Innovative strategies for non-invasive treatment of non-melanoma skin cancers

Methotrexate (MTX), a known anti-metabolite of folic acid (FA), has given promising results against keratoacanthoma and specified cases of squamous cell carcinoma, upon intralesional injection (off-label). However, this is a painful and invasive procedure and shows adverse effects due to systemic absorption. The aim of the project was to develop innovative formulations for the topical administration of MTX in a non-invasive or minimally invasive way, to treat more efficaciously non melanoma skin cancers, improving topical bioavailability and reducing transdermal absorption. Given MTX toxicity, FA was selected as a model drug due to the similarities in the physicochemical properties and in vitro skin behavior. To support the skin retention and permeation data obtained in in vitro permeation experiments, two-photon microscopy technique was used as an innovative tool for drug visualization in the tissue, based on its fluorescence properties. The images obtained suggest a preferential drug retention in hair follicles, which is worth further investigation. The next step of the research was to test the effect of a minimally invasive approach based on the use of microneedle roller to improve FA skin retention: in particular the effect of the number of passes and of the needle length was evaluated. The effect of the application time was considered as well. Four passes of microneedle roller equipped with 0.5 mm long microneedles guaranteed to maximize drug retention and minimize drug permeation through the skin, after the application of a solution for 6 hours. Since the application of a solution is not suitable for clinical treatment, different topical formulations were developed and tested in vitro in passive condition or after pretreatment with microneedle roller. Topical films composed by hydrophilic polymers (polyvinyl alcohol-PVA and polyvinylpyrrolidone- PVP) were developed, but the results of skin retention were not satisfactory. The attention then moved to semisolid formulations, like hydrogels and emulsions: PVA- and PVP-based hydrogels were developed, but the results were not optimal compared to those obtained with drug solution. The use of biphasic systems gave better results: in particular, a o/w emulsion containing Tefose® applied after pretreatment with microneedle roller, guaranteed a retention of drug over than 35 µg/cm2, much higher than the reference solution, without increasing significantly the amount permeated. The final attempt was to include FA nanosuspension in soluble microneedles, but the amount retained in the skin was lower compared to application of the emulsion on pre-treated skin. Finally, the best performing formulation (Tefose® o/w emulsion) was prepared also with the active ingredient methotrexate: the results obtained were comparable for the two drugs, confirming that all the data produced with folic acid can be reasonably extended to methotrexate. The general conclusion of this work is that the topical administration of methotrexate, to be used as an alternative of intradermal injection, can be realized by combining a traditional formulation (such as an emulsion) with a minimally invasive technique, such as skin pretreatment with microneedles.