Chemotherapy Drug Vincristine Increases Pain-Signaling Peptide Substance P in the Spinal Cord

What the researchers found

Vincristine treatment (0.1 mg/kg/day i.p. for 14 days) significantly increased substance P expression by 30.3% ± 2.4% in the superficial layers of the rat spinal dorsal horn compared to saline controls, confirmed by both immunohistochemistry and direct measurement of substance P levels in spinal cord tissue.

The neurokinin 1 (NK1) receptor antagonist aprepitant (20 mg/kg, s.c.) significantly inhibited the mechanical allodynia and hyperalgesia caused by vincristine, demonstrating that substance P signaling through the NK1 receptor is a key mediator of this chemotherapy-induced neuropathic pain.

Why it matters

Chemotherapy-induced peripheral neuropathy affects many cancer patients and is a major reason for dose reductions or treatment discontinuation. Understanding that substance P — a well-known pain peptide — mediates vincristine-induced pain opens the door to using existing NK1 receptor antagonists like aprepitant (already FDA-approved for nausea) as potential treatments for this debilitating side effect.

How the study worked

Sprague-Dawley rats received intraperitoneal vincristine at 0.1 mg/kg/day. After 14 days, mechanical pain sensitivity was assessed using von Frey filaments to measure allodynia and hyperalgesia. Substance P expression in the spinal dorsal horn was quantified using immunohistochemistry, and substance P levels in spinal cord tissue were measured directly. The NK1 receptor antagonist aprepitant was administered subcutaneously to test whether blocking substance P signaling could reduce the pain.

What this study cannot tell us

The study was conducted in rats, so the findings may not directly translate to human chemotherapy patients. Specific group sizes were not reported in the abstract. The study only examined vincristine, so results may not apply to other chemotherapy drugs that cause neuropathy. Long-term effects of aprepitant on neuropathic pain and potential interactions with cancer treatment were not assessed.

How to read the evidence

This is a preclinical animal study using a rat model of chemotherapy-induced neuropathy. While it provides clear mechanistic evidence with specific quantitative findings, the results require validation in human clinical studies.

When this study was published

Published in 2022, this study builds on established knowledge about substance P and pain signaling while providing specific new evidence about its role in vincristine neuropathy.

The bigger picture

This study connects two well-established fields — chemotherapy toxicology and neuropeptide pain signaling. Substance P has long been studied in pain research, but its specific role in chemotherapy-induced neuropathy has been less clear. By demonstrating that vincristine directly increases spinal substance P and that blocking its receptor reduces pain, the study provides a mechanistic rationale for repurposing NK1 antagonists in oncology supportive care.

Questions still open

• Could aprepitant or other NK1 receptor antagonists be effective for managing chemotherapy-induced neuropathy in human cancer patients?
• Do other chemotherapy drugs that cause neuropathy also increase spinal substance P levels?
• What is the optimal timing for NK1 antagonist treatment — preventive during chemotherapy or therapeutic after neuropathy develops?

Common questions

Read the original research

Vincristine increased spinal cord substance P levels in a peripheral neuropathy rat model.

Drug and chemical toxicology, 45(1), 393-397

Citation

Chiba, Terumasa; Kambe, Toshie; Yamamoto, Ken; Kawakami, Kazuyoshi; Taguchi, Kyoji; Abe, Kenji. (2022). Vincristine increased spinal cord substance P levels in a peripheral neuropathy rat model.. Drug and chemical toxicology, 45(1), 393-397. https://doi.org/10.1080/01480545.2019.1706547