Neuropilin-1 is a T cell memory checkpoint limiting long-term antitumor immunity.

Robust CD8+ T cell memory is essential for long-term protective immunity but is often compromised in cancer, where T cell exhaustion leads to loss of memory precursors. Immunotherapy via checkpoint blockade may not effectively reverse this defect, potentially underlying disease relapse. Here we report that mice with a CD8+ T cell-restricted neuropilin-1 (NRP1) deletion exhibited substantially enhanced protection from tumor rechallenge and sensitivity to anti-PD1 immunotherapy, despite unchanged primary tumor growth. Mechanistically, NRP1 cell-intrinsically limited the self-renewal of the CD44+PD1+TCF1+TIM3- progenitor exhausted T cells, which was associated with their reduced ability to induce c-Jun/AP-1 expression on T cell receptor restimulation, a mechanism that may contribute to terminal T cell exhaustion at the cost of memory differentiation in wild-type tumor-bearing hosts. These data indicate that blockade of NRP1, a unique 'immune memory checkpoint', may promote the development of long-lived tumor-specific Tmem that are essential for durable antitumor immunity.

A Pilot Study of Pembrolizumab in Combination With Y90 Radioembolization in Subjects With Poor Prognosis Hepatocellular Carcinoma.

BACKGROUND: Combination checkpoint inhibition therapy with yttrium-90 (Y90) radioembolization represents an emerging area of interest in the treatment of advanced hepatocellular carcinoma (HCC). HCRN GI15-225 is an open-label, single-arm multicenter, pilot study (NCT03099564). METHODS: Eligible patients had poor prognosis, localized HCC defined as having portal vein thrombus, multifocal disease, and/or diffuse disease that were not eligible for liver transplant or surgical resection. Patients received pembrolizumab 200 mg intravenously every 3 weeks in conjunction with glass yttrium-90 (Y90) radioembolization TheraSphere. Primary endpoint was 6-month progression-free survival (PFS6) per RECIST 1.1. Secondary endpoints included time to progression (TTP), objective response rate (ORR), overall survival (OS), and safety/tolerability. RESULTS: Between October 23, 2017 and November 24, 2020, 29 patients were enrolled: 2 were excluded per protocol. Fifteen of the remaining 27 patients were free of progression at 6 months (55.6%; 95% CI, 35.3-74.5) with median PFS 9.95 months (95% CI, 4.14-15.24) and OS 27.30 months (95% CI, 10.15-39.52). One patient was not evaluable for response due to death; among the remaining 26 patients, ORR was 30.8% (95% CI, 14.3-51.8) and DCR was 84.6% (95% CI, 65.1-95.6). CONCLUSION: In patients with localized, poor prognosis HCC, pembrolizumab in addition to glass Y90 radioembolization demonstrated promising efficacy and safety consistent with prior observations (ClinicalTrials.gov Identifier: NCT03099564; IRB Approved: 16-3255 approved July 12, 2016).

Fewer LAG-3+ T Cells in Relapsing-Remitting Multiple Sclerosis and Type 1 Diabetes.

The coinhibitory receptor lymphocyte activation gene 3 (LAG-3) is an immune checkpoint molecule that negatively regulates T cell activation, proliferation, and homeostasis. Blockade or deletion of LAG-3 in autoimmune-prone backgrounds or induced-disease models has been shown to exacerbate disease. We observed significantly fewer LAG-3+ CD4 and CD8 T cells from subjects with relapsing-remitting multiple sclerosis (RRMS) and type 1 diabetes. Low LAG-3 protein expression was linked to alterations in mRNA expression and not cell surface cleavage. Functional studies inhibiting LAG-3 suggest that in subjects with RRMS, LAG-3 retains its ability to suppress T cell proliferation. However, LAG-3 expression was associated with the expression of markers of apoptosis, indicating a role for low LAG-3 in T cell resistance to cell death. In T cells from subjects with RRMS, we observed a global dysregulation of LAG-3 expression stemming from decreased transcription and persisting after T cell stimulation. These findings further support the potential clinical benefits of a LAG-3 agonist in the treatment of human autoimmunity.

SPaRTAN, a computational framework for linking cell-surface receptors to transcriptional regulators.

