Abigail Altabef

Activation of the PD-1 Pathway Contributes to Immune Escape in EGFR-Driven Lung Tumors

UNLABELLED The success in lung cancer therapy with programmed death (PD)-1 blockade suggests that immune escape mechanisms contribute to lung tumor pathogenesis. We identified a correlation between EGF receptor (EGFR) pathway activation and a signature of immunosuppression manifested by upregulation of PD-1, PD-L1, CTL antigen-4 (CTLA-4), and multiple tumor-promoting inflammatory cytokines. We observed decreased CTLs and increased markers of T-cell exhaustion in mouse models of EGFR-driven lung cancer. PD-1 antibody blockade improved the survival of mice with EGFR-driven adenocarcinomas by enhancing effector T-cell function and lowering the levels of tumor-promoting cytokines. Expression of mutant EGFR in bronchial epithelial cells induced PD-L1, and PD-L1 expression was reduced by EGFR inhibitors in non-small cell lung cancer cell lines with activated EGFR. These data suggest that oncogenic EGFR signaling remodels the tumor microenvironment to trigger immune escape and mechanistically link treatment response to PD-1 inhibition. SIGNIFICANCE We show that autochthonous EGFR-driven lung tumors inhibit antitumor immunity by activating the PD-1/PD-L1 pathway to suppress T-cell function and increase levels of proinflammatory cytokines. These findings indicate that EGFR functions as an oncogene through non-cell-autonomous mechanisms and raise the possibility that other oncogenes may drive immune escape.

A murine lung cancer co-clinical trial identifies genetic modifiers of therapeutic response

Targeted therapies have demonstrated efficacy against specific subsets of molecularly defined cancers. Although most patients with lung cancer are stratified according to a single oncogenic driver, cancers harbouring identical activating genetic mutations show large variations in their responses to the same targeted therapy. The biology underlying this heterogeneity is not well understood, and the impact of co-existing genetic mutations, especially the loss of tumour suppressors, has not been fully explored. Here we use genetically engineered mouse models to conduct a ‘co-clinical’ trial that mirrors an ongoing human clinical trial in patients with KRAS-mutant lung cancers. This trial aims to determine if the MEK inhibitor selumetinib (AZD6244) increases the efficacy of docetaxel, a standard of care chemotherapy. Our studies demonstrate that concomitant loss of either p53 (also known as Tp53) or Lkb1 (also known as Stk11), two clinically relevant tumour suppressors, markedly impaired the response of Kras-mutant cancers to docetaxel monotherapy. We observed that the addition of selumetinib provided substantial benefit for mice with lung cancer caused by Kras and Kras and p53 mutations, but mice with Kras and Lkb1 mutations had primary resistance to this combination therapy. Pharmacodynamic studies, including positron-emission tomography (PET) and computed tomography (CT), identified biological markers in mice and patients that provide a rationale for the differential efficacy of these therapies in the different genotypes. These co-clinical results identify predictive genetic biomarkers that should be validated by interrogating samples from patients enrolled on the concurrent clinical trial. These studies also highlight the rationale for synchronous co-clinical trials, not only to anticipate the results of ongoing human clinical trials, but also to generate clinically relevant hypotheses that can inform the analysis and design of human studies.

Loss of Lkb1 and Pten Leads to Lung Squamous Cell Carcinoma with Elevated PD-L1 Expression

Lung squamous cell carcinoma (SCC) is a deadly disease for which current treatments are inadequate. We demonstrate that biallelic inactivation of Lkb1 and Pten in the mouse lung leads to SCC that recapitulates the histology, gene expression, and microenvironment found in human disease. Lkb1;Pten null (LP) tumors expressed the squamous markers KRT5, p63 and SOX2, and transcriptionally resembled the basal subtype of human SCC. In contrast to mouse adenocarcinomas, the LP tumors contained immune populations enriched for tumor-associated neutrophils. SCA1(+)NGFR(+) fractions were enriched for tumor-propagating cells (TPCs) that could serially transplant the disease in orthotopic assays. TPCs in the LP model and NGFR(+) cells in human SCCs highly expressed Pd-ligand-1 (PD-L1), suggesting a mechanism of immune escape for TPCs.

STK11/LKB1 Deficiency Promotes Neutrophil Recruitment and Proinflammatory Cytokine Production to Suppress T-cell Activity in the Lung Tumor Microenvironment

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 the inactivation of tumor suppressor genes, such as STK11/LKB1, exerts 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 IL6-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.

