Development and Validation of a Spectrofluorimetric Method for the Determination of Erlotinib in Spiked Human Plasma

Abstract

A rapid and sensitive spectrofluorimetric method was developed and validated for the determination of erlotinib (ETB), a potent anticancer drug, in spiked human plasma without any derivatization. The described method was validated and the analytical parameters of linearity, accuracy, precision (intra- and inter-day), limit of detection (LOD), and limit of quantification (LOQ) were evaluated. The relation between the fluorescence intensity and concentration was found to be linear (r(2) 0.9998) over the range 125 to 1000 ng/mL with the detection limit of 15 ng/mL. A simple liquid-liquid extraction method was followed in order to extract the drug from spiked plasma. The mean absolute recoveries of ETB were 85.59 % (±0.57), 86.91 % (±1.77) and 89.31 % (±3.01) at spiked plasma ETB concentration of 5000, 3750 and 2500 ng/mL, respectively. The spectrofluorimetric method presented here is a rapid, simple, specific, and reproducible method and can be used to characterize the plasma pharmacokinetics of ETB.

Full text

SHORT COMMUNICATION
Development and Validation of a Spectrofluorimetric Method
for the Determination of Erlotinib in Spiked Human Plasma
Bivash Mandal &Pavan Balabathula &Nivesh Mittal &
George C. Wood &Himanshu Bhattacharjee
Received: 2 March 2012 /Accepted: 27 June 2012 / Published online: 9 August 2012
#
Abstract A rapid and sensitive spectrofluorimetric method
was developed and validated for the determination of erlo-
tinib (ETB), a potent anticancer drug, in spiked human
plasma without any derivatization. The described method
was validated and the analytical parameters of linearity,
accuracy, precision (intra- and inter-day), limit of detection
(LOD), and limit of quantification (LOQ) were evaluated.
The relation between the fluorescence intensity and concen-
tration was found to be linear (r
2
0.9998) over the range 125
to 1000 ng/mL with the detection limit of 15 ng/mL. A
simple liquid-liquid extraction method was followed in or-
der to extract the drug from spiked plasma. The mean
absolute recoveries of ETB were 85.59 % (±0.57),
86.91 % (±1.77) and 89.31 % (±3.01) at spiked plasma
ETB concentration of 5000, 3750 and 2500 ng/mL, respec-
tively. The spectrofluorimetric method presented here is a
rapid, simple, specific, and reproducible method and can be
used to characterize the plasma pharmacokinetics of ETB.
Keywords Erlotinib .Spectrofluorimetric .Spiked human
plasma .Validation
Introduction
The epidermal growth factor receptor (EGFR) tyrosine ki-
nase (TK) is recognized as an important molecular target
expressed in various types of solid tumors [1]. Erlotinib, N-
(3-ethynylphenyl)-6,7-bis(2-methoxyethoxy)quinazolin-4-
amine,(ETB) is a highly selective and potent inhibitor of
EGFR TK [2]. It is clinically used for the treatment of
several advanced malignancies including non-small cell
lung cancer (NSCLC), pancreatic, ovarian, head and neck,
breast, prostate, colorectal, hepatic, and renal cancers [3].
Several techniques such as high performance liquid chro-
matography with tandem mass spectrometry (LC-MS) [4,5]
or UV visible spectrophotometry [6,7], hydrophilic interac-
tion liquid chromatography with tandem mass spectrometry
(HILIC-MS/MS) [8] have been reported for the determina-
tion of ETB in human plasma. However, these techniques
are time-consuming, complex, expensive and require trained
personnel for clinical analysis of plasma samples.
A preliminary study in our lab showed the intrinsic
fluorescence property of ETB. Further evaluation of this
phenomenon led to the hypothesis that the application of
fluorescence spectrometry could be one of the viable alter-
natives for the determination of ETB in human plasma.
Fluorescence spectrometry is a very simple, rapid, efficient,
selective, and highly sensitive technique for determination
of drug in plasma [9–12]. A thorough survey of the literature
on bio-analytical methods for ETB reveals a lack of sup-
porting information employing spectrofluorimetric method
for the analysis of ETB in biological fluids. Although a
study was published concerning the application of fluores-
cence spectroscopy and UV-visible spectrometry to investi-
gate the binding ability of ETB with bovine serum albumin
[13], it did not report bio-analytical assay of ETB in plasma.
Therefore, the aim of the current study is to develop and
validate a simple and rapid spectrofluorimetric method for
the in vitro determination of ETB in spiked human plasma.
This method does not require derivatization of the drug due
to the intrinsic fluorescent activity of ETB. Results from this
B. Mandal :P. Balabathula :N. Mittal :G. C. Wood :
H. Bhattacharjee (*)
Plough Center for Sterile Drug Delivery Systems, Department of
Pharmaceutical Sciences, College of Pharmacy,
University of Tennessee Health Science Center,
26 South Dunlap Street,
Memphis, TN 38163, USA
e-mail: himanshu_b@me.com
J Fluoresc (2012) 22:1425–1429
DOI 10.1007/s10895-012-1103-8
Springer Science+Business Media, LLC 2012

