A Green-Absorbing, Red-Fluorescent Phenalenone-Based Photosensitizer as a Theranostic Agent for Photodynamic Therapy

Article abstract of DOI:10.1021/acsmedchemlett.1c00284

Phenalenone is a synthetically accessible, highly efficient photosensitizer with a near-unity singlet oxygen quantum yield. Unfortunately, its UV absorption and lack of fluorescence has made it unsuitable for fluorescence-guided photodynamic therapy against cancer. In this work, we synthesized a series of phenalenone derivatives containing electron-donating groups to red-shift the absorption spectrum and bromine(s) to permit good singlet oxygen production via the heavy-atom effect. Of the derivatives synthesized, the phenalenone containing an amine at the 6-position with bromines at the 2- and 5-positions (OE19) exhibited the longest absorption wavelength (i.e., green) and produced both singlet oxygen and red fluorescence efficiently. OE19 induced photocytotoxicity with nanomolar potency in 2D cultured PANC-1 cancer cells as well as light-induced destruction of PANC-1 spheroids with minimal dark toxicity. Overall, OE19 opens up the possibility of employing phenalenone-based photosensitizers as theranostic agents for photodynamic cancer therapy.

Full text of DOI:10.1021/acsmedchemlett.1c00284

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Letter
A Green-Absorbing, Red-Fluorescent Phenalenone-Based
Photosensitizer as a Theranostic Agent for Photodynamic Therapy
Esther G. Kaye, Karishma Kailass, Oleg Sadovski, and Andrew A. Beharry*
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ABSTRACT: Phenalenone is a synthetically accessible, highly
efficient photosensitizer with a near-unity singlet oxygen quantum
yield. Unfortunately, its UV absorption and lack of fluorescence has
made it unsuitable for fluorescence-guided photodynamic therapy
against cancer. In this work, we synthesized a series of phenalenone
derivatives containing electron-donating groups to red-shift the
absorption spectrum and bromine(s) to permit good singlet oxygen
production via the heavy-atom effect. Of the derivatives synthesized,
the phenalenone containing an amine at the 6-position with bromines
at the 2- and 5-positions (OE19) exhibited the longest absorption
wavelength (i.e., green) and produced both singlet oxygen and red fluorescence efficiently. OE19 induced photocytotoxicity with
nanomolar potency in 2D cultured PANC-1 cancer cells as well as light-induced destruction of PANC-1 spheroids with minimal dark
toxicity. Overall, OE19 opens up the possibility of employing phenalenone-based photosensitizers as theranostic agents for
photodynamic cancer therapy.
KEYWORDS: Photodynamic therapy, photosensitizer, fluorescence, phenalenone, theranostic
hotodynamic therapy (PDT) is a cancer treatment known
for its minimal invasiveness and noncumulative resistance
simple, comprising of three fused phenyl rings with one ketone,
making it synthetically accessible, while its low molecular
weight and relatively nonpolar nature make it capable of
permeating cells for PDT.12 However, the requirement of UV-
A to violet light excitation (360−415 nm) limits PN for cancer
treatment,15 and its nonfluorescent nature does not permit
real-time fluorescence imaging of cancerous tissue. Thus, a PN
derivative capable of exerting high phototoxicity of cancer cells
using long irradiation wavelengths (i.e., >415 nm) while
permitting simultaneous fluorescence imaging is highly
warranted.
Several groups have synthesized PN derivatives, which have
provided some insight into the influence of substituents on the
photophysical properties of PN. For example, it was found that
the installation of methylene bridges does not lead to spectral
red shifts or impact the PN singlet oxygen/fluorescence
quantum yield.16−19 In contrast, extending the π conjugation
via ring substitution decreases the singlet oxygen yield13 with
no significant red shift in the absorption and only modest
increases in fluorescence.13,20 Sandoval-Altamirano et al.
