Suramin inhibits DNA damage in human prostate cancer cells treated with topoisomerase inhibitors in vitro

Suramin, a highly sulfonated drug, has been reported to be effective against several human malignancies in vitro and in vivo, and currently is undergoing clinical trials against prostate tumors. The biochemical and molecular mechanisms for suramin's antiproliferative activity are not clear. In order to define the biochemical basis for its antitumor activity and to enhance suramin's chemotherapeutic potential while decreasing its toxicity, we have examined interactions of suramin with topoisomerase I and 11 and several clinically active anticancer drugs against the human prostate (PC3 and LNCaP) cancer cell line. While etoposide, m-AMSA, camptothecin, and SN-38 (the active metabolite of CPT-11) were active in killing prostate cells as single agents, combinations of suramin and these agents were antagonistic against these cells. We found that suramin inhibited activities of purified topoisomerase I and II in vitro as measured by relaxation and cleavage assays. Further studies indicated that suramin also inhibited the drug-induced DNA damage in vitro and in isolated nuclei. These findings indicate that combinations of suramin with topoisomerase inhibitors, for example, VP-16, m-AMSA, or CPT, may not be beneficial to patients receiving suramin-containing chemotherapy. © 1993 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America

.     

Sequential doxorubicin and topotecan in relapsed/refractory aggressive non-Hodgkin's lymphoma: results of CALGB 59906

Topoisomerase enzymes are critical components of genomic replication and function to minimize torsional stress on DNA. Sequential administration of a topoisomerase II inhibitor followed by a topoisomerase I inhibitor is potentially synergistic due to increased target enzyme levels. Patients with relapsed or refractory aggressive non-Hodgkin's lymphomas (NHL) were eligible for this phase II study of doxorubicin 25 mg/m² intravenous (IV) on day 1 and topotecan 1.75 mg/m²/day IV on days 3 - 5, every 21 days. The trial objectives included the overall response rate, progression-free survival, and toxicity. Twenty-six patients were enrolled and 25 patients are assessable for toxicity and response. The median age was 58 (range 23 - 74) years. The patients had received a median of two (range one to five) prior regimens, including five patients with a prior stem cell transplant. Five patients (20%, 95% confidence interval 0.07, 0.42) responded with two (8%) complete remissions and three (12%) partial remissions; an additional four (16%) patients had stable disease. Both patients achieving a complete remission had Burkitt's lymphoma. There were no treatment-related deaths. In conclusion, the combination of doxorubicin and topotecan is well tolerated and has modest activity in relapsed/refractory NHL, with occasional patients having a prolonged remission. The activity in Burkitt's lymphoma should be investigated further.     

Safety,pharmacokinetics, and activity of EZN‐2208, a novel conjugate of polyethylene glycol and SN38, in patients with advanced malignancies

BACKGROUND:

EZN‐2208 is a water‐soluble, polyethylene glycol drug conjugate of SN38, which is the active moiety of irinotecan. In this study, the authors evaluated the tolerability, pharmacokinetics (PK), and activity of EZN‐2208 in adult patients with advanced solid tumors.

METHODS:

Patients in sequential cohorts (3 + 3 design) received intravenous EZN‐2208 at doses between 1.25 mg/m² and 25 mg/m² once every 21 days.

RESULTS:

Thirty‐nine patients received EZN‐2208. The median number of prior therapies was 2 (range, 0‐10 prior therapies). Seventeen patients received prior irinotecan. Two maximum tolerated doses (MTDs) were defined: EZN‐2208 with (16.5 mg/m²) and without (10 mg/m²) granulocyte‐colony–stimulating factor (G‐CSF). The dose‐limiting toxicity (DLT) was febrile neutropenia. Two of 19 patients who were heterozygous for a polymorphism in the uridine diphosphate glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) gene (UGT1A1*28) developed DLTs (dose, 25 mg/m² with G‐CSF), and 2 patients who were homozygous for UGT1A1*28 were treated without DLTs (dose, 5 mg/m²). PK analysis indicated a mean terminal half‐life of 19.4 ± 3.4 hours. Sixteen patients (41%) achieved stable disease, including 6 of 39 patients (15%) who had stable disease that lasted ≥4 months. One patient with cholangiocarcinoma (no prior irinotecan) achieved a short‐lived 32% tumor regression. Among 6 patients who had stable disease that lasted for ≥4 months, 3 had received prior irinotecan, and 1 had KRAS‐positive colorectal cancer.

CONCLUSIONS:

EZN‐2208 was well tolerated and produced stable disease that lasted for ≥4 months/unconfirmed partial responses in 7 of 39 heavily pretreated patients (18%) with advanced solid tumors, including those who had failed prior irinotecan therapy. Cancer 2012. © 2012 American Cancer Society.     

