Phase I and pharmacokinetic study of exatecan mesylate (DX-8951f): a novel camptothecin analog

TOP1-DNA Trapping by Exatecan and Combination Therapy with ATR Inhibitor

Exatecan and deruxtecan are antineoplastic camptothecin derivatives in development as tumor-targeted-delivery warheads in various formulations including peptides, liposomes, polyethylene glycol nanoparticles, and antibody-drug conjugates. Here, we report the molecular pharmacology of exatecan compared with the clinically approved topoisomerase I (TOP1) inhibitors and preclinical models for validating biomarkers and the combination of exatecan with ataxia telangiectasia and Rad3-related kinase (ATR) inhibitors. Modeling exatecan binding at the interface of a TOP1 cleavage complex suggests two novel molecular interactions with the flanking DNA base and the TOP1 residue N352, in addition to the three known interactions of camptothecins with the TOP1 residues R364, D533, and N722. Accordingly, exatecan showed much stronger TOP1 trapping, higher DNA damage, and apoptotic cell death than the classical TOP1 inhibitors used clinically. We demonstrate the value of SLFN11 expression and homologous recombination (HR) deficiency (HRD) as predictive biomarkers of response to exatecan. We also show that exatecan kills cancer cells synergistically with the clinical ATR inhibitor ceralasertib (AZD6738). To establish the translational potential of this combination, we tested CBX-12, a clinically developed pH-sensitive peptide-exatecan conjugate that selectively targets cancer cells and is currently in clinical trials. The combination of CBX-12 with ceralasertib significantly suppressed tumor growth in mouse xenografts. Collectively, our results demonstrate the potency of exatecan as a TOP1 inhibitor and its clinical potential in combination with ATR inhibitors, using SLFN11 and HRD as predictive biomarkers.

Cancer therapies utilizing the camptothecins: a review of the in vivo literature

This review summarizes the in vivo assessment-preliminary, preclinical, and clinical-of chemotherapeutics derived from camptothecin or a derivative. Camptothecin is a naturally occurring, pentacyclic quinoline alkaloid that possesses high cytotoxic activity in a variety of cell lines. Major limitations of the drug, including poor solubility and hydrolysis under physiological conditions, prevent full clinical utilization. Camptothecin remains at equilibrium in an active lactone form and inactive hydrolyzed carboxylate form. The active lactone binds to DNA topoisomerase I cleavage complex, believed to be the single site of activity. Binding inhibits DNA religation, resulting in apoptosis. A series of small molecule camptothecin derivatives have been developed that increase solubility, lactone stability and bioavailability to varying levels of success. A number of macromolecular agents have also been described wherein camptothecin(s) are covalently appended or noncovalently associated with the goal of improving solubility and lactone stability, while taking advantage of the tumor physiology to deliver larger doses of drug to the tumor with lower systemic toxicity. With the increasing interest in drug delivery and polymer therapeutics, additional constructs are anticipated. The goal of this review is to summarize the relevant literature for others interested in the field of camptothecin-based therapeutics, specifically in the context of biodistribution, dosing regimens, and pharmacokinetics with the desire of providing a useful source of comparative data. To this end, only constructs where in vivo data is available are reported. The review includes published reports in English through mid-2009.

XMT-1001, a novel polymeric camptothecin pro-drug in clinical development for patients with advanced cancer

An overview of XMT-1001 is provided in the context of other topoisomerase I inhibitors conjugated to polymers or encapsulated in liposomes. XMT-1001 is a novel polymeric pro-drug derivative of camptothecin (CPT) with a molecular weight of 70 kDa, in which CPT is chemically tethered to a hydrophilic, biodegradable polyacetal polymer, poly(1-hydroxymethylethylene hydroxymethylformal), also called PHF or Fleximer(R). XMT-1001 releases CPT via intermediates camptothecin-20-O-(N-succinimidoglycinate) (CPT-SI), and camptothecin-20-O-(N-succinamidoyl-glycinate) (CPT-SA) over an extended time period. XMT-1001 has an improved therapeutic window compared to CPT and irinotecan in human tumor xenograft models, providing a compelling rationale for clinical development. A unique feature of XMT-1001 is its dual phase release mechanism for CPT which may result in lower levels of CPT in the urine and less bladder toxicity, a serious dose limiting toxicity associated with CPT and CPT conjugated to other polymers. XMT-1001 is being evaluated in patients with advanced cancer in an ongoing Phase 1 trial.

