Adose-ﬁndingstudywithanovel water ...download.xuebalib.com/4qncUXIedkg8.pdf · 244...

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



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.



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.



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



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



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



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



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



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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