The increasing prevalence of chronic and hospital-acquired infections produced by multidrug-resistant (MDR) or extensively drug-resistant (XDR) Pseudomonas aeruginosa strains is associated with significant morbidity and mortality. This growing threat results from the extraordinary capacity of this pathogen for developing resistance through chromosomal mutations and from the increasing prevalence of trans- ferable resistance determinants, particularly those encoding carbapenemases or extended-spectrum -lactamases (ESBLs). P. aeruginosa has a nonclonal epidemic population structure, composed of a limited number of widespread clones which are selected from a background of a large quantity of rare and unre- lated genotypes that are recombining at high frequency. Indeed, recent concerning reports have provided evidence of the existence of MDR/XDR global clones, denominated high-risk clones, disseminated in hos- pitals worldwide; ST235, ST111, and ST175 are likely those more widespread. Noteworthy, the vast majority of infections by MDR, and specially XDR, strains are produced by these and few other clones worldwide. Moreover,the association of high-risk clones, particularly ST235, with transferable resistance is overwhelming; nearly 100 different horizontally-acquired resistance elements and up to 39 different acquired -lactamases have been reported so far among ST235 isolates. Likewise, MDR internationally- disseminated epidemic strains, such as the Liverpool Epidemic Strain (LES, ST146), have been noted as well among cystic fibrosis patients. Here we review the population structure, epidemiology, antimicrobial resistance mechanisms and virulence of the P. aeruginosa high-risk clones. The phenotypic and genetic factors potentially driving the success of high-risk clones, the aspects related to their detection in the clinical microbiology laboratory and the implications for infection control and public health are also discussed.

Azole resistance is an emerging problem in Aspergillus fumigatus and is associated with a high probability of treatment failure. An azole resistance mechanism typically decreases the activity of multiple azole compounds, depending on the mutation. As alternative treatment options are limited and in some iso- lates the minimum inhibitory concentration (MIC) increases by only a few two-fold dilutions steps, we investigated if voriconazole and posaconazole have a role in treating azole-resistant Aspergillus disease. The relation between resistance genotype and phenotype, pharmacokinetic and pharmacodynamic prop- erties, and (pre)clinicaltreatment efficacy were reviewed. The results were used to estimate the exposure needed to achieve the pharmacodynamic targetfor each MIC. For posaconazole adequate exposure can be achieved only for wild type isolates as dose escalation does not allow PD target attainment. However, the new intravenous formulation might result in sufficient exposure to treat isolates with a MIC of 0.5 mg/L. For voriconazole our analysis indicated that the exposure needed to treat infection due to isolates with a MIC of 2 mg/L is feasible and maybe isolates with a MIC of 4 mg/L. However, extreme caution and strict monitoring of drug levels would be required, as the probability of toxicity will also increase.

Over the past decade, the proteasome inhibitor bortezomib (Velcade) has not only gained a cornerstone position in the treatment of hematological malignancies, particularly multiple myeloma and mantle cell lymphoma, but also in experimental therapeutics of acute leukemia. However, the therapeutic efficacy of bortezomib is hampered by the emergence of acquired resistance, for which multifactorial mechanisms have been identified. This review summarizes the current status ofthe molecular mechanisms underlying resistance to proteasome inhibitors that emerged in preclinical therapeutic studies, and discusses these findings in the clinical perspective of novel therapeutic modalities of hematological malignancies. The specific topics that will be addressed in the current review include the recently established mechanisms of resistance to proteasome inhibitors: the role of constitutive and immunoproteasomes, mutations in pro- teasome subunits, unfolded protein response, XBP1 and MARCKS proteins, multidrug efflux transporters, aggresomes and autophagy, as well as the impact of pro-survival signaling pathways and bone mar- row microenvironment. The growing knowledge of the determinants that confer bortezomib resistance and/or toxicity has provided the basis for the rational development of second generation proteasome inhibitors, some of which were recently approved or that are undergoing clinical evaluation as novel strategies to overcome bortezomib resistance as well as to enhance clinical therapeutic efficacy along with minimal side effects. Collectively, these combined approaches should enhance therapeutic efficacy and outcome in patients with hematological malignancies.

