P039 Human papillomavirus 8-associated skin field cancerization demonstrates signal transducer and activator of transcription 3 pathway activation: a novel therapeutic target
Authors: Creamer Katharine , Morgan Huw , Olivero Carlotta , Shorning Boris Y , Gibbs Alex , Phillips Alexandra , Ananthan Lokapriya , Lim Annabelle Xiao Hui , Martuscelli Licia , Borgogna Cinzia , De Andrea Marco , Hufbauer Martin , Akgul Baki , Gariglio Marisa , Patel Girish 
Published: June 2024

Abstract
Improved understanding and targeting of pathways involved in actinic keratoses (AK) could reduce the incidence of keratinocyte carcinoma. The objective of this study was to elucidate pathways involved in AK as potential therapeutic targets. In total, 443 AK samples were analysed after ethics approval was obtained. Nine transgenic mouse models were used to elucidate the biology of AK with approval. Analysis of 161 human AKs identified the presence of epidermal koilocytes in 70% of tissue samples (Table), indicating viral aetiology. The presence of koilocytes was more common in men (P &lt; 0.05), but was not affected by age, site or type. Genotyping of AKs with koilocytes indicated the presence of human papillomavirus (HPV)8, with 100% sensitivity and 98% positive predictive value (P &lt; 0.01). A triple cross HPV8tg:Lrig1CreERT2:R26RConfetti mouse model, in which HPV8 early region genes were expressed throughout the skin, led to epidermal changes of AK. Analysis of HPV8 mouse models determined these epidermal changes to be derived from a polyclonal expansion of hair follicle junctional zone, but not bulge, keratinocyte stem cells. A ­colony-forming assay confirmed that the epidermal keratinocytes retained the phenotype of keratinocyte stem cells (P &lt; 0.01). Furthermore, this population had no melanin ‘cap’, suggesting increased susceptibility to ultraviolet mutagenesis. Comparison of HPV8 and wildtype mouse keratinocyte stem cell populations identified activation of the signal transducer and activator of transcription (STAT)3 pathway in the HPV8 mouse hair follicle junctional zone, suggesting this is involved in AK development. When evaluating human AK samples the STAT3 pathway is also activated. Blocking STAT3 (with siRNA) or its upstream signalling component Src kinase (with siRNA or tirbanibulin) prevented the epidermal changes of AK and subsequent tumorigenesis, suggesting that the STAT3 pathway is an important therapeutic target. In conclusion, understanding the pathogenesis of AK is critical for skin cancer prevention. These findings redefine the biological basis of AK, in which HPV8 viral reactivation drives proliferation of hair follicle keratinocyte stem cells to create AK without need for DNA mutations. This study identifies an essential targetable signalling pathway for future drug development. Grants were received from LEO Foundation and Almirall.All AK (n = 164)AK with koilocytes (n = 117)AK without koilocytes (n = 47)Age (years), mean (SD); range70 (10); 42–9071 (10); 42–9069 (10); 48–84Sex, n (%); male, female57 (46), 68 (54)45 (79), 39 (57)12 (21), 29 (43)Site, n (%) Head/neck101 (66)70 (65)31 (70) Torso12 (8)10 (9)2 (5) Arm28 (18)19 (18)9 (20) Leg11 (8)9 (8)2 (5)Pathology findings, n (%) Bowenoid15 (9)14 (12)1 (2) Acantholytic3 (2)2 (2)1 (2) Hyperkeratotic or hypertrophic lesion20 (12)18 (15)2 (4) Lichenoid infiltrate16 (10)8 (7)8 (17)Percentages are based on available data.