The serine/threonine kinase mechanistic target of rapamycin (mTOR) plays a pivotal role in the regulation of cell proliferation, survival, and motility in response to availability of energy and nutrients as well as mitogens. The mTOR signaling axis regulates important biological processes, including cellular growth, metabolism, and survival in many tissues. In the skin, dysregulation of PI3K/AKT/mTOR pathway may lead to severe pathological conditions characterized by uncontrolled proliferation and inflammation, including skin hyperproliferative as well as malignant diseases. Herein, we provide an update on the current knowledge regarding the pathogenic implication of the mTOR pathway in skin diseases with inflammatory features (such as psoriasis, atopic dermatitis, pemphigus, and acne) and malignant characteristics (such as cutaneous T cell lymphoma and melanoma) while we critically discuss current and future perspectives for therapeutic targeting of mTOR axis in clinical practice.

Background: The combination of JAK/STAT and HDAC inhibitors exerted beneficial effects in haematological malignancies, presenting promising therapeutic CTCL targets. We aim to investigate the efficacy of JAK1/2i ruxolitinib in combination with HDACi resminostat in CTCL in vitro. Material & methods: Non-toxic concentrations of ruxolitinib and/or resminostat were administered to MyLa (MF) and SeAx (SS) cells for 24h. Cytotoxicity, cell proliferation and apoptosis were estimated through MTT, BrdU/7AAD and Annexin V/PI assay. Multi-pathway analysis was performed to investigate the effect of JAK1/2i and/or HDACi on JAK/STAT, Akt/mTOR and MAPK signalling pathways. Results: Both drugs and their combination were cytotoxic in MyLa (p<0.05) and in SeAx cell line (p<0.001), inhibited proliferation of MyLa (p<0.001) and SeAx (p<0.001) at 24h, compared to untreated cells. Moreover, combined drug treatment induced apoptosis after 24h (p<0.001) in MyLa, and SeAx (p<0.001). The combination of drugs had a strong synergistic effect with a CI<1. Importantly, the drugs’ combination inhibited phosphorylation of STAT3 (p<0.001), Akt (p<0.05), ERK1/2 (p<0.001) and JNK (p<0.001) in MyLa, while it reduced activation of Akt (p<0.05) and JNK (p<0.001) in SeAx. Conclusion: The JAKi/HDACi combination exhibited substantial anti-tumor effects in CTCL cell lines, and may represent a promising novel therapeutic modality for CTCL patients.

The combination of Resminostat (HDACi) and Ruxolitinib (JAKi) exerted cytotoxic effects and inhibited proliferation of CTCL cell lines (MyLa, SeAx) in previously published work. A xenograft tumor formation was produced by implanting the MyLa or SeAx cells on top of the chick embryo chorioallantoic membrane (CAM). The CAM assay protocol was developed to monitor the metastatic properties of CTCL cells and the effects of Resminostat and/or Ruxolitinib in vivo. In the spontaneous CAM assays, Resminostat and Ruxolitinib treatment inhibited the cell proliferation (p < 0.001) of MyLa and SeAx, and induced cell apoptosis (p < 0.005, p < 0.001, respectively). Although monotherapies reduced the size of primary tumors in the metastasis CAM assay, the drug combination exhibited a significant inhibition of primary tumor size (p < 0.0001). Furthermore, the combined treatment inhibited the intravasation of MyLa (p < 0.005) and SeAx cells (p < 0.0001) in the organs, as well as their extravasation to the liver (p < 0.0001) and lung (p < 0.0001). The drug combination also exerted a stronger inhibitory effect in migration (p < 0.0001) rather in invasion (p < 0.005) of both MyLa and SeAx cells. It further reduced p-p38, p-ERK, p-AKT, and p-STAT in MyLa cells, while it decreased p-ERK and p-STAT in SeAx cells in CAM tumors. Our data demonstrated that the CAM assay could be employed as a preclinical in vivo model in CTCL for pharmacological testing. In agreement with previous in vitro data, the combination of Resminostat and Ruxolitinib was shown to exert antitumor effects in CTCL in vivo.

Angiogenesis plays a pivotal role in the growth and metastasis of tumors, including the development and progression of cutaneous lymphomas. The chick embryo CAM model has been utilized in various studies to assess the growth rate, angiogenic potential, and metastatic capability of different tumor types and malignant cell lines. However, the precise mechanisms of angiogenesis in CTCL and the influence of Ruxolitinib or Resminostat on angiogenesis in hematological malignancies and solid tumors are not well understood. Recent in vitro and in vivo data have demonstrated the synergistic inhibition of tumorigenesis and metastasis in experimental models of CTCL when using the combination of Resminostat (HDACi) with Ruxolitinib (JAKi). The present work aims to elucidate the effects of this combination on the tumor microenvironment’s vascular components. We investigated the effects of Ruxolitinib (JAKi) in combination with Resminostat (HDACi) treatment in transendothelial migration of CTCL cells (10⁶ MyLa and SeAx) by using a transwell-based transendothelial migration assay and tumor angiogenesis in vivo. We used the CTCL chick embryo CAM model with xenografted tumors derived from implanted MyLa and SeAx cells and administered topically 15 μM ruxolitinib and 5 μM Resminostat every two days during a 5-day period. JAKi and HDACi inhibited CTCL cell transendothelial migration by 75% and 82% (p < 0.05) in both CTCL engrafted cells (MyLa and SeAx, respectively) compared to the untreated group. Moreover, the combination of ruxolitinib with resminostat blocked angiogenesis by significantly reducing the number of blood vessel formation by 49% and 34% in both MyLa and SeAx, respectively (p < 0.05), indicating that the proposed combination exerted significant anti-angiogenic effects in the CAM CTCL model. Overall, these data provide valuable insights into potential therapeutic strategies targeting angiogenesis in CTCL, paving the way for more effective treatment approaches in the future.