Markedly improved efficacy of edatrexate compared to methotrexate in a high-dose regimen with leucovorin rescue against metastatic murine solid tumors.

10-Ethyl-10-deazaaminopterin (EDX, edatrexate) exhibits therapeutic activity against methotrexate (MTX)-resistant tumors in animals and patients. In an effort to improve its efficacy among more chemoresistant tumors, studies were initiated in murine models of advanced metastatic disease comparing EDX and MTX at their maximum tolerated dose alone and in a high-dose regimen incorporating low-dose, delayed Ca leucovorin (LCV) rescue. Both twice-weekly x 3 and weekly x 3 schedules of administration were used with LCV given 16, 20, and 24 h after EDX. The LCV dose required to protect mice was 1/40 and 1/20 of the EDX or MTX dose, respectively, on either schedule. Therapy was initiated 5 or 6 days following i.v. implant of 5 x 10(5) cells of the E0771 mammary adenocarcinoma, T241 fibrosarcoma, Lewis lung carcinoma, B16 melanoma, or C38 colon carcinoma. MTX was essentially ineffective (increase in life span = < 30%) when given alone and either ineffective or only modestly effective (increase in life span = 20-80%) in increasing survival when given in the high-dose regimen to tumor-bearing mice. EDX alone was more effective than MTX when it was given in either regimen of therapy. Also, EDX given in the high-dose regimen (either twice-weekly or weekly x 3) was markedly more effective than EDX alone. Increased survival with this regimen was 2-3-fold greater than EDX alone against all 5 tumors, and long-term survivors were obtained with E0771 (20%), T241 (30-40%), Lewis lung (10-15%), B16 (20%), and C38 (40%) tumors. The administration of 6 doses rather than 3 doses on the twice-weekly schedule against T241 and Lewis lung tumors required a modest increase in the LCV dose but substantially improved efficacy, with as much as 70% long-term survivors (T241 tumor). We conclude that the use of a high-dose regimen with delayed LCV rescue markedly improved the therapeutic effectiveness of EDX against advanced metastatic disease in tumor-bearing mice. These studies should provide a framework for further clinical work with EDX, using this modality of therapy.

Intracavitary therapy of murine ovarian cancer with cis-diamminedichloroplatinum(II) and 10-ethyl-10-deazaaminopterin incorporating systemic leucovorin protection.

Administration i.p. of 10-ethyl-10-deazaaminopterin (10EDAM) with cis-diamminedichloroplatinum(II) (cis-Pt) had significant antitumor activity against the murine ovarian tumor. This tumor is a teratoma originating in the ovary with pathogenesis and metastatic properties similar to those of human ovarian cancer. Drug was given on a schedule of once every 3 days for 3 doses 1 or 2 days after i.p. implant of 10(7) tumor cells. Despite the 2-fold attenuation of dosage required, antitumor activity of the combination (increased life span, 161%) was approximately twice that obtained with maximum tolerated doses of either agent alone and tumor-free, long-term survivors were obtained. Incorporation of s.c. calcium leucovorin administration 16 h after each dose of 10EDAM and cis-Pt allowed a 4-fold increase in dosage of 10-EDAM without an increase in toxicity, increased median survival by an additional 120%, and quadrupled the number of tumor-free, long-term survivors to 40% of treated animals. By comparison, methotrexate was only modestly active against this tumor model either as a single agent, with cis-Pt, or with delayed s.c. calcium leucovorin administration. These results appear to suggest that 10EDAM with cis-Pt may have considerable potential for intracavitary therapy of human cancer, including ovarian carcinoma, particularly when incorporating delayed systemic calcium leucovorin administration.

New folate analogs of the 10-deaza-aminopterin series. Further evidence for markedly increased antitumor efficacy compared with methotrexate in ascitic and solid murine tumor models.

A group of folate analogs of the 10-deaza-aminopterin series, which were designed on the basis of the results of an intensive biochemical and pharmacokinetic program, have been examined in therapy experiments utilizing a group of murine tumor models. These new analogs were found to be markedly superior to methotrexate against four of five ascites tumors (L1210 leukemia, Sarcoma 180, Ehrlich carcinoma and Tapper carcinosarcoma) and against four of five solid tumors (S180, Tapper carcinosarcoma, E0771 mammary adenocarcinoma, Lewis lung carcinoma, and T241 sarcoma). Analogs alkylated (methyl or ethyl) at the 10 position of 10-deaza-aminopterin were found to be the most effective of the group. These analogs achieved log10 reduction in tumor burden several-fold greater in magnitude than methotrexate against L1210 and S180 ascites tumors and there were also long-term survivors. 10-Deaza-aminopterin itself gave a result intermediate between those obtained with the 10-alkyl derivatives and methotrexate. Against the solid forms of the Tapper tumor some partial regressions were obtained with methotrexate and 10-deaza-aminopterin, but a far greater number, extending over a longer period were obtained with the 10-ethyl derivative of 10-deaza-aminopterin. Against the E0771 tumor, 10-deaza-aminopterin was 2-fold and the ethyl derivative of 10-deaza-aminopterin was greater than 5-fold more effective than methotrexate in retarding tumor growth. Evidence for partial regressions and marked effects against metastatic disease were also obtained in the case of the 10-alkyl derivative. Similar results were also obtained with the T241 sarcoma. For Lewis lung carcinoma the relative potency was about the same but overall antitumor effects were more modest.

Antitumor tests of amygdalin in spontaneous animal tumor systems.

In a series of 6 experiments with CD8F1 mice with spontaneous mammary adenocarcinomas Sugiura noted by macrovisual observation with some histology an overall average of 21% of mice with lung metastases when treated with 1,000--2,000 mg/kg/day of amygdalin compared with 90% of the control mice. The significance attributed to those early observations is seriously challenged by the negative findings of 3 independent investigators, by 2 out of 3 negative cooperative experiments in which Sugiura participated, and particularly by the blind experiment in which he and others under blind readings found no anticancer activity. Treatment of Swiss albino mice showed no destructive effect upon their spontaneous mammary adenocarcinomas. Of the treated mice, 22% were found by macrovisual observation to have lung metastases while 91% were noted among the controls. The results are subject to questions raised in the discussion. Amygdalin at 2,000 mg/kg/day was ineffective both in treating and preventing the development of spontaneous leukemia in AKR mice. At 1,000 mg/kg/day it was not found effective in preventing or significantly delaying the development of spontaneous mammary tumors in CD8F1 mice. In summary, we do not have evidence to support taking amygdalin to clinical trial, although other considerations may require that one be conducted.

Antitumor tests of amygdalin in transplantable animal tumor systems.

Except for oral administration, there was no grossly observed toxicity from carefully administered high doses of amygdalin in the experimental systems used. The compound in high doses was ineffective against the DMBA-induced rat mammary carcinoma and the following transplanted experimental tumors: Sarcoma 180, plasma cell tumor LPC-1, leukemia L1210, Mecca lymphosarcoma, Ridgway osteogenic sarcoma, sarcoma T241, mammary carcinoma E0771, Taper liver tumor, Ehrlich carcinoma (solid and ascites), and Walker carcinosarcoma 256. Amygdalin did not noticeably influence the toxicity or impair the efficacy of these chemotherapeutic agents in their respective systems: Cytosine arabinoside, methotrexate, cytoxan, or 5-fluorouracil in L1210; the latter two in LPC-1; 6-mercaptopurine in Ridgway osteogenic sarcoma; estradiol-17beta or 2alpha-methyldihydrotestosterone propionate in the DMBA-induced rat mammary carcinoma.