A phase I dose-escalation study of the immunocytokine EMD 521873 (Selectikine) in patients with advanced solid tumours

Facts and Hopes on Chimeric Cytokine Agents for Cancer Immunotherapy

Cytokines are key mediators of immune responses that can modulate the antitumor activity of immune cells. Cytokines have been explored as a promising cancer immunotherapy. However, there are several challenges to cytokine therapy, especially a lack of tumor targeting, resulting in high toxicity and limited efficacy. To overcome these limitations, novel approaches have been developed to engineer cytokines with improved properties, such as chimeric cytokines. Chimeric cytokines are fusion proteins that combine different cytokine domains or link cytokines to antibodies (immunocytokines) or other molecules that can target specific receptors or cells. Chimeric cytokines can enhance the selectivity and stability of cytokines, leading to reduced toxicity and improved efficacy. In this review, we focus on two promising cytokines, IL2 and IL15, and summarize the current advances and challenges of chimeric cytokine design and application for cancer immunotherapy. Most of the current approaches focus on increasing the potency of cytokines, but another important goal is to reduce toxicity. Cytokine engineering is promising for cancer immunotherapy as it can enhance tumor targeting while minimizing adverse effects.

A novel dual mechanism-of-action bispecific PD-1-IL-2v armed by a "βγ-only" interleukin-2 variant

Introduction

Interleukin-2 (IL-2) is one of the first cytokines to be discovered as an immune agonist for cancer immunotherapy. Biased IL-2 variants had been discovered to eliminate Treg activation or enhance the tumor specific T cell cytotoxicity. However, all the biased IL-2 variants pose the risk to overstimulate immune response at a low-dose range. Here, we introduce a novel dual-MOA bispecific PD-1-IL-2v molecule with great anti-tumor efficacy in a high dosed manner.

Methods

The novel IL-2 variant was designed by structural truncation and shuffling. The single armed bispecific PD-1-IL-2v molecule and IL-2v were studied by immune cell activations in vitro and in vivo and anti-tumor efficacy in mouse model.

Results and discussion

The IL-2 variant in this bispecific antibody only binds to IL-2Rβγ complex in a fast-on/off manner without α, β or γ single receptor binding. This IL-2v mildly activates T and NK cells without over stimulation, meanwhile it diminishes Treg activation compared to the wild type IL-2. This unique bispecific molecule with "βγ-only" IL-2v can not only "in-cis" stimulate and expand CD8 T and NK cells moderately without Treg activation, but also block the PD-1/L1 interaction at a similar dose range with monoclonal antibody.

IL-2Rα-biased agonist enhances antitumor immunity by invigorating tumor-infiltrating CD25+CD8+ T cells

To avoid regulatory T cell promotion and vascular toxicity, the interleukin-2 receptor-β/interleukin-2 receptor-γ (IL-2Rβγ)-biased approach is used by most IL-2 analogs in immuno-oncology. However, recent clinical disappointments in these IL-2 agonists have questioned this strategy. Here we show that both wild-type (IL-2wt) and IL-2Rβγ-attenuated (IL-2α-bias) agonists that preserve IL-2Rα (CD25) activities can effectively expand tumor-specific CD8+ T cells (TSTs) and exhibit better antitumor efficacy and safety than the 'non-α' counterpart (IL-2nα). Mechanistically, TSTs coexpress elevated CD25 and PD-1 and are more susceptible to stimulation by IL-2Rα-proficient agonists. Moreover, the antitumor efficacy of anti-PD-1 depends on activation of PD-1+CD25+ TSTs through autocrine IL-2-CD25 signaling. In individuals with cancer, a low IL-2 signature correlates with non-responsiveness to anti-PD-1 treatment. In mouse models, IL-2α-bias, but not IL-2nα, restores the IL-2 signature and synergizes with anti-PD-1 to eradicate large established tumors. These findings underscore the indispensable function of CD25 in IL-2-based immunotherapy and provide rationales for evaluating IL-2Rα-biased agonists in individuals with cancer.

Engineering cytokines for cancer immunotherapy: a systematic review

Cytokines are pivotal mediators of cell communication in the tumor microenvironment. Multiple cytokines are involved in the host antitumor response, but the production and function of these cytokines are usually dysregulated during malignant tumor progression. Considering their clinical potential and the early successful use of cytokines in cancer immunotherapy, such as interferon alpha-2b (IFNα-2b; IntronA^®) and IL-2 (Proleukin^®), cytokine-based therapeutics have been extensively evaluated in many follow-up clinical trials. Following these initial breakthroughs, however, clinical translation of these natural messenger molecules has been greatly limited owing to their high-degree pleiotropic features and complex biological properties in many cell types. These characteristics, coupled with poor pharmacokinetics (a short half-life), have hampered the delivery of cytokines via systemic administration, particularly because of severe dose-limiting toxicities. New engineering approaches have been developed to widen the therapeutic window, prolong pharmacokinetic effects, enhance tumor targeting and reduce adverse effects, thereby improving therapeutic efficacy. In this review, we focus on the recent progress and competitive landscape in cytokine engineering strategies and preclinical/clinical therapeutics for cancer. In addition, aiming to promote engineered cytokine-based cancer immunotherapy, we present a profound discussion about the feasibility of recently developed methods in clinical medicine translation.

