Albumin inhibition of the antileukemic activity of hydroxylated phenothiazines.

Trifluoperazine (TFP) shows cytotoxic activity against human acute lymphatic leukemia (ALL) in vitro. This activity is inhibited by increasing serum concentration and by albumin. Despite its in vitro activity, the drug is inactive in vivo. To determine if increased phenothiazine hydrophilicity could protect against albumin inhibition of antileukemic activity, we compared ALL cytotoxic median effective dose concentrations of a series of hydroxylated phenothiazines in 5% fetal bovine serum (FBS) and in 5% FBS supplemented with albumin. Albumin inhibits the activity of all drugs. A representative derivative 7,8-dihydroxychlorpromazine, although active in vitro, is inactive against L1210 and P388 murine leukemias in vivo.

Cyclosporin A corrects daunorubicin resistance in Ehrlich ascites carcinoma.

We have previously developed a daunorubicin resistant subline of Ehrlich ascites carcinoma (EA/DR) for studies on the reversal of daunorubicin resistance. The mean survival of untreated BALB/c mice bearing drug sensitive parental tumour (EA/DS) is 18.4 +/- 0.6 days, mice bearing EA/DS treated with five daily doses of 0.3 mg kg-1 daunorubicin greater than 60 days, and mice bearing EA/DR treated with the same daunorubicin regimen, 21.1 +/- 1.4 days. We now report complete reversal of daunorubicin resistance in EA/DR by cyclosporin A (CsA). The in vitro daunorubicin IC50, defined as that concentration of daunorubicin required to inhibit 50% of DNA synthesis, in EA/DR was 6.7 +/- 1.15 micrograms ml-1 compared to 2.8 +/- 0.72 micrograms ml-1 in EA/DS. This value was reduced to 2.8 +/- 0.52 and 2.1 +/- 0.10 micrograms ml-1 daunorubicin by 3.3 and 13.2 micrograms ml-1 CsA respectively, P less than 0.05. The MST of groups of host mice bearing EA/DR either untreated, treated with five daily doses of 0.3 mg kg-1 daunorubicin, treated with 80 mg kg-1 CsA in five divided daily doses or treated with combined daunorubicin-CsA were 19.0 +/- 1.0, 21.1 +/- 1.4, 24.0 +/- 2.6 and greater than 60 days respectively. The mean survival of groups of host mice bearing EA/DR treated with 5 mg kg-1 or 10 mg kg-1 CsA simultaneously with daunorubicin for five days was also greater than 60 days. These differences are highly significant.

Verapamil potentiation of VP-16-213 in acute lymphatic leukemia and reversal of pleiotropic drug resistance.

Verapamil, the calcium-influx-blocking agent, has previously been shown to have favorable interactions with antineoplastic drugs. Our study of human T cell acute lymphatic leukemia (ALL) GM3639 indicates that verapamil enhances the in vitro cytotoxicity of VP-16-213 against drug-sensitive ALL by reducing the concentration of VP-16-213, resulting in 50% cell viability from 104.5 +/- 26.6 nM to 46.0 +/- 2.7 nM (P less than 0.05). The addition of verapamil to VP-16-213 treatment of BDF/1 mice bearing L1210 leukemia increases their mean survival from 21.2 +/- 3.6 to 50.4 +/- 4.3 days (P less than 0.01) and the survival of CD2F/l mice bearing P388 leukemia from 27.8 +/- 3.7 to 49.1 +/- 5.0 days (P less than 0.01). The 30-day survival is significantly increased in L1210 and P388 leukemia mice, and 60-day survival is significantly increased in P388 leukemic mice by verapamil. We developed a vincristine (VCR)-resistant subline of GM3639 T cell ALL, L23, by continuous exposure of drug-sensitive cells to VCR. This subline demonstrates pleiotropic cross resistance to VP-16-213 and daunorubicin. The addition of verapamil to VCR, to VP-16-213, and to daunorubicin completely restores responsiveness to these drugs, as indicated by the normalization of the VCR and VP-16-213 concentrations required for cytotoxicity and the concentration of daunorubicin required for inhibition of thymidine incorporation.

Verapamil restoration of daunorubicin responsiveness in daunorubicin-resistant Ehrlich ascites carcinoma.

We have studied the influence of verapamil hydrochloride on the in vitro and in vivo effects of daunorubicin in Ehrlich ascites carcinoma. Daunorubicin-sensitive tumor was rendered resistant to daunorubicin by the continuous treatment of sequential generations of tumor-bearing BALB/c mice. The ability of daunorubicin to inhibit [(3)H]uridine and [(3)H]thymidine incorporation and the effect of daunorubicin on the mean survival time of host animals bearing daunorubicin-sensitive and daunorubicin-resistant Ehrlich ascites carcinoma were compared. The addition of verapamil to daunorubicin in vitro reduced the concentration of daunorubicin required to inhibit 50% of DNA and RNA synthesis in the daunorubicin-resistant tumor to that required in the daunorubicin-sensitive tumor, from 6 and 4.4 mug/ml to 1.5 and 1.3 mug/ml, respectively. Verapamil also restored drug sensitivity to daunorubicin-resistant Ehrlich ascites carcinoma in vivo. The 21.7+/-0.7 d mean survival time (MST) of BALB/c mice bearing daunorubicin-resistant tumor treated with daunorubicin alone rose to 44.0+/-0.7 d when the same tumor was treated with verapamil and daunorubicin, P < 0.001. This in vivo effect is specific for daunorubicin-resistant Ehrlich ascites carcinoma, since there is no alteration in MST of BALB/c mice bearing daunorubicin-sensitive or daunorubicin-resistant tumor when they are treated with verapamil alone or when BALB/c mice bearing daunorubicin-sensitive tumor are treated with daunorubicin and verapamil.

Combined interferon--antimetabolite therapy of murine L1210 leukemia.

To assess the interaction of interferon with estabished chemotherapeutic agents, L1210 murine leukemia in BDF/1 mice was treated with methotrexate, 6-mercaptopurine. Adriamycin, cytosine arabinoside or cyclophosphamide alone or in combination with mouse L-cell (Newcastle disease virus-induced) interferon or with interferon-free tissue culture medium. Also studied was the effect of interferon on the combined 6-mercaptopurine-methotrexate therapy of this tumor. Interferon failed to enhance the response of L1210 leukemia to 6-mercaptopurine, adriamycin, cytosine arabinoside or cyclophosphamide. The addition of interferon to all methotrexate-containing regimens increased mean survival time (P less than 0.05). The increase in survival of host animals treated with 6-mercaptopurine-methotrexate and interferon was sustained though four transfer generations despite evolving resistance to this antimetabolite combination.