Novel 7-oxyiminomethyl derivatives of camptothecin with potent in vitro and in vivo antitumor activity

The antimicrobial potential of adarotene derivatives against Staphylococcus aureus strains

Multidrug-resistant (MDR) pathogens are severely impacting our ability to successfully treat common infections. Here we report the synthesis of a panel of adarotene-related retinoids showing potent antimicrobial activity on Staphylococcus aureus strains (including multidrug-resistant ones). Fluorescence and molecular dynamic studies confirmed that the adarotene analogues were able to induce conformational changes and disfunctions to the cell membrane, perturbing the permeability of the phospholipid bilayer. Since the major obstacle for developing retinoids is their potential cytotoxicity, a selected candidate was further investigated to evaluate its activity on a panel of human cell lines. The compound was found to be well tolerated, with IC50 5-15-fold higher than the MIC on S. aureus strains. Furthermore, the adarotene analogue had a good pharmacokinetic profile, reaching a plasma concentration of about 6 μM after 0.5 h after administration (150 mg/kg), at least twice the MIC observed against various bacterial strains. Moreover, it was demonstrated that the compound potentiated the growth-inhibitory effect of the poorly bioavailable rifaximin, when used in combination. Overall, the collected data pave the way for the development of synthetic retinoids as potential therapeutics for hard-to-treat infectious diseases caused by antibiotic-resistant Gram-positive pathogens.

A camptothecin-based, albumin-binding prodrug enhances efficacy and safety in vivo

The albumin-based drug delivery system is an effective drug delivery strategy for traditional chemotherapeutic drugs that can improve their antitumour efficacies and reduce systemic toxicities. The camptothecin derivative CPTS0001 has excellent antitumour activity in vitro, but it shows toxicity and side effects in vivo. In this study, we report the synthesis and biological evaluation of the β-glucuronidase-reactive albumin-binding prodrug Mal-glu-CPTS0001 based on quaternary ammonium. After intravenous administration, the compound covalently binds to plasma albumin through Michael addition, enabling it to accumulate in tumours, where tumour-associated β-glucuronidase triggers the selective release of CPTS0001. This prodrug significantly reduced the toxicity of the parent drug, and the maximum tolerated dose was increased by 2.5 times. At the same time, this prodrug enhanced the selectivity in vivo and improved the preferential accumulation of prodrug in tumours. Notably, this prodrug exhibited excellent in vivo antitumour effects in a murine breast cancer xenograft model without visible pathological toxicity.

Putative SARS-CoV-2 Mpro Inhibitors from an In-House Library of Natural and Nature-Inspired Products: A Virtual Screening and Molecular Docking Study

A novel coronavirus (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2) has been the cause of a recent global pandemic. The highly contagious nature of this life-threatening virus makes it imperative to find therapies to counteract its diffusion. The main protease (Mpro) of SARS-CoV-2 is a promising drug target due to its indispensable role in viral replication inside the host. Using a combined two-steps approach of virtual screening and molecular docking techniques, we have screened an in-house collection of small molecules, mainly composed of natural and nature-inspired compounds. The molecules were selected with high structural diversity to cover a wide range of chemical space into the enzyme pockets. Virtual screening experiments were performed using the blind docking mode of the AutoDock Vina software. Virtual screening allowed the selection of structurally heterogeneous compounds capable of interacting effectively with the enzymatic site of SARS-CoV-2 Mpro. The compounds showing the best interaction with the protein were re-scored by molecular docking as implemented in AutoDock, while the stability of the complexes was tested by molecular dynamics. The most promising candidates revealed a good ability to fit into the protein binding pocket and to reach the catalytic dyad. There is a high probability that at least one of the selected scaffolds could be promising for further research.

Hybrid topoisomerase I and HDAC inhibitors as dual action anticancer agents

Recent studies have shown that HDAC inhibitors act synergistically with camptothecin derivatives in combination therapies. To exploit this synergy, new hybrid molecules targeting simultaneously topoisomerase I and HDAC were designed. In particular, a selected multivalent agent containing a camptothecin and a SAHA-like template showed a broad spectrum of antiproliferative activity, with IC₅₀ values in the nanomolar range. Preliminary in vivo results indicated a strong antitumor activity on human mesothelioma primary cell line MM473 orthotopically xenografted in CD-1 nude mice and very high tolerability.

