Licensure of gemtuzumab ozogamicin for the treatment of selected patients 60 years of age or older with acute myeloid leukemia in first relapse

Pharmacokinetic/Pharmacodynamic Modeling to Support the Re-approval of Gemtuzumab Ozogamicin

Gemtuzumab ozogamicin (Mylotarg; Pfizer, New York, NY) was the first antibody-drug conjugate to be approved for CD33-positive acute myeloid leukemia (AML). However, it was voluntarily withdrawn from the US market due to lack of clinical benefit in the confirmatory phase III trial. In 2012, several investigator cooperative studies using a different dosing regimen showed efficacy, but pharmacokinetic (PK) data were not collected in these trials. Through simulation of expected concentrations for new dosing regimens, PK/pharmacodynamic modeling was able to support the safety and efficacy of these regimens. Significant exposure-response relationships were found for the attainment of complete remission with and without platelet recovery, attainment of blast-free status, the time course of myelosuppression, several grade ≥ 3 hepatic adverse events, and veno-occlusive disease. Gemtuzumab ozogamicin received full approval by the US Food and Drug Administration (FDA) in September 2017 for newly diagnosed and relapsed AML in adult patients and relapsed AML in pediatric patients aged 2-17 years.

Cancer Therapy with Radiolabeled and Drug/Toxin-conjugated Antibodies

Radioimmunotherapy and antibody-directed chemotherapy have emerged as cancer treatment modalities with the regulatory approval of products for non-Hodgkin's lymphoma and acute myeloid leukemia. Antibody-toxin therapy is likewise on the verge of clinical fruition. Accumulating evidence suggests that radioimmunotherapy may have the best impact in minimal-disease and adjuvant settings, especially with radioresistant solid tumors. For the latter, ongoing efforts in ‘pretargeting’ to increase deliverable tumor radiation dose, combination therapies, and locoregional applications are also of importance. Antibody-drug conjugates have the potential to increase the therapeutic index of chemotherapy by minimizing systemic toxicity and improving tumor targeting. The design of optimal drug conjugates in this regard is predicated upon the proper choice of the target antigen, the cleavable-linker, and the drug. In respect of antibody-toxin conjugates, considerable progress has been made in chemical and recombinant immunotoxin designs, and in the advancement of many products to clinical trials. Continued development of antibody-directed therapies should expand the options available for the management of cancer.

Therapeutic application of monoclonal antibodies in cancer: advances and challenges

INTRODUCTION

Monoclonal antibody (mAb)-based products are highly specific for a particular antigen. This characteristic feature of the molecules makes them an ideal tool for many applications including cancer diagnosis and therapy.

SOURCES OF DATA

We performed comprehensive searches of PubMed, Medline and the Food and Drug Administration website using keywords such as 'therapeutic antibodies' and 'anti-cancer antibodies'.

AREAS OF AGREEMENT

Treatment of cancer patients with antibodies when used alone or in combination with chemotherapy and radiotherapy, or conjugated to drugs or radioisotopes, prolongs overall survival in cancer patients. Currently, there are 14 mAb-based drugs that have been approved for the treatment of cancer patients.

AREAS OF CONTROVERSY

The response of cancer patients to antibody therapy can be of short duration. Therapeutic antibodies are expensive and may have side effects. There are no reliable predictive biomarkers for sensitivity or resistance to certain therapeutic antibodies. FUTURE FOCUS: There should be additional studies to discover novel therapeutic targets, to develop more effective antibody-based drugs with fewer side effects, to identify more reliable predictive biomarker(s) for response to therapy with antibody-based drugs and to develop alternative strategies (e.g. transgenic plants, transgenic farm animals) for production of large quantities and more affordable batches of therapeutic antibodies.

AREAS TIMELY FOR DEVELOPING RESEARCH

A better understanding of cancer biology, the hallmarks of human cancers and the immune system would lead to identification of additional cell surface biomarkers. These in turn would facilitate the development of novel and biosimilar antibody-based drugs and their routine use as 'magic bullets' for the targeted therapy of human cancers.

Gemtuzumab ozogamicin for the treatment of acute promyelocytic leukemia: mechanisms of action and resistance, safety and efficacy

INTRODUCTION

Acute promyelocytic leukemia (APL) is characterized by peculiar biological features and high sensitivity to therapeutic agents such as anthracyclines, all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). Because cure rates of up to 80 - 90% have been reported using various combinations of the above agents, future strategies will probably aim at reducing therapy-related toxicity while maintaining therapeutic efficacy. Gemtuzumab ozogamicin (GO) is a calicheamicin-conjugated mAb directed against CD33, a surface antigen highly expressed on APL blasts. GO has been shown to be effective in this disease and better tolerated than conventional chemotherapy.

