An amphipathic Bax core dimer forms part of the apoptotic pore wall in the mitochondrial␣membrane.

Bax proteins form pores in the mitochondrial outer membrane to initiate apoptosis. This might involve their embedding in the cytosolic leaflet of the lipid bilayer, thus generating tension to induce a lipid pore with radially arranged lipids forming the wall. Alternatively, Bax proteins might comprise part of the pore wall. However, there is no unambiguous structural evidence for either hypothesis. Using NMR, we determined a high-resolution structure of the Bax core region, revealing a dimer with the nonpolar surface covering the lipid bilayer edge and the polar surface exposed to water. The dimer tilts from the bilayer normal, not only maximizing nonpolar interactions with lipid tails but also creating polar interactions between charged residues and lipid heads. Structure-guided mutations demonstrate the importance of both types of protein-lipid interactions in Bax pore assembly and core dimer configuration. Therefore, the Bax core dimer forms part of the proteolipid pore wall to permeabilize mitochondria.

Self-Assembled Antibody-Oligonucleotide Conjugates for Targeted Delivery of Complementary Antisense Oligonucleotides.

Antibody-oligonucleotide conjugate (AOC) affords preferential cell targeting and enhanced cellular uptake of antisense oligonucleotide (ASO).  Here, we have developed a modular AOC (MAOC) approach based on accurate self-assembly of separately prepared antibody and ASO modules. Homogeneous multimeric AOC with defined ASO-to-antibody ratio were generated by L-DNA scaffold mediated precise self-assembly of antibodies and ASOs. The MAOC approach has been implemented to deliver exon skipping ASOs via transferrin receptor (TfR1) mediated internalization. We discovered an anti-TfR1 sdAb that can greatly enhance nuclear delivery of ASOs. Cryo-EM structure of the sdAb-TfR1 complex showed a new epitope that does not overlap with the binding sites of endogenous TfR1 ligands. In vivo functional analyses of MAOCs with one ASO for single exon skipping and two ASOs for double exon skipping showed that both ASO concentration and exon skipping efficacy of MAOC in cardiac and skeletal muscles are dramatically higher than conventional ASOs in the transgenic Duchenne muscular dystrophy (DMD) mouse model. MAOC treatment was well tolerated in vivo and not associated with any toxicity-related morbidity or mortality. Collectively, our data suggest that the self-assembled MAOC is a viable option for broadening the therapeutic application of ASO via multi-specific targeting and delivery.

Self-Assembled L-DNA Linkers for Rapid Construction of Multi-Specific Antibody-Drug Conjugates Library.

One of the key challenges of improving clinical outcomes of antibody drug conjugates (ADCs) is overcoming cancer resistance to the antibody and/or drug components of ADCs, and hence the need for ADC platforms with high combinatory flexibility. Here, we introduce the use of self-assembled left-handed DNA (L-DNA) oligonucleotides to link combinatory single-domain antibodies and toxin payloads for tunable and adaptive delivery of ADCs. We demonstrate that the method allows convenient construction of a library of ADCs with multi-specific targeting, multi-specific payloads, and exact drug-antibody ratio. The newly constructed ADCs with L-DNA scaffold showed favorable properties of in vitro cell cytotoxicity and in vivo suppression and eradication of solid tumors. Collectively, our data suggest that the L-DNA based modular ADC (MADC) platform is a viable option for generating therapeutic ADCs and for potentially expanding ADC therapeutic window via multi-specificity.

DNA-Mediated Assembly of Multispecific Antibodies for T Cell Engaging and Tumor Killing.

Targeting T-cells against cancer cells is a direct means of treating cancer, and has already shown great responses in clinical treatment of B-cell malignancies. A simple way to redirect T-cells to cancer cells is by using multispecific antibody (MsAb) that contains different arms for specifically "grabbing" the T-cells and cancer cells; as such, the T-cells are activated upon target engagement and the killing begins. Here, a nucleic acid mediated protein-protein assembly (NAPPA) approach is implemented to construct a MsAb for T-cell engaging and tumor killing. Anti -CD19 and -CD3 single-chain variable fragments (scFvs) are conjugated to different l-DNAs with sequences that form the Holliday junction, thus allowing spontaneous assembly of homogeneous protein-DNA oligomers containing two anti-CD19 and one anti-CD3 scFvs. The new MsAb shows strong efficacy in inducing Raji tumor cell cytotoxicity in the presence of T-cells with EC50 ≈ 0.2 × 10-9 m; it also suppresses tumor growth in a Raji xenograft mouse model. The data indicates that MsAbs assembled from protein-DNA conjugates are effective macromolecules for directing T-cells for tumor killing. The modular nature of the NAPPA platform allows rapid generation of complex MsAbs from simple antibody fragments, while offering a general solution for preparing antibodies with high-order specificity.