Liposomal clodronate treatment for tumour macrophage depletion in dogs with soft-tissue sarcoma.

Increased numbers of tumour-associated macrophages correlate with rapid tumour growth and metastasis in tumours. Thus, macrophage depletion has potential as a novel cancer therapy and positive responses have been reported in rodent tumour models. To investigate the effectiveness of this approach in dogs with cancer, we evaluated the effects of the macrophage-depleting agent liposomal clodronate (LC) in dogs with soft-tissue sarcoma (STS). To this end, we conducted a clinical trial of LC therapy in 13 dogs with STS. Repeated LC administration was well tolerated clinically. Preliminary examination of tumour biopsy sets from 5 of the 13 dogs demonstrated that the density of CD11b(+) macrophages was significantly decreased after LC treatment. Circulating concentrations of interleukin-8 were also significantly reduced. These preliminary studies are the first to suggest that LC can be used as a systemic macrophage-depleting agent in dogs to reduce numbers of tumour-associated macrophages.

Bisphosphonates significantly increase the activity of doxorubicin or vincristine against canine malignant histiocytosis cells.

Canine malignant histiocytosis (MH) is an aggressive neoplasm of macrophages and dendritic cells. It carries a poor prognosis because of the development of widespread metastasis and poor sensitivity to chemotherapy. Thus, there is a large need for new treatments for MH. We hypothesized that bisphosphonates might be useful to increase the effectiveness of cytotoxic chemotherapy against MH. To address this question, we conducted in vitro screening studies using MH cell lines and a panel of 6 chemotherapy and 5 bisphosphonate drugs. The combination of clodronate with vincristine was found to elicit synergistic killing which was associated with a significant increase in cell cycle arrest. Second, zoledronate combined with doxorubicin also significantly increased cell killing. Zoledronate significantly increased the uptake of doxorubicin by MH cells. On the basis of these findings, we conclude that certain bisphosphonate drugs may increase the overall effectiveness of chemotherapy for MH in dogs.

Combination chemotherapy with continuous L-asparaginase, lomustine, and prednisone for relapsed canine lymphoma.

BACKGROUND: The combination of lomustine, L-asparaginase, and prednisone (LAP) is an effective rescue treatment for canine lymphoma (LSA). In a previous study, we reported that remission was typically lost around the time L-asparaginase was discontinued. HYPOTHESIS: Use of L-asparaginase with each lomustine treatment will be well tolerated and efficacious as a rescue therapy for canine LSA. ANIMALS: Forty-eight client-owned dogs with cytologically confirmed multicentric LSA whose disease had relapsed after a cyclophosphamide, doxorubicin, vincristine, and prednisone-based chemotherapy protocol were included. METHODS: Lomustine was administered orally at 3-week intervals, concurrently with subcutaneous or intramuscular L-asparaginase for a total of 5 doses or until disease progression. Prednisone was administered at a tapering dose for the duration of the protocol. RESULTS: The overall response rate (ORR) for dogs treated with this protocol was 77%, with 65% achieving a complete response (CR). The median time to progression (TTP) was 70 days. Based on loose comparison, these findings are not significantly different from our previously reported historical control. The actual CCNU dosage administered did not affect response rate or remission duration. CONCLUSIONS/CLINICAL IMPORTANCE: These findings support previous data concluding that the LAP protocol is a viable rescue treatment option for dogs with LSA. However, results from this study suggest that continued use of L-asparaginase with each lomustine treatment does not significantly increase remission duration and toxicity appears greater.