Growth inhibition of human ovarian carcinoma by a novel AvidinOX-anchored biotinylated camptothecin derivative

Oxidized form of avidin, named AvidinOX, provides stable fixation of biotinylated molecules in tissues thus representing a breakthrough in topical treatment of cancer. AvidinOX proved to be a stable receptor for radiolabeled biotin, biotinylated antibodies and cells. In order to expand applicability of the AvidinOX-based delivery platform, in the present study we investigated the possibility to hold biotinylated chemotherapeutics in AvidinOX-treated sites. A novel biotinylated gimatecan-derived camptothecin, coded ST8161AA1, was injected at suboptimal doses into human tumors xenografted in mice alone or pre-complexed to AvidinOX. Significantly higher growth inhibition was observed when the drug was anchored to AvidinOX suggesting the potential utility of this delivery modality for the local treatment of inoperable tumors.

Design, semisynthesis and potent cytotoxic activity of novel 10-fluorocamptothecin derivatives

Fluorination is a well-known strategy for improving the bioavailability of bioactive molecules in the lead optimization phase of drug discovery projects. In an attempt to improve the antitumor activity of camptothecins (CPTs), novel 10-fluoro-CPT derivatives were designed, synthesized and evaluated for cytotoxicity against five human cancer cell lines (A-549, MDA-MB-231, KB, KB-VIN and MCF-7). All of the derivatives showed more potent in vitro cytotoxic activity than the clinical CPT-derived drug irinotecan against the tumor cell lines tested, and most of them showed comparable or superior potency to topotecan. Remarkably, compounds 16b (IC₅₀, 67.0nM) and 19b (IC₅₀, 99.2nM) displayed the highest cytotoxicity against the multidrug-resistant (MDR) KB-VIN cell line and merit further development as preclinical drug candidates for treating cancer, including MDR phenotype. Our study suggested that incorporation of a fluorine atom into position 10 of CPT is an effective method for discovering new potent CPT derivatives.

Engineering Camptothecin-Derived Norbornene Polymers for Theranostic Application

A multifunctional stimuli-responsive nanotheranostic agent provides huge benefits in nanomedicine by combining both the diagnostic agent and the drug molecule in a single system. This nanosystem is capable of doing multiple tasks, for example, diagnosis, drug delivery, and monitoring the therapeutic response. Hence, theranostic agents are expected to play a significant role in personalized medicine. Herein, a new class of nanotheranostic agents, Pnr-Cbt-Cpt-Pg-Bn, is proposed for the effective delivery of camptothecin. This new class of polymer has been functionalized with a superparamagnetic norbornene cobalt unit for its use in magnetic resonance imaging (MRI). The NMR one-dimensional image confirms the MRI capability of this nanotheranostic agent. This is further modified with the poly(ethylene glycol)-biotin moiety for biocompatibility and site-specificity. The uniqueness of the design is confirmed by an in vitro study where a greater uptake of the nanotheranostic agent is observed when compared with free drugs. Hence, this new class of copolymer shows improved potential as nanotheranostic agents in drug delivery.

DNA topoisomerase-targeting chemotherapeutics: what's new?

To resolve the topological problems that threaten the function and structural integrity of nuclear and mitochondrial genomes and RNA molecules, human cells encode six different DNA topoisomerases including type IB enzymes (TOP1 and TOP1mt), type IIA enzymes (TOP2α and TOP2β) and type IA enzymes (TOP3α and TOP3β). DNA entanglements and the supercoiling of DNA molecules are regulated by topoisomerases through the introduction of transient enzyme-linked DNA breaks. The covalent topoisomerase-DNA complexes are the cellular targets of a diverse group of cancer chemotherapeutics, which reversibly stabilize these reaction intermediates. Here we review the structure-function and catalytic mechanisms of each family of eukaryotic DNA topoisomerases and the topoisomerase-targeting agents currently approved for patient therapy or in clinical trials, and highlight novel developments and challenges in the clinical development of these agents.