Despite the major progresses in biomedical research and the development of novel therapeutics and treatment strategies, cancer is still among the dominant causes of death worldwide. One of the crucial challenges in the clinical management of cancer is primary (intrinsic) and secondary (acquired) resistance to both conventional and targeted chemotherapeutics. Multiple mechanisms have been identifiedthat underlie intrinsic and acquired chemoresistance: these include impaired drug uptake, increased drug efflux, deletion of receptors, altered drug metabolism, quantitative and qualitative alterations in drug targets, increased DNA damage repair and various mechanisms of anti-apoptosis. The fast efflux of anticancer drugs mediated by multidrug efflux pumps and the partial or complete reversibility of chemoresistance combined with the absence of genetic mutations suggests a multifactorial process. However, a growing body of recent evidence suggests that chemoresistance is often triggered by the highly acidic microenvironment of tumors. The vast majority of drugs, including conventional chemotherapeutics and more recent biological agents, are weak bases that are quickly protonated and neutralized in acidic environments, such as the extracellular microenvironment and the acidic organelles of tumor cells. It is therefore essential to develop new strategies to overcome the entrapment and neutralization of weak base drugs. One such strategy is the use of proton pump inhibitors which can enhance tumor chemosensitivity by increasing the pH of the tumor microenvironment. Recent clinical trials in animals with spontaneous tumors have indicated that patient alkalization is capable of reversing acquired chemoresistance in a large percentage of tumors that are refractory to chemotherapy. Of particular interest was the benefit of alkalization for patients undergoing metronomic regimens which are becoming more widely used in veterinary medicine. Overall, these results provide substantial new evidence that altering the acidic tumor microenvironment is an effective, well tolerated and low cost strategy for the overcoming of anticancer drug resistance. © 2015 Elsevier Ltd. All rights reserved.

Drug resistance remains a leading cause of chemotherapeutic treatment failure and cancer-related mortality. While some mechanisms of anticancer drug resistance have been well characterized, mul- tiple mechanisms remain elusive. In this respect, passive ion trapping-based lysosomal sequestration of multiple hydrophobic weak-base chemotherapeutic agents was found to reduce the accessibility of these drugs to their target sites, resulting in a markedly reduced cytotoxic effect and drug resis- tance. Recently we have demonstrated that lysosomal sequestration of hydrophobic weak base drugs triggers TFEB-mediated lysosomal biogenesis resulting in an enlarged lysosomal compartment, capable of enhanced drug sequestration. This study further showed that cancer cells with an increased num- ber of drug-accumulating lysosomes are more resistant to lysosome-sequestered drugs, suggesting a model of drug-induced lysosome-mediated chemoresistance. In addition to passive drug sequestration of hydrophobic weak base chemotherapeutics, other mechanisms of lysosome-mediated drug resistance have also been reported; these include active lysosomal drug sequestration mediated by ATP-driven transporters from the ABC superfamily, and a role for lysosomal copper transporters in cancer resistance to platinum-based chemotherapeutics. Furthermore, lysosomal exocytosis was suggested as a mech- anism to facilitate the clearance of chemotherapeutics which highly accumulated in lysosomes, thus providing an additional line of resistance, supplementing the organelle entrapment of chemotherapeu- tics away from their target sites. Along with these mechanisms of lysosome-mediated drug resistance, several approaches were recently developed for the overcoming of drug resistance or exploiting lysoso- mal drug sequestration, including lysosomal photodestruction and drug-induced lysosomal membrane permeabilization. In this review we explore the current literature addressing the role of lysosomes in mediating cancer drug resistance as well as novel modalities to overcome this chemoresistance.

Azole resistance is an emerging problem in Aspergillus fumigatus and is associated with a high probability of treatment failure. An azole resistance mechanism typically decreases the activity of multiple azole compounds, depending on the mutation. As alternative treatment options are limited and in some iso- lates the minimum inhibitory concentration (MIC) increases by only a few two-fold dilutions steps, we investigated if voriconazole and posaconazole have a role in treating azole-resistant Aspergillus disease. The relation between resistance genotype and phenotype, pharmacokinetic and pharmacodynamic prop- erties, and (pre)clinicaltreatment efficacy were reviewed. The results were used to estimate the exposure needed to achieve the pharmacodynamic targetfor each MIC. For posaconazole adequate exposure can be achieved only for wild type isolates as dose escalation does not allow PD target attainment. However, the new intravenous formulation might result in sufficient exposure to treat isolates with a MIC of 0.5 mg/L. For voriconazole our analysis indicated that the exposure needed to treat infection due to isolates with a MIC of 2 mg/L is feasible and maybe isolates with a MIC of 4 mg/L. However, extreme caution and strict monitoring of drug levels would be required, as the probability of toxicity will also increase.

