Development of a novel apigenin prodrug programmed for alkaline-phosphatase instructed self-inhibition to combat cancer

Elevated levels of alkaline phosphatase (ALP) in the tumor microenvironment (TME) are a hallmark of cancer progression and thus inhibition of ALP could serve as an effective approach against cancer. Herein, we developed a novel prodrug approach to tackle cancer that bears self-inhibiting alkaline phosphatase-responsiveness properties that can enhance at the same time the solubility of the parent compound. To probe this novel concept, we selected apigenin as the cytotoxic agent since we first unveiled, that it directly interacts and inhibits ALP activity. Consequently, we rationally designed and synthesized, using a self-immolative linker, an ALP responsive apigenin-based phosphate prodrug, phospho-apigenin. Phospho-apigenin markedly increased the stability of the parent compound apigenin. Furthermore, the prodrug exhibited enhanced antiproliferative effect in malignant cells with elevated ALP levels, compared to apigenin. This recorded potency of the developed prodrug was further confirmed in vivo where phospho-apigenin significantly suppressed by 52.8% the growth of PC-3 xenograft tumors.Communicated by Ramaswamy H. Sarma.

Controlled Self-Assembly of Discrete Amphiphilic Oligourethanes with Cascade Self-Immolative Motif

Discrete polymers offer an excellent platform for comprehending the interplay between precise chain structures, distinctive self-assembly behaviors, and functional applications, whereas the development of discrete polymers with self-immolative properties remains scarce. Here, we modularly synthesize a library of discrete self-immolative oligourethanes containing N-naphthylcarbamate or N-(3-fluorophenyl)carbamate) repeating units via iterative stepwise growth. These oligourethanes undergo not only cascade 1,6-elimination depolymerizations via photo-mediated removal of o-nitrobenzyl carbamate triggers but also selective cleavage of benzyl-O linkages under MS/MS conditions even without UV light irradiation. In aqueous media, these discrete oligourethanes self-assemble into different morphologies such as flat nanosheets, nanofibers, and nanoribbons, depending on the chain lengths and backbone compositions, and further morphological transitions are observed upon annealing treatments.

Electrocatalytic Depolymerization of Self-Immolative Poly(Dithiothreitol) Derivatives

We report the use of electrogenerated anthraquinone radical anion (AQ•-) to trigger fast catalytic depolymerization of polymers derived from poly(dithiothreitol) (pDTT)-a self-immolative polymer (SIP) with a backbone of dithiothreitols connected with disulfide bonds and end-capped via disulfide bonds to pyridyl groups. The pDTT derivatives studied include polymers with simple thiohexyl end-caps or modified with AQ or methyl groups by Steglich esterification. All polymers were shown to be depolymerized using catalytic amounts of electrons delivered by AQ•-. For pDTT, as little as 0.2 electrons per polymer chain was needed to achieve complete depolymerization. We hypothesize that the reaction proceeds with AQ•- as an electron carrier (either molecularly or as a pendant group), which transfers an electron to a disulfide bond in the polymer in a dissociative manner, generating a thiyl radical and a thiolate. The rapid and catalytic depolymerization is driven by thiyl radicals attacking other disulfide bonds internally or between pDTT chains in a chain reaction. Electrochemical triggering works as a general method for initiating depolymerization of pDTT derivatives and may likely also be used for depolymerization of other disulfide polymers.

Dual-Responsive Material Based on Catechol-Modified Self-Immolative Poly(Disulfide) Backbones

Functional materials engineered to degrade upon triggering are in high demand due their potentially lower impact on the environment as well as their use in sensing and in medical applications. Here, stimuli-responsive polymers are prepared by decorating a self-immolative poly(dithiothreitol) backbone with pendant catechol units. The highly functional polymer is fashioned into stimuli-responsive gels, formed through pH-dependent catecholato-metal ion cross-links. The gels degrade in response to specific environmental changes, either by addressing the pH responsive, non-covalent, catecholato-metal complexes, or by addition of a thiol. The latter stimulus triggers end-to-end depolymerization of the entire self-immolative backbone through end-cap replacement via thiol-disufide exchanges. Gel degradation is visualized by release of a dye from the supramolecular gel as it itself is converted into smaller molecules.

