Mitochondria and fungal pathogenesis: drug tolerance, virulence, and potential for antifungal therapy

Recently, mitochondria have been identified as important contributors to the virulence and drug tolerance of human fungal pathogens. In different scenarios, either hypo- or hypervirulence can result from changes in mitochondrial function. Similarly, specific mitochondrial mutations lead to either sensitivity or resistance to antifungal drugs. Here, we provide a synthesis of this emerging field, proposing that mitochondrial function in membrane lipid homeostasis is the common denominator underlying the observed effects of mitochondria in drug tolerance (both sensitivity and resistance). We discuss how the contrasting effects of mitochondrial dysfunction on fungal drug tolerance and virulence could be explained and the potential for targeting mitochondrial factors for future antifungal drug development.     

Systematic Phenotyping of a Large-Scale Candida glabrata Deletion Collection Reveals Novel Antifungal Tolerance Genes

The opportunistic fungal pathogen Candida glabrata is a frequent cause of candidiasis, causing infections ranging from superficial to life-threatening disseminated disease. The inherent tolerance of C. glabrata to azole drugs makes this pathogen a serious clinical threat. To identify novel genes implicated in antifungal drug tolerance, we have constructed a large-scale C. glabrata deletion library consisting of 619 unique, individually bar-coded mutant strains, each lacking one specific gene, all together representing almost 12% of the genome. Functional analysis of this library in a series of phenotypic and fitness assays identified numerous genes required for growth of C. glabrata under normal or specific stress conditions, as well as a number of novel genes involved in tolerance to clinically important antifungal drugs such as azoles and echinocandins. We identified 38 deletion strains displaying strongly increased susceptibility to caspofungin, 28 of which encoding proteins that have not previously been linked to echinocandin tolerance. Our results demonstrate the potential of the C. glabrata mutant collection as a valuable resource in functional genomics studies of this important fungal pathogen of humans, and to facilitate the identification of putative novel antifungal drug target and virulence genes.     

The concept of a changing receptor concentration: implications for the theory of drug action

Drugs are considered to produce their effects on biological tissues either by altering some physical property of cells or by interacting with specific cellular components, called receptors. Most drugs and endogenous neurotransmitters act on highly selective receptors located on the outer surface membrane of cells. These receptors were believed, until recently, to be stationary on the cell surface and to be present in unvarying numbers. Consequently, most early theorists modeled the drug-receptor interaction on the basis of stationary and static receptor molecules. The substantial advances in our understanding of drug action based on these models have partly justified this view. However, recent electron microscopic studies have revealed the presence of structures, including "coated" pits and vesicles, that appear to provide a mechanism by which cell surface receptors might be internalized in a process of endocytosis. The precise intracellular fate of these internalized receptors is unknown, but based on present understanding, it seems reasonable to believe that some are destroyed intracellularly whereas others are recycled to the cell surface. The importance of such processes to pharmacologic theory is a new awareness of a cellular pathway that is capable of internalizing drugs, receptors, or both. The implications of such a process to the theory of drug action extends to some unexplained drug phenomena such as down regulation, drug tolerance, tachyphyllaxis, and partial agonism. We present herein the theoretical framework for a model of drug action that incorporates the possibility of receptor internalization and subsequent degradation, recycling, or replacement.     

Addiction and the brain: the neurobiology of compulsion and its persistence

People take addictive drugs to elevate mood, but with repeated use these drugs produce serious unwanted effects, which can include tolerance to some drug effects, sensitization to others, and an adapted state - dependence - which sets the stage for withdrawal symptoms when drug use stops. The most serious consequence of repetitive drug taking, however, is addiction: a persistent state in which compulsive drug use escapes control, even when serious negative consequences ensue. Addiction is characterized by a long-lasting risk of relapse, which is often initiated by exposure to drug-related cues. Substantial progress has been made in understanding the molecular and cellular mechanisms of tolerance, dependence and withdrawal, but as yet we understand little of the neural substrates of compulsive drug use and its remarkable persistence. Here we review evidence for the possibility that compulsion and its persistence are based on a pathological usurpation of molecular mechanisms that are normally involved in memory.     

Comparative metabolism of the amphetamine drugs of dependence in man and monkeys.

The use of animal models to study drug dependence and tolerance requires that the species used metabolizes the drugs like man, a condition frequently not fulfilled by non-primate species. The metabolic fate of several amphetamine drugs, namely amphetamine, norephedrine, chlorphentermine and phenmetrazine, in the rhesus monkey and the tamarin and two non-primate species has been investigated and compared to that found for man. The findings show that the two primate species metabolize these drugs in a manner similar to that in man.     

Functional dissociation of mu opioid receptor signaling and endocytosis: implications for the biology of opiate tolerance and addiction.

