The scientific community hopes to find the same success with the dry form.
Len V. Hua
Download and mail the CE Quiz
Increased vascularity in tumors and its importance in tumor growth was
observed more than a century ago. Over the next few decades, a number of
theories postulated that tumors may produce signaling factors to stimulate
angiogenesis, supporting their rapid proliferation.
However, the first theoretical clinical application of anti-angiogenesis
in cancer was not made until 1971, when Judah Folkman hypothesized that tumor
growth could be stopped if angiogenesis could be inhibited. Although the
concept was intriguing, it did not gain much traction because no angiogenic
factor was known then.
‘VEGF’ introduced in 1989
It was not until 1989 that the term vascular endothelial growth factor
(VEGF) was introduced as an endothelial-specific mitogen by Napoleone Ferrara
of Genentech. In the same year the molecular cloning of VEGF was completed and
published by Monsanto Company.
The remarkable characteristics of VEGF recognized early on were its
ability to induce endothelial cell proliferation and cause vascular leak and
edema. The first study that established the dominance of VEGF in tumor
angiogenesis was the demonstration by Genentech that mouse monoclonal antibody
designed to block VEGF could strongly inhibit tumor growth in an animal model.
This preliminary and seminal finding, however, did not immediately convince
others in the pharmaceutical industry to emphasize VEGF as an exciting new drug
target for cancer because various other targets with equal potential were being
investigated at the time.
Scientists at Genentech continued to develop the next version of the
humanized antibody against VEGF and named it bevacizumab (Avastin), which first
entered clinical trials in 1997 and achieved U.S. Food and Drug Administration
approval in 2004 as a first-line treatment for metastatic colorectal cancer in
combination with chemotherapy. Bevacizumab has since gained additional FDA
approvals for other cancer therapies and still remains the standard for
While the roles of VEGF in angiogenesis were investigated with respect
to tumor growth, its propensity to cause vascular leak and edema was studied by
other investigators. Retinal swelling and edema as commonly seen in wet
age-related macular degeneration (AMD) and proliferative diabetic retinopathy
were the ocular conditions of interest for therapeutic testing. With
collaboration from Genentech, bevacizumab was shown to also be effective in
reducing ocular neovascularization and edema in animal models in 1994.
Bevacizumab, however, was not the first anti-VEGF therapy approved for clinical
treatment of wet AMD.
This fundus photo shows advanced AMD in a patient’s left
Image: Hua LV
Pegaptanib (Macugen, Pfizer), an RNA aptamer directed against VEGF-165
isoform was shown in clinical trials to slow progressive visual loss in wet
AMD. The data on clinical safety and efficacy of pegaptanib was gathered in the
ensuing years and led to the FDA approval in 2004 for the treatment of wet
Although Genentech did not get to the market first for using an
anti-VEGF antibody for the treatment of wet AMD, the company knew it had a more
effective VEGF blocker. However, the concern was that a full-length antibody,
bevacizumab, might not dissolve well enough to reach the retina for optimal
efficacy, so a smaller version was designed and named ranibizumab (Lucentis).
In addition to being smaller size, ranibizumab had a much higher affinity for
multiple VEGFs and, thus, was effective at a lower concentration than
In comparison to the data from clinical studies of pegaptanib, which
merely slowed vision loss, ranibizumab was able to produce vision gain and
maintain these gains over time with a monthly intravitreal injection. With
subsequent data on clinical safety and efficacy, ranibizumab was approved for
the treatment of wet AMD in 2006 and recently also gained approval for the
treatment of retinal vein occlusion. Currently, about a quarter of a million
patients around the world are treated with ranibizumab annually.
Fittingly and timely, the 2010 Lasker DeBakey Clinical Research Award
went to Napoleone Ferrara of Genentech for the discovery of VEGF as a major
mediator of angiogenesis and for the development of an effective anti-VEGF
therapy for wet AMD.
As one more brief historical perspective, the use of antibody as therapy
for ocular complication was first reported in the 1895 by Henri Coppez, a
Belgian ophthalmologist who applied anti-diphtheritic serum to treat
conjunctival diphtheria in two young children, with astounding success. A
century later, therapeutic antibody re-emerges as a remarkable therapy for
ocular angiogenesis and edema.
