Linker Technology Research Articles

Exploring alternative dosing regimens of single-agent belantamab mafodotin on safety and efficacy in patients with relapsed or refractory multiple myeloma: DREAMM-14.

TPS8073 Background: Belantamab mafodotin (belamaf: BLENREP) is a first-in-class, monomethyl auristatin F (MMAF)-containing, B-cell maturation antigen (BCMA)-directed antibody–drug conjugate (ADC). In the DREAMM-2 study, belamaf showed deep responses with a manageable safety profile in patients with relapsed/refractory multiple myeloma (RRMM). At 13 months of follow-up, the median duration of response was 11 months and overall survival was 13.7 months at the 2.5 mg/kg Q3W dose. Corneal events are common and expected with belamaf and other MMAF-containing ADCs. In DREAMM-2, corneal events were managed with dose modifications. Clinical responses were observed even with prolonged dose holds, suggesting alternative dosing regimens may lower corneal event rates without compromising efficacy. The DREAMM-14 study (NCT05064358) will investigate if an improved benefit/risk profile of single-agent belamaf can be achieved by modifying the dose, schedule, or both, relative to the approved dosing regimen (2.5 mg/kg Q3W). Methods: This Phase II, randomized, open-label study will include adults with RRMM who had ≥3 prior lines of therapy (LOT), including an anti-CD38 monoclonal antibody, an immunomodulatory agent, and a proteasome inhibitor. Patients with corneal epithelial disease (except nonconfluent superficial punctate keratitis) or with prior exposure to BCMA-targeted therapies, or ADCs will be excluded. Patients will be randomized into Arms A–D (n=40 each) and Arm E (n=20) in parallel and stratified by the International Staging System (I vs II vs III) and prior LOT (3 vs ≥4). Belamaf will be administered as follows—Arm A: 2.5 mg/kg Q3W; Arm B: 1.9 mg/kg Q3W; Arm C: 2.5 mg/kg Q6W; Arm D: 1.9 mg/kg Q6W; Arm E: 1.9 mg/kg Q6W with ocular event-related dose modifications based on oncology staff assessment of ocular symptoms (patient-reported symptoms using the Ocular Surface Disease Index), and visual acuity (Snellen chart or equivalent) in addition to corneal findings assessed by an eye care specialist. Patients in all Arms will have response assessments, safety assessments, and ophthalmic exams performed by an eye care specialist Q3W regardless of dosing schedule. Ocular event-related dose modifications (except in Arm E) will be guided by a modified Keratopathy and Visual Acuity scale. The primary endpoint will be incidence of ocular events. Key secondary endpoints include ocular safety and tolerability, overall safety and tolerability, pharmacokinetics, and efficacy outcomes. Follow-up for progression-free survival will be Q3W until progressive disease, start of new anticancer therapy, withdrawal of consent, end of study, or death. Status: Recruitment is ongoing. Funding: GSK (Study 209628); drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. Clinical trial information: NCT05064358.

Safety and clinical activity of belantamab mafodotin with lenalidomide plus dexamethasone in patients with relapsed/refractory multiple myeloma (RRMM): DREAMM-6 arm-A interim analysis.

8017 Background: Belantamab mafodotin (belamaf; BLENREP) is a B-cell maturation antigen-targeting antibody–drug conjugate approved for patients (pts) with RRMM as monotherapy at 2.5 mg/kg Q3W. Preclinical data demonstrate synergy between belamaf and lenalidomide (Len), suggesting added benefit when combined with standard of care such as Len + dexamethasone (Dex). DREAMM-6 (NCT03544281) Arm A is evaluating belamaf in combination with LenDex in pts with RRMM. Methods: This ongoing, two-part, two-arm, open-label study included pts with RMMM previously treated with ≥1 line of therapy (LOT). Pts received 4 belamaf doses/schedules (1.9 mg/kg Q8W or Q4W; 2.5 mg/kg Q4W or Q4W SPLIT dose [50% on Days (D)1, 8] IV) in combination with Len (20 mg PO D1–21) and Dex (20 mg PO/IV D1, 8, 15, 22). Primary objectives were safety (including treatment-related [TR]AEs related to the combination belamaf and LenDex), tolerability, and efficacy (including overall response rate [ORR] defined as ≥partial response). Results: As of this interim analysis (data cut: July 23, 2021), 45 pts received ≥1 dose (12 at 1.9 mg/kg Q8W; 4 at 1.9 mg/kg Q4W; 16 at 2.5 mg/kg Q4W; 13 at 2.5 mg/kg Q4W SPLIT). Across cohorts, the median age was 68 y (range: 36–80). Thirteen pts (29%) had high-risk cytogenetics and 6 (13%) had extramedullary disease. Median prior LOT was 3 (range: 1–11) and 26 (58%) had prior Len treatment. The median duration of follow-up and ORR ranged across cohorts (Table). The median duration of response was only reached in the 1.9 mg/kg Q4W cohort (11.1 mo [95% CI: 3.7–not reached [NR]). At the time of data cut, median progression-free survival was not reached in the 1.9 mg/kg Q8W or 2.5 mg/kg Q4W cohorts. Gr ≥3 TRAEs occurred in 42–85%. Gr ≥3 keratopathy occurred in 0 pts in 1.9 mg/kg Q8W, 1 pt (25%) in 1.9 mg/kg Q4W, 8 pts (50%) in 2.5 mg/kg Q4W, and 6 pts (46%) in 2.5 mg/kg Q4W SPLIT cohorts. Conclusions: Belamaf + LenDex had a tolerable safety profile, with no new safety signals identified in pts with RRMM. AEs, including keratopathy, were common but manageable with dose modifications. Encouraging clinical activity is observed with this combination in pts with RRMM. Follow-up/correlative studies are ongoing. Funding: GSK (Study 207497); drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. Clinical trial information: NCT03544281. [Table: see text]

Homogeneity of antibody-drug conjugates critically impacts the therapeutic efficacy in brain tumors.

