Novel sphingosine-containing analogues selectively inhibit sphingosine kinase (SK) isozymes, induce SK1 proteasomal degradation and reduce DNA synthesis in human pulmonary arterial smooth muscle cells

Article abstract of DOI:10.1039/c3md00201b

Sphingosine 1-phosphate (S1P) is involved in hyper-proliferative diseases such as cancer and pulmonary arterial hypertension. We have synthesized inhibitors that are selective for the two isoforms of sphingosine kinase (SK1 and SK2) that catalyze the synthesis of S1P. A thiourea adduct of sphinganine (F02) is selective for SK2 whereas the 1-deoxysphinganines 55-21 and 77-7 are selective for SK1. (2S,3R)-1-Deoxysphinganine (55-21) induced the proteasomal degradation of SK1 in human pulmonary arterial smooth muscle cells and inhibited DNA synthesis, while the more potent SK1 inhibitors PF-543 and VPC96091 failed to inhibit DNA synthesis. These findings indicate that moderate potency inhibitors such as 55-21 are likely to have utility in unraveling the functions of SK1 in inflammatory and hyperproliferative disorders.

Full text of DOI:10.1039/c3md00201b

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Novel sphingosine-containing analogues selectively
inhibit sphingosine kinase (SK) isozymes, induce SK1
proteasomal degradation and reduce DNA synthesis in
human pulmonary arterial smooth muscle cells†
Cite this: Med. Chem. Commun., 2013,
4, 1394
a
b
b
b
a
*
Hoe-Sup Byun, Susan Pyne, Neil MacRitchie, Nigel J. Pyne and Robert Bittman
Sphingosine 1-phosphate (S1P) is involved in hyper-proliferative diseases such as cancer and pulmonary
arterial hypertension. We have synthesized inhibitors that are selective for the two isoforms of
sphingosine kinase (SK1 and SK2) that catalyze the synthesis of S1P. A thiourea adduct of sphinganine
(F02) is selective for SK2 whereas the 1-deoxysphinganines 55-21 and 77-7 are selective for SK1. (2S,3R)-
1-Deoxysphinganine (55-21) induced the proteasomal degradation of SK1 in human pulmonary arterial
smooth muscle cells and inhibited DNA synthesis, while the more potent SK1 inhibitors PF-543 and
VPC96091 failed to inhibit DNA synthesis. These findings indicate that moderate potency inhibitors such
as 55-21 are likely to have utility in unraveling the functions of SK1 in inflammatory and
hyperproliferative disorders.
Received 16th July 2013
Accepted 5th August 2013
DOI: 10.1039/c3md00201b
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prepared in order to reduce cancer cell survival but only very few
have been found to be isoform selective. For example,
Introduction
(2R,3S,4E)-N-methyl-5-(40-pentylphenyl)-2-amino-4-pentene-1,3-
diol (commonly referred to as SK1-I and BML-258) is a selective
SK1 inhibitor that enhances the survival of mice in an ortho-
topic intracranial tumor model.8 An analogue of the oral
multiple sclerosis drug FTY720 (Gilenyaꢀ), (2R)-2-amino-2-
Sphingosine kinase (SK), which catalyzes the conversion of
sphingosine (Sph) to sphingosine 1-phosphate (S1P), exists as
two isoforms, SK1 and SK2. The isoforms are encoded by
distinct genes and differ in their biochemical properties,
subcellular localization, and function.1 There is accumulating
evidence that SK1 is involved in hyperproliferative diseases; for
instance, SK1 mRNA transcript and/or protein expression are
increased in various human tumors.2 Moreover, siRNA knock-
down of SK1 reduces proliferation of glioblastoma cells3 and
androgen-independent PC-3 prostate cancer cells.4 Sustained
hypoxia increases SK1 expression in proliferating human
pulmonary arterial smooth muscle cells (PASMC), which might
contribute to their increased survival5 and vascular remodeling
in pulmonary arterial hypertension. There is also evidence that
