Biomedical subjects

Y M Rustum

Publications and source records attributed to Y M Rustum.

At least 37 records · Page 2Linked to original sources

PubMed1999

Characterisation of a synergistic interaction between a thymidylate synthase inhibitor, ZD1694, and a novel lipophilic topoisomerase I inhibitor karenitecin, BNP1100: mechanisms and clinical implications.

We developed a combination protocol for inhibitors of thymidylate synthase (TS) and DNA topoisomerase I (Topo I) that can exert highly lethal effects in vitro against HCT-8 human colorectal cancer cells. The specific schedule was constructed so that a TS inhibitor could induce not only primary DNA damage but also cellular conditions optimal for the efficient action of a Topo I inhibitor. The initial drug treatment consisted of a brief exposure to a quinazoline-based antifolate, ZD1694. After an interval of approximately one cell-doubling time, cells were exposed for 8-24 h to BNP1100, a Karenitecin-class 7-thiomethyl-camptothecin, in the presence of 1-10 microM thymidine; the latter acted as a crucial factor to promote the collision of moving replication forks with the drug-stabilised DNA-Topo I cleavable complexes even under continuous TS inhibition. Clonogenic analyses confirmed that these mechanistically distinct drugs at clinically achievable concentrations worked in a highly synergistic manner, with a maximum effect abolishing the viability of virtually all cancer cells (> 99.9%). The pretreatment with ZD1694 increased the amount of DNA-bound Topo I by up to 4-fold and the DNA-damaging capability of BNP1100 by up to 15-fold. The possibility of at least four DNA-damaging pathways is proposed which might have resulted from the individual actions of TS and Topo I inhibitors as well as their concerted actions. Taken together, the present findings provided a logically permissible explanation as to why TS and Topo I inhibitors in concerted interactions induced a highly lethal effect which was more than a simple additive effect. Since these drugs are effective specifically on actively proliferating cancer cells, but not on non-cycling G0/G1 cells, this mechanism-based protocol may warrant consideration for clinical verification.

Antimetabolites, Antineoplastic↗

PubMed1999

Reversal of MDR1-associated resistance to topotecan by PAK-200S, a new dihydropyridine analogue, in human cancer cell lines.

Recent data suggest that expression of the membrane P170-glycoprotein (P-gp) may confer resistance to the topoisomerase-I-interactive agent topotecan. The present study describes the cellular effects of a new dihydropyridine analogue, PAK-200S, on P-gp-mediated resistance to topotecan in human breast and ovarian tumour cells. PAK-200S at a non-cytotoxic concentration of 2.0 microM completely reversed resistance to topotecan in P-gp-expressing MCF-7/adr (breast) and A2780/Dx5 (ovarian) tumour cells, respectively, with no effects on parental cells. Cellular pharmacokinetic studies by reversed-phase high-performance liquid chromatography analysis showed significantly lower cellular drug concentrations of the pharmacologically active closed-ring lactone of topotecan in multidrug-resistant cells than in parental cells. PAK-200S was effective in restoring the cellular lactone concentrations of topotecan in resistant MCF-7/adr cells to levels comparable to those obtained in parental cells. Furthermore, exposure of MCF-7/adr cells to topotecan in the presence of PAK-200S significantly increased the induction of protein-linked DNA breaks. PAK-200S did not alter nuclear topoisomerase I-mediated ex vivo pBR322 DNA plasmid unwinding activity and topoisomerase-I protein expression. These results suggest that reversal of P-gp-mediated resistance to topotecan by PAK-200S was related to the restoration of cellular drug concentrations of the active lactone form of topotecan rather than a direct effect on topoisomerase-I function.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1999

Phase I study of a weekly schedule of irinotecan, high-dose leucovorin, and infusional fluorouracil as first-line chemotherapy in patients with advanced colorectal cancer.