Multiple isoforms of VEGF proteins
Molecular and biochemical studies over the past decade have identified
six main spliced VEGF isoforms from eight exons of human VEGF-A gene: 121, 145,
165, 183, 189 and 206 amino acids. VEGF121, the smallest isoform, is free,
whereas the larger forms, VEGF189 and VEGF206, are bound to extracellular
matrix. The intermediate VEGF165 exists in both free and bound forms. In
addition, multiple shorter diffusible forms are made as a result of protein
breakdown by extracellular matrix metalloproteinases.
Currently, there are three anti-VEGF agents available for treating
retinal neovascularization. Pegaptanib (Macugen) binds specifically to VEGF165
and spares other isoforms, while bevacizumab (Avastin) and ranibizumab
(Lucentis) bind broadly to all VEGF isoforms, thus perhaps yielding greater
potency of VEGF inhibitions and better efficacy.
Bevacizumab vs. ranibizumab
In spite of its superior efficacy over pegaptanib in the treatment of
wet AMD, the cost of approximately $2,000 per ranibizumab injection was
alarming to many patients, insurance carriers and clinicians. At the same time,
another anti-VEGF, bevacizumab, also made by Genentech, was available in the
market at a much lower cost for treating colorectal cancer.
With the knowledge that anti-VEGF was beneficial to many wet AMD
patients and frustration of the high cost of ranibizumab, a group of retinal
specialists conducted a pilot study using bevacizumab off-label to treat wet
AMD via international collaboration.
The first prospective study using intravitreal bevacizumab off-label for
treatment of neovascular AMD was performed in 17 eyes of 17 patients at the
American University of Beirut Medical Center, Lebanon. The dose was monthly
injection of 2.5 mg in 0.1 mL, twice the dose currently used by most
clinicians. The report corroborated the initial hypothesis that bevacizumab
could be effective for treating wet AMD at a cheaper price. After 3 months of
treatment with bevacizumab, eyes with choroidal neovascularization (CNV) due to
AMD showed significant improvement both in retinal anatomy and visual
This finding ushered in a worldwide clinical adoption of bevacizumab for
neovascular AMD. Over the last few years, the off-label use of bevacizumab as
an anti-angiogenesis and anti-edema treatment for retinal diseases has become
so popular and widespread that it superseded ranibizumab both in applications
and publications. This phenomenon could be due to an approximately 40 times
lower cost per injection with significant efficacy, despite concerns that have
been raised about the clinical safety of off-label use of a large antibody in
The National Eye Institute (NEI) realized the potential pharmacoeconomic
value and safety concern of bevacizumab off-label for not only AMD but
potentially for other ocular disorders. As a result, NEI sponsored a
head-to-head Comparison of AMD Treatment Trial (CATT) study of bevacizumab vs.
ranibizumab in AMD in 2008. The purposes of the trial were to evaluate the
relative efficacy and safety of ranibizumab and bevacizumab and to determine
whether an as-needed regimen would be adequate as compared with a monthly
In this multicenter, single-masked, randomized prospective trial, 1,208
patients with neovascular AMD were assigned to ranibizumab monthly, bevacizumab
monthly or ranibizumab or bevacizumab as needed with monthly vision exam,
dilated exam and ocular coherence tomography (OCT). The final goal of
comparison was the mean change in visual acuity at 1 year, with a
noninferiority deviation of five letters on the eye chart.
In April of 2011, the 1-year findings of CATT were published in the
New England Journal of Medicine. The results indicated that
monthly injection with bevacizumab was equivalent to monthly injection with
ranibizumab, with a gain of approximately eight letters. Moreover,
administration as needed yielded a gain of about six letters for both drugs.
Ranibizumab as needed was adequate and did not compromise visual acuity as
compared to monthly ranibizumab; and the comparison between bevacizumab as
needed and monthly bevacizumab was equivalent for 9 months, but monthly
bevacizumab was slightly better (2.1 letters) than as needed bevacizumab at the
end of the year. However, the significance of this small difference remains to
be answered with longer follow-up. It is remarkable to note the outstanding
efficacy of the two drugs in the study, because more than 90% of patients did
not have a decrease in visual acuity of greater than 15 letters from baseline,
and about 30% of patients gained at least 15 letters at the 1-year mark.
