Citations

Abstract CD36 is an endothelial cell (EC) receptor that mediates angiostatic activity and oxidative stress, which are important in ischemic disease and tumor progression. CD36 interacts with TSR domain proteins including thrombospondin-1. This results in a signal that is likely to initiate an antiangiogenic “switch," subsequently converting a growth factor-mediated proangiogenic response to an antiangiogenic response. However, in pathologic settings including malignant tumors, robust angiogenesis occurs despite the abundance of TSR-containing proteins in the microenvironment. This suggests that there is a mechanism by which TSR-mediated antiangiogenesis could be blunted via the localized downregulation of EC CD36 transcription. We previously reported that lysophosphatidic acid (LPA), a bioactive signaling phospholipid mediator, down-regulates microvascular EC (MVEC) CD36 transcription by protein kinase PKD-1 signaling via G protein coupled receptor LPA1,3. However, further elucidating the CD36 transcriptional mechanisms is critical to understanding the antiangiogenic switch. To this end, we recently discovered that obesity-derived LPA inhibited CD36 expression in tumor-associated ECs (TAECs). Similarly, inducing the constitutively active PKD-1 or PKD-CA expression also resulted in CD36 downregulation. Mechanistically, LPA treatment led to nuclear accumulation of PKD-1, HDAC7 and FoxO1. Furthermore, LPA-mediated PKD-1 signaling enhanced FoxO1-HDAC7 interaction in the nucleus. This interaction was attenuated with PKD-1 silencing. Intriguingly, doxycycline induced PKD-CA expression increased ephrin B2 expression and ERK activation, which are two critical “molecular signatures” involved in arteriogenesis. Functionally, FGF-2 induced a potent proangiogenic response even in the presence of TSP-1 in ECs pre-treated with LPA. Doxycycline induced PKD-CA expression stimulated robust arterial EC branching in a 3D spheroid assay. This angiogenic response was inhibited by a novel PKD-1 specific inhibitor. Moreover, in a mouse Lewis lung carcinoma model, we detected a minimal level of endothelial CD36 expression with robust tumor angiogenesis. The role of PKD-1 signaling in CD36 transcriptional repression and tumor arteriogenesis is a critical yet underexplored and underappreciated field. We propose that the LPA-PKD-FoxO1 signaling axis is essential for CD36 transcriptional repression and arteriogenic signaling and responses. The PKD-1 stimulated nuclear signaling network is critical to epigenetic suppression of CD36 transcription and silencing of CD36 antiangiogenic switch, subsequently turning on the angiogenic switch and stimulating the arteriogenic responses. Targeting the LPA-PKD1-FoxO1 signaling axis could have therapeutic potential in the ischemic disease and malignant tumors. Citation Format: Jacob D. Kohlenberg, Yiliang Chen, Brad Best, Peter Storz, Randall T. Peterson, Roy Silverstein, Bin Ren. A novel LPA-PKD1-FoxO1 pathway in endothelial cells provides an angiogenic switch via down-regulation of CD36 transcription and induction of arteriogenic responses . [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 LB-338. doi:10.1158/1538-7445.AM2013-LB-338

Abstract Background: Fluoro-deoxyglucose positron emission tomography (FDG-PET) scans are used for diagnosis and staging of known or suspected non-small cell lung cancer (NSCLC). Single institution studies examining the impact of avidity on survival have reported mixed results. The purpose of this study is to evaluate the association between FDG-PET avidity and survival in the national prospective ACOSOG Z4031 trial in patients with pathological Stage I NSCLC. Methods: Between 2004 and 2006, 1074 patients with known or suspected clinical stage I (cT1-2N0M0) NSCLC were enrolled in the ACOSOG Z4031 trial and underwent surgical resection. FDG-PET results were abstracted from radiology interpretations included in the case report forms. FDG-PET avidity was categorized based on either radiologist description or reported maximum standard uptake value (SUV). The four categories were: 1) not avid and not cancerous (SUV=0), 2) low avidity and likely not cancerous (SUV>0 and <2.5), 3) avid and probably cancerous (SUV≥2.5 and <5) and 4) highly avid and likely cancerous (SUV≥5). The lesion was classified as avid if in categories 3 or 4. The final diagnosis was determined by pathological examination and all cause mortality was reported. Cox proportional hazard regression was used to assess the impact of FDG-PET avidity on survival. The covariates used in the model included pStage, gender, age, race, and preoperative lesion size. Kaplan-Meier survival curves were calculated and the log-rank test was used to determine differences in survival based on FDG-PET avidity. Results: There were 51 enrolling sites in 39 cities with 969 eligible participants. Preoperative FDG-PET results were available for 540 participants with NSCLC and 81% had FDG-PET avid or highly avid lesions. 