426
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Singh SS, Smith KM, Brown DM. Drug retention following intravesical delivery of fluorouracil therapeutic adhesive in C3H mouse bladder. Anticancer Drugs 1996; 7:507-13. [PMID: 8862715 DOI: 10.1097/00001813-199607000-00002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We have developed a fibrinogen-based, sustained-retention drug delivery system, therapeutic adhesive (TA), for application to resected tumor beds to reduce local tumor recurrences. In this study we evaluated the feasibility, safety and retention of the TA formulated with 5-fluorouracil (5-FU TA) after intravesical administration in a mouse bladder model. Radiolabeled [14C]5-FU TA or [14C]5-FU solution was delivered intravesically to C3H/He female mice. After drug administration, retention of 14C in the bladder was quantified by storage-phosphor autoradiography. A 2.6-fold increase in retention was observed with 5-FU TA when compared with 5-FU solution. The AUC(2 min-5 h) for 5-FU TA was 685 nmol h/mm2 compared with 260 nmol h/mm3 for 5-FU solution. No signs of toxicity in the bladder tissue or treatment-associated adverse effects were observed in the mice.
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427
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Li Y, Ito S, Cheng W, Ishii Y. Combined effect of 5-fluorouracil and recombinant tumor necrosis factor against human gastric carcinoma cell lines. Anticancer Res 1996; 16:1771-4. [PMID: 8712699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
This study was performed to investigate the direct effects of recombinant human tumor necrosis factor (rH-TNF) and recombinant human interleukin-2 (rH-IL-2), either alone or in combination, on the cytotoxicity of 5-FU measured by MTT assay against human gastric adenocarcinoma cell lines (MKN-28 and MKN-45), and also to determine the optimal schedule for their combination. The antitumor activity of rH-TNF was enhanced more than 42% by 10(2) U/ml of rH-IL-2. The enhancing effects of rH-TNF and rH-IL-2 on the cytotoxicity of 5-FU were evaluated in terms of Modification Index(MI), the MI value at 10 U/ml rH-TNF was 1.6; the MI at the same concentration of rH-TNF in the presence of 10(2) U/ml of rH-IL-2 was 2.1. These results demonstrated that the antitumor effect of 5-FU was enhanced 1.6 times by 10 U/ml of rH-TNF and further enhanced by the combined use of rH-TNF and rH-IL-2. The combined effect of equal concentrations of 5-FU and rH-TNF was superior or equivalent to that of 5-FU or rH-TNF alone. The sequence of 5-FU followed by rH-TNF and rH-IL-2 showed a higher inhibitory effect than the reverse sequence. This sequence combination seems worthy of further consideration for the treatment of gastric cancer.
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428
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Tanigawa N, Kitaoka A, Yamakawa M, Tanisaka K, Kobayashi H. In vitro chemosensitivity testing of human tumours by collagen gel droplet culture and image analysis. Anticancer Res 1996; 16:1925-30. [PMID: 8712722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
It is necessary to develop an in vitro test to overcome the problems often associated with in vitro chemosensitivity tests on individual human tumours. We have developed a collagen gel droplet culture technique that allows for a three-dimensional in vitro growth and drug response assay for human solid tumour cells. Important features of chemosensitivity testing by the collagen gel droplet culture technique include the maintenance of high cloning efficiencies resulting in the need for fewer tumour cells, sufficient suppression of the in vitro proliferation of contaminating non-malignant cells by serum-free medium, and the application of the image analysis system which automatically discriminates between cancer cell colonies and fibroblasts. We described in vitro-in vivo correlations for drug response using 7 human lung cancer xenografts grown in the collagen gel droplet culture and as xenografts in nude mice. Results demonstrated significant correlations with the in vitro drug concentration at 1/10 of the peak plasma concentrations (1/10 Cmax) with the correlation coefficient 0.84 for all four drugs tested. We have cultured 206 tumours thus far obtaining 86% of evaluability for drug response. The drug response data of the fresh lung cancers were similar to not only to data for lung cancer lines but the reported clinical pattern. These results suggested that the collagen gel droplet culture at 1/10 Cmax may have potential in predicting clinical drug responses.
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429
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Menei P, Boisdron-Celle M, Croué A, Guy G, Benoit JP. Effect of stereotactic implantation of biodegradable 5-fluorouracil-loaded microspheres in healthy and C6 glioma-bearing rats. Neurosurgery 1996; 39:117-23; discussion 123-4. [PMID: 8805147 DOI: 10.1097/00006123-199607000-00023] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
OBJECTIVE Poly(lactic acid-co-glycolic acid) (PLAGA) microspheres are promising systems for interstitial chemotherapy of brain tumors. They can be readily implanted by stereotaxy and are biocompatible with the brain, in which they are totally biodegraded within 2 months. 5-Fluorouracil (5-FU) was selected for encapsulation, because this hydrophilic and antimetabolic drug is not directly neurotoxic and does not readily cross the blood-brain barrier. Also, its anticancer activity may be improved by sustained administration. Furthermore, it is a potent radiosensitizer. METHODS To study their fate and toxicity, two types of 5-FU-loaded PLAGA microspheres were implanted in healthy rats by stereotaxy. One type presented a fast in vitro release profile (FR), and the second exhibited a slow in vitro release pattern (SR) (100% of the encapsulated 5-FU is released within 72 hours and 18 days, respectively). Periodically, rats were killed for microscopic examination. The efficacy of these microspheres on rat glioma was then evaluated. Seven days after stereotactic implantation of C6 malignant glioma cells in the brain, the rats were treated by intratumoral injection of 5-FU solution, blank microspheres, or 5-FU-loaded microspheres (FR and SR types). The mortality of these treated groups was compared by the log-rank test with that of an untreated group. RESULTS After implantation of two types of 5-FU-loaded PLAGA microspheres, no sign of clinical or histological toxicity was observed. Entrapped 5-FU crystals were observed until Days 12 and 20 postimplantation within FR and SR microspheres, respectively, which suggests a longer releasing period in vivo than in vitro. In the therapeutic evaluation, only intratumoral implantation of SR-type 5-FU-loaded microspheres significantly decreased the mortality (P = 0.017). CONCLUSION 5-FU-loaded PLAGA microspheres were implanted in rat brains without evident toxicity. Histological examination suggested a longer sustained delivery period in vivo than in vitro. Intratumoral implantation of SR-type 5-FU-loaded microspheres decreased the mortality of C6 tumor-bearing rats. This effect can be related to the local and the sustained delivery of the drug, because 5-FU administered systemically is ineffective against brain tumors.
