Chemotherapeutic agent CPT-11 induces the new expression of the apoptosis initiator to the cytoplasm

Circadian Rhythm of Irinotecan Tolerability in Mice

The toxicity of irinotecan (CPT-11), a topoisomerase-I inhibitor largely used in cancer patients, was investigated as a function of the circadian time of its administration in mice, with mortality, body weight loss, leukopenia, neutropenia, intestinal lesions, and bone marrow cell cycle phase distribution as end points. Four experiments were performed on a total of 773 male mice standardized with 12h light/12h darkness. Irinotecan was administered daily for 4 or 10 consecutive days (D1-4 and D1-10, respectively, in different experiments) at one of six circadian stages expressed in hours after light onset (HALO). The survival curves differed significantly as a function of the dosage and circadian time of drug administration by the D1-10 schedule, with 70% survival at 7 or 11 HALO and 51% at 19 or 23 HALO (p=0.039 from log rank test). CPT-11 administration at 19 or 23 HALO resulted in (1) greatest mean body weight loss at nadir; (2) most severe colic and bone marrow lesions and/or slowest recovery; and (3) deepest neutropenia nadir and/or slowest hematologic recovery. These circadian treatment time-related differences were statistically validated. The bone marrow cell cycle data revealed a four to eight-fold larger G2-M phase arrest following irinotecan administration at 19 or 23 HALO in comparison to the other times of drug administration, apparently representative of the repair of more extensive DNA damage (p < 0.001 from ANOVA) when the medication was given at these circadian times. Overall, CPT-11 was better tolerated by mice treated during the light (animals' rest) span. The results support the administration of CPT-11 to cancer patients in the second half of the night, during sleep, in order to improve drug tolerability.

Loss of one allele of the p53 gene in the lens epithelial tumor in transgenic mice suppresses apoptosis induced by a topoisomerase I inhibitor (CPT-11)

To examine whether CPT-11 can induce apoptosis in the mouse lens tumor, it was administered to pregnant alphaT3 mice, which developed epithelial tumors in the lens during the perinatal stage. Three different p53 genotypes were generated to analyze the influence of p53 status on tumor cells under chemotherapy. On day 16--17 of gestation, alphaT3 mice received an i.p. injection of CPT-11, and fetal lens tumors were examined 2 days later. Apoptosis in the tumors was observed in both a CPT-11 dose- and p53 gene copy-dependent manner. In addition, it was found that CPT-11 could also induce apoptosis via a p53-independent pathway.

Antitumoral effect of irinotecan (CPT-11) on an experimental model of malignant neuroectodermal tumor

Irinotecan (CPT-11) is a topoisomerase I inhibitor with antitumor activity on a wide variety of neoplasms in several preclinical studies, but it showed poor efficacy in patients with nervous system tumors. We have carried out an experimental study in order to evaluate the effect of CPT-11 on the growth of a subcutaneously implanted malignant neuroectodermal tumor, after administration by different routes. The results showed that CPT-11 administration by intraperitoneal injections (at dose 10 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period--one course--to a total of two courses) had no significant antitumor effect. Nevertheless, continuous infusion by intraperitoneal osmotic minipump over 28 days (at an infusion rate of 4.4 microg/h) showed a significant delay in tumor growth in 4 weeks of the implantation. The best antitumor effects were observed after CPT-11 intratumoral administration (at dose of 5 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period, to a total of three courses) reaching tumor regression in the treated animals. These results suggest the utility of CPT-11, by means of intralesional administration, on malignant tumors of the nervous system.

Inductions of fibroblast-like morphology and high growth activity by low-dose CPT-11 in PC12 cells: role of tenascin

The chemotherapeutic agent CPT-11 induces apoptotic cell death in various cells. In the present study we examined the effect of CPT-11 in rat pheochromocytoma PC12 cells. When PC12 cells were treated with CPT-11, two distinct reactions were encountered. A high dose of CPT-11 induced apoptotic cell death mediated by caspase cascade, whereas a low dose of CPT-11 induced irreversible cell morphological changes. The cell shape of the transformed PC12 cells was similar to fibroblasts, and these were termed FLTP12 (fibroblast-like transformed PC12). FLTP12 cells showed some differences from the original PC12 cells. In addition, cultured media of passed FLTP12 cells induced same cell transformation in PC12 cells. To examine how this transformation may be triggered, the possible involvement of a growth factor(s) was investigated. Among those tested, the possible involvement of basic fibroblast growth factor (basic-FGF) was observed, whereas basic FGF antibody did not affect the induction of cell transformation. Molecular sieve analysis revealed that transformation-inducing factor is large molecule protein like cell attachment factors (>100K), and we demonstrated the direct involvement of tenascin in the transformation of PC12 cell.

