvironment, tumor immunity and response to therapy has prompted extensive translational and clinical research in melanoma. There is a growing evidence that genomic and immune features of pre-treatment tumor biopsies may correlate with response in patients with melanoma and other cancers, but they have yet to be fully characterized and implemented clinically. Development of novel biomarker platforms may help to improve diagnostics and predictive accuracy for selection of patients for specific treatment. Overall, the future research efforts in melanoma therapeutics and translational research should focus on several aspects including: (a) developing robust biomarkers to predict efficacy of therapeutic modalities to guide clinical decision-making and optimize treatment regimens, (b) identifying mechanisms of therapeutic resistance to immune checkpoint inhibitors that are potentially actionable, (c) identifying biomarkers to predict therapy-induced adverse events, and (d) studying mechanism of actions of therapeutic agents and developing algorithms to optimize combination treatments. During the Melanoma Bridge meeting (December 2nd-4th, 2021, Naples, Italy) discussions focused on the currently approved systemic and local therapies for advanced melanoma and discussed novel biomarker strategies and advances in precision medicine as well as the impact of COVID-19 pandemic on management of melanoma patients.

Enhancing PD-L1 Degradation by ITCH during MAPK Inhibitor Therapy Suppresses Acquired Resistance

MAPK inhibitor (MAPKi) therapy in melanoma leads to the accumulation of tumor-surface PD-L1/L2, which may evade antitumor immunity and accelerate acquired resistance. Here, we discover that the E3 ligase ITCH binds, ubiquitinates, and downregulates tumor-surface PD-L1/L2 in MAPKi-treated human melanoma cells, thereby promoting T-cell activation. During MAPKi therapy in vivo, melanoma cell-intrinsic ITCH knockdown induced tumor-surface PD-L1, reduced intratumoral cytolytic CD8+ T cells, and accelerated acquired resistance only in immune-competent mice. Conversely, tumor cell-intrinsic ITCH overexpression reduced MAPKi-elicited PD-L1 accumulation, augmented intratumoral cytolytic CD8+ T cells, and suppressed acquired resistance in BrafV600MUT, NrasMUT, or Nf1MUT melanoma and KrasMUT-driven cancers. CD8+ T-cell depletion and tumor cell-intrinsic PD-L1 overexpression nullified the phenotype of ITCH overexpression, thereby supporting an in vivo ITCH-PD-L1-T-cell regulatory axis. Moreover, we identify a small-molecular ITCH activator that suppresses acquired MAPKi resistance in vivo. Thus, MAPKi-induced PD-L1 accelerates resistance, and a PD-L1-degrading ITCH activator prolongs antitumor response.

SIGNIFICANCE

MAPKi induces tumor cell-surface PD-L1 accumulation, which promotes immune evasion and therapy resistance. ITCH degrades PD-L1, optimizing antitumor T-cell immunity. We propose degrading tumor cell-surface PD-L1 and/or activating tumor-intrinsic ITCH as strategies to overcome MAPKi resistance. This article is highlighted in the In This Issue feature, p. 1825.

A Genome-Wide Screen Identifies PDPK1 as a Target to Enhance the Efficacy of MEK1/2 Inhibitors in NRAS Mutant Melanoma

Melanomas frequently harbor activating NRAS mutations. However, limited advance has been made in developing targeted therapy options for patients with NRAS mutant melanoma. MEK inhibitors (MEKi) show modest efficacy in the clinic and their actions need to be optimized. In this study, we performed a genome-wide CRISPR-Cas9-based screen and demonstrated that loss of phosphoinositide-dependent kinase-1 (PDPK1) enhances the efficacy of MEKi. The synergistic effects of PDPK1 loss and MEKi was validated in NRAS mutant melanoma cell lines using pharmacologic and molecular approaches. Combined PDPK1 inhibitors (PDPK1i) with MEKi suppressed NRAS mutant xenograft growth and induced gasdermin E-associated pyroptosis. In an immune-competent allograft model, PDPK1i+MEKi increased the ratio of intratumoral CD8+ T cells, delayed tumor growth, and prolonged survival; the combination treatment was less effective against tumors in immune-deficient mice. These data suggest PDPK1i+MEKi as an efficient immunostimulatory strategy against NRAS mutant melanoma.