A systematic review of interleukin-2-based immunotherapies in clinical trials for cancer and autoimmune diseases

BACKGROUND

The cytokine interleukin-2 (IL-2) can stimulate both effector immune cells and regulatory T (Treg) cells. The ability of selectively engaging either of these effects has spurred interest in using IL-2 for immunotherapy of cancer and autoimmune diseases. Thus, numerous IL-2-based biologic agents with improved bias or delivery towards effector immune cells or Treg cells have been developed. This study systematically reviews clinical results of improved IL-2-based compounds.

METHODS

We searched the ClinicalTrials.gov database for registered trials using improved IL-2-based agents and different databases for available results of these studies.

FINDINGS

From 576 registered clinical trials we extracted 36 studies on different improved IL-2-based compounds. Adding another nine agents reported in recent literature reviews and based on our knowledge totalled in 45 compounds. A secondary search for registered clinical trials of each of these 45 compounds resulted in 141 clinical trials included in this review, with 41 trials reporting results.

INTERPRETATION

So far, none of the improved IL-2-based compounds has gained regulatory approval for the treatment of cancer or autoimmune diseases. NKTR-214 is the only compound completing phase 3 studies. The PIVOT IO-001 trial testing the combination of NKTR-214 plus Pembrolizumab compared to Pembrolizumab monotherapy in metastatic melanoma missed its primary endpoints. Also the PIVOT-09 study, combining NKTR-214 with Nivolumab compared to Sunitinib or Cabozantinib in advanced renal cell carcinoma, missed its primary endpoint. Trials in autoimmune diseases are currently in early stages, thus not allowing definite conclusions on efficacy.

FUNDING

This work was supported by public funding agencies.

Targeted Cytokine Delivery for Cancer Treatment: Engineering and Biological Effects

Anti-tumor properties of several cytokines have already been investigated in multiple experiments and clinical trials. However, those studies evidenced substantial toxicities, even at low cytokine doses, and the lack of tumor specificity. These factors significantly limit clinical applications. Due to their high specificity and affinity, tumor-specific monoclonal antibodies or their antigen-binding fragments are capable of delivering fused cytokines to tumors and, therefore, of decreasing the number and severity of side effects, as well as of enhancing the therapeutic index. The present review surveys the actual antibody-cytokine fusion protein (immunocytokine) formats, their targets, mechanisms of action, and anti-tumor and other biological effects. Special attention is paid to the formats designed to prevent the off-target cytokine-receptor interactions, potentially inducing side effects. Here, we describe preclinical and clinical data and the efficacy of the antibody-mediated cytokine delivery approach, either as a single therapy or in combination with other agents.

Interleukin-2–based therapies in cancer

Molecular insights into the mechanism of beneficial and adverse effects of interleukin-2 (IL-2) have resulted in the development of improved IL-2 formulations with IL-2 receptor bias and tissue-targeting properties. Several of these compounds are currently in clinical development and are ushering IL-2 therapy into the current era of cancer immunotherapy.

Emerging new therapeutic antibody derivatives for cancer treatment

Monoclonal antibodies constitute a promising class of targeted anticancer agents that enhance natural immune system functions to suppress cancer cell activity and eliminate cancer cells. The successful application of IgG monoclonal antibodies has inspired the development of various types of therapeutic antibodies, such as antibody fragments, bispecific antibodies, and antibody derivatives (e.g., antibody–drug conjugates and immunocytokines). The miniaturization and multifunctionalization of antibodies are flexible and viable strategies for diagnosing or treating malignant tumors in a complex tumor environment. In this review, we summarize antibodies of various molecular types, antibody applications in cancer therapy, and details of clinical study advances. We also discuss the rationale and mechanism of action of various antibody formats, including antibody–drug conjugates, antibody–oligonucleotide conjugates, bispecific/multispecific antibodies, immunocytokines, antibody fragments, and scaffold proteins. With advances in modern biotechnology, well-designed novel antibodies are finally paving the way for successful treatments of various cancers, including precise tumor immunotherapy, in the clinic.

