CD33 is expressed on plasma cells of a significant number of myeloma patients, and may represent a therapeutic target

Radiolabeled Antibodies for Cancer Imaging and Therapy

Simple Summary

Monoclonal antibodies (mAbs) have the ability to specifically target tumor-cell antigens. This unique property has led to their use in the delivery of radioisotopes to tumor sites (scintigraphic imaging and radioimmunotherapy (RIT)). The choice of the radionuclide depends on its unique physical properties and intended use. Using radiolabeled mAbs with imaging techniques provides critical data that are essential for predicting side effects and determining an optimal antibody dose and treatment schedule. While RIT has been successful in the management of hematological malignancies, the treatment of solid tumors remains challenging. Various strategies are being investigated to improve the efficacy of RIT in solid tumors.

Abstract

Radioimmunoconjugates consist of a monoclonal antibody (mAb) linked to a radionuclide. Radioimmunoconjugates as theranostics tools have been in development with success, particularly in hematological malignancies, leading to approval by the US Food and Drug Administration (FDA) for the treatment of non-Hodgkin’s lymphoma. Radioimmunotherapy (RIT) allows for reduced toxicity compared to conventional radiation therapy and enhances the efficacy of mAbs. In addition, using radiolabeled mAbs with imaging methods provides critical information on the pharmacokinetics and pharmacodynamics of therapeutic agents with direct relevance to the optimization of the dose and dosing schedule, real-time antigen quantitation, antigen heterogeneity, and dynamic antigen changes. All of these parameters are critical in predicting treatment responses and identifying patients who are most likely to benefit from treatment. Historically, RITs have been less effective in solid tumors; however, several strategies are being investigated to improve their therapeutic index, including targeting patients with minimal disease burden; using pre-targeting strategies, newer radionuclides, and improved labeling techniques; and using combined modalities and locoregional application. This review provides an overview of the radiolabeled intact antibodies currently in clinical use and those in development.

Flow cytometric myeloma measurable residual disease testing in the era of targeted therapies

Therapies in myeloma are rapidly advancing with a host of new targeted therapies coming to market. While these drugs offer significant survival benefits and better side-effect profiles compared with conventional chemotherapeutics, they raise significant difficulties in monitoring post-therapy disease status by flow cytometry due to assay interference and/or selection of phenotypically different sub-clones. The principal culprit, anti-CD38 monoclonal antibodies, limits the ability to detect plasma cells based on classical CD38/CD45 gating. Other markers, such as CD138, are known to be suboptimal by flow cytometry. Various techniques have been proposed to overcome this problem. The most promising of these techniques has been the marker VS38c, a monoclonal antibody targeting an endoplasmic reticulum protein which has shown high sensitivity for plasma cells. Alternative techniques for gating plasma cells, while variably effective in the near term are already the subject of several targeted therapies rendering their usefulness limited in the longer term. Likewise, future targets of these therapies may render present aberrancy markers ineffective in MRD testing. These therapies pose challenges that must be overcome with new markers and novel panels in order for flow cytometric MRD testing to remain relevant.

225Ac-labeled CD33-targeting antibody reverses resistance to Bcl-2 inhibitor venetoclax in acute myeloid leukemia models

Purpose

Despite the availability of new drugs, many patients with acute myeloid leukemia (AML) do not achieve remission and outcomes remain poor. Venetoclax is a promising new therapy approved for use in combination with a hypomethylating agent or with low‐dose cytarabine for the treatment of newly diagnosed older AML patients or those ineligible for intensive chemotherapy. ²²⁵Actinium‐lintuzumab (²²⁵Ac‐lintuzumab) is a clinical stage radioimmunotherapy targeting CD33 that has shown evidence of single‐agent activity in relapsed/refractory AML. Increased expression of MCL‐1 is a mediator of resistance to venetoclax in cancer.

Experimental design

Here we investigated the potential for ²²⁵Ac‐lintuzumab‐directed DNA damage to suppress MCL‐1 levels as a possible mechanism of reversing resistance to venetoclax in two preclinical in vivo models of AML.

