This phase 2b trial is a randomized, double-masked, parallel-group, multi-center study in approximately 156 patients with DME to evaluate the efficacy and safety of CU06-1004 orally administered once daily for 24 weeks. The study will have a 1:1:1 randomization (CU06-1004 200mg: CU06-1004 300mg: Placebo).

Inclusion Criteria:

Patients will be eligible for inclusion in the study if they meet all of the following criteria:

1. Have read, understood, and signed the informed consent form.
2. Patient is willing and able to comply with all study procedures, and is likely to complete the study, based on the investigator's judgment.
3. Male and female patients must be ≥18 years of age at the time of screening visit. Race and ethnicity information will be collected based on National Institutes of Health criteria.
4. Has a diagnosis of Type 1 or Type 2 diabetes mellitus.
5. Has definite retinal thickening due to DME in the center of the macula of the study eye (either treatment-naïve or previously treated patients).
6. The study eye has a BCVA of 25 to 69 (approximate Snellen equivalent of 20/50 to 20/320) at an initial distance of 4 meters, as assessed by the ETDRS letter score at screening.
7. Has a study eye with CST of ≥320 µm for men or ≥305 µm for women as determined by Heidelberg Spectralis (or equivalent) SD-OCT (or Zeiss Cirrus OCT: 305 µm for men or 290 µm for women) and confirmed by the CRC at screening.
8. Has a DRSS score of ≥43 confirmed by the CRC.
9. Has media clarity, pupillary dilation, and patient cooperation sufficient for adequate fundus photographs.
10. Is willing to abide by the contraceptive requirements.

Exclusion Criteria:

Patients will be excluded from the study if they meet any of the following criteria:

1. Has only 1 functional eye, even if the eye met all other study requirements, or has and/or is likely to have amblyopia, amaurosis, or an ocular disorder with BCVA ≤25 ETDRS letter score (approximate Snellen equivalent of <20/320) in the fellow eye.

2. Concurrent and/or history (where indicated) of an ocular condition including one or more of the following in the study eye:

   1. Active proliferative diabetic retinopathy (PDR) or preretinal fibrosis involving the macula.

      Note: Patients with mild PDR without high-risk features will be allowed in the study.

   2. Vitreomacular traction or epiretinal membrane that is expected to affect central vision.

   3. Iris neovascularization, vitreous hemorrhage, or tractional retinal detachment.

   4. Uncontrolled glaucoma or filtration surgery for glaucoma in the past or likely to be needed in the future

   5. Intraocular pressure (IOP) >24 mmHg at screening and randomization. IOP will be assessed by applanation tonometry (Goldmann tonometer, Tono-pen™, or an equivalent device).

   6. Spherical equivalent of the refractive error of more than 6 diopters myopia or any signs of myopic chorioretinopathy.

   7. Structural damage to the center of the macula that is likely to preclude improvement in BCVA following the resolution of macular edema, including atrophy of the RPE, subretinal fibrosis or scar, significant macular ischemia, or organized hard exudates.

   8. Disease other than DME, that could compromise visual acuity, require medical or surgical intervention during the study period, or could confound interpretation of the results (including retinal vascular occlusion, retinal detachment, macular hole, or choroidal neovascularization of any cause) as assessed by the investigator.

   9. Macular edema is of nondiabetic retinopathy etiology (eg, secondary to vitreomacular interface abnormalities).

   10. Inability to obtain fundus and OCT images due to, but not limited to, insufficient media clarity or inadequate pupil dilation.

   11. Aphakia or absence of the posterior capsule. Absence of an intact posterior capsule is allowed if it occurred because of Yttrium-aluminum-garnet (YAG) laser posterior capsulotomy in association with prior posterior chamber intraocular lens implantation longer than 2 months before screening.

3. Concurrent and/or history (where indicated) of ocular condition including one or more of the following in either eye:

   1. There is evidence of external ocular infection, including conjunctivitis, chalazion, or significant blepharitis. However, a patient who has completely recovered from the infection at Week 1 (baseline) is allowed to be enrolled in the study at the investigator's discretion.
   2. Has any active intraocular inflammatory disease such as uveitis or a history of intraocular inflammatory disease other than what would be expected in the normal postoperative course following prior routine ocular surgery such as cataract surgery.

