Phase I study of topotecan for pediatric patients with malignant solid tumors

Oral topotecan for refractory and relapsed neuroblastoma: a retrospective analysis

PURPOSE

Among patients with multiply relapsed neuroblastoma refractory to conventional chemotherapy, oral topotecan has often been used for palliation. Although toxicity was generally thought to be mild, the efficacy of such an approach remains unproven.

METHODS

The authors retrospectively analyzed patients with multiply relapsed or refractory neuroblastoma who were treated with oral topotecan for palliation. Each course was generally 1 mg/m2/d in two divided doses, for 21 consecutive days, repeated after a 1-week rest in patients without symptoms of progressive disease. Disease status was assessed by radiographic studies, urine catecholamine levels, and multiple bone marrow aspirations and biopsies.

RESULTS

Twenty patients between the ages of 3 and 34 (median 13 years) received 1 (n = 7), 2 (n = 3), 3 (n = 4), 4 (n = 2), 6 (n = 2), and 12 courses (n = 2). Prior treatments included multiple cycles of high-dose alkylator-based chemotherapy (n = 20), high-dose intravenous topotecan (n = 8), myeloablative chemotherapy or radioimmunotherapy (n = 10), or experimental biologic agents (n = 16). Anti-neuroblastoma effects were seen in five patients lasting 6 to 12 months; two additional patients remained stable for 4 months. Thirteen patients had progressive disease (11 after one or two cycles). Toxicity included diarrhea (n = 12) requiring a dose adjustment in three patients and discontinuation of the drug in a fourth, and myelosuppression (n = 11) requiring transfusion and/or granulocyte-colony stimulating factor support.

CONCLUSIONS

Oral topotecan therapy has antitumor activity in a small percentage of patients with relapsed or refractory neuroblastoma. Toxicities, including diarrhea and myelosuppression, may necessitate a dose adjustment in this patient population. Low-dose oral topotecan may have utility in the treatment of neuroblastoma.

[Topotecan for pediatric patients with resistant and recurrent solid tumors]

BACKGROUND

Topotecan is a cytotoxic drug isolated from the Camptotheca acuminata tree (from China). It is able to block the enzyme DNA topoisomerase I and has recently been used in the treatment of pediatric cancer.

OBJECTIVES

To evaluate our preliminary experience with topotecan in the second line treatment of refractory solid tumors in the pediatric age group. PATIENTS AND MEHTODS: We performed a retrospective study of 10 patients with various recurrent solid tumors resistant to first line treatment who were treated with topotecan alone or in association with other chemotherapeutic agents.

RESULTS

Ten patients with recurrent solid tumors or tumors that were refractory to conventional treatment (two neuroblastomas, three rhabdomyosarcoma, two PNET/Ewing's sarcoma, one anaplastic astrocytoma, one soft tissue sarcoma and one synovial sarcoma) were included. Five patients showed favorable responses (two had complete responses, two had partial responses and one had stable disease). Five patients showed no response. All patients showed grade II-IV hematological toxicity.

CONCLUSIONS

In our experience, topotecan is beneficial in some refractory or recurrent solid tumors, especially neuroblastomas and soft tissue sarcomas. Myelosuppression was tolerable with the use of granulocyte colony-stimulating factors. Patients with a complete response to topotecan could benefit from high-dose chemotherapy and autologous stem cell rescue therapy.

Treatment of Ewing sarcoma family of tumors: current status and outlook for the future

BACKGROUND

The Ewing sarcoma family of tumors (ESFT) comprises a group of well-characterized neoplasms with aggressive behavior. Despite significant progress with the use of intensive multiagent chemotherapy and local control measures, a significant proportion of patients die of disease progression. Chemotherapy dose intensification and autologous hematopoietic stem cell transplant (HSCT) have been explored by many institutions without obvious benefit in high-risk patients. Our current understanding in the biology and treatment of ESFT suggests that a more rational approach to the development of risk-adapted therapy should be undertaken.

PROCEDURE

We performed a review of the most relevant data regarding the current status in the treatment of ESFT. The results of the major American and European cooperative groups were analyzed, including the treatment strategies used and the prognostic factors identified for both localized and metastatic ESFT.

RESULTS

The intensification of alkylating agents and topoisomerase-II inhibitors is feasible and has resulted in some survival improvement for selected patients. This benefit seems to be restricted to patients with localized disease, and a proportion of survivors are at risk of developing treatment-related hematologic malignancies. Nevertheless, these advances have resulted in a re-definition of prognostic factors, which may help to define risk groups based on tumor load parameters as well as biologic factors (type of fusion transcript and histologic response to chemotherapy). Patients with advanced metastatic disease may benefit from HSCT. New strategies such as immunotherapy and the use of biologic modifiers may have a role in the treatment of ESFT.

CONCLUSIONS

Future treatment for ESFT should consider risk-adapted strategies and the inclusion of newer therapies such as biologic modifiers for the minimal residual disease. A modified risk-adapted therapy is proposed.

Protracted intermittent schedule of topotecan in children with refractory acute leukemia: a pediatric oncology group study

PURPOSE

To determine dose-limiting toxicity (DLT) and maximum-tolerated dose (MTD) of a protracted, intermittent schedule of daily 30-minute infusions of topotecan (TPT) for up to 12 consecutive days, every 3 weeks, in children with refractory leukemia.

PATIENTS AND METHODS

Forty-nine children were enrolled onto this phase I trial (24 with acute nonlymphoblastic leukemia [ANLL] and 25 with acute lymphoblastic leukemia [ALL]). TPT dosage was escalated from 2.0 to 5.2 mg/m(2)/d for 5 days and 2.4 mg/m(2)/d from 7 days to the same dose for 9 and 12 days in cohorts of three to six patients when no DLT was identified. TPT pharmacokinetics were studied in 33 children once or twice (first and last doses in patients who received TPT for > 7 days).

