Activity of the Ubiquitin-activating Enzyme Inhibitor TAK-243 in Adrenocortical Carcinoma Cell Lines, Patient-derived Organoids, and Murine Xenografts

Current treatment options for metastatic adrenocortical carcinoma (ACC) have limited efficacy, despite the common use of mitotane and cytotoxic agents. This study aimed to identify novel therapeutic options for ACC. An extensive drug screen was conducted to identify compounds with potential activity against ACC cell lines. We further investigated the mechanism of action of the identified compound, TAK-243, its synergistic effects with current ACC therapeutics, and its efficacy in ACC models including patient-derived organoids and mouse xenografts. TAK-243, a clinical ubiquitin-activating enzyme (UAE) inhibitor, showed potent activity in ACC cell lines. TAK-243 inhibited protein ubiquitination in ACC cells, leading to the accumulation of free ubiquitin, activation of the unfolded protein response, and induction of apoptosis. TAK-243 was found to be effluxed out of cells by MDR1, a drug efflux pump, and did not require Schlafen 11 (SLFN11) expression for its activity. Combination of TAK-243 with current ACC therapies (e.g., mitotane, etoposide, cisplatin) produced synergistic or additive effects. In addition, TAK-243 was highly synergistic with BCL2 inhibitors (Navitoclax and Venetoclax) in preclinical ACC models including patient-derived organoids. The tumor suppressive effects of TAK-243 and its synergistic effects with Venetoclax were further confirmed in a mouse xenograft model. These findings provide preclinical evidence to support the initiation of a clinical trial of TAK-243 in patients with advanced-stage ACC. TAK-243 is a promising potential treatment option for ACC, either as monotherapy or in combination with existing therapies or BCL2 inhibitors.

SIGNIFICANCE

ACC is a rare endocrine cancer with poor prognosis and limited therapeutic options. We report that TAK-243 is active alone and in combination with currently used therapies and with BCL2 and mTOR inhibitors in ACC preclinical models. Our results suggest implementation of TAK-243 in clinical trials for patients with advanced and metastatic ACC.

The novel ATR inhibitor M1774 induces replication protein overexpression and broad synergy with DNA-targeted anticancer drugs

Ataxia Telangiectasia and Rad3-related (ATR) checkpoint kinase inhibitors are in clinical trials. Here we explored the molecular pharmacology and therapeutic combination strategies of the oral ATR inhibitor M1774 (Tuvusertib) with DNA damaging agents (DDAs). As single agent, M1774 suppressed cancer cell viability at nanomolar concentrations, showing greater activity than ceralasertib and berzosertib, but less potency than gartisertib and elimusertib in the small-cell lung cancer H146, H82, and DMS114 cell lines. M1774 also efficiently blocked the activation of the ATR-CHK1 checkpoint pathway caused by replication stress induced by TOP1 inhibitors. Combination with non-toxic dose of M1774 enhanced TOP1 inhibitor-induced cancer cell death by enabling unscheduled replication upon replicative damage, thereby increasing genome instability. Tandem mass tag (TMT)-based quantitative proteomics uncovered that M1774, in the presence of DDA, forces the expression of proteins activating replication (CDC45) and G2/M-progression (PLK1 and CCNB1). In particular, the fork protection complex proteins (TIMELESS and TIPIN) were enriched. Low dose of M1774 was found highly synergistic with a broad spectrum of clinical DDAs including TOP1 inhibitors (SN-38/irinotecan, topotecan, exatecan, and exatecan), the TOP2 inhibitor etoposide, cisplatin, the RNA polymerase II inhibitor lurbinectedin, and the PARP inhibitor talazoparib in various models including cancer cell lines, patient-derived organoids, and mouse xenograft models. Furthermore, we demonstrate that M1774 reverses chemoresistance to anticancer DDAs in cancer cells lacking SLFN11 expression, suggesting that SLFN11 can be utilized for patient selection in upcoming clinical trials.

Schlafen 11 (SLFN11) Kills Cancer Cells Undergoing Unscheduled Re-replication

Schlafen 11 (SLFN11) is an increasingly prominent predictive biomarker and a molecular sensor for a wide range of clinical drugs: topoisomerases, PARP and replication inhibitors, and platinum derivatives. To expand the spectrum of drugs and pathways targeting SLFN11, we ran a high-throughput screen with 1,978 mechanistically annotated, oncology-focused compounds in two isogenic pairs of SLFN11-proficient and -deficient cells (CCRF-CEM and K562). We identified 29 hit compounds that selectively kill SLFN11-proficient cells, including not only previously known DNA-targeting agents, but also the neddylation inhibitor pevonedistat (MLN-4924) and the DNA polymerase α inhibitor AHPN/CD437, which both induced SLFN11 chromatin recruitment. By inactivating cullin-ring E3 ligases, pevonedistat acts as an anticancer agent partly by inducing unscheduled re-replication through supraphysiologic accumulation of CDT1, an essential factor for replication initiation. Unlike the known DNA-targeting agents and AHPN/CD437 that recruit SLFN11 onto chromatin in 4 hours, pevonedistat recruited SLFN11 at late time points (24 hours). While pevonedistat induced unscheduled re-replication in SLFN11-deficient cells after 24 hours, the re-replication was largely blocked in SLFN11-proficient cells. The positive correlation between sensitivity to pevonedistat and SLFN11 expression was also observed in non-isogenic cancer cells in three independent cancer cell databases (NCI-60, CTRP: Cancer Therapeutics Response Portal and GDSC: Genomic of Drug Sensitivity in Cancer). The present study reveals that SLFN11 not only detects stressed replication but also inhibits unscheduled re-replication induced by pevonedistat, thereby enhancing its anticancer efficacy. It also suggests SLFN11 as a potential predictive biomarker for pevonedistat in ongoing and future clinical trials.

Replication-associated formation and repair of human topoisomerase IIIα cleavage complexes

Topoisomerase IIIα (TOP3A) belongs to the conserved Type IA family of DNA topoisomerases. Here we report that human TOP3A is associated with DNA replication forks and that a "self-trapping" TOP3A mutant (TOP3A-R364W) generates cellular TOP3A DNA cleavage complexes (TOP3Accs). We show that trapped TOP3Accs that interfere with replication, induce DNA damage and genome instability. To elucidate how TOP3Accs are repaired, we explored the role of Spartan (SPRTN), the metalloprotease associated with DNA replication, which digests proteins forming DNA-protein crosslinks (DPCs). We find that SPRTN-deficient cells show elevated TOP3Accs, whereas overexpression of SPRTN lowers cellular TOP3Accs. SPRTN is deubiquitinated and epistatic with TDP2 in response to TOP3Accs. In addition, we found that MRE11 can excise TOP3Accs, and that cell cycle determines the preference for the SPRTN-TDP2 vs. the ATM-MRE11 pathways, in S vs. G2, respectively. Our study highlights the prevalence of TOP3Accs repair mechanisms to ensure normal DNA replication.

