Immunotoxins in the treatment of refractory hairy cell leukemia

Diagnosis and treatment of hairy cell leukemia as the COVID-19 pandemic continues

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, usually driven by the BRAF V600E mutation. For 30 years, untreated and relapsed HCL was successfully treated with purine analogs, but minimal residual disease (MRD) remained in most patients, eventually causing relapse. Repeated purine analogs achieve decreasing efficacy and increasing toxicity, particularly to normal T-cells. MRD-free complete remissions (CRs) are more common using rituximab with purine analogs in both 1^st-line and relapsed settings. BRAF inhibitors and Ibrutinib can achieve remission, but due to persistence of MRD, must be used chronically to prevent relapse. BRAF inhibition combined with Rituximab can achieve high MRD-free CR rates. Anti-CD22 recombinant immunotoxin moxetumomab pasudotox is FDA-approved in the relapsed setting and is unique in achieving high MRD-free CR rates as a single-agent. Avoiding chemotherapy and rituximab may be important in ensuring both recovery from COVID-19 and successful COVID-19 vaccination, an area of continued investigation.

Development of Recombinant Immunotoxins for Hairy Cell Leukemia

Hairy cell leukemia (HCL) is an indolent B-cell malignancy with excellent initial response to purine analogs pentostatin or cladribine, but patients are rarely, if ever, cured. Younger patients will usually need repeat chemotherapy which has declining benefits and increasing toxicities with each course. Targeted therapies directed to the BRAF V600E mutation and Bruton's tyrosine kinase may be helpful, but rarely eradicate the minimal residual disease (MRD) which will eventually lead to relapse. Moxetumomab pasudotox (Moxe) is an anti-CD22 recombinant immunotoxin, which binds to CD22 on HCL cells and leads to apoptotic cell death after internalization and trafficking of the toxin to the cytosol. Phase I testing achieved a complete remission (CR) rate of 57% in relapsed/refractory HCL. Most CRs were without MRD and eradication of MRD correlated with prolonged CR duration. Patients were often MRD-free after five years. Important mild-moderate toxicities included capillary leak and hemolytic uremic syndromes which could be prevented and managed conservatively. A phase 3 trial met its endpoint of durable CR with acceptable toxicity, leading to FDA approval of Moxe for relapsed/refractory HCL, under the name Lumoxiti. Moxe combined with rituximab is currently being evaluated in relapsed/refractory HCL to improve the rate of MRD-free CR.

Pore-Forming Proteins from Cnidarians and Arachnids as Potential Biotechnological Tools

Animal venoms are complex mixtures of highly specialized toxic molecules. Cnidarians and arachnids produce pore-forming proteins (PFPs) directed against the plasma membrane of their target cells. Among PFPs from cnidarians, actinoporins stand out for their small size and molecular simplicity. While native actinoporins require only sphingomyelin for membrane binding, engineered chimeras containing a recognition antibody-derived domain fused to an actinoporin isoform can nonetheless serve as highly specific immunotoxins. Examples of such constructs targeted against malignant cells have been already reported. However, PFPs from arachnid venoms are less well-studied from a structural and functional point of view. Spiders from the Latrodectus genus are professional insect hunters that, as part of their toxic arsenal, produce large PFPs known as latrotoxins. Interestingly, some latrotoxins have been identified as potent and highly-specific insecticides. Given the proteinaceous nature of these toxins, their promising future use as efficient bioinsecticides is discussed throughout this Perspective. Protein engineering and large-scale recombinant production are critical steps for the use of these PFPs as tools to control agriculturally important insect pests. In summary, both families of PFPs, from Cnidaria and Arachnida, appear to be molecules with promising biotechnological applications.

Authentic caring occasions for patients in hairy cell leukemia clinical trials

BACKGROUND

Rare diseases present challenges for patients, healthcare providers, and researchers. Rare disease communities exist for collaboration, dissemination of information, and to promote support for all community members. Patients with a rare disease desire to be supported through a rare disease community. Hairy cell leukemia (HCL) is a rare adult B-cell lymphocytic cancer that currently has no cure.

