Research

The cornerstone of the Drug Discovery Lab (as the name would imply) is identification and development of "small molecules" as potential new therapeutics for AD. These small molecules are mostly chemical compounds that are tested to determine if they have the desired effect, if they enter the brain, and if they are safe. Many of our small molecule candidates are multifunctional and can address multiple network components, with the idea that a single molecule with a combination of biological activities may deliver a more powerful, synergistic therapeutic effect. To date, we have designed and synthesized over 100 promising "new chemical entities" (NCEs), that is, chemical compounds that have never been created previously. We rely on our extensive expertise of our chemists to design these new molecules, and our screening team to determine if a new compound is effective. NCEs must undergo complete pre-clinical and clinical testing for both safety and efficacy. One of our NCEs, under development with the support of a corporate sponsor, has even advanced to pre-clinical testing in anticipation of a clinical trial.

Many of our compounds are "repurposed". Repurposed compounds are typically approved drugs currently used for another, non-AD condition. We determine if they have anti-AD effects in our assays. The great advantage of our testing existing drugs is that they have already passed rigorous safety testing and have known pharmacological effects. This knowledge allows rapid progression to clinical trials to look for anti-AD effects (efficacy). Many "clinical compound libraries" exist containing thousands of compounds and can be screened rapidly. In fact, one of our repurposed compounds we identified by screening a library is currently in a clinical trial to treat Mild Cognitive Impairment (MCI), a condition that often precedes development of full-blown AD. Since this drug is already known to be safe, if it shows clinical efficacy by improving memory and cognitive skills in MCI patients, it could rapidly move forward as a new therapy for AD.

Several of our other promising NCE and repurposed drug candidates in our drug discovery pipeline need support so that they may too progress towards clinic testing. This is one of the key areas where we need support in our efforts to find a treatment for this devastating disease.

We already have one compound moving towards clinical trials as a result of using a straightforward approach to identify novel AD therapeutics based on their ability to increase sAPPα and the sAPPα/Aβ ratio. Through our screening and medicinal chemistry, we identified "DDL110" as an agent that increased those parameters. We compared DDL110 to two currently approved AD therapeutic drugs (memantine and donepezil) and saw greater improvements in memory in a mouse model of AD with DDL110. DDL110 is "multifunctional", that is, it interacts with at least two different receptors involved in cognitive function as well as APP itself.

As one of the key pathological characteristics of AD is the presence of amyloid plaques comprising amyloid-β (Aβ) peptide in brain tissue, we and many others would like to reduce the production and/or increase the clearance of Aβ. While Aβ plaque clearance alone has not yet resulted in significant clinical results, reduction of Aβ production itself may play a role in effective combination therapy. Aβ originates from a much larger protein named amyloid precursor protein (APP) — an apt name — and is generated by that large protein being cut (cleaved) first by an enzyme called BACE1, generating βCTF, as shown in purple above. Then a second enzyme, gamma (γ) secretase, cuts βCTF, producing Aβ that can link together to form oligomers or form large clusters that, with other components, become plaque. Because drugs that inhibit γ secretase were found to be too toxic by other groups, we targeted identification of BACE inhibitors. Our BACE inhibitors are selected on their ability to reduce BACE cleavage of APP selectively, rather than all proteins than can be cleaved by that enzyme. Inhibition of cleavage of non-APP proteins may lead to unwanted side effects, and so we are attempting to avoid this phenomenon.

Perhaps our most innovative way of reducing Aβ is not by going after reduction of the activity of the enzymes that make Aβ, but by increasing a protein that is good for the functioning of synapses (sAPPα) and that, when it is increased, leads to a reduction in Aβ and could suppress the progression of the disease.

In normal, healthy brain, most APP is not cleaved by BACE and then γ secretase (although some of this cleavage is normal), but by an enzyme called "ADAM10" (shown in green). ADAM10 produces a protein termed soluble APPα (sAPPα) that is important for cell-to-cell connections in the brain. The critical cell type for this communication is the neuron, and neurons communicate through synapses. Synaptic health is supported by sAPPα.

