bropirimine and Leukemia-P388

At least three marked differences were noted in the results compared from two parallel experiments using identical protocols with virus-free mice and mouse hepatitis virus (MHV) infected mice inoculated with P388 leukemia. First, the therapeutic effect of cyclophosphamide (CY), a cytotoxic antitumor drug, was apparently augmented in MHV-infected mice. A 162% increase of life span (ILS) was obtained in MHV-infected mice compared to a 100% ILS in uninfected mice. Second, the experimental error in terms of the range of animal survival time was much larger with MHV-infected mice than with uninfected mice. In MHV-infected mice, the therapeutic effect of the combination treatment with CY and pyrimidinone was not statistically different from that of the treatment with CY alone. In uninfected mice, the effects of the combination therapy at all doses of pyrimidinone were statistically more effective than that of CY treatment alone.

Topics: Animals; Antineoplastic Agents; Cyclophosphamide; Cytosine; Drug Therapy, Combination; Female; Hepatitis, Viral, Animal; Leukemia P388; Leukemia, Experimental; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Murine hepatitis virus; Pyrimidinones

Bropirimine (ABPP), a pyrimidinone, is currently under clinical trial for its antitumor potential. Bropirimine alone was marginally active against some experimental tumors such as B16 melanoma but was ineffective against others such as P388 or L1210 leukemia. However, it produced statistically significant synergistic activity against P388 leukemia when used in combination with cyclophosphamide (CY). The aim of this investigation was to determine whether the synergism could be achieved with different types of cytotoxic drugs. Actinomycin D (act D), adriamycin, 5-azacytidine, cisplatin, melphalan, mitomycin C, and vincristine were selected. Using an experimental protocol identical to that of CY and bropirimine combination therapy, and using a more or less equally effective dosage of the drug for the initial reduction of tumor burden (i.e., around 100% increase of life span), cisplatin and bropirimine also produced a statistically significant synergism over the treatment with cisplatin alone. The combination of bropirimine with either adriamycin, mitomycin, or vincristine was beneficial but the effect was not as consistent or as striking as that seen with the CY and bropirimine combination. It is clear, however, that the combination of act D and bropirimine was not synergistic under the experimental conditions. Since the antitumor activity of pyrimidinone has been reported to be mediated in part by its stimulation of natural killer cell activity, the effect of these cytotoxic drugs on the immunomodulatory activity of bropirimine was investigated. Like CY, cisplatin did not alter the augmentation of natural killer cell activity by bropirimine. However, adriamycin, mitomycin, or vincristine showed a marked inhibition (25-50%) of the augmentation. Act D completely inhibited the immunomodulating activity of bropirimine 4 days after drug administration and continued to show marked inhibition 18 days later. This may partially explain the reasons for lack of synergism between act D and bropirimine. A prolonged immunosuppressive effect exhibited by act D and the degree of tumor repopulation during this period could render bropirimine ineffective. In addition to the magnitude of initial tumor burden reduction by the chemotherapeutic drugs, the present results indicate that the immunosuppressive property of these drugs may also affect the outcome of chemoimmunotherapy.

Topics: Animals; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Cisplatin; Cyclophosphamide; Cytosine; Cytotoxicity, Immunologic; Dactinomycin; Drug Synergism; Killer Cells, Natural; Leukemia P388; Leukemia, Experimental; Male; Mice; Mice, Inbred Strains

Since increasing evidence indicates that combination modality of cancer treatment is preferable, and a series of 5-halo-6- phenylpyrimidinones has been found to induce interferon production and to stimulate a variety of immune responses, several were tested alone or in combination with cyclophosphamide (CY) against B 16 melanoma and P388 leukemia. Thus far, 2-amino-5-bromo-6-(3-fluorophenyl)-4(3H)pyrimidinone ( ABMFPP ) and its sister compound 2-amino-5-bromo-6-(2-fluorophenyl)-4(3H)pyrimidinone ( ABOFPP ) were found to be superior to other pyrimidinones including 2-amino-5-bromo-6-(6-phenyl)-4-pyrimidinone which is currently under clinical investigation. Neither ABMFPP nor ABOFPP alone had any significant activity against P388 leukemia. However, a marked synergistic effect was observed when a single i.p. injection of CY at 24 hr after tumor inoculation (10(6) cells/mouse) was followed by multiple i.p. injections of either ABMFPP or ABOFPP . For instance, the increase of life span was about 180% when animals received both CY (150 mg/kg) and ABMFPP (125 mg/kg/injection) as compared to 100% increased life span when animals received CY alone, and 0% increased life span when animals received ABMFPP alone. Also, 80% of the animals were long-term survivors (greater than 30 days) when animals received the combination therapy as compared to 20% survivors when animals received CY alone. The synergistic effect exhibited by ABMFPP or ABOFPP correlated positively to the initial reduction of tumor burden by CY. The optimal gap between CY and pyrimidinone administration was one day. The best therapeutic response was observed when pyrimidinone was given every 4 days for a total of 7 injections; however, other schedules and dosing frequencies also gave significant responses. The synergistic effect was also observed with B 16 melanoma when animals received the combination therapy. The significance of these findings, in terms of theoretical consideration as well as drug development, is discussed.

Topics: Animals; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Cell Line; Combined Modality Therapy; Cyclophosphamide; Cytosine; Drug Synergism; Immunotherapy; Leukemia P388; Leukemia, Experimental; Melanoma; Mice; Mice, Inbred Strains