Daniel S. Martin

Combination clinical trials with thymidine and fluorouracil: A phase I and clinical pharmacologic evaluation

Phase I observations of combined therapy with thymidine (TdR) and 5‐fluorouracil (FU) have demonstrated that when TdR is administered by rapid infusion at a dose of 7.5 or 15g and FU is given by bolus injection 60 minutes after the start of the TdR dose, the biologic activity of FU is increased five‐ to eight‐fold. The observed toxicity is primarily hematopoietic: 15g TdR and 7.5 or 10mg/kg FU produced median white blood count nadirs of 2,600 on day 16 and platelet count nadirs of 150,000 on day 14. The combined therapy produced two partial remissions in 18 patients with colon cancer, 17 of which had experienced progression of disease on FU containing regimens. Partial remissions were also obtained in two heavily pretreated patients with ovarian cancer and diffuse, poorly differentiated lymphocytic lymphoma. Plasma analyses for TdR and FU and their metabolic products by high pressure liquid chromatography have demonstrated a marked elevation and prolongation of FU levels. The β phase T1/2 for 7.5mg/kg FU were: FU alone 6 minutes, 7.5g TdR + FU 135 minutes, 15g TdR + FU 188 minutes, and TdR 45g + FU 190 minutes. The addition of TdR all but eliminated oxidative metabolism of FU; renal clearance became the primary detoxification route. Thymidine levels exceeded 10−3M; the β phase T1/2 of TdR varied with the administered dose: 3g TdR, 7 minutes; 7.5g TdR, 24 minutes; 15g TdR, 52 minutes; and 45g TdR, 98 minutes.

Use of oral uridine as a substitute for parenteral uridine rescue of 5-fluorouracil therapy, with and without the uridine phosphorylase inhibitor 5-benzylacyclouridine

SummaryInitial clinical trials have demonstrated that uridine (Urd) rescue given i.v. over at least 3 days can ameliorate 5-fluorouracil (FUra) toxicity; to avoid Urd-induced phlebitis in the peripheral veins of patients, a central vein is used. The latter necessity, along with the need for 3 days of i.v. administration, makes Urd rescue by parenteral means a cumbersome and complicated clinical procedure. It would appear preferable to use oral Urd; however, the oral Urd dose in the clinic is limited, as high doses cause diarrhea. Therefore, using a tumor-bearing murine model we investigated as to whether low doses of oral Urd coupled with a Urd phosphorylase inhibitor benzylacyclouridine (BAU), would effect safe rescue of FUra toxicity with preservation of antitumor activity. A high-dose FUra-containing drug combination that included parenteral Urd rescue was used as a control; other groups of tumor-bearing mice received the same drug combination, except that p.o. Urd was substituted for i.p. Urd. In the absence of BAU, p.o. Urd could effect rescue while maintaining an antitumor effect comparable to that obtained with i.p. Urd. When given concomitantly with BAU, a 50% reduction in the oral Urd dose (i.e., from 4,000 to 2,000 mg/kg) enabled the achievement of a comparable therapeutic index. Intraperitoneal Urd produces very high (6–8 mM) plasma and tissue Urd levels, which remain above 100 μM for at least 6 h. In contrast, neither oral Urd nor oral BAU alone raised plasma Urd concentrations above about 50 μM. However, the combination of oral Urd plus oral BAU gave a peak plasma Urd level of about 300 μM, and the level was maintained above 100 μM for 6 h. Following oral Urd administration, gut tissue levels of Urd were in the mM range and those of BAU were in the range of 10–20 μg/g tissue, a level sufficient to result in substantial inhibition of Urd phosphorylase. Oral Urd plus oral BAU appears to be a promising clinical alternative to parenteral administration of Urd for selective rescue of FUra toxicity.

Biochemical modulation of 5-fluorouracil with leucovorin or delayed uridine rescue. Correlation of antitumor activity with dosage and FUra incorporation into RNA.