SIGNIFICANCE

Targeting PDPK1 stimulates antitumor immunity and sensitizes NRAS mutant melanoma to MEK inhibition, providing rationale for the clinical development of a combinatorial approach for treating patients with melanoma.

HRS phosphorylation drives immunosuppressive exosome secretion and restricts CD8+ T-cell infiltration into tumors

The lack of tumor infiltration by CD8⁺ T cells is associated with poor patient response to anti-PD-1 therapy. Understanding how tumor infiltration is regulated is key to improving treatment efficacy. Here, we report that phosphorylation of HRS, a pivotal component of the ESCRT complex involved in exosome biogenesis, restricts tumor infiltration of cytolytic CD8⁺ T cells. Following ERK-mediated phosphorylation, HRS interacts with and mediates the selective loading of PD-L1 to exosomes, which inhibits the migration of CD8⁺ T cells into tumors. In tissue samples from patients with melanoma, CD8⁺ T cells are excluded from the regions where tumor cells contain high levels of phosphorylated HRS. In murine tumor models, overexpression of phosphorylated HRS increases resistance to anti-PD-1 treatment, whereas inhibition of HRS phosphorylation enhances treatment efficacy. Our study reveals a mechanism by which phosphorylation of HRS in tumor cells regulates anti-tumor immunity by inducing PD-L1⁺ immunosuppressive exosomes, and suggests HRS phosphorylation blockade as a potential strategy to improve the efficacy of cancer immunotherapy.

DNTTIP1 promotes nasopharyngeal carcinoma metastasis via recruiting HDAC1 to DUSP2 promoter and activating ERK signaling pathway

Background

Distant metastasis remains the leading cause of treatment failure in patients with nasopharyngeal carcinoma (NPC), making it critical to identify efficient therapeutic targets for metastatic NPC. Previous studies have demonstrated that deoxynucleotidyltransferase terminal-interacting protein 1 (DNTTIP1) is associated with the development of various types of cancer. However, its role and mechanism in NPC have not been explored.

Methods

RNA-seq profiling was performed for three pairs of NPC and normal nasopharynx tissues. DNTTIP1 expression in NPC specimens was detected by immunohistochemistry. In vitro and in vivo assays were used to investigate the function of DNTTIP1. The molecular mechanism was determined using RT-qPCR, western blotting, RNA-seq, luciferase reporter assays, ChIP assays, and co-IP assays.

Findings

DNTTIP1 was found to be significantly upregulated in NPC tissues. Furthermore, DNTTIP1 promoted NPC growth and metastasis in vitro and in vivo. Upregulation of DNTTIP1 in NPC indicated poor clinical outcomes. Mechanistically, DNTTIP1 suppressed DUSP2 gene expression via recruiting HDAC1 to its promoter and maintaining a deacetylated state of histone H3K27. The downregulation of DUSP2 resulted in aberrant activation of the ERK signaling and elevated MMP2 levels, promoting NPC metastasis. Chidamide, an HDAC inhibitor, was shown to suppress NPC metastasis by regulating the DNTTIP1/HDAC1-DUSP2 axis.

Interpretation

Our findings demonstrate that DNTTIP1 not only regulates NPC metastasis but also independently predicts NPC prognosis. Furthermore, targeting DNTTIP1/HDAC1 by Chidamide may benefit NPC patients with metastasis.

Funding

This work was supported by the National Natural Science Foundation of China (No. 81872464, 82073243).

