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Antimicrobial Agents and Chemotherapy, November 2000, p. 3235-3236, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Suppression of Posttreatment Recurrence of Experimental Visceral
Leishmaniasis in T-Cell-Deficient Mice by Oral Miltefosine
Henry W.
Murray*
Department of Medicine, Weill Medical College
of Cornell University, New York, New York 10021
Received 19 April 2000/Returned for modification 5 June
2000/Accepted 5 August 2000
 |
ABSTRACT |
T-cell-deficient nude mice infected with Leishmania
donovani were treated with miltefosine and then given either no
treatment or intermittent miltefosine. Intracellular visceral infection recurred in untreated mice but was suppressed by once- or twice-weekly oral administration of miltefosine. Miltefosine may be useful as oral
maintenance therapy for T-cell-deficient patients with visceral leishmaniasis.
 |
TEXT |
In an experimental model of visceral
leishmaniasis caused by the intracellular protozoan Leishmania
donovani, the activities of a new oral antileishmanial agent,
hexadecylphosphocholine (miltefosine) (6, 17, 18), in
T-cell-deficient athymic (nude) and T-cell-intact euthymic mice proved
comparable (12). This result raised the possibility that
miltefosine may have a role as an initial oral treatment approach to
the growing problem of AIDS-associated visceral leishmaniasis
(kala-azar) in CD4 cell-depleted patients (1, 4, 11).
A second, related therapeutic issue in this clinical setting is relapse
of infection once any initially effective treatment is discontinued
(1, 2, 7, 8, 11, 13, 15; R. N. Davidson and R. Russo, Letter, Clin. Infect. Dis. 91:560, 1994). Since
successful host defense against this disease, including the prevention
of posttreatment relapse, is T-cell dependent and driven by CD4 (Th1)
cell-derived cytokines (9, 11, 13, 14), it is not surprising
that recurrence of AIDS-related kala-azar is predictable if therapy is
stopped (1, 2, 7, 8, 11, 13, 15; Davidson and Russo,
Letter, Clin. Infect. Dis., 1994). This study extended the analysis
of miltefosine by testing whether it may also be useful as a long-term
treatment to prevent recrudescence of visceral infection in the
T-cell-deficient host.
Materials and Methods. (i) Animals and visceral infection.
Athymic (nude) BALB/c mice (20 to 30 g) (Charles Rivers
Laboratories, Wilmington, Mass.) were injected via the tail vein with 1.5 × 107 hamster spleen-derived L. donovani amastigotes (one Sudan strain) (12). Visceral
infection was monitored microscopically using Giemsa-stained liver
imprints, and liver parasite burdens were measured by calculating, in a
blinded fashion, the number of amastigotes per 500 cell nuclei
multiplied by the liver weight (in milligrams) (Leishman-Donovan units
[LDU]) (12). The histologic reaction in the liver was
assessed using formalin-fixed, stained tissue sections (12).
(ii) Initial and maintenance treatment.
Two weeks after
L. donovani challenge, liver parasite burdens
were determined for 4 of 28 infected mice, and then the animals received either no treatment (n = 4) or oral
miltefosine by gavage (n = 20). Miltefosine, generously
provided as a powder by ASTA Medica AG (Frankfurt, Germany), was
dissolved in tap water and administered once daily at 25 mg/kg of body
weight in a volume of 0.3 ml for five consecutive days (12).
Two days after treatment ended, four untreated and four treated mice
were sacrificed. LDU at this point (week 3) were compared to initial
LDU (at week 2) to determine the extent of initial parasite killing
(12). The remaining 16 treated mice were randomly divided
into four groups to receive, for the next 9 weeks, either no further
treatment or single doses of miltefosine (25 mg/kg) given twice weekly, once weekly, or every 2 weeks. Twelve weeks after infection, liver parasite burdens were determined for all animals.
Results and discussion.
