Mark J. Coster

Mitochondrial Targeting of Vitamin E Succinate Enhances Its Pro-apoptotic and Anti-cancer Activity via Mitochondrial Complex II

Mitochondrial complex II (CII) has been recently identified as a novel target for anti-cancer drugs. Mitochondrially targeted vitamin E succinate (MitoVES) is modified so that it is preferentially localized to mitochondria, greatly enhancing its pro-apoptotic and anti-cancer activity. Using genetically manipulated cells, MitoVES caused apoptosis and generation of reactive oxygen species (ROS) in CII-proficient malignant cells but not their CII-dysfunctional counterparts. MitoVES inhibited the succinate dehydrogenase (SDH) activity of CII with IC50 of 80 μm, whereas the electron transfer from CII to CIII was inhibited with IC50 of 1.5 μm. The agent had no effect either on the enzymatic activity of CI or on electron transfer from CI to CIII. Over 24 h, MitoVES caused stabilization of the oxygen-dependent destruction domain of HIF1α fused to GFP, indicating promotion of the state of pseudohypoxia. Molecular modeling predicted the succinyl group anchored into the proximal CII ubiquinone (UbQ)-binding site and successively reduced interaction energies for serially shorter phytyl chain homologs of MitoVES correlated with their lower effects on apoptosis induction, ROS generation, and SDH activity. Mutation of the UbQ-binding Ser68 within the proximal site of the CII SDHC subunit (S68A or S68L) suppressed both ROS generation and apoptosis induction by MitoVES. In vivo studies indicated that MitoVES also acts by causing pseudohypoxia in the context of tumor suppression. We propose that mitochondrial targeting of VES with an 11-carbon chain localizes the agent into an ideal position across the interface of the mitochondrial inner membrane and matrix, optimizing its biological effects as an anti-cancer drug.

Stereocontrolled Total Synthesis of (+)‐Altohyrtin A/Spongistatin 1

As an exceptionally potent antimitotic macrolide, altohyrtin A/spongistatin 1 shows great promise in cancer chemotherapy but its extreme scarcity in the natural sponges has halted its further preclinical development. A highly stereocontrolled total synthesis, which exploits boron-mediated aldol bond constructions, has been realized to provide, for the first time, a useful amount of synthetic material.

Mitochondrial targeting of α-tocopheryl succinate enhances its pro-apoptotic efficacy: A new paradigm for effective cancer therapy

Mitochondria are emerging as intriguing targets for anti-cancer agents. We tested here a novel approach, whereby the mitochondrially targeted delivery of anti-cancer drugs is enhanced by the addition of a triphenylphosphonium group (TPP(+)). A mitochondrially targeted analog of vitamin E succinate (MitoVES), modified by tagging the parental compound with TPP(+), induced considerably more robust apoptosis in cancer cells with a 1-2 log gain in anti-cancer activity compared to the unmodified counterpart, while maintaining selectivity for malignant cells. This is because MitoVES associates with mitochondria and causes fast generation of reactive oxygen species that then trigger mitochondria-dependent apoptosis, involving transcriptional modulation of the Bcl-2 family proteins. MitoVES proved superior in suppression of experimental tumors compared to the untargeted analog. We propose that mitochondrially targeted delivery of anti-cancer agents offers a new paradigm for increasing the efficacy of compounds with anti-cancer activity.

A Concise Route to Dihydrobenzo[b]furans: Formal Total Synthesis of (+)-Lithospermic Acid

A sequence of Sonogashira coupling, Pd(II)-catalyzed carbonylative annulation, and benzofuran reduction (Mg, MeOH, NH(4)Cl) provides a convergent and modular synthetic route to trans-2-aryl-2,3-dihydrobenzo[b]furan-3-carboxylates, which are a structural feature of numerous biologically active natural products. This versatile strategy was applied to the formal total synthesis of the anti-HIV natural product (+)-lithospermic acid.

Molecular Probes for P2X7 Receptor Studies

The ionotropic P2X7 receptor (P2X7R) has become the focus of intense research interest for a number of reasons: i) it is a cation selective ion channel that is modulated by extracellular ATP. Upon stimulation by high concentrations of ATP it generates a non-selective membrane pore which is permeable to hydrophilic molecules with molecular weight up to 900 Da. ii) Though its physiological function is yet to be fully understood, there is high P2X7R expression in microglia. Importantly, this implies a pivotal role for the P2X7R in neuro-inflammatory and -degenerative processes. In addition, P2X7R-stimulated release of traditional neurotransmitters in the brain, such as glutamate and GABA, further supports the involvement of P2X7R in neuro-inflammatory and -degenerative processes. P2X7-knockout animals are also found to be resistant to inflammation and neuropathic pain, which suggests that P2X7 antagonists could potentially serve as all-purpose analgesics. Recent advances in the development of P2X7R ligands have resulted in identification of several different classes of P2X7R antagonists, including ATP analogues (oxidized ATP), dyes (Brilliant Blue G), tyrosine derivatives (KN-62 and KN-04), cyclic imides, adamantane and benzamide derivatives. A KN-62 related radioligand has also recently been reported for use in receptor binding assays. A more extensive range of potent, selective P2X7R ligands is required for a better understanding of the cascade of cellular processes associated with the P2X7R. This article will review P2X7R ligands discovered to date, together with their biological activity and therapeutic potential.

Mitochondrially Targeted α-Tocopheryl Succinate Is Antiangiogenic: Potential Benefit Against Tumor Angiogenesis but Caution Against Wound Healing

AIMS A plausible strategy to reduce tumor progress is the inhibition of angiogenesis. Therefore, agents that efficiently suppress angiogenesis can be used for tumor suppression. We tested the antiangiogenic potential of a mitochondrially targeted analog of α-tocopheryl succinate (MitoVES), a compound with high propensity to induce apoptosis. RESULTS MitoVES was found to efficiently kill proliferating endothelial cells (ECs) but not contact-arrested ECs or ECs deficient in mitochondrial DNA, and suppressed angiogenesis in vitro by inducing accumulation of reactive oxygen species and induction of apoptosis in proliferating/angiogenic ECs. Resistance of arrested ECs was ascribed, at least in part, to the lower mitochondrial inner transmembrane potential compared with the proliferating ECs, thus resulting in the lower level of mitochondrial uptake of MitoVES. Shorter-chain homologs of MitoVES were less efficient in angiogenesis inhibition, thus suggesting a molecular mechanism of its activity. Finally, MitoVES was found to suppress HER2-positive breast carcinomas in a transgenic mouse as well as inhibit tumor angiogenesis. The antiangiogenic efficacy of MitoVES was corroborated by its inhibitory activity on wound healing in vivo. INNOVATION AND CONCLUSION We conclude that MitoVES, a mitochondrially targeted analog of α-tocopheryl succinate, is an efficient antiangiogenic agent of potential clinical relevance, exerting considerably higher activity than its untargeted counterpart. MitoVES may be helpful against cancer but may compromise wound healing.

Total Synthesis of (+)-Angelmarin

An efficient 8-step enantioselective total synthesis of (+)-angelmarin, starting from commercially available umbelliferone, has been achieved. Key reactions include olefin cross-metathesis and a Shi epoxidation-cyclization sequence.

Cubyl amides: novel P2X7 receptor antagonists.

Polycyclic amides 2 and 5-9 were successfully synthesised and their lipophilicity profiles were evaluated using reverse-phase HPLC. All synthesised compounds possessed P2X7R antagonistic properties when tested on rat spinal cord microglia cells. Extensive screening for binding to other neuroreceptor subtypes demonstrated their P2X7 selectivity.

Oxo-bridged isomers of aza-trishomocubane sigma (σ) receptor ligands: Synthesis, in vitro binding, and molecular modeling

Isomeric oxo-bridged analogs of aza-trishomocubane sigma (sigma) receptor ligands were synthesized and shown to display a reduced affinity for the sigma receptor. In the case of phenethyl derivative 4, there was a concomitant introduction of high-affinity for the alpha(2C) adrenergic receptor, and moderate affinity for the dopamine transporter. Molecular modeling was undertaken to rationalize these results.

Total synthesis of altohyrtin A (spongistatin 1): an alternative synthesis of the CD-spiroacetal subunit

The CD-spiroacetal containing C16–C28 subunit 2, as used in the total synthesis of the potent cytotoxic macrolide, altohyrtin A (spongistatin 1), was prepared by an alternative route using substrate-based stereocontrol in the two aldol bond constructions generating the acyclic precursor 4.