[CANCER RESEARCH 32, 1195-1200,
June 1972]
Potentiation of Drug Effect by Tween 80 in Chinese Hamster
Cells Resistant to Actinomycin D and Daunomycin1
HansjörgRiehm2 and June L. Biedler
Division of Drug Resistance [H. R., J. L. B.J, Sloan-Kettering Institute for Cancer Research, and Department of Pediatrics [H. R.], Memorial
Hospital for Cancer and Allied Diseases, New York, New York 10021
SUMMARY
In vitro studies of Chinese hamster sublines have indicated
that cellular resistance to actinomycin D and daunomycin is
predominantly
due to decreased uptake of drug. Very
probably, the alteration mediating resistance occurs in the
external cell membrane. For substantiation of these previous
findings, sensitive and resistant sublines were grown in the
presence of graded concentrations
of antibiotics, of the
surface-active, nonionic detergent Tween 80 and of various
combinations of both. Tween 80 caused a marked potentiation
of drug effect, particularly in resistant cells, which exhibited a
considerable degree of cross-resistance to the surfactant.
Increased uptake of tritiated actinomycin D and daunomycin
in the presence of Tween 80 was shown by radioautography to
be directly related to concentration
of detergent. Both
potentiation of drug effect in growth studies and enhancement
of uptake of antibiotics strongly support the concept that
experimentally developed resistance to antibiotics in these
Chinese hamster cells is in large part due to an acquired
alteration manifest at the cellular membrane.
INTRODUCTION
Experimentally
developed resistance to AD3 is associated
with uptake differences as a consequence
of reduced
permeability to drug in several bacterial and mammalian cell
systems, as previously discussed (2). For a graded series of
AD-resistant Chinese hamster sublines, we have provided
evidence suggesting that resistance is likewise due to altered
membrane
permeability.
Dose-response
data
and
radioautographic
determinations
of uptake
of AD-3 H
indicated that degree of resistance is proportional to degree of
cross-resistance to DM and vincristine and proportional to
uptake of AD itself (2). Similarly, reduced permeability to
drug was considered to be principally responsible for the
resistance to DM developing in Chinese hamster cells exposed
to this antibiotic (18). As yet uncharacterized and probably
nonspecific alteration(s) at the surface of the cell may explain
the resistance of these sublines to AD and DM, as well as the
1This investigation was supported in part by TJSPHSResearch Grant
CA 08748.
2Present address: Kinderklinik der Freien Universität,l Berlin 19,
Germany.
3The abbreviations used are: AD, actinomycin D; DM, daunomycin
(daunorubicin); ED50, 50% effective dose; ED80, 80% effective dose.
Received December 17, 1971; accepted March 6, 1972.
cross-resistance to a variety of other antibiotics and alkaloids
that are largely unrelated in mode of action. Whether
mechanisms such as described in other studies (8, 12, 19) may
also contribute to the resistance of these Chinese hamster cells
is unknown.
Investigations carried out by Yamada et al. (21, 22)
suggested that in vitro exposure of rat ascites hepatoma cells
to Tween 80 rendered them more sensitive to the action of
nitrogen mustard. Pilot studies encouraged us to use this
surfactant as a tool for experimentally altering membrane
permeability. Since an appropriate system of cell lines resistant
in different degrees to the antibiotics AD and DM was available
and since resistance was considered to be mediated by
membrane barriers, it was the aim of the present study to
demonstrate potentiation of the effect of the antibiotic by the
nonionic surfactant.
For this purpose, growth response
experiments and determination of uptake by radioautography
were carried out. Preliminary results have been reported (3).
MATERIALS AND METHODS
The source of parental cells used in this study, the
derivation of resistant sublines, the drug sensitivity assay, and
radioautographic technique were described previously (2, 18),
except as noted for individual experiments. Eagle's minimal
essential medium supplemented with 10% fetal calf serum was
used throughout. Resistant sublines were maintained at the
final concentration of drug for at least 6 months before this
study was initiated and were grown in the absence of drug for
10 to 15 days prior to use in experiments.
