Topotecan in colorectal cancer: a phase II study of the EORTC early clinical trials group

Safety and Tolerability of Topotecan-Eluting Radiopaque Microspheres for Hepatic Chemoembolization in a Rabbit Preclinical Model

PURPOSE

Topotecan is a camptothecin analogue with potential advantages over irinotecan for transarterial chemoembolization (TACE) of hepatic colorectal metastases including greater anti-neoplastic activity without enzymatic activation. The purpose of this study was to assess safety and tolerability of topotecan-loaded radiopaque microspheres (ROMTOP) administered by TACE in a rabbit model and to compare the in vitro elution of topotecan from microspheres to irinotecan.

MATERIALS AND METHODS

Topotecan was loaded into radiopaque microspheres (70-150 µm, DC Bead LUMI™, Biocompatibles UK Ltd-Boston Scientific Corporation) to the maximum capacity of 80 mg/mL of microspheres. Six healthy New Zealand White rabbits underwent hepatic TACE with ROMTOP under fluoroscopic guidance until angiographic stasis. Assessment of toxicities included regular liver function tests and complete blood counts until euthanasia 28 days post-TACE. In vitro topotecan elution from the microspheres was assessed using an open-loop flow-through system and compared to irinotecan.

RESULTS

The mean bead volume and topotecan dose delivered were 0.086 mL (0.076-0.105 mL) and 1.99 mg/kg (1.51-2.55 mg/kg), respectively. Aspartate aminotransferase and alanine aminotransferase were elevated post-embolization but resolved within 2 weeks. One rabbit died two days after TACE with pyloric duodenal perforation observed at necropsy, potentially due to non-target embolization. In vitro elution of topotecan from ROMTOP was complete in 10 h compared to 3 h for irinotecan-loaded microspheres.

CONCLUSION

Selective embolization with ROMTOP was tolerated at a dose of 2 mg/kg (24 mg/m²) in rabbits. In vitro topotecan elution from microspheres was more prolonged compared to irinotecan.

In Search of Panacea-Review of Recent Studies Concerning Nature-Derived Anticancer Agents

Cancers are one of the leading causes of deaths affecting millions of people around the world, therefore they are currently a major public health problem. The treatment of cancer is based on surgical resection, radiotherapy, chemotherapy or immunotherapy, much of which is often insufficient and cause serious, burdensome and undesirable side effects. For many years, assorted secondary metabolites derived from plants have been used as antitumor agents. Recently, researchers have discovered a large number of new natural substances which can effectively interfere with cancer cells’ metabolism. The most famous groups of these compounds are topoisomerase and mitotic inhibitors. The aim of the latest research is to characterize natural compounds found in many common foods, especially by means of their abilities to regulate cell cycle, growth and differentiation, as well as epigenetic modulation. In this paper, we focus on a review of recent discoveries regarding nature-derived anticancer agents.

Testing of the topoisomerase 1 inhibitor Genz-644282 by the pediatric preclinical testing program

BACKGROUND

Genz-644282 is a novel non-camptothecin topoisomerase I poison that is in clinical development.

PROCEDURES

Genz-644282 was tested against the PPTP in vitro panel (0.1 nM to 1 µM), and in vivo using three times per week × 2 schedule repeated at day 21 at its maximum tolerated dose (MTD) of 4 mg/kg. Subsequently Genz-644282 was tested at 4, 3, 2, and 1 mg/kg in 3 models to assess the dose-response relationship. mRNA gene signatures predictive for Genz-644282 response in vitro were applied to select 15 tumor models that were evaluated prospectively.

RESULTS

In vitro, Genz-644282 demonstrated potent cytotoxic activity with a median IC(50) of 1.2 nM (range 0.2-21.9 nM). In vivo, Genz-644282 at its MTD (4 mg/kg) induced maintained complete responses (MCR) in 6/6 evaluable solid tumor models. At 2 mg/kg Genz-644282 induced CR or MCR in 3/3 tumor models relatively insensitive to topotecan, but there were no objective responses at 1 mg/kg. Further testing at 2 mg/kg showed that Genz-644282 induced objective regressions in 7 of 17 (41%) models. There was a significant correlation between predictive response scores based on Affymetrix U133Plus2 baseline tumor expression profiles and the observed in vivo responses to Genz-644282.