TOP1-DNA Trapping by Exatecan and Combination Therapy with ATR Inhibitor

Exatecan and deruxtecan are antineoplastic camptothecin derivatives in development as tumor-targeted-delivery warheads in various formulations including peptides, liposomes, polyethylene glycol nanoparticles, and antibody-drug conjugates. Here, we report the molecular pharmacology of exatecan compared with the clinically approved topoisomerase I (TOP1) inhibitors and preclinical models for validating biomarkers and the combination of exatecan with ataxia telangiectasia and Rad3-related kinase (ATR) inhibitors. Modeling exatecan binding at the interface of a TOP1 cleavage complex suggests two novel molecular interactions with the flanking DNA base and the TOP1 residue N352, in addition to the three known interactions of camptothecins with the TOP1 residues R364, D533, and N722. Accordingly, exatecan showed much stronger TOP1 trapping, higher DNA damage, and apoptotic cell death than the classical TOP1 inhibitors used clinically. We demonstrate the value of SLFN11 expression and homologous recombination (HR) deficiency (HRD) as predictive biomarkers of response to exatecan. We also show that exatecan kills cancer cells synergistically with the clinical ATR inhibitor ceralasertib (AZD6738). To establish the translational potential of this combination, we tested CBX-12, a clinically developed pH-sensitive peptide-exatecan conjugate that selectively targets cancer cells and is currently in clinical trials. The combination of CBX-12 with ceralasertib significantly suppressed tumor growth in mouse xenografts. Collectively, our results demonstrate the potency of exatecan as a TOP1 inhibitor and its clinical potential in combination with ATR inhibitors, using SLFN11 and HRD as predictive biomarkers.

Schlafen 11 expression in human acute leukemia cells with gain-of-function mutations in the interferon-JAK signaling pathway

Schlafen11 (SLFN11) is referred to as interferon (IFN)-inducible. Based on cancer genomic databases, we identified human acute myeloid and lymphoblastic leukemia cells with gain-of-function mutations in the Janus kinase (JAK) family as exhibiting high SLFN11 expression. In these cells, the clinical JAK inhibitors cerdulatinib, ruxolitinib, and tofacitinib reduced SLFN11 expression, but IFN did not further induce SLFN11 despite phosphorylated STAT1. We provide evidence that suppression of SLFN11 by JAK inhibitors is caused by inactivation of the non-canonical IFN pathway controlled by AKT and ERK. Accordingly, the AKT and ERK inhibitors MK-2206 and SCH77284 suppressed SLFN11 expression. Both also suppressed the E26 transformation-specific (ETS)-family genes ETS-1 and FLI-1 that act as transcription factors for SLFN11. Moreover, SLFN11 expression was inhibited by the ETS inhibitor TK216. Our study reveals that SLFN11 expression is regulated via the JAK, AKT and ERK, and ETS axis. Pharmacological suppression of SLFN11 warrants future studies.

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SLFN11 expression is high in leukemia and confers response to DNA targeted agents

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SLFN11 expression is driven by the innate immune IFN-JAK signaling pathway

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Leukemia cell lines with JAK-GOF-mutations express high SLFN11 downstream from the AKT/ERK-ETS pathway

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JAK and ETS inhibitors suppress SLFN11 expression

Replication-dependent cytotoxicity and Spartan-mediated repair of trapped PARP1-DNA complexes

The antitumor activity of poly(ADP-ribose) polymerase inhibitors (PARPis) has been ascribed to PARP trapping, which consists in tight DNA-protein complexes. Here we demonstrate that the cytotoxicity of talazoparib and olaparib results from DNA replication. To elucidate the repair of PARP1-DNA complexes associated with replication in human TK6 and chicken DT40 lymphoblastoid cells, we explored the role of Spartan (SPRTN), a metalloprotease associated with DNA replication, which removes proteins forming DPCs. We find that SPRTN-deficient cells are hypersensitive to talazoparib and olaparib, but not to veliparib, a weak PARP trapper. SPRTN-deficient cells exhibit delayed clearance of trapped PARP1 and increased replication fork stalling upon talazoparib and olaparib treatment. We also show that SPRTN interacts with PARP1 and forms nuclear foci that colocalize with the replicative cell division cycle 45 protein (CDC45) in response to talazoparib. Additionally, SPRTN is deubiquitinated and epistatic with translesion synthesis (TLS) in response to talazoparib. Our results demonstrate that SPRTN is recruited to trapped PARP1 in S-phase to assist in the excision and replication bypass of PARP1-DNA complexes.

Precision Oncology with Drugs Targeting the Replication Stress, ATR, and Schlafen 11

Precision medicine aims to implement strategies based on the molecular features of tumors and optimized drug delivery to improve cancer diagnosis and treatment. DNA replication is a logical approach because it can be targeted by a broad range of anticancer drugs that are both clinically approved and in development. These drugs increase deleterious replication stress (RepStress); however, how to selectively target and identify the tumors with specific molecular characteristics are unmet clinical needs. Here, we provide background information on the molecular processes of DNA replication and its checkpoints, and discuss how to target replication, checkpoint, and repair pathways with ATR inhibitors and exploit Schlafen 11 (SLFN11) as a predictive biomarker.