RESULTS

Seventy assessable courses of TPT were administered to 49 children who had refractory leukemia. DLTs were typhlitis, diarrhea, and mucositis, and the MTD was 2.4 mg/m(2)/d for 9 days in this group of heavily pretreated children. In 33 patients, the median TPT lactone clearance after the first dose was 19.2 L/h/m(2) (range, 9.4 to 45.9 L/h/m(2)) and did not change during the course. There were significant responses (one complete response [CR] and four partial responses [PR] in patients with ANLL and one CR and two PRs in patients with ALL), and all but one were at dosages of TPT given for at least 9 days.

CONCLUSION

The MTD was 2.4 mg/m(2)/d for 9 days. Further testing is warranted of TPT's schedule dependence in children with leukemia.

Irinotecan for pediatric solid tumors: the Memorial Sloan-Kettering experience

PURPOSE

Irinotecan is a novel antineoplastic agent that works by inhibiting the enzyme, topoisomerase 1. Although not extensively studied in children, preclinical studies and several phase I trials indicate activity against a variety of relapsed solid tumors when administered on a protracted schedule. This report describes an institutional experience with irinotecan for the treatment of pediatric solid tumors.

PATIENTS AND METHODS

Twenty-two heavily pretreated children with multiply relapsed tumors were treated with courses of irinotecan at 20 mg/m2 per day for 10 days [(every day x 5) x 2].

RESULTS

Of the 19 patients evaluable for response, four achieved an objective response, including two complete responses and one partial response among four patients with rhabdomyosarcoma and one additional patient with an undifferentiated sarcoma with rhabdomyoblastic features, and one patient with a fibrosarcoma had stable disease. Among three patients with non-Hodgkin lymphoma, one achieved a partial response and one had stable disease. Diarrhea was the most commonly observed toxicity.

CONCLUSION

Irinotecan appears to have promising single-agent activity, particularly against rhabdomyosarcoma. with minimal hematopoietic toxicity, making it ideal for further evaluation in patients at high risk with newly diagnosed disease, particularly in combination with other active agents with nonoverlapping toxicities.

Phase I trial of cisplatin and topotecan in children with recurrent solid tumors: Children's Cancer Group Study 0942

OBJECTIVES

To determine the maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs) of cisplatin after a 72-hour continuous infusion of topotecan.

PATIENTS AND METHODS

Thirty-six children younger than age 22 years (range 3-21) with recurrent solid tumors were treated with cisplatin 45 to 75 mg/m2 infused over the course of 6 hours, followed by a 72-hour continuous infusion of topotecan 0.75 or 1 mg/m2 per day, followed by granulocyte colony stimulating factor (G-CSF), either immediately after treatment or when neutropenia developed. Patients were stratified by the presence of bone marrow tumor involvement and previous radiation to the bone marrow.

RESULTS

The DLT was neutropenia (absolute neutrophil count <500/microL for >7 days). The MTD was cisplatin 60 mg/m2 and topotecan 1 mg/m2 per day followed by G-CSF starting 24 hours after chemotherapy for patients without marrow involvement or previous radiation to the bone marrow. An acceptable MTD was not found for patients with previous radiation to the bone marrow or bone marrow involvement or without the use of G-CSF starting 24 hours after chemotherapy was completed. Topotecan clearance and steady-state levels were determined. Limited evidence for antitumor activity with this combination was found in rhabdomyosarcoma.

CONCLUSIONS

The recommended dose for phase II trials is cisplatin 60 mg/m2 followed by a 72-hour infusion of topotecan 1 mg/m2 per day with G-CSF starting 24 hours after the completion of topotecan.

Phase I study of irinotecan in pediatric patients with malignant solid tumors

PURPOSE

To determine the dose-limiting toxicity, maximum tolerated dose, and potential efficacy of irinotecan in children with refractory malignant solid tumors.

PATIENTS AND METHODS

In the present phase I clinical trial, 28 patients received irinotecan 50 to 200 mg/m2 per day by intravenous 2-hour infusion over the course of 3 days, repeated once after an interval of 25 days. Fifty-one treatment courses were administered to these patients.

RESULTS

Dose-limiting toxicities were observed at the dose of 200 mg/m2 per day for 3 days. Diarrhea and hematopoietic toxicities were the dose-limiting factors, and the former required support with intravenous fluid administration. The occurrence of vomiting was variable. Decreases in clinical tumor marker levels were observed in the majority of patients who received two cycles of irinotecan 80 mg/m2 per day to 200 mg/m2 per day over the course of 3 days, and partial response was attained in four patients who received irinotecan in two cycles of 140 mg/m2 per day to 200 mg/m2 per day over the course of 3 days. Pharmacokinetic studies showed that the plasma concentration of irinotecan and its active metabolite SN-38 ranged from 93 to 2,820 ng/mL and 5.2 to 34.8 ng/mL, respectively, during 3-day infusions of irinotecan 200 mg/m2 per day. The mean clearance of irinotecan was 14.54 L/h per m2 (range 8.45-20.83 L/h per m2).

CONCLUSION

The maximum tolerated dose was determined to be a dose of irinotecan between 160 mg/m2 per day and 180 mg/m2 per day administered over the course of 3 consecutive days on an inpatient basis, repeated once after 25 days off, and our results indicate that irinotecan is a promising anticancer agent that is worthy of phase II trials in pediatric solid tumors.

The development of camptothecin analogs in childhood cancers

Camptothecin analogs, agents that target the intranuclear enzyme topoisomerase I, represent a promising new class of anticancer drugs for the treatment of childhood cancer. In preclinical studies, camptothecins, such as topotecan and irinotecan, are highly active against a variety of pediatric malignancies including neuroblastomas, rhabdomyosarcomas, gliomas, and medulloblastomas. In this paper, we review the status of completed and ongoing clinical trials and pharmacokinetic studies of camptothecin analogs in children. These and future planned studies of this novel class of cytotoxic agents are critical to defining the ultimate role of topoisomerase I poisons in the treatment of childhood cancer.

