This experiment validates the mitochondrial dynamics dysfunction hypothesis and tests therapeutic interventions targeting fission/fusion balance restoration in PD.
Determine whether DRP1 inhibition or fusion restoration can slow dopaminergic degeneration in PD models.
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[1].
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[2].
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[3].
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[1:1].
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[4].
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 | [5] |
| 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:
Small molecule inhibitors like Mdivi-1 block DRP1 GTPase activity and have shown neuroprotective effects in PD models.
| 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:
Secondary 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:
Sample size calculation accounts for the expected 40-50% slower progression in the treatment arm compared to placebo, based on preclinical neuroprotection data[1:3].
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[2:1]. 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[1:4].
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[3:1]. 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[7:1].
| 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
DRP1 inhibition protects dopaminergic neurons in vivo. Science Translational Medicine. 2018. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
LRRK2 G2019S drives mitochondrial fission via DRP1 phosphorylation at Ser616. Nature Neuroscience. 2021. ↩︎ ↩︎
Mitochondrial fusion protein OPA1 in PD. Cell Death & Disease. 2020. ↩︎ ↩︎
Fis1 expression correlates with PD severity. Neurobiology of Disease. 2018. ↩︎
DRP1 elevation in PD substantia nigra. Brain. 2017. ↩︎ ↩︎
LRRK2 G2019S knock-in mouse model shows mitochondrial fragmentation. Nature Communications. 2016. ↩︎
Mitochondrial dynamics in neurodegeneration. Journal of Neurochemistry. 2019. ↩︎ ↩︎