Cytokine application in cancer immunotherapy
In recent years, cancer immunotherapy has substantially progressed and greatly improved patients’ prognosis and survival. Currently, the majority of cancer immunotherapy studies focus on the first T cell activation (TCR) signal and the second signal (CD28), whereas the third-signal cytokines have been under researched and not applied clinically. Actually, cytokines represented the first cancer immunotherapy. In 1986, the U.S. Food and Drug Administration (FDA) approved recombinant IFN-α for the treatment of hairy cell leukemia.
Cytokines are a class of small proteins (typically < 30 kDa) possessing various biological activities and being synthesized and secreted by immune and other non-immune cells (endothelial cells, epidermal cells, fibroblasts, etc.). Cytokines mediate intercellular communication in autocrine and paracrine manners, thereby regulating proliferation, differentiation, survival, and effector functions of immune cells. Depending on their functions, they can be classified into interleukins (ILs), interferons (IFNs), tumor necrosis factors (TNFs), colony-stimulating factors (CSTs), and chemokines.
Cytokine drugs
Owing to their indispensable role in the immune response, several cytokines have been recognized as anti-cancer drug candidates based on preclinical and clinical research. Until today, two products of recombinant cytokines have been approved by the FDA for cancer immunotherapy, including Intron A (interferon alfa-2b) and Proleukin (aldesleukin), respectively (Table1). Intron A has been licensed for the treatment of hairy cell leukemia, malignant melanoma, follicular lymphoma, and AIDS-related Kaposi's sarcoma [1], whereas Proleukin has been licensed for the treatment of metastatic renal cell carcinoma and metastatic melanoma [2].
Furthermore, many other cytokines are being developed, including growth-stimulating factors (G-CSF, GM-CSF), vascular endothelial growth factor (VEGF), IL-2, and IFN-γ as the most extensively studied cytokines in clinical trials (Figure1) [3]. In these studies, recombinant cytokine proteins and their highly pure and active receptors are necessary for many functional assays, such as cytotoxicity assay, control experiment of the cytokine drug candidates, and more. Sino Biological provides a wide recombinant cytokines collection, including all cytokine families and their highly active and pure, and multi-label receptors (Figure 2).
Cytokine limitations
Natural cytokines have limitations that need to be further addressed, including their pleiotropic nature and short serum half-life, although some cytokines have been approved for cancer treatment as monotherapy. The pleiotropic nature of cytokines represents an ability to impact various cell types, leading to different or even opposing biological effects. Meanwhile, the short serum half-life of cytokines necessitates large-dose administration to achieve therapeutic efficacy. These limitations are responsible for modest antitumor efficacy and result in severe side effects.
For example, high IFN-α doses result in severe flu-like syndrome as a side effect, including fever, fatigue, headaches, gastrointestinal symptoms, and myalgias[4]. Also, a decrease in platelets, white blood cells, and neutrophils is a common side effect. Furthermore, the possibility of neuropsychiatric disorders is serious. Another example is treatment with IL-2, where high IL-2 doses are linked to excessive vascular permeability, which can cause vascular leak syndrome and even be fatal [5].
Enzyme-linked immunoassay (ELISA)-based assays can be extensively used for cytokine detection, understanding the half-life of drugs, and monitoring the changes of various cytokines in drug-induced immune responses. Sino Biological has developed a variety of ELISA kits to quantitatively detect cytokines with high sensitivity and specificity (Figure 3).
New strategies
With advances in cancer immunotherapy and biotechnology, multiple strategies are emerging for developing new cytokine-based immunotherapies. The first strategy is extending the half-life. Chemical cytokine modification can substantially prolong the half-life and improve its pharmacokinetics. The most frequent forms are protein conjugation with polyethylene glycol (PEG), known as PEGylation, or antibody-cytokine fusion proteins.
For example, NKTR-214 (bempegaldesleukin) is a PEGlyated IL-2 form that contains IL-2 and multiple covalently linked but releasable PEG chains [6]. It preferentially binds to IL-2Rβγ (IL-2 receptor) on CD8+ T cells and NK cells rather than to IL-2Rαβγ on Treg cells, activating CD8+ T cells and NK cells.IL-2 PEGylation effectively extends IL-2 half-life (to approximately 20 hours) and reduces its systemic toxicity by limiting immediate T cells activation in the peripheral blood. Data from phase I/II clinical trials have demonstrated that as monotherapy, NKTR-214had good antitumor effects and significantly reduced tumor size in patients with metastatic melanoma or renal cell carcinoma [7].