Engineered Bifunctional Proteins for Targeted Cancer Therapy: Prospects and Challenges

Bifunctional proteins (BFPs) are a class of therapeutic agents produced through genetic engineering and protein engineering, and are increasingly used to treat various human diseases, including cancer. These proteins usually have two or more biological functions-specifically recognizing different molecular targets to regulate the related signaling pathways, or mediating effector molecules/cells to kill tumor cells. Unlike conventional small-molecule or single-target drugs, BFPs possess stronger biological activity but lower systemic toxicity. Hence, BFPs are considered to offer many benefits for the treatment of heterogeneous tumors. In this review, the authors briefly describe the unique structural feature of BFP molecules and innovatively divide them into bispecific antibodies, cytokine-based BFPs (immunocytokines), and protein toxin-based BFPs (immunotoxins) according to their mode of action. In addition, the latest advances in the development of BFPs are discussed and the potential limitations or problems in clinical applications are outlined. Taken together, future studies need to be centered on understanding the characteristics of BFPs for optimizing and designing more effective such drugs.

Interleukin 2-Based Fusion Proteins for the Treatment of Cancer

Interleukin 2 (IL-2) plays a fundamental role in both immune activation and tolerance and has revolutionized the field of cancer immunotherapy since its discovery. The ability of IL-2 to mediate tumor regression in preclinical and clinical settings led to FDA approval for its use in the treatment of metastatic renal cell carcinoma and metastatic melanoma in the 1990s. Although modest success is observed in the clinic, cancer patients receiving IL-2 therapy experience a wide array of side effects ranging from flu-like symptoms to life-threatening conditions such as vascular leak syndrome. Over the past three decades, efforts have focused on circumventing IL-2-related toxicities by engineering methods to localize IL-2 to the tumor or secondary lymphoid tissue, preferentially activate CD8⁺ T cells and NK cells, and alter pharmacokinetic properties to increase bioavailability. This review summarizes the various IL-2-based strategies that have emerged, with a focus on chimeric fusion methods.

Next-generation cytokines for cancer immunotherapy

Most studies focus on the first and second signals of T cell activation. However, the roles of cytokines in immunotherapy are not fully understood, and cytokines have not been widely used in patient care. Clinical application of cytokines is limited due to their short half-life in vivo, severe toxicity at therapeutic doses, and overall lack of efficacy. Several modifications have been engineered to extend their half-life and increase tumor targeting, including polyethylene glycol conjugation, fusion to tumor-targeting antibodies, and alteration of cytokine/cell receptor-binding affinity. These modifications demonstrate an improvement in either increased antitumor efficacy or reduced toxicity. However, these cytokine engineering strategies may still be improved further, as each strategy poses advantages and disadvantages in the delicate balance of targeting tumor cells, tumor-infiltrating lymphocytes, and peripheral immune cells. This review focuses on selected cytokines, including interferon-α, interleukin (IL)-2, IL-15, IL-21, and IL-12, in both preclinical studies and clinical applications. We review next-generation designs of these cytokines that improve half-life, tumor targeting, and antitumor efficacy. We also present our perspectives on the development of new strategies to potentiate cytokine-based immunotherapy.

Utilizing Immunocytokines for Cancer Therapy

Cytokine therapy for cancer has indicated efficacy in certain diseases but is generally accompanied by severe toxicity. The field of antibody-cytokine fusion proteins (immunocytokines) arose to target these effector molecules to the tumor environment in order to expand the therapeutic window of cytokine therapy. Pre-clinical evidence has shown the increased efficacy and decreased toxicity of various immunocytokines when compared to their cognate unconjugated cytokine. These anti-tumor properties are markedly enhanced when combined with other treatments such as chemotherapy, radiotherapy, and checkpoint inhibitor antibodies. Clinical trials that have continued to explore the potential of these biologics for cancer therapy have been conducted. This review covers the in vitro, in vivo, and clinical evidence for the application of immunocytokines in immuno-oncology.

A highly potential cleavable linker for tumor targeting antibody-chemokines

Chemokines are the large family of chemotactic cytokines that play an important role in leukocyte movement and migration stimulation. Until now, several antibody-cytokine (chemokine) fusion proteins have been investigated in clinical trials because of their ability to evoke the circulating leukocytes far from the tumor site. In this case, creating the concentration gradient regarding the chemokine is very important to recruit the circulating leukocytes with maximum performance to the tumor environment. To achieve a proper gradient, the chemokine separation from the tumor antigen-bounded antibody can be very crucial. Thus, we designed a novel linker that can be cleaved by enzymes presented around the tumor site including cathepsin B, urokinase-type plasminogen activator (uPA) and matrix metalloproteinases (MMPs). Also, it can inhibit tumor progression by competing with the native substrate of key proteases in the tumor microenvironment. The proposed linker was evaluated using some bioinformatics approaches. In silico results showed that the linker is structurally stable and could be detected and cleaved using the mentioned enzymes.Communicated by Ramaswamy H. Sarma.

