Valrubicin activates PKCa in keratinocytes: a conceivable mode of action in treating hyper-proliferative skin diseases.

BACKGROUND: Valrubicin is a semisynthetic anthracycline developed as an anti-cancer drug able to ameliorate psoriasis and non-melanoma skin cancer (NMSC) by topical application in animal models. Valrubicin decreases cell proliferation, and induces apoptosis; however its mode of action is still unknown. Valrubicin localizes in the cytoplasm and its valerate moiety resembles diacylglycerol, an activator of protein kinase C (PKC) α, which belongs to the PKC family of cytoplasmic serine/threonine protein kinases. PKCα is observed in the suprabasal layers of normal skin and is associated to keratinocyte growth arrest and differentiation processes. In hyper-proliferative skin diseases the presence of PKCα is altered. OBJECTIVE: The aim of the present study was to investigate valrubicin's mode of action in keratinocytes by studying its possible effect on PKCα activation. METHODS: PKCα's characteristic to translocate from the cytoplasm to the cellular membrane when activated was assessed by measuring the amount of PKCα in the soluble and membrane-bound protein fractions isolated from valrubicin stimulated keratinocytes and by visualizing PKCα in stimulated cells over time. Downstream signaling was investigated by measuring the amount of phosphorylated Myristoylated Alanine-rich C-kinase substrate (MARCKS) and extracellular signal-regulated kinases (ERK) 1/2 of valrubicin-stimulated keratinocytes. To investigate whether there was a direct interaction between valrubicin and PKCα, an activity assay employing purified PKCα protein was used. RESULTS: Valrubicin activates PKCα in vitro as shown by PKCα's translocation and phosphorylation of downstream signaling molecules. CONCLUSION: Valrubicin stimulates PKCα activity and downstream signaling which may contribute to its beneficial effect in psoriasis and NMSC.

Topical application of valrubicin has a beneficial effect on developing skin tumors.

Valrubicin is a second generation anthracycline characterized by an excellent safety profile presenting no skin toxicity or necrosis upon contact. In its current liquid formulation (Valstar; Indevus Pharmaceuticals, Lexington, MA), it is approved solely for the treatment of bladder cancer. Recently, valrubicin was incorporated in a cream formulation rendering this drug available for topical application. The cytostatic property of valrubicin can, thus, be employed for treating hyperproliferative skin diseases as was recently described for psoriasis. In the present study, the effect of topical application of valrubicin was investigated in skin tumor development; we hypothesized that valrubicin may be employed in treating actinic keratosis, a hyperproliferative skin condition that may transform into malignancy. A two-stage chemical mouse skin carcinogenesis model that represents the multistage etiology of human skin cancer-from developing papillomas to squamous cell carcinoma (SCC) was used. Moreover, two human skin SCC cell lines: DJM-1 and HSC-1 were cultured, to further investigate the effect of valrubicin in vitro. Cell viability was assessed by adenosine triphosphate presence, proliferation as proliferative cell nuclear antigen expression and apoptosis as cytokeratin 18 cleavage, caspase activation, poly-adenosine diphosphate-ribose-polymerase cleavage and bax and bcl-2 regulation. Valrubicin significantly inhibited tumor formation in the mouse skin carcinogenesis model and significantly decreased cell viability of the cultured human skin SCC cells. In both mouse skin and SCC cells, proliferation was significantly decreased. Apoptosis was significantly increased in SCC cells but unchanged in the treated mouse skin at study completion. This study demonstrated that topical application of valrubicin has a beneficial effect in treating developing skin tumors.

Valrubicin in a topical formulation treats psoriasis in a xenograft transplantation model.

Valrubicin is a cytostatic drug currently approved by the American Federal Drug Administration as a trademarked Valstar sterile solution for the treatment of bladder cancer. Valrubicin has shown an excellent therapeutic potential with minimal toxicity. This study investigated the effect in vivo of treating psoriasis with a daily topical application of valrubicin cream in a psoriasis xenograft transplantation model. Psoriasis is characterized by an accelerated keratinocyte proliferation, resulting in increased epidermal thickness. We thus studied the cytostatic potential of valrubicin on epidermal keratinocytes. In vivo, valrubicin treatment resulted in a normalization of epidermal morphology and a reduction in epidermal thickness after 12 days. In addition, the dermal vessel pattern was reduced and the stratum granulosum was regained. Staining for a regenerative proliferation marker showed a decrease in keratinocyte proliferation, and scattered epidermal cells showed apoptosis. In vitro, valrubicin was shown to localize solely to the cell cytoplasm in cultured keratinocytes and to reduce keratinocyte proliferation as well as increase apoptosis by activation of caspases 3, 7, and 9. Our results indicated that valrubicin successfully treats psoriasis in a xenograft transplantation model, suggesting that topical valrubicin may become an upcoming treatment for psoriasis.