Nanotechnology-based delivery systems to overcome drug resistance in cancer.

Cancer nanomedicine is defined as the application of nanotechnology and nanomaterials for the formulation of cancer therapeutics that can overcome the impediments and restrictions of traditional chemotherapeutics. Multidrug resistance (MDR) in cancer cells can be defined as a decrease or abrogation in the efficacy of anticancer drugs that have different molecular structures and mechanisms of action and is one of the primary causes of therapeutic failure. There have been successes in the development of cancer nanomedicine to overcome MDR; however, relatively few of these formulations have been approved by the United States Food and Drug Administration for the treatment of cancer. This is primarily due to the paucity of knowledge about nanotechnology and the fundamental biology of cancer cells. Here, we discuss the advances, types of nanomedicines, and the challenges regarding the translation of in vitro to in vivo results and their relevance to effective therapies.

Hydroxyurea and inactivation of checkpoint kinase MEC1 inhibit transcription termination and pre-mRNA cleavage at polyadenylation sites in budding yeast.

The DNA damage response (DDR) is an evolutionarily conserved process essential for cell survival. The transcription changes triggered by DDR depend on the nature of DNA damage, activation of checkpoint kinases, and the stage of cell cycle. The transcription changes can be localized and affect only damaged DNA, but they can be also global and affect genes that are not damaged. While the purpose of localized transcription inhibition is to avoid transcription of damaged genes and make DNA accessible for repair, the purpose and mechanisms of global transcription inhibition of undamaged genes are less well understood. We show here that a brief cell treatment with hydroxyurea (HU) globally inhibits RNA synthesis and transcription by RNA polymerase I, II, and III (RNAPI, RNAPII, and RNAPIII). HU reduces efficiency of transcription termination and inhibits pre-mRNA cleavage at the polyadenylation (pA) sites, destabilizes mRNAs, and shortens poly(A) tails of mRNAs, indicating defects in pre-mRNA 3' end processing. Inactivation of the checkpoint kinase Mec1p downregulates the efficiency of transcription termination and reduces the efficiency of pre-mRNAs clevage at the pA sites, suggesting the involvement of DNA damage checkpoint in transcription termination and pre-mRNA 3' end processing.

Tolerance to replication stress requires Dun1p kinase and activation of the electron transport chain.

One of the key outcomes of activation of DNA replication checkpoint (DRC) or DNA damage checkpoint (DDC) is the increased synthesis of the deoxyribonucleoside triphosphates (dNTPs), which is a prerequisite for normal progression through the S phase and for effective DNA repair. We have recently shown that DDC increases aerobic metabolism and activates the electron transport chain (ETC) to elevate ATP production and dNTP synthesis by repressing transcription of histone genes, leading to globally altered chromatin architecture and increased transcription of genes encoding enzymes of tricarboxylic acid (TCA) cycle and the ETC. The aim of this study was to determine whether DRC activates ETC. We show here that DRC activates ETC by a checkpoint kinase Dun1p-dependent mechanism. DRC induces transcription of RNR1-4 genes and elevates mtDNA copy number. Inactivation of RRM3 or SGS1, two DNA helicases important for DNA replication, activates DRC but does not render cells dependent on ETC. However, fitness of rrm3Δ and sgs1Δ cells requires Dun1p. The slow growth of rrm3Δdun1Δ and sgs1Δdun1Δ cells can be suppressed by introducing sml1Δ mutation, indicating that the slow growth is due to low levels of dNTPs. Interestingly, inactivation of ETC in dun1Δ cells results in a synthetic growth defect that can be suppressed by sml1Δ mutation, suggesting that ETC is important for dNTP synthesis in the absence of Dun1p function. Together, our results reveal an unexpected connection between ETC, replication stress, and Dun1p kinase.

Replication stress inhibits synthesis of histone mRNAs in yeast by removing Spt10p and Spt21p from the histone promoters.

Proliferating cells coordinate histone and DNA synthesis to maintain correct stoichiometry for chromatin assembly. Histone mRNA levels must be repressed when DNA replication is inhibited to prevent toxicity and genome instability due to free non-chromatinized histone proteins. In mammalian cells, replication stress triggers degradation of histone mRNAs, but it is unclear if this mechanism is conserved from other species. The aim of this study was to identify the histone mRNA decay pathway in the yeast Saccharomyces cerevisiae and determine the mechanism by which DNA replication stress represses histone mRNAs. Using reverse transcription-quantitative PCR and chromatin immunoprecipitation-quantitative PCR, we show here that histone mRNAs can be degraded by both 5' → 3' and 3' → 5' pathways; however, replication stress does not trigger decay of histone mRNA in yeast. Rather, replication stress inhibits transcription of histone genes by removing the histone gene-specific transcription factors Spt10p and Spt21p from histone promoters, leading to disassembly of the preinitiation complexes and eviction of RNA Pol II from histone genes by a mechanism facilitated by checkpoint kinase Rad53p and histone chaperone Asf1p. In contrast, replication stress does not remove SCB-binding factor transcription complex, another activator of histone genes, from the histone promoters, suggesting that Spt10p and Spt21p have unique roles in the transcriptional downregulation of histone genes during replication stress. Together, our data show that, unlike in mammalian cells, replication stress in yeast does not trigger decay of histone mRNAs but inhibits histone transcription.

A micro-solid phase extraction device to prepare a molecularly imprinted porous monolith in a facile mode for fast protein separation.

A molecularly imprinted polymeric monolith was synthesized in an aqueous environment in 15 min via UV-irradiation. The imprinted monolith was composed of hydroxyethyl methacrylate as monomer, dimethyl amino ethyl methacrylate as functional monomer, methylene bisacrylamide and piperazine diacrylamide as crosslinkers and human serum albumin as template molecule. The synthesis took place in a PDMS-based device (2.5 cm long) yielding a micro-solid phase extraction column (3 × 5 mm) with two built-in fingertight connectors for an infusion pump and fraction collector. The imprinted monolith displayed the characteristic features of a porous polymeric monolith, had dimethyl amino ethyl methacrylate and human serum albumin as functional groups within the monolith and showed high permeability (0.51 × 10-13 m2). 85% of the imprinted cavities were readily available for rebinding of human serum albumin with an imprinting factor of 1.3. In comparison to a non-imprinted monolith, molecular imprinting increased human serum albumin adsorption by > 30%. Imprinted monolith displayed selectivity for human serum albumin over other competing proteins (human transferrin, ovalbumin and carbonic anhydrase) with similar or different isoelectric points and size. Human serum albumin was adsorbed (in dynamic mode) with > 98% selectivity from diluted human plasma using the imprinted monolith device. Device to device reproducibility and reusability of the device for 5 cycles showcase the imprinted monolith micro-device efficiency.