AREAS COVERED

This review looks at the mechanism of action, pathways associated with resistance and toxicity profile of GO. Reported experience on the use of GO for relapsed or newly diagnosed APL is also discussed along with evidence on its efficacy and relative tolerability in APL management. In addition to its activity in advanced disease, data suggest that GO in various combinations may replace chemotherapy in APL front-line therapy. This should apply in particular to some subsets such as elderly patients or those unfit to receive conventional chemotherapy.

EXPERT OPINION

GO has proven effective and relatively safe as a single agent in advanced APL. In combinations with ATRA and/or ATO, GO may substitute for conventional chemotherapy of APL, particularly in unfit patients.

The clinical pharmacology of therapeutic monoclonal antibodies in the treatment of malignancy; have the magic bullets arrived?

Monoclonal antibodies (Mabs) are proteins in the immunoglobulin family that bind to specific protein epitope targets on cancer and stromal cells, allowing them to be successfully exploited as therapeutic agents. The prototype Mabs were produced from fusion of mouse B lymphocytes and mouse myeloma cells and were entirely murine in sequence. Subsequent advances in technology have allowed for humanized Mabs, which have different pharmacokinetic properties than murine Mabs in humans. Mabs antitumour activity is mediated through direct interaction with specific target molecules, deployment of immune cytotoxic pathways, or through chaperoning cytotoxic agents to tumour. Mabs are typically administered intravenously, are generally well tolerated and can have powerful anticancer activity. Humanized Mabs have a t(1/2) in human sera of 2-3 weeks, which determines the frequency of administration. At present, nine clinically approved Mabs are used in the treatment of human cancer, and many others are in clinical trials. We discuss the pharmacology, clinical indications, and toxicity of the currently available anticancer Mabs in this review.

Gemtuzumab ozogamicin, cytosine arabinoside, G-CSF combination (G-AraMy) in the treatment of elderly patients with poor-prognosis acute myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is effective as single agent in the treatment of acute myeloid leukemia (AML). We evaluated efficacy and safety of a chemotherapy including growth factors, cytarabine, and GO (G-AraMy) in the treatment of poor-prognosis AML in elderly patients.

PATIENTS AND METHODS

In three Italian hematology departments from September 2003 to September 2006, 53 elderly patients [median age 69 years (range 65-77)] with untreated or primary refractory/relapsed AML were enrolled on the combination G-AraMy administered according to two consecutive schedules (G-AraMy1 and G-AraMy2), with intensified consolidation in the second. Twenty-three of 53 patients had a secondary acute myeloid leukemia (sAML).

RESULTS

The overall response rate was 57%. The most common adverse event was myelosuppression. Seven patients died in induction (13%). No differences for response rate and toxicity profile were observed between untreated and primary resistant/relapsed patients, de novo AML and sAML, and in the two treatment trials. Median disease-free survival and overall survival were 8 months (range 2-23+) and 9 months (range 2-24+).

CONCLUSIONS

G-AraMy therapy may be considered an useful treatment approach for poor-risk elderly AML patients, with a complete remission rate comparable to literature data with reduced side-effects, also in a poor-prognosis population.

Therapeutic potential of CD22-specific antibody-targeted chemotherapy using inotuzumab ozogamicin (CMC-544) for the treatment of acute lymphoblastic leukemia

CMC-544 (inotuzumab ozogamicin) is a CD22-specific cytotoxic immunoconjugate of calicheamicin intended for the treatment of B-lymphoid malignancies. This preclinical study investigated antitumor activity of CMC-544 against CD22+ acute lymphoblastic leukemia (ALL). CMC-544 inhibited in vitro growth of ALL cell lines more potently than that of Ramos B-lymphoma cells. When administered to nude mice with established sc xenografts of REH ALL, CMC-544 caused dose-dependent inhibition of xenograft growth producing complete tumor regression and cures in tumor-bearing mice at the highest dose of 160 microg/kg of conjugated calicheamicin. In contrast, a nonbinding control conjugate was 16-fold less effective than CMC-544 in inhibiting growth of REH ALL xenografts. When REH cells were injected intravenously in scid mice and allowed to disseminate systemically, mice developed hind-limb paralysis that was effectively prevented by treatment with CMC-544. Flow cytometric analysis of cells recovered from the bone marrow from mice with disseminated disease verified the presence of engrafted ALL cells. Significantly reduced numbers of ALL cells were recovered from the bone marrow of CMC-544-treated mice than from vehicle-treated mice with disseminated disease. The anti-leukemia activity of CMC-544 demonstrated here further supports clinical evaluation of CMC-544 for the treatment of CD22+ leukemia.

