Sigma Antagonists for Treatment of Neuropathic Pain Syndromes in Cancer Patients: A Narrative Review

Almost 40% of cancer patients have neuropathic pain or mixed pain with a neuropathic component, which can be intense, debilitating, and challenging to treat. New studies on sigma receptors show these enigmatic ligand-binding protein chaperones may be helpful drug targets for new pharmacologic options to reduce many types of neuropathies, including chemotherapy-induced peripheral neuropathy (CIPN) and other cancer-related neuropathic pain syndromes. Our objective was to review the literature, including preclinical findings, in support of sigma-1 receptor (S1R) antagonists in reducing neuropathic pain and sigma-2 receptor (S2R) agonists for neuroprotection. The mechanisms behind these effects are not yet fully elucidated. The role of S1R antagonists in treating CIPN appears promising. In some cases, combination therapy of an opioid—which is a true analgesic—with a S1R antagonist, which is an anti-hyperalgesic and anti-allodynic agent, has been proposed. Of interest, but not well studied is whether or not S1R antagonists might be effective in treating CIPN in patients with pre-existing peripheral diabetic neuropathy. While neuropathic syndromes may occur with hematologic cancers, the role of S1R agonists may be effective. Sigma receptors are being actively studied now for a variety of conditions ranging from Alzheimer’s disease to Parkinson’s disease as well as neuropathic pain.