Metabolic and Functional Genomic Studies Identify Deoxythymidylate Kinase as a target in LKB1 Mutant Lung Cancer

The LKB1/STK11 tumor suppressor encodes a serine/threonine kinase, which coordinates cell growth, polarity, motility, and metabolism. In non-small cell lung carcinoma, LKB1 is somatically inactivated in 25% to 30% of cases, often concurrently with activating KRAS mutations. Here, we used an integrative approach to define novel therapeutic targets in KRAS-driven LKB1-mutant lung cancers. High-throughput RNA interference screens in lung cancer cell lines from genetically engineered mouse models driven by activated KRAS with or without coincident Lkb1 deletion led to the identification of Dtymk, encoding deoxythymidylate kinase (DTYMK), which catalyzes dTTP biosynthesis, as synthetically lethal with Lkb1 deficiency in mouse and human lung cancer lines. Global metabolite profiling showed that Lkb1-null cells had a striking decrease in multiple nucleotide metabolites as compared with the Lkb1-wild-type cells. Thus, LKB1-mutant lung cancers have deficits in nucleotide metabolism that confer hypersensitivity to DTYMK inhibition, suggesting that DTYMK is a potential therapeutic target in this aggressive subset of tumors.

Co-Clinical Trials Demonstrate Superiority of Crizotinib to Chemotherapy in ALK-Rearranged Non–Small Cell Lung Cancer and Predict Strategies to Overcome Resistance

Purpose: To extend the results of a phase III trial in patients with non–small cell lung cancer with adenocarcinomas harboring EML4-ALK fusion. Experimental Design: We conducted a co-clinical trial in a mouse model comparing the ALK inhibitor crizotinib to the standard-of-care cytotoxic agents docetaxel or pemetrexed. Results: Concordant with the clinical outcome in humans, crizotinib produced a substantially higher response rate compared with chemotherapy, associated with significantly longer progression-free survival. Overall survival was also prolonged in crizotinib- compared with chemotherapy-treated mice. Pemetrexed produced superior overall survival compared with docetaxel, suggesting that this agent may be the preferred chemotherapy in the ALK population. In addition, in the EML4-ALK–driven mouse lung adenocarcinoma model, HSP90 inhibition can overcome both primary and acquired crizotinib resistance. Furthermore, HSP90 inhibition, as well as the second-generation ALK inhibitor TAE684, demonstrated activity in newly developed lung adenocarcinoma models driven by crizotinib-insensitive EML4-ALK L1196M or F1174L. Conclusions: Our findings suggest that crizotinib is superior to standard chemotherapy in ALK inhibitor–naïve disease and support further clinical investigation of HSP90 inhibitors and second-generation ALK inhibitors in tumors with primary or acquired crizotinib resistance. Clin Cancer Res; 20(5); 1204–11. ©2013 AACR.

Kinase domain activation of FGFR2 yields high-grade lung adenocarcinoma sensitive to a pan-FGFR inhibitor in a mouse model of NSCLC

Somatic mutations in FGFR2 are present in 4% to 5% of patients diagnosed with non-small cell lung cancer (NSCLC). Amplification and mutations in FGFR genes have been identified in patients with NSCLCs, and clinical trials are testing the efficacy of anti-FGFR therapies. FGFR2 and other FGFR kinase family gene alterations have been found in both lung squamous cell carcinoma and lung adenocarcinoma, although mouse models of FGFR-driven lung cancers have not been reported. Here, we generated a genetically engineered mouse model (GEMM) of NSCLC driven by a kinase domain mutation in FGFR2. Combined with p53 ablation, primary grade 3/4 adenocarcinoma was induced in the lung epithelial compartment exhibiting locally invasive and pleiotropic tendencies largely made up of multinucleated cells. Tumors were acutely sensitive to pan-FGFR inhibition. This is the first FGFR2-driven lung cancer GEMM, which can be applied across different cancer indications in a preclinical setting.

Abstract B290: Activation of the PD-1 pathway contributes to immune escape in EGFR-driven lung tumors.

The recent clinical success of therapeutic blockade of the immune checkpoint Programmed Death (PD)-1 in advanced lung cancer patients suggests that mechanisms of immune escape may contribute to lung tumor pathogenesis. We identified a correlation between Epidermal Growth Factor Receptor (EGFR) pathway activation and a gene signature indicative of immunosuppression manifested by upregulation of PD-1, PD-L1, cytotoxic T lymphocyte antigen-4 (CTLA-4) and multiple tumor-promoting inflammatory cytokines. Accordingly, we identified a decrease in the number of cytotoxic T cells and an increase in markers of T cell exhaustion in genetically engineered mouse models (GEMMs) of EGFR-driven lung cancer. PD-1 antibody blockade significantly improved the survival of mice with EGFR-driven lung adenocarcinomas by enhancing effector T cell function and lowering the levels of tumor promoting cytokines. Expression of mutant EGFR in human bronchial epithelial cells induced PD-L1 expression, and PD-L1 expression was reduced by treatment with EGFR tyrosine kinase inhibitors (TKIs) in human non-small cell lung cancer (NSCLC) cell lines with an activated EGFR pathway. These data suggest that oncogenic EGFR signaling remodels the tumor microenvironment to trigger immune escape, in addition to established effects on cell proliferation, and mechanistically link treatment response to PD-1 inhibition. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B290. Citation Format: Esra A. Akbay, Shohei Koyama, Julian Carretero, Abigail Altabef, Jeremy Tchaicha, Camilla Christensen, Takeshi Shimamura, Lynette Sholl, Scott Rodig, Gordon Freeman, Peter Hammerman, Glenn Dranoff, Kwok-Kin Wong. Activation of the PD-1 pathway contributes to immune escape in EGFR-driven lung tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B290.

