Engineering high-affinity PD-1 variants for optimized immunotherapy and immuno-PET imaging. Proc Natl Acad Sci U S A. 2015;112:E6506-E6514. [PMID: 26604307 DOI: 10.1073/pnas.1519623112]

Engineered Cellular Vesicles Displaying Glycosylated Nanobodies for Cancer Immunotherapy

Immune checkpoint blockade targeting the CD47/SIRPα axis represents an alluring avenue for cancer immunotherapy. However, the compromised efficacy and safety concerns in vivo of conventional anti-CD47 antibodies impede their wide clinical applications. Here we introduced a single type of high-mannose glycans into the nanobody against CD47 (HM-nCD47) and subsequently displayed HM-nCD47 on cellular vesicles (CVs) for enhanced cancer immunotherapy. In this platform, the CVs significantly improved the circulation time of HM-nCD47-CVs, the nCD47 enabled the blockade of the CD47/SIRPα axis, and the HM enhanced recognition of mannose-binding lectin, all synergistically activating the macrophage-mediated antitumor immunity. In both subcutaneous and metastatic murine tumor models, the HM-nCD47-CVs possessed significantly extended half-lives and increased accumulation at the tumor site, resulting in a remarkable macrophage-dependent inhibition of tumor growth, a transcriptomic remodeling of the immune response, and an increase in survival time. By integrating the chemical biology toolbox with cell membrane nanotechnology, the HM-nCD47-CVs represent a new immunotherapeutic platform for cancer and other diseases.

Short Peptides as Powerful Arsenal for Smart Fighting Cancer

Short peptides have been coming around as a strong weapon in the fight against cancer on all fronts-in immuno-, chemo-, and radiotherapy, and also in combinatorial approaches. Moreover, short peptides have relevance in cancer imaging or 3D culture. Thanks to the natural 'smart' nature of short peptides, their unique structural features, as well as recent progress in biotechnological and bioinformatics development, short peptides are playing an enormous role in evolving cutting-edge strategies. Self-assembling short peptides may create excellent structures to stimulate cytotoxic immune responses, which is essential for cancer immunotherapy. Short peptides can help establish versatile strategies with high biosafety and effectiveness. Supramolecular short peptide-based cancer vaccines entered clinical trials. Peptide assemblies can be platforms for the delivery of antigens, adjuvants, immune cells, and/or drugs. Short peptides have been unappreciated, especially in the vaccine aspect. Meanwhile, they still hide the undiscovered unlimited potential. Here, we provide a timely update on this highly active and fast-evolving field.

Biotechnological Advances Utilizing Aptamers and Peptides Refining PD-L1 Targeting

While monoclonal antibodies have shown success in cancer immunotherapy, their limitations prompt exploration of alternative approaches such as aptamers and peptides targeting programmed death ligand 1 (PD-L1). Despite the significance of these biotechnological tools, a comprehensive review encompassing both aptamers and peptides for PD-L1 targeting is lacking. Addressing this gap is crucial for consolidating recent advancements and insights in this field. Biotechnological advances leveraging aptamers and peptides represent a cutting-edge approach in refining the targeting proteins. Our review aims to provide valuable guidance for researchers and clinicians, highlighting the biotechnological advances utilizing aptamers and peptides refining PD-L1 targeting.

Modulating macrophage-mediated programmed cell removal: An attractive strategy for cancer therapy

Macrophage-mediated programmed cell removal (PrCR) is crucial for the identification and elimination of needless cells that maintain tissue homeostasis. The efficacy of PrCR depends on the balance between pro-phagocytic "eat me" signals and anti-phagocytic "don't eat me" signals. Recently, a growing number of studies have shown that tumourigenesis and progression are closely associated with PrCR. In the tumour microenvironment, PrCR activated by the "eat me" signal is counterbalanced by the "don't eat me" signal of CD47/SIRPα, resulting in tumour immune escape. Therefore, targeting exciting "eat me" signalling while simultaneously suppressing "don't eat me" signalling and eventually inducing macrophages to produce effective PrCR will be a very attractive antitumour strategy. Here, we comprehensively review the functions of PrCR-activating signal molecules (CRT, PS, Annexin1, SLAMF7) and PrCR-inhibiting signal molecules (CD47/SIRPα, MHC-I/LILRB1, CD24/Siglec-10, SLAMF3, SLAMF4, PD-1/PD-L1, CD31, GD2, VCAM1), the interactions between these molecules, and Warburg effect. In addition, we highlight the molecular regulatory mechanisms that affect immune system function by exciting or suppressing PrCR. Finally, we review the research advances in tumour therapy by activating PrCR and discuss the challenges and potential solutions to smooth the way for tumour treatment strategies that target PrCR.

Bio-orthogonal click chemistry strategy for PD-L1-targeted imaging and pyroptosis-mediated chemo-immunotherapy of triple-negative breast cancer

BACKGROUND

The combination of programmed cell death ligand-1 (PD-L1) immune checkpoint blockade (ICB) and immunogenic cell death (ICD)-inducing chemotherapy has shown promise in cancer immunotherapy. However, triple-negative breast cancer (TNBC) patients undergoing this treatment often face obstacles such as systemic toxicity and low response rates, primarily attributed to the immunosuppressive tumor microenvironment (TME).

METHODS AND RESULTS

In this study, PD-L1-targeted theranostic systems were developed utilizing anti-PD-L1 peptide (APP) conjugated with a bio-orthogonal click chemistry group. Initially, TNBC was treated with azide-modified sugar to introduce azide groups onto tumor cell surfaces through metabolic glycoengineering. A PD-L1-targeted probe was developed to evaluate the PD-L1 status of TNBC using magnetic resonance/near-infrared fluorescence imaging. Subsequently, an acidic pH-responsive prodrug was employed to enhance tumor accumulation via bio-orthogonal click chemistry, which enhances PD-L1-targeted ICB, the pH-responsive DOX release and induction of pyroptosis-mediated ICD of TNBC. Combined PD-L1-targeted chemo-immunotherapy effectively reversed the immune-tolerant TME and elicited robust tumor-specific immune responses, resulting in significant inhibition of tumor progression.

CONCLUSIONS

Our study has successfully engineered a bio-orthogonal multifunctional theranostic system, which employs bio-orthogonal click chemistry in conjunction with a PD-L1 targeting strategy. This innovative approach has been demonstrated to exhibit significant promise for both the targeted imaging and therapeutic intervention of TNBC.

A pan-allelic human SIRPα-blocking antibody, ES004-B5, promotes tumor killing by enhancing macrophage phagocytosis and subsequently inducing an effective T-cell response

As a major immune cell type in the tumor microenvironment, tumor-associated macrophages secrete suppressive factors that can inhibit antitumor immunity and promote tumor progression. One approach trying to utilize macrophages for immunotherapy has been to block the CD47-SIRPα axis, which mediates inhibitory signaling, to promote phagocytosis of tumor cells. Many CD47-targeted agents, namely, anti-CD47 antibodies and SIRPα fusion proteins, were associated with a diverse spectrum of toxicities that limit their use in clinical settings. Universal expression of CD47 also leads to a severe "antigen sink" effect of CD47-targeted agents. Given that the CD47 receptor, SIRPα, has a more restricted expression profile and may have CD47-independent functions, targeting SIRPα is considered to have distinct advantages in improving clinical efficacy with a better safety profile. We have developed ES004-B5, a potentially best-in-class pan-allelic human SIRPα-blocking antibody using hybridoma technology. ES004-B5 binds to major human SIRPα variants through a unique epitope with high affinity. By blocking CD47-induced inhibitory "don't-eat-me" signaling, ES004-B5 exerts superior antitumor activity in combination with anti-tumor-associated antigen antibodies in vitro and in vivo. Unlike CD47-targeted agents, ES004-B5 exhibits an excellent safety profile in nonhuman primates. ES004-B5 has potential to be an important backbone for SIRPα-based combination therapy and/or bispecific antibodies, which will likely overcome the limitations of CD47-targeted agents encountered in clinical settings.

