support

# Practical Drug Development Assessment: Hyperconnectivity Hypotheses in AD

## Executive Summary

These seven hypotheses address a critical therapeutic question: how to distinguish adaptive from maladaptive network changes in early AD. From a drug development perspective, **only two targets have meaningful clinical tractability**, and the field must confront fundamental questions about target validation before investment is warranted. The most advanced programs cluster around **complement inhibition** and **metabolic support strategies**, while several hypotheses rely on targets with significant druggability concerns.

---

## Hypothesis 1: Astrocyte LDHA/MCT4 Metabolic Coupling

### Druggability Assessment

**LDHA (Lactate Dehydrogenase A)**
| Aspect | Assessment |
|--------|------------|
| Target Class | Metabolic enzyme (tetrameric protein) |
| Chemical Matter | Multiple small molecule inhibitors exist |
| Existing Compounds | **FX11** (selective LDHA inhibitor, Cayman Chemical), **Galloflavin** (competitive inhibitor), **Gossypol/AT-101** (pan-LDH inhibitor, clinical-stage oncology) |
| Clinical Candidates | AT-101 completed Phase I for solid tumors (Mayo Clinic/Southern Oncology); no CNS indication |
| Druggability Score | **Moderate** — enzyme is druggable but active site is challenging for selectivity |

**MCT4 (SLC16A3)**
| Aspect | Assessment |
|--------|------------|
| Target Class | Monocarboxylate transporter (MCT family) |
| Chemical Matter | No selective pharmacological activators exist |
| Existing Compounds | **AR-C155858** (MCT1 inhibitor, not MCT4-selective), **α-Cyano-4-hydroxycinnamic acid** (pan-MCT inhibitor, used in vitro only) |
| Druggability Score | **Low-Moderate** — transporter enhancers generally lacking; genetic approaches would be required |

### Critical Development Concerns

1. **LDHA agonists don't exist**: The therapeutic prediction requires *increasing* LDHA activity, but virtually all pharmacological tool compounds are inhibitors, not activators. Developing enzyme activators is notoriously difficult and few successful precedents exist.

2. **MCT4 enhancers are nonexistent**: Without pharmacological tools to enhance lactate export, testing the compensatory hypothesis in vivo requires genetic approaches (viral overexpression), which limits rapid translational development.

3. **The lactate hypothesis has been substantially challenged**: Recent literature increasingly suggests that brain lactate accumulation in AD is *pathological*, not compensatory. MRS studies show elevated lactate correlates with worse outcomes (PMID: 29727722), and TSPO-PET demonstrates microglial activation underlies early hypermetabolism (PMID: 29100300).

### Competitive Landscape

| Company | Program | Modality | Stage | Indication |
|---------|---------|----------|-------|------------|
| No targeted AD programs identified | — | — | — | — |

No pharmaceutical or biotech programs specifically targeting astrocytic lactate metabolism for neurodegeneration have entered clinical development.

### Safety Concerns

- LDHA inhibition would suppress glycolysis in all tissues; oncology safety data with AT-101 showed metabolic toxicity
- Enhancing lactate shuttle could have bidirectional effects depending on context
- Blood-brain barrier penetration required; no current compounds have demonstrated adequate CNS exposure

### Cost/Timeline Estimate

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Target validation (genetic) | $800K–$1.5M | 18–24 months |
| Lead optimization (MCT4 activator) | Not feasible currently | N/A |
| IND-enabling studies | N/A | N/A |

**Practical Assessment**: This hypothesis has **low immediate translatability** because the therapeutic prediction (enhance lactate shuttle) requires pharmacology that doesn't exist. The scientific premise has also been substantially challenged by recent TSPO-PET and MRS data. If pursuing, the field should first establish whether lactate is truly compensatory using genetic tools before investing in drug discovery.