PURPOSE: To determine the maximum-tolerated dose (MTD) of a weekly schedule of irinotecan (CPT-11), leucovorin (LV), and a 24-hour infusion of fluorouracil (5-FU24h) as first-line chemotherapy in advanced colorectal cancer and to assess preliminary data on the antitumor activity. PATIENTS AND METHODS: Twenty-six patients with measurable metastatic colorectal cancer were entered onto this phase I study. In the first six dose levels, fixed doses of CPT-11 (80 mg/m2) and LV (500 mg/m2) in combination with escalated doses of 5-FU24h ranging from 1.8 to 2.6 g/m2 were administered on a weekly-times-four (dose levels 1 to 4) or weekly-times-six (dose levels 5 to 6) schedule. The dose of CPT-11 was then increased to 100 mg/m2 (dose level 7). RESULTS: Seventy-nine cycles of 5-FU24h/LV with CPT-11 were administered in an outpatient setting. No dose-limiting toxicities were observed during the first cycle at dose levels 1 to 6, but diarrhea of grade 4 (National Cancer Institute common toxicity criteria) was observed in three patients after multiple treatment cycles. Other nonhematologic and hematologic side effects, specifically alopecia and neutropenia, did not exceed grade 2. With the escalation of CPT-11 to 100 mg/m2 (dose level 7), diarrhea of grade 3 or higher was observed in four of six patients during the first cycle; thus, the MTD was achieved. Sixteen of 25 response-assessable patients (64%; 95% confidence interval, 45% to 83%) achieved an objective response. CONCLUSION: The recommended doses for further studies are CPT-11 80 mg/m2, LV 500 mg/m2, and 5-FU24h 2.6 g/m2 given on a weekly-times-six schedule followed by a 1-week rest period. The addition of CPT-11 to 5-FU24h/LV seems to improve the therapeutic efficacy in terms of tumor response with manageable toxicity.

Adolescent↗

PubMed1999

Persistent induction of apoptosis and suppression of mitosis as the basis for curative therapy with S-1, an oral 5-fluorouracil prodrug in a colorectal tumor model.

In an effort to improve the therapeutic selectivity of 5-fluorouracil (FUra) against colorectal cancer, S-1, a combination agent including a prodrug of FUra with two modulators, was recently developed by Taiho Pharmaceuticals Co. S-1 is a combination of tegafur (FT), 5-chloro-2,4-hydroxypyridine, and potassium oxonate in the molar ratio of 1.0:0.4:1.0, with the latter two components as inhibitors of dihydropyrimidine dehydrogenase and phosphoribosylpyrophosphate transferase, respectively. In this study, the therapeutic selectivity and efficacy of S-1 (oral) was compared with FT (oral) and FUra (i.v. infusion) in rats bearing advanced colorectal cancer by using clinically relevant schedules. The maximum tolerated doses (MTDs) of S-1, FT, and FUra were 31.5, 200, and 25 mg/kg/d for 7 days and 22.5, 150, and 12.5 mg/kg/d for 28 days, respectively. The therapeutic index of S-1 was 4- to 5-fold higher than that of either FT or FUra. S-1 achieved 100% complete tumor regression (CR) at its MTD in both 7-day and 28-day schedules. Furthermore, the high incidences of stomatitis, alopecia, and diarrhea observed with FUra and FT, were not observed with S-1. In an attempt to understand the basis for the observed superior therapeutic selectivity with S-1, we studied pharmacokinetic analysis of FUra, drug-induced apoptosis, suppression of mitosis, and inhibition of thymidylate synthase (TS) after S-1, FUra, or FT administration. The peak plasma FUra concentrations derived from FUra or S-1 (FT) at comparable MTDs were similar, but the plasma level of FUra was higher with S-1 than with FUra. Induction of high and sustained apoptosis was achieved with S-1. Although the initial level of apoptosis induced by FUra was comparable to S-1, it was not sustained. The sustained level of apoptosis appears to correlate with tumor growth inhibition. Mitotic figures were more greatly suppressed with S-1 treatment than with FUra. Studies on TS inhibition indicated that, although both S-1 and FUra caused a 4- to 6-fold induction of total TS protein, single oral administration of S-1 was superior to 24-h infusion of FUra in suppressing free TS. The data are consistent with the observation that the therapeutic efficacy of S-1 (100% cure) over FUra is associated with high and sustained levels of drug-induced apoptosis, greater suppression of mitosis, and inhibition of free TS in tumor tissues.

