Chronomodulation of chemotherapy against metastatic colorectal cancer. International Organization for Cancer Chronotherapy

Chrono-tailored drug delivery systems: recent advances and future directions

Circadian rhythms influence a range of biological processes within the body, with the central clock or suprachiasmatic nucleus (SCN) in the brain synchronising peripheral clocks around the body. These clocks are regulated by external cues, the most influential being the light/dark cycle, in order to synchronise with the external day. Chrono-tailored or circadian drug delivery systems (DDS) aim to optimise drug delivery by releasing drugs at specific times of day to align with circadian rhythms within the body. Although this approach is still relatively new, it has the potential to enhance drug efficacy, minimise side effects, and improve patient compliance. Chrono-tailored DDS have been explored and implemented in various conditions, including asthma, hypertension, and cancer. This review aims to introduce the biology of circadian rhythms and provide an overview of the current research on chrono-tailored DDS, with a particular focus on immunological applications and vaccination. Finally, we draw on some of the key challenges which need to be overcome for chrono-tailored DDS before they can be translated to more widespread use in clinical practice.

Why does circadian timing of administration matter for immune checkpoint inhibitors' efficacy?

BACKGROUND

Tolerability and antitumour efficacy of chemotherapy and radiation therapy can vary largely according to their time of administration along the 24-h time scale, due to the moderation of their molecular and cellular mechanisms by circadian rhythms. Recent clinical data have highlighted a striking role of dosing time for cancer immunotherapy, thus calling for a critical evaluation.

METHODS

Here, we review the clinical data and we analyse the mechanisms through which circadian rhythms can influence outcomes on ICI therapies. We examine how circadian rhythm disorders can affect tumour immune microenvironment, as a main mechanism linking the circadian clock to the 24-h cycles in ICIs antitumour efficacy.

RESULTS

Real-life data from 18 retrospective studies have revealed that early time-of-day (ToD) infusion of immune checkpoint inhibitors (ICIs) could enhance progression-free and/or overall survival up to fourfold compared to late ToD dosing. The studies involved a total of 3250 patients with metastatic melanoma, lung, kidney, bladder, oesophageal, stomach or liver cancer from 9 countries. Such large and consistent differences in ToD effects on outcomes could only result from a previously ignored robust chronobiological mechanism. The circadian timing system coordinates cellular, tissue and whole-body physiology along the 24-h timescale. Circadian rhythms are generated at the cellular level by a molecular clock system that involves 15 specific clock genes. The disruption of circadian rhythms can trigger or accelerate carcinogenesis, and contribute to cancer treatment failure, possibly through tumour immune evasion resulting from immunosuppressive tumour microenvironment.

CONCLUSIONS AND PERSPECTIVE

Such emerging understanding of circadian rhythms regulation of antitumour immunity now calls for randomised clinical trials of ICIs timing to establish recommendations for personalised chrono-immunotherapies with current and forthcoming drugs.

Personalized Chronomodulated 5-Fluorouracil Treatment: A Physiologically-Based Pharmacokinetic Precision Dosing Approach for Optimizing Cancer Therapy

The discovery of circadian clock genes greatly amplified the study of diurnal variations impacting cancer therapy, transforming it into a rapidly growing field of research. Especially, use of chronomodulated treatment with 5-fluorouracil (5-FU) has gained significance. Studies indicate high interindividual variability (IIV) in diurnal variations in dihydropyrimidine dehydrogenase (DPD) activity - a key enzyme for 5-FU metabolism. However, the influence of individual DPD chronotypes on chronomodulated therapy remains unclear and warrants further investigation. To optimize precision dosing of chronomodulated 5-FU, this study aims to: (i) build physiologically-based pharmacokinetic (PBPK) models for 5-FU, uracil, and their metabolites, (ii) assess the impact of diurnal variation on DPD activity, (iii) estimate individual DPD chronotypes, and (iv) personalize chronomodulated 5-FU infusion rates based on a patient's DPD chronotype. Whole-body PBPK models were developed with PK-Sim(R) and MoBi(R). Sinusoidal functions were used to incorporate variations in enzyme activity and chronomodulated infusion rates as well as to estimate individual DPD chronotypes from DPYD mRNA expression or DPD enzymatic activity. Four whole-body PBPK models for 5-FU, uracil, and their metabolites were established utilizing data from 41 5-FU and 10 publicly available uracil studies. IIV in DPD chronotypes was assessed and personalized chronomodulated administrations were developed to achieve (i) comparable 5-FU peak plasma concentrations, (ii) comparable 5-FU exposure, and (iii) constant 5-FU plasma levels via "noise cancellation" chronomodulated infusion. The developed PBPK models capture the extent of diurnal variations in DPD activity and can help investigate individualized chronomodulated 5-FU therapy through testing alternative personalized dosing strategies.

