Determine whether DRP1 inhibition or fusion restoration can slow dopaminergic degeneration in PD models and whether these interventions can restore mitochondrial network balance toward a physiological state.
| Arm | Intervention | Model | n |
|-----|--------------|-------|---|
| A1 | Vehicle | iPSC-DA neurons (WT) | 12 |
| A2 | Mdivi-1 (50μM) | iPSC-DA neurons (WT) | 12 |
| A3 | Vehicle | iPSC-DA neurons (LRRK2 G2019S) | 12 |
| A4 | Mdivi-1 (50μM) | iPSC-DA neurons (LRRK2 G2019S) | 12 |
| A5 | Vehicle | iPSC-DA neurons (SNCA A53T) | 12 |
| A6 | Mdivi-1 (50μM) | iPSC-DA neurons (SNCA A53T) | 12 |
| Arm | Intervention | Model | n |
|-----|------------|-------|---|
| B1 | Vehicle | C57BL/6J mice | 15 |
| B2 | Mdivi-1 (10mg/kg IP, daily) | C57BL/6J mice | 15 |
| B3 | Vehicle | LRRK2 G2019S KI mice | 15 |
| B4 | Mdivi-1 (10mg/kg IP, daily) | LRRK2 G2019S KI mice | 15 |
| Arm | Intervention | Population | n |
|-----|------------|-----------|---|
| C1 | Standard of care | Early PD (H&Y 1-2) | 30 |
| C2 | Mdivi-1 (investigational) | Early PD (H&Y 1-2) | 30 |
The dose-response arms (A2-A4) establish the optimal Mdivi-1 concentration that maximizes neuroprotection while minimizing cytotoxicity. Previous studies have shown dose-dependent effects with optimal neuroprotection at 25-50μM in some models but cytotoxicity at higher concentrations[@rappold2018].
Phase 1b: Genetic Stratification
Arms A5-A10 determine whether LRRK2 G2019S and SNCA A53T neurons show differential responsiveness to DRP1 inhibition. Given that LRRK2 G2019S directly drives fission through DRP1 phosphorylation, we hypothesize these neurons will show the strongest response to Mdivi-1[@janda2021].
Phase 1c: Combination Therapy
Arm A13 tests the hypothesis that combining DRP1 inhibition (to block excessive fission) with MFN1 overexpression (to restore fusion) may produce synergistic benefits, addressing both sides of the fission-fusion balance[@chen2020].
This phase translates the in vitro findings to mammalian models, assessing behavioral outcomes and target engagement in the brains of live animals.
| Arm | Intervention | Model | n | Duration |
|-----|------------|-------|---|----------|
| B1 | Vehicle (saline + DMSO) | C57BL/6J mice | 15 | 8 weeks |
| B2 | Mdivi-1 (10mg/kg IP, daily) | C57BL/6J mice | 15 | 8 weeks |
| B3 | Mdivi-1 (25mg/kg IP, daily) | C57BL/6J mice | 15 | 8 weeks |
| B4 | Vehicle | LRRK2 G2019S KI mice | 15 | 8 weeks |
| B5 | Mdivi-1 (10mg/kg IP, daily) | LRRK2 G2019S KI mice | 15 | 8 weeks |
| B6 | Mdivi-1 (25mg/kg IP, daily) | LRRK2 G2019S KI mice | 15 | 8 weeks |
| B7 | AAV-MFN1 (bilateral SNc) | LRRK2 G2019S KI mice | 15 | 8 weeks post-surgery |
| B8 | AAV-OPA1 (bilateral SNc) | LRRK2 G2019S KI mice | 15 | 8 weeks post-surgery |
| B9 | Mdivi-1 + AAV-MFN1 | LRRK2 G2019S KI mice | 15 | 8 weeks |
MPTP Challenge Model
At week 4 of treatment, all mice will receive a subthreshold MPTP challenge (10mg/kg IP, every 2 hours × 4) to induce dopaminergic toxicity while preserving sufficient neurons to detect neuroprotective effects of the intervention[@rappold2018].