Plasticity of Extrachromosomal and Intrachromosomal BRAF Amplifications in Overcoming Targeted Therapy Dosage Challenges

Focal amplifications (FA) can mediate targeted therapy resistance in cancer. Understanding the structure and dynamics of FAs is critical for designing treatments that overcome plasticity-mediated resistance. We developed a melanoma model of dual MAPK inhibitor (MAPKi) resistance that bears BRAFV600 amplifications through either extrachromosomal DNA (ecDNA)/double minutes (DM) or intrachromosomal homogenously staining regions (HSR). Cells harboring BRAFV600E FAs displayed mode switching between DMs and HSRs, from both de novo genetic changes and selection of preexisting subpopulations. Plasticity is not exclusive to ecDNAs, as cells harboring HSRs exhibit drug addiction-driven structural loss of BRAF amplicons upon dose reduction. FA mechanisms can couple with kinase domain duplications and alternative splicing to enhance resistance. Drug-responsive amplicon plasticity is observed in the clinic and can involve other MAPK pathway genes, such as RAF1 and NRAS. BRAF FA-mediated dual MAPKi-resistant cells are more sensitive to proferroptotic drugs, extending the spectrum of ferroptosis sensitivity in MAPKi resistance beyond cases of dedifferentiation.

SIGNIFICANCE

Understanding the structure and dynamics of oncogene amplifications is critical for overcoming tumor relapse. BRAF amplifications are highly plastic under MAPKi dosage challenges in melanoma, through involvement of de novo genomic alterations, even in the HSR mode. Moreover, BRAF FA-driven, dual MAPKi-resistant cells extend the spectrum of resistance-linked ferroptosis sensitivity. This article is highlighted in the In This Issue feature, p. 873.

KRAS acting through ERK signaling stabilizes PD-L1 via inhibiting autophagy pathway in intrahepatic cholangiocarcinoma

Background

While the correlation between PD-L1 expression and KRAS mutation has been previously reported in other solid tumors such as non-small cell lung cancer (NSCLC), whether PD-L1 can be modulated by ERK signaling downstream of KRAS in intrahepatic cholangiocarcinoma (iCCA) and the underlying molecular regulatory mechanism remain unclear.

Methods

The expression of ERK, p-ERK, PD-L1 and autophagy markers following KRAS knockdown or Ras/Raf/MEK/ERK signaling inhibitors treatment was examined in two human iCCA cell lines (HuCCT1 and RBE) using western blotting and immunofluorescence. Both pharmacological autophagy inhibitors and short-interfering RNA against ATG7 were applied to inhibit autophagy. The apoptosis rates of iCCA cell lines were detected by flow cytometry and CCK-8 after co-culturing with CD3/CD28-activated human CD8⁺ T lymphocytes. Immunohistochemistry was applied to detect the correlation of ERK, p-ERK and PD-L1 in 92 iCCA tissues.

Results

The present study demonstrated that the PD-L1 expression level was distinctly reduced in KRAS-mutated iCCA cell lines when ERK signaling was inhibited and ERK phosphorylation levels were lowered. The positive association between p-ERK and PD-L1 was also verified in 92 iCCA tissue samples. Moreover, ERK inhibition induced autophagy activation. Both inhibiting autophagy via autophagy inhibitors and genetically silencing the ATG7 expression partially reversed the reduced PD-L1 expression caused by ERK inhibition. In addition, ERK-mediated down-regulation of PD-L1 via autophagy pathways induced the apoptosis of iCCA cells when co-cultured with CD3/CD28-activated human CD8⁺ T lymphocytes in vitro.

Conclusions

Our results suggest that ERK signaling inhibition contributes to the reduction of PD-L1 expression through the autophagy pathway in iCCA. As a supplement to anti-PD-1/PD-L1 immunotherapy, ERK-targeted therapy may serve as a potentially novel treatment strategy for human KRAS-mutated iCCA.

