The anticancer potential of organic salts and ionic liquids (OSILs) has been widely
discussed recently. Their attractiveness for pharmaceutical production is attributed
to such advantageous properties as simplicity in preparation and purification, low
costs, tunable permeability through biological barriers, etc.
Here we report a group of OSILs with cytotoxic activity against cancerous cells
comparable with that of carboplatin and much lower against noncancerous cells.
Biological tests of the obtained compounds have demonstrated that they possess
inhibitory activity against two ectonucleotidase isozymes, which could be one of
their main antiproliferation mechanisms of action. At the same time,
physicochemical tests have shown that at room temperature and deemed light these
compounds possess antioxidant effect acting as free radical scavengers, while their
irradiation with 365 nm light makes them photosensitizers inducing singlet oxygen
production in water suspensions.
Most of the previous studies by other groups on OSILs with more or less selective
cytotoxicity against different lines of cancerous cells have mainly demonstrated the
antiproliferative activity but did not go further to study their potential cytotoxic
mechanisms. Other works made attempts for structure-cytotoxic activity
relationship studies that demonstrated higher toxicity for OSILs containing cations
with longer chains and lower toxicity for compounds with functionalized side
chains in cations as compared to non-functionalized ones. Wang et al.1 studied
cytotoxicity of a group of ionic liquids and their precursors in HeLa cells and
determined increase in reactive oxygen species production (ROS) and a consequent
reduction of mitochondrial membrane potential.
While it is well known that intracellular generation of singlet oxygen equally
induces cell death in both cancerous and noncancerous cells, extracellular singlet
oxygen has a more selective action on tumor cells via membrane-associated catalase
inhibition and reactivation of intracellular ROS/RNS-dependent apoptosis-inducing
signaling, while having no effect on non-malignant cells. Previously, we have
demonstrated that some of the benzylamine derivatized OSILs synthesized by us
possess photosensibilizing properties with formation of ROS.2

Imidazolium-bearing OSILs 1-8 have been synthesized and tested against two
isozymes of ecto-5’-nucleotidase i.e. h-e5’NT and r-e5’NT. Most of the compounds
from both series exhibited maximum inhibitory potential towards both isozymes but
few derivatives from either series exhibited selective inhibition towards human
isozymes. Among all imidazole derivatives compound 4 was found as the potent
inhibitor. This compound exhibited non-selective and almost equipotent behavior
towards both isozymes i.e. against h-e5NT and r-e5’NT it showed IC50 value of
1.14±0.05 and 1.93±0.21 μM. It can be suggested that the presence of methyl group
is responsible for its maximum inhibition towards both h-e5’NT and r-e5’NT.
The anticancer potential of the selected derivatives was determined against HeLa
cells, in comparison to their effect against BHK-21 cells. Almost all the
compounds exhibited more that 50% inhibition of HeLa cells and among those
compounds 2, 5, 6, 7, and 8 exhibited 68%, 62%, 67%, 64%, and 67% inhibition
respectively. While compound 3 exhibited 73% inhibition respectively. The
maximum inhibition was observed in case of 4, 87%. The results were in correlation
with the enzyme inhibition data. From both series the compounds which were
identified as the most potent inhibitor of h-e5’NT were also found to inhibit
maximum cell growth of HeLa cells. 4 caused maximum inhibition and it was
further selected for the determination of IC50 value and it was found about
2.92±0.11 μM was found approximately 2 fold higher as that of positive control
used i.e. carboplatin (5.13±0.45 μM) at the same concentration i.e. 100 μM. These
compounds were found safe and did not exhibit ≥10 inhibition of normal cells.

Antioxidant activity of the compounds 1 – 8 was measured with application of
DPPH method and compared to that of the ascorbic acid. In general, compounds 1 -
4 have shown higher levels of antioxidant activity. At the same time, there is no
clear correlation between the antioxidant activity of the compounds within the
groups and their structural particularities. Thus, the main structural difference
within both groups is the radical at the imidazole cycle: methyl, ethyl, vinyl, and
butyl. However, there is no clear influence of the radical nature on the antioxidant
activity of the compounds. For example, the highest antioxidant activity represented
by lower EC50 has been determined for the vinyl derivative 2 in the 1-4 group with
salicylic aldehyde moiety and for the methyl derivative 8 in the group 5 – 8.
Moreover, the general trend of the antioxidant activity change in the group of
derivatives 1 – 4 in comparison to ascorbic acid (AA) is the following: AA > vinyl
> butyl > methyl > ethyl. While the same trend among the 5 – 8 derivatives and
ascorbic acid is: AA > methyl > butyl > vinyl > ethyl.

Another series of ILs was obtained via conversion of carbonitriles into primary
amine cyclic ether quaternized salts.3 The obtained compounds were checked for
their antiproliferative activity in HeLa cells line. All these compounds
demonstrated an efficient cytotoxic behavior against HeLa cells as compared to a
standard anticancer drug Vincristine. The IC50 values for these compounds vary in
the limits of 0.97 – 2.37 μM with percent inhibition of Vero cells growth at 10 μM
varying from 10 -28%.
Compound [Me]Cl (9) displayed the highest inhibition activity towards HeLa with
SI10μM ≥ 5.0, while the [2HE]Tf2N (10) showed the lowest selectivity index within
the substituted 1-amino-2,8-dioxa-5-azoniabiciclo[3.3.1]nonanium salts (SI10μM ≥
2.5).
REFERENCES
(1) Wang, X.; Ohlin, C. A.; Lu, Q.; Fei, Z.; Hu, J.; Dyson, P. J. Green Chem., 2007, 9, 1191-
1197.
(2) Neamțu, M.; Macaev, F.; Boldescu, V.; Hodoroaba, V-D.; Nădejde, C.; Schneider, R. J.;
Paul, A; Ababei, G.; Panne, U. Appl. Catal. B. 2016, 183, 335-342.
(3) Prodius, D.; Shah, H.S.; Iqbal, J.; Macaeva, A.; Dimoglo, A.; Kostakis, G. E.; Zill, N.;
Macaev, F.; Powell A.K. Chem. Comm. 2014, 50, 4888-4890.
Acknowledgements: the authors are grateful for the funding support offered by 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