Rationale and objective
Intravenous infusions of nicotine appear to exert little primary reinforcing effects in adult rats but, instead, maintain self-administration behavior at least, in part, by ...increasing the intrinsic reinforcing effects of drug-paired sensory stimuli. The present study examined instead the impact of a motivationally neutral cue on self-administration.
Methods
Adult male Long-Evans rats were permitted to self-administer nicotine (0.015 mg/kg IV given over 30 s, 2 h/day) or saline presented with or without a sensory stimulus (light, white noise). Fixed and progressive ratio reinforcement schedules of nicotine reinforcement were tested. Experiment 2 determined whether noncontingent nicotine or mecamylamine (nicotinic antagonist) would induce lever pressing for either sensory stimulus. Experiment 3 tested whether the white noise stimulus alone could maintain responding after repeated pairing with self-administered nicotine. Finally, the sensory stimuli were assessed for possible aversive properties.
Results
Nicotine infusions alone were at best weakly reinforcing. The white noise stimulus, presented alone, was neither reinforcing nor aversive, whereas the white light appeared marginally reinforcing. Both stimuli, however, facilitated intravenous nicotine self-administration. Neither nicotine nor mecamylamine challenge rendered the white noise reinforcing. The white noise, after being self-administered with nicotine, failed to maintain self-administration behavior on its own.
Conclusions
Even a motivationally neutral sensory stimulus, lacking detectable primary or secondary reinforcing properties, can facilitate self-administration of nicotine. Possibly, drug-paired stimuli provide a "response marker" or serve as a temporal bridge between the operant response and drug effect. Motivationally neutral stimuli may therefore serve to isolate primary reinforcing effects of nicotine.
Project portfolio management deals with the dynamic selection of research and development (R&D) projects and determination of resource allocations to these projects over a planning period. Given the ...uncertainties and resource limitations over the planning period, the objective is to maximize the expected total discounted return or the expectation of some other function for all projects over a long time horizon. We develop a detailed formal description of this problem and the corresponding decision process, and then model it as a multistage stochastic integer program with endogenous uncertainty. Accounting for this endogeneity, we propose an efficient solution approach for the resulting model, which involves the development of a formulation technique that is amenable to scenario decomposition. The proposed solution algorithm also includes an application of the sample average approximation method, where the sample problems are solved through Lagrangian relaxation and a new lower bounding heuristic. The performance of the overall solution procedure is demonstrated using several implementations of the proposed approach.
Understanding the prebiotic genesis of 2-deoxy-d-ribose, which forms the backbone of DNA, is of crucial importance to unravelling the origins of life, yet remains open to debate. Here we demonstrate ...that 20 mol% of proteinogenic amino esters promote the selective formation of 2-deoxy-d-ribose over 2-deoxy-d-threopentose in combined yields of ≥4%. We also demonstrate the first aldol reaction promoted by prebiotically-relevant proteinogenic amino nitriles (20 mol%) for the enantioselective synthesis of d-glyceraldehyde with 6% ee, and its subsequent conversion into 2-deoxy-d-ribose in yields of ≥ 5%. Finally, we explore the combination of these two steps in a one-pot process using 20 mol% of an amino ester or amino nitrile promoter. It is hence demonstrated that three interstellar starting materials, when mixed together with an appropriate promoter, can directly lead to the formation of a mixture of higher carbohydrates, including 2-deoxy-d-ribose.
The initiation of apoptosis in response to the disruption of mitosis provides surveillance against chromosome instability. Here, we show that proteolytic destruction of the key regulator Mcl‐1 during ...an extended mitosis requires the anaphase‐promoting complex or cyclosome (APC/C) and is independent of another ubiquitin E3 ligase, SCFFbw7. Using live‐cell imaging, we show that the loss of Mcl‐1 during mitosis is dependent on a D box motif found in other APC/C substrates, while an isoleucine‐arginine (IR) C‐terminal tail regulates the manner in which Mcl‐1 engages with the APC/C, converting Mcl‐1 from a Cdc20‐dependent and checkpoint‐controlled substrate to one that is degraded independently of checkpoint strength. This mechanism ensures a relatively slow but steady rate of Mcl‐1 degradation during mitosis and avoids its catastrophic destruction when the mitotic checkpoint is satisfied, providing an apoptotic timer that can distinguish a prolonged mitotic delay from normal mitosis. Importantly, we also show that inhibition of Cdc20 promotes mitotic cell death more effectively than loss of APC/C activity through differential effects on Mcl‐1 degradation, providing an improved strategy to kill cancer cells.
Synopsis
The APC/C ubiquitin ligase mediates mitotic degradation of the anti‐apoptotic regulator Mcl‐1 independent of its activator Cdc20. This atypical mechanism provides a timer for cell death induction upon prolonged mitotic arrest, and an opportunity to kill cancer cells in combination with drugs that cause such an arrest.
Live‐cell imaging shows that mitotic Mcl‐1 destruction depends on the APC/C‐targeting D box motif.
A C‐terminal APC/C‐interaction IR tail converts Mcl‐1 into a Cdc20‐ and checkpoint‐independent substrate.
