Clinical advances in therapies targeting the interleukin-2 receptor.
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Since the discovery of human immunodeficiency virus (HIV) as a pathogenic retrovirus linked to acquired immunodeficiency syndrome (AIDS), a number of potentially useful strategies for antiretroviral therapy of AIDS and its related diseases have emerged. One such strategy involves use of the broad family of 2',3'-dideoxynucleosides, to which 3'-azido-2',3'-dideoxythymidine (AZT) belongs. AZT has been shown to reduce the replication of HIV in vivo and to confer significant clinical benefits in patients in both early and advanced stages of infection. Other members of the family, 2',3'-dideoxycytidine (ddC), 2',3'-dideoxyinosine (ddI), and 2',3'-didehydro-2',3'-dideoxythymidine (d4T), have also been reported to be active against HIV in short-term clinical trials. The armamentarium of antiretroviral agents is rapidly growing. Various nonnucleoside agents have recently been identified to be active against HIV in vitro. HIV-1 protease inhibitors are notable as possible new therapies for HIV-1-related diseases. However, we have faced several new challenges in the antiretroviral therapy in AIDS. These include long-term drug-related toxicities; emergence of drug-resistant HIV variants; and development of various cancers, particularly as effective therapies prolong survival. Progress in understanding structure-activity relations and clinical effectiveness will continue with dideoxynucleoside analogs. However, it seems certain that a variety of nonnucleoside analogs affecting multiple steps in viral replication will become available before long, and combination therapies using multiple antiretroviral drugs will be available. Such therapies will exert major effects against the moribidity and mortality caused by HIV.
The mammalian cell cycle is exquisitely controlled by the cyclin-dependent kinases, which regulate cell cycle progression. Cell cycle transitions are, in turn, controlled by checkpoints that monitor the integrity and replication status of the genetic material before cells commit to either replicate or segregate their DNA. On activation, checkpoints interface with cyclin-Cdk complexes to block the cell cycle. Pharmacologic compounds that exploit our current knowledge of cell cycle and checkpoint pathway regulation offer insights into the development of novel therapeutic strategies.
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Topoisomerase II enzymes play an essential role in human DNA metabolism. They are also recognized as primary targets of a number of anti-cancer drugs used in the treatment of breast cancer, which remains a leading cause of cancer-related death in women. While topoisomerase inhibitors have produced significant response rates in this disease, their use has been limited both by toxicity and by the development of resistance. In this article we review the extensive work which has not only increased our understanding of the biochemistry and molecular biology of type II topoisomerases but also enabled more rational drug design. Such knowledge should translate into increased clinical efficacy in the treatment of breast cancer and other malignancies.
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A possible selective therapeutic approach to corneal graft rejection will aim at IL-2 receptor-bearing antigen-activated T-lymphocytes with monoclonal anti IL-2R antibodies. In a rat penetrating keratoplasty model (Lewis x Lewis-BN) comparing to controls (median, 8 days), a significant delay of the allograft reaction was achieved by applying a therapeutic dose (15 mg/kg bw) of cyclosporin A (median, 18 days; p < 0.01), an intraperitoneal (1.0 mg/kg bw) (median, 13.5 days; p < 0.05) or a subconjunctival injection of IL-2R mab (0.5 mg/kg bw ART-18) (median, 16 days; p < 0.01) with low-dose Cyclosporin A (1.5 mg/kg bw). In pharmacokinetic experiments, the corneal radioactivity 24 h after intraperitoneal injection of 125I-labeled ART-18 was < 1% (p < 0.01) of the values obtained by subconjunctival injection, whereas the serum radioactivity values (p > 0.05) were in the same range. The above results suggest that the onset of an allograft reaction in perforating keratoplasty seems to depend on the locally achievable antibody concentration and can be delayed with a high level of IL-2 R mab present in the immediate surrounding of the foreign antigen-expressing cells.