Effects of interleukin-2 in immunostimulation and immunosuppression

Distinctions in the nature and spatiotemporal expression of IL-2R subunits on conventional versus regulatory T cells are exploited to manipulate IL-2 immunomodulatory effects. Particularly, low-dose IL-2 and some recombinant derivatives are being evaluated to enhance/inhibit immune responses for therapeutic purposes.

Historically, interleukin-2 (IL-2) was first described as an immunostimulatory factor that supports the expansion of activated effector T cells. A layer of sophistication arose when regulatory CD4⁺ T lymphocytes (Tregs) were shown to require IL-2 for their development, homeostasis, and immunosuppressive functions. Fundamental distinctions in the nature and spatiotemporal expression patterns of IL-2 receptor subunits on naive/memory/effector T cells versus Tregs are now being exploited to manipulate the immunomodulatory effects of IL-2 for therapeutic purposes. Although high-dose IL-2 administration has yielded discrete clinical responses, low-dose IL-2 as well as innovative strategies based on IL-2 derivatives, including “muteins,” immunocomplexes, and immunocytokines, are being explored to therapeutically enhance or inhibit the immune response.

Antibody-cytokine fusion proteins: A novel class of biopharmaceuticals for the therapy of cancer and of chronic inflammation

Antibody-cytokine fusion proteins represent a novel class of biopharmaceuticals, with the potential to increase the therapeutic index of cytokine 'payloads' and to promote leukocyte infiltration at the site of disease. In this review, we present a survey of immunocytokines that have been used in preclinical models of cancer and in clinical trials. In particular, we highlight how antibody format, choice of target antigen and cytokine engineering, as well as combination strategies, may have a profound impact on therapeutic performance. Moreover, by using anti-inflammatory cytokines, antibody fusion strategies can conveniently be employed for the treatment of auto-immune and chronic inflammatory conditions.

The challenges and molecular approaches surrounding interleukin-2-based therapeutics in cancer

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IL2-based cancer therapies are limited by their toxicity and pleiotropy.

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Current engineering approaches target IL2 half-life and cell/receptor specificity.

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IL2 may enhance the efficacy of checkpoint inhibitors and CAR-T-based therapies.

Interleukin-2 has had a long history as a promising cancer therapeutic, being capable of eliciting complete and durable remissions in patients with metastatic renal cell carcinoma and metastatic melanoma. Despite high toxicity and efficacy limited to only certain patient subpopulations and cancer types, the prospective use of novel, engineered IL2 formats in combination with the presently expanding repertoire of immuno-oncological targets remains very encouraging. This is possible due to the significant research efforts in the IL2 field that have yielded critical structural and biological insights that have made IL2 more effective and more broadly applicable in the clinic. In this review, we discuss some of the molecular approaches that have been used to further improve IL2 therapy for cancer.

Antibody-cytokine fusion proteins: Biopharmaceuticals with immunomodulatory properties for cancer therapy

Cytokines have long been used for therapeutic applications in cancer patients. Substantial side effects and unfavorable pharmacokinetics limit their application and may prevent dose escalation to therapeutically active regimens. Antibody-cytokine fusion proteins (often referred to as immunocytokines) may help localize immunomodulatory cytokine payloads to the tumor, thereby activating anticancer immune responses. A variety of formats (e.g., intact IgGs or antibody fragments), molecular targets (e.g., extracellular matrix components and cell membrane antigens) and cytokine payloads have been considered for the development of this novel class of biopharmaceuticals. This review presents the basic concepts on the design and engineering of immunocytokines, reviews their potential limitations, points out emerging opportunities and summarizes key features of preclinical and clinical-stage products.

Human and murine IL2 receptors differentially respond to the human-IL2 component of immunocytokines

The humanized immunocytokine, hu14.18-IL2 (ICp), leads to the immune cell-mediated destruction of GD2-expressing tumors in mouse models, resulting in potent antitumor effects with negligible IL2-related toxicity. In contrast, when ICp is used clinically, antitumor activity is accompanied by dose-limiting IL2-related toxicities. These species-specific differences in ICp toxicity may be linked to differential binding to mouse vs. human IL2 receptors (IL2Rs). We evaluated immunocytokines genetically engineered to preferentially bind either high-affinity αβγ-IL2Rs or intermediate-affinity βγ-IL2Rs. These ICs have the IL2 fused to the C-terminus of the IgG light chains rather than the heavy chains. We found that IC35, containing intact huIL2, maintained activation of human and mouse αβγ-IL2Rs but exhibited a 20-fold reduction in the ability to stimulate human βγ-IL2Rs, with no activation of mouse βγ-IL2Rs at the concentrations tested. The reduced ability of IC35 to stimulate human βγ-IL2Rs (associated with IL2-toxicities) makes it a potential candidate for clinical trials where higher clinical IC doses might enable better tumor targeting and increased antitumor effects with less toxicity. Contrastingly, ICSK (IC with an IL2 mutein that has enhanced binding to the IL2R β-chain) showed increased activation over ICp on mouse βγ-IL2Rs, with a dose-response curve similar to that seen with IC35 on human βγ-IL2Rs. Our data suggest that ICSK might be used in mouse models to simulate the anticipated effects of IC35 in clinical testing. Understanding the differences in species-dependent IL2R activation should facilitate the design of reagents and mouse models that better simulate the potential activity of IL2-based immunotherapy in patients.