SK2 may play an important role in cancer. For example, siRNA
knockdown of SK2 enhances doxorubicin-induced apoptosis of
breast or colon cancer cells6 and reduces cancer cell prolifera-
tion and migration/invasion.7
(methoxymethyl)-4-(40-n-octylphenyl)butan-1-ol
((R)-FTY720-
OMe, ROME), is a selective, enantioselective, competitive (with
Sph) inhibitor of SK2.9 Treatment of MCF-7 breast cancer cells
with ROME abrogates the enrichment of actin into lamellipodia
in response to S1P.9 Another SK2-selective inhibitor is the
nonlipid molecule 4-pyridinemethyl 3-(40-chlorophenyl)-ada-
mantane-1-carboxamide (ABC294640), which is also a compet-
itive (with Sph) inhibitor of SK2 activity. ABC294640 reduces
formation of intracellular S1P in cancer cells and prevents
tumor progression in mice with mammary adenocarcinoma
xenogras.10 The Ki values for inhibition of SK2 by (R)-FTY720-
OMe and ABC294640 are very similar (16.5 mM vs. 10 mM,
respectively).9,10 Recently, 3-(2-amino-ethyl)-5-[3-(4-butoxyl-
phenyl)-propylidene]-thiazolidine-2,4-dione (K145) was identi-
ed as a selective inhibitor of SK2.11 This compound reduced
S1P levels, inhibited growth and suppressed ERK/AKT signaling
in U937 cells and inhibited tumor growth in vivo.11
As SK1 and SK2 are potential and promising targets for
cancer chemoprevention, a number of SK inhibitors have been
aDepartment of Chemistry and Biochemistry, Queens College, The City University of
New York, Flushing, NY 11367-1597, USA. E-mail: robert.bittman@qc.cuny.edu; Tel:
+1 718-997-3279
Diastereomers of diverse saturated sphingoid bases such as
sphinganine,12 sangol (L-threo-sphinganine, the rst putative
SK1 inhibitor to enter a phase I trial),13 fumonisin B1,14 spisu-
losine ((2S,3R)-1-deoxysphinganine, ES-285),15 enigmols (1-
deoxy-3,5-dihydroxysphinganines),16 and phytosphingosine
(PHS)17 were found to disrupt the normal biosynthesis of
bCell Biology Group, Strathclyde Institute of Pharmacy and Biomedical Sciences,
University of Strathclyde, Glasgow G4 0RE, UK
† Electronic supplementary information (ESI) available: Detailed synthetic
procedures and NMR spectra, and SK assay information. See DOI:
10.1039/c3md00201b
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various signaling sphingolipids and to possess pro-apoptotic with NaBH4 gave 2-azido-1,3-diol 2, which was converted to the
properties via multiple mechanisms in numerous cell types. In 2-azido-1,3-cyclic sulfate intermediate 3 by reaction with SOCl2
previous work, we showed that N-phenethylisothiocyanate in the presence of pyridine, followed by oxidation of resulting
derivatives of sphingosine and sphinganine have a higher cyclic sulte with catalytic RuO4. Without further purication, 3
cytotoxic activity to HL-60 leukemic cells than sphinganine and was subjected to reduction with sodium borohydride in DMF in
sangol.18 These ndings suggest that adducts of synthetic the presence of sodium iodide, which removed the primary
saturated sphingoid bases may be putative inhibitors of either hydroxyl group and reduced the azide, affording (2S,3R)-2-
or both SK isoforms. In this communication, we report the amino-3-octadecanol (55-21) in 79% yield. The reaction of 55-21
synthesis of a series of saturated D-erythro long-chain bases and with formaldehyde in the presence of NaBH3CN in MeOH fur-
an assessment of their ability to inhibit the two isoforms of SK. nished the N,N-dimethylamino derivative 55-22 in 82% yield. N-
Our data have identied new isoform-selective SK inhibitors, of Methylation of 55-22 with methyl tosylate in THF gave the
which 55-21 is also able to induce proteasomal degradation of N,N,N-trimethylammonium tosylate salt, 77-13.