The identity and functions of specialized cell types are dependent on the complex interplay between signaling and transcriptional networks. Recently single-cell technologies have been developed that enable simultaneous quantitative analysis of cell-surface receptor expression with transcriptional states. To date, these datasets have not been used to systematically develop cell-context-specific maps of the interface between signaling and transcriptional regulators orchestrating cellular identity and function. We present SPaRTAN (Single-cell Proteomic and RNA based Transcription factor Activity Network), a computational method to link cell-surface receptors to transcription factors (TFs) by exploiting cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) datasets with cis-regulatory information. SPaRTAN is applied to immune cell types in the blood to predict the coupling of signaling receptors with cell context-specific TFs. Selected predictions are validated by prior knowledge and flow cytometry analyses. SPaRTAN is then used to predict the signaling coupled TF states of tumor infiltrating CD8+ T cells in malignant peritoneal and pleural mesotheliomas. SPaRTAN enhances the utility of CITE-seq datasets to uncover TF and cell-surface receptor relationships in diverse cellular states.

Intractable Coronavirus Disease 2019 (COVID-19) and Prolonged Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Replication in a Chimeric Antigen Receptor-Modified T-Cell Therapy Recipient: A Case Study.

A chimeric antigen receptor-modified T-cell therapy recipient developed severe coronavirus disease 2019, intractable RNAemia, and viral replication lasting >2 months. Premortem endotracheal aspirate contained >2 × 1010 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA copies/mL and infectious virus. Deep sequencing revealed multiple sequence variants consistent with intrahost virus evolution. SARS-CoV-2 humoral and cell-mediated immunity were minimal. Prolonged transmission from immunosuppressed patients is possible.

The Impact of Estrogen in the Tumor Microenvironment.

Tumor immune escape is now a hallmark of cancer development, and therapies targeting these pathways have emerged as standard of care. Specifically, immune checkpoint signal blockade offers durable responses and increased overall survival. However, the majority of cancer patients still do not respond to checkpoint blockade immune therapy leading to an unmet need in tumor immunology research. Sex-based differences have been noted in the use of cancer immunotherapy suggesting that sex hormones such as estrogen may play an important role in tumor immune regulation. Estrogen signaling already has a known role in autoimmunity, and the estrogen receptor can be expressed across multiple immune cell populations and effect their regulation. While it has been well established that tumor cells such as ovarian carcinoma, breast carcinoma, and even lung carcinoma can be regulated by estrogen, research into the role of estrogen in the regulation of tumor-associated immune cells is still emerging. In this chapter, we discuss the role of estrogen in the tumor immune microenvironment and the possible immunotherapeutic implications of targeting estrogen in cancer patients.

The Role of the Estrogen Pathway in the Tumor Microenvironment.

Estrogen receptors are broadly expressed in many cell types involved in the innate and adaptive immune responses, and differentially regulate the production of cytokines. While both genomic and non-genomic tumor cell promoting mechanisms of estrogen signaling are well characterized in multiple carcinomas including breast, ovarian, and lung, recent investigations have identified a potential immune regulatory role of estrogens in the tumor microenvironment. Tumor immune tolerance is a well-established mediator of oncogenesis, with increasing evidence indicating the importance of the immune response in tumor progression. Immune-based therapies such as antibodies that block checkpoint signals have emerged as exciting therapeutic approaches for cancer treatment, offering durable remissions and prolonged survival. However, only a subset of patients demonstrate clinical response to these agents, prompting efforts to elucidate additional immunosuppressive mechanisms within the tumor microenvironment. Evidence drawn from multiple cancer types, including carcinomas traditionally classified as non-immunogenic, implicate estrogen as a potential mediator of immunosuppression through modulation of protumor responses independent of direct activity on tumor cells. Herein, we review the interplay between estrogen and the tumor microenvironment and the clinical implications of endocrine therapy as a novel treatment strategy within immuno-oncology.

Therapeutic targeting of regulatory T cells in cancer.

The success of immunotherapy in oncology underscores the vital role of the immune system in cancer development. Regulatory T cells (Tregs) maintain a fine balance between autoimmunity and immune suppression. They have multiple roles in the tumor microenvironment (TME) but act particularly in suppressing T cell activation. This review focuses on the detrimental and sometimes beneficial roles of Tregs in tumors, our current understanding of recruitment and stabilization of Tregs within the TME, and current Treg-targeted therapeutics. Research identifying subpopulations of Tregs and their respective functions and interactions within the complex networks of the TME will be crucial to develop the next generation of immunotherapies. Through these advances, Treg-targeted immunotherapy could have important implications for the future of oncology.