Novel and Highly Potent ATR Inhibitor M4344 Kills Cancer Cells With Replication Stress, and Enhances the Chemotherapeutic Activity of Widely Used DNA Damaging Agents

Although several ATR inhibitors are in development, there are unresolved questions regarding their differential potency, molecular signatures of patients with cancer for predicting activity, and most effective therapeutic combinations. Here, we elucidate how to improve ATR-based chemotherapy with the newly developed ATR inhibitor, M4344 using in vitro and in vivo models. The potency of M4344 was compared with the clinically developed ATR inhibitors BAY1895344, berzosertib, and ceralasertib. The anticancer activity of M4344 was investigated as monotherapy and combination with clinical DNA damaging agents in multiple cancer cell lines, patient-derived tumor organoids, and mouse xenograft models. We also elucidated the anticancer mechanisms and potential biomarkers for M4344. We demonstrate that M4344 is highly potent among the clinically developed ATR inhibitors. Replication stress (RepStress) and neuroendocrine (NE) gene expression signatures are significantly associated with a response to M4344 treatment. M4344 kills cancer cells by inducing cellular catastrophe and DNA damage. M4344 is highly synergistic with a broad range of DNA-targeting anticancer agents. It significantly synergizes with topotecan and irinotecan in patient-derived tumor organoids and xenograft models. Taken together, M4344 is a promising and highly potent ATR inhibitor. It enhances the activity of clinical DNA damaging agents commonly used in cancer treatment including topoisomerase inhibitors, gemcitabine, cisplatin, and talazoparib. RepStress and NE gene expression signatures can be exploited as predictive markers for M4344.

Abstract 1055: Novel and highly potent ATR inhibitor M4344 kills cancer cells with replication stress and enhances the chemotherapeutic activity of widely used DNA damaging agents

Purpose: Although several ATR inhibitors are in development, there are unresolved questions regarding their differential potency, molecular signatures of cancer patients for predicting activity and most effective therapeutic combinations. Here, we elucidate how to improve ATR-based chemotherapy with the newly developed ATR inhibitor, M4344 using in vitro and in vivo models.

Experimental design: The potency of M4344 was compared with the clinically developed ATR inhibitors BAY1895344, berzosertib, and ceralasertib. The anticancer activity of M4344 was investigated as monotherapy and combination with clinical DNA damaging agents in multiple cancer cell lines, patient-derived tumor organoids and mouse xenograft models. We also elucidated the anticancer mechanisms and potential biomarkers for M4344.

Results: M4344 is highly potent among the clinically developed ATR inhibitors. Replication stress (RepStress) and neuroendocrine (NE) gene expression signatures are significantly associated with a response to M4344 treatment. M4344 kills cancer cells by inducing cellular catastrophe and DNA damage. M4344 is highly synergistic with a broad range of DNA-targeting anticancer agents. It significantly synergizes with topotecan and irinotecan in patient-derived tumor organoids and xenograft models.

Conclusions: M4344 is a promising and highly potent ATR inhibitor. It enhances the activity of clinical DNA damaging agents commonly used in cancer treatment including topoisomerase inhibitors, gemcitabine, cisplatin and talazoparib. RepStress and NE gene expression signatures can be exploited as predictive markers for M4344.

Citation Format: Ukhyun Jo, Ilya Senatorov, Astrid Zimmermann, Liton Kumar Saha, Yasuhisa Murai, Se Hyun Kim, Vinodh N Rajapakse, Fathi Elloumi, Nobuyuki Takahashi, Christopher Schultz, Anish Thomas, Frank Zenke, Yves Pommier. Novel and highly potent ATR inhibitor M4344 kills cancer cells with replication stress and enhances the chemotherapeutic activity of widely used DNA damaging agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1055.

SLFN11 Inactivation Induces Proteotoxic Stress and Sensitizes Cancer Cells to Ubiquitin Activating Enzyme Inhibitor TAK-243

Schlafen11 (SLFN11) inactivation occurs in approximately 50% of cancer cell lines and in a large fraction of patient tumor samples, which leads to chemoresistance. Therefore, new therapeutic approaches are needed to target SLFN11-deficient cancers. To that effect, we conducted a drug screen with the NCATS mechanistic drug library of 1,978 compounds in isogenic SLFN11-knockout (KO) and wild-type (WT) leukemia cell lines. Here we report that TAK-243, a first-in-class ubiquitin activating enzyme UBA1 inhibitor in clinical development, causes preferential cytotoxicity in SLFN11-KO cells; this effect is associated with claspin-mediated DNA replication inhibition by CHK1 independently of ATR. Additional analyses showed that SLFN11-KO cells exhibit consistently enhanced global protein ubiquitylation, endoplasmic reticulum (ER) stress, unfolded protein response (UPR), and protein aggregation. TAK-243 suppressed global protein ubiquitylation and activated the UPR transducers PERK, phosphorylated eIF2α, phosphorylated IRE1, and ATF6 more effectively in SLFN11-KO cells than in WT cells. Proteomic analysis using biotinylated mass spectrometry and RNAi screening also showed physical and functional interactions of SLFN11 with translation initiation complexes and protein folding machinery. These findings uncover a previously unknown function of SLFN11 as a regulator of protein quality control and attenuator of ER stress and UPR. Moreover, they suggest the potential value of TAK-243 in SLFN11-deficient tumors. SIGNIFICANCE: This study uncovers that SLFN11 deficiency induces proteotoxic stress and sensitizes cancer cells to TAK-243, suggesting that profiling SLFN11 status can serve as a therapeutic biomarker for cancer therapy.

DNA and RNA Cleavage Complexes and Repair Pathway for TOP3B RNA- and DNA-Protein Crosslinks

The present study demonstrates that topoisomerase 3B (TOP3B) forms both RNA and DNA cleavage complexes (TOP3Bccs) in vivo and reveals a pathway for repairing TOP3Bccs. For inducing and detecting cellular TOP3Bccs, we engineer a “self-trapping” mutant of TOP3B (R338W-TOP3B). Transfection with R338W-TOP3B induces R-loops, genomic damage, and growth defect, which highlights the importance of TOP3Bcc repair mechanisms. To determine how cells repair TOP3Bccs, we deplete tyrosyl-DNA phosphodiesterases (TDP1 and TDP2). TDP2-deficient cells show elevated TOP3Bccs both in DNA and RNA. Conversely, overexpression of TDP2 lowers cellular TOP3Bccs. Using recombinant human TDP2, we demonstrate that TDP2 can process both denatured and proteolyzed TOP3Bccs. We also show that cellular TOP3Bccs are ubiquitinated by the E3 ligase TRIM41 before undergoing proteasomal processing and excision by TDP2.

Saha et al. introduce an approach to generate and detect the catalytic intermediates of TOP3B in DNA and RNA by engineering a self-poisoning enzyme, R338W-TOP3B. They reveal the cellular consequences of abortive TOP3Bcc formation and a repair pathway involving TRIM41, the proteasome, and TDP2 for processing of TOP3Bcc.

