The dual topoisomerase inhibitor, BN 80927, is highly potent against cell proliferation and tumor growth

Population pharmacokinetic/pharmacodynamic modeling of drug-induced adverse effects of a novel homocamptothecin analog, elomotecan (BN80927), in a Phase I dose finding study in patients with advanced solid tumors

PURPOSE

To characterize the pharmacokinetic profile of elomotecan, a novel homocamptothecin analog, evaluate the dose-limiting toxicities, and establish the relationship between exposure and toxicity in the first Phase I study in patients with advanced malignant solid tumors. Preliminary antitumor efficacy results are also provided.

DESIGN

Elomotecan was administered as a 30-min intravenous infusion at doses ranging from 1.5 to 75 mg once every 3 weeks to 56 patients with advanced solid tumors. Plasma concentration data and adverse effects were modeled using the population approach.

RESULTS

Elomotecan showed linear pharmacokinetics, and clearance was decreased with age. The model predicts a 47 and 61 % reduction in CL for patients aged 60 and 80 years, respectively, when compared with younger patients (30 years). Neutropenia represented the dose-limiting toxicity. The maximum tolerated dose and the recommended dose (RD) were 75 and 60 mg, respectively. Elomotecan elicited a 20, 5, 2, and 2 % severe (grade 4) neutropenia, asthenia, nausea, and vomiting at the RD, respectively. Of the subjects in the RD cohort, 41.7 % had a stable disease mean duration of 123.6 ± 43.4 days.

CONCLUSIONS

The pharmacokinetic parameters and the toxicity pattern of elomotecan suggest that this novel homocamptothecin analog should be further explored in the clinical setting using a dose of 60 mg administered as a 30-min intravenous infusion, once every 3 weeks.

Chiral capillary electrophoretic determination of the enantiomeric purity of homocamptothecin derivatives, promising antitumor topoisomerase I inhibitors, using highly sulfated CDs and fluorescence detection

EKC methods for the enantiomeric resolution of homocamptothecin derivatives, potent anticancer agents targeting DNA topoisomerase I selected for clinical trials, were developed using highly sulfated beta-CD as chiral selectors at acidic pH. Optimal electrophoretic conditions, with migration times under 15 min, were as follows: for the neutral homocamptothecin analog 1, a BGE of 75 mM phosphate buffer pH 2.5 (H(3)PO(4) + triethanolamine)/ACN - 95/5 v/v, with 7.5% w/v highly S-beta-CD, an applied field of 0.2 kV/cm and a fused capillary temperature control of 30 +/- 0.1 degrees C (typical current approximately 175 microA); for the cationic homocamptothecin 2, a BGE of 25 mM phosphate buffer pH 2.5 (H(3)PO(4) + TEA)/ACN - 90/10 v/v, with 2.5% w/v highly S-beta-CD, an applied field of 0.15 kV/cm and a fused capillary temperature control of 25 +/- 0.1 degrees C (typical current approximately 45 muA), and both are validated. The best results in terms of LOQ were obtained by EC with fluorescence detection: 10 ng/mL and 20 ng/mL for 1 and 2, respectively (LOQ divided by 150 for 1 and 5 for 2 with respect to UV), thus making this method particularly convenient for enantiomeric purity determination of galenic forms. UV detection appears to be an alternative to fluorescence for the analysis of the main component either for the control of galenic forms or for therapeutic adaptation. Moreover, this method exhibits better performances than HPLC.

Phase I dose-finding study and a pharmacokinetic/pharmacodynamic analysis of the neutropenic response of intravenous diflomotecan in patients with advanced malignant tumours

PURPOSE

To determine the maximum tolerated dose (MTD) of intravenous (iv) diflomotecan administered once every 3 weeks, and to characterize the relationship between pharmacokinetics and neutropenic effect, using a semi-mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model.

EXPERIMENTAL DESIGN

Twenty-four patients received a total of 75 cycles of iv diflomotecan that was administered as 20-min infusion, once every 3 weeks at escalating doses of 2, 4, 5, and 6 mg/m2. Haematological and non-haematological toxicities were evaluated. Plasma concentrations of diflomotecan were measured after the first drug administration.