Perspectives on Biologically Active Camptothecin Derivatives

Camptothecins (CPTs) are cytotoxic natural alkaloids that specifically target DNA topoisomerase I. Research on CPTs has undergone a significant evolution from the initial discovery of CPT in the late 1960s through the study of synthetic small‐molecule derivatives to investigation of macromolecular constructs and formulations. Over the past years, intensive medicinal chemistry efforts have generated numerous CPT derivatives. Three derivatives, topotecan, irinotecan, and belotecan, are currently prescribed as anticancer drugs, and several related compounds are now in clinical trials. Interest in other biological effects, besides anticancer activity, of CPTs is also growing exponentially, as indicated by the large number of publications on the subject during the last decades. Therefore, the main focus of the present review is to provide an ample but condensed overview on various biological activities of CPT derivatives, in addition to continued up‐to‐date coverage of anticancer effects.     

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/m² of DE-310 (as equvalent 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.     

Identification of gene polymorphisms of human DNA topoisomerase I in the National Cancer Institute panel of human tumour cell lines

Topoisomerase 1 (Top1), a nuclear enzyme involved in DNA relaxation, is the target of several anticancer drugs. TOP1 mutations occur in camptothecin-resistant tumour cell lines. We explored, in the NCI panel of 60 human tumour cell lines, whether polymorphic variations in the TOP1 gene could explain differences in drug sensitivity. The 21 exons of the gene were fully studied as well as five intronic domains that had previously been shown to harbour single nucleotide polymorphisms (SNPs) or mutations. PCR products covering the whole exonic sequences or the relevant intronic domains were subjected to denaturing high-performance liquid chromatography. Nucleotide variations were then determined by sequencing. Discrimination between intronic common and variant homozygous samples was performed using a restriction fragment length polymorphism technique. Only one exonic mutation was detected, at the heterozygous state; it occurs in exon 19 of a colon cancer cell line (HCT-15) and consists of a G>A transition at position 75, resulting in a Met675Ile change. The intronic sequences studied harboured the SNPs expected with allelic frequencies between 20 and 40%. Three major haplotypes, generating 92% of the 10 genotypes encountered, were defined as containing none of the intronic SNPs, or three of them, or all of them. No significant relationship was evidenced between Top1 expression and the TOP1 polymorphisms studied. However, when comparing the cytotoxicity of 138 drugs as a function of the genotypes, several drug groups, namely Top1 inhibitors, antifolates and taxanes, had significantly different IC(50)s as a function of the distribution of the intronic SNPs of the TOP1 gene.     

Effect of Cyclodextrin Complexation on the Liposome Permeability of a Model Hydrophobic Weak Acid

Purpose  This study examines the effect of a chemically modified β-cyclodextrin on the liposome bilayer permeability of a liposomally entrapped model hydrophobic weak acid, DB-67 (7-t-butyldimethylsilyl-10-hydroxycamptothecin). Materials and Methods  Permeability studies were conducted in liposomes prepared by hydration–extrusion in the presence or absence of entrapped hydroxypropyl-β-cyclodextrin (HPβCD). A gradient HPLC method with evaporative light scattering detection was developed for analysis of HPβCD. DB-67 was analyzed by HPLC with fluorescence detection. Results  HPβCD entrapped in the aqueous compartment of liposomes was found to be membrane impermeable. Gel phase liposomes were stable in the presence of HPβCD. HPβCD complexation did not significantly alter the apparent permeability of DB67 lactone, due to its high membrane binding. However, lactone ring-opening and ionization significantly decreased the apparent permeability and improved the liposomal retention of DB-67, an effect that was amplified in the presence of 50 mM HPβCD. Conclusions  In liposomes, cyclodextrin complexation competes with liposomal membrane binding which may temper the potential benefit of complexation in prolonging hydrophobic drug retention. Cyclodextrin complexation combined with drug ionization may nevertheless significantly enhance the retention of ionizable hydrophobic drugs in liposomes as complexation may compete more favorably with membrane binding when the drug is ionized.     

Targeting topoisomerase I: molecular mechanisms and cellular determinants of response to topoisomerase I inhibitors

Background: Topoisomerase I is required for DNA relaxation during critical cellular functions. The identification of camptothecins as specific enzyme inhibitors and their clinical efficacy have stimulated extensive efforts to exploit topoisomerase I as a tumor target and explain the putative mechanisms of antitumor-specific action. Objective: This review provides an overview of the recent achievements in the development of topoisomerase I inhibitors and in the explanation of the biological pathways involved in tumor response. Results/conclusion: In spite of the difficulty to identify novel topoisomerase I inhibitors with improved pharmacological properties, a growing body of evidence supports the possibility of optimizing the therapeutic profile of available agents. The explanation of defense mechanisms and the molecular determinants of tumor cell response is expected to provide a basis for the design of combination approaches for optimization of topoisomerase I inhibitors-based therapy.