Two strategies for modulation of 5-fluorouracil (FUra) activity were compared in vivo in advanced murine CD8F1 breast tumors with regard to three parameters: chemotherapeutic activity, inhibition of thymidylate synthase (TSase) activity, and incorporation of FUra into RNA, (FU)RNA. Inhibition of TSase by FUra was modulated by leucovorin (LV), and the incorporation of FUra into RNA was increased by the administration of otherwise lethal doses of FUra followed by uridine rescue. Thymidylate synthase activity was inhibited substantially (49%) by low-dose FUra at 25 mg/kg, but was not further enhanced (48%) by repeated daily treatments at the same dose (FUra25 x 4). Inhibition of TSase was somewhat enhanced (55%) by the addition of LV to FUra25 x 4, and a greater therapeutic effect was obtained with FUra25 x 4 + LV over FUra25 x 4 alone. FUra as a single agent at the maximum tolerated weekly dose of 100 mg/kg inhibited TSase activity 66-73%. This inhibition was further enhanced slightly by the addition of LV (71-82%), and its therapeutic efficacy was greater than with FUra25 x 4 with or without LV. However, in contrast to low dose FUra25 x 4, the antitumor effect of FUra100 was not enhanced by LV. (FU)RNA increased with FUra dose from 0.4 (FUra25) to 2.2 nmol/mg DNA (FUra100). At a very-high-dose of FUra (200-225 mg/kg) followed by uridine rescue, TSase inhibition was not further enhanced, but both (FU)RNA (4.8 nmol/mg DNA) and the therapeutic efficacy were increased. Since TSase could not be further inhibited at doses above FUra100, the increased chemotherapeutic efficacy correlated with increased (FU)RNA.

Biochemical Modulation of Tumor Cell Energy in Vivo: II. A Lower Dose of Adriamycin is Required and a Greater Antitumor Activity is Induced when Cellular Energy is Depressed

A quadruple drug combination--consisting of a triple-drug combination of N-(phosphonacetyl)-L-aspartate (PALA) + 6-methylmercaptopurine riboside (MMPR) + 6-amino-nicotinamide (6-AN), designed to primarily deplete cellular energy in tumor cells, + Adriamycin (Adria)--yielded significantly enhanced anticancer activity (i.e., tumor regressions) over that produced by either Adria alone at maximum tolerated dose (MTD) or by the triple-drug combination, against large, spontaneous, autochthonous murine breast tumors. The adenosine triphosphate (ATP)-depleting triple-drug combination administered prior to Adria resulted in a 100% tumor regression rate (12% complete regression; 88% partial regression) of spontaneous tumors. Histological examination of treated tumors demonstrated that the treatment-induced mechanism of cancer cell death was by apoptosis. The augmented therapeutic results (100% tumor regressions) were obtained with approximately one-half the MTD of Adria as a single agent and suggest the potential clinical benefit of longer, more effective, and safer treatment by low doses of Adria when combined with the triple-drug combination. Two likely mechanisms of action are discussed: (1) prevention of DNA repair; (2) complementary disruption of biochemical pathways by both the triple-drug combination and the biochemical cascade of apoptosis that is induced by a DNA-damaging anticancer agents such as Adria.

Perspective: The Chemotherapeutic Relevance of Apoptosis and a Proposed Biochemical Cascade for Chemotherapeutically Induced Apoptosis

Cancer cells that are sufficiently damaged by cancer chemotherapeutic agents (as well as radiotherapy) eventually die in an ordered sequential biochemical process known as apoptosis. Apoptosis is a general physiological mechanism for controlled cell deletion that is an active (i.e., an energy-dependent, at least initially), inherent (gene-directed) program of cell death, and therefore sometimes referred to as cell suicide and programmed cell death (1,2). The apoptotic biochemical events occurring after the anticancer agents interaction with its biochemical target is the actual process of cell death and is a secondary phenomenon following the primary drug-target interaction. Thus, anticancer agents, despite having different primary biochemical targets (e.g., inhibition of thymidylate synthase, microtubule damage, topoisomerase inhibitors, DNA crosslinking agents, etc.), all ultimately kill by inducing the biochemical cascade of apoptosis (3,4). However, there is a “qualitative” and “quantitative” heteroge...

