Continued survival of more than ten years, without resection of metastatic disease, in patients with metastatic colorectal cancer treated with biomodulated fluorouracil: report of two cases.

The treatment of metastatic colorectal cancer by chemotherapy alone was considered palliative and without the potential to cure patients unless patients were rendered resectable. We report two patients with metastatic colorectal cancer involving the liver who were considered inoperable and were treated with systemic chemotherapy using biomodulated 5-fluorouracil. Both patients received 5-fluorouracil and N-(phosphonoacetyl)-l-aspartic acid; one also received methotrexate, leucovorin, and triacetyluridine with the N-(phosphonoacetyl)-l-aspartic acid and 5-fluorouracil. Both patients had a complete remission with chemotherapy and are still alive with no evidence of cancer ten years after the diagnosis of unresectable metastatic disease. These patients provide evidence that prolonged survival can be achieved withsystemic chemotherapy without the use of surgery or other forms of local therapy. These patients also confirm the importance of continued investigation of fluorouracil modulating agents, which may further enhance the recent progress made with fluorouracil-based combination chemotherapy for colorectal cancer.

A phase II pilot study of high-dose 24-hour continuous infusion of 5-FU and leucovorin and low-dose PALA for patients with colorectal cancer: a Southwest Oncology Group study.

PURPOSE: The purpose of this phase II multi-institutional study was to define the efficacy and toxicity of infusional 5-FU in combination with PALA and leucovorin in patients with advanced colorectal cancer. PATIENTS AND METHODS: Patients were required to have histologically confirmed colorectal cancer with distant metastases. The treatment regimen consisted of 5-FU 2600 mg/m(2) as a 24-hours continuous infusion given once a week, concurrently with leucovorin (LV) at 500 mg/m(2) as a 24-hour continuous infusion. PALA was administered 24 hours prior to 5-FU/LV at a dose of 250 mg/m(2) iv over 15 minutes weekly. Patients were continued on the assigned treatment regimen until progression of disease, unacceptable toxicity, or the patient declined further therapy. RESULTS: This study accrued 28 patients and all were eligible and evaluable for toxicity. Four patients had inadequate assessment of response and are considered non-responders. There was one complete response and five partial responses for an overall response rate of 6/28 or 21% (95% confidence interval 8-41%). Estimated median survival was 17.4 months (95% confidence interval 13.3-20.5 months). One patient died of a treatment related infection. This patient also had grade 4 diarrhea and vomiting. CONCLUSION: The combination of 5-FU, leucovorin, and PALA in the doses and schedule used here, produces a response rate similar to other modulated schedules of 5-FU with similar survival and toxicity profiles.

A phase II study of high-dose 24 hour continuous infusion 5-FU and leucovorin and low-dose PALA for patients with advanced pancreatic adenocarcinoma: a Southwest Oncology Group Study.

PURPOSE: The purpose of this phase II multi-institutional study was to define the efficacy and toxicity of infusional 5-FU in combination with PALA and leucovorin in patients with advanced pancreatic cancer. PATIENTS AND METHODS: Patients were required to have histologically confirmed pancreatic cancer that was locally advanced, unresectable or disseminated. The treatment regimen consisted of weekly 5-FU 2600 mg/m(2) given concurrently with leucovorin at 500 mg/m(2). Both drugs were administered by 24-hour continuous infusion. PALA was administered 24 hours prior to the administration of 5-FU/LV at a dose of 250 mg/m(2) IV over 15 minutes weekly. Patients were continued on the assigned treatment regimen until progression of disease, unacceptable toxicity, or the patient declined further therapy. RESULTS: This study accrued 30 patients. Four of these patients were ineligible. All 26 eligible patients were evaluated for toxicity. One patient had inadequate assessment of response and was considered a non-responder. Three of the twenty-six eligible patients had partial responses, for a response rate of 12% (95% confidence interval 2% to 30%). All 26 eligible patients have died and the median overall survival was 7 months (95% confidence interval: 5.2 to 9 months). Four patients experienced grade 4 toxicities, including bilirubin increase (2 patients), vomiting (1 patient) and non-local skin ulceration (1). Two patients discontinued therapy due to toxicity. CONCLUSION: The dual modulation of 5-FU with PALA and leucovorin in the dose and schedule used here, has a response rate similar to other single agents in pancreatic cancer and can result in some long term survival while having relatively mild toxicity.

