Circadian regulation of mouse topoisomerase I gene expression by glucocorticoid hormones

Molecular Aspects of Circadian Pharmacology and Relevance for Cancer Chronotherapy

The circadian timing system (CTS) controls various biological functions in mammals including xenobiotic metabolism and detoxification, immune functions, cell cycle events, apoptosis and angiogenesis. Although the importance of the CTS is well known in the pharmacology of drugs, it is less appreciated at the clinical level. Genome-wide studies highlighted that the majority of drug target genes are controlled by CTS. This suggests that chronotherapeutic approaches should be taken for many drugs to enhance their effectiveness. Currently chronotherapeutic approaches are successfully applied in the treatment of different types of cancers. The chronotherapy approach has improved the tolerability and antitumor efficacy of anticancer drugs both in experimental animals and in cancer patients. Thus, chronobiological studies have been of importance in determining the most appropriate time of administration of anticancer agents to minimize their side effects or toxicity and enhance treatment efficacy, so as to optimize the therapeutic ratio. This review focuses on the underlying mechanisms of the circadian pharmacology i.e., chronopharmacokinetics and chronopharmacodynamics of anticancer agents with the molecular aspects, and provides an overview of chronotherapy in cancer and some of the recent advances in the development of chronopharmaceutics.

Identification of Circadian Determinants of Cancer Chronotherapy through In Vitro Chronopharmacology and Mathematical Modeling

Cancer chronotherapy aims at enhancing tolerability and efficacy of anticancer drugs through their delivery according to circadian clocks. However, mouse and patient data show that lifestyle, sex, genetics, drugs, and cancer can modify both host circadian clocks and metabolism pathways dynamics, and thus the optimal timing of drug administration. The mathematical modeling of chronopharmacology could indeed help moderate optimal timing according to patient-specific determinants. Here, we combine in vitro and in silico methods, in order to characterize the critical molecular pathways that drive the chronopharmacology of irinotecan, a topoisomerase I inhibitor with complex metabolism and known activity against colorectal cancer. Large transcription rhythms moderated drug bioactivation, detoxification, transport, and target in synchronized colorectal cancer cell cultures. These molecular rhythms translated into statistically significant changes in pharmacokinetics and pharmacodynamics according to in vitro circadian drug timing. The top-up of the multiple coordinated chronopharmacology pathways resulted in a four-fold difference in irinotecan-induced apoptosis according to drug timing. Irinotecan cytotoxicity was directly linked to clock gene BMAL1 expression: The least apoptosis resulted from drug exposure near BMAL1 mRNA nadir (P < 0.001), whereas clock silencing through siBMAL1 exposure ablated all the chronopharmacology mechanisms. Mathematical modeling highlighted circadian bioactivation and detoxification as the most critical determinants of irinotecan chronopharmacology. In vitro-in silico systems chronopharmacology is a new powerful methodology for identifying the main mechanisms at work in order to optimize circadian drug delivery.

Mechanism of the 24-hour rhythm of tumor necrosis factor-alpha formed by onset of rheumatoid arthritis

OBJECTIVE

Morning stiffness and plasma cytokine levels in rheumatoid arthritis (RA) patients exhibit 24-hour variations. Tumor necrosis factor-α (TNF-α) plays a central role in RA clinical conditions, including the invasion of inflammatory cells, destruction of cartilage, systemic inflammatory response and its levels show a 24-hour rhythm after the onset of RA. In this study, we investigated what cytokines and/or transcriptional factors are involved in the formation of 24-hour variations in TNF-α levels after the onset of RA using MRL/Mpj-Tnfrsf6(lpr) (MRL/lpr) mice.

METHOD

Blood was drawn at six different times from MRL/lpr mice to measure cytokines, serum amyloid A (SAA), IgG rheumatoid factor (IgG-RF) and corticosterone levels. Cytokine and transcriptional factor levels at the different times were measured in 10- and/or 15-week-old MRL/lpr mice. The promoter activity of TNF-α by lymphotoxins (LTs) was investigated using a dual-luciferase assay.

