Leukemia (2001) 15, 764–771
 2001 Nature Publishing Group All rights reserved 0887-6924/01 $15.00
www.nature.com/leu
Combined action of PSC 833 (Valspodar), a novel MDR reversing agent, with
mitoxantrone, etoposide and cytarabine in poor-prognosis acute myeloid leukemia
G Visani1, D Milligan2, F Leoni3, J Chang4, S Kelsey5, R Marcus6, R Powles7, S Schey8, A Covelli9, A Isidori1, M Litchman10,
PP Piccaluga10, H Mayer9, M Malagola9 and C Pfister9
1
Istituto di Ematologia e Oncologia Medica ‘L & A Seragnoli’, Università degli Studi di Bologna, Azienda Ospedaliera Policlinico
‘Sant’Orsola-Malpighi’, Bologna, Italy; 2Department of Haematology, Birmingham Heartlands Hospital, Birmingham, UK; 3Università degli
Studi di Firenze, Unità Operativa di Ematologia, Azienda Ospedaliera ‘Careggi’, Firenze, Italy; 4Christie Hospital BHS Trust, Manchester;
5
Department of Haematology, Royal London Hospital, London; 6Department of Haematology, Addenbrookes Hospital, Cambridge;
7
Leukaemia and Myeloma Unit, Royal Marsden Hospital, Sutton; 8Department of Haematology, Guys Hospital, London, UK; 9Novartis
Pharma AG, Basel, Switzerland; and 10Novartis Pharmaceuticals Corporation Inc., East Hanover, NJ USA
PSC 833 (Valspodar) can reverse multidrug resistance (MDR)
in patients with hematologic malignancies, but alters the pharmacokinetics of concomitant anticancer agents. A phase I,
dose-finding study was initiated to define a safe and effective
regimen of mitoxantrone, etoposide, and cytarabine (MEC)
when administered with PSC 833 to patients with early relapsed
or refractory acute myeloid leukemia (AML). Poor-prognosis
AML patients refractory to first-line induction therapy or relapsing within 9 months of attaining complete remission (CR) were
treated with cytarabine (1.0 g/m2/day), etoposide (30
mg/m2/day), and mitoxantrone at a dose of either 3.0 mg/m2/day
(cohort 1) or 4.5 mg/m2/day (cohorts 2 and 3) for 6 days plus
continuous-infusion PSC 833 (10 mg/kg/24 h with a 2.0 mg/kg
loading dose) for 6 or 7 days each 21-day cycle. Patients
achieving CR were given a 4-day MEC plus PSC 833 consolidation cycle. Twenty-three patients were enrolled (eight with
primary refractory AML and 15 in relapse). Dose-limiting toxicity occurred in one of six patients in cohort 2 (grade 4
mucositis) and one of seven patients in cohort 3 (grade 4
hyperbilirubinemia). The maximum tolerated dose of mitoxantrone was defined as 4.5 mg/m2/day. Clinically significant grade
4 hyperbilirubinemia, possibly related to PSC 833, occurred in
four patients. Hematologic toxicities were as expected in this
patient population, but were not dose limiting. Mild to moderate
cerebellar ataxia and paresthesia occurred in six (26%) and five
(22%) patients, respectively, but were not dose limiting. Overall,
six of 23 (26%) patients achieved CR, including five patients
with demonstrated P-glycoprotein expression and/or function.
The median overall survival was 4 months. All six patients with
a CR were alive and four (17%) patients were disease free at
12 months. Blood levels of PSC 833 were well above the target
level of 1000 ng/ml, a concentration that is known to reverse
MDR in vitro. PSC 833 reduced the clearance of etoposide by
approximately two-fold. No correlation was observed between
the mitoxantrone or etoposide area under the curve and
response. In conclusion, the MEC plus PSC 833 tested regimen
was well tolerated and the 26% CR rate warrants further testing
of this regimen in a randomized, phase III trial. Leukemia (2001)
15, 764–771.
Keywords: acute myeloid leukemia; multidrug resistance; reversing agents; cytosine arabinoside; mitoxantrone
Introduction
Failure of conventional chemotherapy in refractory acute
myeloid leukemia (AML) is frequently linked to the expression
of a multidrug resistance (MDR) phenotype. One of the most
important mechanisms of MDR is mediated by the MDR gene-
Correspondence: G Visani, Institute of Hematology and Medical
Oncology ‘L & A Seragnoli’, Università degli Studi di Bologna, Az.
