Development of an attenuated interleukin-2 fusion protein that can be activated by tumour-expressed proteases

Emerging trends and therapeutic applications of monoclonal antibodies

Monoclonal antibodies (mAbs) are being used to prevent, detect, and treat a broad spectrum of malignancies and infectious and autoimmune diseases. Over the past few years, the market for mAbs has grown exponentially. They have become a significant part of many pharmaceutical product lines, and more than 250 therapeutic mAbs are undergoing clinical trials. Ever since the advent of hybridoma technology, antibody-based therapeutics were realized using murine antibodies which further progressed into humanized and fully human antibodies, reducing the risk of immunogenicity. Some of the benefits of using mAbs over conventional drugs include a drastic reduction in the chances of adverse reactions, interactions between drugs, and targeting specific proteins. While antibodies are very efficient, their higher production costs impede the process of commercialization. However, their cost factor has been improved by developing biosimilar antibodies, which are affordable versions of therapeutic antibodies. Along with biosimilars, innovations in antibody engineering have helped to design bio-better antibodies with improved efficacy than the conventional ones. These novel mAb-based therapeutics are set to revolutionize existing drug therapies targeting a wide spectrum of diseases, thereby meeting several unmet medical needs. In the future, mAbs generated by applying next-generation sequencing (NGS) are expected to become a powerful tool in clinical therapeutics. This article describes the methods of mAb production, pre-clinical and clinical development of mAbs, approved indications targeted by mAbs, and novel developments in the field of mAb research.

Tumor-activated IL-2 mRNA delivered by lipid nanoparticles for cancer immunotherapy

Interleukin-2 (IL-2) exhibits the unique capacity to modulate immune functions, potentially exerting antitumor effects by stimulating immune responses, making it highly promising for immunotherapy. However, the clinical use of recombinant IL-2 protein faces significant limitations due to its short half-life and systemic toxicity. To overcome these challenges and fully exploit IL-2's potential in tumor immunotherapy, this study reports the development of a tumor-activated IL-2 mRNA, delivered via lipid nanoparticles (LNPs). Initially, ionizable lipid U-101 derived nanoparticles (U-101-LNP) were prepared using microfluidic technology. Subsequent in vitro and in vivo delivery tests demonstrated that U-101-LNP achieved more effective transfection than the approved ALC-0315-LNP. Following this, IL-2F mRNAs, encoding fusion proteins comprising IL-2, a linker, and CD25 (IL-2Rα), were designed and synthesized through in vitro transcription. A cleavable linker, consisting of the peptide sequence SGRSEN↓IRTA, was selected for cleavage by matrix metalloproteinase-14 (MMP-14). IL-2F mRNA was then encapsulated in U-101-LNP to create U-101-LNP/IL-2F mRNA complexes. After optimization, assessments of expression efficiency, masking, and release characteristics revealed that IL-2F with linker C4 demonstrated superior performance. Finally, the antitumor activity of IL-2F mRNA was evaluated. The results indicated that U-101-LNP/IL-2F mRNA achieved the strongest antitumor effect, with an inhibition rate of 70.3%. Immunohistochemistry observations revealed significant expressions of IL-2, IFN-γ, and CD8, suggesting an up-regulation of immunomodulation in tumor tissues. This effect could be ascribed to the expression of IL-2F, followed by the cleavage of the linker under the action of MMP-14 in tumor tissue, which sustainably releases IL-2. H&E staining of tissues treated with U-101-LNP/IL-2F mRNA showed no abnormalities. Further evaluations indicated that the U-101-LNP/IL-2F mRNA group maintained proper levels of inflammatory factors without obvious alterations in liver and renal functions. Taken together, the U-101-LNP/IL-2F mRNA formulation demonstrated effective antitumor activity and safety, which suggests potential applicability in clinical immunotherapy.

Pharmacokinetics, pharmacodynamics, and toxicity of a PD-1-targeted IL-15 in cynomolgus monkeys

