Biological Effects of Ingenol Mebutate Gel in Moderate to Severe Actinic Fields Assessed by Reflectance Confocal Microscopy: A Phase I Study.

Ingenol mebutate represents a topical treatment for fields with actinic keratosis (AK). The biological effects of ingenol mebutate in AK, subclinical (SC)-AK, and reference-skin were assessed and graded by in vivo reflectance confocal microscopy (RCM) and histology. Patients with AK and SC-AK lesions in one 25 cm(2) field on hands or forearms, and with an area of reference skin on the inner upper arm, were included. The two fields were each treated with ingenol mebutate 0.05% gel (n=16), or vehicle (n=8), on 2 consecutive days; clinical and RCM assessments were performed on days 1, 2, 3, 8, and 57, and biopsies on day 3. Local skin responses were more pronounced in AK fields (6.1 (mean) +/- 2.6 (SD)) compared with reference skin (3.5 +/- 1.5). The clinical AK lesion reduction was 43.8% and 6.3% with ingenol mebutate and vehicle, respectively. RCM and histology evaluations showed that ingenol mebutate induced a significant pronounced cell death and immune response in AK and SC-AK lesions, compared with reference skin. Ingenol mebutate induced RCM-measured reduction in (investigator-1/investigator-2): AK lesions (34/28%), SC-AK lesions (72/56%), and solar elastosis in AK fields (mean, -0.22/-0.25). In conclusion, ingenol mebutate showed selective pronounced biological responses in AK and SC-AK as compared with reference skin.