Continual reassessment method vs. traditional empirically based design: modifications motivated by Phase I trials in pediatric oncology by the Pediatric Brain Tumor Consortium

In this article we provide additional support for the use of a model-based design in pediatric Phase I trials and present our modifications to the continual reassessment method (CRM), which were largely motivated by specific challenges we encountered in the context of the Pediatric Brain Tumor Consortium trials. We also summarize the results of our extensive simulations studying the operating characteristics of our modified approach and contrasting it to the empirically based traditional method (TM). Compared to the TM, our simulations indicate that the modified version of CRM is more accurate, exposes fewer patients to potentially toxic doses, and tends to require fewer patients. Further, the CRM-based MTD has a consistent definition across trials, which is important, especially in a consortium setting where multiple agents are being tested in studies that are often running simultaneously and accruing from the same patient population.

Gemcitabine in the treatment of metastatic pancreatic cancer

Gemcitabine (2 ,2 -difluorodeoxycytidine) is a deoxycytidine-analog antimetabolite with broad activity against a variety of solid tumors and lymphoid malignancies. It was approved as standard of care in patients with pancreatic cancer one decade ago, based primarily on improvement in clinical benefit response such as pain reduction, improvement in Karnofsky performance status and increase in body weight. This article gives an overview of the pharmacodynamics and pharmacokinetics of gemcitabine, highlights the clinical activity of gemcitabine and summarizes the treatment options in metastatic pancreatic cancer with focus on gemcitabine-based chemotherapy. The emerging role of combinations of gemcitabine with novel targeted agents, including small-molecule inhibitors and other investigational drugs, is also discussed.

Cytotoxic Therapy for Advanced Pancreatic Adenocarcinoma

Pancreatic adenocarcinoma is a highly lethal disease with anecdotal long-term survivorship when the disease is inoperable at presentation. A new era in the treatment of advanced pancreatic cancer commenced a decade ago with the advent of gemcitabine as a standard of care. While many large phase III trials have been conducted in the last 10 years, it has proved a difficult challenge to advance beyond the modest bar set by gemcitabine. For the most part, gemcitabine-combination cytotoxic studies have been negative where the principal end point has been overall survival with only a few noted exceptions; however, for vigorous individuals with bulky or symptomatic disease, a gemcitabine-based fluoropyrimidine or platinum combination is considered a standard of care and these data are reviewed in detail. In this new era of targeted therapy, the addition of erlotinib to gemcitabine has provided an alternate standard option to single-agent gemcitabine or gemcitabine-based cytotoxic combinations, a topic which will be discussed in a separate chapter. Other phase III studies of gemcitabine and bevacizumab and gemcitabine and cetuximab, respectively, which were both preliminarily reported as negative, have provided an indirect endorsement for the relative value of cytotoxic therapy in advanced pancreatic cancer. This underscores the major therapeutic hurdles that we have to surmount in this most challenging of human malignancies.

New cytotoxic agents: a review of the literature

The goal of treatment for patients with advanced cancer is to prolong survival, control symptoms, and reduce disease-related complications. Despite the introduction of many cytotoxic agents during the past decade, only modest improvement in survival has been achieved. In order to urgently improve these situations, new cytotoxic agents as well as molecular-targeted agents are now under investigation. In this article, we reviewed the latest information regarding antitumor activity, toxicity, pharmacokinetics, and clinical application of the new cytotoxic agents.