A Phase II study of Bcl-2 antisense (oblimersen sodium) combined with gemtuzumab ozogamicin in older patients with acute myeloid leukemia in first relapse

Oblimersen selectively targets Bcl-2 mRNA and has been shown to enhance the apoptotic activity of various antileukemic agents, including gemtuzumab ozogamicin (GO), in preclinical studies. We evaluated the efficacy and safety of oblimersen combined with GO in patients > or =60 years of age in first relapse with CD33+ acute myeloid leukemia. Oblimersen 7 mg/kg/day was given as a continuous intravenous infusion on days 1-7 and 15-21. GO 9 mg/m2 was given intravenously on days 4 and 18. Twelve of 48 patients (25%) achieved a major response (five, complete response and seven, complete response without platelet recovery). Ten of the 12 patients who achieved a major response survived >6 months compared with six of 36 non-responders. Serious adverse events for the oblimersen/GO combination were qualitatively similar to those reported for GO alone. Oblimersen can be safely combined with GO. Assessment of incremental benefit will require a randomized trial.

The role of gemtuzumab ozogamicin in acute leukaemia therapy

Gemtuzumab ozogamicin (GO) is an immunoconjugate that binds to CD33 on the surface of acute myeloid leukaemia (AML) blasts and, after internalisation, releases a cytotoxic drug, calicheamicin. GO is approved by the US Food and Drug Administration for the treatment of CD33-positive AML at first relapse in patients 60 years and older who are not candidates for other cytotoxic therapy. GO as a single agent has low antileukaemic activity. When given to patients meeting the criteria noted above, it produces a complete response (CR) rate of only 12%, with another 12% achieving CR with inadequate platelet recovery (CRp). The median survival of patients treated with GO monotherapy is 11.2 months. GO therapy at 9 mg/m(2) is complicated with hepatic veno-occlusive disease in 5-10% of patients, particularly prior to or following stem cell transplantation. GO at lower doses combined with chemotherapy as induction or postremission therapy is promising, however, and phase III trials are ongoing. GO is probably most active in acute promyelocytic leukaemia (APL). It is used for induction regimens in high-risk APL and for the elimination of minimal residual APL. Case reports suggest that GO also has activity in CD33-positive acute lymphoblastic leukaemia. In conclusion, single agent GO can induce responses in patients with CD33-positive AML in first recurrence. The future of GO is its use in combination with other cytotoxic agents. Ongoing clinical trials may better define the role of GO combinations, particularly in untreated AML.

Uncialamycin, A New Enediyne Antibiotic

[structure: see text] Laboratory cultures of an undescribed streptomycete obtained from the surface of a British Columbia lichen produce uncialamycin (1), a new enediyne antibiotic. The structure of uncialamycin (1) has been elucidated by analysis of spectroscopic data. Uncialamycin (1) exhibits potent in vitro antibacterial activity against gram-positive and gram-negative human pathogens, including Burkholderia cepacia, a major cause of morbidity and mortality in patients with cystic fibrosis.

Tumour-targeted chemotherapy with immunoconjugates of calicheamicin

Antibody-targeted chemotherapy is a therapeutic strategy in cancer therapy that involves a monoclonal antibody specific for a tumour-associated antigen, covalently linked via a suitable linker to a potent cytotoxic agent. Tumour-targeted delivery of a cytotoxic agent in the form of an immunoconjugate is expected to improve its antitumour activity and safety. Calicheamicin is a cytotoxic natural product isolated from Micromonospora echinospora that is at least 1000-fold more potent than conventional cytotoxic chemotherapeutics. Calicheamicin binds DNA in the minor groove and causes double-strand DNA breaks, leading to cell death. Immunoconjugates of calicheamicin targeted against tumour-associated antigens exhibit tumour-specific cytotoxic effects and cause regression of established human tumour xenografts in nude mice. Gemtuzumab ozogamicin is the first clinically validated cytotoxic immunoconjugate in which a humanised anti-CD33 antibody is linked to a derivative of calicheamicin. Gemtuzumab ozogamicin is indicated for the treatment of elderly patients with relapsed acute myeloid leukaemia. A similar conjugate, inotuzumab ozogamicin, is being evaluated at present in Phase I clinical trials in patients with non-Hodgkin's lymphoma. A number of tumour-targeted immunoconjugates of calicheamicin are being explored preclinically at present for their therapeutic applications.