SK1 and reduce DNA synthesis in human pulmonary arterial
smooth muscle cells (PASMC).
As shown in Scheme 2, the synthesis of oxyspisulosine analog
77-7, which contains an oxygen atom in the aliphatic chain,
started with rac-1-O-tetradecylglycerol (4).21 Oxidative cleavage of
vicinal diol 4 with NaIO4 afforded aldehyde 5. HWE reaction of 5
with (EtO)2P(O)CH2CO2Et in aqueous 2-propanol the presence
of K2CO3 afforded (E)-a,b-unsaturated ester 6 with good E
selectivity. Asymmetric dihydroxylation of ester 6 with AD-mix-b
proceeded smoothly, providing chiral 2,3-diol ester 7 in 89%
yield. Conversion of diol 7 to cyclic sulfate intermediate 8,
followed by regioselective azidation gave azidoester 9, and
reduction of the ester functionality in 9 with NaBH4 gave
2-azido1,3-diol 10. We next attempted to remove the primary
hydroxyl group from 1,3-diol 10 by the cyclic sulfate method-
ology shown in Scheme 1. However, when the cyclic sulfate of 10
was reduced with NaBH4 we found that the oxygen atom in the
aliphatic chain affected the regioselectivity of the reduction,
resulting in a mixture of primary and secondary alcohols that
was difficult to purify. Therefore, we devised a novel route
Results and discussion
Fig. 1 shows the structures of the 1-deoxysphingoid bases 55-21,
55-22, 77-7, and 77-13; the thiourea-sphinganine bases F01 and
F02; the 4-sphingenine (sphingosine) adducts 67-320 and 67-
330; the thiourea adduct of 2-epi-pachastrissamine19 67-341;
and the thiourea-PHS derivatives 67-301, 67-306, 67-310, and
the urea-PHS derivative 67-311.
Scheme 1 outlines the preparation of 1-deoxysphinganine
analogues 55-21 and 55-22 via cyclic sulfate intermediates of
(2S,3R)-2-azidosphinganine. Azidoester 1 was prepared by
asymmetric dihydroxylation of ethyl octadecenoate using AD-
mix-b ((DHQD)2PHAL), followed by conversion to a cyclic sulfate
intermediate and regioselective azidation with sodium azide in
aqueous acetone as described previously.20 Reduction of ester 1
Fig. 1 Structures of sphingoid bases evaluated as SK inhibitors.
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Scheme 1 Synthesis of 1-deoxysphingoid derivatives 55-21, 55-22, and 77-13 via cyclic sulfate chemistry. Reagents and conditions: (a) NaBH4, THF, MeOH, ꢁ78 ꢂC – rt;
(b) SOCl2, py, CH2Cl2, ꢁ78 ꢂC, 2 h, then rt, 2 h; (c) cat. RuCl3$3H2O, NaIO4, MeCN/H2O (5 : 1), rt, 2 h; (d) NaBH4 (2 equiv.), NaI (1 equiv.), DMF, 0 ꢂC – rt, 48 h, then aq. HCl
(79%); (e) CH2O (10 equiv.), NaBH3CN (11 equiv.), MeOH, 0 ꢂC – rt, 48 h (82%); (f) p-TsOMe, THF, rt, overnight (100%).
involving a dibutylstannane intermediate (11) to synthesize 77-7 hydrolysis of the N-protecting group with NaOH in MeOH
(Scheme 2). Reaction of 10 with dibutyltin oxide followed by (Scheme 3). Thiourea derivatives F-01 and F-02 were prepared by
tosylation of 11 gave intermediate 12, which was converted to 77- the reaction of sphinganine with an aryl isothiocyanate (ESI†).
