Jonas A. Nilsson

Exosomes, the endogenous nanocarriers that can deliver biological information between cells, were recently introduced as new kind of drug delivery system. However, mammalian cells release relatively low quantities of exosomes, and purification of exosomes is difficult. Here, we developed bioinspired exosome-mimetic nanovesicles that deliver chemotherapeutics to the tumor tissue after systemic administration. The chemotherapeutics-loaded nanovesicles were produced by the breakdown of monocytes or macrophages using a serial extrusion through filters with diminishing pore sizes (10, 5, and 1 μm). These cell-derived nanovesicles have similar characteristics with the exosomes but have 100-fold higher production yield. Furthermore, the nanovesicles have natural targeting ability of cells by maintaining the topology of plasma membrane proteins. In vitro, chemotherapeutic drug-loaded nanovesicles induced TNF-α-stimulated endothelial cell death in a dose-dependent manner. In vivo, experiments in mice showed that the chemotherapeutic drug-loaded nanovesicles traffic to tumor tissue and reduce tumor growth without the adverse effects observed with equipotent free drug. Furthermore, compared with doxorubicin-loaded exosomes, doxorubicin-loaded nanovesicles showed similar in vivo antitumor activity. However, doxorubicin-loaded liposomes that did not carry targeting proteins were inefficient in reducing tumor growth. Importantly, removal of the plasma membrane proteins by trypsinization eliminated the therapeutic effects of the nanovesicles both in vitro and in vivo. Taken together, these studies suggest that the bioengineered nanovesicles can serve as novel exosome-mimetics to effectively deliver chemotherapeutics to treat malignant tumors.

Antioxidants are widely used to protect cells from damage induced by reactive oxygen species (ROS). The concept that antioxidants can help fight cancer is deeply rooted in the general population, promoted by the food supplement industry, and supported by some scientific studies. However, clinical trials have reported inconsistent results. We show that supplementing the diet with the antioxidants N-acetylcysteine (NAC) and vitamin E markedly increases tumor progression and reduces survival in mouse models of B-RAF- and K-RAS-induced lung cancer. RNA sequencing revealed that NAC and vitamin E, which are structurally unrelated, produce highly coordinated changes in tumor transcriptome profiles, dominated by reduced expression of endogenous antioxidant genes. NAC and vitamin E increase tumor cell proliferation by reducing ROS, DNA damage, and p53 expression in mouse and human lung tumor cells. Inactivation of p53 increases tumor growth to a similar degree as antioxidants and abolishes the antioxidant effect. Thus, antioxidants accelerate tumor growth by disrupting the ROS-p53 axis. Because somatic mutations in p53 occur late in tumor progression, antioxidants may accelerate the growth of early tumors or precancerous lesions in high-risk populations such as smokers and patients with chronic obstructive pulmonary disease who receive NAC to relieve mucus production.

Antioxidants in the diet and supplements are widely used to protect against cancer, but clinical trials with antioxidants do not support this concept. Some trials show that antioxidants actually increase cancer risk and a study in mice showed that antioxidants accelerate the progression of primary lung tumors. However, little is known about the impact of antioxidant supplementation on the progression of other types of cancer, including malignant melanoma. We show that administration of N-acetylcysteine (NAC) increases lymph node metastases in an endogenous mouse model of malignant melanoma but has no impact on the number and size of primary tumors. Similarly, NAC and the soluble vitamin E analog Trolox markedly increased the migration and invasive properties of human malignant melanoma cells but did not affect their proliferation. Both antioxidants increased the ratio between reduced and oxidized glutathione in melanoma cells and in lymph node metastases, and the increased migration depended on new glutathione synthesis. Furthermore, both NAC and Trolox increased the activation of the small guanosine triphosphatase (GTPase) RHOA, and blocking downstream RHOA signaling abolished antioxidant-induced migration. These results demonstrate that antioxidants and the glutathione system play a previously unappreciated role in malignant melanoma progression.

c-Myc promotes cell growth and transformation by ill-defined mechanisms. c-myc(-/-) mice die by embryonic day 10.5 (E10.5) with defects in growth and in cardiac and neural development. Here we report that the lethality of c-myc(-/-) embryos is also associated with profound defects in vasculogenesis and primitive erythropoiesis. Furthermore, c-myc(-/-) embryonic stem (ES) and yolk sac cells are compromised in their differentiative and growth potential. These defects are intrinsic to c-Myc, and are in part associated with a requirement for c-Myc for the expression of vascular endothelial growth factor (VEGF), as VEGF can partially rescue these defects. However, c-Myc is also required for the proper expression of other angiogenic factors in ES and yolk sac cells, including angiopoietin-2, and the angiogenic inhibitors thrombospondin-1 and angiopoietin-1. Finally, c-myc(-/-) ES cells are dramatically impaired in their ability to form tumors in immune-compromised mice, and the small tumors that sometimes develop are poorly vascularized. Therefore, c-Myc function is also necessary for the angiogenic switch that is indispensable for the progression and metastasis of tumors. These findings support the model wherein c-Myc promotes cell growth and transformation, as well as vascular and hematopoietic development, by functioning as a master regulator of angiogenic factors.