The use of bevacizumab in cancer therapy has been associated with
arteriothrombic events, venous thrombotic events, gastrointestinal perforation
and hemorrhage, wound-healing complications and hypertension. The dosage of
bevacizumab for cancer therapy however is about 500 times that used in
intravitreal injections. In this study, the relative safety of bevacizumab and
ranibizumab were similar with respect to rates of death, myocardial infarction
and stroke, except bevacizumab was found to slightly increase the risk of at
least one serious systemic event. But the overall significance of this
difference is unknown and requires a bigger and longer study to elucidate.
Suggested frequency of administration
The initial FDA approval for ranibizumab (Lucentis, Genentech), based on
clinical trial data from MARINA (Minimally Classic/Occult Trial of the
Anti-VEGF Antibody Ranibizumab in the Treatment of Neovascular AMD) and ANCHOR
(Anti-VEGF Antibody for the Treatment of Predominantly Classic Choroidal
Neovascularization in AMD) studies, in 2006 was for neovascular AMD and macular
edema following retinal vein occlusion. The dosage was 0.5 mg (0.05 mL)
administered by intravitreal injection once a month (about every 28 days).
Although monthly injection was recommended for ranibizumab, other possible
dosing schedules have been of collective interest to scientists, clinicians and
patients. Over the last few years, there have been a few studies conducted to
explore variable dosing schedules compared to monthly injection.
The PIER (Phase 3b, Multicenter, Randomized, Double Masked, Sham
Injection Controlled Study of the Efficacy and Safety of Ranibizumab in
Subjects With Subfoveal CNV With or Without Classic CNV Secondary to AMD) study
was the first to evaluate the 12-month efficacy of dosing ranibizumab (0.3 mg
and 0.5 mg) every 3 months after the initial three consecutive monthly
injections (six doses per year) vs. the recommended 12 doses per year. The
findings published in 2008 confirmed that both 0.3-mg and 0.5-mg ranibizumab
injections yielded significant visual acuity improvement compared with sham
treatment, but quarterly ranibizumab dosing groups had minimal average gain in
visual acuity of less than two letters compared to those of monthly dosing
regimens of greater than seven letters in earlier MARINA and ANCHOR studies.
Thus, the study concluded that a quarterly dosing regimen was less effective
than monthly dosing.
PrONTO (Prospective OCT Imaging of Patients With Neovascular AMD Treated
With Intraocular Ranibizumab) is another study that investigated a variable
dosing schedule. In this case it attempted to evaluate an as-needed dosing
based on monthly OCT imaging for central retinal thickness (CRT) and quarterly
fluorescein angiography (FA) assessment. Patients with neovascular AMD received
three consecutive monthly intravitreal injections of ranibizumab (0.5 mg).
Afterward, retreatment with ranibizumab was administered only if OCT CRT
increased more than 100 µm, VA loss was greater than five letters or any
qualitative increase in the amount of fluid was detected. In 2008, at the end
of 2 years and an average of 10 injections, 37 patients completed the study
with mean VA improvement of 11.1 letters and OCT CRT decrease by 212 µm.
Even though the study population was relatively small, PrONTO showed that with
regular monitoring by OCT and FA assessments, an as-needed dosing regimen was
effective and economical.
The EXCITE (Efficacy and Safety of Monthly vs. Quarterly Ranibizumab
Treatment in Neovascular AMD) study made a direct comparison between monthly
and quarterly dosing regimens and was an extension of the PIER study. In the
EXCITE study, patients had better VA improvement of about four letters in the
0.3-mg quarterly group compared to 1.6 letters achieved in the PIER study, but
the final analysis still indicated that VA gain was higher in the monthly
regimen than the quarterly regimen at month 12. Thus, the efficacy results from
the EXCITE study further supported the earlier findings of the PIER study that
quarterly ranibizumab treatment was not as efficacious as monthly treatment.
