Antibody-Based Treatment of Acute Myeloid Leukemia

Recent Advances in Material Technology for Leukemia Treatments

Leukemia is a widespread hematological malignancy characterized by an elevated white blood cell count in both the blood and the bone marrow. Despite notable advancements in leukemia intervention in the clinic, a large proportion of patients, especially acute leukemia patients, fail to achieve long-term remission or complete remission following treatment. Therefore, leukemia therapy necessitates optimization to meet the treatment requirements. In recent years, a multitude of materials have undergone rigorous study to serve as delivery vectors or direct intervention agents to bolster the effectiveness of leukemia therapy. These materials include liposomes, protein-based materials, polymeric materials, cell-derived materials, and inorganic materials. They possess unique characteristics and are applied in a broad array of therapeutic modalities, including chemotherapy, gene therapy, immunotherapy, radiotherapy, hematopoietic stem cell transplantation, and other evolving treatments. Here, an overview of these materials is presented, describing their physicochemical properties, their role in leukemia treatment, and the challenges they face in the context of clinical translation. This review inspires researchers to further develop various materials that can be used to augment the efficacy of multiple therapeutic modalities for novel applications in leukemia treatment.

Immunotherapy in AML: a brief review on emerging strategies

Acute myeloid leukemia (AML), the most common form of leukemia amongst adults, is one of the most important hematological malignancies. Epidemiological data show both high incidence rates and low survival rates, especially in secondary cases among adults. Although classic and novel chemotherapeutic approaches have extensively improved disease prognosis and survival, the need for more personalized and target-specific methods with less side effects have been inevitable. Therefore, immunotherapeutic methods are of importance. In the following review, primarily a brief understanding of the molecular basis of the disease has been represented. Second, prior to the introduction of immunotherapeutic approaches, the entangled relationship of AML and patient's immune system has been discussed. At last, mechanistic and clinical evidence of each of the immunotherapy approaches have been covered.

A general view of CD33+ leukemic stem cells and CAR-T cells as interesting targets in acute myeloblatsic leukemia therapy

Acute myeloblastic leukemia (AML) is the most frequent acute leukemia in adulthood with very poor overall survival rates. In the past few decades, significant progresses had led to the findings of new therapeutic approaches and the better understanding of the molecular complexity of this hematologic malignancy. Leukemic stem cells (LSCs) play a key role in the initiation, progression, regression, and drug resistance of different types of leukemia. The cellular and molecular characteristics of LSCs and their mechanism in the development of leukemia had not yet been specified. Therefore, determining their cellular and molecular characteristics and creating new approaches for targeted therapy of LSCs is crucial for the future of leukemia research. For this reason, the recognition of surface maker targets on the cell surface of LSCs has attracted much attention. CD33 has been detected on blasts in most AML patients, making them an interesting target for AML therapy. Genetic engineering of T cells with chimeric antigen receptor (CAR-T cell therapy) is a novel therapeutic strategy. It extends the range of antigens available for use in adoptive T-cell immunotherapy. This review will focus on CAR-T cell approaches as well as monoclonal antibody (mAB)-based therapy, the two antibody-based therapies utilized in AML treatment.

New and Emerging Targeted Therapies for Pediatric Acute Myeloid Leukemia (AML)

The relapse rate for children with acute myeloid leukemia (AML) remains high despite advancements in risk classification, multi-agent chemotherapy intensification, stem cell transplantation, and supportive care guidelines. Prognosis for this subgroup of children with relapsed/refractory AML remains poor. It is well known that the ceiling of chemotherapy intensification has been reached, limited by acute and chronic toxicity, necessitating alternative treatment approaches. In the last several years, our improved understanding of disease biology and critical molecular pathways in AML has yielded a variety of new drugs to target these specific pathways. This review provides a summary of antibody drug conjugates (ADCs), small molecule inhibitors, and tyrosine kinase inhibitors with an emphasis on those that are currently under clinical evaluation or soon to open in early phase trials for children with relapsed/refractory AML.

