Academic literature on the topic 'Delayed Death Inhibitors'

ABSTRACTToxoplasma gondiiand related human parasites contain an essential plastid organelle called the apicoplast. Clinically used antibiotics and other inhibitors that disrupt apicoplast biogenesis cause a mysterious “delayed-death” phenotype in which parasite growth is unaffected during the first lytic cycle of inhibitor treatment but is severely inhibited in the second lytic cycle even after drug removal. Critical to understanding the complex downstream cellular effects of these drug classes are the timing of apicoplast loss during inhibitor treatment and how it relates to this peculiar growth phenotype. Here we show that, upon treatment with diverse classes of apicoplast inhibitors, newly replicatedT. gondiiparasites in the first lytic cycle initially form apicoplasts with defects in protein import or genome replication and eventually fail to inherit the apicoplast altogether. Despite the accumulation of parasites with defective or missing apicoplasts, growth is unaffected during the first lytic cycle, as previously observed. Strikingly, concomitant inhibition of host cell isoprenoid biosynthesis results in growth inhibition in the first lytic cycle and unmasks the apicoplast defects. These results suggest that defects in and even the complete loss of the apicoplast inT. gondiiare partially rescued by scavenging of host cell metabolites, leading to death that is delayed. Our findings uncover host cell interactions that can alleviate apicoplast inhibition and highlight key differences in delayed-death inhibitors betweenT. gondiiandPlasmodium falciparum.

ABSTRACT Targeting of apicoplast replication and protein synthesis in the apicomplexan Toxoplasma gondii has conventionally been associated with the typical “delayed death” phenotype, characterized by the death of parasites only in the generation following drug intervention. We demonstrate that antibiotics like clindamycin, chloramphenicol, and tetracycline, inhibitors of prokaryotic protein synthesis, invoke the delayed death phenotype in Plasmodium falciparum, too, as evident from a specific reduction of apicoplast genome copy number. Interestingly, however, molecules like triclosan, cerulenin, fops, and NAS-91, inhibitors of the recently discovered fatty acid synthesis pathway, and succinyl acetone, an inhibitor of heme biosynthesis that operates in the apicoplast of the parasite, display rapid and striking parasiticidal effects. Our results draw a clear distinction between apicoplast functions per se and the apicoplast as the site of metabolic pathways, which are required for parasite survival, and thus subserve the development of novel antimalarial therapy.

Protein tyrosine phosphorylation plays an important role in the regulation of neuronal function. We examined the effects of inhibition of tyrosine phosphorylation on ischemic neuronal damage in the CA1 region of the hippocampus. In the gerbil hippocampus, genistein and lavendustin A, tyrosine kinase inhibitors, were administered 30 min before initiation of 5-min ischemia and reperfusion. Both genistein and lavendustin A blocked tyrosine phosphorylation and prevented delayed neuronal death (DND). However, genistin, an inactive analogue of genistein, did not block DND. Genistein was dose-dependent in the inhibition of DND after ischemia and reperfusion. Administration of genistein 5 to 10 min after ischemia and reperfusion was ineffective in blocking DND in the CA1 region of the hippocampus. The tyrosine kinase inhibitors selectively blocked the phosphorylation of microtubule-associated protein (MAP)-2 kinase following ischemia and reperfusion injury. These results suggest that tyrosine phosphorylation in the ischemic brain is important for neuronal injury and that MAP-2 kinase may play a role in the onset of delayed neuronal death.

We show that mouse sperm die spontaneously within 1–2 days in culture and that treatment with either staurosporine (STS) and cycloheximide (CHX) or a peptide caspase inhibitor does not accelerate or delay the cell death. Chicken erythrocytes, by contrast, are induced to die by either serum deprivation or treatment with STS and CHX, and embryonic erythrocytes are more sensitive than adult erythrocytes to both treatments. Although these erythrocyte deaths display a number of features that are characteristic of apoptosis, they are not blocked, or even delayed, by peptide caspase inhibitors, and most of the cells die without apparently activating caspases. A small proportion of the dying erythrocytes do activate caspase-3, but even these cells, which seem to be the least mature erythrocytes, die just as quickly in the presence of caspase inhibitors. Our findings raise the possibility that both mouse sperm and chicken erythrocytes have a death programme that may not depend on caspases and that chicken erythrocytes lose caspases as they mature. Chicken erythrocytes may provide a useful ‘stripped down’ cell system to try to identify the protein components of such a death programme, which may serve to back-up the conventional caspase-dependent suicide mechanism in many cell types.