Biochemical modulation of bolus fluorouracil by PALA in patients with advanced colorectal cancer.

PURPOSEnN-(phosphonacetyl)-L-aspartic acid (PALA) is a pyrimidine synthesis inhibitor that modulates fluorouracil (FU) cytotoxicity. Two previous studies of patients with colorectal carcinoma documented complete response (CR) and partial response (PR) rates of 40% and 43% using weekly low-dose PALA followed by a 24-hour FU infusion. We investigated whether comparable results could be obtained with biochemical modulation by low-dose PALA using bolus instead of infusional FU.nnnPATIENTS AND METHODSnForty-five patients without prior chemotherapy who had advanced colorectal carcinoma were treated with PALA 250 mg/m2 followed 24 hours later by bolus FU at three dose levels, 600, 700, 800 mg/m2, repeated weekly for 6 weeks followed by a 2-week break.nnnRESULTSnThe CR and PR rate was 15 of 43 patients or 35% (95% confidence interval [CI], 21% to 49%), with an overall median survival of 18 months. Grade 3 or 4 diarrhea was the major toxicity observed in 24% of patients receiving FU at 700 mg/m2 and in 43% of patients receiving 800 mg/m2. Hematologic toxicity was observed only with an FU dose of 800 mg/m2, and 29% (four of 14) of patients developed grade 4 leukopenia. We also noted the development of ascites in six patients, mild hyperbilirubinemia in 16 patients, and a decreased albumin level in 22 patients; these abnormalities occurred more frequently in responding patients.nnnCONCLUSIONSnThe observed response rate, median survival, and toxicity in this study are similar to those obtained with PALA plus infusional FU and with other methods of FU modulation. Larger phase III studies are needed to compare bolus FU/PALA regimens with other PALA and non-PALA-containing combinations. Our future focus will be attenuate this regimens toxicity while maintaining or improving its response rates and survival.

Loss of murine tumor thymidine kinase activity in vivo following 5-fluorouracil (FUra) treatment by incorporation of FUra into RNA

The effects of 5-fluorouracil (FUra) treatment on thymidine kinase (TKase) activity were examined in vivo in CD8F1 mice bearing first generation CD8F1 mouse mammary tumors. TKase activity was not affected by low dose FUra25 (25 mg/kg), a dose which substantially inhibited thymidylate synthase (TSase), but was severely inhibited 24 hr following treatment with FUra100, a weekly maximally tolerated dose, as judged by activity measurements and labeling of DNA with [3H]thymidine. The amount of (FU)RNA was increased markedly with increasing FUra dose from 0.4 nmol/mg DNA at FUra25 to 2.2 nmol/mg DNA at FUra100. At FUra100, TKase activity gradually declined over 24 hr to less than 10% of the control value, remained low for a further 48 hr, and then was gradually restored to control levels by 168 hr. The loss of TKase activity followed the incorporation of FUra into RNA which peaked at 4-5 hr. TKase activity was not restored by removal of endogenous inhibitors but was restored by treatment with uridine. TKase activity was not inhibited by therapeutic levels of methotrexate (300 mg/kg). TKase from murine colon 38 carcinoma was also severely inhibited, but the activity from colon 26 was only partially (50%) inhibited. Ornithine decarboxylase was also inhibited by FUra100 treatment in the CD8F1 tumor. These results demonstrate that certain short-lived, proliferation-related enzymes are affected by FUra doses higher than those required for TSase inhibition, and this effect appears to correlate with incorporation of FUra into RNA. Thus, in some tumors high doses of FUra can inhibit salvage as well as de novo synthesis of thymidylate providing an increased block of DNA synthesis and increased therapeutic advantage.

Status of methylthioadenosine phosphorylase and its impact on cellular response to L-alanosine and methylmercaptopurine riboside in human soft tissue sarcoma cells.