---

## Hypothesis 2: ADAMTS4/5 (PNN Degradation)

### Druggability Assessment

| Aspect | Assessment |
|--------|------------|
| Target Class | Aggrecanase (zinc-dependent metalloprotease) |
| Chemical Matter | Multiple small molecule inhibitor chemotypes exist |
| Existing Compounds | **Selective ADAMTS4/5 inhibitors** in pre-clinical development for osteoarthritis by Bioiberica, Pfizer (Phase I for musculoskelet al); **GLPG1972** (Sanofi/Galapagos, completed Phase I for OA) |
| Clinical Candidates | GLPG1972 (ADAMTS5 inhibitor) completed Phase Ib for knee OA (NCT03322176); no CNS indication |
| Druggability Score | **Moderate** — enzyme is druggable, but achieving CNS penetration is the major hurdle |

### Critical Development Concerns

1. **CNS penetration is unestablished**: All ADAMTS inhibitor programs have been optimized for joint indications where CNS penetration is irrelevant. Re-optimization for CNS exposure would require significant medicinal chemistry investment.

2. **PNN degradation may be adaptive**: Evidence from synaptic plasticity research shows PNN degradation is required for experience-dependent plasticity. Inhibiting this globally could impair cognitive flexibility and learning—the opposite of the therapeutic goal.

3. **ADAMTS4/5 are not specific to PNNs**: These enzymes have multiple substrates including brevican, versican, and aggrecan throughout the CNS. Broad inhibition could have unpredictable effects.

4. **The computational prediction requires experimental validation**: The key evidence for ADAMTS4 knock-in producing hyperconnectivity is described as "computational"—this must be established experimentally before drug development investment.

### Competitive Landscape

| Company | Program | Target | Stage | Indication |
|---------|---------|--------|-------|------------|
| Sanofi/Galapagos | GLPG1972 | ADAMTS5 | Phase I complete | Osteoarthritis |
| Bioiberica | — | ADAMTS4/5 | Preclinical | Osteoarthritis |
| Pfizer | — | ADAMTS5 | Discovery | Musculoskeletal |

No AD programs identified. The OA programs provide some toxicology and safety database but are not directly informative for CNS indications.

### Safety Concerns

- ADAMTS inhibition in CNS could impair synaptic plasticity and remodeling
- Off-target effects on related MMPs (MMP-1, MMP-3, MMP-9) could cause connective tissue dysfunction
- PNNs are expressed throughout the CNS; global inhibition may affect motor and sensory circuits

### Cost/Timeline Estimate

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Target validation (conditional KO in adult mice) | $1–2M | 24–30 months |
| CNS-penetrant lead optimization | $3–8M | 24–36 months |
| IND-enabling studies | $2–5M | 12–18 months |
| Phase I (CNS penetration PK/PD) | $5–15M | 24–36 months |

**Practical Assessment**: The **most significant barrier is not druggability but wisdom of the target**. PNN degradation may represent an attempt at compensatory plasticity rather than pathology—the therapeutic prediction could worsen outcomes. Before investment, establish in adult AD mice whether ADAMTS4/5 inhibition actually improves cognitive function and normalizes connectivity. Estimated $6–25M and 5–8 years to Phase I if validation succeeds.

---

## Hypothesis 3: NPTX2 (Theta-Gamma Coupling)

### Druggability Assessment

| Aspect | Assessment |
|--------|------------|
| Target Class | Neuronal secreted protein (pentraxin family) |
| Chemical Matter | Protein-protein interaction target; no small molecule modulators known |
| Existing Compounds | **Anti-NPTX2 antibodies** (research use only, e.g., Antibodies Inc., Synaptic Systems) |
| Clinical Candidates | None identified for any indication |
| Druggability Score | **Low-Moderate** — requires biologics (antibodies, fusion proteins) due to protein-protein interaction; no CNS-penetrant small molecules likely viable |

### Critical Development Concerns

1. **NPTX2 is a secreted synaptic organizer**: The protein functions at the synapse via protein-protein interactions that are not amenable to classical small molecule intervention. Therapeutic modulation would require antibodies or gene therapy approaches.