Abstract LB-121: The novel ATR inhibitor M4344 and CHK1 inhibitor SRA737 overcome chemoresistance in SLFN11-negative cells in combination treatment with DNA-damaging agents

Precision medicine is an unmet need for DNA-damaging agents with potentially severe side effects. Loss of Schlafen 11 (SLFN11) expression is frequently detected in ~50% cancer cell lines of the NCI, the Broad Institute cancer cell line panel (CCLE), and the Genomics of Drug Sensitivity in Cancer project (GDSC). Deficiency of SLFN11 expression causes chemoresistance to a broad range of DNA-damaging agents, including topoisomerase I (TOP1) inhibitors, topoisomerase II (TOP2) inhibitors, alkylating agents, DNA synthesis inhibitors and PARP inhibitors. Moreover, gene silencing of SLFN11 is observed in small cell lung cancer patient-derived xenograft models with acquired drug resistance. To identify synthetic lethal therapeutic targets to overcome chemoresistance in SLFN11 deficient cells, we performed a genome-wide RNAi screen with the human druggable genome siRNA library by using camptothecin (CPT), a TOP1 inhibitor, in SLFN11 wild-type (WT) and knock-out (KO) prostate cancer DU145 cells. Gene Ontology analysis identified the inhibition of ATR-mediated DNA repair pathway genes (ATR, CHK1, BRCA2 and RPA1) is synergistic with CPT in SLFN11 KO cells, whereas inhibition of the RNA metabolism-related genes (POLR2, PSMD3, POLR2F and PSMD11) had higher combination effects in SLFN11 WT cells. The synergistic effects by depletion of ATR-mediated DNA repair pathway in SLFN11 KO cells were validated by additional siRNAs-mediated cell viability assays. To determine whether inhibition of ATR-mediated pathway can be applied clinically, we tested the new clinical ATR (M4344) and CHK1 (SRA737) inhibitors. Treatment with non-toxic-doses of M4344 and SRA737 reversed drug resistance of the SLFN11 KO cells to TOP1 inhibitors [CPT, and clinically used topotecan and LMP400 (indotecan)]. Additionally, the same synergistic effects by combination of the ATR/CHK1inhibitors and CPT were detected in isogenic CCRF-CEM SLFN11 WT and KO leukemic lymphoblasts cells and non-isogenic DMS114 and H446 small cell lung cancer cells. We also confirmed synergy with ATR/CHK1 inhibitors in combination of other clinical DNA-damaging agents (TOP2 inhibitor: etoposide, alkylating agent: cisplatin, and PARP inhibitor: talazoparib). Molecular changes induced by the combination treatment were examined in the cell cycle by assessing DAPI and EdU incorporation, cell death with Annexin V, and DNA damage response by confocal microscopy with M4344 and CPT. Co-treatment with ATR inhibitor and CPT resulted in G2/M arrest and apoptotic cell death, and formation of micronuclei and fragmented nuclei in SLFN11 KO cells, compared with SLFN11 WT cells. Collectively, our results provide a new therapeutic rationale for the clinical development of combination treatments of chemotherapeutic DNA-targeted agents with ATR/CHK1 inhibitors based on SLFN11 status.

Citation Format: Ukhyun Jo, Yasuhisa Murai, Junko Murai, Shar-yin N Huang, Sirisha Chakka, Lu Chen, Ken Cheng, Yves Pommier. The novel ATR inhibitor M4344 and CHK1 inhibitor SRA737 overcome chemoresistance in SLFN11-negative cells in combination treatment with DNA-damaging agents [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-121.

Conditional degradation of SDE2 by the Arg/N-End rule pathway regulates stress response at replication forks

Multiple pathways counteract DNA replication stress to prevent genomic instability and tumorigenesis. The recently identified human SDE2 is a genome surveillance protein regulated by PCNA, a DNA clamp and processivity factor at replication forks. Here, we show that SDE2 cleavage after its ubiquitin-like domain generates Lys-SDE2^Ct, the C-terminal SDE2 fragment bearing an N-terminal Lys residue. Lys-SDE2^Ct constitutes a short-lived physiological substrate of the Arg/N-end rule proteolytic pathway, in which UBR1 and UBR2 ubiquitin ligases mediate the degradation. The Arg/N-end rule and VCP/p97^UFD1-NPL4 segregase cooperate to promote phosphorylation-dependent, chromatin-associated Lys-SDE2^Ct degradation upon UVC damage. Conversely, cells expressing the degradation-refractory K78V mutant, Val-SDE2^Ct, fail to induce RPA phosphorylation and single-stranded DNA formation, leading to defects in PCNA-dependent DNA damage bypass and stalled fork recovery. Together, our study elucidates a previously unappreciated axis connecting the Arg/N-end rule and the p97-mediated proteolysis with the replication stress response, working together to preserve replication fork integrity.

A Selective FGFR inhibitor AZD4547 suppresses RANKL/M-CSF/OPG-dependent ostoclastogenesis and breast cancer growth in the metastatic bone microenvironment

Aberrant activation of fibroblast growth factor receptor (FGFR) signalling contributes to progression and metastasis of many types of cancers including breast cancer. Accordingly, FGFR targeted tyrosine kinase inhibitors (TKIs) are currently under development. However, the efficacy of FGFR TKIs in the bone microenvironment where breast cancer cells most frequently metastasize and also where FGFR is biologically active, has not been clearly investigated. We investigated the FGFR-mediated interactions among cancer and the bone microenvironment stromal cells (osteoblasts and osteoclasts), and also the effects of FGFR inhibition in bone metastasis. We showed that addition of culture supernatant from the MDA-MB-134-VI FGFR-amplified breast cancer cells-activated FGFR siganalling in osteoblasts, including increased expression of RANKL, M-CSF, and osteoprotegerin (OPG). Further in vitro analyses showed that AZD4547, an FGFR TKI currently in clinical trials for breast cancer, decreased RANKL and M-CSF, and subsequently RANKL and M-CSF-dependent osteoclastogenesis of murine bone marrow monocytes. Moreover, AZD4547 suppressed osteoclastogenesis and tumor-induced osteolysis in an orthotopic breast cancer bone metastasis mouse model using FGFR non-amplified MDA-MB-231 cells. Collectively, our results support that FGFR inhibitors inhibit the bone microenvironment stromal cells including osteoblasts and osteoclasts, and effectively suppress both tumor and stromal compartments of bone metastasis.

