Contemporary nuclear medicine imaging of neuroendocrine tumours

Neuroendocrine tumours (NETs) are rare, heterogeneous, and often hormonally active neoplasms. Nuclear medicine (NM) imaging using single photon- and positron-emitting radiopharmaceuticals allows sensitive and highly specific molecular imaging of NETs, complementary to anatomy-based techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI). Somatostatin-receptor scintigraphy is a whole-body imaging technique widely used for diagnosis, staging and restaging of NETs. The increasing availability of hybrid single-photon emission CT (SPECT)/CT cameras now offers superior accuracy for localization and functional characterization of NETs compared to traditional planar and SPECT imaging. The potential role of positron-emission tomography (PET) tracers in the functional imaging of NETs is also being increasingly recognized. In addition to 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG), newer positron-emitting radiopharmaceuticals such as (18)F-dihydroxyphenylalanine (DOPA) and (68)Ga-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) peptides, show promise for the future. This article will summarize the role of current and emerging radiopharmaceuticals in NM imaging of this rare but important group of tumours.

A capillary electrophoresis sequencing method for the identification of mutations in the inverted terminal repeats of adeno-associated virus

Inverted terminal repeat (ITR) integrity is critical for the replication, packaging, and transduction of recombinant adeno-associated virus (rAAV), a promising gene therapy vector. Because AAV ITRs possess 70% GC content and are palindromic, they are notoriously difficult to sequence. The purpose of this work was to develop a reliable ITR sequencing method. The ITRs of two molecular clones of AAV2, pTZAAV and pAV2, were (1) sequenced directly from plasmid DNA in the presence of denaturant (direct sequencing method, DSM) or (2) first amplified in a reaction in which 7-deaza-dGTP was substituted for dGTP and the resultant amplification product sequenced (amplification sequencing method, ASM). The DSM and ASM techniques yielded clear chromatograms, read through the ITR hairpin, and revealed hitherto unreported mutations in each ITR. pTZAAV and pAV2 possess identical mutations at the upstream MscI site of the 5' ITR (T>G, nt 2) and the downstream MscI site of the 3' ITR (del. nt 4672-4679). The chromatograms for pAV2 also revealed that the ITRs of this construct were arranged in a FLOP/FLOP orientation. In addition, the DSM was successfully employed to recover ITR-chromosomal junction sequences from a variety of rAAV-transduced tissue types. Both the DSM and ASM can be employed to sequence through the AAV ITR hairpin, and both techniques reliably detect mutations in the ITR. Because the DSM and ASM offer a way to verify ITR integrity, they constitute powerful tools for the process development of rAAV gene therapy.

Combined EGFR/MET or EGFR/HSP90 inhibition is effective in the treatment of lung cancers codriven by mutant EGFR containing T790M and MET

Tyrosine kinase inhibitors (TKI) that target the EGF receptor (EGFR) are effective in most non-small cell lung carcinoma (NSCLC) patients whose tumors harbor activating EGFR kinase domain mutations. Unfortunately, acquired resistance eventually emerges in these chronically treated cancers. Two of the most common mechanisms of acquired resistance to TKIs seen clinically are the acquisition of a secondary "gatekeeper" T790M EGFR mutation that increases the affinity of mutant EGFR for ATP and activation of MET to offset the loss of EGFR signaling. Although up to one-third of patient tumors resistant to reversible EGFR TKIs harbor concurrent T790M mutation and MET amplification, potential therapies for these tumors have not been modeled in vivo. In this study, we developed a preclinical platform to evaluate potential therapies by generating transgenic mouse lung cancer models expressing EGFR-mutant Del19-T790M or L858R-T790M, each with concurrent MET overexpression. We found that monotherapy targeting EGFR or MET alone did not produce significant tumor regression. In contrast, combination therapies targeting EGFR and MET simultaneously were highly efficacious against EGFR TKI-resistant tumors codriven by Del19-T790M or L858R-T790M and MET. Our findings therefore provide an in vivo model of intrinsic resistance to reversible TKIs and offer preclinical proof-of-principle that combination targeting of EGFR and MET may benefit patients with NSCLC.

Abstract 2016: A subset of small cell lung cancer (SCLC) cell lines is Mcl-1-dependent and responds to cyclin-dependent kinase (cdk)9 inhibition in vitro and in vivo

