Ординатура / Офтальмология / Английские материалы / Diabetic Retinopathy_Lang_2007

ICAM-1 and in producing leukocyte adhesion and blood-retinal barrier breakdown in a diabetic retinopathy model [14]. Moreover, leukocyte adhesion and breakdown of the blood-retinal barrier were significantly suppressed in both early and late diabetes by intravitreous injection of pegaptanib, which specifi-

cally targets VEGF165/164 [14]. Although suppression of blood-retinal barrier breakdown was somewhat diminished in established diabetes, these results sug-

gest that pegaptanib has the potential to reverse many of the features of diabetic retinopathy.

Ishida et al. [23] have provided further evidence of the inflammatory role of VEGF165 in hypoxia-related ocular neovascularization, which may also have relevance to diabetic retinopathy. Using a mouse model system approximating retinopathy of prematurity, VEGF164 was dramatically increased, compared with VEGF120, in retinas undergoing pathological neovascularization. Injection of a VEGFR-Fc fusion protein that provides a pan-isoform blockade inhibited both physiological and pathological neovascularization, while pegaptanib inhibited

only the pathological form [23]. Since pegaptanib is specific to VEGF164/165, this finding suggested that VEGF164/165 is especially important in mediating pathologic neovascularization yet is dispensable for normal physiological vas-

cularization in the eye. Studies in transgenic mice lacking VEGF164 yielded similar results in that VEGF164-deficient mice exhibited no negative effects with respect to physiological vascularization [23]. VEGF164 has also been found to be dispensable for VEGF-mediated neuroprotective effects in the rat eye,

providing further evidence that the actions of VEGF164/165 can be inactivated without producing adverse ocular effects [29].

These data support a proinflammatory role of VEGF165 in pathological neovascularization and suggest that pegaptanib, by targeting only the VEGF165 isoform, could be both an effective and safe treatment for ocular neovascular diseases, findings that have been confirmed in clinical trials of pegaptanib in the treatment of age-related macular degeneration and DME [16].

Development of the Anti-VEGF Aptamer Pegaptanib

Pegaptanib is a nuclease-resistant, 28-nucleotide RNA aptamer that binds to VEGF165 with high affinity (with a dissociation constant of approximately 0.2 nM) while showing little affinity for VEGF121 [110]. It is highly stable in biological fluids due to chemical modifications designed to increase resistance to nucleases and has also been modified by addition of a 40-kDa polyethylene glycol moiety to the 5 terminus to increase bioavailability by decreasing clearance from the vitreous [data on file, (OSI) Eyetech, Inc.; 110 –112]. Pegaptanib is a potent inhibitor of the interaction between VEGF165 and its cellular receptors,

with the concentration for 50% inhibition of 125I-labeled VEGF (10 ng/ml) binding to cultured human endothelial cells ranging from 0.75 to 1.4 nM; total inhibition of VEGF binding occurs at 10 nM [15].

Perhaps the finding most relevant to diabetic retinopathy is that pegaptanib is able to inhibit VEGF-mediated endothelial cell mitogenic and vascular permeability effects. Specifically, cultured endothelial cell proliferative responses to VEGF165, but not to VEGF121, were inhibited when cells were pretreated with pegaptanib [15]. In addition, vessel leakage produced in response to VEGF (as demonstrated using an animal microvascular permeability assay) was inhibited by 83% when VEGF was preincubated with 0.1 M pegaptanib [110]. These findings were further supported by studies demonstrating that intravitreous injection of pegaptanib significantly reduced ocular neovascularization using rodent models of corneal angiogenesis and retinopathy of prematurity [113].

Studies in rhesus monkeys demonstrated that the pharmacokinetic properties of pegaptanib were appropriate for a therapeutic agent, with elimination half-lives following intravenous or subcutaneous injections of 9.3 and 12.0 h, respectively [114]. Additional work in monkeys established that pegaptanib was removed from the eye following intravitreous injection through plasma clearance, with a half-life of approximately 94 h [111]. Pegaptanib was detectable in the eye for 28 days after a single 0.5-mg intravitreous injection and retained full biological activity [111].

Such preclinical studies led to early phase I/II clinical trials testing the safety of pegaptanib when administered by intravitreous injection to patients with age-related macular degeneration [113, 115]. The efficacy of pegaptanib in treating age-related macular degeneration was demonstrated in 2 concurrent phase III trials, the VISION trials, involving a total of 1,208 patients [16]. Pegaptanib (0.3, 1 or 3 mg) or sham injections were administered intravitreously every 6 weeks for a period of 48 weeks. In a combined analysis, 70% (206/ 294) of patients receiving 0.3 mg of pegaptanib (p 0.001), 71% (213/300) receiving 1 mg (p 0.001) and 65% (193/296) receiving 3 mg (p 0.03) lost15 letters of VA on the study eye chart between baseline and week 54, compared with 55% (164/296) of patients receiving sham injections (primary efficacy endpoint). There was no evidence of a dose-response relationship. The 0.3-mg pegaptanib dose also showed significant benefits for additional secondary endpoints (table 3) [16], including mean change in VA (fig. 2), VA loss of 30 letters or more, and the likelihood of maintaining or gaining VA. Pegaptanib demonstrated clinical benefits irrespective of angiographic subtype, size of lesion, baseline VA, sex, age, race or iris pigmentation [16, 116]. Early detection and treatment with pegaptanib appeared to result in superior vision outcomes [117].

Table 3. Maintenance, gain and severe loss of VA with pegaptanib and sham injection [16]

Data are indicated as number of patients, with figures in parentheses as percentages. Where data were missing, the last-observation-carried-forward method was used. Loss of 30 or more letters was defined as severe loss of VA.

p values were calculated with the use of the Cochran-Mantel-Haenszel test.

Fig. 2. Mean change in VA at week 54 in patients receiving 0.3 mg of pegaptanib or sham injection in the pivotal phase III VISION trials. With permission from Ng and Adamis [116].

The VISION trials established that pegaptanib was well tolerated with a low risk of serious complications, such as endophthalmitis, retinal detachment or traumatic lens injury [16]. These complications were related to the intravitreous injection procedure itself (and therefore modifiable) rather than to the drug. An important safety finding is that there was no evidence that pegaptanib was associated with major systemic adverse events, such as hypertension, thromboembolism or serious hemorrhage, that have been reported with systemically administered, pan-isoform VEGF blockade [42, 44–47]. The positive findings of the VISION trials led to US Food and Drug Administration approval of pegaptanib for the treatment of neovascular age-related macular degeneration. This was a notable milestone in that pegaptanib represented the first aptamer therapeutic approved by a government regulatory agency and the first antiVEGF agent for treatment of an ocular neovascular disease.

Phase II Trial of Pegaptanib in Patients with DME

The accumulating body of evidence supporting an important role of VEGF165 in the pathogenesis of diabetic retinopathy (see above), coupled with the preclinical findings demonstrating that pegaptanib was able to suppress leukostasis and blood-retinal barrier breakdown in established diabetes [14], provided strong theoretical support for evaluating pegaptanib as a therapeutic agent for DME. Intravitreous pegaptanib was evaluated in a phase I study, which identified no safety issues that would preclude the use of pegaptanib in patients with DME [data on file, (OSI) Eyetech, Inc.]. A phase II trial was conducted to further explore the safety and efficacy of pegaptanib in patients with DME [17]. The design and important outcomes of the phase II trial are described below.

Study Design

The randomized, sham-controlled, double-masked, dose-finding phase II trial enrolled patients of 18 years and older with type 1 or type 2 diabetes [17]. To be eligible, study eyes had to have macular edema involving the center of the macula, as confirmed by optical coherence tomography (OCT), together with leakage from microaneurysms, retinal telangiectasis, or both, demonstrable on fluorescein angiography, and retinal thickening of at least half a disc area involving the central macula. An independent fundus photograph and angiogram reading center confirmed eligibility and appropriate retinal thickness classification (both for study entry and subsequent randomization and stratification) according to baseline fluorescein angiography and OCT assessments. Only patients for whom the investigator judged that photocoagulation could be safely

withheld for 16 weeks could be enrolled. A best-corrected VA in the study eye from 20/50 to 20/320 and at least 20/100 in the fellow eye were required. Principal exclusion criteria included a history of panretinal, focal photocoagulation, other retinal treatments within the previous 6 months, or abnormalities that would interfere with measurements of VA and fundus photography. Patients with glycosylated hemoglobin levels 13%, with evidence of severe cardiac disease, clinically significant peripheral vascular disease, or uncontrolled hypertension were excluded.

In all, 172 patients were randomized to 4 treatment arms (0.3, 1 and 3 mg pegaptanib or sham injections). Randomization was stratified by study site, size of the thickened retina area ( 2.5 vs. 2.5 disc areas) and baseline VA (letter score 58 vs. 58). Injections were given at baseline, week 6 and week 12 for a minimum of 3 injections. Thereafter, additional injections were given every 6 weeks up to week 30 (for a maximum of 6 injections) at the discretion of the investigators. Final assessments were made at week 36 or 6 weeks after the last injection. Refraction, VA, an ophthalmologic examination and OCT were performed at baseline and at each visit. Color fundus photography was performed at baseline and every 6 weeks while fluorescein angiography was carried out at baseline and 6 weeks after the last injection. Overall, 169 patients received at least 1 injection, and more than 90% of patients in each treatment group completed the study; among the pegaptanib-treated patients, 49% received the maximum of 6 injections from baseline to week 30 (table 4) [17].

Results

Visual Outcomes. Visual outcomes were evaluated in terms of a mean change in best-corrected VA (number of lines and letters gained or lost) and the proportion of patients maintaining baseline VA (0 lines lost) or gaining 5 (1 line), 10 (2 lines) or 15 letters (3 lines). At week 36, all pegaptanib groups demonstrated better VA relative to the sham group. Compared with baseline, 93, 98, 93 and 90% of patients in the 0.3-, 1-, 3-mg and sham groups, respectively, avoided losing 3 or more lines of VA. In the same treatment groups, gains of 0 letters were seen in 73, 72, 60 and 51% (0.3 mg vs. sham; p 0.023), gains of 5 letters were seen in 59, 44, 31 and 34% (0.3 mg vs. sham; p 0.010), gains of 10 letters were seen in 34, 30, 14 and 10% (0.3 mg vs. sham; p 0.003), and gains of 15 letters were seen in 18, 14, 7 and 7% (0.3 mg vs. sham; p 0.012). In these same respective groups, mean changes in VA also favored pegaptanib treatment, with changes of 4.7, 4.7, 1.1 and –0.4 letters (p 0.04, 0.05 and 0.55 for the 0.3-, 1- and 3-mg groups compared with the sham group) (table 5) [17]. Moreover, more patients in all the pegaptanib groups maintained or gained acuity, with a 22% absolute increase and a 43% relative increase in the 0.3-mg group compared with the sham group (fig. 3) [17].

Table 4. Treatment summary (safety population, n 169)

Figures in parentheses are percentages.

With permission from the Macugen Diabetic Retinopathy Study Group [17].

Table 5. Changes from baseline to week 36 in VA (intention-to-treat population, n 172)

For missing baseline data, day 0 data were used for the analysis. For missing data at subsequent time points, the last observation was carried forward. There were missing relevant data for 1 patient each in the 1-mg and sham groups.

1The analysis of covariance model was adjusted for the baseline retinal thickening area and baseline vision; p values of pairwise comparisons were unadjusted for multiplicity.

With permission from the Macugen Diabetic Retinopathy Study Group [17].

Fig. 3. Percentage of patients treated with pegaptanib maintaining or gaining VA from baseline to week 36 (intention-to-treat population, n 172). *p 0.05; **p 0.01. With permission from the Macugen Diabetic Retinopathy Study Group [17].

Retinal Thickness. Changes in central retinal thickness were evaluated as an anatomic proxy for the presence and extent of macular edema. Mean changes in retinal thickness from baseline to week 36 as determined at the center point were –68.0, –22.7 and –5.3 m for the 0.3-, 1- and 3-mg groups, respectively, compared with 3.7 m for the sham group (0.3 mg vs. sham; p 0.021). More patients in the pegaptanib-treated groups experienced an absolute decrease of 75, 100 and 200 m compared with the sham group. Differences in the 0.3-mg group were especially marked, with 49% showing a decrease of 75 m compared with 19% in the sham group (p 0.008); in addition, 42% of the 0.3-mg pegaptanib group had an decrease of 100 m compared with 16% in the sham arm (p 0.02) (table 6) [17]. Baseline and week 36 color fundus photographs and OCT images from a representative patient are presented in figure 4 [17].

Need for Laser Photocoagulation. In the sham group, 48% of patients required additional intervention with photocoagulation therapy between weeks 12 and 36 while only 25, 30 and 40% of patients in the 0.3-, 1- and 3-mg groups needed such treatment (p 0.042, 0.090 and 0.537, respectively, compared

Table 6. Changes from baseline to week 36 in retinal thickness of the center point of the central subfield (intention-to-treat population, n 172)

Figures in parentheses are percentages. For missing baseline data, day 0 data were used for the analysis. For missing data at week 36, the last observation was carried forward. There are missing relevant data for 1 patient in the 0.3-mg, 5 patients in the 1-mg, 6 patients in the 3-mg and 5 patients in the sham groups.

1Analysis of covariance model adjusted for the baseline retinal thickening area, baseline vision, and baseline retinal thickness; p value indicates the difference in least square means between each dose group and the sham group.

2The Cochran-Mantel-Haenszel test was adjusted for the baseline retinal thickening area and baseline vision; p value indicates the difference in odds ratios between each dose group and the sham group.

With permission from the Macugen Diabetic Retinopathy Study Group [17].

with sham). For the 0.3-mg group, this difference meant a relative decrease of 44% compared with the sham group (table 7) [17].

Retinal Neovascularization. Fundus photographs of all study patients were graded for severity of diabetic retinopathy by an independent reading center at baseline, week 36 and week 52 using the Early Treatment Diabetic

Fig. 4. a, b Baseline color fundus photograph (a) and optical coherence tomography image (b) before treatment with intravitreous pegaptanib 0.3 mg show intraretinal hemorrhage, microaneurysm formation and exudates as well as a retinal thickness of 422 M with cystic spaces evident at the center of the macula. VA at the time of study entry was 68 Early Treatment Diabetic Retinopathy Study chart letters (Snellen acuity, approximately 20/50). Laser photocoagulation was administered 6 months before enrollment. Adapted from the Macugen Diabetic Retinopathy Study Group [17]. c, d Fundus photograph at week 36 (c) and optical coherence tomography image (d) after 4 intravitreous injections (at day 0, weeks 6, 12 and 24) of pegaptanib 0.3 mg show partial resolution of retinal microaneurysms, hemorrhages and exudates, as well as a marked decrease in retinal thickness to 267 M. VA at week 36 was 79 Early Treatment Diabetic Retinopathy Study chart letters (Snellen acuity, approximately 20/25). No focal laser photocoagulation treatments were administered after enrollment. Adapted from the Macugen Diabetic Retinopathy Study Group [17].

Retinopathy Study severity scale; fluorescein angiograms were also graded in a masked fashion for the presence of neovascularization. A review of all subjects identified 19 of 172 patients who had retinal neovascularization ( 0.5 disc area in one or more fields) in the study eye at baseline [118]. A retrospective analysis of these patients was done to evaluate the effects of pegaptanib on retinal neovascularization. One of the 19 patients was excluded due to a protocol violation (scatter photocoagulation 13 days before randomization), and 2 were excluded due to the unavailability of follow-up photographs. Of the remaining cohort of

Table 7. Patients receiving focal/grid laser at week 12 or later in the study eye (intention-to-treat population, n 172)

Figures in parentheses are percentages. p values based on the Cochran-Mantel-Haenszel test were adjusted for the baseline retinal thickening area and baseline vision.

With permission from the Macugen Diabetic Retinopathy Study Group [17].

16 patients included in this analysis, 8 had photocoagulation more than 6 months prior to the study and 1 had photocoagulation during the study. Four patients had retinal neovascularization in the fellow eye [118].

Thirteen of these patients received pegaptanib, while the remaining 3 patients received sham injections. Eight of 13 patients (61%) in the pegaptanib group, including the patient receiving photocoagulation during follow-up, had regression of neovascularization demonstrated by fundus photography, diminished or absent fluorescein leakage on fluorescein angiography, or both at 36 weeks. In contrast, none of the 3 patients in the sham group and none of the 4 fellow eyes showed regression of neovascularization. Moreover, 3 of the 8 patients (including the patient receiving photocoagulation) who had regression of neovascularization while receiving pegaptanib experienced a return of neovascularization between weeks 36 and 52, when pegaptanib had been discontinued (fig. 5) [118]. These findings provide further support that VEGF165 plays an important role in the pathogenesis of diabetic retinopathy and suggest that early treatment, before the most destructive sequelae caused by neovascularization have occurred, is likely to be beneficial.

Safety. Pegaptanib was well tolerated, with the majority of adverse events being transient, injection procedure related and mild to moderate in severity. Few serious adverse events were noted, and none were attributed to the pegaptanib drug itself. There was one incident of endophthalmitis (culture negative)