Original Article DOI: 10.1111/j.1476-5829.2011.00314.x
A dose-finding study with a novelwater-soluble formulation of paclitaxelfor the treatment of malignant high-gradesolid tumours in dogs
H. von Euler1, P. Rivera1,∗,, H. Nyman2, J. Haggstrom1 and O. Borga3
1Department of Clinical Sciences, Division of Small Animal Clinical Sciences, Swedish University ofAgricultural Sciences (SLU), Uppsala, Sweden2Department of Clinical Sciences, Division of Diagnostic Imaging, Faculty of Veterinary Medicine and AnimalSciences, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden3Borga PK Consulting, Stockholm, Sweden
AbstractA new formulation of water-soluble paclitaxel (Paccal® Vet) has been developed for canine cancer
patients, without the need for pre-medication (traditionally required in non-water-soluble paclitaxel
formulations). The objective of the study was to determine a clinically safe and efficacious dose of
Paccal Vet and to estimate progression-free and overall survival and to evaluate single-dose
pharmacokinetics in tumour-bearing dogs. A positive risk:benefit ratio was established for Paccal Vet
administered at 150 mg m–2 intravenous (IV) for three or more treatment cycles. Preliminary efficacy
was demonstrated by best objective response rate (86%), median time to response (14 days) and
median progression-free survival (131 days). Paccal Vet was associated with expected adverse events
(AE) (e.g. myelosuppression), however the majority were transient, clinically silent and manageable.
This is the first clinical report of a water-soluble formulation of paclitaxel suggesting successful
administration and being safely used without pre-medication in dogs.
Keywordscancer, canine, malignant,paclitaxel, translationaloncology, tumour
Introduction
Solid tumours, with or without metastatic disease
are one of the most common neoplastic conditions
in the dog – although difficult to accurately estimate
approximately 50% of dogs will develop tumours
during their life.1–3 The most common types are
mammary tumour, malignant melanoma, haeman-
giosarcoma, osteosarcoma, mast cell tumour and
squamous cell carcinoma (SCC). Without effective
treatments for multicentric solid tumours, most
∗Present address: Stromsholm Small Animal ReferralHospital, Stromsholm, Sweden
dogs will progress to die of their disease within
months.
Primary treatment for solid tumours is often
surgery. However, for late stage disease or highly
malignant tumours, metastatic foci may already be
present or develop soon after surgery. Metastatic
disease generally manifests in the lungs, liver,
spleen and/or regional lymph nodes. Uncontrolled
metastatic disease will ultimately have a severe
impact on the animal’s quality of life. The objective
of chemotherapy is to induce a remission or
prevent disease progression [i.e. stable disease
(SD)], while maintaining an acceptable quality of
life for both the companion animal and caregiver.
Correspondence address:H. von EulerDepartment of ClinicalSciencesDivision of Small AnimalClinical SciencesSwedish University ofAgricultural Sciences (SLU)UppsalaSwedene-mail:[email protected]
© 2012 Blackwell Publishing Ltd 243
244 H. von Euler et al.
Paclitaxel is a widely used chemotherapeutic
agent with a broad spectrum of activity in human
cancers.4 Combinations of paclitaxel with other
forms of cancer therapy including conventional
chemotherapy, small molecule inhibitors and/or
radiation therapy has extended its use to can-
cers such as angiosarcoma,5 Kaposi’s sarcoma,6
endometrial cancer,7 malignant melanoma,8 non-
small-cell lung cancer,9,10 bladder cancer,11 and
cervical carcinoma.12 Indeed, paclitaxel has been
approved for use in combination with trastuzumab
in the treatment of metastatic breast cancer.13
Paclitaxel was originally isolated from the bark
of the Pacific yew tree, Taxus brevifolia in 1971.14
Taxanes exert their cytotoxic effect, at least in
part, by arresting mitosis through microtubule
stabilization, resulting in cellular apoptosis.15 The
development history for paclitaxel has resulted in
extensive experience with the toxicities linked to its
use in rodents, dogs, primates and humans. Com-
mon side effects predicted by the mechanism of
action of paclitaxel include bone marrow suppres-
sion, nausea, vomiting, loss of appetite, change in
taste, thinned or brittle hair, transient joint pain
and paraesthesia.15 Because of the low aqueous sol-
ubility of paclitaxel, Taxol® formulations include
cremophor-EL (polyoxyethylated castor oil) and
ethanol (1:88). This formulation allows solubiliza-
tion of paclitaxel for parenteral use.16 Cremophor-
induced complement activation is believed to be
the cause of hypersensitivity reactions related to
Taxol use in humans and other species.17 In dogs,
the published clinical experiences are few. A clinical
study conducted in client-owned animals demon-
strated that 165 mg m–2 of paclitaxel (containing
the excipient cremophor-EL) given intravenously
in 3-week cycles, showed activity against a vari-
ety of cancers in dogs.18 Despite pre-medication
with anti-histamines and corticosteroids to reduce
hypersensitivity reactions to cremophor-EL, 64%
of dogs still experienced hypersensitivity reactions.