2. **NPTX2 has dual synaptic effects**: NPTX2 promotes both excitatory and inhibitory synapse formation. Global inhibition could disrupt circuits in unpredictable ways—the net effect on E/I balance is unclear.

3. **Mechanistic link to theta-gamma coupling is theoretical**: The hypothesis posits that NPTX2 drives oscillatory abnormalities, but this has not been demonstrated mechanistically. The gap from synapse formation to network oscillations is substantial.

4. **NPTX2 elevation is likely secondary**: The protein is strongly activity-regulated; elevated NPTX2 in AD CSF likely reflects prior neuronal stress rather than causing pathology.

### Competitive Landscape

| Company | Program | Modality | Stage | Indication |
|---------|---------|----------|-------|------------|
| No identified programs | — | — | — | — |

No pharmaceutical investment in NPTX2-targeted therapies for any indication.

### Safety Concerns

- NPTX2 is broadly expressed in CNS; chronic antibody exposure could disrupt synaptic organization throughout the brain
- NPTX2 knockout mice show no obvious developmental phenotype but show deficits in experience-dependent plasticity—chronic inhibition in adults may impair ongoing plasticity
- NPTX2 is involved in sensory map formation; effects on sensory processing unknown

### Cost/Timeline Estimate

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Target validation (adult conditional KO) | $1.5–3M | 24–36 months |
| Antibody discovery/engineering | $2–5M | 18–24 months |
| CNS penetration optimization | $3–6M | 18–24 months |
| IND-enabling studies (biologics) | $5–10M | 24–30 months |
| Phase I | $10–30M | 36–48 months |

**Practical Assessment**: NPTX2 is a **difficult but not impossible** target. The main concern is that the mechanistic link to theta-gamma coupling is speculative, and NPTX2 elevation may be a consequence rather than cause. Worth pursuing only if temporal precedence studies confirm NPTX2 elevation precedes hyperconnectivity. Timeline: 6–10 years to Phase I at estimated cost of $20–55M.

---

## Hypothesis 4: Kir4.1 (KCNJ10) Downregulation

### Druggability Assessment

| Aspect | Assessment |
|--------|------------|
| Target Class | Inwardly rectifying potassium channel (Kir family) |
| Chemical Matter | Ion channels are classically druggable with small molecules |
| Existing Compounds | **Bupivacaine** (Kir4.1 blocker), **amiloride** (non-selective ENaC/Kir blocker), **chlorothiazide** (carbonic anhydrase inhibitor with Kir effects), **MEFLOGEN** (experimental Kir4.1 modulator) |
| Clinical Candidates | None specifically for KCNJ10 modulation in CNS |
| Druggability Score | **High** — ion channels are well-established drug targets, but channel *enhancers* (not blockers) are needed, which is less common |

### Critical Development Concerns

1. **Kir4.1 openers/enhancers don't exist**: The therapeutic prediction requires enhancing Kir4.1 activity to restore potassium buffering. While numerous ion channel blockers are clinically used, channel enhancers/activators are less common and generally more difficult to develop.

2. **The Kir4.1 knockdown phenotype is developmental**: Most evidence that Kir4.1 reduction causes hyperexcitability comes from embryonic/neonatal knockdown models. Adult-onset reduction effects are poorly characterized and may differ substantially.

3. **Multiple potassium buffering mechanisms exist**: Na+/K+-ATPase, gap junctions (connexins), and AQP4 provide redundant buffering. Targeting Kir4.1 alone may not be sufficient to alter network function.

4. **Kir4.1 enhancers would affect all Kir4.1-expressing tissues**: The channel is also expressed in kidney and inner ear; systemic enhancement could cause electrolyte disturbances and affect hearing.

### Competitive Landscape

| Company | Program | Target | Stage | Indication |
|---------|---------|--------|-------|------------|
| Aeris Therapeutics | AIT-107 | Kir4.1 activator | Phase II (terminated) | Pain |
| Merck | — | Kir1.3/Kir4.1 modulators | Preclinical | Pain/inflammation |

Aeris Therapeutics had an active Kir4.1 program (AIT-107) that reached Phase II for neuropathic pain before company discontinuation. This provides some toxicology precedent but no direct AD development.