Design, synthesis and potent cytotoxic activity of novel 7-(N-[(substituted-sulfonyl)piperazinyl]-methyl)-camptothecin derivatives

In an effort to discover potent camptothecin-derived antitumor agents, novel camptothecin analogues with sulfonylpiperazinyl motifs at position-7 were designed and synthesized. They were evaluated for in vitro cytotoxicity with the sulforhodamine-B (SRB) method in five types of human tumor cell lines, A-549, MDA-MB-231, KB, KB-VIN and MCF-7. With IC50 values in the low μM to nM level, most of the new analogues showed greater cytotoxicity activity than the reference compounds irinotecan and topotecan. Furthermore, compounds 12l (IC50, 1.2nM) and 12k (IC50, 20.2nM) displayed the highest cytotoxicity against the multidrug-resistant (MDR) KB-VIN cell line and merit further development as preclinical drug candidates for treating cancer, including MDR phenotype. Our study suggested that integration of sulfonylpiperazinyl motifs into position-7 of camptothecin is an effective strategy for discovering new potent cytotoxic camptothecin derivatives.

Design and synthesis of new 7-(N-substituted-methyl)-camptothecin derivatives as potent cytotoxic agents

A series of novel 7-(N-substituted-methyl)-camptothecin derivatives was designed, synthesized, and evaluated for in vitro cytotoxicity against four human tumor cell lines, A-549, MDA-MB-231, KB, and KBvin. All of the derivatives showed promising in vitro cytotoxic activity against the tested tumor cell lines, with IC50 values ranging from 0.0023 to 1.11 μM, and were as or more potent than topotecan. Compounds 9d, 9e, and 9r exhibited the highest antiproliferative activity among all prepared derivatives. Furthermore, all of the compounds were more potent than paclitaxel against the multidrug-resistant (MDR) KBvin subline. With a concise efficient synthesis and potent cytotoxic profiles, especially significant activity towards KBvin, compounds 9d, 9e, and 9r merit further development as a new generation of camptothecin-derived anticancer clinical trial candidates.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

Design, modeling, synthesis and biological activity evaluation of camptothecin-linked platinum anticancer agents

The design, modeling, synthesis and biological activity evaluation of two hybrid agents formed by 7-oxyiminomethylcamptothecin derivatives and diaminedichloro-platinum (II) complex are reported. The compounds showed growth inhibitory activity against a panel of human tumor cell lines, including sublines resistant to topotecan and platinum compounds. The derivatives were active in all the tested cell lines, and compound 1b, the most active one, was able to overcome cisplatin resistance in the osteosarcoma U2OS/Pt cell line. Platinum-containing camptothecins produced platinum-DNA adducts and topoisomerase I-mediated DNA damage with cleavage pattern and persistence similar to SN38, the active principle of irinotecan. Compound 1b exhibited an appreciable antitumor activity in vivo against human H460 tumor xenograft, comparable to that of irinotecan at lower well-tolerated dose levels and superior to cisplatin. The results support the interpretation that the diaminedichloro-platinum (II) complex conjugated via an oxyiminomethyl linker at the 7-position of the camptothecin resulted in a new class of effective antitumor compounds.

Preclinical evaluation of the novel 7-substituted camptothecin Namitecan (ST1968) in paediatric tumour models

PURPOSE

The present study aimed to evaluate the new water soluble camptothecin analogue Namitecan (ST1968) in preclinical paediatric tumour models of the nervous system comprehensive of neuroblastoma, primitive neuroectodermal tumours/PNET and medulloblastoma where the drug was compared to Irinotecan.

METHODS

Cellular sensitivity to the drug was assessed by MTT and clonogenic assays. Propidium iodide staining was used for cell cycle perturbation studies. The genotoxic effects were quantified by Comet assay, whereas apoptosis was assessed by PARP cleavage and sub-G1 accumulation. Tumour response was investigated in xenograft models in nude mice.