To this end, a new formulation of paclitaxel was
developed for administration to dogs abrogating
hypersensitivity reactions and removing the need
for pre-medication.19 The new veterinary formula-
tion (Paccal® Vet), was made water-soluble by using
a mixed micelle preparation with a surfactant based
on a derivative of retinoic acid; the novel excipient
(XR-17) in Paccal Vet forms nanoparticles. Pac-
cal Vet is presently under clinical development in
canine oncology.
The objective of this first-in-dog study was to
determine a clinically safe and efficacious dose of
Paccal Vet for treatment of canine solid tumours.
Additional objectives were to estimate progression
free and overall survival and to evaluate single-dose
pharmacokinetics in tumour-bearing dogs.
Materials and methods
Study design
The study was designed as an open-label, single-
arm, dose-escalating clinical field study and was
conducted at a single site in Sweden (SLU, Uppsala)
in compliance with good clinical practice. All
therapies and sample collections were approved
by the Swedish Animal Ethical Committee and the
Swedish Animal Welfare Agency. Owner informed
consent was obtained in writing before initiating
any study-related procedures.
Selection criteria
Client-owned dogs of either sex and any breed,
age or weight with a confirmed diagnosis of clin-
ically measurable multicentric solid tumours were
screened for inclusion. The intention was to enroll
25 dogs. Dogs were excluded if they (1) had
been treated with systemic glucocorticoids within
2 months prior to the study; (2) had previously
received chemotherapy, radiation therapy, hor-
monal or other anti-neoplastic therapy; (3) were
pregnant or lactating; (4) had a life expectancy
of less than 1 month; (5) had an active infec-
tion or a clinically significant abnormality in vital
organ function; or (6) had a global activity score of
disabled.20
Study procedures
Within 7 days prior to the first paclitaxel treatment,
the veterinarian obtained owner consent; recorded
animal demographics, medical history, con-
comitant medications and physical examination
findings; identified and measured (length and
width) up to three tumour target lesions; and
performed complete blood count, serum chemistry
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
Paccal Vet for canine malignant tumours 245
and urinalysis evaluations on all dogs considered
eligible for the study. On day 0, dogs were clinically
staged based on haematology, clinical chemistry,
thoracic radiography, abdominal ultrasound,
regional lymph node fine-needle aspiration biopsy
(if palpably enlarged), buffy coat analysis, biopsy
for histopathology and tumour grading, where
indicated.
Dogs were withdrawn from the study for any
of the following reasons: death or euthanasia,
investigator or owner non-compliance with the
protocol, unacceptable adverse events, delay of
Paccal Vet treatment for more than 28 days or
progressive disease (PD).
Paccal Vet was supplied in vials of 60 mg
of lyophilized powder for injection and was
reconstituted in 60 mL of Ringers acetate to a
paclitaxel concentration of 1 mg mL–1 immediately
prior to administration. On the first day of paclitaxel
treatment (day 0), Paccal Vet (175 mg m–2) was
to be administered by slow intravenous (IV)
infusion over 15–30 min. Dogs were monitored
for adverse events, and if observed, the infusion was
immediately stopped and symptomatic treatment
was provided. If severe (Veterinary Co-operative
Oncology Group – common terminology criteria
for adverse events (VCOG–CTCAE) grade III or
higher)21 adverse events were not observed in the
first 3 dogs enrolled, the dose was to be increased
to 200 mg m–2 for the next cohort of three dogs
and the same dose-escalation scheme was applied to
subsequent cohorts. Dogs were treated with Paccal
Vet for at least three cycles and up to five cycles
(separate infusions approximately 21 days apart).
If a dose-limiting toxicity (DLT) was observed in a
given dog, the next dose of Paccal Vet was delayed
(up to 28 days) until the event had resolved. A
DLT was defined as ≥ grade III for any adverse
event with the exception of neutropenia, where a
grade III neutropenia that resolved prior to the
next scheduled treatment was not deemed dose-
limiting. Any grade IV neutropenia was deemed
a DLT.
While concomitant anti-cancer therapies were
prohibited during the study period, dogs were
permitted to receive other supportive therapies
(e.g. antibiotics and fluids) for the management
of adverse events or disease progression.
