This study is a multicenter, double-blinded, randomized, placebo-controlled, dose-ranging study to evaluate the safety, tolerability, PK, and efficacy of Isuzinaxib compared with placebo in subjects with DKD.

Inclusion Criteria:

1. Male/female subject aged ≥19 years inclusive at the time of informed consent.
2. Clinical diagnosis of type 2 diabetes and DKD.
3. 18.5 kg/m² < body mass index < 35 kg/m².
4. Stable UACR values prior to screening visit.
5. UACR between 200 and 3000 mg/g.
6. Hemoglobin A1c ≤10% at Screening Visit.
7. Subject who has been taking unchanged dosage of angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blockers (ARB) medication.
8. Subject who has been on stable anti-hyperglycemic prior to screening.
9. Females of childbearing potential/sexually active males with a partner of childbearing potential: commitment to consistently and correctly use an acceptable method of birth control.
10. Willing to be under dietary management for diabetes.
11. Willing to comply with all study procedures and availability for the duration of the study.
12. Capable of understanding the content of and able voluntarily to provide a signed and dated written informed consent form (ICF) prior to any study procedures.

Exclusion Criteria:

1. History of type 1 diabetes mellitus or gestational diabetes.
2. Subject's renal impairment and/or albuminuria is considered to be of origin other than DKD.
3. History of renal transplant and/or plan to undergo a renal transplant during the study.
4. History of acute kidney injury or renal dialysis.
5. Subject with uncontrolled blood pressure.
6. Subject taking immunosuppressant.
7. Subject with known or suspected hypersensitivity to any components of the APX-115 formulation.
8. Clinically significant abnormal laboratory findings at screening.
9. History of drug or alcohol abuse within 1 year prior to screening.
10. History of any cardiovascular event or cardiovascular procedure planned during the clinical study.
11. Current or history of New York Heart Association class III or IV heart failure.
12. Clinically significant electrocardiogram (ECG) abnormalities.
13. Known significant liver disease.
14. Subject with active urinary tract infection or has not fully recovered before randomization.
15. History of malignancy within 5 years prior to screening.
16. Administration of any investigational product.
17. Major surgery within 28 days or not fully recovered surgery prior to randomization or major surgery planned during the next 6 months.
18. Positive hepatitis B surface antigen.
19. Female subject who is pregnant or breastfeeding.
20. Other medical history which in the opinion of the Investigator would make the subject unsuitable for participation in the study.
21. Subject who, in the judgment of the Investigator, is likely to be non-compliant or uncooperative during the study or unable to cooperate because of a language problem or poor mental status.