Development of Recombinant Toxins to Treat Hematologic Malignancies

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

Overview. We focus on targeted therapy for hematologic malignancies, particularly hairy cell leukemia (HCL), and other new therapies for HCL. Moxetumomab pasudotox (Moxe) contains truncated Pseudomonas exotoxin (PE) fused to an anti-CD22 Fv fragment. Previously called HA22 or CAT-8015, it is an affinity-matured form of a previous molecule BL22 for targeting hematologic malignancies, particularly HCL. We test combinations of chemotherapy and rituximab to help determine the optimal therapy of newly diagnosed and multiply relapsed HCL, and to better understand the behavior of HCL in immunotoxin-treated patients. We also test small molecules as targeted therapy for HCL and poor-prognosis variants like HCLv. In the lab, we use clinical samples from patients to investigate treatment efficacy and toxicity, and to better understand the biology and pathogenesis of HCL/HCLv. Development of anti-CD22 recombinant immunotoxins for CD22+ B-cell malignancies. We reported multicenter phase 1 and 3 results for Moxe. Of 49 patients enrolled on the phase I trial, 33 received the highest dose level, 50 ug/Kg x3, and in this group the complete remission (CR) rate was 64% with overall response rate (ORR) 88%. We published that most of the evaluable CRs (11 of 20) were without minimal residual disease (MRD), using the highest sensitivity standard assay, bone marrow aspirate (BMA) flow cytometry. For the first time in HCL, we reported that eradication of MRD was associated with a significantly longer CR duration. A worldwide pivotal trial in 80 patients, including 26 at NIH, met its primary endpoint with a durable CR rate of 36%. The most important toxicities, reported earlier with BL22, included reversible capillary leak syndrome (CLS) and hemolytic uremic syndrome (HUS), the latter a combination of transient thrombocytopenia and renal insufficiency resolving without treatment. On 9/13/18 the FDA approved Moxe for patients with relapsed/refractory HCL, the first time in decades that a new treatment was approved for HCL and the first FDA approval for a recombinant immunotoxin. To improve efficacy in HCL, we began a trial at NIH testing Moxe with rituximab, the latter to decrease immunogenicity and to help kill HCL cells and to hasten MRD-free CR. We presented the first 9 patients at ASCO 2021, reporting an MRD-free CR rate of 78%. Development of MAb-chemotherapy combinations for early and relapsed/refractory HCL. For the past 30-35 years, cladribine alone, or less commonly pentostatin alone, was the standard 1st and 2nd line treatment of HCL, but without cure in most patients. To determine the value of rituximab added to cladribine, newly diagnosed or once-relapsed HCL patients were randomized to cladribine with either immediate or 6-month delayed rituximab, and MRD at 6 months and other time points measured. As published in 2020, for 68 purine-analog naive HCL patients randomized 1:1, 1st line concurrent cladribine-rituximab (CDAR) eradicates MRD in 97%, vs 32% of patients with cladribine alone (CDA) (p0.0001). In this protocol, delayed rituximab was given when MRD was detected in blood and eradicates MRD in 2/3 of patients with most MRD-free CRs persisting at a median follow-up of 6.5 years. Patients could get up to 2 courses of 8 weekly doses of Rituximab. Of 68 patients treated with either approach, only 1 progressed to the point of needing next treatment, vs 28% of 90 historical patients treated with CDA alone and followed until retreatment was needed for relapse (p0.0001). Thus, while CDAR is superior with respect to long-term MRD-free CR, CDA alone with delayed rituximab is also established as a new standard of care for treatment of newly diagnosed HCL. Once-relapsed HCL patients are continuing to be randomized on the trial. In the poor prognosis HCL variant (HCLv), concurrent rituximab + cladribine was highly effective, establishing CDAR as a new standard of care for early HCLv. We recently published long-term data from the 20 patient-cohort of HCLv showing a 95% CR rate, and 80% MRD-free CR rate. Eradication of MRD improved progression free survival (PFS) and overall survival (OS), and TP53 mutations in HCLv decreased PFS and OS. To study pentostatin-rituximab and bendamustine-rituximab (BR) combinations in HCL prospectively, a randomized trial showed both regimens as a highly effective combination, particularly in eradicating MRD, albeit with chemotherapy toxicities. Targeted therapy for HCL. Although the BRAF V600E mutation is thought to be present in 100% of classic HCL, we showed that up to 20% lack V600E (wild-type, WT), particularly those with unmutated IGHV4-34 immunoglobulin rearrangement, which characterizes a variant first described by our group in 2009. For the first time in HCL, we began treating BRAF V600E+ HCL patients by inhibiting both BRAF with Dabrafenib and its downstream pathway MEK with Trametinib. This trial is part of a Novartis-sponsored multicenter registration trial in many different BRAF V600E+ histologies, which completed accrual. As part of this trial, we treated several patients with anaplastic thyroid cancer (ATC), a rapidly fatal disease also expressing BRAF V600E, leading to the approval of Dabrafenib and Trametinib by the FDA for the treatment of ATC. To continue development of BRAF/MEK inhibition for HCL, we initiated a trial of BRAF inhibitor Encorafenib and MEK inhibitor Binimetinib in HCL. For HCLv, which is BRAF WT, and those more aggressive HCL cases which are also BRAF WT, we have initiated a trial of Binimetinib alone. As part of this trial, we are determining if response to Binimetinib depends on the presence of MEK mutations, which we have reported in about half of BRAF WT HCL/HCLv. Finally, we treated 20 of the 37 patients enrolled on the multicenter BTK inhibitor Ibrutinib study run by Ohio State University, and the report published. While agents targeting BRAF, MEK and BTK generally do not eliminate MRD, they can achieve regression of nodal disease and may be useful as a bridge to Moxe or Moxe-R which can then eliminate MRD. Laboratory research with other therapies for hematologic malignancies. To better target HCL/HCLv, new potential drugs are also being tested in cytotoxicity assays, including BRAF, MEK, BTK, and BCL-2 inhibitors. Using clinical samples from HCL/HCLv patients, we are sequencing immunoglobulin rearrangements (IgH) unique to each HCL patient, to study HCL biology and to design patient-specific PCR assays for MRD. The RQ-PCR test can detect 1 HCL cell in 1 million normal cells, and we are testing deep sequencing (MiSeq) for determining MRD as well. We are performing whole exome sequencing and RNA transcriptome analysis for HCLv and BRAF WT HCL samples to determine what causes disease in these variant cells. We have found genes which are characteristic of patients with HCL and/or HCLv, including Myf6 which as we published is the most common gene expressed in HCL compared to HCLv, and is expressed in 100% of HCL patients. Our work with this and other genes may shed light on pathogenesis of HCL/HCLv and possible new treatments for these disorders. We began several projects related to the COVID-19 pandemic. The first project, started very early in the COVID pandemic, was to study the humoral immune symptom via its immunoglobulin repertoire in otherwise healthy people acutely infected with COVID. The 2nd project was to study the humoral immune system in HCL patients infected with COVID with respect to time since their most recent treatment, and with respect to their normal B-cell *TRUNCATED*