Effect of topical vasoconstrictor exposure upon tumoricidal radiotherapy

Abstract

Topical application of the alpha adrenergic vasoconstrictors norepinephrine, phenylephrine or epinephrine to skin or mucosa in alcohol:water-based delivery vehicles minutes before irradiation has recently been shown to protect skin and mucosa cells against radiotherapy-induced toxicities in both preclinical and clinical studies. The protective mechanism is thought to involve transient skin or mucosal vasoconstriction with secondary, transient hypoxia and associated radioprotection. Regarding possible protection of tumor cell nests within the radiotherapy field, the endothelial cell-abnormal stroma constructed blood vessels generally found in human tumors commonly lack adrenergic receptor-containing smooth muscle cells that are required to achieve vasoconstriction. Consistent with this, we show here that topical application of norepinephrine or phenylephrine to broken or intact skin over human Cal-27 or A-431 xeonograft, or mouse solid L1210 allograft tumors growing subcutaneously in nude mice, showed no effect upon radiation-induced tumor growth inhibition. Although vasoconstrictor-induced nude mouse skin blanch was seen minutes after topical application of 600 mM norepinephrine, no blanching was seen within the A-431 xenograft tumors. Radiation dermatitis was severe 11 days post-irradiation (2 × 13.8 Gy) in the irradiated field containing xenograft tumors in mice that received topical delivery vehicle, but was absent in mice that received topical norepinephrine. Topical vasoconstrictor-conferred prevention of radiation dermatitis without discernible radioprotection of three histologically diverse xenograft or allograft tumors supports further development of the topical vasoconstrictor therapeutic strategy in humans.