Treatment of intracranial rat glioma model with implant of radiosensitizer and biomodulator drug combined with external beam radiotherapy.

PURPOSE: To evaluate an intracranial polymer implant containing bromodeoxyuridine (BrdUrd) and N-(phosphonacetyl)-L-aspartic acid (PALA) in combination with external beam radiotherapy (EBRT) in the treatment of a rat glioma. METHODS AND MATERIALS: Combinations of the biomodulators 5-fluorouracil, methotrexate, or PALA with BrdUrd were evaluated as radiosensitizers in vitro by clonogenic assay. In in vivo experiments, BrdUrd and PALA were incorporated into a polyanhydride-based polymer, bis(p-carboxyphenoxy)propane sebacic acid, and implanted in the C6 rat glioma growing intracranially. The effectiveness of treatment was evaluated on the basis of survival. EBRT was given as 10-MV X-rays. RESULTS: In tissue culture experiments, C6 cells were refractory to radiosensitization by BrdUrd even when the thymidine analog was combined with a biomodulator intended to reduce de novo thymidine synthesis. The most effective compound in vitro was PALA. When PALA and BrdUrd in a polymer formulation were implanted intracranially and combined with 10-Gy EBRT, the treatment was highly effective, with 83% of treated rats surviving 180 days. CONCLUSION: Although the in vitro results were not encouraging, the combination of intratumoral BrdUrd and PAL with 10-Gy EBRT was highly effective in treating a rat glioma. These results indicate the clinical potential of combined and mixed modality treatments involving intratumoral sustained-release drug delivery.

Thymidylate synthase protein expression in primary colorectal cancer: lack of correlation with outcome and response to fluorouracil in metastatic disease sites.

PURPOSE: The aim of this study was to investigate the utility of quantitating thymidylate synthase (TS) in the primary tumor as a surrogate for metastatic disease sites to predict the likelihood of response and outcome to fluorouracil (FU) treatment in patients with metastatic colorectal cancer. METHODS: TS protein expression was evaluated using the TS 106 antibody and the avidin biotin labeling immunohistochemical technique in primary tumor samples from 219 patients with metastatic colorectal cancer. The patients were a representative sample of those patients enrolled into the Eastern Cooperative Oncology Group E2290 protocol that evaluated five separate FU-containing regimens in patients with metastatic residual or recurrent colorectal carcinoma. RESULTS: Our retrospective analysis found that the level and extent of TS protein expression in the primary tumor did not correlate with overall survival in patients with metastatic or recurrent colorectal cancer. A trend toward a direct correlation between the level of TS protein expression and response was noted in tumors that expressed high TS levels. This response advantage for patients expressing high TS levels in the primary tumor was apparent regardless of what FU-based treatment the patient received but was most apparent in the subgroup treated with leucovorin, in which the level of TS expression and response to FU and leucovorin reached statistical significance (P =.034). No significant interaction could be detected between the addition of leucovorin to FU and the level of TS expression in the primary tumor. CONCLUSION: This study demonstrated that measurement of TS protein levels in the primary tumor tissue does not aid in predicting outcome or response to FU in a metastatic disease site. These assays must be performed on biopsy tissue from the metastatic disease site that is used to radiologically assess response and outcome to treatment.

High-dose 5-fluorouracil plus low dose methotrexate plus or minus low-dose PALA in advanced colorectal cancer: a randomised phase II-III trial of the EORTC Gastrointestinal Group.

The aim of this study was to investigate whether N-(phosphonacetyl)-L-aspartic acid (PALA) can enhance the activity of low-dose methotrexate (LD-MTX) modulated infusional 5-fluorouracil (5-FU) in patients with advanced colorectal cancer. 198 patients were randomised either to (i) 5-FU 60 mg/kg as a continuous infusion over 48 h, to be given weekly four times and thereafter every 2 weeks, with methotrexate 40 mg/m(2) administered just before 5-FU (control regimen) or to (ii) PALA 250 mg/m(2) as a 15 min infusion administered 24 h before 5-FU and methotrexate which was given as described in the control regimen. The response rate was 13% in the patients randomised to the control arm and 7% in the patients randomised to the experimental arm. If stabilisation of the disease was also considered as a positive response, these figures become 54 and 46%, respectively. All these differences did not reach statistical significance. The median durations of progression-free survival (PFS) in the two treatment groups were not significantly different. The median duration of survival was 13.1 months in the control arm and 11.9 months in the experimental arm (P=0.31). No benefit was obtained by adding PALA to LD-MTX+infusional FU. Taking into account data from US trials, the modulating effect of PALA, although 'promising' in phase II, could not be substantiated in randomised studies.

