Faculty Bibliography

Non-small cell lung cancer (NSCLC) has a poor prognosis, with substantial mortality rates even among patients diagnosed with early-stage disease. There are few effective measures to block the development or progression of NSCLC. Antiangiogenic drugs represent a new class of agents targeting multiple aspects of tumor progression, including cell proliferation, invasion, migration, and outgrowth of metastatic deposits. We tested the multitargeted angiogenesis inhibitor sunitinib in a novel endogenous mouse model of NSCLC, which expresses a conditional activating mutation in Kras with or without conditional deletion of Lkb1; both alterations are frequent in human NSCLC. We showed that daily treatment with sunitinib reduced tumor size, caused tumor necrosis, blocked tumor progression, and prolonged median survival in both the metastatic (Lkb1/Kras) and nonmetastatic (Kras) mouse models; median survival was not reached in the nonmetastatic model after 1 year. However, the incidence of local and distant metastases was similar in sunitinib-treated and untreated Lkb1/Kras mice, suggesting that prolonged survival with sunitinib in these mice was due to direct effects on primary tumor growth rather than to inhibition of metastatic progression. These collective results suggest that the use of angiogenesis inhibitors in early-stage disease for prevention of tumor development and growth may have major survival benefits in the setting of NSCLC.

Somatic mutations that activate phosphoinositide 3-kinase (PI3K) have been identified in the p110-alpha catalytic subunit (encoded by PIK3CA). They are most frequently observed in two hotspots: the helical domain (E545K and E542K) and the kinase domain (H1047R). Although the p110-alpha mutants are transforming in vitro, their oncogenic potential has not been assessed in genetically engineered mouse models. Furthermore, clinical trials with PI3K inhibitors have recently been initiated, and it is unknown if their efficacy will be restricted to specific, genetically defined malignancies. In this study, we engineered a mouse model of lung adenocarcinomas initiated and maintained by expression of p110-alpha H1047R. Treatment of these tumors with NVP-BEZ235, a dual pan-PI3K and mammalian target of rapamycin (mTOR) inhibitor in clinical development, led to marked tumor regression as shown by positron emission tomography-computed tomography, magnetic resonance imaging and microscopic examination. In contrast, mouse lung cancers driven by mutant Kras did not substantially respond to single-agent NVP-BEZ235. However, when NVP-BEZ235 was combined with a mitogen-activated protein kinase kinase (MEK) inhibitor, ARRY-142886, there was marked synergy in shrinking these Kras-mutant cancers. These in vivo studies suggest that inhibitors of the PI3K-mTOR pathway may be active in cancers with PIK3CA mutations and, when combined with MEK inhibitors, may effectively treat KRAS mutated lung cancers.

PURPOSE: Current therapy for lung cancer involves multimodality therapies. However, many patients are either refractory to therapy or develop drug resistance. KRAS and epidermal growth factor receptor (EGFR) mutations represent some of the most common mutations in lung cancer, and many studies have shown the importance of these mutations in both carcinogenesis and chemoresistance. Genetically engineered murine models of mutant EGFR and KRAS have been developed that more accurately recapitulate human lung cancer. Recently, using cell-based experiments, we showed that platinum-based drugs and the antidiabetic drug rosiglitazone (PPARgamma ligand) interact synergistically to reduce cancer cell and tumor growth. Here, we directly determined the efficacy of the PPARgamma/carboplatin combination in these more relevant models of drug resistant non-small cell lung cancer. EXPERIMENTAL DESIGN: Tumorigenesis was induced by activation of either mutant KRAS or EGFR. Mice then received either rosiglitazone or carboplatin monotherapy, or a combination of both drugs. Change in tumor burden, pathology, and evidence of apoptosis and cell growth were assessed. RESULTS: Tumor burden remained unchanged or increased in the mice after monotherapy with either rosiglitazone or carboplatin. In striking contrast, we observed significant tumor shrinkage in mice treated with these drugs in combination. Immunohistochemical analyses showed that this synergy was mediated via both increased apoptosis and decreased proliferation. Importantly, this synergy between carboplatin and rosiglitazone did not increase systemic toxicity. CONCLUSIONS: These data show that the PPARgamma ligand/carboplatin combination is a new therapy worthy of clinical investigation in lung cancers, including those cancers that show primary resistance to platinum therapy or acquired resistance to targeted therapy.