Results

We demonstrated that ²²⁵Ac‐lintuzumab in combination with venetoclax induced a synergistic increase in tumor cell killing compared to treatment with either drug alone in venetoclax‐resistant AML cell lines through both an induction of double‐stranded DNA breaks (DSBs) and depletion of MCL‐1 protein levels. Further, this combination led to significant tumor growth control and prolonged survival benefit in venetoclax‐resistant in vivo AML models.

Conclusions

There results suggest that the combination of ²²⁵Ac‐lintuzumab with venetoclax is a promising therapeutic strategy for the treatment of patients with venetoclax‐resistant AML.

Clinical trial of this combination therapy (NCT03867682) is currently ongoing.

Targeted Alpha-Particle Therapy for Hematologic Malignancies

The short range and high linear energy transfer of α-particles offer the potential for efficient tumor killing while sparing normal bystander cells. Hematologic malignancies are ideally suited to targeted α-particle therapy (TAT) due to easy accessibility of malignant cells in blood, bone marrow, lymph nodes, and spleen as well as their radiosensitivity. Most clinical trials using α-particle therapy for hematologic malignancies have focused on acute myeloid leukemia (AML); however, preclinical studies have shown activity against other diseases such as non-Hodgkin's lymphoma and multiple myeloma. To date, the short-lived radionuclide bismuth-213 (²¹³Bi) and its parent actinium-225 (²²⁵Ac) have been used clinically, but trials with astatinie-211 (²¹¹At) have recently begun, and thorium-227 (²²⁷Th) has shown promising preclinical results. Lintuzumab is a humanized monoclonal antibody that targets the cell surface antigen CD33, which is expressed on the vast majority of AML cells. Initial studies showed that ²¹³Bi-labeled lintuzumab had antileukemic activity and could produce remissions after partial cytoreduction with cytarabine. An initial phase I trial demonstrated that a single infusion of ²²⁵Ac-lintuzumab could be given safely at doses upto 111 kBq/kg with antileukemic activity across all dose levels. A second phase I study showed that fractionated-dose ²²⁵Ac-lintuzumab could be safely combined with low-dose cytarabine and produced objective responses in 28% of older patients with untreated AML. In a phase II study, treatment with ²²⁵Ac-lintuzumab monotherapy for a similar patient population resulted in remission in 69% of patients receiving two fractions of 74 kBq/kg and 22% of patients receiving two 55.5-kBq/kg fractions. Additionally, TAT may be useful in intensifying antileukemic therapy prior to hematopoietic cell transplantation, and pretargeting strategies offer the possibility for improved tumor-to-normal organ dose ratios.

Clinical effects of CD33 and MPC-1 on the prognosis of multiple myeloma treated with bortezomib

In the present study, the effects of immunophenotyping on the prognoses of patients with MM treated with bortezomib as induction therapy were investigated. A total of 118 patients with MM were examined, and the prognostic significance of the immunophenotyping and other factors were investigated. Immature and plasmablastic cell types and high-risk cytogenesis were more frequently observed in patients with CD33+ and MPC-1-. CD33+ and MPC-1- have potential as prognostic factors and correlated with lower progression-free survival and overall survival in a Kaplan-Meier analysis. Moreover, the present results demonstrated that at the relapse of disease, the percentage of CD33 increased (median 48.7%) and MPC-1 decreased (median 14.1%), respectively, therefore, both of these antigens may be associated with the refractory disease status. The present study showed that the expression of CD33 and MPC-1 in neoplastic plasma cells from patients with MM was associated with patient prognosis independent of other prognostic factors.

