In Vitro Sarcoma Cells Release a Lipophilic Substance That Activates the Pain Transduction System via TRPV1

Despite success in treating many forms of cancer, pain associated with malignancy remains a serious clinical issue with a poorly understood etiology. This study determined if certain sarcoma cell lines produced a soluble factor that activates the TRPV1 ion channel expressed on nociceptive sensory neurons, thereby activating a major pain transduction system. Trigeminal ganglia were harvested from rats and cultured. A rhabdomyosarcoma (CRL1598) and osteosarcoma (CRL 1543) cell line were grown to 75% confluency. Conditioned media (CM) was collected after 24 h of exposure and subjected to reverse phase chromatography. Neuronal activation in the presence of CM was measured using iCGRP RIA and calcium imaging after treatment with vehicle or I-RTX, a potent TRPV1 antagonist. Data were analyzed by ANOVA/Bonferroni or t test. The rhabdomyosarcoma CM produced a 4-fold increase in iCGRP release compared with control media (P < 0.001). The osteosarcoma cell line CM produced a 7-fold increase in iCGRP release compared with control media (P < 0.001). This evoked iCGRP release was via TRPV1 activation since the effect was blocked by the antagonist I-RTX. The application of rhabdomyosarcoma CM produced about a 4-fold increase in [Ca(2+)]I levels (P < 0.001), and this effect was blocked by pretreatment with the TRPV1 antagonist, I-RTX. We have shown that certain sarcoma cell lines produce a soluble, lipophilic factor that activates the peripheral nociceptor transduction system via TRPV1 activation, thereby contributing to cancer pain. Further investigations are needed to develop tumor-specific analgesics that do not produce unwanted or harmful side-effects.