Targeting oncogene and non-oncogene addiction to inflame the tumour microenvironment

Immune checkpoint inhibitors (ICIs) have revolutionized the clinical management of multiple tumours. However, only a few patients respond to ICIs, which has generated considerable interest in the identification of resistance mechanisms. One such mechanism reflects the ability of various oncogenic pathways, as well as stress response pathways required for the survival of transformed cells (a situation commonly referred to as 'non-oncogene addiction'), to support tumour progression not only by providing malignant cells with survival and/or proliferation advantages, but also by establishing immunologically 'cold' tumour microenvironments (TMEs). Thus, both oncogene and non-oncogene addiction stand out as promising targets to robustly inflame the TME and potentially enable superior responses to ICIs.

Response and recurrence correlates in individuals treated with neoadjuvant anti-PD-1 therapy for resectable oral cavity squamous cell carcinoma

Neoadjuvant PD-1 blockade may be efficacious in some individuals with high-risk, resectable oral cavity head and neck cancer. To explore correlates of response patterns to neoadjuvant nivolumab treatment and post-surgical recurrences, we analyzed longitudinal tumor and blood samples in a cohort of 12 individuals displaying 33% responsiveness. Pretreatment tumor-based detection of FLT4 mutations and PTEN signature enrichment favors response, and high tumor mutational burden improves recurrence-free survival. In contrast, preexisting and/or acquired mutations (in CDKN2A, YAP1, or JAK2) correlate with innate resistance and/or tumor recurrence. Immunologically, tumor response after therapy entails T cell receptor repertoire diversification in peripheral blood and intratumoral expansion of preexisting T cell clones. A high ratio of regulatory T to T helper 17 cells in pretreatment blood predicts low T cell receptor repertoire diversity in pretreatment blood, a low cytolytic T cell signature in pretreatment tumors, and innate resistance. Our study provides a molecular framework to advance neoadjuvant anti-PD-1 therapy for individuals with resectable head and neck cancer.

Anti-PD-1/L1 lead-in before MAPK inhibitor combination maximizes antitumor immunity and efficacy

Rationally sequencing and combining PD-1/L1-and MAPK-targeted therapies may overcome innate and acquired resistance. Since increased clinical benefit of MAPK inhibitors (MAPKi) is associated with previous immune checkpoint therapy, we compare the efficacies of sequential and/or combinatorial regimens in subcutaneous murine models of melanoma driven by BrafV600, Nras, or Nf1 mutations as well as colorectal and pancreatic carcinoma driven by KrasG12C. Anti-PD-1/L1 lead-in preceding MAPKi combination optimizes response durability by promoting pro-inflammatory polarization of macrophages and clonal expansion of interferon-γhi, and CD8+ cytotoxic and proliferative (versus CD4+ regulatory) T cells that highly express activation genes. Since therapeutic resistance of melanoma brain metastasis (MBM) limits patient survival, we demonstrate that sequencing anti-PD-1/L1 therapy before MAPKi combination suppresses MBM and improves mouse survival with robust T cell clonal expansion in both intracranial and extracranial metastatic sites. We propose clinically testing brief anti-PD-1/L1 (± anti-CTLA-4) dosing before MAPKi co-treatment to suppress therapeutic resistance.

Drug combination screening as a translational approach toward an improved drug therapy for chordoma

Purpose

Drug screening programmes have revealed epidermal growth factor receptor inhibitors (EGFR_is) as promising therapeutics for chordoma, an orphan malignant bone tumour, in the absence of a known genetic driver. Concurrently, the irreversible EGFR_i afatinib (Giotrif®) is being evaluated in a multicentric Phase II trial. As tyrosine kinase inhibitor (TKI) monotherapies are invariably followed by resistance, we aimed to evaluate potential therapeutic combinations with EGFR_is.

Methods

We screened 133 clinically approved anticancer drugs as single agents and in combination with two EGFR_is (afatinib and erlotinib) in the clival chordoma cell line UM-Chor1. Synergistic combinations were analysed in a 7 × 7 matrix format. The most promising combination was further explored in clival (UM-Chor1, MUG-CC1) and sacral (MUG-Chor1, U-CH1) chordoma cell lines. Secretomes were analysed for receptor tyrosine kinase ligands (EGF, TGF-α, FGF-2 and VEGF-A) upon drug treatment.

