Chronic myeloid leukemia blast phase (CML-BP) cells commonly express the multidrug transporter, P-glycoprotein (Pgp). To determine whether Pgp inhibition improves treatment outcome in CML-BP, the Southwest Oncology Group performed a randomized, controlled trial testing the benefit of the Pgp modulator, cyclosporin A (CsA). Seventy-three eligible patients were assigned to treatment with cytarabine and infusional daunorubicin with or without intravenous CsA. Treatment with CsA yielded no improvement in treatment outcome as measured by the frequency of induction resistance (68% vs 53%), rate of complete remission or restored chronic phase (CR/CP, 8% vs 30%), and survival (3 vs 5 months). Blast expression of Pgp (63%) and LRP (71%) was common, whereas only Pgp adversely impacted the rate of CR/CP (P = .025). We conclude that Pgp has prognostic relevance in CML-BP but that the modulation of Pgp function with CsA as applied in this trial is ineffective.

Blast transformation of chronic myeloid leukemia (CML-BP), the terminal phase of the disease, remains an important therapeutic challenge. Attempts to induce remission or to restore chronic phase with chemotherapy regimens active in acute myeloid leukemia (AML) are generally ineffective, yielding median overall survival (OS) of 2 to 4 months.1,2 Resistance to cytotoxic therapy in CML-BP extends to high-dose chemoradiotherapy conditioning with allogeneic stem cell rescue, offering a potential for extended survival rate that rarely exceeds 10%.1 The bcr/abl fusion gene product is singularly responsible for the hematologic manifestations of chronic phase CML3 and contributes to cellular resistance to cytotoxic therapy by the up-regulation of antiapoptotic molecules and other survival signals.4-8 In CML-BP, however, chemotherapy resistance is multifactorial and cannot be ascribed solely to bcr/abl. Although the bcr/abl-specific tyrosine kinase inhibitor, imatinib mesylate (Gleevec; Novartis, Basel, Switzerland), has shown promising activity in patients with CML-BP, responses in CML-BP are short-lived because of the acquisition of alternative mechanisms of resistance that contribute to treatment failure.9 10 

P-glycoprotein (Pgp) is a highly conserved plasma membrane glycoprotein that functions as an ATP-dependent multidrug exporter with broad specificity for natural product-derived antineoplastics.11-13 In adult AML, the overexpression of Pgp is associated with reduced cellular accumulation and in vitro resistance to anthracyclines that can be overcome by concurrent exposure to competitive Pgp antagonists such as cyclosporin A (CsA).14-16 Indeed in AML, Pgp overexpression is associated with a lower rate of complete remission and with inferior rates of disease-free and overall survival in patients receiving conventional anthracycline-containing induction and consolidation regimens.17-20 Southwest Oncology Group trial SWOG-9126 showed that adding CsA to a chemotherapy regimen containing infusional daunorubicin (DNR) significantly reduces induction resistance in patients with high-risk AML and prolongs the duration of remission and survival, implicating Pgp as an important cellular mechanism of resistance in myeloid leukemia.21 Pgp expression is demonstrable in myeloblasts in as many as 70% of patients with CML-BP.22-24 To determine whether the inhibition of Pgp export function improves survival in CML-BP, the SWOG conducted a randomized trial in adults (18-70 years old) with CML in previously untreated BP (SWOG-9032) comparing treatment with the same induction and consolidation regimen containing infusional DNR and high-dose cytarabine (HDAC) used in SWOG-9126, with or without the addition of CsA. Patients were required to have serum bilirubin levels lower than 1.5 times the institutional upper limit of normal, adequate cardiac function, and performance status of 0 to 2 by SWOG criteria.

