Role of fluoropyrimidine Schedule and (6R,S)leucovorin dose in a preclinical animal model of colorectal carcinoma

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.

Polyglutamylation of the dihydrofolate reductase inhibitor gamma-methylene-10-deazaaminopterin is not essential for antitumor activity

As part of a continuing program aimed at developing nonpolyglutamylatable inhibitors of dihydrofolate reductase that are less toxic and more specific in their action, we herein report the therapeutic efficacy and toxicity of gamma-methylene-10-deazaaminopterin (MDAM) in athymic nude mice bearing advanced human HCT-8 ileocecal xenografts and its antitumor activity in C57BL/6 x DBA/2 F1 (hereafter called B6D2F1) mice bearing P388 murine leukemia. For the xenograft study, MDAM was administered at the maximum tolerated dose by the following dose schedules: (a) 5-day continuous i.v. infusion at 1.0 mg/kg/day (schedule I); and (b) i.v. push, daily for 5 days at 50 mg/kg/day (schedule II). The maximum tolerated dose values for methotrexate (MTX) under these conditions were 0.2 and 1.0 mg/kg/day for schedule I and schedule II, respectively. MTX did not exhibit any significant antitumor activity in this model system by both schedules; however, MDAM induced complete responses of 13 and 25% and partial responses of 25 and 50% by schedules I and II, respectively. MDAM also exhibited antitumor activity significantly superior to that of MTX in the P388 tumor model. One of the enantiomers of MDAM, which possesses the natural configuration at the gamma-methyleneglutamate moiety (l-MDAM), has been shown to be a better inhibitor of human recombinant dihydrofolate reductase and H35 hepatoma cell growth than D,L-MDAM. L-MDAM inhibited the uptake of radiolabeled folinic acid to H35 hepatoma cells eight times more efficiently than MTX. The results indicate that the superior activity of MDAM relative to MTX may be partially due to a combination of enhanced transport to tumor cells and slower deactivation by aldehyde oxidase.

[Reversion of malignant phenotypes of human lung squamous carcinoma cells by ornithine decarboxylase antisense RNA]

Abnormally elevated activity of ornithine decarboxylase (ODC), with subsequent polyamine accumulation are intimately associated with the genesis, development and metastasis of cancer. Therefore, ODC antisense RNA was used to transfect human lung squmous carcinoma cell line LTEP-78. Compared with the parental cells, growth of the antisense transfected LTEP-78 cells arrested in G0/G1 phase and colony formation in soft agar and tumorigenicity in nude mice were significantly reduced. Nucleic acid hybridization demonstrated the expression of ODC antisense RNA and the content of ODC mRNA was markedly reduced. The results suggest that the reversion of malignant phenotypes of human lung squamous carcinoma cells is associated with the control of polyamine biosynthesis.

PAK-104P, a pyridine analogue, reverses paclitaxel and doxorubicin resistance in cell lines and nude mice bearing xenografts that overexpress the multidrug resistance protein

Multidrug resistance (MDR) is considered multifactorial and has been associated with overexpression of the multidrug resistance protein (MRP). However, effective compounds for reversal of MRP-related MDR are limited. In the present study, the modulatory activity of the novel pyridine analogue PAK-104P on MRP-mediated resistance to doxorubicin and paclitaxel was investigated in two doxorubicin-selected human tumor cell lines [HT1080/DR4 (sarcoma) and HL60/ADR (leukemia)] and compared with the nonimmunosuppressive cyclosporine analogue PSC-833. In cell lines HT1080/DR4 (MRP/lung resistance-related protein phenotype) and HL60/ADR (MRP phenotype), doxorubicin resistance was significantly higher (250-fold and 180-fold, respectively) than that to paclitaxel (6-fold and 9-fold, respectively). With noncytotoxic concentrations of PAK-104P (1 and 5 microM), the reversal of doxorubicin resistance was significant but partial in HT1080/DR4 and HL60/ADR cells (dose-modifying factor for 5.0 microM PAK-104P, 25.0 and 31.2, respectively), whereas complete reversal of paclitaxel resistance was achieved in HL60/ADR cells. In contrast, PSC-833 modulation of doxorubicin and paclitaxel resistance was modest. Cellular drug uptake and retention studies by flow cytometry analysis demonstrated that PAK-104P was effective in restoring cellular doxorubicin concentrations in resistant cells to levels comparable to those obtained in parental cells. In athymic nude mice, PAK-104P significantly potentiated the therapeutic efficacy of doxorubicin and paclitaxel against resistant HT1080/DR4 xenografts. Of significance is that the maximum tolerated doses of doxorubicin and paclitaxel were administered in combination with PAK-104P, documenting improvement in the therapeutic index of these agents. In addition to reversing P-glycoprotein-mediated MDR, the pyridine analogue PAK-104P provides an example of an effective in vivo modulator of MRP-mediated MDR.