Fluorouracil modulation in colorectal cancer: lack of improvement with N -phosphonoacetyl- l -aspartic acid or oral leucovorin or interferon, but enhanced therapeutic index with weekly 24-hour infusion schedule--an Eastern Cooperative Oncology Group/Cancer and Leukemia Group B Study.

PURPOSE: To investigate mechanism-directed regimens in maximizing the efficacy of fluorouracil (5-FU) in advanced colorected cancer. PATIENTS AND METHODS: Based on promising phase II data, a randomized comparison of various methods for the biochemical modulation of 5-FU was undertaken in patients with advanced colorectal cancer. The control group received single-agent 5-FU as a 24-hour infusion weekly. Patients (N = 1,120) with no prior chemotherapy for metastatic disease were randomized to one of the following arms: arm A, 5-FU 2,600 mg/m2 by 24-hour infusion, weekly; arm B, N-phosphonoacetyl-l-aspartic acid 250 mg/m2 day l, 5-FU 2,600 mg/m2 by 24-hour infusion day 2, weekly; arm C, 5-FU 600 mg/m2 with oral leucovorin (LV) 125 mg/m2 hourly for the preceding 4 hours, weekly; arm D, 5-FU 600 mg/m2 with intravenous (IV) LV 600 mg/m2, weekly; arm E, 5-FU 750 mg/m2/d IV by continuous infusion for 5 days, then 750 mg/m2 weekly, and recombinant interferon alfa-2a 9 million units subcutaneously three times weekly. Median follow-up was 4.8 years. RESULTS: Of the 1,098 assessable patients, 57% had measurable disease. The toxicity of all the regimens was tolerable. Grade 4 or worse toxicity occurred in 11%, 11%, 30%, 24%, and 22% on each arm, respectively; diarrhea was the most common adverse effect. These toxicity patterns favored significantly (P <.001) the 24-hour infusion arms. Median survival (months) by arm was A, 14.8; B, 11.9; C, 13.5; D, 13.6; and E, 15.2. These survival durations did not differ significantly. CONCLUSION: We conclude that a weekly infusion regimen of 5-FU is significantly less toxic than and as effective as 5-FU bolus regimens modulated by either LV or interferon in patients with metastatic colorectal cancer.

N-(phosphonacetyl)-L-aspartate and calcium leucovorin modulation of fluorouracil administered by constant rate and circadian pattern of infusion over 72 hours in metastatic gastrointestinal adenocarcinoma.

BACKGROUND: We have reported that N-(phosphonacetyl)-L-aspartic acid (PALA) 1266 mg/m2 can safely be given 24 hours prior to the start of a 72-hour infusion of fluorouracil (FUra) and leucovorin (LV) at doses of 2000 and 500 mg/m2/day. Since inhibition of aspartate carbamoyltransferase (ACTase) activity was evident 4 hours post PALA, we wished to evaluate PALA given 1 hour prior to FUra. Further, we studied the toxicity and pharmacokinetics with FUra given by either fixed- or variable-rate infusion. PATIENTS AND METHODS: Twenty-seven patients with gastrointestinal tract adenocarcinomas were treated with PALA 1266 mg/m2/15 min followed by a 72-hour infusion of FUra and LV (1750 & 500 mg/m2/day) given by fixed- or variable-rate (peak at 4:00 A.M.). RESULTS: Clinical toxicity was similar in two consecutive cycles in 17 patients receiving fixed- and variable-rate infusion at the same FUra dose. Overall, grade 3 stomatitis and hand-foot syndrome occurred in 12% and 4% patients receiving fixed- and in 16% and 10.5% of patients receiving variable-rate infusions. Six of 24 evaluable patients (25%) had a partial response. The profile of FUra plasma levels (Cp) over a 24-hour period during fixed- and variable-rate infusions were strikingly different, but the average Cp and area under the concentration-time curves were comparable. ACTase activity was significantly decreased at 4 and 24 hours after PALA (12% and 18% of baseline; P < 0.001), but enzyme activity had recovered to 40% by 72 hours. CONCLUSIONS: This regimen was active and well tolerated with similar toxicities with FUra given by either fixed- or variable rate infusion. PALA 1266 mg/m2 significantly inhibited ACTase activity for at least 24 hours.