6b in two steps and 66% overall yield from 10. In contrast to the
We assessed the effects of uorine and triuoromethyl
reduction of 3, the azido group was not completely reduced even substitution in the benzene ring of the putative inhibitors
in DMF at elevated temperature. Therefore, catalytic hydro- (Fig. 2). The N-(4-uorophenyl)thiourea-PHS derivative 67-301 is
genolysis was necessary to complete the reduction of tosylate 12. a weak and nonselective SK inhibitor, but effectiveness for SK1
The N-arylthiourea and -arylurea derivatives were prepared versus SK2 is improved by insertion of ve uorine atoms into the
by the addition of the amino group of Sph, sphinganine, or D- benzene ring to afford 67-306, albeit the inhibition remains
ribo-PHS to the electrophilic carbon of an aryl isothiocyanate or moderate. Thiourea 67-310 and urea 67-311, which are both
aryl cyanate in CHCl3/CH3OH (1 : 1) (ESI†). 67-341 was prepared p-triuoromethylphenyl PHS derivatives, are moderately effec-
from 2-epi-pachastrissamine (15)19 and pentauorophenyl iso- tive SK2 inhibitors (64.5 ꢀ 4.9% and 53.9 ꢀ 0.9% inhibition
thiocyanate. Cyclic amine 15 was obtained by regioselective at 50 mM, respectively). Notably, the N-(4-uorophenyl)thiourea-
tosylation of triuoroacetamido-D-ribo-PHS 14 followed by Sph derivative 67-320 is
a more effective SK2 inhibitor
Scheme 2 Synthesis of 1-deoxysphingoid derivative 77-7 via dibutylstannane-mediated monotosylation of 1,3-diol 10. Reagents and conditions: (a) NaIO4, THF/H2O,
0 ꢂC – rt, 2 h; (b) (EtO)2P(O)CH2CO2Et, K2CO3, 2-PrOH/H2O (1 : 1), 0 ꢂC – rt, overnight; (c) AD-mix b, MeSO2NH2, t-BuOH/H2O (1 : 1), rt; (d) SOCl2, py, CH2Cl2, 0 ꢂC; (e) cat.
RuCl3$3H2O, NaIO4, MeCN/H2O (5 : 2); (f) NaN3 (3 equiv.), Me2CO/H2O (2 : 1), then Et2O, aq. H2SO4; (g) NaBH4, THF/MeOH (100 : 1), 0 ꢂC – rt; (h) Bu2SnO, toluene,
reflux; (i) p-TsCl, CH2Cl2, 0 ꢂC – rt, overnight; (j) NaBH4, THF, 0 ꢂC – rt; (k) Pd(OH)2/C, MeOH, rt; (l) CH2O, NaBH3CN (12.5 equiv.), MeOH, 0 ꢂC – rt, 48 h (80%).
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Scheme 3 Synthesis of 67-341, a thiourea derivative of 2-epi-pachastrissamine. Reaction conditions: (a) CF3CO2Et, MeOH, rt, overnight (95%); (b) p-TsCl (1.1 equiv.),
py/CH2Cl2 (1 : 1), 0 ꢂC – rt (80%); (c) NaOH, MeOH, reflux, 3 h (100%); (d) C6F5NCS.
(79.2
ꢀ
1.9% inhibition at 50 mM) whereas its p-tri-
uoromethylphenyl analogue 67-330 is a weak inhibitor of both
SK isoforms. The cyclic N-(pentauorophenyl)thioureido deriv-
ative 67-341 is a more effective SK1 inhibitor (64.7 ꢀ 5.3% inhi-
bition at 50 mM). Sphinganine thiourea derivative F-02 is more
effective for SK2 (80 ꢀ 2% inhibition at 50 mM), but its analogue
F-01 is less effective. 1-Deoxysphinganine analog 55-21 and its
N,N-dimethyl derivative 55-22 are more effective SK1 inhibitors.