The epidermal growth factor receptor (EGFR) secondary kinase domain T790M non-small cell lung cancer (NSCLC) mutation enhances receptor catalytic activity and confers resistance to the reversible tyrosine kinase inhibitors gefitinib and erlotinib. Currently, irreversible inhibitors represent the primary approach in clinical use to circumvent resistance. We show that higher concentrations of the irreversible EGFR inhibitor CL-387,785 are required to inhibit EGFR phosphorylation in T790M-expressing cells compared with EGFR mutant NSCLC cells without T790M. Additionally, CL-387,785 does not fully suppress phosphorylation of other activated receptor tyrosine kinases (RTK) in T790M-expressing cells. These deficiencies result in residual Akt and mammalian target of rapamycin (mTOR) activities. Full suppression of EGFR-mediated signaling in T790M-expressing cells requires the combination of CL-387,785 and rapamycin. In contrast, Hsp90 inhibition overcomes these limitations in vitro and depletes cells of EGFR, other RTKs, and phospho-Akt and inhibits mTOR signaling whether or not T790M is present. EGFR-T790M-expressing cells rendered resistant to CL-387,785 by a kinase switch mechanism retain sensitivity to Hsp90 inhibition. Finally, Hsp90 inhibition causes regression in murine lung adenocarcinomas driven by mutant EGFR (L858R) with or without T790M. However, efficacy in the L858R-T790M model requires a more intense treatment schedule and responses were transient. Nonetheless, these findings suggest that Hsp90 inhibitors may be effective in T790M-expressing cells and offer an alternative therapeutic strategy for this subset of lung cancers.

Endometrial cancer has been generally categorized into two broad groups of tumors, type I (TI) and type II (TII), with distinct epidemiological/clinical features and genetic alterations. Because telomere attrition appears to trigger genomic instability in certain cancers, we explored the role of telomere dysfunction in endometrial cancer by analyzing telomeres and other markers of telomere status in both tumor types. We describe a new method, telomere chromogenic in situ hybridization, which permitted us to detect cells with short telomeres relative to control (stromal) cells within the same tissue section. Using this method, we found that both types of tumor cells had short telomeres. However, only TII tumors were significantly associated with critical telomere shortening in adjacent, morphologically normal epithelium, suggesting that telomere shortening contributes to the initiation of TII but not TI tumors. To explore this hypothesis, we analyzed mice with critically short telomeres and documented distinctive endometrial lesions that histologically resembled the in situ precursor of TII serous carcinomas; these lesions have not been observed previously in TI mouse models of endometrial cancer. Based on this and previous studies, we propose a model in which telomere attrition contributes to the initiation of TII and progression of TI endometrial cancers.

Mutational activation of the gene for epidermal growth factor receptor (EGFR) is 1 of the main ways by which this receptor induces non-small cell lung cancers (NSCLC). Variant III EGFR (EGFRvIII) is a potential therapeutic target in NSCLC treatment because of the high frequency of deletion mutations in this protein. This study used noninvasive magnetic resonance imaging (MRI) to investigate the role of an EGFRvIII mutant in lung tumorigenesis and tumor maintenance as well as its response to the EGFR small molecule inhibitor erlotinib (Tarceva) on bitransgenic mice. Both spin-echo and gradient-echo sequences with and without cardiac and respiratory gating were performed to image the invasive mouse lung tumor driven by EGFRvIII mutation. Tumor volumes were measured based on 2-dimensional axial MRI; 3-dimensional rendering of the images were obtained to demonstrate the spatial location and distribution of the tumor in the lung. The MRI results indicated that the tumor driven by the EGFRvIII mutation was generated and maintained in the bitransgenic mice with the use of doxycycline. Tumor monitoring via MRI showed that Erlotinib can significantly inhibit the growth of tumor in vivo. MRI has the ability to image mouse lung tumor with different sequences focusing on tissue contrasts between tumor and surroundings. The MRI approaches in this work can be applied on other antitumor drug treatment evaluation in vivo when appropriate sequences are chosen.