RESULTS

SAA and TNF-α concentrations clearly exhibited 24-hour rhythms with higher levels at the light phase and lower levels at the dark phase after RA crisis. The expression of LT-α and LT-β showed significant 24-hour rhythms in 15-week-old MRL/lpr mice and the phases of LT-α and LT-β levels were antiphase compared with that of TNF-α. AP-1 binding sites were found in LT-α and LT-β promoter regions, and jun mRNA expression corresponded to LT-α and LT-β levels. TNF-α promoter activity was decreased due to the co-transfection of LT-α and LT-β.

CONCLUSION

LT-α and LT-β controls the 24-hour rhythm in TNF-α levels after the onset of RA in order to suppress TNF-α promoter activity.

Rhythmic binding of Topoisomerase I impacts on the transcription of Bmal1 and circadian period

The Bmal1 gene is essential for the circadian system, and its promoter has a unique open chromatin structure. We examined the mechanism of topoisomerase I (Top1) to understand the role of the unique chromatin structure in Bmal1 gene regulation. Camptothecin, a Top1 inhibitor, and Top1 small interfering RNA (siRNA) enhanced Baml1 transcription and lengthened its circadian period. Top1 is located at an intermediate region between two ROREs that are critical cis-elements of circadian transcription and the profile of Top1 binding indicated anti-phase circadian oscillation of Bmal1 transcription. Promoter assays showed that the Top1-binding site is required for transcriptional suppression and that it functions cooperatively with the distal RORE, supporting that Bmal1 transcription is upregulated by Top1 inhibition. A DNA fragment between the ROREs, where the Top1-binding site is located, behaved like a right-handed superhelical twist, and modulation of Top1 activity by camptothecin and Top1 siRNA altered the footprint profile, indicating modulation of the chromatin structure. These data indicate that Top1 modulates the chromatin structure of the Bmal1 promoter, regulates Bmal1 transcription and influences the circadian period.

Role of circadian clocks in the development and therapeutics of cancer

Circadian clocks are endogenous molecular time-keeping systems that underlie daily fluctuations in multiple physiological and biochemical processes. It is now well recognized that dysfunction of the circadian system may be associated with a heightened incidence of cancer. This brief review presents evidence supporting the important role played by circadian clocks in the development of cancer and the therapeutic efficacy of anticancer agents. A number of circadian clock genes have been identified, which include transcription factors that regulate gene expression. Continued research in this area should increase understanding of the role of circadian clocks which could, ultimately, reduce the incidence of cancer in people with disrupted sleep-wake cycles, such as 24-h shift workers and flight attendants, and provide optimal chronopharmacology for cancer treatment.

Sex and dosing-time dependencies in irinotecan-induced circadian disruption

Circadian disruption accelerates malignant growth; thus, it should be avoided in anticancer therapy. The circadian disruptive effects of irinotecan, a topoisomerase I inhibitor, was investigated according to dosing time and sex. In previous work, irinotecan achieved best tolerability following dosing at zeitgeber time (ZT) 11 in male and ZT15 in female mice, whereas worst toxicity corresponded to treatment at ZT23 and ZT3 in male and female mice, respectively. Here, irinotecan (50 mg/kg intravenous [i.v.]) was delivered at the sex-specific optimal or worst circadian timing in male and female B6D2F1 mice. Circadian disruption was assessed with rest-activity, body temperature, plasma corticosterone, and liver mRNA expressions of clock genes Rev-erbα, Per2, and Bmal1. Baseline circadian rhythms in rest-activity, body temperature, and plasma corticosterone were more prominent in females as compared to males. Severe circadian disruption was documented for all physiology and molecular clock endpoints in female mice treated at the ZT of worst tolerability. Conversely, irinotecan administration at the ZT of best tolerability induced slight alteration of circadian physiology and clock-gene expression patterns in female mice. In male mice, irinotecan produced moderate alterations of circadian physiology and clock-gene expression patterns, irrespective of treatment ZT. However, the average expression of Rev-erbα, Per2, and Bmal1 were down-regulated 2- to 10-fold with irinotecan at the worst ZT, while being minimally or unaffected at the best ZT, irrespective of sex. Corticosterone secretion increased acutely within 2 h with a sex-specific response pattern, resulting in a ZT-dependent phase-advance or -delay in both sex. The mRNA expressions of irinotecan clock-controlled metabolism genes Ce2, Ugt1a1, and Top1 were unchanged or down-regulated according to irinotecan timing and sex. This study shows that the circadian timing system represents an important toxicity target of irinotecan in female mice, where circadian disruption persists after wrongly timed treatment. As a result, the mechanisms underling cancer chronotherapeutics are expectedly more susceptible to disruption in females as compared to males. Thus, the optimal circadian timing of chemotherapy requires precise determination according to sex, and should involve the noninvasive monitoring of circadian biomarkers.

