Phase I trial of 9-aminocamptothecin in children with refractory solid tumors: a Pediatric Oncology Group study

A comparison of safety and efficacy of cytotoxic versus molecularly targeted drugs in pediatric phase I solid tumor oncology trials

BACKGROUND

Prior reviews of phase I pediatric oncology trials involving primarily cytotoxic agents have reported objective response rates (ORRs) and toxic death rates of 7.9-9.6% and 0.5%, respectively. These data may not reflect safety and efficacy in phase I trials of molecularly targeted (targeted) drugs.

METHODS

A systematic review of pediatric phase I solid tumor trials published in 1990-2013 was performed. The published reports were evaluated for patient characteristics, toxicity information, and response numbers.

RESULTS

A total of 143 phase I pediatric clinical trials enrolling 3,896 children involving 53 targeted and 48 cytotoxic drugs were identified. A meta-analysis demonstrated that the ORR is 2.1-fold higher with cytotoxic drugs (0.066 vs. 0.031 per subject; P = 0.007). By contrast, the pooled estimate of the stable disease rate (SDR) is similar for cytotoxic and targeted drugs (0.2 vs. 0.23 per subject; P = 0.27).  The pooled estimate of the dose-limiting toxicity rate is 1.8-fold larger with cytotoxic drugs (0.24 vs. 0.13 per subject; P = 0.0003). The hematologic grade 3-4 (G3/4) toxicity rate is 3.6-fold larger with cytotoxic drugs (0.43 vs. 0.12 per treatment course; P = 0.0001); however, the nonhematologic G3/4 toxicities and toxic deaths occur at similar rates for cytotoxic and targeted drugs.

CONCLUSIONS

In phase I pediatric solid tumor trials, ORRs were significantly higher for cytotoxic versus targeted agents. SDRs were similar in targeted and cytotoxic drug trials. Patients treated with cytotoxic agents were more likely to experience hematologic G3/4 toxicities than those patients receiving targeted drugs.

Phase I trial of continuous infusion 9-aminocamptothecin in patients with advanced solid tumors: 21-day infusion is an active well-tolerated regimen

This study's objectives were to determine the maximum tolerated dose (MTD) of 9-aminocamptothecin (9-AC), given as a prolonged continuous infusion (CI) for 7-21 days, when formulated in dimethylacetamide/polyethylene glycol 400 (DMA) and then later as a colloidal dispersion (CD), and to determine the steady-state pharmacokinetics of 9-AC. Patients with solid tumors refractory to standard therapy were enrolled on this study. Total dose/cycle of 9-AC/DMA was initially escalated by duration (7-21 days), while keeping the dose rate constant at 6.2 microg/m/h (1.04-3.12 mg/m/4-week cycle). Then, the dose rate was escalated from 6.2 to 21.1 microg/m/h (3.12-10.6 mg/m/4-week cycle) while keeping the infusion duration constant at 21 days. CD formulation was escalated from 14.1 to 25 microg/m/h (7.11-12.60 mg/m/4-week cycle) while keeping the infusion duration constant at 21 days and then escalated from 28.1 to 37.5 microg/m/h (9.44-12.60 mg/m/3-week cycle) while keeping the infusion duration constant at 14 days. Sixty-two patients were evaluable for toxicity; 61 received prior chemotherapy (median 3 regimens/patient). No consistent dose-limiting toxicity (DLT) was encountered with the DMA formulation until dose level 10.60 mg/m/cycle, when two patients experienced DLTs. With the 21-day CD formulation, the MTD was 12.60 mg/m/cycle with three DLTs out of five patients. When 9-AC was given on the 14-day schedule, DLT was seen at 9.44, 11.20 and 12.60 mg/m/cycle, with consistent DLT at the two highest dose levels. All DLTs for both formulations were grade 4 hematologic toxicities (neutropenia and/or thrombocytopenia), while non-hematologic toxicities were relatively mild (including gastrointestinal toxicities and fatigue). One patient with ovarian cancer had a complete response and three had partial responses (PRs). One patient each with non-Hodgkin's lymphoma and cancer of unknown primary had a PR. Pharmacokinetic studies of both formulations of 9-AC revealed a linear relationship between increasing plasma 9-AC lactone concentration and dose. The median plasma 9-AC lactone concentration for 9-AC/CD was approximately twice that achieved by 9-AC/DMA for the same dose level. Both 9-AC formulations, given as a 21-day CI, were well tolerated with dose-limiting myelosupression at the MTD. This dose intensity exceeds that of other 9-AC phase I/II schedules. The recommended phase II dose (RPTD) is 9.42 mg/m/4-week cycle, given as a 21-day infusion. The 14-day schedule of 9-AC/CD was equally myelosuppressive with the RPTD of 9.44 mg/m/3-week cycle, although two heavily pre-treated patients (one with pelvic radiotherapy) could not tolerate this dose. Objective responses were observed in six out of 57 heavily pre-treated patients, most of which had ovarian cancer.