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430
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Potten CS. Protection of the small intestinal clonogenic stem cells from radiation-induced damage by pretreatment with interleukin 11 also increases murine survival time. Stem Cells 1996; 14:452-9. [PMID: 8843547 DOI: 10.1002/stem.140452] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effect of administering recombinant human interleukin 11 in conjunction with cytotoxic insults to the gastrointestinal tract has been studied using the crypt microcolony assay for stem cell function and whole-animal survival time studies. The cytotoxic regimens include single doses of gamma rays; single doses of 5-fluorouracil (5-FU) and multiple doses of 5-FU spaced 6 h apart. Interleukin 11 (IL-11) (100 micrograms/kg) delivered over a period of time prior to cytotoxic exposure afforded protection to the clonogenic cells in the crypts as seen with the microcolony assay and prolonged the animal survival time following radiation exposure. Continuing this dose of IL-11 after cytotoxic exposure afforded little additional protection. Three doses of 5-FU 6 h apart generated crypt survival curves similar to those obtained after a single dose of gamma rays. IL-11 given prior to two doses of 5-FU effectively abolished the cytotoxic effect of the second dose of 5-FU; i.e., 2.5-3.0 times more crypts survived if IL-11 was administered when the higher 5-FU doses are considered. IL-11 given before a dose of 12 Gy of gamma rays prolonged the survival time of animals by three to four days. This confirms earlier studies demonstrating that protecting clonogenic cells in the crypt survival assay can result in beneficial effects on whole-animal survival times.
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431
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Szilvassy SJ, Weller KP, Lin W, Sharma AK, Ho AS, Tsukamoto A, Hoffman R, Leiby KR, Gearing DP. Leukemia inhibitory factor upregulates cytokine expression by a murine stromal cell line enabling the maintenance of highly enriched competitive repopulating stem cells. Blood 1996; 87:4618-28. [PMID: 8639830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Attempts to maintain or expand primitive hematopoietic stem cells in vitro without the concomitant loss of their differentiative and proliferative potential in vivo have largely been unsuccessful. To investigate this problem, we compared the ability of three cloned bone marrow (BM) stromal cell lines to support the growth of primitive Thy-1lo Sca-1+H-2Khi cells isolated by fluorescence-activated cell sorting from the BM of Ly-5.2 mice treated 1 day previously with 5-fluo- rouracil. Sorted cells were highly enriched in cobblestone area-forming cells (CAFC), but their frequency was dependent on the stromal cell lines used in this assay (1 per 45 cells on SyS-1; 1 per 97 cells on PA6). In the presence of recombinant leukemia inhibitory factor (LIF), CAFC cloning efficiency was increased to 1 per 8 cells on SyS-1 and 1 per 11 cells on PA6, thus showing the high clonogenicity of this primitive stem cell population. More primitive stem cells with competitive repopulating potential were measured by injecting the sorted cells into lethally irradiated Ly-5.1 mice together with 10(5) radioprotective Ly-5.1 BM cells whose long-term repopulating ability has been "compromised" by two previous cycles of marrow transplantation and regeneration. Donor-derived lymphocytes and granulocytes were detected in 66% of animals injected with 50 sorted cells. To quantitate the maintenance of competitive repopulating units (CRU) by stromal cells, sorted cells were transplanted at limiting dilution before and after being cultured for 2 weeks on adherent layers of SyS-1, PA6, or S17 cells. CRU represented 1 per 55 freshly sorted cells. CRU could be recovered from cocultures supported by all three stromal cell lines, but their numbers were approximately-sevenfold less than on day 0. In contrast, the addition of LIF to stromal cultures improved CRU survival by 2.5-fold on S17 and PA6 cells (approximately two-fold to threefold decline), and enabled their maintenance on SyS-1. LIF appeared to act indirectly, because alone it did not support the proliferation of Thy-1lo Sca-1+H-2Khi cells in stroma-free cultures. Polymerase chain reaction (RT-PCR) analysis revealed that Interleukin-1beta (IL-1 beta) IL-2, IL-6, granulocyte-colony stimulating factor, granulocyte macrophage-colony stimulating factor, transforming growth factors, LIF, and Steel Factor (SLF) mRNAs were upregulated in SyS-1 within 1 to 6 hours of LIF-stimulation. To determine if increased expression of SLF by LIF-stimulated SyS-1 cells could account for their capacity to support stem cells, sorted calls were cocultured on simian CV-E cells that were transfected with an expression vector encoding membrane-bound SLF, or supplemented with soluble SLF. In both cases, SLF synergized with IL-6 produced endogenously by CV-E cells enabling CAFC growth equivalent to that on LIF-stimulated SyS-1. CAFC development on LIF-stimulated SyS-1 could also be completely abrogated by an anti-SLF antibody. These data provide evidence for a role of LIF in the support of long-term repopulating stem cells by indirectly promoting cytokine expression by BM stroma. Furthermore, we have used quantitative assays to show a maintenance of CRU numbers, with retention of in vivo function following ex vivo culture.