Time-Dependent Efficacy of Checkpoint Inhibitor Nivolumab: Results from a Pilot Study in Patients with Metastatic Non-Small-Cell Lung Cancer

Simple Summary

Initial clinical observations revealed strikingly longer follow-up for metastatic non-small-cell lung cancer (NSCLC) patients receiving nivolumab infusions predominantly in the morning as compared to those treated in the afternoon. Prior experimental and human studies have demonstrated the temporal distributions of immune cells’ proliferation, trafficking, and antigen recognition and destruction over the 24 h. Here, we hypothesized that circadian timing could play an important role in nivolumab’s efficacy, as previously shown for the toxicity and/or efficacy of chronomodulated chemotherapy in colorectal and lung cancer patients. Following project validation by an internal scientific review board, the dosing times of each of the 1818 nivolumab infusions given to 95 consecutive patients as a standard treatment for metastatic NSCLC were retrieved from the day-hospital records. Adverse events and radiologically documented tumor responses were retrieved and reviewed from patients’ clinical charts. Patients were allocated to ‘morning’ (N = 48 patients) or ‘afternoon’ (N = 47 patients) groups, according to whether they had received the majority of nivolumab infusions before or after 12:54, i.e., the median time of all infusions, respectively. ‘Morning’ nivolumab dosing nearly quadrupled median progression-free and overall survival as compared to ‘afternoon’ dosing. ‘Morning’ nivolumab was significantly more effective irrespective of age, sex, performance status, prior treatments, tumor histology, or PD-L1 expression. In contrast, nivolumab primary resistance was most often observed following ‘afternoon’ dosing. Randomized trials are warranted both to further identify the optimal timing of checkpoint inhibitors in individual cancer patients, and to determine the main mechanisms that precisely drive immunotherapy efficacy and resistance along the circadian timescale.

Abstract

Hypothesis: Prior experimental and human studies have demonstrated the circadian organization of immune cells’ proliferation, trafficking, and antigen recognition and destruction. Nivolumab targets T(CD8) cells, the functions, and trafficking of which are regulated by circadian clocks, hence suggesting possible daily changes in nivolumab’s efficacy. Worse progression-free survival (PFS), and overall survival (OS) were reported for malignant melanoma patients receiving more than 20% of their immune checkpoint inhibitor infusions after 16:30 as compared to earlier in the day. Methods: Consecutive metastatic non-small-cell cancer (NSCLC) patients received nivolumab (240 mg iv q 2 weeks) at a daily time that was ‘randomly’ allocated for each course on a logistical basis by the day-hospital coordinators. The median time of all nivolumab administrations was computed for each patient. The study population was split into two timing groups based upon the median value of the median treatment times of all patients. CTCAE-toxicity rates, iRECIST-tumor responses, PFS and OS were computed according to nivolumab timing. PFS and OS curves were compared and hazard ratios (HR) were computed for all major categories of characteristics. Multivariable and sensitivity analyses were also performed. Results: The study accrued 95 stage-IV NSCLC patients (PS 0–1, 96%), aged 41–83 years. The majority of nivolumab administrations occurred between 9:27 and 12:54 for 48 patients (‘morning’ group) and between 12:55 and 17:14 for the other 47 (‘afternoon’ group). Median PFS (95% CL) was 11.3 months (5.5–17.1) for the ‘morning’ group and 3.1 months (1.5–4.6) for the ‘afternoon’ one (p < 0.001). Median OS was 34.2 months (15.1–53.3) and 9.6 months (4.9–14.4) for the ‘morning’ group and the ‘afternoon’ one, respectively (p < 0.001). Multivariable analyses identified ‘morning’ timing as a significant predictor of longer PFS and OS, with respective HR values of 0.26 (0.11–0.58) and 0.17 (0.08–0.37). The timing effect was consistent across all patient subgroups tested. Conclusions: Nivolumab was nearly four times as effective following ‘morning’ as compared to ‘afternoon’ dosing in this cohort of NSCLC patients. Prospective timing-studies are needed to minimize the risk of resistance and to maximize the benefits from immune checkpoint inhibitors.