study suggest that this method can afford a rapid, simple,
accurate and sensitive technique to determine ETB in
plasma.
Experimental
Chemicals and Reagents
ETB, free base (98 % purity) was purchased from Cayman
Chemical (MI, USA). Glycine, analytical grade and sodium
hydroxide, analytical grade were supplied by Fisher (NJ,
USA). All solvents (water, HPLC grade; acetonitrile, HPLC
grade; hexane, HPLC grade and ethyl acetate, ACS grade)
were also supplied by Fisher (NJ, USA). Drug free human
plasma was obtained from Innovative Research (MI, USA)
and stored at −80 °C until analysis.
Instruments
All fluorescent measurements were performed using a Hita-
chi F-2500 fluorescence spectrophotometer (Tokyo, Japan)
equipped with xenon lamp. Slit widths for both excitation
and emission monochromators were set at 5 nm and all
measurements were made in quartz cells with path length
of 1.0×1.0 cm. Thermo scientific IEC CL31R multispeed
centrifuge (NC, USA) with Eppendorf rotor (F16-48 ×1.5/
2.0, Fibrolite
®
, Piramoon Technol. Inc., CA, USA) was used
to separate insoluble components.
Standards and Sample Preparations
An accurately weighed sample (20.00 mg) of ETB was
transferred into a 100 mL volumetric flask, dissolved in
about 80 mL of acetonitrile and made up to the volume with
acetonitrile to prepare standard ETB stock solution. The
ETB stock solution was found to be stable for at least
30 days. Working solutions with concentrations ranging
from 125 to 1000 ng/mL were made by appropriate serial
dilution with acetonitrile.
Procedure for Calibration Curve
The ETB stock solution was diluted with acetonitrile to
obtain standard solutions of concentration ranging from
125 to 1000 ng/mL. The fluorescence intensity of the
standard solutions was measured at 470 nm following
an excitation at 247 nm (Fig. 1). The intensity of the
blank solution without ETB was measured. The cor-
rected fluorescence intensity (actual intensity less blank
intensity) was plotted against the corresponding drug
concentrations to obtain the calibration curve. The
Fig. 1 Excitation (a) and emission (b) spectrum of ETB in acetonitrile at room temperature
Table 1 Validation data for analysis of ETB using spectrofluorimetry
Parameter Result
Linearity range (ng/mL) 125.00–1000.00
λ
ex
/λ
em
(nm) 247/470
Regression equation I
F
08.8922 C–91.6566
Correlation coefficient (r
2
) 0.9998
Slope ± SD 8.8922±0.0331
Standard error of slope 0.019
Intercept ± SD 91.6566± 44.6161
Standard error of intercept 25.7591
Lower limit of detection 15.0523
Lower limit of quantification 50.1744
λ
ex
maximum wavelength of excitation; λ
em
maximum wavelength of
emission; I
F
corrected fluorescence intensity; Cconcentration; SD
standard deviation
1426 J Fluoresc (2012) 22:1425–1429