4. Had major surgery within 3 months prior to randomization or has major surgery planned during the next 6 months.

5. Had unstable angina, myocardial infarction, transient ischemic attack, cerebral infarction, coronary artery bypass surgery, or transluminal coronary angioplasty within 6 months before screening.

6. Has the following illness or abnormal laboratory test values:

   1. Persisting elevations of aspartate aminotransferase or alanine aminotransferase >2 × upper limit of normal (ULN)
   2. Uncontrolled hypertension (systolic blood pressure of >180 mmHg or diastolic blood pressure of >100 mmHg).
   3. Uncontrolled diabetes (hemoglobin A1c >12.0%).
   4. Total bilirubin >1.5× upper limit of normal.
   5. Positive results for HIV or hepatitis B or C viruses.
   6. Other clinically significant abnormal laboratory values per the investigator's judgment.

7. Has severe renal impairment, defined as an estimated glomerular filtration rate ≤ 30 mL/min/1.73 m².

8. Has an ocular condition (other than diabetes) that, in the opinion of the investigator, might affect macular edema or alter visual acuity during the course of the study (eg, vein occlusion, uveitis or other ocular inflammatory disease, neovascular glaucoma, Irvine-Gass Syndrome, foveal atrophy, pigmentary changes, dense subfoveal hard exudates, or a nonretinal condition).

9. Is expected to have no improvement of decreased visual acuity in the opinion of the investigator, even if macular edema is resolved (eg, foveal atrophy, abnormal pigmentation, dense subfoveal hard exudate).

10. Have administered vaccinium myrtillus extract or calcium dobesilate within 2 weeks before randomization.

11. Have a hypersensitivity to any excipients of the investigational product or similar class of drug and ingredient.

12. A pregnant woman, lactating woman, or a female or male patient of childbearing potential who does not accept appropriate contraceptive measures for at least 6 months prior to the first dose of the study treatment (hormonal contraceptives, intrauterine contraceptive device, sterilization of spouse [eg, vasectomy, tubal ligation], double-barrier method [eg, combinational use of spermicides and condoms, diaphragm, contraceptive sponge, or FemCap], sexual abstinence).

13. Has a medical condition that, in the opinion of the investigator, would preclude participation in the study (eg, unstable medical status including blood pressure, cardiovascular disease, and glycemic control or a significant medical condition including end-stage renal disease and severe liver diseases).

    Patients with a study eye that meets any of the following criteria may not participate in this study:

14. Has history of intravitreal (IVT) treatment with anti-VEGF agents prior to randomization: A 3-month washout for ranibizumab and bevacizumab, and a 4-month washout for aflibercept 2mg, (and 6 months for longer-acting agents such as faricimab or aflibercept 8mg) are required. Any patients with a history of prior brolucizumab use in the study eye will be excluded from this study.

15. Has history of treatment with IVT or periocular triamcinolone acetonide or IVT dexamethasone within 12 months of screening or has received an IVT dexamethasone implant (Ozurdex), or fluocinolone acetonide implant (Iluvien) or Susvimo (ranibizumab) implant any time prior to randomization.

16. Has history of panretinal scatter photocoagulation (PRP) or is anticipated to require PRP in the 3 months following randomization.

17. Has history of focal laser treatment (focal/grid laser photocoagulation) within 3 months prior to randomization and/or focal laser scar in the fovea that could limit BCVA improvement in the study eye.

18. Has history of ocular surgery (including cataract extraction, any intraocular surgery, etc) within 3 months prior to screening or anticipated within the next 6 months following randomization.

19. Has history of retinal detachment or retinal detachment repair surgery.

20. Has history of vitrectomy.

21. Participation in another interventional clinical trial for DME in either eye within 90 days before screening or any previous participation in a clinical trial of systemic antiangiogenic drugs with receipt of a previous study drug within 180 days before screening or 5 times the half-life of the study drug used, whichever is longer.