Blockade of Platelet-Derived Growth Factor Receptor-Beta by CDP860, a Humanized, PEGylated di-Fab',...

Blockade of Platelet-Derived Growth FactorReceptor-Beta by CDP860, a Humanized, PEGylateddi-Fab’, Leads to Fluid Accumulation and Is AssociatedWith Increased Tumor Vascularized VolumeG.C. Jayson, G.J.M. Parker, S. Mullamitha, J.W. Valle, M. Saunders, L. Broughton, J. Lawrance,B. Carrington, C. Roberts, B. Issa, D.L. Buckley, S. Cheung, K. Davies, Y. Watson,K. Zinkewich-Peotti, L. Rolfe, and A. Jackson

From the Cancer Research UKDepartments of Medical Oncology andRadiology, Christie Hospital; ImagingScience and Biomedical Engineering,University of Manchester,Manchester; Oncology Group,Celltech R & D Ltd, Slough, UK.

Submitted January 8, 2004; acceptedAugust 12, 2004.

Supported by Celltech R & D Ltd,Slough, UK.

Terms in blue are defined in the glossary,found at the end of this issue and onlineat www.jco.org.

Authors’ disclosures of potentialconflicts of interest are found at theend of this article.

Address reprint requests to GordonJayson, FRCP, PhD, Cancer ResearchUK, Department of Medical Oncology,Christie Hospital, Manchester M20 4BX,United Kingdom; e-mail: [email protected].

2005 by American Society of ClinicalOncology

0732-183X/05/2305-973/$20.00

DOI: 10.1200/JCO.2005.01.032

A B S T R A C T

PurposeCDP860 is an engineered Fab’ fragment-polyethylene glycol conjugate, which binds to andblocks the activity of the beta-subunit of the platelet-derived growth factor receptor(PDGFR-�). Studies in animals have suggested that PDGFR-� inhibition reduces tumor inter-stitial fluid pressure, and thus increases the uptake of concomitantly administered drugs. Thepurpose of this study was to determine whether changes in tumor vascular parameters couldbe detected in humans, and to assess whether CDP860 would be likely to increase the uptakeof a concurrently administered small molecule in future studies.

Patients and MethodsPatients with advanced ovarian or colorectal cancer and good performance status received in-travenousinfusionsofCDP860ondays0and28.Patientshadserialdynamiccontrast-enhancedmagnetic resonance imaging studies to measure changes in tumor vascular parameters.

ResultsThree of eight patients developed significant ascites, and seven of eight showed evidence offluid retention. In some patients, the ratio of vascular volume to total tumor volume increasedsignificantly (P� .001) within 24 hours following CDP860 administration, an effect suggestiveof recruitment of previously non-functioning vessels.

ConclusionThese observations suggest that inhibition of PDGFR-� might improve delivery of a concur-rently administered therapy. However, in cancer patients, further exploration of the dosingregimen of CDP860 is required to dissociate adverse effects from beneficial effects. The find-ings challenge the view that inhibition of PDGF alone is beneficial, and confirm that effects ofPDGFR kinase inhibition mediate, to some extent, the fluid retention observed in patientstreated with mixed tyrosine kinase inhibitors.

J Clin Oncol 23:973-981. 2005 by American Society of Clinical Oncology

INTRODUCTION

Platelet-derived growth factor (PDGF) isa homo- or heterodimeric protein com-posed of A- and B-100 amino acid disulfidebonded polypeptides. The dimers signalthrough � and � tyrosine kinase receptors.While all forms of PDGF A and B can signalthrough PDGF receptor (PDGFR) -��, only

PDGF BB can signal through PDGFR-��.1 The PDGF receptors are mostly foundon fibroblasts and smoothmuscle cells.1 Re-cently, two other isoforms of PDGF,PDGF C and D, have been identified.2-4

PDGFR-� is expressed on many tumortypes,5 including ovarian 5,6 and colon can-cers.5,7,8 In addition, the receptors areexpressed on pericytes,9 suggesting that

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131.104.62.10Information downloaded from jco.ascopubs.org and provided by at ACQUISITIONS SECTION on May 8, 2012 from

Copyright © 2005 American Society of Clinical Oncology. All rights reserved.

PDGF signaling may be involved in the regulation ofangiogenesis.10 Inhibition of pericyte and endothelialfunction is associated with enhanced tumor growthinhibition9 in animals.

