PROJECT ABSTRACT Microneedles (MNs) are micron scale projections that allow for improved drug delivery through the skin via formation of transient micropores. For successful transdermal drug delivery, it is crucial that the micropores remain open (drug delivery ceases rapidly after micropore closure, usually within ~48 hrs). Delaying micropore closure would be advantageous by allowing a longer period of drug delivery from each MN treatment. Previous methods that have been explored for delaying micropore closure timeframes did not account for the biochemical differences seen in diverse skin types; further, previous studies did not address the physiological processes that impact micropore closure. We have shown that darker skin types have longer micropore closure timeframes. This could result in altered therapeutic outcomes from unexpected drug delivery windows in diverse skin types, which may be especially problematic for drugs with narrow therapeutic windows. Catecholamines such as dopamine play a role in cutaneous wound healing and may mediate micropore closure, but the direct role of dopamine in micropore closure has never been studied. Dopamine may alter wound healing through dopamine receptor binding and subsequent cAMP modulation. Interestingly, melanin production (responsible for skin color) also relies on the same dopaminergic precursors and alters intracellular cAMP production. Therefore, we hypothesize that drug delivery through micropores in diverse skin types will differ in a manner dependent upon micropore closure times, and variability in micropore closure among skin types is influenced by dopamine secretion and receptor signaling. To test this, we will establish a translational approach through two Aims. In Aim 1 we will assess the impact of differences in micropore closure times on model drug absorption using a pharmacokinetic study. In Aim 2 we will investigate how dopamine D1/D2 receptor signaling alters microwound recovery using a dual in-vitro knockdown approach. The overall goal is to identify a possible pharmaceutical target for delaying micropore closure, ultimately improving MN-assisted transdermal drug delivery and informing development of better MN products for diverse populations.

PROJECT NARRATIVE Microneedles facilitate drug delivery by forming micropores in the skin. Variability in micropore closure times in diverse skin types may reduce efficacy of this drug delivery approach. In this project we will 1) determine the impact of micropore closure times on delivery of a model drug through the skin, and 2) explore the role of dopamine signaling in microwound closure timeframes in diverse skin types. The overall goal is to identify a possible pharmaceutical target for delaying micropore closure and improving microneedle assisted transdermal drug delivery.