Clinical assessments
Each dog was evaluated by the veterinarian at 4, 7
and 21 (±2) days after each treatment infusion
(the day-21 assessment was made immediately
prior to the next cycle’s treatment infusion),
and if available at 14–21 days after completing
the last cycle. Follow-up contact at 6 and
12 months was conducted by phone or office
visit.
A physical examination was performed, global
activity score was assessed and samples were
collected for haematology and clinical chemistry
analyses on days 4, 7 and 21 of each cycle. Samples
for analysis of troponin-1 were obtained at 8
and 24 h after the first Paccal Vet treatment and
additionally on day 4 of cycle 2. All blood analyses
were performed at the division of clinical chem-
istry, University Animal Hospital, SLU, Uppsala.
Electrocardiography was periodically used to
monitor cardiac safety. Global activity score criteria
were: 0 = fully active, able to walk and run without
evidence of dyspnea, tiredness or emaciation;
1 = able to walk and run; slight tiredness, or dysp-
nea after severe exertion and/or slight emaciation;
2 = apparent tiredness, or dyspnea after moderate
to severe exertion and/or distinct emaciation;
3 = spontaneous tiredness or dyspnea (without
exertion), often lies on the floor; 4 = unable to care
for itself, recumbent; 5 = moribund.20
Biopsy, radiography and ultrasound were also
periodically used as needed to monitor disease
progression. Tumour measurements (sum of the
longest perpendicular diameter) were recorded
and response outcome was assessed 21 days after
each treatment infusion. Adverse events were
recorded from the time of first infusion of Paccal
Vet administration for up to 6 months or last visit.
An adverse event was defined as any undesirable
event, expected or not, occurring in a dog during
the study, whether considered as having a causal
relation to Paccal Vet or not. Serious adverse events
were defined as any life-threatening or morbid
event.
Pharmacokinetics
Two millilitres of blood was sampled via venipunc-
ture of the cephalic vein contralateral to the infusion
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
246 H. von Euler et al.
site on day 0 at 0 (pre-infusion), 8 and 15 min, and
1, 2, 4, 8, 12 and 24 h after the start of paclitaxel
infusion. Samples were stored at room temperature
for 30 min, and then centrifuged at 3000 × g for
5 min. Plasma was separated and transferred into
polystyrene vials and snap-frozen at −20 ◦C, then
stored at −70 ◦C.
Paclitaxel in plasma was quantified by Quin-
tiles AB (Uppsala, Sweden) using a validated
high-performance liquid chromatography (HPLC)
method with ultraviolet (UV) detection. Paclitaxel
analysis was performed with a lower limit of
quantification (LLOQ) of 40 ng mL–1 using 250 μL
samples. Blank plasma from each dog was analyzed
to ascertain no endogenous interfering peaks
(<20% of the peak height of the LLOQ). The crite-
ria for calibration samples (when back-calculated)
and quality control (QC) samples was ±15% of the
nominal value. The calibration curve comprised a
minimum of six standards and each analytical run
included four QC samples spiked at 120, 800, 1600
and 4000 ng mL–1. The following performance data
were obtained from the five runs of duplicate QC
samples; within-run precision 2.5–6.2% coefficient
of variation (CV) and between-run precision
3.8–4.5% (CV). Calibration curve r2 values varied
from 0.996 to 1.000. Pharmacokinetic parameters
were calculated only for dogs with a minimum of
plasma concentration data from five time points;
the last point was required to be at least 8 h after
the start of drug administration.
Variables
Response outcome [change in tumour size
according to World Health Organization (WHO)
criteria]was categorized relative to baseline
measurements as: complete response (CR, 100%
disappearance of all lesions); partial response
(PR, ≥50% decrease); PD, ≥25% increase; and SD,
any change not qualifying as CR, PR or PD. Global
activity score after treatment was compared with
values before treatment.
Time to objective response was defined as the
time from study start to the first observation of CR
or PR. Progression-free survival time was defined
as the time from study start to the first observation
of disease progression or death from any cause.
Values were censored at the last known visit for
dogs that were still alive and had not progressed.
Overall survival was defined as the time from study
start to the date of death. Values were censored
at the last known visit for dogs that were still
alive.
Pharmacokinetic variables included the area
under the plasma concentration time curve
from time zero to infinity (AUC), clearance
(CL), volume of distribution at steady state
(V ss), maximum concentration (Cmax), distribu-
tion half-life (T1/2α) and elimination half-life
(T1/2β).
Haematology and serum chemistry values after
treatment were compared with before treatment.