measured the photophysical behavior of hydroxy- and
P
compared with traditional therapies.1 The procedure uses three
components: a photosensitizer (PS), light, and molecular
oxygen. Once the PS absorbs an appropriate wavelength of
light, it undergoes intersystem crossing to the triplet excited
state (*T), from which its energy is transferred either to
molecular oxygen (3O2) to generate singlet oxygen (1O2)
(Type II mechanism) or to biomolecules to produce radical
species (Type I mechanism),2 with both mechanisms
ultimately leading to cell death via apoptosis or necrosis
mechanisms.3 For optimal clinical applications, the PS should
undergo excitation at long wavelengths to minimize toxicity to
healthy cells and afford deep tissue penetration,4 and in
addition to producing reactive oxygen species (ROS), it should
be capable of fluorescing to permit image guidance alongside
PDT, a feature often used to determine the optimal irradiation
time and to assess the degree of cell death.5
Phenalenone (PN) (also known as 1H-phenalen-1-one or
perinaphthenone) represents a class of natural products widely
found in plants and fungi that possess antimicrobial roles as
phytoalexins and phytoanticipins.6 It is also well-known as an
extremely efficient Type II photosensitizer having a near-unity
singlet oxygen quantum yield across a wide range of solvents.7
In fact, PNs have been described to display ROS-mediated
activity against bacteria,8 mosquito larvae,9 parasitic nemat-
odes,9,10 and fungi11 and more recently as a PDT agent against
cancer.12,13 In contrast to other types of PSs (e.g., porphyrins,
BODIPYs, xanthenes),14 the PN core structure is relatively
Received: May 18, 2021
Accepted: July 7, 2021
https://doi.org/10.1021/acsmedchemlett.1c00284
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Scheme 1. Synthetic Pathway to Phenalenone Derivatives
ethoxy-PN derivatives in organic solvents21 and found that
these electron-donating groups cause red shifts and increase
the fluorescence emission but reduce the singlet oxygen yield
compared with native PN.21 Unfortunately, whether these
compounds have the ability to induce photocytotoxicity in
cancer cells was not determined.
phosphate-buffered saline (PBS) containing 1% dimethyl
sulfoxide (DMSO) (Tables 1 and 2). PN possesses an n →
Table 1. Absorption Maxima and Singlet Oxygen Quantum
a
Yields of Phenalenone Derivatives 1−5 and 7
We sought to develop a PN derivative capable of absorbing
long-wavelength light while producing sufficient singlet oxygen
and fluorescence to kill and image cancer cells, respectively.
Using the notion that electron-donating groups have the
potential to cause spectral red shifts but undesirably reduce the
singlet oxygen quantum yield, we reasoned the latter may be
offset by the incorporation of heavy atoms to promote
intersystem crossing to the triplet state22 while not impacting
the absorption spectrum significantly. To test this, we
evaluated the effects of oxygen- and nitrogen-based electron
donors in combination with bromination on the PN ring
(Scheme 1). We note that although derivatives 1−3, 5, and 6
were previously synthesized, their singlet oxygen quantum
yields were not determined.23−26
PN and derivative 1 were synthesized as previously reported
by the reaction of commercially available trans-cinnamoyl
chloride with either naphthalene or 2-methoxynapthalene,
respectively.25 Methylation of derivative 1 with methyl iodide
via an SN2 mechanism gave derivative 2,23 and subsequent
bromination using N-bromosuccinimide (NBS) yielded
derivative 3.27 To install an electron-donating amine group,
compound 1 was nitrated through electrophilic aromatic
substitution, which was directed to position 5 by the ortho/
para electron-donating effect of the 9-hydroxy group.
a
All of the experiments were performed at room temperature in PBS
(pH 7.4). The reference for derivatives 1−5 and 7 was phenalenone
(ΦΔ ≈ 1).7 The reference for derivative 4 was eosin Y (ΦΔ ≈ 0.57).29
π* transition from 330 to 430 nm (λmax = 360 nm) with an
extinction coefficient of 10 000 M−1 cm−1.17,28 We found that
all of the derivatives having the addition of electron-donating
groups (hydroxy, methoxy, amino), regardless of position on
the ring, exhibited a red shift of the n → π* band compared
with native PN (Figures 1 and S1−S3). As expected,
bromination did not significantly impact the absorption spectra
compared with the corresponding parent scaffolds (2 vs 3, 5 vs
7, and 6 vs OE19). Installation of the amine at the 5-position
(i.e., 5) produced a red shift of ∼100 nm relative to PN, which
increased to 125 nm when there was a hydroxyl group at the 9-
position (i.e., 4). Interestingly, moving the amine from the 5-
position to the 6-position (i.e., 6) induced an additional ∼100
nm red shift in the absorption spectrum, thereby producing the
most red-shifted compound in our series.
Subsequent reduction using SnCl2 produced derivative 4.26
A
similar nitration and reduction procedure was performed on
native PN, which yielded amino derivatives 5 and 6.