Opiate analgesia, tolerance, and addiction are mediated by drug-induced activation of the mu opioid receptor. A fundamental question in addiction biology is why exogenous opiate drugs have a high liability for inducing tolerance and addiction while native ligands do not. Studies indicate that highly addictive opiate drugs such as morphine are deficient in their ability to induce the desensitization and endocytosis of receptors. Here, we demonstrate that this regulatory mechanism reveals an independent functional property of opiate drugs that can be distinguished from previously established agonist properties. Moreover, this property correlates with agonist propensity to promote physiological tolerance, suggesting a fundamental revision of our understanding of the role of receptor endocytosis in the biology of opiate drug action and addiction.     

Phosphodiesterase 4 inhibitors and drugs of abuse: current knowledge and therapeutic opportunities

Background

Long-term exposure to drugs of abuse causes an upregulation of the cAMP-signaling pathway in the nucleus accumbens and other forebrain regions, this common neuroadaptation is thought to underlie aspects of drug tolerance and dependence. Phosphodiesterase 4 (PDE4) is an enzyme that the selective hydrolyzes intracellular cAMP. It is expressed in several brain regions that regulate the reinforcing effects of drugs of abuse.

Objective

Here, we review the current knowledge about central nervous system (CNS) distribution of PDE4 isoforms and the effects of systemic and brain-region specific inhibition of PDE4 on behavioral models of drug addiction.

Methods

A systematic literature search was performed using the Pubmed.

Results

Using behavioral sensitization, conditioned place preference and drug self-administration as behavioral models, a large number of studies have shown that local or systemic administration of PDE4 inhibitors reduce drug intake and/or drug seeking for psychostimulants, alcohol, and opioids in rats or mice.

Conclusions

Preclinical studies suggest that PDE4 could be a therapeutic target for several classes of substance use disorder. We conclude by identifying opportunities for the development of subtype-selective PDE4 inhibitors that may reduce addiction liability and minimize the side effects that limit the clinical potential of non-selective PDE4 inhibitors. Several PDE4 inhibitors have been clinically approved for other diseases. There is a promising possibility to repurpose these PDE4 inhibitors for the treatment of drug addiction as they are safe and well-tolerated in patients.

     

Regulated endocytosis of opioid receptors: cellular mechanisms and proposed roles in physiological adaptation to opiate drugs

Opiate drugs such as morphine and heroin are among the most effective analgesics known. Prolonged or repeated administration of opiates produces adaptive changes in the nervous system that lead to reduced drug potency or efficacy (tolerance), as well as physiological withdrawal symptoms and behavioral manifestations such as craving when drug use is terminated (dependence). These adaptations limit the therapeutic utility of opiate drugs, particularly in the treatment of chronically painful conditions, and are thought to contribute to the highly addictive nature of opiates. For many years it has been proposed that physiological tolerance to opiate drugs is associated with a modification of the number or functional activity of opioid receptors in specific neurons. We now understand certain mechanisms of opioid receptor desensitization and endocytosis in considerable detail. However, the functional roles that these mechanisms play in the complex physiological adaptation of the intact nervous system to opiates are only beginning to be explored.     

A theory of drug tolerance and dependence I: a conceptual analysis

A mathematical model of drug tolerance and its underlying theory is presented. The model extends a first approach, published previously. The model is essentially more complex than the generally used model of homeostasis, which is demonstrated to fail in describing tolerance development to repeated drug administrations. The model assumes the development of tolerance to a repeatedly administered drug to be the result of a regulated adaptive process. The oral detection and analysis of exogenous substances is proposed to be the primary stimulus for the mechanism of drug tolerance. Anticipation and environmental cues are in the model considered secondary stimuli, becoming primary only in dependence and addiction or when the drug administration bypasses the natural-oral-route, as is the case when drugs are administered intravenously. The model considers adaptation to the effect of a drug and adaptation to the interval between drug taking autonomous tolerance processes. Simulations with the mathematical model demonstrate the model's behavior to be consistent with important characteristics of the development of tolerance to repeatedly administered drugs: the gradual decrease in drug effect when tolerance develops, the high sensitivity to small changes in drug dose, the rebound phenomenon and the large reactions following withdrawal in dependence. The mathematical model verifies the proposed theory and provides a basis for the implementation of mathematical models of specific physiological processes. In addition, it establishes a relation between the drug dose at any moment, and the resulting drug effect and relates the magnitude of the reactions following withdrawal to the rate of tolerance and other parameters involved in the tolerance process. The present paper analyses the concept behind the model. The next paper discusses the mathematical model.     

On the relationship between drug’s size,cell membrane mechanical properties and high levels of multi drug resistance: a comparison to published data

Multi drug resistance (MDR) or cross resistance to drugs was initially explained on the basis that MDR cells express drug transporters that expel membrane-embedded drugs. However, it is now clear that transporters are a single piece from a complex puzzle. An issue that has been solved recently is, given that these transporters have to handle drugs, why should a membrane-embedded drug and a transporter meet? To solve this problem, a theory has been suggested considering the interaction between the cell membrane mechanical properties and the size of drugs. In simple terms, this theory proposes that an excess in the packing of lipid in the inner leaflet of the membrane of MDR cells is responsible for blocking drugs mechanically as a function of their sizes at the membrane level, thus impairing their flux into the cytosol. In turn it is expected that this would allow any membrane embedded drug to diffuse toward transporters. The study concluded that the size of drugs is necessarily important regarding the mechanical interaction between the drug and the membrane, and likely to be central to MDR. Remarkably, an experimental study based on MDR and published years ago concluded that the molecular weight (MW) of drugs was central to MDR (Biedler and Riehm in Cancer Res 30:1174–1184, 1970). Given that size and MW are linked together, I have compared the former theory to the latter experimental data and demonstrate that, indeed, basic membrane mechanics is involved in high levels of cross resistance to drugs in Pgp expressing cells.     

