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Antimicrobial Agents and Chemotherapy, February 2000, p. 473-474, Vol. 44, No. 2
0066-4804/00/$04.00+0
LETTERS TO THE EDITOR
May the Drug Transporter P Glycoprotein Affect the Antiviral
Activity of Human Immunodeficiency Virus Type 1 Proteinase Inhibitors?
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LETTER |
Several studies have demonstrated that human immunodeficiency
virus (HIV) proteinase inhibitors (PIs) are substrates of the multidrug
transporter P glycoprotein (P-gp) (2, 3, 5).
In a recent article Srinivas and coworkers (4), in addition to
confirming previous observations, demonstrated for the first time that
HIV PIs interact also with MRP1, another multidrug transporter protein
(1). They have also observed that HIV PIs are equally effective against
HIV in wild-type cells and in a P-gp-expressing cell line, suggesting
that cellular resistance to HIV PIs might not be a major therapeutic
concern. It is our opinion that the possibility that P-gp expression
may affect the antiviral activity of PIs should be further addressed.
In the framework of a project aimed to address the role played by
cellular resistance in HIV infection treatment failure, we have
performed similar experiments. The results, however, are not perfectly
consistent with those reported by Srinivas et al. We found that the
cell line CEMVBL 100, expressing a high level of P-gp (as measured by
fluorescein-activated cell sorter analysis with a specific monoclonal
antibody and by reverse transcriptase PCR designed to detect mRNA for
P-gp), is less sensitive to PI antiviral activity than the parental
cell line, not expressing P-gp.
Figure 1 shows the results. It can be seen that saquinavir and
indinavir display at the indicated concentrations significantly reduced
antiviral activities in CEMVBL100 cells compared to CEM cells.
Specifically, 50 and 5 nM saquinavir reduced HIV yield in the parental
cell line by 90 and 70%, respectively. In contrast, the same compound
in CEMVBL100 at the same concentrations inhibited HIV yield by 80 and
40%. In repeated experiments this small difference becomes significant
(P < 0.05).
Basically, the same results were obtained using indinavir. Importantly,
both drugs partially recover the ability to inhibit replication of
HIV-1 in the presence of nontoxic concentratioin of verapamil, an
inhibitor of P-gp function (6), thus indicating that P-gp expression
may affect the antiviral activity of PIs.
The inhibitory effect exerted by P-gp against PIs, however, occurs only
at intermediate dosage, which approximately corresponds to the 90%
effective dose (ED90) reported by Srinivas et al. At higher
doses PIs are able to inhibit HIV replication in CEMVBL100 cells also,
whereas at lower doses they do not affect HIV replication.
Together these findings suggest that P-gp expression may influence the
antiviral activity of PIs at least at a certain
dosage.
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FIG. 1.
Antiviral activities of saquinavir and indinavir in CEM
and CEMVBL100 cells in the presence or absence of verapamil (2 µM).
Cells of both types were infected with HIVpnl43 at a
multiplicity of infection of 0.1. After 5 days of incubation, percent
viral-yield reduction was determined by measuring the level of p24
antigen. Data are means with standard deviations for three independent
experiments.
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Srinivas et al. reported a higher ED90 for CEMVBL100 cells
than that for the parental line, but the difference was not
significant. Using a different calculation
comparing percent
viral-yield reductionthe difference between the two cell lines
becomes significant. We do not want to overemphasize such a small
difference. However, in light of the recent demonstration that all PIs
are first-rate substrates of the P-gp pump, we believe that the
question of whether P-gp mediated cellular resistance to anti-HIV drugs
exists is still open.
| |
FOOTNOTES |
*
Phone: 39-06-4470-0223 Fax:
39-06-446-9024 E-mail:
Virosap{at}flashnet.it
| |
REFERENCES |
| 1.
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1996.
Multidrug resistance associated with overexpression of MRP.
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B. Leake,
A. J. J. Wood, and D. M. Roden.
1998.
The drug transporter P-glycoprotein limits oral absorption and brain entry of HIV-1 proteinase inhibitors.
J. Clin. Invest.
101:289-294[Medline].
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Lee, C. G. L.,
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HIV-1 protease inhibitors are substrates for the MDR1 multidrug transporter.
Biochemistry
37:3594-3601[CrossRef][Medline].
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| 4.
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Srinivas, R. V.,
D. Middlemas,
P. Flynn, and a. Fridland.
1998.
Human immunodeficiecy cirus protease inhibitors serve as substrates for multidrug transporter proteins MDR1 and NRP1 but retain antibiral efficacy in cell lines expressing these transporters.
Antimicrob. Agents Chemother.
42:3157-3162[Abstract/Free Full Text].
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| 5.
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Washington, C. B.,
G. E. Duran,
M. C. Man,
B. I. Sikic, and T. F. Blaschke.
1998.
Interaction of anti-HIV proteinase inhibitors with the multidrug transporter P-glycoprotein (P-gp) in human cultured cells.
J. Acquired Immune Defic. Syndr. Human Retrovirol.
19:203-209[Medline].
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| 6.
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Y7usa, K., and T. Tsuruo.
1989.
Reversal mechanism of multidrug resistance by verapamil: direct binding of verapamil to P-glycoprotein on specific sites and transport of verapamil outward across the plasma membrane of K562/ADM cells.
Cancer Res.
49:5002-5006[Abstract/Free Full Text].