Animals↗

PubMed1999

Antitumor activity of ZD1694 (tomudex) against human head and neck cancer in nude mouse models: role of dosing schedule and plasma thymidine.

We studied the antitumor activity and toxicity of ZD1694 (tomudex), a specific inhibitor of thymidylate synthase (TS), in nude mice bearing human head and neck squamous cell carcinoma A253 and FaDu xenografts. Mice were treated by single i.v. push (i.v. x 1), i.v. push once a week for 3 weeks (weekly x 3), and i.v. push once a day for 5 days (daily x 5), and the maximum tolerated doses (MTDs) of ZD1694 were 300 mg/kg, 60 mg/kg/week, and 30 mg/kg/day, respectively. ZD1694 was moderately active against both A253 and FaDu xenografts. Antitumor activity was schedule-dependent in both tumors: weekly x 3 > or = i.v. x 1 >> daily x 5. In contrast, the rank order of toxicity was daily x 5 >> weekly x 3 > or = i.v. x 1. ZD1694 at the MTD produced 20% complete tumor regression and 20% partial tumor regression (PR) with i.v. x 1 and weekly x 3 schedules and 12-day tumor growth delay with daily x 5 schedule against FaDu xenografts. No complete tumor regression was achieved with ZD1694 with any schedule against A253; a 20% PR, 40% PR, and 10-day tumor growth delay were observed with i.v. x 1, weekly x 3, and daily x 5 schedules, respectively. The data indicate that ZD1694 was slightly more effective against FaDu than against A253. Of interest and potential clinical importance was the observation that ZD1694 was still active at doses lower than the MTD (> or =1/3 MTD), which showed a high therapeutic index and wide safety margin. Study of ZD1694 compared with 5-fluorouracil and 5-fluoro-2'-deoxyuridine at the MTD revealed that the antitumor activity of ZD1694 was comparable with or superior to 5-fluorouracil and 5-fluoro-2'-deoxyuridine against both A253 and FaDu xenografts, with less toxicity. High plasma thymidine in mouse relative to human (approximately 1.3 microM and <0.1 microM, respectively) may complicate the study of antitumor activity and toxicity of TS inhibitors with human tumor xenografts grown in the mouse. To test this hypothesis, we preadministered methoxypolyethyleneglycol-conjugated thymidine phosphorylase (MPEG-TPase; 2500 units/kg/dose) to reduce mouse plasma thymidine, then treated with various doses of ZD1694 using the daily x 5 or i.v. x 1 schedules in the A253 tumor model. MPEG-TPase significantly increased the toxicity of ZD1694; the MTD of ZD1694 plus MPEG-TPase was reduced 3- and 10-fold compared with ZD1694 alone for i.v x 1 and daily x 5 schedules, respectively. However, preadministration of MPEG-TPase did not potentiate the antitumor activity of ZD1694 with either schedule. The data indicate that the study of TS inhibitors in rodent models may not be suitable for predicting a safe dose for clinical study. However, rodent models, particularly human tumor xenografts, are still useful models for evaluation of antitumor activity and schedule selection for TS inhibitors.

Animals↗

PubMed1999

Clinical implications of 5-FU modulation.

In recent years, due to the advent of sensitive instrumentation and methodologies, it has been possible to identify parameters that predict the quality of response of individual patients to treatments for specific selected diseases, e.g., colon carcinoma and breast carcinoma. Ongoing studies are attempting to identify sensitive patients in order to select treatment regimens suitable for the individual patient. The critical question that remains is whether the basis for drug resistance is due in part to insufficient delivery of drugs to target tumor cells or to the resistance of target tumor cells by various mechanisms, including, in the case of 5-fluorouracil (5-FU), drug transport, metabolism, expression of the target enzyme thymidylate synthase (dTMPS), depletion of folate cofactors, and/or level of competing substrate deoxyuridine monophosphate. Also in recent years, attempts have been made to delineate mechanisms of resistance to the fluoropyrimidines. On the basis of such studies, it may be possible to develop approaches aimed at the selective modulation of the therapeutic efficacy of these agents in tumor tissues with varying degrees of sensitivity of fluoropyrimidines, e.g., patients with advanced colorectal cancer. One such approach is the use of calcium folinate to modulate the therapeutic efficacy of 5-FU.