Small cell lung cancer (SCLC) accounts for approximately 13% of lung cancer cases, and current treatment options are limited to radiation and/or chemotherapy, which frequently lead to drug resistance. Recently, multiple SCLC cell lines have been found to be responsive to the Bcl-2/Bcl-xL inhibitor, ABT-737, both in vitro and in vivo. Clinical trials of the related orally-bioavailable compound ABT-263 have shown promising activity in SCLC patients. However, a subset of SCLC cell lines that express Mcl-1, another anti-apoptotic protein, are resistant to ABT-737. Therefore, drugs targeting Mcl-1 may be particularly useful in this disease. Here, we have investigated dependence of a panel of SCLC cell lines on Mcl-1 for survival. A subset of Mcl-1-expressing SCLC cell lines, including NCI-H82, NCI-N417 and SHP-77, demonstrate apoptosis upon Mcl-1 knockdown. However, other SCLC cell lines, including NCI-H69, NCI-H196 and SW1271, are not responsive to Mcl-1 knockdown. In addition, the dependence of SCLC cell lines on Mcl-1 for survival can be predicted by BH3 profiling, a methodology that measures dependence of a cell on a variety of anti-apoptotic proteins. We have also investigated the efficacy of Flavopiridol, a potent inhibitor of the transcriptional cyclin-dependent kinase (cdk)9, against the panel of SCLC cell lines. Flavopiridol acutely down-regulates Mcl-1 expression in all SCLC cell lines tested; however, only Mcl-1-dependent cells, including NCI-H82, NCI-N417 and SHP-77, undergo abrupt apoptosis. In contrast, cells that were not found to be Mcl-1 dependent are not effectively killed by Flavopiridol. We have further investigated the activity of Flavopiridol against Mcl-1-dependent SCLC in vivo utilizing nude mice bearing NCI-H82 xenografts. Flavopiridol treatment results in substantial tumor growth inhibition in this aggressive and chemotherapy-refractory model. To potentially stratify patients who would be predicted to be responsive to Flavopiridol treatment, we have performed MCL-1 gene fluorescence in situ hybridization in SCLC cell lines and deidentified patient specimens. MCL-1 gene copy number gains exist in both patient and cell line samples, and copy number gain of MCL-1 or MYC in cell lines correlates with Mcl-1 dependence. Strategies for targeting MCL-1 and MYC copy number gains will be discussed further. Finally, we have demonstrated that the combination of Flavopiridol and ABT-737 significantly reduces viability in Mcl-1-independent SW1271 cells compared to treatment with either drug alone. Taken together, our studies suggest that Flavopiridol-mediated cdk9 inhibition may effectively target Mcl-1-dependent SCLCs, including those resistant to Bcl-2/Bcl-xL inhibition.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2016. doi:1538-7445.AM2012-2016

Metformin prevents liver tumorigenesis by inhibiting pathways driving hepatic lipogenesis

A number of factors have been identified that increase the risk of hepatocellular carcinoma (HCC). Recently it has become appreciated that type II diabetes increases the risk of developing HCC. This represents a patient population that can be identified and targeted for cancer prevention. The biguanide metformin is a first-line therapy for the treatment of type II diabetes in which it exerts its effects primarily on the liver. A role of metformin in HCC is suggested by studies linking metformin intake for control of diabetes with a reduced risk of HCC. Although a number of preclinical studies show the anticancer properties of metformin in a number of tissues, no studies have directly examined the effect of metformin on preventing carcinogenesis in the liver, one of its main sites of action. We show in these studies that metformin protected mice against chemically induced liver tumors. Interestingly, metformin did not increase AMPK activation, often shown to be a metformin target. Rather metformin decreased the expression of several lipogenic enzymes and lipogenesis. In addition, restoring lipogenic gene expression by ectopic expression of the lipogenic transcription factor SREBP1c rescues metformin-mediated growth inhibition. This mechanism of action suggests that metformin may also be useful for patients with other disorders associated with HCC in which increased lipid synthesis is observed. As a whole these studies show that metformin prevents HCC and that metformin should be evaluated as a preventive agent for HCC in readily identifiable at-risk patients.

Metformin prevents liver tumorigenesis by inhibiting pathways driving hepatic lipogenesis

A number of factors have been identified that increase the risk of hepatocellular carcinoma (HCC). Recently it has become appreciated that type II diabetes increases the risk of developing HCC. This represents a patient population that can be identified and targeted for cancer prevention. The biguanide metformin is a first-line therapy for the treatment of type II diabetes in which it exerts its effects primarily on the liver. A role of metformin in HCC is suggested by studies linking metformin intake for control of diabetes with a reduced risk of HCC. Although a number of preclinical studies show the anticancer properties of metformin in a number of tissues, no studies have directly examined the effect of metformin on preventing carcinogenesis in the liver, one of its main sites of action. We show in these studies that metformin protected mice against chemically induced liver tumors. Interestingly, metformin did not increase AMPK activation, often shown to be a metformin target. Rather metformin decreased the expression of several lipogenic enzymes and lipogenesis. In addition, restoring lipogenic gene expression by ectopic expression of the lipogenic transcription factor SREBP1c rescues metformin-mediated growth inhibition. This mechanism of action suggests that metformin may also be useful for patients with other disorders associated with HCC in which increased lipid synthesis is observed. As a whole these studies show that metformin prevents HCC and that metformin should be evaluated as a preventive agent for HCC in readily identifiable at-risk patients.

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.