Bromination of 5 and 6 using NBS yielded compound 7 and
the key derivative OE19. NMR spectroscopy revealed that
while derivative 5 was monobrominated at position 6,
derivative 6 was dibrominated at positions 2 and 5 (see the
Supporting Information). We note that monobromination of
derivative 6 proved to be difficult, and thus, excess equivalents
of NBS were introduced to push the reaction toward
dibromination.
We determined the photophysical properties of each
compound by first measuring their absorption spectra in
B
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methoxy group (2) did cause a decrease in the singlet oxygen
yield. However, the singlet oxygen yield was nearly recovered
by the addition of Br at the 2-position (3), in agreement with
our initial hypothesis.
Table 2. Photophysical Properties of Compound 6 and
OE19
a
Addition of the more strongly electron-donating amino
group at the 5-position (5) led to a decrease in the singlet
oxygen yield, and adding the 9-hydroxy group (4) abolished
the singlet-oxygen-generating capability. Unfortunately, unlike
compound 2 versus 3, the introduction of bromine at the 6-
position (i.e., 7) could not recover the singlet oxygen
production but rather led to a decrease in the yield compared
with 5. This result suggests that the ability of a bromine
substituent to induce intersystem crossing and subsequent
singlet oxygen production depends on the position of the
bromine on the PN scaffold. Such a position dependence has
been previously observed for BODIPY-based PSs.31
Similar to derivative 4, direct modification of the π ring
system with the electron-donating amino group at the 6-
position (6) led to a complete loss of singlet oxygen
production. However, in this case, bromination at the 2- and
5-positions (OE19) resulted in a significant increase in the
singlet oxygen yield. Since previously characterized 6 is known
to be a good fluorophore,26 we asked whether the increase in
singlet oxygen production in OE19 came at the expense of
fluorescence. Interestingly, OE19 was found to retain
fluorescence emission at ∼600 nm with a quantum yield
similar to that of its parent compound 6, while compounds 1−
5 and 7 did not exhibit any significant fluorescence (Φf <
0.05). Thus, among the derivatives synthesized, OE19 exhibits
the best combination of long-wavelength absorption and good
fluorescence and singlet oxygen quantum yields, making it the
most promising candidate in the series.
a
b
All of the experiments were performed at room temperature. ΦΔ,
1
Φf, and λem. max. were measured in DMSO. The reference for the O2
quantum yield was rose bengal (ΦΔ = 0.76), and rhodamine B (Φf =
0.5) was the reference for the fluorescence quantum yield.32
c
d
Determined in PBS.26 Determined in PBS with 100 μg/mL BSA.
The above photophysical properties of OE19 were measured
in DMSO, as solubility/aggregation was found to occur in PBS
(although 6 was stable in PBS, measurements were performed
in DMSO for better comparison to OE19). Specifically, we
observed the fluorescence of OE19 to decrease with time in
PBS (Figure S7), which also resulted in a reduction in singlet
oxygen production (Figure S8). However, we found that this
aggregation effect can be diminished by the addition of bovine
serum albumin (BSA) to the PBS or by dissolving OE19 in cell
medium (DMEM) containing 10% fetal bovine serum (FBS)
(Figure S9). These results are consistent with studies using
high-protein environments as preventative measures against
small-molecule aggregation,33,34 as dissolving OE19 in medium
with reduced serum (Opti-MEM) or no serum at all resulted in
aggregation (Figure S9). Thus, given these observations, we
reasoned that OE19 may still function in cells, where
intracellular molecular crowding would reduce aggregation,
thereby permitting fluorescence and singlet oxygen production.
We note that under our irradiation conditions, the absorbance
of OE19 in PBS containing BSA remained constant, suggesting
that OE19 exhibits high photostability (Figure S10), a
characteristic that is also desirable for cellular applications.
To test OE19 in cells, we prepared a stock solution in
DMSO, which was diluted to a final concentration of 2 μM in
wells containing the pancreatic cancer cell line PANC-1 in
reduced-serum medium (Opti-MEM). After incubation for 3 h,
we observed bright red fluorescence signals diffuse within the
cytosol, suggesting that OE19 is cell-permeable (Figure 2).
Interestingly, we also observed good fluorescence contrast of
cells without removal of OE19 from the medium. We
hypothesize that this is likely the case because although
Figure 1. Spectra of phenalenone derivatives. (a) Lowest-energy
absorption band of hydroxy- or methoxy-PN compounds 1−3 in PBS.