Pharmacotherapy of malignant astrocytomas of children and adults: current strategies and future trends

This article reviews the conceptual progression in the pharmacological therapy of malignant astrocytoma (MA) over the past decade, and its future trends. It is a selective rather than an exhaustive inventory of literature citations. The experience of the Brain Tumour Cooperative Group (BTCG) and earlier phase III trials are summarised to place subsequent phase II and I studies of single and combination agent chemotherapy in perspective. The BTCG experience of the 1970s to 1980s may be summarised to indicate that external beam radiotherapy (EBRT) is therapeutic, although not curative, and not further improved upon by altering fractionation schedules, or the addition of radioenhancers. Whole brain and reduced whole brain EBRT with focal boost were comparable regimens. Nitrosourea-based, adjuvant chemotherapy provided a modest improvement in survival among adult patients, which was comparable with that of other single drugs or multidrug regimes. The multiagent schedules, however, had a correspondingly higher toxicity rate. Intra-arterial administration was associated with significant risk, which conferred no therapeutic advantage. The trend of the past decade has been towards multiagent chemotherapy although its benefit cannot be predicted from the classic prognostic factors. Published experience with investigational trials utilising myeloablative chemotherapy with autologous bone marrow or peripheral blood stem cell haemopoietic support, drug delivery enhancement methods and radiosensitisers is critically reviewed. None of these approaches have achieved wide-spread acceptance in the treatment of adult patients with MA. Greater attention is placed on recent 'chemoradiotherapy' trials, which attempt to integrate and maximise the cytoreductive potential of both modalities. This approach holds promise as an effective means to delay or overcome the evolution of tumour resistance, which is probably one of the dominant determinants of prognosis. However, the efficacy of this approach remains unproven. New chemotherapeutic agents as well as biological response modifiers, protein kinase inhibitors, angiogenesis inhibitors and gene therapy are also discussed; their role in the therapeutic armamentarium has not been defined.

Phase I study of combination topotecan and carboplatin in pediatric solid tumors

PURPOSE

We conducted a phase I trial of escalating doses of topotecan (TOPO) in association with a fixed systemic exposure of carboplatin (CARBO) with or without granulocyte colony-stimulating factor (G-CSF) in children.

PATIENTS AND METHODS

Two separate cohorts of patients (pts) with solid tumors were studied: (A) pts with refractory or recurrent disease and (B) pts with no prior myelosuppressive therapy or newly diagnosed tumors for which there was no standard chemotherapy. CARBO was given on day 1 at an area under the curve of 6.5, followed by TOPO as a continuous infusion for 3 days; the starting dose of TOPO was 0.50 mg/m(2)/d. Cycles were repeated every 21 days. G-CSF was given at a dose of 5 microg/kg/d starting on day 4.

RESULTS

Forty-eight of 51 pts were assessable for toxicity. In group A, dose-limiting myelosuppression persisted despite de-escalation of TOPO to 0.3 mg/m(2)/d and use of G-CSF. In group B, the maximum-tolerated dose of TOPO was 0.5 mg/m(2)/d for 3 days, and 0.6 mg/m(2)/d for 3 days with G-CSF. No significant nonhematologic toxicities were observed. Among 46 pts assessable for response, one had complete response, five had partial response, and 18 had stable disease.

CONCLUSION

Although this combination possesses antineoplastic activity in pediatric solid tumors, hematologic toxicity precluded any meaningful TOPO dose escalation. The addition of G-CSF did not alter this. The potential for preservation of activity and diminution of toxicity with alternative sequences and schedules of administration (topoisomerase followed by alkylating or platinating agents) should be evaluated.

Topotecan combined with myeloablative doses of thiotepa and carboplatin for neuroblastoma, brain tumors, and other poor-risk solid tumors in children and young adults

Topotecan appears to be relatively unaffected by the most common multidrug resistance mechanisms, may potentiate cytotoxicity of alkylators, has good penetration into the central nervous system, is active against a variety of neoplasms, and has myelosuppression as its paramount toxicity. We present our experience with a myeloablative regimen that includes topotecan. Twenty-one patients with poor-prognosis tumors and intact function of key organs received topotecan 2 mg/m2 by 30-min intravenous (i.v.) infusion on days -8, -7, -6, -5, -4; thiotepa 300 mg/m2 by 3 h i.v. infusion on days -8, -7, -6; and carboplatin by 4 h i.v. infusion on days -5, -4, -3 with a daily dose derived from the pediatric Calvert formula, using a targeted area under the curve of seven mg/ml* min ( approximately 500 mg/m2/day). Stem cell rescue was on day 0. The patients were 1 to 29 (median 4) years old; 18 were in complete remission (CR) and three in partial remission (PR). Early toxicities were severe mucositis and erythema with superficial peeling in all patients and a seizure, hypertension, and renal insufficiency followed by veno-occlusive disease in one patient each. Post-transplant treatment included radiotherapy alone (four patients) or plus biological agents (11 patients with neuroblastoma). With a follow-up of 6+ to 32+ (median 11+) months, event-free survivors include 10/11 neuroblastoma patients (first CR), 4/5 brain tumor patients (second PR or CR), 1/3 patients with metastatic Ewing's sarcoma (first or second CR), and a patient transplanted for multiply recurrent immature ovarian teratoma; a patient with desmoplastic small round-cell tumor (second PR) had progressive disease at 8 months. Favorable results for disease control, manageable toxicity, and the antitumor profiles of topotecan, thiotepa, and carboplatin, support use of this three-drug regimen in the treatment of neuroblastoma and brain tumors; applicability to other tumors is still uncertain.

