Browsing Pathways

Vorapaxar also known as Zontivity, is an inhibitor for platelet aggregation used to treat patients with a history of myocardial infarction or peripheral arterial disease to reduce the chance of thrombotic cardiovascular events. Vorapaxar inhibits protease-activated receptor 1 (PAR-1), which is a G protein-coupled receptor that is expressed on the platelet. Inhibition of PAR-1 prevents platelet aggregation and activation. Vorapaxar is administered orally and rapidly absorbs and travels through the bloodstream. It is metabolized to major metabolites M20 and M19 by CYP3A4 and CYP2J2. This is then eliminated primarily through feces and urine. Due to the anticoagulant and antiplatelet nature, herbs and supplements with similar activity should be avoided such as garlic, ginger, bilberry, danshen, piracetam and ginkgo biloba. St.John's Wort should also be avoided as it induces CYP3A metabolism and will reduce the concentration of Vorapaxar. Caution should be exercised with grapefruit products, as coadministration with strong inhibitors should be avoided.

Viomycin is an antibiotic used to treat Mycobacterium tuberculosis and binds to the ribosome displacing structures leading to inhibition of protein synthesis. It binds to the interface between helix 44 of the small ribosomal subunit and helix 69 of the large ribosomal subunit which stops tRNA from binding to the A site and the addition of amino acids to a polypeptide chain.

Vinorelbine is a semi-synthetic third generation vinca alkaloid used in chemotherapy treatment for cervical, lung, breast, and esophageal cancers. It is differentiated from natural alkaloids by its eight-catharanine ring. Administered intravenously, vinorelbine acts on tumorous cells in the body to suppress their growth. Its main mechanism of action works by binding microtubules that are formed during the M phase of mitosis. This ceases the polymerization of microtubules, effectively pausing the cell at its G2/M phase. The disarray of microtubules induces two proteins; cellular tumor antigen p53 and cyclin-dependent kinase inhibitor p21. The latter protein works to inhibit cyclin-dependent kinases in the cell, which disrupt the phosphorylation of the apoptosis inhibitor Bcl-2. Bcl-2 suppresses apoptosis by regulating the permeability of the mitochondrial membrane but is unable to do so due to interrupted phosphorylation. The former protein, p53, acts on BAK and BAX to enact conformational changes, creating pores in the mitochondrial membrane that allow the exit of cytochrome c. Cytochrome c further activates caspases in the cell, which cleave essential cellular proteins. In this way, p53 and p21 work alongside each other to promote apoptosis and terminate unhealthy cells. Vinorelbine is especially valuable as a drug because it binds specifically to mitotic microtubules, likely decreasing its neurotoxicity.

Vinorelbine (also named Navelbine) is a semisynthetic vinca alkaloid. Vinorelbine are used as chemotherapy medication such as an antimitotic anticancer agent. The mechanism of vinorelbine is the inhibition of microtubule dynamics that would cause mitotic arrest and eventual cell death. As a microtubule destabilizing agent, vinorelbine stimulates mitotic spindle destruction and microtubule depolymerization at high concentrations. At lower clinically relevant concentrations, vinorelbine can block mitotic progression. Unlike the taxanes, which bind poorly to soluble tubulin, vinorelbine can bind both soluble and microtubule-associated tubulin. To be able stabilizing the kinetics of microtule, vinorelbine rapidly and reversibly bind to soluble tubulin which can increase the affinity of tublin by the induction of conformational changes of tubulin. Vinorelbine binds to β-tubulin subunits at the positive end of microtubules at a region called the _Vinca_-binding domain. Binding between vinorelbine and solubale tubulin decreases the rate of microtubule dynamics (lengthening and shortening) and increases the duration of attenuated state of microtubules. Therefore, the proper assembly of the mitotic spindle could be prevented; and the tension at the kinetochores of the chromosomes could be reduced. Subsequently, chromosomes can not progress to the spindle equator at the spindle poles. Progression from metaphase to anaphase is blocked and cells enter a state of mitotic arrest. The cells may then undergo one of several fates. The tetraploid cell may undergo unequal cell division producing aneuploid daughter cells. Alternatively, it may exit the cell cycle without undergoing cell division, a process termed mitotic slippage or adaptation. These cells may continue progressing through the cell cycle as tetraploid cells (Adaptation I), may exit G1 phase and undergo apoptosis or senescence (Adaption II), or may escape to G1 and undergo apoptosis during interphase (Adaptation III). Another possibility is cell death during mitotic arrest. Alternatively, mitotic catastrophe may occur and cause cell death. Vinca alkaloids are also thought to increase apoptosis by increasing concentrations of p53 (cellular tumor antigen p53) and p21 (cyclin-dependent kinase inhibitor 1) and by inhibiting Bcl-2 activity. Increasing concentrations of p53 and p21 lead to changes in protein kinase activity. Phosphorylation of Bcl-2 subsequently inhibits the formation Bcl-2-BAX heterodimers. This results in decreased anti-apoptotic activity. One way in which cells have developed resistance against the vinca alkaloids is by drug efflux. Drug efflux is mediated by a number of multidrug resistant transporters as depicted in this pathway.