The roles played by cholesterol in cancer development and the potential of therapeutically targeting cholesterol homeostasis is a controversial area in the cancer community. Several epidemiologic studies report an association between cancer and serum cholesterol levels or statin use, while others suggest that there is not one. Furthermore, the Cancer Genome Atlas (TCGA) project using next-generation sequencing has profiled the mutational status and expression levels of all the genes in diverse cancers, including those involved in cholesterol metabolism, providing correlative support for a role of the cholesterol pathway in cancer development. Finally, preclinical studies tend to more consistently support the role of cholesterol in cancer, with several demonstrating that cholesterol homeostasis genes can modulate development. Because of space limitations, this review provides selected examples of the epidemiologic, TCGA, and preclinical data, focusing on alterations in cholesterol homeostasis and its consequent effect on patient survival. In melanoma, this focused analysis demonstrated that enhanced expression of cholesterol synthesis genes was associated with decreased patient survival. Collectively, the studies in melanoma and other cancer types suggested a potential role of disrupted cholesterol homeostasis in cancer development but additional studies are needed to link population-based epidemiological data, the TCGA database results, and preclinical mechanistic evidence to concretely resolve this controversy. Cancer Res; 76(8); 2063–70. ©2016 AACR.

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 protein promotes cell survival and tumor development in 43 to 60% of nonfamilial melanomas. The predominant Akt isoform active in melanomas was identified by showing that small interfering RNA (siRNA) against only Akt3, and not Akt1 or Akt2, lowered the amount of phosphorylated (active) Akt in melanoma cells. The amount of active Akt3 increased progressively during melanoma tumor progression with highest levels present in advanced-stage metastatic melanomas. Mechanisms of Akt3 deregulation occurred through a combination of overexpression of Akt3 accompanying copy number increases of the gene and decreased PTEN protein function occurring through loss or haploinsufficiency of the PTEN gene. Targeted reduction of Akt3 activity with siRNA or by expressing active PTEN protein stimulated apoptotic signaling, which reduced cell survival by increasing apoptosis rates thereby inhibiting melanoma tumor development. Identifying Akt3 as a selective target in melanoma cells provides new therapeutic opportunities for patients in the advanced stages of this disease.

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 β₂ integrin expression by 75% to 100%. Intercellular adhesion molecule-1 on melanoma cells and β₂ integrin on neutrophils interacted, promoting anchoring to vascular endothelium. Decreasing IL-8 secretion from melanoma cells lowered extracellular levels by 20% to 50%, decreased β₂ 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. Cancer Res; 70(14); 6071–82. ©2010 AACR.

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 ^V599EB-Raf 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 ^V599EB-Raf in melanoma tumors. This inhibition led to reduced activity of the mitogen-activated protein kinase–signaling cascade and inhibited tumor development in animals. Targeted reduction of mutant ^V599EB-Raf expression (activity) in melanoma cells before tumor formation inhibited tumorigenesis by reducing the growth potential of melanoma cells. In contrast, reduction of mutant ^V599EB-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 ^V599EB-RAF promotes melanoma development and show the effectiveness of targeting this protein to inhibit melanoma tumor growth.

Introduction: The biggest challenge faced by the scientific community involved in drug development is to deliver safe and effective dosage of drugs without causing systemic toxicity. Therefore, nov...