Topoisomerase I inhibition with topotecan: pharmacologic and clinical issues

Topoisomerase I (topo-I) inhibitors are a new class of anticancer agents with a mechanism of action aimed at interrupting DNA replication in cancer cells, the result of which is cell death. Most, if not all, topo-I inhibitors are derivatives of the plant extract camptothecin. Topotecan is a derivative of camptothecin which has been structurally modified to increase water solubility. The pharmacokinetic profile of topotecan is usually characterised by a two-compartment model and is linear in the dose range of 0.5 - 3.5 mg/m(2). Current clinical trials suggest antitumour activity against a variety of human tumour types, including ovarian cancer, non-small cell lung cancer (NSCLC) and non-lymphocytic haematologic malignancies. The main dose-limiting toxicity (DLT) is non-cumulative myelosuppression. Non-haematologic toxicities are usually mild. Based on several Phase I studies, the recommended Phase II dose was 1.5 mg/m(2)/day iv. for 5 days. Current Phase I and Phase II trials are evaluating the combination of topotecan with other chemotherapeutic agents to increase the therapeutic benefits of topotecan. The DLT in these trials is mainly myelosuppression.

Phase I topotecan preparative regimen for high-risk neuroblastoma, high-grade glioma, and refractory/recurrent pediatric solid tumors

We evaluated the toxicity and maximum tolerated dose of topotecan in a novel myeloablative regimen as treatment for high-risk pediatric tumors. Patients received an assigned topotecan dosage in combination with fixed doses of carboplatin and thiotepa, followed by autologous hematopoietic stem cells infusion. Topotecan dose was escalated in cohorts of four patients until the maximum tolerated dose of topotecan was defined or until accrual of 30 patients. Pharmacokinetics of topotecan were examined, and event-free survival was estimated. We describe preliminary results following treatment of 25 pediatric patients with high-risk solid tumors.

Pilot study of topotecan and high-dose cyclophosphamide for resistant pediatric solid tumors

BACKGROUND

The recommended dosages of topotecan and cyclophosphamide in combination for prior-treated patients-3.75 mg/m(2) and 1,250 mg/m(2) in children, 5 mg/m(2) and 600 mg/m(2) in adults, respectively-are well below those of each agent when used singly. We tested the hypothesis that much higher dosing would meet critical goals of salvage therapy: antitumor effect and a lack of toxicity to key organs, so as not to preclude subsequent consolidative treatments needed for cure.

PROCEDURE

Patients with resistant pediatric solid tumors received cyclophosphamide 4,200 mg/m(2) by 48 hr infusion, and topotecan 6 mg/m(2) by 72 hr infusion (HD-Cy/Topo). Mesna and granulocyte colony-stimulating factor were used. Cycles were repeated when neutrophil counts were >1,000/uL and platelet counts were >75,000/uL.

RESULTS

Twenty-eight patients, aged 2 to 33 years (median, 14), received one (n = 4), two (n = 15), or > or =3 (n = 9) cycles of HD-Cy/Topo. All patients had previously received > or =6 cycles of other therapy, high-dose alkylator-based chemotherapy, and/or etoposide- and doxorubicin-containing regimens. HD-Cy/Topo was given in an outpatient setting. Profound myelosuppression was the major toxicity, but retreatment was possible by day 28, and preliminary results with peripheral blood stem cell collections showed a sparing effect on hemopoietic stem cells. Mucositis was uncommon. After HD-Cy/Topo, cardiac, renal, hepatic, and pulmonary function remained within the normal range. Partial or minor responses were noted in neuroblastoma, desmoplastic small round-cell tumor, Ewing sarcoma, rhabdomyosarcoma, and osteosarcoma.

CONCLUSIONS

Its antitumor potential and limited toxicity make HD-Cy/Topo an attractive choice for inclusion in aggressive salvage programs aimed at achieving cures of resistant tumors. It may also merit incorporation into frontline treatment protocols.

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 for the treatment of recurrent or progressive central nervous system tumors - a pediatric oncology group phase II study

Topotecan was studied as a 72 h infusion given every 3 weeks. Treatment began at a dose of 1.0 mg/m2/day and was increased to 1.25 mg/m2/day after the first 6 patients tolerated this higher dose without excessive toxicities. Eighty-eight evaluable children were accrued in 6 strata. There were no complete nor partial responses. Twenty subjects had stable disease (astrocytoma 5/11, malignant glioma 5/13, medulloblastoma 0/12, brain stem tumor 4/19, ependymoma 5/17, and miscellaneous histologies 1/16). Two patients (astrocytoma, ependymoma) completed the maximum 18 topotecan courses. The remaining 68 children developed progressive disease within 2 months. Myelosuppression was the main toxicity. Grade 4 leukopenia, neutropenia, anemia, and thrombocytopenia were observed in 18, 32, 5, and 23 participants, respectively. It was concluded that topotecan as given according to this schedule showed insufficient activity to promote it to frontline protocol usage.

Current aspects of biology, risk assessment, and treatment of neuroblastoma

Neuroblastoma is one of the most intensely studied solid malignancies that affect the pediatric age groups; its clinical presentation, treatment strategies and ultimate prognosis vary greatly. The biologic and genetic character of each tumor has an important impact on disease behavior, and clinical staging now incorporates these factors to generate an overall therapy plan. The clinical presentation of neuroblastoma is related to primary tumor location, production of metabolically active substances, and the presence of metastatic disease. There are also prognostically important associated syndromes including opsoclonus-myoclonus, Horner's syndrome, neurofibromatosis, and a variety of other neurocristopathies. The histologic features of the tumor are of prognostic significance and are utilized in treatment stratification. The International Neuroblastoma Staging System (INSS) has unified classic clinical staging. Features at diagnosis and those determined by initial operation are combined with biologic prognostic factors to achieve risk group assignment for virtually all patients. There are groups of children in which limited therapy is curative and intermediate-risk situations where standard multimodality treatment provides favorable outcomes. Unfortunately, there are many patients with high-risk disease that require intensive strategies, but success is still limited. It is in these most resistant patients that innovative approaches are being undertaken and novel strategies are being investigated.

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.