(b) Lowest-energy absorption band of amino-containing compounds
4−7 and OE19 in PBS. (c) Fluorescence spectra of compound 6 and
OE19 in DMSO after excitation at 518 and 525 nm (0.13 AU at each
maximum), respectively.
We next determined the singlet oxygen quantum yields of
our derivatives using the singlet oxygen sensor 9,10-
anthracenediylbis(methylene)dimalonic acid (ABDA). ABDA
is selectively photobleached by singlet oxygen into its
corresponding endoperoxide, turning off its characteristic
absorption.30 Thus, a decrease the ABDA absorption at 401
nm can be monitored with increasing irradiation time for each
derivative, and the resulting slopes can be compared with those
of standards with known quantum yields irradiated under the
same conditions (Figures S4−S6). Although the introduction
of the electron-donating 9-hydroxy group in 1 produced a
bathochromic shift, it did not largely affect the singlet oxygen
production efficiency compared with native PN (Table 1). In
contrast, methylation of the hydroxy group to generate the
C
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Figure 3. Cell viability of PANC-1 cancer cells. Cells were treated
with increasing concentrations (0−2 μM) of OE19 in the dark or
under light conditions (15 min using a lamp with a green filter with an
emission maximum at 525 nm, 16.61 J/cm2). Cells treated with OE19
Figure 2. Fluorescence imaging of OE19 and intracellular ROS
production in PANC-1 cells. Top row: before irradiation, bright red
fluorescence from OE19 (2 μM) was observed, but no green
fluorescence from DCF (the product of ROS oxidation and esterase
cleavage from DCFH2-DA) was observed. Bottom row: after
irradiation (530 nm, 10 min, 11.14 J/cm2), bright green fluorescence
from DCF was observed, indicative of ROS production by OE19.
Scale bar = 50 μm.
displayed a dose-dependent response in viability under light (IC50
=
166 nM) but not in the dark (IC50 > 2 μM). Data are presented as
mean SD (n = 9).
aggregation of OE19 occurs in reduced-serum medium,
leading to fluorescence quenching (Figure S9), the intracellular
envrionment is capable of reducing the aggregation, thereby
“turning on” the fluorescence. Given these promising results,
we next determined whether OE19 is capable of producing
ROS intracellularly by employing the cell-permeable ROS
sensor 2′,7′-dichlorofluorescein diacetate (DCFH2-DA). When
DCFH2-DA is deactylated by intracellular esterases and
oxidized by ROS, the green-fluorescent product 2′,7′-
dichlorofluorescein (DCF) is produced.35 Irradiation of
PANC-1 cells treated with both DCFH2-DA and OE19
produced substantially stronger green fluorescence in compar-
ison with PANC-1 cells treated without irradiation (Figure 2)
or treated with only DCFH2-DA or OE19 and irradiated
(Figures S11 and S12). To evaluate whether the light-induced
ROS production by OE19 can induce photocytotoxicity,
PANC-1 cells were treated with OE19 (0−2 μM) in the dark
or with green-light irradiation (using a lamp with a green filter
with an emission maximum at 525 nm, 16.61 J/cm2) for 15
min. After the cells were cultured in the dark for 24 h, the cell
viability was determined using a standard MTT assay. We
found that irradiation induced cytotoxicity in a dose-dependent
manner with nanomolar potency (IC50 = 166 nM) (Figure 3).
In contrast, cells treated and kept in the dark displayed no
significant dark toxicity (IC50 > 2 μM) (Figure 3).
The mechanism of cell death was investigated by employing
annexin V−FITC, which binds to phosphatidylserine trans-
located to cell membrane exteriors during apoptosis, producing
green fluorescence.36 Cells were also stained with propidium
iodide, which permeates only damaged cell and nuclear
membranes.37 However, since propidium iodide and OE19
have overlapping emission, red fluorescence in the nuclei was
used only to confirm cell death (Figure S13). PANC-1 cells
were incubated with 0.5 μM OE19, irradiated for 15 min with
green light (using a lamp with a green filter with an emission
maximum at 525 nm, 16.61 J/cm2), and then stained with
annexin V−FITC 30 min, 80 min, 3 h, or 24 h after PDT. We
observed green fluorescence over background at all time
points, with the strongest signals produced at 24 h, suggesting
that the cells died by apoptosis (Figure 4). PANC-1 cells
incubated with OE19 (0.5 μM, 3 h) but kept in the dark lacked
Figure 4. Mechanism of cell death. PANC-1 cells were stained with
annexin V−FITC after treatment with OE19 (0.5 μM) and irradiation
for 15 min with green light (using a lamp with a green filter with an
emission maximum at 525 nm, 16.61 J/cm2). Shown are (top row)
bright-field images and (bottom row) fluorescence images of cells
stained with annexin V−FITC 30 min, 80 min, 3 h, and 24 h after
irradiation. 20× magnification, scale bars = 50 μm.
green emission from annexin-V−FITC, indicating that no dark
toxicity was exerted by OE19 (Figure S14).