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432
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de Haan G, Donte B, Engel C, Loeffler M, Nijhof W. Prophylactic pretreatment of mice with hematopoietic growth factors induces expansion of primitive cell compartments and results in protection against 5-fluorouracil-induced toxicity. Blood 1996; 87:4581-8. [PMID: 8639826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The aim of this study was to expand the primitive and committed hematopoietic cell compartments in vivo in order to confer resistance of the blood cell forming system against the cytotoxic, cell cycle specific drug 5-fluorouracil (5-FU). Possible chemoprotective effects of such a pretreatment could result from increased numbers of hematopoietic cells, present before 5-FU administration. In addition, we hypothesized that an enhanced number of primitive and progenitor calls would result in a reduced cycling activity, ie, 5-FU sensitivity, of these same cells, due to normal physiological feedback loops. Administration of stem cell factor (SCF) plus interleukin-11 (IL-11) to mice was shown to result in expansion of the various immature cell compartments in marrow and, in particular, spleen. The total body content of the primitive cobblestone area forming cells (CAFC)-day 28 was increased to 140%, whereas the more committed cells (CAFC-day 7, erythroid and granuloid progenitors) were increased to 500%. This in vivo expansion resulted in a decreased 5-FU sensitivity of the hematopoietic system. In particular, mice that had received 5-FU 24 hours after discontinuation of growth factor pretreatment showed significantly less toxicity of committed cell stages. Compared with mice not pretreated, it appeared that in pretreated mice, 24 hours after 5-FU administration, the absolute number, but also the fraction of surviving CAFC, was much higher in both marrow and spleen. This was caused by a decrease in the cycling activity of all primitive cell subsets. To explore the possible use of this finding in a chemotherapeutic setting, we determined the interval between two subsequent doses of 5-FU (160 mg/kg) that was required to prevent drug-induced mortality. When control mice received a second dose of 5-FU 7, 10, or 14 days after the first, respectively 0%, 20%, and 80% survived. In contrast, 40% and 100% of mice that received SCF + IL-11 before the first dose of 5-FU, survived a second dose of 5-FU given respectively after 7 or 10 days. To assess whether chemoprotection in this setting could be ascribed to protection of the hematopoietic system, we transplanted a high number of normal bone marrow cells (sufficient to compensate for any hematopoietic deficiency) to normal and pretreated mice after they had been administered 2 doses of 5-FU, given 7 days apart. Bone marrow transplantation (BMT) could only rescue 50% of mice not pretreated, showing that a significant part of the mortality was because of nonhematologic toxicity. However, a BMT given to growth factor pretreated mice saved all mice, indicating that in this setting SCF + IL-11 had additional protective effects on cell systems other than hematopoiesis. In conclusion, our study showed fundamental knowledge about the behavior of primitive cells in vivo and has shown that manipulation of these and other cell compartments with appropriate growth factors may confer resistance against cytotoxic drugs.
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433
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Konishi F, Mitsuyama M, Okuda M, Tanaka K, Hasegawa T, Nomoto K. Protective effect of an acidic glycoprotein obtained from culture of Chlorella vulgaris against myelosuppression by 5-fluorouracil. Cancer Immunol Immunother 1996; 42:268-74. [PMID: 8706047 PMCID: PMC11037657 DOI: 10.1007/s002620050281] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
An acidic glycoprotein prepared from a culture of Chlorella vulgaris (CVS) was examined for its protective effect on 5-fluorouracil(5FU)-induced myelosuppression and indigenous infection in mice. Subcutaneous administration of CVS greatly reduced the mortality of non-tumor-bearing mice given a high dose of 5FU, and could increase the LD50 value of 5FU for these mice. After 5FU treatment, indigenous infection developed probably as a result of the impairment of the host defense system. CVS reduced the incidence of indigenous infections and this effect was attributable to the acceleration of recovery from 5FU-induced myelosuppression. Early recovery of hematopoietic stem cells, or cells responding to interleukin-3 or granulocyte/macrophage-colony-stimulating factor, was especially observed in the bone marrow of CVS-treated mice on days 4-9 after the injection of 5FU. When tumor-bearing mice were given CVS during treatment with 5FU, CVS prolonged the survival of mice without affecting the antitumor activity of 5FU. In addition, CVS was itself shown to exert an antitumor effect. These results suggested that CVS may be beneficial for the alleviation of side-effects in cancer chemotherapy without affecting the antitumor activity of the chemotherapeutic agent.
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434
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Neta R, Keller JR, Ali N, Blanchette F, Dubois CM. Contrasting mechanisms of the myeloprotective effects of interleukin-1 against ionizing radiation and cytotoxic 5-fluorouracil. Radiat Res 1996; 145:624-31. [PMID: 8619029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Pretreatment with a single dose of interleukin-1 (IL-1) counteracts the myelosuppressive effects of radiation. In contrast, multiple doses are required to protect against several cytoablative drugs, suggesting different mechanisms. We examined the possibility that myeloprotection is due to IL-1-induced cycling of primitive progenitor cells. First, we evaluated the effect of the time between administration of IL-1 and 5-fluorouracil (5-FU), which kills cycling cells but spares quiescent early progenitors, on their interaction. Pretreatment with a single dose of IL-1 resulted in the death of mice treated with 5-FU provided IL-1 was given 18 h, but not 4 or 48 h, prior to administration of sublethal doses of 5-FU. Second, evaluation of primitive hematopoietic progenitor cells, 13-day spleen colony-forming units (CFU-S) and CFU with high proliferative potential revealed that treatment with 5-FU 18 h after administration of IL-1 results in reduction of CFU-S by 98% and of CFU with high proliferative potential by 65%, but only a 7 and 10% reduction, respectively, at 48 h. Third, in contrast to protection from death by pretreatment with a single dose of IL-1 at 24 h, two injections of IL-1 at 72 and 24 h before irradiation abrogated such protection. Similarly, the toxicity of 5-FU to progenitor cells was reduced when two injections of IL-1 were administered 48 h apart. This correlates with the time of up-regulation in the bone marrow cells of TGF-beta. These findings suggest that, depending on the schedule of treatment, administration of IL-1 may result in cycling of primitive progenitors, to protect against radiation, and may cause inhibition of cycling to protect against chemotherapeutic drugs.
