Targeting V600EB-Raf and Akt3 Using Nanoliposomal-Small Interfering RNA Inhibits Cutaneous Melanocytic Lesion Development

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Abstract
Most events promoting early melanoma development are yet to be identified, but deregulation of the B-Raf and Akt3 signaling cascades is an important regulator of this process. Approximately 90% of normal moles and ∼60% of early invasive cutaneous melanomas contain a T1799A B-Raf mutation (V600EB-Raf), leading to 10 times higher enzyme activity and constitutive activation of the mitogen-activated protein kinase pathway. Furthermore, ∼70% of melanomas have elevated Akt3 signaling due to increased gene copy number and PTEN loss. Therefore, targeting V600EB-Raf and Akt3 signaling is necessary to prevent or treat cutaneous melanocytic lesions. Agents specifically targeting these proteins are needed, having fewer side effects than those inhibiting both normal and mutant B-Raf protein or targeting all three Akt isoforms. In this study, a unique nanoliposomal-ultrasound–mediated approach has been developed for delivering small interfering RNA (siRNA) specifically targeting V600EB-Raf and Akt3 into melanocytic tumors present in skin to retard melanoma development. Novel cationic nanoliposomes stably encapsulate siRNA targeting V600EB-Raf or Akt3, providing protection from degradation and facilitating entry into melanoma cells to decrease expression of these proteins. Low-frequency ultrasound using a lightweight four-cymbal transducer array enables penetration of nanoliposomal-siRNA complex throughout the epidermal and dermal layers of laboratory-generated or animal skin. Nanoliposomal-mediated siRNA targeting of V600EB-Raf and Akt3 led to a cooperatively acting ∼65% decrease in early or invasive cutaneous melanoma compared with inhibition of each singly with negligible associated systemic toxicity. Thus, cationic nanoliposomes loaded with siRNA targeting V600EB-Raf and Akt3 provide an effective approach for targeted inhibition of early or invasive cutaneous melanomas. [Cancer Res 2008;68(18):7638–49]

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