Development of an in vitro melanoma skin model for transdermal drug delivery applications

Melanoma is the fifth most commonly diagnosed type of cancer and has a 5-year survival rate of only 15% in advanced stages. Current treatments for melanoma include surgical removal, chemotherapy, and immune- and molecularly targeted therapies. However, melanoma often presents a high resistance to therapies resulting in a low treatment efficacy, and severe sys-temic side effects. To overcome this limited efficacy and reduce side effects, an adhesive trans-dermal drug delivery (TDD) system was developed and tested to locally deliver fluorescent dyes to melanoma sites, forming one part of the work presented in the thesis. The gel adhered to skin due to the polyphenol tannic acid, without leaving residues after removal from the skin. Microparticles were embedded in the gel, which allowed encapsulation of drugs in particles as well as suspended throughout the gel. Release of fluorescent dyes from microparticles and gels to spheroids showed diffusive release of drugs is possible. However, one limitation in the development of such novel drug delivery systems is the lack of biologically relevant 3D culture systems for evaluation. This often leads to the failure of many drugs in preclinical or later clinical trials, as complexities and interactions with the extracellular matrix (ECM) and other cells, crucial for evaluating the efficacy of novel drug systems, are com-monly lacking in conventional 2D cultures. Cancer-associated fibroblasts (CAFs) are one of the most important cellular components of the tumor microenvironment (TME) in melanoma that lead to increased matrix deposition, tumor progression, and survival. Furthermore, the TME has been shown to play a role in cancer progression due to the presence of important structural and signaling molecules. Therefore, the second goal of this project was to develop an in vitro 3D melanoma model with high resemblance to the in vivo melanoma tumor site in humans. This model was used to test the developed transdermal drug delivery application. First, a 3D spheroid model, consisting of melanoma cells and fibroblasts, was developed. The addition of fibroblasts led to increased structural stability, matrix deposition, and resis-tance to chemotherapy. The use of a fibroblast-modulating drug led to increased effects of the chemotherapy treatment in 2D and 3D models but showed increased resistance in the 3D model, indicating the relevance of drug testing in 3D cultures. The formed 3D spheroids were then injected into de- and recellularized skin matrices to increase their morphological relevance due to the presence of ECM. The addition of fibroblasts led to aggregate formation, similar to tumor formation. Comparison of tumor morphology, growth, and treatment response at different time points can be achieved with the melanoma model. In conclusion, the 3D in vitro melanoma model shows potential as a drug testing platform for transdermal drug delivery and for investi-gating tumor progression, migration, and interaction with multiple cell types.