Among 82 patients with previously untreated CML-BP registered between September 1992 and January 1998, 5 were ineligible because of prior treatment intended to restore chronic phase or to control leukocytosis 7 days or less before registration (3 patients), performance status 3 (1 patient), or unwillingness to accept randomization (1 patient). All 73 eligible patients with centrally reviewed pretreatment cytogenetics had the Philadelphia chromosome (Ph). Randomization between the HDAC/DNR (40 patients) and HDAC/DNR+CsA (37 patients) arms was stratified by age (younger than 55 vs 55 or older) and blast lineage (myeloid vs lymphoid vs undifferentiated). Blast expression of Pgp, multidrug resistance protein-1 (MRP1), the major vault protein lung resistance protein (LRP), and Pgp dye efflux capacity were assessed by flow cytometry as previously described.20 21 

Characteristics of the eligible patients were generally similar in the CsA and control arms, except that CsA patients had higher leukocyte and peripheral blast counts (Tables1-4). Expression of Pgp and LRP were slightly more common in the CsA arm, but CsA-inhibitable DiOC2 efflux and expression of MRP1 were not. Among 75 eligible patients evaluable for induction toxicity, 8 (21%; 95% confidence interval [CI], 10%, 37%) of 38 controls died of induction toxicity compared with 7 (19%; 95% CI, 8%, 35%) of 37 CsA patients (one-tailed test, P = .48). Grade 4 hyperbilirubinemia was more frequent with CsA (P < .0001; 14 [38%] HDAC/DNR+CsA vs 1 [3%] HDAC/DNR).

Table 1.

Demographic features by treatment arm

HDAC/DNR,
n = 40
HDAC/DNR + CsA, n = 37
No.PercentageNo.Percentage
Female 14 35 20 54  
Aged 55 to 70 y 15 38 14 38  
Blast lineage, myeloid/lymphoid/undiff 32/3/5 80/8/13 31/1/5 84/3/14 
Performance status 2 12 30 14 38  
Prior myelosuppression therapy 14 35 10 27 
HDAC/DNR,
n = 40
HDAC/DNR + CsA, n = 37
No.PercentageNo.Percentage
Female 14 35 20 54  
Aged 55 to 70 y 15 38 14 38  
Blast lineage, myeloid/lymphoid/undiff 32/3/5 80/8/13 31/1/5 84/3/14 
Performance status 2 12 30 14 38  
Prior myelosuppression therapy 14 35 10 27 
Table 2.

Pretreatment hematologic features by treatment arm

HDAC/DNR,
n = 40
HDAC/DNR + CsA,
n = 37
MedianRangeMedianRange
Age, y 51 21 -67 50 24 -70  
Marrow blasts, % 51 10 -95 43 11 -95  
WBC, 1000/μL 31.6 0.8 -175 60.1 3.4 -312  
Peripheral blasts, % 27 0 -84 35 1 -96  
Peripheral blasts, 1000/μL 10.6 0.0 -82.6 19.4 0.4 -123  
Hemoglobin, g/dL 9.2 5.5 -27.4 9.4 6.6 -15.1  
Platelets, 1000/μL 82 8 -5000 88 6 -199 
HDAC/DNR,
n = 40
HDAC/DNR + CsA,
n = 37
MedianRangeMedianRange
Age, y 51 21 -67 50 24 -70  
Marrow blasts, % 51 10 -95 43 11 -95  
WBC, 1000/μL 31.6 0.8 -175 60.1 3.4 -312  
Peripheral blasts, % 27 0 -84 35 1 -96  
Peripheral blasts, 1000/μL 10.6 0.0 -82.6 19.4 0.4 -123  
Hemoglobin, g/dL 9.2 5.5 -27.4 9.4 6.6 -15.1  
Platelets, 1000/μL 82 8 -5000 88 6 -199 
Table 3.

Multidrug resistance phenotype by treatment arm

HDAC/DNR, n = 40HDAC/DNR + CsA,
n = 37
No. positive/no. patientsPercentageNo. positive/no. patientsPercentage
Duplicate Ph 5/37 14 5/36 14 
Pgp* 20/36 56 22/36 61  
CsA-inhibited DiOC2 efflux 22/36 61 21/36 58 
MRP1* 8/36 22 5/36 14 
LRP* 23/35 66 28/36 78 
HDAC/DNR, n = 40HDAC/DNR + CsA,
n = 37
No. positive/no. patientsPercentageNo. positive/no. patientsPercentage
Duplicate Ph 5/37 14 5/36 14 
Pgp* 20/36 56 22/36 61  
CsA-inhibited DiOC2 efflux 22/36 61 21/36 58 
MRP1* 8/36 22 5/36 14 
LRP* 23/35 66 28/36 78 
Table 4.