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435
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Breul J, Tief G, Hartung R. Enhancement of 5-fluorouracil cytotoxicity by folinic acid in different cell-lines of human renal cell carcinoma. Eur J Med Res 1996; 1:339-42. [PMID: 9364036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Results of cytotoxic chemotherapy in metastatic renal cell carcinoma are not impressive. Remission rates range between 0 and 20%. One of the substances which show a marginal effect is 5-fluorouracil (5-FU). The cytotoxicity of 5-FU can be modulated by combination with folinic acid as shown in various cell lines and clinical trials. We were interested to see whether such a biomodulation also occurs in renal cell cancer. The antiproliferative effect of 5-fluorouracil on two human cell lines of RCC and its potentiation by folinic acid was investigated in a monolayer proliferation assay. It could be shown that folinic acid enhanced the cytotoxic potential of 5-FU 6-8-fold. Our results indicate that the combination of these two drugs in the treatment of metastatic renal cell cancer might lead to better response rates.
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436
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Cao S, Frank C, Rustum YM. Role of fluoropyrimidine Schedule and (6R,S)leucovorin dose in a preclinical animal model of colorectal carcinoma. J Natl Cancer Inst 1996; 88:430-6. [PMID: 8618234 DOI: 10.1093/jnci/88.7.430] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
BACKGROUND Fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd), used alone or in combination with other cytotoxic agents, exhibit limited efficacy in the treatment of advanced gastrointestinal cancer. (6R,S)leucovorin (LV), a source of reduced folate cofactor, can modulate (i.e., enhance) the therapeutic efficacy of treatment with these fluoropyrimidines (FPs). The role of FP schedule and lv dose in modulating FP antitumor activity, using clinically relevant drug doses and schedules, has not been fully documented. PURPOSE We evaluated the antitumor activities and the toxic effects of 5-FU and FdUrd, used either alone or in combination with LV, by following three clinically relevant treatment schedules in rats bearing advanced ward colorectal carcinomas. METHODS Maximum tolerated doses (MTDs), i.e., doses producing a reversible body weight loss of no more than 20% with no lethality, of 5-FU and FdUrd, either individually or in combination with LV, were used in the following treatment schedules: (I) 4 days of continuous intravenous FP infusion (with or without a daily 2-hour lv infusion); (II) a daily FP intravenous push for 4 days (LV, when given, was administered as a 2-hour infusion, with the FP push given after the first hour of LV treatment); and (III) an FP intravenous push given weekly for 3 weeks (the coadministration of LV and FP was performed as in schedule II). In these studies, LV was given at either a low dose (20 mg/kg [body weight] per day) or a high dose (200 mg/kg per day). The MTDs of 5-FU and FdUrd, with or without LV, were defined in normal rats. Antitumor activities were assessed in animals 12-14 days after they received subcutaneous tumor implants. Toxic effects at the MTD were evaluated in both normal and tumorbearing animals. RESULTS With schedules I and II, the MTD of 5-FU alone was 35 mg/kg per day; with schedule III, it was 100 mg/kg per week. For FdUrd alone, the MTD was 100 mg/kg per day with schedules I and II and 400 mg/kg per week with schedule III. Coadministration of LV reduced the MTD of both 5-FU and FdUrd by approximately 25%-30%, irrespective of the LV dose used. The dose-limiting toxic effects of treatment with 5-FU and FdUrd were diarrhea and/or stomatitis, the relative severity of which depended on the schedule of FP administration. The profile of toxic effects was not altered by LV when used at either dose. FP antitumor activity was modulated by LV in all three treatment schedules, but the greatest effects were seen using schedule III, where more complete tumor regression was seen with high-dose LV than with low dose LV. LV potentiated the antitumor activity of FdUrd to a greater extent than that observed with 5-FU. CONCLUSIONS In this rat model of colorectal carcinoma, the extent to which FP antitumor activity is modulated by LV depends on the schedule of FP administration and the dose of LV used.
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437
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Doroshow JH. Biochemical modulation of fluoropyrimidines: is there an optimal (6R,S) leucovorin dose and schedule? J Natl Cancer Inst 1996; 88:393-5. [PMID: 8618231 DOI: 10.1093/jnci/88.7.393] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
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438
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Bessler H, Straussberg R, Alexandrova S, Beilin B, Djaldetti M, Hart J. Effect of oral chemotherapy on the mitochondrial size of mouse intestinal cells. Cancer Chemother Pharmacol 1996; 38:35-8. [PMID: 8603449 DOI: 10.1007/s002800050444] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Since orally given cytotoxic agents may cause intestinal disfunction, the effect of oral administration of three cytotoxics, i.e., methotrexate (MTX), cyclophosphamide (CPA), and ftoral, a derivative of 5-fluorouracil (5-FU), on the gastric, liver, and small-intestine cells of C57B1 mice was studied by transmission electron microscopy. Although no ultrastructural alterations could be detected in the cells of the first two organs, the epithelial cells of the small intestine showed a marked increase in size of their mitochondria. In the control animals the mitochondrial size was in the range of 0.04-1.8 micron (mean +/- SE 0.54 +/- 0.01 micron). In the treated animals the size of the mitochondria ranged between 0.15 and 4.33 micron (mean +/- SE 0.73 micron) for those treated with MTX, 0.24-2.88 micron (mean +/- SE 0.80 +/- 0.02 micron) for those given CPA, and 0.28-5.3 micron (mean +/- SE 1.18 +/- 0.48 micron) for those treated with 5-FU. These findings were significantly different from those obtained in controls (P < 0.0001). In addition, in animals treated with MTX the mitochondria of the jejunal cells were surrounded by channels of rough endoplasmic reticulum. The cytoplasm contained long, winding channels of smooth endoplasmic reticulum, vacuoles, and myelin figures. Fluid retention in the small intestine due to administration of cytotoxic drugs is suggested as a possible mechanism for distention of the mitochondria.