Clinical pharmacology of camptothecins

Camptothecins (CPTs) are a unique class of chemotherapeutic agent which inhibit DNA synthesis by inhibiting topoisomerase I activity. Structure-activity studies on the original CPT alkaloid led to the development of the new analogues irinotecan (CPT-11), topotecan, and 9-aminocamptothecin, which have improved water solubility and lower toxicity. CPT analogues exhibit interesting pharmacokinetic/pharmacodynamic and metabolic properties that are of major research and clinical interest. This review describes the clinical pharmacology of these 3 CPT analogues. Specific areas such as absorption after extravascular administration, pharmacokinetic/pharmacodynamic variability, metabolism, and administration in special populations are discussed.

Neuroblastoma

The neuroblastic tumours originate from primordial neural crest cells that normally develop into sympathetic nervous system, including the adrenal medulla. Neuroblastoma is the most intriguing pediatric neoplasm displaying diverse clinical and biologic characteristics and natural history. It has the highest rate of spontaneous regression of all human cancers, yet exhibits extremely malignant behaviour in older children with regional and disseminated disease. In the last 30 years, only a nominal improvement has occurred in the outlook of older children with metastatic disease at diagnosis. Tremendous gains in understanding of the biology of neuroblastoma in recent years have led to development of risk-related therapy based on age, stage and biological characteristics of neuroblastoma.

Phase I therapy trials in children with cancer

PURPOSE

This study examined the response and toxicity rates of antineoplastic drugs evaluated in phase I clinical trials in children to identify trends in response and toxicity over time.

PATIENTS AND METHODS

Full length, peer-reviewed articles describing the results of single agent phase I therapy trials in children younger than 21 years with cancer were reviewed. Tumor-specific response data and doses of drugs that resulted in objective responses were noted. Deaths that occurred on study caused by drug toxicity, progressive disease (PD), or complications of marrow aplasia were identified, along with drug doses that resulted in toxic death. Temporal trends in response rates, toxicity, and number of patients entered in trials were examined.

RESULTS

A total of 1,606 patients with cancer were enrolled in 56 single-agent pediatric phase I therapy trials published between 1978 and 1996. Of these, 1,257 were evaluated for response by tumor type. The overall objective response rate was 7.9%. Response rates were highest for patients with neuroblastoma (17.7%) and acute myelogenous leukemia (11.6%). Patients with osteosarcoma and rhabdomyosarcoma had response rates of < 3%. Sixty percent of responses in patients with solid tumors occurred at 81 to 100% of the maximum tolerated dose (MTD), although 42% of responses in patients with leukemia occurred at > 100% of the MTD. Death on study was noted in 7.0% of all patients entered in trials. Only 0.7% of patients experienced a death related to drug toxicity. PD accounted for the death of 5.6% of study participants. A trend of increasing response rate despite smaller trial size was noted over the last 7 years of this period.

CONCLUSION

Phase I trials in children with cancer represent a safe mechanism to determine the MTD, toxicity profile, and pharmacokinetics of new agents for use in children with cancer.

Topoisomerase I inhibitors and drug resistance

DNA topoisomerase I is a nuclear enzyme which catalyzes the conversion of the DNA topology by introducing single-strand breaks into the DNA molecule. This enzyme represents a novel and distinct molecule target for cancer therapy by antitopoisomerase drugs belonging to the campthotecin series of antineoplastics. As many tumors can acquire resistance to drug treatment and become refractary to the chemotherapy it is very important to investigate the mechanisms involved in such a drug resistance for circumventing the phenomenon. This article describes the role of topoisomerase I in cell functions and the methods used to assess its in vitro catalytic activity. It reviews the mechanisms of cytotoxicity of the most specific antitopoisomerase I drugs by considering also the phenomenon of drug resistance. Some factors useful to drive the future perspectives in the development of new topoisomerase I inhibitors are also evidenced and discussed.

Relationship between topotecan systemic exposure and tumor response in human neuroblastoma xenografts

BACKGROUND

Topotecan is a topoisomerase I inhibitor with activity against xenografts of childhood solid tumors and established clinical activity against neuroblastoma and rhabdomyosarcoma. We have studied the relationship between systemic exposure to and the antitumor activity of topotecan lactone (the active form of the drug) in the xenograft models. Furthermore, we determined whether the responses seen in these models occur at systemic exposure levels that are tolerable in children.

METHODS

Neuroblastoma xenografts derived from the tumors of six different patients were established subcutaneously in immune-deprived mice. Topotecan was administered by intravenous bolus injection 5 days a week for 2 consecutive weeks, repeated every 21 days for three cycles. The minimum daily doses that induced complete responses (CRs) and partial responses (PRs) were determined. Topotecan lactone pharmacokinetic studies were performed in both tumor-bearing and nontumor-bearing mice.

RESULTS

The minimum doses associated with CRs and PRs in four of the six neuroblastoma xenografts were 0.61 and 0.36 mg/kg body weight, respectively. The topotecan lactone single-day systemic exposures associated with these doses were 88 and 52 ng x hr/mL, respectively. There was an approximately sixfold difference in topotecan lactone systemic exposure (290 ng x hr/mL versus 52 ng x hr/mL) associated with achieving CRs in the least-sensitive and most-sensitive tumors, respectively.

CONCLUSIONS

Neuroblastoma xenografts are highly sensitive to topotecan therapy, and responses in mice are achieved at systemic exposures similar to those that are clinically effective and tolerable in children. These results support the concept of deriving preclinical data relating systemic exposure to antitumor activity in xenograft models. Such data may be valuable in making informed decisions regarding the clinical development of new agents.

