Vitamin D as a potential enhancer of aminolevulinate-based photodynamic therapy for nonmelanoma skin cancer

摘要

Vitamin D3 (Vit D3) is a hormone essential for normal bone and cardiovascular health, and may participate in preventing nonmelanoma skin cancers (NMSC). Calcitriol (1,25 dihydroxyD3) is the active form of the hormone. We showed previously that calcitriol is a potent inducer of protoporphyrin IX (PpIX) in skin keratinocytes grown in organotypic cultures. Here, we investigated the ability of Vit D3 to enhance PpIX levels within skin tumors in vivo. Squamous tumors, generated by chemical carcinogenesis in mice, were pretreated for 3 days with topical calcitriol. Then 5-aminolevulinic acid (5-ALA) was applied topically, and PpIX levels were measured by noninvasive fluorimetry and in biopsied tissue. Calcitriol pretreatment resulted in a 3 to 4-fold elevation of PpIX in tumors, relative to no pretreatmen, providing significantly more photosensitizer available for tumor destruction. For deep tumors, topical calcitriol may not penetrate sufficiently. Therefore we explored whether systemic Vit D3, given short-term (3 days), might elevate PpIX within NMSC in a deep tumor model (subcutaneously-implanted A431 human squamous carcinoma cells). Defined amounts of calcitriol were injected into the mice for 3 d, followed by systemic 5-ALA, tissue biopsy, and confocal microscopic measurement of PpIX in frozen tissues. PpIX was clearly elevated after systemically delivered calcitriol. More work is needed, but if the amount of calcitriol required to elevate PpIX levels proves to be small, then the approach may ultimately prove attractive. Since most Americans are currently Vitamin D deficient, a small increase in calcitriol might be possible without risk of hypercalcemia.