Rapamycin circumvents anti PD-1 therapy resistance in colorectal cancer by reducing PD-L1 expression and optimizing the tumor microenvironment

The unresectable or postoperative recurrence of advanced metastatic colorectal cancer (CRC) is the difficulty of its clinical management, and pharmacological therapy is the main source of benefit. Immune checkpoint inhibitors are therapeutic options but are effective in approximately 5 % of patients with deficient mismatch repair (MMR)/microsatellite instability CRC and are ineffective in patients with MMR-proficient (pMMR)/microsatellite stable (MSS) CRCs, which may be associated with the tumor microenvironment (TME). Here, we propose a new combination strategy and evaluate the efficacy of rapamycin (Rapa) combined with anti-PD-1 (αPD-1) in CT26 tumor-bearing mice, azoxymethane (AOM)/dextran sodium sulfate (DSS) inflammation-associated CRC mice, CT26-Luc tumor-bearing mice with postoperative recurrence, and CT26 liver metastasis mice. The results revealed that Rapa improved the therapeutic effect of αPD-1 and effectively inhibited colorectal carcinogenesis, postoperative recurrence, and liver metastasis. Mechanistically, Rapa improved the anticancer effect of αPD-1, associated with Rapa reprograming of the immunosuppressive TME. Rapa effectively depleted α-SMA+ cancer-associated fibroblasts and degraded collagen in the tumor tissue, increasing T lymphocyte infiltration into the tumor tissue. Rapa induced the downregulation of programed cell death 1 ligand 1 (PD-L1) protein and transcript levels in CT26 cells, which may be associated with the inhibition of the mTOR/P70S6K signaling axis. Furthermore, co-culture of tumor cells and CD8+ T lymphocytes demonstrated that Rapa-induced PD-L1 downregulation in tumor cells increased spleen-derived CD8+ T lymphocyte activation. Therefore, Rapa improves the anti-tumor effect of αPD-1 in CRCs, providing new ideas for its use to improve combinatorial strategies for anti-PD-1 immunotherapy.

Tumor-associated macrophages in anti-PD-1/PD-L1 immunotherapy for hepatocellular carcinoma: recent research progress

Hepatocellular carcinoma (HCC) is one of the cancers that seriously threaten human health. Immunotherapy serves as the mainstay of treatment for HCC patients by targeting the programmed cell death protein 1/programmed cell death 1 ligand 1 (PD-1/PD-L1) axis. However, the effectiveness of anti-PD-1/PD-L1 treatment is limited when HCC becomes drug-resistant. Tumor-associated macrophages (TAMs) are an important factor in the negative regulation of PD-1 antibody targeted therapy in the tumor microenvironment (TME). Therefore, as an emerging direction in cancer immunotherapy research for the treatment of HCC, it is crucial to elucidate the correlations and mechanisms between TAMs and PD-1/PD-L1-mediated immune tolerance. This paper summarizes the effects of TAMs on the pathogenesis and progression of HCC and their impact on HCC anti-PD-1/PD-L1 immunotherapy, and further explores current potential therapeutic strategies that target TAMs in HCC, including eliminating TAMs in the TME, inhibiting TAMs recruitment to tumors and functionally repolarizing M2-TAMs (tumor-supportive) to M1-TAMs (antitumor type).

In Search of Better Peptide-(Derived from PD-L2)-Based Immune Checkpoint Inhibitors

Current anti-cancer immune checkpoint therapy relies on antibodies that primarily target the PD-1/PD-L1(-L2) negative regulatory pathway. Although very successful in some cases for certain cancers, these antibodies do not help most patients who, presumably, should benefit from this type of therapy. Therefore, an unmet clinical need for novel, more effective drugs targeting immune checkpoints remains. We have developed a series of high-potency peptide inhibitors interfering with PD-1/PD-L1(-L2) protein-protein interaction. Our best peptide inhibitors are 12 and 14 amino acids long and show sub-micromolar IC50 inhibitory activity in the in vitro assay. The positioning of the peptides within the PD-1 binding site is explored by extensive modeling. It is further supported by 2D NMR studies of PD-1/peptide complexes. These results reflect substantial progress in the development of immune checkpoint inhibitors using peptidomimetics.

Engineering PD-1-targeted small protein variants for in vitro diagnostics and in vivo PET imaging

BACKGROUND

Programmed cell death 1 (PD-1) belongs to immune checkpoint proteins ensuring negative regulation of the immune response. In non-small cell lung cancer (NSCLC), the sensitivity to treatment with anti-PD-1 therapeutics, and its efficacy, mostly correlated with the increase of tumor infiltrating PD-1+ lymphocytes. Due to solid tumor heterogeneity of PD-1+ populations, novel low molecular weight anti-PD-1 high-affinity diagnostic probes can increase the reliability of expression profiling of PD-1+ tumor infiltrating lymphocytes (TILs) in tumor tissue biopsies and in vivo mapping efficiency using immune-PET imaging.

METHODS

We designed a 13 kDa β-sheet Myomedin scaffold combinatorial library by randomization of 12 mutable residues, and in combination with ribosome display, we identified anti-PD-1 Myomedin variants (MBA ligands) that specifically bound to human and murine PD-1-transfected HEK293T cells and human SUP-T1 cells spontaneously overexpressing cell surface PD-1.

RESULTS

Binding affinity to cell-surface expressed human and murine PD-1 on transfected HEK293T cells was measured by fluorescence with LigandTracer and resulted in the selection of most promising variants MBA066 (hPD-1 KD = 6.9 nM; mPD-1 KD = 40.5 nM), MBA197 (hPD-1 KD = 29.7 nM; mPD-1 KD = 21.4 nM) and MBA414 (hPD-1 KD = 8.6 nM; mPD-1 KD = 2.4 nM). The potential of MBA proteins for imaging of PD-1+ populations in vivo was demonstrated using deferoxamine-conjugated MBA labeled with 68Galium isotope. Radiochemical purity of 68Ga-MBA proteins reached values 94.7-99.3% and in vitro stability in human serum after 120 min was in the range 94.6-98.2%. The distribution of 68Ga-MBA proteins in mice was monitored using whole-body positron emission tomography combined with computerized tomography (PET/CT) imaging up to 90 min post-injection and post mortem examined in 12 mouse organs. The specificity of MBA proteins was proven by co-staining frozen sections of human tonsils and NSCLC tissue biopsies with anti-PD-1 antibody, and demonstrated their potential for mapping PD-1+ populations in solid tumors.

CONCLUSIONS

Using directed evolution, we developed a unique set of small binding proteins that can improve PD-1 diagnostics in vitro as well as in vivo using PET/CT imaging.

Checkpoint inhibitor-expressing lentiviral vaccine suppresses tumor growth in preclinical cancer models

BACKGROUND

While immunotherapy has been highly successful for the treatment of some cancers, for others, the immune response to tumor antigens is weak leading to treatment failure. The resistance of tumors to checkpoint inhibitor therapy may be caused by T cell exhaustion resulting from checkpoint activation.

METHODS

In this study, lentiviral vectors that expressed T cell epitopes of an experimentally introduced tumor antigen, ovalbumin, or the endogenous tumor antigen, Trp1 were developed. The vectors coexpressed CD40 ligand (CD40L), which served to mature the dendritic cells (DCs), and a soluble programmed cell death protein 1 (PD-1) microbody to prevent checkpoint activation. Vaccination of mice bearing B16.OVA melanomas with vector-transduced DCs induced the proliferation and activation of functional, antigen-specific, cytolytic CD8 T cells.

RESULTS

Vaccination induced the expansion of CD8 T cells that infiltrated the tumors to suppress tumor growth. Vector-encoded CD40L and PD-1 microbody increased the extent of tumor growth suppression. Adoptive transfer demonstrated that the effect was mediated by CD8 T cells. Direct injection of the vector, without the need for ex vivo transduction of DCs, was also effective.

CONCLUSIONS

This study suggests that therapeutic vaccination that induces tumor antigen-specific CD8 T cells coupled with a vector-expressed checkpoint inhibitor can be an effective means to suppress the growth of tumors that are resistant to conventional immunotherapy.

Development, Characterization, and Radiation Dosimetry Studies of 18F-BMS-986229, a 18F-Labeled PD-L1 Macrocyclic Peptide PET Tracer

PURPOSE

In cancer immunotherapy, the blockade of the interaction between programmed death-1 and its ligand (PD-1:PD-L1) has proven to be one of the most promising strategies. However, as mechanisms of resistance to PD-1/PD-L1 inhibition include variability in tumor cell PD-L1 expression in addition to standard tumor biopsy PD-L1 immunohistochemistry (IHC), a comprehensive and quantitative approach for measuring PD-L1 expression is required. Herein, we report the development and characterization of an 18F-PD-L1-binding macrocyclic peptide as a PET tracer for the comprehensive evaluation of tumor PD-L1 expression in cancer patients.

PROCEDURES

18F-BMS-986229 was characterized for PD-L1 expression assessment by autoradiography or PET imaging. 18F-BMS-986229 was utilized to evaluate tumor PD-L1 target engagement in competition with a macrocyclic peptide inhibitor of PD-L1 (BMS-986189) over a range of doses using PET imaging. A whole-body radiation dosimetry study of 18F-BMS-986229 in healthy non-human primates (NHPs) was performed.

RESULTS

In vitro autoradiography showed an 8:1 binding ratio in L2987(PD-L1 +) vs. HT-29 (PD-L1-) tumors, more than 90% of which could be blocked with 1 nM of BMS-986189. Ex vivo autoradiography showed that 18F-BMS-986229 detection was penetrant over a series of sections spanning the entire L2987 tumor. In vivo PET imaging in mice demonstrated a 5:1 tracer uptake ratio (at 90-100 min after tracer administration) in L2987 vs. HT-29 tumors and demonstrated 83%-93% specific binding of BMS-986189 within those dose ranges. In a healthy NHP dosimetry study, the resultant whole-body effective dose was 0.025 mSv/MBq.