Sensitivity Assay for Combined Effect of Inhibitors. For
comparison of the effectiveness of 2 inhibitors, alone and in
combination, a method described by Elion et al. (7) and used
with bacteria was modified and adapted to conditions of
mammalian cell culture. The sensitivity assay (2) is based on
determination of total cell number in cell cultures growing in
the presence or absence (controls) of graded concentrations of
inhibitor for 72 ±2 hr. Essentially the same technique was
used for testing Tween 80 in combination with another
chemical agent. When 2 to 4 concentrations of 2 compounds
and 4 times 4 combinations were used to obtain growth
response data, it was possible to determine ED50 and ED80
values for each combination.
The fractional inhibitory
concentration was calculated by dividing the effective dose
value of the inhibitor, when present in the combination, by
the effective dose value of the same inhibitor that would be
required to give the same degree of inhibition (50 or 80%) by
JUNE 1972
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1195
HansjörgRiehm and June L. Biedler
Table l
Drug concentrations at which resistant lines were maintained; response of cell lines to Tween
80 in terms of ED s0 and ED 80; and degree of resistance and cross-resistance
MaintenanceconcentrationCell
toAD137624501022791960DM12976231883290Tween
of resistance"
(%)ED800.0200.0410.0450.0520.0810.050Degree
8011.72.32.84.42.4
lineDC-3FDC-3F/AD
IVDC-3F/AD
XDC-3F/DM
IDC-3F/DM
XXDC-3F/AD
IV/DMDrugADADDMDMDMHg/ml1.010.02.010.05.0TweenED500.0100.0180.0240.0290.0460.02480
" Resistance is expressed as ratio of ED5 0 values for resistant subline to parental line.
Table 2
inhibition of growth of parental DC-3F line and resistant subline
DC-3F/AD X by various concentrations of AD and
Tween 80 in combination
Concentration of agent
Fractional inhibitory
concentration
80(%)ADTween
Cell lineAD
DC-3F
80
(Mg/ml)Tween
0.0023
0.0017
0.0011
0.00072
0.00062
0.00052
0.0
0.0
0.001
0.002
0.005
0.0075
0.01
0.012
1.0
0.74
0.48
0.31
0.27
0.23
0.0
0.0
0.083
0.17
0.42
0.63
0.83
1.0
points are located along a straight line connecting 1.0 on the
abscissa with 1.0 on the ordinate. Deviation to the left or right
of this connecting line indicates synergism (potentiation) or
antagonism (interference). Straight lines connecting unities of
abscissa and ordinate with experimental points intersect at a
point
indicating
the
minimal
fractional
inhibitory
concentration of both compounds. If the sum of fractional
inhibitory concentration of the most effective combination (7)
is near 1.0, additive effect is assumed; the smaller the sum the
greater the degree of synergism.
Chemical Agents. The source of most of the chemical agents
used in these studies was given previously (2, 18). Tween 80
was obtained from Mann Research Laboratories, Inc., New
York, N. Y.; Triton WR-1339 from Ruger Chemical Co.,
Irvington-on-Hudson, N. Y.; dimethyl sulfoxide, from J. T.
Baker Chemical Co., Phillipsburg, N. J.; and neuraminidase,
from Worthington Biochemicals Corp., Freehold, N. J.
ED,
0.0054
0.0045
0.0037
0.0020
0.0018
0.0012
0.0
0.0
0.001
0.002
0.005
0.0075
0.01
0.023
1.0
0.83
0.69
0.37
0.33
0.22
0.0
0.0
0.044
0087
0.22
RESULTS
Response to Tween 80. Chinese hamster cell lines, resistant
in
various degrees to the antibiotics AD and DM, exhibited an
0.33
approximately
2- to 4-fold increase in resistance to the
0.44
1.0
surfactant, Tween 80 (Table 1). The response to the surfactant
could be expressed by a straight line in a semilogarithmic plot,
ED,
as previously shown for other chemical agents (1, 2, 18).
Cross-resistance to Tween 80 was demonstrably greater for the
DC-3F/AD X
0.0
1.0
0.0
4.5
DM-resistant than for the AD-resistant sublines. However,
0.002
0.58
0.077
2.6
0.005
0.22
0.19
0.98
despite the differential response of antibiotic-sensitive and
0.01
0.093
0.38
0.42
-resistant cells in the 3-day drug sensitivity assay, the
0.02
0.018
0.77
0.082
attachment of cells to glass at the ED5 0 level of the detergent
0.026
0.0
0.0
1.0
was not noticeably different following inoculation.