The increasing prevalence of chronic and hospital-acquired infections produced by multidrug-resistant (MDR) or extensively drug-resistant (XDR) Pseudomonas aeruginosa strains is associated with significant morbidity and mortality. This growing threat results from the extraordinary capacity of this pathogen for developing resistance through chromosomal mutations and from the increasing prevalence of trans- ferable resistance determinants, particularly those encoding carbapenemases or extended-spectrum -lactamases (ESBLs). P. aeruginosa has a nonclonal epidemic population structure, composed of a limited number of widespread clones which are selected from a background of a large quantity of rare and unre- lated genotypes that are recombining at high frequency. Indeed, recent concerning reports have provided evidence of the existence of MDR/XDR global clones, denominated high-risk clones, disseminated in hos- pitals worldwide; ST235, ST111, and ST175 are likely those more widespread. Noteworthy, the vast majority of infections by MDR, and specially XDR, strains are produced by these and few other clones worldwide. Moreover,the association of high-risk clones, particularly ST235, with transferable resistance is overwhelming; nearly 100 different horizontally-acquired resistance elements and up to 39 different acquired -lactamases have been reported so far among ST235 isolates. Likewise, MDR internationally- disseminated epidemic strains, such as the Liverpool Epidemic Strain (LES, ST146), have been noted as well among cystic fibrosis patients. Here we review the population structure, epidemiology, antimicrobial resistance mechanisms and virulence of the P. aeruginosa high-risk clones. The phenotypic and genetic factors potentially driving the success of high-risk clones, the aspects related to their detection in the clinical microbiology laboratory and the implications for infection control and public health are also discussed.

Azole resistance is an emerging problem in Aspergillus fumigatus and is associated with a high probability of treatment failure. An azole resistance mechanism typically decreases the activity of multiple azole compounds, depending on the mutation. As alternative treatment options are limited and in some iso- lates the minimum inhibitory concentration (MIC) increases by only a few two-fold dilutions steps, we investigated if voriconazole and posaconazole have a role in treating azole-resistant Aspergillus disease. The relation between resistance genotype and phenotype, pharmacokinetic and pharmacodynamic prop- erties, and (pre)clinicaltreatment efficacy were reviewed. The results were used to estimate the exposure needed to achieve the pharmacodynamic targetfor each MIC. For posaconazole adequate exposure can be achieved only for wild type isolates as dose escalation does not allow PD target attainment. However, the new intravenous formulation might result in sufficient exposure to treat isolates with a MIC of 0.5 mg/L. For voriconazole our analysis indicated that the exposure needed to treat infection due to isolates with a MIC of 2 mg/L is feasible and maybe isolates with a MIC of 4 mg/L. However, extreme caution and strict monitoring of drug levels would be required, as the probability of toxicity will also increase.

Over the past decade, the proteasome inhibitor bortezomib (Velcade) has not only gained a cornerstone position in the treatment of hematological malignancies, particularly multiple myeloma and mantle cell lymphoma, but also in experimental therapeutics of acute leukemia. However, the therapeutic efficacy of bortezomib is hampered by the emergence of acquired resistance, for which multifactorial mechanisms have been identified. This review summarizes the current status ofthe molecular mechanisms underlying resistance to proteasome inhibitors that emerged in preclinical therapeutic studies, and discusses these findings in the clinical perspective of novel therapeutic modalities of hematological malignancies. The specific topics that will be addressed in the current review include the recently established mechanisms of resistance to proteasome inhibitors: the role of constitutive and immunoproteasomes, mutations in pro- teasome subunits, unfolded protein response, XBP1 and MARCKS proteins, multidrug efflux transporters, aggresomes and autophagy, as well as the impact of pro-survival signaling pathways and bone mar- row microenvironment. The growing knowledge of the determinants that confer bortezomib resistance and/or toxicity has provided the basis for the rational development of second generation proteasome inhibitors, some of which were recently approved or that are undergoing clinical evaluation as novel strategies to overcome bortezomib resistance as well as to enhance clinical therapeutic efficacy along with minimal side effects. Collectively, these combined approaches should enhance therapeutic efficacy and outcome in patients with hematological malignancies.