corresponding regression equation was derived to vali-
date the method.
Method Validation
The validation of the method was carried out by establishing
linearity, accuracy, precision (intra- and inter-day), limit of
detection (LOD), and limit of quantification (LOQ).
Procedure for Extraction of Drug from Spiked Human
Plasma
The extraction protocol was based on liquid-liquid extrac-
tion, adapted from published work by Masters et al [4].
Briefly, frozen human plasma samples (stored in a −80 °C
freezer) were thawed to ambient temperature. A 0.1 mL
aliquot of the human plasma was placed in a 1.5 mL
Fig. 2 Calibration curve of ETB in acetonitrile
Table 2 Accuracy of the spec-
trofluorimetric method for de-
termining ETB
SD standard deviation; SEM
standard error of mean; RSD
relative standard deviation; 1,2,3
represents measurements
obtained on day 1, day 2 and day
3 respectively (n03 for each
day)
Actual Mean ± SD % % % SEM
Days Conc. (ng/mL) Conc. (ng/mL) Nominal RSD Bias
1 125 131.61 0.35 105.29 0.26 5.29 0.20
2 125 133.12 0.06 106.50 0.05 6.50 0.04
3 125 133.23 0.17 106.58 0.13 6.58 0.10
1 250 250.02 0.24 100.01 0.10 0.01 0.14
2 250 252.38 0.23 100.95 0.09 0.95 0.13
3 250 252.20 0.43 100.88 0.17 0.88 0.25
1 500 508.10 2.60 101.62 0.51 1.62 1.50
2 500 493.44 0.72 98.69 0.15 −1.31 0.41
3 500 501.63 1.58 100.33 0.31 0.33 0.91
1 750 756.07 0.40 100.81 0.05 0.81 0.23
2 750 757.35 1.30 100.98 0.17 0.98 0.75
3 750 756.70 0.62 100.89 0.08 0.89 0.36
1 1000 1003.13 1.39 100.31 0.14 0.31 0.80
2 1000 1005.24 1.14 100.52 0.11 0.52 0.66
3 1000 1005.09 0.58 100.51 0.06 0.51 0.33
J Fluoresc (2012) 22:1425–1429 1427

