Multimodal biochemical modulation of 5-fluorouracil activity in advanced colorectal cancer with allopurinol, folinic acid and dipyridamol

Leucovorin + 5-Fluorouracil plus Dipyridamole in Leucovorin + 5-Fluorouracil-Pretreated Patients with Advanced Colorectal Cancer: A Pilot Study of Three Different Dipyridamole Regimens

Dipyridamole, an inhibitor of nucleoside transport, increases the activity of 5-fluorouracil in a dose-dependent manner. The purpose of the present study was to determine whether dipyridamole with 5-fluorouracil and leucovorin gave an improved therapeutic outcome. Sixty patients entered in the present pilot study had previously received 5-fluorouracil (450 mg/m2) and leucovorin (100 mg/m2), every week, and relapsed during this treatment, which ended at least 6 weeks prior to study entry. Dipyridamole was administered at three different dosing schedules (DS) and methods of administration in three groups of patients. DS I: dipyridamole, 30 mg/m2 in normal saline solution, in 90 min iv infusion, followed by leucovorin, 100 mg/m2 iv push, followed by 5-fluorouracil, 450 mg/m2 in normal saline solution, in 60 min iv infusion, dipyridamole tablets (75 mg) every 12 hrs, continuously during the time of chemotherapy. DS II: dipyridamole, 50 mg/m2 in normal saline solution, in 90 min iv infusion, and the rest was the same as DS I. DS III: without oral dipyridamole, patients received dipyridamole (50 mg/m2) iv in the same manner as in DS I and II. Treatment was continued until tumor progression or unacceptable toxicity. All patients (n = 60) entered in the present study were assessable for response and toxicity. No complete response was observed. No patient at DS I responded, whereas 2 patients at DS II and 3 at DS III had a partial response (P <0.1). Stable disease was found with DS I (n = 1), DS II (n = 8) and DS III (n = 9) (P <0.01). More patients progressed at DS I (n = 19) than at DS II (n = 10) and DS III (n = 8) (P <0.0007). The median duration of response was 11 weeks (range, 8-16). Time to progression was 17 weeks for DS I, 15 weeks (range, 10-19) for DS II, and 14 weeks (range, 11-21) for DS III (P = 0.43). Median survival did not differ significantly between DS I (29 weeks; range, 14-48), DS II (31.5 weeks; range, 17-63) and DS III (36 weeks; range, 16-58) (P = 0.2). Neutropenia was most severe with DS I (grade 2, P <0.01) and DS II (grade 1, P <0.05) and nausea/vomiting with DS I (grade 0, P < 0.0005, grade 1, P <0.0002, grade 2, P <0.02) and DS III (grade 3, P <0.0009). Diarrhea was most severe in DS II (grade 3, P <0.005). Mucositis was increased in DS II (grade 0, P <0.008), anorexia in DS II (grade 0, P <0.032) and fatigue in DS I (grade 0, P <0.003). More patients in DS I than with the other two DS experienced headache (P <0.044). According to the response achieved at DS III (15% partial response and 45% stable disease) and the toxicity which was well tolerated mainly in this DS (except for nausea and vomiting grade 3, P <0.009), it can be stated that DS III is the appropriate dose and the simplest schedule of administration (administration of dipyridamole during therapy only). In conclusion, it appears that dipyridamole might still have a role in enhancing the clinical activity of drugs involved in the inhibition of the thymidylate synthetase biochemical pathway and its activity in combination with these agents (5-fluorouracil + leucovorin) as frontline treatment should therefore be explored in future phase II studies.