We describe sustained hyposmotic stress as a novel type of environmental condition enforcing apoptosis. In a dose- and time-dependent fashion, hyposmotic stress leads to a delayed type of apoptosis with considerable variations in constitutive sensitivity among different cell types. For example, after 48 h at 84 mosmol/l, the death rate ranged from 10.8 ± 0.7% in AsPc1 human pancreatic carcinoma cells to 72.0 ± 1.6% in HK-2 human kidney tubule cells. Caspase inhibitors rendered cells more resistant to hyposmolar stress; the caspase 3 inhibitor Ac-Asp-Glu-Val-aspartic acid aldehyde was the most efficient. After 24 h of stress, HT-29 colon carcinoma and HK-2 cells had increased their mitochondrial mass. This went along with an increase in mitochondrial membrane potential in HT-29 cells but with a decrease in HK-2 cells. Starting at 2 h of stress, we detected transient CD95L transcription followed by surface expression of CD95L in HT-29 but not in HK-2 cells. Inhibitory CD95L antibody partially inhibited specific death in HT-29 but not in HK-2 cells. Thus, as in other types of stress-induced apoptosis, the CD95/CD95L system is one of the different routes to suicide optionally used by hyposmotically stressed cells. Our findings may have clinical implications for the prevention and treatment of tissue damage caused by severe hyposmolar states.

There is an unmet need for economical snakebite therapies with long shelf lives that are effective even with delays in treatment. The orally bioavailable, heat-stable, secretory phospholipase A2 (sPLA2) inhibitor, LY333013, demonstrates antidotal characteristics for severe snakebite envenoming in both field and hospital use. A murine model of lethal envenoming by a Papuan taipan (Oxyuranus scutellatus) demonstrates that LY333013, even with delayed oral administration, improves the chances of survival. Furthermore, LY333013 improves the performance of antivenom even after it no longer reverses neurotoxic signs. Our study is the first demonstration that neurotoxicity from presynaptic venom sPLA2S can be treated successfully, even after the window of therapeutic antivenom has closed. These results suggest that sPLA2 inhibitors have the potential to reduce death and disability and should be considered for the initial and adjunct treatment of snakebite envenoming. The scope and capacity of the sPLA2 inhibitors ability to achieve these endpoints requires further investigation and development efforts.

Maedi–visna virus (MVV) causes encephalitis, pneumonia and arthritis in sheep. In vitro, MVV infection and replication lead to strong cytopathic effects characterized by syncytia formation and subsequent cellular lysis. It was demonstrated previously that MVV infection in vitro induces cell death of sheep choroid plexus cells (SCPC) by a mechanism that can be associated with apoptotic cell death. Here, the relative implication of several caspases during acute infection with MVV is investigated by employing diverse in vitro and in situ strategies. It was demonstrated using specific pairs of caspase substrates and inhibitors that, during in vitro infection of SCPC by MVV, the two major pathways of caspase activation (i.e. intrinsic and extrinsic pathways) were stimulated: significant caspase-9 and -8 activities, as well as caspase-3 activity, were detected. To study the role of caspases during MVV infection in vitro, specific, cell-permeable, caspase inhibitors were used. First, these results showed that both z-DEVD-FMK (a potent inhibitor of caspase-3-like activities) and z-VAD-FMK (a broad spectrum caspase inhibitor) inhibit caspase-9, -8 and -3 activities. Second, both irreversible caspase inhibitors, z-DEVD-FMK and z-VAD-FMK, delayed MVV-induced cellular lysis as well as virus growth. Third, during SCPC in vitro infection by MVV, cells were positively stained with FITC-VAD-FMK, a probe that specifically stains cells containing active caspases. In conclusion, these data suggest that MVV infection in vitro induces SCPC cell death by a mechanism that is strongly dependent on active caspases.