In vitro cytotoxic effect of N-(phosphonacetyl)-L-aspartic acid in liposome against C-26 murine colon carcinoma.

We have investigated the in vitro cytotoxic effect of liposome-encapsulated N-(phosphonacetyl)-L-aspartic acid (PALA) against C-26 murine colon cancer cells, and have compared it in this regard to free PALA. Three different PALA-containing liposomal formulations using distearoylphosphatidylcholine (DSPC), distearoylphosphatidylglycerol (DSPG), and polyethyleneglycol-derivatized distearoylphosphatidylethanolamine (PEG-DSPE) were made and their cytotoxicity was measured. In 72 hr continuous exposure experiment with C-26 cells, the 50% growth inhibitory concentration (IC50) of DSPG-PALA liposome formulation was 0.09 microM, which showed about 65-fold more potent than unencapsulated free PALA (5.1 microM). Similar degree of increase in cytotoxicity was also observed in 1 hr exposure experiment. However, the IC50 of PEG-DSPE-PALA liposome and DSPC-PALA liposome were 10.7 microM and 11.8 microM, respectively, which showed slightly less potent than unencapsulated free PALA. Physical characteristics of PALA-liposomes, such as the size and drug:lipid ratio were also determined. In conclusion, negatively-charged DSPG-PALA liposome showed the highest cytotoxic effect among tested on the C-26 cells in vitro.

Where do we stand with 5-fluorouracil?

For nearly four decades, 5-fluorouracil (5-FU) has been the mainstay of treatment for colorectal cancer. Due to the lack of other agents with significant activity, tremendous efforts have been undertaken to increase the efficacy of 5-FU by investigating alternative schedules of delivery and biomodulation. However, bolus 5-FU in combination with folinic acid (FA), either as the Mayo Clinic or Roswell Park protocol, still represents the standard treatment for adjuvant and first-line palliative chemotherapy of colorectal cancer. In a recent meta-analysis, infusional protocols of 5-FU demonstrated increased response rates (14% to 22%) and a marginal, but significant survival benefit of 3 weeks (11.3 to 12.1 months). In view of the much higher costs and complicated management of infusional 5-FU regimens, this marginal survival benefit does not yet allow protracted 5-FU application to be defined as standard therapy. However, protracted 5-FU infusion in combination with radiation can be considered standard therapy as adjuvant treatment of rectal cancer, since it has demonstrated a significant increase in survival. In the future, oral 5-FU prodrugs may be substituted for infusional 5-FU. Furthermore, current data indicate that 5-FU will also be an essential component of combination chemotherapy protocols with the new active agents oxaliplatin, irinotecan, and raltitrexed. Preclinical studies show synergistic antitumor activity of 5-FU with these agents, which corresponds well with clinical response rates of 50% in untreated and 15% to 25% in 5-FU-refractory patients. Moreover, 5-FU-based pro-drug-active drug systems serve as excellent models for tumor-targeted gene therapy.

Sequential biochemical modulation of fluorouracil with folinic acid, N-phosphonacetyl-L-aspartic acid, and interferon alfa-2a in advanced colorectal cancer.