The second strategy is enhancing cytokine specificity. Using mutagenesis techniques, cytokines are modified to change their specificity and affinity to their receptors and improve their antitumor responses. For example, IL-18, an important pro-inflammatory factor belonging to IL-1 family, can bind to its receptor, IL-18R, on the surface of T cells and NK cells to enhance the immune function of these cells. Owing to its immune-activating function, recombinant IL-18 was once used for cancer immunotherapy. However, it failed to show efficacy in phase II clinical trials [8] because IL-18 can induce expression of IL-18BP, an IL-18 decoy receptor and its natural inhibitor, on cancer cells. IL-18BP binds IL-18 with ultra-high affinity and prevents IL-18 from binding to IL-18R, thereby inhibiting the immune-activating function of IL-18.
To address this issue, scientists used directed evolution with yeast surface display to create a “decoy-resistant” IL-18 variant, DR-18, that binds only IL-18R but not IL-18BP [9]. DR-18 showed therapeutic effects no lower than anti-PD-1 in various animal tumor models and could also be used in combination with anti-PD-1 to produce a synergistic effect. Next, DR-18 will be tested in clinical trials.
Another strategy is combination drugs. Therapeutic cytokines are used in combination with other anti-cancer therapies, including monoclonal antibodies or CAR-T cells, to achieve optimal efficacy. Currently, numerous clinical trials on combination drugs are underway [10]. For example, NKTR-214 is being evaluated in phase II and III trials in combination with PD-1 inhibition (NCT03138889 and NCT03635983) or dual CTLA4 and PD-1 inhibition (NCT02983045). PEGylated IL-10 has also been evaluated in combination with pembrolizumab or nivolumab for patients with melanoma, non-small cell lung cancer, or renal cell carcinoma.
Conclusion
Recombinant cytokines have a great potential for cancer immunotherapy. Although only a few drugs have yet been approved, numerous novel cytokines designed by different strategies have entered the clinical trials stage and achieved project milestones. Meanwhile, based on the well-established recombinant protein and antibody technology platform, Sino Biological has developed a series of cytokine-related research reagents, such as recombinant cytokines and their receptors, antibodies, ELISA kits, genes, etc., to support cytokine studies.
References
[1] PRODUCT INFORMATION INTRON A (Interferon alfa-2b). www.fda.gov, accessed January 21, 2022. Reference ID: 4160510
[2] PRODUCT INFORMATION PROLEUKIN (aldesleukin). www.fda.gov, accessed January 21, 2022. Reference ID: 3165255
[3] Qiu Y, Su M, Liu L, Tang Y, Pan Y, Sun J. Clinical Application of Cytokines in Cancer Immunotherapy. Drug Des Devel Ther. 2021;15:2269-2287. doi:10.2147/DDDT.S308578
[4] Waldmann TA. Cytokines in Cancer Immunotherapy. Cold Spring Harb Perspect Biol. 2018;10(12):a028472. doi:10.1101/cshperspect.a028472
[5] Dutcher JP, Schwartzentruber DJ, Kaufman HL, et al. High dose interleukin-2 (Aldesleukin) - expert consensus on best management practices-2014. J Immunother Cancer. 2014;2(1):26. doi:10.1186/s40425-014-0026-0
[6] Doberstein SK. Bempegaldesleukin (NKTR-214): a CD-122-biased IL-2 receptor agonist for cancer immunotherapy. Expert Opin Biol Ther. 2019;19(12):1223-1228. doi:10.1080/14712598.2019.1685489
[7] Bentebibel SE, Hurwitz ME, Bernatchez C, et al. A First-in-Human Study and Biomarker Analysis of NKTR-214, a Novel IL2Rβγ-Biased Cytokine, in Patients with Advanced or Metastatic Solid Tumors. Cancer Discov. 2019;9(6):711-721. doi:10.1158/2159-8290.CD-18-1495
[8] Tarhini AA, Millward M, Mainwaring P, et al. A phase 2, randomized study of SB-485232, rhIL-18, in patients with previously untreated metastatic melanoma. Cancer. 2009; 115(4): 859-868. doi:10.1002/cncr.24100
[9] Zhou T, Damsky W, Weizman OE, et al. IL-18BP is a secreted immune checkpoint and barrier to IL-18 immunotherapy. Nature. 2020;583(7817):609-614. doi:10.1038/s41586-020-2422-6
[10] Propper DJ, Balkwill FR. Harnessing cytokines and chemokines for cancer therapy. Nat Rev Clin Oncol. 2022;10.1038/s41571-021-00588-9. doi:10.1038/s41571-021-00588-9
