Clinical and Histological Characterization of Toxic Keratopathy From Depatuxizumab Mafodotin (ABT-414), an Antibody-Drug Conjugate

Incidence and Mitigation of Corneal Pseudomicrocysts Induced by Antibody-Drug Conjugates (ADCs)

Purpose of Review

This study is to highlight the incidence of corneal pseudomicrocysts in FDA-approved antibody-drug conjugates (ADCs), and success of preventive therapies for pseudomicrocysts and related ocular surface adverse events (AEs).

Recent Findings

ADCs are an emerging class of selective cancer therapies that consist of a potent cytotoxin connected to a monoclonal antibody (mAb) that targets antigens expressed on malignant cells. Currently, there are 11 FDA-approved ADCs with over 164 in clinical trials. Various AEs have been attributed to ADCs, including ocular surface AEs (keratitis/keratopathy, dry eye, conjunctivitis, blurred vision, corneal pseudomicrocysts). While the severity and prevalence of ADC-induced ocular surface AEs are well reported, the reporting of corneal pseudomicrocysts is limited, complicating the development of therapies to prevent or treat ADC-related ocular surface toxicity.

Summary

Three of 11 FDA-approved ADCs have been implicated with corneal pseudomicrocysts, with incidence ranging from 41 to 100% of patients. Of the six ADCs that reported ocular surface AEs, only three had ocular substudies to investigate the benefit of preventive therapies including topical steroids, vasoconstrictors, and preservative-free lubricants. Current preventive therapies demonstrate limited efficacy at mitigating pseudomicrocysts and other ocular surface AEs.

Antibody-Drug Conjugates and Ocular Toxicity

Antibody-drug conjugates (ADCs) are a growing class of chemotherapeutic agents for the purpose of treating cancers that often have relapsed or failed first- and second-line treatments. ADCs are composed of extremely potent cytotoxins with a variety of side effects, one of the most significant being ocular toxicity. The available literature describes these toxicities as varying in severity and in incidence, although with disparate methods of evaluation and management. Some of the most common toxicities include microcyst-like epithelial keratopathy and dry eye. We discuss proposed mechanisms of ocular toxicity and describe the reports that mention these toxicities. We focus on ADCs with the most published literature and the most significant effects on ocular tissue. We propose areas for further investigation and possible ideas of future management. We provide a comprehensive look at the reports of ADCs in current literature to better inform clinicians on an expanding drug class.

Corneal Findings Associated to Belantamab-Mafodotin (Belamaf) Use in a Series of Patients Examined Longitudinally by Means of Advanced Corneal Imaging

Belantamab mafodotin (belamaf) is a novel antibody–drug conjugate developed for the treatment of patients with relapsed or refractory multiple myeloma (RRMM). Although the drug has demonstrated a good efficacy, corneal adverse events have been reported. In this prospective study, consecutive patients with RRMM who received belamaf infusions were included. The standard ophthalmological visit was implemented with anterior segment (AS)-optical coherence tomography (OCT) and in vivo confocal microscopy (IVCM). Five patients (three males, two females; mean age 66 ± 6.0 years) with MMRR and unremarkable ocular findings at baseline who received belamaf infusion were included. After a median time of 28 days from the first infusion, four of them developed corneal alterations with transient vision reduction to a variable extent. In particular, corneal deposits of microcyst-like epithelial changes (MECs) were detected centrally in one patient and peripherally in three patients. AS-OCT scans showed a bilateral heterogeneous increase in signal intensity, together with hyper-reflective lesions confined within the epithelium in all cases, except for one case in which they also involved the stroma. Corneal maps showed a transient increase in epithelial thickness in the first phase that was followed by a diffuse decrease in the subsequent phase. IVCM scans showed MECs as hyper-reflective opacities located at the level of corneal epithelium, largely intracellular. Multimodal corneal imaging may implement the current clinical scale, helping us to detect corneal abnormalities in patients under belamaf therapy. This workup provides useful data for monitoring over time corneal findings and for optimizing systemic therapy.

Characterization and Potential Mitigation of Corneal Effects in Nonclinical Toxicology Studies in Animals Administered Depatuxizumab Mafodotin

Purpose: To characterize the ocular toxicity of an antibody-drug conjugate (ADC), depatuxizumab mafodotin (Depatux-m), in nonclinical species and to evaluate the effects of drug-antibody ratios (DARs), variations of the ADC construct, and potential methods for mitigation of the corneal toxicity. Depatux-m contains the potent cytotoxic agent monomethyl auristatin F as the ADC payload. Methods: Depatux-m was administered intravenously to cynomolgus monkeys at doses up to 30 mg/kg and to mice up to 100 mg/kg. Ocular toxicity was evaluated by clinical ophthalmic examinations and histopathology. Potential mitigation was tested through agents to block target engagement and multiple topical ophthalmic treatments (antioxidant, vasoconstrictor, tear stimulant). Results: Effects primarily involved corneal epithelium and were dose-dependent with respect to onset, severity, and time to reversal in both monkeys and mice. On slit lamp biomicroscopy, the initial effect in monkeys was superficial multifocal punctate opacities (granularity), which migrated axially and were followed by pigmentation and multifocal punctate fluorescein staining. Microscopically, findings were characterized by single-cell necrosis, pigmentation, disordered basilar layer, and thinning of the corneal epithelium. Increased toxicity was associated with a higher DAR or more stably attached linker. Treatment with agents to block target engagement did not affect toxicity, and none of the topical treatments was successful. Conclusions: The corneal findings observed were similar to the effects described in clinical trials with Depatux-m and other ADCs. Collectively, these studies and available literature support the hypothesis that ADC-mediated toxicity is driven primarily by mechanism of action of the payload.

Belantamab mafodotin associated corneal microcyst-like epithelial changes

Purpose

To report a case of bilateral corneal microcyst-like epithelial changes associated with belantamab mafodotin (belamaf) therapy.

Observations

A 70-year-old man with refractory multiple myeloma was placed on belamaf, a recently FDA-approved treatment for relapsed or refractory multiple myeloma. He developed decreased visual acuity and bilateral corneal microcyst-like peripheral epithelial changes. Belamaf was withheld.

Anterior segment OCT showed intra-epithelial opacities at various depths. After resolution of corneal changes and recovery of vision, belamaf was restarted. The patient underwent two additional treatments, each time with recurrence of diffuse microcyst-like corneal epithelial changes. It took a total of 8, 11.5 and 17 weeks after each respective infusion for the microcyst-like epithelial changes to resolve. This suggested a longer recovery time after each subsequent infusion.

Conclusions and importance

The care for patients on belamaf requires the collaboration of eye care providers and hematologists-oncologists to assess for ocular adverse effects and adjust treatment as necessary. Further study is needed to illustrate the mechanism of corneal microcyst-like epithelial changes and its effects on limbal stem cells.