PURPOSE: Several agents have been evaluated for their effect as biochemical modulators of fluorouracil (5-FU) in the treatment of metastatic colorectal carcinoma. In this study, we used folinic acid (FA), N-phosphonacetyl-L-aspartic acid (PALA), and recombinant interferon alfa-2a (IFNalpha-2a) in a sequential order to assess the efficacy of this approach in patients with metastatic colorectal carcinoma. PATIENTS AND METHODS: Forty-four patients with metastatic colorectal carcinoma were enrolled onto the study. The treatment course consisted of three cycles: (cycle 1) FA 20 mg/m(2) followed by 5-FU 425 mg/m(2) on days 1 to 5; (cycle 2) PALA 250 mg/m(2) on days 29, 36, 43, and 50 and 5-FU 2,600 mg/m(2) as a 24-hour infusion on days 30, 37, 44, and 51; and (cycle 3) IFNalpha-2a 9 million units (MU) three times a week for 5 weeks beginning on day 57, with a continuous infusion of 5-FU 750 mg/m(2) on days 57 to 61, and then weekly bolus of 5-FU 750 mg/m(2)/wk on days 71, 78, and 85. Response was determined after cycle 3. RESULTS: All patients had a Zubrod performance status >/= 2, measurable disease, and had received no prior chemotherapy for their metastatic disease. A total of 212 cycles were given. Thirty-six patients were assessable for response. No complete responses were seen. Seven patients had a partial response, eight had stable disease, and 15 had progressive disease. The median duration of response was 25 weeks, and the median survival was 53 weeks. Grade 3 and 4 toxic effects included granulocytopenia, stomatitis, diarrhea, rash, nausea, and fatigue. CONCLUSION: This trial provided no evidence that sequential biochemical modulation of 5-FU in patients with metastatic colorectal carcinoma had any therapeutic advantage over conventional treatment regimens of 5-FU plus FA.

Phase II study of N-phosphonacetyl-L-aspartate, recombinant interferon-alpha, and fluorouracil infusion in advanced squamous cell carcinoma of the head and neck.

BACKGROUND: 5-Fluorouracil (5-FU), as a single agent, produces a 15% response rate in advanced squamous cell carcinoma of the head and neck (SCCHN). N-phosphonacetyl-L-aspartate (PALA) inhibits pyrimidine biosynthesis and increases incorporation of 5-FU metabolites into ribonucleic acid (RNA). Recombinant alpha interferon-2b (rIFN-alpha-2b) may inhibit 5-FU clearance and blunt reflex rise in thymidylate synthetase, therefore enhancing inhibition of the target enzyme of 5-FU. METHODS: In an attempt to exploit their potential therapeutic synergy, we initiated a phase II trial combining PALA 250 mg/m2 by intravenous (IV) bolus day 1 with 5-FU 2600 mg/m2 24-hour IV infusion initiated 24 hours after PALA, followed by rIFNalpha-2b 10 million units (MU) by subcutaneous injection days 2, 3, and 4 in patients with advanced, measurable SCCHN incurable with surgery or radiotherapy. Treatment was repeated weekly; patients were assessed every 4-6 weeks. Pretreatment tumor specimens were analyzed for p53 mutations in exons 5-8 and for protein expression using the p53 polyclonal antibody CM-1. RESULTS: Nineteen patients were enrolled from November 1991 through February 1994. Median age was 59 years (range, 31-72 years). All had previously received definitive radiotherapy, and all but two had undergone surgical resection. Seven patients (37%) had received prior adjuvant chemotherapy. Median time from initial diagnosis to protocol enrollment was 17 months (range, 5 months to 10 years). Median performance status (PS) was 1. Primary tumor sites included oral cavity (8 patients), larynx (7 patients), oropharynx (3 patients), and hypopharynx (1 patient). The median serum transferrin was 241 (range, 141-333). Sixteen patients (84%) had sufficient pretreatment biopsy material for p53 analysis. Patients received a median of 6 weeks of treatment (range, 2-30 weeks). Six patients (32%) in the absence of disease progression failed to finish the first 6 weeks of treatment: 3 died of pulmonary insufficiency or pneumonia and 3 were removed from study during the first 6 weeks due to toxicity. Grade 2-3 flulike symptoms occurred in 17 patients (89%); grade > or = 3 fatigue occurred in 12 patients (63%), and grade > or = 2 stomatitis occurred in 5 (26%). Gastrointestional toxicity was minimal and myelosuppression mild. Of 13 evaluable patients, there were 2 partial responses (15%) lasting 3 months and 20 months; 5 patients with stable disease lasting 2, 2, 2.5, 3, and 4.5 months; and 6 with disease progression. For all 19 patients, the overall response rate was 11%, the median survival was 6 months and 1-year survival rate 26%. Lower transferrin values (< or =241) were associated with shortened median survival 2.5 vs 11 months). Increased p53 protein expression but not p53 mutations in pretreatment specimens also predicted inferior survival (median, 6 vs 11 months) after enrollment in study (p = .0124). CONCLUSIONS: Biochemical modulation of 5-FU by rIFNalpha-2b and PALA does not enhance its efficacy in patients with advanced SCCHN whose disease has progressed after prior radiotherapy. Serum transferrin and p53 protein expression segregate outcome in this group of uniformly treated patients.

