Nailing down another HIV target

Enfuvirtide: a fusion inhibitor for the treatment of HIV infection

BACKGROUND

Drug resistance continues to be a major challenge in the treatment of HIV-1 infection. Virtually all currently available antiretroviral medications inhibit the viral reverse transcriptase or protease. Enfuvirtide is the first fusion inhibitor approved by the US Food and Drug Administration for use in combination with other antiretroviral agents for the treatment of HIV-1 infection in treatment-experienced patients.

OBJECTIVE

This paper describes the pharmacologic properties and clinical usefulness of enfuvirtide.

METHODS

Relevant information was identified through searches of MEDLINE (1990 to October 2003), International Pharmaceutical Abstracts (1970 to October 2003), and meeting abstracts of major HIV/AIDS conferences (1996-2003) using the search terms enfuvirtide, pentafuside, T-20, DP-178, and fusion inhibitor.

RESULTS

In vitro, enfuvirtide exhibits activity against HIV-1 isolates that are resistant to all other classes of anti-retroviral medications. Enfuvirtide blocks the entry of HIV-1 into host cells by interfering with virus-cell fusion, making it unique among licensed antiretroviral medications. In human adults, enfuvirtide has a volume of distribution of 5.48 L, is highly bound to plasma protein (92%), has a plasma elimination half-life of 3.8 hours, and is catabolized by peptidases and proteinases in various tissues. Dose adjustment does not appear necessary on the basis of age, race, or body weight, but may be warranted in women weighing <50 kg. A literature review did not identify any data on the disposition of enfuvirtide in patients with hepatic or renal insufficiency. Clinical trials suggest that enfuvirtide reduces plasma HIV-1 RNA levels in highly treatment-experienced patients taking an optimized antiretroviral regimen. Pivotal trials indicated a mean change in HIV-1 RNA of -1.48 log(10) copies/mL in the enfuvirtide arm at week 48, compared with -0.63 log(10) copy/mL in the control arm ( P<0.001 ). The mean absolute increase on CD4 cell count was 46 cells/mm(3) (91 cells/mm(3)) in the enfuvirtide arm vs 45 cells/mm(3) in the control arm; P<0.001 ). The most commonly reported (>15 cases per 100 patient-years of exposure) adverse events (AEs) in clinical trials included injection-site reactions, diarrhea, nausea, fatigue, insomnia, peripheral neuropathy, headache, vomiting, and fever. The most commonly reported (> or =2%) laboratory abnormalities (grade III or IV) were eosinophilia, anemia, and increases in amylase, lipase, triglycerides, creatine phosphokinase, alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase. In clinical trials, serious AEs leading to study discontinuation occurred in 12.9% ( 114/885 ) of patients in the enfuvirtide arm, compared with 10.7% ( 12/112 ) in the control arm ( P = NS ). The recommended dosage of enfuvirtide is 90 mg SC BID in adults and 2 mg/kg SC BID in children. Efficacy studies in children are ongoing.

CONCLUSION

Although additional studies are needed, enfuvirtide appears to be a promising agent, in combination with other antiretroviral agents, for the treatment of HIV infection in treatment-experienced patients.

Enfuvirtide (T-20): a novel human immunodeficiency virus type 1 fusion inhibitor

The development of highly active antiretroviral therapy has improved life expectancy and reduced progression to acquired immunodeficiency syndrome in human immunodeficiency virus (HIV)-infected patients. However, resistance to currently available classes of antiretroviral drugs has become a problem, limiting the options for patients with advanced disease who have been heavily treated. Enfuvirtide (T-20; ENF), a synthetic peptide, is the first of a new class of antiretrovirals that block entry of virus into host cells. ENF interferes with conformational changes required for membrane fusion and injection of virus into the host cell. Optimal treatment of HIV infection will likely require combinations of drugs that target novel stages of HIV type 1 entry and replication.