A combined experimental and mathematical approach for molecular-based optimization of irinotecan circadian delivery

Circadian timing largely modifies efficacy and toxicity of many anticancer drugs. Recent findings suggest that optimal circadian delivery patterns depend on the patient genetic background. We present here a combined experimental and mathematical approach for the design of chronomodulated administration schedules tailored to the patient molecular profile. As a proof of concept we optimized exposure of Caco-2 colon cancer cells to irinotecan (CPT11), a cytotoxic drug approved for the treatment of colorectal cancer. CPT11 was bioactivated into SN38 and its efflux was mediated by ATP-Binding-Cassette (ABC) transporters in Caco-2 cells. After cell synchronization with a serum shock defining Circadian Time (CT) 0, circadian rhythms with a period of 26 h 50 (SD 63 min) were observed in the mRNA expression of clock genes REV-ERBα, PER2, BMAL1, the drug target topoisomerase 1 (TOP1), the activation enzyme carboxylesterase 2 (CES2), the deactivation enzyme UDP-glucuronosyltransferase 1, polypeptide A1 (UGT1A1), and efflux transporters ABCB1, ABCC1, ABCC2 and ABCG2. DNA-bound TOP1 protein amount in presence of CPT11, a marker of the drug PD, also displayed circadian variations. A mathematical model of CPT11 molecular pharmacokinetics-pharmacodynamics (PK-PD) was designed and fitted to experimental data. It predicted that CPT11 bioactivation was the main determinant of CPT11 PD circadian rhythm. We then adopted the therapeutics strategy of maximizing efficacy in non-synchronized cells, considered as cancer cells, under a constraint of maximum toxicity in synchronized cells, representing healthy ones. We considered exposure schemes in the form of an initial concentration of CPT11 given at a particular CT, over a duration ranging from 1 to 27 h. For any dose of CPT11, optimal exposure durations varied from 3h40 to 7h10. Optimal schemes started between CT2h10 and CT2h30, a time interval corresponding to 1h30 to 1h50 before the nadir of CPT11 bioactivation rhythm in healthy cells.

Treatment timing within the 24-h timescale, that is, circadian (circa, about; dies, day) timing, can change by several fold the tolerability and antitumor efficacy of anticancer agents both in experimental models and in cancer patients. Chronotherapeutics aims at improving the tolerability and/or the efficacy of medications through the administration of treatments according to biological rhythms. Recent findings highlight the need of individualizing circadian delivery schedules according to the patient genetic background. In order to address this issue, we propose a combined experimental and mathematical approach in which molecular mathematical models are fitted to experimental measurements of critical biological variables in the studied experimental model or patient. Optimization procedures are then applied to the calibrated mathematical model for the design of theoretically optimal circadian delivery patterns. As a first proof of concept we focused on the anticancer drug irinotecan. A mathematical model of the drug molecular PK-PD was built and fitted to experimental data in Caco-2 colon cancer cells. Numerical algorithms were then applied to theoretically optimize the chronomodulated exposure of Caco-2 cells to irinotecan.

Glucocorticoid-dependent expression of O(6)-methylguanine-DNA methyltransferase gene modulates dacarbazine-induced hepatotoxicity in mice