Osp. Policlinico ‘Sant’Orsola-Malpighi’, Via G. Massarenti, 9, 40138
Bologna, Italy; Fax: 0039-(0)51–6364037
Received 27 July 2000; accepted 15 February 2001
1 (mdr-1),1–4 which encodes a 170-kDa transmembrane glycoprotein known as permeability glycoprotein (P-gp).5–9
The correlation between mdr-1 gene expression and poor
treatment outcome is well documented in AML.10–29 There has
thus been a remarkable interest in developing pharmacologic
strategies for MDR reversal in vivo. Although several comparative studies with P-gp modulators have been limited by
the unacceptable toxicities of available agents, recent clinical
phase I/II studies have demonstrated the feasibility of this strategy.30–39 PSC 833 (Valspodar; Novartis Pharma Corporation,
East Hanover, NJ, USA), a cyclosporine analog without
immunosuppressive or nephrotoxic toxicity, is approximatively five-fold to 30-fold more potent than cyclosporine A
(CsA) in vitro, and, unlike CsA, is a high-affinity noncompetitive inhibitor of P-gp.40–42 A few studies investigating the use
of PSC 833 in human malignancies have shown the improvement of clinical response in patients with AML,30–36 as well
as with other refractory malignancies.37–39 Older and
relapsed/refractory AML patients, however, are burdened by
an unacceptable toxicity when treated with aggressive regimens, and schemes with low-toxic profile seem to be appropriate in these kinds of patients. A regimen of mitoxantrone
and etoposide, with intermediate-dose cytarabine (MEC), has
been shown to be effective, with acceptable toxicity, in
relapsed or refractory AML.43–46 However, although complete
remission rates in relapsed/refractory AML patients treated
with a MEC regimen range from 39% to 44%, only 3% of
patients are disease-free after 2 years, in part probably due to
MDR. Therefore, addition of an MDR modulator such as PSC
833 to a mitoxantrone–etoposide-based regimen seemed a
logical step. Encouraging results have been shown from very
recent studies30,35 (comprising a partial, preliminary report of
the present data31) investigating the use of a regimen of mitoxantrone and etoposide, with or without intermediate-dose
cytarabine. Chauncey et al35 studied older patients with
untreated AML and suggested that the addition of PSC 833
to a mitoxantrone–etoposide regimen for older patients with
untreated AML is well tolerated but requires a reduction in
mitoxantrone–etoposide dosing to avoid increased toxicity. In
effect, grade III–IV hyperbilirubinemia according to WHO
grading scale, as well as cerebellar dysfunction and paresthesias were frequently observed. Thus, appropriate dose
reductions are required when these cytotoxic agents are coadministered with PSC 833 to avoid increased toxicity, because
PSC 833 can affect the normal physiologic transport and
excretion of cytotoxic agents that are substrates for P-gp.47
This could be particularly important for heavily pretreated
patients, such as relapsed-refractory AML.
Basing on this, we planned a phase I study to establish a
safe and effective regimen consisting of mitoxantrone, etopo-
PSC 833 in poor-prognosis AML
G Visani et al
side, and cytarabine (MEC) when combined with PSC 833 in
patients with refractory or early relapsed AML.
Patients and methods
The study was an open-label, multicenter, phase I dose-escalation study to determine the maximum tolerated dose of
mitoxantrone in combination with etoposide and cytarabine
when coadministered with PSC 833 in patients with poorprognosis AML. The study protocol was approved by the Institutional Review Boards of the participating hospitals. All
patients provided written informed consent.
Patient population
Adult patients between 18 and 65 years of age with a diagnosis of AML by the French–American–British classification,48
who had either failed to obtain a complete response to firstline induction therapy (ie, refractory patients) or were in first
or subsequent relapse within 9 months of attaining CR, were
enrolled. Refractory patients had to have received at least two
cycles of an anthracycline-containing induction regimen
before entry into this study. Other eligibility criteria included
World Health Organization (WHO) performance status ⭐2
and suitability for intensive chemotherapy in the opinion of
the treating physician.
Criteria for exclusion included the following: documented
central nervous system involvement; left ventricular ejection
fraction ⬍50%, as measured by cardiac radionuclide-gated
blood pool scan; severe rhythm abnormalities; other severe
cardiac dysfunction; serum creatinine ⭓175 ␮mol/l; serum
bilirubin ⭓2.5-fold the institutional upper limit of normal;
positive hepatitis B surface antigen, a known history of hepatitis C, or HIV infection; known hypersensitivity to CsA; prior
treatment with radiotherapy to the pelvis and/or spinal axis in
the 4 weeks prior to study entry; and chronic granulocytic
leukemia in blast cell crisis.