New Insights Into Cancer Chronotherapies

Circadian clocks participate in the coordination of various metabolic and biological activities to maintain homeostasis. Disturbances in the circadian rhythm and cancers are closely related. Circadian clock genes are differentially expressed in many tumors, and accelerate the development and progression of tumors. In addition, tumor tissues exert varying biological activities compared to normal tissues due to resetting of altered rhythms. Thus, chronotherapeutics used for cancer treatment should exploit the timing of circadian rhythms to achieve higher efficacy and mild toxicity. Due to interpatient differences in circadian functions, our findings advocate an individualized precision approach to chronotherapy. Herein, we review the specific association between circadian clocks and cancers. In addition, we focus on chronotherapies in cancers and personalized biomarkers for the development of precision chronotherapy. The understanding of circadian clocks in cancer will provide a rationale for more effective clinical treatment of tumors.

Circadian Influences on Chemotherapy Efficacy in a Mouse Model of Brain Metastases of Breast Cancer

Chemotherapy is more effective in the treatment of peripheral tumors than brain metastases, likely reflecting the reduced ability of chemotherapy to cross the blood-brain barrier (BBB) and blood-tumor barrier at efficacious concentrations. Recent studies demonstrate circadian regulation of the BBB. Thus, we predicted that optimally timed chemotherapy would increase anti-tumor efficacy in a model of brain metastases of breast cancer (BMBC). First, we characterized novel daily alterations in BBB permeability to a commonly used chemotherapeutic, 14C-paclitaxel, within BMBC following injections given at four time points across the day. Peak and trough 14C-paclitaxel concentrations within BMBC occurred during the mid-dark phase and at the beginning of the light phase, respectively. Notably, chemotherapy injections during the dark phase increased cell death within BMBC and delayed onset of neurological symptoms relative to injections during the light phase. These data provide strong evidence for the beneficial effects of chrono-chemotherapy for the treatment of BMBC.

Cell-intrinsic, Bmal1-dependent Circadian Regulation of Temozolomide Sensitivity in Glioblastoma

The safety and efficacy of chemotherapeutics can vary as a function of the time of their delivery during the day. This study aimed to improve the treatment of glioblastoma (GBM), the most common brain cancer, by testing whether the efficacy of the DNA alkylator temozolomide (TMZ) varies with the time of its administration. We found cell-intrinsic, daily rhythms in both human and mouse GBM cells. Circadian time of treatment affected TMZ sensitivity of murine GBM tumor cells in vitro. The maximum TMZ-induced DNA damage response, activation of apoptosis, and growth inhibition occurred near the daily peak in expression of the core clock gene Bmal1. Deletion of Bmal1 (Arntl) abolished circadian rhythms in gene expression and TMZ-induced activation of apoptosis and growth inhibition. These data indicate that tumor cell-intrinsic circadian rhythms are common to GBM tumors and can regulate TMZ cytotoxicity. Optimization of GBM treatment by timing TMZ administration to daily rhythms should be evaluated in prospective clinical trials.

Current status and future perspectives on treatment of liver metastasis in colorectal cancer (Review)

Liver metastasis is the most common site of colorectal cancer (CRC) metastasis. Approximately half of all colorectal cancer patients will develop liver metastases. Although radical surgery is the standard treatment modality, only 10-20% of patients are deemed eligible for resection. Despite advances in survival with chemotherapy, surgical resection is still considered the only curative option for patients with liver metastases. Much effort has been expended to address patients with metastatic liver disease. The majority of evidence stated a significant survival benefit with surgical resection to reach an overall 5-year survival rate of 35-55% after hepatic resection. However, still majority of patients will experience disease recurrence even after a successful resection. In this review, we describe current status and controversies related to treatment options for CRC liver metastases and its potential for enhancing oncologic outcomes and improving quality of life.

Imaging multidimensional therapeutically relevant circadian relationships

Circadian clocks gate cellular proliferation and, thereby, therapeutically target availability within proliferative pathways. This temporal coordination occurs within both cancerous and noncancerous proliferating tissues. The timing within the circadian cycle of the administration of drugs targeting proliferative pathways necessarily impacts the amount of damage done to proliferating tissues and cancers. Concurrently measuring target levels and associated key pathway components in normal and malignant tissues around the circadian clock provides a path toward a fuller understanding of the temporal relationships among the physiologic processes governing the therapeutic index of antiproliferative anticancer therapies. The temporal ordering among these relationships, paramount to determining causation, is less well understood using two- or three-dimensional representations. We have created multidimensional multimedia depictions of the temporal unfolding of putatively causative and the resultant therapeutic effects of a drug that specifically targets these ordered processes at specific times of the day. The systems and methods used to create these depictions are provided, as well as three example supplementary movies.

