Comparison of the cytotoxic effects of single and divided treatment of 4-hydroxycyclophosphamide at the same total dosage amount in canine lymphoma cell lines

Cyclophosphamide is widely used in combination chemotherapy to treat dogs with lymphoma. The metabolite of cyclophosphamide, acrolein, can irritate the urinary bladder and cause sterile haemorrhagic cystitis. The divided administration of cyclophosphamide across multiple days may reduce the occurrence of the cystitis. However, the therapeutic effect of this modification has not been evaluated and compared to the traditional single maximum-tolerated dose. It is difficult to evaluate the cytotoxic effect by the single chemotherapeutic drug in dogs. In order to verify the effect of the single and divided treatment of cyclophosphamide in canine lymphoma, we used two canine lymphoma cell lines (CLBL-1, B-cell lymphoma and UL-1, T-cell lymphoma) to imitate the clinical conditions. The cell viability in the CLBL-1 and UL-1 cells treated by a single dosage of 4-hydroxycyclophosphamide after 48 h were 70.4% and 61.5%, respectively. The cell viability in the CLBL-1 and UL-1 cells treated by the divided dosage of 4-hydroxycyclophosphamide after 48 h were 109.4% and 50.8%. There were no significant differences between the two administration methods in the T-cell lymphoma cell line (P = 0.215). The single full dosage of 4-hydroxycyclophosphamide exhibited a significant cytotoxic effect rather than the divided dosage in B-cell lymphoma cell line (P = 0.007) did. The maximum-tolerated dose of cyclophosphamide is still recommended to be used in dogs with B-cell lymphoma.