Treatment outcome by assigned therapy

HDAC/DNR,
n = 40
HDAC/DNR + CsA,
n = 37
Estimate95% CIEstimate95% CI
Median survival, mos, P = .77 4 -7 2 -5 
6-mo survival probability, % 47 37 -62 32 17 -48 
Complete response, P = .95 18 7 -33 1 -18  
Complete response or RCP, P = .99,4-151 30 17 -47 2 -22  
Resistant disease, P = .91 53 36 -68 68 50 -82 
HDAC/DNR,
n = 40
HDAC/DNR + CsA,
n = 37
Estimate95% CIEstimate95% CI
Median survival, mos, P = .77 4 -7 2 -5 
6-mo survival probability, % 47 37 -62 32 17 -48 
Complete response, P = .95 18 7 -33 1 -18  
Complete response or RCP, P = .99,4-151 30 17 -47 2 -22  
Resistant disease, P = .91 53 36 -68 68 50 -82 

Undiff indicates undifferentiated; RCP, restored chronic phase.

F4-150

Pgp expression was defined by flow cytometry detection of MRK16 reactivity with Kolmogorv-Smirnov (KS) D ≥ 0.20, MRP1 by MRPm6antibody with KS D ≥ 0.20, and LRP by the LRP56 antibody with KS D ≥ 0.25.

F4-151

CsA-inhibited DiOC2 efflux was defined by Kolmogorv-Smirnov D ≥ 0.25.

One-tailed P for superior outcome in CsA arm, based on PH or logistic regression models for survival and response, respectively, adjusted for stratification by age group and blast lineage (lymphoid and undifferentiated combined in analyses of response).

Twelve controls (30%; 95% CI, 17%, 47%) achieved complete response (CR; 7 patients) or restored chronic phase (CP; 5 patients) compared with 3 CsA patients (8%; 95% CI, 2%, 22%; 2 CRs, 1 CP). Twenty-one controls (53%; 95% CI, 36%, 68%) had resistant disease compared with 25 (68%; 95% CI, 50%, 82%) CsA patients. All responses (CR or restored CP) were achieved with one course of induction therapy. Twelve of 15 responding patients (2 CsA, 10 controls) had cytogenetic follow-up, and 3 of these (2 with CR and 1 with restored CP, all controls) achieved cytogenetic CR.

Estimated median OS time was 5 months (95% CI, 4-7 months) in the control arm versus 3 months (95% CI, 2-5 months) in the CsA arm (one-tailed test, P = .77). Because the CsA-treated cohort had higher leukocyte and peripheral blast counts and higher Pgp expression, additional analyses were performed to assess whether such differences confounded the treatment comparison. In unstratified proportional hazards (PH) regression models, survival decreased with increasing WBC (2-tailed test, P = .074) or absolute blast count (P = .19), but it varied little in relation to level of Pgp expression (P = .47) or efflux (P = .14). However, in multivariate analysis, the absence of benefit of CsA was not explained by confounding effects of these factors (results not shown).

To determine whether pretreatment multidrug resistance phenotype has prognostic relevance in CML-BP, we examined the relation between blast expression of Pgp and other drug resistance proteins to treatment outcome in univariate analysis. With both treatment arms combined, response to treatment (CR, CR/CP, or RD) was significantly associated with Pgp expression and function (Table5), whereas neither MRP1 nor LRP expression adversely influenced induction outcome. As in the analysis of OS, the lack of benefit of CsA could not be explained by confounding effects of drug resistance protein expression or efflux.

Table 5.