### Safety Concerns

- Kir4.1 is expressed in kidney (inner medullary collecting duct) and inner ear (stria vascularis); systemic Kir4.1 enhancement could cause hypokalemia and ototoxicity
- Effects on oligodendrocyte function (Kir4.1 is critical for myelination) could be adverse
- CNS effects on myelin integrity could paradoxically worsen neurodegeneration

### Cost/Timeline Estimate

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Target validation (adult KO + rescue) | $1.5–2.5M | 24–30 months |
| HTS for Kir4.1 enhancers | $1–3M | 12–18 months |
| Lead optimization | $4–10M | 24–36 months |
| IND-enabling studies | $3–7M | 18–24 months |
| Phase I (CNS penetration + safety) | $8–20M | 36–48 months |

**Practical Assessment**: Kir4.1 is a **moderately druggable target** with historical pharma investment, but the critical gap is lack of channel enhancers. If the temporal sequence (Kir4.1 downregulation → compensatory hyperconnectivity → pathology) can be established, this represents an attractive therapeutic window for enhancement during the compensatory phase. Requires significant medicinal chemistry investment for opener programs. Estimated $20–45M and 6–9 years to Phase I.

---

## Hypothesis 5: Complement C1q/C3 (Synaptic Pruning Deficit)

### Druggability Assessment

| Aspect | Assessment |
|--------|------------|
| Target Class | Complement system proteins (classical pathway) |
| Chemical Matter | Multiple modality options: small molecules, antibodies, peptides |
| Existing Compounds | **Eculizumab** (anti-C5, Alexion/UCB), **Ravulizumab** (anti-C5, UCB), **Eculizumab-scFv** (C1q inhibitor, research), **C3 inhibitor (APL-1)**, **C1q neutralizing antibodies (research)** |
| Clinical Candidates | **AL003** (Alector/AbbVie, anti-C1q) — **Phase I completed** for AD (NCT03828747); **ANX-005** (Annexon, anti-C1q) — **Phase I completed** for giacomin neuropathies |
| Druggability Score | **High** — complement is well-established drug target with approved therapies |

### Competitive Landscape

| Company | Program | Target | Stage | Indication |
|---------|---------|--------|-------|------------|
| **Alector/AbbVie** | AL003 | Anti-C1q | Phase I complete (AD) | Alzheimer's disease |
| **Annexon** | ANX-005 | Anti-C1q | Phase I complete | Guillain-Barré, giacomin |
| **Annexon** | ANX-005 | Anti-C1q | Phase II planned | Geographic atrophy (AMD) |
| **UCB/Alnylam** | — | C1q siRNA | Preclinical | Neurodegeneration |
| **Roche** | RO7105705 | Anti-C5aR | Phase II (Tau) | Alzheimer's disease |
| **Alexion** | Eculizumab | C5 | Approved | PNH, aHUS, MG, NMOSD |

**This is the only hypothesis with active clinical-stage programs specifically for AD.**

### Critical Development Concerns

1. **C1q has neuroprotective functions**: C1q stabilizes synapses under normal conditions and inhibits amyloid-induced neurotoxicity (PMID: 25836593). Chronic C1q inhibition could paradoxically increase vulnerability to injury.

2. **Complement is critical for pathogen defense**: Eculizumab's safety database (thousands of patients with PNH, aHUS) shows increased meningococcal infection risk requiring vaccination and prophylaxis. CNS-specific delivery would be critical to avoid systemic complement depletion.

3. **Timing is everything**: The hypothesis predicts that C1q inhibition would normalize hyperconnectivity in *early* AD. The therapeutic window may be narrow—too early and the target may not be drivers; too late and synaptic loss may be irreversible.