ED,
Cells growing in the presence of detergent exhibited a
densely
granular
appearance
which
was related
to
10.16.23.21.350.440.00.00.0020.0050.010.020.0481.00.610.320.130.0440.00.00.0420.100.210.421.0
concentration and which tended to disappear gradually after
removal of the agent. When the concentration of fetal calf
serum was increased from 10 to 20%, the toxicity in terms of
ED5 o was decreased by about one-half.
Tween
80 and Antibiotics
in Combination.
The
combination
experiments
were performed to determine
itself. When fractional inhibitory concentrations and effective
whether the surfactant would potentiate the action of AD and
dose values for both compounds were matched, it was possible
DM on cells sensitive or resistant to these agents. The
to plot corresponding fractional inhibitory concentrations in a calculation of fractional inhibitory concentrations (Table 2)
coordinate system. Drug effect is considered additive when obviated the problem of quantitative differences in response of
1196
CANCER RESEARCH VOL. 32
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Cellular Resistance and Tween 80
the various sublines to antibiotic or to Tween 80. The
dose-response curves for the DC-3F/AD X subline, at the
equivalent concentrations of Tween 80, showed a somewhat
wider spread with respect to concentration of AD than for
parental DC-3F cells, indicating a higher degree of potentiated
growth inhibition of resistant cells. The synergistic effect with
AD occurred even at demonstrably nontoxic concentrations of
Tween 80 for sensitive and resistant cells. A higher
concentration
of the surfactant was tested because of
cross-resistance of the AD-resistant cells. From the plot of the
sums of fractional inhibitory concentrations of the most
effective combination, only moderate synergism of drug action
against DC-3F is indicated (Chart 1), whereas a much higher
degree of synergistic action was exhibited for AD-resistant cell
lines. For all resistant sublines, Tween 80 markedly
potentiated the action of AD (Table 3). At the ED80 level, the
0.1 0.2
0.3 0.4
0.5 0.6 07
08
effect was more pronounced than at the EDSO level (Table 3;
Chart 1). Combination experiments with DM revealed drug
potentiation with both parental and resistant cells. Differential
potentiation in respect to DC-3F and DC-3F/AD IV cells
manifested by AD in combination with Tween 80 was also
demonstrated when the antibiotic mithramycin was tested
(Table 3). In a previous study, the DC-3F/AD IV subline was
found to be highly cross-resistant to this antibiotic (2).
Experiments performed with Chinese hamster cell lines
resistant in various degrees to amethopterin (1) revealed no, or
only moderate, synergism when tested in the same system
(Chart 2).
Uptake of AD-3 H and DM-3 H in Presence of Tween 80. The
uptake of tritiated AD by parental DC-3F cells and resistant
subline DC-3F/AD IV in the presence of a variety of chemical
agents was determined according to the schedule outlined in
Table 4. Radioautograms were prepared from cells exposed to
EDSO and 10 times EDSO levels of the test agent in
O.9 10
TWEEN 80
FRACTIONAL INHIBITORY CONCENTRATION
0.1
Chart 1. Effectiveness of combinations of AD and Tween 80 in terms
of fractional inhibitory concentrations determined from ED80 values.
»,parental DC-3F (2 experiments); •¿,
DC-3F/AD IV; o, DC-3F/AD X.
Intersections of straight lines, sums of the fractional inhibitory
concentrations of the most effective combination. The sums are given
in Table 3.
02
03
04
05
06
07
08
09
10
TWEEN 80
FRACTIONAL INHIBITORY CONCENTRATION
Chart 2. Effectiveness of combinations of amethopterin and Tween
80 against amethopterin-resistant sublines determined as described in
Chart 1. •¿,
DC-3F8/A55 (4,455-fold resistance); •¿,
DC-3F/A3
(108,400-fold resistance); *, CLM-7/A XVIII (32,200-fold resistance).
Table 3
Sum of fractional inhibitory concentrations of most effective combination of Tween 80
with other agents, for parental DC-3F and resistant sublines
The procedure for obtaining fractional inhibitory concentration is described in "Materials
and Methods" and illustrated in Charts 1 and 2.