OBJECTIVES

Patients with relapsed or refractory HCL may need to consider participation in a clinical trial. The research nurse can initiate a planned caring occasion based on Watson's Theory of Human Caring. The purpose of the planned caring occasion for patients with HCL in clinical trials is to establish authentic intentional caring encounters between the research nurse and patients and meaningful caring encounters between patients.

OBSERVATIONS

Relapsed or refractory patients enrolled in an HCL clinical trial identify the trial as a microcommunity and the research nurse as an advocate and liaison. Patients seek support, empowerment, and the opportunity to connect with other patients with HCL. The planned caring occasion has the potential to provide a healing environment and facilitate shared experiences of living with HCL. The potential outcome for patients is strengthened holistic wellness.

Antibody-based therapeutics for the treatment of human B cell malignancies

The dynamic expression of various phenotypic markers during B cell development not only defines the particular stage in ontogeny but also provides the necessary growth, differentiation, maturation and survival signals. When a B cell at any given stage becomes cancerous, these cell surface molecules, intracellular signaling molecules, and the over-expressed gene products become favorite targets for potential therapeutic intervention. Various adaptive and adoptive immunotherapeutic approaches induce T cell and antibody responses against cancer cells, and successful remission leading to minimal residual disease has been obtained. Nonetheless, subsequent relapse and development of resistant clones prompted further development and several novel strategies are evolving. Engineered monoclonal antibodies with high affinity and specificity to target antigens have been developed and used either alone or in combination with chemotherapeutic drugs. They are also used as vehicles to deliver cytotoxic drugs, toxins, or radionuclides that are either directly conjugated or encapsulated in liposomal vesicles. Likewise, genetically engineered T cells bearing chimeric antigen receptors are used to redirect cytotoxicity to antigen-positive target cells. This review describes recent advancements in some of these adoptive immunotherapeutic strategies targeting B cell malignancies.

B-cell prolymphocytic leukemia and hairy cell leukemia: new advances in biology and treatment

SUMMARY B-cell prolymphocytic leukemia and hairy cell leukemia are mature lymphoid neoplasms recognized by WHO classification as distinct entities. The diagnosis relies on a constellation of clinical and laboratory features. B-cell prolymphocytic leukemia is a rare disease that lacks a genetic signature and represents a challenge to clinicians, due to the limited information on its pathogenesis, the difficulty of setting up prospective clinical trials and its refractoriness to treatments used in other chronic lymphoid neoplasms. By contrast, major advances have taken place in the understanding of the pathogenesis of hairy cell leukemia, as well as in the therapeutic armamentarium available for this disease. In this review, data will be presented on the natural history, pathogenesis, diagnosis and current therapies for these two leukemias.

Renal excretion of recombinant immunotoxins containing pseudomonas exotoxin

Recombinant immunotoxins BL22 (CAT-3888) and LMB-2, composed of Fv fragments of anti-CD22 and CD25 MAbs, respectively, have produced major responses in patients with hematologic malignancies, and are also associated with renal toxicity, particularly with BL22. Characterization of the renal excretion of recombinant immunotoxins, which have 2-4 h half-lives in plasma, has not been reported in humans. To study the renal excretion of recombinant immunotoxins, urine from patients treated with BL22 was collected and the recombinant protein visualized after trichloroacetic acid (TCA) precipitation or anion exchange chromatography. BL22 viewed by immunoblot was found in the urine of patients within 8 h after dosing as an intact protein, and progressively degraded to fragments of <20 kDa within 1 day. We studied the stability of BL22 and LMB-2 added to urine at different time points and pH. When exposed to urine ex vivo, BL22 time-dependent proteolysis was similar to that observed in treated patients. By N-terminal sequencing, proteolysis was documented at positions 348-349 and 350-351 of BL22, and 339-340 and 341-342 of LMB-2, and other proteolytic sites were observed as well. Our data suggest that BL22 is excreted into the urine in a potentially cytotoxic form, even after its plasma level declines, and may remain intact long enough to cause renal toxicity.