CONCLUSIONS

Genz-644282 was highly active within a narrow dose range (2-4 mg/kg), typical of other topoisomerase I poisons. As with other topoisomerase I poisons, how accurately these data will translate to clinical activity will depend upon the drug exposures that can be achieved in children treated with this agent.

Chemotherapeutic agents and the skin: An update

Chemotherapeutic agents give rise to numerous well described adverse effects that may affect the skin, hair, mucous membranes, or nails. The mucocutaneous effects of longstanding agents have been extensively studied and reviewed. Over the last 2 decades, a number of new molecular entities for the treatment of cancer have been approved by the United States Food and Drug Administration (FDA). This article reviews the cutaneous toxicity patterns of these agents. It also reviews one drug that has not received FDA approval but is in use outside the United States and is important dermatologically. Particular emphasis is placed on the novel signal transduction inhibitors as well as on newer literature pertaining to previously described reactions.

LEARNING OBJECTIVES

At the completion of this learning activity, participants should able to list the newer chemotherapeutic agents that possess significant mucocutaneous side effects and describe the range of reactions that are seen with each drug. In addition, they should be able to formulate appropriate management strategies for these reactions.

Randomised phase II study comparing topotecan/carboplatin administration for 5 versus 3 days in the treatment of extensive-stage small-cell lung cancer

BACKGROUND

Topotecan is an active drug in small-cell lung cancer (SCLC). In our previous study, a combination of topotecan with cisplatin was associated with a median overall survival of 7.6 or 8.7 months, depending on the duration of treatment. We have replaced cisplatin by carboplatin in this trial, with the objective of creating a more convenient schedule for our patients. Furthermore, we have also compared the standard 5-day schedule with an experimental 3-day schedule.

PATIENTS AND METHODS

A total of 100 patients with metastatic disease were included. Patients were randomly assigned to receive either topotecan 0.75 mg/m2, days 1-5, and carboplatin AUC 5, day 5 (arm A) or topotecan 1.25 mg/m2, days 1-3, and carboplatin AUC 5, day 3 (arm B). Six cycles were given at a 3-week interval.

RESULTS

A total of 91 patients were assessable for response. The response during therapy was 86.9% in arm A and 80.0% in arm B. Median survival in arm A was 11.8 months and in arm B 11.6 months (P=0.37).

CONCLUSIONS

The combination of topotecan and carboplatin is active in extensive-disease SCLC. Toxicity and median survival were comparable in both arms. Three days of treatment seems to be similar to the 5-day regimen.

Dermatologic toxicity of chemotherapeutic agents

Due to its high metabolic rate, skin represents one of the major target organs of chemotherapy-associated toxicity. Reactions range from common, nonspecific exanthematous eruptions to rare but distinctive cutaneous lesions that may not become apparent until a drug transitions from clinical trials to widespread oncologic use. The challenge of the physician is to recognize reaction patterns that reflect a drug reaction, identify a likely causative drug, and determine whether the reaction is a dose-limiting toxicity. This review will focus on the cutaneous side effects of the newer classes of chemotherapy drugs, including targeted monoclonal antibody therapy and small molecule inhibitors.

Topotecan, an active new antineoplastic agent: review and current status

Topotecan (Hycamtin) is a water soluble semisynthetic analogue of the alkaloid camptothecin which has antitumour activity in preclinical models in vitro and in vivo. A range of Phase I studies has been performed and a daily x 5 iv. schedule, which showed most promising evidence of activity, was selected for extensive clinical evaluation. To date, topotecan has been shown to be active in a number of malignancies, including metastatic ovarian cancer, recurrent small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), breast cancer, colorectal cancer and myelodysplastic syndrome. In ovarian cancer, response rates of around 15% were identified in patients who had failed standard chemotherapy, and in a randomised, comparative study with paclitaxel response rates of 20% (topotecan) and 13% (paclitaxel) were observed. In addition, overall time to progression was impressive at 23 weeks (topotecan) compared with 14 weeks (paclitaxel). In recurrent SCLC, topotecan has shown good activity in sensitive patients with a response rate of 39%, although the response rate in refractory patients was considerably lower (7%). Median survival of all patients was 5.4 months, acceptable for this difficult clinical scenario. Topotecan is well-tolerated in the majority of patients and subjective toxicities are uncommon. The principal side-effect is myelosuppression, mainly neutropenia. Serious clinical sequelae are relatively uncommon and non-cumulative. Nonhaematological toxicities are generally mild and not dose-limiting. In clinical use, topotecan has exhibited activity in multiple tumour types, with a side-effect profile that is predictable and manageable. The drug is under evaluation in other tumour types and in combination chemotherapy regimens.

