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. 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. Development of anti-CD22 recombinant immunotoxins for CD22+ B-cell malignancies. We reported phase 1 and 3 results of Moxe, both from international multicenter studies. In phase 1, no dose limiting toxicity (DLT) was observed, but two patients had grade 2 hemolytic uremic syndrome (HUS), a syndrome with transient renal insufficiency and thrombocytopenia. Of the 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%. 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 in NIH testing Moxe with rituximab, the latter to decrease immunogenicity and to help kill HCL cells and shorten the time to 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 years, cladribine alone, or less commonly pentostatin alone, has been the standard 1st and 2nd line treatment of HCL, but is non-curative 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), and delayed rituximab, when needed for MRD in blood, 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, with 6 more patients left to fill accrual. In the poor prognosis HCL variant (HCLv), concurrent rituximab + cladribine is highly effective, with our published report supporting this combination as a new standard of care for early HCLv. We have completed the 20 patient-cohort of HCLv and at ASH 2019 reported a 95% CR rate, and 80% MRD-free CR rate. To study pentostatin-rituximab and bendamustine-rituximab (BR) combinations in HCL prospectively, a randomized trial is ongoing in multiply relapsed HCL which will complete accrual with 1 more patient. Our report establishes BR as a highly effective combination, particularly in eradicating MRD. However, since these regimens contain chemotherapy-type toxicities, more preferred options include Moxe and other targeted therapies. 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 the poor prognosis IGHV4-34 immunoglobulin rearrangement, 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 will determine 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 19 of the 37 patients enrolled on the multicenter BTK inhibitor Ibrutinib study run by Ohio State University, and the manuscript was recently accepted by Blood. 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 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. This RQ-PCR test can detect 1 HCL cell in 1 million normal cells, and we are testing deep sequencing 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 #1 gene expressed more commonly 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.