A new paclitaxel prodrug for use in ADEPT strategy

NQO1-activated multifunctional theranostic probe for imaging-guided mitochondria-targeted photodynamic therapy and boosting immunogenic cell death

NAD(P)H: quinine oxidoreductase (NQO1) is overexpressed in many types of cancer cells, and have been used as a biomarker for cancer diagnosis and targeted therapy. The development of activatable theranostic agents is highly desirable for precise cancer diagnosis and therapy. Herein, a NQO1-activated near-infrared multifunctional theranostic probe I-HCy-Q is successfully developed for imaging guided photodynamic therapy. The NIR fluorescence (λex/em = 685/703 nm) and capacity of reactive oxygen species generation are sensitive controllable by the level of NQO1, the linear detection range of NQO1 and limit of detection are 0.05-1.5 μg/mL and 5.66 ng/mL, respectively. On the one hand, I-HCy-Q can monitor the activity of NQO1 and distinguish the NQO1 positive cancer cells; on the other hand, the capacity of mitochondria-targeted photodynamic therapy makes I-HCy-Q an effective inducer of apoptosis and immunogenic cell death. Attribute to its complementary advantages, I-HCy-Q holds potential for the imaging and treatment of tumors in complex organisms.

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

Bioorthogonal Uncaging of Cytotoxic Paclitaxel through Pd Nanosheet-Hydrogel Frameworks

The promising potential of bioorthogonal catalysis in biomedicine is inspiring incremental efforts to design strategies that regulate drug activity in living systems. To achieve this, it is not only essential to develop customized inactive prodrugs and biocompatible metal catalysts but also the right physical environment for them to interact and enable drug production under spatial and/or temporal control. Toward this goal, here, we report the first inactive precursor of the potent broad-spectrum anticancer drug paclitaxel (a.k.a. Taxol) that is stable in cell culture and labile to Pd catalysts. This new prodrug is effectively uncaged in cancer cell culture by Pd nanosheets captured within agarose and alginate hydrogels, providing a biodegradable catalytic framework to achieve controlled release of one of the most important chemotherapy drugs in medical practice. The compatibility of bioorthogonal catalysis and physical hydrogels opens up new opportunities to administer and modulate the mobility of transition metal catalysts in living environs.

Dually Enzyme- and Acid-Triggered Self-Immolative Ketal Glycoside Nanoparticles for Effective Cancer Prodrug Monotherapy

The use of glycoside prodrugs is a promising strategy for developing new targeted medicines for chemotherapy. However, the in vivo utility of such prodrugs is hindered by insufficient activation and the lack of convenient synthetic methods. We have developed an innovative strategy for synthesizing ketal glycoside prodrugs that are unique in being activated by a dual enzyme- and acid-triggered self-immolative mechanism. Amphiphilic glucosyl acetone-based ketal-linked etoposide glycoside prodrug isomers were synthesized and fabricated into excipient-free nanoparticles for effective cancer prodrug monotherapy. Hydrolysis of the glycosidic linkage or the ketal linkage triggered hydrolysis of the other linkage, which resulted in spontaneous self-immolative hydrolysis of the prodrugs. Nanoparticles of the prodrug isomer that was the most labile in a lysosome-mimicking environment displayed high intratumoral accumulation and strong antitumor activity in an A549 xenograft mouse model. Our strategy may be useful for the development of stimulus-responsive self-immolative prodrugs and their nanomedicines.

Fast Cyclization of a Proline-Derived Self-Immolative Spacer Improves the Efficacy of Carbamate Prodrugs

Self-immolative (SI) spacers are sophisticated chemical constructs designed for molecular delivery or material degradation. We describe herein a (S)-2-(aminomethyl)pyrrolidine SI spacer that is able to release different types of anticancer drugs (possessing either a phenolic or secondary and tertiary hydroxyl groups) through a fast cyclization mechanism involving carbamate cleavage. The high efficiency of drug release obtained with this spacer was found to be beneficial for the in vitro cytotoxic activity of protease-sensitive prodrugs, compared with a commonly used spacer of the same class. These findings expand the repertoire of degradation machineries and are instrumental for the future development of highly efficient delivery platforms.