Sum of fractional inhibitory concentrations at ED80 andED50 levels
Cell une
Tween 80 and AD
Tween 80 and DM
ED,
ED8C
ED,
ED,
Tween 80 and
mithramycin
ED8(
ED,
DC-3FDC-3F/AD
IVDC-3F/AD
XDC-3F/DM
IDC-3F/DM
XXDC-3F/AD
IV/DM0.610.220.220.310.310.220.660.400.310.380.370.270.320.490.530.400.310.450.710.770.620.450.800.391.000.76
JUNE 1972
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1197
HansjörgBiehm and June L. Biedler
Table 4
Uptake of AD-3 H by parental DC-3F cells and resistant subline DC-3F/A DIV
in presence of various agents at ED 50 and 10 times ED s 0
Cells were exposed simultaneously to either 0. l MgAD-3H per ml (DC-3F) or 1.0 tig AD-3H per ml (DC-3F AD IV) and the
test agent for 2 hr prior to preparation of the radioautograms.
Mean no. of grains per nucleus in cells
IV10XED501.31.51.30.9C0.71.51.91.70.50
IV0.0120.50.231.0°1500.2110.0b0.150.0230.30.05°0.02aED503.33.33.14.52.94.83.86.26.9DC-3F10
agentNoneAmethopterinDMDemecolcineDimethyl
Test
ED503.73.51.7c3.63.96.13.34.5cED51.40.81.41.21.71.82.01.50.70.45.817.0
X
sulfoxideHydrocortisone6-MercaptopurincNeuraminidaseNitrogen
mustard4-Nitroquinoline-A^-oxideProflavine
sulfateTriton
339Tween
WR-1
80ED50DC-3F0.0120.0160.0131.0"2000.421.0b0.350.0230.140.05°0.01°(Mg/ml)DC-3F/AD
a % values.
b ED50 not determined; these concentrations were tested.
c Determinations were technically impossible because of detachment of cells from coverslips.
combination with AD-3H. Only Tween 80 markedly enhanced
uptake (about 13-fold) in terms of mean number of grains per
nucleus in resistant cells, while parental cells were affected to a
minor degree (less than 2-fold), at the EDSO level. For the
parental cell line, neuraminidase
and another nonionic
detergent, Triton WR-1339, also appeared to cause slight
augmentation of uptake. However, for the resistant subline,
the only additional agent to influence grain number was Triton
WR-1339 with which there were 4- and 7-fold increases at the
2 concentrations used.
Sensitive cells (DC-3F) were shown to take up AD-3 H and
DM-3H to about the same extent (less than a 2-fold difference
in grain number) in the absence or presence of various
concentrations
of Tween 80 (Chart 3). For the AD- and
DM-resistant sublines, at the EDSO levels of Tween 80 (Table
1), there was an increase in grain number of approximately 10to 20-fold. All resistant sublines exhibited higher grain
numbers with the increase in concentration of surfactant
(0.002 to 0.05%). The dynamics of uptake for sensitive cells
was clearly different, as substantiated by the mean grain
number determined at the different concentrations of Tween
80 when the concentration of AD-3 H was reduced 10-fold
(Chart 3).
DISCUSSION
Tween 80 is described as a nonionic, surface-active
detergent, polyoxyethylene sorbitan monooleate. Tween 80
and some other nonionic and ionic surfactants appear to
increase permeability of the cell membrane and to enhance
uptake of dyes and proteins (9-11,
13, 14, 16). The
mechanism of action is poorly understood. The surface of cells
exposed to Tween 60, for example, increases more than twice
1198
(13), probably as a result of a flattening of the undulated
membranes during swelling by the opening of microtubules to
the cell surface (15, 17). In the present study, Tween 80
enhanced uptake of the antibiotics AD and DM, especially in
drug-resistant cells, as demonstrated by radioautography and
as suggested by growth response in combination experiments.
Increased uptake, therefore, may have effected potentiation of
drug action at the pharmacological sites.
According to our findings, AD- and DM-resistant cells are
characterized, in proportion to degree of resistance, by a
marked reduction in nuclear uptake of tritiated drug (2, 18).
However, after fixation with methanol, labeling of both
sensitive and resistant cells was markedly heavier; the density
of nuclear label exceeded by 3 to 5 times that of sensitive cells
exposed to drug before fixation (unpublished observations).