Topoisomerase I Inhibitors in the Treatment of Gastrointestinal Cancer: From Intravenous to Oral Administration

This article reviews the current status of the topoisomerase I (top I) inhibitors in the treatment of gastrointestinal (GI) malignancies. We focus on oral drug administration, the mode of administration that is generally preferred by patients with cancer. However, the great majority of the studies have been performed with intravenous (I.V.) administration. The most extensively investigated GI malignancy in phase I/II studies is colorectal cancer (CRC), for which I.V. irinotecan is currently approved in the United States and Europe. We discuss the activity and efficacy of irinotecan as a single agent in CRC and in combination regimens. Also, results obtained with monotherapy and in combination treatment in other GI malignancies such as esophageal, gastric, and pancreatic cancer are discussed. Few phase I studies have been performed with oral irinotecan and its clinical activity has not yet been fully determined. Several top I inhibitors are discussed, including topotecan, 9-aminocamptothecin, rubitecan, exatecan, and lurtotecan. None of these agents, given orally or intravenously, have shown activity in CRC similar to that of I.V. irinotecan. However, several agents show promising results in other GI malignancies, eg, rubitecan and exatecan in pancreatic cancer. A complicating factor in the oral administration of the top I inhibitors is the often encountered low and variable oral bioavailability. This can partly be explained by the high affinity for the drug efflux pumps BCRP (ABCG2) and P-glycoprotein, which are highly expressed in the epithelial apical membrane of the GI tract. A novel approach to improve the oral bioavailability of the top I inhibitors by temporary blockade of the drug transporter BCRP is described.

Phase I and pharmacokinetic study of the combination of topotecan and ifosfamide administered intravenously every 3 weeks

To determine the maximum-tolerated dose (MTD), dose-limiting toxicities, and pharmacokinetics of topotecan administered as a 30-min intravenous (i.v.) infusion over 5 days in combination with a 1-h i.v. infusion of ifosfamide (IF) for 3 consecutive days every 3 weeks. Patients with advanced malignancies refractory to standard therapy were entered into the study. The starting dose of topotecan was 0.4 mg m⁻² day⁻¹ × 5 days. Ifosfamide was administered at a fixed dose of 1.2 g m⁻² day⁻¹ × 3 days. In all, 36 patients received 144 treatment courses. Owing to toxicities, the schedule of topotecan administration was reduced from 5 to 3 days. The MTD was reached at topotecan 1.2 mg m⁻² day⁻¹ × 3 days with IF 1.2 g m⁻² day⁻¹ × 3 days. Haematological toxicities were dose limiting. Neutropenia was the major toxicity. Thrombocytopenia and anaemia were rare. Nonhaematological toxicities were relatively mild. Partial responses were documented in three patients with ovarian cancer dosed below the MTD. Topotecan and IF did not appear to interact pharmacokinetically. The relationships between the exposure to topotecan lactone and total topotecan, and the decrease in absolute neutrophil count and the decrease in thrombocytes, were described with sigmoidal–E_max models. The combination of 1.0 mg m⁻² day⁻¹ topotecan administered as a 30-min i.v. infusion daily times three with 1.2 g m⁻² day⁻¹ IF administered as a 1-h i.v. infusion daily times three every 3 weeks was feasible. However, the combination schedule of topotecan and IF did result in considerable haematological toxicity and in conjunction with previously reported pronounced nonhaematological toxicities and treatment related deaths, it may be concluded that this is not a favourable combination.