Molecular insight into the biology and clinical course of hairy cell leukemia utilizing immunoglobulin gene analysis

The B cell receptor (BCR) is the functional distinguishing unit that defines any B cell. Immunoglobulin gene (IG) status is preserved in the neoplastic B cell clone and can provide an indicator of the maturation stage reached by the B cell prior to transformation. In hairy cell leukemia (HCL), several pieces of data from IG analysis provide clear hints regarding the cell of origin and the ongoing selective interactions of the tumor BCR with environmental stimuli. HCLs have variable levels of IG somatic mutations, and continue somatic mutations at low levels as well as IG class switching after transformation. More recent data also show the occurrence of selective events in the light chain of the BCR, suggesting a dominant role for IG status in the pathogenesis of HCL. Moreover, it has recently emerged that an unmutated status of the HCL IG can be associated with failure to respond to cladribine, genetic abnormalities indicative of poor outcome, and aggressive disease. These observations suggest that IG analysis may have biological and prognostic relevance in HCL and merits further characterization.

On the interaction of Clostridium perfringens enterotoxin with claudins

Clostridium perfringens causes one of the most common foodborne illnesses, which is largely mediated by the Clostridium perfringens enterotoxin (CPE). The toxin consists of two functional domains. The N-terminal region mediates the cytotoxic effect through pore formation in the plasma membrane of the mammalian host cell. The C-terminal region (cCPE) binds to the second extracellular loop of a subset of claudins. Claudin-3 and claudin-4 have been shown to be receptors for CPE with very high affinity. The toxin binds with weak affinity to claudin-1 and -2 but contribution of these weak binding claudins to CPE-mediated disease is questionable. cCPE is not cytotoxic, however, it is a potent modulator of tight junctions. This review describes recent progress in the molecular characterization of the cCPE-claudin interaction using mutagenesis, in vitro binding assays and permeation studies. The results promote the development of recombinant cCPE-proteins and CPE-based peptidomimetics to modulate tight junctions for improved drug delivery or to treat tumors overexpressing claudins.

How I treat hairy cell leukemia

The description of hairy cell leukemia as a specific clinical entity was published 50 years ago. The clinical outcome for patients was hampered by ineffective chemotherapy, and splenectomy was the major therapeutic approach to improve peripheral blood counts. The median survival after diagnosis was 4 years. With the introduction of alpha-interferon in 1984, marked improvements in patient responses were observed. Shortly thereafter, the introduction of the purine nucleoside analogs transformed this disease into a highly treatable form of leukemia, and patients with the classic form of this rare leukemia now have a near-normal life expectancy. However, other clinical entities mimicking this disease do not respond; thus, accurate diagnosis is important. Immunophenotypic features in classic hairy cell leukemia show that the leukemic cells express CD11c, CD25, CD103, and CD123 and display bright CD20. Despite the high percentage of durable complete remissions with modern therapy, the long-term disease-free survival curves have not reached a plateau. Many patients who achieve a complete remission by morphologic criteria have minimal residual disease demonstrable by either flow cytometry or immunohistochemical staining, and this population may be at higher risk for earlier relapse. Continued clinical research is essential to optimize therapy for this disease.

Initial characterization of an immunotoxin constructed from domains II and III of cholera exotoxin