Prolyl isomerization of FAAP20 catalyzed by PIN1 regulates the Fanconi anemia pathway

The Fanconi Anemia (FA) pathway is a multi-step DNA repair process at stalled replication forks in response to DNA interstrand cross-links (ICLs). Pathological mutation of key FA genes leads to the inherited disorder FA, characterized by progressive bone marrow failure and cancer predisposition. The study of FA is of great importance not only to children suffering from FA but also as a model to study cancer pathogenesis in light of genome instability among the general population. FANCD2 monoubiquitination by the FA core complex is an essential gateway that connects upstream DNA damage signaling to enzymatic steps of repair. FAAP20 is a key component of the FA core complex, and regulated proteolysis of FAAP20 mediated by the ubiquitin E3 ligase SCF^FBW7 is critical for maintaining the integrity of the FA complex and FA pathway signaling. However, upstream regulatory mechanisms that govern this signaling remain unclear. Here, we show that PIN1, a phosphorylation-specific prolyl isomerase, regulates the integrity of the FA core complex, thus FA pathway activation. We demonstrate that PIN1 catalyzes cis-trans isomerization of the FAAP20 pSer48-Pro49 motif and promotes FAAP20 stability. Mechanistically, PIN1-induced conformational change of FAAP20 enhances its interaction with the PP2A phosphatase to counteract SCF^FBW7-dependent proteolytic signaling at the phosphorylated degron motif. Accordingly, PIN1 deficiency impairs FANCD2 activation and the DNA ICL repair process. Together, our study establishes PIN1-dependent prolyl isomerization as a new regulator of the FA pathway and genomic integrity.

Fanconi anemia (FA) is a devastating disease of children that leads to birth defects, bone marrow failure, and a variety of cancers early in their lives. Germ-line mutations in FA genes disrupt the DNA repair process, namely the FA pathway, resulting in genome instability and clinical features of FA patients. Thus, understanding the molecular mechanisms by which the FA pathway is regulated is critical for alleviating the burden of children suffering from FA and related cancer. A critical step in this pathway is the monoubiquitination of FANCD2 by a multi-subunit ubiquitin E3 ligase called the FA core complex, and the FAAP20 subunit is required for its functional integrity. Here, we show that proline-directed structural change of FAAP20 catalyzed by the PIN1 prolyl cis-trans isomerase is essential for the FAAP20 stability by counteracting phosphorylation-dependent proteolytic signaling of FAAP20 and thus promotes FANCD2 activation and DNA repair. Our findings reveal how PIN1-mediated phosphorylation signaling cascade and proteolysis preserves genomic integrity and how its deregulation is associated the pathogenesis of FA. Our knowledge on a new regulatory mechanism governing FA pathway activation may lead to the development of a new target for FA and FA-related malignancy.

FBW7 regulates DNA interstrand cross-link repair by modulating FAAP20 degradation

Mutations that deregulate protein degradation lead to human malignancies. The SCF ubiquitin E3 ligase complex degrades key oncogenic regulators, thereby limiting their oncogenic potential. FBW7 is a substrate recognition subunit of SCF^FBW7 and is among the most commonly mutated ubiquitin-proteasome system proteins in cancer. FBW7-mutated cancer cells display increased genome instability, but the molecular mechanism by which FBW7 preserves genome integrity remains elusive. Here, we demonstrate that SCF^FBW7 regulates the stability of FAAP20, a critical component of the Fanconi anemia (FA) DNA interstrand cross-link (ICL) repair pathway. Phosphorylation of the FAAP20 degron motif by GSK3β provides a platform for recognition and polyubiquitination of FAAP20 by FBW7, and its subsequent degradation by the proteasome. Accordingly, enhanced GSK3β-FBW7 signaling disrupts the FA pathway. In cells expressing non-phosphorylatable FAAP20 mutant, the turnover of its binding partner, FANCA, is deregulated in the chromatin during DNA ICL repair, and the FA pathway is compromised. We propose that FAAP20 degradation, which is prompted by its phosphorylation, controls the dynamics of the FA core complex required for completing DNA ICL repair. Together, this study provides insights into how FBW7-mediated proteolysis regulates genome stability and how its deregulation is associated with tumorigenesis.

Abstract 1403: PCNA-dependent cleavage and degradation of SDE2 regulates response to replication stress

Maintaining genomic integrity during DNA replication is essential for cellular survival and for preventing tumorigenesis. Proliferating cell nuclear antigen (PCNA) functions as a processivity factor for DNA replication, and posttranslational modification of PCNA plays a key role in coordinating DNA repair against replication-blocking lesions by providing a platform to recruit factors required for DNA repair and cell cycle control. Here, we identify human SDE2 as a new genome surveillance factor regulated by PCNA interaction. SDE2 contains an N-terminal ubiquitin-like (UBL) fold, which is cleaved at a diglycine motif via a PCNA-interacting peptide (PIP) box and deubiquitinating enzyme activity. The cleaved SDE2 is required for negatively regulating ultraviolet damage-inducible PCNA monoubiquitination and counteracting replication stress. The cleaved SDE2 products need to be degraded by the CRL4CDT2 ubiquitin E3 ligase in a cell cycle- and DNA damage-dependent manner, and failure to degrade SDE2 impairs S phase progression and cellular survival. Collectively, this study uncovers a new role for CRL4CDT2 in protecting genomic integrity against replication stress via regulated proteolysis of PCNA-associated SDE2 and provides insights into how an integrated UBL domain within linear polypeptide sequence controls protein stability and function. Knowledge on such mechanism will be useful to identify novel cancer therapeutic interventions exploiting deregulated ubiquitin signaling and SDE2 activities in cancer.

Citation Format: Ukhyun Jo, Winson Cai, Jingming Wang, Yoojin Kwon, Alan D. D’Andrea, Hyungjin Kim. PCNA-dependent cleavage and degradation of SDE2 regulates response to replication stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1403. doi:10.1158/1538-7445.AM2017-1403

PCNA-Dependent Cleavage and Degradation of SDE2 Regulates Response to Replication Stress

Maintaining genomic integrity during DNA replication is essential for cellular survival and for preventing tumorigenesis. Proliferating cell nuclear antigen (PCNA) functions as a processivity factor for DNA replication, and posttranslational modification of PCNA plays a key role in coordinating DNA repair against replication-blocking lesions by providing a platform to recruit factors required for DNA repair and cell cycle control. Here, we identify human SDE2 as a new genome surveillance factor regulated by PCNA interaction. SDE2 contains an N-terminal ubiquitin-like (UBL) fold, which is cleaved at a diglycine motif via a PCNA-interacting peptide (PIP) box and deubiquitinating enzyme activity. The cleaved SDE2 is required for negatively regulating ultraviolet damage-inducible PCNA monoubiquitination and counteracting replication stress. The cleaved SDE2 products need to be degraded by the CRL4^CDT2 ubiquitin E3 ligase in a cell cycle- and DNA damage-dependent manner, and failure to degrade SDE2 impairs S phase progression and cellular survival. Collectively, this study uncovers a new role for CRL4^CDT2 in protecting genomic integrity against replication stress via regulated proteolysis of PCNA-associated SDE2 and provides insights into how an integrated UBL domain within linear polypeptide sequence controls protein stability and function.