Fluoride-Triggered Self-Degradation of Poly(2,4-disubstitued 4-hydroxybutyric acid) Derivatives

Self-immolative polymers are a special kind of degradable polymers that depolymerize into small molecules through a cascade of reactions upon stimuli-triggered cleavage of the polymer chain ends. This work reports the design and synthesis of a fluoride-triggered self-immolative polyester. A 2,4-disubstitued 4-hydroxy butyrate is first confirmed to quickly cyclize in solution to form a γ-butyrolactone derivative. Then, the Passerini three component reaction (P-3CR) of an AB dimer (A: aldehyde, B: carboxylic acid) with tert-butyl isocyanide or oligo(ethylene glycol) isocyanide affords two poly(2,4-disubstitued 4-hydroxybutyrate) derivatives (P2 and P3). Two silyl ether end-capped polymers (P4 and P5) are abtained from P2 and P3, and their degradation in solution is examined by NMR spectrum and size exclusion chromatography. Polymers P4 and P5 are stable in the absence of tetrabutylammonium fluoride (TBAF), while in the presence of TBAF, the molar masses of P4 and P5 gradually decrease with time together with the increase of the amount of formed 2,4-disubstitued γ-butyrolactone. The depolymerization mechanism is proposed. The first step is the fast removal of the silyl ether by fluoride. Then, the released hydroxyl group initiates the quick head-to-tail depolymerization of the polyester via intramolecular cyclization.

Designing Mesoporous Silica Nanoparticles to Overcome Biological Barriers by Incorporating Targeting and Endosomal Escape

The several biological barriers that nanoparticles might encounter when administered to a patient constitute the major bottleneck of nanoparticle-mediated tumor drug delivery, preventing their successful translation into the clinic and reducing their therapeutic profile. In this work, mesoporous silica nanoparticles have been employed as a platform to engineer a versatile nanomedicine able to address such barriers, achieving (a) excessive premature drug release control, (b) accumulation in tumor tissues, (c) selective internalization in tumoral cells, and (d) endosomal escape. The nanoparticles have been decorated with a self-immolative redox-responsive linker to prevent excessive premature release, to which a versatile and polyvalent peptide that is able to recognize tumoral cells and induce the delivery of the nanoparticles to the cytoplasm via endosomal escape has been grafted. The excellent biological performance of the carrier has been demonstrated using 2D and 3D in vitro cell cultures and a tumor-bearing chicken embryo model, demonstrating in all cases high biocompatibility and cytotoxic effect, efficient endosomal escape and tumor penetration, and accumulation in tumors grown on the chorioallantoic membrane of chicken embryos.

A Selective, Dual Emission β-Alanine Aminopeptidase Activated Fluorescent Probe for the Detection of Pseudomonas aeruginosa, Burkholderia cepacia, and Serratia marcescens

Selective detection of β-alanyl aminopeptidase (BAP)-producing Pseudomonas aeruginosa, Serratia marcescens, and Burkholderia cepacia was achieved by employing the blue-to-yellow fluorescent transition of a BAP-specific enzyme substrate, 3-hydroxy-2-(p-dimethylaminophenyl)flavone derivative, incorporating a self-immolative linker to β-alanine. Upon cellular uptake and accumulation of the substrate by viable bacterial colonies, blue fluorescence was generated, while hydrolysis of the N-terminal peptide bond by BAP resulted in the elimination of the self-immolative linker and the restoration of the original fluorescence of the flavone derivative.

Self-Propagating Amplification Reactions for Molecular Detection and Signal Amplification: Advantages, Pitfalls, and Challenges

Self-propagating cascade reactions are a recent development for chemo-sensing protocols. These cascade reactions, in principle, offer low limits of detection by virtue of exponential signal amplification, and are initiated by a specific, pre-planned molecular detection event. This combination of selectivity for a detection event followed by in situ signal amplification is achieved by exploitation of mechanistic organic chemistry, and thus has resulted in various chemo-sensing protocols that employ one or more reagents to achieve the desired selectivity and sensitivity for an assay. Species such as hydrogen peroxide, thiols, and fluoride, have been used as active reagents to initiate the first examples of self-propagating signal amplification reactions, although many other active reagents should be compatible with the approaches. A common feature of the reagents that support the self-propagating signal amplification reactions is the involvement of quinonemethide intermediates resulting from elimination of optical reporters and/or active reagents, where the latter propagates the signal amplification reaction. The early examples of these amplification sequences, however, are slow to reach full signal, thus leaving time for background reactions to generate non-specific signals. This issue of background has limited practical applications of these self-propagating signal amplification reactions, as has challenging synthetic routes to the reagents, as well as the potential for other chemical species to interfere with the detection and signal amplification processes. Thus, the goal of this review is to summarize the progress of self-propagating signal amplification technology, identify the pitfalls of current designs, and by doing so, to stimulate future studies in this growing and promising research area.