Multiple roles of cyclin-dependent kinase 4/6 inhibitors in cancer therapy

BACKGROUND

Cyclin-dependent kinases (CDKs) regulate cell proliferation and coordinate the cell cycle checkpoint response to DNA damage. Although inhibitors with varying selectivity to specific CDK family members have been developed, selective CDK4/6 inhibitors have emerged as the most attractive antineoplastic agents because of the importance of CDK4/6 activity in regulating cell proliferation and the toxic effects associated with inhibition of other CDKs (eg, CDK1 and CDK2).

METHODS

FVB/N wild-type mice (n = 13) were used to evaluate carboplatin-induced myelosuppression in bone marrow by complete blood cell counts after treatment with the CDK4/6 inhibitor PD0332991. Genetically engineered murine models of retinoblastoma (Rb)-competent (MMTV-c-neu) and Rb-incompetent (C3-TAg) breast cancer (n = 16 MMTV-c-neu mice in the carboplatin plus vehicle control group, n = 17 MMTV-c-neu mice in the carboplatin plus PD0332991 group, n = 17 C3-TAg mice in the carboplatin plus vehicle control group, and n = 14 C3-TAg mice in the carboplatin plus PD0332991 group) were used to investigate the antitumor activity of PD0332991 alone or in combination with chemotherapy. All statistical tests were two-sided.

RESULTS

Coadministration of PD0332991 with carboplatin compared with carboplatin alone in FVB/N wild-type mice increased hematocrit (51.2% vs 33.5%, difference = 17.7%, 95% confidence interval [CI] = -26.7% to -8.6%, P < .001), platelet counts (1321 vs 758.5 thousand cells per μL, difference = 562.5 thousand cells per μL, 95% CI = -902.8 to -222.6, P = .002), myeloid cells (granulocytes and monocytes; 3.1 vs 1.6 thousand cells per μL, difference = 1.5 thousand cells per μL, 95% CI = -2.23 to -0.67, P < .001), and lymphocytes (7.9 vs 5.4 thousand cells per μL, difference = 2.5 thousand cells per μL, 95% CI = -4.75 to -0.18, P = .02). Daily administration of PD0332991 exhibited antitumor activity in MMTV-c-neu mice as a single agent. However, the combination of carboplatin plus PD0332991 decreased antitumor activity compared with carboplatin alone in Rb-competent mice (mean percent change in tumor volume at day 21 = -52.6% vs 3.7% for carboplatin and carboplatin plus PD0332991, respectively, difference = 56.3%, 95% CI = -109.0% to -3.6%, P = .04). In contrast, Rb-deficient tumors in C3-Tag mice were resistant to PD0332991, and coadministration of PD0332991 plus carboplatin had no effect on in vivo tumor growth (mean percent change in tumor volume at day 21 = 118.8% and 109.1% for carboplatin and carboplatin plus PD0332991, respectively, difference = 9.7%, 95% CI = -183.5% to 202.9%, P = .92). Finally, in tumor-bearing mice, coadministration of PD0332991 with carboplatin provided statistically significant protection of platelets (P = .04).

CONCLUSION

We believe that the present data support a possible role for CDK4/6 inhibitors in a majority of patients with advanced cancer: to either inhibit tumor growth in CDK4/6-dependent tumors or ameliorate the dose-limiting toxicities of chemotherapy in CDK4/6-indepdendent tumors. Our data also suggest CDK4/6 inhibitors should not be combined with DNA-damaging therapies, such as carboplatin, to treat tumors that require CDK4/6 activity for proliferation.

Receptor tyrosine kinases exert dominant control over PI3K signaling in human KRAS mutant colorectal cancers

Therapies inhibiting receptor tyrosine kinases (RTKs) are effective against some human cancers when they lead to simultaneous downregulation of PI3K/AKT and MEK/ERK signaling. However, mutant KRAS has the capacity to directly activate ERK and PI3K signaling, and this is thought to underlie the resistance of KRAS mutant cancers to RTK inhibitors. Here, we have elucidated the molecular regulation of both the PI3K/AKT and MEK/ERK signaling pathways in KRAS mutant colorectal cancer cells and identified combination therapies that lead to robust cancer cell apoptosis. KRAS knockdown using shRNA suppressed ERK signaling in all of the human KRAS mutant colorectal cancer cell lines examined. However, no decrease, and actually a modest increase, in AKT phosphorylation was often seen. By performing PI3K immunoprecipitations, we determined that RTKs, often IGF-IR, regulated PI3K signaling in the KRAS mutant cell lines. This conclusion was also supported by the observation that specific RTK inhibition led to marked suppression of PI3K signaling and biochemical assessment of patient specimens. Interestingly, combination of RTK and MEK inhibitors led to concomitant inhibition of PI3K and MEK signaling, marked growth suppression, and robust apoptosis of human KRAS mutant colorectal cancer cell lines in vitro and upon xenografting in mice. These findings provide a framework for utilizing RTK inhibitors in the treatment of KRAS mutant colorectal cancers.