PF-07209960 is a novel bispecific fusion protein composed of an anti-PD-1 antibody and engineered IL-15 cytokine mutein with reduced binding affinity to its receptors. The pharmacokinetics (PK), pharmacodynamics (PD), and toxicity of PF-07209960 were evaluated following once every other week subcutaneous (SC) or intravenous (IV) administration to cynomolgus monkeys in a repeat-dose PKPD (0.01-0.3 mg/kg/dose) and GLP toxicity study (0.1-3 mg/kg/dose). PF-07209960 showed dose dependent pharmacokinetics with a terminal T1/2 of 8 and 13 hours following IV administration at 0.03 and 0.1 mg/kg, respectively. The clearance is faster than a typical IgG1 antibody. Slightly faster clearance was also observed following the second dose, likely due to increased target pool and formation of anti-drug antibodies (ADA). Despite a high incidence rate of ADA (92%) observed in GLP toxicity study, PD-1 receptor occupancy, IL-15 signaling (STAT5 phosphorylation) and T cell expansion were comparable following the first and second doses. Activation and proliferation of T cells were observed with largest increase in cell numbers found in gamma delta T cells, followed by CD4+ and CD8+ T cells, and then NK cells. Release of cytokines IL-6, IFNγ, and IL-10 were detected, which peaked at 72 hours postdose. There was PF-07209960-related mortality at ≥1 mg/kg. At scheduled necropsy, microscopic findings were generalized mononuclear infiltration in various tissues. Both the no observed adverse effect level (NOAEL) and the highest non severely toxic dose (HNSTD) were determined to be 0.3 mg/kg/dose, which corresponded to mean Cmax and AUC48 values of 1.15 μg/mL and 37.9 μg*h/mL, respectively.

BRAIDing receptors for cell-specific targeting

Systemic toxicity is a major challenge in the development of therapeutics. Consequently, cell-type-specific targeting is needed to improve on-target efficacy while reducing off-target toxicity. Here, we describe a cell-targeting system we have termed BRAID (BRidged Activation by Intra/intermolecular Division) whereby an active molecule is divided into two inactive or less active parts that are subsequently brought together via a so-called 'bridging receptor' on the target cell. This concept was validated using the WNT/β-catenin signaling system, demonstrating that a multivalent WNT agonist molecule divided into two inactive components assembled from different epitopes via the hepatocyte receptor βKlotho induces signaling specifically on hepatocytes. These data provide proof of concept for this cell-specific targeting strategy, and in principle, this may also allow activation of multiple signaling pathways where desirable. This approach has broad application potential for other receptor systems.

Innate Immunity in Cancer Biology and Therapy

Immunotherapies including adaptive immune checkpoint inhibitors (ICIs) and chimeric antigen receptor (CAR) T cells, have developed the treatment of cancer in clinic, and most of them focus on activating T cell immunity. Although these strategies have obtained unprecedented clinical responses, only limited subsets of cancer patients could receive long-term benefits, highlighting the demand for identifying novel targets for the new era of tumor immunotherapy. Innate immunity has been demonstrated to play a determinative role in the tumor microenvironment (TME) and influence the clinical outcomes of tumor patients. A thorough comprehension of the innate immune cells that infiltrate tumors would allow for the development of new therapeutics. In this review, we outline the role and mechanism of innate immunity in TME. Moreover, we discuss innate immunity-based cancer immunotherapy in basic and clinical studies. Finally, we summarize the challenges in sufficiently motivating innate immune responses and the corresponding strategies and measures to improve anti-tumor efficacy. This review could aid the comprehension of innate immunity and inspire the creation of brand-new immunotherapies for the treatment of cancer.

A split, conditionally active mimetic of IL-2 reduces the toxicity of systemic cytokine therapy

The therapeutic potential of recombinant cytokines has been limited by the severe side effects of systemic administration. We describe a strategy to reduce the dose-limiting toxicities of monomeric cytokines by designing two components that require colocalization for activity and that can be independently targeted to restrict activity to cells expressing two surface markers. We demonstrate the approach with a previously designed mimetic of cytokines interleukin-2 and interleukin-15-Neoleukin-2/15 (Neo-2/15)-both for trans-activating immune cells surrounding targeted tumor cells and for cis-activating directly targeted immune cells. In trans-activation mode, tumor antigen targeting of the two components enhanced antitumor activity and attenuated toxicity compared with systemic treatment in syngeneic mouse melanoma models. In cis-activation mode, immune cell targeting of the two components selectively expanded CD8+ T cells in a syngeneic mouse melanoma model and promoted chimeric antigen receptor T cell activation in a lymphoma xenograft model, enhancing antitumor efficacy in both cases.

Strategies for Conditional Regulation of Proteins

Design of the next-generation of therapeutics, biosensors, and molecular tools for basic research requires that we bring protein activity under control. Each protein has unique properties, and therefore, it is critical to tailor the current techniques to develop new regulatory methods and regulate new proteins of interest (POIs). This perspective gives an overview of the widely used stimuli and synthetic and natural methods for conditional regulation of proteins.