Response to induction therapy by pretreatment Pgp expression and efflux, MRP, and LRP expression

PatientComplete responseCR or restored chronic phaseResistant disease
% CR95% CIP% CR or RCP95% CIP% RD95% CIP
Pgp (MRK16) D < 0.20 30 23 10 -42 .0071 27 12 -46 .025 53 34 -72 .18  
 D ≥ 0.20 42 1 -16 — 12 4 -26 — 67 50 -80 —  
CsA-inhibited D < 0.25 29 21 8 -40 .030 24 10 -44 .028 52 33 -71 .0033 
DiOC2 efflux D ≥ 0.25 43 1 -19 — 14 5 -28 — 67 51 -81 —  
MRP D < 0.20 59 12 5 -23 .75 17 8 -29 .81 59 46 -72 .29 
 D ≥ 0.20 13 15 2 -45 — 23 5 -54 — 69 39 -91 — 
LRP D < 0.25 20 10 1 -32 .55 20 6 -44 .80 45 23 -68 .37  
 D ≥ 0.25 51 14 6 -26 — 18 8 -31 — 67 52 -79 — 
PatientComplete responseCR or restored chronic phaseResistant disease
% CR95% CIP% CR or RCP95% CIP% RD95% CIP
Pgp (MRK16) D < 0.20 30 23 10 -42 .0071 27 12 -46 .025 53 34 -72 .18  
 D ≥ 0.20 42 1 -16 — 12 4 -26 — 67 50 -80 —  
CsA-inhibited D < 0.25 29 21 8 -40 .030 24 10 -44 .028 52 33 -71 .0033 
DiOC2 efflux D ≥ 0.25 43 1 -19 — 14 5 -28 — 67 51 -81 —  
MRP D < 0.20 59 12 5 -23 .75 17 8 -29 .81 59 46 -72 .29 
 D ≥ 0.20 13 15 2 -45 — 23 5 -54 — 69 39 -91 — 
LRP D < 0.25 20 10 1 -32 .55 20 6 -44 .80 45 23 -68 .37  
 D ≥ 0.25 51 14 6 -26 — 18 8 -31 — 67 52 -79 — 

Two-tailed P for test of trend in response rate with Pgp, MRP1, or LRP expression level (MRK16), or efflux Dtreated as a quantitative (continuous) variable in simple (univariate) logistic regression, that is, without adjustment for stratification or treatment assignment.

This controlled trial was designed so that the survival comparison between treatment arms would have 91% statistical power if the true CsA:control mortality hazards ratio was 0.5 (one-sided test at critical level, 5%), and this level of power was achieved. Therefore, the results of this study provided compelling evidence that the addition of CsA to an HDAC/DNR-containing induction and consolidation regimen offers no survival benefit of practical importance over chemotherapy alone in patients with CML-BP. We cannot exclude the possibility that failure to achieve blood concentrations of CsA sufficient for Pgp blockade impacted the results of this trial. However, the analogous regimen studied in patients with high-risk AML (SWOG-9126) consistently yielded CsA blood concentrations exceeding 1500 ng/mL and significantly improved survival in Pgp-positive patients.21 Our data indicate that Pgp expression and function represent adverse prognostic variables impacting induction outcome in CML-BP, analogous to the data reported for AML. The negative results of this study do not exclude the potential benefit of more potent, so-called second-generation Pgp antagonists in CML-BP, but they raise the notion that Pgp expression reflects an alternative antigenic marker of a primitive blast phenotype that, in this disease, represents only one of many redundant cell defense mechanisms or survival signals. Indeed, recently characterized large genomic deletions on the derivative chromosome 9 adjacent to the t(9;22) breakpoint identify a subgroup of CML patients with particularly poor prognosis and inferior survival, independent of clinical prognostic variables.25 Strategies to inhibit Pgp function may merit further study in CML-BP when combined with the bcr-abl tyrosine kinase inhibitor, imatinib mesylate, and conventional cytotoxics.26 Imatinib mesylate interrupts the constitutive kinase-induced antiapoptotic signals to yield additive cytotoxicity or synergy with many antineoplastics.27Indeed, Pgp has been implicated as an important cellular mechanism contributing to in vitro resistance to imatinib mesylate. The farnesyl transferase inhibitor SCH66336, a downstream inhibitor of ras-mediated signaling by BCR-ABL, directly inhibits Pgp transport function with a potency comparable to that of CsA.28-30Inhibition of Pgp might accentuate cytotoxicity by augmenting imatinib mesylate and antineoplastic cellular accumulation and, as a consequence, potentially limit the molecular adaptation toBCR-ABL recognized with extended imatinib mesylate treatment.31 

The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked “advertisement” in accordance with 18 U.S.C. section 1734.