Down-regulation of endothelin receptors by transforming growth factor beta1 in hepatic stellate cells

BACKGROUND/AIMS

Hepatic endothelin-1 (ET-1) receptor density as well as the levels of both ET-1 and transforming growth factor beta1 (TGF-beta1) increase in liver cirrhosis. Considering their potent contractile (ET-1) and fibrogenic (TGF-beta1) actions on myofibroblastic stellate cells found in the fibrotic/cirrhotic liver, we aimed to investigate the effects of TGF-beta1 on ET-1 receptors and ET-1 synthesis in these cells.

METHODS

Stellate cells isolated from rat liver by enzymatic digestion were cultured and subjected to TGF-beta1 treatment. Cellular ET-1 receptors and ET-1 released in the medium were determined.

RESULTS

TGF-beta1 treatment produced time- and dose-dependent decrease in ET-1 binding sites, but did not affect the affinity of the receptors for ET-1. TGF-beta1 also stimulated the release of ET-1 from stellate cells. The extent of TGF-beta1-induced inhibition of [125I]ET-1 binding was much greater for ETB subtype (73+/-18% inhibition), which comprised a major portion (78+/-12%) of the total ET-1 receptors, than for ETA subtype (35+/-11% inhibition). The mRNA expression of the ET-1 receptors also was reduced by TGF-beta1 treatment. TGF-beta1-induced reduction in ET-1 receptor density was coupled to the inhibition of ET-1-stimulated release of [3Hlarachidonic acid from the prelabeled cells. The effects of TGF-beta1 were inhibited by a TGF-beta1 neutralizing monoclonal antibody.

CONCLUSIONS

These results suggest that the TGF-beta1-induced decrease in ET-1 receptor density may be an important mechanism in limiting the pathologic actions of ET-1 on stellate cells in chronic liver disease.

Superoxide-induced changes in endothelin (ET) receptors in hepatic stellate cells

BACKGROUND/AIMS

Reactive oxygen species are mediators of various pathophysiologic events, including postischemic reperfusion injury and inflammation. Generation of reactive oxygen species and consequent organ injury are associated with increased levels of a powerful vasoconstrictor peptide endothelin-1. Current evidence suggests that actions of endothelin-1 on the contractile and fibrogenic transdifferentiated stellate cells may play a critical role in hepatic pathophysiology. The aim of this investigation was to determine whether reactive oxygen species modulate the synthesis of endothelin-1 and its receptors in stellate cells.

METHODS

Primary cultures of transdifferentiated stellate cells were exposed to reactive oxygen species-generating system, hypoxanthine/xanthine oxidase, before determination of endothelin-1 and its receptors.

RESULTS

The treatment caused an initial decrease in ET-1 receptor density (about 30% at 30 min), followed by a significant increase over the basal level at 6 h. The increase in the receptors, which occurred specifically in the ET(B) subtype, progressed thereafter up to 24 h and was accompanied by an augmented functional response, as indicated by an enhanced endothelin-1-induced release of [3H]arachidonic acid from the prelabeled cells. Furthermore, treatment of cells for 24 h but not 30 min caused increased expression of ET(B) mRNA as determined by semi-quantitative polymerase chain reaction. The release of endothelin-1 in the culture medium was also enhanced by hypoxanthine/xanthine oxidase treatment. These effects of hypoxanthine/xanthine oxidase were inhibited by superoxide dismutase and dimethyl sulfoxide. ET-1-induced [3H]arachidonic acid release was also inhibited by the ET(B) receptor antagonist BQ788, but not by the ET(A) receptor antagonist BQ123.

CONCLUSIONS

These findings indicate that interactions between ET-1 and stellate cells during episodes of the generation of reactive oxygen species can be an important mechanism in the pathophysiology of hepatic disorders.

Necessity of interleukin-1beta converting enzyme cascade in taxotere-initiated death signaling

Taxotere is a new type chemotherapeutic agent which targets tubulin. In the present study, we investigated the molecular machinery of taxotere-initiated death signaling. Taxotere induced cell death in mouse fibroblast L929 cells. Cell morphological analysis revealed that this effect showed characteristics of apoptotic and necrotic cell death. To further examine taxotere-induced cell death, we investigated the direct involvement of caspase. When cells were pretreated with the synthesized tetrapeptide inhibitor of caspase, YVAD-CHO (Ac-Tyr-Val-Ala-Asp-aldehyde: inhibitor of interleukin-1beta converting enzyme (ICE) subfamily) or DEVD-CHO (Ac-Asp-Glu-Val-Asp-aldehyde: inhibitor of CPP32 subfamily), taxotere-induced cell death was prevented. In addition, time course experiments demonstrated that activation of the ICE subfamily preceded activation of the CPP32 subfamily in taxotere-initiated death signaling, suggesting the direct involvement of the ICE cascade in taxotere-initiated death signaling. On the basis of these results, we suggest that taxotere causes the initiation of ICE cascade in its death signaling pathway and that the down-stream site of taxotere-initiated death signaling is the same as that of other chemotherapeutic agents.