CONCLUSION

18F-BMS-986229 has been preclinically characterized and exhibits high target specificity, low background uptake, and a short blood half-life supportive of same day imaging in the clinic. As the PET tracer, 18F-BMS-986229 shows promise in the quantification of PD-L1 expression, and its use in monitoring longitudinal changes in patients may provide insights into PD-1:PD-L1 immuno-therapy treatment outcomes.

Evaluating immunotherapeutic outcomes in triple-negative breast cancer with a cholesterol radiotracer in mice

Evaluating the response to immune checkpoint inhibitors (ICIs) remains an unmet challenge in triple-negative breast cancer (TNBC). The requirement for cholesterol in the activation and function of T cells led us to hypothesize that quantifying cellular accumulation of this molecule could distinguish successful from ineffective checkpoint immunotherapy. To analyze accumulation of cholesterol by T cells in the immune microenvironment of breast cancer, we leveraged the PET radiotracer, eFNP-59. eFNP-59 is an analog of cholesterol that our group validated as an imaging biomarker for cholesterol uptake in preclinical models and initial human studies. In immunocompetent mouse models of TNBC, we found that elevated uptake of exogenous labeled cholesterol analogs functions as a marker for T cell activation. When comparing ICI-responsive and -nonresponsive tumors directly, uptake of fluorescent cholesterol and eFNP-59 increased in T cells from ICI-responsive tumors. We discovered that accumulation of cholesterol by T cells increased in ICI-responding tumors that received anti-PD-1 checkpoint immunotherapy. In patients with TNBC, tumors containing cycling T cells had features of cholesterol uptake and trafficking within those populations. These results suggest that uptake of exogenous cholesterol analogs by tumor-infiltrating T cells allows detection of T cell activation and has potential to assess the success of ICI therapy.

Engineering a Programmed Death-Ligand 1-Targeting Monobody Via Directed Evolution for SynNotch-Gated Cell Therapy

Programmed death-ligand 1 (PD-L1) is a promising target for cancer immunotherapy due to its ability to inhibit T cell activation; however, its expression on various noncancer cells may cause on-target off-tumor toxicity when designing PD-L1-targeting Chimeric Antigen Receptor (CAR) T cell therapies. Combining rational design and directed evolution of the human fibronectin-derived monobody scaffold, "PDbody" was engineered to bind to PD-L1 with a preference for a slightly lower pH, which is typical in the tumor microenvironment. PDbody was further utilized as a CAR to target the PD-L1-expressing triple negative MDA-MB-231 breast cancer cell line. To mitigate on-target off-tumor toxicity associated with targeting PD-L1, a Cluster of Differentiation 19 (CD19)-recognizing SynNotch IF THEN gate was integrated into the system. This CD19-SynNotch PDbody-CAR system was then expressed in primary human T cells to target CD19-expressing MDA-MB-231 cancer cells. These CD19-SynNotch PDbody-CAR T cells demonstrated both specificity and efficacy in vitro, accurately eradicating cancer targets in cytotoxicity assays. Moreover, in an in vivo bilateral murine tumor model, they exhibited the capability to effectively restrain tumor growth. Overall, CD19-SynNotch PDbody-CAR T cells represent a distinct development over previously published designs due to their increased efficacy, proliferative capability, and mitigation of off-tumor toxicity for solid tumor treatment.

Structure-Guided Discovery of PD-1/PD-L1 Interaction Inhibitors: Peptide Design, Screening, and Optimization via Computation-Aided Phage Display Engineering

Cancer immunotherapy harnesses the immune system to combat tumors and has emerged as a major cancer treatment modality. The PD-1/PD-L1 immune checkpoint modulates interactions between tumor cells and T cells and has been extensively targeted in cancer immunotherapy. However, the monoclonal antibodies known to target this immune checkpoint have considerable side effects, and novel PD-1/PD-L1 inhibitors are therefore required. Herein, a peptide inhibitor to disrupt PD-1/PD-L1 interactions was designed through structure-driven phage display engineering coupled to computational modification and optimization. BetaPb, a novel peptide library constructed by using the known structure of PD-1/PD-L, was used to develop inhibitors against the immune checkpoint, and specific peptides with high affinity toward PD-1 were screened through enzyme-linked immunosorbent assays, homogeneous time-resolved fluorescence, and biolayer interferometry. A potential inhibitor, B8, was preliminarily screened through biopanning. The binding affinity of B8 toward PD-1 was confirmed through computation-aided optimization. Assessment of B8 variants (B8.1, B8.2, B8.3, B8.4, and B8.5) demonstrated their attenuation of PD-1/PD-L1 interactions. B8.4 exhibited the strongest attenuation efficiency at a half-maximal effective concentration of 0.1 μM and the strongest binding affinity to PD-1 (equilibrium dissociation constant = 0.1 μM). B8.4 outperformed the known PD-1/PD-L1 interaction inhibitor PL120131 in disrupting PD-1/PD-L1 interactions, revealing that B8.4 has remarkable potential for modification to yield an antitumor agent. This study provides valuable information for the future development of peptide-based drugs, therapeutics, and immunotherapies for cancer.

Discovery of galectin-8 as an LILRB4 ligand driving M-MDSCs defines a class of antibodies to fight solid tumors

LILRB4 is an immunosuppressive receptor, and its targeting drugs are undergoing multiple preclinical and clinical trials. Currently, the absence of a functional LILRB4 ligand in solid tumors not only limits the strategy of early antibody screening but also leads to the lack of companion diagnostic (CDx) criteria, which is critical to the objective response rate in early-stage clinical trials. Here, we show that galectin-8 (Gal-8) is a high-affinity functional ligand of LILRB4, and its ligation induces M-MDSC by activating STAT3 and inhibiting NF-κB. Significantly, Gal-8, but not APOE, can induce MDSC, and both ligands bind LILRB4 noncompetitively. Gal-8 expression promotes in vivo tumor growth in mice, and the knockout of LILRB4 attenuates tumor growth in this context. Antibodies capable of functionally blocking Gal-8 are able to suppress tumor growth in vivo. These results identify Gal-8 as an MDSC-driving ligand of LILRB4, and they redefine a class of antibodies for solid tumors.

Recent Advances in the Development of Non-Invasive Imaging Probes for Cancer Immunotherapy

The last two decades have witnessed a major revolution in the field of tumor immunology including clinical progress using various immunotherapy strategies. These advances have highlighted the potential for approaches that harness the power of the immune system to fight against cancer. While cancer immunotherapies have shown significant clinical successes, patient responses vary widely due to the complex and heterogeneous nature of tumors and immune responses, calling for reliable biomarkers and therapeutic strategies to maximize the benefits of immunotherapy. Especially, stratifying responding individuals from non-responders during the early stages of treatment could help avoid long-term damage and tailor personalized treatments. In efforts to develop non-invasive means for accurately evaluating and predicting tumor response to immunotherapy, multiple affinity-based agents targeting immune cell markers and checkpoint molecules have been developed and advanced to clinical trials. In addition, researchers have recently turned their attention to substrate and activity-based imaging probes that can provide real-time, functional assessment of immune response to treatment. Here, we highlight some of those recently designed probes that image functional proteases as biomarkers of cancer immunotherapy with a focus on their chemical design and detection modalities and discuss challenges and opportunities for the development of imaging tools utilized in cancer immunotherapy.

Inhibitors of Immune Checkpoints: Small Molecule- and Peptide-Based Approaches

The revolutionary progress in cancer immunotherapy, particularly the advent of immune checkpoint inhibitors, marks a significant milestone in the fight against malignancies. However, the majority of clinically employed immune checkpoint inhibitors are monoclonal antibodies (mAbs) with several limitations, such as poor oral bioavailability and immune-related adverse effects (irAEs). Another major limitation is the restriction of the efficacy of mAbs to a subset of cancer patients, which triggered extensive research efforts to identify alternative approaches in targeting immune checkpoints aiming to overcome the restricted efficacy of mAbs. This comprehensive review aims to explore the cutting-edge developments in targeting immune checkpoints, focusing on both small molecule- and peptide-based approaches. By delving into drug discovery platforms, we provide insights into the diverse strategies employed to identify and optimize small molecules and peptides as inhibitors of immune checkpoints. In addition, we discuss recent advances in nanomaterials as drug carriers, providing a basis for the development of small molecule- and peptide-based platforms for cancer immunotherapy. Ongoing research focused on the discovery of small molecules and peptide-inspired agents targeting immune checkpoints paves the way for developing orally bioavailable agents as the next-generation cancer immunotherapies.