1
Faderl
S
Talpaz
M
Estrov
Z
et al
The biology of chronic myeloid leukemia.
N Engl J Med.
341
1999
165
172
2
Kantarjian
HM
Talpaz
M
Kontoyiannis
D
et al
Treatment of chronic myelogenous leukemia in accelerated and blastic phases with daunorubicin, high-dose cytarabine, and granulocyte-macrophage colony-stimulating factor.
J Clin Oncol.
10
1992
398
405
3
Daley
GQ
Van Etten
RA
Baltimore
D
Induction of chronic myelogenous leukemia in mice by the P210bcr/abl gene of the Philadelphia chromosome.
Science.
247
1990
824
830
4
Deininger
MWN
Goldman
JM
Melo
JV
The molecular biology of chronic myeloid leukemia.
Blood.
96
2000
3343
3356
5
Cortez
D
Stoica
G
Pierce
JH
Pendergast
AM
The BCR-ABL tyrosine kinase inhibits apoptosis by activating a Ras-dependent signaling pathway.
Oncogene.
13
1996
2589
2594
6
Chai
SK
Nichols
GL
Rothman
P
Constitutive activation of JAKs and STATs in BCR-Abl–expressing cell lines and peripheral blood cells derived from leukemic patients.
J Immunol.
159
1997
4720
4728
7
Skorski
T
Kanakaraj
P
Nieborowska-Skorska
M
et al
Phosphatidylinositol-3 kinase activity is regulated by BCR/ABL and is required for the growth of Philadelphia chromosome-positive cells.
Blood.
85
1995
726
736
8
Amarante-Mendes
GP
McGahan
AJ
Nishioka
WK
Afar
DE
Witte
ON
Green
DR
Bcl-2–independent Bcr-Abl–mediated resistance to apoptosis: protection is correlated with up regulation of Bcl-xL.
Oncogene.
16
1998
1383
1390
9
Druker
BJ
Sawyers
CL
Kantarjian
H
et al
Activity of a specific inhibitor of the BCR-ABL tyrosine kinase in the blast crisis of chronic myeloid leukemia and acute lymphoblastic leukemia with the Philadelphia chromosome.
N Engl J Med.
344
2001
1038
1042
10
Druker
BJ
Talpaz
M
Resta
DJ
et al
Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia.
N Engl J Med.
344
2001
1031
1037
11
Gerlach
JH
Endicott
JA
Juranka
PF
et al
Homology between P-glycoprotein and a bacterial haemolysin transport protein suggests a model for multidrug resistance.
Nature.
324
1986
485
489
12
Ng
WF
Sarangi
F
Zastawny
RL
Veinot-Drebot
L
Ling
V
Identification of members of the P-glycoprotein multigene family.
Mol Cell Biol.
9
1989
1224
1232
13
Ueda
K
Cardarelli
C
Gottesman
MM
Pastan
I
Expression of a full-length cDNA for the human “MDR1” gene confers resistance to colchicine, doxorubicin, and vinblastine.
Proc Natl Acad Sci U S A.
84
1987
3004
3008
14
Nooter
K
Sonneveld
P
Oostrum
R
Herweijer
H
Hagenbeek
T
Valerio
D
Overexpression of the mdr 1 gene in blast cells from patients with acute myelocytic leukemia is associated with decreased anthracycline accumulation that can be restored by cyclosporin-A.
Int J Cancer.
45
1990
263
268
15
Coley
HM
Twentyman
PR
Workman
P
Improved cellular accumulation is characteristic of anthracyclines which retain high activity in multidrug resistant cell lines, alone or in combination with verapamil or cyclosporin A.
Biochem Pharmacol.
38
1989
4467
4475
16
Naito
M
Tsuge
H
Kuroko
C
et al
Enhancement of cellular accumulation of cyclosporine by anti–P-glycoprotein monoclonal antibody MRK-16 and synergistic modulation of multidrug resistance.
J Natl Cancer Inst.
85
1993
311
316
17
Pirker
R
Wallner
J
Geissler
K
et al
MDR1 gene expression and treatment outcome in acute myeloid leukemia.
