The ribonucleoside analog ribavirin (1-beta-D-ribofuranosyl-1,2, 4-triazole-3-carboxamide) shows antiviral activity against a variety of RNA viruses and is used in combination with interferon-alpha to treat hepatitis C virus infection. Here we show in vitro use of ribavirin triphosphate by a model viral RNA polymerase, poliovirus 3Dpol. Ribavirin incorporation is mutagenic, as it templates incorporation of cytidine and uridine with equal efficiency. Ribavirin reduces infectious poliovirus production to as little as 0. 00001% in cell culture. The antiviral activity of ribavirin correlates directly with its mutagenic activity. These data indicate that ribavirin forces the virus into 'error catastrophe'. Thus, mutagenic ribonucleosides may represent an important class of anti-RNA virus agents.

Innate immune responses to pathogens critically impact the development of adaptive immune responses. However, it is not completely understood how innate immunity controls the initiation of adaptive immunities or how it determines which type of adaptive immunity will be induced to eliminate a given pathogen. Here we show that viral stimulation not only triggers natural interferon (IFN)-α/β–producing cells (IPCs) to produce vast amounts of antiviral IFN-α/β but also induces these cells to differentiate into dendritic cells (DCs). IFN-α/β and tumor necrosis factor α produced by virus-activated IPCs act as autocrine survival and DC differentiation factors, respectively. The virus-induced DCs stimulate naive CD4+ T cells to produce IFN-γ and interleukin (IL)-10, in contrast to IL-3–induced DCs, which stimulate naive CD4+ T cells to produce T helper type 2 cytokines IL-4, IL-5, and IL-10. Thus, IPCs may play two master roles in antiviral immune responses: directly inhibiting viral replication by producing large amounts of IFN-α/β, and subsequently triggering adaptive T cell–mediated immunity by differentiating into DCs. IPCs constitute a critical link between innate and adaptive immunity.

No abstract

Drugs that target DNA topoisomerase II (Top2), including etoposide (VP-16), doxorubicin, and mitoxantrone, are among the most effective anticancer drugs in clinical use. However, Top2-based chemotherapy has been associated with higher incidences of secondary malignancies, notably the development of acute myeloid leukemia in VP-16-treated patients. This association is suggestive of a link between carcinogenesis and Top2-mediated DNA damage. We show here that VP-16-induced carcinogenesis involves mainly the ␤ rather than the ␣ isozyme of Top2. In a mouse skin carcinogenesis model, the incidence of VP-16-induced melanomas in the skin of 7,12-dimethylbenz[a]anthracene-treated mice is found to be significantly higher in TOP2␤ ؉ than in skin-specific top2␤-knockout mice. Furthermore, VP-16-induced DNA sequence rearrangements and double-strand breaks (DSBs) are found to be Top2␤-dependent and preventable by cotreatment with a proteasome inhibitor, suggesting the importance of proteasomal degradation of the Top2␤-DNA cleavage complexes in VP-16-induced DNA sequence rearrangements. VP-16 cytotoxicity in transformed cells expressing both Top2 isozymes is, however, found to be primarily Top2␣-dependent. These results point to the importance of developing Top2␣-specific anticancer drugs for effective chemotherapy without the development of treatment-related secondary malignancies.DNA rearrangements ͉ melanoma ͉ skin-specific topoisomerase II␤-knockout ͉ tumor cell killing ͉ carcinogenesis A nticancer drugs that target DNA topoisomerase II (Top2), including etoposide (VP-16), doxorubicin, and mitoxantrone, are often referred to as Top2 poisons and are among the most effective and widely used anticancer drugs in the clinic. However, life-threatening toxic side effects, including drug-induced secondary malignancies, have been noted in patients receiving Top2-based chemotherapy. An association between infant leukemia and in utero exposure to Top2 poisons has also been reported (reviewed in refs. 1-3). In all cases, the molecular basis underlying carcinogenesis in Top2-based chemotherapy is unclear.Clinical evidence for a direct link between VP-16 treatment and treatment-related acute myeloid leukemia (t-AML) is particularly strong (1-3). VP-16-induced t-AML is frequently associated with balanced translocations between the mixed lineage leukemia (MLL) gene on chromosome 11q23 and Ͼ50 partner genes (the MLL gene is also known as ALL-1, hTRX, or HRX) (4-7). These rearrangements, as well as those found in infant leukemia, cluster within a well characterized 8.3-kb breakpoint cluster region (bcr) (8-16). The bcr of MLL is AT-rich and contains Alu sequences, putative recognition sites of Top2-mediated DNA cleavage, and chromosome scaffold/matrix attachment regions (SAR/MAR) (5,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). There is substantial evidence that chromosome 11q23 translocations in t-AML and infant leukemia are a consequence of drug-induced formation of double-strand breaks (DSBs) (6-9). VP-16 is known to induce DSBs by the format...

No abstract