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. Based on published phase 1 and 3 results for Moxe, the FDA approved Moxe for relapsed/refractory HCL in September of 2018. 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. To improve efficacy in HCL, we began a trial at NIH testing Moxe with rituximab (MoxeR), 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%. The primary endpoint of the MoxeR trial was safety, which was met after 13 patients were enrolled. To determine whether MoxeR was more effective than Moxe in achieving MRD-free CR, AstraZeneca (AZ) allowed additional patients to be enrolled with the NIH supplying the Rituximab biosimilar Ruxience. After enrolling a total of 18 patients, the MRD-free CR rate (defined by negative bone marrow flow cytometry and immunohistochemistry) was 72% for MoxeR, compared to 47% (30 of 64 evaluable patients) after Moxe alone, which was a significant difference (1-sided p=0.05, Fisher's exact). We proposed testing MoxeR as a method to eliminate MRD after therapy for indolent Non-Hodgkin's lymphoma (NHL), including follicular lymphoma (FL), marginal zone lymphoma (MZL), mantle cell lymphoma (MCL), and lymphoplasmacytic lymphoma (LPL). We found that MCL and MZL cells were sensitive to the cytotoxicity of Moxe like HCL cells. To make Moxe easier and safer to administer as an outpatient, we proposed testing MoxeR in HCL every 2 weeks rather than every other day for 3 doses on 4-week cycles. Unfortunately, AZ was not interested in developing Moxe further, returned the license to the NIH, and at this time another company is considering taking over development of this lifesaving therapy. 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, 1st line concurrent cladribine-rituximab (CDAR) eradicates MRD in 97%, vs 32% of patients with cladribine alone (CDA) (p0.0001). 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. 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. Cladribne with rituximab is a new option for 1st line HCL treatment in the NCCN guidelines. Once-relapsed HCL patients are continuing to be enrolled 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. Long-term data from the 20 patient-cohort of HCLv showed 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 which recently complete accrual showed both regimens as highly effective, particularly in eradicating MRD, albeit with chemotherapy toxicities. Targeted therapy for HCL. The BRAF V600E mutation is present in 80-90% of classic HCL. Those lacking V600E include those with unmutated IGHV4-34 immunoglobulin rearrangement, first described by our group in 2009. For the first time in HCL, we treated BRAF V600E+ HCL patients by inhibiting both BRAF with Dabrafenib and its downstream pathway MEK with Trametinib. This trial was part of a Novartis-sponsored multicenter registration trial in many different BRAF V600E+ histologies, and the HCL results were recently published. We also 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 HCL cases which are also BRAF WT, we began 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. We treated 20 of the 37 patients enrolled on the multicenter BTK inhibitor Ibrutinib study run by Ohio State University, and the published report showed low response rates but excellent progression-free survival (PFS). 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. In our trials, patients may receive rituximab or other CD20 Mab combined with of Binimetinib +/- Encorafenib if patients achieve MRD+ CR with Binimetinib +/- Encorafenib alone. Finally, the BCL-2 inhibitor Venetoclax was recently published by others to achieve responses in a few patients with relapsed/refractory HCL/HCLv, and after several years of negotiating with the Cancer Therapy Evaluation Program (CTEP) and recently with Abbvie-Genentech, we have been given approval to lead a multicenter trial of Venetoclax in HCL/HCLv. Laboratory research to study HCL/HCLv biology and treatment. 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 test MRD by RQ-PCR and next-gen sequencing (NGS). 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 and are studying 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.