The mechanism of non-steroidal anti-inflammatory drugs’ (NSAIDs) action is based on the preferential or non-preferential inhibition of the activity of cyclooxygenase-2 (COX-2, the inducible form). This enzyme takes part in the pathway of arachidonic acid transformations which result in the formation of prostanoids. These compounds are involved in the inflammation process and contribute to the development of pain, swelling, or fever. By reducing COX-2 action with the use of NSAIDs, it is possible to reduce prostanoid synthesis, and thereby the activity, extent, and intensity of inflammatory processes. NSAIDs are commonly used in veterinary medicine not only because of their anti-inflammatory effect but also due to their analgaesic and antipyretic properties. However, their most interesting feature is their potential anticancer effect.
Osteosarcoma is a primary malignant bone tumour of mesenchymal origin with a very diverse histological structure. Osteosarcoma is diagnosed in approximately. 80%–85% of dogs with bone cancer, making it the most common lesion in this group of tumours. Seen in the context of all cancer types diagnosed in dogs, however, the frequency of osteosarcoma is considered moderate. Osteosarcoma usually occurs in adult individuals in the age range of 2–15 years. Large and giant breeds, such as the German Shepherd, St. Bernard, Irish Setter, Great Dane, Bernese Mountain Dog, Boxer, Golden Retriever, Rottweiler, and Doberman Pinscher (17, 21), are most predisposed to this disease. The area prone to develop this type of cancer in dogs are the long bones which are most exposed to overloads and related microtraumata, which explains their markedly more frequent occurrence in large and giant breeds (15). Osteosarcoma is less commonly encountered in flat bones (the maxilla, mandibula, skull, scapulae, ribs, and pelvis). This cancer belongs to the group of particularly aggressive proliferative lesions causing bone damage visible in radiographic images. It spreads quickly to the surrounding soft tissues and also often metastasises to nearby (regional) lymph nodes and lungs as well as other bones, the skin and the liver (8, 11, 19).
The treatment consists primarily in the amputation of the tumour-affected extremity and adjuvant chemotherapy. The most commonly used drugs include: platinum derivatives (cisplatin and carboplatin) and anthracycline antibiotics (doxorubicin). To alleviate pain symptoms associated with osteosarcoma, NSAIDs are used very often, while opioid receptor agonists are administered less frequently.
The objective of this experiment was to assess how NSAIDs from different groups varying in terms of their chemical structure affect cell viability in a specific cell line (D-17) of canine osteosarcoma, and whether they show any evidence of antitumour activity.
Etodolac, flunixin, and tolfenamic acid were dissolved in 70% ethyl alcohol (Stanlab, Poland). Carprofen and ketoprofen were dissolved in a 1:1 mixture of 70% ethyl alcohol and double distilled water.
Etodolac, flunixin, and tolfenamic acid were tested at concentrations of 0.05, 0.1, 0.5, 1, 5, 10, and 20 μg/ml, while carprofen and ketoprofen assay concentrations were the same and additionally 40μg/ml. The concentrations in which these compounds were tested were established based on those in the literature (20), the maximum concentrations they reach in canine serum, and the permissible maximum non-cytotoxic solvent concentration. As a positive control, non-treated cells were used, and as a negative control, cells were challenged with doxorubicin at a concentration of 0.5 μg/ml.
The cells treated with indicated concentrations of the tested drugs were incubated for 72 h, and then their viability was assessed with the MTT assay. Each well on the culture plate was supplied with 20 μl of MTT solution (Sigma-Aldrich, USA), and the cells were incubated for an additional 4 h. Then 80 μl of lysis buffer was added to the samples. After 24 h, the optical density of the samples was measured with an ELx800 plate reader (BioTek, USA). Four independent repetitions were performed for each of the test drugs, and their results are provided as the average. In addition to a viability assessment, an attempt was made to determine the EC50 (
Effect of etodolac, flunixin, and tolfenamic acid on the viability of D-17 canine osteosarcoma cell line
Effect of carprofen and ketoprofen on the cell viability of D-17 canine osteosarcoma cell line
Carprofen displayed concentration-dependent cytotoxicity within the tested concentration ranges (Fig. 2). The strongest cytotoxic effect of the test drug was observed in the samples treated with concentrations of 20 and 40 μg/ml, where the cell viability was 71.98 ± 1.16% and 21.56 ± 3.33%, respectively.
Ketoprofen showed no cytotoxic activity in any but the highest concentration tested, which was only used for experimental purposes, because it is not possible to achieve such a concentration in the patients’ serum (Fig. 2). The maximum obtainable concentration was approximately 2 μg/ml.
Statistical analysis showed significantly different values for the tested compounds compared to the positive and negative controls (P = 0.03 for each compound). From the graph of Fig. 2, we can see that carprofen possessed the strongest cytotoxic activity against canine osteosarcoma cells, however, due to the low number of repetitions made during this study, the statistical picture only demonstrates that it works more strongly than etodolac (P = 0.02).
EC50 values for the drugs tested
Drug | EC50 |
Etodolac | > 20 μg/mL |
Flunixin | > 20 μg/mL |
Tolfenamic acid | > 20 μg/mL |
Carprofen | 28.71 ± 2.31 μg/mL |
Ketoprofen | > 40 μg/mL |
The NSAIDs we used in the experiment are applied with lower or higher frequency in anti-inflammatory and analgesic therapies in dogs. The most widely used NSAID is carprofen, which turned out to have the strongest cytotoxic activity, as the analysis of results and their comparison with the results across the complement of drugs proved. It is interesting and promising that cytotoxic concentrations are easily achieved in the serum of patients through the administration of a standard anti-inflammatory and analgaesic dose,
It is worth highlighting that carprofen is generally very well tolerated by patients, which may be an additional argument in favour of using this drug in the treatment of osteosarcoma in dogs. However, to make an unequivocal statement that carprofen can be introduced for routine use in the treatment of this type of tumours a series of additional studies would be required. The results obtained in this experiment may be a starting point for further research. It should be emphasised that there is little information available in the literature on the effect of carprofen on animal cancer cells.
Tolfenamic acid showed cytotoxic activity at a concentration greater than its obtainable level in canine serum after the application of a standard dose. However, Wilson
The investigation showed that at obtainable concentrations in canine serum, flunixin does not produce a satisfactory cytotoxic effect. There are also no reports on studies conducted on animal cancer cell lines with this drug. The results we obtained are not promising and raise questions as to the desirability of further testing with flunixin and possibility of its use in the treatment of osteosarcoma in dogs. Testing higher concentrations of flunixin is pointless, because higher serum concentrations with potentially cytotoxic effects might cause an overdose. Unfortunately, there are no clinical studies showing the symptoms of flunixin overdose. The situation with ketoprofen is similar. The maximum obtainable concentration is approximately 2 μg/ml. It does not manifest any cytotoxic action, unlike carprofen which comes from the same chemical group. There are also few data on
In this study, no cytotoxic effect of etodolac on canine osteosarcoma cells from the D-17 line was recorded. Research literature contains several reports confirming its inhibitory action on cancer cells but it must be noted that these reports regard human and not animal cells. There is no information available on trials with animal cells. For human cell lines, satisfactory results were obtained in studies using prostate cancer or bladder cancer cells, among others (12, 18). Chen
In summary, the studies we completed are only preliminary and limited to the assessment of any potential cytotoxic action of the test drugs. Among all the NSAIDs used in the experiment, the most effective and promising are carprofen and tolfenamic acid. The possibility of their introduction into the routine treatment of osteosarcoma in dogs should be considered. However, further