Chemotherapy treatment
All patients were scheduled to receive one or two identical
induction cycles of a minimum duration of 21 days. For each
of the first 6 days of the induction cycle(s), the patients
received cytarabine at a fixed dose of 1.0 g/m2/day as a 6-h
infusion and etoposide at a fixed dose of 30.0 mg/m2/day as
a 1-h infusion. Mitoxantrone was administered as a bolus
injection at 3.0 mg/m2/day in cohort 1 and 4.5 mg/m2/day in
cohorts 2 and 3. PSC 833 was administered at a dose of
10 mg/kg/24 h CIV. On day 1, the continuous infusion was
started concomitantly with a loading dose of 2 mg/kg given
over 2 h. The continuous infusion of PSC 833 was given for
168 h (7 days) in cohorts 1 and 2, and for 144 h (6 days) in
cohort 3. The duration of PSC 833 administration was shortened in cohort 3 because pharmacokinetic (PK) data indicated
that PSC 833 levels remained ⬎1000 ng/ml for 24 h after the
completion of the continuous infusion.
Treatment in subsequent cycles depended on the patient’s
response to therapy in the prior induction cycle using previously established criteria for response.49 If the bone marrow
after the first induction cycle showed ⭓25% blasts, and/or
extramedullary disease was diagnosed, the patient was considered a treatment failure and treatment was discontinued. If
the bone marrow after the first induction cycle showed
between 5% and 25% blasts, and there were no signs of extramedullary disease, a second course of induction chemotherapy was given. If the bone marrow after the first or second
induction cycle showed ⬍5% blasts and no signs of extramedullary disease, the patient was to receive consolidation therapy after peripheral blood recovery (ie, absolute neutrophil
count ⭓1500 cells/ml and a transfusion-independent platelet
count ⭓100 000/ml).
765
Response criteria
Complete remission (CR) required adequate marrow cellularity with ⬍5% of blasts documented at the preconsolidation
evaluation, no peripheral blasts, an absolute neutrophil count
⭓1500/␮l, platelet count ⭓100 000/␮l, and no evidence of
extramedullary leukemia. Partial remission (PR) required all
criteria as in CR except that the bone marrow may have contained 5% to 25% blasts, or the bone marrow had ⬍5% blasts,
in the presence of moderate thrombocytopenia (50–
100 000/␮l). Failure was defined as leukemia-associated or
caused by early death (ie, within 30 days of completion of
treatment). Leukemia-related causes of failure were refractory
disease (inability to achieve hypoplasia despite one cycle of
chemotherapy) and regrowth resistance, a term used to indicate cases in which ⬎25% bone marrow blasts were noted
on recovery despite adequate marrow hypoplasia having
been achieved.49
Determination of maximum tolerated dose and doselimiting toxicity
This was an open-label, multicenter phase I dose-escalation
study to determine the MTD of mitoxantrone and etoposide
given in combination with fixed doses of PSC 833 and cytarabine in patients with poor-prognosis acute myelogenous leukemia. Patients were assigned sequentially to cohorts and
dose escalation of either mitoxantrone or etoposide proceeded
until the MTD could be defined. The anticipated dose range
of mitoxantrone tested was 4–8 mg/m2/day and for etoposide
60–100 mg/m2/day. However, these planned dose ranges
were subsequently modified in a protocol amendment, when
information from a similar US study became available.30
According to this trial, it was decided not to escalate the doses
of mitoxantrone and etoposide above cumulated doses per
induction cycle of 25 mg/m2 and 250 mg/m2, respectively.
The following algorithm was used to determine mitoxantrone or etoposide dose escalation:
• If 0/3 patients in any cohort experienced DLT, then escalation to the next cohort was allowed.
• If 1/3 patients in any cohort experienced DLT, then an
additional three patients were enrolled. If no further DLT
occurred, dose escalation to the next cohort continued.
• If ⬎1 patient in any cohort experienced DLT there was no
further dose escalation and the MTD of cytarabine, mitoxantrone and etoposide in combination with PSC833 was
defined as the dose combination of the previous cohort.
The MTD was defined as the dose below the dose associated with DLT in 2/6 patients in the first cycle.
Dose-limiting toxicities were based on NCIC Expanded
Common Toxicity Criteria, divided into hematological and
non-hematological types and defined as follows.
Leukemia
PSC 833 in poor-prognosis AML
G Visani et al
766
Non-hematological DLT:
CTC grade 3/4 non-hematological toxicity occurring up to 14 days after cessation of PSC833
infusion but excluding nausea, vomiting, alopecia, infectious
causes and grade 3 reversible cerebellar dysfunction. Grade 4
hyperbilirubinemia was considered dose limiting if it was the
only reason for treatment discontinuation, ie resulting in a
delay of treatment ⬎7 days.
The definitions of cerebellar dysfunction used in the NCIC
CTC are ill-suited to classifying the actual dysfunction
observed in patients, therefore the following revised
definitions for cerebellar toxicity were used.
Grade 1: Slight subjective sense of incoordination. No difficulty walking. Physical examination normal or
equivocally normal.