Colorectal cancer surgery of octogenarians in Hong Kong: who will survive?

OBJECTIVE. To assess the accuracy of the Association of Coloproctology of Great Britain and Ireland scoring system in predicting the 30-day mortality after surgery for colorectal cancer in Hong Kong elderly (aged 80 years or more) patients. DESIGN. Early mortality outcome audit in a historical cohort. SETTING. Queen Elizabeth Hospital, Hong Kong. PATIENTS. All Chinese patients (aged 80 years or more) who underwent elective or emergency surgery for colorectal cancer in the Department of Surgery between January 2005 and December 2009. MAIN OUTCOME MEASURES. Receiver operating characteristic curve analyses were used to estimate the predictive ability of the score. RESULTS. In all, 180 patients with colorectal cancer were included in this review. The overall 30-day and hospital mortality rates were 29/180 (16%) and 31/180 (17%), respectively. The Association of Coloproctology of Great Britain and Ireland score was significantly higher among patients who died within 30 days (4.2 vs 3.1, P=0.0001), and was the only independent predictor for 30-day mortality by logistic regression (P=0.009; odds ratio=2.555; 95% confidence interval, 1.277-4.932). The mean score of this study population was 3.22 (median, 3.10), giving a predicted 30-day mortality rate of 16.0 to 17.4%, which corresponded with an observed 30-day mortality of 16.1% encountered in this study. The score had a significantly larger area under the curve for the 30-day mortality rates (odds ratio=0.811; 95% confidence interval, 0.722-0.849) as compared to the American Society of Anesthesiologists score (0.664; 0.589-0.735) [P=0.0001]. CONCLUSION. The Association of Coloproctology of Great Britain and Ireland scoring system can accurately predict the 30-day mortality rate of elderly Hong Kong Chinese patients (aged 80 years or more) operated on for colorectal cancer.

Molecular imaging in the management of thyroid cancer

Thyroid cancer is the most common endocrine malignancy in adults. The disease is classified into papillary, follicular, medullary and anaplastic types, each with characteristic histology and patterns of biological behavior. Diagnosis of thyroid cancer is usually made by needle aspiration of suspicious thyroid nodules. Disease management of well-differentiated thyroid cancer relies upon characteristic accumulation of radioisotopes of iodine that continues to play a central role in detection and treatment of disease. Recombinant human thyrotropin (rhTSH) is used as an alternative to thyroid hormone withdrawal to provide TSH stimulation necessary for diagnostic radioiodine scintigraphy and preparation for thyroid remnant ablation and cancer therapy. Hybrid SPECT/CT cameras combining functional scintigraphic information with CT anatomy are replacing stand-alone gamma cameras and these devices have been shown to outperform traditional planar and SPECT imaging techniques. Similarly, clinical application of novel radioisotopes like [124I]iodine with PET/CT for thyroid cancer imaging provides improved lesion resolution and direct tumor dosimetry. Alternative tracers such as [18F]fluorodeoxyglucose (FDG) can be used to evaluate well-differentiated thyroid cancers that no longer express the Na+/I- symporter, with a role in staging Hürthle cell, poorly differentiated, and anaplastic thyroid cancers. Medullary thyroid cancer recurrences are often difficult to detect using conventional imaging and traditional radionuclide studies, whereas [18F]FDG and [18F]fluorodihydroxyphenylalanine (DOPA) PET and PET/CT show promise for localizing the often elusive source (s) of elevated calcitonin in these patients.

Cigarette smoking increases copy number alterations in nonsmall-cell lung cancer

Cigarette smoking has been a well-established risk factor of lung cancer for decades. How smoking contributes to tumorigenesis in the lung remains not fully understood. Here we report the results of a genome-wide study of DNA copy number and smoking pack-years in a large collection of nonsmall-cell lung cancer (NSCLC) tumors. Genome-wide analyses of DNA copy number and pack-years of cigarette smoking were performed on 264 NSCLC tumors, which were divided into discovery and validation sets. The copy number-smoking associations were investigated in three scales: whole-genome, chromosome/arm, and focal regions. We found that heavy cigarette smokers (>60 pack-years) have significantly more copy number gains than non- or light smokers (≤60 pack-years) (P = 2.46 × 10(-4)), especially in 8q and 12q. Copy number losses tend to occur away from genes in non/light smokers (P = 5.15 × 10(-5)) but not in heavy smokers (P = 0.52). Focal copy number analyses showed that there are strong associations of copy number and cigarette smoking pack-years in 12q23 (P = 9.69 × 10(-10)) where IGF1 (insulin-like growth factor 1) is located. All of the above analyses were tested in the discovery set and confirmed in the validation set. DNA double-strand break assays using human bronchial epithelial cell lines treated with cigarette smoke condensate were also performed, and indicated that cigarette smoke condensate leads to genome instability in human bronchial epithelial cells. We conclude that cigarette smoking leads to more copy number alterations, which may be mediated by the genome instability.