ART-18, a mouse antirat IL-2R mAb inhibits IL-2 binding and IL-2-dependent T cell growth. Although both (LEW x BN)F1 kidney and heart allografts survive ca. 3 weeks in ART-18-treated LEW rats (acute rejection occurs within 10 days, P less than 0.001), the host responses against the two organs vary. In the heart model, the splenic CD4:CD8 ratio as determined by FMF was similar both in untreated and treated animals, but decreased significantly in kidney recipients conditioned with ART-18. In both mAb-modulated animal groups, splenocytes inhibited test MLR and prolonged test cardiac allograft survival in a donor-specific fashion upon adoptive transfer, suggesting that ART-18 mediates "sparing" of Ts. However, both CD4+ and CD8+ cells from kidney-grafted hosts conferred suppression in vivo; only the CD8+ subset was effective in the heart model. Immunohistologically, IL-2R+ cells were absent in the heart grafts of treated hosts; a significant proportion of the kidney cell infiltrate remained IL-2R+ despite continuous mAb administration. Although ART-18 therapy prolonged renal graft survival significantly, function was poor and the rats remained uremic. However, when one of the native kidneys was retained and the rat continued to enjoy normal renal function, IL-2R+ cells were abolished from the graft infiltrate, as shown by FMF and immunohistology. Thus, ART-18 treatment influences host responses differentially against kidney and heart allografts (modulation and depletion of IL-2R+ cells, respectively) despite increasing their survival comparably. The uremic state in the kidney model prevents elimination of infiltrating IL-2R+ mononuclear cells by a mAb directed specifically against them.
The immunosuppressive effects of RIB-5/2, a nondepleting anti-rat CD4 monoclonal antibody (mAb), were analyzed in a well-defined model of accelerated cardiac allograft rejection. (LEW x BN)F1 hearts are rejected within 24 hours in LEW hosts presensitized with BN skin grafts at day -7. Treatment with RIB-5/2 mAb (3.5 mg/day i.v.) at days -7 and -1, prolonged cardiac allograft survival to the median of >62 days. The long-term recipients rejected acutely third-party (Wistar-Furth) test skin grafts, without an adverse effect on the survival of the original cardiac transplants. Lymphocytes harvested from mAb-treated hosts significantly decreased proliferative responses of donor cells in mixed leukocyte reaction. The cell activation and cytokine elaboration patterns were evaluated at the mRNA and protein levels by competitive template reverse transcriptase polymerase chain reaction and immunohistochemistry, respectively. Cardiac allografts in CD4 mAb-treated rats at 24 hours displayed reduced CD3, CD25, tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-2, interferon (IFN)-gamma, and IL-10 mRNA levels as compared to those in rejecting grafts. Equal amounts of IL-4 mRNA were detected throughout in both animal groups; the expression of IL-10 mRNA increased progressively in the treated hosts. In contrast, IFN-gamma was consistently depressed after mAb therapy. The mRNA levels coding for CD3, CD25, tumor necrosis factor-alpha, IL-1-beta, and IL-2 genes were comparable in long-surviving and rejecting allografts. The staining for IL-2R, IL-2, and IFN-gamma was diminished, whereas the staining for IL-4 was either unaffected or enhanced in well-functioning grafts in RIB-5/2 mAb-treated hosts. The untreated recipients elicited strong circulating IgM allo-Ab response, which peaked around the time of cardiac rejection and then switched to IgG allo-Ab 4-7 days after heart transplantation. Treatment with RIB-5/2 mAb decreased IgM and prevented the switch into the IgG allo-Ab response. In conclusion, the ability of RIB-5/2 mAb treatment to combat accelerated rejection and to produce long-term graft acceptance is unprecedented in our experience in this model. These data provide new insights into the complexities of the cellular and humoral responsiveness, contributing to the the induction of donor-specific unresponsiveness in sensitized hosts. This study, along with our previous reports, indicate that an immune deviation in which intragraft Th1-type cytokines (primarily IFN-gamma) are diminished and Th2-type cytokines (IL-4 and IL-10) are maintained represents the common effector mechanism of CD4 mAb regimens in recipients of vascularized organ allografts.
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