Antimetabolites, Antineoplastic↗

PubMed1999

Dimerization of mitochondrial Bax is associated with increased drug response in Bax-transfected A253 cells.

Human head and neck squamous cell carcinoma A253 cells, which do not express p53 and p21 proteins, were engineered to stably express about 50-fold higher level of Bax protein (A253/Bax) than the mock-transfected (A253/vec) or parental cells. Using these cell lines, studies were carried out to evaluate the role of Bax in response to anticancer drugs and to study the associated mechanisms. A253/Bax cells exhibited a significant increase in in vitro sensitivity to various anticancer drugs, including tomudex (9.5-fold), SN-38 (13.8-fold), doxorubicin (7.9-fold), taxol (3.1-fold), 5-FU (2.7-fold), and 5-FU/LV (4.5-fold). Increased level of drug-induced apoptosis was observed in A253/Bax cells in a drug concentration-dependent manner. In untreated A253/Bax cells, Bax was expressed in a monomeric state. Treatment with tomudex induced the formation of Bax dimer in a drug concentration-dependent manner. Dimerization of Bax occurred only in mitochondria, while the cytosolic Bax was retained in the monomeric state. Low level of Bax dimerization was also detected in parental A253 cells following tomudex exposure. In addition, Bax dimer formation was associated with mitochondrial cytochrome c release and activation of caspases in A253/Bax cells. The data suggest that Bax overexpression increases drug response by enhancing drug-induced apoptosis. Furthermore, dimerization of mitochondrial Bax and downstream mechanisms are associated with drug-induced apoptotic cell death and increased drug sensitivity.

Apoptosis↗

PubMed1999

New drugs in therapy of colorectal cancer: preclinical studies.

For years, 5-fluorouracil (5-FU) was the only chemotherapeutic agent for the treatment of patients with advanced colorectal cancer. Based on laboratory data, modulation of 5-FU by leucovorin (LV) was proven to be an active alternative. In addition, a number of 5-FU prodrugs and antifolate antimetabolites became available for preclinical and clinical evaluation. With the 5-FU prodrugs, the overall aim was to improve the therapeutic efficacy and selectivity of 5-FU and to provide an oral form of therapy. In preclinical systems, several of the 5-FU prodrugs, eg, capecitabine, uracil/ ftorafur (UFT)/LV, and S- , are active and offer significant therapeutic advantages over 5-FU/LV. A direct and specific new thymidylate synthase (TS) inhibitor, Tomudex (raltitrexed, ZDI694; Zeneca Pharmaceuticals, Macclesfield, UK), is active in several preclinical and clinical settings. The major focus of this report will be on the preclinical development of selected fluoropyrimidine prodrugs.

Animals↗

PubMed1999

Phase I and pharmacokinetic study of weekly 5-fluorouracil administered with granulocyte-macrophage colony-stimulating factor and high-dose leucovorin: a potential role for growth factor as mucosal protectant.

Diarrhea is dose-limiting with weekly 5-fluorouracil (5-FU) plus high-dose leucovorin (LV). Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been associated with a decrease in chemotherapy-associated mucosal toxicity. This study was conducted to determine the maximum tolerated dose (MTD) of weekly 5-FU when administered with GM-CSF and high-dose LV. Patients were treated with intravenous LV 500 mg/m2 plus 5-FU weekly for six doses followed by a 2-week rest. GM-CSF 250 mg/m2 was administered subcutaneously 5 days each week. Cohorts were treated with 5-FU at 600, 700, and 800 mg/m2 weekly. Twenty-nine patients were treated. The MTD of 5-FU in this schedule was 700 mg/m2/week, with diarrhea dose-limiting. 5-FU delivered dose intensity at the MTD was 424 +/- 23.7 mg/m2/week, including rest periods. 5-FU and LV pharmacokinetics were not altered by concurrent treatment with GM-CSF. In a weekly schedule with high-dose LV and GM-CSF, the MTD of 5-FU and 5-FU delivered dose intensity were higher than previously reported with 5-FU and LV administered without GM-CSF.