Beyond checkpoint inhibition - Immunotherapeutical strategies in combination with radiation

The revival of cancer immunotherapy has taken place with the clinical success of immune checkpoint inhibition. However, the spectrum of immunotherapeutic approaches is much broader encompassing T cell engaging strategies, tumour-specific vaccination, antibodies or immunocytokines. This review focuses on the immunological effects of irradiation and the evidence available on combination strategies with immunotherapy. The available data suggest great potential of combined treatments, yet also poses questions about dose, fractionation, timing and most promising multimodal strategies.

Cergutuzumab amunaleukin (CEA-IL2v), a CEA-targeted IL-2 variant-based immunocytokine for combination cancer immunotherapy: Overcoming limitations of aldesleukin and conventional IL-2-based immunocytokines

We developed cergutuzumab amunaleukin (CEA-IL2v, RG7813), a novel monomeric CEA-targeted immunocytokine, that comprises a single IL-2 variant (IL2v) moiety with abolished CD25 binding, fused to the C-terminus of a high affinity, bivalent carcinoembryonic antigen (CEA)-specific antibody devoid of Fc-mediated effector functions. Its molecular design aims to (i) avoid preferential activation of regulatory T-cells vs. immune effector cells by removing CD25 binding; (ii) increase the therapeutic index of IL-2 therapy by (a) preferential retention at the tumor by having a lower dissociation rate from CEA-expressing cancer cells vs. IL-2R-expressing cells, (b) avoiding any FcγR-binding and Fc effector functions and (c) reduced binding to endothelial cells expressing CD25; and (iii) improve the pharmacokinetics, and thus convenience of administration, of IL-2. The crystal structure of the IL2v-IL-2Rβγ complex was determined and CEA-IL2v activity was assessed using human immune effector cells. Tumor targeting was investigated in tumor-bearing mice using 89Zr-labeled CEA-IL2v. Efficacy studies were performed in (a) syngeneic mouse models as monotherapy and combined with anti-PD-L1, and in (b) xenograft mouse models in combination with ADCC-mediating antibodies. CEA-IL2v binds to CEA with pM avidity but not to CD25, and consequently did not preferentially activate Tregs. In vivo, CEA-IL2v demonstrated superior pharmacokinetics and tumor targeting compared with a wild-type IL-2-based CEA immunocytokine (CEA-IL2wt). CEA-IL2v strongly expanded NK and CD8+ T cells, skewing the CD8+:CD4+ ratio toward CD8+ T cells both in the periphery and in the tumor, and mediated single agent efficacy in syngeneic MC38-CEA and PancO2-CEA models. Combination with trastuzumab, cetuximab and imgatuzumab, all of human IgG1 isotype, resulted in superior efficacy compared with the monotherapies alone. Combined with anti-PD-L1, CEA-IL2v mediated superior efficacy over the respective monotherapies, and over the combination with an untargeted control immunocytokine. These preclinical data support the ongoing clinical investigation of the cergutuzumab amunaleukin immunocytokine with abolished CD25 binding for the treatment of CEA-positive solid tumors in combination with PD-L1 checkpoint blockade and ADCC competent antibodies.

