Image: Flickr - Adrian Miles Huntington’s disease (HD) is a genetic disorder caused by mutations in the huntingtin gene. The altered huntingtin protein (htt) causes gradual neurological damage; HD usually develops between the ages of 30 and 50 and symptoms get worse over the next 20 or more years. Defects in macroautophagy – a lysosomal system for removing toxic and unwanted proteins – have been suggested to play a role in the cell’s inability to clear mutant htt, but the exact mechanisms are poorly understood.
Researchers at the Albert Einstein College of Medicine have now shown that mutant htt interferes directly with the function of the autophagosome. Normally, cellular debris is sequestered in double-membraned autophagosomes and delivered to lysosomes for degradation following fusion of the vesicles. In cells from two mouse models of HD and in cells from people with the disease, fusion of the two vesicles and enzymatic activity of the lysosome were unaffected but mutant htt was found to stick to the inner membrane of the autophagosome and prevent normal loading of proteins destined for recycling. As a result, the autophagosomes are empty when they arrive at the lysosomes and cellular debris accumulates and probably contributes to cell death. Although defects in autophagy have been linked to other neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, the researchers believe that the defect in cargo loading seen in the present study has not been described before.
The study, which is published in Nature Neuroscience, also suggests that proposed treatments for HD which involve activating lysosomes are unlikely to be effective. Professor Ana Maria Cuervo, the senior author of the study, likened autophagosomes to ‘garbage bags’ and lysosomes to ‘garbage trucks’ – there is no point in more trucks if the bags are not being filled.
Image: Flickr - elektroholunder One problem associated with the treatment of solid tumours is that chemotherapeutic agents have difficulty in penetrating more than a few cell diameters from the vasculature. Higher doses of drug are required and, because some tumour cells are not reached, the risk of recurrence is high. To address this issue, researchers at Sanford-Burnham Medical Research Institute have now described a peptide able to enhance the ability of drugs to access tumour tissue.
Some years ago it was shown that peptides containing the RGD (Arg-Gly-Asp) sequence recognise a family of cell-surface receptors, integrins, which mediate the interaction of cells with the extracellular matrix (ECM) components fibronectin and type I collagen and are important for the migration and invasion of tumour cells. RGD peptides have been used for homing to malignant tissue and the Sanford-Burnham team have taken this a step further. The new agent is a cyclic nona-peptide (CRGDK/RGPD/EC), referred to as iRGD. The contained RGD sequence targets the agent to tumour tissue where it is cleaved to reveal a ‘CendR’ sequence that binds to neuropilin-1, mediating an active transport system.
In a paper published in Cancer Cell late last year, the research team showed that coupling iRGD to anti-cancer drugs allowed them to penetrate deep into tumours, effectively increasing the activity of the drugs. In their latest study, published in Science, the team have shown that the chemotherapeutic agents do not need to be conjugated to the peptide. Co-administration of iRGD with a variety of drugs, including a small molecule (doxorubicin), nanoparticles (nab-paclitaxel and doxorubicin liposomes), and a monoclonal antibody (trastuzumab), improved their therapeutic index.
The team hope that iRGD may be a valuable adjunct to enhance efficacy of anti-cancer agents, whilst reducing side-effects.
Image: Wikimedia Commons For many people, the word ‘arsenic’ conjures up thoughts of murder mysteries and, in fact, arsenic has been a popular murder weapon since the middle ages. In the Victorian era, arsenic trioxide found favour as a cosmetic and it has also been used in both Chinese and Western medicine. Most recently, arsenic trioxide has been used to treat acute promyelocytic leukaemia (APL) that is unresponsive to first line therapies.
Arsenic trioxide is able to induce complete remission in patients with relapsed or refractory APL and is generally well-tolerated with minimal chemotherapy-related side effects. How arsenic trioxide kills cancer cells is not clear but scientists in China and France believe they have made a key step towards solving the mystery. APL cells are characterised by the occurrence of chromosomal translocations involving the retinoic acid receptor α gene (RARα)and the promyelocytic leukaemia gene (PML). These translocations lead to production of a fusion protein, PML-RORα that has altered functions and protects the cells from apoptosis. Arsenic trioxide triggers small ubiquitin-like modifier (SUMO) proteins to tag PML-RORα as part of a degradation mechanism. The new study has shown that the arsenic binds directly to cysteine residues in zinc fingers located within RBCC (N-terminal RING finger/B-box/coiled coil) domains of PML causing cross-linking and oligomerisation. The aggregated protein then undergoes SUMO modification and degradation. The identification of PML as a direct target of arsenic trioxide provides new insights into how the drug is able to treat APL and may lead to new treatment options.