PDGF probably plays a role in the control of tissue in-terstitial fluid pressure (IFP). Evidence suggests that PDGFis an important signaling molecule for the maintenance ofthe interaction ofmyofibroblasts with collagen in the extra-cellular matrix, via �1 integrins.

11 It was previously shownthat PDGF effects on IFP were specific to PDGF BB. In a ratmodel, administrationof PDGFBB, but not PDGFAA, nor-malizeddermal IFP that hadbeenexperimentally lowered.12

Studies using rodent tumor models showed that inhibitionof PDGF using the tyrosine kinase inhibitor imatinib, or ananti-PDGF BDNA aptamer, was associated with a decreasein tumor IFP.13Theauthorshypothesized that the reductionin IFP by PDGF inhibition would increase the blood flow–driven uptake of small molecules, and confirmed thehypothesis using 51Cr-EDTA,13 and subsequently, [3H]-paclitaxel14 and epothilone B.15 In the Pietras et al study,15

imatinib increased the tumor uptake of epothilone B with-out increasinguptake in liver, kidney, or intestinal tract, andwithout reduction in the tolerability of the cytotoxic agent.

In patients with colorectal and ovarian carcinoma, wereport the phase II evaluation of a pegylated di-Fab’ mole-cule,16 CDP860, which binds to and inhibits PDGFR-�.CDP860 cross-reacts with PDGFR-� from cynomolgusmon-key, and was well tolerated in toxicology evaluation in thisspecies at doses up to 400 mg/kg, given weekly for 4 weeks.

One hypothetical benefit of inhibiting PDGF is the po-tential toprevent coronaryartery restenosis after stent inser-tion. Primate models of neointimal formation suggesteda role for PDGFR-� in intimal hyperplasia.17,18 A studywas performed inwhich 145patients undergoing intracoro-nary stent insertion received placebo or 25 mg/kg CDP860(nZ 76), the drug having beenwell tolerated at doses up to30 mg/kg in a healthy volunteer study. Although there wasno improvement in restenosis rate, 47 of the patients receiv-ing CDP860 developed peripheral or facial edema between2 hours and 3 weeks after dosing. These observations wereattributed to the mode of action of CDP860.19

In total, 97 volunteers and patients had receivedCDP860 before this study. Following the reported effectsof PDGF BB inhibition on IFP in animal models, wewanted to determine if changes in tumor vascular param-eters could be detected in humans, and to assess whetherCDP860 would be likely to increase the uptake of a concur-rently administered small molecule in future studies.

PATIENTS AND METHODS

CDP860

CDP860 is an engineered Fab’ fragment-polyethylene glycolconjugate, which binds to and blocks the activity of the �-subunit

of the PDGF receptor. The parent antibody was a murinehybridoma-derived monoclonal antibody, m162, identified byZymogenetics Inc (Seattle, WA), and humanized at Celltech(Slough, UK).20 Each molecule of CDP860 has two constituents:first, a humanized antibody di-Fab’, composed of two moleculesof Fab’ crosslinked covalently and site-specifically at their hingeregion using a maleimide crosslinker; secondly, 40 kD polyethyl-ene glycol (PEG) attached directly to the crosslinker. The addi-tion of PEG is designed to increase the plasma half-life of themolecule.21 The molecular weight of CDP860 is approximately140 kd, and it has a dissociation constant of 2.1 � 10�10 M forPDGFR-�, as measured by surface plasma resonance (Biacore,Neuchatel, Switzerland).

Phase II Evaluation of CDP860 in Advanced Ovarian

and Colorectal Cancer

Aims of the study. The study examined changes in tumorvascular parameters assessed using dynamic contrast-enhancedmagnetic resonance imaging (DCE-MRI) in patients with ad-vanced colorectal or ovarian cancer who had received CDP860.The primary end point was the change in tumor vascular perme-ability measured for up to 45 days after administration of theCDP860. Secondary end points were effects of CDP860 on othervascular parameters including tumor blood flow, safety and toler-ability ofCDP860, plasmapharmacokinetics, and tumor response.

Patients. Patients with measurable primary or secondarycolon or ovarian cancer over 18 years of age, an Eastern Cooper-ative Oncology Group score between 0 and 2, and life expectancyof at least 3 months were eligible. They were required to have ad-equate liver (normal bilirubin and transaminases� 2.5� the up-per limit of normal), renal (creatinine � 1.5� the upper limit ofnormal), and hematologic (hemoglobin �10 g/dL, white cellcount � 3 � 109/L, and platelet count �100 � 109/L) function,as well as normal coagulation (prothrombin time and activatedpartial thromboplastin time) and a normal ECG.