Antibodies targeting conserved non-canonical antigens and endemic coronaviruses associate with favorable outcomes in severe COVID-19.

While there have been extensive analyses characterizing cellular and humoral responses across the severity spectrum in COVID-19, outcome predictors within severe COVID-19 remain less comprehensively elucidated. Furthermore, properties of antibodies (Abs) directed against viral antigens beyond spike and their associations with disease outcomes remain poorly defined. We perform deep molecular profiling of Abs directed against a wide range of antigenic specificities in severe COVID-19 patients. The profiles included canonical (spike [S], receptor-binding domain [RBD], and nucleocapsid [N]) and non-canonical (orf3a, orf8, nsp3, nsp13, and membrane [M]) antigenic specificities. Notably, multivariate Ab profiles directed against canonical or non-canonical antigens are equally discriminative of survival in severe COVID-19. Intriguingly, pre-pandemic healthy controls have cross-reactive Abs directed against nsp13, a protein conserved across coronaviruses. Consistent with these findings, a model built on Ab profiles for endemic coronavirus antigens also predicts COVID-19 outcome. Our results suggest the importance of studying Abs targeting non-canonical severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and endemic coronavirus antigens in COVID-19.

Systemic Immune Dysfunction in Cancer Patients Driven by IL6 Induction of LAG3 in Peripheral CD8+ T Cells.

Many cancer patients do not develop a durable response to the current standard-of-care immunotherapies, despite substantial advances in targeting immune inhibitory receptors. A potential compounding issue, which may serve as an unappreciated, dominant resistance mechanism, is an inherent systemic immune dysfunction that is often associated with advanced cancer. Minimal response to inhibitory receptor (IR) blockade therapy and increased disease burden have been associated with peripheral CD8+ T-cell dysfunction, characterized by suboptimal T-cell proliferation and chronic expression of IRs (e.g., PD1 and LAG3). Here, we demonstrated that approximately a third of cancer patients analyzed in this study have peripheral CD8+ T cells that expressed robust intracellular LAG3 (LAG3IC), but not surface LAG3 (LAG3SUR) due to a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) cleavage. This is associated with poor disease prognosis and decreased CD8+ T-cell function, which could be partially reversed by anti-LAG3. Systemic immune dysfunction was restricted to CD8+ T cells, including, in some cases, a high percentage of peripheral naïve CD8+ T cells, and was driven by the cytokine IL6 via STAT3. These data suggest that additional studies are warranted to determine if the combination of increased LAG3IC in peripheral CD8+ T cells and elevated systemic IL6 can serve as predictive biomarkers and identify which cancer patients may benefit from LAG3 blockade.

COVID-19 versus Non-COVID-19 Acute Respiratory Distress Syndrome: Comparison of Demographics, Physiologic Parameters, Inflammatory Biomarkers, and Clinical Outcomes.

Rationale: There is an urgent need for improved understanding of the mechanisms and clinical characteristics of acute respiratory distress syndrome (ARDS) due to coronavirus disease (COVID-19).Objectives: To compare key demographic and physiologic parameters, biomarkers, and clinical outcomes of COVID-19 ARDS and ARDS secondary to direct lung injury from other etiologies of pneumonia.Methods: We enrolled 27 patients with COVID-19 ARDS in a prospective, observational cohort study and compared them with a historical, pre-COVID-19 cohort of patients with viral ARDS (n = 14), bacterial ARDS (n = 21), and ARDS due to culture-negative pneumonia (n = 30). We recorded clinical demographics; measured respiratory mechanical parameters; collected serial peripheral blood specimens for measurement of plasma interleukin (IL)-6, IL-8, and IL-10; and followed patients prospectively for patient-centered outcomes. We conducted between-group comparisons with nonparametric tests and analyzed time-to-event outcomes with Kaplan-Meier and Cox proportional hazards models.Results: Patients with COVID-19 ARDS had higher body mass index and were more likely to be Black, or residents of skilled nursing facilities, compared with those with non-COVID-19 ARDS (P < 0.05). Patients with COVID-19 had lower delivered minute ventilation compared with bacterial and culture-negative ARDS (post hoc P < 0.01) but not compared with viral ARDS. We found no differences in static compliance, hypoxemic indices, or carbon dioxide clearance between groups. Patients with COVID-19 had lower IL-6 levels compared with bacterial and culture-negative ARDS at early time points after intubation but no differences in IL-6 levels compared with viral ARDS. Patients with COVID-19 had longer duration of mechanical ventilation but similar 60-day mortality in both unadjusted and adjusted analyses.Conclusions: COVID-19 ARDS bears several similarities to viral ARDS but demonstrates lower minute ventilation and lower systemic levels of IL-6 compared with bacterial and culture-negative ARDS. COVID-19 ARDS was associated with longer dependence on mechanical ventilation compared with non-COVID-19 ARDS. Such detectable differences of COVID-19 do not merit deviation from evidence-based management of ARDS but suggest priorities for clinical research to better characterize and treat this new clinical entity.