Insertion of an oxygen atom into the aliphatic chain afforded
77-7, which is also an effective SK1 inhibitor; however, the N,N,N-
trimethylammonium salt 77-13 is a nonselective SK inhibitor.
To further establish the selectivity for SK1 or SK2 of the most
effective compounds identied above, we determined the rela-
tive IC50 values for F-02, 55-21, and 77-7. As shown in Fig. 3A,
F-02 inhibited SK2 activity with an IC50 of 21.8 ꢀ 4.2 mM and SK1
activity with an IC50 of 69 ꢀ 5.5 mM. Fig. 3B shows that 55-21
inhibited SK1 activity with an IC50 of 7.1 ꢀ 0.75 mM and SK2
Fig. 2 Effect of inhibitors on SK1 or SK2 activity (n ¼ 3 for each compound, mean
of % control ꢀ S.D.). Compounds were used at 50 mM. The Sph concentrations
were 3 and 10 mM, corresponding to the Km values of SK1 and SK2, respec-
tively.9,22 BML-258 at 50 mM inhibited SK1 activity by 74.5 ꢀ 3.3%. The control is
set at 100% and denotes the activity against Sph alone.
Fig. 3 Concentration-dependent inhibition of (A) SK2 activity (upper graph) and SK1 activity (lower graph) by F-02; (B) SK1 activity (upper graph) and SK2 activity
(lower graph) by 55-21. Results are expressed as mean of % control ꢀ S.D. of control (n ¼ 3–6); the control is set to 100% and represents the activity with Sph in the
absence of inhibitor. The Sph concentrations were 3 and 10 mM, corresponding to the Km of SK1 and SK2, respectively; (C) effect of 55-21 and F-02 on SK1 expression.
PASMC were treated with or without MG132 (10 mM, 30 min) before addition of 55-21 (10 mM, 24 h) or F-02 (10 mM, 24 h). Cell lysates were western blotted with anti-
SK1 and anti-actin antibodies. Results are representative of three experiments.
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activity with an IC50 of 766 ꢀ 133 mM. 77-7 inhibited SK1 activity
with an IC50 of 27.8 ꢀ 3.2 mM and SK2 activity with an IC50 of
300 ꢀ 62.3 mM (Fig. 4).
Next, the possibility that the compounds that bear a hydroxyl
group may also serve as SK substrates was examined. At 50 mM,
F01, 77-13, 67-341, and 67-302 are weak substrates of SK1 (ESI†),
but probably overlap the Sph binding site in SK1, thereby
inhibiting catalytic phosphorylation of Sph. At 50 mM, F02 and
F01 were very weak substrates of SK2 but 67-302 (cis-Sph) was
efficiently phosphorylated by SK2. None of the other
compounds were SK1 or SK2 substrates.
We have previously shown that inhibition of SK activity in
cells with the SK inhibitors SKi, N,N-dimethyl-Sph, or FTY720
induces proteasomal degradation and removal of SK1 from
PASMC and cancer cell lines.23 Removal of SK1 in response to Fig. 6 Assessment of the effects of PF-543 (10 nM and 100 nM, 24 h),
VPC96091 (300 nM, 24 h), and 55-21 (100 nM and 1 mM, 24 h) on [3H]-thymidine
SKi reduces intracellular S1P and increases C22:0-ceramide
incorporation into DNA in PASMC. Results are expressed as mean of % control ꢀ
S.D. of control (n ¼ 3); the control is set to 100%. ***p < 0.05 versus control.
levels, thereby promoting apoptosis.23 Fig. 3C shows that
treatment of PASMC with the SK1-selective inhibitor 55-21
(10 mM, 24 h) reduced the expression of SK1; this was reversed
by pre-treatment of the cells with the proteasomal inhibitor
MG132. In contrast, treatment of PASMC with the SK2-selective
inhibitor F-02 was without effect on SK1 expression, suggesting
that changes in ceramide-sphingosine-S1P rheostat regulated
by SK2 is not accessible to the proteasome and therefore does
not regulate SK1 turnover.