Selective internal radiation therapy (SIRT): a new modality for treating patients with colorectal liver metastases

BACKGROUND

Selective internal radiation therapy (SIRT) is a new and developing modality for treating non-resectable liver tumours. Evidence is emerging that it is very efficacious in patients with hepatocellular cancer and colorectal liver metastases.

DISCUSSION

SIRT generally involves a single delivery of (90)yttrium micro-spheres into the hepatic artery. Preferential uptake is achieved into liver tumours, because of their predominant hepatic arterial blood supply. Average tumour doses of radiation in excess of 200 Gy are achieved. The treatment is generally well tolerated and has been documented by a number of groups internationally to achieve response rates of around 90% in patients with extensive colorectal cancer (CRC) liver metastases. Since the product obtained FDA approval in the USA in 2002, it is being more widely employed and investigated. Unlike other ablative therapies being applied to non-resectable liver tumours, SIRT is indicated even in patients with an extensive burden of liver tumour. Indications, dosing schedules and expected outcomes will become better defined as more groups take up the treatment.

It's time for chronotherapy!

The EORTC Chronotherapy Group (CTG) stemmed from the International Organisation for Cancer Chronotherapy (IOCC) in 1996. The IOCC was first to initiate large scale multicentre international chronotherapy trials, for the purpose of investigating the relevance of chronomodulated or timed administration of cancer therapy based on biological rhythms. Programmable pumps for cytotoxic chronodelivery and actigraph devices to monitor circadian rhythm alterations linked to cancer were also developed. The unique expertise of the IOCC with regard to cancer chronotherapy furthered its development within the EORTC. The EORTC offers broad expertise in clinical cancer research and opportunities for scientific recognition, intergroup collaborations and translational research. Over the past 5 years, the EORTC CTG has grown from 16 to 48 centres in 12 different countries. It is currently conducting seven multicentre chronotherapy trials which test the relevance of adapting cancer treatment delivery to circadian rhythms. The group aims at developing multiple collaborations to establish a chronotherapy network involving institutions with expertise ranging from experimental chronobiology to new drug testing, disease-specific management and quality of life or survival issues.

Five-year survival following hepatic resection after neoadjuvant therapy for nonresectable colorectal

BACKGROUND

Surgical resection is the most effective treatment for colorectal liver metastases but only a minority of patients are candidates for a potentially curative resection. Our experience with neoadjuvant chemotherapy followed by resection and five years survival analysis of the patients treated is presented.

METHODS

Between February of 1988 and September of 1996, 701 patients with unresectable colorectal liver metastases were treated with neoadjuvant chemotherapy. Four categories of nonresectable disease were defined: large size, ill location, multinodularity, and extrahepatic disease. Liver resection was performed in those patients whose disease became resectable. After resection, the patients were followed up every 3 months. A 5-year survival analysis by the different categories described was performed.

RESULTS

Ninety-five patients (13.5%) were found to be resectable on reevaluation and underwent a potentially curative resection. There was no perioperative mortality, and the complication rate was 23%. As of December of 1999, 87 patients have completed 5 years of follow-up. The overall 5-year survival is 35% from the time of resection and 39% from the onset of chemotherapy. Respective 5-year survival rates are 60% for large tumors, 49% for ill-located lesions, 34% for multinodular disease, and 18% for liver metastases with extrahepatic disease. In this latter category, however, a 35% 5-year survival was found when all the patients with extrahepatic disease were analyzed rather than only those for whom extrahepatic disease was the main cause of nonresectability.

CONCLUSIONS

Neoadjuvant chemotherapy enables liver resection in some patients with initially unresectable colorectal metastases. Long-term survival is similar to that reported for a priori surgical candidates.

Circadian rhythmicity and homeostatic stability in thermoregulation

Stability and circadian variation in core body temperature (Tc) were believed to be homeostatic responses until well into the 20th century. Defense of a narrow thermoneutral range was well documented, whereas circadian oscillations were attributed to episodic biochemical and environmental stimuli or chronological stressors in life routines. Research in thermal physiology has illuminated several of the "black boxes" in the understanding of temperature regulation, and advances in chronobiology have shattered old paradigms. While these discoveries are still evolving, existing information provides valuable clues about physiological responses to heat loss or over-heating that could improve clinical assessment and intervention. Discoveries that circadian rhythm of Tc is regulated by an endogenous "clock" and is remarkably stable have helped to make it the most widely used circadian indicator. More recently, Tc was found to exert its own cyclic rhythm under free-running conditions. While some investigators claim that circadian and homeostatic processes are independent, there are conditions in which clinical distinctions are less clear. This overview reviews contemporary scientific findings about circadian and homeostatic processes in thermoregulation. Examples are drawn from human and animal research. Physiological responses and mechanisms are explained in relation to their relevance to clinical treatment or health care. Gaps in existing research and application are discussed.