Structural analysis of light chain-driven bispecific antibodies targeting CD47 and PD-L1

In contrast to natural antibodies that rely mainly on the heavy chain to establish contacts with their cognate antigen, we have developed a bispecific antibody format in which the light chain (LC) drives antigen binding and specificity. To better understand epitope-paratope interactions in this context, we determined the X-ray crystallographic structures of an antigen binding fragment (Fab) in complex with human CD47 and another Fab in complex with human PD-L1. These Fabs contain a κ-LC and a λ-LC, respectively, which are paired with an identical heavy chain (HC). The structural analysis of these complexes revealed the dominant contribution of the LCs to antigen binding, but also that the common HC provides some contacts in both CD47 and PD-L1 Fab complexes. The anti-CD47 Fab was affinity optimized by diversifying complementary-determining regions of the LC followed by phage display selections. Using homology modeling, the contributions of the amino acid modification to the affinity increase were analyzed. Our results demonstrate that, despite a less prominent role in natural antibodies, the LC can mediate high affinity binding to different antigens and neutralize their biological function. Importantly, Fabs containing a common variable heavy (VH) domain enable the generation of bispecific antibodies retaining a truly native structure, maximizing their therapeutic potential.

In silico evolution of autoinhibitory domains for a PD-L1 antagonist using deep learning models

There has been considerable progress in the development of computational methods for designing protein-protein interactions, but engineering high-affinity binders without extensive screening and maturation remains challenging. Here, we test a protein design pipeline that uses iterative rounds of deep learning (DL)-based structure prediction (AlphaFold2) and sequence optimization (ProteinMPNN) to design autoinhibitory domains (AiDs) for a PD-L1 antagonist. With the goal of creating an anticancer agent that is inactive until reaching the tumor environment, we sought to create autoinhibited (or masked) forms of the PD-L1 antagonist that can be unmasked by tumor-enriched proteases. Twenty-three de novo designed AiDs, varying in length and topology, were fused to the antagonist with a protease-sensitive linker, and binding to PD-L1 was measured with and without protease treatment. Nine of the fusion proteins demonstrated conditional binding to PD-L1, and the top-performing AiDs were selected for further characterization as single-domain proteins. Without any experimental affinity maturation, four of the AiDs bind to the PD-L1 antagonist with equilibrium dissociation constants (KDs) below 150 nM, with the lowest KD equal to 0.9 nM. Our study demonstrates that DL-based protein modeling can be used to rapidly generate high-affinity protein binders.

Ginsenoside Rh2 augmented anti-PD-L1 immunotherapy by reinvigorating CD8+ T cells via increasing intratumoral CXCL10

Profiting from the sustained clinical improvement and prolonged patient survival, immune checkpoint blockade of programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis has emerged as a revolutionary cancer therapy approach. However, the anti-PD-1/PD-L1 antibodies only achieve a clinical response rate of approximately 20%. Herein, we identified a novel combination strategy that Chinese medicine ginseng-derived ginsenoside Rh2 (Rh2) markedly improved the anti-cancer efficacy of anti-PD-L1 antibody in mice bearing MC38 tumor. Rh2 combined with anti-PD-L1 antibody (combo treatment) further triggered the infiltration, proliferation and activation of CD8+ T cells in the tumor microenvironment (TME). Depletion of CD8+ T cells by mouse CD8 blocking antibody abolished the anti-cancer effect of combo treatment totally. Mechanistically, combo treatment further increased the expression of CXCL10 through activating TBK1-IRF3 signaling pathway, explaining the increased infiltration of T cells. Employing anti- CXC chemokine receptor 3 (CXCR3) blocking antibody prevented the T cells infiltration and abolished the anti-cancer effect of combo treatment. Meanwhile, combo treatment increased the percentage of M1-like macrophages and raised the ratio of M1/M2 macrophages in TME. By comparing the anti-cancer effect of combo treatment among MC38, CT26 and 4T1 tumors, resident T cells were considered as a prerequisite for the effectiveness of combo treatment. These findings demonstrated that Rh2 potentiated the anti-cancer effect of PD-L1 blockade via promoting the T cells infiltration and activation, which shed a new light on the combination strategy to enhance anti-PD-L1 immunotherapy by using natural product Rh2.

Site-Selective Functionalized PD-1 Mutant for a Modular Immunological Activity against Cancer Cells

Targeting immune checkpoints is a well-established strategy in cancer therapy, and antibodies blocking PD-1/PD-L1 interactions to restore the immunological activity against cancer cells have been clinically validated. High-affinity mutants of the PD-1 ectodomain have recently been proposed as an alternative to antibodies to target PD-L1 on cancer cells, shedding new light on this research area. In this dynamic scenario, the PD-1 mutant, here reported, largely expands the chemical space of nonantibody and nonsmall-molecule inhibitor therapeutics that can be used to target cancer cells overexpressing PD-L1 receptors. The polyethylene glycol moieties and the immune response-stimulating carbohydrates, used as site-selective tags, represent the proof of concept for future applications.

Engineering high-affinity dual targeting cellular nanovesicles for optimised cancer immunotherapy

Dual targeting to immune checkpoints has achieved a better therapeutic efficacy than single targeting due to synergistic extrication of tumour immunity. However, most dual targeting strategies are usually antibody dependent which facing drawbacks of antibodies, such as poor solid tumour penetration and unsatisfied affinity. To meet the challenges, we engineered a cell membrane displaying a fusion protein composed of SIRPα and PD-1 variants, the high-affinity consensus (HAC) of wild-type molecules, and with which prepared nanovesicles (NVs). Through disabling both SIRPα/CD47 and PD-1/PD-L1 signalling, HAC NVs significantly preserved the phagocytosis and antitumour effect of macrophages and T cells, respectively. In vivo study revealed that HAC NVs had better tumour penetration than monoclonal antibodies and higher binding affinity to CD47 and PD-L1 on tumour cells compared with the NVs expressing wild-type fusion protein. Exhilaratingly, dual-blockade of CD47 and PD-L1 with HAC NVs exhibited excellent therapeutic efficacy and biosafety. This study provided a novel biomaterial against tumoural immune escape and more importantly an attractive biomimetic technology of protein delivery for multi-targeting therapies.

Coengineering specificity, safety, and function into T cells for cancer immunotherapy

Adoptive T-cell transfer (ACT) therapies, including of tumor infiltrating lymphocytes (TILs) and T cells gene-modified to express either a T cell receptor (TCR) or a chimeric antigen receptor (CAR), have demonstrated clinical efficacy for a proportion of patients and cancer-types. The field of ACT has been driven forward by the clinical success of CD19-CAR therapy against various advanced B-cell malignancies, including curative responses for some leukemia patients. However, relapse remains problematic, in particular for lymphoma. Moreover, for a variety of reasons, relative limited efficacy has been demonstrated for ACT of non-hematological solid tumors. Indeed, in addition to pre-infusion challenges including lymphocyte collection and manufacturing, ACT failure can be attributed to several biological processes post-transfer including, (i) inefficient tumor trafficking, infiltration, expansion and retention, (ii) chronic antigen exposure coupled with insufficient costimulation resulting in T-cell exhaustion, (iii) a range of barriers in the tumor microenvironment (TME) mediated by both tumor cells and suppressive immune infiltrate, (iv) tumor antigen heterogeneity and loss, or down-regulation of antigen presentation machinery, (v) gain of tumor intrinsic mechanisms of resistance such as to apoptosis, and (vi) various forms of toxicity and other adverse events in patients. Affinity-optimized TCRs can improve T-cell function and innovative CAR designs as well as gene-modification strategies can be used to coengineer specificity, safety, and function into T cells. Coengineering strategies can be designed not only to directly support the transferred T cells, but also to block suppressive barriers in the TME and harness endogenous innate and adaptive immunity. Here, we review a selection of the remarkable T-cell coengineering strategies, including of tools, receptors, and gene-cargo, that have been developed in recent years to augment tumor control by ACT, more and more of which are advancing to the clinic.

Development of an Albumin-Masked mutPD-1Ig as a Tumor Lesion-Selective Immune Checkpoint Inhibitor

The antitumor effects elicited by immune checkpoint inhibitors (ICIs) have transformed cancer treatments. However, severe immune-related adverse events (irAEs) resulting from these treatments have restricted the application of ICIs. To overcome the adverse events, we developed a tumor lesion-selective pro-PD-1Ig that is activated by proteases overexpressed in tumors. We genetically linked albumin to the N-terminus of a modified PD-1Ig (termed mutPD-1Ig hereafter) via an MMP substrate sequence to form Alb-hinge-mutPD-1Ig. We demonstrate that the binding activity of nondigested Alb-hinge-mutPD-1Ig is approximately 11-folds lower than mutPD-1Ig. However, digestion by type IV collagenase restored the binding activity of Alb-hinge-mutPD-1Ig to a level comparable to that of native mutPD-1Ig. In order to enhance the masking efficiency of Alb-mutPD-1Ig, we simulated the effects of diverse MMP substrate linkers for connecting albumin and PD-1 at various starting positions by bioinformatics tools. Our validation experiments indicate Alb-hinge-mutPD-1Ig displayed the best masking efficiency among all simulated constructs. Our study suggests that albumin may be best applicable to mask a target protein whose binding motif is centralized and in the proximity of the N-terminus of the protein.