5-Ethynyluracil (776C85): effects on the antitumor activity and pharmacokinetics of tegafur, a prodrug of 5-fluorouracil

We studied the effects of 5-ethynyluracil (776C85 and 776C), a potent mechanism-based inactivator of dihydropyrimidine dehydrogenase, on the antitumor efficacy and pharmacokinetics of tegafur (FT), a prodrug of 5-fluorouracil (5-FU), in rats with large s.c. colon carcinoma. Rats were dosed p.o. once daily for 7 days with either FT, FT and uracil in a 1:4 molar ratio (UFT), FT 1 h after 776C (776C/FT), or UFT 1 h after 776C (776C/UFT). 776C, which was dosed at 1 mg/kg, had neither intrinsic antitumor activity nor toxicity. The rank order in antitumor efficacy at the maximal tolerated dose of the FT (mg/kg/day) component was 776C/FT (5 mg/kg/day) > or = UFT (80 mg/kg/day) = 776C/UFT (5 mg/kg/day) >> FT (200 mg/kg/day). One-hundred % of rats treated with 776C/FT had complete and sustained tumor regression with no severe toxicity. The area under the plasma 5-FU concentration versus the time curve generated from UFT, FT, and 776C/FT at their maximum tolerated dose was 140, 50, and 27 microM.h, respectively. The area under the concentration in plasma versus time curve did not correlate with the rank order of antitumor efficacy. The vast majority of 5-FU derived from FT (alone) appeared to be rapidly catabolized. Furthermore, plasma exposure of 5-FU derived from UFT was more variable than that from 776C/FT. Each therapy also produced different levels of plasma uracil. Endogenous plasma uracil levels (1-3 microM) were not affected by FT but increased to 100 microM after dosing with 776C. Plasma uracil from UFT was 800 microM 1 h after dosing. These results suggest that moderately elevated uracil (776C/FT) may be beneficial, whereas uracil that is greatly elevated during the first 5 h (UFT) and 5-FU catabolites (FT alone) may interfere with antitumor efficacy. 776C, coadministered with FT, could provide once-a-day oral therapy for cancer patients.

5-Fluorouracil prodrug: role of anabolic and catabolic pathway modulation in therapy of colorectal cancer

Following p.o. administration to rats bearing advanced colorectal carcinoma, Ftorafur (FT) is converted to 5-fluorouracil (FUra) by microsomal P450 in the liver. To optimize the therapeutic selectivity of the FUra generated from FT, three approaches were utilized: (a) inhibition of FUra degradation to dihydrofluorouracil by uracil as an alternative substrate for uracil reductase in the molar ratio of 4 uracil:1 FT (UFT); (b) modulation of drug inhibition of thymidylate synthase by leucovorin (LV); and (c) by increasing the level of FUra incorporation into cellular RNA by N-(phosphonacetyl)-L-aspartate (PALA), an inhibitor of aspartate transcarbomylase. The maximum tolerated dose (MTD) of FT and UFT, administered 3 times a day for 28 days, was 150 mg/kg/day and 60 mg/kg/day, respectively. The MTDs were not significantly modified by LV (150 or 600 mg/kg/day), administered by the p.o. route with the drugs, or by PALA (100 mg/kg) administered weekly by the i.v. route. The dose-limiting toxicity of FT alone and in combination with the modulators was stomatitis. The severe alopecia observed with FT alone was reduced significantly by uracil. At the MTD, the antitumor activity of UFT was superior to those of FT and FUra alone and in combination with LV and/or PALA. The 3-month sustained complete tumor regression for UFT, FT, and FUra was 38%, 0%, and 13% (for the weekly schedule), respectively. Although uracil, LV, and PALA individually increased the antitumor activity of FT at its MTD, the combination of the three modulators produced the highest therapeutic efficacy in rats bearing advanced colorectal carcinoma, in which 100% of the treated animals achieved complete and sustained tumor regression. The therapeutic efficacy observed with FT modulation could not be achieved with FUra administered by different schedules, each at its MTD alone or in combination with either LV or PALA. In brief, modulation of FT produced greater therapeutic efficacy and selectivity than FUra. Furthermore, the combined use of modulators capable of inhibiting the degradation pathway of FUra and potentiating the effects of the anabolic metabolites action appears to offer the greatest therapeutic potential.

[Clinical application of luteinizing hormone releasing hormone agonist and its impact on bone metabolism]

OBJECTIVES

To evaluate the efficacy of luteinizing hormone releasing hormone agonist (LHRH-A) in the treatment of endometriosis (Em), uterine leiomyoma and adenomyosis, and its impact on bone metabolism.