Prodrugs in medicinal chemistry and enzyme prodrug therapies

Prodrugs are cunning derivatives of therapeutic agents designed to improve the pharmacokinetics profile of the drug. Within a prodrug, pharmacological activity of the drug is masked and is recovered within the human body upon bioconversion of the prodrug, a process that is typically mediated by enzymes. This concept is highly successful and a significant fraction of marketed therapeutic formulations is based on prodrugs. An advanced subset of prodrugs can be engineered such as to achieve site-specific bioconversion of the prodrug - to comprise the highly advantageous "enzyme prodrug therapy", EPT. Design of prodrugs for EPT is similar to the prodrugs in general medicinal use in that the pharmacological activity of the drug is masked, but differs significantly in that site-specific bioconversion is a prime consideration, and the enzymes typically used for EPT are non-mammalian and/or with low systemic abundance in the human body. This review focuses on the design of prodrugs for EPT in terms of the choice of an enzyme and the corresponding prodrug for bioconversion. We also discuss the recent success of "self immolative linkers" which significantly empower and diversify the prodrug design, and present methodologies for the design of prodrugs with extended blood residence time. The review aims to be of specific interest for medicinal chemists, biomedical engineers, and pharmaceutical scientists.

Synthesis and biological analysis of novel glycoside derivatives of l-AEP, as targeted antibacterial agents

To develop targeted methods for treating bacterial infections, the feasibility of using glycoside derivatives of the antibacterial compound l-R-aminoethylphosphonic acid (l-AEP) has been investigated. These derivatives are hypothesized to be taken up by bacterial cells via carbohydrate uptake mechanisms, and then hydrolyzed in situ by bacterial borne glycosidase enzymes, to selectively afford l-AEP. Therefore the synthesis and analysis of ten glycoside derivatives of l-AEP, for selective targeting of specific bacteria, is reported. The ability of these derivatives to inhibit the growth of a panel of Gram-negative bacteria in two different media is discussed. β-Glycosides (12a) and (12b) that contained l-AEP linked to glucose or galactose via a carbamate linkage inhibited growth of a range of organisms with the best MICs being <0.75mg/ml; for most species the inhibition was closely related to the hydrolysis of the equivalent chromogenic glycosides. This suggests that for (12a) and (12b), release of l-AEP was indeed dependent upon the presence of the respective glycosidase enzyme.

An investigation of nitrile transforming enzymes in the chemo-enzymatic synthesis of the taxol sidechain

Paclitaxel (taxol) is an antimicrotubule agent widely used in the treatment of cancer. Taxol is prepared in a semisynthetic route by coupling the N-benzoyl-(2R,3S)-3-phenylisoserine sidechain to the baccatin III core structure. Precursors of the taxol sidechain have previously been prepared in chemoenzymatic approaches using acylases, lipases, and reductases, mostly featuring the enantioselective, enzymatic step early in the reaction pathway. Here, nitrile hydrolysing enzymes, namely nitrile hydratases and nitrilases, are investigated for the enzymatic hydrolysis of two different sidechain precursors. Both sidechain precursors, an openchain α-hydroxy-β-amino nitrile and a cyanodihydrooxazole, are suitable for coupling to baccatin III directly after the enzymatic step. An extensive set of nitrilases and nitrile hydratases was screened towards their activity and selectivity in the hydrolysis of two taxol sidechain precursors and their epimers. A number of nitrilases and nitrile hydratases converted both sidechain precursors and their epimers.

Antineoplastic agents. 600. From the South Pacific Ocean to the silstatins

The recent advances in the development of antibody and other drug conjugates for targeted cancer treatment have further increased the need for powerful cancer cell growth inhibitors. Toward that objective we have extended our earlier discovery of the remarkable anticancer bacillistatins 1 and 2 from Bacillus silvestris to SAR and other structural modifications such as availability of a free hydroxy group for antibody-drug conjugate (ADC) and other prodrug linkage. That direction has resulted in seven structural modifications designated silstatins 1-8 (7a, 8a, 8b, 14a, 15a, 15b, 18a, and 18b), where the exceptional cancer cell growth inhibition of some of them are in the range GI50 10(-3)-10(-4) μM/mL. Silstatin 7 (18a) was converted to a glucuronic conjugate (28) that displayed an impressive reduction in toxicity during transport.

β-Glucuronidase-responsive prodrugs for selective cancer chemotherapy: an update

The design of novel antitumor agents allowing the destruction of malignant cells while sparing healthy tissues is one of the major challenges in medicinal chemistry. In this context, the use of non-toxic prodrugs programmed to be selectively activated by beta-glucuronidase present at high concentration in the microenvironment of most solid tumors has attracted considerable attention. This review summarizes the major progresses that have been realized in this field over the past ten years. This includes the new prodrugs that have been designed to target a wide variety of anticancer drugs, the prodrugs employed in the course of a combined therapy, the dendritic glucuronide prodrugs and the concept of β-glucuronidase-responsive albumin binding prodrugs.

