Researchers led by a team at the Wilmer Eye Institute, Johns Hopkins Medicine, have discovered why vision in some patients with neovascular (nv) or “wet” age-related macular degeneration (nvAMD, or wet AMD) fails to improve following treatment that targets vascular endothelial growth factor (VEGF).
Their studies, including samples from human patients, indicated that anti-VEGF therapies may actually contribute to a lack of vision improvement by triggering the overexpression of a second protein, ANGPTL4. Further work in a mouse model found that an experimental drug, 32-134D, which inhibits HIF-1—a protein known to be involved in wet AMD and diabetic eye disease for its role in switching on VEGF production—could be used in combination with existing anti-VEGF treatment to improve response.
“This work exposes a way to improve anti-VEGF therapy for all patients and potentially help a subset of patients with wet AMD who still lose vision over time despite treatment,” said Akrit Sodhi, MD, PhD, associate professor of ophthalmology and the Branna and Irving Sisenwein Professor of Ophthalmology at the Johns Hopkins University School of Medicine and the Wilmer Eye Institute. “Our hope is that this [project] will further the three goals we have related to wet AMD: make current therapies as effective as possible, identify new therapies, and prevent people from ever getting wet AMD.”
Sodhi is corresponding author of the team’s published paper in PNAS, titled “VEGF inhibition increases expression of HIF-regulated angiogenic genes by the RPE limiting the response of wet AMD eyes to aflibercept.” In their paper, the authors concluded “Collectively, these results help explain why many patients with nvAMD respond inadequately to anti-VEGF therapy and suggest that the HIF inhibitor 32-134D will be an effective drug—alone or in combination with current anti-VEGF therapies—for the treatment of patients with this blinding disease.”
Wet AMD, one of two kinds of AMD, is a progressive eye condition caused by choroidal neovascularization (CNV), an overgrowth of abnormal leaky blood vessels in the retina, which is the light-sensing tissue in the eye that also relays vision signals to the brain. These blood vessels—caused by overexpression of the protein VEGF, which leads to blood vessel growth—then leak fluid or bleed and damage the retina, causing vision loss. The authors further explained, “Expression of VEGF in the eyes of patients with nvAMD is regulated by the transcription factor, hypoxia-inducible factor (HIF)-1. Increased expression of VEGF by HIF-1, in turn, promotes the growth of the abnormal leaky vessels that compromise vision in patients with nvAMD.”
Despite the severe vision loss often experienced by people with wet AMD, less than half of patients treated with monthly eye injections of anti-VEGF therapies show any major vision improvements. And most of those who do benefit with improved vision will lose those gains over time. “Why many patients with nvAMD treated with anti-VEGF therapies fail to respond adequately to treatment remains unclear,” the team continued.
The Wilmer-led team of researchers has now uncovered anti-VEGF therapies may actually contribute to lack of vision improvements by triggering the overexpression of a second protein, known as angiopoietin-like 4 (ANGPTL4), an angiogenic mediator which is similar to VEGF, as it can also stimulate overproduction of abnormal blood vessels in the retina.
The team compared VEGF and ANGPTL4 levels in the eye fluid of 52 patients with wet AMD at various stages of anti-VEGF treatment. Prior to anti-VEGF injections, patients with wet AMD had high levels of ANGPTL4 and VEGF proteins. After treatment, their VEGF levels predictably decreased, but ANGPTL4 levels rose higher, indicating ANGPTL4 remained active following the anti-VEGF injections and the treatments contributed to an increase in ANGPTL4. Such ANGPTL4 activity can lead to blood vessel overgrowth and lack of vision improvement.
“We have previously reported that ANGPTL4 was increased in patients who did not respond well to anti-VEGF treatment,” said Sodhi. “What we saw in this paper was a paradoxical increase of ANGPTL4 in patients that received anti-VEGF injections—the anti-VEGF therapy itself turned on expression of this protein.” The researchers also investigated the effects of anti-VEGF therapy in a mouse model of wet AMD, with similar results to those observed in humans. “… these observations demonstrate that anti-VEGF therapy promotes increased ANGPTL4 mRNA and protein expression in a mouse model for CNV.”
Describing their collective findings, the authors noted, “… these results demonstrate that treatment of patients with nvAMD with anti-VEGF therapy results in a therapeutic decrease in VEGF, but a countertherapeutic increase in the expression of ANGPTL4, supporting a role for ANGPTL4 in limiting the treatment response of patients with nvAMD to anti-VEGF therapy.”
They next investigated ways to bridge the gap between patients with increased ANGPTL4 following anti-VEGF treatments by testing in a mice model an experimental drug, 32-134D, which decreases levels of HIF-1. The researchers believed that 32-134D would have a similar effect on ANGPTL4 following anti-VEGF treatment, since ANGPTL4 production is also turned on by HIF-1. “… we set out to evaluate the therapeutic efficacy of targeting HIF-1α for the treatment of CNV,” they explained.
Analyses of mice receiving only the anti-VEGF therapy aflibercept first corroborated the team’s findings in human patients. In these animals levels of VEGF were lower, yet ANGPTL4 levels rose, preventing anti-VEGF therapies from fully working to prevent blood vessel growth and associated vision loss. Conversely, in mice treated using 32-134D there was a decrease in HIF-1 levels and VEGF, as well as decreased levels of ANGPTL4 and blood vessel overgrowth. “32-134D prevented the expression of both VEGF and ANGPTL4 and was at least as effective as aflibercept in treating CNV in mice,” they wrote, “… demonstrating that 32-134D could be an effective monotherapy for the treatment of patients with nvAMD.”
In a further set of experiments the researchers determined that combining 32-134D with anti-VEGF treatment prevented the increase in HIF-1, VEGF, and ANGPTL4. This treatment combination was more effective than was either drug alone. “By preventing the increase in HIF-1α accumulation in response to anti-VEGF therapy, combining 32-134D with aflibercept was more effective for choroidal neovascularization (CNV) treatment in mice than either drug alone,” they stated. “This suggests that combining 32-134D with current therapies may overcome the inadequate response of patients with nvAMD to anti-VEGF monotherapy … Collectively, these studies provide the foundation for a clinical study assessing 32-134D, alone or in combination with anti-VEGF therapies, for the treatment of patients with nvAMD.”
