Background: Current melphalan-based intravitreal regimens for retinoblastoma (RB) vitreous seeds cause retinal toxicity. We assessed the efficacy and toxicity of topotecan monotherapy compared with melphalan in our rabbit model and patient cohort.Methods: Rabbit experiments: empiric pharmacokinetics were determined following topotecan injection. For topotecan (15 μg or 30 µg), melphalan (12.5 µg) or saline, toxicity was evaluated by serial electroretinography (ERG) and histopathology, and efficacy against vitreous seed xenografts was measured by tumour cell reduction and apoptosis induction. Patients: retrospective cohort study of 235 patients receiving 990 intravitreal injections of topotecan or melphalan.Results: Intravitreal topotecan 30 µg (equals 60 µg in humans) achieved the IC₉₀ across the rabbit vitreous. Three weekly topotecan injections (either 15 µg or 30 µg) caused no retinal toxicity in rabbits, whereas melphalan 12.5 µg (equals 25 µg in humans) reduced ERG amplitudes 42%–79%. Intravitreal topotecan 15 µg was equally effective to melphalan to treat WERI-Rb1 cell xenografts in rabbits (96% reduction for topotecan vs saline (p=0.004), 88% reduction for melphalan vs saline (p=0.004), topotecan vs melphalan, p=0.15). In our clinical study, patients received 881 monotherapy injections (48 topotecan, 833 melphalan). Patients receiving 20 µg or 30 µg topotecan demonstrated no significant ERG reductions; melphalan caused ERG reductions of 7.6 μV for every injection of 25 µg (p=0.03) or 30 µg (p<0.001). Most patients treated with intravitreal topotecan also received intravitreal melphalan at some point during their treatment course. Among those eyes treated exclusively with topotecan monotherapy, all eyes were salvaged.Conclusions: Taken together, these experiments suggest that intravitreal topotecan monotherapy for the treatment of RB vitreous seeds is non-toxic and effective.

Purpose: To use our intra-arterial chemotherapy (IAC) rabbit model to assess the impact of IAC procedure, drug, dose, and choice of technique on ocular structure and function, to study the nature and etiology of IAC toxicity, and to compare to observations in patients. Methods: Rabbits received IAC melphalan (0.4-0.8 mg/kg), carboplatin (25–50 mg), or saline, either by direct ophthalmic artery cannulation, or with a technique emulating nonocclusion. Ocular structure/function were assessed with examination, electroretinography (ERG), fundus photography, fluorescein angiography, optical coherence tomography (OCT), and OCT angiography, prior to and 5 to 6 weeks after IAC. Blood counts were obtained weekly. We reviewed our last 50 IAC treatments in patients for evidence of ocular or systemic complications. Results: No toxicity was seen in the saline control group. With standard (0.4 mg/kg) melphalan, no vascular/microvascular abnormalities were seen with either technique. However, severe microvascular pruning and arteriolar occlusions were seen occasionally at 0.8 mg/kg doses. ERG reductions were dose-dependent. Histology showed melphalan dose-dependent degeneration in all retinal layers, restricted geographically to areas of greatest vascular density. Carboplatin caused massive edema of ocular/periocular structures. IAC patients experienced occasional periocular swelling/rash, and only rarely experienced retinopathy or vascular events/hemorrhage in eyes treated multiple times with triple (melphalan/carboplatin/topotecan) therapy. Transient neutropenia occurred after 46% of IAC procedures, generally after triple therapy. Conclusions: IAC toxicity appears to be related to the specific drug being used and is dose-dependent, rather than related to the IAC procedure itself or the specific technique selected. These rabbit findings are corroborated by our clinical findings in patients.