Etorphine inhibits cell growth and induces apoptosis in SK-N-SH cells: involvement of pertussis toxin-sensitive G proteins

Opiates have been used extensively in the treatment of pain but with the severe side effect of addiction, which is believed to be related to opiates' direct (primary) or indirect (secondary) neurotoxicity. In this study, the effects of opioids on cell growth and apoptosis have been examined in human neuroblastoma cell line SK-N-SH. Etorphine, a wide-spectrum and potent agonist of opioid receptors, was found to significantly inhibit cell growth and to induce apoptosis. The inhibitory and apoptotic activities of etorphine followed a dose- and time-dependent manner. The more specific agonists of opioid receptors such as morphine, [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAGO), [D-Pen2, D-Pen5]-enkephalin (DPDPE), dynorphin A and nociceptin/orphanin FQ did not show similar toxic activities under the same conditions. In addition, the effects of etorphine could not be blocked by the opioid receptor antagonist naloxone, suggesting that the effects of etorphine might not be mediated by a classical opioid receptor. However, pretreatment of SK-N-SH cells with pertussis toxin (PTX) blocked the inhibition of cell growth and apoptosis induced by etorphine, indicating the involvement of PTX-sensitive G proteins in the processes. It was also shown that etorphine-induced apoptosis was prevented by actinomycin D (AD) and interleukin-1beta converting enzyme inhibitor I. Interestingly, etorphine was similarly potent to inhibit growth of pheochromocytoma (PC12) cells but less effective in SH-SY5Y neuroblastoma cells and C6 glioma cells. We propose that inhibition of cell growth and induction of apoptosis may be one mechanism of opioid neurotoxicity.

Clinical pharmacokinetics of irinotecan

This article reviews the clinical pharmacokinetics of a water-soluble analogue of camptothecin, irinotecan [CPT-11 or 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptoth eci n]. Irinotecan, and its more potent metabolite SN-38 (7- ethyl-10-hydroxy-camptothecin), interfere with mammalian DNA topoisomerase I and cancer cell death appears to result from DNA strand breaks caused by the formation of cleavable complexes. The main clinical adverse effects of irinotecan therapy are neutropenia and diarrhoea. Irinotecan has shown activity in leukaemia, lymphoma and the following cancer sites: colorectum, lung, ovary, cervix, pancreas, stomach and breast. Following the intravenous administration of irinotecan at 100 to 350 mg/m2, mean maximum irinotecan plasma concentrations are within the 1 to 10 mg/L range. Plasma concentrations can be described using a 2- or 3-compartment model with a mean terminal half-life ranging from 5 to 27 hours. The volume of distribution at steady-state (Vss) ranges from 136 to 255 L/m2, and the total body clearance is 8 to 21 L/h/m2. Irinotecan is 65% bound to plasma proteins. The areas under the plasma concentration-time curve (AUC) of both irinotecan and SN-38 increase proportionally to the administered dose, although interpatient variability is important. SN-38 levels achieved in humans are about 100-fold lower than corresponding irinotecan concentrations, but these concentrations are potentially important as SN-38 is 100- to 1000-fold more cytotoxic than the parent compound. SN-38 is 95% bound to plasma proteins. Maximum concentrations of SN-38 are reached about 1 hour after the beginning of a short intravenous infusion. SN-38 plasma decay follows closely that of the parent compound with an apparent terminal half-life ranging from 6 to 30 hours. In human plasma at equilibrium, the irinotecan lactone form accounts for 25 to 30% of the total and SN-38 lactone for 50 to 64%. Irinotecan is extensively metabolised in the liver. The bipiperidinocarbonylxy group of irinotecan is first removed by hydrolysis to yield the corresponding carboxylic acid and SN-38 by carboxyesterase. SN-38 can be converted into SN-38 glucuronide by hepatic UDP-glucuronyltransferase. Another recently identified metabolite is 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC). This metabolite is a weak inhibitor of KB cell growth and a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). Numerous other unidentified metabolites have been detected in bile and urine. The mean 24-hour irinotecan urinary excretion represents 17 to 25% of the administered dose. Recovery of SN-38 and its glucuronide in urine is low and represents 1 to 3% of the irinotecan dose. Cumulative biliary excretion is 25% for irinotecan, 2% for SN-38 glucuronide and about 1% for SN-38. The pharmacokinetics of irinotecan and SN-38 are not influenced by prior exposure to the parent drug. The AUC of irinotecan and SN-38 correlate significantly with leuco-neutropenia and sometimes with the intensity of diarrhoea. Certain hepatic function parameters have been correlated negatively with irinotecan total body clearance. It was noted that most tumour responses were observed at the highest doses administered in phase I trials, which indicates a dose-response relationship with this drug. In the future, these pharmacokinetic-pharmacodynamic relationships will undoubtedly prove useful in minimising the toxicity and maximise the likelihood of tumour response in patients.

