ACS Medicinal Chemistry Letters
Letter
with MIC value in the range (0.125−4 μg/mL) displayed the
broader antimicrobial spectrum than other compounds; it can
inhibit the activity of Candida. pp. and A. fum. In summary,
these target compounds can maintain the antifungal activity,
and their fragment groups can lead to some of the change in
biologic activity and antifungal spectrum.
Fluconazole, as a representative antifungal drug, has been
widely used in clinical antifungal treatment, and it achieved
good therapeutic effect. However, the more and more
pathogenic fungi have developed the phenomenon of drug
resistance with the increase of clinical treatment time.
Therefore, it is of important significance to evaluate the
antiresistant fungal activity of these compounds. The preferred
compounds (7a-1, 7a-2, and 7c-2) were selected, and their
antifungal activity is summarized in Table 6. The target
Figure 9. Changes of fungal cell (C. alb. ATCC SC5314) density were
observed in different concentrations (A1, 2‑1: 0 nmol/mL; A1, 2‑2: 50
nmol/mL; A1, 2‑3: 5 nmol/mL). A1‑1, 2, 3: Treated with naftifine;
A2‑1, 2, 3: Treated with compound 7a-2.
Table 6. Anti-Fluconazole Resistant Fungal Activity of the
Preferred Compounds in Vitro
10B1, 2). The result indicated that the compound has destroyed
the external structure of the fungal cells.
MIC, μg/mL
Strain
CaR
Strain
Strain
901
Strain
632
Strain
904
Compd
7a-1
7a-2
7c-2
Naftifine
Fluconazole
17#
8
4
4
4
>16
>16
4
>16
8
4
4
>16
>16
>16
>16
8
>16
8
>16
>16
8
8
>16
>16
>16
a
Abbreviations: Strain CaR, Strain 17#, Strain 901, Strain 632, and
Strain 904, fluconazole-resistant strains of Candida albicans. These
Figure 10. Transmission electron microscopy (TEM) results. B1:
Untreated; B2: Treated with compound 7a-2.
strains were provided by Shenyang Pharmaceutical University.
It was an important condition for drugability to investigate
the stability of the compound in plasma. In this study,
compounds 7a-2 and 7c-2 with higher antifungal activity were
selected to be incubated with human plasma, which was shown
in Table 7; we can see that they exhibit high stability at 120
min (remaining 91.6% and 83.5%, respectively).
compounds 7a-1 and 7c-2 with MIC values > 16 μg/mL did
not demonstrate the significant inhibitory activity against the
strains 17# and Strain 632, which was isolated from AIDS
patients. It was worth noting that compound 7a-2 with MIC
value 4 μg/mL showed moderate inhibitory activity against
Strain 17#, Strain CaR, and Strain 901.
Fungal cell density is an important index, which can directly
reflect their growth status. In theis study, the different
concentrations (0 nmol/mL, 50 nmol/mL and 5 nmol/mL)
of naftifine and compound 7a-2 were set in the solution of C.
alb.
Table 7. Stability of Target Compounds 7a-2 and 7c-2
Compd.
% Incubating for 60 min
% Incubating for 120 min
7a-2
7c-2
94.5
87.3
91.6
83.5
We can see that fungal cell displayed the proliferation ability
at the concentration of 0 nmol/mL, and some fungal cells
display the phenomenon of spore proliferation in the solution;
their cell density is significantly higher than the other
concentration groups (Figure 9 A1, 2‑1). In the high and low
concentration treated groups (50 nmol/mL, 5 nmol/mL) with
compound 7a-2 and naftifine, the cell proliferation of C. alb.
was inhibited, and their cell density decreased significantly
compared with the untreated group (Figure. 9A1, 2−2, 3).
Subsequently, TEM was further performed to observe the
cell morphological changes of C. alb. In the early stage, the
fungal cell showed the elliptical structure, their nucleus and
organelles were distributed in the center of cells, and the cell
wall and membrane structure were covered on the cell surface.
It is worth noting that some fungal cells show a tendency to
divide. With the prolonged treatment of fungal cells with
compound 7a-2, the phenomenon of fungal cell division
disappeared, and the structure of cell walls and cell membranes
began to become uneven. At the same time, some fungal cells
showed internal material exuding from the cells (Figure
LC-MS was performed to study the change of sterol
composition in different treatment groups; the result was
summarized in Table 8. It can reflect the biological mechanism
of compound 7a-2.28,29 In the blank control, ergosterol was the
dominant component, which contained 96.7%, while eburicol
only accounted for 1.2%. At the same time, there is no
squalene in this component. When the C. alb. were treated
with different concentrations of naftifine and compound 7a-2
(0.125−4 μg/mL), the proportion of ergosterol in the cell
membrane decreased to 28.4% and 31.7% from 96.7%, and the
contents of squalene, eburicol, and unknown sterol were
accumulated. In particular, the content of squalene increased
sharply to 64.5% and 58.9%, respectively. Therefore, they
showed the same changing trend of ergosterol and squalene.
The possible reason was that ergosterol synthesis was blocked
by inhibiting the target enzyme SE.
Molecular docking can guide the design and optimization of
target compounds by determining the binding mode of
molecules. The target compound 7a-2 and naftifine with
F
ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX