Citations

Abstract The central importance of the ERBB/RAS signal transduction cascade has been well established in human cancer. As such, novel approaches to counteract activated ERBB/RAS signals constitute important measures to reverse tumorigenesis and metastasis in human cancers. Instead of targeting an upstream signaling module such as ERBB/RAS/MEK/MAPK/AKT/mTOR, we targeted the most downstream signaling module in the ERBB/RAS pathway called the SIAH-dependent proteolytic machinery. SIAHs are the human homologs of Seven-In-Absentia (SINA), an evolutionarily conserved RING E3 ligase, an essential downstream signaling module and a critical “gatekeeper” required for proper Drosophila RAS signal transduction. Guided by the insights and principles learned from Drosophila RAS signaling pathway, we conducted preclinical studies to examine SIAH function in the context of RAS-mediated tumorigenesis and metastasis in human cancer cells.We found that (1) SIAH is a novel biomarker for human cancer, i.e. it specifically decorates proliferating tumor cells (not stromal cells in the tumor microenvironment). SIAH expression is progressively and markedly upregulated as human cancer progresses to the advanced stages in human pancreatic, lung, breast and prostate cancers; and (2) inhibiting the proteolytic function of SIAH is highly effective to abolish tumorigenesis and metastasis in eight of the most aggressive human cancer cell lines known in the literature that include pancreatic cancer cells (MiaPaCa and Panc-1), lung cancer cells (A549), invasive breast cancer cells (MDA-MB-231, MDA-MB-468 and MDA-MB-435) and hormonal-refractory prostate cancer cells (PC-3 and DU-145) in soft agar as well as in athymic nude mice. These findings suggest that SIAH may be an attractive new therapeutic target for novel anti-RAS and anti-cancer therapy in human cancer. As a highly evolutionarily conserved E3 ligase and consistent with its “gatekeeper” function identified in the ERBB/RAS signaling pathway, SIAH is well positioned to become a next-generation and potent anticancer drug target to block the tumor-promoting RAS pathway and to treat the most aggressive types of human cancers. “Using anti-SIAH molecules to block active RAS signaling in human cancer” may be another example of “from the bench [basic science from fruitflies (model organism) to human cancers] to the bedside story [translational medicine in the near future]”. Anti-SIAH-based anticancer strategy may aid in expanding our arsenal of novel anticancer therapies. By attacking the oncogenic ERBB/RAS pathway using multi-pronged synergistic inhibitions at upstream (EGFR/HER2 membrane receptors), midstream (RAS/RAF/MEK/mTOR) and downstream (SIAH E3 ligase) signaling modules in parallel, we may be in a great position to halt the genesis, progression and metastasis of the most aggressive and lethal types of human cancers. If successful, we hope to translate our findings to the cancer clinics to treat many cancer patients with metastatic diseases in the future. Citation Information: Cancer Res 2009;69(23 Suppl):A1.

Glioblastoma, the most common primary malignant cancer of the brain, is characterized by rapid tumor growth and infiltration of tumor cells throughout the brain. These traits cause glioblastomas to be highly resistant to current therapies with a resultant poor prognosis. Although aberrant oncogenic signaling driven by signature genetic alterations, such as EGF receptor (EGFR) gene amplification and mutation, plays a major role in glioblastoma pathogenesis, the responsible downstream mechanisms remain less clear. Here, we report that EGFRvIII (also known as ΔEGFR and de2-7EGFR), a constitutively active EGFR mutant that is frequently co-overexpressed with EGFR in human glioblastoma, promotes tumorigenesis through Src family kinase (SFK)-dependent phosphorylation of Dock180, a guanine nucleotide exchange factor for Rac1. EGFRvIII induces phosphorylation of Dock180 at tyrosine residue 722 (Dock180 Y722 ) and stimulates Rac1-signaling, glioblastoma cell survival and migration. Consistent with this being causal, siRNA knockdown of Dock180 or expression of a Dock180 Y722F mutant inhibits each of these EGFRvIII-stimulated activities. The SFKs, Src, Fyn, and Lyn, induce phosphorylation of Dock180 Y722 and inhibition of these SFKs by pharmacological inhibitors or shRNA depletion markedly attenuates EGFRvIII-induced phosphorylation of Dock180 Y722 , Rac1 activity, and glioblastoma cell migration. Finally, phosphorylated Dock180 Y722 is coexpressed with EGFRvIII and phosphorylated Src Y418 in clinical specimens, and such coexpression correlates with an extremely poor survival in glioblastoma patients. These results suggest that targeting the SFK-p-Dock180 Y722 -Rac1 signaling pathway may offer a novel therapeutic strategy for glioblastomas with EGFRvIII overexpression.