Image: Flickr - Joanna Vaughan The relatively rapid development of drug resistance is a major obstacle to successful chemotherapy. Resistance is frequently attributed to the outgrowth of cells within the tumour which have a genetic survival advantage in the presence of drug treatment such as enhanced drug efflux, impaired drug binding or the ability to use alternative survival pathways. More recently, it has been found that acquired drug resistance does not necessarily need a stable, heritable genetic alteration and, moreover, that response to treatment can be restored following a ‘drug holiday’. Whilst modelling the acute response to a variety of anti-cancer drugs in treatment-sensitive human tumour cell lines, researchers at Massachusetts General Hospital Cancer Center and the Dana-Farber Cancer Institute consistently found a small subpopulation of reversibly ‘drug-tolerant’ cells. They found that whereas the vast majority of EGFR mutant non-small cell lung cancer-derived cells (PC9 cells) were killed by exposure to a high concentration (100 x IC50) of EGFR tyrosine kinase inhibitors (TKIs), a small fraction of cells survived. Similar populations of ‘drug-tolerant persisters’ (DTPs) were found when PC9 cells were treated with cisplatin and also in several other cancer cell lines with established drug sensitivity, suggesting that a drug-tolerant cell subpopulation is broadly present in tumour-derived cell lines.
Although DTPs are largely quiescent, about 20% eventually resume proliferation in the presence of drug to give colonies of cells referred to as ‘drug-tolerant expanded persisters’ (DTEPs) which can propagate indefinitely in the presence of drug. DTPs rapidly regain sensitivity when grown in drug-free media whereas restoration of sensitivity in DTEPs occurs at higher passage number. The reduced drug-sensitivity of both DTPs and DTEPs was linked to increased expression of a gene that encodes a chromatin-modifying enzyme, KDM5A. Although there are, as yet, no inhibitors of KDM5A, its known association with histone deacetylases (HDACs) led the team to test the effect of HDAC inhibitors on DTPs and DTEPs. Trichostatin A, an inhibitor of class I/II HDACs was found to rapidly kill PC9-derived DTPs and DTEPs but to have no effect on parental PC9 cells or TKI-resensitised DTEPs. The team went on to show that continous treatment with HDAC inhibitors, whilst having no effect on growth and survival of parental P9 cells, can prevent the emergence of EGFR TKI resistance. As well as HDAC inhibitors, a selective inhibitor of the insulin-like growth factor 1 receptor (IGF-1R) kinase also virtually eliminated the emergence of EGFR TKI-tolerant DTEPs. IGF-1R signalling was found to be necessary for drug-tolerant phenotypes in other cancer cell lines and to be mediated by the histone-demethylating activity of KDM5A.
The team hope that the results seen in cell culture experiments will extend to cancer patients and have already begun a clinical trial to see whether a combination of a chromatin-modifying agent with the EGFR TKI, erlotinib, may prevent or delay the development of resistance. Although the trial is not yet completed, early data indicate that the inclusion of a chromatin-modifying agent can dramatically improve clinical benefit in a subset of patients demonstrating acquired TKI resistance.
Image: Flickr - Untitled Blue The retrovirus, xenotropic murine leukemia virus-related virus (XMRV), has been – controversially – linked to both prostate cancer and chronic fatigue syndrome (CFS). In an attempt to clarify the association of XMRV with disease, researchers at Emory University are developing a serum-based assay to detect neutralising antibodies to the virus which should begin to answer basic questions about how widespread the virus is, and how it is transmitted. The team found good agreement between their serum based assay and polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH) tests carried out on prostate samples from cancer patients, and showed that at least some of the patients had been infected with XMRV. The study is published in the April issue of Urology.