Grade 2: Definite subjective incoordination on walking, but
able to walk without assistance. On examination,
broad-based gait and/or mild dysdiadochokinesias
and difficulty walking heel-to-toe.
Grade 3: Unable to walk without assistance from another
person or a walker. On examination, markedly
abnormal gait and inability to walk heel-to-toe.
Grade 4: Unable to walk, because of incoordination, even
with assistance.
Hematological DLT:
Hypoplastic death during the first
cycle occurring between 34 and 45 days from the start of
chemotherapy with no evidence of persisting AML (if disease
was still evident hypoplastic death was not dose limiting);
neutropenia after the first cycle (only if patient was in CR)
defined as ANC ⬍0.5 × 109/l for ⬎45 days after it was first
measured; thrombocytopenia after the first cycle (only if
patient was in CR) defined as platelets ⬍20 × 109/l for ⬎45
days after it was first measured.
Pharmacokinetic analysis
The pharmacokinetics of PSC 833, mitoxantrone, and etoposide were assessed in induction cycle 1 and during consolidation. In induction cycle 1, plasma concentrations of etoposide and mitoxantrone were determined during concomitant
administration of PSC 833. In the consolidation cycle a PK
profile was performed on day 1 in the absence of PSC 833.
Blood samples (2 ml) for PK analysis of PSC 833 were drawn
on day 1 just after completing the loading dose and before
starting CIV, and thereafter at the same time daily on each
day of PSC 833 administration in the induction cycle. The PSC
833 concentration in whole blood was determined using a
radioimmunoassay as previously published.50 Blood samples
(5 ml) for measurement of etoposide and mitoxantrone plasma
concentrations were taken just before drug administration and
at 1, 2, 3, 4, 6, 8, 10, 12, 24, and 36 h (this last sample only
in the induction cycle) after the start of administration. Plasma
levels were assayed using high-performance liquid chromatography as previously described.51,52
The plasma concentration-time data for etoposide and
mitoxantrone were analyzed separately by standard noncompartmental methods. The following parameters were derived:
area under the curve (AUC) over a 24-h dosing interval by
trapezoidal summation; total body clearance (CL =
Dose/AUC); and distribution volume associated with the terminal phase (Vz = CL/lambda) and terminal disposition rate
constant (lambda) by log-linear regression of the terminal porLeukemia
tion of the profile. The corresponding half-life (t1/2) was calculated as t1/2 = ln2/lambda.
Determination of P-gp expression and function
Bone marrow aspirates (3 ml) from the sternum or the posterior iliac crest were collected at diagnosis and stored at 0° to
4°C in 2 ml of Dulbecco’s modified Eagle’s medium (DMEM)
(Gibco BRL, Paisley, UK) containing 5000 IU of heparin.
Mononuclear bone marrow cells were collected by centrifugation over Lymphoprep (Nycomed, Oslo, Norway) and suspended at a concentration of 4 × 106 cells/ml in DMEM supplemented with 10% fetal calf serum and gentamycin. P-gp
expression was determined by staining with monoclonal antibodies against P-gp: MRK16 (Kamiya Biomedical Company,
Seattle, WA, USA) at a concentration of 10 ␮g/ml. An isotypematched murine immunoglobulin (Ig)G2a control antibody
(Sigma, St Louis, MO, USA) was used at a concentration of
10 ␮g/ml. Cell-bound antibodies were detected using fluorescein isothiocyanate-conjugated rabbit anti-mouse antibodies (DAKO, Glostrup, Denmark). Fluorescence was measured using a FACScalibur (Becton Dickinson, San Jose, CA,
USA). Results were expressed as the ratio of cell-associated
fluorescence of cells incubated with the anti-P-gp antibody to
the mean of cell-associated fluorescence of cells incubated
with the nonspecific control antibody as previously
described.18
Function of P-gp was measured by incubating cells for 1 h
at 37°C at 5% CO2 in the presence or absence of 2 ␮m PSC
833, followed by incubation with 200 ng/ml rhodamine-123
(Sigma). Fluorescence was measured using a FACScalibur.
Results are expressed as the ratio of the mean intracellular
rhodamine fluorescence of cells exposed to PSC 833 to the
mean intracellular fluorescence of cells not exposed to PSC
833.