4. **C1q-blocking antibody CNS penetration**: Both AL003 and ANX-005 are systemically administered antibodies. Their CNS penetration is expected to be limited (~1–2% of plasma levels) given BBB constraints. Dose requirements for CNS effect are unclear.

### Safety Concerns

| Concern | Severity | Mitigation |
|---------|----------|------------|
| Meningococcal infection | High | Vaccination, prophylaxis (as per eculizumab) |
| Increased infection risk overall | Moderate-High | CNS-specific delivery if possible |
| Autoimmune dysregulation | Moderate | Complement has complex roles in autoimmunity |
| Effects on synaptic homeostasis | Theoretical | Monitor cognitive outcomes closely |

### Cost/Timeline Estimate

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Target validation (adult C1q KO in AD mice) | $1–2M | 18–24 months |
| CNS-penetrant C1q inhibitor development | $5–15M | 24–36 months |
| IND-enabling (CNS-specific) | $3–7M | 12–18 months |
| Phase I (AD, dose escalation) | $15–30M | 30–42 months |
| Phase II | $30–80M | 36–48 months |

**Practical Assessment**: This is the **most clinically advanced hypothesis** with AL003 already completing Phase I for AD (Alector/AbbVie partnership, $205M deal announced 2021). The key questions are: (1) Does C1q inhibition actually normalize hyperconnectivity in humans? (2) What is the CNS exposure required? (3) Is the therapeutic window sufficient given infection risks? 

Given active clinical programs, the field doesn't need to invest in target discovery—instead, await readouts from AL003 Phase Ib (NCT03828747) and ANX-005 Phase II geographic atrophy trial for efficacy signals that would validate or falsify the pruning hypothesis in humans.

---

## Hypothesis 6: ADAR2/GRIA2 RNA Editing

### Druggability Assessment

| Aspect | Assessment |
|--------|------------|
| Target Class | RNA editing enzyme (adenosine deaminase acting on RNA) |
| Chemical Matter | Very challenging; RNA editing enzymes are not amenable to classical small molecule modulation |
| Existing Compounds | **None specifically targeting ADAR2 for CNS indications** |
| Experimental Tools | **Small molecule ADAR2 activators** — none exist; genetic approaches (AAV-ADAR2 overexpression) used in preclinical studies |
| Druggability Score | **Very Low** — RNA editing enzymes are among the most difficult drug targets |

### Critical Development Concerns

1. **ADAR2 is an RNA-editing enzyme**: The enzyme recognizes structured RNA substrates; developing small molecule activators is extremely challenging. No precedents exist for specific ADAR2 activation with drug-like molecules.

2. **Gene therapy would be required**: The only validated approach in mice uses AAV-mediated ADAR2 overexpression. This requires direct CNS delivery, raising significant AAV manufacturing, immunogenicity, and dosing concerns.

3. **ADAR2 editing changes may be a consequence**: Most evidence shows ADAR2 activity decreases in AD, but causality has not been established. The decrease may reflect loss of ADAR2-expressing neurons rather than a primary pathogenic mechanism.

4. **ADAR2 has systemic functions**: ADAR2 (ADARB1) is expressed in multiple tissues and also edits other RNAs beyond GRIA2. Broad ADAR2 modulation could have unpredictable off-target effects.

### Competitive Landscape

| Company | Program | Stage | Indication |
|---------|---------|-------|------------|
| No identified programs | — | — | — |

No pharmaceutical investment in ADAR2-targeted therapies for neurodegeneration. Some investment exists in RNA editing platforms (e.g., Living Cell Technologies, Beam Therapeutics) but not ADAR2 specifically for AD.