Bcl-xL antisense oligonucleotides chemosensitize human glioblastoma cells

BACKGROUND

Resistance to chemotherapy in glioblastoma has been linked to the expression of antiapoptotic Bcl-2 family members including Bcl-xL.

METHODS

Bcl-xL expression was specifically reduced in M059K glioblastoma cells with antisense oligonucleotides (ISIS 16009, ISIS 16967) as assessed by Western blotting. Induction of apoptosis by treatment with antisense oligonucleotides in combination with paclitaxel in cell culture was monitored by WST-1 assays and flow cytometric analysis.

RESULTS

Antisense oligonucleotide-mediated reduction of Bcl-xL levels led to enhanced cytotoxicity in M059K cells when compared to the use of a mismatch control oligonucleotide (p < 0.001). A decreased threshold for the induction of apoptosis led to significantly enhanced cytotoxic responses to paclitaxel treatment in WST-1 assays (p < 0.001) and flow cytometric analyses.

CONCLUSION

Combination treatment using Bcl-xL antisense oligonucleotides and paclitaxel may qualify as a promising strategy to ultimately improve the clinical outcome of glioblastoma.

Immunohistochemically detectable bcl-2 expression in metastatic melanoma: association with survival and treatment response

OBJECTIVE

The antiapoptotic protein Bcl-2 is supposed to influence the treatment responsiveness of different malignancies. In the present study the prognostic and predictive significance of Bcl-2 expression for survival and response to an administered therapy was explored in patients with metastatic melanoma. Also, the correlation between Bcl-2 expression and proliferation activity of tumor cells was defined to examine the regulatory role of Bcl-2 in proliferation.

MATERIALS AND METHODS

Sixty metastatic melanomas obtained from patients treated with chemoimmunotherapy were examined by immunohistochemistry with anti-Bcl-2 and anti-Ki-67 (MIB-1) antibodies. Proliferation activity was expressed in percentages as MIB-1 index.

RESULTS

The presence of Bcl-2 immunoreactivity was associated with a significantly lower MIB-1 index (p = 0.016), and a longer disease-free survival (p = 0.004). The lack of Bcl-2 expression was related to a higher response rate to therapy in comparison to a diffuse and focal pattern of Bcl-2 expression (p = 0.017). Although the presence of Bcl-2 immunoreactivity as such did not correlate with survival after the initiation of chemoimmunotherapy, the focal Bcl-2 expression pattern was strongly associated with a worse prognosis compared to a diffuse expression or a lack of Bcl-2 staining (p < 0.0001).

CONCLUSIONS

Our results support the role of Bcl-2 in the regulation of cell proliferation and suggest that an increase of metastatic potential and progression of malignant melanoma is associated with a loss of Bcl-2 expression. The lack of Bcl-2 expression could be a predictor of the response to chemoimmunotherapy, whereas the Bcl-2 expression pattern, possibly indicating the heterogeneity of the tumors, might be a potential prognostic factor for survival after the initiation of therapy.

Syncytium formation amplifies apoptotic signals: a new view on apoptosis in HIV infection in vitro

Infection of CD4+ cells with HIV in vitro causes extensive cytopathology. The mechanism that underlies this process is unclear and conflicting data exist regarding whether cytotoxicity is due to necrosis or apoptosis. It was previously reported and is shown here that the coculture of HIV glycoprotein-expressing cells with CD4+ cells results in apoptosis within several hours. This study demonstrates that apoptosis did not occur in single cells and was mediated neither by CD4 nor by coreceptor signaling, indicating that apoptosis was not induced by intra- or intercellular glycoprotein-receptor interaction. Detection of apoptosis required cell-to-cell fusion and undetectable levels of apoptotic cell death were substantially amplified upon syncytium formation. Similar results were obtained with syncytium-forming cultures of measles virus glycoprotein-expressing cells. These findings indicate that the apoptotic cell death observed in cultures of HIV and other syncytium-forming viruses is primarily due to amplification of background apoptosis in the wake of cell-to-cell fusion.