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N588K-KCNH2 and V307L-KCNQ1 mutations decrease carvedilol's inhibition of the IKs or IKr tail but increase carvedilol's IKr end-pulse inhibition and metoprolol's inhibition of tail and end-pulse currents. These different effects on SQT1 and SQT2 mutated channels should be considered when using β-blocker therapy in SQTS patients.

Introduction and Hypothesis: Short QT syndrome is an inherited ion channelopathy with an accelerated cardiac repolarization due to gain-of-function mutations in K+ channel genes. Patients are prone to ventricular tachycardia and sudden cardiac death (SCD). Detailed knowledge about mechanisms of arrhythmogenesis is lacking. We aimed at generating transgenic SQT1 rabbits as novel tool to investigate these mechanisms. Methods: FLAG-HA-tagged HERG-N588K cDNA and the b-MyHC promoter were integrated into a pBSII SK vector and microinjected into rabbit oocytes. SQT1 rabbits and their wildtype (WT) littermates were subjected to in vivo ECG and ex vivo monophasic action potential (AP) measurements. Electrical remodeling was investigated using real-time PCR. Results: We successfully generated 3 transgenic SQT1 founder rabbits. One of the founders died suddenly at the age of 60 days. In SQT1 rabbits (F1) not subjected to any experiments 3/11 died around day 40 vs. 0/8 WT rabbits (p<0.05). SQT1 founder rabbits and their offspring demonstrated a shortened QT interval compared to WT (QT, ms, SQT1, n=44, 147.8±1.7 vs. WT, n=24, 166.4±2.9, p<0.0001, heart-rate corrected QTi, %, 91.6±0.7 vs. 98.1±1.1, p<0.0001) with no gender differences among SQT1 rabbits. Moreover, in SQT1, AP duration was shortened in all segments of LV base, mid, and apex (LV base-lat, APD90, ms, SQT1, n=7, 118.6±5.1 vs. WT, n=9, 154.4±2.2, p<0.0001; APD75, 93.1±6.8 vs. 127.1±1.9, p<0.0001). Ventricular fibrillation (VF) occurred more often during AP measurements in SQT1 than in WT rabbits (SQT1, 5/13 vs. WT, 0/8, p<0.05). FLAG-HA-HERG-N588K channels expressed in HEK cells demonstrated increased IKr steady currents and impaired inactivation indicative of a gain-of-function. Remodeling of ion channels and Ca2+ handling proteins occurred in SQT1 rabbits with a downregulation of L-type Ca2+ channel mRNA in LV septum-mid (SQT1, n=4, 0.84±0.1 vs. WT, n=6, 1.03±0.1, p<0.05) and of RyR2 in LV septum-apex (0.85±0.1 vs. 1.08±0.1, p<0.05). Conclusion: These first transgenic SQT1 rabbits over-expressing a HERG-N588K gain-of-function mutation mimic the human phenotype with shortening of QT and APD, a high rate of VF and SCD. These models are thus a useful tool to explore arrhythmogenic mechanisms in SQTS.

Background: Merkel cell polyomavirus (MCPyV) is detected in approximately 80% of Merkel cell carcinomas (MCC). A number of previous studies have shown that MCC patients are at a significantly increased risk to develop chronic lymphocytic leukemia (CLL) and vice versa. Until recently, clonal integration and truncating mutations of the Large T antigen (LTAg) of MCPyV were restricted to MCC. We have recently reported the presence of the MCPyV in highly purified tumor cells of CLL (n = 19/70, 27.1%) (Blood. 2010 Sep 3). Of these, six revealed a novel 246 bp deletion in the helicase gene of the LTAg. The presence of MCPyV was confirmed by immunohistochemistry. Material and Method: Here we aimed to determine the presence of MCPyV by fluorescence in situ hybridization (FISH) analysis in CLL cells in order to evaluate whether MCPyV was integrated or episomal. For this purpose we performed FISH analysis as previously described (Int J Cancer. 2005, 115:419-428) using the MCPyV genome as FISH probe. We tested 2 of the previously reported MCPyV positive CLL cases (EDTA decalcified bone marrow trephines) and MCPyV-positive MCC (n = 5). In addition, we tested MCPyV-negative tumors, e.g. breast and colon cancers. All tissues were formalin-fixed and paraffin-embedded. Results: Specific MCPyV DNA by FISH analysis was detected in the nuclei of MCPyV-positive CLL and MCC cells. In contrast to particularly punctate FISH signals in MCC indicating viral integration, the nuclear FISH signals of the CLL cases revealed especially granular signals, indicative for integrated MCPyV DNA together with transcribed viral RNA (Int J Cancer. 2008, 122:2656-2664). No signals were obtained by MCPyV FISH in breast or colon cancer specimens. Conclusion: The specific detection of MCPyV in CLL cells further supports our previous report of a possible involvement of MCPyV in a significant subset of CLL. The specific but rather granular nuclear FISH signals in MCPyV positive CLL cells needs further study to evaluate if it is also generated by co-existing episomal virus copies, by viral RNA or by the decalcification process. In addition, more CLL cases will be analyzed for the presence of MCPyV. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2717. doi:10.1158/1538-7445.AM2011-2717