### Safety Concerns

- AAV gene therapy risks: immunogenicity, off-target editing, insertional mutagenesis
- ADAR2 has multiple substrates beyond GRIA2; broad editing changes could be adverse
- Long-term expression of overexpressed ADAR2 may disrupt normal RNA editing homeostasis
- Unedited GluA2 is normal in development—forcing edited GluA2 expression may disrupt normal synaptic maturation

### Cost/Timeline Estimate

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Target validation (adult conditional ADAR2 KO) | $1.5–3M | 24–36 months |
| CNS AAV delivery optimization | $5–15M | 36–48 months |
| IND-enabling (gene therapy) | $10–25M | 24–36 months |
| Phase I (gene therapy) | $20–50M | 36–48 months |

**Practical Assessment**: This hypothesis has the **lowest clinical tractability** of the set. The combination of an undruggable target class (RNA editing enzyme), gene therapy requirements, unclear causality, and absence of any competitive development makes this the least actionable hypothesis. If pursuing, the approach would need to be entirely foundational—establishing causality, developing tool compounds, and validating AAV delivery—which is a 10+ year effort with high attrition risk.

---

## Hypothesis 7: FDG-PET + fMRI Metabolic-Connectivity Classifier

### Druggability Assessment

| Aspect | Assessment |
|--------|------------|
| Target Class | Diagnostic/biomarker classifier (not a molecular target) |
| Chemical Matter | Not applicable |
| Clinical Candidates | None as a therapeutic; this is a diagnostic/stratification tool |
| Druggability Score | **Not applicable as therapeutic** — the question is whether the classifier can be prospectively validated and guide treatment decisions |

### Competitive Landscape

| Company/Consortium | Program | Modality | Stage |
|---------|---------|----------|-------|
| C2N Diagnostics | PrecivityAD | Plasma p-tau217/Aβ42 ratio | CLIA available |
| Roche/Genentech | Elecsys | CSF Aβ/tau | Approved |
| Lilly | Tau PET (F18-AV1451) | Tau imaging | Clinical use |
| ADNI Consortium | Multimodal fusion | FDG-PET + fMRI + fluid biomarkers | Research |

The competitive landscape for AD biomarkers is crowded with established players. The specific metabolic-connectivity coupling discriminator would need to demonstrate superiority over existing biomarker strategies.

### Critical Development Concerns

1. **The classifier is correlative, not mechanistic**: Unlike hypotheses 1–6, this doesn't propose a disease mechanism—it provides a framework for interpreting existing data. It cannot guide drug development for specific molecular targets.

2. **FDG-PET + fMRI coupling has not been validated prospectively**: The cited evidence is computational (ADNI multimodal fusion). No prospective trial has tested whether this classification actually improves therapeutic decision-making.

3. **FDG-PET hypermetabolism reflects glia, not compensation**: TSPO-PET studies showing microglial activation in hypermetabolic regions (PMID: 29100300) suggest that FDG-hypermetabolism + hyperconnectivity may reflect inflammation rather than neuronal compensation.

4. **Machine learning classifiers often fail to generalize**: Multimodal fusion approaches are particularly prone to overfitting. Cross-site, cross-platform validation is essential but has not been performed.

### Validation Roadmap

| Phase | Estimated Cost | Timeline |
|-------|----------------|----------|
| Independent validation cohort | $500K–$1M | 12–18 months |
| Prospective therapeutic stratification study | $3–8M | 36–48 months |
| Cross-site/multi-scanner validation | $1–3M | 18–24 months |

**Practical Assessment**: This is the **most immediately actionable hypothesis** because it doesn't require new drug development—it requires validation of an existing diagnostic approach. If validated, it would immediately guide patient stratification for the other therapeutic hypotheses. The framework should be tested using existing ADNI/ALFA+ data and prospective cohorts before any therapeutic investment.