Prediction of non-linear pharmacokinetics in humans of an antibody-drug conjugate (ADC) when evaluation of higher doses in animals is limited by tolerability: Case study with an anti-CD33 ADC

For antibody-drug conjugates (ADCs) that carry a cytotoxic drug, doses that can be administered in preclinical studies are typically limited by tolerability, leading to a narrow dose range that can be tested. For molecules with non-linear pharmacokinetics (PK), this limited dose range may be insufficient to fully characterize the PK of the ADC and limits translation to humans. Mathematical PK models are frequently used for molecule selection during preclinical drug development and for translational predictions to guide clinical study design. Here, we present a practical approach that uses limited PK and receptor occupancy (RO) data of the corresponding unconjugated antibody to predict ADC PK when conjugation does not alter the non-specific clearance or the antibody-target interaction. We used a 2-compartment model incorporating non-specific and specific (target mediated) clearances, where the latter is a function of RO, to describe the PK of anti-CD33 ADC with dose-limiting neutropenia in cynomolgus monkeys. We tested our model by comparing PK predictions based on the unconjugated antibody to observed ADC PK data that was not utilized for model development. Prospective prediction of human PK was performed by incorporating in vitro binding affinity differences between species for varying levels of CD33 target expression. Additionally, this approach was used to predict human PK of other previously tested anti-CD33 molecules with published clinical data. The findings showed that, for a cytotoxic ADC with non-linear PK and limited preclinical PK data, incorporating RO in the PK model and using data from the corresponding unconjugated antibody at higher doses allowed the identification of parameters to characterize monkey PK and enabled human PK predictions.

Targeting Notch-1 positive acute leukemia cells by novel fucose-bound liposomes carrying daunorubicin

Complete remission by induction therapy in acute myelogenous leukemia (AML) can be achieved due to improvements in supportive and optimized therapy. However, more than 20% of patients will still need to undergo salvage therapy, and most will have a poor prognosis. Determining the specificity of drugs to leukemia cells is important since this will maximize the dose of chemotherapeutic agents that can be administered to AML patients. In turn, this would be expected to lead to reduced drug toxicity and its increased efficacy. We targeted Notch-1 positive AML cells utilizing fucose-bound liposomes, since activation of Notch-1 is required for O-fucosylation. Herein, we report that intravenously injected, L-fucose-bound liposomes containing daunorubicin can be successfully delivered to AML cells that express fucosylated antigens. This resulted in efficient tumor growth inhibition in tumor-bearing mice and decreased proliferation of AML patient-derived leukemia cells. Thus, biological targeting by fucose-bound liposomes that takes advantage of the intrinsic characteristics of AML cells could be a promising new strategy for Notch-1 positive-AML treatment.

Current applications of multiparameter flow cytometry in plasma cell disorders

Multiparameter flow cytometry (MFC) has become standard in the management of patients with plasma cell (PC) dyscrasias, and could be considered mandatory in specific areas of routine clinical practice. It plays a significant role during the differential diagnostic work-up because of its fast and conclusive readout of PC clonality, and simultaneously provides prognostic information in most monoclonal gammopathies. Recent advances in the treatment and outcomes of multiple myeloma led to the implementation of new response criteria, including minimal residual disease (MRD) status as one of the most relevant clinical endpoints with the potential to act as surrogate for survival. Recent technical progress led to the development of next-generation flow (NGF) cytometry that represents a validated, highly sensitive, cost-effective and widely available technique for standardized MRD evaluation, which also could be used for the detection of circulating tumor cells. Here we review current applications of MFC and NGF in most PC disorders including the less frequent solitary plasmocytoma, light-chain amyloidosis or Waldenström macroglobulinemia.

Small-lymphoid cells and myeloid antigen expression in a patient with IgG myeloma: A case report

Multiple myeloma is defined as a malignant proliferation of a single clone of plasma cells resulting in monoclonal immunoglobulin production. Due to the number of plasma cell morphological variants, difficulty is often faced during morphological diagnosis. The current study describes the case of a 49-year-old woman presenting with atypical plasma cell morphology detected by a bone marrow examination. Flow cytometric immunophenotyping determined the nature of the neoplastic cells as monoclonal myeloma cells with myeloid antigen expression. Serum electrophoresis with immunofixation and subsequent clinical findings confirmed this diagnosis. Therefore, the immunophenotyping of plasma cells in myelomas may be useful for the diagnosis of cases with atypical plasma cell morphology.