Preserving genomic integrity during DNA replication is essential for preventing tumorigenesis. The CRL4^CDT2 ubiquitin E3 ligase plays a unique role in this pathway by coupling proteolysis to interaction with the DNA replication processivity factor PCNA, in order to ensure selective elimination of key factors in cell cycle regulation. However, the mechanisms by which CRL4^CDT2 directly regulates replication-associated DNA repair remain elusive. In this work, we identify a new human protein called SDE2 that helps cells relieve replication stress and ensure completing DNA replication process, whose activity is regulated by PCNA interaction and CRL4^CDT2. We show that SDE2 is cleaved by PCNA interaction and ubiquitin signaling to generate a functional C-terminal product. The cleaved SDE2 negatively regulates PCNA monoubiquitination required for relieving replication stress. Conversely, the cleaved SDE2 fragments need to be degraded, and failure to degrade SDE2 impairs S phase progression and cellular survival. Our findings uncover the role of CRL4^CDT2-proteolytic signaling coupled to PCNA in protecting genomic integrity against replication stress. Knowledge on such mechanism will be useful to identify novel cancer therapeutic interventions exploiting deregulated ubiquitin signaling and SDE2 activities in cancer.

Caveolin-1 Modulates Docetaxel-Induced Cell Death in Breast Cancer Cell Subtypes through Different Mechanisms

Purpose

Caveolin-1 (CAV-1) expression is more associated with basal-like cancers than estrogen receptor- or ErbB-2–expressing breast cancers. However, the biological relevance of different levels of CAV-1 expression according to subtype in the epithelial compartment of breast cancer remains unclear.

Materials and Methods

We investigated whether CAV-1 functions as a tumor suppressor and/or modulator of the cytotoxic activity of docetaxel (DTX) in subtypes of breast cancer using in vitro and xenograft models.

Results

The levels of CAV-1 expression were closely associated with DTX sensitivity in triple-negative breast cancer cells. In addition, CAV-1 significantly inhibited cell proliferation and modulated DTX-induced apoptosis through cell cycle arrest in the G2/M phase. The mechanisms underlying DTX-induced apoptosis differed in breast cancers according to the levels of CAV-1 expression. DTX robustly enhanced Bcl-2 inactivation by CAV-1 in MDA-MB-231 cells, while p53-mediated cell cycle arrest by DTX was more pronounced in CAV-1–low but p53-functional MCF-7 cells. In parallel with the data from breast cancer cell lines, CAV-1–transfected MCF-7 cells showed higher efficacy of DTX treatment in a xenograft model.

Conclusion

We clearly demonstrated cooperative effects between CAV-1 and DTX in mediating apoptosis, suggesting that the levels of CAV-1 expression might be an important indicator for DTX use in breast cancer.

Exploiting the Fanconi Anemia Pathway for Targeted Anti-Cancer Therapy

Genome instability, primarily caused by faulty DNA repair mechanisms, drives tumorigenesis. Therapeutic interventions that exploit deregulated DNA repair in cancer have made considerable progress by targeting tumor-specific alterations of DNA repair factors, which either induces synthetic lethality or augments the efficacy of conventional chemotherapy and radiotherapy. The study of Fanconi anemia (FA), a rare inherited blood disorder and cancer predisposition syndrome, has been instrumental in understanding the extent to which DNA repair defects contribute to tumorigenesis. The FA pathway functions to resolve blocked replication forks in response to DNA interstrand cross-links (ICLs), and accumulating knowledge of its activation by the ubiquitin-mediated signaling pathway has provided promising therapeutic opportunities for cancer treatment. Here, we discuss recent advances in our understanding of FA pathway regulation and its potential application for designing tailored therapeutics that take advantage of deregulated DNA ICL repair in cancer.

Abstract 2763: EGFR endocytosis is a rational target in lung cancer with wild-type EGFR

Oncogenic alterations of epidermal growth factor receptor (EGFR) signaling are frequently observed in lung cancer patients with worse differentiation and poor prognosis. However, the therapeutic efficacy of EGFR-tyrosine kinase inhibitors (TKIs) is currently limited in selected patients with EGFR mutations. Therefore, in this study, we investigated the potential molecular mechanism that contributes to cell viability and the response of gefitinib, one of the EGFR-TKIs, in lung cancer models with wide-type EGFR (wtEGFR). Interestingly, we found that EGF-induced EGFR endocytosis is existed differently between gefitinib-sensitive and -insensitive lung cancer cell lines. Suppressing EGFR endocytos decreased cell viability and increased apoptotic cell death in gefitinib-insensitive lung cancer with wtEGFR in vitro and in vivo. In addition, we found that Rab25 was differentially expressed in between gefitinib-sensitive and -insensitive lung cancer cells. Rab25 knockdown caused the changed EGFR endocytosis and reverted the gefitinib response in gefitinib-sensitive lung cancer with wtEGFR in vitro and in vivo. Taken together, our findings suggest a novel insight that EGFR endocytosis is a rational therapeutic target in lung cancer with wtEGFR, in which the combined efficacy with gefitinib is expected. Furthermore, we demonstrated that Rab25 plays an important role in EGFR endocytosis and gefitinib therapy.

