TriTACs, a Novel Class of T-Cell-Engaging Protein Constructs Designed for the Treatment of Solid Tumors

Nonclinical Investigation of Cytokine Mitigation Strategies for T-cell-Engaging Bispecifics in the Cynomolgus Macaque

SUMMARY

T-cell-directed cancer therapies such as T-cell-engaging bispecifics (TCBs) are commonly associated with cytokine release syndrome and associated clinical signs that can limit their tolerability and therapeutic benefit. Strategies for reducing cytokine release are therefore needed. Here, we report on studies performed in cynomolgus monkeys to test different approaches for mitigating cytokine release with TCBs. A "priming dose" as well as subcutaneous dosing reduced cytokine release compared with intravenous dosing but did not affect the intended T-cell response to the bispecific. As another strategy, cytokines or cytokine responses were blocked with an anti-IL-6 antibody, dexamethasone, or a JAK1/TYK2-selective inhibitor, and the effects on toxicity as well as T-cell responses to a TCB were evaluated. The JAK1/TYK2 inhibitor and dexamethasone prevented CRS-associated clinical signs on the day of TCB administration, but the anti-IL-6 had little effect. All interventions allowed for functional T-cell responses and expected damage to target-bearing tissues, but the JAK1/TYK2 inhibitor prevented the upregulation of activation markers on T cells, suggesting the potential for suppression of T-cell responses. Our results suggest that short-term prophylactic dexamethasone treatment may be an effective option for blocking cytokine responses without affecting desired T-cell responses to TCBs.

Development of pharmacological immunoregulatory anti-cancer therapeutics: current mechanistic studies and clinical opportunities

Immunotherapy represented by anti-PD-(L)1 and anti-CTLA-4 inhibitors has revolutionized cancer treatment, but challenges related to resistance and toxicity still remain. Due to the advancement of immuno-oncology, an increasing number of novel immunoregulatory targets and mechanisms are being revealed, with relevant therapies promising to improve clinical immunotherapy in the foreseeable future. Therefore, comprehending the larger picture is important. In this review, we analyze and summarize the current landscape of preclinical and translational mechanistic research, drug development, and clinical trials that brought about next-generation pharmacological immunoregulatory anti-cancer agents and drug candidates beyond classical immune checkpoint inhibitors. Along with further clarification of cancer immunobiology and advances in antibody engineering, agents targeting additional inhibitory immune checkpoints, including LAG-3, TIM-3, TIGIT, CD47, and B7 family members are becoming an important part of cancer immunotherapy research and discovery, as are structurally and functionally optimized novel anti-PD-(L)1 and anti-CTLA-4 agents and agonists of co-stimulatory molecules of T cells. Exemplified by bispecific T cell engagers, newly emerging bi-specific and multi-specific antibodies targeting immunoregulatory molecules can provide considerable clinical benefits. Next-generation agents also include immune epigenetic drugs and cytokine-based therapeutics. Cell therapies, cancer vaccines, and oncolytic viruses are not covered in this review. This comprehensive review might aid in further development and the fastest possible clinical adoption of effective immuno-oncology modalities for the benefit of patients.

Combination of T cell-redirecting strategies with a bispecific antibody blocking TGF-β and PD-L1 enhances antitumor responses

T cell-based immunotherapies for solid tumors have not achieved the clinical success observed in hematological malignancies, partially due to the immunosuppressive effect promoted by the tumor microenvironment, where PD-L1 and TGF-β play a pivotal role. However, durable responses to immune checkpoint inhibitors remain limited to a minority of patients, while TGF-β inhibitors have not reached the market yet. Here, we describe a bispecific antibody for dual blockade of PD-L1 and TFG-β, termed AxF (scFv)2, under the premise that combination with T cell redirecting strategies would improve clinical benefit. The AxF (scFv)2 antibody was well expressed in mammalian and yeast cells, bound both targets and inhibited dose-dependently the corresponding signaling pathways in luminescence-based cellular reporter systems. Moreover, combined treatment with trispecific T-cell engagers (TriTE) or CAR-T cells significantly boosted T cell activation status and cytotoxic response in breast, lung and colorectal (CRC) cancer models. Importantly, the combination of an EpCAMxCD3×EGFR TriTE with the AxF (scFv)2 delayed CRC tumor growth in vivo and significantly enhanced survival compared to monotherapy with the trispecific antibody. In summary, we demonstrated the feasibility of concomitant blockade of PD-L1 and TGF-β by a single molecule, as well as its therapeutic potential in combination with different T cell redirecting agents to overcome tumor microenvironment-mediated immunosuppression.