Synergistic interaction of β-galactosyl-pyrrolidinyl diazeniumdiolate with cisplatin against three tumor cells

Cisplatin is a platinum-based compound that is largely employed as an effective antitumor drug against a wide spectrum of solid neoplasms for many years. Despite of its initial therapeutic success, cisplatin often results in high incidence of chemoresistance and high-dose cytotoxicity. Consequently, considerable efforts in hopes of reducing the dose-dependent side effects of cisplatin while retaining, or even enhancing, its antitumor properties have been undertaken throughout the past three decades. Nitric oxide (NO) is a small lipophilic free radical gas possessing versatile biological functions, including antitumor activities. However, NO, of itself, is difficult to be used, because of its extreme instability and short half-life. Previously, we have reported a stable NO donor, β-galactosyl-pyrrolidinyl diazeniumdiolate (β-Gal-NONOate), which exerts tumor killing effects through site-specific intracellular release of exogenous NO. In this study, we further investigated the combined inhibitory effect of β-Gal-NONOate and cisplatin against C6/LacZ, 9L/LacZ, and HeLa/LacZ tumor cells. It was shown that, in combination with β-Gal-NONOate, the antitumor effects of cisplatin against these common tumor cell lines were increased in a dose-dependent manner. Furthermore, the combination of these chemicals resulted in a synergistic suppression on tumor growth, which was achieved under a much lower cisplatin dosage. Collectively, our findings indicate that β-Gal-NONOate can synergistically improve the antitumor effect of cisplatin, and may therefore reduce its side effects caused by high dose cisplatin monochemotherapies. Accordingly, β-Gal-NONOate is an important therapeutic assistant reagent with great potential of clinical applicability, and thus worth of continuous research in the coming future.

Analogue-based drug discovery: Contributions to medicinal chemistry principles and drug design strategies. Microtubule stabilizers as a case in point (Special Topic Article)

The benefits of utilizing marketed drugs as starting points to discover new therapeutic agents have been well documented within the IUPAC series of books that bear the title Analogue-based Drug Discovery (ABDD). Not as clearly demonstrated, however, is that ABDD also contributes to the elaboration of new basic principles and alternative drug design strategies that are useful to the field of medicinal chemistry in general. After reviewing the ABDD programs that have evolved around the area of microtubule-stabilizing chemo-therapeutic agents, the present article delineates the associated research activities that additionally contributed to general strategies that can be useful for prodrug design, identifying pharmacophores, circumventing multidrug resistance (MDR), and achieving targeted drug distribution.

Improved biochemical strategies for targeted delivery of taxoids

Paclitaxel (Taxol) and docetaxel (Taxotere) are very important anti-tumor drugs in clinical use for cancer. However, their clinical utility is limited due to systemic toxicity, low solubility and inactivity against drug resistant tumors. To improve chemotherapeutic levels of these drugs, it would be highly desirable to design strategies which bypass the above limitations. In this respect various prodrug and drug targeting strategies have been envisioned either to improve oral bioavailability or tumor specific delivery of taxoids. Abnormal properties of cancer cells with respect to normal cells have guided in designing of these protocols. This review article records the designed biochemical strategies and their biological efficacies as potential taxoid chemotherapeutics.

Protecting Groups for Glucuronic Acid: Application to the Synthesis of New Paclitaxel (Taxol) Derivatives

To prepare two new glucuronide conjugates, allyl ester and allyl carbonates were used as protecting groups of the glucuronic moiety. In this way, an aniline glycosyl carbamate spacer linked to the 2'-OH of paclitaxel was obtained. By using palladium chemistry, an efficient one-step removal of all the allyl groups at the end of the synthesis afforded the desired compounds in good yields.

Prodrogues glucuronylées du paclitaxel (Taxol®) activables au niveau des tumeurs

Three glucuronyl prodrugs of paclitaxel have been synthesized in order to be activated by the B-glucuronidase present within the necrotic areas of tumors. As three compartments containing prodrugs, they include a specifier, a self immolative spacer and the drug. In vitro testing clearly indicates that the two former prodrugs are stable and are more or less detoxified. As expected, in the presence of E. coli B-glucuronidase, the glycosidic linkage is hydrolyzed with a rate depending on the nature of the spacer but, once this hydrolysis has occurred, the self immolative spacer is soon eliminated leading to the liberation of the paclitaxel.

First enzymatically activated Taxotere prodrugs designed for ADEPT and PMT

Described here are the syntheses and preliminary biological evaluations of the first two enzymatically activated prodrugs of docetaxel (Taxotere) reported to date. These prodrugs were designed as potential candidates for selective chemotherapy in ADEPT or PMT. They are constituted of a glucuronic acid moiety, a double spacer and the cytotoxic drug, differing only by the spacer substitution. The prodrugs were stable in a buffer, and the in vitro studies showed good detoxification and hydrolysis kinetics. As docetaxel was efficiently released in both cases, these compounds are very valuable candidates for further biological evaluations.