400 patients had pStage I NSCLC and the 5 year survival was 70% with 95%CI (65%, 75%). FDG-PET avidity, male gender, age, and lesion size negatively impacted survival. FDG-PET avidity in pStage I disease still negatively impacted survival (p=0.03) when controlling for lesion size. The 5 year survival for Stage I disease was 80% with 95%CI (68%, 88%) in FDG-PET negative patients and 67% with 95% CI (61%, 72%) in FDG-PET positive patients (p=0.02). Conclusions: In a national surgical population with pathological stage I NSCLC, FDG-PET avidity negatively impacted five year survival, independently of lesion size. Further work should be done to determine if chemotherapy would be beneficial in patients with PET avid lesions and pStage I NSCLC. Citation Format: Eric L. Grogan, Stephen A. Deppen, Heidi Chen, Karla V. Ballman, Francys C. Verdial, Melinda C. Aldrich, Paul A. Decker, David H. Harpole, Robert J. Cerfolio, Robert J. Keenan, David R. Jones, Thomas A. D'Amico, Joseph B. Shrager, Bryan F. Meyers, Joe B. Putnam. FDG-PET avidity negatively impacts survival in pStage I NSCLC in the ACOSOG Z4031 trial. [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 LB-296. doi:10.1158/1538-7445.AM2013-LB-296

Abstract Janus kinase-2 (JAK2)/STAT pathway activation is commonly observed in myeloproliferative neoplasms and plays an important role in disease development and progression. The V617F activating mutation in the JAK2 pseudokinase domain is found in 95% of patients with polycythemia vera (PV) and in 50-70% of patients with primary myelofibrosis (MF) or essential thrombocythemia (ET). Studies have shown the clinical efficacy of JAK2 inhibitors in treating MF in terms of a reduction in splenomegaly and relief of constitutional symptoms. A reduction in the JAK2V617F allele burden after treatment with a JAK2-targeted agent could be a surrogate for a disease-modifying effect of this therapy. To demonstrate this, a robust method that can accurately measure the JAK2V617F allele burden is required. Here, we report the development of a sensitive quantitative PCR (qPCR) assay to determine the JAK2V617F allele burden in patients treated with SAR302503, the validation of the assay in a Phase 0 clinical study and implementation in a phase II study using samples from patients with MF. The assay demonstrated robust performance, with high sensitivity (LLOD=0.05% and LLOQ=0.5%) and accuracy. A phase 0 study in MF, PV, and ET patients showed that (1) there was minimal intra-subject sampling variability in JAK2V617F allele burden, and (2) whole-blood samples are stable for at least 48 hours at ambient conditions for DNA preparation without a significant impact on JAK2V617F allele burden measurement.Of the 31 patients with intermediate-2 or high-risk MF enrolled in a phase II clinical study (NCT01420770), baseline samples were available for 29 patients and of these, 26 were JAK2V617F-positive using this assay. Of the 19/26 patients for whom samples were available at all 3 time points, the median allele burden was 93% at baseline, 87% at the end of Cycle 3, and 78% at the end of Cycle 6. Among the 24 patients who were JAK2V617F-positive and for whom spleen measurements were available at the end of Cycle 6, a total of 15 (63%) had a spleen response (≥ 35% reduction in spleen volume by MRI versus baseline). In contrast, two JAK2V617F-negative patients did not have a spleen response. Patients with baseline allele burden levels of 0 to <25%, 25% to 75%, and ≥75% showed spleen response rates of 50%, 44%, and 69%, respectively, at the end of Cycle 6. JAK2V617F allele burden will continue to be assessed every 3 cycles. Longer follow up is needed to determine the clinical effect of allele burden reduction. Citation Format: Feng Liu, Moshe Talpaz, Animesh Pardanani, Catriona Jamieson, Nashat Gabrail, Ayalew Tefferi, Tianlei Lei, Rita Greco, Francisco Adrian, Nikki Daskalakis, Claudia Lebedinsky, Pamela Cohen, Donald Bergstrom. Determination of JAK2V617F allele burden in a phase II study of patients with myelofibrosis treated with SAR302503 using a sensitive and robust allele-specific qPCR assay. [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 LB-294. doi:10.1158/1538-7445.AM2013-LB-294