A Protease Activatable Interleukin-2 Fusion Protein Engenders Antitumor Immune Responses by Interferon Gamma-Dependent and Interferon Gamma-Independent Mechanisms

Cytokines are powerful mediators of immune responses and some, such as interleukin-2 (IL-2), have achieved dramatic responses as cancer immunotherapies. Unfortunately, systemic administration often results in deleterious side effects, prompting exploration of strategies to localize cytokine activity to the tumor microenvironment (TME). To this end, we constructed an IL-2/IL2Ra fusion protein (IL-2FP) with an MMP2/9-specific cleavage site, designed to exploit the dysregulated protease activity in the TME to selectively activate IL-2 in the tumor. To determine if TME protease activity is sufficient to cleave the FP and if FP activity is due to specific cleavage, we created Colon 38 tumor cell lines expressing similar levels of IL-2FPs with either a functional cleavage site [H11(cs-1FP)] or a scrambled, noncleavable sequence [H2(scramFP)]. H11(cs-1FP) tumors demonstrated reduced tumor growth, characterized by regressions not observed in H2(scramFP) tumors. Analysis through qRT-PCR, flow cytometry, and immunohistochemistry indicate robust CD8 responses in the H11(cs-1FP) tumors. Interferon gamma (IFNg) knockout mice revealed that the immune effects of the cleavable FP are mediated through both IFNg-dependent and IFNg-independent mechanisms. Collectively, these data suggest that matrix metalloproteinases (MMPs) in the TME can cleave the IL-2FP specifically, thus enhancing an antitumor response, and provide a rationale for further developing this approach.

Masking the immunotoxicity of interleukin-12 by fusing it with a domain of its receptor via a tumour-protease-cleavable linker

Immune-checkpoint inhibitors have shown modest efficacy against immunologically 'cold' tumours. Interleukin-12 (IL-12)-a cytokine that promotes the recruitment of immune cells into tumours as well as immune cell activation, also in cold tumours-can cause severe immune-related adverse events in patients. Here, by exploiting the preferential overexpression of proteases in tumours, we show that fusing a domain of the IL-12 receptor to IL-12 via a linker cleavable by tumour-associated proteases largely restricts the pro-inflammatory effects of IL-12 to tumour sites. In mouse models of subcutaneous adenocarcinoma and orthotopic melanoma, masked IL-12 delivered intravenously did not cause systemic IL-12 signalling and eliminated systemic immune-related adverse events, led to potent therapeutic effects via the remodelling of the immune-suppressive microenvironment, and rendered cold tumours responsive to immune-checkpoint inhibition. We also show that masked IL-12 is activated in tumour lysates from patients. Protease-sensitive masking of potent yet toxic cytokines may facilitate their clinical translation.

Exploiting protease activation for therapy

Proteases have crucial roles in homeostasis and disease; and protease inhibitors and recombinant proteases in enzyme replacement therapy have become key therapeutic applications of protease biology across several indications. This review briefly summarises therapeutic approaches based on protease activation and focuses on how recent insights into the spatial and temporal control of the proteolytic activation of growth factors and interleukins are leading to unique strategies for the discovery of new medicines. In particular, two emerging areas are covered: the first is based on antibody therapies that target the process of proteolytic activation of the pro-form of proteins rather than their mature form; the second covers a potentially new class of biopharmaceuticals using engineered, proteolytically activable and initially inactive pro-forms of antibodies or effector proteins to increase specificity and improve the therapeutic window.

Massively parallel, computationally guided design of a proenzyme

Proteins have shown promise as therapeutics and diagnostics, but their effectiveness is limited by our inability to spatially target their activity. To overcome this limitation, we developed a computationally guided method to design inactive proenzymes or zymogens, which are activated through cleavage by a protease. Since proteases are differentially expressed in various tissues and disease states, including cancer, these proenzymes could be targeted to the desired microenvironment. We tested our method on the therapeutically relevant protein carboxypeptidase G2 (CPG2). We designed Pro-CPG2s that are inhibited by 80 to 98% and are partially to fully reactivatable following protease treatment. The developed methodology, with further refinements, could pave the way for routinely designing protease-activated protein-based therapeutics and diagnostics that act in a spatially controlled manner.

Confining the activity of a designed protein to a specific microenvironment would have broad-ranging applications, such as enabling cell type-specific therapeutic action by enzymes while avoiding off-target effects. While many natural enzymes are synthesized as inactive zymogens that can be activated by proteolysis, it has been challenging to redesign any chosen enzyme to be similarly stimulus responsive. Here, we develop a massively parallel computational design, screening, and next-generation sequencing-based approach for proenzyme design. For a model system, we employ carboxypeptidase G2 (CPG2), a clinically approved enzyme that has applications in both the treatment of cancer and controlling drug toxicity. Detailed kinetic characterization of the most effectively designed variants shows that they are inhibited by ∼80% compared to the unmodified protein, and their activity is fully restored following incubation with site-specific proteases. Introducing disulfide bonds between the pro- and catalytic domains based on the design models increases the degree of inhibition to 98% but decreases the degree of restoration of activity by proteolysis. A selected disulfide-containing proenzyme exhibits significantly lower activity relative to the fully activated enzyme when evaluated in cell culture. Structural and thermodynamic characterization provides detailed insights into the prodomain binding and inhibition mechanisms. The described methodology is general and could enable the design of a variety of proproteins with precise spatial regulation.