O(6)-methylguanine-DNA methyltransferase (MGMT) plays a crucial role in the defense against the alkylating agent-induced cytotoxic lesion O(6)-alkylguanine in DNA. Although a significant circadian variation in MGMT activity has been found in the liver of mice, the exact mechanism of the variation remains poorly understood. In this study, we present evidence that glucocorticoids were required for the 24-h oscillation of MGMT expression in mouse liver. The exposure of mouse hepatic cells (Hepa1-6) to dexamethasone (DEX) significantly increased the mRNA levels of MGMT in a dose-dependent manner. The DEX-induced increase in MGMT expression was reversed by concomitant treatment with RU486 [11beta-[p-(dimethylamino) phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one], a glucocorticoid receptor antagonist. The mRNA levels of MGMT and its enzymatic activity in the liver of mice showed significant 24-h oscillations, which were not observed in adrenalectomized mice. A single administration of DEX to adrenalectomized mice significantly increased the mRNA levels of MGMT in the liver. These findings suggest that the 24-h oscillation in the hepatic expression of MGMT is caused by the endogenous rhythm of glucocorticoid secretion. Dacarbazine (DTIC), a potent O(6)-guanine-alkylating agent, causes serious hepatotoxicity accompanied by hepatocellular necrosis and hepatic vein thrombosis. DTIC-induced hepatotoxicity in mice was attenuated by administering the drug at the time of day when MGMT expression was abundant. The present findings suggest that glucocorticoid-regulated oscillation in the hepatic MGMT expression is the underlying cause of dosing time-dependent changes in DTIC-induced hepatotoxicity.

Circadian Timing in Cancer Treatments

The circadian timing system is composed of molecular clocks, which drive 24-h changes in xenobiotic metabolism and detoxification, cell cycle events, DNA repair, apoptosis, and angiogenesis. The cellular circadian clocks are coordinated by endogenous physiological rhythms, so that they tick in synchrony in the host tissues that can be damaged by anticancer agents. As a result, circadian timing can modify 2- to 10-fold the tolerability of anticancer medications in experimental models and in cancer patients. Improved efficacy is also seen when drugs are given near their respective times of best tolerability, due to (a) inherently poor circadian entrainment of tumors and (b) persistent circadian entrainment of healthy tissues. Conversely, host clocks are disrupted whenever anticancer drugs are administered at their most toxic time. On the other hand, circadian disruption accelerates experimental and clinical cancer processes. Gender, circadian physiology, clock genes, and cell cycle critically affect outcome on cancer chronotherapeutics. Mathematical and systems biology approaches currently develop and integrate theoretical, experimental, and technological tools in order to further optimize and personalize the circadian administration of cancer treatments.

The molecular mechanism regulating the autonomous circadian expression of Topoisomerase I in NIH3T3 cells

To identify whether Topoisomerase I (TopoI) has autonomous circadian rhythms regulated by clock genes, we tested mouse TopoI (mTopoI) promoter oscillation in NIH3T3 cells using a real-time monitoring assay and TopoI mRNA oscillations using real-time RT-PCR. Analysis of the mTopoI promoter region with Matlnspector software revealed two putative E-box (E1 and E2) and one DBP/E4BP4-binding element (D-box). Luciferase assays indicated that mTopoI gene expression was directly regulated by clock genes. The real-time monitoring assay showed that E-box and D-box response elements participate in the regulation of the circadian expression of mTopoI. Furthermore, a gel-shift assay showed that E2 is a direct target of the BMAL1/CLOCK heterodimer and DBP binds to the putative D-site. These results indicate that TopoI is expressed in an autonomous circadian rhythm in NIH3T3 cells.

Modulation of circadian rhythm of DNA synthesis in tumor cells by inhibiting platelet-derived growth factor signaling

Circadian synchronization of cell proliferation is observed not only in normal healthy tissues but also in malignant solid tumors. However, the proliferation rhythm of tumor cells is often different from that of normal cells. We reported here that the peculiar rhythm of tumor cell proliferation was modulated by inhibition of platelet-derived growth factor (PDGF) signaling. DNA synthesis in tumor cells implanted in mice showed a 24-h oscillation apparently differing from that of normal bone marrow cells. Continuous administration of AG1295 (10 microg/h, s.c.), a PDGF receptor tyrosine kinase inhibitor, substantially suppressed DNA synthesis in the implanted tumor cells but not in the healthy bone marrow cells. During the administration of this drug, the rhythm of DNA synthesis in the tumor cells was synchronized with that in bone marrow cells. The present results suggest that the circadian rhythm of DNA synthesis in tumor cells is modulated by PDGF receptor signaling, which is activated following tumor progression. Because the rhythmic patterns of clock gene expression in tumor cells did not differ significantly from those in other healthy tissues, the enhanced signal transduction of PDGF receptor may cause an alteration in the rhythmicity of tumor cell proliferation without changing in the intracellular molecular clockwork.