SUMMARYGlioblastoma multiforme (GBM) is the most aggressive and fatal disease of all brain tumor types. Most therapies rarely provide clinically meaningful outcomes in the treatment of GBM. Although antibody-drug conjugates (ADCs) are promising anticancer drugs, no ADCs have been clinically successful for GBM, primarily because of poor blood-brain barrier (BBB) penetration. Here, we report that ADC homogeneity and payload loading rate are critical parameters contributing to this discrepancy. Although both homogeneous and heterogeneous conjugates exhibit comparable in vitro potency and pharmacokinetic profiles, the former shows enhanced payload delivery to brain tumors. Our homogeneous ADCs provide improved antitumor effects and survival benefits in orthotopic brain tumor models. We also demonstrate that overly drug-loaded species in heterogeneous conjugates are particularly poor at crossing the BBB, leading to deteriorated overall brain tumor targeting. Our findings indicate the importance of homogeneous conjugation with optimal payload loading in generating effective ADCs for intractable brain tumors.

A Patent Review on FDA-Approved Antibody-Drug Conjugates, Their Linkers and Drug Payloads.

Antibody-drug conjugates (ADCs) have emerged as a promising class of biologics since the first approval of Gemtuzumab ozogamicin in 2000. Compared to small molecule drugs, ADCs are structurally much more complex as they comprise of an antibody conjugated to cytotoxic payloads by specially-designed linkers. Correspondingly, the ADC patent landscape is also much more complex. This review collates and discusses the patents protecting ADCs approved by the FDA up to 31 December 2021, with particular emphasis on their linker and cytotoxin payload technologies.

Single Mutation on Trastuzumab Modulates the Stability of Antibody-Drug Conjugates Built Using Acetal-Based Linkers and Thiol-Maleimide Chemistry.

Antibody-drug conjugates (ADCs) are a class of targeted therapeutics used to selectively kill cancer cells. It is important that they remain intact in the bloodstream and release their payload in the target cancer cell for maximum efficacy and minimum toxicity. The development of effective ADCs requires the study of factors that can alter the stability of these therapeutics at the atomic level. Here, we present a general strategy that combines synthesis, bioconjugation, linker technology, site-directed mutagenesis, and modeling to investigate the influence of the site and microenvironment of the trastuzumab antibody on the stability of the conjugation and linkers. Trastuzumab is widely used to produce targeted ADCs because it can target with high specificity a receptor that is overexpressed in certain breast cancer cells (HER2). We show that the chemical environment of the conjugation site of trastuzumab plays a key role in the stability of linkers featuring acid-sensitive groups such as acetals. More specifically, Lys-207, located near the reactive Cys-205 of a thiomab variant of the antibody, may act as an acid catalyst and promote the hydrolysis of acetals. Mutation of Lys-207 into an alanine or using a longer linker that separates this residue from the acetal group stabilizes the conjugates. Analogously, Lys-207 promotes the beneficial hydrolysis of the succinimide ring when maleimide reagents are used for conjugation, thus stabilizing the subsequent ADCs by impairing the undesired retro-Michael reactions. This work provides new insights for the design of novel ADCs with improved stability properties.

DREAMM-5 Study: Investigating the Synergetic Effects of Belantamab Mafodotin Plus Inducible T-Cell Co-Stimulator Agonist (aICOS) Combination Therapy in Patients with Relapsed/Refractory Multiple Myeloma

DREAMM-5 Study: Investigating the Synergetic Effects of Belantamab Mafodotin Plus Inducible T-Cell Co-Stimulator Agonist (aICOS) Combination Therapy in Patients with Relapsed/Refractory Multiple Myeloma

Can Patient-Reported Ocular Symptoms Guide Dose Modifications in Patients with Relapsed/Refractory Multiple Myeloma Receiving Belantamab Mafodotin?

Can Patient-Reported Ocular Symptoms Guide Dose Modifications in Patients with Relapsed/Refractory Multiple Myeloma Receiving Belantamab Mafodotin?