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MESH Headings
- Administration, Oral
- Animals
- Antimetabolites, Antineoplastic/administration & dosage
- Antimetabolites, Antineoplastic/toxicity
- Antineoplastic Agents, Alkylating/administration & dosage
- Antineoplastic Agents, Alkylating/toxicity
- Cyclophosphamide/administration & dosage
- Cyclophosphamide/toxicity
- Endoplasmic Reticulum, Rough/drug effects
- Endoplasmic Reticulum, Rough/pathology
- Endoplasmic Reticulum, Smooth/drug effects
- Endoplasmic Reticulum, Smooth/pathology
- Fluorouracil/administration & dosage
- Fluorouracil/metabolism
- Fluorouracil/toxicity
- Gastric Mucosa/cytology
- Gastric Mucosa/drug effects
- Intestine, Small/cytology
- Intestine, Small/drug effects
- Jejunum/cytology
- Jejunum/drug effects
- Methotrexate/administration & dosage
- Methotrexate/toxicity
- Mice
- Mice, Inbred C57BL
- Mitochondria/drug effects
- Mitochondria/ultrastructure
- Mitochondria, Liver/drug effects
- Mitochondria, Liver/ultrastructure
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439
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Judde JG, Spangler G, Magrath I, Bhatia K. Use of Epstein-Barr virus nuclear antigen-1 in targeted therapy of EBV-associated neoplasia. Hum Gene Ther 1996; 7:647-53. [PMID: 8845390 DOI: 10.1089/hum.1996.7.5-647] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
To target expression of toxic genes to Epstein-Barr virus (EBV)-associated tumor cells, we have developed an EBV-driven enzyme prodrug system (EDEPS) that takes advantage of the trans-activating properties of EBNA1, a latent protein expressed in all EBV-containing cells, to direct expression of cytosine deaminase (CD) at high levels in those cells only. Plasmids were constructed in which the CD gene or a luciferase reporter gene were cloned downstream of the herpes simplex virus thymidine kinase (tk) promoter and the family of repeats (FR) sequence from the oriP region of EBV. Analysis of luciferase activity after transient transfection into a panel of EBV-negative or -positive human cell lines showed that the presence of the FR element enhanced transcription from the tk promoter in all EBV-positive cell lines, whereas transcription from tk was repressed in all EBV-negative cell lines, including B, T, and fibroblast cell lines. In clonogenicity assays following transfection with the CD vector, the presence of 5-fluorocytosine (5-FC) in the culture medium completely abolished cell growth in EBV-positive cell lines, but did not affect the growth of EBV-negative cell lines. This vector system should have wide applicability in that it allows targeted expression of any gene of interest to tumors that carry EBV, irrespective of the role EBV plays in their pathogenesis.
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440
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Kavlock RJ, Setzer RW. The road to embryologically based dose-response models. ENVIRONMENTAL HEALTH PERSPECTIVES 1996; 104 Suppl 1:107-121. [PMID: 8722115 PMCID: PMC1469576 DOI: 10.1289/ehp.96104s1107] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The goal of researchers working in the area of developmental toxicology is to prevent adverse reproductive outcomes (early pregnancy loss, birth defects, reduced birth weight, and altered functional development) in humans due to exposures to environmental contaminants, therapeutic drugs, and other factors. To best achieve that goal, it is important that relevant information be gathered and assimilated in the risk assessment process. One of the major challenges of improved risk assessment is to better use all pertinent biological and mechanistic information. This may be done qualitatively (e.g., demonstrating that the experimental model is not appropriate for extrapolation purposes); semiquantitatively (using information to reduce the degree of uncertainty present under default extrapolation procedures), or quantitatively (formally describing the relationships between exposure and adverse outcome in mathematical forms, including components that directly reflect individual steps in the overall progression of toxicity). In this paper we review the recent advances in the risk assessment process for developmental toxicants and hypothesize on future directions that may revolutionize our thinking in this area. The road to these changes sometimes appears to be a well-mapped course on a relatively smooth surface; at other times the path is bumpy and obscure, while at still other times it is only a wish in the eye of the engineer to cross an uncharted and rugged environment.