2612 Background: Activated MAPK and PI3K pathway signaling are associated with poor prognosis in triple negative breast cancer (TNBC). Although some TNBC cell models are sensitive to MEK inhibition, feedback activation of the PI3K pathway mediates resistance. Thus, suppression of both arms of the MAPK/PI3K/mTOR network is a rational approach to targeting TNBC. Here we explore the anti-tumor efficacy of combinations of MEK inhibitor with PI3K, AKT, or mTOR inhibitors with a focus on biomarker development. Methods: Combinations of the MEK inhibitor PD-0325901 with the PI3K inhibitor GDC-0941, AKT inhibitor MK-2206, dual mTORC 1/2 inhibitor Torin 1, or the rapalog temsirolimus were evaluated in TNBC cell lines. Synergy was assessed using the combination index method of Chou and Talalay. We utilized reverse-phase protein array to map the signaling architecture of the treated lines to verify target suppression and identify pharmacodynamic biomarkers. Results: All combinations demonstrated synergy that was mediated by both suppression of proliferation and cell death in a dose-dependent manner. Cell death was delayed, peaking at least 96 hours post-dosing, and was associated with sustained suppression of target proteins in both pathways, including pERKT202/Y204, pS6rpS235/236, p4EBP-1S65, and pPRAS40T246. However, suppression of pAKT (at T308 or S473) was variable and not consistently required for cell death. Pathway mapping identified a protein network ‘signature’ specific to all combination therapies that emerged at 72 hours and was associated with cell death. Thus, all combinations appear to share common downstream effectors. All combinations showed promising efficacy and will be evaluated in a human-in-mouse model of TNBC. Conclusions: These data support therapeutic strategies for TNBC that simultaneously inhibit both arms of the MAPK/PI3K/mTOR signaling network. For continued biomarker development, we stress the importance of studying the delayed effects of combination therapy. This strategy coupled with a protein network based approach uncovered a unique functional signaling ‘signature’.

Malaria is caused by mosquito-borne parasites of the genus Plasmodium which were responsible for ~435,000 of deaths annually, with >90% caused by the deadliest species, P. falciparum. Over the last two decades, global implementation of vector control and artemisinin combination therapies have resulted in significant reductions in the global burden of malaria. Of current concern is the spread of multi-drug resistant parasites that have severely limited the efficacy of antimalarials, including front-line artemisinins, highlighting the urgent need to identify new antimalarials for use as treatments. The aim of this thesis was to investigate novel antimalarial development avenues and identify new chemotypes that could be used in the near future as treatments. The macrolide antibiotic azithromycin is known to target the malaria parasites remnant plastid organelle (the apicoplast’s) bacterial-like ribosome and causes slow-killing ‘delayed death’, where the parasite dies in the second replication cycle (4 days). Azithromycin has also been shown to inhibit invading merozoites and kill blood stages within the first replication cycle (2 days) via an unidentified mechanism, proposed to be independent of delayed death. Thus, we hypothesised that azithromycin could be redeveloped into an antimalarial with two different mechanisms of action against parasites: delayed death and quick-killing. Over 100 azithromycin analogues that featured a high proportion of different structural profiles were obtained, leading to improved quick-killing activities over azithromycin. Quick-killing was also confirmed to be completely unrelated to delayed death, as blood stage parasites lacking the apicoplast were equally susceptible to quick-killing of azithromycin and analogues. Two different avenues were also confirmed for azithromycin’s antimalarial re-development: delayed death and quick-killing or quick-killing only, which could be modulated depending on the location of added functional groups. Azithromycin and analogues were found to be active across blood stage development, with only short treatments required to kill parasites. The metabolomics signatures of parasites treated with azithromycin and analogues suggested that quick-killing acts multi-factorially, with the parasite’s food vacuole and mitochondria being likely targets. Finally, in vitro activities of two subtypes of tri-peptide proteasome-like inhibitors, vinyl sulfone and aldehydes, were addressed against P. falciparum and the zoonotic malaria parasite P. knowlesi. All compounds exhibited low-nanomolar activities against both Plasmodium spp. and showed excellent selectivity for parasites over human cells, suggesting these inhibitors provide viable chemical scaffolds for optimisation. There was no evidence of increased protein ubiquitination upon treating parasites with these compounds, suggesting they do not target the proteasome. We also investigated whether hypoxia inducible pro-drug proteasome-like inhibitors could be used to reduce host toxicity of antimalarials. However, these pro-drugs could be not activated in in vitro culture conditions and there was limited evidence suggesting this strategy would be applicable in malaria. These studies build on previous findings on the drug-killing efficacy, mechanism of action and possible application of redeveloping azithromycin analogues as new and improved antimalarials. I also identified new proteasome inhibitor-like scaffolds as starting points for further development. This body of work provides thorough biological characterisation of a panel of compounds that could lead to new avenues for antimalarial development.
Thesis (Ph.D.) -- University of Adelaide, School of Biololgical Sciences, 2020