Prevalence of intratumoral regulatory T cells expressing neuropilin-1 is associated with poorer outcomes in patients with cancer.

Despite the success of immune checkpoint blockade therapy, few strategies sufficiently overcome immunosuppression within the tumor microenvironment (TME). Targeting regulatory T cells (Tregs) is challenging, because perturbing intratumoral Treg function must be specific enough to avoid systemic inflammatory side effects. Thus, no Treg-targeted agents have proven both safe and efficacious in patients with cancer. Neuropilin-1 (NRP1) is recognized for its role in supporting intratumoral Treg function while being dispensable for peripheral homeostasis. Nonetheless, little is known about the biology of human NRP1+ Tregs and the signals that regulate NRP1 expression. Here, we report that NRP1 is preferentially expressed on intratumoral Tregs across six distinct cancer types compared to healthy donor peripheral blood [peripheral blood lymphocyte (PBL)] and site-matched, noncancer tissue. Furthermore, NRP1+ Treg prevalence is associated with reduced progression-free survival in head and neck cancer. Human NRP1+ Tregs have broad activation programs and elevated suppressive function. Unlike mouse Tregs, we demonstrate that NRP1 identifies a transient activation state of human Tregs driven by continuous T cell receptor (TCR) signaling through the mitogen-activated protein kinase pathway and interleukin-2 exposure. The prevalence of NRP1+ Tregs in patient PBL correlates with the intratumoral abundance of NRP1+ Tregs and may indicate higher disease burden. These findings support further clinical evaluation of NRP1 as a suitable therapeutic target to enhance antitumor immunity by inhibiting Treg function in the TME.

People critically ill with COVID-19 exhibit peripheral immune profiles predictive of mortality and reflective of SARS-CoV-2 lung viral burden.

Despite extensive analyses, there remains an urgent need to delineate immune cell states that contribute to mortality in people critically ill with COVID-19. Here, we present high-dimensional profiling of blood and respiratory samples from people with severe COVID-19 to examine the association between cell-linked molecular features and mortality outcomes. Peripheral transcriptional profiles by single-cell RNA sequencing (RNA-seq)-based deconvolution of immune states are associated with COVID-19 mortality. Further, persistently high levels of an interferon signaling module in monocytes over time lead to subsequent concerted upregulation of inflammatory cytokines. SARS-CoV-2-infected myeloid cells in the lower respiratory tract upregulate CXCL10, leading to a higher risk of death. Our analysis suggests a pivotal role for viral-infected myeloid cells and protracted interferon signaling in severe COVID-19.

Bifurcated monocyte states are predictive of mortality in severe COVID-19.

Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 infection presents with varied clinical manifestations1, ranging from mild symptoms to acute respiratory distress syndrome (ARDS) with high mortality2,3. Despite extensive analyses, there remains an urgent need to delineate immune cell states that contribute to mortality in severe COVID-19. We performed high-dimensional cellular and molecular profiling of blood and respiratory samples from critically ill COVID-19 patients to define immune cell genomic states that are predictive of outcome in severe COVID-19 disease. Critically ill patients admitted to the intensive care unit (ICU) manifested increased frequencies of inflammatory monocytes and plasmablasts that were also associated with ARDS not due to COVID-19. Single-cell RNAseq (scRNAseq)-based deconvolution of genomic states of peripheral immune cells revealed distinct gene modules that were associated with COVID-19 outcome. Notably, monocytes exhibited bifurcated genomic states, with expression of a cytokine gene module exemplified by CCL4 (MIP-1ß) associated with survival and an interferon signaling module associated with death. These gene modules were correlated with higher levels of MIP-1ß and CXCL10 levels in plasma, respectively. Monocytes expressing genes reflective of these divergent modules were also detectable in endotracheal aspirates. Machine learning algorithms identified the distinctive monocyte modules as part of a multivariate peripheral immune system state that was predictive of COVID-19 mortality. Follow-up analysis of the monocyte modules on ICU day 5 was consistent with bifurcated states that correlated with distinct inflammatory cytokines. Our data suggests a pivotal role for monocytes and their specific inflammatory genomic states in contributing to mortality in life-threatening COVID-19 disease and may facilitate discovery of new diagnostics and therapeutics.

