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Modulation of Alkylating Agents by Etanidazole and Fluosol-DA/Carbogen in the FSaIIC Fibrosarcoma and EMT6 Mammary Carcinoma¹

Dana-Farber Cancer Institute [B. A. T., T. S. H., J. T., S. A. H., E. F. III], Joint Center for Radiation Therapy [B. A. T., T. S. H., C. N. C.], and Beth Israel Hospital [J. P. E., G. B.], Boston, Massachusetts 02115

Tumor cell survival assay in the FSaIIC murine fibrosarcoma demonstrated that when the modulator Fluosol-DA (0.3 ml; 12 ml/kg i.v.) was administered just prior to an alkylating agent plus carbogen breathing for 6 h or the modulator etanidazole (1 g/kg i.p.) was administered just prior to an alkylating agent, the combination treatment produced significantly more tumor cell killing across the dosage range of each alkylating agent tested compared with the alkylating agent alone. Each alkylating agent produced a dose-dependent log-linear tumor cell survival curve. There was an increase in tumor cell killing of 5–10-fold when either Fluosol-DA/carbogen or etanidazole was added to treatment with the alkylating agent. For cis-diamminedichloroplatinum(II) (CDDP) and N,N',N''-triethylenethiophosphoramide, the modulators used in combination increased tumor cell killing by only 2–3-fold over that obtained with a single modulator, but for the other alkylating agents, tumor cell killing was increased by 10–50-fold when the combination of modulators was used. Bone marrow granulocyte-macrophage colony-forming unit survival assays showed that the combination of modulators with the alkylating agents resulted in only small increases in bone marrow toxicity of the alkylating agents except for N,N',N''-triethylenethiophosphoramide and L-phenylalanine mustard (L-PAM), for which the toxicity to the bone marrow granulocyte-macrophage colony-forming unit was increased by 5–10-fold compared with the alkylating agents alone. The Hoechst 33342 dye diffusion defined tumor cell subpopulation assay, also in the FSaIIC tumor, demonstrated that the combination of modulators increased the toxicity of CDDP, cyclophosphamide, L-PAM, and 1,3-bis(2-chloroethyl)-1-nitrosourea by 9–55-fold compared with the alkylating agent alone in both the bright (euxoic-enriched) and dim (hypoxicenriched) cells. For each alkylating agent except 1,3-bis(2-chloroethyl)-1-nitrosourea, the increase in tumor cell killing was greater in the dim cells than in the bright cells. Finally, tumor growth delay studies in both the FSaIIC tumor and the EMT-6 murine mammary adenocarcinoma confirmed that the combination of modulators significantly increased the tumor growth delay caused by CDDP, carboplatin, cyclophosphamide, N,N',N''-triethylenethiophosphoramide, L-PAM, and 1,3-bis(2-chloroethyl)-1-nitrosourea. The greatest increases (4–5-fold were observed for carboplatin and L-PAM in the FSaIIC tumor and CDDP and cyclophosphamide in the EMT-6 tumor. These results suggest that Fluosol-DA/carbogen together with etanidazole may be an effective modulator combination of alkylating agents in the clinic.

¹ This work was supported by National Cancer Institute Grants PO1-CA38493 and PO1-CA19589, a grant from Bristol-Myers Co., Wallingford, CT, and a grant from the Mathers Foundation.

² To whom requests for reprints should be addressed, at Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115.

Received 8/17/90. Accepted 11/29/90.