Inhibition of metastases by anticoagulants

Metastasis involves several distinct steps, including one in which the tumor cell, after entry into the bloodstream, comes to rest in a capillary located at the distant site where a metastatic tumor will ultimately form. Components of the blood-clotting pathway may contribute to metastasis by trapping cells in capillaries or by facilitating adherence of cells to capillary walls. Conceivably, anticoagulants could interfere with this step in the metastatic process. In this review, we have summarized current knowledge on the interaction of malignant cells, clotting factors, and anticoagulants. We used computerized (MEDLINE) and manual searches to identify studies done in humans, in animals, and in in vitro systems that were published in English between 1952 and 1998. We found many reports that the formation of metastatic tumors could be inhibited by heparin, a vitamin K antagonist (warfarin), and inhibitors of platelet aggregation (prostacyclin and dipyridamole). Despite these encouraging preliminary results and a compelling biochemical rationale, only limited information exists on the clinical use of anticoagulants for the prevention or treatment of metastatic cancer because there have been so few controlled and prospectively randomized studies on this topic. In view of the preliminary results, anticoagulants may hold promise for the prevention and treatment of metastases. We believe that larger controlled investigations are strongly warranted to evaluate the clinical potential of anticoagulants for the prevention and treatment of metastases in humans.

Tumor resistance to antimetabolites

1. The inherent or acquired resistance of certain tumors to cytotoxic drug therapy is a major clinical problem. 2. Resistance to the chemotherapeutic antimetabolites (e.g., methotrexate, 5-fluorouracil, tomudex and gemcitabine) is no exception. 3. Mechanisms of resistance include mutations, amplification of target genes, altered drug transport, differences in nucleoside and nucleobase salvage pathways, DNA damage-response pathways and cell cycle control pathways.

Resistance to chemotherapeutic antimetabolites: a function of salvage pathway involvement and cellular response to DNA damage

The inherent or acquired (induced) resistance of certain tumours to cytotoxic drug therapy is a major clinical problem. There are many categories of cytotoxic agent: the antimetabolites, e.g. methotrexate (MTX), N-phosphonacetyl-L-aspartate (PALA), 5-fluorouracil (5-FU), 6-mercaptopurine (6-TG), hydroxyurea (HU) and 1-beta-D-arabinofuranosylcytosine (AraC); the alkylating agents, e.g. the nitrogen mustards and nitrosoureas; the antibiotics, e.g. doxorubicin and mitomycin C; the plant alkaloids, e.g. vincristine and vinblastine; and miscellaneous compounds, such as cisplatin. There are also many mechanisms of drug resistance elucidated principally from in vitro studies. These include mutation of target genes, amplification of target and mutated genes, differences in repair capacity, altered drug transport and differences in nucleoside and nucleobase salvage pathways (Fox et al, 1991). The aim of the present review is to evaluate in detail the mechanisms of response of both normal and tumour cells to three chemotherapeutic antimetabolites, MTX, PALA and 5-FU, which are routinely used in the clinic either alone or in combination to treat some of the commonest solid tumours, e.g. breast, colon, gastric and head and neck. The normal and tumour cell response to these agents will be discussed in relation to the operation of the known alternative 'salvage pathways' of DNA synthesis and current theories of DNA damage response.

