Bexarotene prodrugs: targeting through cleavage by NQO1 (DT-diaphorase)

Quinones as Neuroprotective Agents

Quinones can in principle be viewed as a double-edged sword in the treatment of neurodegenerative diseases, since they are often cytoprotective but can also be cytotoxic due to covalent and redox modification of biomolecules. Nevertheless, low doses of moderately electrophilic quinones are generally cytoprotective, mainly due to their ability to activate the Keap1/Nrf2 pathway and thus induce the expression of detoxifying enzymes. Some natural quinones have relevant roles in important physiological processes. One of them is coenzyme Q₁₀, which takes part in the oxidative phosphorylation processes involved in cell energy production, as a proton and electron carrier in the mitochondrial respiratory chain, and shows neuroprotective effects relevant to Alzheimer's and Parkinson's diseases. Additional neuroprotective quinones that can be regarded as coenzyme Q₁₀ analogues are idobenone, mitoquinone and plastoquinone. Other endogenous quinones with neuroprotective activities include tocopherol-derived quinones, most notably vatiquinone, and vitamin K. A final group of non-endogenous quinones with neuroprotective activity is discussed, comprising embelin, APX-3330, cannabinoid-derived quinones, asterriquinones and other indolylquinones, pyrroloquinolinequinone and its analogues, geldanamycin and its analogues, rifampicin quinone, memoquin and a number of hybrid structures combining quinones with amino acids, cholinesterase inhibitors and non-steroidal anti-inflammatory drugs.

Design and synthesis of NAD(P)H: Quinone oxidoreductase (NQO1)-activated prodrugs of 23-hydroxybetulinic acid with enhanced antitumor properties

A series of NQO1 selectively activated prodrugs were designed and synthesized by introducing indolequinone moiety to the C-3, C-23 or C-28 position of 23-hydroxybetulinic acid (23-HBA) and its analogues. Among them, the representative compound 32j exhibited significant antiproliferative activities against NQO1-overexpressing HT-29 cells and A549 cells, with IC₅₀ values of 1.87 and 2.36 μM, respectively, which were 20-30-fold more potent than those of parent compound 23-HBA. More importantly, it was demonstrated in the in vivo antitumor experiment that 32j effectively suppressed the tumor volume and largely reduced tumor weight by 72.69% with no apparent toxicity, which was more potent than the positive control 5-fluorouracil. This is the first breakthrough in the improvement of in vivo antitumor activities of 23-HBA derivatives. The further molecular mechanism study revealed that 32j blocked cell cycle arrest at G2/M phase, induced cell apoptosis, depolarized mitochondria and elevated the intracellular ROS levels in a dose-dependent manner. Western blot analysis indicated that 32j induced cell apoptosis by interfering with the expression of apoptosis-related proteins. These findings suggest that compound 32j could be considered as a potent antitumor prodrug candidate which deserves to be further investigated for personalized cancer therapy.

Aza-Annulation of 1,2,3,4-Tetrahydro-β-carboline Derived Enaminones and Nitroenamines: Synthesis of Functionalized Indolizino[8,7-b]indoles, Pyrido[1,2-a:3,4-b']diindoles, Indolo[2,3-a]quinolizidine-4-ones and Other Tetrahydro-β-carboline Fused Heterocycles

Aza-annulation of novel 1,2,3,4-tetrahydro-β-carboline derived enaminones and nitroenamines with various 1,2- and 1,3-bis electrophiles, such as oxalyl chloride, maleic anhydride, 1,4-benzoquinone, 3-bromopropionyl chloride, itaconic anhydride, and imines (from formaldehyde and primary amines), has been investigated. These methodologies provide simple one-step pathways for efficient construction of highly functionalized tetrahydro-β-carboline 1,2-fused, five- and six-membered heterocyclic frameworks, such as indolizino[8,7-b]indoles, pyrido[1,2-a:3,4-b']diindoles, indolo[2,3-a]quinolizidines, and pyrimido[1',6':1,2]pyrido[3,4-b]indoles, which are core structures of many naturally occurring indole alkaloids with diverse bioactivity.

Lipophilic activated ester prodrug approach for drug delivery to the intestinal lymphatic system

The intestinal lymphatic system plays an important role in the pathophysiology of multiple diseases including lymphomas, cancer metastasis, autoimmune diseases, and human immunodeficiency virus (HIV) infection. It is thus an important compartment for delivery of drugs in order to treat diseases associated with the lymphatic system. Lipophilic prodrug approaches have been used in the past to take advantage of the intestinal lymphatic transport processes to deliver drugs to the intestinal lymphatics. Most of the approaches previously adopted were based on very bulky prodrug moieties such as those mimicking triglycerides (TG). We now report a study in which a lipophilic prodrug approach was used to efficiently deliver bexarotene (BEX) and retinoic acid (RA) to the intestinal lymphatic system using activated ester prodrugs. A range of carboxylic ester prodrugs of BEX were designed and synthesised and all of the esters showed improved association with chylomicrons, which indicated an improved potential for delivery to the intestinal lymphatic system. The conversion rate of the prodrugs to BEX was the main determinant in delivery of BEX to the intestinal lymphatics, and activated ester prodrugs were prepared to enhance the conversion rate. As a result, an 4-(hydroxymethyl)-1,3-dioxol-2-one ester prodrug of BEX was able to increase the exposure of the mesenteric lymph nodes (MLNs) to BEX 17-fold compared to when BEX itself was administered. The activated ester prodrug approach was also applied to another drug, RA, where the exposure of the MLNs was increased 2.4-fold through the application of a similar cyclic activated prodrug. Synergism between BEX and RA was also demonstrated in vitro by cell growth inhibition assays using lymphoma cell lines. In conclusion, the activated ester prodrug approach results in efficient delivery of drugs to the intestinal lymphatic system, which could benefit patients affected by a large number of pathological conditions.

Ultrasound assisted one-pot synthesis of benzo-fused indole-4, 9-dinones from 1,4-naphthoquinone and α-aminoacetals

A one-pot synthesis of benzo[f]indole-4,9-diones from 1,4-naphthoquinone with α-aminoacetals has been developed. This method provides a straightforward synthesis of benzo[f]indole-4,9-diones via intramolecular nucleophilic attack of aminoquinones to aldehydes under mild reaction conditions. The detailed mechanism was also investigated.