Biomodulation of Fluorouracil in colorectal cancer.

5-Fluorouracil (5-FU) remains the agent of choice for the treatment of colorectal cancer. Research has focused on the biomodulation of 5-FU in order to attempt to improve the cytotoxity and therapeutic effectiveness of this drug in the treatment of advanced colorectal cancer. Modulation of 5-FU by methotrexate (MTX), trimetrexate (TMTX), interferon-alpha (IFN-alpha), leucovorin (LV), or N-(phosphonacetyl)-L-asparte acid (PALA) has produced higher response rates than those observed with 5-FU alone. Methotrexate may improve the durability of response to or survival with 5-FU, but with inferior results compared with those in trials of 5-FU and leucovorin. Trimetrexate produces a number of responses, and further phase III trials are in progress to confirm the results of promising phase II trials with this drug. IFN-alpha has shown therapeutic efficiency when combined with 5-FU alone or with 5-FU and leucovorin, but latest studies with these combinations have shown increased toxicity. Initial single-institution phase I trials with 5-FU and PALA reported promising responses, but the latter responses with PALA were not substantiated in randomized multicenter trials. Leucovorin enhances the cytotoxic activity of 5-FU in vitro and in vivo, and several clinical trials have shown improved response rates and possible trends in improved survival when such therapy is compared with the use of 5-FU as a single-agent. More recent randomized trials have focused their attention on determining the optimal dose and schedule with this combination for producing a better clinical response with minimal toxicity. Schedules using infusional 5-FU appear to be the most active regimens when 5-FU is used as a single agent, as demonstrated by recent randomized trials. The Southwest Oncology Group (SWOG) and the Eastern Cooperative Oncology Group (ECOG) have performed separate randomized trials and have shown that the optimal regimens employ infusional 5-FU as a single agent, and that these are the least toxic regimens, perhaps more effective, and associated with a better quality of life. Future studies will focus on infusional regimens involving either short-term, high-dose protracted or long-term, low-dose protracted infusion of 5-FU, since these regimens have shown the most favorable toxicity spectrum and produced the longest survival times. Future research will also focus on the evaluation of various methods of delivery of 5-FU, including oral administration of the drug in combination with compounds that can modify its catabolism.

Effects of PALA on the pharmacokinetics of 5-fluorouracil.

N-(phosphonacetyl)-L-aspartate (PALA) modulates the activity of 5-fluorouracil (5-FU) by inhibiting pyrimidine biosynthesis. A cross-over study was conducted to determine whether PALA affects the pharmacokinetic parameters of 5-FU in patients given 5-FU/folinic acid (FA). Six patients (3 males, 3 females) aged 63 4.3 (mean SD) years (body surface area of 1.84 18 m2) with metastatic colorectal carcinoma were given two courses of treatment. The treatment consisted of 250 mg/m2 of PALA on day 1 followed by 20 mg/m2 FA and 400 mg/m2 5-FU (5 min i.v. bolus injection) on days 2-5 in one cycle of treatment (PALA+). In another treatment cycle, these doses of 5-FU and FA were given for all 5 days without PALA (PALA-). The two courses were given four weeks apart. It was determined by random selection whether the course with PALA was given before or after the course without PALA. Blood samples were collected over a period of three hours, starting from the beginning of 5-FU infusion on days 2 and 5 of both courses. Plasma concentrations of 5-FU were determined by an HPLC technique. Pharmacokinetic parameters were calculated using a non-compartmental model. While there were no significant differences between pharmacokinetic parameters in the PALA+ vs PALA- courses, there was a trend towards a decreasing area under the curve (AUC) and increasing clearance (Cl) in PALA+ courses of treatment.