J Natl Cancer Inst.
83
1991
708
712
18
Campos
L
Guyotat
D
Archimbaud
E
et al
Clinical significance of multidrug resistance P-glycoprotein expression in acute nonlymphoblastic leukemia cells at diagnosis.
Blood.
79
1992
473
476
19
List
AF
Spier
CM
Cline
A
et al
Expression of the multidrug resistance gene product (P-glycoprotein) in myelodysplasia is associated with a stem cell phenotype.
Br J Haematol.
78
1992
28
34
20
Leith
CP
Kopecky
KJ
Godwin
J
et al
Acute myeloid leukemia in the elderly: assessment of multidrug resistance (MDR1) and cytogenetics distinguishes biologic subgroups with remarkably distinct responses to standard chemotherapy: a Southwest Oncology Group Study.
Blood.
89
1997
3323
3329
21
List
AF
Kopecky
KJ
Willman
CL
et al
Benefit of cyclosporine modulation of drug resistance in patients with poor-risk acute myeloid leukemia: a Southwest Oncology Group study.
Blood.
98
2001
3212
3220
22
Carulli
G
Petrini
M
Marini
A
Ambrogi
F
P-glycoprotein in acute non-lymphoblastic leukemia and in the blastic crisis of myeloid leukemia.
N Engl J Med.
319
1988
797
798
23
Kuwazuru
Y
Yoshimura
A
Hanada
S
et al
Expression of the multidrug transporter, P-glycoprotein, in chronic myelogenous leukemia cells in blast crisis.
Br J Haematol.
74
1990
24
29
24
Herquijer
H
Sonneveld
P
Baas
F
Nooter
K
Expression of mdr 1 and mdr 3 multidrug-resistance genes in human acute and chronic leukemias and association with stimulation of drug accumulation by cyclosporine.
J Natl Cancer Inst.
82
1990
1133
1140
25
Huntly
HJP
Reid
AG
Bench
AJ
et al
Deletions of the derivative chromosome 9 occur at the time of the Philadelphia translocation and provide a powerful and independent prognostic indicator in chronic myeloid leukemia.
Blood.
98
2001
1732
1738
26
Mahon
FX
Deininger
MW
Schultheis
B
et al
Selection and characterization of BCR-ABL positive cell lines with differential sensitivity to the tyrosine kinase inhibitor STI571: diverse mechanisms of resistance.
Blood.
96
2000
1070
1079
27
Thiessing
JT
Ohno-Jones
S
Kolibaba
KS
Druker
BJ
Efficacy of STI71, an Abl tyrosine kinase inhibitor, in conjunction with other antileukemic agents against Bcr-Abl-positive cells.
Blood.
96
2000
3195
3199
28
Peters
DG
Hoover
RR
Gerlach
MJ
et al
Activity of the farnesyl protein transferase inhibitor SCH66336 against BCR/ABL-induced murine leukemia and primary cells from patients with chronic myeloid leukemia.
Blood.
97
2001
1404
1412
29
Reichert
A
Heisterkamp
N
Daley
GQ
Groffen
J
Treatment of Bcr/Abl-positive acute lymphoblastic leukemia in P190 transgenic mice with the farnesyl transferase inhibitor SCH66336.
Blood.
97
2001
1399
1403
30
Wang
EJ
Casciano
CN
Clement
RP
Johnson
WW
The farnesyl protein transferase inhibitor SCH66336 is a potent inhibitor of MDR1 product P-glycoprotein.
Cancer Res.
61
2001
7525
7529
31
Gorre
ME
Mohammed
M
Ellwood
K
et al
Clinical resistance to STI-571 cancer therapy caused by BCR-ABL gene mutation and amplification.
Science.
293
2001
876
880

Author notes

Alan F. List, Southwest Oncology Group (SWOG-9126), Operations Office, 14980 Omicron Dr, San Antonio, TX 78245-3217.

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