Lysine-specific demethylase 2B (KDM2B)-let-7-enhancer of zester homolog 2 (EZH2) pathway regulates cell cycle progression and senescence in primary cells

Sustained expression of the histone demethylase, KDM2B (Ndy1/FBXL10/JHDM1B), bypasses cellular senescence in primary mouse embryonic fibroblasts (MEFs). Here, we show that KDM2B is a conserved regulator of lifespan in multiple primary cell types and defines a program in which this chromatin-modifying enzyme counteracts the senescence-associated down-regulation of the EZH2 histone methyltransferase. Senescence in MEFs epigenetically silences KDM2B and induces the tumor suppressor miRNAs let-7b and miR-101, which target EZH2. Forced expression of KDM2B promotes immortalization by silencing these miRNAs through locus-specific histone H3 K36me2 demethylation, leading to EZH2 up-regulation. Overexpression of let-7b down-regulates EZH2, induces premature senescence, and counteracts immortalization of MEFs driven by KDM2B. The KDM2B-let-7-EZH2 pathway also contributes to the proliferation of immortal Ink4a/Arf null fibroblasts suggesting that, beyond its anti-senescence role in primary cells, this histone-modifying enzyme functions more broadly in the regulation of cellular proliferation.

Exploiting cancer cell vulnerabilities to develop a combination therapy for ras-driven tumors

Ras-driven tumors are often refractory to conventional therapies. Here we identify a promising targeted therapeutic strategy for two Ras-driven cancers: Nf1-deficient malignancies and Kras/p53 mutant lung cancer. We show that agents that enhance proteotoxic stress, including the HSP90 inhibitor IPI-504, induce tumor regression in aggressive mouse models, but only when combined with rapamycin. These agents synergize by promoting irresolvable ER stress, resulting in catastrophic ER and mitochondrial damage. This process is fueled by oxidative stress, which is caused by IPI-504-dependent production of reactive oxygen species, and the rapamycin-dependent suppression of glutathione, an important endogenous antioxidant. Notably, the mechanism by which these agents cooperate reveals a therapeutic paradigm that can be expanded to develop additional combinations.

Characterization of the cell of origin for small cell lung cancer

Small cell lung carcinoma (SCLC) is a neuroendocrine subtype of lung cancer that affects more than 200,000 people worldwide every year with a very high mortality rate. Here, we used a mouse genetics approach to characterize the cell of origin for SCLC; in this mouse model, tumors are initiated by the deletion of the Rb and p53 tumor suppressor genes in the lung epithelium of adult mice. We found that mouse SCLCs often arise in the lung epithelium, where neuroendocrine cells are located, and that the majority of early lesions were composed of proliferating neuroendocrine cells. In addition, mice in which Rb and p53 are deleted in a variety of non-neuroendocrine lung epithelial cells did not develop SCLC. These data indicate that SCLC likely arises from neuroendocrine cells in the lung.

A novel ALK secondary mutation and EGFR signaling cause resistance to ALK kinase inhibitors

Anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors (TKI), including crizotinib, are effective treatments in preclinical models and in cancer patients with ALK-translocated cancers. However, their efficacy will ultimately be limited by the development of acquired drug resistance. Here we report two mechanisms of ALK TKI resistance identified from a crizotinib-treated non-small cell lung cancer (NSCLC) patient and in a cell line generated from the resistant tumor (DFCI076) as well as from studying a resistant version of the ALK TKI (TAE684)-sensitive H3122 cell line. The crizotinib-resistant DFCI076 cell line harbored a unique L1152R ALK secondary mutation and was also resistant to the structurally unrelated ALK TKI TAE684. Although the DFCI076 cell line was still partially dependent on ALK for survival, it also contained concurrent coactivation of epidermal growth factor receptor (EGFR) signaling. In contrast, the TAE684-resistant (TR3) H3122 cell line did not contain an ALK secondary mutation but instead harbored coactivation of EGFR signaling. Dual inhibition of both ALK and EGFR was the most effective therapeutic strategy for the DFCI076 and H3122 TR3 cell lines. We further identified a subset (3/50; 6%) of treatment naive NSCLC patients with ALK rearrangements that also had concurrent EGFR activating mutations. Our studies identify resistance mechanisms to ALK TKIs mediated by both ALK and by a bypass signaling pathway mediated by EGFR. These mechanisms can occur independently, or in the same cancer, suggesting that the combination of both ALK and EGFR inhibitors may represent an effective therapy for these subsets of NSCLC patients.