The nuclear hormone receptor family round the clock

Daily rhythms in behavior and physiology are observed in most organisms. These rhythms are controlled by internal self-sustained circadian ( approximately 24 h) clocks, which are present in virtually all cells. The 24-h oscillations are generated by a molecular mechanism entrained by external or internal time cues and which, in turn, regulate rhythmic outputs. In mammals, the circadian system comprises a master clock located in the hypothalamus that is directly entrained by the light-dark cycle and which coordinates the phases of local clocks in the periphery in order to ensure optimal timing of the physiology. Nuclear receptors (NRs) form a large family of transcription factors that include both ligand-inducible and orphan receptors. These NRs are key regulators of major biological processes such as reproduction, development, cell growth and death, inflammation, immunity, and metabolic homeostasis. Recent observations indicate that several NR signaling pathways play a critical role in central and peripheral circadian clocks. The REV-ERB/retinoid-related orphan receptor orphan NR subfamily regulates the expression of core clock genes and contributes to the robustness of the clock mechanism. Glucocorticoid and retinoic acid receptors are involved in the resetting of peripheral clocks. Several other NRs such as peroxisome proliferator-activated receptor-alpha, short heterodimer partner, and constitutive androstane receptor act as molecular links between clock genes and specific rhythmic metabolic outputs. The expanding functional links between NRs and circadian clocks open novel perspectives for understanding the hormonal regulation of the mammalian circadian system as well as for exploring the role of circadian clocks in the pathogenesis of NR-related diseases such as cancer and metabolic syndrome.

Circadian rhythms: mechanisms and therapeutic implications

The mammalian circadian system is organized in a hierarchical manner in that a central pacemaker in the suprachiasmatic nucleus (SCN) of the brain's hypothalamus synchronizes cellular circadian oscillators in most peripheral body cells. Fasting-feeding cycles accompanying rest-activity rhythms are the major timing cues in the synchronization of many, if not most, peripheral clocks, suggesting that the temporal coordination of metabolism and proliferation is a major task of the mammalian timing system. The inactivation of noxious food components by hepatic, intestinal, and renal detoxification systems is among the metabolic processes regulated in a circadian manner, with the understanding of the involved clock output pathways emerging. The rhythmic control of xenobiotic detoxification provides the molecular basis for the dosing time-dependence of drug toxicities and efficacy. This knowledge can in turn be used in improving or designing chronotherapeutics for the patients who suffer from many of the major human diseases.

Glucocorticoid regulation of 24-hour oscillation in interferon receptor gene expression in mouse liver

Although the antiviral effect of interferon (IFN) varies depending on 24-h oscillation in the expression of its specific receptor, the mechanism of oscillation remains to be clarified. Here we report that oscillation in the expression of the IFN receptor gene (IFN-alpha/beta R1) in mouse liver is caused by the endogenous rhythm of glucocorticoid secretion. Brief exposure of mouse hepatic cells (Hepa 1-6) to corticosterone (CORT) resulted in a significant decrease in mRNA levels of IFN-alpha/beta R1. The CORT-induced decrease in IFN-alpha/beta R1 mRNA levels was reversed by pretreating the cells with RU486, a glucocorticoid receptor antagonist. The mRNA levels of IFN-alpha/beta R1 gene in the liver of adrenalectomized mice were consistently increased throughout the day. However, a single administration of CORT to adrenalectomized mice significantly decreased the mRNA levels of IFN-alpha/beta R1 in the liver. Furthermore, the rhythmic phase of IFN-alpha/beta R1 expression was modulated after the alteration of rhythmicity in glucocorticoid secretion, which was induced by restricted daily feeding. As a consequence, under manipulation of the feeding schedule, 2'-5' oligoadenylate synthase activities, as an index of antiviral effect, in plasma and liver at 24 h after IFN-alpha injection also varied depending on the alteration of glucocorticoid secretion rhythm. These results suggest that the endogenous rhythm of glucocorticoid secretion is involved in the circadian regulation of IFN-alpha/beta R1 expression in mouse liver. Our findings also support the notion that monitoring the 24-h variation in IFN receptor function is useful for selecting the most appropriate time of day to administer IFN.