Failure of monotherapeutics

Neurodegenerative disease therapeutics has been, arguably, the field of greatest failure of biomedical therapeutics development. Patients with acute illnesses such as infectious diseases, or with other chronic illnesses, such as cardiovascular disease, osteoporosis, human immunodeficiency virus infection, and even cancer, have access to more effective therapeutic options than do patients with AD or other neurodegenerative diseases such as Lewy body dementia, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis. In the case of Alzheimer’s disease, there is not a single therapeutic that exerts anything beyond a marginal, unsustained symptomatic effect, with little or no effect on disease progression. Furthermore, in the past decade alone, hundreds of clinical trials have been conducted for AD, at an aggregate cost of billions of dollars, without success. This has led some to question whether the approach taken to drug development for AD is an optimal one.

Therapeutic success for other chronic illnesses such as cardiovascular disease, cancer, and HIV, has been improved through the use of combination therapies [5]. In the case of AD and its predecessors, mild cognitive impairment (MCI) and subjective cognitive impairment (SCI), comprehensive combination therapies have not been explored. However, the past few decades of genetic and biochemical research have revealed an extensive network of molecular interactions involved in AD pathogenesis, suggesting that a network-based therapeutics approach, rather than a single target-based approach, may be feasible and potentially more effective for the treatment of cognitive decline due to Alzheimer’s disease.

Preclinical studies

Extensive preclinical studies from numerous laboratories have identified multiple pathogenetic targets for potential intervention. These include, in addition to amyloid-β (Aβ) oligomers and tau, inflammatory mediators, apolipoproteins and lipid metabolism factors, hormonal mediators, trophic factors and their receptors, calcium regulatory pathways, axoplasmic transport machinery, neurotransmitters and their receptors, prion protein, and a host of other potential targets. However, one of the drawbacks of these preclinical studies is that many have implicated single pathways, and shown large effects of targeting one pathway, whereas in human studies, such approaches have not been borne out. There are several possible inferences from such discrepant results: first, it is possible that it will be necessary to target multiple pathways simultaneously in order to effect an improvement in symptoms and pathophysiology. Second, it is possible that targeting a single pathway will be sufficient, but that earlier intervention will be required. Third, it is possible that all of these seemingly disparate pathways will converge on a single critical pathway, so that either a single targeted therapy or a multi-component, multi-targeted approach may be effective. And fourth, of course it is possible that neither of these two types of approaches will be sufficient. It is worth noting, however, that it is possible that addressing multiple targets within the network underlying AD pathophysiology may be successful even when each target is affected in a relatively modest way; in other words, the effects of the various targets may be additive, multiplicative, or otherwise synergistic.

Based on a combination of in vitro and in vivo studies, we have advanced a model in which AD results from an imbalance in endogenous plasticity signaling (Fig. ​(Fig.1),1), 5–9, and in which the β-amyloid precursor protein (APP) is a mediator of such plasticity-related signaling. Thus the model suggests that AD is analogous to other chronic illnesses such as cancer, osteoporosis, and atherosclerosis. In the case of osteoporosis, osteoblastic signaling is chronically exceeded by osteoclastic signaling, resulting in an age-associated chronic illness featuring loss of bone. By analogy, in Alzheimer’s disease, there is a fundamental, age-associated imbalance between the dynamically opposed physiological processes that mediate plasticity, i.e., between synaptoblastic and synaptoclastic activity. This signaling involves physiological mediators of synaptic development, maintenance, repair, and remodeling, including APP, its derivative peptides, ApoE, and tau, and is modulated by all of the many disparate factors associated with Alzheimer’s disease. Furthermore, just as for neoplasia, positive feedback selects and amplifies the disease process; however, whereas in oncogenesis, the positive feedback occurs at the cellular level, in Alzheimer’s disease, the positive feedback occurs at the molecular species level, in the form of prionic loops [5, 8, 9].

Figure 1

Alternative processing of, and signaling by, APP. [5].

In support of this model, the four peptides derived from the amyloidogenic processing of β-amyloid precursor protein (APP)—sAPPβ, Aβ, Jcasp, and C31—have been shown to mediate neurite retraction, synaptic inhibition, caspase activation, and programmed cell death [6, 10–12]; whereas, in contrast, the two peptides derived from the non-amyloidogenic processing of APP—sAPPα and αCTF—mediate neurite extension, and inhibit Aβ production, caspase activation, and programmed cell death 13–15. Thus APP appears to function as a molecular switch, mediating plasticity-related processes, and AD is associated, whether causally or incidentally, with an increase in the ratio of the neurite-retractive peptides to the neurite-extending peptides. Reducing this ratio, whether by affecting BACE (β-site APP cleaving enzyme) or other cleavage of APP, appears to mitigate the AD severity [7, 16, 17].