METHODS

Twenty patients, Em 13 (stage II4, III7, IV2), leiomyoma 4 and adenomyosis 3, were selected to receive LHRH-A 200 micrograms intramuscular daily for 3 months. Clinical and ultrasound features serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), osteocalcin (BGP) concentrations were compared before and at the end of treatment. Furthermore, 24-hour urinary calcium (Ca), phosphate (P) excretions and bone mineral density (BMD) of radius and lumbar spine measured by single photon absorptiometry (SPA) and dual energy X-ray absorptiometry (DEXA) were also analysed before and at the end of treatment. Patients were followed-up 3-19 months after discontinuation of the drug.

RESULTS

At the end of treatment dysmenorrhea disappeared in all 15 cases. Pelvic tenderness and induration improved in 18, endometrioma shrinked in 13 cases. Mean uterine volume of 7 patients with leiomyoma or adenomyosis was reduced by 35% from the basal volume. Serum LH, E2 levels were suppressed significantly (P < 0.05), mean E2 concentration declined from 459.5 +/- 292.0 to 160.3 +/- 110.7 pmol/L (P < 0.001). No significant change was found in serum BGP, urinary Ca, P, and BMD of radius and lumbar spine at the end of therapy, The only side effect was mild not flushes and sweating during treatment. After stopping the drug, 17 patients resumed menses within 2 months. Dysmenorrhea and pelvic mass recurred in 6 months with less severity. One became pregnant in 3 months.

CONCLUSIONS

LHRH-A administration is effective in the treatment of Em, leiomyoma and adenomyosis. No significant adverse effect was shown on bone metabolism at the end of 3-month therapy.

Electric acupuncture treatment of peripheral nerve injury

54 cases of peripheral nerve injury were treated by electric acupuncture and compared with 54 control cases treated with supportive medication. The changes after treatment were observed chiefly by electromyography while sensory and motor improvement were also recorded as auxiliary indicators. The therapeutic results in the acupuncture group were 5 cases cured, 26 markedly effective, 19 improved, and 4 cases failed, a total effective rate of 92.6% in contrast to the 55.6% for the controls. Analysis of the therapeutic results showed that 1) those in the acupuncture group were significantly better than in the control group; 2) nerve injuries should be treated as early as possible; 3) the radial nerve and the common peroneal nerve recovered faster than others; 4) cases not surgically explored recovered faster than those that were, and 5) patients with prompt propagation of the needling sensation recovered significantly faster than those with slow propagation.

Modulation of the antitumour activity of cisplatin alone and in combination with 5-fluoro-2'-deoxyuridine by N-phosphonacetyl-L-aspartate in murine colon carcinoma no. 26

Modulation of the therapeutic efficacy of cisplatin (CDDP) and 5-fluoro-2'-deoxyuridine (FdUrd) alone and in combination with N-phosphonacetyl-L-aspartate (PALA) was evaluated in mice bearing colon carcinoma (C-26) using a weekly intravenous (i.v.) push schedule for 3 weeks. A non-toxic dose of PALA (100 mg/kg) was administered i.v. 24 h prior to the i.v. administration of CDDP +/- FdUrd. The maximum tolerated doses (MTD) of CDDP and FdUrd when used as a single agent were 9 and 400 mg/kg, respectively. In combination, however, the MTD of CDDP and FdUrd were 2.5 and 300 mg/kg, respectively. PALA did not significantly affect the MTD. PALA improved the antitumour activity of CDDP or FdUrd when used alone; however, the highest tumour response, 66% complete tumour regression, was achieved with a PALA modulation of CDDP and FdUrd in combination.

Attenuation of the antitumor activity of 5-fluorouracil by (R)-5-fluoro-5,6-dihydrouracil

5-Ethynyluracil (5-EU; 776C85) is a potent mechanism-based inactivator of dihydropyrimidine dehydrogenase that improves the antitumor activity of 5-fluorouracil (5-FU) to a greater extent than can be accounted for by the improved 5-FU pharmacokinetics that result from preventing the catabolism of 5-FU. We therefore tested the effects of (R)-5-fluoro-5,6-dihydrouracil (5-FUH2), the 5-FU catabolite extensively formed in the absence of 5-EU, on the antitumor activity and toxicity of 5-FU in 5-EU-treated rats bearing large s.c. tumors. Rats were dosed once weekly for 3 weeks with the following regimens: 100 mg/kg 5-FU (maximum tolerated dose), 10 mg/kg 5-FU 1 h after 1 mg/kg 5-EU, or 10 mg/kg 5-FU plus 90 mg/kg 5-FUH2 1 h after 1 mg/kg 5-EU. The latter regimen was designed to approximate the exposure produced from 5-FU in the absence of 5-EU, where > 80% of the dose is catabolized. 5-FU produced complete and sustained tumor regressions in 94% of the animals pretreated with 5-EU. In contrast, 5-FU in combination with 5-FUH2 produced complete regression in only 38% of the 5-EU-treated rats, which was similar to the antitumor activity of 5-FU in the absence of 5-EU. All treatments resulted in 7-11% transient weight loss. 5-FU produced no other notable toxicity in 5-EU-treated rats. However, 5-FUH2 added to this regimen caused transient diarrhea and stomatitis in 13% of the animals, which was similar to the toxicity produced by 5-FU in the absence of 5-EU. Thus, 5-FUH2, or other downstream catabolites of 5-FU, impaired the antitumor activity and slightly increased the toxicity of 5-FU. Accordingly, 5-EU approved to improve the efficacy of 5-FU by preventing the formation of 5-FU catabolites.