Abstract PR05: Targeting of CDK7 inhibits super-enhancer-associated oncogenic programs in MYCN-amplified tumor cells

The MYC oncoproteins are thought to stimulate tumor cell growth and proliferation through amplification of gene transcription, a mechanism that has thwarted most efforts to inhibit MYC function as potential cancer therapy. Using a novel covalent inhibitor of cyclin-dependent kinase 7 (CDK7) to disrupt the transcription of amplified MYCN in neuroblastoma cells, we demonstrate downregulation of the oncoprotein with consequent massive suppression of MYCN-driven global transcriptional amplification. This response translated to significant tumor regression in a mouse model of high-risk neuroblastoma, without the introduction of systemic toxicity. The striking treatment selectivity of MYCN-overexpressing cells correlated with preferential downregulation of super-enhancer-associated genes, including MYCN and other known oncogenic drivers in neuroblastoma. These results indicate that CDK7 inhibition, by selectively targeting the mechanisms that promote global transcriptional amplification in tumor cells, would be useful therapy for cancers that are driven by MYC or its family members. Citation Format: Edmond Chipumuro, Eugenio Marco, Camilla L. Christensen, Nicholas Kwiatkowski, Tinghu Zhang, Clark M. Hatheway, Brian J. Abraham, Bandana Sharma, Caleb Yeung, Abigail Altabef, Antonio Perez-Atayde, Kwok-Kin Wong, Guo-Cheng Yuan, Nathanael S. Gray, Richard A. Young, Rani E. George. Targeting of CDK7 inhibits super-enhancer-associated oncogenic programs in MYCN-amplified tumor cells. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr PR05.

Abstract LB-125: Selective inhibition of CDK7 targets MYCN-driven transcriptional amplification in neuroblastoma

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Oncogenic MYC family transcription factors act as universal amplifiers of the existing gene expression program in many cancer cells, thus reducing rate-limiting constraints on growth and proliferation. Amplification of the MYCN gene defines approximately 50% of high risk neuroblastomas (NB), and is associated with aggressive disease and a poor clinical outcome. Here we exploit MYCN-driven global transcriptional amplification to specifically target MYCN-deregulated NB cells by inhibiting CDK7, a cyclin-dependent kinase with major roles in transcriptional initiation (as part of the TFIIH complex) and elongation (by activating CDK9/P-TEFb). For this purpose, we chose CDK7-IN-1, a newly developed, highly selective, first-in-class covalent inhibitor of CDK7, and then determined the effects of CDK7 inhibition on MYCN expression and global transcriptional activity. NB cells expressing high levels of MYCN were 10 times more sensitive to CDK7 inhibition than normal cells or NB cells not driven by amplified MYCN. CDK7-IN-1 was more active than its reversible (non-covalent) analogue and two pan-CDK inhibitors, roscovitine and flavopiridol. Cytotoxicity in treated MYCN -amplified NB cells resulted from G2 arrest and apoptosis. We observed a dose-dependent decrease in serine 2, 5 and 7 phosphorylation of RNA Pol II C-terminal domain only in MYCN -amplified NB cells, indicating that CDK7-IN-1 selectively inhibits RNA Pol II-mediated transcriptional initiation and elongation. Growth inhibition was accompanied by downregulation of MYCN and MYCN -associated transcriptional programs. CDK7-IN-1 significantly slowed tumor growth in a xenograft model of MYCN -amplified NB (median growth, 56.8% vs. 100% for vehicle-treated mice, P <0.05; n=6 per group) with tumors showing decreased MYCN expression. Mice remained free of toxicity over 4 weeks of CDK7-IN-1 treatment, suggesting that a therapeutic window may exist for NB cells with high MYCN expression. In conclusion, we show for the first time that selective suppression of MYCN expression and MYCN -associated transcriptional activity can be achieved through CDK7 inhibition, with associated antitumor effects in high-risk NB. Thus, CDK7 inhibition warrants further attention as a potential therapeutic strategy for MYCN-deregulated NB and perhaps other MYC-driven cancers. Citation Format: Edmond Chipumuro, Eugenio Marco, Tinghu Zhang, Camilla Christensen, Nicholas Kwiatkowski, Bandana Sharma, Clark Hatheway, Abigail Altabef, Brian J. Abraham, Kwok-Kin Wong, Guo-Cheng Yuan, Richard A. Young, Nathanael S. Gray, Rani E. George. Selective inhibition of CDK7 targets MYCN-driven transcriptional amplification in neuroblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-125. doi:10.1158/1538-7445.AM2014-LB-125