We have already found a drug candidate sAPPα enhancer and are screening the enormous UCLA "compound library" (more than 200,000 known small molecule chemicals!) for more sAPPα enhancers. Increasing sAPPα has the additional benefit of lowering Aβ, so these compounds will have at least two effects.

Another well-known protein found in the brain is implicated in AD. It is an enzyme called Sirtuin 1 (SirT1), and it has been found to be lower in the brain and blood of patients with AD. This is important to know because SirT1 is a major determinant of longevity. Simply put, increasing SirT1 supports healthy aging. Furthermore, increasing SirT1 in the brain has been shown to suppress the tau pathology in an AD model. Therefore, we have targeted enhancing SirT1 in AD. An important aspect of this research is the finding that individuals who have a version of apolipoprotein designated "E4" are at greater risk for AD than people with E3 or E2 and people with E4 may have lower SirT1 even before they have symptoms of AD. We specifically target increasing SirT1 in the presence of ApoE4.

Chronic stress is associated with a higher risk of AD, and there are several known physiological pathways activated or suppressed in individuals under chronic stress (but not under short-term stress). Stress increases on of the other pathological hallmarks of AD brain, neurofibrillary tangles. We already have a potential therapeutic in hand that decreases activation of one of the stress pathways involving corticotropin-releasing factor (CRF) and improves memory performance in a mouse model of AD. We are currently improving this compound and testing new compounds to identify the best one to go into pre-clinical testing.

The tau pathology is implicated in the progression of AD. The enzyme nSMase2 is thought to be a key player in the spread of the tau pathology through exosome-mediated mechanisms. Brain permeable nSMase2 inhibitors would enable us to evaluate this target as a potential new therapeutic approach for Alzheimer's Disease.

In additional to the production of sAPPα and Aβ described on this website, under certain conditions, APP may be cleaved by an enzyme called a caspase. This produces a small fragment, APP-C31, which is particularly toxic and associated with the early pathological stages in AD. Interestingly, this cleavage seems to be upregulated at the same time inflammation increases in response to plaques, so there may be an association. We have already screened for and identified several APP-C31 lowering compounds and are ready to test them in a mouse model of AD.

AD is a disease of the brain, but it can be difficult for many otherwise promising therapeutics to get into the brain due to the blood-brain-barrier (BBB). It is formed by the cells that line the blood vessels and capillaries in the brain, and only certain compounds can get in. To assist with entry of molecules into the brain that would otherwise be excluded, we are using our microfluidic reaction technology to create small membranous particles — liposomes — in which a compound can be encapsulated for brain delivery.

We make our nanovesicles to enhance drug delivery to the brain artificially, but the cells of the body and brain make their own particles that are structurally very similar. These vesicles, called exosomes, can contain cellular components that reflect the physiological state of the cell. Exosomes are expelled from cells and can be found in cerebrospinal fluid, blood, urine, and even saliva. Analysis of these exosomes could be very useful if we can determine the cell type and organ (such as the brain) from which they came. We therefore are developing methods to detect this information. Specifically, we have work underway to use exosomes in saliva to determine state of alertness (cognitive fatigue), and a separate study to use exosomes in plasma to predict disease recurrence.

One of the most cutting edge methods the Drug Discovery Lab is beginning to utilize is a "clinical trial in a dish". This method, as described by Haston and Finkbeiner, and others, involves isolating skin cells from a variety of patients with known genetic differences, and transforming these cells into a type of stem cell — an "induced pluripotential stem cell". As the name implies, these cells can become a variety of different cells types if guided in a specific way. For AD, that might be differentiation into cortical neurons. These neurons then, derived from real and varied human patients, would be treated with a potential therapeutic to see its effects. If the effects differ in cells from individuals, and if a future clinical trial reveals the trial in a dish can be predictive of efficacy, it could then be used to select the right patients for the right drug treatment. This is a form of personalized "macro-medicine".