The foundation of the mononuclear phagocyte system are macrophages that derive
from bone marrow’s monoblasts and promonoblasts. First, monoblasts and
promonoblasts get transformed in circulating monocytes, which, after migration in
extravascular tissue, differentiate into macrophages.
The main role of macrophages is defense of the organism against various infectious
agents. Furthermore, macrophages have been found to play an important part in the
pathology of different diseases: atherosclerosis (foam cells), cancer (tumorassociated
macrophages), infectious diseases for which macrophages play the role
of host cells (e. g. tuberculosis, HIV, leishmaniasis, dengue virus), etc. Thus, recent
studies have detected high viral load in tissue macrophages at all stages of HIV-1,
which persists in them even under combination antiretroviral therapy.1 Therefore,
macrophages make one of important targets for anti-HIV drug design and
development.

The main objective of the current study was design and synthesis of a new group of
non-nucleoside reverse transcriptase inhibitors with targeted activation in
macrophages the feature that would improve pharmacodynamic and
pharmacokinetic parameters of this class of compounds, reduce viral load in
macrophages, and thus improve the outcomes of the antiretroviral therapy.
Human carboxylesterase-1 (hCE-1) is highly expressed in macrophages and,
therefore, could play a role of activator enzyme in activation of prodrugs of nonnucleoside
reverse transcriptase inhibitors targeting these cells.1 Such activation
guarantees a cell-type specific approach and accumulation of the active drug in
higher concentrations on the intracellular level. The occurring intracellular ester
hydrolysis of a drug-ester conjugate results in the production of a potentially active
compound with a charged nature. This would ultimately lead to a drop in the drugs
ability to leave the cell and consequently to a beneficial accumulation in the
targeted cells.2 For a successful delivery of intracellular active compounds to hCE1-
expressing cells, a sensitive motif (see the figure below) for aforementioned
enzyme has to be attached to a drug.

For a specific prodrug concept, based on the research results obtained by Needham
et al.2 and the experience accumulated in our group, the cyclopentanol-ester-of-Lleucine-
based hCE-1 selective motif has been chosen and introduced in the
structures of molecules known to be highly active against HIV-1.
First, a known3,4 reverse transcriptase inhibitor has been obtained and its
diastereomers 1a and 1b have been separated. Compound 1a has been tested
previously in a cell-based HIV reporter infection assay and was identified to have
EC50 = 50 nM.3,4 At the same time, it has been detected that diastereomer 1b is
completely inactive, the fact that suggested that the antiviral activity of 1a is a
result if its specific interaction with reverse transcriptase.3,4 After the separation of
the diastereomers, hydrolysis of the esters has been carried out with formation of
individual cis- and trans-acids 2. Then the isolated cis- and trans-acids have been
subjected to coupling with cyclopentanol ester of L-leucine to obtain compounds
with general formula 3.
The data obtained by Jiang et al.3 indicates that there is a small space for
substitution in position 5 and only small hydrophobic moieties can be introduced
(Cl, Br, CN or vinyl) to allow optimal interaction with reverse transcriptase. In
addition to this, substitution in positions 4, 6, and 7 mostly leads to inactive
compounds.

Interestingly, 1a analogues with different groups (Br, Cl, NO2) in positions 5 and 7
have also shown inhibitory activity against HIV-1 integrase.5 Moreover, only cisanalogs
have demonstrated inhibition, while none of the trans-analogs have shown
any inhibition. Our further work will be directed towards obtaining of new
derivatives active against HIV-1 reverse transcriptase and integrase with attached
esterase sensitive motif.
REFERENCES
(1) Cory, T. J.; Schacker, T. W.; Stevenson, M.; Fletcher, C. V. Current opinion in HIV and AIDS,
2013, 8, 190.
(2) Needham, L. A.; Davidson, A. H.; Bawden, L. J.; Belfield, A.; Bone, E. A.; Brotherton, D. H.
et al. J. Pharmacol. Exp. Ther., 2011, 339, 132-142.
(3) Jiang, T.; Kuhen, K. L.; Wolff, K.; Yin, H.; Bieza, K.; Caldwell, J.; Bursulaya, B.; Wu,
T.Y.H.; He, Y. Bioorg. Med. Chem. Lett., 2006, 16, 2105-2108.
(4) Jiang, T.; Kuhen, K.L.; Wolff, K.; Yin, H.; Bieza, K.; Caldwell, J.; Bursulaya, B.; Tuntland,
T.; Zhang, K.; Karanewsky, D.; He, Y. Bioorg. Med. Chem. Lett., 2006, 16, 2109-2112.
(5) Surmava, S.; Elefthetiou, P.; Geronikaki, A., Petrou, C.; Macaev, F.; Sucman, N. HIV-1
integrase inhibition by novel spiro-isatin-cyclopropane derivatives. In: XVIII International
AIDS Conference. Viena: Austria, 2010, p. 56.
Acknowledgements: the authors are grateful for the funding support from the Science and Technology
Center in Ukraine and the Agency for Research and Development of the Republic of Moldova under
international project 17.80013.8007.10/6245STCU.