laulimalide and ixabepilone

An important aspect of synaptic plasticity in the brain is axonal transport of essential components such as mitochondria from the soma to the synapse. For uninterrupted transport of cellular cargo down the axon, functional microtubules are required. Altered microtubule dynamics induced by changes in expression of microtubule-associated tau protein affects normal microtubule function and interferes with axonal transport. Here we investigate the effects of the nontaxoid-binding-site microtubule-stabilizing agents peloruside A (PelA) and laulimalide, compared with the taxoid-site-binding agents paclitaxel (Ptx) and ixabepilone, on axonal transport of mitochondria in 1-day-old rat pup cerebral cortical neuron cultures. The differences in effects of these two types of compound on mitochondrial trafficking were specifically compared under conditions of excess tau expression. PelA and laulimalide had no adverse effects on their own on mitochondrial transport compared with Ptx and ixabepilone, which inhibited mitochondrial run length at higher concentrations. PelA, like Ptx, was able to partially reverse the blocked mitochondrial transport seen in ECFP-htau40-overexpressing neurons, although at higher concentrations of microtubule-stabilizing agent, the PelA response was improved over the Ptx response. These results support a neuroprotective effect of microtubule stabilization in maintaining axonal transport in neurons overexpressing tau protein and may be beneficial in reducing the severity of neurodegenerative diseases such as Alzheimer's disease.

Topics: Animals; Animals, Newborn; Axonal Transport; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Cerebral Cortex; Epothilones; Green Fluorescent Proteins; Humans; Lactones; Macrolides; Membrane Proteins; Microtubules; Mitochondria; Neurons; Paclitaxel; Rats; Rats, Sprague-Dawley; Transfection; Tubulin Modulators

Microtubule-stabilizing drugs are useful in cancer therapy and show promise for treatment of neurodegenerative diseases. An overlapping binding site between tau and taxoid site drugs has led to a number of research papers investigating the competitive interaction between these drugs and the microtubule. This has implications for cancer treatment since increased tau could confer resistance to paclitaxel. Variations in the tau isoform ratio have also been reported in tauopathies, especially the rise in the levels of the four-repeat tau isoform. Therefore, in conditions of increased or altered expression of tau and its isoforms, a therapy that is not directly affected by changes in tau is desirable. Peloruside A and laulimalide are of particular interest in this respect because of their distinct binding site on the microtubule in relation to the clinically used drugs paclitaxel and ixabepilone. In the present study, we show that peloruside A and laulimalide stabilize microtubules independently of tau overexpression; whereas, the effects of paclitaxel and ixabepilone are masked by the presence of extra tau in the cell.

Topics: Animals; Antineoplastic Agents, Phytogenic; Brain Neoplasms; Bridged Bicyclo Compounds, Heterocyclic; Cell Line, Tumor; Drug Resistance, Neoplasm; Epothilones; HEK293 Cells; Humans; Lactones; Macrolides; Mice; Microtubules; Neuroblastoma; Paclitaxel; Pharmacogenetics; tau Proteins; Tauopathies; Transfection; Tubulin Modulators

Microtubule stabilizing agents (MSAs) comprise a class of drugs that bind to microtubule (MT) polymers and stabilize them against disassembly. Several of these agents are currently in clinical use as anticancer drugs, whereas others are in various stages of development. Nonetheless, there is insufficient knowledge about the molecular modes of their action. Recent studies from our laboratory utilizing hydrogen-deuterium exchange in combination with mass spectrometry (MS) provide new information on the conformational effects of Taxol and discodermolide on microtubules isolated from chicken erythrocytes (CET). We report here a comprehensive analysis of the effects of epothilone B, ixabepilone (IXEMPRA(TM)), laulimalide, and peloruside A on CET conformation. The results of our comparative hydrogen-deuterium exchange MS studies indicate that all MSAs have significant conformational effects on the C-terminal H12 helix of α-tubulin, which is a likely molecular mechanism for the previously observed modulations of MT interactions with microtubule-associated and motor proteins. More importantly, the major mode of MT stabilization by MSAs is the tightening of the longitudinal interactions between two adjacent αβ-tubulin heterodimers at the interdimer interface. In contrast to previous observations reported with bovine brain tubulin, the lateral interactions between the adjacent protofilaments in CET are particularly strongly stabilized by peloruside A and laulimalide, drugs that bind outside the taxane site. This not only highlights the significance of tubulin isotype composition in modulating drug effects on MT conformation and stability but also provides a potential explanation for the synergy observed when combinations of taxane and alternative site binding drugs are used.

Topics: Animals; Binding Sites; Brain; Brain Chemistry; Bridged Bicyclo Compounds, Heterocyclic; Cattle; Epothilones; Lactones; Macrolides; Mass Spectrometry; Microtubules; Nerve Tissue Proteins; Protein Structure, Secondary; Tubulin; Tubulin Modulators