Thermal Stability of RNA Structures with Bulky Cations in Mixed Aqueous Solutions.

Bulky cations are used to develop nucleic-acid-based technologies for medical and technological applications in which nucleic acids function under nonaqueous conditions. In this study, the thermal stability of RNA structures was measured in the presence of various bulky cations in aqueous mixtures with organic solvents or polymer additives. The stability of oligonucleotide, transfer RNA, and polynucleotide structures was decreased in the presence of salts of tetrabutylammonium and tetrapentylammonium ions, and the stability and salt concentration dependences were dependent on cation sizes. The degree to which stability was dependent on salt concentration was correlated with reciprocals of the dielectric constants of mixed solutions, regardless of interactions between the cosolutes and RNA. Our results show that organic solvents affect the strength of electrostatic interactions between RNA and cations. Analysis of ion binding to RNA indicated greater enhancement of cation binding to RNA single strands than to duplexes in media with low dielectric constants. Furthermore, background bulky ions changed the dependence of RNA duplex stability on the concentration of metal ion salts. These unique properties of large tetraalkylammonium ions are useful for controlling the stability of RNA structures and its sensitivity to metal ion salts.

Prospective observational study of bevacizumab combined with paclitaxel as first- or second-line chemotherapy for locally advanced or metastatic breast cancer: the JBCRG-C05 (B-SHARE) study.

PURPOSE: To investigate the effectiveness and safety of bevacizumab-paclitaxel combination therapy as first- or second-line chemotherapy for HER2-negative locally advanced or metastatic breast cancer in daily clinical practice. METHODS: In this prospective multicenter observational study, bevacizumab-paclitaxel was administered at the discretion of attending physicians. Cohorts A and B had hormone receptor-positive and triple-negative breast cancer (TNBC), respectively. Primary endpoint was overall survival (OS). Multivariate analyses were conducted to identify prognostic factors. RESULTS: Between November 2012 and October 2014, 767 patients were enrolled from 155 institutions across Japan. Effectiveness was analyzed in 754 eligible patients (cohort A, 539; cohort B, 215) and safety in 750 treated patients (median observation period, 19.7 months). Median OS (95% CI) was 21.7 (19.8-23.6) months in eligible patients; 25.2 (22.4-27.4) months and 13.2 (11.3-16.6) months in cohorts A and B, respectively; and 24.4 (21.9-27.2) months and 17.6 (15.2-20.0) months in patients receiving first- and second-line therapy, respectively. Factors affecting OS (hazard ratio 95% CI) were TNBC (1.75, 1.44-2.14), second-line therapy (1.35, 1.13-1.63), ECOG performance status ≥ 1 (1.28, 1.04-1.57), taxane-based chemotherapy (0.65, 0.49-0.86), cancer-related symptoms (0.56, 0.46-0.68), and visceral metastasis (0.52, 0.40-0.66). Incidences of grade ≥ 3 AEs hypertension, neutropenia, peripheral neuropathy, proteinuria, and bleeding were 35.7%, 27.2%, 7.2%, 3.7%, and 0.3%, respectively. CONCLUSIONS: In Japanese clinical practice, combined bevacizumab-paclitaxel was as effective as in previous studies. Factors that independently predicted poor prognosis in the present study are consistent with those identified previously. TRIAL REGISTRATION: Trial no. UMIN000009086.

Stabilization of DNA Loop Structures by Large Cations.

The DNA-binding properties of large cations differ from those of metal ions due to steric exclusion from base-paired regions. In this study, the thermal stability of DNA secondary structures, including duplexes, internal loops, bulge loops, hairpin loops, dangling ends, and G-quadruplexes, was investigated in the presence of cations of different sizes. Large cations, such as tetrabutylammonium and tetrapentylammonium ions, reduced the stability of fully matched duplexes but increased the stability of duplexes with a long loop. The cations also increased the stability of G-quadruplexes with a long loop, and the degree of stabilization was greater for low-stability G-quadruplexes. Analysis of the salt concentration dependence indicates that large cations bind to the loop nucleotides, leading to counteracting the destabilization effect on base pairing. It is likely that binding occurs when loop nucleotides are sufficiently flexible to allow for greater accessibility for large cations. These results provide insight into nucleic acid interactions with large cationic molecules and suggest a potential method for stabilizing noncanonical DNA structures under intracellular conditions.