The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
Nelfinavir mesylate is a protease inhibitor that is used in the treatment of human immunodeficiency virus. NFV has been shown to have good efficacy in HIV-infected patients, with decreased HIV viral load and increased CD4+ T cell counts resulting following treatment (Bardsley-Elliot and Plosker, 2000). Because HIV can infect cells of the immune system such as CD4+ T cells, it is important to establish if drugs designed to treat the infection can impact the various functions of the immune system. While other HIV drugs, such as zidovudine, have been well-studied for potential immunomodulatory effects, those drugs of the protease inhibitor class, including NFV and saquinavir, have not been thoroughly evaluated. An immunotoxicity evaluation of NFV in Sprague Dawley rats following one or six months of exposure has been reported (Burns-Naas et al., 2005). In that study, splenocyte phenotyping, spleen cell proliferation, and natural killer cell activity were evaluated, and no overall treatment-related effects were observed.
The National Toxiclogy Program requested that range-finding studies be conducted to establish the effects of NFV on the various components of the immune system. These studies were conducted in female B6C3F1/N mice. Animals were treated with the vehicle control or NFV daily for 28 days at one of three doses (336, 672, and 1008 mg/kg). NFV was prepared weekly in the vehicle 2-hydroxypropyl betacyclodextrin (50% w/v).
Toxicological Studies: Fifteen animals treated with 1008 mg/kg NFV did not survive the treatment period, with no signs of gavage error, suggesting that these deaths may have been compound-related. No effects were observed on combined body weights at any point during the study. However, significant increases were observed in body weight gain for all NFV-treated animals at interim points during the 28-day study. These differences were absent at study termination (i.e., Day 29 - Day 1). Liver weights were increased at NFV doses ≥ 672 mg/kg, while the weights of the spleen, thymus, lung, and kidneys were unaffected. Significant decreases in erythrocyte numbers, hemoglobin, and hematocrit were observed at the 1008 mg/kg dose level. Mean corpuscular hemoglobin was significantly decreased at NFV doses ≥ 672 mg/kg. Mean corpuscular volume was significantly decreased at the 672 mg/kg dose only. Blood leukocyte counts, platelets, and the absolute number of lymphocytes were increased at the 672 mg/kg dose level in one study but were unaffected in another study.
Immunological Studies: Spleen cell numbers were unaffected. Absolute numbers of T helper cells, T cytotoxic cells, and NK cells were decreased at the 672 mg/kg dose, while the absolute number of T cells was decreased at both 672 and 1008 mg/kg NFV. The percentage of T cells was decreased at doses ≥ 672 mg/kg. The percentage of B cells was increased, while the percentages of TCTL and NK cells were decreased at the 672 mg/kg dose.
The antibody-forming cell response to sheep red blood cells was decreased in two of three studies when evaluated as AFC/106 spleen cells (Specific Activity). When evaluated as AFC/Spleen (Total Spleen Activity), effects were observed in only one study. The serum IgM antibody responses to sRBC and keyhole limpet hemocyanin were unaffected, suggesting that NFV treatment had minimal effects on humoral immunity. Furthermore, cell-mediated immune functions (the mixed leukocyte response, anti-CD3 proliferation, cytotoxic T-lymphocyte activity, and the delayed-type hypersensitivity response) were unaffected. Finally, no effects were observed on innate immunity, when the functional activity of the mononuclear phagocytic system (MPS) and the cytotoxic activity of NK cells were evaluated.
In conclusion, NFV treatment for 28 days produced dose-related increases in liver weights and hematological changes, including decreases in erythrocytes, hemoglobin concentration and hematocrit. Furthermore, a significant number of animals treated with 1008 mg/kg NFV died, indicating overt toxicity at this dose level. At doses that were not overtly toxic (i.e., < 1008 mg/kg), minimal effects were observed on humoral, cell-mediated, or innate immunity.
Bardsley-Elliot A. & Plosker G.L. (2000). Nelfinavir: an update on its use in HIV infection. Drugs. 59(3):581-620.
Burns-Naas L.A., White K.L., McCay J.A., Ivett J., Webber S., & Zorbas M. (2005). Immunotoxicity evaluation of nelfinavir in rats. Human Exp Toxicol 24:67-78.