This phase tests the leading intervention in early Parkinson's disease patients, establishing safety, tolerability, and preliminary efficacy.
| Arm | Intervention | Population | n | Duration |
|-----|------------|-----------|---|----------|
| C1 | Standard of care + placebo | Early PD (H&Y 1-2, MDS-UPDRS ≤ 40) | 30 | 52 weeks |
| C2 | Standard of care + Mdivi-1 (low dose) | Early PD (H&Y 1-2, MDS-UPDRS ≤ 40) | 30 | 52 weeks |
| C3 | Standard of care + Mdivi-1 (high dose) | Early PD (H&Y 1-2, MDS-UPDRS ≤ 40) | 30 | 52 weeks |
Patient Selection Rationale
Early PD patients (within 2 years of diagnosis) are selected because they retain sufficient dopaminergic neurons for potential rescue. Patients with LRRK2 G2019S or GBA variants will be enrichment through genetic testing to increase the likelihood of detecting a response, as these genetic backgrounds show the strongest mitochondrial dynamics dysfunction[@kumar2018].
Mitochondrial dynamics are particularly crucial in neurons due to their unique morphology and energy requirements:
| Process | Key Players | Function |
|---------|-------------|----------|
| Fission | DRP1, FIS1, MFF | Mitochondrial division |
| Fusion | MFN1, MFN2, OPA1 | Mitochondrial networking |
| Transport | Kinesin, Milton, Miro | Process distribution |
| Mitophagy | PINK1, Parkin, LC3 | Quality control |
Neurons require precise spatial distribution of mitochondria at:
Multiple genetic and environmental factors in PD affect mitochondrial dynamics:
| Factor | Effect on Dynamics | Reference |
|--------|-------------------|----------|
| LRRK2 G2019S | Increased fission, DRP1 activation | [@gomez2017] |
| PINK1 loss | Impaired mitophagy, fission initiation | [@ Scar19] |
| Parkin loss | Failed mitochondrial quality control | [@geisler2020] |
| SNCA A53T | Drp1 recruitment, fragmentation | [@kazi2021] |
| MPTP/toxin exposure | Acute fission induction | [@ba2019] |
Post-mortem studies in PD substantia nigra show:
DRP1 (Dynamin-related protein 1) is the master regulator of mitochondrial fission:
| Arm | Cell Type | n | Treatment |
|-----|-----------|---|-----------|
| A1 | iPSC-DA neurons (WT) | 12 | Vehicle |
| A2 | iPSC-DA neurons (WT) | 12 | Mdivi-1 (50μM) |
| A3 | iPSC-DA neurons (LRRK2 G2019S) | 12 | Vehicle |
| A4 | iPSC-DA neurons (LRRK2 G2019S) | 12 | Mdivi-1 (50μM) |
| A5 | iPSC-DA neurons (SNCA A53T) | 12 | Vehicle |
| A6 | iPSC-DA neurons (SNCA A53T) | 12 | Mdivi-1 (50μM) |
Endpoints:
| Arm | Intervention | Mechanism | n |
|-----|--------------|-----------|---|
| B1 | OPA1 overexpression | Fusion promotion | 12 |
| B2 | MFN2 overexpression | Outer membrane fusion | 12 |
| B3 | Mdivi-1 + OPA1 | Combined approach | 12 |
| B4 | Vector control | Baseline | 12 |
| Arm | Model | Intervention | Dose | n |
|-----|-------|--------------|------|---|
| C1 | C57BL/6J | Vehicle | IP daily | 15 |
| C2 | C57BL/6J | Mdivi-1 | 10mg/kg IP daily | 15 |
| C3 | LRRK2 G2019S KI | Vehicle | IP daily | 15 |
| C4 | LRRK2 G2019S KI | Mdivi-1 | 10mg/kg IP daily | 15 |
| C5 | Thy1-SynA53T | Vehicle | IP daily | 15 |
| C6 | Thy1-SynA53T | Mdivi-1 | 10mg/kg IP daily | 15 |
| Arm | Model | MPTP | Mdivi-1 | n |
|-----|-------|------|--------|---|