Abstract Background: Polo-like kinase 1 (PLK1) is a serine/threonine kinase that regulates multiple critical aspects of cell progression. PLK1 is over-expressed in many human tumor types and its over-expression is a negative prognostic indicator of patient outcome in a variety of cancers. TKM-080301 is a lipid nanoparticle formulation of a small interfering RNA (siRNA) directed against PLK1 that has been shown to effect highly selective reductions in PLK1 mRNA in vitro and in tumor xenograft models in mice. Methods: A phase I multi-center, open-label, non-randomized, dose-escalation study of TKM-080301 is ongoing in patients with advanced solid tumors or lymphoma. Sequential cohorts of 3 to 6 patients receive TKM-080301 as a 30-minute IV infusion on Days 1, 8, and 15 of a 28-day cycle. Primary objectives include determination of safety, maximum tolerated dose (MTD) and dose limiting toxicities (DLTs). Secondary objectives include characterization of pharmacokinetics (PK) and preliminary assessment of anti-tumor activity and pharmacodynamic effects. Pre-and post-dose biopsy samples are being collected from patients treated after DLT has been established. Results: Twenty-three (23) patients, receiving a cumulative total of 128 doses, have been treated with TKM-080301 at doses ranging from 0.15 to 0.9 mg/kg/week. The most common drug-related adverse events have been mild-to-moderate infusion related reactions with delayed onset, pyrexia, chills, nausea, vomiting, and fatigue. Mild, transient increases in certain cytokines (e.g., IL-6, IL-8, MCP-1) have been observed at dose levels ≤0.75 mg/kg/week and generally correlated with the timing of delayed infusion reactions. DLTs were observed at 0.9 mg/kg/week and included hypoxia/dyspnea in one patient (with a previous history of asthma) and thrombocytopenia in another patient. The dose level was subsequently reduced to 0.75 mg/kg/week. Pharmacokinetic parameters determined after the first dose in Cycles 1 and 2 demonstrated dose proportional Cmax and AUC and no obvious accumulation. Two patients have received TKM-080301 for at least 6 months (6 cycles) with no evidence of cumulative toxicity, including one patient with stable disease (colon) and one patient with a durable confirmed partial response (carcinoid tumor) who has received 8+ cycles of treatment. Conclusions: Preliminary results from this first-in-human trial indicate TKM-080301 was generally well-tolerated by the majority of patients. Preliminary antitumor efficacy has been observed, supporting PLK1 as a therapeutic target. As two DLTs were observed at the dose of 0.9 mg/kg/week, patient accrual is continuing at the 0.75 mg/kg/week dose level. Citation Format: Ramesh K. Ramanathan, Solomon I. Hamburg, Mitesh J. Borad, Mahesh Seetharam, Madappa N. Kundranda, Peter Lee, Paul Fredlund, Mark Gilbert, Cathy Mast, Sean C. Semple, Adam D. Judge, Brynne Crowell, Linda Vocila, Ian MacLachlan, Donald W. Northfelt. A phase I dose escalation study of TKM-080301, a RNAi therapeutic directed against PLK1, in patients with advanced solid tumors. [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 LB-289. doi:10.1158/1538-7445.AM2013-LB-289

Abstract Despite significant progress in the treatment of breast cancer particularly through the use of targeted therapy, relapse and chemo-resistance remain a major hindrance in the fight to minimize the burden of the disease. Accumulating evidence suggest that breast cancer stem cells (BCSCs), which show resistance to chemotherapy and radiation, drive tumor initiation and disease recurrence. It is becoming increasingly clear that a rare subpopulation of cells known as cancer stem cells (CSC), able to be generated through epithelial to mesenchymal transition (EMT) and capable of tumor initiation and self-renewal, contributes to treatment resistance and metastases. This means that a more effective therapy should target both the chemoresistant CSCs and the proliferating epithelial cells that give rise to them in order