Exploring Alternative Dosing Regimens of Single-Agent Belantamab Mafodotin on Safety and Efficacy in Patients with Relapsed or Refractory Multiple Myeloma: DREAMM-14

Exploring Alternative Dosing Regimens of Single-Agent Belantamab Mafodotin on Safety and Efficacy in Patients with Relapsed or Refractory Multiple Myeloma: DREAMM-14

A Phase 1, Open-Label, Dose-Escalation Study of the Safety and Efficacy of Anti-CD38 Antibody Drug Conjugate (STI-6129) in Patients with Relapsed or Refractory Multiple Myeloma

Background: With the advent of several new agents in the treatment of multiple myeloma, including proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), and anti-CD38 monoclonal antibodies (mAb), the overall survival (OS) has significantly improved in the past two decades. However, most patients become refractory to currently available therapies along the disease trajectory. The median OS in triple-class-refractory patients (i.e., anti-CD 38 mAb, PIs, and IMiDs) is 6 months (Gandhi et al. Leukemia. 2019). Although BCMA-targeted therapies are a major advance in such patients, none of them are curative thus far, with the median progression-free survival (PFS) ranging from 3 months in BCMA-antibody drug conjugates (ADCs) to approximately 1 year in BCMA chimeric antigen receptor T-cell (CAR T-cell) therapies. Furthermore, unique toxicities of BCMA-targeted agents such as ocular toxicity (ADCs), cytokine release syndrome, or neurotoxicity (CAR Ts and BiTEs) may preclude their use in many patients. Hence, there is a critical unmet need in patients with triple-class-refractory myeloma.The STI-6129 ADC is produced by conjugating STI-5171, a fully human anti-CD38 mAb, with a covalently bound tubulin inhibitor, duostatin 5.2 (DUO-5.2), using a proprietary linker technology with a 3:1 drug-antibody ratio. STI-6129 binds to different CD38 epitopes than daratumumab. Upon binding to CD38, STI-6129 ADC is internalized by the cancer cell and undergoes lysosomal degradation, releasing DUO-5.2. This in turn leads to G2-phase cell cycle arrest, followed by caspase 3/7-dependent apoptosis and cell death. In studies on cynomolgus monkeys, the serum level of DUO-5.2 remained undetectable at all doses except at the highest dose of 4.5 mg/kg, indicating low likelihood of off-target toxicity. In vitro studies of primary human plasma cells, human tumor models, and animal xenograft models have demonstrated target elimination of CD38-positive human plasma cells by STI-6129. Importantly, STI-6129 has demonstrated cytotoxic activity in human multiple myeloma cells isolated from daratumumab-refractory patients (Figure 1). Hence, further investigation on clinical activity of STI-6129 is warranted.Study Design: The 38-ADC-RRMM-101 study is a two-stage, multicenter, open-label, dose-finding phase 1/2 trial. The phase 1 trial is designed to identify the recommended phase 2 dose (RP2D) of STI-6129 by assessing safety, preliminary efficacy, and pharmacokinetics in patients with relapsed/refractory (RR) myeloma. The phase 2a stage of the trial will be a single-arm study to investigate the efficacy of STI-6129 in an expansion cohort of RR myeloma patients. Up to 25 patients will be enrolled in the phase 1 stage and 30 in the phase 2 stage of the study. The key inclusion criteria are the following: (a) RR myeloma with at least 3 prior lines of therapy in addition to being refractory to at least 1 PI, 1 IMiD, and 1 anti-CD 38 mAb; (b) measurable disease. The key exclusion criteria are: (a) receipt of the last dose of any anti-CD mAb within 90 days; (b) grade ≥3 neuropathy or grade 2 neuropathy with pain; (c) current history of CTCAE grade 3 muscle paresis, eyelid conditions, glaucoma, or any other ocular disorder that is CTCAE grade 2; (d) estimated creatinine clearance <60 ml/min; (e) left ventricular ejection fraction<40%. The primary endpoint of phase 1 stage of the study is safety, particularly any dose limiting toxicities. The primary endpoint of the phase 2 part of the study is overall response rate as per IMWG criteria. The dosing cohorts in the dose escalation phase will range from 0.25 mg/kg to 3.68 mg/kg. Given the potential for on-target off-tumor toxicity due to expression of CD38 on non-clonal plasma cells and other hematopoietic cells, blood counts and immunoglobulin levels will be closely monitored. While neurotoxicity or ocular toxicity were not observed with STI-6129 in animal models, including non-human primates, such event will be considered as adverse events of special interest (AESI) and comprehensive neurology and ocular (including slit lamp) examinations will be performed at baseline and study completion, and at any AESI. STI-6129 will be administered intravenously once in a 4-week cycle, with the intention being to treat patients until disease progression or unacceptable toxicity. [Display omitted] DisclosuresYan: Sorrento Therapeutics: Current Employment. Royal: Sorrento Therapeutics: Current Employment.

DREAMM-9: Phase I Study of Belantamab Mafodotin Plus Standard of Care in Patients with Transplant-Ineligible Newly Diagnosed Multiple Myeloma

DREAMM-9: Phase I Study of Belantamab Mafodotin Plus Standard of Care in Patients with Transplant-Ineligible Newly Diagnosed Multiple Myeloma

Prostate-Specific Membrane Antigen-Targeted Turn-on Probe for Imaging Cargo Release in Prostate Cancer Cells.

