**4.2 Observation**

The DRCR Network, Protocol V study, addressed the management of well-controlled DM with center involving DME (CI - DME) and good vision. Randomization of study participants was to observation, focal laser, and intravitreal Aflibercept [121]. The results suggest that patients with CI-DME and good vision (20/25 or better) can be managed initially with observation and close followup. These eyes should receive treatment if they suffer a decrease in vision.

For many years, focal and or grid macular laser photocoagulation (MLP) was the gold standard for DME treatment; newer laser techniques are now available. These minimize the side effects of a traditional laser. Intravitreal anti-Vascular endothelial growth factor (anti-VEGF) injections are now the mainstay of CI-DME. Although intravitreal anti-VEGFs have become popular, intravitreal steroids are often indicated in the treatment of DME. Vitrectomy is also used to treat DME. Combination therapy is another strategy employed for treating DME.

## **4.3 Intravitreal anti-vascular endothelial growth factors (anti VEGF).**

Anti VEGFs inhibit upregulated VEGF, which has been implicated in the pathogenesis of DME. The efficacy of anti-VEGF injections in DME has been demonstrated by several studies [122–125]. Anti-VEGF therapy, however, requires frequent intravitreal

injections that are difficult to transpose to clinical practice. Thus, fewer injections are administered in clinical practice than in clinical trials; this contributes to decreased efficacy as the results of clinical trials have been difficult to replicate in real life [126].

#### *4.3.1 Pegaptanib*

The first anti-VEGF drug used to treat DME was Pegaptanib (Macugen®, Bausch and Lomb, Rochester, NY, USA), which selectively blocks the 165-isoform of VEGF [127]. A phase II trial by the Macugen Diabetic Retinopathy Study Group reported that at 36 weeks, Pegaptanib led to better BCVA gain, a more significant reduction in central macular thickness (CMT), and less requirement for laser in DME when compared to sham [128]. However, it has been observed that Pegaptanib is less effective at improving visual outcomes than other anti-VEGF agents that target all VEGF-A isoforms [129].

#### *4.3.2 Bevacizumab*

Bevacizumab, a humanized monoclonal antibody that inhibits VEGF, was initially developed as a concomitant medication for use in combination with existing metastatic colorectal cancer regimens [130]. The FDA does not approve it for the treatment of DR or DME. However, the intravitreal Bevacizumab or laser therapy in the management of diabetic macular edema (BOLT) study examined the efficacy of Bevacizumab versus focal laser for DME and reported that Bevacizumab is superior to focal laser alone [131].

Patients in the Bevacizumab group showed significant BCVA improvement over patients in the laser group [131]. Bevacizumab costs much less than the FDAapproved intravitreal anti-VEGF drugs [132]. It is, therefore, more cost-effective in treating DME than Ranibizumab or Aflibercept [133, 134]. It is usually given as a 1.25 mg in 0.05 ml dose. The incidence of severe ocular and monocular adverse events was low for intravitreal Bevacizumab [135].

#### *4.3.3 Ranibizumab*

Ranibizumab (IVR, Lucentis®, Novartis, Basel, Switzerland) is a fully-humanized monoclonal antibody fragment that binds to VEGF-A's multiple variants [136]. The Ranibizumab for Diabetic Macular Edema (A Study of Ranibizumab Injection in Subjects With Clinically Significant Macular Edema With Center Involvement Secondary to Diabetes Mellitus (RIDE) and A Study of Ranibizumab Injection in Subjects With Clinically Significant Macular Edema With Center Involvement Secondary to Diabetes Mellitus (RISE) trials investigated the use of monthly Ranibizumab given in two doses—0.5 and 0.3 mg—for the treatment of DME [137]. The FDA approves it for the treatment of DME and DR at a dose of 0.3 mg monthly.

Port Delivery System (PDS) with Ranibizumab is a permanent refillable eye implant, approximately the size of a grain of rice, designed to deliver a customized formulation of Ranibizumab continuously over an extended duration, i.e., six months; potentially reducing the treatment burden associated with frequent eye injections [138].

The LADDER trial demonstrated that PDS with the 100 mg/mL formulation is non-inferior to monthly intravitreal injections of Ranibizumab in terms of visual and anatomical outcomes in neovascular age related macular degeneration (AMD) eyes [139]. In the ARCHWAY trial, 98.4% of PDS patients could go six months without needing additional treatment and achieved vision outcomes equivalent to in AMD patients receiving monthly Ranibizumab injections, a

current standard of care [138]. Therefore, PDS could reduce the number of anti-VEGF treatments to two per year.

It is surgically implanted via a specialized tool through an incision in the sclera and pars plana. Reported adverse effects include conjunctival bleb, vitreous hemorrhage, conjunctival erosion, conjunctival retraction, endophthalmitis, rhegmatogenous retinal detachment, and hyphaema [138].

Two trials, PAGODA (will evaluate the efficacy, safety, and pharmacokinetics of the PDS With Ranibizumab in participants with DME compared with intravitreal Ranibizumab) and PAVILION (a multicenter, randomized study in participants with diabetic retinopathy without center-involved DME to evaluate the efficacy, safety, and pharmacokinetics of Ranibizumab delivered via the PDS relative to the comparator arm) are underway to study the safety and efficacy of PDS in subjects with DME and those with DR without CI-DME [140, 141].