Citation Format: Ukhyun Jo, Kyong Hwa Park, Young Mi Whang, Jae Sook Sung, Nam Hee Won, Jong Kuk Park, Yeul Hong Kim. EGFR endocytosis is a rational target in lung cancer with wild-type EGFR. [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 2763. doi:10.1158/1538-7445.AM2014-2763

Abstract 3746: Association with the sonic hedgehog pathway between gastric cancer stem cells

Cancer stem cells (CSCs) have been hypothesized to drive the growth, metastasis and chemoresistance capacity. Activation of sonic hedgehog (SHH) signaling has been implicated in progression of variety of tumors. In this study, we investigated potentiality that activation of the SHH pathway maintained the characteristics of gastric CSCs. First, we establish spheres culture system from 5 human gastric cancer cells and identified spheres from 3 gastric CSCs (MKN45, SNU638, SNU601). Compared with parent cells, spheres had more self-renewing capacity and multipotent capacity. Gastric cancer spheres shown that increased expression of stem cell markers (Oct4 and Nanog) and decreased epithelial maker (Cytokeratin 18). However, expressions of CSCs markers (CD44, CD24, CD54 and CD133) were not significantly. Spheres showed more CSCs characteristics, such as more colony formation and more resistance to conventional chemotherapeutic drugs (5-FU, cisplatin and paclitaxel) compared to parent cells. Next, western blot showed that the expression levels of SHH related pathway (Ptch, Smo and Gli1) were significantly higher in spheres than in parent cells. Further analysis, we found that SHH pathway blocked by cyclopamine enhanced the efficacy of chemotherapeutic drugs in spheres. In the further study, we will confirm SHH dependence and in vivo xenograft study. In conclusion, our data suggest that sonic hedgehog blockade could improve the antitumor efficacy of chemotherapy of human gastric cancer. [This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. A010250)]

Citation Format: Jae Sook Sung, Jong Won Lee, Ukhyun Jo, Yeul Hong Kim. Association with the sonic hedgehog pathway between gastric cancer stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3746. doi:10.1158/1538-7445.AM2013-3746

Abstract 4458: EGFR endocytosis is associated with susceptibility to gefitinib in lung cancer cells with wild-type EGFR

Although epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) is a rational targeted drug with dramatic survival benefit in lung cancer, susceptibility to the drug is restricted in lung cancer with activating mutations of EGFR. Nevertheless, the EGFR-TKI still remains an attractive anticancer drug in lung cancer with wild-type EGFR (wtEGFR). Therefore, in this study, we aimed to investigate unknown mechanism which can contribute to response of the EGFR targeted therapy using gefitinib, a well-known EGFR-TKI, in eight lung cancer cells with wtEGFR. We first examined differential effects of gefitinib on cell survival, morphology, motility, cell cycle and EGFR signaling between the TKI-sensitive and -resistant cells. As a result, although the TKI-resistant cells did not show any changes in cell phenotype by gefitinib treatment, phosphorylation of EGF induced EGFR and downstream effectors was inhibited by the drug treatment as if those in the TKI-sensitive cells. Additionally, we found difference in cellular distribution of EGF induced EGFR after gefitinib treatment between the TKI-sensitive and -resistant cells and it was associated with EGFR endocytosis. Based on our results, we next investigated that regulation of EGFR endocytosis could affect on the response of gefitinib in lung cancer cells with wtEGFR. Inhibition of EGFR endocytosis by combination treatment with gefitinib and two endocytosis inhibitors, dynasore and dynole 34-2, led to significantly decreased cell viability in the TKI-resistant cells compared with treatment of these drugs alone. Moreover, the reduced cell survival after the combination treatment was concerned with increased apoptotic cell death, accompanying by elevated cleavage of poly ADP ribose polymerase (PARP) and decreased myeloid cell leukemia-1 (Mcl-1), X-linked inhibitor of apoptosis protein (XIAP), Survivin and Livin among anti-apoptotic proteins. In addition, we found differentially expressed Rab25, a member of the RAS superfamily of small GTPases, between the TKI-sensitive and-resistant cells through genome-wide gene expression analysis. The expression status of Rab25 was partially associated with response of gefitinib in lung cancer cells with wtEGFR. Furthermore, the silencing of Rab25 in the TKI-sensitive cells with its normal expression reversed sensitivity to gefitinib treatment. In conclusion, our results provided molecular evidences that EGFR endocytosis might contribute to cell survival and response to the EGFR-TKI as a bypass survival mechanism in lung cancer with wtEGFR. Thus, targeting EGFR endocytosis could help us to overcome therapeutic limitation of EGFR-TKI in lung cancer with wtEGFR and Rab25 expression may be an important tool for predicting efficacy of the drug treatment.

Citation Format: Ukhyun Jo, Young Mi Whang, Jae Sook Sung, Kyong Hwa Park, Seung Tae Kim, Yeul Hong Kim. EGFR endocytosis is associated with susceptibility to gefitinib in lung cancer cells with wild-type EGFR. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4458. doi:10.1158/1538-7445.AM2013-4458

Wnt5a is associated with cigarette smoke-related lung carcinogenesis via protein kinase C

Wnt5a is overexpressed during the progression of human non-small cell lung cancer. However, the roles of Wnt5a during smoking-related lung carcinogenesis have not been clearly elucidated. We investigated the associations between Wnt5a and the early development of cigarette smoke related lung cancer using human bronchial epithelial (HBE) cells (NHBE, BEAS-2B, 1799, 1198 and 1170I) at different malignant stages established by exposure to cigarette smoke condensate (CSC). Abnormal up-regulation of Wnt5a mRNA and proteins was detected in CSC-exposed transformed 1198 and tumorigenic 1170I cells as compared with other non-CSC exposed HBE cells. Tumor tissues obtained from smokers showed higher Wnt5a expressions than matched normal tissues. In non-CSC exposed 1799 cells, treatment of recombinant Wnt5a caused the activations of PKC and Akt, and the blockage of Wnt5a and PKC significantly decreased the viabilities of CSC-transformed 1198 cells expressing high levels of Wnt5a. This reduced cell survival rate was associated with increased apoptosis via the down-regulation of Bcl2 and the induction of cleaved poly ADP-ribose polymerase. Moreover, CSC-treated 1799 cells showed induction of Wnt5a expression and enhanced colony-forming capacity. The CSC-induced colony forming efficiency was suppressed by the co-incubation with a PKC inhibitor. In conclusion, these results suggest that cigarette smoke induces Wnt5a-coupled PKC activity during lung carcinogenesis, which causes Akt activity and anti-apoptosis in lung cancer. Therefore, current study provides novel clues for the crucial role of Wnt5a in the smoking-related lung carcinogenesis.

Association between -276 C/T polymorphism of the ERBB3 gene and lung cancer risk in a Korean population

BACKGROUND/AIM

The associations between the polymorphisms in the promoter region of the V-erb-b2 erythroblastic leukemia viral oncogene homolog 3 (ERBB3) gene and lung cancer risk were investigated.