Clinical pharmacokinetics and administration of established platinum drugs

We review the pharmacology and clinical administration of the commonly used platinum-based anticancer drugs cisplatin and carboplatin, and the more recently approved diamminocyclohexane-based oxaliplatin. The development of analogues of cisplatin has been focused upon identifying compounds with less toxicity and with a different spectrum of activity. Carboplatin exemplifies the former, while the initial data with oxaliplatin support its activity in cisplatin-resistant tumours. The clinical pharmacokinetics of the drugs are reviewed. Incorporation of these data into the design of clinical regimens has permitted individualised therapy with carboplatin, and has enhanced safety. Additional investigation of the pharmacodynamics of all of these agents is expected to result in their selective application. The clinical effects of these analogues are discussed.

Surgery after downstaging of unresectable hepatic tumors with intra-arterial chemotherapy

BACKGROUND

This retrospective study was performed to assess the outcome among patients who underwent hepatic resection or tumor ablation after hepatic artery infusion (HAI) therapy down-staged previously unresectable hepatocellular carcinoma (HCC) or liver metastases from colorectal cancer (CRC).

METHODS

Between 1983 and 1998, 25 patients with HCC and 383 patients with hepatic CRC metastases were treated with HAI therapy for unresectable liver disease. We retrospectively reviewed the records of 26 (6%) of these patients who underwent subsequent surgical exploration for tumor resection or ablation.

RESULTS

At a median of 9 months (range 7-12 months) after HAI treatment, four patients (16%) with HCC underwent exploratory surgery; two underwent resection with negative margins, and the other two were given radiofrequency ablation (RFA) because of underlying cirrhosis. At a median postoperative follow-up of 16 months (range 6-48 months), all four patients were alive with no evidence of disease. At a median of 14.5 months (range 8-24 months) after HAI therapy, 22 patients with hepatic CRC metastases underwent exploratory surgery; 10 underwent resection, 6 underwent resection and RFA or cryotherapy, and 2 underwent RFA only. At a median follow-up of 17 months, 15 (83%) of the 18 patients with CRC who had received surgical treatment had developed recurrent disease; the other 3 died of other causes (1 of postoperative complications) within 7 months of the surgery. One patient in whom disease recurred underwent a second resection and was disease-free at 1 year follow-up.

CONCLUSIONS

Hepatic resection or ablation after tumor downstaging with HAI therapy is a viable option for patients with unresectable HCC. However, given the high rate of recurrence of metastases from CRC, hepatic resection or ablation after downstaging with HAI should be used with caution.

Basis for effective combination cancer chemotherapy with antimetabolites

Most current chemotherapy regimens for cancer consist of empirically designed combinations, based on efficacy and lack of overlapping toxicity. In the development of combinations, several aspects are often overlooked: (1) possible metabolic and biological interactions between drugs, (2) scheduling, and (3) different pharmacokinetic profiles. Antimetabolites are used widely in chemotherapy combinations for treatment of various leukemias and solid tumors. Ideally, the combination of two or more agents should be more effective than each agent separately (synergism), although additive and even antagonistic combinations may result in a higher therapeutic efficacy in the clinic. The median-drug effect analysis method is one of the most widely used methods for in vitro evaluation of combinations. Several examples of classical effective antimetabolite-(anti)metabolite combinations are discussed, such as that of methotrexate with 6-mercaptopurine or leucovorin in (childhood) leukemia and 5-fluorouracil (5FU) with leucovorin in colon cancer. More recent combinations include treatment of acute-myeloid leukemia with fludarabine and arabinosylcytosine. Other combinations, currently frequently used in the treatment of solid malignancies, include an antimetabolite with a DNA-damaging agent, such as gemcitabine with cisplatin and 5FU with the cisplatin analog oxaliplatin. The combination of 5FU and the topoisomerase inhibitor irinotecan is based on decreased repair of irinotecan-induced DNA damage. These combinations may increase induction of apoptosis. The latter combinations have dramatically changed the treatment of incurable cancers, such as lung and colon cancer, and have demonstrated that rationally designed drug combinations offer new possibilities to treat solid malignancies.

