BACKGROUND Extracorporeal photopheresis (ECP) has been approved for the treatment of advanced cutaneous T‐cell lymphoma since 1988. While the precise mechanisms resulting in clinical effects are not fully understood, the photoactivation of mononuclear cells (MNCs) using ultraviolet A (UVA) light and methoxsalen is believed to be the predominant initiating process. The effects of MNC passage through the instrument without photoactivation are unknown. The objective of this study was to evaluate the effect of cell processing through the photopheresis instruments on MNCs. STUDY DESIGN AND METHODS Fourteen healthy male subjects underwent one simulated ECP procedure without reinfusion of buffy coats (BCs) in a two‐center, open‐label, prospective trial. Baseline peripheral blood BC, apheresis‐separated untreated BC (BC1), and photoactivated BC (BC2) were evaluated in culture for viability by dye exclusion, apoptosis by annexin V binding, and cell proliferation response to phytohemagglutinin (PHA) stimulation by bromodeoxyuridine (BrdU) incorporation. RESULTS Photoactivation (BC2) resulted in 88% expression of annexin V by Day 1 of culture compared with 37 and 39% for baseline and untreated BC1. Cell viability by propidium iodide exclusion was reduced to 10% in BC2 on Day 1 versus 65 and 60% for baseline and BC1. The proliferative response to PHA stimulation was 97% inhibited in the photoactivated BC2. CONCLUSIONS These results demonstrate that the mechanical processes used for cell separation and processing of the BC in the absence of photoactivation do not induce a significant amount of apoptosis compared to the standard ECP with methoxsalen and UVA photoactivation.

PURPOSE: MT-3724, a novel engineered toxin body comprised of an anti-CD20 single-chain variable fragment genetically fused to Shiga-like Toxin A subunit, is capable of binding to and internalizing against CD20, inducing cell killing via permanent ribosomal inactivation. This study evaluated MT-3724 in patients with relapsed/refractory B-cell Non-Hodgkin lymphoma (r/rNHL). METHODS: This open-label, multiple-dose Phase 1a/b trial included a dose escalation in patients with r/rNHL according to a standard 3+3 design. Primary objectives were to determine the maximum tolerated dose (MTD) and pharmacokinetics/pharmacodynamics. In a dose expansion study at MTD in serum rituximab-negative patients with diffuse large B-cell lymphoma (DLBCL), primary objectives were safety, tolerability, and pharmacokinetics/pharmacodynamics. RESULTS: Twenty-seven patients enrolled. MTD was 50 µg/kg/dose with 6000 µg/dose cap. Thirteen patients experienced at least one Grade ≥3 treatment-related adverse events; the most common Grade ≥3 event was myalgia (11.1%). Two patients (75 µg/kg/dose) experienced Grade 2 treatment-related capillary leak syndrome. Overall objective response rate was 21.7%. In serum rituximab-negative patients with DLBCL or composite DLBCL (n=12), overall response rate was 41.7% (complete response, n=2; partial response, n=3). In patients with detectable baseline peripheral B-cells, treatment resulted in dose-dependent B-cell depletion. The proportion of patients with anti-drug antibodies (ADAs) increased during treatment and the majority appeared to be neutralizing based on an in vitro assay; nevertheless, tumor regression and responses were observed. CONCLUSIONS: MT-3724 demonstrated efficacy at the MTD in this population of previously treated patients with r/rDLBCL, with mild-to-moderate immunogenic safety events.