Mutations in the DDR2 kinase gene identify a novel therapeutic target in squamous cell lung cancer

While genomically targeted therapies have improved outcomes for patients with lung adenocarcinoma, little is known about the genomic alterations which drive squamous cell lung cancer. Sanger sequencing of the tyrosine kinome identified mutations in the DDR2 kinase gene in 3.8% of squamous cell lung cancers and cell lines. Squamous lung cancer cell lines harboring DDR2 mutations were selectively killed by knock-down of DDR2 by RNAi or by treatment with the multi-targeted kinase inhibitor dasatinib. Tumors established from a DDR2 mutant cell line were sensitive to dasatinib in xenograft models. Expression of mutated DDR2 led to cellular transformation which was blocked by dasatinib. A squamous cell lung cancer patient with a response to dasatinib and erlotinib treatment harbored a DDR2 kinase domain mutation. These data suggest that gain-of-function mutations in DDR2 are important oncogenic events and are amenable to therapy with dasatinib. As dasatinib is already approved for use, these findings could be rapidly translated into clinical trials.

SIGNIFICANCE

DDR2 mutations are present in 4% of lung SCCs, and DDR2 mutations are associated with sensitivity to dasatinib. These findings provide a rationale for designing clinical trials with the FDA-approved drug dasatinib in patients with lung SCCs.

A dual role for the immune response in a mouse model of inflammation-associated lung cancer

Lung cancer is the leading cause of cancer death worldwide. Both principal factors known to cause lung cancer, cigarette smoke and asbestos, induce pulmonary inflammation, and pulmonary inflammation has recently been implicated in several murine models of lung cancer. To further investigate the role of inflammation in the development of lung cancer, we generated mice with combined loss of IFN-γ and the β-common cytokines GM-CSF and IL-3. These immunodeficient mice develop chronic pulmonary inflammation and lung tumors at a high frequency. Examination of the relationship between these tumors and their inflammatory microenvironment revealed a dual role for the immune system in tumor development. The inflammatory cytokine IL-6 promoted optimal tumor growth, yet wild-type mice rejected transplanted tumors through the induction of adaptive immunity. These findings suggest a model whereby cytokine deficiency leads to oncogenic inflammation that combines with defective antitumor immunity to promote lung tumor formation, representing a unique system for studying the role of the immune system in lung tumor development.

Abstract LB-22: A subset of small cell lung cancer (SCLC) cell lines is Mcl-1-dependent and responds to cyclin-dependent kinase (cdk)9 inhibition in vitro and in vivo

Small cell lung cancer (SCLC) accounts for approximately 13% of lung cancer cases, and current treatment options are limited to radiation and/or chemotherapy, which frequently lead to drug resistance. Recently, multiple SCLC cell lines have been found to be responsive to the Bcl-2/Bcl-xL inhibitor, ABT-737, both in vitro and in vivo. Clinical trials of the related orally-bioavailable compound ABT-263 have shown promising activity in SCLC patients. However, a subset of SCLC cell lines that express Mcl-1, another anti-apoptotic protein, are resistant to ABT-737. Therefore, drugs targeting Mcl-1 may be particularly useful in this disease. Here, we have investigated dependence of a panel of SCLC cell lines on Mcl-1 for survival. A subset of Mcl-1-expressing SCLC cell lines, including NCI-H82 and SHP-77, demonstrate apoptosis upon Mcl-1 knockdown. However, other SCLC cell lines, including NCI-H69 and SW1271, are not responsive to Mcl-1 knockdown. In addition, the dependence of SCLC cell lines on Mcl-1 for survival can be predicted by BH3 profiling, a methodology that measures dependence of a cell on a variety of anti-apoptotic proteins. We have also investigated the efficacy of Flavopiridol, a potent inhibitor of the transcriptional cyclin-dependent kinase (cdk)9, against the panel of SCLC cell lines. Flavopiridol acutely down-regulates Mcl-1 expression in all cell lines tested; however, only Mcl-1-dependent cells undergo abrupt apoptosis. In contrast, cells that were not found to be Mcl-1 dependent, including H69 and SW1271 cells, are not effectively killed by Flavopiridol. We have further investigated the activity of Flavopiridol against Mcl-1-dependent SCLC in vivo utilizing nude mice bearing H82 xenografts. Flavopiridol treatment results in substantial tumor growth inhibition in this aggressive and chemotherapy-refractory model. To potentially stratify patients who would be predicted to be responsive to Flavopiridol treatment, we have performed MCL-1 fluorescent in situ hybridization in SCLC cell lines and deidentified patient specimens. MCL-1 gene copy number gains exist in both patient and cell line samples, and copy number gain in cell lines correlates with Mcl-1 dependence. Finally, we have demonstrated that the combination of Flavopiridol and ABT-737 can synergistically kill both Mcl-1-dependent and – independent SCLC cells, with significantly reduced viability in SHP-77 and SW1271 cells compared to treatment with either drug alone. Taken together, our studies suggest that Flavopiridol-mediated cdk9 inhibition may effectively target Mcl-1-dependent SCLCs, including those resistant to Bcl-2/Bcl-xL inhibition.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-22. doi:10.1158/1538-7445.AM2011-LB-22

Abstract 2417: A new mouse model for epithelial ear neoplasms based upon expression of mutant EGFRL858R/T790M