The drug-sensitive cell line RMPI 8226 S and the drugresistant variant 8226 D6, kindly provided by Dr W Dalton
(H Lee Moffitt Cancer Center, Tampa, FL, USA), were used as
negative and positive controls, respectively, for P-gp function
and expression assays. In the P-gp function assay, the mean
ratio of rhodamine-123 fluorescence was 0.91 ± 0.07 for the
negative control vs 7.03 ± 4.69 for the positive control
(mean ± standard deviation, n = 59). Patient bone marrow
samples were considered positive for P-gp function when the
ratio of rhodamine-123 fluorescence was above 1.05, which
was significantly greater than the negative control (P ⬍ 0.05,
two-sided t-test). For P-gp expression, the mean MRK16/IgG2a
ratios were 1.32 ± 0.29 for the negative control vs
30.23 ± 5.01 for the positive control (mean ± standard deviation, n = 59). Patient samples were considered positive for Pgp expression, if the ratio of P-gp fluorescence was above 1.65
(P ⬍ 0.05, two-sided t-test).
Results
Twenty-three patients were enrolled in the study. The majority
of patients (65%) were male and 70% were ⬍50 years of age
(mean age, 41.6 years; range, 18–69 years). Eight patients had
primary refractory disease, 14 patients had relapsed within 6
to 9 months of achieving CR, and one patient had relapsed
11 months after CR. Among the 15 relapsed patients, 13 were
in first relapse and two were in second relapse. Six patients
had AML secondary to myelodysplastic syndrome. Summary
PSC 833 in poor-prognosis AML
G Visani et al
statistics by cohort are presented in Table 1. The cohorts were
comparable with respect to baseline demographic and
clinical characteristics.
Overall, 20 patients went off study before consolidation: 17
after the first induction cycle and three after the second induction cycle. Eleven of 23 (48%) patients discontinued due to
treatment failure (excluding death). Three patients discontinued due to adverse events (one patient in cohort 2 due to
grade 4 hyperbilirubinemia, and two patients in cohort 3 due
to persistent aplasia and abnormal liver function). One patient
in each cohort died during the study as a result of cardiorespiratory arrest (cohort 1), gastrointestinal hemorrhage (cohort 2),
and pneumonia (cohort 3). Three patients withdrew their consent to further treatment; one was in CR after two induction
cycles and did not receive a consolidation cycle; the second
one discontinued the study treatment in order to receive a
bone marrow transplant, and was reported later on to be in
CR; the last one discontinued after the second induction cycle
as a protocol violation, the reason stated by the investigator
being persistent leukopenia and thrombocytopenia.
Table 2
No. of patients with most frequent CTC grade 3 or 4 AEs
(⭓10% in total treatment group)
Cohort 1 Cohort 2 Cohort 3
n (%)
n (%)
n (%)
Patients studied:
Total No. of patients
studied
Total patients with grade
3 or 4 AE
10 (100) 6 (100)
767
Total
n (%)
7 (100) 23 (100)
7 (70)
6 (100)
7 (100) 20 (87)
3
3
1
3
1
2
1
5
5
1
2
2
3
3
1
4
1
2
2
2
2
Grade 3 or 4 adverse
events
Bilirubinemia/jaundice
Bilirubinemia
Jaundice
Fever
Vomiting
Granulocytopenia
Leukopenia
Mucositis (Nos)/Stomatitis
Mucositis (Nos)
Stomatitis
(30)
(30)
(10)
(30)
(10)
(20)
(10)
0
0
0
(83)
(83)
(17)
(33)
(33)
0
0
1 (17)
0
1 (17)
(43)
(43)
(14)
(57)
(14)
(29)
(29)
(29)
(29)
0
11
11
3
9
4
4
3
3
2
1
(48)
(48)
(13)
(39)
(17)
(17)
(13)
(13)
(9)
(4)
Adverse events
Dose-limiting toxicities were grade 4 oral mucositis (one
patient in cohort 2) and grade 4 hyperbilirubinemia with grade
3 raised transaminases (one patient in cohort 3). The incidence of hematologic toxicity did not differ from that expected
in this patient population receiving the full-dose MEC regimen
without PSC 833, and none was dose limiting. Fever, infection, bilirubinemia/jaundice, mucositis/stomatitis, rash,
diarrhea, and nausea were the most frequently observed nonhematologic toxicities in the three cohorts (Table 2).
Bilirubinemia/jaundice was a frequently reported adverse
event, occurring in a total of 13 (57%) patients. Eleven (48%)
patients experienced grade 3 (ie, 3× IULN) or 4 hyperbilirubinemia (ie, ⬎10× ULN), and based on the laboratory data, at
least one grade 3 or 4 bilirubin value was recorded for 16
(70%) patients and at least one grade 4 value was recorded
for 11 (48%) patients. Five (22%) patients had clinically significant grade 4 hyperbilirubinemia; in one patient, this
resulted from a massive gastrointestinal hemorrhage, which
was an aplasia-related event, and from which the patient died
15 days after the start of treatment. The other four cases were
possibly related to treatment. In these patients, grade 4 hyperbilirubinemia started on days 2 to 9, reached a maximum
value of 4× to 21× the upper limit of normal on days 8 to 24,
and subsequently improved. Two of these patients experi-
enced prolonged (ie, ⬎16 days) grade 4 bilirubinemia, but this
resulted in serious adverse event reporting, DLT and discontinuation of only one patient in cohort 3 who also had raised
transaminases. Nevertheless, this patient achieved CR and was
one of the two surviving patients at the last follow-up visit at
18 months. In the other two patients, the prolonged hyperbilirubinemia did not impact their clinical course and was not
considered a DLT. The fourth patient in cohort 2 experienced
prolonged hyperbilirubinemia that did not remain consistently
at grade 4, but ultimately resulted in study discontinuation of
that patient; however, this was not classified as a DLT.
