**8. References**

658 Non-Viral Gene Therapy

presumably, the observed features are related to structural rearrangements and to eventual rupture of vesicle-*NP* adducts with time. In one case, apparently, the sedimentation of adducts takes place after some time. In others, large floating objects are present in the

Depending on the forces active between vesicles and *LYS-NPs*, it is possible that the kinetics of adducts formation follows different pathways. In the case of *SDS*-*CTAB* cat-anionic vesicles (bearing a substantial negative charge), the interaction mechanism obeys a pseudo first-order mechanism, controlled by the number ratio between the components. In the interaction between *DDAB* vesicles and *LYS-NPs*, conversely, the situation is more cumbersome to be rationalized. In this latter case, it is presumed that the interaction mechanism implies the formation of a transient state (characterized by a maximum in *DLS*  plots); after some time the mixed colloid particles rearrange and change in size and shape. It is also possible that the large increase in size observed in this system is due to the incipient

Some questions are still under debate on the biological implications of the above systems. However, when *LYS-ABOP* particles interact with cells, it is expected that the reactive behavior (mostly the one relative to surface adsorption) will be close to that reported in case of cat-anionic surfactant mixtures. In fact, cells are negatively charged and are generally composed by mixtures of oppositely charged lipids. On this regard, thus, catanionic systems are much more effective as bio-mimetic models compared to other currently used lipid dispersions. It must be also considered that the mechanisms controlling the pynocytosis of particles adsorbed onto cells require the deformation of the latter. In fact, vesicles made by different lipids are more prone to be deformed and envaginate (25), as a consequence of local changes in composition associated to adsorption of charged and bulky entities onto them. This implies the migration of the lipid components in the bi-layer and induces a local deformation of vesicles, making possible particles uptake into cells. More dedicated investigation is required to clarify such

Another relevant question deals with use of the above systems in modeling bio-mimetic processes. In nature there are cases of interactions between "*hard*" and "*soft*" particles, as, for instance, in the interactions between viruses and other viral vectors and cells (26,27). From such a point of view, the ones presented here are excellent mimetic models of the above interactions, because viruses are generally covered with enzymes attaching onto the surface of cells and tissues. Preparing nano-particles sharing some properties in common to viruses (having, for instance, a similar surface coverage) would help understanding the physical

This work was made possible through a financial support from La Sapienza University. F.D.P. wishes to acknowledge the Ministry of Education for financing her stay in Barcelona,

Financial support from MICIN CTQ2010-14897, Generalitat de Catalunya, through the 2009SGR1331 grant and COST Action Project on Chemistry at Interfaces, D36, are gratefully

Thanks to A. Scipioni, Dept. of Chemistry at La Sapienza, for help in performing *CD* spectra, and for fruitful discussions on some aspects of the manuscript. Thanks also to G. Risuleo,

nucleation of particles, which precipitate after some time.

grounds underlying the interactions between viruses and cells.

where she completed the characterization of the above mixtures.

dispersing medium.

aspects.

**7. Acknowledgments** 

acknowledged.


**28** 

*Italy* 

*University of Milano* 

**Targeting TRAIL Receptors with Genetically-Engineered CD34+ Hematopoietic Stem Cells** 

Dysregulated apoptosis plays a key role in the pathogenesis and progression of neoplastic disorders, allowing tumor cells to survive beyond their normal life-span, and to eventually acquire chemo-radioresistance (Laconi et al., 2000; Pommier et al., 2004). Thus, targeting either the intrinsic or the extrinsic pathways of apoptosis represent attractive therapeutic strategies for restoring apoptosis sensitivity of malignant cells, or activating agonists of apoptosis (Waxman & Schwartz, 2003). Due to the ability of death receptor ligands to induce cell death, there has been considerable interest in the physiological roles and therapeutic potential of these cytokines as anti-cancer agents. Death receptor ligands of the tumor necrosis factor α (TNFα) superfamily are type II transmembrane proteins that signal to target cells upon cell-cell contact, or after protease-mediated release to the extracellular space (Ashkenazi, 2002). Members of this family, including Fas ligand (FasL), TNFα, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), stand out because of their

Unlike other apoptosis-inducing TNF family members, soluble TRAIL appears to be inactive against normal healthy tissue (Ashkenazi et al., 1999; Lawrence et al., 2001). A variety of preclinical data clearly show that soluble TRAIL is a cancer cell-specific molecule exerting a remarkable antitumor activity both in vitro (Ashkenazi et al., 1999; Gazitt, 1999; Jin et al., 2004; Mitsiades et al., 2001; Pollack et al., 2001; Rieger et al., 1998) as well as in vivo in athymic nude mice or in non-obese diabetic/severe combined immunodeficient (NOD-

The physiological functions of TRAIL are not yet fully understood, but mouse gene knockout studies indicate that this agent has an important role in antitumor surveillance by immune cells, mediates thymocyte apoptosis, and is important in the induction of autoimmune diseases

TRAIL signals by interacting with its receptors. So far, five receptors have been identified, including the two agonistic receptors TRAIL-R1 (Pan et al., 1997b) and TRAIL-R2 (Walczak et al., 1997), and the three antagonistic receptors (Sheridan et al., 1997) TRAIL-R3 (Pan et al.,

ability to induce cell death (Wajant, 2003; Wiley et al., 1995).

SCID) mice (Ashkenazi et al., 1999; Daniel et al., 2007; Kelley et al., 2001).

(Cretney et al., 2002; Lamhamedi-Cherradi et al., 2003; Smyth et al., 2003).

**1. Introduction** 

**2. Soluble TRAIL** 

Carmelo Carlo-Stella, Arianna Giacomini, Silvia L. Locatelli,

*Medical Oncology, Fondazione IRCCS Istituto Nazionale Tumori and* 

Cristiana Lavazza and Alessandro M. Gianni

[27] X. Huang; L.M. Bronstein; J. Retrum; C. Dufort; I. Tsvetkova; S. Aniagyei; B. Stein; G. Stucky; M. McKenna; N. Remmes; D. Baxter; C.C. Kao; B. Dragnea, *Nano Lett.*, 2007, *7*, 2407.