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| | | | |
Ombretta Turriziani*
Paola Di
Marco
Guido Antonelli
Department of Experimental Medicine and
Pathology, University La Sapienza, Viale di Porta
Tiburtina 28, 00185 Rome, Italy
|
| | | | |
Ferdinando Dianzani
Campus Biomedico, Libera
Universita, Rome, Italy
|
| |
AUTHOR'S REPLY |
Turriziani and coworkers show a significant, albeit small, reduction in
the antiviral efficacy of the HIV PI saquinavir in MDR1-overexpressing
CEM-VBL100 cells compared to wild-type CEM cells using virus yield
reduction assays. Indeed, we also observed a slight reduction in the
antiviral efficacy of various HIV PIs in CEM variants that over express
the multidrug transporters, as evidenced by slight increases in the
90% inhibitory concentrations of various HIV-PIs in CEM-VBL100 cells.
These differences, although reproducible, were not statistically
signficant due to the large interassay variations. While it is clear
that the differences observed by Turriziani and coworkers were
statistically significant, the biological signficance of these small
differences in virus yields is hard to evaluate.
The impact of multidrug transporter overexpression in lymphocytes, the
primary targets of HIV, on HIV PI therapy is hard to evaluate since MDR
overexpression per se can modulate the dynamics of HIV infection in
lymphocytes. For example, we have noted that cells that overexpress
MRP-4 are less sensitive to HIV infection (7). Similar findings have
been observed with MDR-1-overexpressing cells. Furthermore, MDR
overexpression among cells of hematopoietic cell lineage may have other
consequences relevant to HIV biology as well. Unlike normal
hematopoietic stem cell (HSC), MDR-1-transduced HSC are capable of ex
vivo expansion and show signficantly greater immune reconstitution (2).
Therefore, while we do not dispute the notion that MDR-1 overexpression
may adversely affect response to PI therapy, we believe that such
effects are more likely to be due to reduced plasma and tissue PI
concentrations resulting from reduced oral uptake and increase
hapatobiliary clearance, rather than selective exclusion from the
target lymphocytes.
While the interaction of MDR-1 P glycoprotein with various HIV PIs is
well documented, the interaction of P glycoprotein with nucleoside
reverse transcription inhibitors (NRTI) has been controversial. Several
investigators, including Turriziani and coworkers, have suggested that
P glycoprotein may confer resistance to zidovudine and other NRTI (1, 3, 4, 6; H. W. Doerr, J. Cinatl, Jr., B. Weber, and J. Cinatl, Abstr.
94th Gen. Meet. Am. Soc. Microbiol. 1994, abstr. T-14, 1994). MDR-1 is
a member of a large family of related multidrug resistance-associated
transporters, and other members of this family may play a role as well.
Earlier we showed that like MDR-1, MRP-1 also interacts with HIV PIs
(8). More recently, we showed that MRP-4, a newly characterized member
of the MDR family, does not interact with HIV PIs but confers cellular
resistance to HIV inhibition by multiple NRTI (5). Given the
complexities of these drug transporter interactions, we agree with
Turriziani and coworkers that further studies are needed to clarify the
role of multidrug transporters in cellular resistance to antiviral therapy.
| |
FOOTNOTES |
Phone: (301) 435-1167 Fax: (301) 480-2241 E-mail:
srinivar{at}csr.nih.gov
| |
REFERENCES |
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AIDS Res. Hum. Retroviruses
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Zidovudine induces the expression of cellular resistance affecting its antiviral antivity.
AIDS Res. Hum. Retroviruses
10:1471-1478[Medline].
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Human immunodeficiency virus I-induced expression of P-glycoprotein.
Biochem. Biophys. Res. Commun.
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Schuetz, J. D.,
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R. V. Srinivas,
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MRP4: a prevously unidentified factor in resistance to nucleoside-based antiviral drugs.
Nat. Med.
5:1048-1051[CrossRef][Medline].
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Signoretti, C.,
G. Romagnoli,
O. Turriziani,
G. Antonelli,
F. Dianzani, and M. Cianfriglia.
1997.
Induction of the multidrug-transporter P-glycoprotien by 3'-azido-3'-deoxythymidine (AZT) treatment in tumor cell lines.
J. Exp. Clin. Cancer Res.
16:29-32[Medline].
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Robbins, B. L.,
M. C. Connelly,
D. R. Marshall,
R. V. Srinivas, and A. Fridland.
1995.
A human T lymphoid cell variant resistant to the acyclic nucleoside phosphonate 9-(2-phosphonylmethoxyethyl)adenine shows a unique combination of a phosphorylation defect and increased efflux of the agent.
Mol. Pharmacol.
47:391-397[Abstract].
|
| 8.
|
Srinivas, R. V.,
D. Middlemas,
P. Flynn, and A. Fridland.
1998.
Human immunodeficiency virus protease inhibitors serve as substrates for multidrug transporter protiens MDR1 and MRP1 but retain antiviral efficacy in cell lines expressing these transporters.
Antimicrob. Agents Chemother.
42:3157-3162.
|
| | | | |
Ranga V. Srinivas
Center for Scientific Review, National Institutes of Health, 6701 Rockledge Dr., Bethesda, MD 20892
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Antimicrobial Agents and Chemotherapy, February 2000, p. 473-474, Vol. 44, No. 2
0066-4804/00/$04.00+0
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