This review is an updated and expanded version of the three prior reviews that were published in this journal in 1997, 2003, and 2007. In the case of all approved therapeutic agents, the time frame has been extended to cover the 30 years from January 1, 1981, to December 31, 2010, for all diseases worldwide, and from 1950 (earliest so far identified) to December 2010 for all approved antitumor drugs worldwide. We have continued to utilize our secondary subdivision of a “natural product mimic” or “NM” to join the original primary divisions and have added a new designation, “natural product botanical” or “NB”, to cover those botanical “defined mixtures” that have now been recognized as drug entities by the FDA and similar organizations. From the data presented, the utility of natural products as sources of novel structures, but not necessarily the final drug entity, is still alive and well. Thus, in the area of cancer, over the time frame from around the 1940s to date, of the 175 small molecules, 131, or 74...

/pdf/natural-products-as-sources-of-new-drugs-over-the-30-years-4p9j38phh8.pdf

Natural Products As Sources of New Drugs over the 30 Years from 1981 to 2010

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(11)60070-6.pdf

Eribulin monotherapy versus treatment of physician's choice in patients with metastatic breast cancer (EMBRACE): A phase 3 open-label randomised study

NTRK gene fusions involving either NTRK1, NTRK2 or NTRK3 (encoding the neurotrophin receptors TRKA, TRKB and TRKC, respectively) are oncogenic drivers of various adult and paediatric tumour types. These fusions can be detected in the clinic using a variety of methods, including tumour DNA and RNA sequencing and plasma cell-free DNA profiling. The treatment of patients with NTRK fusion-positive cancers with a first-generation TRK inhibitor, such as larotrectinib or entrectinib, is associated with high response rates (>75%), regardless of tumour histology. First-generation TRK inhibitors are well tolerated by most patients, with toxicity profiles characterized by occasional off-tumour, on-target adverse events (attributable to TRK inhibition in non-malignant tissues). Despite durable disease control in many patients, advanced-stage NTRK fusion-positive cancers eventually become refractory to TRK inhibition; resistance can be mediated by the acquisition of NTRK kinase domain mutations. Fortunately, certain resistance mutations can be overcome by second-generation TRK inhibitors, including LOXO-195 and TPX-0005 that are being explored in clinical trials. In this Review, we discuss the biology of NTRK fusions, strategies to target these drivers in the treatment-naive and acquired-resistance disease settings, and the unique safety profile of TRK inhibitors.

NTRK fusion-positive cancers and TRK inhibitor therapy

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(15)01283-0.pdf

Eribulin versus dacarbazine in previously treated patients with advanced liposarcoma or leiomyosarcoma: a randomised, open-label, multicentre, phase 3 trial

The largely unexplored marine world that presumably harbors the most biodiversity may be the vastest resource to discover novel ‘validated’ structures with novel modes of action that cover biologically relevant chemical space. Several challenges, including the supply problem and target identification, need to be met for successful drug development of these often complex molecules; however, approaches are available to overcome the hurdles. Advances in technologies such as sampling strategies, nanoscale NMR for structure determination, total chemical synthesis, fermentation and biotechnology are all crucial to the success of marine natural products as drug leads. We illustrate the high degree of innovation in the field of marine natural products, which in our view will lead to a new wave of drugs that flow into the market and pharmacies in the future.

https://www.future-science.com/doi/pdf/10.4155/fmc.11.118

Marine natural products: a new wave of drugs?

Eribulin mesylate (E7389), a synthetic analogue of the marine natural product halichondrin B, is in phase III clinical trials for the treatment of cancer. Eribulin targets microtubules, suppressing dynamic instability at microtubule plus ends through an inhibition of microtubule growth with little or no effect on shortening [Jordan, M. A., et al. (2005) Mol. Cancer Ther. 4, 1086−1095]. Using [3H]eribulin, we found that eribulin binds soluble tubulin at a single site; however, this binding is complex with an overall Kd of 46 μM, but also showing a real or apparent very high affinity (Kd = 0.4 μM) for a subset of 25% of the tubulin. Eribulin also binds microtubules with a maximum stoichiometry of 14.7 ± 1.3 molecules per microtubule (Kd = 3.5 μM), strongly suggesting the presence of a relatively high-affinity binding site at microtubule ends. At 100 nM, the concentration that inhibits microtubule plus end growth by 50%, we found that one molecule of eribulin is bound per two microtubules, indicating that th...