Patients were excluded if they had an additional chronic dis-ease affecting a major organ, infection requiring antibiotics, clin-ically significant ascites or pleural effusion, major surgery withinthe previous 4 weeks, previous history of reaction to biologicagents or drugs containing PEG, a contra-indication to magneticresonance imaging (MRI), history of infection with hepatitis B,C, HIV-1 or HTLV-1, alcohol or drug addiction, or treatmentwithin the previous 4 weeks. Patients were not permitted to takedrugs known to alter vascular flow and they had to have recov-ered from the effects of previous treatments. Patients with knownor suspected brain or CNS disease were excluded.

Study design. Patients were treated at the Christie CancerCenter (Manchester, UK) and received CDP860 25 mg/kgon days 0 and 28. A computed tomography (CT) scan wasperformed during the 2 weeks before treatment, and a post-treatment scan was performed on day 45. CT was also performedas part of the routine clinical monitoring of the patients, on av-erage, 68 days before the first study-specific CT scan. MRI scanswere performed twice at baseline to establish reproducibility,22,23

and on days 1, 7, 27, and 45. Blood samples were taken tomeasure hematologic and biochemical toxicity, CDP860 con-centration, and anti-idiotype responses at screening beforetreatment, and on days 1, 7, 28, 35, and 50. Adverse events wereassessed before treatment and on days 0, 1, 7, 27, 28, 35, 45, and50. Toxicity was assessed using the National Cancer InstituteCommon Toxicity Criteria (version 2.0). Response was assessed

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using Response Evaluation Criteria in Solid Tumors.24 Anypatient with stable disease or better at the end of treatment waseligible to continue treatment for a further 6 months.

All patients gave written informed consent and the studywas approved by the South Manchester Local Research EthicsCommittee and the Christie Hospital Research Committee.

MRI. The location of the tumor to be studied using DCE-MRI was ascertained from the CT scans. All MRIs were per-formed on a Philips Gyroscan NT Intera system (Philips MedicalSystems, Best, Netherlands) at 1.5 T at the University of Man-chester. The MRI protocol consisted of localizer acquisitions, fol-lowed by axial T1-weighted fast field echo (gradient echo), andT2-weighted fast spin echo volumetric acquisitions coveringthe tumor region. The DCE-MRI acquisition series was followedwith a final axial post-contrast T1-weighted acquisition. All im-ages were acquired using the Philips Synergy Body phased arraycoil (Philips Medical Systems).

All image acquisitions for a given patient visit were designedto have the same field of view and slice location to facilitate def-inition of the region of interest (ROI) for DCE-MRI data anal-ysis. The DCE-MRI protocol consisted of three-dimensionalradiofrequency-spoiled fast field echo acquisitions with a tempo-ral resolution of 2.32 sec. Native tissue T1 was determined usingthree separate acquisitions before the DCE-MRI time series, withfour signal averages and flip angles of 2°, 10°, and 30°, and byfitting the standard relationship between T1 and spoiled gradientecho signal intensity,25 dynamic acquisition consisted of 100 sin-gle average volumes (flip angle, 30°). The image matrix for allscans was 128� 128 in-plane, with 20 slices. An elliptical k-spacewindow and over-contiguous slicing (ie, interpolation in the slicedirection within the three-dimensional slab) were utilized tomaintain a short total acquisition time. Repetition time was2.5 msec and echo time was 0.85 msec. Omniscan 0.1 mmol/kg (Amersham Health, Amersham, UK) was administered afterthe fifth dynamic time point as a bolus using a Spectris MR(Medrad Inc, Indianola, PA) power injector at a rate of 3 mL/sec.

DCE-MRI data analysis. Tumor volumes were defined bya radiologist as two-dimensional ROIs on each slice locationcontaining the tumor of interest. ROIs were defined on the pre-contrast T2-weighted images, with the pre- and postcontrastT1-weighted images used to provide additional visual reference.ROIs were defined once all visits for a given patient had beencompleted to ensure the same tumor was always being outlined(on occasion, multiple secondary lesions were visible within thefield of view). The radiologist was not blind to the order of pa-tient visits and was aware of the CDP860 administration sched-ule. Tumor volumes were also determined in the pretreatmentCT scans by the same radiologist.

