Inclusion Criteria:
1. Be able to provide informed consent.
2. Be 18 years or older at the time of informed consent.
3. Disease criteria:
1. Histologically confirmed ACC, any site of origin.
2. Dose Escalation phase ONLY:
* Have locally advanced or metastatic ACC
* Evidence of radiographic progression and/or signs and symptoms associated with their disease (eg, pain, dyspnea, reduced performance status). Participants who have stable disease while being treated with another agent that is not tolerated are eligible after the appropriate washout period.
3. Confirmatory Cohort phase ONLY:
* Have metastatic, recurrent, or unresectable ACC
* Measurable disease at the time of enrollment. At least 1 measurable lesion according to RECIST v1.1 criteria. Participants must have radiographic evidence of disease progression by RECIST v1.1 criteria ≤ 6 months prior to study enrollment. Radiographic eligibility as determined by Central IUO assay.
* MYB poison exon biomarker positive tumor(s) confirmed by central IUO assay.
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
5. Tumor Tissue Requirements
1. Dose Escalation Phase ONLY: be able to provide during Screening a tissue specimen of either a fresh biopsy of a non-target lesion or an archival tumor sample obtained within the last 6 years. A formalin-fixed paraffin-embedded (FFPE) block can be submitted or a minimum of 15 freshly sectioned unstained slides. Agree to an on-treatment biopsy to be obtained \~4-8 weeks after initiation of REM-422 unless medically contraindicated.
2. Confirmatory Cohort phase ONLY: be able to provide, during Pre-Screening, a tissue specimen of either a fresh biopsy of non-targetable lesion or an archival tumor sample obtained within the last 6 years that is interpretable for the biomarker positivity. An FFPE block can be submitted or a minimum of 15 fresh sectioned unstained slides.
6. At least 3 weeks since prior systemic non-investigational therapy at the time of start of REM- 422.
7. Toxicities from prior therapy must be stable or recovered to ≤ Grade 1. Note: Stable chronic and clinically non-significant conditions (≤ Grade 2) that are not expected to resolve are exceptions (eg, neuropathy, myalgia, alopecia, prior therapy-related endocrinopathies, etc.), and patients with these conditions may enroll.
8. Participants must be able to swallow and retain oral medications.
9. Oxygen saturation \> 92% on room air or up to 2 L/min supplemental oxygen by nasal cannula with ≤ Grade 1 dyspnea.
10. Participants of childbearing potential (POCBP) must have a negative serum beta-human chorionic gonadotropin test result.
11. Participants Of Child Bearing Potential must agree to use acceptable, effective methods of contraception as outlined in Appendix 1 and not donate ova from Screening until 6 months after discontinuation of REM- 422. Women who have undergone surgical or ablative sterilization or who have been postmenopausal for ≥ 2 years are not considered to be of childbearing potential.
12. Men must agree to use acceptable, effective methods of contraception and must agree not to donate sperm from the start of receiving REM-422 until 6 months after discontinuation of REM-422.
13. Adequate bone marrow, organ function and laboratory parameters
Exclusion Criteria:
1. Known hypersensitivity or contraindication to any component of REM-422 or to drugs chemically related to REM-422 or its excipients.
2. Clinically significant active infection. Simple urinary tract infection, uncomplicated bacterial pharyngitis responding to active treatment are permitted. Participants receiving intravenous antibiotics ≤ 7 days prior to enrollment are excluded (prophylactic antibiotics, antivirals or antifungals are permitted).
3. Evidence of active HIV infection.
4. Evidence of currently active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection.
5. Primary immunodeficiency.
6. Current or expected need for daily systemic corticosteroid therapy ≥ 10 mg of prednisone equivalent. Topical or inhaled corticosteroids with minimal systemic absorption may enroll and continue minimal corticosteroids if the participant is on a stable dose.
7. Live vaccine ≤ 6 weeks prior to the start of REM-422.
8. Use of strong CYP3A inhibitors or CYP3A inducers
9. Drugs that reduce gastric acidity, such as H2-receptor antagonists (eg, ranitidine, famotidine) and proton pump inhibitors (e.g., omeprazole, esomeprazole) within 7 days prior to the initiation of REM-422 administration or during the study
10. Pregnancy or participants planning to become pregnant during the duration of the study, or lactation.
11. Participants with malabsorption syndrome, a disease significantly affecting gastrointestinal function, or resection of the stomach or bowel.
12. Current use of prohibited medication ≤ 1 week before starting REM-422.
13. Clinically significant cardiovascular disease:
14. Participants who have undergone major surgery (opening a mesenchymal barrier such as the pleural cavity, peritoneum, meninges, or surgical procedures requiring general anesthesia) \< 4 weeks prior to enrollment.
15. History of organ transplant that requires use of immunosuppressive agents.
16. History or current autoimmune disease (eg, Crohn's disease, ulcerative colitis, rheumatoid arthritis, systemic lupus).
17. Radiation therapy ≤ 7 days prior to the start of REM-422.
18. Concurrent or previous other malignancy (other than adenoid cystic carcinoma, hematologic malignancies, or primary central nervous system \[CNS\] malignancies) ≤ 2 years of enrollment, except curatively treated malignancies including basal or squamous cell skin cancer, prostate intraepithelial neoplasm, carcinoma in situ of the cervix.
19. Participants receiving any other investigational treatment for any indication ≤ 3 weeks prior to enrollment.
20. Unwillingness or inability to follow protocol requirements.
21. Any condition that, in the opinion of the Investigator, would interfere with evaluation of REM-422 or interpretation of the participant's safety or study results.
