Discussion
PS of RMS is rare in children and still represents an oncological and
therapeutic challenge . Due to recent promising clinical reports HIPEC
(in combination with CRS) has been established as a novel treatment
option for PS of RMS . Besides significant improvement of the technical
performance of HIPEC in children there is still no consistent treatment
plan regarding the best choice of chemotherapy and concentration,
optimal drug combination and treatment duration. Additionally, it
remains unclear whether CRS or HIPEC are the main factors for treatment
success. Here, we established a feasible and reproducible murine model
for the evaluation of HIPEC in pediatric RMS for the first time. At this
juncture there is no animal model available allowing repeatable
experimental studies of HIPEC within the context of disseminated
intraperitoneal pediatric RMS.
We were able to demonstrate a constant and reliable intraperitoneal
tumor growth of human alveolar RMS (cell line RH-30) in NOD/LtSz-scid
IL2Rγnullmice. This model resembles pediatric RMS in terms of organ
invasion and intraperitoneal tumor spread very well. To evaluate the
tumor dissemination, we adapted the peritoneal carcinomatosis index
(PCI) modelled on Jacquet and Sugarbaker et al. for this animal
model. Furthermore, we developed a feasible and easy way for the
application of liquid hyperthermic intraperitoneal chemotherapy in mice
. MRI scans confirmed the tumor growth and showed the performance of
HIPEC in vivo for the first time. Besides our animal model there
are only few recent comparable HIPEC mouse models but using non
pediatric tumor entities like adult ovarian cancer or performing HIPEC
as pressurized aerosol . Especially pressurized intraperitoneal
chemotherapy (PIPAC) has not been applied in children.
Using TUNEL-assay method we demonstrate different penetration depth (30
- 40 µm) of the HIPEC treatment depending on cisplatin and/or
hyperthermia. Early concentration- or temperature-dependent anti-tumor
effects of cisplatin-based HIPEC on the tumors could be revealed
immediately after treatment. The observed penetration depth of
cisplatin-based HIPEC is considerably more superficial as those
published by Goodman et al . . However, cisplatin has a favorable
area under the curve ratio (maximal the chemotherapeutic dose, minimal
systemic toxicity) for the intraperitoneal application but there is no
clear statement regarding the penetration depth of cisplatin-based HIPEC
for pediatric RMS till now . In the past, cisplatin was used as single
therapeutic agent in different concentrations for HIPEC in children
suffering from intraperitoneal RMS . Whereas the synergy between heat
and drug cytotoxicity could be confirmed, the optimal concentration of
cisplatin for HIPEC remains unclear . Until now cisplatin concentrations
for HIPEC derive from those for intravenous chemotherapy (15-30 mg/m²)
knowing that higher cisplatin dosage with respectively higher
effectiveness and tolerable toxicity are feasible . As final experiment
ending immediately after HIPEC it was not possible to capture late
anti-tumor effects after intraperitoneal chemotherapy lavage knowing
that cellular signal cascades and apoptosis pathway need more time .
Several limitations should be pointed out in this study. Due to ethics
committee approval CRS before HIPEC was not performed. Focusing the
feasibility of a HIPEC animal model for pediatric RMS, we did not do any
cytoreductive surgery before HIPEC compared to existing clinical
studies. The recommendation of administration of HIPEC after CRS is
generally based on clinical studies for adults whereas it remains
unclear if either CRS or HIPEC or the combination of both determines the
therapeutic success in children . Nevertheless, the observed
intraperitoneal tumor growth in our animal model was a disseminated
miliary tumor spread (maximal 3 to 4 cm in diameter) compared to an
incomplete tumor resection in children. In combination with HIPEC
residual tumor of 2,5 cm can be tolerated with the same outcome due to
local tumor control through tumor penetration of HIPEC . All the few
existing data regarding CRS and HIPEC in children were lifted from
restricted clinical case reports . Ethical considerations constrain the
systematic in vivo study of HIPEC in children regarding optimal
drug concentration and combination. With the establishment of an
appropriate animal model this limitation can now be overcome. Our model
allows valid additional insights on the possible efficiency of HIPEC in
pediatric RMS to improve existing treatment strategy and manage the
therapeutic challenge.
In summary, we were able to establish the first animal model for
evaluation of HIPEC in pediatric rhabdomyosarcoma in mice. Using
TUNEL-method early cisplatin- and hyperthermia-dependent apoptotic
effects at the tumor surface (penetration depth 30 – 40 µm) can be
detected. Additionally, statistically significant reduction of early
tumor proliferation depends on cisplatin or hyperthermia. This model
allows valid additional insights on the possible efficiency of HIPEC in
RMS so further studies using other drug combination, concentration and
cytoreduction will follow.