The pyrrolo[2,1‐c][1,4]benzodiazepines (PBDs) are a family of sequence‐selective DNA minor‐groove binding agents that form a covalent aminal bond between their C11‐position and the C2‐NH2 groups of guanine bases. The first example of a PBD monomer, the natural product anthramycin, was discovered in the 1960s, and the best known PBD dimer, SJG‐136 (also known as SG2000, NSC 694501 or BN2629), was synthesized in the 1990s and has recently completed Phase II clinical trials in patients with leukaemia and ovarian cancer. More recently, PBD dimer analogues are being attached to tumor‐targeting antibodies to create antibody–drug conjugates (ADCs), a number of which are now in clinical trials, with many others in pre‐clinical development. This Review maps the development from anthramycin to the first PBD dimers, and then to PBD‐containing ADCs, and explores both structure–activity relationships (SARs) and the biology of PBDs, and the strategies for their use as payloads for ADCs.

Ingestion is the preferred way for drug administration. However, many drugs have poor oral bioavailability, warranting the use of injections. Extracellular vesicles (EVs) from cow milk have shown potential utility in improving oral drug bioavailability. However, EVs produced by intestinal epithelial cells have not been investigated for this application. We compared the capacity of cow milk EVs and intestinal epithelial cell-derived counterparts to enhance oral drug bioavailability. EVs were isolated, fluorescently labelled, and loaded with curcumin (CUR) as a model poorly absorbable drug. These were then characterised before testing in an intestinal model (Caco-2). Epithelial cell-derived EVs showed notably higher cell uptake compared to cow milk EVs. Cell uptake was significantly higher in differentiated compared to undifferentiated cells for both types of EVs. While both milkand cell-derived EVs improved the cell uptake and intestinal permeability of CUR (confirming oral drug bioavailability enhancement potential), epithelial cell EVs demonstrated a superior effect.

Crispene E, a new clerodane-type diterpene, inhibited STAT3 dimerization in a cell-free fluorescent polarisation assay and was found to have significant toxicity against STAT3-dependent MDA-MB 231 breast cancer cell line and selectively inhibited the expression of STAT3 and STAT3 target genes cyclin D1, Fascin and bcl-2. Molecular docking studies suggest the molecule inhibits STAT3 by interacting with its SH2 domain. The compound has been isolated from Tinospora crispa and characterized using standard spectroscopic techniques.

The aim of this study was to probe whether the transferrin (Tf) transport pathway can be exploited for intestinal delivery of nanoparticles. Tf was adsorbed on 100 nm model polystyrene nanoparticles (NP), followed by size characterisation of these systems. Cell uptake of Tf and Tf-adsorbed NP was investigated in intestinal epithelial Caco-2 cells cultured on multi-well plates and as differentiated polarised monolayers. Tf-NP demonstrated a remarkably higher cell uptake compared to unmodified NP in both non-polarised (5-fold) and polarised cell monolayers (16-fold difference). Application of soluble Tf significantly attenuated the uptake of Tf-NP. Notably, Tf-NP displayed remarkably higher rate (23-fold) of epithelial transport across Caco-2 monolayers compared to unmodified NP. This study therefore strongly suggests that the Tf transport pathway should be considered as a candidate biological transport route for orally-administered nanomedicines and drugs with poor oral bioavailability.

Nanomedicines undergo transformation in biological media, which impacts biological effects. Such transformation in the gut environment has implications in use of nanomedicines for oral administration.

Biologics have changed the management of Inflammatory Bowel Disease (IBD), but there are concerns regarding unexpected systemic toxicity and loss of therapeutic response following administration by injection. Local delivery of biologics directly to the inflamed mucosa via rectal enema administration addresses the problems associated with systemic administration. Hydrogels are potentially useful delivery vehicles enabling rectal administration of biologics. Here, we prepared a hydrogel system based on methylcellulose (MC) and hyaluronic acid (HA), which possesses mucosal healing properties, incorporating a model macromolecular drug, namely (fluorescently-labeled) bovine serum albumin (BSA). The BSA-loaded MCHA hydrogel showed temperature-dependent gelation (liquid-like at 20 °C and gel-like at 37 °C) and shear thinning behavior, with these being important and desirable characteristics for rectal application (enabling easy application and retention). BSA release from the MCHA system at 37 °C was linear, with 50% of the loaded drug released within 2 h. The system demonstrated acceptable toxicity towards intestinal (colon) Caco-2 epithelial cells, even at high concentrations. Importantly, application of the BSA-loaded MCHA hydrogel to polarized Caco-2 monolayers, with or without an exemplar absorption enhancer, resulted in transintestinal permeability of BSA. The study therefore indicates that the MCHA hydrogel shows potential for topical (rectal) delivery of biologics in IBD.

Pyrrolobenzodiazepines (PBDs) are covalent-binding DNA-interactive agents with growing importance as payloads in Antibody Drug Conjugates (ADCs). Until now, PBDs were thought to covalently bond to C2-NH2 groups of guanines in the DNA-minor groove across a three-base-pair recognition sequence. Using HPLC/MS methodology with designed hairpin and duplex oligonucleotides, we have now demonstrated that the PBD Dimer SJG-136 and the C8-conjugated PBD Monomer GWL-78 can covalently bond to a terminal guanine of DNA, with the PBD skeleton spanning only two base pairs. Control experiments with the non-C8-conjugated anthramycin along with molecular dynamics simulations suggest that the C8-substituent of a PBD Monomer, or one-half of a PBD Dimer, may provide stability for the adduct. This observation highlights the importance of PBD C8-substituents, and also suggests that PBDs may bind to terminal guanines within stretches of DNA in cells, thus representing a potentially novel mechanism of action at the end of DNA strand breaks.

Full understanding of the barrier property of mucosal tissues is imperative for development of successful mucosal drug delivery strategies, particularly for biologics and nanomedicines. The contribution of the mucosal basement membrane (BM) to this barrier is currently not fully appreciated. This work examined the role of the BM as a barrier to intestinal absorption of model macromolecules (5 kDa and 10 kDa dextrans) and 100 nm polystyrene nanoparticles. Dextrans and nanoparticles were applied either directly to BM-coated inserts or to an intestinal model, namely differentiated intestinal epithelial monolayers (Caco-2) cultured on BM-modified inserts. The work shows that the BM per se does not impact the diffusion of dextran macromolecules, but severely hinders the movement of nanoparticles. However, importantly, Caco-2 monolayers cultured on BMcoated inserts, which show a remarkably different morphology, display a significantly larger barrier to the translocation of one dextran, as well as nanoparticle systems compared to cells cultured on unmodified inserts. Therefore, this work shows that in addition to presenting a direct physical barrier to the movement of nanoparticles, the BM also exerts an indirect barrier effect, likely due to its influence on epithelial cell physiology. This work is important as it highlights the currently unmet need to consider and further study the barrier properties of the BM in mucosal delivery of biologics and nanomedicines.