Absence of both CD56 and CD117 expression on malignant plasma cells is related with a poor prognosis in patients with newly diagnosed multiple myeloma

We retrospectively evaluated the association between the expression of CD56 and CD117 on neoplastic plasma cells and patients prognosis in 50 newly diagnosed multiple myeloma (MM) patients. The overall survival (OS) was measured and Cox proportional hazards model was used to evaluate CD56 and CD117 as possible prognostic factors for OS. CD56+ and CD117+ were detected in 74% and 32% multiple myeloma cases, respectively. In Kaplan-Meier analysis, CD56 and CD117 expression demonstrated potential prognostic impacts and were associated with longer OS (CD56: p=0.004, CD117: p=0.022), absence of both of them showed significantly shorter OS (p=0.046 compared to CD56+/CD117+ group, p=0.014 compared to CD56-/CD117+ or CD56+/CD117- group). Multivariate analysis showed that CD56 was independently prognostic of longer OS (p=0.012). After induction chemotherapy, overall response rates (ORR) was higher in CD56-positive group compared to CD56-negative group (70.6% versus 30.0%, p=0.024), however, there was no difference between CD117-positive and CD117-negative group (69.2% versus 58.1%, p=0.448). This study demonstrated the prognostic value of CD56 and CD117 in patients with newly diagnosed MM patients. Absence of both of them was associated with the poorest prognosis.

Expression of myeloid antigen in neoplastic plasma cells is related to adverse prognosis in patients with multiple myeloma

We evaluated the association between the expression of myeloid antigens on neoplastic plasma cells and patient prognosis. The expression status of CD13, CD19, CD20, CD33, CD38, CD56, and CD117 was analyzed on myeloma cells from 55 newly diagnosed patients, including 36 men (65%), of median age 61 years (range: 38–78). Analyzed clinical characteristics and laboratory parameters were as follows: serum β2-microglobulin, lactate dehydrogenase, calcium, albumin, hemoglobin, serum creatinine concentrations, bone marrow histology, and cytogenetic findings. CD13+ and CD33+ were detected in 53% and 18%, respectively. Serum calcium (P = 0.049) and LDH (P = 0.018) concentrations were significantly higher and morphologic subtype of immature or plasmablastic was more frequent in CD33+ than in CD33− patients (P = 0.022). CD33 and CD13 expression demonstrate a potential prognostic impact and were associated with lower overall survival (OS; P = 0.001 and P = 0.025) in Kaplan-Meier analysis. Multivariate analysis showed that CD33 was independently prognostic of shorter progression free survival (PFS; P = 0.037) and OS (P = 0.001) with correction of clinical prognostic factors. This study showed that CD13 and CD33 expression associated with poor prognosis in patients with MM implicating the need of analysis of these markers in MM diagnosis.

Immunophenotype of normal and myelomatous plasma-cell subsets

Plasma cells (PCs) are essentially characterized by the co-expression of CD138 and CD38, which allows their identification in flow cytometry in bone marrow (BM), peripheral blood, or cell suspensions from tissues. These terminally differentiated B-cells may lose the expression of surface CD19 and that of CD20 while retaining CD27. When malignant, they can gain a number of other markers such as CD28, CD33, CD56, or CD117 and lose CD27. Moreover, since each PC is only able to produce a single type of immunoglobulins (Igs), they display isotypic restriction and clonal malignant PCs can be further characterized by their homogeneous expression of either kappa or lambda light chains. In multiple myeloma (MM), such PC clones produce the Ig identified in plasma as an abnormal peak. In the BM where they essentially accumulate, these PCs may however display various immunophenotypes. The latter were explored in a two-way approach. Firstly, the various subsets delineated by the selective or common expression of CD19 together with combined CD56/CD28 were explored in normal and MM BM. Then, other aberrant markers’ expression was investigated, i.e., CD20, CD27, CD33, CD56, CD117. These data were compared to literature information. They underline the vast heterogeneity of MM PCs possibly accounting for the various answers to therapy of MM patients.