Of particular interest for the development of a therapeutic program whose goal is to correct the hypothesized chronic synaptoblastic:synaptoclastic imbalance is the feedback mechanism: whereas homeostatic (negative) feedback is utilized by biological systems with single goal outcomes (e.g., serum pH) and no requirement for amplification, prionic loop (positive) feedback is utilized by biological systems with multi-goal outcomes and a requirement for rapid amplification (e.g., thrombus formation or, potentially, synapse modulation), and such systems therefore function as molecular switches [9]. In these latter systems, the positive feedback feature of the systems dictates that the molecular mediators involved, or a subset thereof, beget more of themselves, or enhance their own activities. Thus such amplifying systems are prionic, with the degree of infectivity depending on the stability of the molecular species involved. In the case of APP signaling, binding of a trophic ligand such as netrin-1 increases the production of sAPPα [18], which inhibits BACE cleavage [19], with the complementary fragment, αCTF, inhibiting γ-secretase cleavage [14]; thus cleavage at the α-site produces fragments that inhibit cleavage at the β-site and γ-site rather than feeding back to reduce α-site cleavage. Similarly, cleavage at the β-site and γ-site to produce Aβ feeds back positively to increase APP-C31 production [20], thus favoring the pro-AD, anti-trophic processing of APP. Moreover, Aβ itself has been shown to exhibit prionic properties [21], although the mechanism by which it does so has not been clarified.

Thus APP processing displays positive feedback, and therefore APP and its derivative peptides function as a molecular switch. This has critical implications for therapeutic development, since it offers a mechanism by which a threshold effect occurs. We have taken advantage of this phenomenon to develop drug candidates that increase the anti-AD, trophic APP signaling, while reducing the pro-AD, anti-trophic APP signaling [22] and enhancing cognition [23].

We have found that the manipulation of the plasticity balance that is mediated or reflected by the APP-derivative peptide balance (Fig. ​(Fig.1),1), whether genetically or pharmacologically, leads to predictable effects on learning and memory. Mutation of the caspase site at Asp664 inhibits the synaptic loss, memory deficits, and dentate gyral atrophy that otherwise occurs in the PDAPP transgenic mouse model of AD [7, 17, 24–26]. Furthermore, knock-in studies of a wild type mouse D664A support the notion that APP is indeed involved fundamentally in plasticity. (Kane, et al, unpublished data, 2014)

Patient one: therapeutic program

As noted above, and following an extended discussion of the components of the therapeutic program, the patient began on some but not all of the system: (1) she eliminated all simple carbohydrates, leading to a weight loss of 20 pounds; (2) she eliminated gluten and processed food from her diet, and increased vegetables, fruits, and non-farmed fish; (3) in order to reduce stress, she began yoga, and ultimately became a yoga instructor; (4) as a second measure to reduce the stress of her job, she began to meditate for 20 minutes twice per day; (5) she took melatonin 0.5mg po qhs; (6) she increased her sleep from 4-5 hours per night to 7-8 hours per night; (7) she took methylcobalamin 1mg each day; (8) she took vitamin D3 2000IU each day; (9) she took fish oil 2000mg each day; (10) she took CoQ₁₀ 200mg each day; (11) she optimized her oral hygiene using an electric flosser and electric toothbrush; (12) following discussion with her primary care provider, she reinstated HRT (hormone replacement therapy) that had been discontinued following the WHI report in 2002; (13) she fasted for a minimum of 12 hours between dinner and breakfast, and for a minimum of three hours between dinner and bedtime; (14) she exercised for a minimum of 30 minutes, 4-6 days per week.

Patient two: history

A 69-year-old entrepreneur and professional man presented with 11 years of slowly progressive memory loss, which had accelerated over the past one or two years. In 2002, at the age of 58, he had been unable to recall the combination of the lock on his locker, and he felt that this was out of the ordinary for him. In 2003, he had FDG-PET (fluoro-deoxyglucose positron emission tomography), which was read as showing a pattern typical for early Alzheimer’s disease, with reduced glucose utilization in the parietotemporal cortices bilaterally and left > right temporal lobes, but preserved utilization in the frontal lobes, occipital cortices, and basal ganglia. In 2003, 2007, and 2013, he had quantitative neuropsychological testing, which showed a reduction in CVLT (California Verbal Learning Test) from 84%ile to 1%ile, a Stroop color test at 16%ile, and auditory delayed memory at 13%ile. In 2013, he was found to be heterozygous for ApoE4 (3/4). He noted that he had progressive difficulty recognizing the faces at work (prosopagnosia), and had to have his assistants prompt him with the daily schedule. He also recalled an event during which he was several chapters into a book before he finally realized that it was a book he had read previously. In addition, he lost an ability he had had for most of his life: the ability to add columns of numbers rapidly in his head.