DE-310, a macromolecular prodrug of the topoisomerase-I-inhibitor exatecan (DX-8951), in patients with operable solid tumors

BACKGROUND

DE-310 is composed of the topoisomerase-I-inhibitor DX-8951 (exatecan) and a biodegradable macromolecular carrier, which are covalently linked by a peptidyl spacer. In pre-clinical studies, high levels and prolonged retention of conjugated DX-8951 (carrier-bound DX-8951) have been observed in tumor tissues following DE-310 administration. This phenomenon is explained as the enhanced permeability and retention (EPR) effect. DX-8951 and G-DX-8951 (glycyl-DX-8951) exerting anti-tumor activity in vivo are released from DE-310 by enzymatic cleavage of the spacer.

METHODS

To quantify the concentration of conjugated DX-8951, DX-8951 and G-DX-8951 in human tissues, six patients with different solid tumor types received 6.0 mg/m(2) of DE-310 (as equivalent of DX-8951) as a single three-hour infusion administered 7 days (+/-2 days) prior to scheduled tumor resection. Drug concentrations were then determined in the resected tissues. To evaluate the plasma PK of DE-310, plasma samples were taken up to 42 days post dosing.

RESULTS

There were no severe side effects of the DE-310 infusion. Concentrations of conjugated DX-8951, DX-8951 and G-DX-8951 were in general similar in tumor and relevant normal tissue samples and preferential accumulation of DE-310, DX-8951 and G-DX-8951 in human tumor tissues was not observed.

CONCLUSIONS

These data indicate that there is distribution of DE-310 into tissue and that DX-8951 and G-DX-8951 are released slowly over an extended period from DE-310 providing prolonged exposure similar to a continuous infusion. However, the similarity in the concentrations in tumor and relevant normal tissues does not support the EPR concept in the studied human cancers.

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.

Emerging treatments for ovarian cancer

The survival at 5 years, of patients with ovarian cancer, has steadily improved since 1960, when surgery and alkylating agents were the only initial modalities employed to cope with the usual late presentation of the disease. In the 1980s, cisplatin and then carboplatin became established as the most active drugs, alone or in combination with other drugs. In the last decade, the antimicrotubulin drug paclitaxel, and the topoisomerase I inhibitor topotecan were noted to be active after failure of platinum drugs. These drugs, as well as others with known activity in the second-line setting, such as the pegylated liposomal doxorubicin, gemcitabine and oral etoposide, all play a role in the treatment of these patients and likely prolong survival without eradicating the disease. The plight of these patients has stimulated new areas of drug development. Here, the evolution of the current therapeutic strategy, the scientific rationale for cytotoxic and non-cytotoxic agents and their status at present are reviewed. 'Targeted' drug trials, in contrast to trials studying cytotoxic drug analogues, currently represent only a minor portion of clinical trials in ovarian cancer.

Camptothecins in clinical development

Following the realisation that DNA topoisomerase I is a useful therapeutic target to be exploited for the design of potential inhibitors, topoisomerase I inhibitors now represent an established class of effective agents. In spite of intense efforts in the field, only camptothecins have a clinical relevance. Several options in chemical manipulation of natural camptothecin have been explored to overcome the major drawbacks of the drug, which include water insolubility, lactone instability, reversibility of the drug-target interaction and drug resistance. Several analogues are currently in clinical development, including water soluble camptothecins, lipophilic camptothecins and polymer-bound camptothecins. The therapeutic advantages of novel camptothecins over the two analogues (topotecan and irinotecan) approved for clinical use remain to be defined. This article is an overview of the relevant features of the analogues that are undergoing clinical development.

Phase I and Pharmacokinetic Study of DE-310 in Patients with Advanced Solid Tumors

Purpose: To assess the maximum-tolerated dose, toxicity, and pharmacokinetics of DE-310, a macromolecular prodrug of the topoisomerase I inhibitor exatecan (DX-8951f). in patients with advanced solid tumors.

