ßIII-tubulin enhances efficacy of cabazitaxel as compared with docetaxel.

Cabazitaxel is a novel taxane approved for treatment of metastatic hormone-refractory prostate cancer in patients pretreated with docetaxel. Cabazitaxel, docetaxel, and paclitaxel bind specifically to tubulin in microtubules, disrupting functions essential to tumor growth. High levels of ßIII-tubulin isotype expression are associated with tumor aggressivity and drug resistance. To understand cabazitaxel's increased efficacy, we examined binding of radio-labeled cabazitaxel and docetaxel to microtubules and the drugs' suppression of microtubule dynamic instability in vitro in microtubules assembled from purified bovine brain tubulin containing or devoid of ßIII-tubulin. We found that cabazitaxel suppresses microtubule dynamic instability significantly more potently in the presence of ßIII-tubulin than in its absence. In contrast, docetaxel showed no ßIII-tubulin-enhanced microtubule stabilization. We also asked if the selective potency of cabazitaxel on ßIII-tubulin-containing purified microtubules in vitro extends to cabazitaxel's effects in human tumor cells. Using MCF7 human breast adenocarcinoma cells, we found that cabazitaxel also suppressed microtubule shortening rates, shortening lengths, and dynamicity significantly more strongly in cells with normal levels of ßIII-tubulin than after 50% reduction of ßIII-tubulin expression by siRNA knockdown. Cabazitaxel also more strongly induced mitotic arrest in MCF7 cells with normal ßIII-tubulin levels than after ßIII-tubulin reduction. In contrast, docetaxel had little or no ßIII-tubulin-dependent selective effect on microtubule dynamics or mitotic arrest. The selective potency of cabazitaxel on purified ßIII-tubulin-containing microtubules and in cells expressing ßIII-tubulin suggests that cabazitaxel may be unusual among microtubule-targeted drugs in its superior anti-tumor efficacy in tumors overexpressing ßIII-tubulin.

A Caenorhabditis elegans Model Elucidates a Conserved Role for TRPA1-Nrf Signaling in Reactive α-Dicarbonyl Detoxification.

Reactive α-dicarbonyls (α-DCs), like methylglyoxal (MGO), accumulate with age and have been implicated in aging and various age-associated pathologies, such as diabetic complications and neurodegenerative disorders like Alzheimer's and Parkinson's diseases. Evolutionarily conserved glyoxalases are responsible for α-DC detoxification; however, their core biochemical regulation has remained unclear. We have established a Caenorhabditis elegans model, based on an impaired glyoxalase (glod-4/GLO1), to broadly study α-DC-related stress. We show that, in comparison to wild-type (N2, Bristol), glod-4 animals rapidly exhibit several pathogenic phenotypes, including hyperesthesia, neuronal damage, reduced motility, and early mortality. We further demonstrate TRPA-1/TRPA1 as a sensor for α-DCs, conserved between worms and mammals. Moreover, TRPA-1 activates SKN-1/Nrf via calcium-modulated kinase signaling, ultimately regulating the glutathione-dependent (GLO1) and co-factor-independent (DJ1) glyoxalases to detoxify α-DCs. Interestingly, this pathway is in stark contrast to the TRPA-1 activation and the ensuing calcium flux implicated in cold sensation in C. elegans, whereby DAF-16/FOXO gets activated via complementary kinase signaling. Finally, a phenotypic drug screen using C. elegans identified podocarpic acid as a novel activator of TRPA1 that rescues α-DC-induced pathologies in C. elegans and mammalian cells. Our work thus identifies TRPA1 as a bona fide drug target for the amelioration of α-DC stress, which represents a viable option to address aging-related pathologies in diabetes and neurodegenerative diseases.