Epithelial neoplasms of the ear are rare and difficult to detect before the development of audiovestibular or facial nerve dysfunction. Complete resection is often difficult because of location and the late stage at diagnosis, so effective chemotherapy is required. No preclinical models exist for these tumors. During the generation of mice using CC10 or surfactant protein C (SP-C) promoters to drive expression of mutant EGFR (EGFRL858R/T790M) in lung tissues, we observed that no SP-C mice developed lung tumors, but approximately 30% of them developed head tilt and a circular gait by 25 wk. MRI scans showed bilateral ear tumors located in the tympanic cavity that partially invaded into temporal bone, which suggested the presence of middle ear tumors or endolymphatic sac tumors (ELSTs). Histology of the ear tumors showed well-differentiated adenocarcinomas with multiple papillary and microcystic structures. Immunohistochemical (IHC) analysis showed that the mutant EGFR was active and selectively expressed in the tumors, and that downstream components of EGFR signaling such as Akt, mTOR and ERK were activated. SP-C expression was also detected, suggesting that surfactant proteins are expressed in ear epithelium at specific times during tumor development. To determine if these tumors were addicted to EGFR signaling, EGFR-based therapies were tested in symptomatic mice. Consistent with the T790M mutation in EGFR conferring resistance to reversible EGFR tyrosine kinase inhibitors (TKI), erlotinib was ineffective. In contrast, the combination of an irreversible EGFR TKI (BIBW-2992) with an antibody against EGFR (cetuximab), or a chemically optimized analogue of BIBW-2992 (WZ4002) used alone, was highly effective. All mice treated with the combination or WZ4002 alone had normalization of gait and complete responses by MRI, suggesting that these tumors are dependent upon mutant EGFR. To assess the possible clinical relevance of this mouse model, 2 human middle ear adenocarcinomas and a human ELST were stained for active EGFR using IHC. 3/3 displayed increased EGFR activation. These studies describe a new mouse model for human epithelial ear tumors based on EGFR activation, and raise the possibility that EGFR-based therapies might have clinical efficacy in these rare neoplasms.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2417. doi:10.1158/1538-7445.AM2011-2417

Abstract 2836: Rapamycin prolongs overall survival and progression-free survival in a mouse model of lung cancer in never smokers resistant to erlotinib

Lung cancer in never smokers accounts for approximately 25,000 cases/yr in the US, and is characterized by distinct molecular alterations such as mutations in EGFR. Despite initial responses to EGFR inhibitors such as erlotinib, tumors invariably recur with selection of tumor cells that have mutations in EGFR that confer resistance. Previously we showed that rapamycin, an inhibitor of mTOR, could inhibit tobacco carcinogen-induced lung tumorigenesis. Here, we used an inducible, genetically engineered mouse model of lung cancer in never smokers resistant to erlotinib (CC10-rtTA, EGFRL858R/T790M) to test whether rapamycin could prevent lung tumorigenesis. Prior to detection of tumors, mTOR was activated in lung tissues by the mutant EGFR transgene. When given to achieve trough drug levels achievable in humans, rapamycin decreased tumor incidence by 52% compared to vehicle at 8 wk, as assessed by microCT. Rapamycin increased overall survival by more than 3 fold (HR=0.075, p&lt;0.0001), which was dependent upon continued rapamycin treatment. To extend these studies, we treated mice with a new irreversible EGFR TKI, WZ4002, and randomised them to consolidation treatment with rapamycin or vehicle. Mice treated with rapamycin had increased progression-free survival and overall survival (p = 0.014 and 0.0007, respectively). Tumors from mice that progressed on rapamycin continued to show inhibition of mTOR, with no evidence of feedback activation of Akt. In a series of 7 resected human NSCLC specimens with T790M mutations, 7/7 displayed increased mTOR activation, highlighting the potential clinical application of rapamycin as a chemopreventive agent in EGFR-driven lung cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2836. doi:10.1158/1538-7445.AM2011-2836

Abstract 956: Receptor tyrosine kinases, not KRAS, activate PI3K in KRAS mutant colorectal cancers

Introduction: Therapies inhibiting receptor tyrosine kinases (RTKs) are effective when they lead to simultaneous downregulation of phosphoinositide 3-kinase (PI3K)-AKT and mitogen-activated protein kinase (MEK)-ERK signaling. Although cetuximab has demonstrated activity in KRAS wildtype cancers, it remains unknown if RTK inhibition alone can suppress one or both of these pathways in colorectal cancers, especially in cancers with KRAS mutations.