Haemoglobin and absolute leukocyte, platelet and
neutrophil counts, and alanine aminotransferase
(ALAT), alkaline phosphatase (ALP) and aspartate
aminotransferase (ASAT) were graded according to
VCOG–CTCAE.21 Abnormal clinical examination
findings, clinically significant laboratory abnormal-
ities or other clinically significant observations were
reported as adverse events, classified according
to the veterinary dictionary for drug regulatory
activities (VeDDRA)22 and graded according to
VCOG–CTCAE.21
Statistical and pharmacokinetic analyses
Formal statistical modelling and hypothesis test-
ing were not used in this exploratory study,
however descriptive statistics for each variable
were calculated. Nine dogs were not included
in the per-protocol analysis of efficacy (n =23) because of major protocol violations in the
study, but were all included in the analysis of
safety (n = 32). Pharmacokinetic analysis was con-
ducted using the WinNonlin software (Pharsight,
St Louis, MO, USA). An open two-compartment
model was found to adequately describe the data,
and model fitting was obtained by minimizing the
weighted sum of squares of the deviation between
the function curve (described by the parameters)
and the experimentally observed points. Examina-
tion of results from different weighting schemes
demonstrated that a weight of 1/(Yhat)2 was most
appropriate, where Yhat represented the estimated
dependent variable of the fitted curve of plasma
concentration.
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
Paccal Vet for canine malignant tumours 247
Results
Demographic information
Thirty-two dogs with a mean weight of 27 ± 13
(range 4–59) kg and mean age of 8 ± 3 (range
0.4–14) years were enrolled in the study. Female
dogs (n = 19; 59%) outnumbered male dogs
(n = 13; 41%). Dogs from 24 breeds were
enrolled; the most prevalent were mixed breed
(5), Boxer (3), Dachshund (2) and Rottweiler
(2). The distribution of tumour diagnoses was
mast cell tumour (8), mammary tumour (8),
lymphoma (4), squamous cell carcinoma (3) and
one each of anal sac carcinoma, bladder transitional
cell carcinoma, fibrosarcoma, haemangiosarcoma,
histiocytoma, malignant melanoma, mediastinal
mass, osteosarcoma and synovial cell sarcoma.
Of the 32 enrolled dogs, there were 9 major
protocol violations in the study – 7 dogs did
not receive the protocol-mandated three treatment
cycles of Paccal Vet; 2 dogs were enrolled but were
found to violate the inclusion/exclusion criteria
or were not compliant with protocol procedures.
These nine dogs were not included in the per-
protocol analysis of efficacy (n = 23), but were
included in the analysis of safety (n = 32).
On average, the dogs were in the study for 72 ± 31
(range 41–184) days. Twenty-five dogs received
three cycles of Paccal Vet; seven dogs remained
in the study to receive four cycles, and three
dogs remained in the study to receive five cycles
of treatment (Table 1). Because of unacceptable
toxicity only the first dog in the study was treated
once with 175 mg m–2 Paccal Vet; the remainder
of dogs at all cycles were treated with 100–150 mg
m–2. The most commonly administered dose of
Paccal Vet was 150 mg m–2 (≥67% dogs at each
cycle) (Table 1). Median treatment infusion time
was 15 min (range 10–24 min).
Clinical efficacy
Nineteen of the 23 dogs (82%) in the per-protocol
data set used for analysis of efficacy experienced
objective response of CR (n = 8) or PR (n = 11)
(Table 2). Three dogs with mast cell tumor (MCT)
had a CR. The other diagnoses with CR were SCC
(n=2) and one each of mammary adenocarcinoma,
Table 1. Number of dogs treated with Paccal Vet by doseand treatment cycle
Dose Cycle Cycle Cycle Cycle Cycle(mg m–2) 1 2 3 4 5
100 3 2 2 0 0
110 1 1 0 0 0
120 1 1 1 0 0
125 0 1 0 0 0
135 1 1 0 0 0
140 0 2 1 1 1
145 0 1 3 0 0
150 25 20 18 6 2
175 1 0 0 0 0
Total 32 29 25 7 3
Table 2. Summary of descriptive statistics for objectiveresponse, global activity and time to event variables
Statistic
Variable Category No. of dogs % (n = 23)
Best response CR 8 35%
PR 11 47%
SD 2 9%
PD 2 9%
Global activitya 0 19 83%
1 2 9%
2 1 4%
3 0 0%
4 1 4%
5 0 0%
Median Range
Time to CR or PR, d 19 14 3–64
Progression -free 23 131 20–416
survival, d
aScore at end of study or last observation (for withdrawn dogs). 0
= fully active, able to walk and run without evidence of dyspnea,
tiredness or emaciation; 1 = able to walk and run; slight tiredness,
or dyspnea after severe exertion and/or slight emaciation; 2 =apparent tiredness, or dyspnea after moderate to severe exertion
and/or distinct emaciation; 3 = spontaneous tiredness or dyspnea
(without exertion), often lies on the floor; 4 = unable to care for
itself, recumbent; 5 = moribund.
malignant lymphoma and histiocytic sarcoma.
