K65R, a lysine to arginine change at codon 65 of HIV-1 reverse transcriptase (RT), has been selected in vitro by many NRTIs (nucleoside analog RT inhibitors), but until recently, was infrequently detected in patients. Located in the fingers subdomain of RT, K65R causes NRTI resistance through a discrimination mechanism by increasing selectivity for natural deoxynucleotide triphosphate substrates (dNTP) incorporation over triphosphorylated NRTI incorporation. The thymidine analog mutations (TAMs) include the following amino acid changes in RT: M41L, D67N, K70R, L210W, T215F/Y and K219Q. Different combinations of TAMs facilitate AZT resistance by a primer unblocking mechanism, also known as an excision mechanism, in which the chain-terminating NRTI is removed from the nascent DNA strand to allow polymerization to resume. From in vitro and clinical observations, we proposed that K65R and TAMs represent two different pathways of NRTI resistance that exhibit bi-directional phenotypic antagonism and counterselection in vivo. We have generated several lines of evidence in support of this hypothesis: (1) HIV encoding K65R has reduced susceptibility to all NRTIs tested except those with a 3 azido in the pseudosugar component (AZT and AZA); (2) in a large clinical database, K65R is increasing in prevalence in patient isolates, whereas TAMs are decreasing in prevalence; (3) a strong negative relation exists between the frequency of K65R and specific TAMs among HIV-1 isolates in a large clinical database; (4) K65R reverses viral resistance to AZT caused by TAMs and TAMs reverse resistance to abacavir and tenofovir caused by K65R; (5) K65R antagonizes the primer unblocking activity of TAMs and TAMs antagonize discrimination by K65R; and (6) in plasma samples in which both K65R and TAMs were detected by population sequencing, K65R was not found on the same genome with T215F/Y and 2 or more other TAMs, except when the Q151M multi-drug resistance complex was also present. HIV-1 drug resistance is a significant public health problem. This work contributes to the understanding of NRTI resistance and will help to optimize current and future therapy for HIV-1 infection.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-07292005-120606 |
| Date | 14 September 2005 |
| Creators | Parikh, Urvi Mahendra |
| Contributors | Phalguni Gupta, PhD, Michael Parniak, PhD, Ronald Montelaro, PhD, John W. Mellors, MD |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-07292005-120606/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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