The reconstruction of transcriptional networks reveals critical genes with implications for clinical outcome of multiple myeloma

PURPOSE

The combined use of microarray technologies and bioinformatics analysis has improved our understanding of biological complexity of multiple myeloma (MM). In contrast, the application of the same technology in the attempt to predict clinical outcome has been less successful with the identification of heterogeneous molecular signatures. Herein, we have reconstructed gene regulatory networks in a panel of 1,883 samples from MM patients derived from publicly available gene expression sets, to allow the identification of robust and reproducible signatures associated with poor prognosis across independent data sets.

EXPERIMENTAL DESIGN

Gene regulatory networks were reconstructed by using Algorithm for the Reconstruction of Accurate Cellular Networks (ARACNe) and microarray data from seven MM data sets. Critical analysis of network components was applied to identify genes playing an essential role in transcriptional networks, which are conserved between data sets.

RESULTS

Network critical analysis revealed that (i) CCND1 and CCND2 were the most critical genes; (ii) CCND2, AIF1, and BLNK had the largest number of connections shared among the data sets; (iii) robust gene signatures with prognostic power were derived from the most critical transcripts and from shared primary neighbors of the most connected nodes. Specifically, a critical-gene model, comprising FAM53B, KIF21B, WHSC1, and TMPO, and a neighbor-gene model, comprising BLNK shared neighbors CSGALNACT1 and SLC7A7, predicted survival in all data sets with follow-up information.

CONCLUSIONS

The reconstruction of gene regulatory networks in a large panel of MM tumors defined robust and reproducible signatures with prognostic importance, and may lead to identify novel molecular mechanisms central to MM biology.

Immunophenotyping in multiple myeloma and related plasma cell disorders

Plasma cell disorders form a spectrum ranging from the asymptomatic presence of small monoclonal populations of plasma cells to conditions like plasma cell leukemia and multiple myeloma, in which the bone marrow can be replaced by the accumulation of neoplastic plasma cells. Immunophenotyping has become an invaluable tool in the management of hematological malignancies and is increasingly finding a role in the diagnosis and monitoring of plasma cell disorders. Multiparameter flow cytometry has evolved considerably during the past decade with an increasing ability to screen large numbers of events and to detect multiple antigens at the same time. This, along with a better understanding of the phenotypic heterogeneity of the clonal plasma cells in different disorders, has made immunophenotyping an indispensible tool in the diagnosis, prognostic classification and management of plasma cell disorders. This book chapter addresses the approaches taken to evaluate monoclonal plasma cell disorders, and the different markers and techniques that are important for the study of these diseases.

Update on the Diagnosis and Classification of the Plasma Cell Neoplasms

The plasma cell neoplasms are malignancies of the most terminally differentiated cells in B-cell ontogeny and are usually associated with the production of a monoclonal immunoglobulin molecule or M protein. These malignancies include tumors whose clinical manifestations are directly attributable to the end-organ damage induced by the dysregulated proliferation of neoplastic plasma cells. In contrast, disorders, such as primary amyloidosis, have a paradoxically low burden of neoplastic plasma cells, rendered highly pathogenic by the end-organ damage induced by deposition of the secreted paraprotein. In this article, discussion focuses on plasma cell myeloma. The molecular pathogenesis of plasma cell myeloma is reviewed and the diagnosis of the plasma cell neoplasms discussed.

Utility of flow cytometry immunophenotyping in multiple myeloma and other clonal plasma cell-related disorders

In recent years, multiparameter flow cytometry (MFC) immunophenotyping has become mandatory in the clinical management of hematological malignancies, both for diagnostic and monitoring purposes. Multiple myeloma (MM) and other clonal plasma cell-related (PC) disorders should be no exception to this paradigm, but incorporation of immunophenotypic studies in the management of patients with PC disorders is still far from being routinely established in many diagnostic flow cytometry laboratories. For clonal PC disorders, MFC is of clear and established clinical relevance in: (1) the differential diagnosis between MM and other PC-related disorders; (2) the identification of high-risk MGUS and smoldering MM; (3) minimal residual disease investigation after therapy; additionally it may also be useful for (4) the definition of prognosis-associated antigenic profiles; and (5) the identification of new therapeutic targets. In this article, we review the clinical value of MFC in the study of PC disorders, with specific emphasis in those areas where consensus exists on the need to incorporate MFC into routine evaluation of MM and other clonal PC-related disorders.