Interestingly, it is between months 3 and 4 that there was a prominent
dissociation between monthly and quarterly regimens suggesting a possible
optimal dosing frequency somewhere between 1 and 3 months.
PIER, EXCITE and PrONTO are important studies in establishing dosage and
frequency of administration for ranibizumab. The results from these studies
have encouraged many retinal specialists to give three consecutive monthly
injections of 0.3 mg of ranibizumab followed by as-needed administration based
on OCT or FA findings. While there was no study to establish dosing for
bevacizumab prior to the CATT study, most clinicians have used dosing regimens
similar to that for ranibizumab. Fortuitously, the findings from the latest
CATT trial indicating that less-than-monthly dosing of 1.25 mg of bevacizumab
was as effective as a monthly injection provided solid support to the way many
clinicians have been using it off-label for the past few years. At the moment,
individualized and as-needed dosing after the initial three consecutive monthly
injections for both drugs is used by most retinal experts.
Issues in optometric comanagement
When it comes to comanagement of neovascular AMD, optometrists as
primary eye care providers play an essential role in educating patients about
the disease and necessary treatment, in providing surgeons with medical and
ocular history of the patient prior to treatment and continuing patient care
after each treatment. Thus, it is important that optometrists keep up with the
latest findings from clinical trials on efficacy and safety of intravitreal
No one likes to have a needle stuck in the eye, not even once, but with
the current treatment paradigm, patients will have to put up with the uneasy
feelings almost once a month for at least a few years. So, it is critical to
emphasize that “it sounds worse than it actually is” and, if
possible, refer the patient to other patients who have been through the process
a few times as support.
Current tailored dosing frequency (modified from
In addition to educating and calming the patient about intravitreal
injection, information about potential adverse effects from the treatment
should be discussed and made available. Based on multiple clinical studies with
hundreds of patients and thousands of injections, common ocular adverse effects
for ranibizumab injections included conjunctival hemorrhage, eye pain and
transient increase in intraocular pressure; therefore, it is important to check
IOP after every injection. Because it is an invasive procedure,
endophthalmitis, uveitis, retinal detachment, vitreous hemorrhage and cataract
have rarely (less than 1% incidence) been associated with intravitreal
Nonocular adverse effects including nasopharyngitis and hypertension
were more common with ranibizumab, whereas incidence of arteriothrombotic
events (myocardial infarctions or cerebral vascular events) were relatively
low. In the CATT study, endophthalmitis developed in less than 0.1% of treated
patients. Uveitis, retinal detachment, vein occlusion, retinal tear and
vitreous hemorrhage each occurred in less than 1% of patients.
The proportions of patients with arteriothrombotic events, such as
myocardial infarction and transient ischemic attack, were similar with
ranibizumab and bevacizumab at about 2.5%, which is within the expected
incidence in the general population of patients with AMD. Therefore,
ranibizumab may not significantly increase the risks for arteriothrombotic
events, but it is difficult to prove either way. In response of this concern,
Genentech issued a letter of warning that patients with a history of stroke may
have a higher risk of subsequent stroke. On a positive note, many patients can
appreciate the improvement of vision in a relative short time, because the two
drugs are effective and can substantially reduce the total retinal thickness as
early as a month after the initial injection.
Indications beyond wet AMD
Angiogenesis was one of the properties discovered in the initial
investigation of the role of VEGF; the other was its association to vascular
leakage and edema, which is a common sequelae to other retinal disorders. Thus,
it was anticipated at an early stage of anti-VEGF development that the molecule
could be useful in relieving retinal edema for various conditions in addition
to neovascular AMD. After receiving FDA approval in 2006 for treating wet AMD,
the focus was broadened to study ranibizumab for treating retinal vein
BRAVO (a Study of the Efficacy and Safety of Ranibizumab Injection in
Patients With Macular Edema Secondary to Branch Retinal Vein Occlusion)
demonstrated that monthly intravitreal injections of 0.3 mg or 0.5 mg of
ranibizumab provided rapid, effective treatment for macular edema after branch
retinal vein occlusion (BRVO). At 6 months, the percentage of patients who
gained at least 15 letters in best corrected visual acuity was about 60% in the
ranibizumab groups and 30% in the sham group. The median percent reduction in
excess foveal thickness was about 97% and 28%, respectively.