Identification of Nanobodies against the Acute Myeloid Leukemia Marker CD33

Nanobodies (Nbs) are the smallest antigen-binding, single domain fragments derived from heavy-chain-only antibodies from Camelidae. Among the several advantages over conventional monoclonal antibodies, their small size (12-15 kDa) allows them to extravasate rapidly, to show improved tissue penetration, and to clear rapidly from blood, which are important characteristics for cancer imaging and targeted radiotherapy. Herein, we identified Nbs against CD33, a marker for acute myeloid leukemia (AML). A total of 12 Nbs were generated against recombinant CD33 protein, out of which six bound natively CD33 protein, expressed on the surface of acute myeloid leukemia THP-1 cells. The equilibrium dissociation constants (KD) of these six Nbs and CD33 range from 4 to 270 nM, and their melting temperature (Tm) varies between 52.67 and 67.80 °C. None of these Nbs showed leukemogenicity activity in vitro. The selected six candidates were radiolabeled with 99mTc, and their biodistribution was evaluated in THP-1-tumor-bearing mice. The imaging results demonstrated the fast tumor-targeting capacity of the Nbs in vivo. Among the anti-CD33 Nbs, Nb_7 showed the highest tumor uptake (2.53 ± 0.69 % injected activity per gram (IA/g), with low background signal, except in the kidneys and bladder. Overall, Nb_7 exhibits the best characteristics to be used as an anti-CD33 targeting vehicle for future diagnostic or therapeutic applications.

Reinforcing the primary immunotherapy modulators against acute leukemia; monoclonal antibodies in AML

Recent therapeutic advances in cancer treatment recruit immune system potentiation against malignant cells. Numerous ongoing clinical trials on immunotherapy methods, either monotherapy or combination therapy, are investigating the impeding factors on the way of acute myeloid leukemia (AML) treatment. Due to the genetic diversity in AML progenitors, combining various strategies is more likely to be useful for improving patient outcomes. This review describes the details of applying monoclonal antibodies against AML, focusing on CD33, CD123, FLT3, CD45 and CD66 targeting. Furthermore, it clarifies the importance of immunotoxins, bispecific antibodies, chimeric antigen receptor (CAR)-T cells and T cell receptor-modified cells as reinforcing agents for monoclonal antibodies.

SS30, a novel thioaptamer targeting CD123, inhibits the growth of acute myeloid leukemia cells

AIMS

CD123 represents an important acute myeloid leukemia (AML) therapeutic target. CD123 aptamers may potentially serve as tumor-homing ligands with excellent affinity and specificity for AML targeted therapy, but their complexity, laborious preparation and nuclease digestion limited pharmacological application. The aim of this study was to develop the first CD123 thioaptamer to overcome these obstacles.

MAIN METHODS

Flow cytometry was utilized to assess the binding specificity, affinity and anti-nuclease ability of thioaptamer. CCK8, Annexin-V/DAPI, and colony forming assays were used to evaluate the anti-cancer ability of thioaptamer in vitro. The tumor volume, weights, survival rate, H&E staining of organs, and serum level of organ damage biomarkers of animal model were applied to investigate the anti-cancer ability of thioaptamer in vivo. Furthermore, we explored the binding mechanism between thioaptamer and CD123.

KEY FINDINGS

CD123 thioaptamer SS30 was able to bind to CD123 structure with high specificity in complex nuclease environment, the dissociation constant of 39.1 nM for CD123 peptide and 287.6 nM for CD123⁺ AML cells, while exhibiting minimal cross-reactivity to albumin. Furthermore, SS30 inhibited the proliferation and survival of AML cell lines and human AML blasts selectively in vitro (P < 0.01). In addition, SS30 prolonged the survival and inhibited tumor growth in a mouse xenograft tumor model in vivo. Of note, SS30 blocked the interaction between IL-3 and CD123, and decreased expression of p-STAT5 and p-AKT.

SIGNIFICANCE

The proliferation inhibition and nuclease resistance ability of SS30 made it as a more promising functional molecule for AML targeted therapy.