The tunable nature of phosphoramidate linkers enables broad applicability as pH-triggered controlled-release platforms, particularly in the context of antibody- and small-molecule-drug conjugates (ADCs and SMDCs), where there remains a need for new linker technology. Herein, we explored in-depth the release of turn-on fluorogenic payloads from a homoserinyl-based phosphoramidate acid-cleavable linker. Kinetics of payload release from the scaffold was observed in buffers representing the pH conditions of systemic circulation, early and late endosomes, and lysosomes. It was found that payload release takes place in two key consecutive steps: (1) P-N bond hydrolysis and (2) spacer immolation. These two steps were found to follow pseudo-first-order kinetics and had opposite dependencies on pH. P-N bond hydrolysis increased with decreasing pH, while spacer immolation was most rapid at physiological pH. Despite the contrasting release kinetics of these two steps, maximal payload release was observed at the mildly acidic pH (5.0-5.5), while minimal payload release occurred at physiological pH. We integrated this phosphoramidate-payload linker system into a PSMA-targeted fluorescent turn-on probe to study the intracellular trafficking and release of a fluorescent payload in PSMA-expressing prostate cancer cells. Results showed excellent turn-on and accumulation of the coumarin payload in the late endosomal and lysosomal compartments of these cells. The release properties of this linker mark it as an attractive alternative in the modular design of ADCs and SMDCs, which demand selective intracellular payload release triggered by the pH changes that accompany intracellular trafficking.

P-202: Characterization of ocular adverse events in patients receiving Belantamab Mafadotin for ≥12 months: post-hoc analysis of DREAMM-2 study in relapsed/refractory Multiple Myeloma

<h3>Background</h3> The B-cell maturation antigen–targeting antibody–drug conjugate belantamab mafodotin (belamaf; GSK2857916) is approved for the treatment of adult patients with heavily pretreated relapsed or refractory multiple myeloma (RRMM). Ocular symptoms (eg, dry eye, blurred vision), eye examination findings (including keratopathy; superficial punctate keratopathy and/or microcyst-like epithelial changes), and visual acuity changes are common with belamaf. This post-hoc analysis characterizes the safety profile of belamaf 2.5 mg/kg Q3W in patients treated for ≥12 months in the DREAMM-2 study. <h3>Methods</h3> Patients with RRMM who had ≥3 prior therapies, including an immunomodulatory agent and proteasome inhibitor, refractory and/or intolerant to an anti-CD38 monoclonal antibody, received single-agent belamaf. Eye examinations were conducted at baseline and prior to each dose. Dose modifications were based on the most severe Keratopathy and Visual Acuity scale grading, which considers corneal exam findings and best corrected visual acuity (BCVA) changes from baseline. Recovery was defined as Grade 1 exam finding/no exam finding, and ≤1-line decline in BCVA vs baseline. Patient-reported ocular symptoms were graded per Common Terminology Criteria for Adverse Events version 4.03. <h3>Results</h3> At 13-month follow-up, the clinical benefit rate (≥minimal response) in patients receiving belamaf 2.5 mg/kg (n=97) was 36%; 14 patients (15%) had received ≥12 months of treatment. All 14 patients experienced ≥1 ocular event (maximum grade: 2 [14%]; 3 [79%]; 4 [7%]), and required ≥2 dose delays, with dose reduction to 1.92 mg/kg in 12 patients (86%). Dose modifications permitted ocular event recovery, so belamaf was resumed in all 14 patients. Patients had a mean of 3.6 dose delays (median: 3.5; range: 2–6). Median duration of dose delays was 41 days (range: 4–212); 10 patients (71%) had dose delays ≥63 days. Long delays did not appear to negatively impact clinical response to belamaf: 12 (86%) had a clinical response (≥partial response; 11 [79%] for ≥6 months). All 14 patients had keratopathy. Ocular symptoms occurred in 13 patients (93%); blurred vision 57%, dry eye 36%, visual acuity reduced 21%, and photophobia 21%. No patients had permanent complete vision loss. <h3>Conclusions</h3> In this subset of patients receiving belamaf treatment for ≥12 months, dose modification was effective in managing ocular symptoms and decreasing findings at eye examination, and allowed patients the clinical benefit gained from continuing treatment with belamaf. The safety profile of belamaf will be further characterized in ongoing analyses and studies. <h3>Funding</h3> GlaxoSmithKline (Study 205678, NCT03525678). Drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. © 2021 European Hematology Association, Inc. Reused with permission. This abstract was accepted and previously presented at the 2021 EHA Annual Meeting. All rights reserved.

P-219: Relationship between corneal exam findings, best-corrected visual acuity, and ocular symptoms in patients with relapsed or refractory multiple myeloma receiving belantamab mafodotin