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441
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Gamelin EC, Danquechin-Dorval EM, Dumesnil YF, Maillart PJ, Goudier MJ, Burtin PC, Delva RG, Lortholary AH, Gesta PH, Larra FG. Relationship between 5-fluorouracil (5-FU) dose intensity and therapeutic response in patients with advanced colorectal cancer receiving infusional therapy containing 5-FU. Cancer 1996; 77:441-51. [PMID: 8630950 DOI: 10.1002/(sici)1097-0142(19960201)77:3<441::aid-cncr4>3.0.co;2-n] [Citation(s) in RCA: 161] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND A phase II prospective trial was carried out to study the concept of 5-fluorouracil (5-FU) dose-intensity in patients with advanced colorectal cancer. Forty patients were treated with 5-FU plus leucovorin (LV), with individually increasing doses of 5-FU. A 5-FU pharmacokinetic follow up was performed and a relationship was sought between its metabolism and its response to treatment, and between 5-FU's toxicity and patient survival. METHODS 5-FU was administered weekly by 8 hour continuous infusion. The initial dose of 1000 mg/m2 was individually increased every 3 weeks by 250 mg/m2 steps, potentiated by 400 mg/m2 LV. 5-FU plasma concentrations were determined weekly by liquid chromatography. RESULTS Eighteen overall objective responses and 22 minor responses, stabilizations, or progressions (NR) were observed. 5-FU plasma levels were significantly higher in cases of complete or partial response, whatever the dose. They reached about 2000 micrograms/l as early as the second dose level (1250 mg/m2). Only seven patients who experienced NR reached equivalent levels after the fourth step (1750 mg/m2). High 5-FU plasma levels were predictive of an objective response and better survival (difference not significant). The acute toxicity, whatever the type, was correlated with 5-FU levels > 3000 micrograms/l and not with the dose. CONCLUSIONS This study shows the wide variability of 5-FU metabolism, whatever the dose, the clear relationship between 5-FU plasma levels, toxicity, and efficacy. This relationship points out the problem of the polymorphism of 5-FU metabolism, the usefulness of the therapeutic range determination and the usefulness of the individual 5-FU dose adaptation.
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442
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DeYoung DJ, Bantle JA, Hull MA, Burks SL. Differences in sensitivity to developmental toxicants as seen in Xenopus and Pimephales embryos. BULLETIN OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 1996; 56:143-150. [PMID: 9026148 DOI: 10.1007/s001289900021] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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443
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Thompson MJ, Abdhul-Rahmann S, Baker TG, Bibby MC. Potentiation of testicular cytotoxicity by the alkyltransferase inhibitor O6 benzylguanine and the 5-fluorouracil/N-(2-chloroethyl)-N-nitrosourea molecular combination, B.4152. Reprod Toxicol 1996; 10:71-7. [PMID: 8998388 DOI: 10.1016/0890-6238(95)02020-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Alkylating agents are a group of compounds that have a cytotoxic effect due to their ability to form adducts with DNA. Cells possess the ability to repair this damage via an enzyme, O6-alkylguanine-DNA alkyltransferase (AGT). To study the effect of inhibiting this repair mechanism upon testicular cytotoxicity in BALB/c mice, the AGT inhibitor O6 benzylguanine (O6BG) was used in conjunction with the potential anticancer drug B.4152. Paraffin sections were stained and examined using Chalkley scoring to identify the cells affected by the treatment. Using B.4152 alone the maximal effect upon the spermatogenic tissue was found to be after 32 days. The damage found was minor, with the spermatocytes and spermatids most affected. Using this time point it was found that the combined treatment produced widespread damage, with significant depletion of the majority of spermatogenic cell types. These results therefore, indicate that differentiating spermatogenic cells are normally protected from B.4152 induced damage by AGT, depletion of which significantly potentiates B.4152 toxicity.
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444
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Kiremitçi-Gümüşderelioglu M, Gökçe M, Akata RF. A novel MMC-loaded pHEMA drainage device for the treatment of glaucoma: in vitro and in vivo studies. JOURNAL OF BIOMATERIALS SCIENCE. POLYMER EDITION 1996; 7:857-69. [PMID: 8836832 DOI: 10.1163/156856296x00039] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Administration of subconjunctival 5-fluorouracil (5-FU) and topical mitomycin-C (MMC) has been shown to improve the success rate of glaucoma-filtering surgery. However, corneal toxicity and administrative problems remain. To overcome this limitation, drainage devices for the sustained release of 5-FU and MMC were designed and tested in vitro and in vivo. This paper presents only the results of our studies which were carried out on MMC-loaded devices. Here, the drainage devices were prepared from MMC-loaded poly(hydroxyethyl methacrylate) (pHEMA) matrices in different cross-linking ratios and in different drug loading capacities, i.e. 0.2, 0.5, and 2.0 mg MMC per device. These devices released MMC at approximately 6.0-90.0 micrograms day-1 for over 2 months depending on cross-linking density and initial drug loading. The diffusional release of MMC from glassy and swollen copolymers showed that diffusion mechanism is Fickian in both cases. The usability of the pHEMA implants were investigated by in vivo experiments which were done on eight dog's eye. In the treatment eyes, intraocular pressures remained significantly lower than the control eyes throughout the experimental period (4 months). Subconjunctival implantations revealed no clinical and histological evidence for toxicity. The results of in vitro and in vivo studies indicate that an implantable release system delivering MMC for over 2 months can improve the prognosis for filtering surgery by preventing postoperative fibrosis.
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445
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Clarke E, Rice GC, Weeks RS, Jenkins N, Nelson R, Bianco JA, Singer JW. Lisofylline inhibits transforming growth factor beta release and enhances trilineage hematopoietic recovery after 5-fluorouracil treatment in mice. Cancer Res 1996; 56:105-12. [PMID: 8548748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The effectiveness of endogenous or exogenously administered colony-stimulating factors may be modulated by the presence of hematopoietic inhibitory molecules. Cytotoxic therapy may result in the induction of hematopoietic inhibitors contributing to prolonged myelosuppression, whereas preventing the induction of such inhibitors may accelerate multilineage recovery. Lisofylline [LSF; (R)-1-(5-hydroxyhexyl)-3,7, dimethyl-xanthine], inhibits the signaling and/or release of certain hematopoietic inhibitory molecules such as tumor necrosis factor alpha, macrophage inflammatory protein 1 alpha, transforming growth factor beta, and IFN-gamma. Treatment of murine bone marrow cells with the cytotoxic agent 5-fluorouracil (5-FU) results in the release of a nondialyzable inhibitor of progenitor (colony-forming unit-granulocyte macrophage; CFU-GM) proliferation. When murine bone marrow cells were treated with 5-FU plus LSF, release of this inhibitor of CFU-GM proliferation was blocked. Neutralizing antibody and Western blot analysis indicated that the inhibitor was TGF-beta. We tested the effect of LSF (100 mg/kg i.p., b.i.d.) on multilineage regeneration after high-dose 5-FU or thiotepa treatment in BALB/c mice. In 4 of 5 experiments, LSF significantly accelerated neutrophil recovery (P < or = 0.05, Wilcoxon paired-signed test). In addition, platelet, reticulocyte, and CFU-GM regeneration were significantly accelerated in mice treated with LSF compared to control mice (P < or = 0.05). LSF had no significant effects on the ability of 5-FU to kill hematopoietic progenitor cells, nor did LSF stimulate or inhibit proliferation of CFU-GM. LSF had no effect on chemotherapy-induced killing of tumor cells in vitro, nor on the antitumor activity of 5-FU or thiotepa in BALB/c mice implanted with P388 leukemia cells. Inhibition of hematopoietic inhibitor release may accelerate multilineage recovery after cytotoxic therapy and, as such, may represent an alternative or additional therapy to the use of positively acting lineage specific colony-stimulating factors.