Between week 2 and week 3, the period
during which miltefosine was initially administered, liver parasite
burdens increased in untreated nude mice from 2,124 ± 269 (Fig.
1) to 2,994 ± 212 LDU (mean ± the standard error of the mean [SEM]) (n = 8, data not shown). In mice treated for 5 days, LDU (mean ± SEM) at week 3 were reduced to 496 ± 87, indicating 77% initial killing 1 week after therapy began (Fig. 1). Treated mice were then given either no additional miltefosine or single doses twice per week, once per
week, or every second week for the next 9 weeks. As shown in Fig. 1,
parasite replication resumed in treated mice that were given no
additional drug, and liver burdens at week 12 were 3.5-fold higher than
those at week 3. While miltefosine administered biweekly did not
prevent recurrence of visceral replication, treatment given once or
twice weekly was clearly active in suppressing infection for the
duration of the experiment. Histologic examination of the livers at
week 12 confirmed these effects (Fig. 2).

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FIG. 1.
Initial effect of miltefosine treatment in nude BALB/c
mice and prevention of subsequent relapse. Two weeks after infection,
nude mice were initially treated with drug for 5 days. Two days later
(end of week 3), treated mice either were given no further drug or
received single doses every second week, once weekly, or twice weekly
for the next 9 weeks. Results are from two experiments and are
means ± SEMs for seven to eight mice per group.
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FIG. 2.
Photomicrographs of livers of nude mice 12 weeks after
L. donovani infection. (a) Mice treated with miltefosine
during week 2 to 3 only (no maintenance therapy) show recurrent
infection, with multiple heavily parasitized foci (arrows).
Magnification, ×500. (b) In contrast, mice treated during week 2 to 3 and twice weekly thereafter show markedly reduced liver parasite
burdens at week 12, with only one infected focus in a lower-power field
(arrow). Magnification, ×315.
|
|
Intracellular
Leishmania organisms are probably seldom, if
ever, entirely eradicated even from healthy hosts by either
antileishmanial
chemotherapy or the T-cell-dependent, cytokine-driven
mechanism
which develops to regulate successful acquired resistance and
prevention of relapse in visceral infection (
3,
9,
10,
13,
14,
16). In T-cell-depleted or -deficient hosts with
kala-azar, such
as individuals with advanced human immunodeficiency
virus disease
(
1) or immunosuppressed transplant recipients
(
5), not only may an initial response to treatment be
difficult
to induce, but also relapse after such an apparent response
is
frequent once therapy is discontinued (
1,
2,
5,
7,
8,
11,
13,
15; Davidson and Russo, Letter, Clin. Infect.
Dis.,
1994). Although not yet well studied, current evidence regarding
AIDS-related kala-azar suggests that maintenance treatment with
once-monthly injections of pentavalent antimony may suppress recurrent
infection (
15); however, monthly pentamidine injections
(
7)
or daily oral allopurinol use appears to have little
effect (
15).
While it still needs to be tested in patients coinfected with human
immunodeficiency virus, miltefosine is remarkably active
in kala-azar
(
6,
17,
18) and has additional advantages:
(i) a long
circulating half-life (~8 days) (
17) and (ii) experimental
antileishmanial efficacy which is direct and does not require
a host
T-cell-dependent response for full expression (
12). The
results reported here suggest that miltefosine has promise as
a
convenient oral treatment to suppress or prevent relapse of
visceral
infection in the T-cell-deficient
host.
 |
ACKNOWLEDGMENTS |
This study was supported by NIH grant AI 16963.
 |
FOOTNOTES |
*
Mailing address: Department of Medicine, Weill Medical
College of Cornell University, 1300 York Ave., New York, NY 10021. Phone: (212) 746-6330. Fax: (212) 746-6332. E-mail:
hwmurray{at}mail.med.cornell.edu.
 |
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Antimicrobial Agents and Chemotherapy, November 2000, p. 3235-3236, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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