Immune Checkpoint Blockade in Oncogene-Driven Non-Small-Cell Lung Cancer.

Patients with oncogene-driven lung cancer have limited therapeutic options after progressing on their targeted tyrosine kinase inhibitor (TKI) therapy. Given the growing role of immune checkpoint inhibitor (ICI) therapy in the treatment of lung cancer, oncogene-driven cancer has warranted further evaluation regarding ICI therapy. However, initial ICI studies have suggested that ICI monotherapy is not only lacking in efficacy, but that it may be less tolerable in oncogene-driven non-small-cell lung cancer (NSCLC). We performed a detailed review of the literature using Pubmed, and present the current and impactful findings here. Studies evaluating the use of concurrent ICI therapy and TKI therapy have also suggested increased toxicity and lack of increased activity in these patients. Larger studies have suggested that the sequence of ICI therapy and TKI, such as utilizing ICI therapy after TKI as opposed to before TKI, may play a role in reducing toxicity (hepatotoxicity, pneumonitis); however, these studies are limited in number. Novel methods of patient selection, including low tumor mutational burden, inflamed phenotyping, and  high CD8 + tumor infiltrating lymphocytes, may aid in determining ideal patients to give ICI therapy. Novel therapeutic combinations including the addition of anti-VEGF (vascular endothelial growth factor) therapy or radiotherapy show promising findings for these patients. Given the growing unmet need for therapeutic options in patients with oncogene-driven NSCLC who have failed TKI therapy, further research is warranted.

Resistance to PD1 blockade in the absence of metalloprotease-mediated LAG3 shedding.

Mechanisms of resistance to cancer immunotherapy remain poorly understood. Lymphocyte activation gene-3 (LAG3) signaling is regulated by a disintegrin and metalloprotease domain-containing protein-10 (ADAM10)- and ADAM17-mediated cell surface shedding. Here, we show that mice expressing a metalloprotease-resistant, noncleavable LAG3 mutant (LAG3NC) are resistant to PD1 blockade and fail to mount an effective antitumor immune response. Expression of LAG3NC intrinsically perturbs CD4+ T conventional cells (Tconvs), limiting their capacity to provide CD8+ T cell help. Furthermore, the translational relevance for these observations is highlighted with an inverse correlation between high LAG3 and low ADAM10 expression on CD4+ Tconvs in the peripheral blood of patients with head and neck squamous cell carcinoma, which corresponded with poor prognosis. This correlation was also observed in a cohort of patients with skin cancers and was associated with increased disease progression after standard-of-care immunotherapy. These data suggest that subtle changes in LAG3 inhibitory receptor signaling can act as a resistance mechanism with a substantive effect on patient responsiveness to immunotherapy.

The next generation of immunotherapy: keeping lung cancer in check.

Lung cancer is the deadliest malignancy with more cancer deaths per year than the next three cancers combined. Despite remarkable advances in targeted therapy, advanced lung cancer patients have not experienced a significant improvement in mortality. Lung cancer has been shown to be immunogenic and responsive to checkpoint blockade therapy. Checkpoint signals such as CTLA-4 and PD-1/PD-L1 dampen T cell activation and allow tumors to escape the adaptive immune response. Response rates in patients with pretreated, advanced NSCLC were much higher and more durable with PD-1 blockade therapy compared to standard-of-care, cytotoxic chemotherapy. Therefore, PD-1 inhibitors such as nivolumab and pembrolizumab were rapidly approved for both squamous and nonsquamous lung cancer in the pretreated population. The advent of these new therapies have revolutionized the treatment of lung cancer; however, the majority of NSCLC patients still do not respond to PD-1/PD-L1 inhibition leaving an unmet need for a large and growing population.Immunotherapy combinations with chemotherapy, radiation therapy, or novel immunomodulatory agents are currently being examined with the hope of achieving higher response rates and improving overall survival rate. Chemotherapy and radiation therapy has been theorized to increase the release of tumor antigen leading to increased responses with immunotherapy. However, cytotoxic chemotherapy and radiation therapy may also destroy actively proliferating T cells. The correct combination and order of therapy is under investigation. The majority of patients who do respond to immunotherapy have a durable response attributed to the effect of adaptive immune system's memory. Unfortunately, some patients' tumors do progress afterward and investigation of checkpoint blockade resistance is still nascent.This review will summarize the latest efficacy and safety data for early and advanced NSCLC in both the treatment-naïve and pretreated settings. The emerging role of immunotherapy for the treatment of small cell lung cancer and malignant mesothelioma will also be discussed.