Pediatric Phase I Trials in Oncology: An Analysis of Study Conduct Efficiency

Purpose

To determine the efficacy and safety of pediatric phase I oncology trials in the era of dose-intensive chemotherapy and to analyze how efficiently these trials are conducted.

Methods

Phase I pediatric oncology trials published from 1990 to 2004 and their corresponding adult phase I trials were reviewed. Dose escalation schemes using fixed 30% dose increments were studied to theoretically determine whether trials could be completed utilizing fewer patients and dose levels.

Results

Sixty-nine pediatric phase I oncology trials enrolling 1,973 patients were identified. The pediatric maximum-tolerated dose (MTD) was strongly correlated with the adult MTD (r = 0.97). For three-fourths of the trials, the pediatric and adult MTD differed by no more than 30%, and for more than 85% of the trials, the pediatric MTD was less than or equal to 1.6 times the adult MTD. The median number of dose levels studied was four (range, two to 13). The overall objective response rate was 9.6%, the likelihood of experiencing a dose-limiting toxicity was 24%, and toxic death rate was 0.5%.

Conclusion

Despite the strong correlation between the adult and pediatric MTDs, more than four dose levels were studied in 40% of trials. There appeared to be little value in exploring dose levels greater than 1.6 times the adult MTD. Limiting pediatric phase I trials to a maximum of four doses levels would significantly shorten the timeline for study conduct without compromising safety.

A predictive model of human myelotoxicity using five camptothecin derivatives and the in vitro colony-forming unit granulocyte/macrophage assay

PURPOSE

Many promising anticancer drugs are limited by myelosuppression. It is difficult to evaluate human myelotoxicity before a Phase I study because of the susceptibility of humans and animals to hematotoxicity. The purpose of this study was to establish a reliable method to predict the human maximum tolerated dose (MTD) of five camptothecin derivatives: SN-38, DX-8951f, topotecan, 9-aminocamptothecin, and camptothecin.

EXPERIMENTAL DESIGN

The myelotoxicity of SN-38 and DX-8951f were evaluated on bone marrow from mice, dogs, and humans using a 14-day colony-forming unit, granulocyte-macrophage (CFU-GM) assay to determine the 50%, 75%, and 90% inhibitory concentration values (IC50, IC75, and IC90, respectively).

RESULTS

Species differences in myelotoxicity were observed for SN-38 and DX-8951f. Using human and murine IC90s for myelotoxicity of these compounds and other camptothecin compounds (topotecan, 9-aminocamptothecin, and camptothecin), in vivo toxicological data, and pharmacokinetic parameters (data referred to in the literature), human MTDs were predicted retrospectively. The mechanism-based prediction model that is proposed uses the in vitro camptothecin assay and in vivo parameters on the basis of free fraction of area under the concentration-curve at the MTD (r2 = 0.887) and suggests that the human MTDs were well predicted for the five camptothecin derivatives by this model rather than by other models.