The DCE-MRI time series was analyzed using a softwarepackage written in-house. We aimed to produce parameter val-ues reflecting tumor microvasculature using methods that havecommonly been applied in previous studies of antivascularagents (see methods 1 and 2), and more advanced methods thatare designed to provide more specific physiologic information(see methods 3 and 4): (1) Initial area under the tissue contrastagent concentration time curve (IAUC), defined over 60 sec be-ginning at the point of bolus administration26; (2) standard Toftsand Kermode kinetic modeling to derive estimates of the volumetransfer coefficient for contrast agent between the blood pool andthe tissue extracellular extravascular space Ktrans (often approxi-mated to the capillary wall permeability surface area product)

and the volume of the extracellular extravascular space as a frac-tion of total tissue volume ve

27; a standardized arterial inputfunction (AIF) was assumed for all patients28; (3) kinetic mod-eling incorporating an estimate of vascular plasma volume vp

29;for this method, as well as method 4, we defined the AIF in eachpatient at each visit using an automated AIF extraction method.30

This method also produces estimates of Ktrans and ve; and (4) tis-sue homogeneity model. This model (St Lawrence and Lee31) al-lows estimates of Ktrans, ve, and vp to be made, plus estimates ofblood flow and capillary permeability-surface area product.

The use of methods 1 and 2 was intended to provide a di-rectly comparable output to previous studies of antivascularagents. Methods 3 and 4 were additionally applied with theaim of providing a more accurate characterization of the vascularstate of the tumors studied.

The change in tissue signal intensity due to contrast agentover time was converted into estimates of contrast agent concen-tration via estimation of T1.

32 Each voxel within the tumor wasidentified as ‘‘enhancing’’ if the signal intensity rose above 3 stan-dard deviations of the data noise level during the dynamic series;otherwise it was classified as ‘‘nonenhancing’’ and no modelingwas performed for that voxel. The total volume occupied by en-hancing and nonenhancing tumor was recorded. For each de-rived parameter (IAUC, three estimates of Ktrans and ve, andtwo estimates of vp), the median and mean values calculatedwithin the enhancing tumor volume were recorded.

Pharmacokinetics. Concentrations of CDP860 were as-sessed using a sandwich enzyme-linked immunosorbent assay(ELISA) consisting of a murine Fc-PDGFR fusion-coated plateand a goat anti-human kappa-horse radish peroxide conjugateas the detection layer. The limit of quantification for this assay(allowing for the minimum 1/100 dilution) was 1.20 �g/mL.Antibodies to CDP860 were assessed using a double antigensandwich ELISA consisting of a CDP860 coated plate anda CDP860 biotin detection system. Samples were quantifiedagainst a rabbit anti-CDP860 high titer standard and the limitof quantification was 0.6 units/mL.

Statistical design. We planned to recruit six patients withcolon cancer and six patients with ovarian cancer. Acceptinga standard deviation of 0.019 min�1, identified from previous

Table 1. Patient Demographics

Patient Demographics No. of Patients

Total 8Colon cancer

Male 3Female 2

Ovarian cancer 3Age, years

Median 59Range 34-72

No. of previous treatmentsMedian 2Range 1-3

No. of months treatment-free intervalMedian 0Range 0-15

No. of disease sitesMedian 3Range 1-4

Patients receiving CDP860One cycle 5Two cycles 3

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reproducibility studies in glioma,22,23 and using a two-sided � Z0.05 significance level, this study had an 80% power to detecta 0.025 min�1 change in Ktrans.

RESULTS

Drug Administration and Toxicity

Eight of the planned 12 patients were treated in thisstudy and their characteristics are shown in Table 1.The median number of organs involved by tumor wasthree (range, one to four organs). The median numberof previous chemotherapy regimens was two. Tumor typesand locations studied by MRI are summarized in Table 2.

Three patients received two drug administrationswhile the others received only one. The study was stoppedafter three patients developed dramatic and rapid onset as-cites and/or pleural effusions. These data and the othertoxicities are summarized in Tables 3 and 4. Largely, theyshow that besides the fluid accumulation toxicities, the an-tibody was well tolerated with only grade I and II toxicitiesthat typify the complications seen in patients with ad-vanced cancer (Table 3). All of the patients had progressive

disease or developed such marked toxicity in the form offluid accumulation that further treatment was not possibleand they were withdrawn from the study.