The aim of this study was to examine the expression of methylthioadenosine phosphorylase (MTAP) in 21 fresh tumor samples from patients with soft tissue sarcomas (STS) and 11 human soft tissue sarcoma cell lines, and to determine if loss of expression of this enzyme was correlated with increased sensitivity to L-alanosine and/or 6-methylmercaptopurine. We used a polyclonal antibody to measure the expression of MTAP in soft tissue sarcoma cell lines and in fresh tumor samples. Transfection of the HT-1080 cell line with a plasmid containing the cDNA for the MTAP gene was also performed to generate cell lines for in vitro and in vivo comparative sensitivity studies. MTAP was not expressed in 8 of 21 fresh STS tumors. The expression of MTAP was also not detectable in 3 of the 11 soft tissue sarcoma cell lines (HT-1080, HS42, and M-9 110). These three cell lines were more sensitive to L-alanosine, a potent inhibitor of de novo AMP synthesis, and to an inhibitor of de novo purine nucleotide synthesis, 6-methylmercaptopurine riboside (MMPR). The IC50 values for L-alanosine and MMPR were >20-fold lower in MTAP-deficient cells than in MTAP-positive cells. Restoration of MTAP into HT-1080 MTAP-deficient cells also led to decreased sensitivity to L-alanosine and MMPR. An in vivo study using HT-1080 cell tumors with and without MTAP expression confirmed that tumors lacking MTAP were more sensitive to L-alanosine than tumors expressing MTAP. These results provide the basis for selective therapy using inhibitors of de novo purine nucleotide synthesis such as L-alanosine or MMPR to treat patients with STS lacking this enzyme.

Biochemical modulation of tumor cell energy IV: Evidence for the contribution of adenosine triphosphate (ATP) depletion to chemotherapeutically-induced tumor regression

DNA-damaging agents, e.g. Adriamycin (ADR), are reported to cause tumor regression by induction of apoptosis. A reduction in the intracellular content of ATP is part of the biochemical cascade of events that ultimately results in programmed death of the cell, or apoptosis. A chemotherapeutic three-drug combination (PMA) consisting of N-(phosphonacetyl)-L-aspartate (PALA) + 6-methylmercaptopurine riboside (MMPR) + 6-aminonicotinamide (6AN) significantly lowers levels of ATP in CD8F1 murine breast tumors in vivo and produces tumor regression by apoptosis. Addition of the DNA-damaging antitumor agent ADR to PMA was found to further significantly deplete ATP in CD8F1 murine breast tumors in vivo with a concomitant significant increase in the number of tumor regressions. The correlative biochemical and therapeutic results are consistent with, and support, the hypothesis that ATP depletion is a significant factor and, therefore, is a worthy therapeutic target in the production of apoptosis.

A New Syndrome: Ascites, Hyperbilirubinemia, and Hypoalbuminemia after Biochemical Modulation of Fluorouracil with N-Phosphonacetyl-L-Aspartate (PALA)

OBJECTIVEnTo report a new syndrome of ascites, hyperbilirubinemia, and hypoalbuminemia after treatment with N-phosphonacetyl-L-aspartate (PALA) and fluorouracil for metastatic colorectal cancer.nnnDESIGNnRetrospective analysis.nnnSETTINGnRegional cancer treatment center.nnnPATIENTSnForty-four previously untreated patients with metastatic colorectal cancer in a phase I-II trial of PALA-fluorouracil.nnnMEASUREMENTS AND MAIN RESULTSnOne or more transient hepatic abnormalities frequently occurred in 15 of the 17 responding patients. Within the first 10 weeks of treatment, 5 patients developed ascites, 12 had a decrease in the serum albumin level, 6 developed bilirubin elevations, and 7 had transaminase elevations, all in the presence of a complete or partial tumor response. Prolongations of the prothrombin time and elevations of serum glucose levels were also seen.nnnCONCLUSIONSnAn unusual syndrome of ascites, hyperbilirubinemia, and hypoalbuminemia is associated with a PALA-fluorouracil regimen. These abnormalities, which may be related to decreased hepatic protein synthesis, occurred more often in patients whose tumor was responding to chemotherapy. Clinicians must recognize that in patients undergoing chemotherapy with these agents, ascites and elevated liver function tests may be secondary to drug administration and are not necessarily due to disease progression.