Nerve terminals in the tumor microenvironment as targets for local infiltration analgesia.

Nerve terminals within the tumor microenvironment as potential pain-mitigating targets for local infiltration analgesia is relatively less explored. In this study, we examine the role of key analgesics administered as local infiltration analgesia in a model of cancer-induced bone pain (CIBP). CIBP was induced by administration of allogenic MRMT1 breast cancer cells in the proximal tibia of rats, and tumor mass characterized using radiogram, micro-CT, and histological analysis. In vitro responsiveness to key analgesics δ-opioid receptor agonist (DOPr), Ca2+ channel and TRPV1 antagonists was assessed using ratiometric Ca2+ imaging in sensory neurons innervating the tumor site. Effectiveness of locally infiltrated analgesics administered independently or in combination was assessed by quantifying evoked limb withdrawal thresholds at two distinct sites for up to 14 days. CIBP animals demonstrated DOPr, N-, and L-type and TRPV1 expression in lumbar dorsal root ganglion neurons (DRG), comparable to controls. Evoked Ca2+ transients in DRG neurons from CIBP animals were significantly reduced in response to treatment with compounds targeting DOPr, N-, L-type Ca2+ channels and TRPV1 proteins. Behaviourally, evoked hyperalgesia at the tumor site was strongly mitigated by peritumoral injection of the DOPr agonist and T-type calcium antagonist, via its activity on bone afferents. Results from this study suggest that nerve terminals at tumor site could be utilized as targets for specific analgesics, using local infiltration analgesia.

Secretome mediated interactions between sensory neurons and breast cancer cells.

The role of the nervous system in aiding cancer progression and metastasis is an important aspect of cancer pathogenesis. Interaction between cancer cells and neurons in an in vitro platform is a simple and robust method to further understand this phenomenon. In our study, we aimed to examine in vitro reciprocal effect between breast cancer cells and cancer-sensitized peripheral primary sensory neurons. Secretome obtained from either cultured DRG neurons from tumor-burdened rats, or MRMT1 breast cancer cells were used to study neuronal and cancer cell reciprocity. We utilized neurite analysis, modified cell migration assay and cell signaling pathway inhibitors to determine neurite growth patterns and cell migration in PC12/DRG neurons and MRMT1 cells, respectively. MRMT1 secretome was found to induce significant neurite outgrowth in PC12 and primary sensory neurons. Secretome-induced neurite growth in PC12 cells was partly mediated by PI3K and ERK pathways, but not by adenylyl cyclase. Conversely, secretome from tumor-sensitized sensory neuron cultures induced increased rate of migration in cultured MRMT1 cells. Results from our study provide additional support to the hypothesis that both breast cancer cells and nerve terminals secrete signaling messengers that have a reciprocal effect on each other.

A Brief Review of In Vitro Models for Injury and Regeneration in the Peripheral Nervous System.

Nerve axonal injury and associated cellular mechanisms leading to peripheral nerve damage are important topics of research necessary for reducing disability and enhancing quality of life. Model systems that mimic the biological changes that occur during human nerve injury are crucial for the identification of cellular responses, screening of novel therapeutic molecules, and design of neural regeneration strategies. In addition to in vivo and mathematical models, in vitro axonal injury models provide a simple, robust, and reductionist platform to partially understand nerve injury pathogenesis and regeneration. In recent years, there have been several advances related to in vitro techniques that focus on the utilization of custom-fabricated cell culture chambers, microfluidic chamber systems, and injury techniques such as laser ablation and axonal stretching. These developments seem to reflect a gradual and natural progression towards understanding molecular and signaling events at an individual axon and neuronal-soma level. In this review, we attempt to categorize and discuss various in vitro models of injury relevant to the peripheral nervous system and highlight their strengths, weaknesses, and opportunities. Such models will help to recreate the post-injury microenvironment and aid in the development of therapeutic strategies that can accelerate nerve repair.

Effect of gold nanoparticle treated dorsal root ganglion cells on peripheral neurite differentiation.

The use of gold nanoparticles (AuNps) in applications connected to the peripheral nervous system (PNS) holds much promise in terms of therapeutic and diagnostic strategies. Despite their extensive use, a clear understanding of their effects on neurons and glia in the PNS is lacking. In this study, we set out to examine the effects of AuNps on dorsal root ganglion (DRG) cells, and how such AuNp-exposed cells could in-turn affect neurite differentiation. DRG cultures were exposed to mono-dispersed spherical-shaped AuNps of diameter 24.3 ± 2.3, 109.2 ± 14.7 or 175 ± 19.2 nm at varying concentrations. Cellular uptake and viability were quantified using flow-cytometry. Neurite differentiation was quantified using neurite tracing analysis in PC-12 and DRG neurons exposed to conditioned media derived from AuNp-treated DRG cells. Both neurons and glia were found to internalize AuNps. DRG cell viability was significantly reduced upon treatment with higher concentration of 175 nm sized AuNps, while 24 nm and 109 nm sized AuNps had no effect. Further, conditioned media from AuNp-treated DRG cells produced comparable neurite outgrowth and neurite branching measurement as controls in PC-12 and DRG neurons. DRG cells were quite resilient to AuNp exposure in mild-moderate concentration. AuNp-exposed DRG cells, irrespective of size and concentration range tested, did not affect neuronal differentiation.