Adult↗

PubMed1999

Image analysis for quantitation of solid tumor drug sensitivity.

BACKGROUND: A method of assessing chemosensitivity of tissue has been described by Rotman et al. The aim of this study was to use image analysis to provide a more rapid and quantitative means of assessing drug effect on tissue proliferative capacity. METHOD: Fluoropyrimidine sensitive Ward rat colon adenocarcinoma tumor was implanted onto collagen impregnated cellulose fibers suspended on metal grids at an air-fluid interface and kept in a 95% air/5% CO2 incubator at 37 degrees C. The fluorescent microscopic image captured by a silicon intensified target (low light detecting) camera and linked to an image processing unit was measured for fluorescent brightness and tumor image area. Blinded 5-Fluorouracil (5-FU) drug treatment was begun 8 days after tumor explantation on the collagen-cellulose matrix. Tumor image area and fluorescent brightness were measured at 24 h pretreatment, 48 h posttreatment, and at 48 h post drug removal. RESULTS: Nontreated tumor cultures demonstrated an increase in area and fluorescent brightness with time following tumor implantation on the collagen gel. Dose responsiveness was seen with increasing concentrations of 5-FU. At the highest clinically achievable concentration of 5-FU (500 microM), there was a 39% decrease in area compared with the nontreated group, 113%. Linear dose responsiveness was not demonstrated between 50 and 150microM 5-FU. CONCLUSIONS: Fluoropyrimidine activity was demonstrated with the implemented image analysis system. The in vitro tumor sensitivity to FU using collagen gel was consistent with responsiveness of tumors in vivo borne by rats.

Adenocarcinoma↗

PubMed1998

Modeling of the time-dependency of in vitro drug cytotoxicity and resistance.

For potential clinical extrapolation of in vitro findings, it is of interest to relate the measured effect of an anticancer agent to concentration and exposure time. The Hill model (A. V. Hill, J. Physiol., 40: iv-vii, 1910) is commonly used to describe pharmacodynamic (PD) effects, including drug-induced growth inhibition of cancer cells in vitro. The IC(X)n x T = k relationship, in which IC(X) is the concentration of agent required to reduce cell growth by X%, T is the exposure time, and n and k are estimable parameters, was first applied to bacterial disinfectant action and then was successfully used to model anticancer drug potency as a function of exposure time (D. J. Adams, Cancer Res., 49: 6615-6620, 1989). Our goal was to create a new global PD modeling paradigm to facilitate the quantitative assessment of the growth-inhibitory effect of anticancer agents as a function of concentration and exposure time. Wild-type human ovarian A2780 and ileocecal HCT-8 carcinoma cells and sublines that were resistant to cisplatin (A2780/CP3), doxorubicin (A2780/DX5B), and raltitrexed (RTX) (HCT-8/DW2) were exposed to various anticancer agents, cisplatin, doxorubicin, paclitaxel, trimetrexate, RTX, methotrexate, and AG2034, for periods ranging from 1 to 96 h. Cell growth inhibition was measured with the sulforhodamine B protein dye assay. Patterns of time-dependency of drug potency, slope of the concentration-effect curves, and relative degree of resistance were characterized. Empirical mathematical expressions were built into a global concentration-time-effect model. The global PD model was then fit to the concentration-time-effect data with iteratively reweighted nonlinear regression. Under specific treatment conditions, the examination of the slope and the shape of the concentration-effect curves revealed a large heterogeneity in drug response, e.g., shallow concentration-effect curve or double or triple Hill "roller coaster" concentration-effect curve. These patterns, which were observed at intermediate exposure times in parental and resistant cells for paclitaxel and trimetrexate or only in resistant HCT-8/DW2 cells for RTX, methotrexate, and AG2034, revealed mechanistic insights for the former cases but possible methodological artifacts for the latter cases. The comprehensive PD modeling of the cytotoxic effect of anticancer agents showed that it was possible to modulate drug effect, response heterogeneity, and drug resistance by altering the time of exposure to the agents. This approach will be useful for: (a) describing complex concentration-time-effect surfaces; (b) refining biological interpretations of data; (c) providing insights on mechanisms of drug action and resistance; and (d) generating leads for clinical use of anticancer drugs.

