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A tumor-selective non-lytic retroviral replicating vector (RRV), Toca 511, and an extended-release formulation of 5-fluorocytosine (5-FC), Toca FC, are currently being evaluated in clinical trials in patients with recurrent high-grade glioma (NCT01156584, NCT01470794 and NCT01985256). Tumor-selective propagation of this RRV enables highly efficient transduction of glioma cells with cytosine deaminase (CD), which serves as a prodrug activator for conversion of the anti-fungal prodrug 5-FC to the anti-cancer drug 5-fluorouracil (5-FU) directly within the infected cells. We investigated whether, in addition to its direct cytotoxic effects, 5-FU generated intracellularly by RRV-mediated CD/5-FC prodrug activator gene therapy could also act as a radiosensitizing agent. Efficient transduction by RRV and expression of CD were confirmed in the highly aggressive, radioresistant human glioblastoma cell line U87EGFRvIII and its parental cell line U87MG (U87). RRV-transduced cells showed significant radiosensitization even after transient exposure to 5-FC. This was confirmed both in vitro by a clonogenic colony survival assay and in vivo by bioluminescence imaging analysis. These results provide a convincing rationale for development of tumor-targeted radiosensitization strategies utilizing the tumor-selective replicative capability of RRV, and incorporation of radiation therapy into future clinical trials evaluating Toca 511 and Toca FC in brain tumor patients.

Retroviral replicating vectors (RRVs) have been shown to achieve efficient tumor transduction and enhanced therapeutic benefit in a wide variety of cancer models. Here we evaluated two different RRVs derived from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV), in human malignant mesothelioma cells. In vitro, both RRVs expressing the green fluorescent protein gene efficiently replicated in most mesothelioma cell lines tested, but not in normal mesothelial cells. Notably, in ACC-MESO-1 mesothelioma cells that were not permissive for AMLV-RRV, the GALV-RRV could spread efficiently in culture and in mice with subcutaneous xenografts by in vivo fluorescence imaging. Next, GALV-RRV expressing the cytosine deaminase prodrug activator gene showed efficient killing of ACC-MESO-1 cells in a prodrug 5-fluorocytosine dose-dependent manner, compared with AMLV-RRV. GALV-RRV-mediated prodrug activator gene therapy achieved significant inhibition of subcutaneous ACC-MESO-1 tumor growth in nude mice. Quantitative reverse transcription PCR demonstrated that ACC-MESO-1 cells express higher PiT-1 (GALV receptor) and lower PiT-2 (AMLV receptor) compared with normal mesothelial cells and other mesothelioma cells, presumably accounting for the distinctive finding that GALV-RRV replicates much more robustly than AMLV-RRV in these cells. These data indicate the potential utility of GALV-RRV-mediated prodrug activator gene therapy in the treatment of mesothelioma.

We have recently developed a novel and highly efficient strategy that exclusively uses the purine analog 6-thioguanine (6TG) for both pretransplantation conditioning and post-transplantation chemoselection of hypoxanthine-guanine phosphoribosyltransferase (HPRT)-deficient bone marrow (BM). In a mouse BM transplantation model, combined 6TG preconditioning and in vivo chemoselection consistently achieved >95% engraftment of HPRT-deficient donor BM and long-term reconstitution of histologically and immunophenotypically normal hematopoiesis in both primary and secondary recipients, without significant toxicity and in the absence of any other cytotoxic conditioning regimen. To translate this strategy for combined 6TG conditioning and chemoselection into a clinically feasible approach, it is necessary to develop methods for genetic modification of normal hematopoietic stem cells (HSC) to render them HPRT-deficient and thus 6TG-resistant. Here we investigated a strategy to reduce HPRT expression and thereby confer protection against 6TG myelotoxicity to primary murine BM cells by RNA interference (RNAi). Accordingly, we constructed and validated a lentiviral gene transfer vector expressing short-hairpin RNA (shRNA) that targets the murine HPRT gene. Our results showed that lentiviral vector-mediated delivery of HPRT-targeted shRNA could achieve effective and long-term reduction of HPRT expression. Furthermore, in both an established murine cell line as well as in primary murine BM cells, lentiviral transduction with HPRT-targeted shRNA was associated with enhanced resistance to 6TG cytotoxicity in vitro. Hence this represents a translationally feasible method to genetically engineer HSC for implementation of 6TG-mediated preconditioning and in vivo chemoselection.

