Site-specific antibody-drug conjugates with variable drug-to-antibody-ratios for AML therapy

Genetically reprogrammed exosomes for immunotherapy of acute myeloid leukemia

Current treatments for acute myeloid leukemia (AML) remain challenging and are characterized by poor clinical outcomes. Exosomes, cell-derived membranous vesicles, have been emerging as a new modality of therapy. Here, we designed and generated genetically reprogrammed exosomes with surface-displayed antibodies and immunoregulatory proteins, namely programmed immune-engaging exosomes (PRIME Exos). By simultaneously targeting T cells and AML cells expressing C-type lectin-like molecule-1 (CLL-1), PRIME Exos can elicit tumor-specific immune responses and sustain cellular immunity against AML by modulating programmed death 1 (PD-1)- and CD27-mediated immune checkpoint pathways. In preclinical models of AML, PRIME Exos have shown promising efficacy and safety for suppressing leukemia expansion. This study developed a new exosome-based approach for AML immunotherapy.

Bispecific Aptamer-Drug Conjugates Selectively Eliminate Malignant Hematologic Cells for Treating Acute Myeloid Leukemia

Surface antigen-directed immunotherapy is a curative treatment modality for acute myeloid leukemia (AML) that is characterized by the abundance and stability expression of surface antigens. However, current surface antigen-directed immunotherapies have shown poor outcomes and undesirable mortality rates in treating AML patients, primarily due to acquired resistance that arises from using single-target therapies to address the heterogeneous expression of surface antigens. Hence, in order to improve the efficacy of antigen-specific therapies for treating AML, we designed a bispecific aptamer-drug conjugate. In particular, cell-SELEX incorporating cell lysate-SELEX for aptamers with HEL cells yielded AptCD117, which specifically binds to CD117 (a highly expressed marker on both hematopoietic stem cells and primary AML cells) and has excellent performance in targeting human AML cells. Combined with CD71-binding aptamer LXD-11b (another broadly expressed surface antigen on leukemia cells), bispecific aptamers were designed to couple with monomethyl auristatin F (MMAF) for fabricating aptamer-drug conjugates. Results demonstrated that bispecific aptamer-MMAF conjugates efficiently kill different CD117 and CD71 expression levels of target AML cell lines in vitro. Importantly, the exposure of AML marrow specimens to bispecific aptamer-MMAF conjugates resulted in the selective elimination of primary AML cells in vitro and had no effect on healthy lymphocytes within the same specimens. Thus, these results provide a proof of concept for the generation of bispecific aptamer-drug conjugates directed against human AML cells, which hold the promise of advancing treatment strategies and improving AML patient outcomes.

Nicotinamide Riboside and CD38: Covalent Inhibition and Live-Cell Labeling

Nicotinamide adenine dinucleotide (NAD+) is required for a myriad of metabolic, signaling, and post-translational events in cells. Its levels in tissues and organs are closely associated with health conditions. The homeostasis of NAD+ is regulated by biosynthetic pathways and consuming enzymes. As a membrane-bound protein with robust NAD+ hydrolase activity, cluster of differentiation 38 (CD38) is a major degrader of NAD+. Deficiency or inhibition of CD38 enhances NAD+ levels in vivo, resulting in various therapeutic benefits. As a metabolic precursor of NAD+, nicotinamide mononucleotide can be rapidly hydrolyzed by CD38, whereas nicotinamide riboside (NR) lacks CD38 substrate activity. Given their structural similarities, we explored the inhibition potential of NR. To our surprise, NR exhibits marked inhibitory activity against CD38 by forming a stable ribosyl-ester bond with the glutamate residue 226 at the active site. Inspired by this discovery, we designed and synthesized a clickable NR featuring an azido substitution at the 5'-OH position. This cell-permeable NR analogue enables covalent labeling and imaging of both extracellular and intracellular CD38 in live cells. Our work discovers an unrecognized molecular function of NR and generates a covalent probe for health-related CD38. These findings offer new insights into the role of NR in modulating NAD+ metabolism and CD38-mediated signaling as well as an innovative tool for in-depth studies of CD38 in physiology and pathophysiology.

Synthesis of site-specific Fab-drug conjugates using ADP-ribosyl cyclases

Targeted delivery of small-molecule drugs via covalent attachments to monoclonal antibodies has proved successful in clinic. For this purpose, full-length antibodies are mainly used as drug-carrying vehicles. Despite their flexible conjugation sites and versatile biological activities, intact immunoglobulins with conjugated drugs, which feature relatively large molecular weights, tend to have restricted tissue distribution and penetration and low fractions of payloads. Linking small-molecule therapeutics to other formats of antibody may lead to conjugates with optimal properties. Here, we designed and synthesized ADP-ribosyl cyclase-enabled fragment antigen-binding (Fab) drug conjugates (ARC-FDCs) by utilizing CD38 catalytic activity. Through rapidly forming a stable covalent bond with a nicotinamide adenine dinucleotide (NAD+ )-based drug linker at its active site, CD38 genetically fused with Fab mediates robust site-specific drug conjugations via enzymatic reactions. Generated ARC-FDCs with defined drug-to-Fab ratios display potent and antigen-dependent cytotoxicity against breast cancer cells. This work demonstrates a new strategy for developing site-specific FDCs. It may be applicable to different antibody scaffolds for therapeutic conjugations, leading to novel targeted agents.

Antibody-platinum (IV) prodrugs conjugates for targeted treatment of cutaneous squamous cell carcinoma

Antibody-drug conjugates (ADCs) are a new type of targeting antibodies that conjugate with highly toxic anticancer drugs via chemical linkers to exert high specificity and efficient killing of tumor cells, thereby attracting considerable attention in precise oncology therapy. Cetuximab (Cet) is a typical antibody that offers the benefits of good targeting and safety for individuals with advanced and inoperable cutaneous squamous cell carcinoma (cSCC); however, its anti-tumor activity is limited to a single use. Cisplatin (CisPt) shows good curative effects; however, its adverse effects and non-tumor-targeting ability are major drawbacks. In this study, we designed and developed a new ADC based on a new cytotoxic platinum (IV) prodrug (C8Pt(IV)) and Cet. The so-called antibody-platinum (IV) prodrugs conjugates, named Cet-C8Pt(IV), showed excellent tumor targeting in cSCC. Specifically, it accurately delivered C8Pt(IV) into tumor cells to exert the combined anti-tumor effect of Cet and CisPt. Herein, metabolomic analysis showed that Cet-C8Pt(IV) promoted cellular apoptosis and increased DNA damage in cSCC cells by affecting the vitamin B6 metabolic pathway in tumor cells, thereby further enhancing the tumor-killing ability and providing a new strategy for clinical cancer treatment using antibody-platinum (IV) prodrugs conjugates.

Rational design of humanized antibody inhibitors for cathepsin S

Cathepsin S (CTSS) is involved in pathogenesis of many human diseases. Inhibitors blocking its protease activity hold therapeutic potential. In comparison to small-molecule inhibitors, monoclonal antibodies capable of inhibiting CTSS enzymatic activity may possess advantageous pharmacological properties. Here we designed and produced inhibitory antibodies targeting human CTSS by genetically fusing the propeptide of procathepsin S (proCTSS) with antibodies in clinic. The resulting antibody fusions in full-length or fragment antigen-binding format could be stably expressed and potently inhibit CTSS proteolytic activity in high specificity. These fusion antibodies not only demonstrate a new approach for facile synthesis of antibody inhibitors against CTSS, but also represent novel anti-CTSS therapeutic candidates.