Experimental Procedures and Results: Colorectal cancer cells were treated with gefitinib (1 μM) or Cetuximab (10 μg/mL) to compare the consequences of EGFR inhibition on downstream signaling events between KRAS wt (n=6) and mt (n=8) cell lines. In KRAS wt cancers, either cetuximab or gefitinib led to loss of ERK phosphorylation, but had only a modest effect on PI3K signaling. However, in most KRAS mutant cancers, EGFR inhibition minimally impacted ERK signaling and had neglible effects on PI3K signaling. To determine if KRAS constitutively activates ERK and PI3K signaling in KRAS mutant colorectal cancers, we utilized shRNA in eight KRAS mutant cancer cell lines and abruptly turned off KRAS expression in an vivo transgenic model. In all models, the phosphorylation of ERK was markedly decreased by KRAS knockdown, but this was not associated with downregulation of PI3K signaling. To determine how PI3K was activated in KRAS mutant cancers, we immunoprecipitated the p85 regulatory subunit and identified that IRS proteins co-precipitated with PI3K in KRAS mutant cancer. These complexes were disrupted by an IGF-IR inhibitor, NVP-AEW541, but not by gefitinib, and accordingly, NVP-AEW541 led to loss of AKT phosphorylation. Of the eight KRAS mutant cell lines, we found p85/IRS-1 or p85/IRS-2 complexes in 7 cell lines. We also observed that a monoclonal anti-IGF-IR antibody R1507 (18 mg/kg twice a week) downregulated PI3K signaling in SW837 xenografts in vivo. Biochemical assessment of patient specimens with KRAS mutations also suggested that PI3K was regulated primarily by IGF-IR. Importantly, by combining RTK inhibitors with MEK inhibitors in KRAS mutant cancers, both the PI3K and ERK pathways were concomitantly downregulated leading to marked growth suppression and robust apoptosis. Furthermore, combining R1507 (18 mg/kg twice a week) with a MEK inhibitor (AZD6244 25 mg/kg twice daily) induced marked tumor regressions of a KRAS mutant colorectal cancer in vivo.

Conclusions: In this study, we provide evidence that KRAS does not drive PI3K signaling in KRAS mutant cancers, and demonstrate that specific RTK inhibition potently suppresses PI3K signaling in vitro and in vivo. These findings provide a framework for utilizing RTK inhibitors in the treatment of KRAS mutant colorectal cancers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 956. doi:10.1158/1538-7445.AM2011-956

Abstract LB-399: Chronic inhibition of mutant EGFR in NSCLC leads to EGFR TKI resistance by TGF-β1 mediated epithelial to mesenchymal transition

In NSCLC, activating EGFR mutations underlie responsiveness of NSCLCs to reversible EGFR tyrosine kinase inhibitors (TKIs), including gefitinib and erlotinib. Despite initial responses, acquired resistance invariably develops, mediated by the emergence of the secondary T790M mutation and by focal amplification of MET, in approximately 50% and 30% of patients, respectively. The resistance mechanisms for the remaining 20% of cases remain elusive. EGFR TKI-sensitive HCC827 cells were exposed to graded concentrations of erlotinib for 6 months. Approximately 70% of the isolated clones were resistant to erlotinib and harbored MET amplification, and were sensitive to dual EGFR/MET inhibition. The remaining 30% of clones were resistant to EGFR/MET dual-inhibition and demonstrated less than 1.4-fold increase in MET copy number and no secondary T790M mutation. Interestingly, 38 plex Luminex growth factor assays revealed that the 30% of clones for which the mechanism of resistance to erlotinib is unknown secrete high levels of TGF-1. In NSCLC, TGF-β1 has been identified as a potent inducer of epithelial to mesenchymal transition (EMT). Subsequent gene expression profiles of HCC827 erlotinib-resistant clones without MET amplification and secondary EGFR T790M mutation exhibit significant enrichment of genes unique to EMT and clustered separately from gene expression profiles of clones with MET amplification. In agreement with genomic analyses, Western blots confirmed the EMT phenotype in the subset of clones. Additionally, phosphoprotein arrays of the clones demonstrated markedly decreased expression of EGFR, ERBB3, and MET receptors, while maintaining high level of PI3-K MAPK, and SRC activities. Importantly, clones from HCC827 cells with stable EGFR knockdown (HCC827shEGFR) was established and all clones displayed EMT markers, suggesting induction of the EMT phenotype is not due to off-target effects of erlotinib, but rather is primarily due to the sustained loss of EGFR signaling in HCC827 cells. Multiplex Luminex growth factor assays identified TGF-β1 as the most abundant growth factor secreted from HCC827shEGFR clones. Overexpression of mutant EGFR in HCC827shEGFR clones re-sensitized the clones to EGFR TKIs and partially reversed EMT phenotype. To test the roles of TGF-β1in the emergence of EGFR TKI resistance, HCC827 cells were cultured in the media supplemented with TGF-1 for 30 days. MTS assays revealed that HCC827 cells became insensitive to EGFR TKIs after chronic exposure to TGF-β1 for 30 days. However, subsequent removal of TGF-β1 for 30 days re-sensitizes the cells to EGFR TKIs. Consequently, it is hypothesized that sustained suppression of EGFR in HCC827 cells promotes TGF-β1 secretion and subsequent induction of EMT processes, which modulate signaling and apoptosis pathways contributing to the development of resistance to erlotinib.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-399. doi:10.1158/1538-7445.AM2011-LB-399