Malignant melanoma is the skin cancer with the most significant impact on man, carrying the highest risk of death from metastasis. Both incidence and mortality rates continue to rise each year, with no effective long-term treatment on the horizon. In part, this reflects lack of identification of critical genes involved and specific therapies targeted to correct these defects. We report that selective activation of the Akt3

Activating mutations of the B-RAF gene are observed in >60% of human melanomas. Approximately 90% of these mutations occur in the activation segment of the kinase domain as a single-base substitution that converts a valine to glutamic acid at codon 599 (V599E) in exon 15. This mutation causes activation of the kinase as well as downstream effectors of the mitogen-activated protein kinase-signaling cascade, leading to melanoma tumor development by an as yet unknown mechanism. In this study, we have identified the role of V599E BRaf in melanoma tumor development by characterizing the mechanism by which this mutant protein promotes melanoma tumorigenesis. Small interfering RNA targeted against B-Raf or a Raf kinase inhibitor (BAY 43-9006) was used to reduce expression and/or activity of V599E B-Raf in melanoma tumors. This inhibition led to reduced activity of the mitogenactivated protein kinase-signaling cascade and inhibited tumor development in animals. Targeted reduction of mutant V599E B-Raf expression (activity) in melanoma cells before tumor formation inhibited tumorigenesis by reducing the growth potential of melanoma cells. In contrast, reduction of mutant V599E B-Raf activity in preexisting tumors prevented further vascular development mediated through decreased vascular endothelial growth factor secretion, subsequently increasing apoptosis in tumors. These effects in combination with reduced proliferative capacity halted growth, but did not shrink the size of preexisting melanoma tumors. Thus, these studies identify the mechanistic underpinnings by which mutant V599E B-RAF promotes melanoma development and show the effectiveness of targeting this protein to inhibit melanoma tumor growth. (Cancer Res 2005; 65(6): 2412-21)

It is unknown why only a minority of circulating tumor cells trapped in lung capillaries form metastases and involvement of immune cells remains uncertain. A novel model has been developed in this study showing that neutrophils regulate lung metastasis development through physical interaction and anchoring of circulating tumor cells to endothelium. Human melanoma cells were i.v. injected into nude mice leading to the entrapment of many cancer cells; however, 24 hours later, very few remained in the lungs. In contrast, injection of human neutrophils an hour after tumor cell injection increased cancer cell retention by ∼3-fold. Entrapped melanoma cells produced and secreted high levels of a cytokine called interleukin-8 (IL-8), attracting neutrophils and increasing tethering β 2 integrin expression by 75% to 100%. Intercellular adhesion molecule-1 on melanoma cells and β 2 integrin on neutrophils interacted, promoting anchoring to vascular endothelium. Decreasing IL-8 secretion from melanoma cells lowered extracellular levels by 20% to 50%, decreased β 2 integrin on neutrophils by ∼50%, and reduced neutrophil-mediated extravasation by 25% to 60%, resulting in ∼50% fewer melanoma cells being tethered to endothelium and retained in lungs. Thus, transendothelial migration and lung metastasis development decreased by ∼50%, showing that targeting IL-8 in melanoma cells has the potential to decrease metastasis development by disrupting interaction with neutrophils.

B-Raf is the most mutated gene in melanoma; however, the mechanism through which it promotes early melanomas remains uncertain. Most nevi contain activated V600E B-Raf but few develop into melanoma, and expression in melanocytes is inhibitory with low protein levels present in surviving cells, suggesting unknown cooperative oncogenic events are necessary for melanoma development. Because many melanomas have V600E

Malignant melanoma is the most invasive and deadly form of skin

Paradigm-shifting modalities to more efficiently deliver drugs to cancerous lesions require the following attributes: nanoscale-size, targetability and stability under physiological conditions. Often, these nanoscale drug delivery vehicles are limited due to agglomeration, poor solubility or cytotoxicity. Thus, we have designed a methodology to encapsulate hydrophobic antineoplastic chemotherapeutics within a 20-30 nm diameter, pH-responsive, non-agglomerating, non-toxic calcium phosphate nanoparticle matrix. In the present study, we report on calcium phosphate nanocomposite particles (CPNP) that encapsulate both fluorophores and chemotherapeutics, are colloidally stable in physiological solution for extended time at 37°C and can efficaciously deliver hydrophobic antineoplastic agents, such as ceramide, in several cell model systems.

In vitro tumor cell culture models have illuminated the potential therapeutic utility of elevating the intracellular concentration of the antimitogenic and proapoptotic sphingolipid, ceramide. However, although cell-permeable, short-chain ceramide is an effective apoptotic agent in vitro, its use as an in vivo, systemically delivered therapeutic is limited by its inherent lipid hydrophobicity and physicochemical properties. Here, we report that the systemic i.v. delivery of C 6 -ceramide (C 6 ) in a pegylated liposomal formulation significantly limited the growth of solid tumors in a syngeneic BALB/c mouse tumor model of breast adenocarcinoma. Over a 3-week treatment period, a well-tolerated dose of 36 mg/kg liposomal-C 6 elicited a >6-fold reduction in tumor size compared with empty ghost liposomes. Histologic analyses of solid tumors from liposomal-C 6 -treated mice showed a marked increase in the presence of apoptotic cells, with a coincident decrease in cellular proliferation and in the development of a microvessel network. Liposomal-C 6 accumulated within caveolae and mitochondria, suggesting putative mechanisms by which ceramide induces selective cancer cell cytotoxicity. A pharmacokinetic analysis of systemic liposomal-C 6 delivery showed that the pegylated liposomal formulation follows first-order kinetics in the blood and achieves a steady-state concentration in tumor tissue. Confirming the therapeutic utility of i.v. liposomal-C 6 administration, we also shown diminution of solid tumor growth in a human xenograft model of breast cancer. Together, these results indicate that bioactive ceramide analogues can be incorporated into pegylated liposomal vehicles for improved solubility, drug delivery, and antineoplastic efficacy.Sphingolipids not only serve a structural role in membranes but also are substrates for the generation of bioactive second messengers that influence mitogenesis and apoptosis. Metabolism of sphingomyelin, the major sphingolipid in membranes, forms ceramide, a potent lipid-derived second messenger that modulates the induction of cell differentiation, cell cycle arrest, and/or apoptosis (1 -4). In addition, chemotherapeutic agents (5 -7) and ionizing radiation (8, 9) are two of the multiple cellular stressors (10 -16) that lead to the accumulation of ceramide within membranes. We and others have shown that ceramide-mediated signaling cascades induce apoptosis in part via the inhibition of Akt prosurvival pathways, mitochondrial dysfunction, and the stimulation of caspase activity, which ultimately leads to DNA fragmentation and cell death (17 -21).Although short-chain, cell-permeable ceramides, such as C 6 -ceramide (C 6 ), have been shown to be antiproliferative and proapoptotic in numerous cancer cell types in vitro (22, 23), there are obstacles to the delivery of ceramide for systemic applications, such as cancer chemotherapy. Despite being more efficacious than physiologic long-chain ceramides (C 18 -C 24 -ceramide), the effectiveness of cell-permeable ceramide analogues re...

Most events promoting early melanoma development are yet to be identified but deregulation of the B-Raf and Akt3 signaling cascades are important regulators 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 10X higher enzyme activity and constitutive activation of the MAP 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 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 4-cymbal transducer array enables penetration of nanoliposomal-siRNA complex throughout 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 to 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.