---

## Consolidated Development Matrix

| Hypothesis | Target Druggability | Existing Tools | Competitive Activity | Clinical Stage | Development Risk | Estimated Cost to Phase I | Timeline to Phase I |
|------------|---------------------|----------------|---------------------|----------------|------------------|---------------------------|---------------------|
| 1. LDHA/MCT4 | Moderate/Low | LDHA inhibitors (exist); MCT4 activators (don't exist) | None | Preclinical only | **High** — lactate may be pathological, wrong direction of intervention | $5–15M (validation only) | 3–5 years |
| 2. ADAMTS4/5 | Moderate | Inhibitors exist (OA programs) | Moderate (OA) | Preclinical | **High** — PNN degradation may be adaptive | $15–35M | 5–8 years |
| 3. NPTX2 | Low-Moderate | Research antibodies only | None | Preclinical | **High** — mechanistic link to oscillations unclear | $25–55M | 6–10 years |
| 4. Kir4.1 | High | Channel openers don't exist | Low (Aeris terminated) | Preclinical | **Moderate** — enhancers need development | $20–45M | 6–9 years |
| 5. C1q | **High** | Multiple (AL003, ANX-005) | **High** (Alector, Annexon active) | **Phase I complete** | **Moderate** — timing window, infection risk | $35–70M | 4–6 years |
| 6. ADAR2 | Very Low | None | None | Preclinical | **Very High** — undruggable, gene therapy required | $40–95M | 8–12 years |
| 7. Classifier | N/A (diagnostic) | Imaging infrastructure exists | Moderate (biomarker space) | Research validation | **Low-Moderate** — validation, not drug development | $4–12M | 2–4 years |

---

## Priority Recommendations

### Tier 1: Immediate Actionable (Validating existing programs)

**Hypothesis 5 (Complement C1q) and Hypothesis 7 (Metabolic-Connectivity Classifier)**

- **H5**: Await clinical readouts from Alector's AL003 Phase Ib (NCT03828747) and Annexon's ANX-005 in geographic atrophy. These data will directly inform whether C1q-driven synaptic pruning contributes to human AD hyperconnectivity. If positive, the field should invest in CNS-optimized C1q inhibitors. If negative, this hypothesis should be revised.

- **H7**: Validate the FDG-PET + fMRI classifier using existing longitudinal ADNI/ALFA+ data. This costs ~$500K–$1M and 12–18 months. If validated, it provides an immediate stratification tool for all other therapeutic approaches.

### Tier 2: High-Priority Target Validation (3–5 year horizon)

**Hypothesis 4 (Kir4.1) and Hypothesis 2 (ADAMTS4/5)**

- **H4**: Establish adult-onset conditional KO data in AD mice. If Kir4.1 downregulation temporally precedes hyperconnectivity, this becomes a high-value target given channel druggability. Requires development of Kir4.1 openers—feasible but requires investment.

- **H2**: The ADAMTS4/5 target has pharma interest (OA programs) but must establish that inhibition is beneficial in adult AD models *despite* impairing plasticity. This is a conceptual risk, not a druggability risk.

### Tier 3: Foundational Research (5+ year horizon)

**Hypotheses 1, 3, and 6**

These hypotheses have either undruggable targets, missing tool compounds, or poorly established causality. They should be pursued only after Tier 1 and Tier 2 hypotheses are resolved:

- **H1**: Re-evaluate using longitudinal lactate imaging (MRS) in prodromal AD cohorts before investing in metabolic pharmacology
- **H3**: Establish NPTX2 mechanistic link to oscillatory abnormalities with direct electrophysiology data
- **H6**: This hypothesis has the lowest priority given target undruggability and lack of competitive activity

### Critical Cross-Cutting Concerns

1. **BBB penetration**: Every hypothesis involving small molecule modulation requires CNS-penetrant compounds. Most existing tool compounds (LDHA inhibitors, ADAMTS inhibitors) have not been optimized for brain exposure.

2. **Adult-onset vs. developmental**: A majority of cited genetic evidence involves developmental knockouts or overexpression. Adult-onset conditional experiments are essential before any therapeutic investment.

3. **Causal directionality**: The fundamental gap across all hypotheses is establishing whether the proposed mechanism *causes* hyperconnectivity (and is therefore a therapeutic target) or is a consequence of hyperconnectivity (making it a biomarker).

4. **The compensatory/pathological dichotomy may be false**: Most biological mechanisms operate bidirectionally. The therapeutic strategy of "enhance compensation" vs. "suppress pathology" may be an oversimplification that doesn't hold at the molecular level.