Modulation of the antitumor-activity of 5-Fluorouracil and cisplatinum by N-phosphonacetyl-L-aspartate in the murine colon-carcinoma number-26

Modulation of the antitumor activity of cisplatinum (CDDP) alone or in combination with 5-fluorouracil (FUra) by N-phosphonacetyl-L-aspartate (PALA) was investigated in Balb/c mice bearing colon 26 adenocarcinoma, using weekly i.v. push schedule (days 1, 7 and 14) with PALA (100 mg/kg) been administered 24 h prior to each drug treatment. Antitumor activity was assessed at the maximum tolerated dose (MTD) of treatment by determining tumor doubling time (TD), ratio of tumor size in drug treated to control values (T/C) and by kinetic of tumor regression, being partial (PR) or complete (CR) tumor regression. In this model system, FUra and CDDP alone and in combination did not produce significant antitumor activity. Although tumor reduction by these agents was primarily in the form of PR, regrowth of tumor was apparent following termination of treatment. In contrast, pretreatment with a nontoxic dose of PALA produced significant increase in CR rates, ranged from 6% of treated animals with CDDP to 19% of animals treated with FUra. Furthermore, the greatest therapeutic efficacy was achieved when PALA was used to modulate the antitumor activity of the combination of FUra and CDDP. Under these conditions 70% and 30% of treated animals achieved PR and CR, respectively. With the weekly schedule use herein, PALA did not potentiate significantly the toxicity of either FUra or CDDP. Potentiation of CDDP toxicity by PALA was observed when the drug was used in combination with FUra, requiring approximately 6 fold reduction in CDDP dose. In brief, using the optimal doses of FUra and CDDP in combination, PALA potentiated significantly the antitumor activity of the combination in mice bearing a tumor relatively resistant to FUra and CDDP when used as a single agent and in combination.

5-Ethynyluracil (776C85): modulation of 5-fluorouracil efficacy and therapeutic index in rats bearing advanced colorectal carcinoma

5-Ethynyluracil (EU; 776C85) is a potent inactivator of dihydropyrimidine dehydrogenase, the enzyme that rapidly degrades 5-fluorouracil (FUra). We have investigated the antitumor activity and toxicity of FUra alone and in combination with EU in rats bearing advanced colon carcinoma. Two schedules were studied: (a) FUra daily for 4 days i.v. push (daily x 4); and (b) FUra administered i.v. push weekly for 3 weeks (weekly x 3). EU was administered at 1 mg/kg 1 h before FUra and for two additional days post-FUra therapy. The maximum tolerated doses of FUra alone were 35 and 100 mg/kg/day and for FUra plus EU were 10 and 15 mg/kg/day for the daily x 4 and weekly x 3 schedules, respectively. The dose-limiting toxicities were diarrhea and stomatitis both for FUra alone and for FUra in combination with EU. Although EU was not toxic and not active as an antitumor agent, it markedly improved the efficacy and therapeutic index of FUra. The antitumor activity of FUra was schedule dependent, yielding 13% complete and sustained tumor regression on the weekly schedule and no complete and sustained tumor regression on the daily schedule. The combination of FUra and EU produced 100% complete and sustained tumor regression on both schedules. The therapeutic index was < or = 1 for FUra alone and 6 for FUra with EU. EU was considerably more effective than either leucovorin or N-(phosphonacetyl)-L-aspartate as a modulator of FUra. Leucovorin or N-(phosphonacetyl)-L-aspartate induced minimum improvements on the daily schedule and only increased the therapeutic index to 1.5 on the weekly schedule. Because a 4-day continuous infusion of FUra alone at the maximum tolerated dose did not improve FUra therapy, we conclude that the improvements by EU involve additional modulations that complement the enhanced exposure of FUra.