Considerations for selecting second-line treatment in patients with progressive small cell lung cancer and the use of Lurbinectedin in this setting

Small cell lung cancer (SCLC) is characterized by high initial responses to platinum-based chemotherapy plus immune checkpoint inhibitors; however, most patients quickly relapse and require subsequent treatment. Second-line treatment options in SCLC remain limited, and treatment algorithms are not completely consistent across the available guidelines in this setting. This review highlights key considerations regarding selection of second-line treatment for patients with relapsed SCLC. In particular, the role of lurbinectedin, which was first approved in 2020, representing the first significant addition to treatment algorithms in this setting for decades, is summarized. Future directions, including the identification of SCLC subtypes and the need for predictive biomarkers to guide patient selection and targeted therapy, are also discussed.

Design and engineering of bispecific antibodies: insights and practical considerations

Bispecific antibodies (bsAbs) have attracted significant attention due to their dual binding activity, which permits simultaneous targeting of antigens and synergistic binding effects beyond what can be obtained even with combinations of conventional monospecific antibodies. Despite the tremendous therapeutic potential, the design and construction of bsAbs are often hampered by practical issues arising from the increased structural complexity as compared to conventional monospecific antibodies. The issues are diverse in nature, spanning from decreased biophysical stability from fusion of exogenous antigen-binding domains to antibody chain mispairing leading to formation of antibody-related impurities that are very difficult to remove. The added complexity requires judicious design considerations as well as extensive molecular engineering to ensure formation of high quality bsAbs with the intended mode of action and favorable drug-like qualities. In this review, we highlight and summarize some of the key considerations in design of bsAbs as well as state-of-the-art engineering principles that can be applied in efficient construction of bsAbs with diverse molecular formats.

Nanobody-based trispecific T cell engager (Nb-TriTE) enhances therapeutic efficacy by overcoming tumor-mediated immunosuppression

BACKGROUND

T cell engagers (TCEs) have been established as an emerging modality for hematologic malignancies, but solid tumors remain refractory. However, the upregulation of programmed cell death 1 (PD-1) is correlated with T cell dysfunction that confer tumor-mediated immunosuppression. Developing a novel nanobody-based trispecific T cell engager (Nb-TriTE) would be a potential strategy to improve therapeutic efficacy.

METHODS

Given the therapeutic potential of nanobodies (Nbs), we first screened Nb targeting fibroblast activation protein (FAP) and successfully generated a Nb-based bispecific T cell engager (Nb-BiTE) targeting FAP. Then, we developed a Nb-TriTE by fusing an anti-PD-1 Nb to the Nb-BiTE. The biological activity and antitumor efficacy of the Nb-TriTE were evaluated in vitro and in both cell line-derived and patient-derived xenograft mouse models.

RESULTS

We had for the first time successfully selected a FAP Nb for the generation of novel Nb-BiTE and Nb-TriTE, which showed good binding ability to their targets. Nb-TriTE not only induced robust tumor antigen-specific killing, potent T cell activation and enhanced T cell function in vitro, but also suppressed tumor growth, improved survival and mediated more T cell infiltration than Nb-BiTE in mouse models of different solid tumors without toxicity.

CONCLUSIONS

This novel Nb-TriTE provides a promising and universal platform to overcome tumor-mediated immunosuppression and improve patient outcomes in the future.

