, indicating that CyPA is the chief mediator of the observed CsA resistance. The dependency on CyPA for replication was observed for both genotype (GT) 1a and 1b replicons as well as a GT 2a infectious virus. An interaction between CyPA and HCV RNA as well as the viral polymerase that is sensitive to CsA treatment in wild-type but not in resistant replicons was detected. These findings reveal the molecular mechanism of CsA resistance and identify CyPA as a critical cellular cofactor for HCV replication and infection.

Human mesenchymal stem cell (hMSC) resistance to the apoptotic effects of chemotherapeutic drugs has been of major interest, as these cells can confer this resistance to tumor microenvironments. However, the effects of internalized chemotherapeutics upon hMSCs remain largely unexplored. In this study, cellular viability and proliferation assays, combined with different biochemical approaches, were used to investigate the effects of Paclitaxel exposure upon hMSCs. Our results indicate that hMSCs are highly resistant to the cytotoxic effects of Paclitaxel treatment, even though there was no detectable expression of the efflux pump P-glycoprotein, the usual means by which a cell resists Paclitaxel treatment. Moreover, Paclitaxel treatment induces hMSCs to adopt a non-proliferative fibroblastic state, as evidenced by changes to morphology, cellular markers, and a reduction in differentiation potential that is not directly coupled to the cytoskeletal effects of Paclitaxel. Taken together, our results show that Paclitaxel treatment does not induce apoptosis in hMSCs, but does induce quiescence and phenotypic changes.

Activation of the type I interferon (IFN) pathway by small interfering RNA (siRNA) is a major contributor to the off-target effects of RNA interference in mammalian cells. While IFN induction complicates gene function studies, immunostimulation by siRNAs may be beneficial in certain therapeutic settings. Various forms of siRNA, meeting different compositional and structural requirements, have been reported to trigger IFN activation. The consensus is that intracellularly expressed short-hairpin RNAs (shRNAs) are less prone to IFN activation because they are not detected by the cell-surface receptors. In particular, lentiviral vector-mediated transduction of shRNAs has been reported to avoid IFN response. Here we identify a shRNA that potently activates the IFN pathway in human cells in a sequence- and 5′-triphosphate-dependent manner. In addition to suppressing its intended mRNA target, expression of the shRNA results in dimerization of interferon regulatory factor-3, activation of IFN promoters and secretion of biologically active IFNs into the extracellular medium. Delivery by lentiviral vector transduction did not avoid IFN activation by this and another, unrelated shRNA. We also demonstrated that retinoic-acid-inducible gene I, and not melanoma differentiation associated gene 5 or toll-like receptor 3, is the cytoplasmic sensor for intracellularly expressed shRNAs that trigger IFN activation.

We describe a family of hybrid compounds for the most efficient light-activated double-strand (ds) DNA cleavage known to date. This family represents the second generation of "switchable" molecular systems for pH-gated ds DNA-cleavage which combine a potent DNA-photocleaver and a pH-regulated part derived from a dipeptide. Design of the pH-switchable part utilizes amino groups of different basicity. Whereas the basic amino groups are protonated throughout the biologically relevant pH range, the pH-gating amines undergo protonation at the pH threshold which separates cancer and normal cells. Control over the reactivity and selectivity is achieved via transformation of the initial protonation state (a monocation or a dication) into a trication at the acidic pH. This change leads to an extraordinary increase in the efficiency of ds DNA cleavage leading to the ds:ss ratios comparable with the most efficient nonenzymatic ds DNA cleavers. Statistical analysis reveals that these high ds:ss ratios result from the combination of several factors: (a) true double-stranded cleavage, and (b) conversion of single-stranded (ss)-scission into ds cleavage. Considerable part of ds cleavage is also produced via the combination of ss cleavage events.

Research over the past decade has identified several of the key limiting features of multidrug resistance (MDR) in cancer therapy applications, such as evolving glycoprotein receptors at the surface of the cell that limit therapeutic uptake, metabolic changes that lead to protection from multidrug resistant mediators which enhance degradation or efflux of therapeutics, and difficulty ensuring retention of intact and functional drugs once endocytosed. Nanoparticles have been demonstrated to be effective delivery vehicles for a plethora of therapeutic agents, and in the case of nucleic acid based agents, they provide protective advantages. Functionalizing cell penetrating peptides, also known as protein transduction domains, onto the surface of fluorescent quantum dots creates a labeled delivery package to investigate the nuances and difficulties of drug transport in MDR cancer cells for potential future clinical applications of diverse nanoparticle-based therapeutic delivery strategies. In this study, eight distinct cell penetrating peptides were used (CAAKA, HSV1-VP22, HIV-TAT, HIV-gp41, Ku-70, hCT(9-32), integrin-β3, and K-FGF) to examine the different cellular uptake profiles in cancer versus drug resistant melanoma (A375 & A375-R), mesothelioma (MSTO & MSTO-R), and glioma (rat 9L and 9L-R, and human U87 & LN18) cell lines. The results of this study demonstrate that cell penetrating peptide uptake varies with drug resistance status and cell type, likely due to changes in cell surface markers. This study provides insight into developing functional nanoplatform delivery systems in drug resistant cancer models.