In the present study, we compared the therapeutic effect of tumor-selective retroviral replicating vectors (RRV) expressing the yeast cytosine deaminase (CD) delivered by convection-enhanced delivery (CED) or simple injection, followed by systemic administ

The behavior of the self-excited chatter in cutting was investigated from the space phase point of view; the space phase is defined as that between outer and inner modulation. Records of oscillation for the horizontal motion of the work and those for the horizontal component of the cutting force were stored in a newly developed measurement system. The amplitude of the vibration increases for decreasing cutting speed and vice versa, the amplitude for the cutting force does not increase as the amplitude of the work motion does. Amplified and damped amplitudes for the decreasing and the increasing cutting speed are shown to be closely related to decreasing and increasing space phases, respectively. The mechanism of this phenomenon was analyzed on the complex plane by taking the cutting dynamics and the structural compliance into account. Attempts to suppress the chatter amplitude were conducted on the basis of these phenomena.

The gas cluster ion beam technique has been used to smooth the bottom NiFe magnetic shield for magnetic tunnel junction read heads. This approach allows the production an ultrathin tunneling barrier for magnetic tunnel junction read heads.

Magnetic tunnel junctions are fabricated by using radical oxidation to form an AlOx tunneling barrier. The results are discussed in terms of the E-model based on the field-induced distortion of atomic bonds in the oxide barrier.

A study was conducted to analyze the canting of exchange coupling direction in spin valve supporting different pinned layers. Films were prepared on silicon or AltiC substrates at room temperature by the direct current magnetron sputtering system. Experimental results indicated that the exposure of the the spin valve to heat and magnetic field correlates with increases in cant.

In this work, the frequency response in magnetic tunnel junction (MTJ) heads was studied. Both stray capacitance and junction resistance, forming a low-pass-filter, have to be reduced to improve the cutoff frequency in MTJ heads. By employing an Ar gas cluster ion beam (GCIB) process, junctions grown on the magnetic shield show a resistance area product as low as 3.6 [Omega][micro][m.sup.2] and tunneling magneto-resistance over 14%. The dominant capacitance in common lead and shield MTJ heads was found mainly resulting from the shield-to-shield spacing, whose capacitance can be reduced by using an Si[O.sub.2] gap layer instead of [Al.sub.2][O.sub.3] layer and thus leading to an improved frequency response. Simple analysis indicates that a read amplifier design with low impedance could be helpful to realize a high data transfer rate, and a rate of around 800 Mbps for 100 Gbits/[in.sup.2] recording system can be thus expected. Index Terms--Common lead and shield, cut off frequency, data transfer rate, input impedance, magnetic recording/magnetic tunnel junction heads, stray capacitance.

Magnetic tunnel junction (MTJ) heads have been successfully fabricated using the free layer as flux guide to prevent electrical short during the definition of the air bearing surface (ABS). For a 6 Gbits/[in.sup.2] design, an output as high as 5740 [micro]Vpp was achieved for 3 mA sense current, and the output waveform was stable and noise free. Noise analysis confirmed that shot noise is prevailing in these MTJ heads, suggesting that the junction resistance has to be further reduced to challenge spin-valve heads in term of signal to noise ratio. Landau-Lifshitz-Gilbert simulations showed that for 20 Gbits/[in.sup.2] application, the flux guide height should not exceed 0. [micro]m. Index Terms--Magnetic recording/magnetic tunnel junction heads, front flux guide, shot noise, micromagnetic simulation.

A first attempt to longitudinally bias magnetic tunnel junctions for the application in magnetic read heads is presented. A design wherein the free layers uncovered lateral extensions is a promising candidate since good transfer curves could be simulated using either permanent magnets (PM) or AF slabs, deposited on top of the lateral extensions.