Mild to moderate cerebellar toxicity resulting in ataxia or
paresthesia was reported in six (26%) and five (22%) patients,
respectively; no patient experienced grade 3 or 4 cerebellar
toxicity. Paresthesia led to interruption of the PSC 833 infusion
for 22 h in one patient, but otherwise neither ataxia nor paresthesia was severe enough to be dose limiting. A conservative evaluation of the patients with possible ataxia used the
preferred adverse event terms of dizziness, cerebellar syndrome, and gait abnormal, and these were included in the
ataxia group.
Response
Table 1
Baseline demographic characteristics by cohort
Patients, n (%)
Age (years)
Mean
Sex, n (%)
Male
Female
Prior disease
status, n (%)
Refractory
First relapse
Second
relapse
Cohort 1
Cohort 2
Cohort 3
Total
10 (100)
6 (100)
7 (100)
23 (100)
42.5
49.3
33.6
41.6
7 (70)
3 (30)
3 (50)
3 (50)
5 (71)
2 (29)
15 (65)
8 (35)
4 (40)
4 (40)
2 (20)
2 (33)
4 (33)
0
2 (29)
5 (71)
0
8 (35)
13 (56)
2 (9)
Overall, six (26%) patients achieved CR, including the one
patient who withdrew after only one induction cycle for a
bone marrow transplant (Table 3). In addition, one patient
achieved partial remission. Among 14 patients who failed
chemotherapy, 10 patients had absolute or relative drug resistance, three patients had marrow regeneration failure, and one
patient died with indeterminate response to therapy. Two
additional patients died on study and their response to therapy
was not evaluable. Three patients, all in cohort 1, achieved
CR after the first cycle and received a subsequent consolidation cycle. One patient in cohort two was in CR after two
induction cycles and did not receive a consolidation cycle.
Two additional patients, one each in cohorts 2 and 3, achieved CR after the first induction cycle and refused further
treatment. The median overall survival was 4 months. The 1Leukemia
PSC 833 in poor-prognosis AML
G Visani et al
768
Table 3
Treatment outcome
Patients, n (%)
Cohort 1 Cohort 2 Cohort 3
No. of patients
Complete remission
Partial remission
Failure to respond
Drug resistance
Regeneration failure
Indeterminate (death)
Not evaluable (death)
10 (100) 6 (100)
3 (30)
2 (33)
0
1 (17)
6 (60)
3 (50)
6 (60)
2 (33)
0
0
0
1 (17)
1 (10)
0
Total
7 (100) 23 (100)
1 (14)
6 (26)
0
1 (4)
5 (71)
14 (61)
2 (28)
10 (44)
3 (43)
3 (13)
0
1 (4)
1 (14)
3 (13)
year event-free and overall survival rates were 17% and
26%, respectively.
P-gp expression and function
Sixteen (70%) patients were assessed for P-gp expression, and
12 (52%) patients were assessed for P-gp function at baseline;
seven patients were not evaluable for either (Table 4). Overall,
13 of 16 assessable patients tested positive for P-gp expression
and/or function, and four patients tested positive for both
expression and function. Five of 13 (38%) patients who tested
positive for P-gp expression and/or function achieved CR.
Three patients were negative for both P-gp expression and
function, but none of these patients responded to treatment.
One
patient
who
was
unevaluable
for
P-gp
expression/function achieved CR.
Figure 1
Mean (± standard deviation) whole blood concentrations
of PSC 833. Number of patients is indicated at each data point.
Table 5
1 only)
Selected pharmacokinetic parameters of etoposide (cycle
Cmax(mg/l) t1/2(h)
Mean (n = 13)
Standard
deviation
Median
Minimum
Maximum
AUC␶ Vz (l/m2)
(h·mg/l)
CL
(l/h/m2)
6.69
2.10
8.20
2.00
52.92
14.43
6.93
1.39
0.629
0.278
6.73
2.97
10.89
8.63
4.53
11.6
54.1
20.1
80.6
6.83
4.71
9.78
0.555
0.372
1.496
Cmax, time to maximal concentration.