Background Belantamab mafodotin (belamaf; GSK2857916) is a B-cell maturation antigen (BCMA)-targeting antibody–drug conjugate approved in the United States and European Union as a monotherapy for heavily pretreated adult patients with relapsed or refractory multiple myeloma (RRMM). Ocular events (OEs) during the pivotal DREAMM-2 trial (NCT03525678) included corneal exam findings (superficial punctate keratopathy and/or microcyst-like epithelial changes), decline in best-corrected visual acuity (BCVA), and ocular symptoms. Dose reductions or delays based on corneal exam findings and BCVA were used to manage OEs. Here we performed a post hoc investigation of relationships between corneal exam findings, BCVA changes, and patient-reported ocular symptoms to explore if BCVA decline and symptoms could guide dosing, rather than corneal exams. Methods Eye evaluations (including a corneal exam and BCVA assessment of Snellen visual acuity) were performed on all patients receiving single-agent belamaf (2.5 mg/kg) by ophthalmologists at baseline and prior to each belamaf dose. Changes in the corneal epithelium (keratopathy) and BCVA were both assessed as per protocol-defined criteria and assessment of grade (GR) was based on the worse eye. BCVA grading was relative to baseline. Patient-reported ocular symptoms were reported as per the Common Terminology Criteria for Adverse Events. Results In 12.5% of eye evaluations, GR 3–4 keratopathy was associated with minimal or no (GR ≤1) BCVA changes. When patient-reported ocular symptoms were also considered, GR 3–4 keratopathy with GR ≤1 BCVA changes and no ocular symptoms was observed in only 7.5% of evaluations. Mild or no (GR ≤2) keratopathy was associated with GR ≤1 BCVA changes in 59.5% of evaluations, or in 38.8% of evaluations with no ocular symptoms reported. Overall, GR 3–4 keratopathy was found in 24.9% of evaluations; by contrast, patients had GR 2–4 BCVA changes or ocular symptoms in 53.6% of evaluations. Conclusions These findings suggest that BCVA changes and ocular symptoms should be further investigated to determine if they can be used as potential surrogate markers (eg, frequency of eye examinations based on symptoms) for the management of belamaf dosing to potentially reduce the burden on patients and healthcare professionals. Funding Source GSK (205678; NCT03525678). Drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. Encore Statement ©2021 American Society of Clinical Oncology, Inc. Reused with permission. This abstract was accepted and previously presented at the 2021 ASCO Annual Meeting. All rights reserved. Belantamab mafodotin (belamaf; GSK2857916) is a B-cell maturation antigen (BCMA)-targeting antibody–drug conjugate approved in the United States and European Union as a monotherapy for heavily pretreated adult patients with relapsed or refractory multiple myeloma (RRMM). Ocular events (OEs) during the pivotal DREAMM-2 trial (NCT03525678) included corneal exam findings (superficial punctate keratopathy and/or microcyst-like epithelial changes), decline in best-corrected visual acuity (BCVA), and ocular symptoms. Dose reductions or delays based on corneal exam findings and BCVA were used to manage OEs. Here we performed a post hoc investigation of relationships between corneal exam findings, BCVA changes, and patient-reported ocular symptoms to explore if BCVA decline and symptoms could guide dosing, rather than corneal exams. Eye evaluations (including a corneal exam and BCVA assessment of Snellen visual acuity) were performed on all patients receiving single-agent belamaf (2.5 mg/kg) by ophthalmologists at baseline and prior to each belamaf dose. Changes in the corneal epithelium (keratopathy) and BCVA were both assessed as per protocol-defined criteria and assessment of grade (GR) was based on the worse eye. BCVA grading was relative to baseline. Patient-reported ocular symptoms were reported as per the Common Terminology Criteria for Adverse Events. In 12.5% of eye evaluations, GR 3–4 keratopathy was associated with minimal or no (GR ≤1) BCVA changes. When patient-reported ocular symptoms were also considered, GR 3–4 keratopathy with GR ≤1 BCVA changes and no ocular symptoms was observed in only 7.5% of evaluations. Mild or no (GR ≤2) keratopathy was associated with GR ≤1 BCVA changes in 59.5% of evaluations, or in 38.8% of evaluations with no ocular symptoms reported. Overall, GR 3–4 keratopathy was found in 24.9% of evaluations; by contrast, patients had GR 2–4 BCVA changes or ocular symptoms in 53.6% of evaluations. These findings suggest that BCVA changes and ocular symptoms should be further investigated to determine if they can be used as potential surrogate markers (eg, frequency of eye examinations based on symptoms) for the management of belamaf dosing to potentially reduce the burden on patients and healthcare professionals.

P-212: DREAMM-5 platform trial: Belantamab mafodotin (belamaf; GSK2857916) in combination with five different novel agents in patients with relapsed/refractory multiple myeloma (RRMM)

<h3>Background</h3> Single-agent belamaf, a B-cell maturation antigen-targeting antibody-drug conjugate, induced durable responses with a manageable safety profile in patients with RRMM at 13 months of follow-up (DREAMM-2; NCT03525678). The unique multimodal mechanisms of action (MoAs) of belamaf, in combination with MoAs of selected agents, have the potential to achieve synergistic effects in RRMM to further enhance the benefit-risk profile. Belamaf is being evaluated in DREAMM-5 in various lines of treatment, as monotherapy or in combination with other agents. <h3>Methods</h3> DREAMM-5 (NCT04126200) is a phase 1/2 platform study that utilizes a master protocol with separate sub-studies comprised of sequential dose-exploration (DE) and cohort-expansion (CE) phases to identify effective belamaf combinations compared with a shared single-agent belamaf control arm (CE phase only). In the DE phase, patients will be assigned to one of the multiple belamaf dosing combination cohorts by a predetermined algorithm (N≤10 per cohort). A recommended phase 2 dose (RP2D) for each combination will be identified based on safety and preliminary efficacy in the DE phase. An interim analysis of safety, pharmacokinetic, biomarker, and efficacy data will be performed for each combination to determine if it should move forward to the CE phase. Patients in the CE phase (N≥35 per cohort) will be randomized to a sub-study, and within a sub-study, to either the combination arm or belamaf control arm. Patients will also be stratified by number of prior therapies; eligible patients will have received ≥3 prior lines, including an immunomodulatory agent, proteasome inhibitor, and anti-CD38 antibody. All patients will provide informed consent for participation. Primary objectives of the study are to identify the RP2D (DE phase), the overall response rate (≥partial response, CE phase), and safety and tolerability for each combination. Sub-study 1 (combination with GSK3174998, OX40 agonist antibody) is no longer open to enrollment. Sub-studies 2 (combination with GSK3359609, feladilimab, anti-ICOS agonist), 3 (combination with nirogacestat [PF-03084014; SpringWorks Therapeutics], gamma-secretase inhibitor), and 4 (combination with dostarlimab, PD-1 antagonist antibody) are currently open to enrollment. Sub-study 5 (combination with isatuximab [Sanofi], CD38 antagonist antibody) will be open to enrollment soon. Additional sub-studies will be explored based on scientific rationale and/or available preclinical combination data. <h3>Funding</h3> GSK (208887; NCT04126200). Belamaf drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. Nirogacestat and isatuximab produced by and used in collaboration with SpringWorks Therapeutics and Sanofi, respectively <h3>Encore Statement</h3> ©2021 European Hematology Association, Inc. Reused with permission. This abstract was accepted and previously presented at the 2021 EHA Annual Meeting. All rights reserved.

