Assembly of pH-Responsive Antibody-Drug-Inspired Conjugates.

With the advent of chemical strategies that allow the design of smart bioconjugates, peptide- and protein-drug conjugates are emerging as highly efficient therapeutics to overcome limitations of conventional treatment, as exemplified by antibody-drug conjugates (ADCs). While targeting peptides serve similar roles as antibodies to recognize overexpressed receptors on diseased cell surfaces, peptide-drug conjugates suffer from poor stability and bioavailability due to their low molecular weights. Through a combination of a supramolecular protein-based assembly platform and a pH-responsive linker, the authors devise herein the convenient assembly of a trivalent protein-drug conjugate. The conjugate should ideally possess distinct features of ADCs such as 1) recognition sites that recognize cell receptor and are arranged on 2) distinct locations on a high molecular weight protein scaffold, 3) a stimuli-responsive linker, as well as 4) an attached payload such as a drug molecule. These AD-like conjugates target cancer cells that overexpress somatostatin receptors, can enable controlled release in the microenvironment of cancer cells through a new pH-responsive biotin linker, and exhibit stability in biological media.

Controlled Supramolecular Assembly Inside Living Cells by Sequential Multistaged Chemical Reactions.

Synthetic assembly within living cells represents an innovative way to explore purely chemical tools that can direct and control cellular behavior. We use a simple and modular platform that is broadly accessible and yet incorporates highly intricate molecular recognition, immolative, and rearrangement chemistry. Short bimodular peptide sequences undergo a programmed sequence of events that can be tailored within the living intracellular environment. Each sequential stage of the pathways beginning with the cellular uptake, intracellular transport, and localization imposes distinct structural changes that result in the assembly of fibrillar architectures inside cells. The observation of apoptosis, which is characterized by the binding of Annexin V, demonstrates that programmed cell death can be promoted by the peptide assembly. Higher complexity of the assemblies was also achieved by coassembly of two different sequences, resulting in intrinsically fluorescent architectures. As such, we demonstrate that the in situ construction of architectures within cells will broaden the community's perspective toward how structure formation can impact a living system.

Control over Imidazoquinoline Immune Stimulation by pH-Degradable Poly(norbornene) Nanogels.

The reactivation of the innate immune system by toll-like receptor (TLR) agonists holds promise for anticancer immunotherapy. Severe side effects caused by unspecific and systemic activation of the immune system upon intravenous injection prevent the use of small-molecule TLR agonists for such purposes. However, a covalent attachment of small-molecule imidazoquinoline (IMDQ) TLR7/8 agonists to pH-degradable polymeric nanogels could be shown to drastically reduce the systemic inflammation but retain the activity to tumoral tissues and their draining lymph nodes. Here, we introduce the synthesis of poly(norbornene)-based, acid-degradable nanogels for the covalent ligation of IMDQs. While the intact nanogels trigger sufficient TLR7/8 receptor stimulation, their degraded version of soluble, IMDQ-conjugated poly(norbornene) chains hardly activates TLR7/8. This renders their clinical safety profile, as degradation products are obtained, which would not only circumvent nanoparticle accumulation in the body but also provide nonactive, polymer-bound IMDQ species. Their immunologically silent behavior guarantees both spatial and temporal control over immune activity and, thus, holds promise for improved clinical applications.

Sequence Programming with Dynamic Boronic Acid/Catechol Binary Codes.

The development of a synthetic code that enables a sequence programmable feature like DNA represents a key aspect toward intelligent molecular systems. We developed herein the well-known dynamic covalent interaction between boronic acids (BAs) and catechols (CAs) into synthetic nucleobase analogs. Along a defined peptide backbone, BA or CA residues are arranged to enable sequence recognition to their complementary strand. Dynamic strand displacement and errors were elucidated thermodynamically to show that sequences are able to specifically select their partners. Unlike DNA, the pH dependency of BA/CA binding enables the dehybridization of complementary strands at pH 5.0. In addition, we demonstrate the sequence recognition at the macromolecular level by conjugating the cytochrome c protein to a complementary polyethylene glycol chain in a site-directed fashion.

Orthogonally Stimulated Assembly/Disassembly of Depsipeptides by Rational Chemical Design.

Controlling the assembly and disassembly of cross-ß-sheet-forming peptides is one of the predominant challenges for this class of supramolecular material. As they constitute a continuously propagating material, every atomic change can be exploited to bring about distinct responses at the architectural level. We report herein that, by using rational chemical design, serine and methionine can both be used as orthogonal chemical triggers to signal assembly/disassembly through their corresponding stimuli. Serine is used to construct an ester-bond oligopeptide that can undergo O,N-acyl rearrangement, whereas methionine is sensitive to oxidation by H2 O2 . Using the example peptide sequence, KIKISQINM, we demonstrate that assembly and disassembly can be independently controlled on demand.