Nucleoside transport in normal and neoplastic cells

The permeation of nucleosides across the plasma membrane of mammalian cells is complex and mediated by at least five distinct transporters that differ in their sensitivity to inhibitors and in their specificity for nucleosides. The basic properties and permeant specificity of these transporters are summarized in Table 3. It appears that there may be differences in the distribution of these transporters in tumors and normal tissues that might be exploited for chemotherapeutic purposes. The human tumor cell lines examined express predominantly the NBMPR-sensitive equilibrative transporter es which can be blocked by low concentrations of NBMPR and dipyridamole. It is reasonable to expect that tumors with transport properties similar to the CCRF-CEM and Rh28 cell lines (Table 1) that have no detectable NBMPR-insensitive transport activity will be highly susceptible to the therapeutic approach of combining a transport inhibitor such as dipyridamole or NBMPR with an inhibitor of de novo pyrimidine biosynthesis. On the other hand, this approach to therapy is unlikely to succeed against tumors with transport phenotypes similar to the WI-L2 cell line that may permit the salvage nucleosides in the presence of these inhibitors. The majority of tumor cells examined, however, fall between these extremes, and it is not yet known what level of NBMPR-insensitive transport activity can be tolerated without seriously compromising this therapeutic approach. With respect to normal tissues, the mature absorptive cells of the intestine have predominantly Na(+)-dependent nucleoside transporters that are insensitive to NBMPR and dipyridamole. The proliferating crypt cells also appear to have Na(+)-dependent nucleoside transport, although they may also have an NBMPR-sensitive component of transport (Belt, unpublished data). Bone marrow granulocyte-macrophage progenitor cells also appear to have one or more concentrative nucleoside transporters. Thus these tissues, which are most vulnerable to the toxicity of antimetabolites, may be able to salvage nucleosides in the presence of inhibitors of equilibrative transport and be protected from the toxicity of de novo synthesis inhibitors. It is likely, however, that a successful application of this therapeutic approach will require the analysis of the nucleoside transport phenotype of individual tumors in order to identify those patients that may benefit from such therapy. Since the development of antibodies and cDNA probes for the various nucleoside transporters is currently underway in several laboratories, it is likely that analysis of the nucleoside transport phenotype of tumors from biopsy material will be feasible in the future.

Factors that influence the therapeutic activity of 5-fluorouracil [6RS]leucovorin combinations in colon adenocarcinoma xenografts

The therapeutic activity of FUra alone or combined with [6RS]LV doses ranging from 50 to 1,000 mg/m2 was examined in eight colon adenocarcinoma xenografts, of which five were established from adult neoplasms (HxELC2, HxGC3, HxVRC5, HxHC1, and HxGC3/c1TK-c3 selected for TK deficiency) and three were derived from adolescent tumors (HxSJC3A, HxSJC3B, and HxSJC2). The growth-inhibitory effects of FUra were potentiated by higher doses of [6RS]LV (500-1,000 mg/m2) in three lines (HxGC3/c1TK-c3, HxSJC3A, and HxSJC3B) and by a low dose of [6RS]LV in only one tumor (HxVRC5). Expansion of pools of CH2-H4PteGlun+H4PteGlun (greater than or equal to 2.4-fold) in response to higher doses of [6RS]LV was obtained in all lines except HxHC1. Metabolism of [6RS]LV was high in HxVRC5, with high levels of 5-CH3-H4PteGlu being detected, but not in HxHC1, in which levels of 5-CH3-H4PteGlu and CH = H4PteGlu+10-CHO-H4PteGlu remained relatively low. In the adolescent tumors, levels of CH = H4PteGlu+10-CHO-H4PteGlu were consistently higher than those of 5-CH3-H4PteGlu following [6RS]LV administration, and in HxSJC3A, in which pools of CH2-H4PteGlun+H4PteGlun were significantly expanded, 5-CH3-H4PteGlu concentrations were lower than those observed in the other two lines. The sensitivity of tumors to FUra +/- [6RS]LV and the characteristics of [6S]LV metabolism did not correlate with the activity of CH = H4PteGlu synthetase, the enzyme responsible for the initial cellular metabolism of [6S]LV to CH = H4PteGlu. Thus, no single metabolic phenotype correlated with the [6RS]LV-induced expansion of CH2-H4PteGlun+H4PteGlun pools. Potentiation of the therapeutic efficacy of FUra by [6RS]LV was observed in HxGC3/c1TK-c3 xenografts but not in parent HxGC3 tumors, demonstrating the influence of dThd salvage capability in the response to FUra-[6RS]LV combinations. Plasma dThd concentrations in CBA/CaJ mice were high (1.1 microM). The present data therefore demonstrate the importance of (1) higher doses of [6RS]LV, (2) expansion of pools of CH2-H4PteGlun+H4PteGlun, and (3) dThd salvage capability in potentiation of the therapeutic efficacy of FUra in colon adenocarcinoma xenografts. The plasma levels of FUra achieved in mice are presented.