Pharmacokinetics
Blood concentrations of PSC 833 were measured daily in 21
patients. After the loading dose, levels ranged from 1400 to
8900 ng/ml. Serum levels of PSC 833 were well above
1000 ng/ml in all patients, a concentration shown to reverse
MDR in resistant cell lines in vitro.36 Overall mean values up
to the last day of PSC 833 dosing in all cohorts are shown
in Figure 1.
The terminal elimination phase of etoposide was defined.
The decrease over time in the concentration of etoposide followed a monoexponential decay with a mean CL of
0.63 l/h/m2. This is about half the value reported in the literature; etoposide CL values of approximately 1.2 l/h/m2
(20 ml/min/m2) have been reported.52 This is consistent with
Table 4
P-gp
expression
P-gp
function
Positive
Positive
Negative
NA
Negative
NA
NA, not available.
Leukemia
Pharmacokinetic/Pharmacodynamic relationship
Figure 2 shows the AUC0-tz for mitoxantrone and AUC0-⬁
values for etoposide for patients who showed CR or partial
response and for nonresponders. No relationship between the
P-gp expression and response to treatment
No. of patients, all/complete responses
Cohort 1 Cohort 2 Cohort 3
Positive
Negative
Positive
Positive
Negative
NA
the observation that concurrent administration of PSC 833,
even at low doses, has a profound effect on etoposide CL.53
Descriptive statistics of selected PK parameters for etoposide
are given in Table 5. The PK of mitoxantrone was highly variable between patients. Only two patients had PK sampling
for mitoxantrone and etoposide in both the induction and the
consolidation cycles. Thus, a within-study comparison of the
PK parameters of mitoxantrone and etoposide with and without concurrent PSC 833 was not possible.
2/1
1/0
3/1
1/1
2/0
1/0
1/0
0
0/0
2/2
0/0
3/0
1/0
0
1/0
1/0
1/0
3/1
Total
4/1
1/0
4/1
4/3
3/0
7/1
Figure 2
Area under the curve (AUC) values for mitoxantrone and
etoposide vs responses. PR, partial response; NR, no response.
PSC 833 in poor-prognosis AML
G Visani et al
AUC of these two agents and response to therapy was
apparent.
Discussion
Reversal of MDR is clearly an important goal in patients with
relapsed and refractory AML. The clinical challenge when
using MDR modulators such as PSC 833 is the PK interactions
between PSC 833 and chemotherapy agents, such as etoposide, that are substrates for P-gp. The results of this and the
previously reported ECOG trial have established a safe and
well-tolerated modified MEC regimen that has activity in this
group of poor-prognosis patients.
In particular, regarding poor-risk AML patients, Estey et al54
have recently proposed to place these patients in four categories that correlated their responses to conventional treatment
with presenting clinical features. These patients were categorized as being in one of four prognostic risk groups, based on
their treatment history. Group 1 patients had expected CR
rates of approximately 70% (patients with a first CR lasting
⬎2 years being treated with conventional therapy); group 2
patients had expected CR rates of approximately 40%
(patients with a first CR duration of 1 to 2 years being treated
with conventional treatment); group 3 patients had expected
CR rates of approximately 10 to 20% (patients with a first CR
lasting ⬍1 year, or with no initial CR, who were receiving
their initial salvage attempt with conventional treatment); and
group 4 patients had expected CR rates of ⬍1% (patients with
an initial CR ⬍1 year, or with no initial CR, who were receiving a second or subsequent salvage regimen, having not
responded to a first salvage attempt with conventional drugs).
The patient population studied here contains only poor-prognosis AML patients, and is virtually categorized as being in
the very poor prognostic risk groups 3 and 4 (Table 1). Of the
23 patients enrolled in the current study, 21 (91%) would fall
into group 3 and two (9%) would fall into group 4. Therefore,
despite these poor-risk features, the observed CR rates (22%)
were higher than expected for this patient population, as were
the CR rates reported from other studies investigating the use
of PSC 833 to modulate MDR in poor-prognosis relapsed or
refractory AML patients.30–36
The observed CR rates achieved with this regimen are
encouraging and provide a rationale for further investigation
of this regimen in relapsed or refractory AML patients. Previously, Advani et al30 reported a 32% CR rate in 37 evaluable, poor-risk (groups 3 and 4), relapsed/refractory AML
patients treated with a 5-day MEC plus PSC 833 regimen on
the ECOG protocol. Among this cohort were 27 patients with
de novo AML and 10 patients with secondary AML. The 22%
CR rate reported here compares favorably with the ECOG
experience and with reports from studies investigating intermediate- and high-dose cytarabine-containing regimens.55
Taken together, these studies show the antileukemic effectiveness of the PSC-MEC regimen suggesting its promising activity
in relapsed and refractory AML patients who have a low probability of response and long-term disease-free survival.
