Microtubules have long been considered an ideal target for anticancer drugs because of the essential role they play in mitosis, forming the dynamic spindle apparatus. As such, there is a wide variety of compounds currently in clinical use and in development that act as antimitotic agents by altering microtubule dynamics. Although these diverse molecules are known to affect microtubule dynamics upon binding to one of the three established drug domains (taxane, vinca alkaloid, or colchicine site), the exact mechanism by which each drug works is still an area of intense speculation and research. In this study, we review the effects of microtubule-binding chemotherapeutic agents from a new perspective, considering how their mode of binding induces conformational changes and alters biological function relative to the molecular vectors of microtubule assembly or disassembly. These “biological vectors” can thus be used as a spatiotemporal context to describe molecular mechanisms by which microtubule-targeting drugs work.

Noscapine, a microtubule-interfering agent, has been shown to arrest mitosis, to induce apoptosis, and to have potent antitumor activity. We report herein that two brominated derivatives of noscapine, 5-bromonoscapine (5-Br-nosc) and reduced 5-bromonoscapine (Rd 5-Br-nosc), have higher tubulin binding activity than noscapine and affect tubulin polymerization differently from noscapine. In addition, they are able to arrest cell cycle progression at mitosis at concentrations much lower than noscapine. Interestingly, whereas noscapine-arrested cells have nearly normal bipolar spindles, cells arrested by 5-Br-nosc and Rd 5-Br-nosc form multipolar spindles. Nevertheless, noscapine and the two derivatives all affect the attachment of chromosomes to spindle microtubules and they impair the tension across paired kinetochores to similar degrees. 5-Br-nosc and Rd 5-Br-nosc are also more active than noscapine in inhibiting the proliferation of various human cancer cells, including those that are resistant to paclitaxel and epothilone. Our results thus indicate a great potential for the use of 5-Br-nosc and Rd 5-Br-nosc both as biological tools for studying microtubule-mediated processes and as chemotherapeutic agents for the treatment of human cancers.

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Cilia are hair-like organelles extending from the cell surface with important sensory and motility functions. Ciliary defects can result in a wide range of human diseases known as ciliopathies. However, the molecular mechanisms controlling ciliogenesis remain poorly defined. Here we show that cylindromatosis (CYLD), a tumor suppressor protein harboring deubiquitinase activity, plays a critical role in the assembly of both primary and motile cilia in multiple organs. CYLD knockout mice exhibit polydactyly and various ciliary defects, such as failure in basal body anchorage and disorganization of basal bodies and axenomes. The ciliary function of CYLD is partially attributed to its deconjugation of the polyubiquitin chain from centrosomal protein of 70 kDa (Cep70), a requirement for Cep70 to interact with γ-tubulin and localize at the centrosome. In addition, CYLD-mediated inhibition of histone deacetylase 6 (HDAC6), which promotes tubulin acetylation, constitutes another mechanism for the ciliary function of CYLD. Small-molecule inhibitors of HDAC6 could partially rescue the ciliary defects in CYLD knockout mice. These findings highlight the importance of protein ubiquitination in the modulation of ciliogenesis, identify CYLD as a crucial regulator of this process, and suggest the involvement of CYLD deficiency in ciliopathies.

Phytochemical complexity of plant extracts may offer health-promoting benefits including chemotherapeutic and chemopreventive effects. Isolation of 'most-active fraction' or single constituents from whole extracts may not only compromise the therapeutic efficacy but also render toxicity, thus emphasizing the importance of preserving the natural composition of whole extracts. The leaves of Annona muricata, commonly known as Graviola, are known to be rich in flavonoids, isoquinoline alkaloids and annonaceous acetogenins. Here, we demonstrate phytochemical synergy among the constituents of Graviola leaf extract (GLE) compared to its flavonoid-enriched (FEF) and acetogenin-enriched (AEF) fractions. Comparative quantitation of flavonoids revealed enrichment of rutin (~7-fold) and quercetin-3-glucoside (Q-3-G, ~3-fold) in FEF compared to GLE. In vivo pharmacokinetics and in vitro absorption kinetics of flavonoids revealed enhanced bioavailability of rutin in FEF compared to GLE. However, GLE was more effective in inhibiting in vitro prostate cancer proliferation, viability and clonogenic capacity compared to FEF. Oral administration of 100mg/kg bw GLE showed ~1.2-fold higher tumor growth-inhibitory efficacy than FEF in human prostate tumor xenografts although the concentration of rutin and Q-3-G was more in FEF. Contrarily, AEF, despite its superior in vitro and in vivo efficacy, resulted in death of the mice due to toxicity. Our data indicate that despite lower absorption and bioavailability of rutin, maximum efficacy was achieved in the case of GLE, which also comprises of other phytochemical groups including acetogenins that make up its natural complex environment. Hence, our study emphasizes on evaluating the nature of interactions among Graviola leaf phytochemcials for developing favorable dose regimen for prostate cancer management to achieve optimal therapeutic benefits.