Combined topoisomerase I inhibition for the treatment of metastatic colon cancer

The objective of this study was to define the maximally tolerated dose (MTD) and response rate of a combination of two topoisomerase I inhibitors, topotecan and irinotecan, in patients with metastatic colon cancer. Eleven patients, the majority with previously progressive disease on 5-fluorouracil-based regimens, were enrolled onto a phase I/II dose escalation trial utilizing continuous infusion topotecan for 2 weeks and weekly irinotecan x 3 with cycles repeated every 28 days. Dosages of topotecan utilized included 0.2 and 0.25mg/m2/day. Irinotecan was administered at a dose of 62 mg/m2 by i.v. bolus. Patients were followed for toxicity and response. The MTD of the combination of agents was found to be 0.25mg/m2/day for topotecan and 62 mg/m2 for irinotecan. The most common serious toxicities were diarrhea and nausea/vomiting. Only one patient experienced grade III neutropenia. There were no complete or partial responses. However, four patients had prolonged disease stabilization (SD) of up to 324 days and this group remained on protocol therapy for an average of 227 days (p=0.0005 versus patients not achieving SD). We concluded that the MTD for this combination of topoisomerase I inhibitors, given on this particular schedule, has been defined. This combination cannot be recommended as a first- or second-line therapy for patients with metastatic colon cancer based on the responses observed. However, approximately one-third of patients achieved prolonged disease stabilization. Topotecan with irinotecan may be useful as a palliative regimen for a subgroup of colon cancer patients.

The camptothecins

Supported by detailed understanding of their mechanism of action, and facilitated by chemical manipulations that have amplified their solubility, the camptothecins have advanced to the forefront of several areas of therapeutic and developmental chemotherapy. Additive and synergistic laboratory interactions with other cytotoxic drugs have been exploited to allow development of camptothecin-based multidrug regimens, which are showing important activity in several malignancies. Topotecan and irinotecan are already in widespread use in clinical practice, and newer agents with promising preclinical activity are in various stages of clinical assessment. As knowledge of molecular and biochemical mechanisms of action and resistance continues to expand, newer and better camptothecin-based strategies for treatment of malignant disease are likely to evolve.

Simple and efficient liposomal encapsulation of topotecan by ammonium sulfate gradient: stability, pharmacokinetic and therapeutic evaluation

Topotecan (TPT), a topoisomerase I inhibitor, is presently undergoing clinical evaluation worldwide. Previous studies have shown that entrapping TPT within multi-lamellar vesicle liposome can stabilize the lactone moiety, which is structurally important for biological activity. However, low drug:lipid ratios due to the amphipathic character and small entrapment volume in the unilamellar vesicle limits the development of pharmaceutically acceptable liposomal formulation. With an aim to improve on this drawback, we herein describe a method that utilizes the ammonium sulfate gradient to entrap TPT into liposomes. By this method, the encapsulation efficiency was over 90% and a drug:lipid molar ratio as high as 1:5.4 was reached. In comparison with free drug, liposome-encapsulated TPT is more stable in physiological conditions and shows higher in vitro cytotoxicity. Because of increased blood circulation time, the initial plasma concentration and area under the plasma concentration of liposomal drugs were 14 and 40 times, respectively, of those of free drug. Furthermore, liposome encapsulation enhanced the antitumor activity of TPT in syngeneic murine C-26 and human HTB-9 xenograft models in vivo. At a dose of 5 mg/kg, the tumor growth delay of liposomal formulation was significantly than that of free TPT. Based on these results, we believe that this liposomal TPT formulation is worthy of further clinical study.

Clinical phase II study and pharmacological evaluation of rubitecan in non-pretreated patients with metastatic colorectal cancer-significant effect of food intake on the bioavailability of the oral camptothecin analogue

A randomised, open label phase II study was performed in patients with advanced colorectal cancer to evaluate the safety, toxicity and antineoplastic activity of the topoisomerase I-inhibitor rubitecan. A cross-over design was chosen to determine the intrapatient variation of the bioavailability and pharmacokinetics of the anticancer agent depending on the timing of food intake in relation to the oral drug administration. Patients with previously untreated metastatic disease received two single oral doses of rubitecan 1.5 mg/m2 for assessment of the pharmacokinetics. They were randomised to have the first administration either after an overnight fasting period or immediately after a high calorie breakfast, and crossed over to the alternative schedule after a one-week washout period. After completion of the pharmacokinetic sampling, treatment continued with rubitecan given orally at a dose of 1.5 mg/m2/day, to be increased up to 2.0 mg/m2/day, under fasting conditions for 5 consecutive days per week until disease progression. 19 patients entered the trial after informed consent was obtained. A total number of 35 treatment cycles (median 2, range 1-4) were administered. All patients were evaluable for safety. The toxicity profile of rubitecan was generally mild to moderate, with sporadic cases of grade 4 toxicities (Common Toxicity Criteria (CTC) version 2.0) diarrhoea, leucopenia and neutropenia. None of 15 evaluable patients achieved an objective response. The majority had early disease progression. 14 patients were evaluable for pharmacokinetic analysis. The bioavailability of rubitecan was found to be strongly dependent on the timing of food intake with a fasted-to-fed ratio for C(max) of 1.98 (two-tailed P<0.001; ANOVA), T(max) 0.49 (P<0.001), AUC(0-8 h) 2.52 (P<0.001) and AUC(0-24 h) 1.64 (P=0.003). Rubitecan is well tolerated, but clinically inactive in colorectal cancer at the currently recommended dose and schedule. The bioavailability is strongly dependent on the timing of food intake in relation to the oral administration of the drug. The topoisomerase I-inhibitor should be administered under fasting conditions to achieve adequate drug exposure in future prospective trials in other tumour types.