RESULTS

Dose limiting toxicity (DLT) following the first cycle occurred in 12 patients and a total of 16 patients experienced DLT at some point in the trial. During the first cycle of treatment the number of patients in the 5 and 6 mg/m2 dose groups that experienced DLT was 3 of 4, and 3 of 3, respectively. Therefore, the dose of 5 mg/m2 was considered the MTD and the dose of 4 mg/m2 the recommended dose (RD). During the first cycle, 12 patients experienced DLT, six had either infection of haematological toxicity and eight complained of fatigue. The best response was a partial response in one patient treated at the 6 mg/m2 dose level. Disease stabilization was observed in seven patients (four patients treated at 4 mg/m2 and one patient at each dose level of 2, 5, and 6 mg/m2). The remaining patients had all progressive disease. The median time to progression for all patients was 5.9 weeks. Pharmacokinetics of diflomotecan was described with a three-compartmental model. Mean population parameter estimates of the apparent volume of distribution of the central compartment (V c) increased linearly with body surface area (BSA) as: V c (L) = 41.5 x (BSA/1.85), and the mean population estimate of the apparent volume of distribution of the shallow compartment was lower in females (29.5 vs 48.8 L). Computer simulations showed the lack of clinical significance of these covariates. The time course of the neutropenic response was adequately described by a semi-mechanistic model that includes cellular processes and drug effects.

CONCLUSIONS

The MTD and RD after a 20-min iv infusion of diflomotecan every 3 weeks are 4 and 5 mg/m2, respectively. Diflomotecan showed linear pharmacokinetic behaviour and the selected PK/PD model described adequately the time course of neutropenia. The mean model predicted values of nadir and time to nadir after a 20-min iv infusion of 4 mg/m2 of diflomotecan was 0.86 x 10(9) /L neutrophil cell counts and 11 days, respectively.

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

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

BN80927

BN80927 belongs to a novel family of camptothecin analogs, the homocamptothecins, developed on the concept of topoisomerase I (Topo I) inhibition and characterized by a stable seven-membered beta-hydroxylactone ring. Preclinical data reported here show that BN80927 retains Topo I poisoning activity in cell-free assay (DNA relaxation) as well as in living cells, in which in vivo complexes of topoisomerase experiments and quantification of DNA-protein-complexes stabilization, have confirmed the higher potency of BN80927 as compared with the Topo I inhibitor SN38. In addition, BN80927 inhibits Topo II-mediated DNA relaxation in vitro but without cleavable-complex stabilization, thus indicating catalytic inhibition. Moreover, a Topo I-altered cell line (KBSTP2), resistant to SN38, remains sensitive to BN80927, suggesting that a part of the antiproliferative effects of BN80927 are mediated by a Topo I-independent pathway. This hypothesis is also supported by in vitro data showing an antiproliferative activity of BN80927 on a model of resistance related to the noncycling state of cells (G(0)-G(1) synchronized). In cell growth assays, BN80927 is a very potent antiproliferative agent as shown by IC(50) values consistently lower than those of SN38 in tumor cell lines as well as in their related drug-resistant lines. BN80927 shows high efficiency in vivo in tumor xenograft studies using human androgen-independent prostate tumors PC3 and DU145. Altogether, these data strongly support the clinical development of BN80927.

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.

Camptothecins

Camptothecin analogues and derivatives appear to exert their antitumour activity by binding to topoisomerase I and have shown significant activity against a broad range of tumours. In general, camptothecins are not substrates for either the multidrug-resistance P-glycoprotein or the multidrug-resistance-associated protein (MRP). Because of manageable toxicity and encouraging activity against solid tumours, camptothecins offer promise in the clinical management of human tumours. This review illustrates the proposed mechanism(s) of action of camptothecins and presents a concise overview of current camptothecin therapy, including irinotecan and topotecan, and novel analogues undergoing clinical trails, such as exatecan (DX-8951f), IDEC-132 (9-aminocamptothecin), rubitecan (9-nitrocamptothecin), lurtotecan (GI-147211C), and the recently developed homocamptothecins diflomotecan (BN-80915) and BN-80927.