The Cfr methyltransferase confers combined resistance to five different classes of antibiotics that bind to the peptidyl transferase center of bacterial ribosomes. The Cfr-mediated modification has previously been shown to occur on nucleotide A2503 of 23S rRNA and has a mass corresponding to an additional methyl group, but its specific identity and position remained to be elucidated. A novel tandem mass spectrometry approach has been developed to further characterize the Cfr-catalyzed modification. Comparison of nucleoside fragmentation patterns of A2503 from Escherichia coli cfr+ and cfrÀ strains with those of a chemically synthesized nucleoside standard shows that Cfr catalyzes formation of 8-methyladenosine. In addition, analysis of RNA derived from E. coli strains lacking the m 2 A2503 methyltransferase reveals that Cfr also has the ability to catalyze methylation at position 2 to form 2,8-dimethyladenosine. The mutation of single conserved cysteine residues in the radical SAM motif CxxxCxxC of Cfr abolishes its activity, lending support to the notion that the Cfr modification reaction occurs via a radical-based mechanism. Antibiotic susceptibility data confirm that the antibiotic resistance conferred by Cfr is provided by methylation at the 8 position and is independent of methylation at the 2 position of A2503. This investigation is, to our knowledge, the first instance where the 8-methyladenosine modification has been described in natural RNA molecules.

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Due to increased lactate production during glucose metabolism, tumor cells heavily rely on efficient lactate transport to avoid intracellular lactate accumulation and acidification. Monocarboxylate transporter 4 (MCT4/SLC16A3) is a lactate transporter that plays a central role in tumor pH modulation. The discovery and optimization of a novel class of MCT4 inhibitors (hit 9a), identified by a cellular screening in MDA-MB-231, is described. Direct target interaction of the optimized compound 18n with the cytosolic domain of MCT4 was shown after solubilization of the GFP-tagged transporter by fluorescence cross-correlation spectroscopy and microscopic studies. In vitro treatment with 18n resulted in lactate efflux inhibition and reduction of cellular viability in MCT4 high expressing cells. Moreover, pharmacokinetic properties of 18n allowed assessment of lactate modulation and antitumor activity in a mouse tumor model. Thus, 18n represents a valuable tool for investigating selective MCT4 inhibition and its effect on tumor biology.

Cell type, morphology, and functioning are key variables in the construction of efficient "drug-vehicle" hybrids in magnetic drug delivery. Iron-encapsulated multiwall carbon nanotubes (Fe@MWCNTs) appear as promising candidates for theranostics due to in situ chemical catalytic vapor deposition (c-CVD) synthesis, straightforward organic functionalization, and nanoneedle (1D) behavior. Here, model hybrids were synthesized by exploring C-sp 2 chemistry ((1+2)-cycloaddition of nitrenes and amidation) of the outer MWCNT walls combined with anticancer agents, that is, 5-fluorouracil (5FU), purpurin (Purp), and 1,8-naphthalimide DNA intercalators (NIDIs), via linkers. Analyses of the Fe@MWCNT vehicles by SEM, TEM, and Raman spectroscopy revealed their morphology while Mössbauer spectroscopy confirmed the presence of encapsulated ferromagnetic iron-based nanodomains. Cytotoxicity of the hybrids was studied using a 24 h MTS assay combined with the apoptosis and life cycle assays against human melanoma (Me45), colon carcinoma (HCT116+), and colon adenocarcinoma (Caco-2). The cells had different sensitivity to the vehicles themselves as well as to the hybrids. MWCNT-based covalent hybrids of 5FU and Purp emerged as the most promising systems against Me45 and HCT116+ cell lines with the highest in vitro cytotoxicity and proapoptotic activity. Furthermore, nanotubes bearing 4-nitro-and 4-(N-morpholinyl)-1,8-naphthalimide DNA intercalators appear as a promising candidate for the treatment of Caco-2.

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