Meanwhile, other researchers at Emory University/Atlanta Veterans Affairs Medical Center and the University of Utah have been looking for ways to treat XMRV should it turn out to have a causal role in prostate cancer or chronic fatigue syndrome. The team evaluated 45 compounds, mostly drugs approved for the treatment of HIV/AIDS, and found that four of them were able to inhibit XMRV with EC50 values of < 1µM. XMRV replication was studied in both MCF-7 cells (generated from human breast cancer) and LNCaP cells (generated from human prostate cancer). The most effective compounds were two nucleoside reverse transcriptase inhibitors (zidovudine and tenofovir disoproxil fumarate) and two integrase inhibitors (raltegravir and L-000870812). Despite the lack of homology (only 14% identity) between HIV-1 integrase and XMRV integrase, raltegravir showed particularly good activity against XMRV with EC50 values of 0.005µM and 0.03µM in MCF-7 and LNCaP cells respectively (cf 0.001µM for HIV-1 grown in PBMCs). The EC90/EC50 ratio was significantly higher for XMRV grown in MCF-7 cells than for XMRV grown in LNCaP cells or for HIV-1 grown in PBMCs (700, 15 and 9 respectively). Synergy studies were carried out in LNCaP cells: combinations of raltegravir and any of the other three compounds were found to act synergistically.
The authors hope that if XMRV is established as a cause of prostate cancer or CFS, existing HIV treatments may prove to be effective therapies for these conditions.
Rapamycin was first isolated from soil samples taken from Rapa Nui (Easter Island)
Image: Flickr - A.www.viajar24h.com Two recent reports from the University of Texas Health Science Center suggest that rapamycin may find a new use in treating Alzheimer’s disease (AD). The first study, published in the Journal of Biological Chemistry, showed that treatment with rapamycin reduced AD-like pathology in 3xTg-AD mice and the more recent study, published in PLoS ONE, showed that rapamycin also improved spatial learning and memory in PDAPP transgenic mice, another murine model of AD. Earlier studies had shown that rapamycin, which blocks the mTOR pathway and is used as an immunosuppressant to prevent rejection following organ transplants, can extend the lifespan of mice, even if treatment is started relatively late in life.
In both 3xTg-AD and PDAPP mice, treatment with rapamycin was found to lower levels of amyloid peptide, Aβ42, a hallmark feature of AD which is believed to be a major cause of neurotoxicity. The reduction in Aβ42 when mTOR activity is reduced may be a consequence of induction of autophagy by high levels of Aβ42. The improved performance of PDAPP mice treated with rapamycin appeared to result entirely from enhanced cognitive performance with no effect on emotions such as anxiety.
The authors suggest that, if the results with mice are borne out by studies in people, rapamycin could be used to prevent or treat AD but the potential benefits will need to be carefully weighed against increased susceptibility to infection and the possible development of some types of malignancy which could result from prolonged immunosuppression.
Last week Medpedia announced the addition of video to its collaborative online medical encyclopaedia. The platform launched with hundreds of medical and health videos from sources including the CDC, the FDA, other institutes of the NIH, as well as from Big Think and other organizations. The videos cover topics ranging from diabetes and H1N1 education, to medical procedures and health care reform.
Like the Clinical Trials system on Medpedia, medical videos are delivered in the appropriate context online. A video can show up in a Medpedia article covering the same topic, it can appear in a personalized feed of someone interested in that disease, or in a patient community related to that condition.
Big Think and other organizations are making hundreds of videos available with more to come. Big Think is an online venue for the growing global conversation about where we are and where we’re headed. Taking cues from elite private institutions and conferences that convene thought leaders from a variety of backgrounds and perspectives to share ideas about pressing global issues, Big Think adapts these models to the web medium to provide public access to expert thinking and the opportunity to engage in dialogue around it. President and co-Founder of Big Think, Peter Hopkins, said:
“Big Think is delighted to share this collection of expert insights and analysis with the Medpedia community. We trust that the addition of this video content will be useful in supporting and enhancing the valuable collaborative efforts being put forth by the medical community.”
As an example, the video below is taken from the Medpedia entry on ‘Hallucination’ and features Oliver Sacks, Professor of Psychiatry at Columbia University.
Image: Flickr - ^riza^ Although interferon-β (IFN-β) is used to reduce the number and severity of relapses in patients with relapsing remitting multiple sclerosis (RRMS), a frustration for both patients and physicians is that the treatment is more effective in some patients than others. Studies by researchers at Stanford University and colleagues have now suggested that there may be two distinct versions of multiple sclerosis and that the effectiveness of β-interferon may depend on the type of disease that the patient has.