The EORTC and drug development. European Organisation for Research and Treatment of Cancer

Early drug development at EORTC has always been subject to structural changes to adapt to the rapid changes that occur in oncological drug development. The expertise of early drug developers has always been cross-fertilised with disease-/tumour-oriented groups and also backwards to the laboratory research groups. This results in the establishment of a solid and dedicated network of medical oncologists with focused expertise in cancer drug development. The EORTC Data Center is fully equipped with all expertise to support clinical research activities and includes regulatory, safety, and quality assurance desks. The EORTC New Drug development Programme (NDDP) provides methodological expertise to early clinical trials and coordinates phase I and phase II studies addressing various approaches. Through NDDP, the early clinical groups and the disease-/tumour-oriented groups have created specific networks to address early drug development in specific tumour types. This results in very efficient networks which have the resources and the patients to address and conduct challenging clinical trials in a standardised fashion ensuring the highest standards in cancer treatment.

Irinotecan in the treatment of colorectal cancer: clinical overview

PURPOSE AND METHODS

For more than three decades, the therapeutic options for patients with advanced colorectal cancer have almost exclusively been based on fluoropyrimidines. With the recognition that topoisomerase-I (TOP-I) is an important therapeutic target in cancer therapy, irinotecan, a semisynthetic TOP-I-interactive camptothecin derivative, has been clinically established in the treatment of colorectal cancer.

RESULTS

Irinotecan was investigated as second-line chemotherapy after prior treatment with fluorouracil (FU)-based regimens in two large randomized phase III trials comparing irinotecan with either best supportive care or an infusional FU/leucovorin (LV) regimen. The outcomes of these trials established irinotecan as the standard therapy in the second-line treatment of colorectal cancer. The therapeutic value of irinotecan in the first-line treatment of metastatic colorectal cancer was investigated in two large randomized phase III trials comparing the combination of irinotecan and FU/LV with FU/LV alone. Both trials demonstrated significant superior efficacy for the combination of irinotecan and FU/LV in terms of response rate, median time to disease progression, and median survival time. Consequently, the combination of irinotecan and FU/LV has been approved as first-line chemotherapy for patients with metastatic colorectal cancer and constitutes the reference therapy against which other treatment options must be tested in the future.

CONCLUSION

In this review, the clinical rationale and update of the present clinical status of irinotecan in the treatment of colorectal cancer and future prospects of irinotecan-based combinations are discussed.

Differential activity of topotecan, irinotecan and SN-38 in fresh human tumour cells but not in cell lines

The topoisomerase I inhibitors topotecan irinotecan (CPT-11) and its metabolite SN-38 were studied in a panel of cell lines and in primary tumour cells from patients, using a non-clonogenic cytotoxicity assay. All three substances showed similar activity patterns in the panel of cell lines established to classify the drugs mechanistically. In the patient tumour cells the drugs had different effects. In haematological and ovarian cancer samples, SN-38 was much more potent than topotecan, followed by irinotecan, while in colorectal cancer samples only irinotecan showed substantial activity. This in vitro activity pattern seems to agree with clinical experiences to date. The inactivity of SN-38 in colorectal cancer suggests irinotecan may also have some other role in addition to being a prodrug to SN-38. This study raises questions as to the role and relevance of early preclinical model systems in anticancer drug development, and suggests that important information can be obtained from studies using primary cultures of human tumour cells.

Clinical use of topoisomerase I inhibitors in anticancer treatment

The camptothecin analogs topotecan and irinotecan have shown to be among the most effective anticancer agents and, as S-phase specific agents, their antitumor effect is maximized when they are administered in protracted schedules. The documented activity as single agents in many adult and pediatric malignancies has been followed by their use in combination with other anticancer agents. These studies have shown promising results, and have placed topotecan and irinotecan in the first line treatment for some malignancies. However, studies to better determine the optimal schedules and sequence of combinations are needed.

