A Phase 2A Multicenter, Randomized, Double Blind, Placebo-Controlled, Parallel-Group Safety and Tolerability Trial of PQ912 in Subjects with early Alzheimer's Disease

1. Signed and dated written informed consent obtained from the subject in accordance with local regulations.
2. Male or surgically sterile or postmenopausal female, aged *50 to *89 years. Male subjects with childbearing potential partners are willing to and should use condoms during study medication treatment and until 28 days after the last dose of study medication.
3. Diagnosis of MCI due to AD or mild dementia due to AD with amnestic presentation, according to Alzheimer Association * National Institute on Aging (AA-NIA) criteria [Albert et al 2011; McKhann et al 2011].
4. MMSE score of 21 to 30 inclusive at screening.
5. Screening visit brain MRI scan consistent with the diagnosis of MCI due to AD or mild dementia due to AD, as judged by central rater.;6. A positive AD signature showing one of the following (either a, b, c, OR d):
a. Screening CSF sample with an A-beta 42 concentration of less than 638 ng/L AND total tau >375 ng/L, as assessed by central laboratory.
b. Screening CSF sample with an A-beta 42 concentration of less than 638 ng/L AND p-tau > 52 ng/L, as assessed by central laboratory.
c. Tau/A-beta ratio > 0.52, as assessed by central laboratory.
d. Positive amyloid PET if available prior to screening.

7. Treatment naïve, this means not having received any prior established specific treatment for MCI due to AD or mild dementia due to AD including no (prior) use of an acetylcholinesterase inhibitor, or memantine. A maximum of two months of prior cumulative treatment with an acetylcholinesterase inhibitor or memantine is allowed if the acetylcholinesterase inhibitor or memantine was
discontinued due to intolerance and if this was done at least two months prior to baseline. Use of Souvenaid will be allowed if Souvenaid was discontinued at least two months prior to baseline, or if the subject is on stable dose for at least six months prior to baseline and is willing to continue during the study on the same dose and frequency. ;8. Fluency in local language and evidence of adequate premorbid intellectual functioning in the opinion of the investigator.
9. Adequate visual and auditory abilities to perform the cognitive and functional assessments in the opinion of the investigator.
10. Outpatient with study partner (age 18 years or older) capable of accompanying the subject on all clinic visits. In accordance to Swedish regulations the availability of a study partner is not applicable for Sweden.
11. The subject and study partner are likely to be able to participate in all scheduled evaluations. In accordance to Swedish regulations the availability of a study partner is not applicable for Sweden.
12. In the opinion of the investigator, the subject and study partner can be compliant and have a high probability of completing the study. In accordance to Swedish regulations the availability of a study partner is not applicable for Sweden.