Role of Serine Proteases at the Tumor-Stroma Interface

During tumor development, invasion and metastasis, the intimate interaction between tumor and stroma shapes the tumor microenvironment and dictates the fate of tumor cells. Stromal cells can also influence anti-tumor immunity and response to immunotherapy. Understanding the molecular mechanisms that govern this complex and dynamic interplay, thus is important for cancer diagnosis and therapy. Proteolytic enzymes that are expressed and secreted by both cancer and stromal cells play important roles in modulating tumor-stromal interaction. Among, several serine proteases such as fibroblast activation protein, urokinase-type plasminogen activator, kallikrein-related peptidases, and granzymes have attracted great attention owing to their elevated expression and dysregulated activity in the tumor microenvironment. This review highlights the role of serine proteases that are mainly derived from stromal cells in tumor progression and associated theranostic applications.

A tumor-specific pro-IL-12 activates preexisting cytotoxic T cells to control established tumors

[Figure: see text].

Tumor-conditional IL-15 pro-cytokine reactivates anti-tumor immunity with limited toxicity

IL-15 is a promising cytokine to expand NK and CD8⁺ T cells for cancer immunotherapy, but its application is limited by dose-limiting, on-target off-tumor toxicity. Here, we have developed a next-generation IL-15 that is activated inside the tumor microenvironment (TME). This pro-IL-15 has the extracellular domain of IL-15Rβ fused to the N-terminus of sIL-15-Fc through a tumor-enriched Matrix Metalloproteinase (MMP) cleavable peptide linker to block its activity. Unlike sIL-15-Fc, pro-IL-15 does not activate the peripheral expansion of NK cells and T cells, thus reducing systemic toxicity, but it still preserves efficient anti-tumor abilities. In various mouse tumors, the anti-tumor effect of pro-IL-15 depends on intratumoral CD8⁺ T cells and IFN-γ. Pro-IL-15 increases the stem-like TCF1⁺Tim-3^-CD8⁺ T cells within tumor tissue and helps overcome immune checkpoint blockade (ICB) resistance. Moreover, pro-IL-15 synergizes with current tyrosine kinase inhibitor (TKI) targeted-therapy in a poorly inflamed TUBO tumor model, suggesting that pro-IL-15 helps overcome targeted-therapy resistance. Our results demonstrate a next-generation IL-15 cytokine that can stimulate potent anti-tumor activity without severe toxicity.

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.

A cytokine receptor-masked IL2 prodrug selectively activates tumor-infiltrating lymphocytes for potent antitumor therapy

As a potent lymphocyte activator, interleukin-2 (IL-2) is an FDA-approved treatment for multiple metastatic cancers. However, its clinical use is limited by short half-life, low potency, and severe in vivo toxicity. Current IL-2 engineering strategies exhibit evidence of peripheral cytotoxicity. Here, we address these issues by engineering an IL-2 prodrug (ProIL2). We mask the activity of a CD8 T cell-preferential IL-2 mutein/Fc fusion protein with IL2 receptor beta linked to a tumor-associated protease substrate. ProIL2 restores activity after cleavage by tumor-associated enzymes, and preferentially activates inside tumors, where it expands antigen-specific CD8 T cells. This significantly reduces IL-2 toxicity and mortality without compromising antitumor efficacy. ProIL2 also overcomes resistance of cancers to immune checkpoint blockade. Lastly, neoadjuvant ProIL2 treatment can eliminate metastatic cancer through an abscopal effect. Taken together, our approach presents an effective tumor targeting therapy with reduced toxicity.