polypropylene microcentrifuge tube. A volume of 0.04 mL
of standard drug solutions (at three different concentrations
of 17500, 13125 and 8750 ng/mL of ETB) was added to the
blank human plasma to achieve spiked plasma concentra-
tions of 5000 ng/mL, 3750 ng/mL and 2500 ng/mL, respec-
tively. The individual tubes were vortexed for 10 seconds
and incubated at room temperature (20–25 °C) for 5 min
following which a 0.1 mL portion of 100 mM NaOH/gly-
cine pH 12 buffer was added. The tube was then mixed for
10 s on a vortex mixer. Next, a volume of 1 mL of hexane:
ethyl acetate (50:50 v/v) was added to the tube and mixed
vigorously for 20 seconds on a vortex mixer. The samples
were then centrifuged at 9800 rpm, 4 °C for 15 min to assure
phase separation. The resulting organic layer was transferred
to a 1.5 mL polypropylene microcentrifuge tube and evap-
orated to dryness using nitrogen purging. Acetonitrile
(1 mL) was added to the tube, mixed for 10 seconds on
the vortex mixer and analyzedinspectrofluorimeter.A
blank solution was prepared in a similar manner using
0.1 mL of human plasma but without addition of ETB.
Results and Discussion
The calibration data with parameters for the analytical
performance of the proposed method are summarized in
Table 1. For evaluation of linearity at the selected con-
ditions, determination of ETB was carried out at five
concentration levels (n03), respectively. The calibration
curves of ETB were linear over the concentration range
of 125–1000 ng/mL with good correlation of coefficient
(r
2
)of0.9998(Fig.2). The LOD and LOQ were cal-
culated employing the following formula [9];
LOD ¼3Sb
m
LOQ ¼10Sb
m
where S
b
is the standard deviation of the intercept of regres-
sion line, and mis the slope of the calibration curve. On this
basis, the LOD and LOQ of the proposed method for standard
ETB solutionwere 15.05 and 50.17 ng/mL, respectively. LOQ
was found to be clinically relevant for the quantification of
ETB in plasma. Phase I studies reported a C
ss, min
of 1200±
620 ng/ml and 1642± 1085 ng/ml in NSCLC patients treated
with the recommended 150 mg daily dose, in western and
Japanese patients, respectively[14] . Overall, the reported data
support that our LOQs are sufficient to quantify plasma ETB
C
ss, min
in NSCLC patients.
Accuracy, intra-day and inter-day precisions of the
method were determined (shown in Tables 2and 3).
Three replicate samples in the same day, as well as on
three consecutive days were assayed for intra-day and
inter-day precision at five different concentrations. Ac-
curacy was calculated as % bias using the following
equation,
%Bias ¼Nominal ETB c oncentration measured ETB mean concentrationðÞ*100
Nominal ETB concentration
The % bias was found to be ranged from −1.31 to 6.58 %,
indicating the accuracy of the method. The intra-day and
inter-day precisions expressed as the % relative standard
deviation (% RSD) for ETB ranged from 0.05 to 0.51 %
and 0.11 to 1.95 %, respectively. The low % RSD indicates
the inter-day and intra-day precision of the method. Hence,
these results indicate that the proposed spectrofluoremetric
method is accurate and precise.
Recovery studies were carried, by spiking varying quan-
tities of pure drug solutions to the human plasma. The
solvent mixture of hexane/ethyl acetate (50:50 v/v) with
NaOH/glycine pH 12 buffer, selected for the liquid-liquid
Table 3 Intra- and inter-day
precision of the proposed
method
Actual Conc
(ng/mL)
Repeatability (intra-day precision) Intermediate Precision (inter-day)
Mean Conc. ± SD
(n03)
SEM % RSD Mean Conc. ± SD (n09) SEM % RSD
125 131.72 ±0.34 0.19 0.26 128.49± 2.51 0.83 1.95
250 249.60 ±0.23 0.13 0.09 247.37± 1.77 0.59 0.72
500 506.72 ±2.59 1.49 0.51 496.88± 8.44 2.81 1.69
750 753.75 ±0.39 0.23 0.05 751.94± 1.59 0.53 0.21
1000 999.88 ±1.38 0.79 0.14 1000.34± 1.15 0.38 0.11
Table 4 Accuracy and recovery data of ETB in spiked human plasma
Spiked
(ng/mL)
Found
(ng/mL)
Accuracy % Mean
Recovery %
±SD % RSD SEM
700 613.13 −12.41 85.59 0.57 0.66 0.33
525 456.28 −13.09 86.91 1.77 2.04 1.03
350 312.59 −10.69 89.31 3.01 3.36 1.74
1428 J Fluoresc (2012) 22:1425–1429

extraction method, showed acceptable recoveries. The mean
absolute recoveries of ETB were 85.59 % (±0.57), 86.91 %
(±1.77) and 89.31 % (±3.01) at spiked plasma ETB
concentration of 5000, 3750 and 2500 ng/mL, respectively.
The three spiked plasma concentrations fall within the
steady state plasma concentration range found in patients
[15,16]. The recovery values are in good agreement with
the findings of Faivre et al. [17] concerning HPLC-UV
method for quantification of ETB in human plasma. The
results reported in Table 4reveal that the % RSD and
percent mean of extraction recovery for spiked plasma
samples are in the range of 0.66–3.36 %, 85.59–
89.31 %, respectively. Relatively, high plasma protein
binding (90–95 % in humans) could be responsible for
low recovery values (below 90 %) [18].
Conclusion
A sensitive and rapid method for the determination of ETB
in spiked human plasma is reported using spectrofluorime-
try based on the intrinsic fluorescence properties of ETB.
The proposed method was optimized and validated for lin-
earity, precision and accuracy. The results of method vali-
dation indicates the linearity over the range from 125 to
1000 ng/mL (r
2
00.9998) with a detection limit of 15 ng/mL,
which is well within the observed therapeutic plasma levels
for ETB. The overall extraction efficiency was greater than
87 % for spiked plasma samples based on simple liquid-liquid
extraction method. Major advantages of this method are
simple sample preparation, low sample volume (0.1 mL),
and high sample throughput.
Acknowledgement The authors thank Plough Center for Sterile
Drug Delivery Systems and College of Pharmacy, University of Ten-
nessee Health Science Center (UTHSC), for financial assistance. Spe-
cial thanks to Prof. Dr. A.P. Naren and his lab workers, department of
physiology, UTHSC for their kind support with the spectrofluorimeter.
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