Amyloid beta-protein induces necrotic cell death mediated by ICE cascade in PC12 cells

A major component of Alzheimer's disease plaque amyloid beta protein (betaAP) showed the cytolytic activity to rat pheochromocytoma PC 12 cells. Nuclear morphological study revealed that betaAP-induced cytolytic activity is due to necrotic cell death, rather than apoptotic cell death. To examine the molecular machinery of betaAP-induced necrotic cell death in detail, I investigated the direct involvement of caspase. When nerve growth factor-treated and -untreated PC12 cells were incubated with the synthesized tetrapeptide inhibitors of caspase, YVAD-CHO (Ac-Tyr-Val-Ala-Asp-CHO) or DEVD-CHO (Ac-Asp-Glu-Val-Asp-CHO), betaAP-induced necrotic cell death was prevented. In addition, the interleukin-1beta converting enzyme (ICE) subfamily activation preceded CPP32 subfamily activation during betaAP-induced necrotic cell death. On the basis of these findings, I suggest that betaAP induces necrotic cell death mediated by the ICE cascade and that the ICE cascade may possibly be involved in Alzheimer's disease.

Involvement of cytoplasmic serine proteinase and CPP32 subfamily in the molecular machinery of caspase 3 activation during Fas-mediated apoptosis

On stimulation by the Fas ligand, the death receptor, Fas, initiates a signal leading to apoptotic cell death. Fas plays an important role in physiological cell death and is closely involved in various disease states. Recent investigations have shown that caspase 3 plays a dominant role in the process of Fas-mediated apoptosis. In the present study, we investigated the molecular machinery of caspase 3 activation in Fas-mediated apoptosis. The results showed that Fas-mediated apoptosis was accompanied by caspase 3 activation, and both Fas-mediated apoptosis and caspase 3 activation were prevented by a serine proteinase inhibitor. In addition, the serine proteinase inhibitor also prevented the caspase 3 activation in cytoplasts, and the specific activation of serineproteinase was encountered in only cytoplasmic proteins. These results suggest that cytoplasmic serineproteinase plays an important role in caspase 3 activation. Interestingly, caspase 3 was cleaved at p3 site immediately after Fas Ab stimulation, and the cleavage at p17 site became detectable later. We also found that among tested proteinases only Staphylococcus aureus V8 serineproteinase initiated caspase 3 activation and specifically cleaved at p3 site. These results strongly suggest that a cytoplasmic S. aureus V8-like serine proteinase is closely involved in caspase 3 activation.

Sequential operation of ceramide synthesis and ICE cascade in CPT-11-initiated apoptotic death signaling

The chemotherapeutic agent CPT-11 induced apoptotic cell death in mouse fibroblast 4B1 cells. To examine the intracellular apoptotic death signal initiated by CPT-11, ceramide synthesis and the ICE cascade were analyzed. CPT-11-initiated cytolytic activity was prevented by both caspase inhibitors YVAD-CHO and DEVD-CHO, or ceramide synthesis inhibitor fumonisin B1, and accelerated by sphingomyelin, suggesting the direct involvement of ceramide synthesis and the interleukin 1-beta converting enzyme (ICE) cascade. In addition, apoptosis was induced by both native and synthesized ceramide and prevented by YVAD-CHO and DEVD-CHO, suggesting the possible involvement of ceramide in ICE cascade operation. To directly demonstrate whether ceramide synthesis operates the ICE cascade, proteolytic activity of ICE- or CPP32-like proteinase was analyzed. ICE-like proteinase activity was prevented by fumonisin B1 and YVAD-CHO, but not by DEVD-CHO. In contrast, fumonisin B1, YVAD-CHO, and DEVD-CHO all prevented CPP32-like proteinase activity. These results suggest that ceramide synthesis acts as a dominant regulator in CPT-11-initiated death signaling and sequentially operates the ICE cascade.