MM-078: Characterization of Ocular Adverse Events in Patients Receiving Belantamab Mafodotin (Belamaf) for ≥12 Months: Post Hoc Analysis of DREAMM-2 Study in Relapsed/Refractory Multiple Myeloma (RRMM)

Context Belamaf is approved for the treatment of adult patients with RRMM. Ocular symptoms (e.g., dry eye, blurred vision), eye examination findings including keratopathy (superficial punctate keratopathy and/or microcyst-like epithelial changes), and visual acuity changes are common with belamaf. Objective To study the safety profile of belamaf 2.5 mg/kg Q3W in patients treated for ≥12 months in the DREAMM-2 study. Methods Patients with RRMM who had ≥3 prior therapies and were refractory to an immunomodulatory agent and proteasome inhibitor and refractory and/or intolerant to an anti-CD38 monoclonal antibody received single-agent belamaf. Eye examinations were conducted at baseline and prior to each dose. Dose modifications were based on the most severe Keratopathy and Visual Acuity Scale grading. Recovery was defined as grade 1 exam findings/no exam findings and ≤1-line decline in BCVA vs baseline; patient-reported ocular symptoms were graded per the Common Terminology Criteria for Adverse Events v4.03. Results At 13-month follow-up, 14 patients (15%) received ≥12 months of treatment. All experienced ≥1 ocular event (maximum grade: 2 [14%]; 3 [79%]; 4 [7%]) and required ≥2 dose delays, with dose reduction to 1.92 mg/kg in 12 patients (86%). Dose modifications permitted ocular event recovery; belamaf was resumed in all 14 patients. Patients had a mean of 3.6 dose delays (median: 3.5; range: 2–6) with a median duration of 41 days (range: 4–212); 10 patients (71%) had dose delays >63 days. Long delays did not appear to negatively impact clinical response to belamaf: 12 patients (86%) had a clinical response (≥partial response; 11 patients [79%] ≥6 months). All 14 patients had keratopathy. Ocular symptoms occurred in 13 patients (93%); blurred vision, 57%; dry eye, 36%; visual acuity reduced, 21%; and photophobia, 21%. No patients had permanent complete vision loss. Conclusions Dose modification managed ocular symptoms, decreased eye examination findings, and allowed patients the clinical benefit gained from continuing belamaf treatment. Funding GSK (Study 205678, NCT03525678). Drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. Presented at 26th Congress of the European Hematology Association (Lonial et al., 2021); submitted with permission of original authors.

MM-103: Relationship Between Corneal Exam Findings, Best-Corrected Visual Acuity (BCVA), and Ocular Symptoms in Patients with Relapsed or Refractory Multiple Myeloma (RRMM) Receiving Belantamab Mafodotin (GSK2857916; Belamaf)

<h3>Context</h3> Belamaf is a B-cell maturation antigen-targeting antibody-drug conjugate approved in the US and EU for the treatment of RRMM. Ocular events (OEs) during the DREAMM-2 trial (NCT03525678) included corneal exam findings (punctate keratopathy and microcyst-like epithelial changes), BCVA changes, and ocular symptoms. Dose reductions or delays based on corneal exam findings and BCVA were used to manage OEs. <h3>Objective</h3> To study relationships between exam findings, BCVA changes, and patient-reported ocular symptoms in a post hoc analysis to explore if BCVA changes and symptoms alone could guide dosing. <h3>Methods</h3> Patients receiving single-agent belamaf (2.5 mg/kg) had eye evaluations (including a corneal exam and BCVA assessment of Snellen visual acuity) performed by ophthalmologists at baseline and prior to each dose. Changes in the corneal epithelium (Ker) and BCVA were assessed per protocol-defined criteria and assessment of grade was based on the worse eye. BCVA grading was relative to baseline. Patient-reported ocular symptoms were reported per the Common Terminology Criteria for Adverse Events. <h3>Results</h3> In 12.5% of eye evaluations Grade 3–4 Ker was associated with minimal or no (Grade ≤1) BCVA changes. When patient-reported ocular symptoms were also considered, only 7.5% of evaluations found Grade 3–4 Ker with Grade ≤1 BCVA changes or ocular symptoms. Mild or no (Grade ≤2) Ker was associated with Grade ≤1 BCVA changes in 59.5% of evaluations, or in 38.8% of evaluations with no ocular symptoms reported. Overall, Grade 3–4 Ker were found in 24.9% of evaluations; by contrast, patients had Grade 2–4 BCVA changes or ocular symptoms in 53.7% of evaluations. <h3>Conclusions</h3> BCVA changes and ocular symptoms should be further investigated to determine if they can be used as alternatives (e.g., frequency of eye examinations based on symptoms) for the management of belamaf dosing to potentially reduce the burden on patients and healthcare professionals. <h3>Funding</h3> GlaxoSmithKline (205678; NCT03525678). Drug linker technology licensed from Seagen Inc.; mAb produced using POTELLIGENT Technology licensed from BioWa. © 2021 American Society of Clinical Oncology, Inc. Reused with permission. This abstract was accepted and previously presented at the 2021 ASCO Annual Meeting. All rights reserved.