ALKS 4230: a novel engineered IL-2 fusion protein with an improved cellular selectivity profile for cancer immunotherapy

BACKGROUND

Interleukin-2 (IL-2) plays a pivotal role in immune homeostasis due to its ability to stimulate numerous lymphocyte subsets including natural killer (NK) cells, effector CD4⁺ and CD8⁺ T cells, and regulatory T cells (T_regs). Low concentrations of IL-2 induce signaling through the high-affinity IL-2 receptor (IL-2R) comprised of IL-2Rα, IL-2Rβ, and common γ chain (γ_c), preferentially expressed on T_regs. Higher concentrations of IL-2 are necessary to induce signaling through the intermediate-affinity IL-2R, composed of IL-2Rβ and γ_c, expressed on memory CD8⁺ T cells and NK cells. Recombinant human IL-2 (rhIL-2) is approved for treatment of metastatic melanoma and renal cell carcinoma (RCC), but adverse events including capillary leak syndrome, potentially mediated through interaction with the high-affinity IL-2R, limit its therapeutic use. Furthermore, antitumor efficacy of IL-2 may also be limited by preferential expansion of immunosuppressive T_regs. ALKS 4230 is an engineered fusion protein comprised of a circularly-permuted IL-2 with the extracellular domain of IL-2Rα, designed to selectively activate effector lymphocytes bearing the intermediate-affinity IL-2R.

RESULTS

ALKS 4230 was equipotent to rhIL-2 in activating human cells bearing the intermediate-affinity IL-2R, and less potent than rhIL-2 on cells bearing the high-affinity IL-2R. As observed in vitro with primary human cells from healthy donors and advanced cancer patients, ALKS 4230 induced greater activation and expansion of NK cells with reduced expansion of T_regs relative to rhIL-2. Similarly, in mice, ALKS 4230 treatment stimulated greater expansion of NK cells and memory-phenotype CD8⁺ T cells at doses that did not expand or activate T_regs. ALKS 4230 treatment induced significantly lower levels of proinflammatory cytokines, including tumor necrosis factor alpha, interleukin-6, and interferon gamma relative to rhIL-2. Furthermore, ALKS 4230 exhibited superior antitumor efficacy in the mouse B16F10 lung tumor model, where ALKS 4230 could be administered via multiple routes of administration and dosing schedules while achieving equivalent antitumor efficacy.

CONCLUSIONS

ALKS 4230 exhibited enhanced pharmacokinetic and selective pharmacodynamic properties resulting in both improved antitumor efficacy and lower indices of toxicity relative to rhIL-2 in mice. These data highlight the potential of ALKS 4230 as a novel cancer immunotherapy, and as such, the molecule is being evaluated clinically.

Development of oncolytic virotherapy: from genetic modification to combination therapy

Oncolytic virotherapy (OVT) is a novel form of immunotherapy using natural or genetically modified viruses to selectively replicate in and kill malignant cells. Many genetically modified oncolytic viruses (OVs) with enhanced tumor targeting, antitumor efficacy, and safety have been generated, and some of which have been assessed in clinical trials. Combining OVT with other immunotherapies can remarkably enhance the antitumor efficacy. In this work, we review the use of wild-type viruses in OVT and the strategies for OV genetic modification. We also review and discuss the combinations of OVT with other immunotherapies.

Development of an Interleukin-12 Fusion Protein That Is Activated by Cleavage with Matrix Metalloproteinase 9

Interleukin-12 (IL-12) is a pleiotropic cytokine that has profound effects on many aspects of cell-mediated responses and can enhance antitumor responses in experimental models. IL-12 has been tested clinically, however, side-effects have limited its use. We are developing an attenuated form of IL-12 whose biological activity could be restricted to sites of tumors by taking advantage of overexpressed tumor proteases that can activate the cytokine. We constructed a panel of fusion proteins (FPs) consisting of IL-12 joined to a specific inhibitor connected by a protease cleavage sequence (cs). We first identified a panel of single-chain Fragment variable (scFv) that bind to 3 independent epitopes on IL-12 and then incorporated them into separate IL-12 FPs containing either a matrix metalloproteinase (MMP) cs or a scrambled (scram) control cs. The intact IL-12 FPs showed attenuation in IL-12 activity compared to free IL-12 in 2 separate in vitro functional assays; proliferation of CTLL-2 and interferon-gamma (IFN-γ) induction by spleen cells. Furthermore, the FP containing the MMPcs showed an increase in biological activity of IL-12 in vitro when cleaved by MMP9. This FP strategy could be applied to other immunomodulators and potentially reduce unwanted side-effects observed with systemic delivery thus improving cytokine immunotherapy strategies.

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.

Modifying the cancer-immune set point using vaccinia virus expressing re-designed interleukin-2

The complex immune tumour microenvironment requires an equally complex immunotherapy approach, especially when the cancer-immune set point is non-inflamed. Oncolytic viruses expressing immune activating cytokines might optimally modify the immune microenvironment and improve the antitumour effects. In this study, we have explored a variety of IL-2 constructs expressed by a tumour-selective oncolytic vaccinia virus, designed to maintain IL-2 in the tumour microenvironment to reduce systemic toxicity. An IL-2 construct combining a glycosylphosphatidylinositol (GPI) anchor with a rigid peptide linker leads to functional IL-2 expression on the tumour cell surface and in the tumour microenvironment. This virus construct effectively modifies the cancer-immune set point and treats a variety of murine tumour models with no toxic side effects. In combination with PD-1/PD-L1 blockade this virus cures most of the mice with a high tumour burden. This combination represents a treatment for cancers which are to date unresponsive to immunotherapy.