VHH CDR-H3 conformation is determined by VH germline usage

VHHs or nanobodies are single antigen binding domains originating from camelid heavy-chain antibodies. They are used as diagnostic and research tools and in a variety of therapeutic molecules. Analyzing variable domain structures from llama and alpaca we found that VHHs can be classified into two large structural clusters based on their CDR-H3 conformation. Extended CDR-H3 loops protrude into the solvent, whereas kinked CDR-H3 loops fold back onto framework regions. Both major families have distinct properties in terms of their CDR-H3 secondary structure, how their CDR-H3 interacts with the framework region and how they bind to antigens. We show that the CDR-H3 conformation of VHHs correlates with the germline from which the antibodies are derived: IGHV3-3 derived antibodies almost exclusively adopt a kinked CDR-H3 conformation while the CDR-H3 adopts an extended structure in most IGHV3S53 derived antibodies. We do not observe any bias stemming from V(D)J recombination in llama immune repertoires, suggesting that the correlation is the result of selection processes during B-cell development. Our findings demonstrate a previously undescribed impact of germline usage on antigen interaction and contribute to a better understanding on how properties of the antibody framework shape the immune repertoire.

Emerging therapies targeting the delta-like ligand 3 (DLL3) in small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive neuroendocrine carcinoma with a poor prognosis. Initial responses to standard-of-care chemo-immunotherapy are, unfortunately, followed by rapid disease recurrence in most patients. Current treatment options are limited, with no therapies specifically approved as third-line or beyond. Delta-like ligand 3 (DLL3), a Notch inhibitory ligand, is an attractive therapeutic target because it is overexpressed on the surface of SCLC cells with minimal to no expression on normal cells. Several DLL3-targeted therapies are being developed for the treatment of SCLC and other neuroendocrine carcinomas, including antibody-drug conjugates (ADCs), T-cell engager (TCE) molecules, and chimeric antigen receptor (CAR) therapies. First, we discuss the clinical experience with rovalpituzumab tesirine (Rova-T), a DLL3-targeting ADC, the development of which was halted due to a lack of efficacy in phase 3 studies, with a view to understanding the lessons that can be garnered for the rapidly evolving therapeutic landscape in SCLC. We then review preclinical and clinical data for several DLL3-targeting agents that are currently in development, including the TCE molecules-tarlatamab (formerly known as AMG 757), BI 764532, and HPN328-and the CAR T-cell therapy AMG 119. We conclude with a discussion of the future challenges and opportunities for DLL3-targeting therapies, including the utility of DLL3 as a biomarker for patient selection and disease progression, and the potential of rational combinatorial approaches that can enhance efficacy.

Trispecific antibodies for cancer immunotherapy

Despite the clinical success of monoclonal and bispecific antibodies, there are still limitations in the therapeutic effect of malignant tumours, such as low response rate, treatment resistance, and so on, inspiring the exploration of trispecific antibodies (TsAbs). TsAbs further improve the safety and efficacy and has great clinical potential through three targets combination and formats optimization. This article reviews the development history and the target combination features of TsAbs. Although there are still great challenges in the clinical application of TsAbs, it is undeniable that TsAbs may be a breakthrough in the development of antibody drugs.

Bispecific PSMA antibodies and CAR-T in metastatic castration-resistant prostate cancer

Prostate cancer is the most common cancer among men and the second leading cause of cancer-related deaths in men in the United States. The treatment paradigm for prostate cancer has evolved with the emergence of a variety of novel therapies which have improved survival; however, treatment-related toxicities are abundant and durable responses remain rare. Immune checkpoint inhibitors have shown modest activity in a small subset of patients with prostate cancer and have not had an impact on most men with advanced disease. The discovery of prostate-specific membrane antigen (PSMA) and the understanding of its specificity to prostate cancer has identified it as an ideal tumor-associated antigen and has revived the enthusiasm for immunotherapeutics in prostate cancer. T-cell immunotherapy in the form of bispecific T-cell engagers (BiTEs) and chimeric antigen receptor (CAR) T-cell therapy have shown exceptional success in treating various hematologic malignancies, and are now being tested in patients with prostate cancer with drug design centered on various target ligands including not just PSMA, but others as well including six-transmembrane epithelial antigen of the prostate 1 (STEAP1) and prostate stem cell antigen (PSCA). This summative review will focus on the data surrounding PSMA-targeting T-cell therapies. Early clinical studies with both classes of T-cell redirecting therapies have demonstrated antitumor activity; however, there are multiple challenges with this class of agents, including dose-limiting toxicity, 'on-target, off-tumor' immune-related toxicity, and difficulty in maintaining sustained immune responses within a complex and overtly immunosuppressive tumor microenvironment. Reflecting on experiences from recent trials has been key toward understanding mechanisms of immune escape and limitations in developing these drugs in prostate cancer. Newer generation BiTE and CAR T-cell constructs, either alone or as part of combination therapy, are currently under investigation with modifications in drug design to overcome these barriers. Ongoing innovation in drug development will likely foster successful implementation of T-cell immunotherapy bringing transformational change to the treatment of prostate cancer.

