Neuropathic pain is a debilitating side effect of many commonly-used chemotherapy drugs, and in severe cases can result in the discontinuation of a cancer treatment. By understanding the mechanisms through which chemotherapeutics induce neuropathic pain, researchers aim to develop effective treatments designed specifically to alleviate the condition. These will combat the dose-limitation imposed on chemotherapeutics, as well as offering utility for conditions including multiple sclerosis, diabetes and HIV.
Neuropathic pain research has historically relied on the use of immortalized cell lines, primary human neuronal cells, or animal models. Immortalized cells have fallen from favor due to concerns over misidentification or phenotypic drift from the original host, while primary human neuronal cells are notoriously difficult to culture. Animal studies are time-consuming and expensive to perform, with findings infrequently translating into humans. For these reasons, researchers are turning to iPSC-derived sensory neuronal cells for neuropathy research. These afford greater physiological relevance, are relatively inexpensive in comparison, and can be generated in large batches for the acquisition of reliable and consistent results.
In our previous blog we have discussed the etiology of neuropathic pain and the potential offered by iPSC-derived sensory neurons as a tool for researching neuropathic pain.
In this article:
We will delve further into models available to researchers and why iPSC-derived sensory neurons are becoming the leading model in this field. It takes 4 minutes to read this article:
Animal nociceptors for the study of neuropathic pain
Nociceptors are specialized peripheral sensory neurons that are implicated in chronic pain conditions such as those related to chemotherapy. Many studies have used rodent nociceptors to understand mechanisms of pain perception. Just one example is the 2015 study by Park et al, who treated mice with Cisplatin , examining the development of neuropathic pain and methods of its alleviation. The authors found that Cisplatin-treated mice exhibited allodynia (a pain response from stimuli that would not usually cause pain) and observed that this could be lessened with the anti-epileptic drug Gabapentin.
While rodent model systems have significantly advanced our understanding of neuropathic pain etiology and treatment, there are several limitations when translating such models into man. One reason may relate to gender differences . For instance, while Paclitaxel and Cisplatin are widely used to treat female patients, most laboratory studies of chemotherapy-induced neuropathic pain have been conducted on male animals. Another possibility is the limited consistency in drug dose or mode of delivery between animal studies.
These limitations are compounded by the fact that rodent and human nociceptors display several key molecular differences. In 2017, Rostock et al performed a detailed comparative analysis of well-known nociceptive markers in human and mouse dorsal root ganglia using fluorescent in situ hybridization. They found co-expression of Trpv1 with TrkA, and of Ret with TrkA, to be greater in human neurons than in mouse neurons. Similar results were observed for Na v 1.8 and Na v 1.9, both of which are implicated in pathological forms of pain. While rodent models still have considerable utility in neuropathy research, caution should be exercised when drawing any experimental conclusions.
iPSC-derived sensory neuron progenitors
Using small molecule inhibitors, we have differentiated iPSC into sensory neuron progenitors which are ideally suited to the study of chemotherapy-induced neuropathic pain. Our thorough characterization process has been used to confirm the cellular expression and function of various ion channels that play a key role in nociception. These include the dorsal root ganglion (DRG) specific voltage-gated sodium channels Na v 1.7, Na v 1.8 and Na v 1.9, and the transient receptor potential (TRP) ion channels, TRPV1, TRPA1 and TRPM8.
We have employed a wide variety of methods to characterize our iPSC-derived sensory neuron progenitors . Sodium channel RNA expression analysis has been measured by cDNA PCR, and we have performed patch clamping to assess various ion channels via electrophysiology . We have also recorded the response to stimuli which include temperature and the natural substances capsaicin, menthol and allyl isothiocyanate (wasabi). Cellular electrical activity has been evaluated with a multi-electrode array system (MEA) , while immunocytochemistry has provided additional visual confirmation of ion channel expression.
The administration of chemotherapy drugs to our iPSC-derived sensory neuron progenitors has demonstrated a clear pain response. The application of Vincristine , for example, showed an acute increase in firing rate, with a slow cellular response in comparison to that seen following application of capsaicin, menthol and allyl isothiocyanate. Oxaliplatin treatment resulted in cold hypersensitivity, a well-documented side effect of this chemotherapeutic, which is understood to be attributable to remodeling of ion channel expression in nociceptors.
To complement our iPSC-derived sensory neuron progenitors, we supply expertly optimized growth media for their successful culture and propagation, along with unrivalled technical support.advance your understanding of neuropathic pain with Axol’s iPSC-derived sensory neuron progenitors