Fluid Accumulation

One of the entry criteria for the study stated that thepatients should not have significant ascites or pleural effu-sions. Despite this, seven of eight patients developed clin-ically significant fluid accumulation that included ascites,pleural effusions, and facial and/or peripheral edema(Table 4). In three patients (patients 3, 4, and 8), the onsetand volume of ascites and pleural effusions were dramatic.

Patient 4 was a 58-year-old woman with advancedovarian adenocarcinoma who had no clinical evidenceof ascites or pleural effusion, although the pretreatmentCT scan revealed loculated pelvic ascites. Eleven days afteradministration of CDP860, she presented with massivetense ascites, which had accumulated over 4 days. Sixteenliters of sterile exudative hemorrhagic ascitic fluid wasdrained over 1 week. A small left-sided pleural effusionwas also noted; however, this did not require any interven-tion and resolved spontaneously. Cytologic examinationof the ascitic fluid revealed malignant cells compatiblewith her ovarian cancer. Following withdrawal from thestudy, the patient did require a further paracentesis, butthe pleural effusion did not recur.

Patient 3 was a 60-year-old woman with advancedgranulosa theca cell ovarian tumor whose pretreatmentCT scan showed minimal pelvic ascites. There was no clin-ical evidence of ascites or pleural effusion.Within 14 days ofdrug administration shewas admitted for therapeutic para-centesis, wherein 3.5 L of hemorrhagic exudative fluid weredrained, although her weight had increased by 11 kg, sug-gesting that she had developed 11 L ascites in total. Afterwithdrawal from the trial, the ascites did not re-accumulate.

Table 3. General Toxicities Associated With CDP860

Colorectal (n Z 5) Ovarian (n Z 3) Total (N Z 8)

Adverse Event No. of Adverse Events No. of Patients No. of Adverse Events No. of Patients No. of Adverse Events No. of Patients

Ascites 3 3 3 3 6 6Lethargy 2 2 4 3 6 5Anemia 4 4 1 1 5 5Edema peripheral 5 3 2 1 7 4Pleural effusion 3 3 1 1 4 4Nausea 3 3 1 1 4 4Periorbital edema 4 3 1 1 5 4Abdominal distension 2 2 2 2 4 4PT prolonged 3 3 1 1 4 4APTT prolonged 3 3 0 0 3 3Weight increased 3 3 0 0 3 3Anorexia 1 1 1 1 2 2Hypokalemia 1 1 1 1 2 2Vomiting 2 2 0 0 2 2

NOTE. All events considered to be possibly, probably, or definitely related to study medication.Abbreviations: PT, prothrombin time; APTT, activated partial thromboplastin time.

Table 2. Tumor Types and Locations Studied Using DCE-MRI

PatientNo.

Primary TumorLocation

Site of LesionStudied With DCE-MRI

1 Colon Adrenal gland2 Colon Liver3 Ovary Spleen4 Ovary Ovary5 Colon Liver6 Colon Liver7 Colon Liver8 Ovary Spleen

Abbreviation: DCE-MRI, dynamic contrast-enhanced magnetic reso-nance imaging.

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Patient 8 was a 54-year-old woman with advancedovarian cancer who had no pretreatment evidence ofa fluid collection. By day 13, she had developed graduallyworsening abdominal distension, and 6 L of hemorrhagicascitic fluid were drained and did not reaccumulate. Bilat-eral small pleural effusions were noted radiologically, butthese resolved spontaneously.

Although these patients had ovarian cancer, the devel-opment of fluid accumulation was noted in seven of theeight patients on the trial, and so the phenomenon wasnot disease-specific. Following the admission of patient8 for paracentesis, recruitment was stopped.

Magnetic Resonance Imaging

Tumor growth. Tumor growth during the study foreach patient was assessed using both MRI and pretreat-

ment CT data. These data (not shown) demonstrate thata characteristically exponential volume increase patternwas not changed by the administration of CDP860. In pa-tient 3, the rate of tumor growth was extremely slow bothbefore and after drug treatment.

