Despite compelling antitumour activity of antibodies targeting the programmed death 1 (PD-1): programmed death ligand 1 (PD-L1) immune checkpoint in lung cancer, resistance to these therapies has increasingly been observed. In this study, to elucidate mechanisms of adaptive resistance, we analyse the tumour immune microenvironment in the context of anti-PD-1 therapy in two fully immunocompetent mouse models of lung adenocarcinoma. In tumours progressing following response to anti-PD-1 therapy, we observe upregulation of alternative immune checkpoints, notably T-cell immunoglobulin mucin-3 (TIM-3), in PD-1 antibody bound T cells and demonstrate a survival advantage with addition of a TIM-3 blocking antibody following failure of PD-1 blockade. Two patients who developed adaptive resistance to anti-PD-1 treatment also show a similar TIM-3 upregulation in blocking antibody-bound T cells at treatment failure. These data suggest that upregulation of TIM-3 and other immune checkpoints may be targetable biomarkers associated with adaptive resistance to PD-1 blockade.

STK11/LKB1 is among the most commonly inactivated tumor suppressors in non-small cell lung cancer (NSCLC), especially in tumors harboring KRAS mutations. Many oncogenes promote immune escape, undermining the effectiveness of immunotherapies, but it is unclear whether inactivation of tumor suppressor genes such as STK11/LKB1 exert similar effects. In this study, we investigated the consequences of STK11/LKB1 loss on the immune microenvironment in a mouse model of KRAS-driven NSCLC. Genetic ablation of STK11/LKB1 resulted in accumulation of neutrophils with T cell suppressive effects, along with a corresponding increase in the expression of T cell exhaustion markers and tumor-promoting cytokines. The number of tumor-infiltrating lymphocytes was also reduced in LKB1-deficient mouse and human tumors. Furthermore, STK11/LKB1 inactivating mutations were associated with reduced expression of PD-1 ligand PD-L1 in mouse and patient tumors as well as in tumor-derived cell lines. Consistent with these results, PD-1 targeting antibodies were ineffective against Lkb1-deficient tumors. In contrast, treating Lkb1-deficient mice with an IL-6 neutralizing antibody or a neutrophil-depleting antibody yielded therapeutic benefits associated with reduced neutrophil accumulation and proinflammatory cytokine expression. Our findings illustrate how tumor suppressor mutations can modulate the immune milieu of the tumor microenvironment, and they offer specific implications for addressing STK11/LKB1 mutated tumors with PD-1 targeting antibody therapies.

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Acquired drug resistance is a major factor limiting the effectiveness of targeted cancer therapies. Targeting tumors with kinase inhibitors induces complex adaptive programs that promote the persistence of a fraction of the original cell population, facilitating the eventual outgrowth of inhibitor-resistant tumor clones. We show that the addition of a newly identified CDK7/12 inhibitor, THZ1, to targeted therapy enhances cell killing and impedes the emergence of drug-resistant cell populations in diverse cellular and cancer models. We propose that targeted therapy induces a state of transcriptional dependency in a subpopulation of cells poised to become drug tolerant, which THZ1 can exploit by blocking dynamic transcriptional responses, promoting remodeling of enhancers and key signaling outputs required for tumor cell survival in the setting of targeted therapy. These findings suggest that the addition of THZ1 to targeted therapies is a promising broad-based strategy to hinder the emergence of drug-resistant cancer cell populations. CDK7/12 inhibition prevents active enhancer formation at genes, promoting resistance emergence in response to targeted therapy, and impedes the engagement of transcriptional programs required for tumor cell survival. CDK7/12 inhibition in combination with targeted cancer therapies may serve as a therapeutic paradigm for enhancing the effectiveness of targeted therapies. .

Small-cell lung cancer (SCLC) has the highest malignancy among all lung cancers, exhibiting aggressive growth and early metastasis to distant sites. For 30 years, treatment options for SCLC have been limited to chemotherapy, warranting the need for more effective treatments. Frequent inactivation of TP53 and RB1 as well as histone dysmodifications in SCLC suggest that transcriptional and epigenetic regulations play a major role in SCLC disease evolution. Here we performed a synthetic lethal screen using the BET inhibitor JQ1 and an shRNA library targeting 550 epigenetic genes in treatment-refractory SCLC xenograft models and identified HDAC6 as a synthetic lethal target in combination with JQ1. Combined treatment of human and mouse SCLC cell line-derived xenograft tumors with the HDAC6 inhibitor ricolinostat (ACY-1215) and JQ1 demonstrated significant inhibition of tumor growth; this effect was abolished upon depletion of NK cells, suggesting that these innate immune lymphoid cells play a role in SCLC tumor treatment response. Collectively, these findings suggest a potential new treatment for recurrent SCLC. These findings identify a novel therapeutic strategy for SCLC using a combination of HDAC6 and BET inhibitors. .