### *4.3.4 Aflibercept*

Aflibercept (IVA; VEGF-trap eye, Eylea, Regeneron Pharmaceuticals, NY, USA) is a recombinant chimeric fusion protein containing the second domain of VEGFR-1 and the third domain of the VEGFR-2 attached Fc portion of human IgG1 [142]. It has a dimeric structure, the molecular weight of the protein is 97kD, and the total molecule after glycosylation is 115kD [143]. Aflibercept acts as a decoy receptor binding VEGF-A, VEGF-B, and PlGF, thereby preventing their binding with their original receptors [144]. VEGF-A binds to both VEGFR-1 and VEGFR-2, but PlGF binds to only VEGFR-1. The FDA approves it for the treatment of DME and DR in patients with DME at a dose of 2 mg. It was studied in the Intravitreal Aflibercept for Diabetic Macular Edema (VISTA and VIVID) trials which compared Aflibercept with a focal laser to treat DME [145]. These studies demonstrated the superiority of Aflibercept over laser in terms of visual acuity improvement.

A comparative effectiveness randomized clinical trial compared Bevacizumab with Ranibizumab and Aflibercept for DME and found that all three agents are effective treatments at the two-year follow-up [146]. However, in eyes with visual acuity of 20/50 or worse, Aflibercept was superior to Ranibizumab and Bevacizumab at one year. In contrast, at two years, Aflibercept was no longer superior to Ranibizumab but remained superior to Bevacizumab [132, 147].

A concomitant effect of intravitreal anti-VEGF treatment for DME noticed with Ranibizumab and Aflibercept is improvement in retinopathy severity or slowing of the rate of progression of retinopathy [148]. Another concomitant effect is thinning of the choroid [149, 150].

#### *4.3.5 Brolucizumab*

Brolucizumab (IVBr, Beovu; Novartis; Basel, Switzerland), a single-chain antibody fragment, was approved for the treatment of nAMD in October 2019 and in February 2020 in the USA and the European Union [151]. The potential benefits of Brolucizumab are assumed to be related to its low molecular weight with subsequent better tissue penetration as well as higher molar concentration [152, 153]. Its use is mentioned here for completeness. It is no longer in "popular" use due to safety concerns. Brolucizumab was associated with reports of intraocular inflammation (IOI) and retinal vasculitis with or without occlusion [154, 155].

Positive 1-year results of the phase III KESTREL and KITE studies, evaluating the efficacy and safety of Beovu (Brolucizumab) 6 mg in DME were reported. Both studies met their primary endpoints of noninferiority in the change in BCVA from

baseline for Beovu 6 mg versus Aflibercept 2 mg at year one [156]. However, the Beovu trials have been discontinued because Beovu was associated with higher rates of intraocular inflammation, including retinal vasculitis and retinal vascular occlusion versus Aflibercept [157].

#### *4.3.6 Faricimab*

Faricimab is a novel anti-Ang-2/anti-VEGF bispecific antibody designed explicitly for intraocular use [158, 159]. It is assembled using Roche's CrossMAb technology (Basel, Switzerland) and binds both VEGF-A and Ang-2 with high affinity and specificity [158, 160]. Faricimab is the first investigational bispecific antibody designed for the eye [161].

It targets two distinct pathways – via angiopoietin-2 (Ang-2) and vascular endothelial growth factor-A (VEGF-A) – that drive several retinal vascular diseases [161]. Ang-2 and VEGF-A contribute to vision loss by destabilizing blood vessels, causing new leaky blood vessels to form and increasing inflammation [162]. By simultaneously blocking both pathways involving Ang-2 and VEGF-A, Faricimab is designed to stabilize blood vessels, potentially improving vision outcomes for a longer duration in patients living with retinal conditions [162].

Faricimab is a promising molecule that is still undergoing investigation primarily for nAMD. The STAIRWAY Phase 2 Randomized Clinical Trial concluded that at week 52, Faricimab dosing every 16 weeks and every 12 weeks resulted in maintenance of initial vision and anatomic improvements comparable with monthly Ranibizumab [163]. TENAYA and LUCERNE phase 3 trials evaluate the efficacy, safety, and extended durability of up to 16 weekly dosing of intravitreal Faricimab in patients with nAMD [164]. YOSEMITE and RHINE are ongoing trials evaluating the efficacy, durability, and safety of Faricimab 8 weekly or a protocol-driven regimen based on treat-and-extend in DME patients [165]. Positive first-year results have been reported for Faricimab, which may emerge as an essential option if equivalent second-year results are reported with no safety flags.

#### **4.4 Regimens**

There is no consensus about the ideal treatment regimen with anti-VEGF agents [166]. Different treatment algorithms have been studied in clinical trials for AMD and applied in clinical practice, including monthly injections (ANCHOR, MARINA, CATT, HARBOR, EXCITE, IVAN, VIEW) as needed 'pro re nata' PRN (SUSTAIN, MONT BLANC, SAILOR, CABERNET, PrONTO, IVAN, CATT, HARBOR, OCTAVE), and 'treat and extend' regimen (TREND, LUCAS) [167].

Monthly maintenance dosing is a tremendous burden for both patients and the healthcare system. It has a real risk of overtreatment. The pro re nata (PRN) regimen is a treatment protocol where follow-up intervals remain fixed. At the same time, decisions to carry out an injection are based on the anatomic findings at each respective visit [168]. The PRN regiment has a risk of undertreatment or overtreatment, and patients may fail to attend. A treat-and-extend regimen (TER) is an individualized dosing scheme of titrating the injection interval based on the patient's response [169]. Therefore, if a patient shows no sign of active disease (e.g., the macula remains dry, without any leakage), intervals will be extended; if there is fluid accumulation, the next interval will be shortened. Fixed dosing lacks long-term practicability in real-world settings due to overtreatment and high costs; thus, PRNs or TERs have been suggested as feasible alternatives [169]. TERs have advantages: their cost-effectiveness due to less frequent visits and increased efficacy based on proactive treatments. However, TER involves more injections than a PRN regimen, leading to overtreatment [170].
