Book of abstract 2008

IL-12 gene therapy of murine sarcoma tumors and metastases combined
with radiotherapy
Gregor Tevž1, Darja Pavlin2, Urška Kamenšek1, Simona Kranjc1, Suzana Mesojednik1,
Maja Čemažar1, Gregor Serša1
1Institute of Oncology Ljubljana, Dept. for Experimental Oncology, Zaloška cesta 2, SI-1000, Ljubljana,
Slovenia; 2University of Ljubljana, Veterinary Faculty, Gerbičeva 60, SI-1115 Ljubljana, Slovenia
Interleukin-12 (IL-12) has immunomodulatory effects on tumors. Unfortunately it’s
associated with toxicity when delivered systemically as a recombinant protein. An
alternative to recombinant protein therapy is delivery of IL-12 by gene therapy. Especially
attractive is IL-12 electrotransfer to skeletal muscle which results in prolonged expression
and secretion and therefore systemic distribution of therapeutic protein. Gene therapy
can be additionally improved when combined with radiation, as IL-12 may have a
radiosensitizing effect.
The aim of our study was to evaluate the antitumor efficacy of intramuscular IL-12
electrotransfer alone or combined with radiation on subcutaneous tumors and induced
lung metastases of two murine sarcomas, LPB and SA-1.
Lung metastases and subcutaneous tumors were induced by intravenous and subcutaneous
injection of tumor cells, respectively. IL-12 electrotransfer was performed by intramuscular
injection of 20 μg of plasmid DNA encoding IL-12 followed by local application of 1
high voltage (600 V/cm, 100 μs, 1Hz) and 4 low voltage (80 V/cm, 100 ms, 1Hz)
square-wave electric pulses. Mice bearing subcutaneous tumors were treated with IL-12
electrotransfer 3-times every second day, starting 24h before tumor irradiation (10 Gy).
Treatment effectiveness was evaluated by tumor growth delay assay. Mice with induced
lung metastases were treated 4-times every second day, starting 1 day before injection of
tumor cells. Eight (SA-1 tumor) or 16 (LPB tumor) days after induction of metastases,
mice were euthanized, their lungs were excised, fixed and colonies counted. In addition,
total IL-12 in serum from the treated mice was determined by ELISA at different times
post-treatment. The growth of subcutaneous tumors treated by IL-12 electrotransfer alone
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was delayed for ~24 days in SA-1 and ~11 days in LPB tumors. Furthermore, 30% of SA-1
tumors responded by complete tumor eradication, which lasted for at least 100 days. In
LPB tumors the complete response was observed in 13%. The number of lung metastases
was significantly reduced after IL-12 electrotransfer; for ~90 % in SA-1 and ~85 % in
LPB tumors. The serum IL-12 levels increased for ~30-times after IL-12 electrotransfer
and peaked on 7 day post-treatment. When IL-12 electrotransfer was combined with
irradiation, 45% of SA-1 tumors responded with complete eradication. Combined therapy
of LPB tumors resulted in 100% of complete responses. Thus, gene therapy with IL-12
showed radiosensitizing effect in both tumors. This study demonstrates that systemic
delivery of IL-12 by intramuscular electrotransfer has a pronounced antitumor effect
on solid subcutaneous tumors as well as on lung metastases of murine sarcomas. Results
of combined therapy indicated on synergistic action of therapies in both LPB and SA-1
tumors.
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