Topotecan: a new topoisomerase I inhibiting antineoplastic agent

OBJECTIVE

To review the pharmacologic, pharmacokinetic, therapeutic, and safety aspects of topotecan, a new antineoplastic agent, and to assess its role in the treatment of cancer.

DATA SOURCES

MEDLINE database English language only, January 1990-March 1998; SmithKline Beecham Pharmaceuticals; published articles, books, and abstracts.

STUDY SELECTION

Studies in humans with cancer, clinical case reports, open clinical trials, and controlled clinical studies. Efficacy studies were limited primarily to trials with at least 20 evaluable patients:

DATA EXTRACTION

Relevant data were extracted only from published reports. Data were obtained from studies in both articles and abstracts. Only articles written in English were reviewed.

DATA SYNTHESIS

Topotecan is an effective second- or third-line therapy for patients with advanced ovarian cancer and is comparable to ifosfamide, liposomal doxorubicin, and paclitaxel. Activity in combination with other agents and as a first-line agent is yet to be determined. Limited data indicate activity in small-cell lung cancer, cancers of the breast and uterus, and in nonlymphocytic leukemia. The dose-limiting toxicity is myelosuppression.

CONCLUSIONS

Topotecan is an effective second-line agent for patients with unresponsive or relapsed cancer of the ovary. It appears to be similar to other active agents in patients with this disease status. Its ultimate role in ovarian cancer and other neoplasms awaits additional evaluation in combination with other agents and as first-line therapy.

Clinical applications of the camptothecins

The camptothecin topoisomerase I-targeting agents are new class of antitumor drugs with demonstrated clinical activity in human malignancies, such as colorectal cancer and ovarian cancer. Currently, irinotecan and topotecan are the most widely used camptothecin analogs in clinical use and clinical trials are ongoing to better characterize their spectra of clinical activity, to determine their optimal schedules of administration and to define their use in combination with other chemotherapeutic agents. Newer camptothecin analogs in clinical development, such as 9-aminocamptothecin, 9-nitrocamptothecin, GI147211 and DX-8951f, are also being studied to determine if they have improved toxicity and efficacy profiles compared with existing analogs. Other potential clinical applications include the use of camptothecin derivatives as radiation sensitizers or as antiviral agents. The successful development of the camptothecins as antitumor agents highlights the importance of topoisomerase I as a target for cancer chemotherapy.

New drugs in the treatment of colorectal carcinoma

BACKGROUND

Treatment with 5-fluorouracil (5-FU) plus leucovorin has been the unofficial standard therapy for patients with colorectal carcinoma (CRC) for more than a decade; however, the optimal dose and schedule remain a matter of debate. Recently several new drugs have shown activity in this disease. These include irinotecan (CPT-11); oxaliplatin; the thymidylate synthase inhibitors raltitrexed, uracil/tegafur (UFT), capecitabine, and S-1; the biochemical modulators trimetrexate and 5-ethynyluracil; and the monoclonal antibody 17-1A.

METHODS

The results of clinical trials with these and other new agents, as well as their current status and main characteristics, were reviewed.

RESULTS

Several of these agents, some with a novel mechanism of action, show promising activity in CRC. In combination with 5-FU and leucovorin, trimetrexate showed encouraging response rates in Phase II studies. Other interesting agents include capecitabine, UFT, and S-1. The biochemical modulator 5-ethynyluracil may allow the oral administration of 5-FU; however, results of Phase II clinical trials are not yet available. CPT-11 is in the most advanced stage of development and, based on consistent data generated in extensive Phase II studies, currently appears to be a reasonable choice for 5-FU-resistant or refractory disease. Another promising agent is oxaliplatin, which showed activity as first-line and second-line treatment.

CONCLUSIONS

Several new agents have shown promise in the treatment of CRC, and changes in the standard treatment of advanced or high risk CRC appear likely in the near future.

High-dose topotecan with granulocyte-colony stimulating factor in fluoropyrimidine-refractory colorectal cancer: a phase II and pharmacodynamic study

PURPOSE

The premise for this study was that topotecan (TPT) resistance in preclinical studies is associated with low level expression of the p-glycoprotein (Pgp) multi-drug transporter conferred by the multi-drug resistant (MDR) phenotype, which might be overcome in clinical practice by administering moderately (2.3-fold) higher doses of TPT that have shown to be feasible with granulocyte colony-stimulating factor (G-CSF) support. This phase II study evaluated the anti-tumor activity of TPT administered at its highest possible solid tumor dose with G-SCF in patients with fluoropyrimidine-refractory advanced colorectal carcinoma. The study also sought to identify pharmacodynamic (PD) determinants of both activity and toxicity.