Pembrolizumab in the treatment of metastatic non-small-cell lung cancer: patient selection and perspectives.

Lung cancer is the leading killer of both men and women in the US, and the 5-year survival remains poor. However, the approval of checkpoint blockade immunotherapy has shifted the treatment paradigm and provides hope for improved survival. The ability of non-small-cell lung cancer (NSCLC) to evade the host immune system can be overcome by agents such as pembrolizumab (MK-3475/lambrolizumab), which is a monoclonal antibody targeting the programmed death 1 (PD-1) receptor. In early studies, treatment with pembrolizumab led to dramatic and durable responses in select patients (PD-L1+ tumors). This remarkable efficacy lead to approval of pembrolizumab in the second-line setting as response rates were almost doubled compared to standard of care (SOC) chemotherapy. Most recently, data in the first-line setting from the KEYNOTE-024 study have redefined the SOC therapy for a selected subset of patients. In patients with ≥50% PD-L1+ tumors, pembrolizumab had a clear progression-free survival and overall survival benefit. Toxicity was mostly immune related and similar to checkpoint blockade toxicities observed in previous studies. The initial approval and subsequent studies of pembrolizumab required and utilized a companion diagnostic test, Dako's IHC 22C3, to assess PD-L1 status of patients. The evaluation and scoring system of this assay has been used by other companies as a reference to develop their own assays, which may complicate selection of patients. Finally, the impact of pembrolizumab in NSCLC is growing as evidenced by the numerous, ongoing trials open for combinations with chemotherapy, chemoradiation, other immunotherapeutics, immunomodulators, tyrosine kinase inhibitors, PI3K inhibitors, MEK inhibitors, hypomethylating agents, and histone deacetylase inhibitors. Further studies are also evaluating pembrolizumab in small-cell lung cancer and malignant pleural mesothelioma. This explosion of studies truly conveys the lack of therapeutic answers for lung cancer patients and the promise of pembrolizumab.

A First-in-Class TWIST1 Inhibitor with Activity in Oncogene-Driven Lung Cancer.

TWIST1, an epithelial-mesenchymal transition (EMT) transcription factor, is critical for oncogene-driven non-small cell lung cancer (NSCLC) tumorigenesis. Given the potential of TWIST1 as a therapeutic target, a chemical-bioinformatic approach using connectivity mapping (CMAP) analysis was used to identify TWIST1 inhibitors. Characterization of the top ranked candidates from the unbiased screen revealed that harmine, a harmala alkaloid, inhibited multiple TWIST1 functions, including single-cell dissemination, suppression of normal branching in 3D epithelial culture, and proliferation of oncogene driver-defined NSCLC cells. Harmine treatment phenocopied genetic loss of TWIST1 by inducing oncogene-induced senescence or apoptosis. Mechanistic investigation revealed that harmine targeted the TWIST1 pathway through its promotion of TWIST1 protein degradation. As dimerization is critical for TWIST1 function and stability, the effect of harmine on specific TWIST1 dimers was examined. TWIST1 and its dimer partners, the E2A proteins, which were found to be required for TWIST1-mediated functions, regulated the stability of the other heterodimeric partner posttranslationally. Harmine preferentially promoted degradation of the TWIST1-E2A heterodimer compared with the TWIST-TWIST1 homodimer, and targeting the TWIST1-E2A heterodimer was required for harmine cytotoxicity. Finally, harmine had activity in both transgenic and patient-derived xenograft mouse models of KRAS-mutant NSCLC. These studies identified harmine as a first-in-class TWIST1 inhibitor with marked anti-tumor activity in oncogene-driven NSCLC including EGFR mutant, KRAS mutant and MET altered NSCLC.Implications: TWIST1 is required for oncogene-driven NSCLC tumorigenesis and EMT; thus, harmine and its analogues/derivatives represent a novel therapeutic strategy to treat oncogene-driven NSCLC as well as other solid tumor malignancies. Mol Cancer Res; 15(12); 1764-76. ©2017 AACR.