Experimental Design: Patients received DE-310 as a 3-hour infusion once every 2 weeks (dose, 1.0-2.0 mg/m2) or once every 6 weeks (dose, 6.0-9.0 mg/m2). Because pharmacokinetics revealed a drug terminal half-life exceeding the 2 weeks administration interval, the protocol was amended to a 6-week interval between administrations also based on available information from a parallel trial using an every 4 weeks schedule. Conjugated DX-8951 (the carrier-linked molecule), and the metabolites DX-8951 and glycyl-DX-8951 were assayed in various matrices up to 35 days post first and second dose.

Results: Twenty-seven patients were enrolled into the study and received a total of 86 administrations. Neutropenia and grade 3 thrombocytopenia, and grade 3 hepatotoxicity with veno-occlusive disease, were dose-limiting toxicities. Other hematologic and nonhematologic toxicities were mild to moderate and reversible. The apparent half-life of conjugated DX-8951, glycyl-DX-8951, and DX-8951 was 13 days. The area under the curve ratio for conjugated DX-8951 to DX-8951 was 600. No drug concentration was detectable in erythrocytes, skin, and saliva, although low levels of glycyl-DX-8951 and DX-8951 were detectable in tumor biopsies. One patient with metastatic adenocarcinoma of unknown primary achieved a histologically proven complete remission. One confirmed partial remission was observed in a patient with metastatic pancreatic cancer and disease stabilization was noted in 14 additional patients.

Conclusions: The recommended phase II dose of DE-310 is 7.5 mg/m2 given once every 6 weeks. The active moiety DX-8951 is released slowly from DE-310 and over an extended period, achieving the desired prolonged exposure to this topoisomerase I inhibitor.

A phase IIA study of the topoisomerase I inhibitor, exatecan mesylate (DX-8951f), administered at two different dose schedules in patients with platinum- and taxane-resistant/refractory ovarian cancer

OBJECTIVES

There is an urgent need for new agents with activity in platinum- and taxane-resistant epithelial ovarian cancer. Exatecan mesylate is a novel topoisomerase I inhibitor with potent activity against ovarian cancer in vitro. A multicentre phase IIA study was conducted in patients with platinum- and taxane-resistant epithelial ovarian cancer.

PATIENTS AND METHODS

Fifty-seven patients with bidimensionally measurable ovarian cancer, previously exposed to platinum and taxanes, whose disease had relapsed within 6 months of platinum-containing chemotherapy were randomised to one of two intravenous schedules of exatecan mesylate; 0.3 mg/m(2) daily for 5 days every 3 weeks (Arm A) or 2.1 mg/m(2) weekly for 3 weeks out of 4 (Arm B).

RESULTS

There were no responses in the weekly arm and a radiological response rate of 5.3% (95% CI 0.3-21.8%) in the daily arm. Principal toxicities were myelosuppression and emesis. Grade 3/4 neutropenia occurred in 29% of patients in Arm A and 6% patients in Arm B. Seventy-one percent of patients in Arm A required red cell transfusions while on treatment.

CONCLUSIONS

Exatecan is well tolerated in this poor prognosis group of patients but only has modest single agent activity when administered in a daily regimen.

Antitumor characteristics of methoxypolyethylene glycol–poly(dl-lactic acid) nanoparticles containing camptothecin

The novel nanoparticles (CPT-NP) were prepared by the solvent evaporation method using methoxypolyethylene glycol-poly(DL-lactic acid) block copolymer as a matrix and camptothecin (CPT) as an antitumor agent, and the antitumor characteristics were examined in vitro and in vivo. The mean diameter of CPT-NP was approximately 250 nm. The drug release from CPT-NP in phosphate-buffered saline, pH 7.4, depended on the particle concentration; in the diluted condition, the initial rapid release was greater and subsequent gradual release was faster. After i.v. administration (0.5 mg CPT eq./kg) in rats, CPT-NP showed a longer plasma retention than CPT solution. In both single (2.5 mg CPT eq./kg) and double (2.5 mg CPT eq./kg x 2) administration to mice bearing sarcoma 180 solid tumor, CPT-NP were much more effective than CPT solution; especially, the tumor disappeared completely in three of the four mice in twice administration of CPT-NP, when the body weight did not decrease markedly. After i.v. administration to the tumor-bearing mice, CPT-NP showed better plasma retention, and high and long tumor localization. CPT-NP are suggested to greatly improve the efficacy of CPT due to their pharmacokinetic features.

