Costimulatory T-cell engagement by PRS-343, a CD137 (4-1BB)/HER2 bispecific, leads to tumor growth inhibition and TIL expansion in a humanized mouse model

Protein scaffolds: Antibody alternative for cancer diagnosis and therapy

Although antibodies are well developed and widely used in cancer therapy and diagnostic fields, some defects remain, such as poor tissue penetration, long in vivo metabolic retention, potential cytotoxicity, patent limitation, and high production cost. These issues have led scientists to explore and develop novel antibody alternatives. Protein scaffolds are small monomeric proteins with stable tertiary structures and mutable residues, which emerged in the 1990s. By combining robust gene engineering and phage display techniques, libraries with sufficient diversity could be established for target binding scaffold selection. Given the properties of small size, high affinity, and excellent specificity and stability, protein scaffolds have been applied in basic research, and preclinical and clinical fields over the past two decades. To date, more than 20 types of protein scaffolds have been developed, with the most frequently used being affibody, adnectin, ANTICALIN®, DARPins, and knottin. In this review, we focus on the protein scaffold applications in cancer therapy and diagnosis in the last 5 years, and discuss the pros and cons, and strategies of optimization and design.

Although antibodies are well developed and widely used in cancer therapy and diagnostic fields, some defects remain, such as poor tissue penetration, long in vivo metabolic retention, potential cytotoxicity, patent limitation, and high production cost.

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.

New insights into affinity proteins for HER2-targeted therapy: Beyond trastuzumab

Human epidermal growth factor receptor 2 (HER2) is known as a potential target for both cancer treatment and diagnosis. One of the most interesting HER2-targeted therapeutics is an affinity protein which selectively recognizes and binds to a defined target. Trastuzumab is a monoclonal antibody which has been approved as the first affinity proteins for treatment of some HER2-positive cancers including breast cancer. Despite initial response to trastuzumab, the majority of patients with metastatic HER2-positive breast cancer still show resistance to the therapy. Recently, various anti-HER2 affinity proteins, including antibodies, antibody fragments (e.g., Fab and scFv) and other protein scaffolds (e.g., affibody and DARPin), alone or fused/conjugated with therapeutic agents (e.g., proteins, drugs and radioisotopes) have been developed to overcome the trastuzumab resistance. Here, we review these engineered affinity proteins which are either clinically approved or under evaluation. Modern technologies and future prospects for their clinical applications in cancer treatment are also discussed.

Novel HER2-targeted therapies for HER2-positive metastatic breast cancer

Human epidermal growth factor receptor 2 (HER2) is overexpressed in approximately 20% of all breast cancers. Before the development of HER2-directed monoclonal antibodies, HER2-positive breast cancer was associated with a rather poor prognosis. With the advent of monoclonal HER2-targeting antibodies (trastuzumab and pertuzumab) and antibody-drug conjugates (trastuzumab emtansine [T-DM1] and trastuzumab deruxtecan), clinical outcomes for HER2-positive breast cancer have dramatically changed, and a greater proportion of patients in the nonmetastatic setting are cured. However, in the metastatic setting, resistance to anti-HER2 treatments still remains a major therapeutic challenge, underscoring the importance of developing novel HER2-directed therapies. Over the last year, there has been a dramatic shift in the current treatment paradigms for HER2-positive metastatic breast cancer, with recent U.S. Food and Drug Administration approvals of trastuzumab deruxtecan (DS-8201), neratinib, and tucatinib in combination with trastuzumab and capecitabine. The authors summarize recent phase 3 data with novel HER2-targeted therapies as well as phase 1 and 2 data with other novel HER2-targeting agents.

The relevance of soluble CD137 in the regulation of immune responses and for immunotherapeutic intervention

CD137 is a potent costimulatory receptor. Several agonistic anti-CD137 antibodies are currently in clinical trials for tumor immunotherapy. Soluble forms of CD137 (sCD137) are generated by differential splicing and antagonize the activities of membrane-bound CD137 (mCD137) and of therapeutic CD137 agonists. sCD137 is found in sera of patients suffering from autoimmune diseases where it is a natural regulator of immune responses, and which has therapeutic potential for immune-mediated diseases. This review summarizes the current knowledge on sCD137, highlights its potential role in immunotherapy against cancer and in autoimmune diseases, and presents important issues to be addressed by future research.

Redrawing the Lines: The Next Generation of Treatment in Metastatic Breast Cancer

Although not considered curative in nature, new therapeutic advances in metastatic breast cancer (MBC) have substantially improved patient outcomes. This article discusses the state-of-the-art and emerging therapeutic options for management of MBC. BC systemic therapy targets multiple key pathways, including estrogen receptor signaling, HER2 signaling, and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling. Other therapeutic strategies include targeting DNA repair, inhibiting immune checkpoints, and developing antibody-drug conjugates. Although surgery historically was reserved for palliation of symptomatic, large, or ulcerating masses, some data suggest a possibly expanding role for more aggressive locoregional therapy in combination with systemic therapy. As technology develops, biomarker-specific, line-agnostic, and receptor-agnostic treatment strategies will redraw the current lines of MBC care. However, tumor heterogeneity remains a challenge. To effectively reshape our approach to MBC, careful consideration of the patient perspective, the costs and value of novel treatments, and accessibility (especially in developing countries) is paramount.

Expanding the Boundaries of Biotherapeutics with Bispecific Antibodies

Bispecific antibodies have moved from being an academic curiosity with therapeutic promise to reality, with two molecules being currently commercialized (Hemlibra® and Blincyto®) and many more in clinical trials. The success of bispecific antibodies is mainly due to the continuously growing number of mechanisms of actions (MOA) they enable that are not accessible to monoclonal antibodies. One of the earliest MOA of bispecific antibodies and currently the one with the largest number of clinical trials is the redirecting of the cytotoxic activity of T-cells for oncology applications, now extending its use in infective diseases. The use of bispecific antibodies for crossing the blood-brain barrier is another important application because of its potential to advance the therapeutic options for neurological diseases. Another noteworthy application due to its growing trend is enabling a more tissue-specific delivery or activity of antibodies. The different molecular solutions to the initial hurdles that limited the development of bispecific antibodies have led to the current diverse set of bispecific or multispecific antibody formats that can be grouped into three main categories: IgG-like formats, antibody fragment-based formats, or appended IgG formats. The expanded applications of bispecific antibodies come at the price of additional challenges for clinical development. The rising complexity in their structure may increase the risk of immunogenicity and the multiple antigen specificity complicates the selection of relevant species for safety assessment.