BACKGROUND
- - Glioblastoma (GBM) is the most common and aggressive primary brain tumour in
adults.
The standard first-line treatment for these tumours features maximized surgery
followed by radiation with concomitant and adjuvant temozolomide. The overall survival (OS)
and progression-free survival (PFS) observed in the clinic with this paradigm are only 14.6
and 6, 9 months respectively. One of the challenges in the treatment of this neoplasm stems
from the severe tumour heterogeneity which translates into unpredictable treatment response.
As a result, newly diagnosed tumours inevitably relapse after the standard first-line
treatment, which is called the Stupp protocol which combines radiation therapy and oral
temozolomide. When recurrence occurs, if the patient's functional status is adequate, this
will mandate other therapeutic strategies. Interestingly, results obtained in most studies in
this setting have been so marginal that there is literally no recognized optimal second and
third line of treatment. Admittedly, the access to active therapies is greatly limited by the
presence of the blood-brain barrier (BBB), which severely reduces the chemotherapy entry to
the CNS.
When one realizes the extensiveness of the vascular network supplying the brain, it appears
obvious that a global delivery strategy via this vascular network as a delivery corridor is
credible and legitimate. The importance of this vascular system has already been detailed by
Bradbury; the author claims that the entire network covers an area of 12 m2/g of cerebral
parenchyma. To understand the extensiveness of the cerebral vascularization in a more prosaic
way, let us just consider that the brain receives about 20% of the total systemic circulation
although it weighs less than 3% of the total body weight.
The access to a patient's cerebral vascular network is technically easy and actually
repeatedly performed in the clinic on a regular basis. Via a simple puncture to access the
femoral artery, a catheter can be introduced and navigated intraarterially to reach one of
the four major cerebral arteries. Once in the target vessel, a therapeutic agent can be
administered via the catheter, that is later withdrawn at the conclusion of the procedure.
The CIAC allows the construct of a regional chemotherapeutic distribution paradigm within the
area irrigated by the targeted vessel.
An increase in the local plasma peak concentration of the drug yields a significantly
improved AUC (concentration of drug according to the time) through the first pass effect.
This consequently translates in an increased local exposure of the target tissue to the
therapeutic agent. Interestingly, as our lab as shown, it is also accompanied by a decreased
systemic drug distribution, hence reducing systemic toxicity and potential side effects.
Consequently, the therapeutic concentration at the targeted tumour cells is increased by a
3.5 to 5-fold factor. This procedure is performed in the angiographic suite under local
anesthesia and typically lasts around 45 minutes.
The IA procedure is a very safe procedure. Indeed, this procedure has been used at our
institution for over 15 years using various chemotherapeutic agents and thus have precise
statistics on the risks and complications. Indeed, 722 different patients have been treated
adding up to 3600 procedures and have compiled the following events. During the MRI that
followed the IA infusion, 66 complications were identified (1.84%), 27 of which were
associated to symptoms (0.75%). During the infusion, 39 episodes of seizures occurred
(1.08%), all of which were successfully controlled with anti-seizure medication. Moreover, a
significant reduction in white, red or platelet blood cell count occurred in 52 patients
during the treatment phase (7.2%). This study will investigate the efficacy of using combined
chemotherapeutic agents described above. Our team currently uses intraarterial (IA) infusion
to alleviate the effects of the BBB. This delivery strategy was shown to be well tolerated,
triggered very few discomforts and side effects, and significantly improved survival. So much
so, that it is nowadays considered a standard of care for relapsing tumours in our
institution.
Like cisplatin, carboplatin is a molecule made of a platinum atom surrounded in a plane by
two ammonia groups and two other ligands in the cis position. Unlike the chloride atoms found
in cisplatin, the ligands in carboplatin are esther functional groups that form a ring
structure. As such, carboplatin is more stable, causes less vomiting and is less neurotoxic,
less ototoxic and less nephrotoxic. Carboplatin's exact mechanism of action remains unclear.
However, it is well known that carboplatin is activated inside the cell into reactive
platinum species. These reactive complexes react with DNA bases to create inter- and
intrastrand crosslinks which prevent cell division by hindering DNA synthesis.
At our institution, carboplatin is the primary chemotherapeutic agent for IA infusions and
yields positive tumour responses in 70% of patients for a median PFS of 5 months. Although
interesting, there is obviously room for improvement in the care of these patients. Hence the
current proposal.
For patients in which carboplatin fails, other chemotherapeutics are chosen arbitrarily from
a list of agents available for IA infusion. As such, our team has successfully treated
relapsing GBM patients with IA delivery of methotrexate, melphalan, etoposide phosphate or
Caelyx (liposomal doxorubicin). At the heart of the present study, carboplatin, which will be
combined with either one of two agents found to be ideally suited in this setting: Caelyx
(liposomal doxorubicin) or etoposide phosphate.
