Development of Recombinant Toxins to Treat Hematologic Malignancies

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

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 answer questions relevant to the optimal therapy of newly diagnosed and multiply relapsed HCL, and to better understand the behavior of HCL in immunotoxin-treated patients. 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 I results of Moxe in 49 patients at 5-50 ug/Kg every other day for 3 doses (QOD x3). Complete remissions (CRs) were observed in 28 (57%), with overall response rate (ORR) 86%. No dose limiting toxicity (DLT) was observed. Two patients had grade 2 HUS, a syndrome with transient renal insufficiency and thrombocytopenia, but milder than HUS with BL22. 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 CR rate was 64% with ORR 88%. As published, we found 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 completed accrual of 80 patients, including 26 at NIH and 1-6 at many centers worldwide. The primary endpoint was met with a durable CR rate of 24 (30%). Most of the CRs were without MRD; for this trial, bone marrow biopsy immunohistochemistry was used for MRD. 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, a trial is beginning soon at NIH testing Moxe with rituximab, the latter to decrease immunogenicity and to help kill HCL cells and shorten the time to MRD-free CR. Once the safety of this combination is known, we plan to include patients with the poor-prognosis HCL variant (HCLv), who compared to classic HCL patients have poorer response to chemotherapy and worse overall survival, but still strongly express CD22 on their HCLv cells. Since the tumor burden in HCLv patients is usually too extensive and fast-growing to respond well to Moxe, we plan to alter the protocol to allow them to be treated when disease burden is minimal and cytopenias have not yet developed. The next step will be to use the Moxe-rituximab combination, possibly in combination with the Bruton's tyrosine kinase inhibitor acalabrutinib, to treat patients with follicular, marginal zone, and mantle-cell lymphoma who have low-level residual disease after therapy and are at high risk for progression. 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 are randomized to cladribine with either immediate or 6-month delayed rituximab, and MRD at 6 months and other time points measured. For newly diagnosed HCL patients, concurrent cladribine + rituximab (CDAR) is highly effective in eradicating MRD, and delayed rituximab, when needed, usually eradicates MRD. Long-term follow-up will determine if concurrent CDAR results prevents or delays the time for additional therapy or leads of cure of HCL. Once-relapsed HCL patients are continuing to be randomized on the trial. 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 are reporting the results, showing 95% CR rate, and 80% MRD-free. To study pentostatin-rituximab and bendamustine-rituximab (BR) combinations in HCL prospectively, a randomized trial is ongoing in multiply relapsed HCL. 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 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 have 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 are preparing 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 are preparing 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 have treated 14 patients with the BTK inhibitor Ibrutinib as part of a multicenter CTEP/Pharmacyclics trial run by Ohio State University. A manuscript is currently being submitted showing major responses. 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 recombinant immunotoxins and other therapies for hematologic malignancies. In collaboration with the multiple myeloma group at NCI and Dr. Ira Pastan's lab, we are working towards developing the anti-B-cell maturation antigen (BCMA) Fab recombinant immunotoxin LMB-70 for a clinical trial in patients with relapsed/refractory multiple myeloma (MM). At the current time, we are investigating methods in the lab to improve the expression of BCMA on MM cells. To better target HCL/HCLv new potential drugs are also being tested in cytotoxicity assays, including BRAF, MEK, BTK, BET, BCL-2, HDAC and PI3K 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, and our work may shed light on the pathogenesis and possible new treatments for these disorders.