Tumor vascularized volume. We examined the rela-tionship between the tumor vascularized volume, definedas the tumor tissue that was found to enhance during theDCE-MRI series, and total tumor volume (Table 5). Figure1 shows the relationship between these measures. In pa-tients 4, 5, and 8, the vascularized volume of the tu-mor appeared to increase following administration ofCDP860 to a greater extent than did the total tumor vol-ume. An independent samples t test on the percentagechange at each patient visit, in comparison with the dis-tribution of percentage variability at baseline, showed

Table 5. Total Tumor Volume and Vascular Tumor Volume

Day of MRI Scan

Patient No. �2 �1 1 7 27 45

1TTV, mL 18.4 18.7 19.0 20.9 38.3 N/DVTV, mL 4.81 5.67 1.99 9.13 17.0 N/DVTV, % 26.1 30.3 10.5* 43.7* 44.3* N/D

2TTV, mL 21.4 20.1 18.1 23.6 35.2 50.6VTV, mL 13.7 15.2 14.2 17.0 22.3 34.1VTV, % 63.9 76.0 78.4 72.1 63.5 67.3

3TTV, mL 194 208 216 199 198 N/DVTV, mL 43.0 80.1 34.3 56.3 65.3 N/DVTV, % 22.2 38.6 15.9* 28.2 32.9 N/D

4TTV, mL 47.7 49.6 50.6 N/D N/D N/DVTV, mL 5.56 6.32 11.5 N/D N/D N/DVTV, % 11.7 12.7 22.7* N/D N/D N/D

5TTV, mL 157 158 189 222 423 N/DVTV, mL 63.5 67.1 161 199 379 N/DVTV, % 40.4 42.3 85.0* 89.8* 89.7* N/D

6TTV, mL 768 814 853 887 1,210 1,290VTV, mL 480 568 505 586 911 880VTV, % 62.5 69.7 59.2 66.1 75.2 68.1

7TTV, mL 10.9 10.5 10.1 12.4 27.2 N/DVTV, mL 5.53 8.38 7.07 6.49 8.04 N/DVTV, % 50.6 80.0 70.1 52.4 29.6* N/D

8TTV, mL 24.3 23.5 26.1 29.6 N/D N/DVTV, mL 14.4 12.0 22.5 28.0 N/D N/DVTV, % 59.3 51.2 86.1* 94.4* N/D N/D

Abbreviations: MRI, magnetic resonance imaging; TTV, total tumor volume; VTV, vascular tumor volume; N/D, not done.*Indicates significant difference from baseline distribution at P � .05 (two-tailed).

Table 4. Toxicities Related to Fluid Accumulation

Ascites Pleural Effusion Facial/Periorbital Edema Peripheral (acral) Edema

Grade No. of Patients Patient Nos. No. of Patients Patient Nos. No. of Patients Patient Nos. No. of Patients Patient Nos.

Grade 1 3 1, 2, 6 4 1,2,3,6 5 1,2,3,6,7 3 1,3,7Grade 2Grade 3 2 3,8 1 6Grade 4 1 4


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visit-specific proportional vascular volume increases aftertreatment in these patients (Table 5). In each case, the in-crease in the ratio of vascular tumor volume to total tumorvolume was evident on the scan taken 1 day after the doseof CDP860 and maintained thereafter in those patients forwhom scans were available (patients 5 and 8). A significantincrease was also noted in patient 1 at days 7 and 27, butnot at day 1. An independent samples t test on the percent-age change over all post-treatment time points in theproportional vascularized volume—when grouping thepatients into numbers 2, 3, 6, 7 and 1, 4, 5, 8—is significantat the P � .001 level (two-tailed).

Vascular permeability and flow. All approaches ap-plied to investigate tumor microvasculature using theDCE-MRI data showed no detectable effect during the ad-ministration of CDP860, suggesting that the drug did notalter tumor IAUC (Table 6) or Ktrans, as determined usingany of the available methods (Table 7). This suggests that

the characteristics of vessels that were patent before ad-ministration of CDP860 were unchanged, and that anynewly recruited or newly patent vessels had similar char-acteristics to the pre-dose viable vessels. Similarly, therewas no observable effect on vascular flow in enhancing ves-sels following CDP860 administration (Table 8).

Pharmacokinetics. The highest geometric meanplasma CDP860 concentration was measured at the endof the infusion on day 0. The geometric mean concentra-tion had decreased on day 1 (261,957 �g/mL) and wasfurther reduced on day 7 (93,220 �g/mL). Each subjectwho received two doses of CDP860 had similar plasmaconcentrations of CDP860 after each dose. The data aresimilar to those in patients without cancer (Celltech, dataon file), and are consistent with a plasma half-life of ap-proximately 5 days. In all subjects, plasma concentrationsof anti-CDP860 antibodies were below the level of quan-tification at all times.