MM-392: Belantamab Mafodotin (Belamaf; GSK2857916) US Expanded Access Program (EAP) for Heavily Pre-Treated Patients with Relapsed/Refractory Multiple Myeloma (RRMM): Baseline Characteristics

<h3>Context</h3> The belamaf US EAP (NCT03763370) provided medicine access to patients unable to participate in a clinical trial prior to regulatory agency approval. <h3>Objective</h3> To obtain insight from the belamaf EAP on patient types potentially eligible for belamaf treatment in a real-world setting. <h3>Methods</h3> The EAP included patients with RRMM who received ≥3 prior lines of therapy and were refractory to proteasome inhibitors, immunomodulatory agents, and anti-CD38 monoclonal antibody. Patients received belamaf 2.5 mg/kg Q3W. Safety was closely monitored, and dose delays/reductions were permitted to manage adverse events. Treating physicians re-evaluated eligibility to continue belamaf at each treatment cycle; patients could withdraw at any time. The EAP closed following US FDA approval of belamaf. We report baseline characteristics from included patients. <h3>Results</h3> In this preliminary analysis (as of 3 Feb 2021), 263 patients were screened; 235 were treated with ≥1 dose of belamaf and were included in this analysis. The most common reasons for withdrawal were lack of continued clinical benefit (n=37) and death (n=21); 23 patients continued therapy beyond closure of the program. Of 235 treated patients, 137 (58.3%) were male. Median age was 66 years, with 106 patients (45.1%) aged <65 years, 86 (36.6%) 65–75 years, and 39 (16.6%) >75 years. Two hundred eighteen patients had further medical history available; 61 (26.0%) had prior treatment-related toxicities, 10 (4.3%) had active renal disease, and 5 (2.1%) had undergone allogeneic stem cell transplant. Two hundred twenty-one patients had ocular baseline characteristics reported; these included prior glaucoma diagnosis (single-eye, n=16 [6.8%]), prior cataract diagnosis (single, n=124 [52.8%]), history of cataract surgery (single, n=66 [28.1%]), and prior dry eye diagnosis (n=46 [19.6%]). The most common prior anticancer therapies included bortezomib, lenalidomide, pomalidomide, and carfilzomib. Data cleaning is ongoing for this study. <h3>Conclusions</h3> This EAP provides insights from a real-world population of US belamaf-treated patients, which, in addition to data from the pivotal DREAMM-2 study, may help practitioners identify patients potentially eligible for belamaf treatment. <h3>Funding</h3> GlaxoSmithKline (213304). Drug linker technology licensed from Seagen Inc.; monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa.

Halogenation at the Phenylalanine Residue of Monomethyl Auristatin F Leads to a Favorable cis/trans Equilibrium and Retained Cytotoxicity.

Halogenation can be utilized for the purposes of labeling and molecular imaging, providing a means to, e.g., follow drug distribution in an organism through positron emission tomography (PET) or study the molecular recognition events unfolding by nuclear magnetic resonance (NMR) spectroscopy. For cancer therapeutics, where often highly toxic substances are employed, it is of importance to be able to track the distribution of the drugs and their metabolites in order to ensure minimal side effects. Labeling should ideally have a negligible disruptive effect on the efficacy of a given drug. Using a combination of NMR spectroscopy and cytotoxicity assays, we identify a site susceptible to halogenation in monomethyl auristatin F (MMAF), a widely used cytotoxic agent in the antibody–drug conjugate (ADC) family of cancer drugs, and study the effects of fluorination and chlorination on the physiological solution structure of the auristatins and their cytotoxicity. We find that the cytotoxicity of the parent drug is retained, while the conformational equilibrium is shifted significantly toward the biologically active trans isomer, simultaneously decreasing the concentration of the inactive and potentially disruptive cis isomer by up to 50%. Our results may serve as a base for the future assembly of a multifunctional toolkit for the assessment of linker technologies and exploring bystander effects from the warhead perspective in auristatin-derived ADCs.