Doxorubicin is an anthracycline, an antineoplastic antibiotic developed from Streptomyces
peucetius subsp. Cassius. It is a very potent antitumour agent and is considered one of the
most active antineoplastic drugs developed to date. Its effect is produced via different
mechanisms: DNA binding and cross-linking, interference with DNA strand separation,
inhibition of RNA polymerase, inhibition of topoisomerase II, formation of free radicals and
membrane peroxidation have all been suggested.
In vitro studies in malignant glial cell lines have demonstrated that doxorubicin induces a
halt in cell growth within 24 hours, and results in apoptosis within 48 hours. It has been
identified as one of the most potent chemotherapeutic drugs against malignant glioma cell
lines in vitro. However, in vivo, the use of doxorubicin is limited by its inability to cross
the BBB.
Doxorubicin is rapidly distributed in the body tissues, and binds to plasma protein and cell
membranes. The clinical application of this agent is unfortunately limited by its
dose-related side effects such as cardiotoxicity and myleotoxicity.
Caelyx is a chlorhydrate of doxorubicin encapsulated within a pegylated liposome. The
liposomal formulation of doxorubicin (Caelyx) exhibits an altered pharmacokinetic profile
favouring the use of this drug formulation in brain tumour treatment. It has a longer
terminal half-life than free doxorubicin, and reaches greater concentration in the tumour.
Because of a decreased uptake by the reticuloendothelial system, the drug remains in
circulation much longer. This seems to be especially true in glioblastoma, where it tends to
accumulate in significant concentration due to the increase in neovascularisation. This has
been shown in experimental settings, as well as in the clinic. Interestingly, because of its
altered pharmacokinetic properties, it also presents a reduced toxicity profile. The
liposomal formulation of doxorubicin causes less myelosuppression, nausea, vomiting and
alopecia than standard doxorubicin. The cardiotoxicity is also reduced.
However, even with the greater accumulation of the drug in the tumour cells, its rate of BBB
penetration when administered via IV infusion remains a limiting factor. Indeed, it is too
low to yield a significant concentration accumulation within the tumour site to produce a
therapeutic benefit.
Etoposide phosphate (Etopophos; Bristol-Myers Squibb Company, Princeton, NJ) is a
water-soluble prodrug of etoposide that is rapidly and completely converted to the parent
compound after intravenous dosing. The pharmacokinetic profile of either etoposide or
etoposide phosphate is identical. Toxicity and clinical activity are also the same. Since
etoposide phosphate is water soluble, solutions of up to 20 mg/mL can be prepared. However,
in high doses, it can only be given as a 5-minute bolus, in small volumes and as a continuous
infusion. Furthermore, it is not formulated with polyethylene glycol, polysorbate 80 (Tween;
ICI Americas, Wilmington, DE), and ethanol, and does not cause acidosis when given at high
doses. The easier-to-use etoposide phosphate represents an improved formulation of etoposide.
Classically, etoposide must be diluted prior to use with sodium chloride (0.9% w/v) or
glucose (5% w/v) solutions to concentration of 0.2 mg/mL (i.e., 1 ml of concentrate in 100 ml
of vehicle) up to 0.4 mg/mL (i.e., 2 ml of concentrate in 100 ml of vehicle). Evidently, this
cannot be something considered in a setting of IA administration, as the volume administered
would be excessive. Hence, the use of etoposide phosphate, for which 100-fold increased
concentration can be prepared in a volume accessible for an IA administration: 200 cc.
STUDY DESIGN
- - This clinical trial will be an open label randomized phase II study in which
intraarterial administration of carboplatin (400 mg/m2) combined with Caelyx (30 mg/m2) will
be compared with intraarterial administration of carboplatin (400 mg/m2) combined with
etoposide phosphate (400 mg/m2).
Patients that have failed the standard first line of
treatment (Stupp protocol) and that are diagnosed with recurrent GBM will be randomly
distributed to one of the two second-line treatment paradigms using the block randomization
method. Each recruited patient will undergo maximal resection before beginning treatments.
Treatment cycles will be administered on a monthly basis until a progression is identified on
the magnetic resonance imaging (MRI) scan or until a total of 12 cycles have been completed.
The cohort will count 120 patients that will be divided into two groups of 60 patients
receiving one of the two chemotherapeutic combinations. As to which of the two combinations
will be best remains to be determined. For that reason, data from our latest published
clinical trial and patients treated with intraarterial carboplatin at our institution will be
used as benchmarks for baseline comparisons (OS of 11 months and PFS of 5 months from study
entry).
AIM
- - By using carboplatin in combination with Caelyx or etoposide phosphate in the setting
of an IA infusion, our intention is to optimally deliver carboplatin-based chemotherapy
combinations to the brain beyond the BBB, and more specifically to the tumour cells.
HYPOTHESES
- - In patients treated with either combination, our prediction is that this will
lead to an improved tumour response and control rate, with minimal impact on the quality of
life.
Our preliminary clinical data seems to support this hypothesis.