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446
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Skretkowicz J, Sekulska M, Danilewicz M, Wagrowska-Danilewicz M, Polakowski P. Effect of some anticancer drugs and combined chemotherapy on renal toxicity. BIOLOGICAL SIGNALS 1996; 5:51-8. [PMID: 8739323 DOI: 10.1159/000109173] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The nephrotoxic action of anticancer drugs such as nitrogranulogen (NG), methotrexate (MTX), 5-fluorouracil (5-FU) and cyclophosphamide (CY) administered alone or in combination [MTX + 5-FU + CY (CMF)] was evaluated in experiments on Wistar rats. After drug administration, creatinine concentrations in the plasma and in the urine of the rats were determined, as well as creatinine clearance. Histopathologic evaluation of the kidneys was also performed. After MTX administration a significant increase (p = 0.0228) in the plasma creatinine concentration and a significant (p = 0.0001) decrease in creatinine clearance was noted compared to controls. After the administration of NG, 5-FU and CY neither a statistically significant increase in creatinine concentration nor an increase in creatinine clearance was observed compared to the group receiving no cytostatics. Following polytherapy according to the CMF regimen, a statistically significant decrease (p = 0.0343) in creatinine clearance was found, but creatinine concentration did not increase significantly compared to controls. CY caused hemorrhagic cystitis in 40% of rats, but it did not cause this complication when combined with 5-FU and MTX. Histologic changes were found in rat kidneys after administration of MTX, CY and NG, while no such change was observed after 5-FU and joint administration of MTX + 5-FU + CY compared to controls. Our studies indicate that nephrotoxicity of MTX + 5-FU + CY administered jointly is lower than in monotherapy.
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447
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Kalechman Y, Rushkin G, Nerubay J, Albeck M, Sredni B. Effect of the immunomodulator AS101 on chemotherapy-induced multilineage myelosuppression, thrombocytopenia, and anemia in mice. Exp Hematol 1995; 23:1358-66. [PMID: 7498364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The immunomodulator AS101 has previously been found to induce mouse and human hematopoietic cells to secrete cytokines such as interleukin-1 alpha (IL-1 alpha), IL-2, tumor necrosis factor-alpha (TNF-alpha), and gamma interferon (IFN-gamma). The compound was shown to protect mice from lethal and sublethal effects of chemotherapy and irradiation. AS101 prevented the decrease in the number of bone marrow (BM) and spleen myeloid progenitor cells, and increased the survival of lethally treated mice. In this study, we show a dose-dependent response of AS101 in the induction of high secretion levels of IL-6, IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF). Since these growth factors are known to induce the proliferation and differentiation of multilineage progenitors, including megakaryocytic and erythroid progenitors, we designed this study to evaluate the role of AS101 in attenuating thrombocytopenia, anemia, and multilineage myelosuppression associated with chemotherapy. We demonstrate that pretreatment of mice with AS101 24 hours before intraperitoneal injection of 250 mg/kg cyclophosphamide (CYP) or intravenous injection of 150 mg/kg 5-fluorouracil (5-FU) significantly increased the number of circulating white blood cells (WBC) and platelets. The numbers of both neutrophils and lymphocytes were significantly increased in AS101-treated mice subjected to chemotherapy. In addition, AS101 attenuated erythropenia caused by 5-FU. It could also increase megakaryocyte and erythroid progenitor cells (CFU-MK and CFU-E) in the BM of treated mice severely affected by chemotherapy. We demonstrate that the protective effect of AS101 could be abrogated by treatment with anti-IL-1R or anti-SCF antibodies. We suggest that the endogenous production of cytokines such as IL-1, IL-6, IL-3, SCF, and GM-CSF in mice treated with AS101 offers protection to circulating blood elements and ameliorates the reconstitution of megakaryocytic and erythroid progenitors. The simultaneous protection by AS101 of multilineage cell compartments is probably due to stimulation by AS101 of a selective subpopulation of primitive stem cells resistant to chemotherapy. On the basis of these studies, phase II clinical trials with patients treated with chemotherapy in combination with AS101 have been initiated.