Despite the major progresses in biomedical research and the development of novel therapeutics and treatment strategies, cancer is still among the dominant causes of death worldwide. One of the crucial challenges in the clinical management of cancer is primary (intrinsic) and secondary (acquired) resistance to both conventional and targeted chemotherapeutics. Multiple mechanisms have been identifiedthat underlie intrinsic and acquired chemoresistance: these include impaired drug uptake, increased drug efflux, deletion of receptors, altered drug metabolism, quantitative and qualitative alterations in drug targets, increased DNA damage repair and various mechanisms of anti-apoptosis. The fast efflux of anticancer drugs mediated by multidrug efflux pumps and the partial or complete reversibility of chemoresistance combined with the absence of genetic mutations suggests a multifactorial process. However, a growing body of recent evidence suggests that chemoresistance is often triggered by the highly acidic microenvironment of tumors. The vast majority of drugs, including conventional chemotherapeutics and more recent biological agents, are weak bases that are quickly protonated and neutralized in acidic environments, such as the extracellular microenvironment and the acidic organelles of tumor cells. It is therefore essential to develop new strategies to overcome the entrapment and neutralization of weak base drugs. One such strategy is the use of proton pump inhibitors which can enhance tumor chemosensitivity by increasing the pH of the tumor microenvironment. Recent clinical trials in animals with spontaneous tumors have indicated that patient alkalization is capable of reversing acquired chemoresistance in a large percentage of tumors that are refractory to chemotherapy. Of particular interest was the benefit of alkalization for patients undergoing metronomic regimens which are becoming more widely used in veterinary medicine. Overall, these results provide substantial new evidence that altering the acidic tumor microenvironment is an effective, well tolerated and low cost strategy for the overcoming of anticancer drug resistance. © 2015 Elsevier Ltd. All rights reserved.

Drug resistance remains a leading cause of chemotherapeutic treatment failure and cancer-related mortality. While some mechanisms of anticancer drug resistance have been well characterized, mul- tiple mechanisms remain elusive. In this respect, passive ion trapping-based lysosomal sequestration of multiple hydrophobic weak-base chemotherapeutic agents was found to reduce the accessibility of these drugs to their target sites, resulting in a markedly reduced cytotoxic effect and drug resis- tance. Recently we have demonstrated that lysosomal sequestration of hydrophobic weak base drugs triggers TFEB-mediated lysosomal biogenesis resulting in an enlarged lysosomal compartment, capable of enhanced drug sequestration. This study further showed that cancer cells with an increased num- ber of drug-accumulating lysosomes are more resistant to lysosome-sequestered drugs, suggesting a model of drug-induced lysosome-mediated chemoresistance. In addition to passive drug sequestration of hydrophobic weak base chemotherapeutics, other mechanisms of lysosome-mediated drug resistance have also been reported; these include active lysosomal drug sequestration mediated by ATP-driven transporters from the ABC superfamily, and a role for lysosomal copper transporters in cancer resistance to platinum-based chemotherapeutics. Furthermore, lysosomal exocytosis was suggested as a mech- anism to facilitate the clearance of chemotherapeutics which highly accumulated in lysosomes, thus providing an additional line of resistance, supplementing the organelle entrapment of chemotherapeu- tics away from their target sites. Along with these mechanisms of lysosome-mediated drug resistance, several approaches were recently developed for the overcoming of drug resistance or exploiting lysoso- mal drug sequestration, including lysosomal photodestruction and drug-induced lysosomal membrane permeabilization. In this review we explore the current literature addressing the role of lysosomes in mediating cancer drug resistance as well as novel modalities to overcome this chemoresistance.

Azole resistance is an emerging problem in Aspergillus fumigatus and is associated with a high probability of treatment failure. An azole resistance mechanism typically decreases the activity of multiple azole compounds, depending on the mutation. As alternative treatment options are limited and in some iso- lates the minimum inhibitory concentration (MIC) increases by only a few two-fold dilutions steps, we investigated if voriconazole and posaconazole have a role in treating azole-resistant Aspergillus disease. The relation between resistance genotype and phenotype, pharmacokinetic and pharmacodynamic prop- erties, and (pre)clinicaltreatment efficacy were reviewed. The results were used to estimate the exposure needed to achieve the pharmacodynamic targetfor each MIC. For posaconazole adequate exposure can be achieved only for wild type isolates as dose escalation does not allow PD target attainment. However, the new intravenous formulation might result in sufficient exposure to treat isolates with a MIC of 0.5 mg/L. For voriconazole our analysis indicated that the exposure needed to treat infection due to isolates with a MIC of 2 mg/L is feasible and maybe isolates with a MIC of 4 mg/L. However, extreme caution and strict monitoring of drug levels would be required, as the probability of toxicity will also increase.