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Jahnke, Anika (2008): Intratumoraler Transfer der felinen Zytokin-Gene IL-2, IFN-gamma und GM-CSF unter Verwendung der Magnetofektion als neoadjuvante Behandlung des Fibrosarkoms der Katze: Eine klinische Phase-I-Studie. Dissertation, LMU München: Tierärztliche Fakultät



The prognosis for cats with fibrosarcoma is still poor as the treatment options existing to date do not lead to satisfying results. After sole surgical removal of the tumor, up to 70 % of the cats develop local recurrences. Even with adjuvant radiation and/or chemotherapy, the recurrence rate can just be reduced to at most 40 %. In the present work an alternative treatment method in terms of neoadjuvant immunostimulatory gene therapy should be established. Via plasmids, three feline cytokine genes were transferred into the tumor. The plasmids coded for feIL-2, feIFN-γ and feGM-CSF. Using magnetofection, gene transfer should be optimized. The aim of this clinical dose escalation study was to define a well tolerated dose, which can be tested for its efficacy in a subsequent phase-II trial. Therefore the cats were examined at defined time points for treatment-related toxicity up to 180 days after surgery. Two more check-ups on day 270 and 360 after surgery were performed to elongate the observation period for local recurrences. Prerequisite for a cat’s admission to the study was the localization of the fibrosarcoma (primary tumor or recurrence) on the trunk. The tumor had to be excised in one setting without limb amputation. Affected cats were neither allowed to be pretreated with chemo-, radiation- or gene therapy nor with corticosteroids within the past six weeks. Further exclusion criteria were hints for metastases or other severe illnesses which reduce life expectancy to less than one year. Due to the potential teratogenic effect of the expressed cytokines, pregnancy had to be ruled out. Only cats with histopathologically confirmed fibrosarcoma continued the study after surgery. As this was a scientific study with a drug not registered yet, written informed consent from the owners was a prerequisite for the participation of each cat. Four treatment groups with defined dose escalation were prospectively fixed. The dose of the feline cytokines was 15, 50, 150 and 450 µg per plasmid in group I, II, III and IV. The initial dose (3 x 15 µg) was oriented to the total dose for small oral melanomas in dogs (400 µg) established by DOW et al. and is 1/10 of it. Plasmids as non-viral vectors were chosen for several reasons. Their handling is not liable to such strict regulations as the potentially more dangerous viral vectors. Their production is simple and affordable. They induce fewer side effects than viral vectors. Therefore plasmids are more suitable for application in veterinary clinical practice. Equal amounts of the plasmids were brought into 0.9 % saline. The positively charged magnetic nanoparticles were brought into solution with aqua for injections and were mixed with the plasmid formulation in a 1:1 ratio. This formulation had a total volume of 500 µl and was injected twice intratumorally in weekly intervals. Transfection was enhanced and targeted to the tumor area by the application of a neodymium-iron-boron magnet for the duration of 60 minutes. One week after the second application, wide en-bloc resection of the tumor was performed. Four cats were assigned to each treatment group. As questionable toxicity occured in group IV, four more cats were added to this group. A control group also consisting of four cats received surgery without neoadjuvant therapy. For ethical reasons, the application of empty plasmids was avoided so that in this group surgery could be performed without delay. Medical care of all the cats was carried out by the same team of internists, anesthetists and surgeons. Clinical and laboratory parameters were evaluated according to the VCOG-CTCAE system. All adverse events were registered, classified with severity grades and correlated to treatment. Plasma samples of all cats up to 14 days after surgery were examined for the existence of feGM-CSF and feIFN-γ with commercially available ELISA kits. Statistical analyses were performed comparing the treatment groups themselves as well as treatment groups and the control group regarding body weight, white blood cells and differential blood counts. Only one cat out of group IV showed adverse events during the neoadjuvant treatment period, which were classified as grade 3 and which were probably correlated to treatment (correlation grade 4). For this reason four more cats were treated with the highest dose. None of these cats showed side effects that could be correlate to treatment. The occurrence of early recurrences in four cats of group IV was outstanding, but of course, the expressiveness of this statement is low regarding the small group sizes. However it is known that biological drugs, especially IL-2, often do not have a linear dose-response profile. Therefore the optimal effective dose lies within a strictly defined area and is probably lower than the maximal tolerated dose. The highest applied dose which is 450 µg per plasmid was defined as a well tolerated dose. It can be safely tested for its efficacy in a subsequent phase-II trial. Because of the reflections mentioned above it would undoubtedly be convenient to test the third dose (150 µg per plasmid) in parallel for its effectiveness.