Pharmacologic control of the hormonally modulated immune response. III. Prolongation of allogeneic skin graft rejection and prevention of runt disease by a combination of drugs acting on neuroendocrine functions.

A recently developed pharmacologic means for suppressing acquired immunity by drugs acting on neuroendocrine regulation has been applied to transplantation immune reactions. A number of drugs have been tested singly and in combination for their capacity to suppress the immune response of mice grafted with allogeneic skin. Another model involved newborn F1 hybrid recipients inoculated with spleen cells from donors of parental strains that had been made specifically "unresponsive" by drug and alloantigen treatment. These procedures led to the identification of a combination of four drugs that induced a remarkable delay in allograft rejection and a prolonged unresponsiveness to alloantigens. This combination of drugs also abrogated the graft-vs-host-runting syndrome in newborn hybrid recipients.     

A theory of drug tolerance and dependence II: the mathematical model

The preceding paper presented a model of drug tolerance and dependence. The model assumes the development of tolerance to a repeatedly administered drug to be the result of a regulated adaptive process. The oral detection and analysis of exogenous substances is proposed to be the primary stimulus for the mechanism of drug tolerance. Anticipation and environmental cues are in the model considered secondary stimuli, becoming primary in dependence and addiction or when the drug administration bypasses the natural-oral-route, as is the case when drugs are administered intravenously. The model considers adaptation to the effect of a drug and adaptation to the interval between drug taking autonomous tolerance processes. Simulations with the mathematical model demonstrate the model's behaviour to be consistent with important characteristics of the development of tolerance to repeatedly administered drugs: the gradual decrease in drug effect when tolerance develops, the high sensitivity to small changes in drug dose, the rebound phenomenon and the large reactions following withdrawal in dependence. The present paper discusses the mathematical model in terms of its design. The model is a nonlinear, learning feedback system, fully satisfying control theoretical principles. It accepts any form of the stimulus-the drug intake-and describes how the physiological processes involved affect the distribution of the drug through the body and the stability of the regulation loop. The mathematical model verifies the proposed theory and provides a basis for the implementation of mathematical models of specific physiological processes.     

Anorexia nervosa and bulimia nervosa.

No definitive therapy exists for anorexia nervosa (AN) or bulimia nervosa (BN). Nevertheless, biologic and psychologic research into these disorders has increased over the last decade. We examine the various drugs available for treatment. Advances in pharmacotherapy for AN have been modest and have reflected efforts either to stimulate hunger and weight gain or to control complications of the starvation process. Food remains the "drug" of choice. Antidepressants have been found to be beneficial in the treatment of BN. The meaning of this in the context of a relation between BN and mood disorders remains unclear, since coexistent depression does not predict a positive response to these drugs. Pharmacotherapy represents a single but important dimension of the management of patients with eating disorders. The optimal integration of drug therapy and psychotherapy and the identification of predictors of a positive response to drugs have yet to be addressed by clinical research.     

双刃剑:自噬与肿瘤发生发展的关系及相关靶点小分子药物研究进展

自噬是哺乳动物细胞内重要且复杂的生理活动,同样影响着肿瘤的发生与进展.随着抗肿瘤药物的广泛使用,肿瘤耐药问题日益突出,影响患者预后.多年研究显示,肿瘤自噬与耐药密切相关.目前,已有越来越多的自噬相关小分子药物被用来调节肿瘤自噬活动,以求其能被广泛运用于抗癌方案之中.该文将针对自噬在癌症发生发展过程中的分子机制及相关小分...     

纳米混悬药物传递系统研究进展

在新药研发过程中,约有40%的药物存在溶解性差的问题,限制了药物的开发与应用。纳米混悬剂是20世纪末发展起来的一种纳米药物传递系统,可增加难溶性药物的溶解度和溶出速率、改变药物的体内药物动力学特征、提高口服生物利用度、安全性和有效性。纳米混悬剂不但适用于水溶性差的药物,而且适用于水溶性、脂溶性均较差的药物,其制备方法主要包括"bottom up"和"top down"两种。本文从纳米混悬剂的特点、理论基础、专利技术及应用等方面对纳米混悬剂的研究进展进行了综述。纳米混悬剂对改善难溶性药物的溶出、吸收,提高难溶性药物的有效性、安全性等方面具有显著优势,且适合工业化生产,已有越来越多的产品问世。纳米混悬技术是未来药物传递系统的发展方向之一,将具有良好的应用前景。