Predicting efficacy of immunotherapy in mice with triple negative breast cancer using a cholesterol PET radiotracer

Predicting the response to cancer immunotherapy remains an unmet challenge in triple-negative breast cancer (TNBC) and other malignancies. T cells, the major target of current checkpoint inhibitor immunotherapies, accumulate cholesterol during activation to support proliferation and signaling. The requirement of cholesterol for anti-tumor functions of T cells led us to hypothesize that quantifying cellular accumulation of this molecule could distinguish successful from ineffective checkpoint immunotherapy. To analyze accumulation of cholesterol by T cells in the immune microenvironment of breast cancer, we leveraged a novel positron emission tomography (PET) radiotracer, FNP-59. FNP-59 is an analog of cholesterol that our group has validated as an imaging biomarker for cholesterol uptake in pre-clinical models and initial human studies. In immunocompetent mouse models of TNBC, we found that elevated uptake of exogenous labeled cholesterol analogs functions as a marker for T cell activation. When comparing immune checkpoint inhibitor (ICI)-responsive EO771 tumors to non-responsive AT-3 tumors, we found significantly higher uptake of a fluorescent cholesterol analog in T cells of the ICI-responsive tumors both in vitro and in vivo. Using the FNP-59 radiotracer, we discovered that accumulation of cholesterol by T cells increased further in ICI-responding tumors that received ant-PD-1 checkpoint immunotherapy. We verified these data by mining single cell sequencing data from patients with TNBC. Patients with tumors containing cycling T cells showed gene expression signatures of cholesterol uptake and trafficking. These results suggest that uptake of exogenous cholesterol analogs by tumor-infiltrating T cells predict T cell activation and success of ICI therapy.

Novel Dual-Mode NIR-II/MRI Nanoprobe Targeting PD-L1 Accurately Evaluates the Efficacy of Immunotherapy for Triple-Negative Breast Cancer

Background

Durable responses to immune-checkpoint blocking therapy (ICT) targeting programmed cell death protein-1/ligand-1 (PD-1/PD-L1) have improved outcomes for patients with triple negative breast cancer (TNBC). Unfortunately, only 19-23% of patients benefit from ICT. Hence, non-invasive strategies evaluating responses to therapy and selecting patients who will benefit from ICT are critical issues for TNBC immunotherapy.

Methods

We developed a novel nanoparticle-Atezolizumab (NPs-Ate) consisting of indocyanine green (ICG), gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA), human serum albumin (HSA), and Atezolizumab. The efficiency of Gd-DTPA linking was verified using mass spectrometry, and the size of NPs-Ate was characterized using Nano-flow cytometry. The synthesized NPs-Ate were evaluated for fluorescence stability, penetration depth, and target specificity. TNBC cell lines and tumor-bearing mice models were used to identify the feasibility of this dual-modal second near-infrared/magnetic resonance imaging (NIR-II/MRI) system. Additionally, ICT combination with chemotherapy or radiotherapy in TNBC tumor-bearing mice models were used to assess dynamic changes of PD-L1 and predicted therapeutic responses with NPs-Ate.

Results

Atezolizumab, a monoclonal antibody, was successfully labeled with ICG and Gd-DTPA to generate NPs-Ate. This demonstrated strong fluorescence signals in our NIR-II imaging system, and relaxivity (γ1) of 9.77 mM-1 s-1. In tumor-bearing mice, the NIR-II imaging signal background ratio (SBR) reached its peak of 11.51 at 36 hours, while the MRI imaging SBR reached its highest as 1.95 after 12 hours of tracer injection. NPs-Ate specifically targets cells and tumors expressing PD-L1, enabling monitoring of PD-L1 status during immunotherapy. Combining therapies led to inhibited tumor growth, prolonged survival, and increased PD-L1 expression, effectively monitored using the non-invasive NPs-Ate imaging system.

Conclusion

The NIR-II/MRI NPs-Ate effectively reflected PD-L1 status during immunotherapy. Real-time and non-invasive immunotherapy and response/prognosis monitoring under NIR-II/MRI imaging guidance in TNBC is a promising and innovative technology with potential for extensive clinical applications in the future.

Genetically Engineered-Cell-Membrane Nanovesicles for Cancer Immunotherapy

The advent of immunotherapy has marked a new era in cancer treatment, offering significant clinical benefits. Cell membrane as drug delivery materials has played a crucial role in enhancing cancer therapy because of their inherent biocompatibility and negligible immunogenicity. Different cell membranes are prepared into cell membrane nanovesicles (CMNs), but CMNs have limitations such as inefficient targeting ability, low efficacy, and unpredictable side effects. Genetic engineering has deepened the critical role of CMNs in cancer immunotherapy, enabling genetically engineered-CMN (GCMN)-based therapeutics. To date, CMNs that are surface modified by various functional proteins have been developed through genetic engineering. Herein, a brief overview of surface engineering strategies for CMNs and the features of various membrane sources is discussed, followed by a description of GCMN preparation methods. The application of GCMNs in cancer immunotherapy directed at different immune targets is addressed as are the challenges and prospects of GCMNs in clinical translation.

PD-L1 Blockade Peptide-Modified Polymeric Nanoparticles for Oxygen-Independent-Based Hypoxic Tumor Photo/Thermodynamic Immunotherapy

Distant metastasis of malignant tumors is considered to be the main culprit for the failure of current antitumor treatments. Conventional single treatments often exhibit limited efficacy in inhibiting tumor metastasis. Therefore, there is a growing interest in developing collaborative antitumor strategies based on photothermal therapy (PTT) and free-radical-generated photodynamic therapy (PDT), especially utilizing oxygen-independent nanoplatforms, to address this challenge. Such antitumor strategies can enhance the therapeutic outcomes by ensuring the cytotoxicity of free radicals even in the hypoxic tumor microenvironment, thereby improving the effective suppression of primary tumors. Additionally, these approaches can stimulate the production of tumor-associated antigens and amplify the immunogenic cell death (ICD) effects, potentially feasible for enhancing the therapeutic outcomes of immunotherapy. Herein, we fabricated a functional nanosystem that co-loads IR780 and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]-dihydrochloride (AIPH) to realize PTT-triggered thermodynamic combination therapy via the oxygen-independent pathway for the elimination of primary tumors. Furthermore, the nanocomposites were surface-decorated with a predesigned complex peptide (PLGVRGC-anti-PD-L1 peptide, MMP-sensitive), which facilitated the immunotherapy targeting distant tumors. Through the specific recognition of matrix metalloproteinase (MMP), the sensitive segment on the obtained aNC@IR780A was cleaved. As a result, the freed anti-PD-L1 peptide effectively blocked immune checkpoints, leading to the infiltration and activation of T cells (CTLs). This nanosystem was proven to be effective at inhibiting both primary tumors and distant tumors, providing a promising combination strategy for tumor PTT/TDT/immunotherapy.

Preparation and Bioevaluation of 18F-Labeled Small-Molecular Radiotracers via Sulfur(VI) Fluoride Exchange Chemistry for Imaging of Programmed Cell Death Protein Ligand 1 Expression in Tumors

Nowadays, one of the most effective methods of tumor immunotherapy is blocking programmed cell death protein 1/programmed cell death protein ligand 1 (PD-1/PD-L1) immune checkpoints. However, there is still a significant challenge in selecting patients to benefit from immune checkpoint therapies. Positron emission tomography (PET), a noninvasive molecular imaging technique, offers a new approach to accurately detect PD-L1 expression and allows for a better prediction of response to PD-1/PD-L1 target immunotherapy. Here, we designed and synthesized a novel group of aryl fluorosulfate-containing small-molecule compounds (LGSu-1, LGSu-2, LGSu-3, and LGSu-4) based on the phenoxymethyl-biphenyl scaffold. After screening by the time-resolved fluorescence resonance energy transfer (TR-FRET) assay, the most potent compound LGSu-1 (half maximal inhibitory concentration (IC50): 15.53 nM) and the low-affinity compound LGSu-2 (IC50: 189.70 nM) as a control were selected for 18F-radiolabeling by sulfur(VI) fluoride exchange chemistry (SuFEx) to use for PET imaging. [18F]LGSu-1 and [18F]LGSu-2 were prepared by a one-step radiofluorination reaction in over 85% radioconversion and nearly 30% radiochemical yield. In B16-F10 melanoma cell assays, [18F]LGSu-1 (5.00 ± 0.06%AD) showed higher cellular uptake than [18F]LGSu-2 (2.55 ± 0.04%AD), in which cell uptake could be significantly blocked by the nonradioactivity LGSu-1. In vivo experiments, micro-PET imaging of B16-F10 tumor-bearing mice and radiographic autoradiography of tumor sections showed that [18F]LGSu-1 was more effectively accumulated in the tumor due to the higher binding affinity with PD-L1. The above experimental results confirmed the potential of the small-molecule probe LGSu-1 as a targeting PD-L1 imaging tracer in tumor tissues.