CD123 expression levels in 846 acute leukemia patients based on standardized immunophenotyping

BACKGROUND

While it is known that CD123 is normally strongly expressed on plasmacytoid dendritic cells and completely absent on nucleated red blood cells, detailed information regarding CD123 expression in acute leukemia is scarce and, if available, hard to compare due to different methodologies.

METHODS

CD123 expression was evaluated using standardized EuroFlow immunophenotyping in 139 pediatric AML, 316 adult AML, 193 pediatric BCP-ALL, 69 adult BCP-ALL, 101 pediatric T-ALL, and 28 adult T-ALL patients. Paired diagnosis-relapse samples were available for 57 AML and 19 BCP-ALL patients. Leukemic stem cell (LSC) data was available for 32 pediatric AML patients. CD123 expression was evaluated based on mean fluorescence intensity, median fluorescence intensity, and percentage CD123 positive cells.

RESULTS

EuroFlow panels were stable over time and between laboratories. CD123 was expressed in the majority of AML and BCP-ALL patients, but absent in most T-ALL patients. Within AML, CD123 expression was lower in erythroid/megakaryocytic leukemia, higher in NPM1 mutated and FLT3-ITD mutated leukemia, and comparable between LSC and leukemic blasts. Within BCP-ALL, CD123 expression was higher in patients with (high) hyperdiploid karyotypes and the BCR-ABL fusion gene. Interestingly, CD123 expression was increased in BCP-ALL relapses while highly variable in AML relapses (compared to CD123 expression at diagnosis).

CONCLUSIONS

Authors evaluated CD123 expression in a large cohort of acute leukemia patients, based on standardized and reproducible methodology. Our results may facilitate stratification of patients most likely to respond to CD123 targeted therapies and serve as reference for CD123 expression (in health and disease). © 2018 The Authors. Cytometry Part B: Clinical Cytometry published by Wiley Periodicals, Inc. on behalf of International Clinical Cytometry Society.

An immunological electrospun scaffold for tumor cell killing and healthy tissue regeneration

Antibody-based cancer immune therapy has attracted lots of research interest in recent years; however, it is greatly limited by the easy distribution and burst release of antibodies. In addition, after the clearance of the tissue, healthy tissue regeneration is another challenge for cancer treatment. Herein, we have developed a specific immunological tissue engineering scaffold using the agonistic mouse anti-human CD40 antibody (CD40mAb) incorporated into poly(l-lactide) (PLLA) electrospun fibers through the dopamine (PDA) motif (PLLA-PDA-CD40mAb). CD40mAb is successfully incorporated onto the surface of the electrospun fibrous scaffold, which is proved by immunofluorescence staining, and the PLLA-PDA-CD40mAb scaffold has an anti-tumor effect by locally releasing CD40mAb. Therefore, this immunological electrospun scaffold has very good potential to be developed as a powerful tool for localized tumor treatment, and this is the first to be reported in this area.

An Anti-CLL-1 Antibody-Drug Conjugate for the Treatment of Acute Myeloid Leukemia

PURPOSE

The treatment of acute myeloid leukemia (AML) has not significantly changed in 40 years. Cytarabine- and anthracycline-based chemotherapy induction regimens (7 + 3) remain the standard of care, and most patients have poor long-term survival. The reapproval of Mylotarg, an anti-CD33-calicheamicin antibody-drug conjugate (ADC), has demonstrated ADCs as a clinically validated option to enhance the effectiveness of induction therapy. We are interested in developing a next-generation ADC for AML to improve upon the initial success of Mylotarg.

EXPERIMENTAL DESIGN

The expression pattern of CLL-1 and its hematopoietic potential were investigated. A novel anti-CLL-1-ADC, with a highly potent pyrrolobenzodiazepine (PBD) dimer conjugated through a self-immolative disulfide linker, was developed. The efficacy and safety profiles of this ADC were evaluated in mouse xenograft models and in cynomolgus monkeys.

