Purpose: Subnanogram doses of NGR-tumor necrosis factor (TNF), a TNF-α derivative able to target tumor neovessels, can enhance the antitumor activity of doxorubicin and melphalan in murine models. We have examined the antitumor activity of NGR-TNF in combination with various chemotherapeutic drugs acting via different mechanisms, including, besides doxorubicin and melphalan, cisplatin, paclitaxel, and gemcitabine. Experimental Design: Chemotherapeutic drugs were tested alone and in combination with NGR-TNF (0.1 ng) in murine lymphoma, fibrosarcoma, and mammary adenocarcinoma models. Different administration schedules have been tested and the effects on tumor growth, animal weight, tumor perfusion, and cell cytotoxicity have been investigated. Results: Pretreatment with NGR-TNF enhanced the response to all these drugs although to a different extent. The increased efficacy was not accompanied by increased toxicity at least as judged from the loss of animal weight. The synergistic effect was transient, maximal synergism being observed with a 2-hour delay between NGR-TNF and drug administrations in all models and with all drugs tested. NGR-TNF did not increase the in vitro cytotoxicity of chemotherapeutic drugs against tumor cells, suggesting that the in vivo synergism depends on NGR-TNF effects on host cells rather than on tumor cells. Conclusions: Targeted delivery of low doses of NGR-TNF to the tumor vasculature can increase the efficacy of various drugs acting via different mechanisms. Optimal administration schedule requires 2 hours of pretreatment with NGR-TNF independently from the mechanism of drug cytotoxicity. This work could provide important information for designing clinical studies with NGR-TNF in combination with chemotherapeutic drugs.

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In allogeneic hematopoietic cell transplantation (allo-HCT), the immune recognition of host antigens by donor T lymphocytes leads to a beneficial graft-versus-leukemia (GvL) effect as well as to life-threatening graft-versus-host disease (GvHD). Genetic modification of T lymphocytes with a retroviral vector (RV) expressing the herpes simplex virus-thymidine kinase (TK) suicide gene confers selective sensitivity to the prodrug ganciclovir (GCV). In patients, the infusion of TK ؉ lymphocytes and the subsequent administration of GCV resulted in a time-wise modulation of antihost reactivity for a GvL effect, while controlling GvHD. Because activation required for genetic modification with RV may reduce antihost reactivity, we investigated the requirements for maximizing the potency of human TK ؉ lymphocytes. Whereas T-cell receptor triggering alone led to effector memory (EM)TK IntroductionAllogeneic hematopoietic cell transplantation (allo-HCT) is the curative option for many hematologic malignancies. Moreover, it is being investigated to treat solid tumors. In allo-HCT, the recognition of host antigens by donor T lymphocytes evokes a graft-versusleukemia (GvL) effect. 1 This is associated with the risk of graft-versus-host disease (GvHD). T-cell depletion prevents GvHD but increases the probability of leukemia relapse. Suicide gene therapy offers a pragmatic solution to the "T-cell dilemma" of allo-HCT. 2 A suicide gene codifies for a protein able to convert, at a cellular level, a nontoxic prodrug into a toxic product. Suicide gene modification of donor lymphocytes aims at exploiting allo-HCT for a GvL effect, while providing a selective "switch" to GvHD. 3 The thymidine kinase of herpes simplex virus (TK) is a cell cycledependent suicide gene, that is, it catalyzes the generation of triphosphate ganciclovir (GCV), which is toxic to proliferating cells. 4 In HLA-identical allo-HCT, delayed infusions of TK ϩ lymphocytes were effective against relapsing leukemia, lymphoma, multiple myeloma, and Epstein-Barr virus (EBV)-related lymphoproliferative disorders. 5 When administered at the time of transplantation, TK ϩ lymphocytes facilitated the engraftment of hematopoietic cells. 6,7 In patients developing GvHD, GCV administration eliminated circulating TK ϩ cells and controlled the disease. [5][6][7] Despite these encouraging results, dissemination of the TK technology has been limited by the difficulty in defining optimal conditions for cell manipulation. Current protocols for genetic modification of T lymphocytes with retroviral vectors (RVs) may reduce antigen responsiveness in vitro 8 and antihost reactivity in vivo. 9,10 Given the strict clinical association between GvL and GvHD, it may be postulated that the therapeutic efficacy of TK ϩ lymphocytes will be improved by protocols designed to maximize antihost reactivity in vivo.Genetic modification of T lymphocytes with RVs relies on cell proliferation and leads to a memory phenotype. 11,12 Different models have been proposed to describe mature T-cell differentia...

Interest has been increasingly focused on all-trans-retinoic acid (tRA) and 13-cis-retinoic acid (13cRA) in cancer chemoprevention and treatment. We have examined the in vitro effects of these 2 retinoic acids (

Computer simulations of simple exact lattice models are an aid in the study of protein folding process; they have sometimes resulted in predictions experimentally proved. The contact interactions (CI) method is here proposed as a new algorithm for the conformational search in the low-energy regions of protein chains modeled as copolymers of hydrophobic and polar monomers configured as self-avoiding walks on square or cubic lattices. It may be regarded as an extension of the standard Monte Carlo method improved by the concept of cooperativity deriving from nonlocal contact interactions. A major difference with respect to other algorithms is that criteria for the acceptance of new conformations generated during the simulations are not based on the energy of the entire molecule, but cooling factors associated with each residue define regions of the model protein with higher or lower mobility. Nine sequences of length ranging from 20 to 64 residues were used on the square lattice and 15 sequences of length ranging from 46 to 136 residues were used on the cubic lattice. The CI algorithm proved very efficient both in two and three dimensions, and allowed us to localize energy minima not localized by other searching algorithms described in the literature. Use of this algorithm is not limited to the conformational search, because it allows the exploration of thermodynamic and kinetic behavior of model protein chains.Keywords: conformational search algorithm; hydrophobic interactions; lattice models; protein foldingThe determination of the folding pathway followed by a protein in the conformational space from the denaturated to the native structure is still an unsolved problem. Its difficulty is mainly due to the enormous extension of the conformational space and to its exponential growth when the length of the protein chain increases. How a protein solves the Levinthal paradox (Levinthal, 1968), i.e., how it folds to its native structure without an exhaustive search in the conformational space, has been largely debated in literature (for some recent papers, see for example, Fiebig Abkevich et al., 1994a;Covell, 1994;Dill et al., 1995). The nature of the driving forces inducing the collapse to more compact structures has been discussed and the importance of cooperativity in protein folding evidenced .Models of globular proteins have been used to get a better and better understanding of these phenomena, from the very simple 2D square lattice or 3D cubic lattice to off-lattice, all-heavy-. Reprint requests to: Lucio Toma, Dipartimento di Chimica Organica, Universita di Pavia, Via Taramelli 10, 27100 Pavia, Italy; e-mail: burdisso@ipv85.unipv.it. atoms, or all-atoms models (Hunt et al., 1994; Sali et ai., 1994;Yee et al., 1994; Dill et al., 1995 and references therein cited; Gutin et al., 1995a Gutin et al., , 1995b. With the aid of a cubic lattice model, Dill et al. (1993) demonstrated the importance of nonlocal contact interactions and formulated the hydrophobic zipper hypothesis. This hypothesis derives from t...