An overview of current advances of PD-L1 targeting immuno-imaging in cancers

The programmed death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) pathway plays a significant role in immune evasion. PD-1 or PD-L1 immune checkpoint inhibitors (ICIs) have become a standard treatment for multiple types of cancer. To date, PD-L1 has served as a biomarker for predicting the efficacy of ICIs in several cancers. The need to establish an effective detection method that could visualize PD-L1 expression and predict the efficacy of PD-1/PD-L1 ICIs has promoted a search for new imaging strategies. PD-L1-targeting immuno-imaging could provide a noninvasive, real-time, repeatable, dynamic, and quantitative assessment of the characteristics of all tumor lesions in individual patients. This study analyzed the existing evidence in the literature on PD-L1-based immuno-imaging (2015-2022). Original English-language articles were searched using PubMed and Google Scholar. Keywords, such as "PD-L1," "PET," "SPECT," "PET/CT," and "SPECT/CT," were used in various combinations. A total of nearly 50 preclinical and clinical studies of PD-L1-targeting immuno-imaging were selected, reviewed, and included in this study. Therefore, in this review, we conducted a study of the advances in PD-L1-targeting immuno-imaging for detecting the expression of PD-L1 and the efficacy of ICIs. We focused on the different types of PD-L1-targeting agents, including antibodies and small PD-L1-binding agents, and illustrated the strength and weakness of these probes. Furthermore, we summarized the trends in the development of PD-L1-targeting immuno-imaging, as well as the current challenges and future directions for clinical workflow.

Improving cancer immunotherapy via co-delivering checkpoint blockade and thrombospondin-1 downregulator

The use of checkpoint-blockade antibodies is still restricted in several malignancies due to the modest efficacy, despite considerable success in anti-tumor immunotherapy. The poor response of cancer cells to immune destruction is an essential contributor to the failure of checkpoint therapy. We hypothesized that combining checkpoint therapy with natural-product chemosensitizer could enhance immune response. Herein, a targeted diterpenoid derivative was integrated with the checkpoint blockade (anti-CTLA-4) to improve immunotherapy using thermosensitive liposomes as carriers. In vivo, the liposomes enabled the co-delivery of the two drug payloads into the tumor. Consequently, the regulatory T cell proliferation was restrained, the cytotoxic T cell infiltration was enhanced, and the profound immunotherapeutic effect was achieved. In addition, the immunotherapeutic effect of another clinically used checkpoint antibody, anti-PD-1, also benefited from the diterpenoid derivative. Of note, our mechanism study revealed that the targeted diterpenoid derivative increased the sensitivity of cancer cells to immune attack via THBS1 downregulation and the resultant destruction of THBS1-CD47 interaction. Collectively, co-delivering THBS1 inhibitor and checkpoint blockade is promising to boost cancer immunotherapy. We first time discovered that THBS1 suppression could strengthen checkpoint therapy.

Engineering a CEACAM1 Variant with the Increased Binding Affinity to TIM-3 Receptor

Background

T-cell immunoglobulin domain and mucin domain-3 (TIM-3) is an inhibitory receptor expressed in a variety of cells, including dendritic cells, T-helper 1 lymphocytes, and natural killer cells. Binding of this protein to its ligand, carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), causes T-cell exhaustion, a specific condition in which effector T cells lose their ability to proliferate and produce cytokines. Blocking this inhibitory receptor is known to be an effective strategy for treating cancer and other related diseases. Therefore, in this study, in order to block the inhibitory receptor of TIM-3, we designed and produced recombinantly a protein with a high binding affinity to this receptor.

Methods

The extracellular domain of CEACAM1 involved in binding to TIM-3 was mutated using R script to obtain a variant with the increased binding affinity to TIM-3. The binding energy of the mutant protein was calculated using the FoldX module. Finally, after recombinant production of the most appropriate CEACAM1 variant (variant 39) in E. coli, its secondary structure was determined by CD spectroscopy.

Results

The binding free energy between variant 39 and TIM-3 decreased from -5.63 to -14.49 kcal/mol, indicating an increased binding affinity to the receptor. Analysis of the secondary structure of this variant also showed that the mutation did not significantly alter the structure of the protein.

Conclusion

Our findings suggest that variant 39 could bind to TIM-3 with a higher binding affinity than the wild-type, making it a proper therapeutic candidate for blocking TIM-3.

Engineering a CEACAM1 Variant with the Increased Binding Affinity to TIM-3 Receptor

Background

T-cell immunoglobulin domain and mucin domain-3 (TIM-3) is an inhibitory receptor expressed in a variety of cells, including dendritic cells, T-helper 1 lymphocytes, and natural killer cells. Binding of this protein to its ligand, carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), causes T-cell exhaustion, a specific condition in which effector T cells lose their ability to proliferate and produce cytokines. Blocking this inhibitory receptor is known to be an effective strategy for treating cancer and other related diseases. Therefore, in this study, in order to block the inhibitory receptor of TIM-3, we designed and produced recombinantly a protein with a high binding affinity to this receptor.

Methods

The extracellular domain of CEACAM1 involved in binding to TIM-3 was mutated using R script to obtain a variant with the increased binding affinity to TIM-3. The binding energy of the mutant protein was calculated using the FoldX module. Finally, after recombinant production of the most appropriate CEACAM1 variant (variant 39) in E. coli, its secondary structure was determined by CD spectroscopy.

Results

The binding free energy between variant 39 and TIM-3 decreased from -5.63 to -14.49 kcal/mol, indicating an increased binding affinity to the receptor. Analysis of the secondary structure of this variant also showed that the mutation did not significantly alter the structure of the protein.

Conclusion

Our findings suggest that variant 39 could bind to TIM-3 with a higher binding affinity than the wild-type, making it a proper therapeutic candidate for blocking TIM-3.

PD-L1 ImmunoPET on the basis of Avidin/Biotin pre-targeted cancer imaging

This study aimed to establish the radio-immune imaging protocol on the basis of Avidin/Biotin system. The programmed death-ligand 1 (PD-L1) antibody (Atezolizumab) was employed as the primary molecule in targeting PD-L1, and the two-step strategy, consisting of the first injection of Avidin-conjugated PD-L1 monoclonal antibody (Atezolizumab) and the second injection of 7.4 MBq ⁶⁸Ga-Biotin with a 60 h interval, was then verified on the colon cancer-bearing mice. PET imaging was performed at 30, 90, 180 min to measure the standard uptake value and tumor to liver ratios. Cellular binding experiments and in vivo distribution showed that the conjugation of Avidin did not affect the affinity of Atezolizumab to PD-L1 antigen. Biotin was radio-labeled with ⁶⁸Ga with radiolabeling efficiency of 70.5 ± 3.5% and purification was needed to increase the radiochemical purity. For PD-L1-positive tumors, SUV_max was 0.38 ± 0.06 in the Avidin-Atezolizumab pre-treated mice at 90 min; the tumor/liver ratios of pre-targeting group were 1.06 ± 0.19 and 0.97 ± 0.16 at 30 and 90 min, while the absence of pre-treatment of Avidin was of the lower ratios as 0.88 ± 0.01 and 0.54 ± 0.11 when ⁶⁸Ga-Biotin served as the radiopharmaceutical as well. In conclusion, pre-targeting immunoPET strategy can elevate the target-to-nontarget ratio, decrease the blood background and shorten the interval between injection of radiopharmaceuticals and PET scan, providing a highly PD-L1-specific and sensitive imaging method for the detection of tumorous immune micro-environment.

Systemic administration of mesenchymal stem cells loaded with a novel oncolytic adenovirus carrying a bispecific T cell engager against hepatocellular carcinoma

We previously established a hepatocellular carcinoma (HCC) targeting system of conditionally replicative adenovirus (CRAd) delivered by human umbilical cord-derived mesenchymal stem cells (HUMSCs). However, this system needed to be developed further to enhance the antitumor effect and overcome the limitations caused by the alpha-fetoprotein (AFP) heterogeneity of HCC. In this study, a bispecific T cell engager (BiTE) targeting programmed death ligand 1 controlled by the human telomerase reverse transcriptase promoter was armed on the CRAd of the old system. It was demonstrated on orthotopic transplantation model mice that the new system had a better anti-tumor effect with no more damage to extrahepatic organs and less liver injury, and the infiltration and activation of T cells were significantly enhanced in the tumor tissues of the model mice treated with the new system. Importantly, we confirmed that the new system eliminated the AFP-negative cells on AFP heterogeneous tumor models efficiently. Conclusion: Compared with the old system, the new system provided a more effective and safer strategy against HCC.

Generation of magnetic biohybrid microrobots based on MSC.sTRAIL for targeted stem cell delivery and treatment of cancer

Background

Combining the power of magnetic guidance and the biological activities of stem cells transformed into biohybrid microrobots holds great promise for the treatment of several diseases including cancer.