to reverse EMT and attenuate their conversion to CSCs. Here, we demonstrate a novel function of AXL in acting upstream to induce EMT in normal and immortalized human mammary epithelial cells in an apparent positive feedback loop mechanism and regulate breast CSC (BCSC) self-renewal and chemoresistance. Downregulation of AXL expression using AXL inhibitor MP470 (amuvatinib) or shRNA reversed EMT in mesenchymal normal human mammary epithelial cells and murine BCSCs attenuating self-renewal and restored chemosensitivity of the BCSCs. AXL expression was also found to be associated with expression of stem cell genes, regulation of metastases genes, increased tumorigenicity, and was important for BCSC invasion and migration. Inactivation of AXL also led to downregulation of NFκB pathway and reduced tumor formation in vivo. Together, our data suggest that targeted therapy against AXL, in combination with systemic therapies, has the potential to improve response to anti-cancer therapies and to reduce breast cancer recurrence and metastases. Citation Format: Michael K. Asiedu, Francis Beauchamp-Perez, James N. Ingle, Marshall D. Behrens, Derek C. Radisky, Keith Knutson. AXL induces epithelial to mesenchymal transition and regulates the function of breast 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 LB-272. doi:10.1158/1538-7445.AM2013-LB-272

Abstract Despite limited discovery stages (<1,125 cases), genome-wide association studies (GWAS) have successfully identified 13 loci associated with risk of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL); however, these loci only explain a portion of the heritability. To identify additional genetic loci associated with CLL susceptibility, we conducted the largest meta-analysis of GWAS, to date, including 3,100 CLL cases and 7,667 controls of European ancestry from 25 independent studies genotyped on four different SNP microarrays. Association testing was conducted assuming a log-additive genetic model, adjusting for age, sex, and significant principal components. Meta-analyses were performed using the fixed effects inverse variance method based on the beta estimates and standard errors from each study. Promising loci were taken forward for replication in three additional studies totaling 788 cases and 4,872 controls. In the meta-analysis of both the discovery and replication studies, we conclusively identified ten independent SNPs in nine novel loci that reached genome-wide significance (P<5 x 10−8): 10q23.31 (FAS; P=1.22x10−14), 18q21.33 (BCL2; P=2.66x10−12 and P=7.76x10−11), 11p15.5 (C11orf21; P=2.15x10−10), 4q25 (LEF1; P=4.24x10−10), 2q33.1 (CASP8; P=2.50x10−9), 9p21.3 (CDKN2B-AS1; P=1.27x10−8), 18q21.32 (PMAIP1; P=2.51x10−8), 15q15.1 (BMF; P=2.71x10−10), and 2p22.2 (QPCT; P=1.68x10−8) as well as an independent signal at an established locus (2q13, ACOXL, P=2.08x10−18). We also found evidence for two additional promising loci that reached marginal genome-wide significance (P<2.0x10−7) at 8q22.3 (ODF1; P=5.40x10−8) and 5p15.33 (TERT; P=1.92x10−7). Although further studies are required, the proximity of five of the novel loci to genes involved in apoptosis suggests a possible unifying underlying biological mechanism. Together with the previously established loci, these genetic loci explain ~17% of the familial risk of CLL. Citation Format: Sonja I. Berndt, Christine F. Skibola, Vijai Joseph, Nicola J. Camp, Alexandra Nieters, Zhaoming Wang, Wendy Cozen, Alain Monnereau, Rachel S. Kelly, Silvia de Sanjose, Martha S. Linet, Elio Riboli, Paolo Vineis, Henrik Hjalgrim, James R. Cerhan, Stephen J. Chanock, Nathaniel Rothman, Susan L. Slager. Meta-analysis of genome-wide association studies identifies multiple loci associated with chronic lymphocytic leukemia. [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 LB-23. doi:10.1158/1538-7445.AM2013-LB-23