IL-2 is used systemically for cancer therapy but it is associated with severe toxicity. Here, the authors design a recombinant vaccinia virus expressing membrane-bound IL-2 that shows therapeutic efficacy alone or in combination with checkpoint inhibitors in colon cancer-bearing mice.

IL-2/CD25: A Long-Acting Fusion Protein That Promotes Immune Tolerance by Selectively Targeting the IL-2 Receptor on Regulatory T Cells

Low-dose IL-2 represents an immunotherapy to selectively expand regulatory T cells (Tregs) to promote tolerance in patients with autoimmunity. In this article, we show that a fusion protein (FP) of mouse IL-2 and mouse IL-2Rα (CD25), joined by a noncleavable linker, has greater in vivo efficacy than rIL-2 at Treg expansion and control of autoimmunity. Biochemical and functional studies support a model in which IL-2 interacts with CD25 in the context of this FP in trans to form inactive head-to-tail dimers that slowly dissociate into an active monomer. In vitro, IL-2/CD25 has low sp. act. However, in vivo IL-2/CD25 is long lived to persistently and selectively stimulate Tregs. In female NOD mice, IL-2/CD25 administration increased Tregs within the pancreas and reduced the instance of spontaneous diabetes. Thus, IL-2/CD25 represents a distinct class of IL-2 FPs with the potential for clinical development for use in autoimmunity or other disorders of an overactive immune response.

A factor XIa-activatable hirudin-albumin fusion protein reduces thrombosis in mice without promoting blood loss

Background

Hirudin is a potent thrombin inhibitor but its antithrombotic properties are offset by bleeding side-effects. Because hirudin’s N-terminus must engage thrombin’s active site for effective inhibition, fusing a cleavable peptide at this site may improve hirudin’s risk/benefit ratio as a therapeutic agent. Previously we engineered a plasmin cleavage site (C) between human serum albumin (HSA) and hirudin variant 3 (HV3) in fusion protein HSACHV3. Because coagulation factor XI (FXI) is more involved in thrombosis than hemostasis, we hypothesized that making HV3 activity FXIa-dependent would also improve HV3’s potential therapeutic profile. We combined albumin fusion for half-life extension of hirudin with positioning of an FXIa cleavage site N-terminal to HV3, and assessed in vitro and in vivo properties of this novel protein.

Results

FXIa cleavage site EPR was employed. Fusion protein EPR-HV3HSA but not HSAEPR-HV3 was activated by FXIa in vitro. FVIIa, FXa, FXIIa, or plasmin failed to activate EPR-HV3HSA. FXIa-cleavable EPR-HV3HSA reduced the time to occlusion of ferric chloride-treated murine arteries and reduced fibrin deposition in murine endotoxemia; noncleavable mycHV3HSA was without effect. EPR-HV3HSA elicited less blood loss than constitutively active HV3HSA in murine liver laceration or tail transection but extended bleeding time to the same extent. EPR-HV3HSA was partially activated in citrated human or murine plasma to a greater extent than HSACHV3.

Conclusions

Releasing the N-terminal block to HV3 activity using FXIa was an effective way to limit hirudin’s bleeding side-effects, but plasma instability of the exposed EPR blocking peptide rendered it less useful than previously described plasmin-activatable HSACHV3.

Delivering safer immunotherapies for cancer

Cancer immunotherapy is now a powerful clinical reality, with a steady progression of new drug approvals and a massive pipeline of additional treatments in clinical and preclinical development. However, modulation of the immune system can be a double-edged sword: Drugs that activate immune effectors are prone to serious non-specific systemic inflammation and autoimmune side effects. Drug delivery technologies have an important role to play in harnessing the power of immune therapeutics while avoiding on-target/off-tumor toxicities. Here we review mechanisms of toxicity for clinically-relevant immunotherapeutics, and discuss approaches based in drug delivery technology to enhance the safety and potency of these treatments. These include strategies to merge drug delivery with adoptive cellular therapies, targeting immunotherapies to tumors or select immune cells, and localizing therapeutics intratumorally. Rational design employing lessons learned from the drug delivery and nanomedicine fields has the potential to facilitate immunotherapy reaching its full potential.