Antibody-targeted chemotherapy of B-cell lymphoma using calicheamicin conjugated to murine or humanized antibody against CD22

Antibody-targeted chemotherapy with immunoconjugates of calicheamicin is a clinically validated strategy in cancer therapy. This study describes the selection of a murine anti-CD22 mAb, m5/44, as a targeting agent, its conjugation to a derivative of calicheamicin (CalichDM) via either acid-labile or acid-stable linkers, the antitumor activity of CalichDM conjugated to m5/44, and its subsequent humanization by CDR grafting. Murine IgG1 mAb m5/44 was selected based on its subnanomolar affinity for CD22 and ability to be internalized into B cells. CalichDM conjugated to m5/44 caused potent growth inhibition of CD22+ human B-cell lymphomas (BCLs) in vitro. The conjugate of m5/44 with an acid-labile linker was more potent than an acid-stable conjugate, a nonbinding conjugate with a similar acid-labile linker, or unconjugated CalichDMH in inhibiting BCL growth. CalichDM conjugated to m5/44 caused regression of established BCL xenografts in nude mice. In contrast, both unconjugated m5/44 and a nonbinding conjugate were ineffective against these xenografts. Based on the potent antitumor activity of m5/44-CalichDM conjugates, m5/44 was humanized by CDR grafting to create g5/44, an IgG4 anti-CD22 antibody. Both m5/44 and g5/44 bound CD22 with subnanomolar affinity. Competitive blocking with previously characterized murine anti-CD22 mAbs suggested that g5/44 recognizes epitope A located within the first N-terminal Ig-like domain of human CD22. Antitumor efficacy of CalichDM conjugated to g5/44 against BCL xenografts was more potent than its murine counterpart. Based on these results, a calicheamicin conjugate of g5/44, CMC-544, was selected for further development as a targeted chemotherapeutic agent for the treatment of B-cell malignancies.

Immunophenotyping as a guide for targeted therapy

Immunophenotyping of acute and chronic leukaemias has revealed many lineage- and differentiation-specific antigens. It has now become possible to classify leukaemias according to their unique antigenic expression pattern. Among many lineage- and differentiation-specific antigens, disease-specific antigens are increasingly recognized because of their specific prognostic or therapeutic relevance. Expression of the multidrug resistance proteins of the ABC transporter family is associated with a poor response to treatment and a grave clinical prognosis. Recently, attempts to reverse refractory disease by using P-glycoprotein inhibitors have been performed in acute myeloid leukaemia, so far without evidence of clinical benefit. Other new leads to use antigen expression as a way of designing tumour-specific therapy have resulted in imatinib and Flt3 inhibitors which target tyrosine kinases in the leukaemic cell. Clinical trials are underway to investigate the effect of these new agents. The development of an antibody-calicheamycin complex directed against the myeloid-specific antigen CD33 has shown clinical activity in patients with relapsed acute myeloid leukaemia. The further development of these approaches is discussed.

Antibody-targeted chemotherapy with CMC-544: a CD22-targeted immunoconjugate of calicheamicin for the treatment of B-lymphoid malignancies

Antibody-targeted chemotherapy with gemtuzumab ozogamicin (CMA-676, a CD33-targeted immunoconjugate of N-acetyl-γ-calicheamicin dimethyl hydrazide [CalichDMH], a potent DNA-binding cytotoxic antitumor antibiotic) is a clinically validated therapeutic option for patients with acute myeloid leukemia (AML). Here, we describe the preclinical profile of another immunoconjugate of CalichDMH, CMC-544, targeted to CD22 expressed by B-lymphoid malignancies. CMC-544 comprises a humanized IgG4 anti-CD22 monoclonal antibody (mAb), G5/44, covalently linked to CalichDMH via an acid-labile 4-(4′-acetylphenoxy) butanoic acid (AcBut) linker. Both CMC-544 and unconjugated G5/44 bound human CD22 with subnanomolar affinity. CMC-544, but not unconjugated G5/44, exerted potent cytotoxicity against CD22+ B-cell lymphoma (BCL) cell lines (inhibitory concentration of 50%: 6-600 pM CalichDMH). CMC-544 caused a potent inhibition of growth of small but established BCL xenografts leading to cures (therapeutic index > 10). CMC-544 prevented the establishment of BCL xenografts and also caused regression of large BCLs (> 1.5 g tumor mass). In contrast, unconjugated CalichDMH, unconjugated G5/44, and an isotype-matched control conjugate, CMA-676, were ineffective against these BCL xenografts. Thus, CD22-targeted delivery of CalichDMH is a potent and effective preclinical therapeutic strategy for BCLs. The strong antitumor profile of CMC-544 supports its clinical evaluation as a treatment option for B-lymphoid malignancies.