Multiple myeloma may include microvessel endothelial cells of malignant origin

Multiple myeloma (MM) comprises B and plasma cell compartments that originate from the same parent B cell and share as a cancer signature the same clonotypic IgH VDJ gene rearrangement. Here, we hypothesize that functional interactions between MM plasma cells (MM-PC) and their sister population of MM monocytoid B cells lead to the generation of microvessel endothelium of malignant origin from the monocytoid B cell progenitors. Published reports confirm that endothelial cells can harbor a molecular cancer signature characteristic of a given malignancy. We predict that MM monocytoid B cells-in response to both paracrine and autocrine pathways-contribute to tumor neovascularization in the bone marrow of MM patients. Our hypothesis further predicts that in MM, endothelial cells of malignant origin coexist with those of normal origin. We speculate that malignant development of MM incorporates functionally distinct sister lineages arising from the same MM progenitor that-by working together-ensure survival of the MM clone. We hypothesize that these two arms of the malignant MM clone are functionally interlinked to promote growth of the MM-PC compartment; by providing its own microenvironment, MM clonal evolution may ensure neovascularization to support an expanding malignancy.

Prognostic Value of Immunophenotyping in Multiple Myeloma: A Study by the PETHEMA/GEM Cooperative Study Groups on Patients Uniformly Treated With High-Dose Therapy

Purpose

To analyze the prognostic impact of immunophenotyping in patients with multiple myeloma (MM).

Patients and Methods

We have prospectively analyzed the prognostic impact of antigenic markers, assessed by multiparametric flow cytometry, in a series of 685 newly diagnosed MM patients that were uniformly treated according to the GEM 2000 protocol.

Results

Our results show that expression of both CD19 and CD28 as well as the absence of CD117 were associated with a significantly shorter progression free-survival (PFS) and overall survival (OS). Interestingly, the CD28 expression correlated with t(14;16) and del(17p), while CD117-negative patients were associated with t(4;14) and del(13q). Simultaneous assessment of CD28 and CD117 antigens allowed stratification of patients with MM into three risk categories: poor risk (CD28 positive CD117 negative), intermediate (either both markers negative or both positive), and good risk (CD28 negative CD117 positive), with PFS rates of 30, 37, and 45 months, respectively (P = .01), and OS rates of 45, 68, and not reached, respectively (P = .0001).

Conclusion

To the best of our knowledge, this is the first prospective analysis in which the prognostic impact of a relatively high number of antigenic markers has been simultaneously analyzed in a large series of uniformly treated patients, showing that the expression of several antigens (particularly CD28 and CD117) on bone marrow plasma cells from patients with MM can help to identify patients at high risk of progression.

CD33 detection by immunohistochemistry in paraffin-embedded tissues: a new antibody shows excellent specificity and sensitivity for cells of myelomonocytic lineage

A new monoclonal antibody to CD33 that reacts in paraffin-embedded tissue samples was evaluated. The expected reactivity in granulocytic and monocytic cells was found in a tissue microarray composed of multiple tissue sites. There was no unexpected reactivity found in a wide variety of hematolymphoid and nonhematolymphoid disorders. In cases of acute leukemia, the CD33 antibody showed equivalent results by immunohistochemical analysis compared with flow cytometric analysis. The CD33 antibody was also found to be a useful marker in the workup of myeloid sarcomas. This anti-CD33 antibody will be a useful marker in the workup of acute leukemias and myeloid sarcomas on paraffin-embedded tissue samples.