Encouraged by the high potency and large light−dark
therapeutic window of OE19, we further explored its ability to
exert photocytotoxicity on PANC-1 tumor spheroids.
Compared with 2D cell culture, 3D cell culture systems
more accurately represent the microenvironment of tumors
with respect to their cell physiology, morphology, and spatial
dimensionality, and therefore, spheroids are regarded as a
better assessment of the in vivo therapeutic potential of
compounds.38 PANC-1 spheroids treated with OE19 (0−1.5
μM) for 3 h and kept in the dark exhibited no observable
changes in diameter or overall changes in cell density as
determined by bright-field images (Figure 5a,c). To further
confirm the cell viability of the spheroid, we used the
commercially available ReadyProbes Cell Viability Imaging
Kit, Blue/Green, whereby Hoechst 33342 fluorescently stains
the nuclei of viable and dead cells blue, while only dead cells
are stained with a green fluorescent nuclear dye. Cell death
staining of these spheroids showed bright blue fluorescent
signals with no observable green fluorescent signals, confirming
viability of the spheroids (Figure 5a,c). In contrast, spheroids
treated with OE19 (0−1.5 μM, 3 h incubation) and exposed to
green-light irradiation (using a lamp with a green filter with an
emission maximum at 525 nm, 16.61 J/cm2) for 15 min
showed a decreasing trend in diameter and a difference in
morphology of the spheroids, with total spheroid breakage
D
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healthy cells. However, it may be possible to modify the 6-
amino functional group with substrates for overexpressed
enzymes found in cancer cells, such as quinones for NQO116
or amino acids for peptidases,39 as a means to achieve
selectivity.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acsmedchemlett.1c00284.
■
sı
Synthetic details; 1H NMR, 13C NMR, and HRMS
spectra; photophysical characterization experiments;
absorption spectra; singlet oxygen and fluorescence
quantum yield measurements; solubility assessments;
cell culture details and imaging experiments; cell viability
in 2D and 3D PANC-1 cell culture experiments (PDF)
Figure 5. PDT in PANC-1 tumor spheroids. (a) Spheroids treated
with OE19 (0−1.5 μM) under dark conditions: (top row) bright-field
images with no observable breakage; (middle row) no cell death was
observed using the green fluorescent cell death reagent from the
ReadyProbes Cell Viability Imaging Kit Blue/Green; (bottom panel)
nuclear staining of all cells by Hoechst 33342. (b) Spheroids treated
with OE19 (0−1.5 μM) after irradiation (using a lamp with a green
filter with an emission maximum at 525 nm, 16.61 J/cm2) for 15 min:
(top row) bright-field images show changes in spheroid morphology
and density in a dose-dependent manner; (middle row) green
emission indicative of cell death was observed at 0.38 and 1.5 μM;
(bottom row) blue emission from the nuclei of all cells by Hoechst
33342 using the ReadyProbes Cell Viability Imaging Kit. 10×
magnification, scale bars = 100 μm. (c) Quantification of spheroid
diameter after treatment with OE19 in the dark or after irradiation.
Bars represent averages of three replicate spheroids for each condition
with 12 diameter measurements of each spheroid, and error bars
represent their respective standard deviations. No significant change
in diameter was observed in the dark.
AUTHOR INFORMATION
Corresponding Author
■
Andrew A. Beharry − Department of Chemical and Physical
Sciences, University of Toronto Mississauga, Mississauga, ON
L5L 1C6, Canada; Department of Chemistry, University of
Toronto, Toronto, ON M5S 3H6, Canada;
Email: andrew.beharry@utoronto.ca
Authors
Esther G. Kaye − Department of Chemical and Physical
Sciences, University of Toronto Mississauga, Mississauga, ON
L5L 1C6, Canada; Department of Chemistry, University of
Toronto, Toronto, ON M5S 3H6, Canada
Karishma Kailass − Department of Chemical and Physical
Sciences, University of Toronto Mississauga, Mississauga, ON
L5L 1C6, Canada; Department of Chemistry, University of
Toronto, Toronto, ON M5S 3H6, Canada
observed upon treatment with 1.5 μM OE19 and light (Figure
5b,c). Live/dead cell staining revealed a high degreee of
photocytotoxicty for spheroids treated with 0.38 and 1.5 μM
OE19, consistent with the observed morphological changes
(Figure 5b).