Preclinical development of camptothecin derivatives and clinical trials in pediatric oncology

Although the prognosis of childhood cancers has dramatically improved over the last three decades, new active drugs are needed. Camptothecins represent a very attractive new class of anticancer drugs to develop in paediatric oncology. The preclinical and clinical development of two of these DNA-topoisomerase I inhibitors, i.e. topotecan and irinotecan, is ongoing in paediatric malignancies. Here we review the currently available results of this evaluation. Topotecan proved to be active against several paediatric tumour xenografts. In paediatric phase I studies exploring several administration schedules, myelosuppression was dose-limiting. The preliminary results of topotecan evaluation in phase II study showed antitumour activity in neuroblastoma (response rate: 15% at relapse and 37% in newly diagnosed patients with disseminated disease) and in metastatic rhabdomyosarcoma (40% in untreated patients). Topotecan-containing drug combinations are currently investigated. Irinotecan displayed a broad spectrum of activity in paediatric solid tumour xenografts, including rhabdo-myosarcoma, neuroblastoma, peripheral primitive neuroectodermal tumour, medulloblastoma, ependymoma, malignant glioma and juvenile colon cancer. For several of these histology types, tumour-free survivors have been observed among animals bearing an advanced-stage tumour at time of treatment. The clinical evaluation of irinotecan in children is ongoing. Irinotecan undergoes a complex in vivo biotransformation involving several enzyme systems, such as carboxylesterase, UDPGT and cytochrome P450, in children as well as in adults. Preclinical studies of both drugs have shown that their activity was schedule-dependent. The optimal schedule of administration is an issue that needs to be addressed in children. In conclusion, the preliminary results of the paediatric evaluation of camptothecin derivatives show very encouraging results in childhood malignancies. The potential place of camptothecins in the treatment of paediatric malignant tumours is discussed.

Oral versus intraperitoneal administration of irinotecan in the treatment of human neuroblastoma in nude mice

The present study evaluated the plasma pharmacokinetics of irinotecan (CPT-11) and its effects against a human neuroblastoma in xenograft, given by different administration routes. One-third of the LD50 was administered either intraperitoneally (59 mg/kg mouse weight (MW)) or orally (404 mg/kg MW) to nude mice. The plasma levels of CPT-11 and its active metabolite SN-38 decreased rapidly when CPT-11 was administered intraperitoneally, but remained relatively high for 4-8 h after oral administration. Then, a human neuroblastoma xenograft was inoculated in another set of 21 nude mice. When the estimated tumor weight reached 150-200 mg, CPT-11 was administered in the total LD50 either intraperitoneally or orally in three doses at 4-day intervals (q4d x3) to the mice in each experimental group. Oral administration was found to be superior to intraperitoneal injection in terms of tumor inhibition and to be an effective route for CPT-11 administration in the treatment of human neuroblastoma in nude mice.

Phase II study of cisplatinum and carboplatinum (CACIS) combination in advanced stage neuroblastomas

BACKGROUND

Platinum derivatives are, among others (cyclophosphamide, etoposide, doxorubicin), the most active drugs in neuroblastomas. As the combination of carboplatin (CBDCA) with cisplatinum (CDDP) was proven effective in some carcinomas, we proposed it as a second-line therapy in neuroblastoma.

PROCEDURE

Nineteen children with neuroblastoma and primary refractory disease (seven cases) or relapse either untreated (eight cases) or resistant to second-line therapy (four cases), were treated with cisplatinum and carboplatinum (CACIS) combination. All but one patient had previously received CDDP (median 400: 200 to 1,200 mg/m2) and 15 out of 19 had also received CBDCA (median 1,600:800 to 5,000 mg/m2). Twelve had previously received intensification with megatherapy. The CACIS regimen included CBDCA (100 mg/m2/day as a 1-hour infusion, for 4 days) and simultaneous CDDP (25 mg/m2/day as a 3-hour infusion, for 4 days).

RESULTS

Eight out of 19 patients (42%) achieved a partial response with a duration of response of 3 to 12 months (median 6). No patient achieved a complete response. The toxicity was mainly hematological, though one patient died after two courses of an interstitial pneumonia of unknown origin. Only one patient developed alopecia. The renal toxicity was low.

CONCLUSIONS

The CACIS regimen is an effective combination of platinum derivatives. It may be proposed as second line protocol, especially for children with neuroblastoma who relapse after megatherapy.

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.

Topoisomerase I inhibitors: the relevance of prolonged exposure for present clinical development

Topoisomerase I inhibitors constitute a new class of anti-cancer agents. Recently, topotecan and irinotecan were registered for clinical use in ovarian cancer and colorectal cancer respectively. Cytotoxicity of topoisomerase I inhibitors is S-phase specific, and in vitro and in vivo studies have suggested that, for efficacy, prolonged exposure might be more important than short-term exposure to high concentration. Clinical development of those topoisomerase I inhibitors that have reached this stage is also focused on schedules aiming to achieve prolonged exposure. In this review, we summarize all published preclinical studies on this topic for topoisomerase I inhibitors in clinical development, namely 20-S-camptothecin, 9-nitro-camptothecin, 9-amino-camptothecin, topotecan, irinotecan and GI147211. In addition, preliminary data on clinical studies concerning this topic are also reviewed. The data suggest that prolonged exposure may indeed be relevant for anti-tumour activity. However, the optimal schedule is yet to be determined. Finally, clinical data are yet too immature to draw definitive conclusions.

The impact of column temperature in the high performance liquid chromatographic analysis of topotecan in rat and dog plasma

A sensitive high performance liquid chromatographic (HPLC) assay has been developed and validated for the quantitation of the novel anticancer agent topotecan and topotecan as its lactone plus carboxylate forms in rat and dog plasma. Linear responses in analyte standard peak areas were observed over the concentration ranges 0.10-10 ng ml-1 using 100 microliters of rat plasma and 0.2-100 ng ml-1 using 100 microliters of dog plasma. Due to the instability of the drug in the biological matrix it was necessary to obtain the plasma fraction within 5 min after blood sampling by centrifugation, immediately followed by protein precipitation with cold methanol (-30 degrees C). For the determination of total drug levels (lactone plus lactone ring-opened form), plasma samples were deproteinated with methanol and subsequently acidified with 2% (v/v) perchloric acid. The samples were analysed by HPLC using a Zorbax SB-C18 Stable Bond column and methanol-0.1 M hexane-1-sulfonic acid in methanol-0.01 M N,N,N'N'-tetramethylethylenediamine in distilled water pH 6.0 (25:10:65, v/v/v) as the mobile phase. The detection was performed fluorimetrically. The analytical column was thermostated at 19-21 degrees C to obtain baseline resolution between an interfering endogenous compound in rat and dog plasma and topotecan. This endogenous peak was absent in human plasma. Variation of chromatography temperature appeared to be a very useful tool in the bioanalysis of topotecan. It allowed optimization of the separation between the endogenous compound and the analyte; different mechanisms of solute interactions are apparently involved in this reversed-phase ion-pair chromatographic system.