/pdf/eribulin-binds-at-microtubule-ends-to-a-single-site-on-7ne9g1zxvk.pdf

Eribulin Binds at Microtubule Ends to a Single Site on Tubulin To Suppress Dynamic Instability

Peripheral neuropathy is a serious, dose-limiting side effect of cancer treatment with microtubule-targeting drugs. Symptoms present in a "stocking-glove" distribution, with longest nerves affected most acutely, suggesting a length-dependent component to the toxicity. Axonal transport of ATP-producing mitochondria along neuronal microtubules from cell body to synapse is crucial to neuronal function. We compared the effects of the drugs paclitaxel and ixabepilone that bind along the lengths of microtubules and the drugs eribulin and vincristine that bind at microtubule ends, on mitochondrial trafficking in cultured human neuronal SK-N-SH cells and on axonal transport in mouse sciatic nerves. Antiproliferative concentrations of paclitaxel and ixabepilone significantly inhibited the anterograde transport velocity of mitochondria in neuronal cells, whereas eribulin and vincristine inhibited transport only at significantly higher concentrations. Confirming these observations, anterogradely transported amyloid precursor protein accumulated in ligated sciatic nerves of control and eribulin-treated mice, but not in paclitaxel-treated mice, indicating that paclitaxel inhibited anterograde axonal transport, whereas eribulin did not. Electron microscopy of sciatic nerves of paclitaxel-treated mice showed reduced organelle accumulation proximal to the ligation consistent with inhibition of anterograde (kinesin based) transport by paclitaxel. In contrast, none of the drugs significantly affected retrograde (dynein based) transport in neuronal cells or mouse nerves. Collectively, these results suggest that paclitaxel and ixabepilone, which bind along the lengths and stabilize microtubules, inhibit kinesin-based axonal transport, but not dynein-based transport, whereas the microtubule-destabilizing drugs, eribulin and vincristine, which bind preferentially to microtubule ends, have significantly less effect on all microtubule-based axonal transport. Cancer Res; 76(17); 5115-23. ©2016 AACR.

/pdf/structural-basis-for-induction-of-peripheral-neuropathy-by-18tntaqp9r.pdf

Structural basis for induction of peripheral neuropathy by microtubule-targeting cancer drugs

Eribulin mesylate (Halaven) is a microtubule-targeted anticancer drug used to treat patients with metastatic breast cancer who have previously received a taxane and an anthracycline. It binds at the plus ends of microtubules and has been shown to suppress plus end growth selectively. Because the class III β tubulin isotype is associated with resistance to microtubule targeting drugs, we sought to determine how βIII tubulin might mechanistically influence the effects of eribulin on microtubules. We found that while [3H]eribulin bound to bovine brain soluble tubulin depleted of βIII tubulin in a manner similar to that of unfractionated tubulin, it bound to plus ends of microtubules that were depleted of βIII-depleted tubulin with a maximal stoichiometry (20 ± 3 molecules per microtubule) higher than that of unfractionated microtubules (9 ± 2 molecules per microtubule). In addition, eribulin suppressed the dynamic instability behavior of βIII-depleted microtubules more strongly than and in a manner different...

Effects of eribulin on microtubule binding and dynamic instability are strengthened in the absence of the βIII tubulin isotype.

Many naturally occurring compounds and their synthetic analogs bind to soluble tubulin or to tubulin in microtubules. These compounds are often important drugs or drug candidates. They can potently alter both the dynamics and the polymer mass of microtubules. The binding affinity of a drug for soluble tubulin heterodimers is a common and relatively readily determined biochemical characteristic of a tubulin-targeted drug. However, it is only one important aspect of the drug-tubulin interaction. In solution and in cells, soluble tubulin is in equilibrium with polymerized microtubules. It is as important to determine drug binding to microtubules as it is to determine binding to soluble tubulin, since drug binding to microtubules frequently alters their function. The affinity of a compound for microtubules often differs vastly from its affinity for soluble tubulin. Here, we present detailed instructions for assessing binding stoichiometry and affinity to assembled unstabilized microtubules using radiolabeled drug. In addition, using examples from binding results with several important drugs including vinca alkaloids, colchicine, eribulin, and taxanes, we discuss aspects of the interactions with microtubules that may alter the experimental design of the drug-binding experiments.

Determination of Drug Binding to Microtubules In Vitro

Chemotherapy-induced peripheral neuropathy is a common, dose-limiting side effect of cancer treatment. This conference was the first of its kind to bring together a wide range of clinicians, researchers, and industry professionals to address the potential causes, preventions, and treatments for this drug toxicity. Intraepidermal nerve fiber loss, axonal degeneration, immune cell infiltration, alterations in tubulin protein expression and microtubule stability, axonal transport, and mitochondrial dysfunction were addressed as possible mechanisms. Problems with animal models of the disease were discussed, as well as the potential of patient-derived induced sensory neurons to serve as a novel in vitro model.

https://cancerres.aacrjournals.org/content/canres/early/2015/09/03/0008-5472.CAN-15-1145.full.pdf

Jennifer A. Smith

Papers

Eribulin Binds at Microtubule Ends to a Single Site on Tubulin To Suppress Dynamic Instability

Structural basis for induction of peripheral neuropathy by microtubule-targeting cancer drugs

Effects of eribulin on microtubule binding and dynamic instability are strengthened in the absence of the βIII tubulin isotype.

Determination of Drug Binding to Microtubules In Vitro

Meeting Report: Inaugural Chemotherapy-Induced Peripheral Neuropathy Symposium - Santa Barbara, CA, February 2015.