A subject who meets ANY of the following criteria is not eligible for this study:
1. Significant neurologic disease, other than AD, that may affect cognition.
2. Atypical clinical presentations of MCI due to AD or mild dementia due to AD, such as the visual variant of AD (including posterior cortical atrophy) or the language variant (including logopenic aphasia). ;Concomitant disorders:
3. History of or screening visit brain MRI scan indicative of any other significant abnormality, including but not limited to multiple microhaemorrhages (4 or more, defined as 10 mm or less at the greatest diameter), severe white matter hyper intensities (Fazekas score 3), history or evidence of a single prior haemorrhage >1 cm3, multiple lacunar infarcts or evidence of a single prior infarct >1 cm3, evidence of a cerebral contusion, encephalomalacia, aneurysms, vascular malformations, subdural hematoma, or space-occupying lesions (e.g. brain tumours).
4. Current presence of a clinically important major psychiatric disorder (e.g. major depressive disorder) as defined by DSM-5 criteria, or symptom(s) (e.g. hallucinations) that could affect the subject*s ability to complete the study.
5. Current clinically important systemic illness that is likely to result in clinically relevant deterioration of the subject*s condition or might affect the subject*s safety during the study.
6. History of clinically evident stroke or history of clinically important and symptomatic carotid or vertebrobasilar stenosis or plaque.
7. History of seizures within the last two years prior to the screening visit.
8. Weight > 120 kg (264 lb) at screening.
9. Myocardial infarction within the last six months prior to screening.
10. History of cancer within the last two years prior to screening, with the exception of any of the following conditions: non-metastatic basal cell carcinoma, and squamous cell carcinoma of the skin
or any other cancer if evidence of no residual cancer has been clinically confirmed within the last six months before baseline.
11. History of uncontrolled hypertension (in the opinion of the investigator) within six months prior to screening.
12. Other clinically important diseases or conditions or abnormalities of vital signs, physical examination, neurologic examination, laboratory results, or ECG examination (e.g. atrial fibrillation) that could compromise the study or the safety of the subject.
13. Haemoglobin level less than 11 g/dL (6.8 mmol/L) at screening.
14. Clinically important infection within 30 days prior to screening e.g. chronic persistent or acute infection, such as bronchitis or urinary tract infection.
15. Any known hypersensitivity to any of the excipients contained in the test article formulation.
16. Severe hepatic failure (Child-Pugh C) or kidney failure (creatinine clearance (eGFR) * 30 ml/min/1.73m2) or serum creatinine above 1.5 fold of ULN or AST or ALT above 3 fold of ULN at screening. ;Concomitant Medication/Therapies:
17. The following therapies are not permitted for the given intervals prior to baseline and until V5/End-of-treatment (EOT):
* Anticoagulants (e.g. heparin and vitamin K antagonists) within 30 days prior to baseline. ;NOTE: Platelet anti-aggregants (e.g. clopidogrel bisulfate or the use of carbasalate calcium 100 mg/day, or aspirin 325 mg/day or less) are allowed if they are maintained on a stable dose regimen for at least 30 days prior tobaseline. The combination of clopidogrel and carbasalate calcium or aspirin is not allowed during the time of lumbar puncture.
* Use of experimental medications for AD or any other investigational medications or devices for treatment of indications other than AD within 60 days prior to baseline.
* Treatment with an acetylcholinesterase inhibitor or memantine or Souvenaid, except for an acetylcholinesterase inhibitor or memantine in case of clinically relevant worsening of cognitive performance during the double blind study period, and for Souvenaid if only on stable dose for at least six weeks prior to baseline.
* Treatment with immunosuppressive medications (e.g. systemic corticosteroids in a dose of more than 10 mg/day) within the last 90 days prior to baseline (topical and nasal corticosteroids and inhaled corticosteroids for asthma are permitted).
* Treatment with chemotherapeutic agents for malignancy within the last year prior to baseline.
* Concomitant treatment with strong inhibitors or moderate inducers of the metabolic enzyme CYP 2C19 or substrates with narrow therapeutic margin: fluconazole, fluvoxamin, ticlopidin, rifampicin, S-mephenytoin, repaglinide, phenytoin, phenobarbital and indometacin. A washout phase of at least two weeks before baseline is required for subjects having been treated with any of the above medicinal products.
* Concomitant treatment with St. John*s Wort (a wash out phase of at least two weeks prior to baseline is required).
* Any concomitant treatment which impairs cognitive function and cannot be washed out at least four weeks prior to baseline. ;The following requirements apply to all other medications not intended to treat AD:
* Subjects must be on stable dose for at least four weeks prior to baseline, except for medications which are administered as short courses of treatment (e.g. anti-infective) or which are to be used as needed (PRN).
* Medications which are central nervous system active and may affect cognitive function are not permitted during a period of 72 hours prior to neuropsychological testing (V1, V2 and V5/EOT).
* Hypnotics are not permitted during a period of 72 hours prior to EEG recording (V1 and V5/EOT).
* Subjects who initiate treatment or undertake dose adjustment with drugs not intended for treatment of cognitive impairment during the study may continue in the study if in the opinion of the investigator this will not interfere with study procedures or subject safety. ;Other
18. Blood donation (routine blood donation) in the 90 days prior to screening.
19. History of alcohol or drug dependence or abuse as defined by DSM-5 criteria within the last two years prior to screening.
20. Presence of pacemakers, aneurysm clips, artificial heart valves, ear implants, CSF shunts, claustrophobia, or metal fragments or foreign objects in the eyes, skin, or body that would contraindicate a brain MRI scan.
21. Inadequate venous access to allow multiple blood draws.