CRUISE (a Study of the Efficacy and Safety of Ranibizumab Injection in
Patients With Macular Edema Secondary to Central Retinal Vein Occlusion) also
confirmed that monthly intravitreal injections of 0.3 mg or 0.5 mg of
ranibizumab provided rapid improvement in 6-month visual acuity and macular
edema after central retinal vein occlusion (CRVO). At 6 months, the benefits
found in CRVO patients were even better than what was found for BRVO. The
percentage of patients who gained 15 letters in BCVA at month 6 was 47% in the
ranibizumab group and 17% in the sham group. The median percent reduction in
excess foveal thickness was 96% and 23.9%, respectively. These dramatic
beneficial results led to FDA approval of ranibizumab for treatment of retinal
edema secondary to retinal vein occlusion in 2010. Prior to these studies,
retinal vein occlusions had been managed largely with a
“wait-and-see” approach for the initial few to several months without
an effective treatment guideline.
With evidence that anti-VEGFs are beneficial for treating edema commonly
found in wet AMD and retinal vein occlusion, diabetic macular edema (DME), a
retinal condition with the same theme, is the next natural target. Several
studies (READ-2, RESTORE trials) conducted by the Diabetic Retinal Clinical
Research Network (http://drcrnet.jaeb.org) reported that ranibizumab alone or
in combination with photocoagulation yielded significantly more letters of
visual acuity gain compared to less than one letter gained by laser treatment
alone. In addition, central serous chorioretinopathy is another condition of
retinal edema that had been relieved with anti-VEGF in a number of studies.
The clinical applications of anti-VEGF (ranibizumab or bevacizumab) for
ocular disorders continue to expand as more positive results are found for
other vascular ocular disorders. The arena is now moving more anteriorly from
posterior retina to anterior segment. An increasing number of studies in recent
years have shown the beneficial effects of anti-VEGF, from neovascular glaucoma
to corneal neovascularization. The general theme seems to be as long as
abnormal angiogenesis and edema are part of the pathophysiology of a disease,
anti-VEGF would probably be efficacious in some way, regardless of disease
Future directions – anti-VEGF, laser
The results from various randomized clinical trials to date have
provided concrete evidence on the superb efficacy of ranibizumab and
bevacizumab for the treatment of neovascular AMD. Nonetheless, approximately
one in five patients may not get the full benefit or be nonresponders.
Therefore, retinal specialists have continued to explore combining the new
anti-VEGF with older therapy such as corticosteroids and verteporfin
photodynamic therapy (PDT).
One of the earlier studies to demonstrate the effectiveness of
combination therapy was the FOCUS (Ranibizumab Combined With Verteporfin
Photodynamic Therapy in Neovascular Age-related Macular Degeneration) study.
The study showed that, on average, ranibizumab with PDT had less progression
and greater reduction of retinal edema and required fewer PDT retreatments than
PDT alone. Furthermore, the VIA (Verteporfin and Bevacizumab) study
demonstrated that a combination of PDT with bevacizumab significantly reduced
the number of bevacizumab treatments required over 6 months. In another
combination-therapy study, intravitreal bevacizumab combined with triamcinolone
was administered to patients with neovascular AMD that were resistant to
bevacizumab alone. The results suggested that patients who were nonresponders
to bevacizumab monotherapy may experience mild improvement in vision with
combined intravitreal injection.
Therefore, the field of combination therapy for ocular angiogenesis and
edema is ongoing and evolving as more studies are being carried out. At the
same time, other anti-angiogenic agents are slowly progressing through the drug
pipelines, including VEGF-Trap-Eye (Regeneron/Bayer) with more sustained
Focus shifts to dry AMD
As the saying goes “Dry is the new wet.” Now that a lot of
success has been made in the management of wet AMD, more attention is being
paid to finding effective therapy to stop or reverse dry AMD, which accounts
for the majority of AMD. In addition to AREDS2 (Age-Related Dry Eye Disease
Study 2) in finding a combination of vitamins and antioxidants that can slow
the progression of dry AMD, there are various clinical trials on its potential
For example, complement inhibition with eculizumab for the treatment of
nonexudative AMD is a phase 2 study being conducted by the University of Miami.