Background— Clinical trials have shown that statin therapy reduces cardiovascular morbidity and mortality in patients with coronary artery disease (CAD), even among patients with low-density lipoprotein cholesterol levels <100 mg/dL. We sought to determine the extent to which patients with obstructive CAD in routine outpatient care are treated with statins, nonstatins, or no lipid-lowering therapy. Methods and Results— Within the American College of Cardiology's Practice Innovation and Clinical Excellence (PINNACLE) outpatient registry, we examined rates of treatment with statin and nonstatin medications in 38 775 outpatients with obstructive CAD (history of myocardial infarction or coronary revascularization) and without documented contraindications to statin therapy. Among these patients, 30 160 (77.8%) were prescribed statins, 2042 (5.3%) were treated only with nonstatin lipid-lowering medications, and 6573 (17.0%) were untreated. Lack of medical insurance was associated with no statin treatment, and male sex, coexisting hypertension, and a recent coronary revascularization were associated with statin treatment. Among those not on any lipid-lowering therapy, low-density lipoprotein cholesterol levels were available for 51.2% (3365/6573). Among these untreated patients, low-density lipoprotein cholesterol levels were <100 mg/dL in 1794 patients (53.3%) and ≥100 mg/dL in 1571 patients (46.7%). Conclusions— Despite robust clinical trial evidence, a substantial number of patients with obstructive CAD remain untreated with statins. A small proportion were treated with nonstatin therapy, and 1 in 6 patients was simply untreated; half of the untreated patients had low-density lipoprotein cholesterol values <100 mg/dL. These findings illustrate important opportunities to improve lipid management in outpatients with obstructive CAD.

AbstractA phase 2 study of the oral farnesyltransferase inhibitor tipifarnib was conducted in 93 adult patients with relapsed or refractory lymphoma. Patients received tipifarnib 300 mg twice daily on days 1-21 of each 28-day cycle. The median number of prior therapies was 5 (range, 1-17). For the aggressive B-cell, indolent B-cell, and T-cell and Hodgkin lymphoma (HL/T) groups, the response rates were 17% (7/42), 7% (1/15), and 31% (11/36), respectively. Of the 19 responders, 7 were diffuse large B-cell non-Hodgkin lymphoma (NHL), 7 T-cell NHL, 1 follicular grade 2, and 4 HL. The median response duration for the 19 responders was 7.2 months (mean, 15.8 months; range, 1.8-62), and 5 patients in the HL/T group are still receiving treatment at 29-64+ months. The grade 3/4 toxicities observed were fatigue and reversible myelosuppression. Correlative studies suggest that Bim and Bcl-2 should be examined as potential predictors of response in future studies. These results indicate that tipifarnib has activity in lymphoma, particularly in heavily pretreated HL/T types, with little activity in follicular NHL. In view of its excellent toxicity profile and novel mechanism of action, further studies in combination with other agents appear warranted. This trial is registered at www.clinicaltrials.gov as #NCT00082888.