Recent studies have identied new nonlipid SK1 and SK2
inhibitors with nanomolar potency, including PF-543 and
VPC96091 (see ESI† for structures).24,25 We tested the effect of
PF-543 on SK1 and SK2 activity. Fig. 5 shows that PF-543
inhibited SK1 activity with an IC50 value of 28 ꢀ 6.15 nM. This is
a 10-fold lower potency than previously reported for PF-543.24 In
contrast, PF-543 inhibited SK2 activity by 33.3 ꢀ 3.0% at 5 mM
and 72. 2 ꢀ 3.4% at 50 mM (n ¼ 3), conrming that this
compound is highly selective for SK1 as previously reported.24
Interestingly, we found that treatment of PASMC with 100 nM
PF-543 induced a decrease in cellular SK1 expression, which was
reversed by the proteasomal inhibitor MG132 (Fig. 5). These
ndings indicate that inhibitor-induced proteasomal degrada-
tion of SK1 correlates with a concentration-dependent inhibi-
tion of SK1 activity.
VPC96091 was used at the previously reported Ki concen-
tration for SK1 and SK2.25 VPC96091 at 130 nM inhibited SK1
activity by 41.3 ꢀ 3.0% (n ¼ 3), while 1.5 mM VPC96091 inhibited
SK2 activity by 73.4 ꢀ 1.5% (n ¼ 3). At 50 mM, VPC96091 abol-
ished SK1 and SK2 activity (data not shown). Therefore, both
PF-543 and VPC96091 are more effective inhibitors of SK1 than
the new inhibitors presented herein. However, PF-543 and
VPC96091 are ineffective at reducing DNA synthesis in PASMC,
while 55-21 signicantly inhibited DNA synthesis (Fig. 6).
Fig. 4 Concentration-dependent inhibition of SK1 activity (left graph) and SK2
activity (right graph) by 77-7. Results are expressed as mean of % control ꢀ S.D. of
control (n ¼ 3); the control is set to 100% and represents the activity with Sph in
the absence of inhibitor. The Sph concentrations were 3 and 10 mM, corre-
sponding to the Km values of SK1 and SK2, respectively.
Conclusions
In summary, we have identied new SK inhibitors with isoform
selectivity. Moreover, inhibition of SK1 with selective SK1
Fig. 5 (A) Concentration-dependent inhibition of SK1 activity with PF-543. inhibitors, e.g., 55-21 and RB-005,26 is linked with ubiquitin-
Results are expressed as mean of % control ꢀ S.D. of control (n ¼ 3–6); the control
is set to 100% and represents the activity with Sph in the absence of inhibitor. The
Sph concentration was 3 mM, corresponding to the Km of SK1. (B) Effect of PF-543
on SK1 expression. PASMC were treated with or without MG132 (10 mM, 30 min)
before PF-543 (100 nM, 24 h). Cell lysates were western blotted with anti-SK1 and
anti-actin antibodies. Results are representative of three experiments.
proteasomal degradation of SK1 that might confer enhanced
efficacy of these compounds in terms of abrogating SK1 func-
tion in cells. In addition, we demonstrate here that 55-21 is
effective at reducing DNA synthesis in PASMC, while more
potent SK1 inhibitors, such as PF-543 and VPC96091, are not
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effective. There is substantial evidence to indicate that SK1 has
an essential role on regulating cell growth and survival.2 For
9 K. G. Lim, S. Chaode, R. Bittman, N. J. Pyne and S. Pyne, Cell.
Signalling, 2011, 23, 1590.