Abstract 1842: CD79b targeting ADC with superior pharmacokinetic profile and anti-tumor activity

Abstract Araris' site-specific conjugation technology is improving the safety and efficacy of ADCs without antibody engineering. Our technology is using transglutaminase for site-specific enzymatic payload conjugation to ‘off-the-shelf' antibodies, i.e., without the need to reduce or engineer the antibody. The functionalization takes place site-specifically and stoichiometrically (drug-to-antibody ratio, DAR = 2) at the glutamine residue Q295 in the Fc-part of antibodies. The resulting ADCs show favorable biophysical properties such as high solubility and stability. Additionally, initial data show that linker conjugation does not interfere with Fc-gamma receptor and FcRn binding. Using native polatuzumab (non-engineered, same antibody sequence as present in approved polatuzumab-vedotin) as the targeting antibody and monomethyl auristatin E (MMAE) as payload, we generated within 24 hours highly homogeneous and pure ADCs with a well-defined DAR of 1.9 (LC-MS). Size exclusion chromatography analysis showed a highly monomeric ADC product (&amp;gt; 96% monomer content) that remained stable under stressed conditions at elevated temperatures. In in-vitro assays our ADCs demonstrated potent cytotoxicity in four tested cell-lines, similar to the approved polatuzumab-vedotin (Polivy®). Moreover, our anti-CD79b ADC (termed ARC-01) is highly stable in mouse, cynomolgus and human sera and is resistant to mouse Ces1c cleavage but is cleaved by the lysosomal human Cathepsin B. Most importantly, the resulting ADC is extremely stable as shown in pharmacokinetic studies in mice demonstrating a very long exposure comparable to the unmodified polatuzumab antibody and twice as long as the approved polatuzumab-vedotin (half-life 10d vs 5d). Most importantly, the in vivo efficacy of our ARC-01 (DAR 1.9) as compared with approved polatuzumab-vedotin (DAR 3.5) was assessed in the Granta-519 tumor model. Animals received a single injection of 0.53 or 2.1 mg/kg polatuzumab-vedotin (Polivy®) and either 0.53, 1 or 2.1 mg/kg of ARC-01. ARC-01 provided equal tumor growth inhibition and survival at about half the payload dose relative to polatuzumab-vedotin (comparison of the 2mg/kg doses and 0.53 mg/kg doses). At an approximately equal payload dose, ARC-01 treatment led to a greater antitumor efficacy and a considerable survival advantage with 6/8 complete tumor remissions over polatuzumab-vedotin with 0/8 complete tumor remission (comparison of the 0.53mg/kg dose of polatuzumab-vedotin and 1mg/kg dose of ARC-01). These encouraging results obtained so far indicate that our linker technology a) allows for fast (&amp;lt; 24 hours) and straightforward manufacturing of ADCs without protein engineering efforts, b) results in ADCs with favorable biophysical properties and a clear defined drug-to-antibody ratio, and c) enables the generation of highly potent and stable, thus safer, next-generation ADCs. Citation Format: Philipp René Spycher, Philipp Probst, Romain Bertrand, Ramona Stark, Roger Santimaria, Dragan Grabulovski, Isabella Attinger-Toller. CD79b targeting ADC with superior pharmacokinetic profile and anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1842.

Abstract 50: Targeting Sialyl-Thomsen nouveau (STn) antigen with the SGN-STNV antibody-drug conjugate is effective in preclinical studies

Abstract Targeting glyco-epitopes with antibody-drug conjugates (ADCs) provides a unique advantage as multiple cell surface proteins expressing the same carbohydrate can be harnessed to deliver drug. Sialyl-Thomsen nouveau (STn) is a tumor associated carbohydrate antigen that has historically been difficult to target with specificity. Using glycan array screening, h2G12 was identified as a highly specific human IgG1 antibody, that exclusively binds the STn glyco-epitope independent of protein backbone. Here we introduce SGN-STNV, an investigational antibody-drug conjugate (ADC) targeting monomethyl auristatin E (MMAE) to STn expressing tumor cells with the clinically validated vedotin linker technology. STn has restricted normal tissue expression and is expressed on various solid tumors including ovarian, non-small cell lung, gastric, and endometrial carcinomas. Our work shows correlation of enzyme ST6GALNAC1 expression with STn expression on tumors. Given the frequent O-glycosylation of mucins, we also confirmed high STn expression in mucinous subtypes of ovarian, pancreatic, colorectal, and lung adenocarcinomas. Previous reports have confirmed STn is found on mucins MUC1, MUC5A, and MUC16 (CA-125), as well as cell surface receptors CD44 and integrin β1. These proteins are known to play functional roles in tumor progression and, importantly for ADC delivery, they internalize well to deliver cytotoxic payload. We sought to identify other proteins that may contribute to cytotoxic activity of SGN-STNV and determined that additional surface receptors are tagged with STn. These receptors are internalized and likely contribute to SGN-STNV activity. After binding to STn, SGN-STNV is internalized into cells and releases the microtubule inhibitor MMAE to drive mitotic arrest, apoptosis, and to induce immunogenic cell death. SGN-STNV further mediates anti-tumor response through Fc-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). In preclinical xenograft studies, SGN-STNV monotherapy treatment leveraged h2G12 specificity and ability to target STn on multiple tumor associated proteins to drive durable tumor regressions. SGN-STNV was well tolerated in non-human primates (NHP), with no concerning target-mediated toxicities and a maximum tolerated dose similar to other vedotin-platform ADCs. In summary, the antibody specificity, unique mechanism of targeting a carbohydrate, anti-tumor activity, and tolerability provide a strong rationale for initiation of a phase I study to investigate the therapeutic potential of SGN-STNV. Citation Format: Alyssa Schwartz, Hector Rincon, Nanna Hansen, Robert Lawrence, Sarah Anderson, Nicole Blesie, Kerry Klussman, Angela Epp, Shyra Gardai, William Arthur. Targeting Sialyl-Thomsen nouveau (STn) antigen with the SGN-STNV antibody-drug conjugate is effective in preclinical studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 50.