Kaplan Medical Center is conducting a phase 3 trial with Copaxone (glatiramer
acetate, Teva), a drug for patients with relapsing-remitting multiple
sclerosis. GlaxoSmithKline is working on a tyrosine kinase inhibitor,
pazopanib, that may be formulated as a topical anti-VEGF drop for maintenance
In addition, other modes of therapy are also being investigated such as
localized radiation therapy (EpiRad, NeoVista), rheopheresis (Apheresis
Research Institute) and photobiomodulation (NCT00940407). As defined by the
corresponding companies who ventured in these novel arenas: “Epimacular
beta radiation therapy is approved for the treatment of wet AMD in the European
Union. Rheopheresis is therapeutic apheresis using the methodology of double
filtration plasmapheresis to treat microcirculatory disorders.
Photobiomodulation is the application of nonthermal, nonlaser light of specific
wavelengths and energy directly on the eye to improve retinal function and
delay AMD progression.”
Ultimately, gene therapy may offer a way to deliver anti-VEGF protein or
other therapeutic agents directly to the site of ocular disorders.
In summary, there has been a great leap forward over the past decade in
understanding the mechanism of angiogenesis and management of ocular disorders
resulting from abnormal angiogenesis. Ranibizumab and bevacizumab are the
blockbuster drugs for patients with wet AMD, while the scientific community is
working hard to come up with similar agents for the more common dry form of
AMD. Older therapy such as PDT or photocoagulation and corticosteroids
continues to play an important role as a sole or an adjunct therapy in
combination with the new anti-VEGF molecules for abnormal ocular angiogenesis
as in wet AMD, diabetic retinopathy and BRVO. For optometrists, our roles as
primary eye care providers will not change drastically. As new intravitreal
drugs come into market, the most important thing we can do is to keep up with
developments in eye care, provide excellent care and educate our patients.
- Brown DM, Kaiser PK, Michels M, et al, ANCHOR Study Group. N
Engl J Med. 2006;355:1432-1444.
- Ferrara N. Vascular endothelial growth factor and age-related
macular degeneration: from basic science to therapy. Nat Med.
- Lalwani GA, Rosenfeld PJ, Fung AE, et al. Am J Ophthalmol.
- Magdelaine-Beuzelin, Pinault C, Paintaud G, et al. Therapeutic
antibodies in ophthalmology: old is new again. mAbs.
- Martin DF, Maguire MG, Ying G, et al. CATT Research Group. N
Engl J Med. 2011;364:1897-1908.
- Regillo CD, Brown DM, Abraham P, et al., PIER Study Group. PIER
Study year 1. Am J Ophthalmol. 2008;145:239-248.
- Regillo CD, Brown DM, Abraham P, et al., PIER Study Group. PIER
Study year 2. Am J Ophthalmol. 2010;150:315-324.
- Rosenfeld PJ, Moshfeghi AA, Puliafito CA. Optical coherence
tomography after an intravitreal injection of bevacizumab (Avastin) for
neovascular age-related macular degeneration. Ophthalmic Surg Lasers
- Rosenfeld PJ, Brown DM, Heier JS, et al. Ranibizumab for
neovascular age-related macular degeneration. N Engl J Med.
- Schmidt-Erfurth U, Eldem B, Guymer R, et al. The EXCITE Study
Group. Ophthalmology. 2011;118(5):831-839.
- Tolentino M. Systemic and ocular safety of intravitreal anti-VEGF
therapies for ocular neovascular disease. Surv Ophthalmol.
For more information:
- Len V. Hua, PhD, OD, FAAO, is an assistant professor at Pacific
University College of Optometry. He can be reached at 2043 College Way, Forest
Grove, OR 97116; (503) 352-3059; fax: (503) 352-2929;
- Disclosure: Dr. Hua has no relevant financial disclosures.