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Introduction: Diffuse large B-cell lymphoma (DLBCL) is the most common histologic subtype of non-Hodgkin Lymphoma (NHL) accounting for approximately 30-40% of NHL cases. Approximately 40% of all newly diagnosed DLBCL patients are either refractory or relapsed following initial response to therapy and represent a population with high unmet need for new therapeutic strategies to achieve or regain disease remission. Because of the near ubiquity and persistence of CD20 expression in B-cell malignancies, there is strong rationale to develop compounds with novel mechanisms of action targeting CD20. However, CD20's non-internalizing nature has, to date, leveraged only cytotoxic mechanisms such as antibody-dependent cellular cytotoxicity to which resistance can arise and has impeded the development of agents that internalize a cytotoxic payload. MT-3724 is a novel engineered toxin body designed to overcome this limitation by combining the specific target selectivity of a single chain variable fragment with the lethality of a genetically fused Shiga-like toxin A subunit that facilitates both internalization and cell killing by inactivating ribosomal protein synthesis. MT-3724 has been shown to specifically bind and kill CD20+ malignant human B-cells in vitro (IC50 <1 nM) and in CB17 SCID and PDX mice (Rajagopalan 2016; Huang 2018). As a direct-kill immunotoxin against CD20, MT-3724 has achieved clinical response in subjects with relapsed NHL regardless of acquired resistance to other treatments. Thus, MT-3724 could be a valuable addition to the armamentarium of treating DLBCL. Study Design and Methods: MT-3724 is being evaluated in this Phase 2 study as monotherapy (NCT02361346) in adult subjects with histologically confirmed, relapsed or refractory DLBCL. The primary objective is to determine the efficacy of MT-3724 as monotherapy based on the overall response rate (ORR) by the revised Lugano Classification for Lymphoma adjusted according to immunomodulatory therapy criteria (LYRIC), hereinafter referred to as "revised Lugano Criteria" (Cheson 2014, 2016). Overall response rate is defined as the proportion of subjects with either a complete response or a partial response as determined by independent, blinded central review. Secondary objectives include safety, progression‐free survival, investigator‐assessed ORR, duration of response, and overall survival as well as pharmacokinetics and pharmacodynamics, immunogenicity, and quality of life. To be eligible, patients must have histologically confirmed, relapsed or refractory DLBCL, have received at least 2 standard of care systemic NHL treatment regimens, and have measurable disease according to the revised Lugano criteria. Since rituximab and MT-3724 compete for the same CD20 domain, subjects must have serum rituximab levels < 500 ng/mL before the start of treatment to allow adequate binding of MT-3724. This single arm phase 2 study is being conducted in three stages, where the first two stages will follow the Simon two-stage optimal design [Simon 1989]. Subjects will be enrolled in successive cohorts with each cohort evaluated for efficacy before opening the subsequent cohort, toward a total sample size of 100 subjects. Subjects will receive MT-3724 as an IV infusion over 1 hour on Days 1, 3, 5, 8, 10 and 12 of a 21-day treatment cycle. All subjects will be treated with a 50 µg/kg/dose of MT-3724, which was the recommended Phase 2 dose, as determined in the Phase 1/1b portion of the trial. Sites are open and recruiting in the US, Canada, and Europe. Disclosures Persky: Sandoz: Consultancy; Debiopharm: Other: Member, Independent Data Monitoring Committee; Bayer: Consultancy; Morphosys: Other: Member, Independent Data Monitoring Committee. Musteata:Arensia EM: Other: Principal Investigator; Institute of Oncology: Employment. Strack:Molecular Templates, Inc.: Employment. Burnett:Molecular Templates, Inc.: Employment. Wilson:Molecular Templates, Inc.: Employment. Baetz:Bristol Meyers Squibb: Other: Advisory board; Merck: Other: Advisory board; Gilead: Other: Advisory board; Roche: Other: Advisory board.

Background: Engineered toxin bodies (ETBs), composed of an engineered Shiga-like Toxin A subunit genetically fused to an antibody-binding domain, can force receptor internalization, induce potent cell-kill via enzymatic and permanent inactivation of ribosomes, and may not be subject to resistance mechanisms of other targeted agents. MT-5111, a de-immunized 55 kD ETB targeting HER2 in solid tumors, also binds to an epitope distinct from trastuzumab and pertuzumab, which may permit combination strategies with other HER2 targeting agents. Methods: The primary objective is to determine maximum tolerated dose (MTD) of MT-5111 monotherapy in adult patients (pts) with advanced HER2+ solid tumors. Secondary objectives are PK, efficacy, and immunogenicity. Using a modified 3+3 design, the dose-escalation part of the study includes the following 7 cohorts: 0.5, 1, 2, 3, 4.5, 6.75, and 10 µg/kg. Three dose-expansion cohorts will follow for HER2+ breast cancer, gastro-esophageal cancer, and any other HER2+ tumors. All pts will receive MT-5111 weekly as a 30-min IV infusion in each 21-d treatment (tx) cycle (C) until disease progression (PD), unacceptable toxicity, death, or withdrawn consent (NCT04029922). Results: As of the data cut in December 2020, 16 pts were treated; cancer types included breast (n=6), gastric (n=1), colon (n=1), gallbladder (n=5), and other solid tumors (n=3). Mean age was 64 years (range, 34-78); 37.5% were male. Pts received a median of 4 prior lines of systemic therapies (range, 1-8). No G4 or G5 TEAEs occurred. Six pts had 11 G3 TEAEs; the most common were increased AST and dyspnea (both n=2). Three pts had tx-emergent serious adverse events (abdominal distension [n=1]; dyspnea [n=2]). Tx-related TEAEs occurred in 8 (50%) pts; the most common was fatigue (n=5, 31.3%) and all were ≤ grade 2 in nature, except for one grade 3 event of dyspnea. No cardiac TEAEs, clinically significant changes in cardiac biomarkers (troponin, electrocardiogram, left ventricular ejection fraction), or cases of capillary leak syndrome were observed. Fifteen pts discontinued with PD; 1 pt in cohort 5 (4.5 µg/kg) is on tx with stable disease. To date, no DLTs have been observed and the MTD has not been reached. One pt in cohort 2 (1 µg/kg) had resolution of all hepatic lesions (sub-centimeter lesions pre-tx) at the end of C8; however, the pt came off study due to clinical progression at the end of C10. PK data for the first 5 cohorts matched simulations based on non-human primate studies. Conclusions: MT-5111 was well tolerated with no clinically significant cardiotoxicity. Continued dose escalations are ongoing. Citation Format: Zev A. Wainberg, Monica M. Mita, Minal A. Barve, Erika P. Hamilton, Andrew J. Brenner, Frances Valdes, Daniel Ahn, Joleen Hubbard, Jason Starr, Christine Burnett, Joshua Pelham, Eric T. Williams, Banmeet S. Anand, Thomas Strack, Andrés Machado Sandri, Brian A. Van Tine. Phase 1 study of the novel immunotoxin MT-5111 in patients with HER-2+tumors [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 CT130.