PATIENTS AND METHODS

TPT was administered as a 30-minute infusion daily for five days every three weeks at a dose of 3.5 mg/m2/day to patients with advance colorectal carcinoma who developed progressive disease either during treatment with fluoropyrimidine-based chemotherapy for advanced disease or within six months after receiving fluoropyrimidine-based adjuvant chemotherapy. This dose of TPT was previously determined to be the maximal tolerated dose (MTD) with G-CSF support in a phase I study involving solid tumor patients with similar risk factors for myelosuppression. Plasma sampling with performed during course 1 to characterize the pharmacokinetic (PK) and PD behavior of TPT.

RESULTS

Seventeen patients who received 89 courses of TPT and G-CSF were evaluable for toxicity; 16 patients were evaluable for anti-tumor response. Toxicity, particularly myelosuppression, was substantial. At the 3.5 mg/m2/day dose level, absolute neutrophil counts (ANC) were less than 500/microliters for longer than 5 days in 17% of courses involving seven of seventeen (41%) patients. Severe neutropenia associated with fever occurred in 12.3% of courses; and platelet counts below 25,000/microliters were noted in 26.9% of courses. These toxicities resulted in dose reductions in seven of 17 (41%) patients. Nevertheless, 90% of the planned total dose of TPT was administered. No major responses were observed, though minor activity was noted in several patients. Both the median time to progression and the median survival time were short--2.5 and 4 months respectively. Although interindividual variability in the disposition of total TPT was observed, the lack of objective responses precluded PD assessments related to disease activity. Total TPT exposure was significantly higher than drug exposure achieved in similar patients at an identical dose in a previous phase I study of TPT and G-CSF, which may explain why more severe myelosuppressive effects occurred in the present study. There were no PD relationships evident between relevant PK parameters and the percent decrements in platelets and ANC's during course 1, although patients with severe toxic effects (ANC below 500/microliters for more than five days and/or platelets < 25,000/microliters) had higher drug exposure than patients with less severe toxicity (P < 0.018 and P = 0.09, respectively).

CONCLUSIONS

Based on these results, the true response rate of TPT at its solid tumor MTD with G-CSF support is unlikely to approach 20%. Although a response rate of less than 20% might be viewed as significant in this disease setting and might be confirmed with sufficient statistical certainty by treating additional patients, the substantial toxicity, inconvenience, and cost associated with this high dose TPT/G-CSF regimen does not warrant the acceptance of a lower level of anti-tumor activity as a criterion for further development.

Topoisomerase I inhibitors: review and update

This review presents a summary of preclinical and clinical data on the topoisomerase I (topo I) inhibitors that are under clinical development. To date, all of the topo I inhibitors that have been clinically evaluated are analogues of camptothecin, an extract of the Chinese tree Camptotheca acuminata. The therapeutic development of camptothecin was initially limited by its poor solubility and unpredictable toxicity. More recently, a number of water-soluble camptothecin analogues have undergone extensive evaluation and have demonstrated significant clinical activity. These include irinotecan (CPT-II), topotecan, and 9-aminocamptothecin (9-AC). Preliminary data are also reviewed on other camptothecin analogues (GG-211 and DX-8951f), on oral formulations, and on non-camptothecin topoisomerase I inhibitors. The topoisomerase I inhibitors have already demonstrated a broad spectrum of antitumour activity, most probably due to their unique mechanism of action and lack of clinical cross-resistance with existing antineoplastic compounds. The challenge for the next five years is to identify ways to integrate the topo I inhibitors into multidrug and multimodality therapies to achieve optimal antitumour effect, while keeping the side effects of these therapies manageable.

Experimental chemotherapeutic agents for the treatment of colorectal carcinoma

Colorectal cancer is the third leading cause of cancer mortality for men and women in the United States. For the past 40 years fluorouracil has been the only agent with significant activity in this disease. More recently, advances in our understanding of the molecular biology of cancer have permitted the development of effective new agents for this disease. This article examines the current and future status of these new agents.