Antineoplastic Agents↗

PubMed1998

Interleukin 15 offers selective protection from irinotecan-induced intestinal toxicity in a preclinical animal model.

Irinotecan (CPT-11) is a chemotherapeutic agent that is active in the treatment of a variety of solid tumor malignancies. Diarrhea represents the most common dose-limiting toxicity that is independent of the schedule of administration. A rat model with dose-limiting toxicity profiles that are similar to those observed in patients treated with CPT-11 was developed and used to evaluate the role of interleukin 15 (IL-15) in the modulation of the therapeutic selectivity of CPT-11 in normal rats and rats bearing advanced colorectal cancer. The maximum tolerated dose and lethal dose (LD) of CPT-11 by i.v. push daily x 3 were 150 and 200 mg/kg/day, respectively. CPT-11 at the LD induced a 93-100% incidence of severe diarrhea and an 86-100% incidence of lethality in treated animals. IL-15, a cytokine with multiple mechanisms of action, was used at a 100 or 400 microg/kg/dose with different schedules of administration (3, 8, and 11 doses, i.p.) to protect against CPT-11-induced toxicity. IL-15 offered complete and sustained selective protection against CPT-11-induced delayed diarrhea and lethality. IL-15 also moderately potentiated the antitumor activity of CPT-11 in rats bearing advanced colorectal cancer. Morphological examination of rat intestinal tissues after treatment with LD of CPT-11 revealed dramatic protection of duodenal and colonic tissue architecture by IL-15. CPT-11 alone produced serious damage to duodenal villi and colonic crypts. The results clearly demonstrated the ability of IL-15 to provide significant protection from CPT-11-induced intestinal toxicity with maintenance of antitumor activity, resulting in an increase in the therapeutic index of CPT-11. The clinical relevance of the results obtained in this model system needs to be confirmed.

Animals↗

PubMed1998

Super in vitro synergy between inhibitors of dihydrofolate reductase and inhibitors of other folate-requiring enzymes: the critical role of polyglutamylation.

The combined action among polyglutamylatable and nonpolyglutamylatable antifolates, directed against dihydrofolate reductase (DHFR), glycinamide ribonucleotide formyltransferase (GARFT), 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase (AICARFT), and thymidylate synthase (TS), in human ileocecal HCT-8 cells was examined in a 96-well plate growth inhibition assay (96-h continuous drug exposure). An interaction parameter, alpha, was estimated for each of 95 experiments by fitting a seven-parameter model to data with weighted nonlinear regression. In a representative experiment, raising the folic acid concentration in the medium dramatically increased the Loewe synergy for the combination of trimetrexate (TMTX) and the GARFT inhibitor AG2034 (from a mean alpha +/- SE of 1.50 +/- 0.25 at 2.3 microM folic acid to 146 +/- 20 at 78 microM folic acid). Enhancements were also found for combinations of TMTX with the GARFT inhibitors AG2032, Lometrexol, and LY309887, the AICARFT inhibitor AG2009, and the TS inhibitors LY231514 and Tomudex but not with the GARFT inhibitor LL95509 or with the TS inhibitors AG337, ZD9331, and BW1843U89. Replacing TMTX with methotrexate in two-drug mixtures decreased the intensity of Loewe synergy. Examination of isobolograms at different effect levels revealed informative reproducible changes in isobol patterns. No two-drug combinations among inhibitors of GARFT, AICARFT, and TS exhibited Loewe synergy at either 2.3 or 78 microM folic acid. Thus, the ideal requirement for the folic acid-enhanced synergy is that a nonpolyglutamylatable DHFR inhibitor be combined with a polyglutamylatable inhibitor of another folate-requiring enzyme. A hypothesis to explain this general phenomenon involves the critical role of folylpoly-gamma-glutamate synthetase and the effect of the DHFR inhibitor in decreasing the protection by folic acid of cells to the other antifolates.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1998

Cell cycle: molecular targets for diagnosis and therapy: tumor suppressor genes and cell cycle progression in cancer.