Abstract Introduction: Clear cell renal cell carcinoma (ccRCC) is the most common subtype of RCC, which is the most prevalent kidney cancer among adults. Of the patients who develop this disease, over 1/3 will already present with advanced or metastatic disease during initial diagnosis due to the lack of symptoms in early stages. RCC demonstrates considerable resistance to radiation and traditional chemotherapeutics. Despite advances in the development of targeted anti-cancer treatments, no current drug therapy leads to significant improvement in long term survival in patients with advanced disease with the rare exception of those who respond to immunotherapy. Additionally, patients inevitably develop drug resistance. Therefore new molecular targets for therapy are sorely needed. Our group has identified stearoyl coA desaturase (SCD1) as a novel molecular target in ccRCC. We examined its role in tumor cell growth and viability in vitro and in vivo independently as well as in combination with current FDA approved regimens. Methods: Patient normal and ccRCC tissue samples and cell lines were examined for SCD1 expression. Genetic knockdown models and targeted inhibition of SCD1 through use of a small molecule inhibitor were analyzed for growth, apoptosis, and alterations in gene expression using gene array analysis. Therapeutic models of synergy were evaluated utilizing pharmacologic inhibition of SCD1 with the tyrosine kinase inhibitors (TKI) sunitinib and pazopanib, and the mTOR inhibitor temsirolimus. Results: Our studies identify increased SCD1 expression in all stages of ccRCC. Both genetic knockdown and pharmacologic inhibition of SCD1 decrease tumor cell proliferation and induce apoptosis in vitro and in vivo. Upon gene array, quantitative real-time PCR, and protein analysis of SCDi treated or SCD1 lentiviral knockdown samples, induction of endoplasmic reticulum (ER) stress response signaling was observed, providing mechanistic insight for SCD1 activity in ccRCC. Furthermore, combinatorial application of SCDi with temsirolimus synergistically inhibits tumor growth in vitro and in vivo. Conclusions: Increased SCD1 expression supports ccRCC viability and therefore we propose it as a novel molecular target for therapy either independently or in combination with an mTOR inhibitor for patients whose disease cannot be remedied with surgical intervention, such as in cases of advanced or metastatic disease. These findings support the further evaluation of targeting SCD1 as an anti-cancer strategy in a phase I clinical trial. Citation Format: Christina A. von Roemeling, Laura Marlow, Thomas Caulfield, Kevin Wu, Winston Tan, Han Tun, John A. Copland, Adam Mathias, Chuck Harrison, Louis Dawson, Beth Hollister. Stearoyl-CoA desaturase 1 is a novel molecular therapeutic target for clear cell renal cell carcinoma. [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 LB-210. doi:10.1158/1538-7445.AM2013-LB-210

Abstract Introduction: Symptom control is an important objective in the care of patients with cancer and a critical goal for long-term survivors of antineoplastic treatments. Commonly used chemotherapies, including paclitaxel, are associated with a toxic effect on the peripheral nervous system in a substantial fraction of patients, termed chemotherapy induced peripheral neuropathy (CIPN), that is often debilitating. CIPN cannot be predicted from clinical parameters in neurologically normal subjects, suggesting a genetic basis as the root cause. Patients with hereditary neuropathy (HN) due to one of ~50 recognized genes are prone to developing severe CIPN even if the hereditary predisposition is clinically silent. Assessment of CIPN has usually been an afterthought of cancer treatment studies using crude symptom measurement instruments. N08C1 and N08CA are recent clinical trials_the latter analyzed only in early 2013_focusing on extensive phenotyping by patient reported outcomes (PRO) to support genetic investigations of paclitaxel-related CIPN. Massively parallel (“nextgen”) DNA sequencing is the genetic technology of choice and represents an as-yet unrealized potential to study cancer symptom control. Methods: Exome sequencing_analysis of 20,794 genes at nucleotide resolution_was performed on blood of CIPN cases (n=73) and controls (n=46) from N08C1. The primary endpoint was the association of HN genes with CIPN. Bioinformatic analysis determined SNV and other genetic variations across 6.2x107 nucleotides. The association of genes with CIPN was statistically examined by the over-dispersion test C-alpha. The role of singleton SNV was assessed by a burden test. N08CA served as validation. Results: 386,644 SNV were detected with an estimated sensitivity of 90% and specificity of 99.9%; the orthogonal validation rate (PCR of >1000 genotypes) was 99.7%. The association of the minor allele (C>T) at rs7349683 in the gene EPHA5, previously reported by Baldwin et al. (2012) for CALGB40101, was