A Phase 2 Evaluation of Anti-VEGF Therapy for Diabetic Macular Edema: Bevacizumab (Avastin)

Diabetic retinopathy is a major cause of visual impairment in the United States. Diabetic macular edema (DME) is a manifestation of diabetic retinopathy that produces loss of central vision. Data from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) estimate that after 15 years of known diabetes, the prevalence of diabetic macular edema is approximately 20% in patients with type 1 diabetes mellitus (DM), 25% in patients with type 2 DM who are taking insulin, and 14% in patients with type 2 DM who do not take insulin.

In a review of three early studies concerning the natural history of diabetic macular edema, Ferris and Patz found that 53% of 135 eyes with diabetic macular edema, presumably all involving the center of the macula, lost two or more lines of visual acuity over a two year period. In the Early Treatment Diabetic Retinopathy Study (ETDRS), 33% of 221 untreated eyes available for follow-up at the 3-year visit, all with edema involving the center of the macula at baseline, had experienced a 15 or more letter decrease in visual acuity score (equivalent to a doubling of the visual angle, e.g., 20/25 to 20/50, and termed "moderate visual loss").

In the ETDRS, focal photocoagulation (direct treatment to microaneurysms and grid treatment to diffuse edema) of eyes with clinically significant macular edema (CSME) reduced the risk of moderate visual loss by approximately 50% (from 24% to 12%, three years after initiation of treatment). Therefore, 12% of treated eyes developed moderate visual loss in spite of treatment. Furthermore, approximately 40% of treated eyes that had retinal thickening involving the center of the macula at baseline still had thickening involving the center at 12 months, as did 25% of treated eyes at 36 months.

Although several treatment modalities are currently under investigation, the only demonstrated means to reduce the risk of vision loss from diabetic macular edema are laser photocoagulation, as demonstrated by the ETDRS, intensive glycemic control, as demonstrated by the Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) and blood pressure control, as demonstrated by the UKPDS. In the DCCT, intensive glucose control reduced the risk of onset of diabetic macular edema by 23% compared with conventional treatment. Long-term follow-up of patients in the DCCT show a sustained effect of intensive glucose control, with a 58% risk reduction in the development of diabetic macular edema for the DCCT patients followed in the Epidemiology of Diabetes Interventions and Complications Study.

The frequency of an unsatisfactory outcome with respect to proportion with vision improvement following laser photocoagulation in some eyes with diabetic macular edema has prompted interest in other treatment modalities. One such treatment is pars plana vitrectomy. These studies suggest that vitreomacular traction, or the vitreous itself, may play a role in increased retinal vascular permeability. Removal of the vitreous or relief of mechanical traction with vitrectomy and membrane stripping may be followed by substantial resolution of macular edema and corresponding improvement in visual acuity. However, this treatment may be applicable only to a specific subset of eyes with diabetic macular edema that have a component of vitreomacular traction contributing to the edema. It also requires a complex surgical intervention with its inherent risks, recovery time, and expense. Other treatment modalities such as pharmacologic therapy with oral protein kinase C inhibitors and use of intravitreal corticosteroids are under investigation. The use of antibodies targeted at vascular endothelial growth factor (VEGF), such as in the current study, is another treatment modality that has generated considerable interest, and is currently being investigated in phase 3 trials of choroidal neovascularization in age-related macular degeneration (with pegaptanib or ranibizumab) or diabetic macular edema (with pegaptanib).

Increased VEGF levels have been demonstrated in the retina and vitreous of human eyes with diabetic retinopathy. VEGF, also known as vascular permeability factor, has been demonstrated to increase vessel permeability by increasing the phosphorylation of tight junction proteins, and has been shown to increase retinal vascular permeability in in vivo models. Anti-VEGF therapy, therefore, may represent a useful therapeutic modality which targets the underlying pathogenesis of diabetic macular edema.

Bevacizumab is currently approved for the treatment of metastatic colorectal cancer, and published case reports and widespread clinical use have suggested its efficacy in the treatment of neovascular age-related macular degeneration and macular edema associated with diabetes and central retinal vein occlusion. To date, no evidence of ocular inflammation or other adverse events has been noted in association with intravitreal injection of bevacizumab. However, a study has not been conducted to evaluate its efficacy and safety. In view of the widespread use of bevacizumab, such a study is important to conduct.

From a public health perspective, an intravitreal bevacizumab study is also important to conduct because of the relatively low cost of the bevacizumab drug. As noted earlier, bevacizumab is marketed for systemic use for colon cancer. The dose used in the eye is a fraction of the systemic dose and costs $25 to $50 per dose.

The two doses of bevacizumab being evaluated in this study will be 1.25 mg, which is the dose that has most commonly been used in clinical practice, and 2.5 mg, which has also been used though less commonly. A lower dose than 1.25 mg would create difficulties with dilution and the accuracy of injection of a small volume.

The optimal interval for the bevacizumab doses is not known. Six weeks has been selected for this study as it is not believed that the effect will last longer than this. Retinal thickening and visual acuity will be measured at 3 and 6 weeks to provide the requisite information to judge the duration of effect.

There is expected to be a beneficial cumulative effect of multiple doses. A total of two doses, spaced 6 weeks apart, was selected for the study with the primary outcome 3 weeks after the second dose.