MATERIALS AND METHODS

By direct sequencing, we first found two known polymorphisms (-536 A/G and -276 C/T). Further TaqMan assays and logistic regression analyses were performed in order to characterize the association between the -276 C/T polymorphism of ERBB3 and lung cancer risk in 425 patients with lung cancer and 411 healthy controls. To examine the potential effects of the -276 C/T polymorphism on ERBB3 transcription, luciferase reporter assays were performed in non-small cell lung cancer (NSCLC) cell lines.

RESULTS

The -276 C/T polymorphism was associated with the risk of lung cancer in a recessive model of never-smokers. Interestingly, the T allele conferred significantly lower promoter activity by 32% and 33% than the C allele in H2009 and H358 cell lines.

CONCLUSION

ERBB3 promoter polymorphisms affect ERBB3 gene expression, and contribute to genetic susceptibility to lung cancer in never-smokers.

Abstract 1899: Endocytosis of EGFR and resistance to gefitinib in NSCLC cells with wild-type EGFR

Gefitinib is an oral active, selective epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) and results in clinical benefit in NSCLC patients with EGFR mutations, but objective clinical responses were hardly seen in the majority of NSCLC patients with wild-type EGFR (wtEGFR). However, approximately 10-20% patients with wtEGFR remain responsive to EGFR TKIs, implying that the existence of unexplored mechanisms contribute to susceptibility to gefitinib. Therefore, in this study, we aimed to identify potential mechanism which can predict the response of gefitinib in NSCLC with wtEGFR. Six NSCLC cells (H358, Calu-3, H1703, Calu-1, H441 and H522) with wtEGFR were selected and tested for sensitivity to gefitinib. MTT and cell counting assay revealed that H358 and Calu-3 cells were more sensitive to gefitinib than H1703, Calu-1, H441 and H522 cells. In addition, light microscopy and wound healing assay showed cell morphology change and suppression of motility by gefitinib treatment in the gefitinib-sensitive cells, but not in the gefitinib-resistant cells. Next, changes in phsosphorylation of EGFR and downstream pathway after gefitinib treatment were examined by Western blot assay in the cells with different gefitinib sensitivity. Interestingly, gefitinib inhibited EGF-induced phosphorylation of EGFR and downstream mediators (AKT and ERK) in both gefitinib-sensitive and -resistant cells. EGFR phosphorylation array confirmed decreased activation of multiple phophorylation sites of EGFR in gefitinib-resistant cells, implying that inhibition of tyrosine kinase activity might not a determinant of gefitinib sensitivity in NSCLC with wtEGFR. Since intracellular activity of EGFR has been reported to be important in cell proliferation, we examined whether intracellular distribution of EGFR after gefitinib treatment had different patterns in between gefitinib-sensitive and -resistant cells. Immunofluorescence microscopy assay revealed that EGFR was internalized from cell surface to intracellular region and then formed dot complex after EGF stimulation in both gefitinib-senstive and -resistant cells. Gefitinib treatment inhibited the EGF-induced internalization of EGFR in gefitinib-sensitive cells, but not in gefitinib-resistant cells. Further flowcytometric analysis using fluorescence labeled EGF and EGFR confirmed internalization of EGFR after genfitinib treatment in gefitinib-sensitive cells. Moreover, internalization inhibitors (dynasore and dynole 34.2) significantly decreased cell viability of gefitinib-resistant cells when combined with gefitinib. In conclusion, our results suggest that endocytosis of EGFR might be one of the contributing factors of gefitinib sensitivity in NSCLC with wtEGFR. (This study was supported by a grant of the Korea Healthcare Technology R&D Project, Ministry of Health & Welfare and family Affairs, Republic of Korea (A111218-11-GM04)).

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 1899. doi:1538-7445.AM2012-1899

A study of RET proto-oncogene polymorphisms in association with lung cancer risk in the Korean population

BACKGROUND/AIM

This study examined whether the polymorphisms at the promoter region of RET gene are associated with the risk of lung cancer in the Korean population.

PATIENTS AND METHODS

A total of 409 Korean lung cancer patients and 409 normal subjects were recruited. PCR-RFLP, SNaP Shot assay and logistic regression analyses were performed to characterize the association between polymorphisms of RET and lung cancer risk.

RESULTS

Four SNPs (-1697 C>G, -1260 C>T, -719 C>T, -527 C>A) of RET were selected for large-scale genotyping. Statistical analyses revealed that novel -1260 C > T polymorphism and haplotype 3 (-1697G, -1260T, -719C, and -719C) were associated with the risk of lung cancer; specifically, there were significant associations within subgroups of males and smokers.

CONCLUSION

These results demonstrated that this novel polymorphism of the RET gene is associated with an increased risk of lung cancer in the Korean population.

AKAP12alpha is associated with promoter methylation in lung cancer

PURPOSE

Promoter methylation is an important mechanism for silencing tumor-suppressor genes in cancer and it is a promising tool for the development of molecular biomarkers. The purpose of the present study was to investigate whether inactivation of the A Kinase Anchoring Protein 12 (AKAP12) gene is assoCiated with promoter methylation in lung cancer.

MATERIALS AND METHODS

The AKAP12 expression was examined by reverse transcription-polymerase chain reaction (RT-PCR) in ten lung cancer cell lines. The methylation status of the AKAP12alpha promoter was analyzed by performing bisulfite sequencing analysis in ten lung cancer cell lines, twenty four lung tissues and matched normal tissues.

RESULTS

The AKAP12alpha expression was reduced in 6 of 10 (60%) lung cancer cell lines, whereas the AKAP12beta expression was absent in 1 of 10 (10%) lung cancer cell lines. The AKAP12alpha expression was restored after treatment with the demethylating agent 5-aza-2'-deoxycytidine in three lung cancer cell lines. Methylation of CpG island 1 in the AKAP12alpha promoter was detected in 30% of the lung cancer cell lines, whereas methylation of CpG island 2 in the AKAP12alpha promoter was observed in the immortalized bronchial cell line and in all the lung cancer cell lines. In lung tumors, the CpG island 1 in the AKAP12alpha promoter was infrequently methylated. However, CpG island 2 in the AKAP12alpha promoter was highly methylated in lung tumors compared with the surrounding normal tissues, and this was statistically significant (p=0.0001).

CONCLUSION

Our results suggest that inactivation of the AKAP12alpha expression is assoCiated with DNA methylation of the promoter region in lung cancer, and that AKAP12alpha may play an important role in lung cancer carcinogenesis.