confirmed in N08C1. Two hereditary neuropathy genes were identified as new CIPN candidate genes: Firstly, ARHGEF10 was highly significant with p=5x10-4 based on single gene testing and p<0.02 after Bonferroni correction for multiple testing of 41 hereditary neuropathy genes with non-synonymous SNV. Three SNV were predictive, rs17683288, rs2294039 and rs9657362, the latter with an odds ratio (OR)=3.62. Validation in an independent patient group (n=75) from another paclitaxel CIPN trial, N08CA, confirmed the impact of ARHGEF10 on CIPN (p<0.025; rs9657362 OR=2.51). Secondly, peraxin (PRX) was disrupted by non-synonymous singleton SNV in n=8 cases and n=0 controls (OR=6.4; unadjusted p=0.04). 7 of the 8 mutations were also scored as deleterious by both Polyphen 2 and SIFT. Because PRX SNV were non-recurrent validation was performed in N08C1 by Sanger sequencing. Several neuro-genes across the exome were noted as additional CIPN gene candidates. Conclusions: ARHGEF10 and PRX associations with CIPN suggest that CIPN and HN might share genetic roots in a subset of patients. Construct validity of N08C1 is supported by confirmation of a published result from CALGB40101 relating EPHA5 to CIPN. Germline exome sequencing in cancer patients is highly informative for understanding complex pharmacogenomic traits including outcomes in symptom control research. Citation Format: Andreas S. Beutler, Amit Kulkarni, Rahul Kanwar, Rui Qin, Julie M. Cunningham, Terry M. Therneau, Charles L. Loprinzi. Sequencing symptom control: Results from the Alliance N08C1 and N08CA genetics of chemotherapy neuropathy trials. [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 LB-196. doi:10.1158/1538-7445.AM2013-LB-196

Abstract A p53-dependent mouse spindle checkpoint has been reported since 1995. However the underlying mechanism is still unknown. Here, we found that p53 formed complexes with CHAMP and MAD2L2. Immunofluorescence analysis revealed that p53, CHAMP and MAD2L2 colocalized at spindle fibres from pro-metaphase to anaphase. CHAMP binds MAD2L2 and antagonizes its inhibition function on APC/C. We discovered that p53 enhanced the inhibition of MAD2L2 by CHAMP. P53 knock-down decreased M-phase index. Exogenous expression of p53 increased M-phase index and extended remarkable length of time in M phase. Notably, the regulation of p53 on M phase index was completely abrogated by either CHAMP or MAD2l2 knock-down, suggesting that the regulation of p53 on spindle assembly checkpoint pathway is dependent on CHAMP and MAD2L2. These results demonstrate that p53 participates in a mitotic checkpoint that ensures the maintenance of genetic fidelity during development. Citation Format: Piyan Zhang, Erica Ungewitter, Ettore Appella, Heidi Scrable. Tumor suppressor p53 is involved in a CHAMP-dependent spindle assembly checkpoint pathway. [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 LB-121. doi:10.1158/1538-7445.AM2013-LB-121

Abstract Δ40p53, an N-terminally truncated p53 isoform, is predominantly expressed in embryonic stem cells (ESCs) and during early post-implantation embryogenesis in the mouse. We have discovered that Δ40p53 controls the switch from pluripotency to differentiation by regulating IGF signaling in ESCs. Our studies revealed this isoform of p53 inhibits retinoic acid-induced differentiation and subsequent epithelial-mesenchymal transition (EMT). As ESCs differentiate, Δ40p53 cannot activate the expression of some important developmental genes, such as p21, FGF10, DKK1, lamin A and ZO-1, coincident with decreasing Erk signaling and an enhanced Wnt/β-catenin pathway. ChIP assays suggested that p21, FGF10 and ZO-1 are inhibited at the elongation step. To distinguish between the transcription regulation functions of full-length p53 and Δ40p53, we generated stable HeLa cell lines transfected with Flag-tagged p53 and Δ40p53. qPCR and ChIP assays confirmed that Δ40p53, but not full-length p53, represses gene elongation, with a concomitant decrease in acetylation of histone H4 and H3 in the promoter region. Our studies reveal that Δ40p53, but not p53, is able to block ESC differentiation by regulation of specific gene expression at the elongation step during mouse development. Citation Format: Piyan Zhang, Heidi Scrable. Developmental checkpoint function of Δ40p53. [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 5439. doi:10.1158/1538-7445.AM2013-5439