T-cell-engaging antibodies for the treatment of solid tumors: challenges and opportunities

PURPOSE OF REVIEW

T-cell-engaging antibodies or T-cell engagers (TCEs) can connect a patient's cytotoxic T cells with cancer cells, leading to potent redirected lysis. Until very recently, only one TCE was approved, the CD19/CD3-bispecific blinatumomab. Many new TCEs in late-stage clinical development target various hematopoietic lineage markers like CD20, BCMA, or CD123. Although very compelling single-agent activity of TCEs was observed with various blood-borne cancers, therapy of solid tumor indications has thus far been less successful.

RECENT FINDINGS

The approval in 2022 of the gp100 peptide-major histocompatibility complex (MHC)/CD3 bispecific TCE tebentafusp in uveal melanoma confirms that TCEs can also efficiently work against solid tumors. TCEs targeting peptide-MHC complexes will expand the target space for solid tumor therapy to intracellular targets. Likewise, early clinical trial data from TCEs targeting DLL3 in small cell lunger cancer showed promising antitumor activity. Various technologies for conditional activation of TCEs in the tumor microenvironment (TME) may expand the scope of conventional surface targets that suffer from a narrow therapeutic window. Finally, pharmacological enhancements for TCE therapies by engagement of certain costimulatory receptors and cytokines, or blockade of checkpoints, are showing promise.

SUMMARY

Targeting peptide-MHC complexes, conditional TCE technologies, and concepts enhancing TCE-activated T cells are paving the way towards overcoming challenges associated with solid tumor therapy.

Conditionally active T cell engagers for the treatment of solid tumors: rationale and clinical development

INTRODUCTION

T cell engagers are a class of bispecific molecules that induce highly potent T cell-dependent cytotoxicity by bringing T cell activating receptors into proximity with cancer-associated cell surface antigens. However, because of their high potency, there is a greater risk of on-target/off-tumor toxicity owing to normal tissues having tumor antigen expression even at low levels. To reduce these adverse events, the dysregulated activity of proteases within the tumor microenvironment has recently been explored to create inert prodrugs that become conditionally active engagers after their cleavage by these enzymes.

AREAS COVERED

T-cell engagers that have been introduced for clinical use, and their respective successes and failures are reviewed. The unique challenges of these bispecific molecules for treating solid tumors and prior technologies used to exploit the proteolytic tumor microenvironment to create better-tolerated prodrugs and how that experience has led to the current series of conditionally active T-cell engagers, are discussed.

EXPERT OPINION

Methods for modulating the serum half-life of both inert and activated T cell engagers could have important ramifications in how they infiltrate tumors and prevent toxicity. Alternative features of the tumor microenvironment can also be leveraged in the development of conditional T cell engagers.

Urinary detection of early responses to checkpoint blockade and of resistance to it via protease-cleaved antibody-conjugated sensors

Immune checkpoint blockade (ICB) therapy does not benefit the majority of treated patients, and those who respond to the therapy can become resistant to it. Here we report the design and performance of systemically administered protease activity sensors conjugated to anti-programmed cell death protein 1 (αPD1) antibodies for the monitoring of antitumour responses to ICB therapy. The sensors consist of a library of mass-barcoded protease substrates that, when cleaved by tumour proteases and immune proteases, are released into urine, where they can be detected by mass spectrometry. By using syngeneic mouse models of colorectal cancer, we show that random forest classifiers trained on mass spectrometry signatures from a library of αPD1-conjugated mass-barcoded activity sensors for differentially expressed tumour proteases and immune proteases can be used to detect early antitumour responses and discriminate resistance to ICB therapy driven by loss-of-function mutations in either the B2m or Jak1 genes. Biomarkers of protease activity may facilitate the assessment of early responses to ICB therapy and the classification of refractory tumours based on resistance mechanisms.