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Carlsson G, Gustavsson B, Frösing R, Odin E, Hafström LO, Spears CP, Larsson PA. Antitumour effects of pure diastereoisomers of 5-formyltetrahydrofolate in hepatic transplants of a rodent colon carcinoma model. Biochem Pharmacol 1995; 50:1347-51. [PMID: 7503782 DOI: 10.1016/0006-2952(95)02004-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The effects of the two diastereoisomers of 5-formyltetrahydrofolate on tumour growth, thymidylate synthase (TS, EC 2.1.1.45) levels, and potentiation of 5-fluorouracil cytotoxicity were studied in an in vivo rat colon carcinoma model, transplanted to liver. The animals were randomized into eight groups, treated with daily i.v. tail vein injections of racemic (d,l)-5-formyltetrahydrofolate (5-CHO-FH4), 15 mg/kg, (1)-5-CHO-FH4 7.5 mg/kg, and (d)-5-CHO-FH4 7.5 mg/kg, 5-fluorouracil (FUra) 30 mg/kg, (d,l)-5-CHO-FH4 15 mg/kg+FUra 30 mg/kg, (l) 5-CHO-FH4 7.5 mg/kg+FUra 30 mg/kg, and (d)-5-CHO-FH4 7.5 mg/kg+FUra 30 mg/kg, and a sham-treated control group. The average tumour size of the groups was equal at the start of treatment. After six days' treatment the average tumour sizes were at laparotomy 3.3 +/- 1.0 g in the (d/l)-5-CHO-FH4 treated group, compared to 2.0 +/- 0.1 g in the FUra treated group and 7.1 +/- 3.1 g in the controls. Natural (l)-5-CHO-FH4 promoted tumour growth (average tumour weight 10.8 +/- 4.0 g), whereas the unnatural (d)-5-CHO-FH4 alone retarded it (average tumour weight 1.2 +/- 0.40 g). (l)-5-CHO-FH4 induced a significant increase in tumour tissue TS levels by [3H]FdUMP radioligand assay (27.5 +/- 8.4 pmol/g tumour tissue) compared to controls (16.8 +/- 6.1 pmol/g tumour tissue). Increases in 5,10-methylenetetrahydrofolate and tetrahydrofolate occurred with FUra alone, with a further statistically significant increase in both folates with the addition of (d)-5-CHO-FH4 to FUra.
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Paukovits JB, Paukovits WR. Stem cell stimulation in vitro by the dekapeptide (pEEDCK)2: a single-factor alternative for multifactor cocktails. Leukemia 1995; 9 Suppl 1:S48-52. [PMID: 7475313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Insertion of foreign genes into cellular DNA requires (at least one round of) DNA replication. Since hemopoietic stem cells do not divide rapidly, numerous semi-empirically designed multifactor cocktails have been used to stimulate them. In an attempt to find an alternative to this approach we have investigated the effects of the stem cell stimulatory peptide (pGlu-Glu-Asp-Glys-Lys)2, (pEEDCK)2, on progenitor output in murine long-term bone marrow cultures (LTBMC). (pEEDCK)2 may act by inducing growth factor production in stromal cells. Addition of (pEEDCK)2 to LTBMCs resulted in a three-fold increase in CFU-GM production. For showing an effect of (pEEDCK)2 on primitive hemopoietic cells (long-term-culture initiating cells, (LTC-IC)) LTBMCs were depleted of rapidly dividing progenitors by 5-Fluoro-Uracil (5-FU). LTC-IC survive and repopulate the culture with new CFU-GM. (pEEDCK)2 greatly enhanced this process (eight-fold in the second week after 5-FU). Enhanced progenitor production was observed for several weeks even after discontinuation of (pEEDCK)2 additions to the cultures (100-fold, five weeks after 5-FU, three weeks after end of peptide additions). This increase in progenitor production resulted in increased numbers of total nucleated cells. Our results suggest that (pEEDCK)2 may be a useful alternative for multifactor cocktails when proliferation of primitive stem-cell-like cells is required, as in gene therapy and transplantation. Our experiments also indicate that the redox equilibrium between (stem cell inhibitory) monomeric pEEDCK and (stem cell stimulatory) dimeric (pEEDCK)2, which are both endogenous constituents of LTBMCs may play a role in physiological stem cell regulation.
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Shuey DL, Setzer RW, Lau C, Zucker RM, Elstein KH, Narotsky MG, Kavlock RJ, Rogers JM. Biological modeling of 5-fluorouracil developmental toxicity. Toxicology 1995; 102:207-13. [PMID: 7482555 DOI: 10.1016/0300-483x(95)03049-l] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A biologically-based dose-response (BBDR) model is a mathematical description of the biological events leading to expression of a toxic response. As an alternative to current approaches in non-cancer risk assessment, such models will reduce uncertainty in that they will provide a more comprehensive description of toxicity. We are involved in construction of a BBDR model for the developmental toxicity of 5-fluorouracil (5-FU) in the rat using multiple approaches. First, to identify critical events in the pathogenesis of 5-FU developmental toxicity, thymidylate synthetase (TS) inhibition and alterations in cell kinetics and growth were examined in embryos following maternal administration of 5-FU on day 14 of gestation. A dose-related decline in TS activity was observed within 1 h; however, maximal inhibition and recovery were similar at 10, 20 and 40 mg/kg. Dose-dependent cell cycle alterations were observed within 4 h after exposure and were maximal at 8 h. Hindlimb growth reduction was observed 24 h after exposure to 40 mg/kg, but not at lower doses. At term hindlimb defects were observed at doses above 30 mg/kg. An integrated dose-response model for hindlimb defects was derived from empirical relationships among these events. The resultant dose-response somewhat over-predicted the developmental toxicity of 5-FU, although results of a Monte Carlo simulation indicated that these data were not incompatible with model predictions. Overall, the results suggest that TS inhibition is a key component of the mechanism of 5-FU developmental toxicology, but the model does not capture all of the critical events in the induction of hindlimb defects. A preliminary mechanistic model for the inhibition of embryonic TS, DNA synthesis and cell cycle following maternal exposure to 5-FU, independently derived from literature data to further examine the potential role of this pathway in its developmental toxicity, predicted a dose-response for TS inhibition and DNA synthesis that closely reflected the observed patterns. These results further suggest that TS inhibition, resultant deficits in DNA synthesis and cell cycle perturbations represent a critical mechanistic pathway in the developmental toxicity of 5-FU.
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