The correspondence between molecular weight and degree of
cross-resistance to several biologically active agents probably
unrelated in mode of action to AD and DM has been noted
(2). Incorporation of uridine-3H was relatively less affected by
a high concentration of AD, whereas the more sensitive cells,
including DC-3F, exhibited marked inhibition of RNA
synthesis, as determined radioautographically (2). In a study
of cell hybrids formed from a mixture of amethopterin- and
AD-resistant (DC-3F/AD IV) populations, the membrane
properties of the antibiotic-resistant
cells were apparently
expressed to a major degree in all the hybrid clones studied.
Resistance to AD was close to that of the AD-resistant parent
(20). Increased resistance to AD and DM of the sublines
derived from the spontaneously transformed DC-3F cells
resulted in reduced tumorigenicity in the cheek pouch of
conditioned weanling Syrian hamsters; DC-3F/AD X was
nontumorigenic (4). The antibiotic-resistant cell lines showed a
definite trend toward oriented growth patterns and an increase
CANCER RESEARCH VOL. 32
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Cellular Resistance and Tween 80
100
There is yet no clue as to whether the elevated content of
sialic acid, hexosamine, and hexose in the plasma membranes
of the AD-resistant subline contributes to the phenomenon of
resistance to the antibiotic.
The occurrence
of new
glycoproteins,
as well as the increased synthesis of
glycoproteins, was described. Since the site of action of
nonionic surfactants at the molecular level is unknown, we can
only speculate that the differences in membrane composition
may protect resistant cells from the action of certain drugs and
surfactants as well.
X
IO
Ó
10
O
UJ
ACKNOWLEDGMENTS
The excellent assistance of Miss Roberta A. Devaney and Miss
Barbara A. Spengler is gratefully acknowledged.
REFERENCES
« io
5
o»
'S 100
s
JD
I
IO
t
LO
0005
001
TWEEN 80(%)
002
005
Chart 3. Uptake of AD-3H and DM-3H, in terms of mean number of
grains per nucleus, in the absence and presence of various
concentrations of Tween 80. Cells were exposed simultaneously to
radioactive drug and Tween 80 for 2 hr. The concentration of AD-3H
was 1.0 /¿g/ml,except as indicated, and the concentration of DM-3H
was 5.0 Mg/ml. •¿
and «,DC-3F; T, DC-3F/AD II; m,DC-3F/AD IV; o,
DC-3F/AD X; V, DC-3F/DM I; 0, DC-3F/DM XX.
in adhesiveness to glass substrate, with an increase in degree of
resistance (4). Aggregation characteristics of the sensitive and
drug-resistant
populations
supported
the finding that
resistance to the antibiotics is accompanied by increased
intercellular adhesiveness (5). The findings of the present
study, however, offer the strongest support yet adduced for
our basic concept that altered permeability of the cell
membrane is the primary determinant of resistance for both
the AD- and DM-resistant Chinese hamster sublines.
Quantitative
differences in membrane composition of
DC-3F and DC-3F/AD X cells have been recently reported (6).
JUNE
1. Biedler, ¡.L., Albrecht, A. M., Hutchison, D. Ì.,
and Spengler, B.
A. Drug Response, Dihydrofolate ReducÃ-ase,and Cytogenetics of
Amethoperin-resistant Chinese Hamster Cells in Vitro. Cancer Res.,
32: 153-161, 1972.
2. Biedler, ¡.L., and Riehm, H. Cellular Resistance to Actinomycin D
in Chinese
Hamster
Cells in
Vitro:
Cross-resistance,
Radioautographic, and Cytogenetic Studies. Cancer Res., 30:
1174-1184, 1970.
3. Biedler, 1. L., and Riehm, H. Reduced Cellular Resistance to
Actinomycin D in the Presence of a Detergent. Proc. Am. Assoc.
Cancer Res., 10: 6, 1969.
4. Biedler, ¡.L., and Riehm, H. Reduced Tumor Producing Capacity
of Chinese Hamster Cells Resistant to Actinomycin D and
Daunomycin. Proc. Am. Assoc. Cancer Res., //: 8, 1970.
5. Biedler, }. L., and Spengler, B. A. Aggregation and Growth
Behavior of Cultured Chinese Hamster Cells: Relationship to Drug
Resistance and Oncogenic Potential. In Vitro, 6: 233, 1970.