Immunotoxins are antibody-toxin fusion proteins under development as cancer therapeutics. In early clinical trials, immunotoxins constructed with domains II and III of Pseudomonas exotoxin (termed PE38), have produced a high rate of complete remissions in Hairy Cell Leukemia and objective responses in other malignancies. Cholera exotoxin (also known as cholix toxin) has a very similar three-dimensional structure to Pseudomonas exotoxin (PE) and when domains II and III of each are compared at the primary sequence level, they are 36% identical and 50% similar. Here we report on the construction and activity of an immunotoxin made with domains II and III of cholera exotoxin (here termed CET40). In cell viability assays, the CET40 immunotoxin was equipotent to tenfold less active compared to a PE-based immunotoxin made with the same single-chain Fv. A major limitation of toxin-based immunotoxins is the development of neutralizing antibodies to the toxin portion of the immunotoxin. Because of structure and sequence similarities, we evaluated a CET40 immunotoxin for the presence of PE-related epitopes. In western blots, three-of-three anti-PE antibody preparations failed to react with the CET40 immunotoxin. More importantly, in neutralization studies neither these antibodies nor those from patients with neutralizing titers to PE38, neutralized the CET40-immunotoxin. We propose that the use of modular components such as antibody Fvs and toxin domains will allow a greater flexibility in how these agents are designed and deployed including the sequential administration of a second immunotoxin after patients have developed neutralizing antibodies to the first.

Hairy cell leukemias with unmutated IGHV genes define the minor subset refractory to single-agent cladribine and with more aggressive behavior

Hairy cell leukemia (HCL) is generally responsive to single-agent cladribine, and only a minority of patients are refractory and with poor prognosis. HCLs generally express mutated (M) and, in a minority, unmutated (UM) IGHV. In a multicenter clinical trial in newly diagnosed HCL, we prospectively investigated clinical and molecular parameters predicting response and event-free survival after single-agent cladribine. Of 58 HCLs, 6 expressed UM-IGHV (UM-HCL) and 52 M-IGHV (M-HCL). Beneficial responses were obtained in 53 of 58 patients (91%), whereas treatment failures were observed in 5 of 58 patients (9%). Failures were associated significantly with UM-IGHV (5 of 5 failures vs 1 of 53 beneficial responses had UM-IGHV, P < .001), leukocytosis (3 of 5 vs 3 of 53, P = .006), and bulky spleen (4 of 5 vs 4 of 53, P < .001). The UM-HCL not benefiting from cladribine characteristically had bulky spleen (4 of 5, 80%), leukocytosis (3 of 5, 60%), and TP53 defects (2 of 5, 40%), and progressed rapidly after first treatment (median event-free survival, 7.5 months). Our data suggest that UM-HCLs identify the minor subgroup failing cladribine treatment and with more aggressive disease. High incidence of TP53 dysfunction indicates a potential mechanism of resistance to cladribine in the UM-HCL group. Overall, our data provide new molecular elements relevant for treatment concerns in HCL.

Monoclonal antibodies in therapy of solid tumors

Monoclonal antibodies have become increasingly used therapeutic agents for the treatment of solid cancer. Many are now being tested as components of adjuvant or first-line therapies to assess their efficacy in improving or prolonging survival. Selected unconjugated antibodies can exert clinically significant antitumor effects in many cancers. Antibody conjugates have been used to deliver toxic principles, such as radioactive particles, chemotherapeutic agents, and catalytic toxins, with increasing success in clinical trials.

Emerging drugs for rarer chronic lymphoid leukemias

BACKGROUND

Rarer indolent lymphoid leukemias include well defined mature B-cell and T-cell neoplasm with widely varying natural history and specific morphological, immunophenotypic and molecular characteristics. Among these are prolymphocytic leukemia (PLL), hairy cell leukemia (HCL) and its variants, large granular lymphocyte leukemia (LGLL) and adult T-cell leukemia/lymphoma (ATLL).

OBJECTIVE

To present current therapies and emerging drugs potentially useful in the treatment of rarer chronic lymphoid leukemias.

METHODS

After searching MEDLINE, PubMed and the Current Contents database, and conference proceedings from the previous 3 years of the American Society of Hematology (ASH), the European Society of Hematology (EHA) and the American Society of Clinical Oncology (ASCO) were searched manually; articles written in English and additional relevant publications were then selected.

RESULTS/CONCLUSION

New drugs including monoclonal antibodies (mAbs), new purine analogs, small molecules targeting specific molecular targets and other agents are included. Future research should focus on the novel therapeutic strategies based on the molecular pathogenic mechanisms and the development of new targeted therapies for each distinct chronic lymphoid leukemia.