Among the 11 dogs with PR, the diagnoses were
MCT (n = 4), malignant lymphoma (n = 2),
SCC (n = 2), mammary adenocarcinoma (n =2), fibrosarcoma (n = 1). Two dogs (mammary
tumour and anal sac carcinoma) experienced SD
for a minimum of 6 weeks, and two dogs had
an objective response of PD (mammary tumour
and malignant melanoma). Examples of tumour
response from two dogs are provided in Figs 1 and 2.
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
248 H. von Euler et al.
A B
C
Figure 1. Treatment response for 001–001 (Bella) with grade II mast cell tumour immediately prior (A), 21 days after cycle1 (B) and (C) 6 months after treatment with two cycles of Paccal Vet.
A B
Figure 2. Treatment response for 001–025 (Malou) with oral squamous cell carcinoma immediately prior (A) and 21 daysafter cycle 2 (B) of Paccal Vet treatment.
Global activity score at end of study (or last visit
for dogs that withdrew) was 0 in the majority of
dogs (n = 19; 83%) (Table 2). The incidence of
dogs with a global activity score of 1 was highest
(as many as of 30% of dogs depending on cycle)
on day 4 after each treatment with Paccal Vet. One
dog was observed with a global activity score of
2 on day 1 during the first treatment cycle with
Paccal Vet and two dogs were observed with a score
of 3 on day 1 or 4 during the second treatment
cycle.
The median time to response for the 19 dogs
with CR or PR was 14 days (Table 2). Median
progression-free survival (Table 2 and Fig. 3) and
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
Paccal Vet for canine malignant tumours 249
Figure 3. Kaplan Meier plot for progression-free survival (n = 23 dogs) for dogs receiving at least three cycles of Paccal Vet(100–175 mg/m2 IV). Median progression-free survival time was 131 days. Observations from seven dogs were censored at365 days.
overall survival times (not shown; data similar to
progression-free survival) were both 131 days.
Plasma concentrations of paclitaxel from 21
dogs that received 100–175 mg m−2 Paccal Vet
are provided in Fig. 4. With the exception of
three dogs, plasma concentrations in these dogs
were below the LLOQ (40 ng mL–1) at the
24-h time point. According to the criteria set-
up for pharmacokinetic evaluation, 17 dogs that
received 100–150 mg m–2 Paccal Vet (Table 3)
were evaluable. The clearance values for these dogs
were reasonably within the wide range of values
reported in humans.
Clinical safety
Decreased haemoglobin, ALAT, ALP and ASAT;
leukopenia; thrombocytopenia (all primarily grades
I and II); and neutropenia (primarily grades III and
IV) were observed in the majority of dogs. The
incidence of dogs with leukopenia and neutropenia
tended to be greatest during the first cycle of
treatment compared with later cycles (Table 4).
DLT was observed in several dogs, especially in
the first treatment cycle. The incidence of DLT
appeared to decrease with time (Table 4). None of
the DLT were life-threatening or required delay
in dosing. Five dogs with DLT required dose
reduction; however, for the majority of other dogs
with DLT, there was no relationship between DLT
and dose or dose change. Electrocardiography and
troponin-I values were not considered clinically
significant in any dog during any treatment cycle,
as there were no changes from baseline findings and
the troponin-I values were within normal range.
Adverse events were reported in all study dogs
(range 4–28 events per dog). Forty-three serious
adverse events (neutropenia, n = 39; leukopenia,
n = 4) were observed in 23 dogs. No dogs were
however withdrawn from the study because of
adverse events. The greatest number of adverse
events was observed during the first treatment cycle
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
250 H. von Euler et al.
Figure 4. Plasma concentrations (log scale) of paclitaxel in dogs (n = 21) after an intravenous infusion of paclitaxel asPaccal Vet (100–175 mg/m2). The LLOQ (40 ng/mL) is indicated by the dotted line.