Idiopathic dilated cardiomyopathy is characterized by early ventricular enlargement and systolic contractile dysfunction with congestive heart failure not secondary to recognizable causes. Symptoms of congestive heart failure develop at a later stage, usually between 18 and 50 years of age, although they may occasionally occur earlier as a first manifestation of the underlying disease. Mechanisms of life-threatening arrhythmias are facilitated by subendocardial scarring, electrolyte unbalance, stretch-induced electrophysiological changes, autonomic impairment, conduction delay, or proarrhythmic effects of drug therapy. Sudden death may occur as a consequence of ventricular fibrillation, but electromechanical dissociation or bradycardia may also be a possible underlying cause. Most of the clinical characterization of idiopathic dilated cardiomyopathy is drawn from studies also enrolling patients with cardiomyopathies secondary to variable underlying conditions. Secular trends have improved the ability of early diagnosis, and the therapeutic strategies used to prevent sudden death. Among them are angiotensin-converting enzyme inhibitors, beta blockers, and mineralocorticoids/aldosterone receptor antagonists. The role of implantable cardioverter defibrillator (ICD) therapy for the primary prevention of all-cause mortality is controversial with some studies showing and others questioning the benefit of ICD in this population. Survivors of near-fatal arrhythmias have a high risk of recurrence, which may often be fatal. Idiopathic dilated cardiomyopathy contributes to less than 15% of all such patients. Previous randomized studies conducted in large heterogeneous populations showed that ICD therapy is beneficial and improves survival by about 30%. This therapy is currently recommended for all survivors of a near-fatal arrhythmia regardless of the underlying substrate.

Aspirin, considered the prototypic platelet antagonist, has been available for over a century and currently represents a mainstay both in the prevention and treatment of vascular events that include stroke, myocardial infarction, peripheral vascular occlusion, and sudden death. Aspirin irreversibly acetylates cyclooxygenase (COX), impairing prostaglandin metabolism and thromboxane A2 (TXA2) synthesis. As a result, platelet aggregation in response to collagen, adenosine diphosphate (ADP), and thrombin (in low concentrations) is attenuated (Roth and Majerus, 1975). Because aspirin more selectively inhibits COX-1 activity (found predominantly in platelets) than COX-2 activity (expressed in tissues following an inflammatory stimulus), its ability to prevent platelet aggregation is seen at relatively low doses, compared with the drug’s potential antiinflammatory effects, which require much higher doses (Patrono, 1994). Several alternative mechanisms of platelet inhibition by aspirin have been proposed, including: (1) inhibition of platelet activation by neutrophils and (2) enhanced nitric oxide production. In addition, aspirin may prevent the progression of atherosclerosis by protecting low-density lipoprotein (LDL) cholesterol from oxidation and scavenging hydroxyl radicals. Following oral ingestion, aspirin is promptly absorbed in the proximal gastrointestinal (GI) tract (stomach, duodenum), achieving peak serum levels within 15 to 20 minutes and platelet inhibition within 40 to 60 minutes. Enteric-coated preparations are less well absorbed, causing an observed delay in peak serum levels and platelet inhibition to 60 and 90 minutes, respectively. The antiplatelet effect occurs even before acetylsalicylic acid is detectable in peripheral blood, probably from platelet exposure in the portal circulation. The plasma concentration of aspirin decays rapidly with a circulating half-life of approximately 20 minutes. Despite the drug’s rapid clearance, platelet inhibition persists for the platelet’s life span (7 ± 2 days) due to aspirin’s irreversible inactivation of COX-1. Because 10% of circulating platelets are replaced every 24 hours, platelet activity (bleeding time, primary hemostasis) returns toward normal (≥50% activity) within 5 to 6 days of the last aspirin dose (O’Brien, 1968). A single dose of 100 mg of aspirin effectively reduces the production of TXA2 in many (but not all) individuals.

