Time-limited Treatments Research Articles

Michellamine B, a novel plant alkaloid, inhibits human immunodeficiency virus-induced cell killing by at least two distinct mechanisms

Studies of the mechanism of action of michellamine B, a novel anti-human immunodeficiency virus (HIV) alkaloid from the tropical plant Ancistrocladus korupensis, have revealed that the compound acts at two distinct stages of the HIV life cycle. The compound had no direct effect on HIV virions and did not block the initial binding of HIV to target cells. Postinfection time course studies revealed that the agent partially inhibited HIV-induced cell killing and syncytium formation when added up to 48 h following acute infection; however, viral reproduction was fully inhibited only when the compound was added immediately after infection. Time-limited treatments of HIV-infected cells revealed that michellamine B had to be present continuously to provide maximum antiviral protection. HIV replication in cells in which infection was already fully established or in chronically infected cells was unaffected by michellamine B. Biochemical studies showed that michellamine B inhibited the enzymatic activities of reverse transcriptases (RTs) from both HIV type 1 and HIV type 2 as well as two different nonnucleoside drug-resistant RTs with specific amino acid substitutions. In addition, human DNA polymerases alpha and beta were inhibited by the alkaloid. Michellamine B exerted a potent dose-dependent inhibition of cell fusion in two independent cell-based fusion assays. Thus, michellamine B acts both at an early stage of the HIV life cycle by inhibiting RT as well as at later stages by inhibiting cellular fusion and syncytium formation.

Diarylsulfones, a new chemical class of nonnucleoside antiviral inhibitors of human immunodeficiency virus type 1 reverse transcriptase

A series of variously substituted diarylsulfones and related derivatives were found to prevent human immunodeficiency virus type 1 (HIV-1) replication and HIV-1-induced cell killing in vitro. One of the more potent derivatives, 2-nitrophenyl phenyl sulfone (NPPS), completely protected human CEM-SS lymphoblastoid cells from the cytopathic effects of HIV-1 in cell culture at 1 to 5 microM concentrations. HIV-1 replication, as assessed by the production of infectious virions, viral p24 antigen, and virion reverse transcriptase (RT), was inhibited by NPPS at similar concentrations. There was no evidence of direct cytotoxicity of the drug at concentrations below 100 microM. A variety of other CD4+ T-cell lines as well as cultures of peripheral blood leukocytes and monocytes were protected from HIV-1-induced cytopathicity and/or viral replication. NPPS also inhibited several distinctly different strains of HIV-1 but was ineffective against three strains of HIV-2. Biochemical studies revealed that NPPS inhibited HIV-1 RT but not HIV-2 RT. NPPS had no direct effect on HIV-1 virions, nor did it block the initial binding of HIV-1 to target cells. Time-limited treatments of cells with NPPS found that NPPS had to be present continuously in culture to provide maximum antiviral protection. In addition, HIV-1 replication in cells in which infection was already fully established or in chronically infected cells was also unaffected by NPPS. We conclude that NPPS acts in a reversible manner as a nonnucleoside HIV-1-specific RT inhibitor. Although markedly different in structure from a larger, structurally diverse group of known HIV-1-specific nonnucleoside RT inhibitors, NPPS shares several of the biological properties that characterize this emerging new pharmacologic class.

Oxathiin carboxanilide, a potent inhibitor of human immunodeficiency virus reproduction.

Oxathiin carboxanilide (OC), NSC 615985, a compound originally synthesized as a potential fungicide, was demonstrated to be highly active in preventing human immunodeficiency virus (HIV)-induced cell killing and in inhibiting HIV reproduction. Virus-infected CD4+ lymphocytes were completely protected by 0.5 microM OC, whereas no toxicity was observed at concentrations below 50 microM OC. Production of infectious virus, viral p24 antigen, and virion reverse transcriptase were reduced by OC at concentrations that prevented viral cell killing. A variety of CD4+ T-cell lines were protected by OC from HIV cytopathicity, and OC inhibited two distinct strains of HIV-1. However, HIV-2 infections were unaffected by OC. OC had no direct effect on virions of HIV or on the enzymatic activities of HIV reverse transcriptase or HIV protease. Time-limited treatments of cells with OC before, during, or after exposure of cells to virus failed to protect cells from the eventual cytopathic effects of HIV, and OC failed to inhibit the production of virus from cells in which infection was established or from chronically infected cells. We conclude that the highly active OC has a reversible effect on some early stage of HIV-1 reproduction and cytopathicity. Pilot in vivo experiments showed that circulating concentrations of OC exceeding 1 microM could be achieved and sustained in hamsters for at least a week with no remarkable toxicological sequelae. OC represents a new class of anti-HIV agents that are promising candidates for drug development.

Conceptualizing Short-Term Treatment

Short-term and time-limited treatments have recently received increased interest in the counseling literature. Nevertheless, a great deal of ambiguity exists regarding the structure and substance of these treatments. A classification system is proposed that descriptively orders different types of brief treatments. This system is used to compare and contrast conceptually planned models of short-term therapy. Research and practice implications for counseling psychologists are discussed.