Phase I trial and pharmacokinetic (PK) and pharmacodynamics (PD) study of topotecan using a five-day course in children with refractory solid tumors: a pediatric oncology group study

PURPOSE

A phase I trial was conducted in children with refractory solid tumors to determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), pharmacokinetics, and pharmacodynamics for topotecan administered by a 30-min infusion for 5 consecutive days.

PATIENTS AND METHODS

Forty children with a variety of recurrent solid tumors, including nine patients with neuroblastoma and 10 with brain tumors, were given topotecan as a 30-min infusion for 5 consecutive days, beginning with a dose of 1.4 mg/m2/day. The dose was escalated in 20% increments after establishing that DLT was not present at the prior dose. Drug toxicity was graded using standard criteria. Dose-limiting toxicity was defined as grade 3 or 4 nonhematopoietic toxicity or grade 4 hematopoietic toxicity lasting > 7 days. Pharmacokinetic studies were performed during the first infusion course.

RESULTS

The DLT was hematopoietic and involved both platelets and neutrophils. Grade 4 hematopoietic toxicity of brief duration was seen at all dose levels. Over half of the patients received red blood cell transfusion support, and 19/40 received platelet transfusions. Hospital admissions for fever and neutropenia or for documented infections occurred in 32 of 169 courses of therapy. Gastrointestinal symptoms with nausea and vomiting or diarrhea were mild to moderate in 12 of the 40 patients. Antitumor responses were seen in three patients with neuroblastoma. An additional four patients (one with neuroblastoma, two with anaplastic astrocytomas, one with Ewing) had stable disease with continued therapy for > 6 months. Using a limited sampling model, pharmacokinetic studies were performed in 36 of the 40 patients. Topotecan lactone and total clearance were similar to those reported in other pediatric populations receiving topotecan by continuous infusion. A pharmacodynamic relation between systemic exposure to topotecan lactone and myclosuppression was observed.

CONCLUSIONS

In heavily pretreated children, the MTD for topotecan given by intermittent 30-min infusion for 5 days is 1.4 mg/m2 without GCSF and 2.0 mg/m2/day with GCSF. The dose-limiting toxicity is hematopoietic. Data from this study provide the basis for further studies of topotecan in children with cancer.

Pediatric phase I drug tolerance: a review and comparison of recent adult and pediatric phase I trials

PURPOSE

We evaluated the ratio of pediatric to adult maximum tolerated doses (MTDs) from 70 Phase I studies conducted between 1975 and 1995. The aim of this study was to determine whether previously observed differences in drug tolerance between adult and pediatric Phase I patients have persisted over the 20-year period of this analysis.

PATIENTS AND METHODS

Phase I trials of pediatric and adult patients with solid tumors as the predominant diagnosis and sharing similar dosing regimens were evaluated. For consistent comparison between Phase I studies, the MTD was defined as the drug dose one level below that yielding dose-limiting toxicity in >30% of patients. The ratio of pediatric to adult MTDs was calculated and plotted chronologically by year of pediatric study closure. Statistical evaluation of MTD ratios included regression and correlation analysis. The extent of therapy before Phase I study entry was also examined.

RESULTS

Ninety-three Phase I studies were reviewed. Twenty-one drugs (70 studies) met our criteria for paired review of MTDs and analysis of the variation of ratio with time. The pediatric to adult MTD ratios ranged from 0.4 to 2.8, with a median of 1.2. Regression analysis of the ratio of MTD versus date of pediatric study closure supports a linear relationship of decreasing ratio with time (p<0.01). Analysis of the regression line predicts MTD ratios of 2.02 and 0.76 for 1974 and 1995, respectively. Of patients included in this analysis, 37.1% and 68.6% of adult and pediatric patients, respectively, were considered to have been heavily pretreated before study entry. A significant (p<0.001) downward trend with time was observed in the proportion of adult patients entering Phase I studies who had received both radiation and chemotherapy.

CONCLUSIONS

The results of this review continue to show an equal or greater drug tolerance in the pediatric population when compared with adult patients for most drugs studied during Phase I trials. However, there appears to be significant trend of decreasing differences in drug tolerance between pediatric and adult Phase I patients with time, as defined by the descent of the MTD ratio toward values <1.0. Mechanisms to explain greater drug tolerance in children and the observation of decreasing maximum tolerated dose ratios with time are discussed. Limited data suggest that changes in degree of therapy before Phase I study entry may be influencing the MTD ratio.

Current perspectives on camptothecins in cancer treatment

The camptothecins are a new class of chemotherapeutic agents which have a novel mechanism of action targeting the nuclear enzyme topoisomerase I. Knowledge of the structure-activity relationships of the parent compound camptothecin has led to the development of effective soluble analogues with manageable toxicities. Broad anti-tumour activity shown in preclinical studies has been confirmed in phase I/II studies for irinotecan and topotecan. Two other derivatives, 9-aminocamptothecin and GI 147211C, are undergoing phase I and early phase II evaluation. Although camptothecin is a plant extract, it and most of its derivatives are not affected by the classic P-gpMDR1 mechanism of resistance which may allow the development of novel combination chemotherapeutic regimens. Important areas of future endeavour will include the development of rational combination regimens and the pursuit of randomised trials. Based on single agent data, colorectal cancer and non-small-cell lung cancer should be the focus for future irinotecan studies. Small-cell lung cancer and ovarian carcinoma are logical tumour types to pursue with topotecan. Both 9-aminocamptothecin and GI 147211C are too early in their clinical evaluation to make recommendations about their future roles. Finally, the unfolding story of camptothecin analogue development will give important insights into the predictive value of preclinical observations on relative efficacy, schedule dependency, combination strategies and resistance mechanisms which have helped determine the strategies for clinical evaluation of these agents.