A significant portion of published literature is dedicated to describing the cloning and the characterization of proteins involved in the progression of the cell cycle, which govern cell growth both in cancer and normal ontogenesis. With this abundance of information, the cascading pathways of molecular events that occur in the cell cycle are proving to be exceedingly complicated. The purpose of this conference was to attract the leading clinical and basic science investigators in the growth control field with a final goal to determine how this current wealth of knowledge can be used to impact upon patient care and management by the design of novel adjuvant therapeutics specifically targeted at tumor cells and the identification of molecular diagnostic and/or prognostic markers in an efficient and cost effective manner.

Animals↗

PubMed1998

Interleukin 15 protects against toxicity and potentiates antitumor activity of 5-fluorouracil alone and in combination with leucovorin in rats bearing colorectal cancer.

5-Fluorouracil (FUra) modulated by leucovorin (LV) is active in the treatment of colorectal cancer. Diarrhea and stomatitis are the most common dose-limiting toxicities. We have developed a model system in rats bearing a transplantable colon carcinoma sensitive to FUra therapy with dose-limiting toxicity profiles similar to what is observed in patients treated with either daily or weekly schedules of FUra plus LV. Interleukin 15 (IL-15), a cytokine that shares many biological activities with IL-2, was used at different doses (25, 100, and 400 microg/kg) and schedules (three doses before a single dose of FUra, FUra/LV daily x 5, or before each week of FUra/LV weekly x 4, or three doses before a single dose of FUra or FUra/LV daily x 5, then twice daily x 5 for a total of 11 doses) to evaluate its role in the modulation of the therapeutic selectivity of FUra alone and modulated by LV. IL-15 induced a dramatic decrease in chemotherapy-induced gastrointestinal toxicities, significant potentiation of antitumor activity, and an increased therapeutic index of FUra administered on single dose, daily x 5 and weekly x 4 schedules. In contrast, IL-2 (400 microg/kg) significantly potentiated the toxicity of FUra administered as a single i.v. push, with minimal potentiation of the antitumor activity. Taken together, the results clearly demonstrated the ability of IL-15, but not IL-2, to provide significant improvement of the therapeutic index of FUra alone and in combination with LV. The clinical relevance of the results obtained in this model system needs to be confirmed.

Animals↗

PubMed1998

Novel cellular determinants for reversal of multidrug resistance in cells expressing P170-glycoprotein.

The newly synthesized calcium channel blocker, Ro44-5912, significantly potentiates doxorubicin (Dox)-induced cytotoxicity at non-cytotoxic concentrations in Dox-resistant human ovarian cell line, A2780/DX5, overexpressing P170-glycoprotein (Pgp). Induction of DNA single- and double-strand breaks (ssbs and dsbs) was measured using alkaline elution and constant-field gel electrophoresis (CFGE) assays. The results indicate that potentiation of the cytotoxicity of Dox by Ro44-5912 was accompanied by significant increases in both, Dox-induced DNA ssbs and dsbs in the resistant cells. Pulsed-field gel electrophoresis (PFGE) analysis showed that Dox induced DNA fragments in the 50-800 kilobase (kb) and 0.8-5.7 megabase (Mb) ranges. The majority of the newly synthesized DNA fragments were in the 50-800 kb range. Ro44-5912 treatment resulted in significant potentiation of DNA fragmentation in the 50-800 kb range with a minor increase in 0.8-5.7 Mb DNA fragments, suggesting that the modulator functions by potentiating nascent DNA fragmentation in the resistant cells. Exposure to Dox with Ro44-5912 was associated with a prolonged blockage of cells in the S-phase. In contrast, exposure to Dox alone resulted in temporary blockage of cells in G2/M phase (approximately 24 h) followed by restoration of cell proliferation and normal DNA histograms at 48 h after 2 h drug exposure. Incorporation of BrdUrd by flow cytometric analysis was inhibited by Dox in the presence of Ro44-5912, showing that there is a block of DNA replication. An increased damage in newly synthesized DNA could concur with a blocked DNA replication. Moreover, slowing progression through the S-phase in cells exposed to Dox in combination with Ro44-5912 is accompanied by increased sensitivity of Dox poisons, indicating a correlation of specific S-phase perturbation with the reversal of Dox resistance by Ro44-5912 in cells expressing Pgp. The results suggest that drug-induced augmentation of nascent DNA fragmentation and specific cell-cycle perturbation are potentially important molecular determinants for reversal of multidrug resistance in addition to restoration of intracellular drug retention.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Comparison of 5-fluoro-2'-deoxyuridine with 5-fluorouracil and their role in the treatment of colorectal cancer.