Oleg Sadovski − Department of Chemical and Physical
Sciences, University of Toronto Mississauga, Mississauga, ON
L5L 1C6, Canada; Department of Chemistry, University of
Toronto, Toronto, ON M5S 3H6, Canada
Complete contact information is available at:
In summary, we have developed the first long wavelength
(i.e., green)-absorbing red-fluorescent PN derivative capable of
producing singlet oxygen upon light irradiation. OE19 is cell-
permeable and exerts a high degree of photocytotoxicity in
both 2D and 3D cultured PANC-1 cancer cells with minimal
dark toxicity. OE19 was discovered by an examination of the
effects of electron-donating groups with or without bromina-
tion at various positions on the PN scaffold. Much like native
PN, its synthesis is simple, requiring only four steps using
commercially available, inexpensive reagents. For PDT
applications in vivo, we acknowledge that OE19 falls short
with regard to light excitation within the biological optical
window and suffers from limited solubility for administration.
However, since the derivatives synthesized here also provide
insight into the relationship between the intrinsic molecular
electronic structure of PN and its photophysical properties, it
seems possible that further exploration may lead to a PN
derivative capable of produce singlet oxygen with red- or NIR-
light irradiation. Further derivatization can also be done to
improve the solubility of OE19, such as installation of a
methylene bridge containing moieties bearing charges at pH
7.4 (e.g., a sulfonate or amino group). Lastly, aside from the
enhanced permeability and retention effect, OE19 is not
expected to exhibit a high degree of cancer selectivity over
https://pubs.acs.org/10.1021/acsmedchemlett.1c00284
Author Contributions
The experiments were designed by E.G.K., K.K., and A.A.B.
Synthesis was completed by O.S. and E.G.K. Photophysical
measurements and cell culture experiments were completed by
E.G.K. and K.K. The manuscript was written by E.G.K., K.K.,
and A.A.B. All of the authors approved the final version of the
manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Funding through a Natural Sciences and Engineering Research
Council of Canada (NSERC) Discovery Grant is acknowl-
edged. K.K. acknowledges support from NSERC Postgraduate
Scholarship - Doctoral (PGS-D). E.G.K. acknowledges support
from the University of Toronto Excellence Award (UTEA).
ABBREVIATIONS
■
PDT, photodynamic therapy; PS, photosensitizer; ROS,
reactive oxygen species; UV-A, ultraviolet A; NMR, nuclear
magnetic resonance; LED, light-emitting diode; ABDA, 9,10-
E
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(17) Godard, J.; Brégier, F.; Arnoux, P.; Myrzakhmetov, B.;
Champavier, Y.; Frochot, C.; Sol, V. New Phenalenone Derivatives:
Synthesis and Evaluation of Their Singlet Oxygen Quantum Yield.
ACS Omega 2020, 5 (43), 28264−28272.
(18) Godard, J.; Chapron, D.; Bregier, F.; Rosilio, V.; Sol, V.
Synthesis and Supramolecular Arrangement of New Stearoyl Acid-
Based Phenalenone Derivatives. Colloids Surf., A 2021, 612, 125988.
(19) Godard, J.; Gibbons, D.; Leroy-Lhez, S.; Williams, R. M.;
Villandier, N.; Ouk, T.-S.; Brégier, F.; Sol, V. Development of
Phenalenone-Triazolium Salt Derivatives for aPDT: Synthesis and
Antibacterial Screening. Antibiotics 2021, 10, 626.
anthracenediylbis(methylene)dimalonic acid; DMSO, dimeth-
yl sulfoxide; DCF, 2′,7′-dichlorofluorescein; DCFH2-DA, 2′,7′-
dichlorodihydrofluorescein diacetate; MTT, 3-(4,5-dimethylth-
iazol-2-yl)-2,5-diphenyltetrazolium bromide; IC50, half-maxi-
mal inhibitory concentration; FITC, fluorescein isothiocyanate
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