Abstract The central importance of the HER2/Neu/EGFR/RAS signaling pathway has been well established in the growth, invasion and metastasis of human breast cancer, even though oncogenic RAS mutations are rare in breast cancer, activation of the tumor-promoting ERBB/RAS/MEK/MAPK pathway has been consistently documented in high-grade breast tumors. As such, novel approaches to inhibit activated ERBB/RAS signals constitute important measures to block tumor growth and metastasis in mammary tumors. In this study, instead of targeting an upstream signaling component such as HER2/EGFR/RAS, we targeted the most downstream signaling module identified in the RAS pathway — the SIAH proteolytic machinery. SIAH is an evolutionarily conserved RING E3 ligase that is a critical “gatekeeper” required for RAS signal transduction in human cancer cells. SIAH is specifically expressed in tumor cells in 120 human breast cancer patients examined so far. The increased SIAH expression is correlated with increased grades and aggressiveness of human breast cancer. We then asked whether inhibiting the gatekeeper function of SIAH would be effective in blocking mammary tumorigenesis and metastasis in human breast cancer. Our results indicated that SIAH2-deficiency successfully abolished tumor growth of three breast cancer cell lines (MDA-MB-231, MDA-MB-435 and MDA-MB-468) in soft agar assays as well as in athymic nude mice. Importantly, by inhibiting SIAH2 function in highly aggressive human breast cancer cells, we are able to completely block tumorigenesis and metastasis of two highly invasive and metastatic human breast cancer cell lines (MDA-MB-231 and MDA-MB-435). These findings suggest that SIAH2 may be an attractive new therapeutic target for novel breast cancer therapy and developing anti-SIAH molecules will aid in expanding our arsenal of effective anticancer therapies. More effective breast cancer treatments may be obtained by multi-pronged synergistic inhibitions at upstream (HER2/EGFR membrane receptors), midstream (RAS/RAF/MEK/mTOR) and downstream (SIAH E3 ligase) signaling modules in the HER2/EGFR/RAS pathway in parallel. Thus, by attacking the growth-promoting ERBB/RAS pathway at multiple signaling modules simultaneously, we may be in a great position to halt the genesis, progression and metastasis of human breast cancer. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-15-14.

Abstract Hepatocellular carcinoma (HCC), the primary malignancy of the liver, is the fourth leading cause of cancer deaths worldwide, with a 5-year survival rate of∼10%. Recently, a new multikinase inhibitor, sorafenib (Nexavar®), which mainly targets the VEGFR and the Raf/Mek/Erk pathways, has shown limited response rate and modest survival benefits in patients with advanced stage HCC. We hypothesize that there exist genetic alterations or contexts of vulnerability (COV) in cancer cells that dictate sensitivity to sorafenib. In order to identify specific COVs and obtain an increased understanding of drug's mechanism of action, we performed a custom chemosensitization high-throughput siRNA screen. We developed and optimized a sorafenib chemosensitization assay in 3 HCC cell lines, one of which, Hep3B, a AFP and HBsAg positive cell line, was selected for primary RNAi screening with a kinase siRNA library, which covers 700 genes (4 siRNA sequences per gene). Primary screen data was rigorously evaluated for multiple quality control metrics (transfection efficiency, CV values, accessing plate-to-plate and set-to-set variation) and found to exceed all expected performance parameters. The top sorefenib sensitizing hits were identified and supplemented with additional genes selected based on related biological concepts. This sensitization effect of the genes was further tested and compared in two additional HCC cell lines (HepG2 and PLC). Additionally, based on the sensitizer list from the RNAi screening, 11 chemical compounds were tested for synergistic combination with sorafenib. Notable synergism with sorafenib was observed in the combination with erlotinib or doxorubicin. More strikingly, we also observed synergy between sorafenib and multiple MEK inhibitors as well as gemcitabine in the selected HCC cell lines. Our data suggest that MEK inhibitors might improve the efficacy of sorafenib in HCC treatment in the clinic. Further mechanistic studies are being conducted for this particular combination. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-285.