Table 3. Summary statistics for pharmacokinetic variablesfor dogs receiving Paccal Vet (100–150 mg m–2 IV)
Statistic (n = 17b)Variablea Mean ± SD Median Range
T1/2α , h 0.15 ± 0.11 0.11 0.04–0.44
T1/2β , h 3.6 ± 1.4 3.0 1.9–6.8
Vss, L m–2 54 ± 38 40 16–167
CL, L h–1 m–2 18 ± 6.6 17 11–33
Cmax, mg L–1 14 ± 6.6 14 2.2–27
AUC, mg h L–1 9.4 ± 3.1 9.0 4.6–14
aSee Materials and Methods for abbreviation definitions. Cmax
and AUC are normalized to a dose of 150 mg m−2.bNot including data from 4 of 21 dogs sampled for paclitaxelplasma concentration (see Fig. 4).
and their incidence tended to decrease with time
(Table 5). The vast majority (≥90%) of all adverse
events was graded as mild or moderate. Vomiting
(16%), diarrhoea (19%), leukopenia (38%) and
neutropenia (79%) were graded as severe events.
Hypersensitivity was reported in one dog on two
occasions following Paccal Vet treatment. The
events consisted of mild facial swelling and pruritus
that responded within 1 h to prednisolone.
Death was not an attributable outcome for any
adverse event, however 21 dogs were euthanized or
died because of PD: 4 dogs were euthanized during
the study and an additional 14 were euthanized and
3 died within a year after the study.
The most commonly (80% of dogs) admin-
istered concomitant medications were amoxi-
cillin/clavulanic acid and enrofloxacin, followed
by medetomidine, butorphanol and atipamezole.
Other therapies concurrently administered with
Paccal Vet during the study were ampicillin,
benazepril, betamethasone, carprofen, cimetidine,
electrolytes, fluids, furosemide, metoclopramide,
prednisolone and vitamins. The majority of medi-
cations were given at a single occasion or over a few
days. Prohibited concomitant therapies were not
administered to any study dog.
Discussion
Results from this pilot field study in tumour-bearing
dogs demonstrate that Paccal Vet administered at
100–150 mg m–2 for three treatment cycles every 21
days results in clinically significant tumour response
in a varied population of tumour histologies.
The abandonment of the 175 mg m–2 dose was
justified due to severe adverse events experienced
during the first treatment cycle in a single dog;
however the patient recovered and went on
to receive subsequent dosages at 150 mg m–2
without a schedule delay. As defined below, the
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Paccal Vet for canine malignant tumours 251
Table 4. Number of dogs with leukopenia, neutropenia and dose-limiting toxicity (DLT) by the Veterinary Co-operativeOncology Group (VCOG) and treatment cycle
VCOG Cycle 1 (n = 31) Cycle 2 (n = 29) Cycle 3 (n = 25) Cycle 4 (n = 7) Cycle 5 (n = 3)
Leukopenia I 12 14 11 6 2
II 10 8 10 3 1
III 7 6 3 0 0
IV 3 0 1 0 0
Neutropenia I 7 10 11 1 0
II 6 6 4 2 0
III 8 6 5 1 1
IV 17 10 10 3 1
DLT III or IV 24 17 15 4 2
Table 5. Incidence of dogs with adverse events by treatment cyclea
Event Cycle 1 (n = 32) Cycle 2 (n = 29) Cycle 3 (n = 25)
Total adverse events 32 100% 29 100% 22 88%
Total serious adverse events 16 50% 10 34% 9 36%
Leukopenia 26 81% 24 83% 18 72%
Neutropenia 26 81% 24 83% 19 76%
Fatigue 25 78% 15 52% 7 28%
Vomiting 21 66% 10 35% 13 52%
Anorexia 20 63% 7 24% 11 44%
Diarrhoea 19 59% 9 31% 12 48%
Thrombocytopenia 12 38% 9 31% 5 20%
Dehydration 8 25% 1 3% 4 16%
Pyrexia 3 9% 7 24% 0 0%
Alopecia 3 9% 3 10% 5 20%
Anaemia 2 6% 1 3% 1 4%
Nausea 1 3% 1 3% 0 0%
Hypersensitivity 1 3% 0 0% 1 4%
Weight loss 1 3% 0 0% 1 4%
aDuring the fourth and fifth treatment cycles, three of seven and one of three dogs, respectively, were reported with a seriousadverse event (neutropenia).
standard method of determining whether the
175 mg m–2 dose is indeed dose-limiting would
require additional dogs be evaluated. It is possible,
therefore, that the maximally tolerated dose in the
tumour-bearing companion dog population was
underestimated due to flaws in the trial design.