| D1 | C57BL/6J | Vehicle | Vehicle | 15 |
| D2 | C57BL/6J | MPTP | Vehicle | 15 |
| D3 | C57BL/6J | MPTP | Mdivi-1 (5mg/kg) | 15 |
| D4 | C57BL/6J | MPTP | Mdivi-1 (10mg/kg) | 15 |
| D5 | C57BL/6J | MPTP | Mdivi-1 (20mg/kg) | 15 |
Primary Endpoints:
| Study | Requirements |
|-------|---------------|
| PK/PD | Rodent and non-rodent species |
| Toxicology | 28-day (rodent), 90-day (non-rodent) |
| Safety pharmacology | CNS, cardiovascular, respiratory |
| Formulation | Oral bioavailability |
| Arm | Population | Intervention | n |
|-----|------------|--------------|---|
| E1 | Early PD (H&Y 1-2) | Standard of care | 30 |
| E2 | Early PD (H&Y 1-2) | Mdivi-1 low dose | 30 |
| E3 | Early PD (H&Y 1-2) | Mdivi-1 high dose | 30 |
Primary Endpoint: Change in MDS-UPDRS Part II/III at 52 weeks Secondary Endpoints:
DRP1 (dynamin-related protein 1) is the master regulator of mitochondrial fission. In PD, DRP1 is hyperactivated through phosphorylation at Ser616 by LRRK2 and other kinases[@janda2021]. Elevated DRP1 activity causes excessive mitochondrial fission, generating small, fragmented mitochondria that cannot meet the high energy demands of dopaminergic neurons. Inhibition of DRP1 with Mdivi-1 has shown neuroprotection in multiple PD models, including MPTP-treated mice and 6-OHDA-lesioned rats[@rappold2018].
The mitochondrial fusion machinery (MFN1, MFN2, OPA1) is impaired in PD through multiple mechanisms: alpha-synuclein oligomers directly bind MFN2 and OPA1, reducing their fusogenic activity; oxidative stress activates OMA1 protease, which cleaves OPA1 into fusion-incompetent short forms[@chen2020]. Restoring fusion through AAV-mediated MFN1 or OPA1 overexpression may allow mitochondria to fuse and share content, regenerating a healthy mitochondrial network.
The dual hit of excessive fission (DRP1 hyperactivity) AND impaired fusion (MFN2/OPA1 dysfunction) suggests that combination therapy addressing both defects may be more effective than single-target approaches. This hypothesis will be tested in both in vitro (Arm A13) and in vivo (Arm B9) phases[@berwick2019].
| Milestone | Timeframe |
|-----------|-----------|
| Phase 1 initiation | Month 1 |
| Phase 1 completion | Month 6 |
| Phase 2 initiation | Month 7 |
| Phase 2 completion | Month 14 |
| Phase 3 initiation | Month 15 |
| Interim analysis (Phase 3) | Month 24 |
| Phase 3 completion | Month 30 |
| Final analysis and publication | Month 36 |
PLANNED
Human iPSCs will be differentiated into dopaminergic neurons using a modified dual-SMAD inhibition protocol. Briefly, iPSCs are cultured in neural induction medium containing SB431542 (10μM) and DMH1 (2μM) for 11 days to generate neural progenitor cells. These progenitors are then patterned toward a midbrain identity using SHH (100ng/mL), FGF8 (100ng/mL), and BDNF (20ng/mL) for 15 days. Terminal differentiation occurs over 25 days in maturation medium containing BDNF (20ng/mL), GDNF (10ng/mL), ascorbic acid (200μM), dbcAMP (0.5mM), and TGF-β3 (1ng/mL). Neurons are matured for an additional 30 days before experimentation, yielding tyrosine hydroxylase (TH)-positive neurons with typical dopaminergic electrophysiological properties[@saez2019].
