The purpose of this research study is to assess safety and tolerability of a single intravenous (given through a vein) dose of the investigational retinal tracer AMDX-2011P in patients with neurodegenerative diseases (Parkinson's disease and ALS).

The primary objective of this study is to evaluate the safety and tolerability of three different doses of AMDX-2011P (25mg, 50mg, or 100mg) given as a single intravenous dose in patients with neurodegenerative diseases (Parkinson's disease and ALS). The first cohort of participants taking part in the study will receive the lowest dose of AMDX-2011P (25mg). If no major side effects occur, the dose will be increased for the next group of participants to 50mg and then to 100mg.

Secondary objective of this study is to characterize the pharmacokinetic (PK) profile of AMDX-2011P and AMDX-2011.

Exploratory evaluations of the biological activity of AMDX-2011P in the retina will be performed by imaging.

Inclusion Criteria:

For Subjects with Parkinson's Disease

1. Clinically established Parkinson's disease based on Movement Disorder Society (MDS) Clinical Diagnostic Criteria for Parkinson's disease (Table 8) and a modified Hoehn & Yahr scale of 1-3 (Table 9).

2. No suspected atypical parkinsonian syndromes due to drugs, metabolic disorders, encephalitis, or degenerative diseases.

   For Subjects with ALS

3. Confirmed diagnosis of ALS with both upper and lower motor neuron involvement.

   For All Subjects

4. Ability to undergo retinal imaging.

5. Subject or legally authorized representative must provide signed informed consent (or signed assent form) prior to study entry and have the ability and willingness to attend and comply with the necessary study procedures and visits at the study site. For subjects unable to physically sign the informed consent, a guardian or trusted care giver can sign on their behalf in presence of an independent witness.

6. Contraception use by study subjects of childbearing potential (male and female) and female partners of childrearing potential male subjects should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.

Exclusion Criteria:

1. Presence of any underlying physical or psychological medical condition that would make it unlikely that the subject will complete the study per protocol.
2. Clinically significant laboratory abnormalities assessed by the investigator.
3. Active malignancy and/or history of malignancy in the past 5 years, with the exception of completely excised non-melanoma skin cancer or low-grade cervical intraepithelial neoplasia.
4. Prolonged QTcF (>450 ms for males and >470 ms for females), cardiac arrhythmia, or any clinically significant abnormality in the resting ECG, as judged by the investigator.
5. Presence of any ocular condition that would significantly hinder the ability to detect and quantify hyper-fluorescent puncta (e.g., eyes with significant hyper-autofluorescence that would mask the ability to detect, quantify, and discern post-injection hyper-fluorescent signal from pre-injection hyper-autofluorescence signal).
6. Use of any new prescription therapies or vaccines within 7 days prior to the study drug administration.
7. Drugs with potential phototoxicity per Package Insert are prohibited within 48 hours or 5 half-lives, whichever is longer, prior to first study drug until End-of-study (EOS) visit, except for those required for treatment of underlying disease.
8. Administration of investigational product in another study within 30 days prior to the first study drug administration, or five half-lives, whichever is longer.
9. Females who are pregnant or breastfeeding.

There is no plan to share individual participant data at this time.

From enrollment until end of follow-up, up to 8 days