Constitutive slow Mcl‐1 degradation ensures cell death induction only after prolonged mitotic delay but not during normal mitosis.
Specific inhibition of Cdc20‐dependent APC/C functions enhances mitotic cell death through differential effects on Mcl‐1 and cyclin B stabilities.
By acting in a slow, Cdc20‐independent manner, APC/C‐degradation of apoptotic regulator Mcl‐1 serves as a timer that distinguishes a prolonged mitotic delay from normal mitosis.
Demonstrating intracellular protein target engagement is an essential step in the development and progression of new chemical probes and potential small molecule therapeutics. However, this can be ...particularly challenging for poorly studied and noncatalytic proteins, as robust proximal biomarkers are rarely known. To confirm that our recently discovered chemical probe 1 (CCT251236) binds the putative transcription factor regulator pirin in living cells, we developed a heterobifunctional protein degradation probe. Focusing on linker design and physicochemical properties, we generated a highly active probe 16 (CCT367766) in only three iterations, validating our efficient strategy for degradation probe design against nonvalidated protein targets.
Convergent evidence suggests that amphetamine (AMPH) exerts its rewarding and locomotor stimulating effects via release of dopamine in the nucleus accumbens. However, there is no consensus as to the ...relative contributions of core and medial shell subregions to these effects. Moreover, the literature is based primarily on intracranial administration, which cannot fully mimic the drug distribution achieved by systemic administration. In the present study, the effects of bilateral 6-hydroxydopamine lesions of the accumbens core or medial shell on rewarding and locomotor stimulating effects of systemically administered amphetamine (0.75 mg/kg, i.p.) were examined in a conditioned place preference (CPP) procedure relying solely on tactile cues (floor texture). Residual dopamine innervation was quantified by 125I-RTI-55 binding to the dopamine transporter. When lesions were performed before the conditioning phase, AMPH-induced locomotor stimulation and CPP magnitude were positively correlated with residual dopamine transporter binding in core and medial shell, respectively. Medial shell lesions did not affect morphine CPP, arguing that a sensory or mnemonic deficit was not responsible for the lesion-induced reduction in AMPH CPP. Medial shell lesions performed between the conditioning phase and the test day reduced the expression of amphetamine CPP. These results suggest that after systemic amphetamine administration, rewarding and locomotor stimulating effects of the drug are anatomically dissociated within the nucleus accumbens: the medial shell contributes to rewarding effects, whereas the core contributes to behavioral activation.
A Two‐Step Synthesis of 2‐Spiropiperidines Griggs, Samuel D.; Thompson, Nathan; Tape, Daniel T. ...
Chemistry : a European journal,
July 12, 2017, Letnik:
23, Številka:
39
Journal Article
Recenzirano
Odprti dostop
A general two‐step synthesis of 2‐spiropiperidines has been developed. δ‐Amino‐β‐ketoesters can be reacted with cyclic ketones to generate 2‐spiropiperidines in good to excellent yields. The ...2‐spiropiperidines formed occupy an under‐explored region of 3D‐chemical space and are novel scaffolds for use in drug discovery programs. These 2‐spiropiperidines can be further functionalised to generate small highly sp3‐rich structures, which exhibit an excellent likeness to lead‐molecules in drug discovery.
Spiro‐tastic! 2‐Spiropiperidines have been readily synthesised in good to excellent yields by means of a two‐step procedure. These molecules constitute novel 3D‐scaffolds for use in drug discovery programs, occupying an under‐populated region of chemical space. The 2‐spiropiperidines formed can be readily modified into lead‐like molecules.
Cell-cycle checkpoints induced by DNA damage or replication play critical roles in the maintenance of genomic integrity during cell proliferation. Biochemical analysis of checkpoint pathways has been ...greatly facilitated by the use of cell-free systems made from Xenopus eggs. In the present study, we describe a human cell-free system that reproduces a DNA-dependent checkpoint pathway acting on the Chk1 protein kinase. In this system, double-stranded DNA oligonucleotides induce the phosphorylation of Chk1 at activating sites targeted by ATR ATM (ataxia telangiectasia mutated)- and Rad3-related and ATM kinases. Phosphorylation of Chk1 is dependent on the interaction of Claspin, a protein first identified in Xenopus as a Chk1-binding protein. We show that the DNA-dependent binding of Chk1 to Claspin requires two phosphorylation sites, Thr916 and Ser945, which lie within the Chk1-binding domain of Claspin. Using a phosphopeptide derived from the consensus motif of these sites, we show that the interaction of Claspin with Chk1 is required for the ATR/ATM-dependent phosphorylation of Chk1. Using a panel of protein kinase inhibitors, we provide evidence that Chk1 is phosphorylated at an additional site in response to activation of the checkpoint response, probably by autophosphorylation. Claspin is phosphorylated in the Chk1-binding domain in an ATR/ATM-dependent manner and is also targeted by additional kinases in response to double-stranded DNA oligonucleotides. This cell-free system will facilitate further biochemical analysis of the Chk1 pathway in humans.
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