Higher response rates in colorectal cancer have been observed with regimens that increase the cytotoxicity of fluorouracil (5-FU) by altering the biochemical milieu at its site(s) of action. Phosphonacetyl-L-aspartate (PALA), which inhibits aspartate transcarbamylase and depletes uridine nucleotide pools in vitro and in vivo, selectively potentiates the antitumor activity of 5-FU in preclinical models. In a phase I/II study in patients with advanced colorectal cancer, PALA 250 mg/m2 was given on day 1, followed 24 hours later by 5-FU 2,600 mg/m2 by 24-hour infusion repeated weekly. Through the use of subcutaneous ports and portable infusion pumps, all patients were treated outside the hospital setting. Thirty-nine patients without prior chemotherapy received 884 courses of treatment. The primary site was colon in 31, rectum in eight. Toxicity was generally mild to moderate except among four patients who were escalated to 5-FU 3,250 mg/m2: two developed severe gastrointestinal toxicity and myelosuppression. Among the remaining 35 patients, gastrointestinal and neurologic toxicities predominated, but usually did not develop until the third or fourth month of treatment. Two patients were inevaluable for response. Among the 37 evaluable patients there were three complete and 13 partial remissions for a total response rate of 43% (95% confidence interval [Cl], 27% to 59%). The median duration of response was 5 months (range, 1.5 to 15 months). The projected mean survival is in excess of 17 months. This high response rate is comparable to the best results obtained with other means of modulation of 5-FU. Demonstration of a survival benefit will require larger phase III studies.

The recommended doses of TPT on a daily times-five schedule combined with PTX-24 in these patients were 0.75 mg/m2/d and 135 mg/m2, respectively, with G-CSF support. Although this dose of PTX has significant single-agent activity in ovarian cancer, the dose of TPT is much lower than the TPT dose at which single-agent activity has been observed. Due to the inability to administer near relevant single-agent doses of both drugs in combination, as well as the requirement for G-CSF support, further evaluations of this regimen in women with refractory or recurrent ovarian cancer are necessary before it can be recommended for previously treated patients in this setting.

Amonafide, a benzisoquinoline-1,3-dione with anti-tumor activity in preclinical screens, was administered to patients with recurrent or metastatic bidimensionally measurable colorectal cancer. Fourteen patients with no prior chemotherapy for advanced disease, performance status 0-1, and normal bone marrow, renal, and hepatic function were entered. Amonafide 300 mg/m2 was administered intravenously over 1 hour daily for five consecutive days; courses were repeated every three weeks. The major side effect was neutropenia: Grade 3 or 4 toxicity occurred in 5/14 patients. Other toxicities included nausea and vomiting, flulike symptoms, fever, rash and alopecia. Three patients had stable disease, but there were no responses observed. Amonafide at this dose and schedule has no activity in the treatment of colorectal cancer.

Preclinical and clinical studies demonstrate that the selective antitumor activity of fluorouracil (5-FU) is enhanced by agents which perturb certain intracellular nucleotide pools. We previously demonstrated that the combination of N-phosphonacetyl-L-aspartate (PALA), which depletes pyrimidine nucleotide pools, and 5-FU yielded a 43% response rate among 37 assessable patients with colorectal carcinoma. In preclinical tumor models, 6-methylmercaptopurine riboside (MMPR), an inhibitor of purine synthesis, elevates phosphoribosylpyrophosphate (PRPP) pools and promotes the anabolism of 5-FU to fluorinated nucleotides. In vivo, the addition of MMPR enhances the therapeutic efficacy of PALA-5-FU. In a phase I trial, we sought to determine the optimal dose and schedule of MMPR in combination with PALA (250 mg/m2 on day 1) and 5-FU (1300 mg/m2 by 24-hour infusion on day 2). MMPR (75-225 mg/m2) was given intravenously on day 1 to 27 patients with solid tumors (15 colorectal, seven breast, five other). Toxic effects were mild to moderate and included leukopenia, mucositis, nausea, or rash. Two of seven patients given MMPR at 225 mg/m2 had grade 3 diarrhea. PRPP was measured using a [14C]orotic acid 14CO2 release assay in tumor biopsy specimens obtained before and 12 hours and 24 hours after MMPR doses were given to 20 patients. The addition of MMPR elevated PRPP pools in human solid tumors. At 12 hours after treatment, two (50%) of four patients showed a twofold or greater elevation of PRPP at the MMPR dose level of 75 mg/m2; a similar elevation was observed in five (71%) of seven patients given 150 mg/m2 MMPR and in three (43%) of seven patients given 225 mg/m2 MMPR. At 24 hours after treatment, results for the respective dose levels of MMPR were two (33%) of six patients, one (20%) of five patients, and four (57%) of seven patients. Administration of the two highest MMPR dose levels appeared to result in a greater increase in tumor PRPP levels. However, toxicity was greater at the 225 mg/m2 dose level; therefore, the 150 mg/m2 dose level was favored. Tumor levels of PRPP decreased between 12 hours and 24 hours in nine (56%) of 16 patients. This time course indicates that MMPR should be administered at the beginning of the 24-hour infusion of 5-FU.

In a phase II clinical trial of 5-fluorouracil (5FU) plus N-(phosphonacetyl)-L-aspartate (PALA) therapy administration, a number of slowly developing clinical responses were observed. Because of this, a variety of immune parameters were sequentially studied in 21 patients on this trial. Of the 21 patients studied, 20 provided sufficient samples to compare baseline with subsequent values, 10 of the 20 patients responded to treatment. Responders and non-responders did not differ in any studied parameter at baseline. After 2 months of therapy, non-specific monocyte cytotoxicity (NSMC), antibody-dependent monocyte cytotoxicity (ADMC) and natural killer (NK) activity were higher in the entire study population, but these increases were not statistically significant. When responders and non-responders were evaluated separately, it was apparent that the trend was due solely to the changes observed in the responding patient population. When mean lysis values for each patient group were determined for each studied time point, it was possible to generate a mean area under the cytotoxicity/time curve (AUC) for each studied parameter. NSMC and ADMC did not differ in responders and non-responders. However, NK activity was significantly greater by mean AUC analysis (P = 0.006) in the responding group; NK activity was maintained in the responders, but decreased in non-responders. When lymphocyte and monocyte expression of the surface markers beta 2-microglobulin, HLA-DR, CD56, HNK-1, CD16 and interleukin-2 receptor were evaluated, there were no differences among responders and non-responders at baseline by mean AUC analysis or when comparing baseline with non-baseline values. It is concluded that although baseline immunological characteristics do not identify patients who are likely to respond to weekly 5FU and PALA, treatment is not associated with deleterious effects on the immune effector function parameters evaluated in this study, there being no effects on expression of a variety of associated cell-surface molecules.