Thus, while the methodology was not traditional,
the majority of dogs (n = 25) were part of the
150 mg m–2 dosing group and the grade of adverse
event reported in this cohort are in line with what
is commonly perceived by practicing veterinary
oncologists and their client population as ‘accept-
able’ levels of risk. Hence although the study did
not follow a typical 3 + 3 dose-titration scheme,23
the preponderance of dogs that were successfully
and safely treated at 150 mg m–2 for as many as five
cycles (Table 1) provides a justification for the dose
of Paccal Vet for future clinical trials. The transient
yet expected off-target pharmacodynamic effects
(primarily neutropenia) would suggest that a 3-
week treatment-cycle, standard for most same-class
cytotoxic chemotherapeutics, is also reasonable for
Paccal Vet.
Proof of concept in client-owned tumour-
bearing dogs was successfully demonstrated in
that no fewer than 70% of dogs had a PR or
CR to treatment and the response was durable
(approximately 4 months). Although this early
phase study was not blinded and lacked a
control group, results indicate that Paccal Vet is
biologically active and beneficial relative to other
reports on paclitaxel or to other chemotherapeutic
agents commonly used for the treatment of these
tumour histologies. Additionally, Paccal Vet was
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
252 H. von Euler et al.
not associated with commonly observed severe
hypersensitivity reactions (64%), treatment-related
death (12%), poor response rate (≤20%) and short
duration of progression-free survival (53 days)
that has been reported18 with the formulation of
paclitaxel containing cremophor-EL.
Dogs that are not surgical candidates and/or
have advanced stage tumours need effective
multimodal treatment approaches (e.g. surgery and
chemotherapy). The majority of canine tumour
types (mast cell tumour, mammary tumour,
squamous cell carcinoma) have all been reported in
the veterinary literature to respond to a variety
of chemotherapy including single or multidrug
protocols containing doxorubicin, carboplatin,
vinblastine, docetaxel, gemcitabine, lomustine and
tyrosine kinase receptor inhibitors.24–29 In general,
the reported response rates with single-agent drug
protocols is modest, rarely exceed 40% and are not
durable (i.e. 1–2 months). In contrast, the response
rates and durability of response in the present study
is encouraging.
Paclitaxel is a highly hydrophobic compound,
requiring synthetic solvents for parenteral admin-
istration. The excipient (cremophor-EL) in some
formulations causes life-threatening hypersensitiv-
ity reactions30 and subsequently this agent is not
routinely used in veterinary oncology due in part to
adverse events associated with the excipient. This
report supports the argument that a tolerable tax-
ane (i.e. water-soluble paclitaxel) would represent a
significant improvement over water-insoluble tax-
anes in veterinary cancer treatment. Paccal Vet’s
water-soluble formulation permits paclitaxel to be
dissolved in common innocuous infusions such as
Ringer Acetate or lactated Ringer’s solutions. There
is no longer any need for heavy pre-medication to
tolerate the hydrophilic solvent (i.e. cremophor-
EL) resulting in reduced costs associated with
patient handling and reduced infusion times, thus
increasing the convenience for pets, caregivers and
veterinary professionals. Moreover, the potential
side effects of pre-medication (e.g. steroids) are
avoided.
The pharmacokinetics of paclitaxel, adminis-
tered as Paccal Vet, demonstrated a typical two-
compartment behaviour with a rapid distribution
phase (α-phase), and a slower elimination phase
(β-phase) that could be adequately described by
a two-compartment model. The short distribution
half-life, of the order of 10 min, means that drug
distribution is virtually complete within an hour.
The half-life averaged 3.6 h, which means that the
majority of the drug is eliminated within 24 h. There
was a high variability in clearance between different
dogs. It has long been known that paclitaxel elimi-
nation varies widely in the human population. It is
interesting to note that clearance values in the dogs
fell within the very wide range of values reported in
humans, 5.2–30.2 L h–1 m–2.31
Global activity score was used in the present study
as a surrogate measure of quality of life. Despite
a relatively high incidence of adverse events (see
below), quality of life was reasonably maintained in
dogs receiving Paccal Vet. This is due in large part
to the fact that the adverse events (e.g. neutropenia)
are generally clinically silent, expected and well-
managed by the veterinarian. Clinically ‘silent’
events (e.g. treatable transient effects) related to
the drug’s mechanism are commonly reported for
chemotherapeutics.32
With respect to mast cell disease (the most
common tumour treated in this study), Paccal Vet
achieved a similar objective response rate (≥50%)
as a previous report for toceranib, a registered
drug for treatment of mast cell tumours.29 The
clinical benefit of Paccal Vet is also achieved with
a mechanism of action that is perhaps wider in
its therapeutic scope in that it does not require
c-kit tyrosine kinase receptor aberration in the
tumour (e.g. present in only 20–27% of mast
cell disease).28,29 Further, c-kit mutation must be
documented prior to using masitinib,33 one of
the currently registered veterinary drugs for canine
mast cell disease.