Table 6. Summary of Median IAUC (mM.s)26 – Changes From Baseline

Day 1 Day 7 Day 27 Day 45

No. of patients studied 8 7 6 2Baseline

Mean* 27.91 30.55 31.63 47.15SD 18.825 18.660 20.199

Change from baselineMean 0.32 0.28 �3.18 �1.65SD 4.500 4.138 6.014

95% CI for the difference �3.44 to 4.08 �3.55 to 4.11 �9.50 to 3.13P† .847 .864 .251

Abbreviations: IAUC, initial area under the tissue contrast agent concentration time curve; SD, standard deviation.*Mean of values recorded at days �2 and �1.†P values are derived, using the paired t-test, for exploratory purposes.

10 100 1,000 10,000

Total Tumor Volume (mL)

Vasc

ular

ized

Vol

ume

(mL)

1

1 2 3 4 5 6 7 8 identity

Fig 1. Relationship between totaltumor volume and vascularized vol-ume. Dotted lines indicate sequenceof measurements within each patient.Solid lines indicate uncertainty, ex-pressed as root mean square coeffi-cient of variation of measurementsover all pre-dose measurements.

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DISCUSSION

Wehave performed the first evaluation of a specific PDGFR-� inhibitor inpatientswithcancer.Thetrialwas stoppedearlybecause therewereproblemswithfluid accumulationdespitethe sameorhigherdosehavingbeenadministered to 85otherpatients or volunteers without similar toxicity.

We examined changes in vascular parameters to assesswhether CDP860 administration resulted in changes pre-dictive of increased uptake of concomitantly administereddrug. There was no change in mean tumor Ktrans or bloodflow after CDP860 administration. This suggests thatnewly perfused vessels had similar perfusion and leakagecharacteristics to those originally present.

In some patients, the vascularized volume of the tumorappeared to increase proportionally to a greater extent thanthe total tumor volume following CDP860 administration.This appeared to be independent of both the absolute vol-ume and location of the tumor (Table 5 and Fig 1). The caseof patient 5 is striking, where the vascularized volumemorethandoubled followingCDP860, and the ratio of tumor vol-ume to vascularized volume is subsequently maintained asthe tumor grows (Table 5). One explanation for the increasein vascularizedvolumemight be recruitment of pre-existingblood vessels that were compressed before CDP860 admin-istration, owing to high tumor IFP. This hypothesis is con-

sistentwithpreviously reportedanimal experiments.Firstly,treatment of xenograft-bearing rodents with a DNA ap-tamer against PDGF B is associated with increased tumorvolumetric density and reduced IFP.1 Secondly, there arecompressed blood vessels in rodent xenograft tissue,thought to result from increased IFP.33 Following paclitaxeladministration to animals, which was associated with re-duction in tumor IFP, the vessel density of the xenograft in-creased.33 There is growing evidence for the importance ofPDGF in the establishment of vascular stability and vascularpattern formation in tumors.34 The rapid onset of increasedvascularized tumor volume in a subset of CDP860-treatedpatients is, however, more consistent with the recruitmentof previously poorly perfused unperfused vessels, than it iswith the role of PDGF in tumor angiogenesis.

Seven of eight patients developed adverse events sug-gestive of fluid accumulation. Although two of the patientsmost severely affected also experienced the increase in vas-cular volume (patients 4 and 8), one patient with increasedvascular volume had no apparent fluid accumulation (pa-tient 5). This implies that toxic and potentially beneficialeffects of CDP860 are not always associated.

The exact mechanism of fluid accumulation asso-ciated with CDP860 is unknown. Based on our resultswith this PDGFR-� inhibitor, similar adverse events ob-served with other less specific inhibitors of PDGF (eg,

Table 7. Summary of Median Ktrans (min�1)31 – Changes From Baseline

Median Ktrans per Minute Day 1 Day 7 Day 27 Day 45


Mean* 0.268 0.259 0.227 0.248SD 0.1459 0.1553 0.1414

Change from baselineMean 0.007 0.015 0.025 �0.043SD 0.1297 0.1075 0.1192


Abbrevation: SD, standard deviation.*Mean of values recorded at days �2 and �1.†P values are derived, using the paired t-test, for exploratory purposes.