Interleukin-2: Old and New Approaches to Enhance Immune-Therapeutic Efficacy

Interleukin-2 (IL-2) is a very well-known cytokine that has been studied for the past 35 years. It plays a major role in the growth and proliferation of many immune cells such NK and T cells. It is an important immunotherapy cytokine for the treatment of various diseases including cancer. Systemic delivery of IL-2 has shown clinical benefit in renal cell carcinoma and melanoma patients. However, its use has been limited by the numerous toxicities encountered with the systemic delivery. Intravenous IL-2 causes the well-known "capillary leak syndrome," or the leakage of fluid from the circulatory system to the interstitial space resulting in hypotension (low blood pressure), edema, and dyspnea that can lead to circulatory shock and eventually cardiopulmonary collapse and multiple organ failure. Due to the toxicities associated with systemic IL-2, an aerosolized delivery approach has been developed, which enables localized delivery and a higher local immune cell activation. Since proteins are absorbed via pulmonary lymphatics, after aerosol deposition in the lung, aerosol delivery provides a means to more specifically target IL-2 to the local immune system in the lungs with less systemic effects. Its benefits have extended to diseases other than cancer. Delivery of IL-2 via aerosol or as nebulized IL-2 liposomes has been previously shown to have less toxicity and higher efficacy against sarcoma lung metastases. Dogs with cancer provided a highly relevant means to determine biodistribution of aerosolized IL-2 and IL-2 liposomes. However, efficacy of single-agent IL-2 is limited. As in general, for most immune-therapies, its effect is more beneficial in the face of minimal residual disease. To overcome this limitation, combination therapies using aerosol IL-2 with adoptive transfer of T cells or NK cells have emerged.Using a human osteosarcoma (OS) mouse model, we have demonstrated the efficacy of single-agent aerosol IL-2 and combination therapy aerosol IL-2 and NK cells or aerosol IL-2 and interleukin 11 receptor alpha-directed chimeric antigen receptor-T cells (IL-11 receptor α CAR-T cells) against OS pulmonary metastases. Combination therapy resulted in a better therapeutic effect. A Phase-I trial of aerosol IL-2 was done in Europe and proved to be safe. Others and our preclinical studies provided the basis for the development of a Phase-I aerosol IL-2 trial in our institution to include younger patients with lung metastases. OS, our disease of interest, has a peak incidence in the adolescent and young adult years. Our goal is to complete this trial in the next 2 years.In this chapter, we summarize the different effects of IL-2 and cover the advantages of the aerosol delivery route for diseases of the lung with an emphasis on some of our most recent work using combination therapy aerosol IL-2 and NK cells for the treatment of OS lung metastases.

Antibody fusions with immunomodulatory proteins for cancer therapy

The potential of immunomodulatory proteins, in particular cytokines, for cancer therapy is well recognized, but hampered by the toxicity associated with their systemic application. In order to address this problem, targeted delivery by antibody fusion proteins has been early proposed and their development intensively pursued over the last decade. Here, factors influencing the selection and modification of cytokines and antibody formats for this approach are being discussed, indicating current developments and translational advances in the field.

Novel anti-melanoma treatment: focus on immunotherapy

Melanoma is an intractable cancer that is aggressive, lethal, and metastatic. The prognosis of advanced melanoma is very poor because it is insensitive to chemotherapy and radiotherapy. The incidence of melanoma has been ascending stably for years worldwide, accompanied by increasing mortality. New approaches to managing this deadly disease are much anticipated to enhance the cure rate and to extend clinical benefits to patients with metastatic melanoma. Due to its high degree of immunogenicity, melanoma could be a good target for immunotherapy, which has been developed for decades and has achieved certain progress. This article provides an overview of immunotherapy for melanoma.

NHS-IL2 combined with radiotherapy: preclinical rationale and phase Ib trial results in metastatic non-small cell lung cancer following first-line chemotherapy

BACKGROUND

NHS-IL2 (selectikine, EMD 521873, MSB0010445) consists of human NHS76 (antibody specific for necrotic DNA) fused to genetically modified human interleukin 2 (IL-2) and selectively activates the high-affinity IL-2 receptor. Based on an evolving investigational concept to prime the tumor microenvironment with ionizing radiation prior to initiating immunotherapy, 2 related studies were conducted and are reported here. The first, a preclinical study, tests the systemic effect of the immunocytokine NHS-IL2 and radiotherapy in a lung carcinoma animal model; the second, a phase Ib trial in patients with metastatic non-small cell lung carcinoma (NSCLC), was designed to determine the safety and tolerability of NHS-IL2 in combination with radiotherapy directly following first-line palliative chemotherapy.

METHODS

Tumor-bearing C57Bl/6 mice were treated with NHS-IL2 alone (5 mg/kg; days 7-9), fractionated radiotherapy (3.6 Gy; days 0-4) plus cisplatin (4 mg/kg; day 0), or the triple combination. Metastatic NSCLC patients who achieved disease control with first-line palliative chemotherapy were enrolled in the phase Ib trial. Patients received local irradiation (5x 4 Gy) of a single pulmonary nodule. Dose-escalated NHS-IL2 was administered as 1-h intravenous infusion on 3 consecutive days every 3 weeks.

RESULTS

NHS-IL2 plus radiotherapy induced immune response activation and complete tumor growth regressions in 80%-100% of mice. In patients with metastatic NSCLC treated with NHS-IL2 (3, 3, and 7 patients in the 0.15-mg/kg, 0.30-mg/kg, and 0.45-mg/kg cohorts, respectively), maximum tolerated dose was not reached. Most frequently reported adverse events were fatigue, anorexia, and rash. Transient increases in leukocyte subsets were observed. In 3 patients, thyroid gland dysfunction occurred. No objective responses were reported; long-term survival was observed in 2 patients, including 1 patient with long-term tumor control.

CONCLUSIONS

Combining NHS-IL2 with radiotherapy achieved synergistic antitumor activity in preclinical studies, supporting the use in lung cancer patients. This combination was well tolerated and 2 of 13 patients achieved long-term survival.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00879866.

