Further observations on the inhibition of tumor growth by Corynebacterium parvum with cyclophosphamide. I. Variation in administration of both agents.

Studies from this laboratory have indicated that the administration of cyclophosphamide (CY) and Corynebacterium parvum (CP) over a prolonged time to C3H mice with established measurable tumors resulted in complete arrest of tumor growth as well as partial and complete regressions in many instances. The present investigations on optimal dosage, route, frequency, and sequence of administration of CY and CP in the model system were performed to obtain information that could be useful in the design of chemotherapeutic and immunotherapeutic regimens for the treatment of human tumors. Findings have suggested the need for administration of CP in more than one instance. Although a single dose of CP in combination with weekly injections of CY had a significantly prolonged inhibitory effect, weekly doses of CP and CY were more effective. We also concluded that the time between doses of an immunostimulating agent (I-I interval) as well as between administration of chemotherapy (C-C interval) may be critical for an optimal result. In this model system, C-C and I-I intervals of 7 days inhibited tumor growth most effectively. The time between administration of chemotherapy and immunotherapy (C-I interval) has been considered critical. Whereas slightly better results were achieved in these studies when the immunotherapy was administered 4 days after the CY or when the C-I interval was +4 days, almost equally good results were obtained when both agents were given on the same day, which signified that the C-I interval may not be as critical as other investigators have reported. The present findings confirmed and extended our prior observations and indicated that the iv and ip routes of administration were superior to the im and sc routes in our model. The observed tumor growth inhibition was a result of both chemotherapeutic and immunotherapeutic modalities; also, the inhibitory properties of the regimen were more related to the chemotherapeutic component. Finally, almost identical tumor growth inhibition was observed when CP obtained from two different laboratories was used in conjunction with CY.