Double labelling to obtain S phase subpopulations: application to determine cell kinetics of diploid cells in an aneuploid tumour

We studied the cell kinetics of the murine mammary carcinoma MCa-K using iododeoxyuridine (IdUrd) and chlorodeoxyuridine (CldUrd) given at different times as independently detectable labels of S phase cells. The presence of IdUrd and CldUrd, and the amount of DNA were measured by three-colour flow cytometry making it possible to define three subpopulations within S phase and to measure the progression through the cell cycle during the time following labelling. In DNA histograms of these subpopulations, the diploid and aneuploid cells (which had a DNA index of 1.7) are essentially completely separated. From appropriate combinations of cells labelled with IdUrd only, CldUrd only, or both, it was possible to construct separate DNA distributions for the labelled diploid and aneuploid cells at the times of administration of each label. The kinetics of the diploid and aneuploid cells could be calculated for individual tumours from these two time points without having to make corrections for the presence of the second population. The diploid and aneuploid populations had indistinguishable S and G2 + M phase durations, T(S) and T(G2 + M), of about 9 and 2 h; however, the potential doubling time values for the aneuploid and diploid populations were 30.2 and 101.2 h respectively.

Proliferation kinetics of recruited cells in a mouse mammary carcinoma

Solid tumors contain populations of proliferating (P) and quiescent (Q) cells. Shifting between these populations occurs continuously and cells are recruited from quiescence to proliferate (Q-->P) as a result of exogenously applied or endogenous cell depleting stimuli. Direct measurements of the proliferation kinetics of these Q-->P cells in solid tumors are difficult to make because of the much larger percentage of P-cells. In order to specifically analyze the kinetics of the Q-->P cells, double thymidine analogue labeling was used. This was accomplished by first labeling in vivo all of the P-cells in MCaK tumors using continuous exposure to chlorodeoxyuridine (CldUrd) administered by a minipump over 21 h. About 75% of the aneuploid cells are P-cells based on CldUrd labeling. At different times after the pumps were removed, the tumors were pulse-labeled with iododeoxyuridine (IdUrd) and harvested 6 h later. A 3-color flow cytometry assay was used to simultaneously and independently analyze CldUrd and IdUrd incorporation, as well as DNA content. The Q-->P cells were identified as having only been labeled with IdUrd. The length of their S-phase was calculated from the movement of the Q-->P cells during the 6 h after IdUrd labeling. The results showed the length of S-phase for the recruited cells to be slightly, but significantly, longer than the length of S-phase for the total cells (11 h versus 9 h, respectively). Thus, the recruited cells appear to have slightly slower kinetics than the proliferating cells in the absence of a perturbing stimulus such as radiotherapy or chemotherapy.

Modulation of target enzyme associated with the action of antifolates

The cytotoxicity and molecular effects of antifolate thymidylate synthase inhibitor, ICI-D1694, against human ileocecal carcinoma, were evaluated. The drug concentration for 50% inhibition of cell growth by ICI-D1694 is 73 nM and 3 nM following 2 hr and 72 hr exposure, respectively. The drug induces high level of DNA single strand breaks in a time dependent manner, but subsequent to maximum inhibition of thymidylate synthase. Drug effects can be reversed by thymidine and leucovorin at > 1 microM concentrations. Leucovorin action is primarily at the cell membrane level, competing with the transport and activation of ICI-D1694. Thymidine, however, exerts its competitive effect primarily at the level of thymidylate synthase.

Calculating potential doubling time using monoclonal antibodies specific for two halogenated thymidine analogues

PURPOSE

A new flow cytometric technique that allows for two-incorporated thymidine analogues to be measured simultaneously and independently has been used to improve the accuracy of in vivo cell kinetic estimates, i.e., the length of S-phase (TS) and potential doubling time (Tpot).

METHODS AND MATERIALS

The analogues chlorodeoxyuridine and iododeoxyuridine were injected at different times into mice bearing the mouse mammary tumor MCaK. At different times after labeling, the tumors were harvested and prepared for three color flow cytometric analysis of DNA, chlorodeoxyuridine, and iododeoxyuridine. Control experiments showed that similar estimates of Tpot were obtained from each label when administered singly, or as staggered pulses. Comparisons were made between TS and Tpot calculated from a single label (single point), from the averaged result of the two labels from the same tumor (two point-ave), and from the simultaneous nonlinear fitting of the measured parameters from the two labels, from the same tumor (two point-fit). These estimates of TS and Tpot were then compared to reference values obtained by fitting the pooled measured parameters from all the tumors, that were labeled for different periods of time.

RESULTS

While all of the methods resulted in similar mean estimates of TS and Tpot that were close to the reference values, the fewest assumptions, and the least variability in the results, were obtained using the two point-fit data.

CONCLUSION

The estimation of Tpot using two thymidine analogues is more accurate than that obtained from a single label.

