Disease-modifying Efficacy of Sitagliptin Therapy in Early-stage Parkinson's Disease

A Multicenter, Randomized, Double-blind, Placebo-controlled Phase 2 Trial Evaluating the Disease-modifying Efficacy of Sitagliptin Therapy in Early-stage Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder pathologically characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta and the accumulation of α-synuclein (α-syn) aggregates. To date, all approved treatments, including levodopa, are primarily limited to symptomatic relief, and no disease-modifying therapy (DMT) has been established to fundamentally slow or halt disease progression.

Large-scale epidemiological cohort studies conducted in Taiwan, Sweden, the United Kingdom, and other countries have consistently reported that, among patients with diabetes, DPP-4 inhibitor users had an approximately 30%-40% lower risk of developing Parkinson's disease compared with non-users.

This study aims to evaluate whether 72 weeks of treatment with sitagliptin (100 mg once daily), compared with placebo, delays the time to confirmed motor progression in patients with early-stage PD receiving stable levodopa monotherapy. Confirmed motor progression is defined as an increase of ≥5 points from baseline in the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III score assessed in the OFF state.

Inclusion Criteria:

1. Male or female participants aged 50 to 80 years, inclusive.
2. Participants diagnosed with Clinically Established Parkinson's Disease or Clinically Probable Parkinson's Disease according to the Movement Disorder Society (MDS) Clinical Diagnostic Criteria for Parkinson's Disease (Postuma et al., 2015).
3. Participants diagnosed with Parkinson's disease within 3 years prior to screening.
4. Participants who are either treatment-naïve to antiparkinsonian medications at screening or receiving stable levodopa monotherapy, defined as maintenance of the same levodopa dose for at least 12 weeks immediately prior to screening without concomitant use of other antiparkinsonian medications.
5. Hoehn and Yahr stage 1 or 2 in the ON state.
6. Participants with documented evidence, based on ¹⁸F-FP-CIT PET performed at the investigational site within 36 months prior to screening, of reduced dopamine transporter (DAT) availability in the posterior putamen. Raw DICOM files must be retrievable and suitable for quantitative analysis of standardized uptake value ratio (SUVR) or specific binding ratio (SBR) by the central reader. Participants without an available prior ¹⁸F-FP-CIT PET result must agree to undergo an additional ¹⁸F-FP-CIT PET scan.
7. Participants with documented brain MRI performed at any time prior to screening or during the screening period, confirming exclusion of causes other than Parkinson's disease, including atypical parkinsonian syndromes such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), cerebrovascular disease, normal-pressure hydrocephalus, and brain tumor. The T1-weighted sequence must be suitable for comparison with the follow-up MRI performed at Visit 9.
8. Mini-Mental State Examination (MMSE) score ≥24, to exclude severe cognitive impairment.
9. Participants who understand the clinical trial protocol and voluntarily provide written informed consent.
10. Participants who are able and willing to comply with follow-up visits and study assessments throughout the entire study period.

Exclusion Criteria:

1. Participants with suspected atypical parkinsonian syndromes, including progressive supranuclear palsy (PSP), multiple system atrophy (MSA), corticobasal syndrome (CBS), or other atypical parkinsonian disorders.
2. Participants with vascular parkinsonism, drug-induced parkinsonism, or toxin-induced parkinsonism.
3. Participants with secondary parkinsonism due to causes such as normal-pressure hydrocephalus, brain tumor, or other identifiable secondary causes.
4. Participants currently receiving dopaminergic medications other than levodopa, including dopamine agonists, monoamine oxidase-B (MAO-B) inhibitors, catechol-O-methyltransferase (COMT) inhibitors, amantadine, or other antiparkinsonian medications.
5. Participants with levodopa-induced motor fluctuations or levodopa-induced dyskinesia (LID) that interfere with activities of daily living, defined as a score of ≥2 on MDS-UPDRS Part IV Item 4.1 or 4.2.
6. History of hypersensitivity to sitagliptin or any other dipeptidyl peptidase-4 (DPP-4) inhibitor.
7. Current treatment with a DPP-4 inhibitor or glucagon-like peptide-1 (GLP-1) receptor agonist.
8. History of acute or chronic pancreatitis.
9. Acute cholecystitis or cholangitis.
10. Participants with previously diagnosed diabetes mellitus who are currently receiving antidiabetic medication.However, participants with a diagnosis of diabetes mellitus who are not currently receiving antidiabetic medication, or those found to have HbA1c ≥6.5% during screening, may be enrolled. Participants with HbA1c ≥7.5% will be excluded because combination antidiabetic therapy may be required.
11. Estimated glomerular filtration rate (eGFR) <45 mL/min/1.73 m², indicating moderate or greater renal impairment.
12. Hepatic dysfunction, defined as AST or ALT >3 times the upper limit of normal (ULN).
13. Pancreatic enzyme abnormality, defined as amylase or lipase >3 times the ULN.
14. Clinically significant cardiovascular disease, including New York Heart Association (NYHA) Class III-IV heart failure, myocardial infarction, or stroke within 6 months prior to screening.
15. History of malignancy within 5 years prior to screening, except for completely treated non-melanoma skin cancer.
16. Uncontrolled, clinically significant psychiatric disorder.
17. Participants who are pregnant or breastfeeding, or women of childbearing potential who are unwilling or unable to use an appropriate method of contraception.
18. Participation in another clinical trial within 30 days prior to screening.
19. Participants considered unsuitable for participation in the clinical trial based on the investigator's clinical judgment.