Insights into cytokine-receptor interactions from cytokine engineering

Cytokines exert a vast array of immunoregulatory actions critical to human biology and disease. However, the desired immunotherapeutic effects of native cytokines are often mitigated by toxicity or lack of efficacy, either of which results from cytokine receptor pleiotropy and/or undesired activation of off-target cells. As our understanding of the structural principles of cytokine-receptor interactions has advanced, mechanism-based manipulation of cytokine signaling through protein engineering has become an increasingly feasible and powerful approach. Modified cytokines, both agonists and antagonists, have been engineered with narrowed target cell specificities, and they have also yielded important mechanistic insights into cytokine biology and signaling. Here we review the theory and practice of cytokine engineering and rationalize the mechanisms of several engineered cytokines in the context of structure. We discuss specific examples of how structure-based cytokine engineering has opened new opportunities for cytokines as drugs, with a focus on the immunotherapeutic cytokines interferon, interleukin-2, and interleukin-4.

Use of enhanced interleukin-2 formulations for improved immunotherapy against cancer

The use of interleukin-2 (IL-2) for the stimulation of an effector immune response against metastatic cancer dates back to the early 1980s. Administration of unmodified IL-2, either alone or together with antigen-specific approaches, has resulted in remarkably long-term survival of some patients suffering from metastatic melanoma. However, such treatment is usually hampered by the appearance of toxic adverse effects, which has motivated the engineering of modified IL-2 formulations showing reduced toxicity while being more potent at stimulating anti-tumor effector immune cells. In this review we summarize and discuss the features and biological relevance of several enhanced IL-2 formulations, compare these to IL-15-based therapeutics, and try to foreshadow their potential in immunological research and immunotherapy.

Preclinical evaluation of IL2-based immunocytokines supports their use in combination with dacarbazine, paclitaxel and TNF-based immunotherapy

Antibody-cytokine fusion proteins ("immunocytokines") represent a promising class of armed antibody products, which allow the selective delivery of potent pro-inflammatory payloads at the tumor site. The antibody-based selective delivery of interleukin-2 (IL2) is particularly attractive for the treatment of metastatic melanoma, an indication for which this cytokine received marketing approval from the US Food and drug administration. We used the K1735M2 immunocompetent syngeneic model of murine melanoma to study the therapeutic activity of F8-IL2, an immunocytokine based on the F8 antibody in diabody format, fused to human IL2. F8-IL2 was shown to selectively localize at the tumor site in vivo, following intravenous administration, and to mediate tumor growth retardation, which was potentiated by the combination with paclitaxel or dacarbazine. Combination treatment led to a substantially more effective tumor growth inhibition, compared to the cytotoxic drugs used as single agents, without additional toxicity. Analysis of the immune infiltrate revealed a significant accumulation of CD4(+) T cells 24 h after the administration of the combination. The fusion proteins F8-IL2 and L19-IL2, specific to the alternatively spliced extra domain A and extra domain B of fibronectin respectively, were also studied in combination with tumor necrosis factor (TNF)-based immunocytokines. The combination treatment was superior to the action of the individual immunocytokines and was able to eradicate neoplastic lesions after a single intratumoral injection, a procedure that is being clinically used for the treatment of Stage IIIC melanoma. Collectively, these data reinforce the rationale for the use of IL2-based immunocytokines in combination with cytotoxic agents or TNF-based immunotherapy for the treatment of melanoma patients.

Antibody-cytokine fusion proteins for treatment of cancer: engineering cytokines for improved efficacy and safety

The true potential of cytokine therapies in cancer treatment is limited by the inability to deliver optimal concentrations into tumor sites due to dose-limiting systemic toxicities. To maximize the efficacy of cytokine therapy, recombinant antibody-cytokine fusion proteins have been constructed by a number of groups to harness the tumor-targeting ability of monoclonal antibodies. The aim is to guide cytokines specifically to tumor sites where they might stimulate more optimal anti-tumor immune responses while avoiding the systemic toxicities of free cytokine therapy. Antibody-cytokine fusion proteins containing interleukin (IL)-2, IL-12, IL-21, tumor necrosis factor (TNF)α, and interferons (IFNs) α, β, and γ have been constructed and have shown anti-tumor activity in preclinical and early-phase clinical studies. Future priorities for development of this technology include optimization of tumor targeting, bioactivity of the fused cytokine, and choice of appropriate agents for combination therapies. This review is intended to serve as a framework for engineering an ideal antibody-cytokine fusion protein, focusing on previously developed constructs and their clinical trial results.