instance, siRNA knockdown of SK1 has been shown to induce 10 K. J. French, Y. Zhuang, L. W. Maines, P. Gao, W. Wang,
ceramide-stimulated apoptosis of MCF-7 breast cancer cells.27
V. Beljanski, J. J. Upson, C. L. Green, S. N. Keller and
Therefore, while PF-543 and VPC96091 are more effective
C. D. Smith, J. Pharmacol. Exp. Ther., 2010, 333, 129.
inhibitors of SK1 compared with 55-21, this enhanced binding 11 K. Liu, T. L. Guo, N. C. Hait, J. Allegood, H. I. Parikh, W. Xu,
affinity might result in a lack of specicity toward other
enzymes that can bind sphingosine-based compounds, such as
G. E. Kellogg, S. Grant, S. Spiegel and S. Zhang, PLoS One,
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ceramide synthases. This might effectively negate the effect of 12 W. D. Jarvis, F. A. Fornari Jr, R. S. Traylor, H. A. Martin,
inhibiting SK1 activity on cell growth and survival by preventing
formation of ceramide from sphingosine that has accumulated
L. B. Kramer, R. K. Erukulla, R. Bittman and S. Grant,
J. Biol. Chem., 1996, 271, 8275.
as a result of inhibiting SK1 activity. Indeed, PF-543 fails to 13 M. A. Dickson, R. D. Carvajal, A. H. Merrill Jr, M. Gonen,
increase endogenous ceramide levels in head and neck 1483
carcinoma cells, where it lacks cytotoxicity.24 The novel
L. M. Cane and G. K. Schwartz, Clin. Cancer Res., 2011, 17,
2484.
compounds identied here, e.g. 55-21, have moderate potency, 14 J. M. Soriano, L. Gonzales and A. I. Catala, Prog. Lipid Res.,
which might represent a more favorable prole in terms of 2005, 44, 345.
selectively abrogating SK1 function without exhibiting ‘off- 15 C. Massard, R. Salazar, J. P. Armand, M. Majem, E. Deutsch,
´
´
´
target’ effects on sphingosine/ceramide metabolizing enzymes.
In this regard, 55-21 recapitulates siRNA knockdown and
M. Garcıa, A. Oaknin, E. M. Fernandez-Garcıa, A. Soto and
J. C. Soria, Invest. New Drugs, 2012, 30, 2318.
genetic studies in terms of reducing cell growth; thus 55-21 is 16 H. Symolon, A. Bushnev, Q. Peng, H. Ramaraju, S. G. Mays,
expected to have utility in unraveling the functions of SK1 in
inammatory and hyperproliferative disorders. With the recent
elucidation of the atomic structure of SK1,28 it may be possible
J. C. Allegood, S. T. Pruett, M. C. Sullards, D. L. Dillehay,
D. C. Liotta and A. H. Merrill Jr, Mol. Cancer Ther., 2011,
10, 648.
to dene the binding modalities of these inhibitors in the future 17 H. Stockmann-Juvala and K. Savolainen, Hum. Exp. Toxicol.,
and to optimize the structures of novel inhibitors to achieve
higher potency and selectivity.
2008, 27, 799.
18 C. R. Johnson, J. Chun, R. Bittman and W. D. Jarvis,
J. Pharmacol. Exp. Ther., 2004, 309, 452.
19 Stereoisomers of 4-amino-2-tetradecyltetrahydrofuran-3-ol
(pachastrissamines) are inhibitors of SK and protein
kinase C; see: Y. Yoshimitsu, S. Oishi, J. Miyagaki, S. Inuki,
H. Ohno and N. Fujii, Bioorg. Med. Chem., 2011, 19, 5402.
20 L. He, H.-S. Byun and R. Bittman, J. Org. Chem., 2000, 65,
7618.
Acknowledgements
This work was supported by a British Heart Foundation grant
(29476) to NJP/SP and by NIH Grant HL-083187 to RB. We thank
Dr Dong Jae Baek for preparing VPC96091.
21 C. I. Hong, A. Nechaev, A. J. Kirisits, R. Vig, S.-W. Hui and
C. R. West, J. Med. Chem., 1995, 38, 1629.
Notes and references
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