Engineering carboxypeptidase G2 circular permutations for the design of an autoinhibited enzyme

Carboxypeptidase G2 (CPG2) is an Food and Drug Administration (FDA)-approved enzyme drug used to treat methotrexate (MTX) toxicity in cancer patients receiving MTX treatment. It has also been used in directed enzyme-prodrug chemotherapy, but this strategy has been hampered by off-site activation of the prodrug by the circulating enzyme. The development of a tumor protease activatable CPG2, which could be achieved using a circular permutation of CPG2 fused to an inactivating 'prodomain', would aid in these applications. We report the development of a protease accessibility-based screen to identify candidate sites for circular permutation in proximity of the CPG2 active site. The resulting six circular permutants showed similar expression, structure, thermal stability, and, in four cases, activity levels compared to the wild-type enzyme. We rationalize these results based on structural models of the permutants obtained using the Rosetta software. We developed a cell growth-based selection system, and demonstrated that when fused to periplasm-directing signal peptides, one of our circular permutants confers MTX resistance in Escherichia coli with equal efficiency as the wild-type enzyme. As the permutants have similar properties to wild-type CPG2, these enzymes are promising starting points for the development of autoinhibited, protease-activatable zymogen forms of CPG2 for use in therapeutic contexts.

Role of IL-2 in cancer immunotherapy

Interleukin-2 (IL-2) is one of the key cytokines with pleiotropic effects on immune system. It has been approved for the treatment of metastatic renal cell carcinoma and metastatic melanoma. Recent progress has been made in our understanding of IL-2 in regulating lymphocytes that has led to exciting new directions for cancer immunotherapy. While improved IL-2 formulations might be used as monotherapies, their combination with other anticancer immunotherapies, such as adoptive cell transfer regimens, antigen-specific vaccination, and blockade of immune checkpoint inhibitory molecules, for example cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1) mono-antibodies, would held the promise of treating metastatic cancer. Despite the comprehensive studies of IL-2 on immune system have established the application of IL-2 for cancer immunotherapy, a number of poignant obstacles remain for future research. In the present review, we will focus on the key biological features of IL-2, current applications, limitations, and future directions of IL-2 in cancer immunotherapy.

Animal models of colorectal peritoneal metastasis

Colorectal cancer remains an important cause of mortality worldwide. The presence of peritoneal carcinomatosis (PC) causes significant symptoms and is notoriously difficult to treat. Therefore, informative preclinical research into the mechanisms and possible novel treatment options of colorectal PC is essential in order to improve the prognostic outlook in these patients. Several syngeneic and xenograft animal models of colorectal PC were established, studying a wide range of experimental procedures and substances. Regrettably, more sophisticated models such as those giving rise to spontaneous PC or involving genetically engineered mice are lacking. Here, we provide an overview of all reported colorectal PC animal models and briefly discuss their use, strengths, and limitations.

Characterization of an IL-12 p40/p35 Truncated Fusion Protein That can Inhibit the Action of IL-12

Interleukin-12 (IL-12), a potent inducer of interferon gamma (IFNγ), is a heterodimeric protein consisting of p40 and p35 subunits whose expression is regulated independently. IL-12 is part of a cytokine family (currently consisting of IL-12, IL-23, IL-27, and IL-35) that can have profoundly different immunologic effects, despite sharing subunits. In constructing a single-chain fusion of p40 and p35, we discovered an insert corresponding to an intron in the gene encoding the p35 subunit that would result in a truncated form of p35 if translated. To test its possible role, we constructed, expressed, and analyzed fusions of p40 with the full-length or the truncated form of p35. The fusion protein containing the truncated p35 did not stimulate the proliferation of the IL-12-responsive cell line CTLL-2 nor did it induce IFNγ or the chemokine IFNγ-inducible protein 10 (IP-10, CXCL10) or monokine induced by IFNγ (MIG, CXCL9) from spleen cells. In striking contrast, the full-length IL-12 p40/p35 fusion induced robust responses in both assays. Moreover, the truncated IL-12 fusion protein inhibited the action of the full-length IL-12 p40/p35 fusion in the proliferation assay and also blocked the induction of IFNγ. These findings raise the possibility that alternative splicing may provide an additional regulatory mechanism for IL-12.