Modulation of 5-fluorouracil with methotrexate and low-dose N-(phosphonacetyl)-L-aspartate (PALA) is inactive in advanced pancreatic carcinoma.

PURPOSE: To evaluate the effect of biochemical modulation by PALA and methotrexate on the therapeutic activity of 5-fluorouracil (5-FU) in patients with advanced pancreatic adenocarcinoma. PATIENTS AND METHODS: The treatment protocol consisted of phosphonacetyl-L-aspartate (PALA) 250 mg/m2 i.v. 15-minute infusion followed by methotrexate 200 mg/m2 i.v. 30-minute infusion on day 1 and 5-FU 600 mg/m2 i.v. push on day 2. Folinic acid was given at 15 mg/m2 p.o. every six hours for eight doses, starting 24 hours after methotrexate infusion. Cycles were repeated every two weeks. RESULTS: Thirty patients with advanced chemotherapynaive pancreatic cancer were included; 26 had measurable disease. Median age 56 years (27-72); median PS 1 (0-2). One PR (3.9%) was achieved; nine patients had stable disease. Median time to progression was 91 days. Median survival was 177 days and one year survival was 13.3% (4 of 30 patients). Treatment was well tolerated; diarrhea WHO grade 2 or 3 occurred in six patients; stomatitis WHO grade 2 and 3 in nine patients. CONCLUSIONS: Modulation of 5-FU by PALA and MTX given in this dose and schedule appears to be ineffective in patients with advanced pancreatic adenocarcinoma.

Phase I trial of fluorouracil modulation by N-phosphonacetyl-L-aspartate and 6-methylmercaptopurine ribonucleoside (MMPR), and leucovorin in patients with advanced cancer.

The results of several clinical trials support the hypothesis that biochemical modulation may enhance the antitumor activity of 5-Fluorouracil (5-FU). We have performed a phase I trial using a combination of three different biochemical modulators at the optimal dose established in previous clinical trials. The modulators include: phosphonacetyl-l-aspartate (PALA), which may increase 5-FU incorporation into RNA; leucovorin, which potentiates thymidylate synthase inhibition; and 6-methylmercaptopurine riboside (MMPR), which promotes the intracellular retention of fluorinated nucleotides. The treatment regimen consisted of PALA 250 mg/m2 day 1, followed 24 h later by MMPR 150 mg/m2 as an iv bolus, and the initiation of a 24-hour infusion of 5-FU along with leucovorin 50 mg/m2. This regimen was repeated weekly. Doses of 5-FU were escalated in cohorts of four or more patients from 2,000 to 2,600 mg/m2. Among 20 patients entered, the majority had colorectal cancer, and most had received prior 5-FU treatment. Toxicity was predominantly gastrointestinal, and diarrhea was dose-limiting at a 5-FU dose of 2600 mg/m2. There were three partial remissions observed, two of whom had colorectal cancer. Emerging data that casts doubt on the modulation value of PALA at this dose and schedule suggests that revision of this regimen be considered before Phase II trial.

Apoptosis induced in advanced CD8F1-murine mammary tumors by the combination of PALA, MMPR and 6AN precedes tumor regression and is preceded by ATP depletion.

The drug combination N-(phosphonacetyl)-L-aspartic acid (PALA), methylmercaptopurine riboside (MMPR) and 6-aminonicotinamide (6AN), referred to as PMA, induces regressions of advanced CD8F1 murine mammary carcinomas in vivo. We demonstrated that CD8F1 tumor regressions were preceded by the appearance of apoptotic bodies, as observed by microscopic examination of morphology and TUNEL endlabeling, and fragmentation of DNA into nucleosomal "ladder" patterns. These indications of apoptosis were present as early as 6 h after simultaneous administration of MMPR and 6AN and further increased by over fivefold during the next 3 to 6 h, then remained at 7 to 12.8% (0.6 to 2.4% in saline-treated controls) of the cell population for at least 24 h after MMPR + 6AN administration. The 5'-phosphate derivative of MMRP, MMPR-5P, which inhibits de novo purine biosynthesis, was present at a "steady-state" level, and significant (40%) depletion of ATP had occurred by 3 h and both of these events preceded the onset of apoptosis. In addition, MMPR-5P was retained in CD8F1 tumors at a high level over a prolonged period (> 96 h) even as tumors were undergoing regression. The prolonged presence of MMPR-5P was important for optimal chemotherapeutic effect, since treatment with iodotubercidin (IodoT), an inhibitor of MMPR/adenosine kinase, 6 h after MMPR+6AN administration prevented the prolonged accumulation of MMPR-5P and reversed the regression of CD8F1 tumors. In addition, compared to the PMA-treated group, there was a significant restoration of ATP levels after treatment with IodoT. In individual PMA-treated CD8F1 tumors the degree of ATP depletion was found to correlate with the degree of tumor shrinkage at 24 h, after tumors had sufficient time to respond to treatment. These results define the time-course of drug-induced apoptosis in CD8F1 tumors, show that ATP depletion occurs prior to apoptosis and demonstrate that prolonged retention of MMPR-5P is associated with optimal chemotherapy. Collectively, these results suggest that the depletion of ATP by PMA treatment may be a component of the biochemical apoptotic cascade in the CD8F1 tumor.