Effect of caloric restriction on aflatoxin B1-induced DNA synthesis, AFB1-DNA binding and cell proliferation in Fischer 344 rats

Young adult male Fischer rats maintained on a reduced calorie diet (60% of ad libitum food consumption) for 6 weeks showed a decrease in the binding of aflatoxin B1 (AFB1) to hepatic or renal nuclear DNA and a reduction of AFB1-induced hepatocellular damage. Repeated dosing of rats with AFB1 resulted in the inhibition of hepatic and renal DNA synthesis measured by [3H]thymidine incorporation. However, the rate of DNA synthesis was greater in ad libitum (AL) rats than in calorically restricted (CR) animals. Three days after AFB1 dosing, the rate of DNA synthesis had recovered to the control level. Cell cycle analyses measured by a flow cytometric method on kidney cells of both AL and CR rats showed that there were no significant changes in cell populations in the S phase between these two groups of rats. AFB1 inhibited the cell proliferation on an average of 33%. The restoration of the cell proliferation in kidney cells was found on the third day after AFB1 dosing. The rate of the regenerative cell proliferation was found to be slightly greater in AL rats than in CR animals. The AFB1-induced regenerative DNA synthesis in both liver and kidney was retarded by CR.

[Saponins in the fruit pedicels of Panax notoginseng (Burk.) F.H. Chen (continue)]

Six saponins were isolated from the fruit pedicels of Panax notoginseng. Five of them were identified as gypenoside-XVII, -XV, ginsenoside-Rb1, and notoginsenoside-Fc, -Fa on the basis of chemical methods, spectroscopic analysis and comparison with authentic standards. Quantitative determination of the major saponins in fruit pedicels from the plant was made by thin layer chromatography-densitometry.

[Saponins in fruits pedicels of Panax notoginseng (Burk.). F.H. Chen]

Six saponins were isolated from the fruit pedicels of Panax notoginseng for the first time. They were identified as ginsenoside-Rc, -Rb3, -Re, notoginsenoside-Fe, -R1 and gypenoside IX by chemical and spectroscopic analysis.

Overexpression of the c-erbB-2/neu–encoded p185 protein in primary lung cancer

The c-erbB-2/neu gene encodes a transmembrane protein of 185 kDa (p185) with tyrosine kinase activity and extensive sequence homology to epidermal growth factor receptor. Amplification and overexpression of the c-erbB-2/neu gene has been shown in certain human tumors and is postulated to be important in human carcinogenesis. High levels of expression of the c-erbB-2/neu gene have been reported in non-small-cell lung cancer (NSCLC) cell lines and primary tumors from the United States. Since geographical and cultural factors may contribute to the development of certain types of cancer, we examined p185 examined p185 expression in 120 tumors from Chinese patients with lung cancers of different cell types and used immunohistochemical staining to determine the extent and general significance of p185 expression in human primary lung cancer. Our results demonstrate that 58.8% of the NSCLCs expressed p185 and that expression of p185 was observed only in NSCLC and not in small-cell lung cancers. Thirty-three of 41 adenocarcinomas and 24 of 55 squamous cell carcinomas among the NSCLCs examined were found to express p185 at levels different from those of normal lung. For the squamous cell carcinomas, p185 expression was correlated with lymph node metastasis (P less than 0.01), but for the adenocarcinomas, it was not (P greater than 0.05). In addition, expression of p185 in NSCLC was significantly more frequent in patients in advanced clinical stages. Our findings indicate that p185 expression is a frequent event and a general phenomenon in NSCLC and is correlated with poor clinical prognostic indicators, suggesting that expression of p185 may be of potential prognostic importance in NSCLC.

Cytogenetic studies on a human rectal carcinoma cell line (HR-8348)

Cytogenetic properties of a human rectal carcinoma cell line (HR-8348) established in China are described. The early (29th passage) and late (93rd passage) passage cells were used for chromosome analysis. HR-8348 was found to have an essentially triploid karyotype. This distribution of chromosome numbers was rather dispersed in early passage, whereas it was concentrated in the 65-70 range in late passage. G-banded karyotype analysis also showed that the numerical distribution of chromosomes was dispersed in early passage and was associated with more abnormal chromosomes. In late passage, the numerical distribution became more stable and the number of abnormal chromosomes was reduced. In 60 metaphases analyzed, 10 marker chromosomes were found. The frequencies of M1, M2 and M3 were 100% in both early and late passage cells. The morphological characteristics of these marker chromosomes and their possible origin and role in the pathogenesis of colorectal carcinoma are discussed.