To evaluate the relative efficacy of novel retinoblastoma treatments, eye classification-specific success rates for current standard-of-care intravenous chemotherapy regimens must be known. This meta-analysis included studies if: (1) patients received intravenous chemotherapy for retinoblastoma, (2) globe salvage data was reported, (3) only intravenous chemoreduction (with/without local consolidation) was used. The outcome measure was globe salvage success without need for salvage radiotherapy, subdivided by disease classification and chemotherapy regimen. Data from 27 studies (1483 eyes) were pooled. By Reese–Ellsworth classification, globe salvage rates were 85% (95%CI:73–92%) for Group I, 78% (95%CI:70–85%) for Group II, 68% (95%CI:56–78%) for Group III, 47% (95%CI:34–60%) for Group IV, and 35% (95%CI:26–45%) for Group V (Va: 35% [95%CI:21–54%]; Vb: 42% [95%CI:29–56%]; those without sub-classification: 31% [95%CI:19–47%]). By International Classification, globe salvage rates were 93% (95%CI:80–97%) for Group A, 83% (95%CI:73–89%) for Group B, 73% (95%CI:54–86%) for Group C, 40% (95%CI:31–51%) for Group D, and 19% (95%CI:5–50%) for Group E. Standard carboplatin-etoposide-vincristine out-performed two-drug regimens (odds ratio (OR) = 1.9 (95%CI:1.3–3.0) for Groups I-IV and OR = 2.1 (95%CI:1.3–3.4) for Group V; p = 0.002 for each). For eyes with diffuse vitreous seeds (Vb), an enhanced regimen out-performed standard chemotherapy (OR = 2.4 [95%CI:1.3–4.7]; p = 0.004). In conclusion, two-drug regimens were less effective for all eyes, whereas enhanced regimens were more effective for eyes with vitreous seeds. Novel therapies can now be compared to these baseline globe salvage rates.

To characterize the enhanced depth imaging (EDI) OCT features of ultrasonographically flat choroidal nevi. Retrospective observational study. Patients with ultrasonographically flat choroidal nevi identified over a 3-year period. Comprehensive eye examinations and multimodal imaging were performed every 6 to 12 months. Lesion thickness and features, EDI-OCT findings. A total of 102 nevi (98 patients) were included. Median follow-up was 9 months (range 0-144 months) and 1 to 8 (mean 2.1) OCTs were performed. On OCT, nevi were classified into 5 subtypes: 3.2% were "not visible," 37.2% had "hyperreflectivity confined within normal choroidal thickness," 16.0% had characteristic anteriorly bowed hyperreflectivity with "discrete" borders and cascading edges, 14.9% were "flat with posterior bowing," and 28.7% were "elevated." One nevus of the "elevated" type demonstrated clinically insignificant growth (<10% in thickness) after 22 months of follow-up. Five distinct EDI-OCT patterns of choroidal nevi seemed flat on ultrasonography, and many demonstrated thickness and elevation not measurable on B-scan ultrasonography. Lesion thickness can be measured using EDI-OCT.

Purpose: Current melphalan-based regimens for intravitreal chemotherapy for retinoblastoma vitreous seeds are effective but toxic to the retina. Thus, alternative agents are needed. Based on the known biology of histone deacetylases (HDACs) in the retinoblastoma pathway, we systematically studied whether the HDAC inhibitor belinostat is a viable, molecularly targeted alternative agent for intravitreal delivery that might provide comparable efficacy, without toxicity. Methods: In vivo pharmacokinetic experiments in rabbits and in vitro cytotoxicity experiments were performed to determine the 90% inhibitory concentration (IC₉₀). Functional toxicity by electroretinography and structural toxicity by optical coherence tomography (OCT), OCT angiography, and histopathology were evaluated in rabbits following three injections of belinostat 350 µg (2× IC₉₀) or 700 µg (4× IC₉₀), compared with melphalan 12.5 µg (rabbit equivalent of the human dose). The relative efficacy of intravitreal belinostat versus melphalan to treat WERI-Rb1 human cell xenografts in rabbit eyes was directly quantified. RNA sequencing was used to assess belinostat-induced changes in RB cell gene expression. Results: The maximum nontoxic dose of belinostat was 350 µg, which caused no reductions in electroretinography parameters, retinal microvascular loss on OCT angiography, or retinal degeneration. Melphalan caused severe retinal structural and functional toxicity. Belinostat 350 µg (equivalent to 700 µg in the larger human eye) was equally effective at eradicating vitreous seeds in the rabbit xenograft model compared with melphalan (95.5% reduction for belinostat, P < 0.001; 89.4% reduction for melphalan, P < 0.001; belinostat vs. melphalan, P = 0.10). Even 700 µg belinostat (equivalent to 1400 µg in humans) caused only minimal toxicity. Widespread changes in gene expression resulted. Conclusions: Molecularly targeted inhibition of HDACs with intravitreal belinostat was equally effective as standard-of-care melphalan but without retinal toxicity. Belinostat may therefore be an attractive agent to pursue clinically for intravitreal treatment of retinoblastoma.