Date of Award

January 2023

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Michael Girardi

Abstract

One in five Americans are estimated to develop skin cancer during their lifetime, rendering it the most common malignancy diagnosed in the United States with associated healthcare costs estimated to total over $8 billion annually. The primary environmental risk factor for skin cancer is exposure to ultraviolet radiation (UVR), which can be mitigated through the use of sunscreens. Concerns surrounding the safety and aesthetics of commercial sunscreens have led to our development of a biodegradable bioadhesive nanoparticle (BNP) sunscreen platform. BNPs are unique in their possession of an aldehyde-rich corona that can covalently bind epidermal amines and are produced via conversion from precursor nonadhesive nanoparticles (NNPs). Building upon prior work encapsulating avobenzone (AVO) and octocrylene (OCR) to provide broad-spectrum protection, we have now encapsulated diethylamino hydroxybenzoyl hexyl benzoate (DHHB), a European Union-approved sunscreen with excellent photoprotection, photostability, and compatibility with other sunscreens. DHHB was encapsulated with 30% loading for co-formulation with OCR. Bioadhesion was assessed by applying BNP-DHHB and BNP-OCR to VITRO-SKIN® pieces (4 x 4 cm) that were subsequently subjected to continuous stirring in a water bath. After 1 hour, >86% of BNPs were retained on VITRO-SKIN® compared to 30-45% of NNPs. DHHB and OCR, when formulated as NNPs, had an in vitro SPF of 46 and retained >80% of its maximum absorbance capacity after two hours of UVR exposure. To complement in vitro testing of sunscreen performance, in vivo studies were conducted to assess their ability to prevent UVR-induced mutagenesis, which occurs via direct and indirect pathways. In the direct pathway, immediate damage is caused by the absorption of photons by DNA leading to the formation of a key mutagenic DNA photoproduct: the cyclobutane pyrimidine dimer (CPD). In vivo testing using a murine model revealed that our new formulation of BNP-DHHB,OCR, when combined with natural products, prevented >94% of immediate CPD formation. CPDs additionally result from the indirect pathway via non-DNA chromophores that compromise DNA long after UVR exposure ends, forming so-called dark CPDs (dCPDs). We explored two methods for quantifying dCPDs in murine skin following a single, acute UVA exposure (100 kJ/m2): ELISA and immunofluorescence (IF) staining. In both methods, dCPDs were demonstrated to peak approximately 30 minutes following the end of UVA exposure, lending support to their utility towards assessing sunscreen efficacy in preventing UVR-induced DNA damage in living skin. Together, our results indicate that (1) BNP-encapsulated sunscreens offer improved photoprotection, photostability, bioadhesive properties, and effective in vivo prevention of immediate CPD formation; and (2) both ELISA and IF staining provide ways to assess sunscreen efficacy in preventing UVR-induced DNA damage in living skin.

Comments

This thesis is restricted to Yale network users only. This thesis is permanently embargoed from public release.

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