Results

We found that human MSCs can be readily loaded with magnetic particles and that the resulting biohybrid microrobots could be guided by a rotating magnetic field. Rotating magnetic fields have the potential to be applied in the human setting and steer therapeutic stem cells to the desired sites of action in the body. We could demonstrate that the required loading of magnetic particles into stem cells is compatible with their biological activities. We examined this issue with a particular focus on the expression and functionality of therapeutic genes inside of human MSC-based biohybrid microrobots. The loading with magnetic particles did not cause a loss of viability or apoptosis in the human MSCs nor did it impact on the therapeutic gene expression from the cells. Furthermore, the therapeutic effect of the gene products was not affected, and the cells also did not lose their migration potential.

Conclusion

These results demonstrate that the fabrication of guidable MSC-based biohybrid microrobots is compatible with their biological and therapeutic functions. Thus, MSC-based biohybrid microrobots represent a novel way of delivering gene therapies to tumours as well as in the context of other diseases.

Isolation and characterization of single domain antibodies from banded houndshark (Triakis scyllium) targeting SARS-CoV-2 spike RBD protein

The COVID-19 pandemic has significantly impacted human health for three years. To mitigate the spread of SARS-CoV-2, the development of neutralizing antibodies has been accelerated, including the exploration of alternative antibody formats such as single-domain antibodies. In this study, we identified new variable antigen receptors (VNARs) specific for the receptor binding domain (RBD) of SARS-CoV-2 by immunizing a banded houndshark (Triakis scyllium) with recombinant wild-type RBD. Notably, the CoV₂NAR-1 clone showed high binding affinities in the nanomolar range to various RBDs and demonstrated neutralizing activity against SARS-CoV-2 pseudoviruses. These results highlight the potential of the banded houndshark as an animal model for the development of VNAR-based therapeutics or diagnostics against future pandemics.

Evolving strategies and application of proteins and peptide therapeutics in cancer treatment

Several proteins and peptides have therapeutic potential and can be used for cancer therapy. By binding to cell surface receptors and other indicators uniquely linked with or overexpressed on tumors compared to healthy tissue, protein biologics enhance the active targeting of cancer cells, as opposed to the passive targeting of cells by conventional small-molecule chemotherapeutics. This study focuses on peptide medications that exist to slow or stop tumor growth and the spread of cancer, demonstrating the therapeutic potential of peptides in cancer treatment. As an alternative to standard chemotherapy, peptides that selectively kill cancer cells while sparing healthy tissue are developing. A mountain of clinical evidence supports the efficacy of peptide-based cancer vaccines. Since a single treatment technique may not be sufficient to produce favourable results in the fight against cancer, combination therapy is emerging as an effective option to generate synergistic benefits. One example of this new area is the use of anticancer peptides in combination with nonpeptidic cytotoxic drugs or the combination of immunotherapy with conventional therapies like radiation and chemotherapy. This review focuses on the different natural and synthetic peptides obtained and researched. Discoveries, manufacture, and modifications of peptide drugs, as well as their contemporary applications, are summarized in this review. We also discuss the benefits and difficulties of potential advances in therapeutic peptides.

In silico evolution of protein binders with deep learning models for structure prediction and sequence design

There has been considerable progress in the development of computational methods for designing protein-protein interactions, but engineering high-affinity binders without extensive screening and maturation remains challenging. Here, we test a protein design pipeline that uses iterative rounds of deep learning (DL)-based structure prediction (AlphaFold2) and sequence optimization (ProteinMPNN) to design autoinhibitory domains (AiDs) for a PD-L1 antagonist. Inspired by recent advances in therapeutic design, we sought to create autoinhibited (or masked) forms of the antagonist that can be conditionally activated by proteases. Twenty-three de novo designed AiDs, varying in length and topology, were fused to the antagonist with a protease sensitive linker, and binding to PD-L1 was tested with and without protease treatment. Nine of the fusion proteins demonstrated conditional binding to PD-L1 and the top performing AiDs were selected for further characterization as single domain proteins. Without any experimental affinity maturation, four of the AiDs bind to the PD-L1 antagonist with equilibrium dissociation constants (KDs) below 150 nM, with the lowest KD equal to 0.9 nM. Our study demonstrates that DL-based protein modeling can be used to rapidly generate high affinity protein binders.

Construction of stable membranal CMTM6-PD-L1 full-length complex to evaluate the PD-1/PD-L1-CMTM6 interaction and develop anti-tumor anti-CMTM6 nanobody

CKLF (chemokine-like factor)-MARVEL transmembrane domain containing protein 6 (CMTM6) is a novel regulator to maintain the stability of PD-L1. CMTM6 can colocalize and interact with PD-L1 on the recycling endosomes and cell membrane, preventing PD-L1 from lysosome-mediated degradation and proteasome-mediated degradation thus increasing the half-life of PD-L1 on the cell membrane. The difficulties in obtaining stable full-length PD-L1 and CMTM6 proteins hinder the research on their structures, function as well as related drug development. Using lauryl maltose neopentyl glycol (LMNG) as the optimized detergent and a cell membrane mimetic strategy, we assembled a stable membrane-bound full-length CMTM6-PD-L1 complex with amphipol A8-35. When the PD-1/PD-L1-CMTM6 interactions were analyzed, we found that CMTM6 greatly enhanced the binding and delayed the dissociation of PD-1/PD-L1, thus affecting immunosuppressive signaling and anti-apoptotic signaling. We then used the CMTM6-PD-L1 complex as immunogens to generate immune repertoires in camels, and identified a functional anti-CMTM6 nanobody, called 1A5. We demonstrated that the anti-CMTM6 nanobody greatly decreased T-cell immunosuppression and promoted apoptotic susceptibility of tumor cells in vitro, and mainly relied on the cytotoxic effect of CD8+ T-cells to exert tumor growth inhibitory effects in CT26 tumor-bearing mice. In conclusion, the stable membrane-bound full-length CMTM6-PD-L1 complex has been successfully used in studying PD-1/PD-L1-CMTM6 interactions and CMTM6-targeting drug development, suggesting CMTM6 as a novel tumor immunotherapy target.

De novo design of protein interactions with learned surface fingerprints

Physical interactions between proteins are essential for most biological processes governing life1. However, the molecular determinants of such interactions have been challenging to understand, even as genomic, proteomic and structural data increase. This knowledge gap has been a major obstacle for the comprehensive understanding of cellular protein-protein interaction networks and for the de novo design of protein binders that are crucial for synthetic biology and translational applications2-9. Here we use a geometric deep-learning framework operating on protein surfaces that generates fingerprints to describe geometric and chemical features that are critical to drive protein-protein interactions10. We hypothesized that these fingerprints capture the key aspects of molecular recognition that represent a new paradigm in the computational design of novel protein interactions. As a proof of principle, we computationally designed several de novo protein binders to engage four protein targets: SARS-CoV-2 spike, PD-1, PD-L1 and CTLA-4. Several designs were experimentally optimized, whereas others were generated purely in silico, reaching nanomolar affinity with structural and mutational characterization showing highly accurate predictions. Overall, our surface-centric approach captures the physical and chemical determinants of molecular recognition, enabling an approach for the de novo design of protein interactions and, more broadly, of artificial proteins with function.

Accelerating therapeutic protein design with computational approaches toward the clinical stage

Therapeutic protein, represented by antibodies, is of increasing interest in human medicine. However, clinical translation of therapeutic protein is still largely hindered by different aspects of developability, including affinity and selectivity, stability and aggregation prevention, solubility and viscosity reduction, and deimmunization. Conventional optimization of the developability with widely used methods, like display technologies and library screening approaches, is a time and cost-intensive endeavor, and the efficiency in finding suitable solutions is still not enough to meet clinical needs. In recent years, the accelerated advancement of computational methodologies has ushered in a transformative era in the field of therapeutic protein design. Owing to their remarkable capabilities in feature extraction and modeling, the integration of cutting-edge computational strategies with conventional techniques presents a promising avenue to accelerate the progression of therapeutic protein design and optimization toward clinical implementation. Here, we compared the differences between therapeutic protein and small molecules in developability and provided an overview of the computational approaches applicable to the design or optimization of therapeutic protein in several developability issues.