Cytogenetic studies on peripheral lymphocytes of members from two multiple familial polyposis coli families

Cytogenetic studies were carried out on peripheral lymphocytes of 30 members from two typical familial polyposis coli (FPC) families. It was found that, under low folic acid culture conditions, the chromosome aberration rate of FPC family members (10%) was much higher than that of the control group (2.3%). No significant difference in SCE was found between the two groups. We suggest that the chromosome aberration rate under certain conditions may be used as a parameter for the early detection of FPC in certain FPC families. The analysis of fragile sites sensitive to low folic acid in FPC family members revealed that besides the significant increase of 3p14, which is frequently seen in tumor patients, other unique sites (1p22, 1p32 and 6q21) were also present in most of the FPC patients. Fragile sites 1p22, 1p32 and 6q21 are located near certain well known oncogene loci; thus, they may have something to do with the pathogenesis of FPC. The actual relationship between these fragile sites and FPC remains to be elucidated.

Green tea extract inhibits nucleoside transport and potentiates the antitumor effect of antimetabolites

The present study provides evidence that green tea extract (GTE), consisting of polyphenol components, is a highly active nucleoside transport inhibitor. GTE markedly inhibited radiolabeled thymidine and uridine transport in mouse leukemia L1210 cells, with IC50 values of 3.2 and 8.0 mumol/L, respectively. GTE blocked the rescue effect of exogenous nucleosides and enhanced the cytotoxicity of AraC and MTX to L1210 cells and human hepatoma BEL-7402 cells. GTE markedly potentiated the inhibitory effect of AraC on leukemia L1210 and P388 in mice. These results indicate that GTE is potentially useful when combined with antimetabolites in cancer chemotherapy.

Some observations on the localization of mitomycin C-induced aberrations in human lymphocytes

Actively cycling human lymphocytes were treated with mitomycin C for 1 h (1.4 micrograms/ml) and then grown in medium containing 10 micrograms/ml bromodeoxyuridine. Serial 5-h colcemid accumulation samples were taken up to 35 h and the air-dried methaphase spreads stained for replication banding. A complete cell-cycle subphasing analysis was made, and classified cells scored for all categories of chromatid-type aberrations and their location. In spite of the high dose which produced massive delay and cycle perturbation, there was no evidence for selective lethality of early-S cells, in fact such cells were in excess. Extreme localization of aberrations to late-replicating (mostly centromeric) regions was found at all subphases and in pre-S cells. This rules out 'localization by default' as an explanation for the observed preferential occurrence of 'break points' in these regions. The frequency of incomplete intrachanges, low in late S, rises dramatically in early S to become maximal in pre-S cells.

Comparison between protracted and conventional dose rates of irradiation on the growth of the Bp8 mouse ascites sarcoma

Four days after inoculation, in vivo growing Bp8 mouse ascites sarcoma was irradiated with 1.75, 2.5 and 5 Gy at a dose rate of 0.0185 Gy/min. The results were compared with those obtained previously at a dose rate of 1.33 Gy/min. Using flow-cytometry and the mitotic index, the total number of tumour cells and the proportion of cells in the various parts of the cell cycle were determined up to 10 days after irradiation. In addition, from sequential analyses of the total number of cells in the various compartments of the cell cycle, the flow of cells through cell cycle was calculated. The total number of tumour cells at the plateau phase of growth, the mitotic index and flow calculations indicated that protracted irradiation was more effective than short-time irradiation following 2.5 Gy; no differences were found following 1.75 Gy, and a lesser effect following 5 Gy. While the cells during protracted irradiation were effectively blocked in G2 and in split-dose experiments a good repair capacity has been demonstrated, redistribution of cells in the cell cycle can apparently not explain the results. Induction of repair, dependent both on dose rate and on total dose, may explain the higher efficiency of protracted irradiation.

Repair in irradiated ascites tumour cells growing in vivo. An investigation of split doses related to cell cycle

Split dose irradiation with 2 X 2.5 Gy at intervals of 3 to 48 h was compared with the effect of a single irradiation with a 5 Gy dose in Bp8 mouse ascites sarcoma growing in vivo. The total number of cells and, using rapid-flow cytofluorometry, the proportions of cells in the various parts of the cell cycle were determined up to 10 days after irradiation. In addition, from sequential analyses of the total number of cells in the various compartments of the cell cycle, the flow of cells through the cell cycle was calculated. As judged by the growth in the total number of cells, a rapid repair of at least 20 per cent per h up to 3 h is followed by a slow repair of about one per cent per h during the following 45 h. The proportion of cells in the cell cycle following the conditioning dose did not differ enough to expect a significant influence on the mean radiation sensitivity of the cell population. At split time intervals of 12 to 48 h, after a transient early increase of the flow of cells through the cell cycle, the flow of cells was markedly reduced in all parts of the cell cycle with a maximum 24 to 48 h after the second dose of irradiation. This increase in the cell cycle time was not found following single dose irradiation and may influence the repair of potentially lethal cell damage.