Chemotherapeutically induced DNA damage, ATP depletion, and the apoptotic biochemical cascade.

The biochemical death cascade of apoptosis is separate from, although induced by, the anticancer drug-target interaction. The failure of many of our chemotherapeutic agents reflects an inability of anticancer drugs to induce apoptosis. Understanding the basic cellular mechanisms that control apoptosis will greatly increase our ability to treat cancer. Identification of the components of the apoptotic biochemical cascade will present new targets for complementary enhancement of chemotherapeutically induced cancer cell death. One factor that has been directly implicated in apoptosis is adenosine triphosphate (ATP). Nevertheless, in this regard, ATP is controversial. This commentary takes issue with dogma, and points to the need for additional thought and research in this field. ATP-depleting therapy of tumor-bearing mice has been shown to induce a marked therapeutic result with minimal mortality, and this effect can be further enhanced when combined with chemotherapy. The definitive mechanism of action is still controversial, although several mechanisms for ATP depletion have been implicated in the process. These include reduction in the mitochondrial transmembrane potential, activation of poly (ADP-ribose) polymerase (PARP) and depletion of the coenzyme nicotinamide adenine dinucleotide (NAD+). Even though the definitive experiments have yet to be carried out, the identification of ATP depletion as a critical determinant in apoptosis should allow for the development of new therapeutic strategies in the treatment of human cancer.

Modulation of 5-fluorouracil with methotrexate and low-dose N-(phosphonacetyl)-L-aspartate in patients with advanced colorectal cancer. Results of a phase II study.

Methotrexate (MTX) and N-phosphonacetyl-L-aspartate acid (PALA) have been shown to modulate the cytotoxic effects of 5-fluorouracil (5-FU). A phase II study was initiated to evaluate the feasibility, toxicity and efficacy of PALA/MTX and 5-FU in patients with metastatic colorectal cancer. 26 patients received PALA 250 mg/m2 as an intravenous 15-min infusion plus MTX 200 mg/m2 as a 30-min intravenous (i.v.) infusion on day 1 and 5-FU 600 mg/m2 as i.v. push on day 2. Cycles were repeated every 14 days and the 5-FU dose was escalated in the individual patient in steps of 100 mg/m2 for the third, fifth and seventh cycle in the absence of toxicity. 7 patients had received prior 5-FU-based chemotherapy while 19 patients were chemotherapy naive. Objective responses occurred in 23% of patients (1 CR, 5 PR of which 2 were pretreated), no change in 13 patients (50%) and tumour progression (6 patients) or toxic death (one patient) in 27%. Responses lasted for a median of 7 months (range 6-9), the median time to progression was 4 months and median survival 13 months. Toxicity was mainly gastrointestinal with diarrhoea and mucositis, and severe or life threatening in only 3 patients. In 3 patients an increase in serum glucose levels occurred while being treated with PALA/MTX and 5-FU. 2 patients with insulin-dependent diabetes had a 33% increase in insulin requirement and 1 patient with dietary-controlled diabetes died due to a ketoacidotic coma. PALA/MTX/5-FU in this dose and schedule is active in patients with colorectal cancer. Hyperglycaemia may be a potential side-effect of PALA-containing regimens especially in patients with diabetes. Careful monitoring of serum glucose levels in these patients is indicated.