A Phase II study of intravenous exatecan mesylate (DX-8951f) administered daily for 5 days every 3 weeks to patients with metastatic breast carcinoma

BACKGROUND

The objective of the current study was to determine the antitumor activity, safety, and pharmacokinetic (PK) profile of exatecan mesylate in patients with anthracycline-resistant and taxane-resistant, metastatic breast carcinoma.

METHODS

All patients had clinical evidence of metastatic breast carcinoma; disease resistance or progression after chemotherapy that included anthracyclines and taxanes; no prior chemotherapy with camptothecin derivatives; and bidimensionally measurable disease. The starting dose of exatecan mesylate was either 0.5 mg/m(2) per day or 0.3 mg/m(2) per day, depending on prior chemotherapy exposure. PK blood samples were collected from each patient during the first course of therapy.

RESULTS

Thirty-nine patients received a total of 172 courses of therapy (median, 4 courses; range, 1-16 courses). Three patients (7.7%) had a partial response, and 20 patients (51.3%) had either a minor response or stable disease. Approximately 20% of patients had stable disease for 6 months or longer. The median time to disease progression was 3 months, and the median survival was 14 months. The most frequent severe adverse event was neutropenia. The most frequent severe (Grade 3-4) nonhematologic toxicities were fatigue, nausea, headache, myalgia, constipation, emesis, and paresthesias in 28%, 10%, 10%, 8%, 8%, 5%, and 5% of patients, respectively. Exatecan mesylate displayed linear PK characteristics at the doses administered. The average plasma clearance, total volume of distribution, and terminal elimination half-life were approximately 1.4 L per hour per m(2), 12 L/m(2), and 8 hours, respectively.

CONCLUSIONS

Exatecan mesylate had moderate activity in patients with anthracycline-refractory and taxane-refractory, metastatic breast carcinoma. The toxicity profile of exatecan mesylate was acceptable, and it appeared to have linear PK characteristics on the basis of multiple dose administration.

Phase II study of exatecan mesylate (DX-8951f) as first line therapy for advanced non-small cell lung cancer

BACKGROUND

Exatecan mesylate (DX-8951f) is a water soluble analogue of camptothecin that inhibits topoisomerase I. This multi-centre phase II study evaluated the activity of single agent exatecan in previously untreated patients with advanced non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with histologically or cytologically proven stage IIIb or IV NSCLC were treated with exatecan 0.5 mg/m(2) per day by 30 min intra-venous (i.v.) infusion for 5 days every 3 weeks to a maximum of six cycles. Measurable disease was documented prior to study entry and patients were re-staged every two cycles. Pharmacokinetic (PK) sampling was performed during cycle one.

RESULTS

39 patients (32 patients ECOG performance status 0 or 1; 29 male and ten female; mean age 63 years) were entered into the study. Thirty-three completed at least two cycles of exatecan and 11 completed six cycles. Two patients (5.1%, 95% C.I. 0.3-21.3%) had a partial response, 7 (18.0%) minor response and 8 (20.5%) stable disease. Median time to tumour progression (TTP) was 88 days and median overall survival 262 days. The main toxicity was reversible neutropenia. PK analysis of exatecan demonstrated a mean clearance of 2.28 l/h per m(2), volume of distribution 18.2 l/m(2) and mean elimination half-life of 7.9 h.