The decision as to whether to proceed to a phase 3 trial will be based on the observation of a substantial reduction in retinal thickening in the bevacizumab-treated eyes compared with the laser-treated eyes and at least a suggestion of benefit on visual acuity, plus a safety profile of minimal risk.

The study involves the enrollment of subjects over 18 years of age with diabetic macular edema. Subjects will have one study eye randomly assigned with equal probability (stratified by visual acuity) to one of 5 treatment groups:

Subject-level Inclusion Criteria

To be eligible, the following inclusion criteria (1-3) must be met:

1. Age >= 18 years

2. Diagnosis of diabetes mellitus (type 1 or type 2)

3. Able and willing to provide informed consent.

Exclusion

A subject is not eligible if any of the following exclusion criteria (4-13) are present:

4. Significant renal disease, defined as a history of chronic renal failure requiring dialysis or kidney transplant.

5. A condition that, in the opinion of the investigator, would preclude participation in the study (e.g., unstable medical status including blood pressure, cardiovascular disease, and glycemic control).

6. Participation in an investigational trial within 30 days of randomization that involved treatment with any drug that has not received regulatory approval at the time of study entry.

7. Known allergy to any component of the study drug.

8. Blood pressure > 180/110 (systolic above 180 OR diastolic above 110).

9. Major surgery within 28 days prior to randomization or major surgery planned during the next 6 months.

10. Myocardial infarction, other cardiac event requiring hospitalization, stroke, transient ischemic attack, or treatment for acute congestive heart failure within 6 months prior to randomization.

11. Systemic anti-VEGF or pro-VEGF treatment within 3 months prior to randomization.

12. For women of child-bearing potential: pregnant or lactating or intending to become pregnant within the next 6 months.

13. Subject is expecting to move out of the area of the clinical center to an area not covered by another clinical center during the first 6 months of the study.

Study Eye Criteria

The subject must have one eye meeting all of the inclusion criteria (a-e) and none of the exclusion criteria (f-r) listed below. Subjects can have only one study eye. If both eyes are eligible, the study eye will be selected by the investigator and subject. The eligibility criteria for a study eye are as follows:

Inclusion

a. Best corrected E-ETDRS visual acuity letter score of >= 24 (i.e., 20/320 or better) and <= 78 (i.e., 20/32 or worse) within 8 days of randomization.

b. On clinical exam, definite retinal thickening due to diabetic macular edema involving the center of the macula.

c. OCT central subfield >=275 microns within 8 days of randomization.

d. Media clarity, pupillary dilation, and subject cooperation sufficient for adequate fundus photographs.

e. If prior macular photocoagulation has been performed, the investigator believes that the study eye may possibly benefit from additional photocoagulation.

Exclusions

The following exclusions apply to the study eye only (i.e., they may be present for the nonstudy eye):

f. Macular edema is considered to be due to a cause other than diabetic macular edema.

g. An ocular condition is present such that, in the opinion of the investigator, visual acuity would not improve from resolution of macular edema (e.g., foveal atrophy, pigmentary changes, dense subfoveal hard exudates, nonretinal condition).

h. An ocular condition is present (other than diabetes) that, in the opinion of the investigator, might affect macular edema or alter visual acuity during the course of the study (e.g., vein occlusion, uveitis or other ocular inflammatory disease, neovascular glaucoma, Irvine-Gass Syndrome, etc.).

i. Substantial cataract that, in the opinion of the investigator, is likely to be decreasing visual acuity by 3 lines or more (i.e., cataract would be reducing acuity to 20/40 or worse if eye was otherwise normal).

j. History of treatment for DME at any time in the past 3 months (such as focal/grid macular photocoagulation, intravitreal or peribulbar corticosteroids, anti-VEGF drugs, or any other treatment).

k. History of panretinal scatter photocoagulation (PRP) within 4 months prior to randomization.

l. Anticipated need for PRP in the 6 months following randomization.

m. History of prior pars plana vitrectomy.

n. History of major ocular surgery (including cataract extraction, scleral buckle, any intraocular surgery, etc.) within prior 6 months or anticipated within the next 6 months following randomization.

o. History of YAG capsulotomy performed within 2 months prior to randomization.

p. Aphakia.

q. Uncontrolled glaucoma (in investigator's judgment).

r. Exam evidence of external ocular infection, including conjunctivitis, chalazion, or significant blepharitis.

Fellow Eye Criteria

The fellow eye must meet the following criteria:

a. Best corrected E-ETDRS visual acuity letter score >= 19 (i.e., 20/400 or better).

b. No anti-VEGF treatment within the past 3 months and no expectation of such treatment in next 3 months.

No longer recruiting. Comments:

Completed, with results published. Comments: Long term follow-up for safety.

This study was conducted to provide data to assist in the development of a phase 3 randomized clinical trial protocol and, by design, had a short follow-up period and a modest sample size. Therefore, definitive safety and effectiveness conclusions are limited. Although about half of eyes demonstrated an initial positive response to intravitreal bevacizumab (exceeding an 11% reduction in retinal thickness compared with baseline at either the 3-week or 6-week visit), this response was similar to that observed in the laser group after more than 3 weeks. In addition, the magnitude of the response was not large for most subjects. Thus, these short-term results of the current study should not be generalized to conclude that there is a clinically meaningful benefit in treating DME with intravitreal bevacizumab or other anti-VEGF drugs. This determination of clinical benefit will require the conduct of a large phase 3 randomized clinical trial.