The team found that superficially similar experimental autoimmune encephalitis (EAE), an animal model of multiple sclerosis, can be induced either by T helper type 1 (TH1) cells or by TH17 cells. IFN-β was effective in treating TH1-induced EAE but exacerbated disease caused by TH17 cells. In TH1-induced EAE, treatment was accompanied by increased interleukin-10 (IL-10) production whereas in TH17-induced EAE, IL-10 levels were unaffected by treatment, although IL-17 levels were reduced. Both induction of IL-10 production and suppression of IL-17 levels were dependent on IFN-γ; in the absence of IFN-γ signalling, IFN-β did not reduce the symptoms of EAE.
The team then measured IL-17 levels in blood samples from 26 RRMS patients taken before and about 2 years after starting treatment with IFN-β. When treatment responses were matched to IL-17 levels a clear pattern emerged: patients with a good response had very low levels of the IL-17 family member, IL-17F, whereas those who responded poorly – about 30% of the patients – had high levels of IL-17F. Although the team caution that the results need to be confirmed in larger groups of patients, the study has the potential to transform treatment for MS by stratifying patients into likely IFN-β responders and non-responders. Eventually, a simple blood test could improve the response rate to IFN-β and spare non-responders from the known flu-like side effects of a treatment that could even worsen their disease.
Image: Flickr – Richard0 Conventional wisdom, supported by in vitro experiments, has previously suggested that phosphoinositide 3-kinase (PI3K) plays a protective role in Alzheimer’s disease. However, a team led by researchers at Cold Spring Harbor has now implicated PI3K in the pathogenesis of the disorder.
The team used fruit-flies (Drosophila) that were engineered to produce human β-amyloid in their brains – a model that mimics many of the features of Alzheimer’s, including age-dependent memory loss, neurodegeneration, β-amyloid deposits and plaque formation. In the model, the presence of β-amyloid enhances long term depression (LTD), a process in which nerve signal transmission at particular synapses is depressed for an extended period. The research demonstrated that the enhanced LTD was a consequence of increased PI3K activity and could be abrogated by genetic silencing or pharmacological inhibition of PI3K.
PI3K inhibition restored LTD to a normal level, rescued β-amyloid peptide (Aβ)-induced memory loss and reduced β-amyloid deposits in the Drosophila brain. The data suggest that Aβ42 stimulates PI3K, which in turn causes memory loss in association with increased accumulation of Aβ42 aggregates.
The researchers note that the up-regulation of PI3K may also explain the insulin-resistance observed in the brains of Alzheimer’s victims. Insulin is one of the molecules that normally induce PI3K activity, which in turn mediates the cell’s response to insulin. Since PI3K is already hyperactivated in response to β-amyloid, it may no longer be able to respond to insulin.
Image: Flickr - Jsome1 Although the exact causes of autoimmune diseases such as rheumatoid arthritis are unknown, tissue damage is mediated, at least in part, by the (inappropriate) action of effector T cells. Regulatory T cells are a specialised population of T cells which play a role in ‘self-tolerance’ by suppressing activation of other immune cells: genetic deficiency in regulatory T cells causes severe autoimmune disease in both mice and humans.
Researchers at NYU Langone Medical Center examined blood samples from 25 patients with rheumatoid arthritis and found that regulatory T cell function was inversely correlated with disease severity. The team have now discovered a way to enhance the activity of regulatory T cells which may eventually lead to new treatments for autoimmune diseases such as rheumatoid arthritis or inflammatory diseases such as Crohn’s disease.
In effector T cells, the calcium-independent protein kinase C, PKC-θ, localises at the site of contact between the T cell and the antigen presenting cell, placing it in the proximity of other enzymes that mediate T cell activation. When regulatory T cells become activated, however, the team found that PKC-θ is localised away from the point of cell-cell contact. In cell culture experiments, PKC-θ inhibitors were shown to boost the activity of regulatory T cells around 5-fold. One of the inhibitors was also shown to be protective in a mouse model of Crohn’s disease.
The study is published in Science Express and the PKC-θ inhibitors were provided by Boehringer-Ingelheim Pharmaceuticals, Inc.
