Editorial
Current Alzheimer Research, 2009, Vol. 6, No. 5
407
Editorial A Multi-Targeted Approach for a Complex Multifaceted Disease Alzheimer’s disease (AD), as with other late life diseases, is undoubtedly caused by a multitude of factors that are influenced by stochastic events, an individual’s genetic makeup and environmental exposures. Combination therapy; including preventative treatments, disease modifying therapies, symptomatic agents and lifestyle changes may be our best hope at eradicating Alzheimer’s disease from our society. To this end, the Alzheimer’s Drug Discovery Foundation (ADDF) has funded diverse and novel programs, some of which are highlighted in these proceedings from the 9th International Conference on Alzheimer’s Disease Drug Discovery, that seek to intervene at various stages of the disease process. A similar effort by ADDF was previously highlighted [1]. It is important to consider these independent studies as a joint effort to discover and develop treatments that complement each other as a means to improve the lives of Alzheimer’s disease patients and their families. Studies with human post-mortem brain tissue have given us an invaluable window into the pathological state at the end-stage of the disease. From these studies, scientists have identified the major hallmarks of late stage disease, including amyloid plaques, neurofibrillary tangles, neuronal cell loss and gliosis. However, to this day, we do not fully understand the initiating triggers of the disease or what may be a cause verses a consequence of disease progression. While many valuable studies have been performed in in vitro and in vivo models of AD, our ability to monitor disease progression or analyze pathological changes at early disease stages in humans has been quite limited. Therefore, advances in neuroimaging technology and biomarker assays are crucial for early detection, monitoring of disease progression and response to novel treatments. These efforts can reduce the cost and time of clinical trials, allowing new drugs to reach the market faster. If AD is detected early, before significant symptoms occur, preventative treatments (both pharmacological as well as lifestyle changes) can be initiated at the stage where they can have the most benefit. To this end, Jeff Kuret is working to develop small molecules that would specifically detect neurofibrillary tangles in living human patients as well as inhibit tangle formation (page 409-414). Neurofibrillary tangles, as a marker of neuronal injury and death, closely correlate with cognitive deterioration and clinical disease severity [2, 3]. Therefore, reliable measurements of the quantity and the distribution of tangles in living patients could serve as a valuable surrogate marker for clinical disease progression and aid in treatment development. Understanding genetic risk factors for AD is another method to facilitate early detection of high risk individuals, while also providing insight into disease mechanisms which can lead to the discovery of novel targets and enhance drug discovery efforts. For example, individuals with the apolipoprotein E4 allele (ApoE4) have a significantly greater risk of developing Alzheimer’s disease and often exhibit an earlier age of onset and a more aggressive form of the disease [4]. While ApoE4 is a known risk factor for AD, we still do not fully understand the mechanism of how it influences AD
pathogenesis. To address this issue, Ning Zhong and Karl Weisgraber are working to correlate structural differences in the ApoE isoforms to the functional changes in AD risk (page 415-418). The more we understand about how these isoforms influence AD progression, the more insight we gain into mechanisms behind the variation seen in these genetic pools of AD patients. Identifying genetic subtypes of AD could allow for the development of more individualized therapies as well as aid in the clinical trial design of novel drug therapies. In fact, in the Phase II Bapineuzumab trial initiated by Wyeth and Elan, ApoE4 carriers were separated from non-carriers in the analysis. Only non-carriers demonstrated a significant benefit from the treatment, which would not have been detected had the population been analyzed as a whole [5]. The benefit of developing treatments for a disease as complicated and multifaceted as AD is that there are likely numerous points at which one can intervene. The 9th International Conference on Alzheimer’s Disease Drug Discovery illustrated the diverse spectrum of programs that ADDF funded investigators are pursuing. Neuroprotective and synaptic enhancement strategies as well as anti-oxidant and antiinflammatory strategies complement approaches that are more specifically targeted to disease-associated proteins. For example, H. Uri Saragovi is working on developing novel ligands to modulate neurotrophin receptors and confer neuroprotection (page 419-423). In addition, Hyman Schipper is working on developing inhibitors of glial heme-oxygenase 1 in order to prevent oxidative injury to neurons (page 424430), while Sergey Kalinin and Douglas Feinstein are testing PPARdelta agonists for their ability to decrease amyloid plaque load and inflammation (page 431-437). Since both plaques and tangles, as well as other neurodegenerative disease pathologies, are composed of misfolded protein, ADDF funded investigators are also pursuing general strategies that promote normal protein folding or facilitate degradation of abnormally folded proteins. Along these lines, Ben Bahr is developing lysosomal modulatory drugs to increase misfolded protein disposal (page 438-445). Common pathways exist between many neurodegenerative diseases and efforts are underway to develop treatments that could be effective for multiple diseases. In an effort to promote knowledge sharing between these diseases, a session on Frontotemporal dementia (FTD) and neurofibrillary tangle-targeted therapies was added to the 9th International Conference on Alzheimer’s Disease Drug Discovery. While FTD and AD demonstrate different disease etiologies and are typically distinguishable in the clinic, the end-stage diseases share many similarities including cognitive and behavioral changes as well as neurofibrillary tangle accumulation and neuronal cell loss in the brain [6]. Studying these pathways provides new clues to general mechanisms of neurodegeneration and allows for cross-fertilization of tangle-targeted drug discovery ideas that have the potential to benefit both diseases. To this end, Einar Sigurdsson is working to develop tau-targeted immunotherapy for AD (page 446-450);