A new platform for constructing antibody-cytokine fusion proteins (immunocytokines) with improved biological properties and adaptable cytokine activity

A novel method for constructing immunocytokines has been developed that utilizes fusion of cytokines to the C-terminus of the Ig light chain, rather than fusing to the heavy chain. Such molecules are expressed well in transfected cells, are very stable in normal buffers and have biological properties that are superior to immunocytokines made by fusion to the heavy chain. These properties include longer circulating half-life, increased uptake following subcutaneous dosing and similar or improved antibody effector activities of antibody-dependent cytotoxic activity and complement-dependent cytotoxicity, respectively. Furthermore, the sequestering effect of this fusion junction allows one to adjust intermediate affinity (βγ) interleukin 2 receptor (IL2R) binding and activation by shortening the N-terminus of IL2 at the fusion point. This appears to limit access of the critical contact residue Asp20 of IL2 to the β-chain of βγ IL2R, while maintaining binding and activation of high-affinity (αβγ) IL2R-expressing cells. Several immunocytokine forms with varying degrees of IL2R specificity have been constructed, and some appear to regain their activity for the βγ IL2R when bound to antigen-coated beads. Such molecules may have reduced toxicity in the circulation and enhanced anti-tumor activity.

Immunocytokines: a review of molecules in clinical development for cancer therapy

The concept of therapeutically enhancing the immune system’s responsiveness to tumors is long standing. Several cytokines have been investigated in clinical trials for their therapeutic activity in cancer patients. However, substantial side effects and unfavorable pharmacokinetic properties have been a major drawback hampering the administration of therapeutically relevant doses. The use of recombinant antibody–cytokine fusion proteins promises to significantly enhance the therapeutic index of cytokines by targeting them to the site of disease. This review aims to provide a concise and complete overview of the preclinical data and clinical results currently available for all immunocytokines having reached clinical development.

Polymeric micelles, a promising drug delivery system to enhance bioavailability of poorly water-soluble drugs

Oral administration is the most commonly used and readily accepted form of drug delivery; however, it is find that many drugs are difficult to attain enough bioavailability when administered via this route. Polymeric micelles (PMs) can overcome some limitations of the oral delivery acting as carriers able to enhance drug absorption, by providing (1) protection of the loaded drug from the harsh environment of the GI tract, (2) release of the drug in a controlled manner at target sites, (3) prolongation of the residence time in the gut by mucoadhesion, and (4) inhibition of efflux pumps to improve the drug accumulation. To explain the mechanisms for enhancement of oral bioavailability, we discussed the special stability of PMs, the controlled release properties of pH-sensitive PMs, the prolongation of residence time with mucoadhesive PMs, and the P-gp inhibitors commonly used in PMs, respectively. The primary purpose of this paper is to illustrate the potential of PMs for delivery of poorly water-soluble drugs with bioavailability being well maintained.

Trial Watch: Immunostimulatory cytokines

During the past two decades, the notion that cancer would merely constitute a cell-intrinsic disease has gradually been complemented by a model postulating that the immune system plays a relevant role during all stages of oncogenesis and tumor progression. Along with this conceptual shift, several strategies have been devised to stimulate tumor-specific immune responses, including relatively unselective approaches such as the systemic administration of adjuvants or immunomodulatory cytokines. One year ago, in the July issue of OncoImmunology, we described the main biological features of this large group of proteins and discussed the progress of ongoing clinical studies evaluating their safety and therapeutic potential in cancer patients. Here, we summarize the latest developments in this area of clinical research, focusing on high impact studies that have been published during the last 13 mo and clinical trials launched in the same period to investigate which cytokines can be employed as safe and efficient immunostimulatory interventions against cancer.

T-cell activation by treatment of cancer patients with EMD 521873 (Selectikine), an IL-2/anti-DNA fusion protein

Background

EMD 521873 (Selectikine or NHS-IL2LT) is a fusion protein consisting of modified human IL-2 which binds specifically to the high-affinity IL-2 receptor, and an antibody specific for both single- and double-stranded DNA, designed to facilitate the enrichment of IL-2 in tumor tissue.

Methods

An extensive analysis of pharmacodynamic (PD) markers associated with target modulation was assessed during a first-in-human phase I dose-escalation trial of Selectikine.

Results

Thirty-nine patients with metastatic or locally advanced tumors refractory to standard treatments were treated with increasing doses of Selectikine, and nine further patients received additional cyclophosphamide. PD analysis, assessed during the first two treatment cycles, revealed strong activation of both CD4⁺ and CD8⁺ T-cells and only weak NK cell activation. No dose response was observed. As expected, Treg cells responded actively to Selectikine but remained at lower frequency than effector CD4⁺ T-cells. Interestingly, patient survival correlated positively with both high lymphocyte counts and low levels of activated CD8⁺ T-cells at baseline, the latter of which was associated with enhanced T-cell responses to the treatment.

Conclusions

The results confirm the selectivity of Selectikine with predominant T-cell and low NK cell activation, supporting follow-up studies assessing the clinical efficacy of Selectikine for cancer patients.