Recent findings on the mechanisms involved in tenofovir resistance

Comparative application of derivative spectrophotometric and HPLC techniques for the simultaneous determination of lamivudine and tenofovir disoproxil fumarate in fixed-dose combined drugs

Background

Lamivudine (LAM) and tenofovir disoproxil fumarate (TDF) are part of a fixed-dose combination (FDC) therapy recommended by WHO. Both drugs exhibit similar solubility in many solvent systems and tend to have overlapping spectra with maxima at 260 and 270 nm, respectively, in the UV spectrum—thus making their spectrophotometric assay difficult in FDCs. A third-order derivative (D3, d3A/dλ3) spectrophotometric technique was applied to simultaneously evaluate TDF and LAM in FDC drugs, with amplitudes at 240 and 262.5 nm, respectively. Pharmacopoeia-recommended chromatographic method was also applied for comparative purpose.

Results

Method performance by the proposed D3 technique showed linearity for LAM and TDF from 2–10 µg mL−1 to 8–24 µg mL−1, respectively (R2 ≥ 0.998), while for HPLC method both drugs ranged from 0.25 to 5.0 µg mL−1 (R2 ≥ 0.999). The intercepts and slopes of the regression equations were ≤ 1.62 × 10−4 and ≤ 3.58 × 10−5, respectively, while calculated standard errors were ≤ 8.04 × 10−5. Limits of detection and quantification for both methods were ≤ 0.46 μg mL−1 and ≤ 1.40 μg mL−1, respectively, for LAM, while corresponding limits for TDF were ≤ 2.61 and ≤ 7.90 μg mL−1. The percentage recovery for both drugs and methods ranged from 94.80 to 100.33%. The amount of LAM and TDF in brands I and II was ≥ 99.59 ± 1.19% and ≥ 99.39 ± 0.63%, respectively, for the proposed D3 spectroscopic method, while corresponding values for the HPLC method were ≥ 99.86 ± 0.50 and ≥ 99.87 ± 0.32%. Statistically, both methods were adjudged to have no significant difference at 95% confidence level as the student’s t-test values; experimental paired t- and F-test values were found satisfactory.

Conclusion

The D3 spectrophotometric technique was time saving, cheap, simple and more environmental friendly and shows reliability, precision and accuracy and could be used for routine analysis of FDCs where HPLC is not available.

Graphical abstract

In vitro evaluation of novel reverse transcriptase inhibitors TAF (tenofovir alafenamide) and OBP-601 (2,3-didehydro-3-deoxy-4-ethynylthymidine) against multi-drug resistant primary isolates of HIV-2

New antiretroviral drugs are needed to treat HIV-2 infected patients failing therapy. Herein, we evaluate the activity of novel reverse transcriptase inhibitors tenofovir alafenamide (TAF) and OBP-601(2,3-didehydro-3-deoxy-4-ethynylthymidine) against primary isolates from HIV-2 infected patients experiencing virologic failure. TAF and OBP-601 were tested against twelve primary isolates obtained from nine drug-experienced patients failing therapy and three drug naïve patients using a single-round infectivity assay in TZM-bl cells. The RT-coding region of pol was sequenced and the GRADE algorithm was used to identify resistance profiles and mutations. TAF and OBP-601 inhibited the replication of almost all isolates at a median EC₅₀ of 0.27 nM and 6.83 nM, respectively. Two isolates showed moderate-level resistance to OBP-601 or TAF and two other isolates showed high-level resistance to OBP-601 or to both drugs. With one exception, all resistant viruses had canonical nucleoside reverse transcriptase inhibitors (NRTIs)-associated resistance mutations (K65R, N69S, V111I, Y115F, Q151M and M184V). Our results show that TAF has potent activity against most multi-drug resistant HIV-2 isolates and should be considered for the treatment of HIV-2 infected patients failing therapy.