Challenges and developing solutions for increasing the benefits of IL-2 treatment in tumor therapy

Interleukin-2 (IL-2) is a cytokine with pleiotropic effects on the immune system. Systemic IL-2 treatment has produced durable responses in melanoma and renal cancer patients, but unfortunately this is effective only in a fraction of patients. Moreover, IL-2 treatment also engenders serious side effects, which limit its clinical utility. It is now appreciated that IL-2 not only stimulates NK and effector T cells but also has a critical role in the generation and maintenance of regulatory T cells, which act to dampen immune responses. Thus, successful immunotherapy of cancers using IL-2 has to address two fundamentally important issues: (1) how to limit side effects yet be active where it is needed, and (2) how to preferentially activate effector T cells while limiting the stimulation of Tregs. Strategies are now being developed to address these critical obstacles that may lead to a renaissance of IL-2 therapy.

Generation of a dual-functioning antitumor immune response in the peritoneal cavity

Tumor cell metastasis to the peritoneal cavity is observed in patients with tumors of peritoneal organs, particularly colon and ovarian tumors. Following release into the peritoneal cavity, tumor cells rapidly attach to the omentum, a tissue consisting of immune aggregates embedded in adipose tissue. Despite their proximity to potential immune effector cells, tumor cells grow aggressively on these immune aggregates. We hypothesized that activation of the immune aggregates would generate a productive antitumor immune response in the peritoneal cavity. We immunized mice i.p. with lethally irradiated cells of the colon adenocarcinoma line Colon38. Immunization resulted in temporary enlargement of immune aggregates, and after challenge with viable Colon38 cells, we did not detect tumor growth on the omentum. When Colon38-immunized mice were challenged with cells from the unrelated breast adenocarcinoma line E0771 or the melanoma line B16, these tumors also did not grow. The nonspecific response was long-lived and not present systemically, highlighting the uniqueness of the peritoneal cavity. Cellular depletions of immune subsets revealed that NK1.1(+) cells were essential in preventing growth of unrelated tumors, whereas NK1.1(+) cells and T cells were essential in preventing Colon38 tumor growth. Collectively, these data demonstrate that the peritoneal cavity has a unique environment capable of eliciting potent specific and nonspecific antitumor immune responses.

IFN-γ mediates the antitumor effects of radiation therapy in a murine colon tumor

Cancer treatments using ionizing radiation (IR) therapy are thought to act primarily through the induction of tumor cell damage at a molecular level. However, a new concept has recently emerged, suggesting that the immune system is required for effective IR therapy. Our work here has identified interferon gamma (IFN-γ) as an essential cytokine for the efficacy of IR therapy. Local IR (15 Gy) to mice bearing Colon38, a colon adenocarcinoma, decreases tumor burden in wild-type animals. Interestingly, IR therapy had no effect on tumor burden in IFNγKO mice. We further determined that intratumoral levels of IFN-γ increased 2 days following IR, which directly correlated with a decrease in tumor burden that was not a result of direct cytotoxic effects of IFN-γ on tumor cells. T cells from IR-treated tumors exhibited a far greater capacity to lyse tumor cells in a (51)Cr release assay, a process that was dependent on IFN-γ. CD8(+) T cells were the predominant producers of IFN-γ, as demonstrated by IFN-γ intracellular staining and studies in IFN-γ reporter mice. Elimination of CD8(+) T cells by antibody treatment reduced the intratumoral levels of IFN-γ by over 90%. More importantly, elimination of CD8(+) T cells completely abrogated the effects of radiation therapy. Our data suggest that IFN-γ plays a pivotal role in mediating the antitumor effects of IR therapy.

Local expression of interleukin-2 by B16 melanoma cells results in decreased tumour growth and long-term tumour dormancy

The tumour microenvironment is complex containing not only neoplastic cells but also a variety of host cells. The heterogeneous infiltrating immune cells include subsets of cells with opposing functions, whose activities are mediated either directly or through the cytokines they produce. Systemic delivery of cytokines such as interleukin-2 ( IL-2) has been used clinically to enhance anti-tumour responses, but these molecules are generally thought to have evolved to act locally in a paracrine fashion. In this study we examined the effect of local production of IL-2 on the growth and the immune response to B16 melanoma cells. We found that the local production of IL-2 enhances the number of interferon-γ-expressing CD8 T and natural killer cells in the tumour, as well as inducing expression of vascular cell adhesion molecule 1 on tumour vessels. These responses were largely absent in interferon-γ knockout mice. The expression of IL-2 in the tumour microenvironment decreases tumour growth despite also enhancing Foxp3(+)  CD4(+) regulatory T cells and anti-inflammatory cytokines such as IL-10. Higher levels of IL-2 in the tumour microenvironment eliminated the progressive growth of the B16 cells in vivo, and this inhibition was dependent on the presence of either T cells or, to a lesser extent, natural killer cells. Surprisingly however, the B16 tumours were not completely eliminated but instead were controlled for an extended period of time, suggesting that a form of tumour dormancy was established.