He had a homocysteine of 18 μmol/l, CRP <0.5mg/l, 25-OH cholecalciferol 28ng/ml, hemoglobin A1c 5.4%, serum zinc 78mcg/dl, serum copper 120mcg/dl, ceru-loplasmin 25mg/dl, pregnenolone 6ng/dl, testosterone 610ng/dl, albumin:globulin ratio of 1.3, cholesterol 165mg/dl (on Lipitor), HDL 92, LDL 64, triglyceride 47, AM cortisol 14mcg/dl, free T3 3.02pg/ml, free T4 1.27ng/l, TSH 0.58mIU/l, and BMI 24.9.

He began on the therapeutic program, and after six months, his wife, co-workers, and he all noted improvement. He lost 10 pounds. He was able to recognize faces at work unlike before, was able to remember his daily schedule, and was able to function at work without difficulty. He was also noted to be quicker with his responses. His life-long ability to add columns of numbers rapidly in his head, which he had lost during his progressive cognitive decline, returned. His wife pointed out that, although he had clearly shown improvement, the more striking effect was that he had been accelerating in his decline over the prior year or two, and this had been completely halted.

Patient two: therapeutic program

The patient began on the following parts of the overall therapeutic system: (1) he fasted for a minimum of three hours between dinner and bedtime, and for a minimum of 12 hours between dinner and breakfast; (2) he eliminated simple carbohydrates and processed foods from his diet; (3) he increased consumption of vegetables and fruits, and limited consumption of fish to non-farmed, and meat to occasional grass-fed beef or organic chicken; (4) he took probiotics; (5) he took coconut oil i tsp bid; (6) he exercised strenuously, swimming 3-4 times per week, cycling twice per week, and running once per week; (7) he took melatonin 0.5mg po qhs, and tried to sleep as close to 8 hours per night as his schedule would allow; (8) he took herbs Bacopa monniera 250mg, Ashwagandha 500mg, and turmeric 400mg each day; (9) he took methylcobalamin 1mg, methyltetrahydrofolate 0.8mg, and pyridoxine-5-phosphate 50mg each day; (10) he took citicoline 500mg po bid; (11) he took vitamin C 1g per day, vitamin D3 5000IU per day, vitamin E 400IU per day, CoQ₁₀ 200mg per day, Zn picolinate 50mg per day, and α-lipoic acid 100mg per day; (12) he took DHA (docosahexaenoic acid) 320mg and EPA (eicosapentaenoic acid) 180mg per day.

Patient three: history

A 55-year-old attorney suffered progressively severe memory loss for four years. She accidentally left the stove on when she left her home on multiple occasions, and then returned, horrified to see that she had left it on once again. She would forget meetings, and agree to multiple meetings at the same time. Because of an inability to remember anything after a delay, she would record conversations, and she carried an iPad on which she took copious notes (but then forgot the password to unlock her iPad). She had been trying to learn Spanish as part of her job, but was unable to remember virtually anything new. She was unable to perform her job, and she sat her children down to explain to them that they could no longer take advantage of her poor memory, that instead they must understand that her memory loss was a serious problem. Her children noted that she frequently became lost in mid-sentence, that she was slow with responses, and that she frequently asked if they had followed up on something she thought she had asked them to do, when in fact she had never asked them to do the tasks to which she referred.

Her homocysteine was 9.8μmol/l, CRP 0.16mg/l, 25-OH cholecalciferol 46ng/ml, hemoglobin A1c 5.3%, pregnenolone 84ng/dl, DHEA 169ng/dl, estradiol 275pg/ml, progesterone 0.4ng/ml, insulin 2.7μIU/ml, AM cortisol 16.3mcg/dl, free T3 3.02pg/ml, free T4 1.32ng/l, and TSH 2.04mIU/l.

After five months on the therapeutic program, she noted that she no longer needed her iPad for notes, and no longer needed to record conversations. She was able to work once again, was able to learn Spanish, and began to learn a new legal specialty. Her children noted that she no longer became lost in mid-sentence, no longer thought she had asked them to do something that she had not asked, and answered their questions with normal rapidity and memory.