For whom the T cells troll? Bispecific T-cell engagers in glioblastoma

Glioblastoma is the the most common primary brain tumor in adults. Onset of disease is followed by a uniformly lethal prognosis and dismal overall survival. While immunotherapies have revolutionized treatment in other difficult-to-treat cancers, these have failed to demonstrate significant clinical benefit in patients with glioblastoma. Obstacles to success include the heterogeneous tumor microenvironment (TME), the immune-privileged intracranial space, the blood-brain barrier (BBB) and local and systemic immunosuppressions. Monoclonal antibody-based therapies have failed at least in part due to their inability to access the intracranial compartment. Bispecific T-cell engagers are promising antibody fragment-based therapies which can bring T cells close to their target and capture them with a high binding affinity. They can redirect the entire repertoire of T cells against tumor, independent of T-cell receptor specificity. However, the multiple challenges posed by the TME, immune privilege and the BBB suggest that a single agent approach may be insufficient to yield durable, long-lasting antitumor efficacy. In this review, we discuss the mechanism of action of T-cell engagers, their preclinical and clinical developments to date. We also draw comparisons with other classes of multispecific antibodies and potential combinations using these antibody fragment therapies.

Synthetic biomarkers: a twenty-first century path to early cancer detection

Detection of cancer at an early stage when it is still localized improves patient response to medical interventions for most cancer types. The success of screening tools such as cervical cytology to reduce mortality has spurred significant interest in new methods for early detection (for example, using non-invasive blood-based or biofluid-based biomarkers). Yet biomarkers shed from early lesions are limited by fundamental biological and mass transport barriers - such as short circulation times and blood dilution - that limit early detection. To address this issue, synthetic biomarkers are being developed. These represent an emerging class of diagnostics that deploy bioengineered sensors inside the body to query early-stage tumours and amplify disease signals to levels that could potentially exceed those of shed biomarkers. These strategies leverage design principles and advances from chemistry, synthetic biology and cell engineering. In this Review, we discuss the rationale for development of biofluid-based synthetic biomarkers. We examine how these strategies harness dysregulated features of tumours to amplify detection signals, use tumour-selective activation to increase specificity and leverage natural processing of bodily fluids (for example, blood, urine and proximal fluids) for easy detection. Finally, we highlight the challenges that exist for preclinical development and clinical translation of synthetic biomarker diagnostics.

CAR-T cells and BiTEs in solid tumors: challenges and perspectives

Chimeric antigen receptor (CAR)-modified T cells and BiTEs are both immunotherapies which redirect T cell specificity against a tumor-specific antigen through the use of antibody fragments. They demonstrated remarkable efficacy in B cell hematologic malignancies, thus paving the way for their development in solid tumors. Nonetheless, the use of such new drugs to treat solid tumors is not straightforward. So far, the results from early phase clinical trials are not as impressive as expected but many improvements are under way. In this review we present an overview of the clinical development of CAR-T cells and BiTEs targeting the main antigens expressed by solid tumors. We emphasize the most frequent hurdles encountered by either CAR-T cells or BiTEs, or both, and summarize the strategies that have been proposed to overcome these obstacles.

Changing the History of Prostate Cancer with New Targeted Therapies

The therapeutic landscape of metastatic castration-resistant prostate cancer (mCRPC) is changing due to the emergence of new targeted therapies for the treatment of different molecular subtypes. Some biomarkers are described as potential molecular targets different from classic androgen receptors (AR). Approximately 20–25% of mCRPCs have somatic or germline alterations in DNA repair genes involved in homologous recombination. These subtypes are usually associated with more aggressive disease. Inhibitors of the enzyme poly ADP ribose polymerase (PARPi) have demonstrated an important benefit in the treatment of these subtypes of tumors. However, tumors that resistant to PARPi and wildtype BRCA tumors do not benefit from these therapies. Recent studies are exploring drug combinations with phosphatidylinositol-3-kinase (PI3K) or protein kinase B (AKT) inhibitors, as mechanisms to overcome resistance or to induce BRCAness and synthetic lethality. This article reviews various different novel strategies to improve outcomes in patients with prostate cancer.