CONCLUSIONS

Exatecan mesylate has limited activity in advanced NSCLC and is not recommended for further evaluation as a single agent in this tumour type. PK data from this trial supports results established in phase I studies.

Phase I and pharmacokinetic study of the topoisomerase I inhibitor, exatecan mesylate (DX-8951f), using a weekly 30-minute intravenous infusion, in patients with advanced solid malignancies

BACKGROUND

The topoisomerase I inhibitor exatecan mesylate (DX-8951f ) is a water-soluble hexacyclic analogue of camptothecin that does not require enzymatic activation. This study determined the toxicity, maximum tolerated dose (MTD), pharmacokinetics and pharmacodynamics of a weekly intravenous (i.v.) schedule of DX-8951f.

PATIENTS AND METHODS

Thirty-five patients with advanced solid malignancies, stratified as minimally (MP) or heavily (HP) pre-treated, received escalating doses of DX-8951f as 30-min i.v. infusions for three out of every 4 weeks. Pharmacokinetics were described after the first infusion of DX-8951f.

RESULTS

Infusions (244) of DX-8951f were administered with a median of two cycles (range 1-10). The main toxicity observed was haematological. There was no significant gastrointestinal toxicity. Two patients (6%) had confirmed partial responses. Twelve patients (39%) had stable disease. DX-8951f had a terminal elimination half-life of approximately 8 h and a clearance of 2 l/h/m(2). The area under the plasma concentration versus time curve (AUC( infinity )) and the maximum plasma concentration (C(max)) increased linearly with the dose. A linear relationship was present for the percentage decrease in neutrophil counts or platelet counts and AUC( infinity ) as well as C(max).

CONCLUSIONS

The dose-limiting toxicity of DX-8951f is neutropenia for MP patients and neutropenia and thrombocytopenia for HP patients. Evidence for clinical activity was seen, suggesting phase II study of the drug is indicated. Using this schedule the recommended dose is 2.75 mg/m(2)/week for MP patients and 2.10 mg/m(2)/week for HP patients.

Pharmacokinetic-pharmacodynamic guided trial design in oncology

The application of pharmacokinetic (PK) and pharmacodynamic (PD) modeling in drug development has emerged during the past decades and it is has been suggested that the investigation of PK-PD relationships during drug development may facilitate and optimize the design of subsequent clinical development. Especially in oncology, well designed PK-PD modeling could be extremely useful as anticancer agents usually have a very narrow therapeutic index. This paper describes the application of the current insights in the use of PK-PD modeling to the design of clinical trials in oncology. The application of PK-PD modeling in each separate stage of (pre)clinical drug development of anticancer agents is discussed. The implementation of this approach is illustrated with the clinical development of docetaxel.

Homocamptothecins: potent topoisomerase I inhibitors and promising anticancer drugs

Homocamptothecins (hCPTs) represent a new generation of antitumor agents targeting DNA topoisomerase I. The expanded seven-membered lactone E-ring that characterizes hCPTs enhances the plasma stability of the drug and reinforces the inhibition of topoisomerase I compared with conventional six-membered CPTs. hCPTs are more efficient than the CPTs at promoting cleavage at T/G sites and induce additional cleavage at C/G sites. Compound BN80765 and its difluoro analogue diflomotecan (DN80915) are potent cytotoxic agents and efficiently induce apoptosis in tumor cells. They display strong antiproliferative activities against specific tumor types. Diflomotecan is remarkably efficient at inhibiting the growth of human colon cancer cells in vivo and, administered orally, it also shows superior activities against human prostate cancers compared with the benchmark products topotecan (TPT) and irinotecan (IRT). Diflomotecan has entered phase I clinical testing and antitumor activity has been observed in patients. This 9,10-difluoro-hCPTs derivative is one of the most promising new members of the 'tecan' family. This review summarizes the recent discoveries in the topoisomerase I field and presents the different camptothecin (CPT) analogues currently evaluated as anticancer agents. The specific properties of hCPTs are highlighted.