Long-term survival of patients with unresectable colorectal cancer liver metastases following infusional chemotherapy with 5-fluorouracil, leucovorin, oxaliplatin and surgery

CONTEXT

Long-term survival of patients with metastatic colorectal cancer has been achieved only in patients who underwent complete resection of metastases. Such surgery could be performed in a greater proportion of patients if effective chemotherapy could downstage previously unresectable metastases. This approach has been limited by the low tumor response rate achieved with conventional chemotherapy.

OBJECTIVE

We studied the outcome of patients with initially unresectable liver metastases from colorectal cancer treated with a three-drug chemotherapy regimen followed by liver metastases surgery whenever possible.

PATIENTS AND METHODS

From March 1988 to June 1994, 151 patients with colorectal liver metastases were considered initially unresectable because of large tumor size (> 5 cm), multinodular (> 4) or ill-located metastases. All patients received fully ambulatory chemotherapy with 5-fluorouracil, leucovorin and oxaliplatin (chronotherapy in 83% of them). They were periodically reassessed for surgery by a joint medico-surgical team.

RESULTS

In 151 patients, the size of liver metastases decreased by > 50% in 89 patients (59%) and median overall survival was 24 months (95% confidence interval (95% CI): 19-28 months), with 28% surviving at five years (20%-35%). Surgery with curative intent was attempted in 77 patients (51%), complete resection of liver metastases was achieved in 58 patients (38%). The median survival of the 77 operated patients was 48 months (25-71), with a five-year survival rate of 50% (38-61).

CONCLUSION

This new strategy of combining effective chemotherapy with surgery apparently altered the natural history of unresectable colorectal cancer metastases.

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

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

New developments in cancer treatment with the novel thymidylate synthase inhibitor raltitrexed ('Tomudex')

Following the demonstration of efficacy, tolerability and quality-of-life benefits of raltitrexed ('Tomudex'), principally in advanced colorectal but also in other cancers, an extensive evaluation of combination therapy with other agents in patients with colorectal and other tumour types is being undertaken. This work has been prompted by preclinical observations of enhanced activity of raltitrexed when coadministered with other cytotoxic agents or radiotherapy and by preliminary results showing the activity of raltitrexed in patients with cancers other than colorectal. Raltitrexed is currently being investigated as monotherapy in phase I and II cancer studies, including head and neck cancer, hormone-resistant prostate cancer, paediatric and adult leukaemias and solid tumours, and soft tissue sarcoma. In addition, phase I clinical trials are evaluating the drug in combination with taxanes (paclitaxel) in solid tumours, anthracyclines (doxorubicin) in gastric carcinoma, topoisomerase I inhibitors (CPT-11) and 5-fluorouracil (both infusion and bolus regimens) in advanced colorectal cancer, platinum compounds (oxaliplatin and cisplatin) in a variety of tumours and radiotherapy in rectal cancer. Preliminary reports indicate good tolerability and acceptability of the combinations being investigated, with no dose-limiting toxicity being reported to date, and some early indications of efficacy.

Circadian cell cycle variations of erythro- and myelopoiesis in humans

By use of a multiparameter flow cytometric method with specific surface markers, circadian (24-h) variations in cell cycle distribution have been studied in 19 healthy male volunteers by sampling bone marrow (BM) every 4-5 h during 24-h periods. Admixture of peripheral blood during the sampling was specifically adjusted for, and the fractions of cells in DNA synthetic phase were measured for different hemopoietic cell lineages. Significant circadian variations in DNA S-phase were demonstrated both in myelo- and erythropoiesis of the human BM, with 75% (myeloid) and 80% (erythroid) of the volunteers showing highest activity (values) of DNA S-phase during the day and lowest activity (values) between midnight and 04:00 h. A temporal relationship in the circadian variation of S-phase and G2/M-phase was demonstrated between the myeloid and erythroid cell lineages. The highest fractions of S-phase cells were found in erythropoiesis, while the highest circadian stage dependent variation was found in myelopoiesis. The existence of a similar phasing in DNA synthetic activity for myelopoietic and erythropoietic cells in the human bone marrow indicates that the circadian rhythmicity of hemopoiesis may be caused by a common regulatory mechanism. These findings may be relevant with regard to optimizing the use of cytotoxic drugs and hemopoietic growth factors by taking into consideration the intrinsic (endogenous) circadian variation in proliferative activity of human BM subpopulations.