Despite more than 30 years of intensive studies on new drugs against advanced colorectal cancer, the fluoropyrimidines remain the drugs of choice for systemic treatment and for hepatic artery infusion (HAI). This overview describes new developments in advanced colorectal cancer chemotherapy, providing a rationale for more effective use of the fluoropyrimidines, with biochemical modulation, scheduling or by revealing biochemical mechanisms of action that correlate with antitumour activity. In human colorectal cancer cell lines and various animal tumour model systems 5-fluoro-2'-deoxyuridine (FdUrd) is more effective than 5-fluorouracil (5-FU). Comparably, FdUrd's modulation by leucovorin (LV) is more potent than 5-FU. In animal studies it is shown that intermittent high-bolus administration of FdUrd generates better antitumour activity, compared with equal toxic doses or any other schedule of 5-FU. These effects are related to prolonged-thymidylate synthase (TS) inhibition and the prevention of TS induction, rather than RNA incorporation. Preclinical studies with modulators such as N-phosphonacetyl-L-aspartate (PALA), WR-2721, mitomycin C and platinum derivatives provide a rationale for clinical use in the future. The first choice systemic chemotherapy of patients with advanced colorectal cancer remains 5-FU combined with LV. Some improvement in therapeutic efficacy has been achieved with locoregional HAI. In randomised studies HAI FdUrd improves the quality of life and survival as compared with optimal systemic therapy. Chronomodulation decreases toxicity, allowing dose intensification, while modulators such as LV or dexamethasone increase survival of patients treated with HAI FdUrd to 86% after 1 year. In conclusion, the clinical use of FdUrd has not been fully explored. Intermittent high-dose FdUrd, chronomodulation together with the use of modulators or drugs focused on prolonged TS inhibition, should be studied in large randomised studies.

Antimetabolites, Antineoplastic↗

PubMed1998

Modulation of platinum-induced toxicities and therapeutic index: mechanistic insights and first- and second-generation protecting agents.

Platinum-type drugs have proven to be valuable in the treatment of a variety of solid tumors, beginning with the commercial approval of cisplatin 18 years ago. There are several clinically important toxicities commonly associated with the administration of these drugs. Despite the extensive use of cisplatin and carboplatin, the fundamental chemical transformations and mechanisms that underlie their antitumor and toxic effects have not been fully characterized. Several first-generation protective thiols have been clinically studied in an attempt to reduce the toxicity of platinum-type drugs; while some of these agents appear to protect against certain toxicities, nearly all platinum-protecting drugs have their own intrinsic toxicities, which can be additive to the toxicity of platinum-type drugs. Tumor protection by platinum-protecting drugs is an additional untoward effect that is associated with certain types of agents and must be addressed with care. Recent advances in theoretical and laboratory methods and the use of supercomputers have extended our understanding of the possible major mechanisms underlying platinum drug antitumor activity and toxicity; we present strong evidence that there are two classes of chemical species of platinum drug. One class appears to predominantly account for the antitumor activity, and the other class of chemical species produces many of the toxic effects of platinum drugs. We have discovered a new nontoxic, second-generation platinum-protecting agent, known as BNP7787, which appears to selectively inactivate and eliminate toxic platinum species. BNP7787 has recently entered phase I clinical testing in cancer patients.

Amifostine↗