CONCLUSION

The human MTDs of the camptothecin drugs were successfully predicted using the mechanism-based prediction model. The application of this model for in vitro hematotoxicology could play an important role for the development of new anticancer agents.

Phase I trial of rebeccamycin analog (NSC #655649) in children with refractory solid tumors: a pediatric oncology group study

PURPOSE

To conduct a phase 1 trial of rebeccamycin analog (NSC #655649) in children with solid tumors to establish the dose-limiting toxicity (DLT) and maximum-tolerated dose (MTD); to establish the pharmacokinetic profile in children, and to document any evidence of antitumor activity.

METHODS

A 1-hour infusion of NSC #655649 was administered every 21 days to 17 patients younger than 21 years who had malignant tumors refractory to conventional therapy. Doses ranged from 450 mg/m2 to 760 mg/m2. Pharmacokinetics were done in at least three patients per dose level. The first course was used to determine DLT and MTD.

RESULTS

Sixteen patients on three dose levels were assessable for toxicities. At 760 mg/m2, four patients had dose-limiting neutropenia and thrombocytopenia. Pharmacokinetics were assessable in 13 patients. Plasma concentrations declined triexponentially and concentrations above the range of in vitro antitumor activity were maintained for 3 days. Analysis of urine extracts revealed the presence of an N-de-ethylated metabolite and probable involvement of cytochrome P450 isoenzyme(s) in the metabolism of NSC #655649. Pharmacodynamic studies showed a relationship between the area under the curve and percentage change in absolute neutrophil count in the E(max) model (r2 = 0.56, P = 0.001).

CONCLUSIONS

The recommended phase 2 dose of NSC #655649 administered as a 1-hour infusion every 21 days to children with solid tumors is 585 mg/m2. Both neutropenia and thrombocytopenia were found to be dose-limiting toxicities.

Phase II trial of 9-aminocamptothecin as a 72-h infusion in cutaneous T-cell lymphoma

PURPOSE

To evaluate the role of 9-aminocamptothecin (9-AC), a synthetic camptothecin analog, in advanced cutaneous T-cell lymphoma (CTCL).

METHODS

Eligible patients had stage IIB-IV CTCL. 9-AC was infused over 72 h at a dose of 1,100 microg/m2 per day (approximately 46 microg/m2/h) every 2 weeks, with granulocyte-colony stimulating factor (G-CSF) support.

RESULTS

Twelve patients received a total of 30 cycles of 9-AC. Nine patients had stage IV disease, 5 patients had circulating Sezary cells, and 2 patients had evidence of tranformation to a large cell lymphoma. Most of the patients were heavily pretreated: 10 had received prior chemotherapy (83%), 5 of whom had received 2 or more prior regimens, including a patient who had received high-dose chemotherapy, and 7 had previously received total-skin electron beam therapy. The study was prematurely terminated due to substantial toxicity. Six patients (50%) developed an indwelling central venous catheter-related infection, 5 during a period of neutropenia. Three patients died due to sepsis 4-8 weeks after their last 9-AC treatment. Two of these patients had a previous history of bacterial sepsis. Four patients (33%) developed grade IV thrombocytopenia. Two partial responses were observed (response rate 17%), but the duration of response was brief, 4-8 weeks.

CONCLUSION

9-AC at this schedule and route of administration had activity but resulted in an unacceptable rate of complicated neutropenia and septic deaths in heavily pretreated patients with advanced CTCL who are susceptible to catheter-related infections.

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.

Developmental therapeutics in childhood cancer. A perspective from the Children's Oncology Group and the US Food and Drug Administration

Drug development in pediatric oncology has been reviewed, concentrating on overall development issues and COG studies of cytotoxic compounds. A variety of interesting molecules with more specific targeting are becoming available. The challenges that remain include the availability of such compounds for pediatric trial and their study in a timely fashion, and the subsequent incorporation of the new agents into more up-front regimens, with the ultimate shared goal of curing more children with less toxicity.