The final doses of mitoxantrone and etoposide determined
in this trial were consistent with the final doses established in
a similar phase I/II ECOG study in poor-risk AML patients, in
whom a 5-day MEC plus PSC 833 regimen was investigated.30
Compared with the 6-day regimen tested here, the 5-day regimen investigated in the ECOG study used a slightly lower dose
of mitoxantrone (4.0 mg/m2 vs 4.5 mg/m2), which may have
compensated for the higher etoposide dose (40 mg/m2 vs
30 mg/m2). The PK analysis of the ECOG study indicated that
in the presence of PSC 833 there was a 57% decrease in the
CL of etoposide, and the mean t1/2b of mitoxantrone was
increased 1.8-fold compared with historical controls. In the
present study, the mean etoposide CL value was 0.63 l/h/m2,
which represents a 50% decrease in the expected etoposide
CL of approximately 1.2 l/h/m2 reported in the literature in
the absence of PSC 833.56–57 The high degree of concordance
between published studies indicates that the PK interaction
between PSC 833 and etoposide is highly predictable, and
that concurrent PSC 833, even at low doses, has a profound
effect on etoposide CL.32–35,37,39 With regard to the PK analysis
of mitoxantrone, the sampling schedule during the first 2 h
was not dense enough to determine the first disposition phases
of mitoxantrone, but the observed t1/2b fell well within the
range reported in the literature.58 Therefore, based on cumulative clinical experience with PSC 833, it is now possible to
institute appropriate dose reductions in the scheduled doses
of etoposide and mitoxantrone. These findings, plus the tolerability of the drug, indicated effective dosing of PSC with
this regimen.
Administration of PSC 833 by CIV was well tolerated in this
study and achieved target blood levels capable of modulating
P-gp in vitro. Approximately 25% of patients reported mild to
moderate ataxia or paresthesia, but no patients experienced
grade 3 or higher ataxia. The primary DLTs observed in this
study were nonhematologic (mucositis and hyperbilirubinemia). Clinically significant grade 4 hyperbilirubinemia,
possibly related to treatment, was observed in four patients
but was considered a DLT in only one patient. In two of these
patients hyperbilirubinemia was reversible, was not
accompanied by elevated liver enzymes, and had no major
impact on the patients’ clinical course; therefore, this toxicity
was considered acceptable in the context of the regimen and
patient population. The cause of hyperbilirubinemia is likely
to be multifactorial and to include the effects of hemorrhages,
other coexistent medical conditions, and competition
between PSC 833, concomitant chemotherapy agents, and
bilirubin for the cytochrome P-450 3A metabolic pathways in
the liver.
Although the predictive value of P-gp expression and
inhibitable P-gp-mediated rhodamine-123 efflux as an independent marker of treatment failure has not been clearly
established, studies to date suggest that P-gp expression is an
important determinant of therapeutic outcome in patients with
relapsed or refractory AML, and that reversing MDR due to Pgp expression may benefit patients by improving therapeutic
response to established cytotoxic regimens. Despite a number
of agents inhibiting the function of P-gp blocking efflux of
drugs from the intracellular compartment59–61 (ie verapamil,
cyclosporine and quinine, that are effective in vitro), their
clinical use is limited by side-effects that contribute to the
relatively poor clinical outcome of these patients. In addition,
recent randomized studies62,63 using quinine as an MDR
modulator plus intensive chemotherapy for AML post MDS
and high-risk MDS patients showed that, instead of increasing
CR rate and disease-free survival in patients considered to be
P-gp positive, quinine had no effect on response rate and survival of those who were considered P-gp negative.
Bearing this in mind, two points have to be underlined: (1)
the ability that MEC regimen plus PSC 833 has to produce CR
in patients with an MDR phenotype (five of 13 (38%) P-gppositive patients achieved CR); (2) PSC-833 is relatively free
of side-effects at doses that are adequate to block P-gp
function in vitro and to reverse the MDR phenotype.
769
Leukemia
PSC 833 in poor-prognosis AML
G Visani et al
770
Nevertheless, clinical randomized studies are necessary to
clarify the impact of PSC on therapy of poor-risk AML patients.
In conclusion, we have demonstrated that with appropriate
dose modifications based on the predictable PK interactions
between PSC 833 and chemotherapy agents, PSC 833 can be
safely combined with a modified MEC regimen in patients
with relapsed or refractory AML. Moreover, serum levels of
PSC 833 capable of reversing MDR were achieved and
resulted in a substantial rate of CR in a patient population
with a low probability of CR, including P-gp-positive patients.
These encouraging results warrant further investigation of
this regimen.
Acknowledgements
This study was supported in part by MURST (40%) and
FONDI (60%).
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