The first dog enrolled in the study was
treated per-protocol with 175 mg m–2 IV and
developed a serious adverse event (pyrexia).
The event resolved with symptomatic treatment
(fluids and anti-pyretics) and the dog remained in
the study with 150 mg m–2 IV without further
dose reduction or dose delay. The fact that the
majority of dogs (n = 25; Table 1) also received
150 mg m–2 IV for at least three cycles with the
expected, transient and manageable adverse effects
is commensurate with the perceived risk with
© 2012 Blackwell Publishing Ltd, Veterinary and Comparative Oncology, 11, 4, 243–255
Paccal Vet for canine malignant tumours 253
other cytotoxic chemotherapeutics currently used
by the veterinary oncology community.32,34 Taxane
chemotherapeutics have a well-characterized mech-
anism of action that results in myelosuppression,
occasional gastro intestinal toxicity and transient
fatigue.18,25 The pharmacodynamic effect of tax-
anes are primarily limited to rapidly dividing tissue
compartments as predicted by the anti-replication
mode of action of this and same-class cytotoxic
chemotherapeutic agents. As such, the bone mar-
row, intestinal tract, and hair follicles are most
at risk for off-target (non-cancer cell) effects and
result in an overriding dose-limiting haematopoi-
etic effect (primarily neutropenia). Bone marrow
toxicity was anticipated in the present study and
was used to aid in finding the maximally tolerated
dose. Most cases of neutropenia were considered
subclinical or ‘silent’ as the dogs, in most cases,
maintained acceptable performance status scores.
Recently Vaughan et al.35 reviewed cytotoxic
chemotherapeutics whose mechanism of action is
accompanied by marked bone marrow suppression
and found that dogs with grade III or IV neutrope-
nia had a more favourable tumour response and
longer overall survival time when compared with
dogs without significant neutropenia (grade I or II).
A balance between acceptable clinically silent bone
marrow suppression (i.e. neutropenia) and anti-
tumour activity is commonly sought with the use of
cytotoxic agents. Further confirmatory evidence
that Paccal Vet can achieve satisfactory quality
of life (with a validated instrument for assessing
health-related quality of life),36 while maintaining
sufficient anti-tumour activity, is warranted.
Rare and usually mild anaemia was also detected.
This is a common finding later in the course of
chemotherapy as the treatment also impairs new
red blood cell formation. However, suppression
is usually transient and red blood cells regenerate
after cessation of treatment, as seen in the present
study. The elevations in hepatic enzymes observed
in this study did not result in clinical hepatopathy
or termination of treatment.
In general, adverse events were successfully
managed with supportive care. This is consistent
with principles and recommendations for han-
dling chemotherapy-induced neutropenia and gas-
trointestinal disturbances.32 The cornerstone of
these recommendations include rehydration of the
patient, supportive antibiotics in the case of febrile
neutropenia and non-febrile grade IV neutropenia.
Notably, maropitant was not available at the time
of this trial and metoclopramide was mostly used
as an anti-emetic. The addition of the more active
anti-emetic maropitant may further abrogate gas-
trointestinal adverse events following Paccal Vet
treatment as it has for other commonly used cyto-
toxic chemotherapeutics.37
Antimicrobial therapy was initiated in some dogs
to prevent infection in dogs with significant neu-
tropenia associated with Paccal Vet administration.
Butorphanol, medetomidine and atipamezole were
used primarily as part of the cytoxic safety precau-
tions in place at SLU. Paccal Vet appears compatible
with these and other commonly used canine veteri-
nary medications.
This first-in-dog study assessed the clinical
benefit of Paccal Vet for treatment of canine solid
tumours. Although the study failed to follow a
more traditional dose-titration approach, a positive
benefit to risk ratio was established for Paccal Vet
administered at 150 mg m–2 IV for three or more
treatment cycles. The dose was associated with
expected adverse events; however, the majority was
transient and clinically silent. This is the first report
on a water-soluble formulation of paclitaxel that
can be successfully and safely used without pre-
medication in dogs with cancer.
Acknowledgements
The authors would like to thank and acknowledge
Oasmia Pharmaceutical AB, Uppsala, Sweden for
financial support, and especially Niklas Wikstrom
and the clinical staff at the University Animal
Hospital at SLU for their invaluable assistance
in conducting and managing patients in the
study.
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