Results

Drugs that were active as single agents (n = 45) included TKIs, HDAC and proteasome inhibitors, and cytostatic drugs. Six combinations were analysed in a matrix format: n = 4 resulted in a significantly increased cell killing (crizotinib, dabrafenib, panobinostat and doxorubicin), and n = 2 exhibited no or negligible effects (regorafenib, venetoclax). Clival chordoma cell lines were more responsive to combined EGFR-MET inhibition. EGFR-MET cross-talk (e.g. via TGF-α secretion) likely accounts for the synergistic effects of EGFR-MET inhibition.

Conclusion

Our screen revealed promising combinations with EGFR_is, such as the ALK/MET-inhibitor crizotinib, the HDAC-inhibitor panobinostat or the topoisomerase-II-inhibitor doxorubicin, which are part of standard chemotherapy regimens for various bone and soft-tissue sarcomas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13402-021-00632-x.

Triple Therapy to Outwit the BRAF Oncogene

BRAF-mutant cancers have been knocked down by BRAF and MEK inhibitor combos, yet the cancers always find a way to get back up. Adding a third medicine, namely, a dimer-selective BRAF inhibitor, can knock down longer and better.See related article by Adamopoulos et al., p. 1716.

Perspectives in Melanoma: meeting report from the Melanoma Bridge (December 3rd-5th, 2020, Italy)

Advances in immune checkpoint therapy and targeted therapy have led to improvement in overall survival for patients with advanced melanoma. Single agent checkpoint PD-1 blockade and combination with BRAF/MEK targeted therapy demonstrated benefit in overall survival (OS). Superior response rates have been demonstrated with combined PD-1/CTLA-4 blockade, with a significant OS benefit compared with single-agent PD-1 blockade. Despite the progress in diagnosis of melanocytic lesions, correct classification of patients, selection of appropriate adjuvant and systemic therapies, and prediction of response to therapy remain real challenges in melanoma. Improved understanding of the tumor microenvironment, tumor immunity and response to therapy has prompted extensive translational and clinical research in melanoma. Development of novel biomarker platforms may help to improve diagnostics and predictive accuracy for selection of patients for specific treatment. There is a growing evidence that genomic and immune features of pre-treatment tumor biopsies may correlate with response in patients with melanoma and other cancers but they have yet to be fully characterized and implemented clinically. Overall, the progress in melanoma therapeutics and translational research will help to optimize treatment regimens to overcome resistance and develop robust biomarkers to guide clinical decision-making. During the Melanoma Bridge meeting (December 3rd-5th, 2020, Italy) we reviewed the currently approved systemic and local therapies for advanced melanoma and discussed novel biomarker strategies and advances in precision medicine.

Targeting BRAF and RAS in Colorectal Cancer

Simple Summary

In colorectal cancer, mutations of the KRAS and BRAF genes are quite common and can contribute to the activation of cell signaling pathways that lead to cell proliferation and differentiation. These processes promote cancer growth, and in some cases, they may cause cells to develop resistance to certain types of treatment, notably EGFR inhibitors. We summarize recent knowledge regarding the effects of KRAS and BRAF mutations in the setting of colorectal cancer and discuss the new therapies under development.

Abstract

Colorectal cancer (CRC) is still one of the most frequent forms of cancer in the world in terms of incidence. Around 40% of CRC patients carry a mutation of the Kirsten rat sarcoma (KRAS) gene, while 10% have a mutation in the B-Raf proto-oncogene serine/threonine kinase (BRAF) gene. These mutations are responsible for dysregulation of the mitogen-associated protein kinase (MAPK) pathway, leading to the proliferation, differentiation, angiogenesis, and resistance to apoptosis of cells. Activation of the MAPK pathway results in adaptive therapeutic resistance, rendering EGFR inhibitors ineffective. This review aims to highlight the recent findings that have improved our understanding of KRAS and BRAF mutations in colorectal cancer and to describe new targeted therapies, used alone or in combination.