Table 8. Summary of Median Flow F (mL/min/mL)31 – Changes From Baseline

F (mL/min/mL) Day 1 Day 7 Day 27 Day 45


Mean* 0.816 0.832 0.869 1.295SD 0.4139 0.4442 0.4746

Change from baselineMean �0.033 �0.038 �0.064 �0.465SD 0.0861 0.1634 0.3176


Abbreviation: SD, standard deviation.*Mean of values recorded at days �2 and �1.†P values are derived, using the paired t-test, for exploratory purposes.


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imatinib,35,36 SU101,37,38 SU6668,39-43 and SU1124844)probably resulted from inhibition of PDGF signalingrather than other mechanisms. As some of these drugs(eg, SU11248) affect other receptor kinases, fluid accumu-lation may not occur to the same extent. This might be thecase because either the inhibition of other kinases over-comes the effect of inhibiting PDGFR-� or because the in-hibition of other kinases dominates the dose-limitingtoxicity. Although the mechanism of ascites generationis unclear, it is likely that the dynamic balance between in-travascular and extravascular fluid is more precarious inpatients with diffuse intra-abdominal disease. A perturba-tion such as a reduction in tumor interstitial pressure, me-diated by PDGF antagonists, might tip the balance in favorof extravascular fluid thereby allowing ascites to collect. Infact, two patients had a trace of ascites present initially,and perhaps their dynamic equilibrium was the mostvulnerable to reductions in interstitial pressure. However,it remains striking that in our analyses there was nochange in the Ktrans per unit tissue volume, suggesting thatchanges in vascular permeability were not responsible forthe ascites. It will be particularly interesting to see if otherstudies find similar changes in vascularized volume in pa-tients treated with mixed kinase inhibitors that target thePDGF receptors.

It may be important to consider whether inhibition ofPDGFR-� should be avoided for mixed kinase inhibitors.Kinase inhibitors whose selectivity profiles excludePDGFR may be more clinically useful through their avoid-ance of ascites. Alternatively, the effects observed whenPDGFR-� is specifically inhibited may not occur withmixed inhibitors if inhibition of other kinases can counter-act this biologic effect. As the signaling pathways of PDGFare complex, it will be interesting to determinewhichdown-stream pathways mediate the fluid accumulation effect.Mice expressing PDGFR-� mutated in the PI3K bindingsites were unable to normalize IFP in response to PDGF fol-lowing administrationof amast celldegranulatingagent, in-dicating a role for the PI3K pathway.45 There is evidence tosuggest that inhibition of PDGFR may be clinically useful

through other mechanisms, such as inhibition of autocrineeffects, or inhibition of angiogenesis. As we better under-stand the mechanisms involved in fluid accumulation, wemay learn to manage this side effect. While this study waslimited by the small number of patients, our observationssupport further study of controlled manipulation ofPDGF-mediated IFP through biologic agents such asCDP860, or small molecule antagonists. Modulation ofother pathways may also lead to a decrease in IFP. Willettet al46 have recently shown that inhibition of vascular endo-thelial growth factor causes adecrease in IFP inhumanrectalcarcinomas.

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Acknowledgment

We thank Simon Tickle, Martyn Robinson, and JeffSmith for input into the concept of CDP860 in theoncology setting. We also thank Hilary Done foroperational support of the study, Fran Oates and NaliniParmar for management of the data, Pete Jeffrey forstatistical advice during preparation of the protocol, andJoby Jose for pharmacokinetic and antibody assays.

Authors’ Disclosures of Potential

Conflicts of Interest

The following authors or their immediate familymembers have indicated a financial interest. No conflictexists for drugs or devices used in a study if they arenot being evaluated as part of the investigation. Employ-ment: K. Zinkewich-Peotti, Celltech; L. Rolfe, Celltech.Consultant/Advisory Role: G.C. Jayson, Celltech. StockOwnership: K. Zinkewich-Peotti, Celltech; L. Rolfe, Cell-tech. Honoraria: G.C. Jayson, Celltech. Research Funding:G.C. Jayson, Celltech. For a detailed description of thesecategories, or for more information about ASCO’s conflictof interest policy, please refer to the Author DisclosureDeclaration form and the Disclosures of Potential Con-flicts of Interest section of Information for Contributorsfound in the front of every issue.

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