Research objectives a. Analyze transgenic plants that undergo rapid senescence due to increased expression of hexokinase. b. Determine if hexokinase-induced senescence accelerates natural senescence using senescence specific promoters that drive expression of a reporter gene (GUS) and a cytokinin producing gene (IPT - isopentyl transferase). c. Isolate and analyze plant genes that suppress sugar-induced cell death (SICD) in yeast, genes that potentially are involved in programmed cell death and senescence in plants. Background to the topic Leaf senescence is a regulated process of programmed cell death (PCD) in which metabolites are recycled to other active parts of the plant. Senescence associated genes (SAGs) are expressed throughout leaf senescence. Sugar flux and metabolism is thought to playa fundamental regulatory role in senescence. We found that transgenic tomato plants with high hexokinase activity, the initial enzymatic step of sugar (hexose) metabolism, undergo rapid leaf senescence, directly correlated with hexokinase activity. These plants provide a unique opportunity to analyze the regulatory role of sugar metabolism in senescence, and its relation to cytokinin, a senescence-inhibiting hormone. In addition, we found that sugar induces programmed cells death of yeast cells in direct correlation to hexokinase activity. We proposed to use the sugar induced cell death (SICD) to isolate Arabidopsis genes that suppress SICD. Such genes could potentially be involved in senescence induced PCD in plants. Major conclusions The promoters of Arabidopsis senescence-associated genes, SAG12 and SAGI3, are expressed in senescing tomato leaves similar to their expression in Arabidopsis leaves, indicating that these promoters are good senescence markers for tomato plants. Increased hexokinase activity accelerated senescence and induced expression of pSAG12 and pSAG13 promoters in tomato plants, suggesting that sugar regulate natural senescence via hexokinase. Expression of IPT, a cytokinin producing gene, under pSAG12 and pSAG13 promoters, delayed senescence of tomato leaves. Yet, senescence accelerated by hexokinase was epistatic over cytokinin, indicating that sugar regulation of senescence is dominant over the senescence-inhibiting hormone. A gene designated SFP1, which is similar to the major super family monosaccharide transporters, is induced during leaf senescence in Arabidopsis and may be involved in sugar transport during senescence. Accordingly, adult leaves accumulate sugars that may accelerate hexokinase activity. Light status of the entire plant affects the senescence of individual leaves. When individual leaves are darkened, senescence is induced in the covered leaves. However, whole adult plant placed in darkness show delayed senescence. In a search for Arabidopsis genes that suppress SICD we isolated 8 cDNA clones which confer partial resistance to SICD. One of the clones encodes a vesicle associated membrane protein - VAMP. This is the first evidence that vesicle trafficking might be involved in cell death. Implications Increased hexokinase activity accelerates senescence. We hypothesized that, reduced hexokinase activity may delay senescence. Preliminary experiments using a hexokinase inhibitor support this possible implication. Currently we are analyzing various practical approaches to delay leaf senescence via hexokinase inhibition. .