Oncogenic activation of tyrosine kinases is a common mechanism of carcinogenesis and, given the druggable nature of these enzymes, an attractive target for anticancer therapy. Here, we show that somatic mutations of the fibroblast growth factor receptor 2 (FGFR2) tyrosine kinase gene, FGFR2, are present in 12% of endometrial carcinomas, with additional instances found in lung squamous cell carcinoma and cervical carcinoma. These FGFR2 mutations, many of which are identical to mutations associated with congenital craniofacial developmental disorders, are constitutively activated and oncogenic when ectopically expressed in NIH 3T3 cells. Inhibition of FGFR2 kinase activity in endometrial carcinoma cell lines bearing such FGFR2 mutations inhibits transformation and survival, implicating FGFR2 as a novel therapeutic target in endometrial carcinoma.

The epidermal growth factor receptor (EGFR) has been implicated in the pathophysiology of various cancers, including non-small cell lung cancer (NSCLC). Inhibitors targeting the tyrosine kinase domain of this receptor have been seen to elicit favourable responses in a subset of NSCLC patients. Mutational analysis of the EGFR has revealed that the response to reversible tyrosine kinase inhibitors (TKIs) is a result of the presence of activating mutations present between exons 18 and 21, most frequently the exon 19 deletion and the L858R mutations. After a prolonged treatment with reversible TKIs, patients have been seen to develop resistance that results, in part, from the presence of the secondary T790M mutation in exon 20. Preclinical data suggest that second-generation TKIs may be able to overcome T790M resistance by virtue of their irreversible mode of binding. In addition to the predominant mutations in the EGFR gene, alternative genetic changes between exons 18 and 21 have been observed. Experimental models have demonstrated that TKIs exhibit differential efficacy depending on which mutations are present. Such information may result in the design of highly specific agents that target specific mutations, which could result in more efficacious treatments.

Current mouse models of lung cancer recapitulate signature genetic lesions and some phenotypic features of human lung cancer. However, because mice have long telomeres, models to date do not recapitulate the aspects of lung carcinogenesis-telomere attrition and the genomic instability that ensues-believed to serve as key mechanisms driving lung tumor initiation and progression. To explore the contributions of telomere dysfunction to lung cancer progression, we combined a telomerase catalytic subunit (mTerc) mutation with the well-characterized K-rasG12D mouse lung cancer model. K-ras(G12D) mTerc(-/-) mice with telomere dysfunction but intact p53 exhibited increased lung epithelial apoptosis, delayed tumor formation and increased life span relative to K-ras(G12D) mTerc(+/-) mice with intact telomere function. This demonstrates that by itself, telomere dysfunction acts in a tumor-suppressive mechanism. Introduction of a heterozygous p53 mutation exerted a marked histopathological, biological and genomic impact. K-ras(G12D) mTerc(-/-) p53(+/-) mice developed aggressive tumors with more chromosomal instabilities and high metastatic potential, leading to decreased overall survival. Thus, we have generated a murine model that more faithfully recapitulates key aspects of the human disease. Furthermore, these findings clearly demonstrate (in an in vivo model system) the dual nature of telomere shortening as both a tumor-suppressive and tumor-promoting mechanism in lung cancer, dependent on p53 status.

Mutations in the LKB1 tumor suppressor gene result in the Peutz-Jeghers syndrome, an autosomal dominant condition characterized by hamartomatous polyps of the gastrointestinal tract and a dramatically increased risk of epithelial malignancies at other sites, including the female reproductive tract. Here we show that female mice heterozygous for a null Lkb1 allele spontaneously develop highly invasive endometrial adenocarcinomas. To prove that these lesions were indeed due to Lkb1 inactivation, we introduced an adenoviral Cre vector into the uterine lumen of mice harboring a conditional allele of Lkb1. This endometrial-specific deletion of the Lkb1 gene provoked highly invasive and sometimes metastatic endometrial adenocarcinomas closely resembling those observed in Lkb1 heterozygotes. Tumors were extremely well differentiated and histopathologically distinctive and exhibited alterations in AMP-dependent kinase signaling. Although Lkb1 has been implicated in the establishment of cell polarity, and loss of polarity defines most endometrial cancers, Lkb1-driven endometrial cancers paradoxically exhibit (given their highly invasive phenotype) normal cell polarity and apical differentiation. In human endometrial cancers, Lkb1 expression was inversely correlated with tumor grade and stage, arguing that Lkb1 inactivation or down-regulation also contributes to endometrial cancer progression in women. This study shows that Lkb1 plays an important role in the malignant transformation of endometrium and that Lkb1 loss promotes a highly invasive phenotype.