RESULTS

We demonstrate that CLL-1 shares similar prevalence and trafficking properties that make CD33 an excellent ADC target for AML, but lacks expression on hematopoietic stem cells that hampers current CD33-targeted ADCs. Our anti-CLL-1-ADC is highly effective at depleting tumor cells in AML xenograft models and lacks target independent toxicities at doses that depleted target monocytes and neutrophils in cynomolgus monkeys.

CONCLUSIONS

Collectively, our data suggest that an anti-CLL-1-ADC has the potential to become an effective and safer treatment for AML in humans, by reducing and allowing for faster recovery from initial cytopenias than the current generation of ADCs for AML.

IMGN779, a Novel CD33-Targeting Antibody-Drug Conjugate with DNA-Alkylating Activity, Exhibits Potent Antitumor Activity in Models of AML

The myeloid differentiation antigen CD33 has long been exploited as a target for antibody-based therapeutic approaches in acute myeloid leukemia (AML). Validation of this strategy was provided with the approval of the CD33-targeting antibody-drug conjugate (ADC) gemtuzumab ozogamicin in 2000; the clinical utility of this agent, however, has been hampered by safety concerns. Thus, the full potential of CD33-directed therapy in AML remains to be realized, and considerable interest exists in the design and development of more effective ADCs that confer high therapeutic indices and favorable tolerability profiles. Here, we describe the preclinical characterization of a novel CD33-targeting ADC, IMGN779, which utilizes a unique DNA-alkylating payload to achieve potent antitumor effects with good tolerability. The payload, DGN462, is prototypical of a novel class of purpose-created indolinobenzodiazeprine pseudodimers, termed IGNs. With low picomolar potency, IMGN779 reduced viability in a panel of AML cell lines in vitro Mechanistically, the cytotoxic activity of IMGN779 involved DNA damage, cell-cycle arrest, and apoptosis consistent with the mode of action of DGN462. Moreover, IMGN779 was highly active against patient-derived AML cells, including those with adverse molecular abnormalities, and sensitivity correlated to CD33 expression levels. In vivo, IMGN779 displayed robust antitumor efficacy in multiple AML xenograft and disseminated disease models, as evidenced by durable tumor regressions and prolonged survival. Taken together, these findings identify IMGN779 as a promising new candidate for evaluation as a novel therapeutic in AML. Mol Cancer Ther; 17(6); 1271-9. ©2018 AACR.

Gene-modified NK-92MI cells expressing a chimeric CD16-BB-ζ or CD64-BB-ζ receptor exhibit enhanced cancer-killing ability in combination with therapeutic antibody

Natural killer (NK) cells play a pivotal role in monoclonal antibody-mediated immunotherapy through the antibody-dependent cell-mediated cytotoxicity (ADCC) mechanism. NK-92MI is an interleukin-2 (IL-2)-independent cell line, which was derived from NK-92 cells with superior cytotoxicity toward a wide range of tumor cells in vitro and in vivo. Nonetheless, the Fc-receptor (CD16) that usually mediates ADCC is absent in NK-92 and NK-92MI cells. To apply NK-92MI cell-based immunotherapy to cancer treatment, we designed and generated two chimeric receptors in NK-92MI cells that can bind the Fc portion of human immunoglobulins. The construct includes the low-affinity Fc receptor CD16 (158F) or the high-affinity Fc receptor CD64, with the addition of the CD8a extracellular domain, CD28 transmembrane domains, two costimulatory domains (CD28 and 4-1BB), and the signaling domain from CD3ζ. The resulting chimeric receptors, termed CD16-BB-ζ and CD64-BB-ζ, were used to generate modified NK-92MI cells expressing the chimeric receptor, which were named NK-92MI^hCD16 and NK-92MI^hCD64 cells, respectively. We found that NK-92MI^hCD16 and NK-92MI^hCD64 cells significantly improved cytotoxicity against CD20-positive non-Hodgkin's lymphoma cells in the presence of rituximab. These results suggest that the chimeric receptor-expressing NK-92MI cells may enhance the clinical responses to currently available anticancer monoclonal antibodies.