Neurotoxic lipids as molecular intermediates of paclitaxel induced peripheral neuropathy.
The current proposal addresses the possibility that a specific class of sphingolipids, 1-deoxysphingolipids (deoxySL), play a role as molecular intermediates in paclitaxel-induced peripheral neuropathy (PIPN). PIPN is a major side effect of paclitaxel chemotherapy, which is a widely used systemic therapy for several cancers; these include breast, ovarian, lung, head and neck, and Kaposi's sarcoma. Aside from a diminished quality of life of the patients treated with paclitaxel, in the more severe cases, PIPN can lead to dose reduction or termination of treatment. A recent study in breast cancer patients undergoing paclitaxel chemotherapy showed that in more than one third of the patients (37.3%) paclitaxel therapy had to be reduced or terminated due to PIPN, which resulted in less paclitaxel received by the patients, 9.4% less (dose reduction) and 28.4% less (termination). Therefore, reducing the dose or terminating the treatment due to PIPN has a direct effect on the cancer treatment outcome. The symptoms of PIPN are well-documented in the literature; the molecular mechanism, on the other hand, is not known and there is no treatment or prevention available. The only way PIPN is currently addressed is by dose reduction or treatment termination, which as stated above, affects treatment efficacy.
With our proposal we address the molecular mechanism of PIPN and possible preventive and/or treatment strategies. Our hypothesis is that deoxySL serve as molecular intermediates in PIPN. DeoxySL were shown to be neurotoxic in patients with hereditary sensory and autonomic neuropathy type 1 (HSAN1). The clinical manifestation of peripheral neuropathy in HSAN1 patients is very similar to PIPN experienced by the cancer patients. Importantly, our preliminary studies in breast cancer patients undergoing paclitaxel chemotherapy showed that PIPN symptoms correlated with plasma levels of deoxySL species, e.g. C24 1-deoxyceramide.
Moreover, our preliminary data also showed that treatment of cells with increased concentrations of paclitaxel resulted in a dose dependent increase in deoxySL. DeoxySL are produced when the first biosynthetic enzyme of the sphingolipid pathway, serine palmitoyltransferase (SPT), utilizes L-alanine as its amino acid substrate instead of L-serine (its regular substrate). As a result, deoxySL lack an important functional OH group and cannot be degraded by the last enzyme of the sphingolipid catabolic pathway, sphingosine-1-phosphate lyase. DeoxySL will accumulate if produced in excess. The neurotoxicity of deoxySL was shown in vitro and in cancer patients, where 1-deoxysphinganine was tried as an anticancer drug. Importantly, our preliminary data showed for the first time that treatment of neurons with 1-deoxysphingosine resulted in destabilization in actin dynamics suggesting that aberrant actin dynamics could be involved in the underlying molecular mechanism of PIPN. If our hypothesis that L-alanine derived deoxySL are molecular intermediates in PIPN is proven true, it will allow addressing their overproduction by supplementation with L-serine during paclitaxel treatment. Such a strategy will result in shifting the sphingolipid synthesis to the regular L-serine derived sphingolipid group, which can be metabolically catabolized. Similar strategy with L-serine supplementation has been successfully used in a pilot study with HSAN1 patients. In addition, our proposal is aimed at addressing the mechanism of neurotoxicity by deoxySL by studying the effect of deoxySL on the actin cytoskeleton. Currently the mechanism of deoxySL neurotoxicity is not understood. Our results will provide additional targets for strategies to treat or prevent neuropathy due not only to paclitaxel treatment, but also in other cases where there is an elevation of plasma deoxySL, such as HSAN1 and diabetic patients suffering with comorbid peripheral neuropathy.
The current proposal if funded will provide crucial support to revise an R21 application, which is in response to a special NIH program announcement addressing the mechanisms of chemotherapy-induced peripheral neuropathy (PA-12-083). The project is a collaborative effort with Dr. Kindy from the Department of Neuroscience, who provides essential neuroscience expertise and also the dorsal root ganglion and glia primary cultures necessary for the proposed experiments. Dr. Bielawski, the analytical director of the Lipidomics facility at MUSC, developed a high-quality mass spectrometry method for our project resulting in a precise quantification of deoxySL. The method is indispensable for the success of the current proposal and the long-term success of the project.