National Toxicology Program

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Abstract for IMM90016 - 2'3'-Didehydro-3'-Deoxythymidine (D4T) (CASRN 3056-17-5)

The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program (NTP). The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by the NTP on March 2009 (see http://ntp.niehs.nih.gov/ntp/htdocs/levels/09-3566%20NTP-ITOX-R1.pdf). The findings and conclusions for this study should not be construed to represent the views of the NTP or the US Government.

 

Immunotoxicity of 2'3'-Didehydro-3'-Deoxythymidine (D4T) (CAS No. 3056-17-5) in C57Bl/6 AND DBA/2 Mice

NTP Report Number IMM90016

Introduction

The nucleoside analog, 2'3'-dideoxydidehydrothymidine (D4T), has been shown to be a potent inhibitor of HIV replication in vitro. Clinical trials are being conducted to determine its efficacy in human subjects. This study was undertaken to assess the immunotoxicity and myelotoxicity of D4T in C57BL/6 and DBA/2 mice.

Design

D4T, lot number R060190/05, was obtained from the Raylo Chemical Co. and was determined to be ~98% pure by HPLC. D4T was dissolved in distilled water and administered at dose levels of 125, 250, and 500 mg/kg in both C57BL/6 and DBA/2 female mice. Thirty mice were used in each of the five test groups (control, three dosed groups, and a positive control) with 10 mice per group. With the exception of mice immunized with sheep red blood cells, all positive control mice were dosed i.p. with 100 mg/kg cyclophosphamide (CTX, Sigma Chemical Company, St. Louis, MO), at a volume of 0.1 ml per 10 gm body weight, two days prior to sacrifice. D4T treated mice were dosed daily by oral gavage with a volume of 0.1 ml per 10 g of body weight, 7 days/week, for 30 days.

Results

General toxicological data and immunology data are summarized in Tables 1 and 2 for the two mouse strains. The immunotoxicological effects of this compound were negligible. No dose-related mortality, body weight changes, or gross lesions were observed. All groups of C57BL/6 mice showed normal weight gain over the 30- day period, although DBA/2 mice showed minimal weight gain. There were no significant differences between any of the treatment groups in body weight. Dose-related increases in spleen and liver weights were observed. For boths strains of mice, erythropenia and depressed hematocrits were seen at highest dose. No other hematological parameter was modulated by D4T. There were no D4T- related effects in any of the cell-mediated or humoral immune function assays. Significant decreases in both nucleated cells per femur and CFU-E's were seen with the C57BL/6 mice but not the DBA/2 mice.

Conclusion

Under these experimental conditions, treatment with D4T for 30 days produced no significant effects on cell-mediated immunity, humoral immunity or NK cell activity. However, there was significant hematotoxicity and myelotoxity as measured by nucleated cells per femur, CFU-E, and RBC counts. Based upon these findings it is likely that the observed effects on peripheral RBC was a manifestation of D4T induced suppression of erythropoiesis.

Table 1.

Summary of 2',3'-Dideoxydidehydrothymidine (D4T) Immunotoxicity in C57BL/6 Mice

Parameter Dose (mg/kg) cyclophosphamide

0 125 250 500 100 mg/kg
Body Weight (g) 21 20.4 20.2 20.7

Spleen (mg)

81 94 86 102* 118*

Thymus (mg)

74 69 70 71 55*

Liver (mg)

924 964 957 1070* 1058

Kidney (mg)

241 240 229 239 262

Brain (mg)

397 392 397 412 403

Spleen:Brain

0.20 0.24 0.22 0.25* 0.29*

Thymus:Brain

0.19 0.18 0.18 0.17 0.14*

Liver:Brain

2.3 2.5 2.4 2.6* 2.6

Kidney:Brain

0.61 0.61 0.58 0.58 0.65
Bone Marrow Cell Number:

Nuc. Cells/femur (x 10E6)

10.8 7.7 7.0* 6.4* 2.4*

CFU-E/ 10E5 cells

181 147 59* 7* 334*

CFU-GM/10E5 cells

107 116 113 126 393*

Nuc. cells/spleen (x10E7)

11.0 13.0 11.0 12.0 11.0

PFC/10E6 Spleen cell

354 259 377 314 763*
Cyto. T Lymphocyte 25:1 41.6 42.6 36.4 35.9 34.2
Surface Ig(+) - Spleen cells 59 59 62 65* 59
Mixed Leukocyte Response 5.14 5.50 5.00 5.46 4.07
NK Cell Activity(100:1) 11.1 15.5 22.8 15.7 10.2
Lymphoproliferation:

Concanavalin A

287 346 370 342 162*

Phytohemagglutinin

193 229 235 229 105*

Lipopolysaccharide

66 64 74 72 29*

Anti-Ig

2.9 3.9 3.7 4.2 0.2
note: * = different from vehicle control at p less than 0.05

Table 2.

Summary of 2,3-Dideoxydidehydrothymidine (D4T) Immunotoxicity in DBA/2 Mice

Parameter Dose (mg/kg) cyclophosphamide

0 125 250 500 100 mg/kg
Body Weight (g) 19.2 20.6 20.2 19.5
Organ Weights(mg)

Spleen

87 94 102 117* 116*

Thymus

49 48 45 44 26*

Liver

831 971 1016* 1081* 1018*

Kidney

218 255* 251* 244 275*

Brain

354 358 357 347 374

Spleen:Brain Ratio

0.25 0.26 0.29 0.34* 0.31*

Thymus:Brain Ratio

0.14 0.13 0.13 0.13 0.07*

Liver:Brain Ratio

2.3 2.7 2.9* 3.1* 2.7*

Kidney:Brain Ratio

0.61 0.71* 0.71* 0.71* 0.74*
Bone Marrow Cell Number:

Nuc. Cells/femur (x 10E6)

4.2 3.4 3.5 3.5 0.8*

CFU-E/ 105 cells

86 53 62 61 214*

CFU-GM/105cells

189 167 139 140 239

Nuc. cells/spleen (x 10E8)

0.86 0.89 0.94 1.04 0.69*

PFC/106 Spleen cell

296 220 270 239 72*
Cyto. T Lymphocyte 25:1 13.0 12.7 13.7 12.7 9.1
Surface Ig(+) - Spleen cells 63 65 67 65 59
Mixed Leukocyte Response 2.25 2.10 1.89 1.91 1.02*
NK Cell Activity (100:1) 3.8 4.7 4.0 4.2 3.3
Lymphoproliferation:

Concanavalin A

352 344 84 417 154*

Phytohemagglutinin

148 143 156 158 55*

Lipopolysaccharide

100 92 102 101 29*
note: * = different from vehicle control at P less than 0.05

Report Date: February 1990

NTIS # PB92-140383 [SUMMARY(1-15)]


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