Mitochondria will be imaged using live-cell confocal microscopy (Zeiss LSM 880) with MitoTracker Green FM (100nM, 30min incubation). Image analysis will employ a custom Machine Learning pipeline trained on 10,000+ manually annotated mitochondria:
Cellular ATP will be measured using the CellTiter-Glo 2.0 Luminescent Cell Viability Assay (Promega). Briefly, cells are incubated with CellTiter-Glo reagent (1:1 volume) for 10 minutes at room temperature, and luminescence is measured on a plate reader (Tecan Infinite M1000). ATP levels will be normalized to protein concentration (BCA assay) and expressed as nmol ATP/mg protein.
Protein expression will be assessed by Western blot using the following antibodies:
| Target | Vendor | Catalog | Dilution | Expected Band Size |
|--------|--------|---------|----------|-------------------|
| Total DRP1 | Abcam | ab184247 | 1:1000 | 80kDa |
| p-DRP1 (Ser616) | Cell Signaling | 3455S | 1:500 | 80kDa |
| p-DRP1 (Ser637) | Cell Signaling | 4867S | 1:500 | 80kDa |
| MFN1 | Abcam | ab126024 | 1:1000 | 84kDa |
| MFN2 | Abcam | ab124773 | 1:1000 | 86kDa |
| OPA1 | BD Biosciences | 612607 | 1:500 | 80-100kDa |
| TH | Abcam | ab112 | 1:1000 | 60kDa |
| β-Actin | Sigma | A5441 | 1:5000 | 42kDa |
Mouse brain sections (40μm) will be stained for tyrosine hydroxylase (TH) using immunohistochemistry. Unbiased stereological estimates of TH+ neuron number in the substantia nigra pars compacta will be performed using the optical fractionator method (Stereologer software). The sampling grid size will be 150×150μm, and the dissector height will be 20μm with a 2μm guard zone[@rappold2018].
Motor function will be assessed using a comprehensive battery:
All behavioral testing will be conducted during the animals' active (dark) phase under red light illumination.
DRP1 p-Ser616 in blood: Reflects the primary pharmacological target of Mdivi-1. In PD patient blood, p-Ser616 levels correlate with disease severity and are elevated even in early stages[@janda2021].
Mitochondrial DNA copy number: Serves as a proxy for mitochondrial biogenesis. When fission is inhibited, mitochondria can fuse and undergo mitochondrial biogenesis, increasing mtDNA copy number as a compensatory response.
NfL in CSF: Non-specific marker of neuroaxonal injury but validated in PD progression. A decrease in NfL slope would suggest neuroprotection[@kumar2018].
p-Ser129 α-Syn in CSF: Disease-specific marker of alpha-synuclein pathology. If mitochondrial dynamics intervention reduces alpha-synuclein phosphorylation (through improved mitochondrial function), this would suggest disease modification.
| Timepoint | Blood (EDTA) | CSF | Skin Biopsy | Muscle Biopsy |
|-----------|-------------|-----|------------|---------------|
| Baseline | ✓ | ✓ | ✓ | ✓ |
| Week 12 | ✓ | — | — | — |
| Week 26 | ✓ | ✓ | — | — |
| Week 52 (endpoint) | ✓ | ✓ | ✓ | ✓ |
The primary efficacy endpoint (change in MDS-UPDRS Parts II+III at 52 weeks) will be analyzed using a mixed-effects model for repeated measures (MMRM) with treatment arm, visit, treatment-by-visit interaction, and baseline MDS-UPDRS as covariates. An unstructured covariance matrix will model within-subject correlations.
The hierarchical testing procedure will control family-wise error rate:
Pre-specified subgroups based on genetic status:
Mdivi-1 is a first-generation inhibitor with limitations (limited BBB penetration, potential off-target effects). Several next-generation compounds are in development:
| Compound | Company | Stage | Advantages |
|----------|---------|-------|------------|
| AT-158 | Internal | Preclinical | 10× potency, better selectivity |
| Dynasore analogs | Various | Discovery | Improved brain penetration |
| Small molecule Drp1 modulators | Merck | Preclinical | Allosteric modulation |
AAV-mediated delivery of MFN1, MFN2, or OPA1 directly to the substantia nigra could provide long-term restoration of mitochondrial fusion. This approach would require stereotactic neurosurgery but could provide sustained benefits.
Future trials may combine:
Related Hypotheses: