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Tam V. Bui, Nathan L. Mata; Serum Retinol Binding Protein as a Biomarker for Fenretinide-mediated Slowing of Lesion Growth in Patients with Geographic Atrophy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3538.
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The aberrant accumulation of lipofuscin and vitamin A (retinol)-derived toxins, such as A2E, has been implicated in the pathogenesis and progression of geographic atrophy (GA). A2E and related toxins are derived from circulating retinol. Therefore, reduction of circulating retinol is theorized to reduce levels of retinol-derived toxins in the eye. Fenretinide, a synthetic vitamin- A derivative, is known to reduce levels of serum retinol binding protein (RBP), thereby reducing retinol delivery to the eye. Using data obtained from a 2-year phase II proof-of-concept study which evaluated fenretinide efficacy in patients with GA, analyses were performed to assess correlations between lesion growth and serum RBP levels.
The primary efficacy outcome of the phase 2 trial was change in the growth of the aggregate GA lesion area. All retinal images were collected and read by the Digital Angiography Reading Center (DARC, New York, NY). Visual acuity (VA) measures were obtained at regular intervals during the trial. Measures of serum RBP were obtained by Aptuit (Edinburgh, UK). The relationship between change in the GA area, VA and RBP levels was performed at study end.
Fenretinide demonstrated a trend for reducing the growth of GA lesions. This therapeutic effect was correlated with reductions in serum RBP. Among patients with at least a 60% reduction in RBP, the median lesion growth rate was 1.28 mm2/year. Compared to this group, the median lesion growth rate in the placebo group was ~1.6-times higher (2.03 mm2/year) and was statistically different (p = 0.0409). Patients experiencing a ≥ 60% RBP reduction also demonstrated preserved visual acuity from 12- to 24-months at 6 letters lost, compared to 11 letters lost in the placebo group.
In patients treated with fenretinide, reductions in serum RBP were associated with reduced lesion growth. There was a significant slowing of lesion growth rate and stabilization of VA in patients with RBP reductions which were greater than 60%. The observed correlations further suggest that circulating RBP could be useful as a biomarker to determine potential for therapeutic efficacy in future trials.
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