Multifunctional nanodrug performs sonodynamic therapy and inhibits TGF-β to boost immune response against colorectal cancer and liver metastasis

Liver metastasis is the leading cause of death in colorectal cancer. Immunotherapy using immune checkpoint blockade (ICB) is ineffective due to its immunological cold tumor nature. Herein, we prepared a nanodrug (NCG) encapsulating the transforming growth factor-β receptor inhibitor galunisertib (Gal) and the sonosensitizer chlorin e6 (Ce6), which was aimed to turn this type of cold tumor into a hot one to promote the ICB-based immunotherapy against it. After delivery to the tumor, NCG under ultrasonic irradiation generated reactive oxygen species causing tumor immunogenic cell death and releasing immunostimulatory signals such as calreticulin and HMGB1, which increased tumor immunogenicity and activated the innate T lymphocyte immune response. Moreover, NCG responded to the acidic microenvironment and released Gal, inhibiting phosphorylation and inducing immunosuppressive Smad2/3 signaling. Consequently, the differentiation of MDSCs was inhibited, M1-like polarization of tumor-associated macrophages was induced, and the immunosuppressive barrier of tumor-associated fibroblasts was destroyed to increase the infiltration of effector T cells, which reversed the immunosuppression of the tumor microenvironment and improved the therapeutic efficacy of anti-PD-L1 antibodies. Notably, in the liver metastasis mouse model, combination therapy using NCG (+) and aPD-L1 inhibited the growth of colon cancer liver metastasis, manifesting potential in treating this popular yet intractable malignancy. STATEMENT OF SIGNIFICANCE: Only a limited number of patients with colorectal cancer and liver metastasis can benefit from immune checkpoint blockade therapy, as most of them are microsatellite stable, immunologically cold tumors. Interestingly, there is compelling evidence that sonodynamic therapy (SDT) can convert immunosuppressed cold tumors into hot ones, trigger tumor immunogenic cell death non-invasively, and boost cytotoxic T cells infiltration. However, its therapeutic efficacy is constrained by the abundance of transforming growth factor-β (TGF-β) cytokines in the tumor microenvironment. Here, we reported a TGF-β-targeted inhibitory nanodrug that improved SDT in colon cancer and liver metastasis, reversed the immunosuppressive tumor microenvironment and boosted the immune response to anti-PD-L1 therapy in this cancer. It demonstrated the potential to cure this prevalent but incurable malignancy.

Nanoparticle Targeting with Antibodies in the Central Nervous System

Treatments for disease in the central nervous system (CNS) are limited because of difficulties in agent penetration through the blood-brain barrier, achieving optimal dosing, and mitigating off-target effects. The prospect of precision medicine in CNS treatment suggests an opportunity for therapeutic nanotechnology, which offers tunability and adaptability to address specific diseases as well as targetability when combined with antibodies (Abs). Here, we review the strategies to attach Abs to nanoparticles (NPs), including conventional approaches of chemisorption and physisorption as well as attempts to combine irreversible Ab immobilization with controlled orientation. We also summarize trends that have been observed through studies of systemically delivered Ab-NP conjugates in animals. Finally, we discuss the future outlook for Ab-NPs to deliver therapeutics into the CNS.

Turning a Tumor Microenvironment Pitfall into Opportunity: Discovery of Benzamidoxime as PD-L1 Ligand with pH-Dependent Potency

PD-1/PD-L1 protein complex is attracting a great deal of interest as a drug target for the design of immune therapies able to block its assembly. Although some biologic drugs have entered clinical use, their poor response rate in patients are demanding further efforts to design small molecule inhibitors of PD-1/PD-L1 complex with higher efficacy and optimal physicochemical properties. Dysregulation of pH in the tumor microenvironment is indeed one of the key mechanisms promoting drug resistance and lack of response in cancer therapy. Integrating computational and biophysical approaches, herein we report a screening campaign that has led to identifying VIS310 as a novel ligand of PD-L1, with physicochemical properties enabling a pH-dependent binding potency. Additional optimization efforts by analogue-based screening have been instrumental to disclosing VIS1201, which exhibits improved binding potency against PD-L1 and is able to inhibit PD-1/PD-L1 complex formation in a ligand binding displacement assay. While providing preliminary structure–activity relationships (SARs) of a novel class of PD-L1 ligands, our results lay the foundation for the discovery of immunoregulatory small molecules resilient to tumor microenvironmental conditions for escaping drug-resistance mechanisms.

Design of a protease-activated PD-L1 inhibitor

Immune checkpoint inhibitors that bind to the cell surface receptor PD-L1 are effective anti-cancer agents but suffer from immune-related adverse events as PD-L1 is expressed on both healthy and cancer cells. To mitigate toxicity, researchers are testing prodrugs that have low affinity for checkpoint targets until activated with proteases enriched in the tumor microenvironment. Here, we engineer a prodrug form of a PD-L1 inhibitor. The inhibitor is a soluble PD-1 mimetic that was previously engineered to have high affinity for PD-L1. In the basal state, the binding surface of the PD-1 mimetic is masked by fusing it to a soluble variant of its natural ligand, PD-L1. Proteolytic cleavage of the linker that connects the mask to the inhibitor activates the molecule. To optimize the mask so that it effectively blocks binding to PD-L1 but releases upon cleavage, we tested a set of mutants with varied affinity for the inhibitor. The top-performing mask reduces the affinity of the prodrug for PD-L1 120-fold, and binding is nearly fully recovered upon cleavage. In a cell-based assay measuring inhibition of the PD-1:PD-L1 interaction on the surface of cells, the IC50s of the masked inhibitors were up to 40-fold higher than their protease-treated counterparts. The changes in activity we observe upon protease treatment are comparable to systems currently tested in the clinic and provide evidence that natural binding partners are an excellent starting point for creating a prodrug.

Molecular and functional imaging in cancer-targeted therapy: current applications and future directions

Targeted anticancer drugs block cancer cell growth by interfering with specific signaling pathways vital to carcinogenesis and tumor growth rather than harming all rapidly dividing cells as in cytotoxic chemotherapy. The Response Evaluation Criteria in Solid Tumor (RECIST) system has been used to assess tumor response to therapy via changes in the size of target lesions as measured by calipers, conventional anatomically based imaging modalities such as computed tomography (CT), and magnetic resonance imaging (MRI), and other imaging methods. However, RECIST is sometimes inaccurate in assessing the efficacy of targeted therapy drugs because of the poor correlation between tumor size and treatment-induced tumor necrosis or shrinkage. This approach might also result in delayed identification of response when the therapy does confer a reduction in tumor size. Innovative molecular imaging techniques have rapidly gained importance in the dawning era of targeted therapy as they can visualize, characterize, and quantify biological processes at the cellular, subcellular, or even molecular level rather than at the anatomical level. This review summarizes different targeted cell signaling pathways, various molecular imaging techniques, and developed probes. Moreover, the application of molecular imaging for evaluating treatment response and related clinical outcome is also systematically outlined. In the future, more attention should be paid to promoting the clinical translation of molecular imaging in evaluating the sensitivity to targeted therapy with biocompatible probes. In particular, multimodal imaging technologies incorporating advanced artificial intelligence should be developed to comprehensively and accurately assess cancer-targeted therapy, in addition to RECIST-based methods.

Prophylaxis and treatment of SARS-CoV-2 infection by an ACE2 receptor decoy in a preclinical animal model

The emergence of SARS-CoV-2 variants with highly mutated spike proteins has presented an obstacle to the use of monoclonal antibodies for the prevention and treatment of SARS-CoV-2 infection. We show that a high-affinity receptor decoy protein in which a modified ACE2 ectodomain is fused to a single domain of an immunoglobulin heavy chain Fc region dramatically suppressed virus loads in mice upon challenge with a high dose of parental SARS-CoV-2 or Omicron variants. The decoy also potently suppressed virus replication when administered shortly post-infection. The decoy approach offers protection against the current viral variants and, potentially, against SARS-CoV-2 variants that may emerge with the continued evolution of the spike protein or novel viruses that use ACE2 for virus entry.

Titrating Avidity of Yeast-Displayed Proteins Using a Transcriptional Regulator

Yeast surface display is a valuable tool for protein engineering and directed evolution; however, significant variability in the copy number (i.e., avidity) of displayed variants on the yeast cell wall complicates screening and selection campaigns. Here, we report an engineered titratable display platform that modulates the avidity of Aga2-fusion proteins on the yeast cell wall dependent on the concentration of the anhydrotetracycline (aTc) inducer. Our design is based on a genomic Aga1 gene copy and an episomal Aga2-fusion construct both under the control of an aTc-dependent transcriptional regulator that enables stoichiometric and titratable expression, secretion, and display of Aga2-fusion proteins. We demonstrate tunable display levels over 2-3 orders of magnitude for various model proteins, including glucose oxidase enzyme variants, mechanostable dockerin-binding domains, and anti-PDL1 affibody domains. By regulating the copy number of displayed proteins, we demonstrate the effects of titratable avidity levels on several specific phenotypic activities, including enzyme activity and cell adhesion to surfaces under shear flow. Finally, we show that titrating down the display level allows yeast-based binding affinity measurements to be performed in a regime that avoids ligand depletion effects while maintaining small sample volumes, avoiding a well-known artifact in yeast-based binding assays. The ability to titrate the multivalency of proteins on the yeast cell wall through simple inducer control will benefit protein engineering and directed evolution methodology relying on yeast display for broad classes of therapeutic and diagnostic proteins of interest.