Topoisomerase I interactive drugs in children with cancer

Topotecan, irinotecan, and 9-aminocamptothecin (9-AC) are analogs of the plant alkaloid 20(S)-camptothecin (CMT), the prototypical DNA topoisomerase I interactive agent. These agents interact with the topoisomerase I-DNA complex and prevent resealing topoisomerase I-mediated DNA single-strand breaks. This eventual leads to double-strand DNA breaks and apoptosis or cell death. Topotecan, irinotecan, and 9-AC have shown significant activity in mice bearing pediatric solid tumor xenografts; the greatest antitumor responses were found with protracted continuous schedules. Preclinical data also suggest that maintenance of an exposure-duration threshold (EDT) may be required to achieve optimal cytotoxicity. Pediatric Phase I trials have evaluated the toxicity and safety to camptothecin analogs in children with relapsed solid tumors and relapsed acute leukemia. The primary dose-limiting toxicity (DLT) for the CMT analogs in children has been myelosuppression, except for mucositis observed with the 120-hr continuous topotecan infusion schedule. Pharmacodynamic relationships with these analogs have been reported between systemic exposure, and myelosuppression and mucositis. Although not a primary objective of the early Phase I studies, antitumor responses have been reported. In this review, the pharmacokinetic and pharmacodynamics of the CMT analogs studied in children are summarized, and future studies of these agents are discussed.

High-performance liquid chromatographic determination of the novel antitumour drug topotecan and topotecan as the total of the lactone plus carboxylate forms, in human plasma

A sensitive high-performance liquid chromatographic (HPLC) assay has been developed and validated for the quantitation of the novel anticancer agent topotecan and topotecan as the total of its lactone and carboxylate forms in human plasma. Linear response in analyte standard peak area were observed over the concentration range 0.05-10 ng/ml using 100-microliters plasma samples. The instability of the drug in the biological matrix necessitated that the plasma fraction was obtained within 5 min after blood sampling by centrifugation, immediately followed by protein precipitation with cold methanol (-30 degrees C). Stability studies have indicated that topotecan is stable in these methanolic extracts for at least 4.5 months at -30 degrees C and 2 months at -70 degrees C. For the total determination of the lactone plus lactone ring-opened forms of the drug as topotecan, plasma samples were deproteinated with methanol and, subsequently, acidified with 7% (v/v) perchloric acid. Plasma samples for the measurement of total levels of the lactone and the ring-opened forms of topotecan were stable for at least 4.5 months when stored at -30 degrees C. After centrifugation, the supernatants were analysed by HPLC using a Zorbax SB-C18 Stable Bond column and methanol-0.1 M hexane-1-sulfonic acid in methanol-0.01 M N,N,N',N'-tetramethylethylenediamine (TEMED) in distilled water pH 6.0 (25:10:65, v/v) as the mobile phase. Detection was performed fluorimetrically. Within-run and between-run precision was always less than 12.1% in the concentration range of interest (0.05-10.0 ng/ml). The limit of quantitation is 0.05 ng/ml. Accuracy measurements ranged between 87.6 and 113.5%.

Cerebrospinal fluid pharmacokinetics and penetration of continuous infusion topotecan in children with central nervous system tumors

The purpose of this study was to describe the cerebrospinal fluid (CSF) penetration of topotecan in humans, to generate a pharmacokinetic model to simultaneously describe topotecan lactone and total concentrations in the plasma and CSF, and to characterize the CSF and plasma pharmacokinetics of topotecan administered as a continuous infusion (CI). Plasma and CSF samples were collected from 17 patients receiving 5.5 or 7.5 mg/m2 per day as a 24-h CI (5 patients, 7 courses), or 0.5 to 1.25 mg/m2 per day as a 72-h CI (12 patients, 12 courses). CSF samples were obtained from either a ventricular reservoir (VR) or a lumbar puncture (LP). Topotecan lactone and total (lactone plus hydroxy acid) concentrations were determined by HPLC and fluorescence detection. Using MAP-Bayesian modelling, a three-compartment model was fitted simultaneously to topotecan lactone and total concentrations in the plasma and CSF. The penetration of topotecan into the CSF was determined from the ratio of the CSF to the plasma area under the concentration-time curve. The median CSF ventricular lactone concentrations, obtained prior to the end of infusion (EOI), were 0.86, 1.4, 0.73, 5.3, and 4.6 ng/ml for patients receiving 0.5, 1.0, 1.25, 5.5, and 7.5 mg/m2 per day, respectively. EOI CSF lumbar lactone concentrations measured in three patients were 0.44, 1.1, and 1.7 ng/ml for topotecan doses of 1.0, 5.5, and 7.5 mg/m2 per day, respectively. In two patients receiving 1.25 mg/m2 per day, EOI CSF concentrations were obtained simultaneously from a VR and LP; the lumbar lactone concentrations were 30% and 49% lower than the ventricular concentrations. During a 24-h and a 72-h CI, the median CSF penetration of topotecan lactone was 0.29 (range 0.10 to 0.59) and 0.42 (range 0.11 to 0.86), respectively. A three-compartment model adequately described topotecan lactone and total concentrations in the plasma and CSF. Topotecan was therefore found to significantly penetrate into the CSF in humans. The pharmacokinetic model presented may be useful in the design of clinical studies of topotecan to treat CNS tumors.