6. Bosmann, H. B. Mechanism of Cellular Drug Resistance. Nature,
233: 566-569, 1971.
7. Elion, G. B., Singer, S., and Hitchings, G. H. Antagonists of Nucleic
Acid Derivatives. VIII. Synergism in Combinations
of
Biochemically Related Antimetabolites. ¡. Biol. Chem., 208:
477-488, 1954.
8. Goldstein, M. N., and Zeleny, V. Effect of Actinomycin D on
Sendai-fused Actinomycin D-resistant and -sensitive HeLa Cells. 1.
Cell Biol., 43: 44a, 1969.
9. Höber, R., and Höber,Ì.
The Influence of Detergents on Some
Physiological Phenomena, Especially on the Properties of the
Stellate Cells of the Frog Liver, i. Gen. Physiol., 25: 705-715,
1942.
10. Modes, M. E., Palmer, C. G., and Warren, A. The Effect of Surface
Active Agents on the Permeability to Dye of the Plasma Membrane
of Ehrlich Ascites Cells. Exptl. Cell Res., 21: 164-169, 1960.
11. Kay, E. R. M. The Effects of Tween 80 on the in Vitro Metabolism
of Cells of the Ehrlich-LettréAscites Carcinoma. Cancer Res., 25:
764-769, 1965.
12. Kessel, D., Botterill, V., and Wodinsky, I. Uptake and Retention of
Daunomycin by Mouse Leukemic Cells as Factors in Drug
Response. Cancer Res., 28: 938-941, 1968.
13. Malenkov, A. G., Bogatyreva, S. A., Bozhkova, V. P., Modjanova,
E. A., and Vasiliev, ). M. Reversible Alterations of the Surface of
Ascites Tumor Cells Induced by a Surface-active Substance, Tween
60. Exptl. Cell Res., 48: 307-318, 1967.
14. Miller, G. W., and Janicki, B. W. Further Studies on Selective
Cytotoxicity of Triton WR-1339. Cancer Chemotherapy Rept., 52:
243-249, 1968.
1972
Downloaded from cancerres.aacrjournals.org on June 14, 2017. © 1972 American Association for Cancer Research.
1199
HansjörgRiehm and June L. Biedler
15. Nordling, S., and Mayhew, E. Surface Area Changes and the
Electrophoretic Mobility of Tissue Culture Cells. Exptl. Cell Res.,
43: 77-83, 1966.
16. Palmer, C. G., Modes, M. E., and Warren, A. K. The Action of
Synthetic Surfactants on Membranes of Tumor Cells. I.
Morphological Observations. Exptl. Cell Res., 24: 429-439, 1961.
17. Patinkin, D., and Doljanski, F. The Effect of Volume Expansion on
the Electrophoretic Mobility of Cells. J. Cell. Comp. Physiol., 66:
343-349, 1965.
18. Riehm, H., and Biedler, J. L. Cellular Resistance to Daunomycin in
Chinese Hamster Cells in Vitro. Cancer Res., 31: 409-412, 1971.
1200
19. Simard, R., and Cassingena, R. Actinomycin Resistance in Cultured
Hamster Cells. Cancer Res., 29: 1590-1597, 1969.
20. Sobel, J. S., Albrecht, A. M., Riehm, H., and Biedler, J. L.
Hybridization of Actinomycin D- and Amethopterin-resistant
Chinese Hamster Cells in Vitro. Cancer Res., 31: 297-307, 1971.
21. Yamada, T., and Iwanami, Y. The Transport of Nitrogen Mustard
TV-oxidethrough Cellular Membrane and Its Cytological Effects in
Rat Ascites Hepatoma. Gann, 52: 225-233, 1962.
22. Yamada, T., Iwanami, Y., and Baba, T. The Transport of
14C-labeled Nitrogen Mustard TV-oxidethrough Cellular Membrane
Treated with Tween 80 in Vitro. Gann, 54: 171-176, 1963.
CANCER RESEARCH VOL. 32
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Potentiation of Drug Effect by Tween 80 in Chinese Hamster
Cells Resistant to Actinomycin D and Daunomycin
Hansjörg Riehm and June L. Biedler
Cancer Res 1972;32:1195-1200.
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