Conjugation of camptothecins to poly-(L-glutamic acid)

Conjugation of water-insoluble cancer chemotherapeutic drugs to macromolecular polymers can lead to improved pharmaceutical properties and improved therapeutic ratios due to accumulation of the polymer-drug conjugate in tumor tissue through the enhanced permeability and retention (EPR) to macromolecules associated with tumor vasculature. Pharmaceutical shortcomings of certain active camptothecins including difficulty in formulation and instability of the active lactone form due to interactions with human albumin might be improved by conjugation to polymers. In this report, conjugations of camptothecin (CPT), 10-hydroxy-CPT, and 9-amino-CPT to poly-(L-glutamic acid) (PG) are described; coupling was accomplished either through the 20(S)-hydroxyl or 9 and 10 substituents with and without the use of a glycine linker. Studies using a PG paclitaxel conjugate (PG-TXL), which is currently in Phase I testing, demonstrated that PG enhanced aqueous solubility, prolonged plasma residence time, and greatly increased the distribution of paclitaxel to tumor tissue in a murine model. In this report, we describe the use of similar conjugation technology for CPT derivatives and demonstrate that these difficult to formulate compounds can be rendered water soluble, that their maximum tolerated doses are increased, and that they retain substantial anti-tumor activity in syngeneic and xenogeneic tumor models. Preliminary data suggest that PG with molecular weights between 37 and 50 kDa with CPT loading between 14% and 37% with or without glycine linkers display enhanced efficacy compared with nonconjugated camptothecins administered at their maximum tolerated dose.

The clinical development of 9-aminocamptothecin

9-Aminocamptothecin (9-AC) is a topoisomerase I-targeting agent first synthesized by Wani and Wall in 1986. Because of its potent in vitro effects and promising preclinical activity in colorectal cancer animal models, it was designated a high-priority compound for further drug development by the NCI. In 1993, 9-AC first entered clinical trials as a 72-hour intravenous (i.v.) infusion. Predictable myelosuppression was the major dose-limiting toxicity, and pharmacokinetic studies showed a relatively short plasma half-life and unstable lactone ring. Unfortunately, phase II studies using this schedule showed minimal or no activity in tumors such as colorectal and lung cancer. Modest activity was observed in ovarian cancer and in refractory lymphomas. Efforts to improve systemic drug exposure by utilizing alternative schedules of administration of 9-AC such as prolonged, continuous intravenous infusions have also been tested. However, phase II studies of 120-hour weekly infusions of 9-AC have not shown improved activity against solid tumors such as colorectal cancer. More recently, a daily times 5 days i.v. administration schedule has been tested. Currently, further development of intravenously administered 9-AC for the treatment of colorectal cancer is not promising. Thus, topotecan and irinotecan remain the only two successfully developed topoisomerase I-targeting drugs in the United States. This experience with 9-AC raises important questions regarding how to best select new topoisomerase I-targeting drugs for future clinical development.

Topoisomerase enzymes as drug targets

DNA topoisomerases catalyze changes in the topology of DNA. Recently, other functions have also been reported for these enzymes. For example, topoisomerase I participates in transcription by RNA polymerases I, II, and III, and also has a kinase activity. Topoisomerase I binds directly to at least two helicases, nucleolin and SV40 T antigen, and mechanistic studies show that T antigen alters the function of topoisomerase I. Additional protein and nucleotide interactions for both topoisomerases I and II suggest that each protein is multifunctional. It may be that the multifunctional nature of these enzymes is the basis for the antitumor activity seen with inhibitors of these enzymes. Clinical trials with combinations of CPT-11 and 5-fluorouracil for the treatment of colon cancer, and preclinical studies with CPT-11 and vincristine are particularly encouraging. Protracted schedules of administration of topoisomerase inhibitors will likely have greater antitumor effect than more concentrated, higher dose exposures, but a systematic determination of optimal schedules of administration is needed.