TDK conference 2019

One of the most common neoplasms seen in dogs is lymphoma. Lymphomas are malignant tumours which affect lymphatic cells. Without treatment, most of the dogs diagnosed with lymphoma will die within 4 to 6 weeks but about 50% of the dogs live one more year and 10% survive two years with intensive chemotherapy. After starting the therapy the remission rate is 90% but later the drugs become ineffective because the tumour cells develop resistance against more than one drug and multidrug resistance (MDR) appears. In my in vitro study the central question was how we could prevent these consequences.

One of the main contributors to the mechanisms responsible for MDR is the overexpression of a cell transporter, MDR1 (P-glycoprotein). The function of this pump is measurable by the “calcein-assay” using flow cytometry which helps us to figure out the status of the resistance. The number determined by this method is the multidrug resistance activity factor (MAF) of the tumour. The previously calculated MAF cut-off value for canine lymphoma was 0.2, so every tumour which has higher activity (MAF> 0.2) is considered to be resistant. According to my hypothesis some non-steroidal anti-inflammatory drugs (NSAIDs) can delay the resistance of the tumour.

In this study CLBL-1 (Canine large B-lymphoma) cells were used for our in vitro experiment which had been isolated from a dog with stage IV lymphoma and 5 different treatment groups were compared. One group was treated with doxorubicin (DOX) only in monotherapy which is one of the most commonly used chemotherapeutic drugs and the other 4 groups were treated with a combination of DOX and one of the NSAIDs (meloxicam, celecoxib, firocoxib, mavacoxib). Every group was treated 9 different times and the MAF value was measured with calcein-assay after every third treatment.

Our results proved that DOX monotherapy group showed resistant status after the sixth treatment on the 69th day (MAF: 0.35). Meloxicam-DOX combination group had the similar outcome in the same time (MAF: 0.25). In case of the DOX combination with firocoxib (MAF: 0.22) and mavacoxib (MAF: 0.38) the MAF value reached the 0.2 cut-off value already on the 33th days (after the third treatment). In case of combination of DOX with celecoxib the lymphoma cells preserved the sensitive status during the whole experiment and on the 107th day, and the MAF was only 0.12.

My goal is to prove by an in vivo study that using celecoxib with current chemotherapy protocols for lymphoma can lengthen the survival time of the patients by decreasing tumoral MDR.