Growth kinetics of Bp8 mouse ascites sarcoma after single dose whole body irradiation. I. Analysis of the relative and total numbers of cells in various parts of the cell cycle

The effects of irradiation on the growth of the Bp8 mouse ascites sarcoma were analysed following doses of 1.75, 2.5, 5.0 and 8.0 Gy. From the total number of cells and the percentage of cells in G1, S-phase, G2 + M as measured by flow cytofluorometric DNA analysis and the mitotic index the total number of cells in the various parts of the cell cycle was estimated. After an initial delay in the increase in the cell numbers during the period of rapid growth the total number of cells shows a dose dependent decrease at the plateau stage of the ascites growth. This dose relationship is characterized by a shoulder type of curve with a D0 of about 6.5 Gy and Dq of about 2 Gy. This decrease in the total number of cells is caused by a decreasing number of G1, S-phase and mitotic cells while G2 cells generally remain at unchanged levels. This behaviour of the G2 cells reflects the preference of long-lasting blocking events in G2 of the cell cycle but may also indicate specific regulating processes linked to this type of cell. The ratio between the number of mitotic and G2 cells also decreases in a dose dependent way and is a sensitive indicator for irradiation effects even below the lowest dose (1.75 Gy) used in the present experiments.

Proliferation kinetics and specific behaviour of G2 cells of the Bp8 mouse ascites sarcoma in vivo

Growth characteristics of the Bp8 ascites sarcoma were investigated by means of evaluation of total cell number, the cellular DNA content, the mitotic index and the percentage of dead cells. Following intraperitoneal inoculation of 18 x 10(6) cells into NMRI mice a plateau level of about 1400 x 10(6) cells was reached after 7 days followed by a daily decline of 5 per cent up to day 14, the terminal stage of life. Based on the increase of the cell number and the distribution of cells in the cell cycle the flow rate through and the duration of the various parts of the cell cycle were calculated. Generally, the durations of all phases of the cell cycle including mitosis increased with age, most markedly after day 8 when the durations tended to become infinite. At the plateau phase the total number of G1, S-phase and mitotic cells decreased significantly while G2 cells remained at a constant level. This finding may be of interest in view of the concept of ascites tumour cells behaving as a regulated cell system.

Behaviour of the Bp8 mouse ascites sarcoma after partial body irradiation

Mice bearing the Bp8 mouse ascites sarcoma were 4 days after inoculation irradiated with 2.5, 5 and 8 Gy. By shielding the head and the upper part of the thorax the mice survival, compared with whole body irradiation, was markedly prolonged and the behaviour of the ascites tumour could be evaluated up to 30 days after inoculation. While about 10 days after irradiation the total number of tumour cells started to decrease and amounted to only 4 per cent 20 days later, the ascites volume increased up to 30 ml. Using flow-cytometric cellular DNA analysis, the proportions of cells in the various parts of the cell cycle were determined. After an initial G2 blockage, a partial blockage with an increase proportion of G2 cells was found up to 20 days after inoculation. While the total number of G1, S-phase and mitotic cells started to decrease on day 10, the total number of G2 cells was independent of the dose and was constant up to day 18. This behaviour may indicate specific regulating processes linked to G2 cells.

Growth kinetics of Bp8 mouse ascites sarcoma after single doses of whole body irradiation. II. Analysis of the progression of cells through the cell cycle

Bp8 ascites sarcoma cells growing in vivo were whole body irradiated with doses of 1.75 to 8 Gy. The inflow and outflow rates of cells in the various compartments of the cell cycle were estimated on the basis of sequential analysis of the total number of cells and from the proportion of cells in G1, S-phase, G2 and M. The flow through the compartments was calculated from these data and from the sizes of the cell pools. The durations of the mitotic delay, the G1-depletion and the early G2 blockage were linearly related to the dose. After release of the mitotic division delay the accumulation rate of cells in M and G1 decreased linearly with the dose; for G2, plateau values for the accumulation rate were found after 2.5 Gy. The outflow rates from G2 and M after release of the G2 blockage showed a shoulder type of dose-response with a D0 of 2.5 Gy and a n value of 1.5. In addition to an increase in the duration of G2, generally responsible for the increase in the total cell cycle time at about 24 hours after irradiation and an increase in the duration of the S-phase up to 12 hours after irradiation, an early increase in the duration of G1 and M was observed.

Radiation therapy of nasopharyngeal carcinoma

Carcinoma of the nasopharynx is one of the most frequent malignant tumors in the southern parts of China. A total of 3 263 cases treated with irradiation in the course of the thirty years since the Liberation have been analysed retrospectively. The 5-year survival rate has risen from 27.7 per cent for cases treated during 1955 to 1960 to 54 per cent for those treated in 1973. The technique of irradiation is described, emphasizing the importance of suitable techniques for the treatment of the cervical lymph nodes. The value of elective irradiation of cervical regions not involved clinically is elucidated. Finally, the causes of failure of treatment are discussed.