RESULTS

The cellular response to Namitecan was heterogeneous with IC(50) (2 h) ranging between 0.14 and 13.26 μM, whereas SN38 (the active metabolite of Irinotecan) appeared more effective (IC(50): 0.03-11.7 μM). Interestingly, prolonged drug incubation times up to 72 h enhanced Namitecan cytotoxicity, with similar colony inhibition curves between the two analogues (IC(50), nM-SN38: 0.9 ± 0.2; Namitecan: 0.7 ± 0.4). DNA damage, accumulation in late-S/G2 phases and induction of apoptosis appeared important players of Namitecan cytotoxicity in our models. In vivo, Namitecan was superior to Irinotecan in three out of five xenograft models, with reversible weight loss (10 %). In the sensitive SK-N-AS xenograft, Namitecan showed a high retention in tumours consistently with: high antitumour response, rapid drug-mediated DNA damage (60 % mean TailDNA after 1 h from drug inoculation), persistent cell cycle perturbation (60-40 % G2 accumulation after 48-72 h, respectively) and apoptosis. Studies with Namitecan and platinum agents in this model showed a significant enhancement of antitumour activity of the drugs combination versus single agents.

CONCLUSIONS

Our preclinical data strongly support the interest of further investigations on the well-tolerated Namitecan either as a single agent or in combination in paediatric oncology.

Potent antiviral activity of topoisomerase I and II inhibitors against Kaposi's sarcoma-associated herpesvirus

The lytic DNA replication of Kaposi's sarcoma-associated herpesvirus (KSHV) initiates at an origin (ori-Lyt) and requires trans-acting elements, both viral and cellular. We recently demonstrated that several host cellular proteins, including topoisomerases I and II (Topo I and II), are involved in KSHV lytic DNA replication (Y. Wang, H. Li, Q. Tang, G. G. Maul, and Y. Yuan. J. Virol. 82: 2867-2882, 2008). To assess the importance of these topoisomerases in viral lytic replication, shRNA-mediated gene silencing was used. Depletion of Topo I and II severely inhibited viral lytic DNA replication as well as virion production, suggesting essential roles of these cellular proteins in viral DNA replication. The discovery of Topo I and II as enzymes indispensable for KSHV DNA replication raises a possibility that these cellular proteins could be new targets of therapeutic approaches to halt KSHV replication and treat KSHV-associated diseases. In this report, we examined one Topo I inhibitor and several Topo II inhibitors (inclusive of Topo II poison and catalytic inhibitors) as potential therapeutic agents for blocking KSHV replication. The Topo II catalytic inhibitors in general exhibited marked inhibition on KSHV replication and minimal cytotoxicity. In particular, novobiocin, with the best selectivity index (SI = 31.62) among the inhibitors tested in this study, is effective in inhibiting KSHV DNA replication and virion production but shows little adverse effect on cell proliferation and cycle progression in its therapeutic concentration, suggesting its potential to become an effective and safe drug for the treatment of human diseases associated with KSHV infection.

Inverse virtual screening of antitumor targets: pilot study on a small database of natural bioactive compounds

An inverse virtual screening in silico approach has been applied to natural bioactive molecules to screen their efficacy against proteins involved in cancer processes, with the aim of directing future experimental assays. Docking studies were performed on a panel of 126 protein targets extracted from the Protein Data Bank, to analyze their possible interactions with a small library of 43 bioactive compounds. Analysis of the molecular docking results was performed through the use of tables containing energy data organized in a matrix. The application of this approach may facilitate the prediction of the activity of unknown ligands for known targets involved in the development of cancer and could be applied to other models based on different libraries of ligands and different panels of targets.

Synthesis and biological evaluation of novel 7-acyl homocamptothecins as Topoisomerase I inhibitors

A series of novel 7-acyl derivatives of homocamptothecin (hCPT) were designed and synthesized with the purpose to improve antitumor activity of hCPT, via Minisci free-radical reaction from 10-methoxyhomocamptothecin. All the compounds were evaluated for in vitro cytotoxicity against three cancer cell lines (A549, MDA-MB-435 and HCT116). For MDA-MB-435 cell line, compounds, 6a, 6b, 6k and all of 7-alkylcabonyl homocamptothecin derivatives showed higher in vitro inhibitory activities than topotecan (TPT). Furthermore, compounds 6d, 6e, and 6k showed highly potent inhibitory activities with the IC50 values from less than 1 nM to 2.2 nM. In Topoisomerase I (Topo I)-induced DNA cleavage assay, compounds 6a, 6d, and 6k, as compared to CPT, revealed higher Topo I inhibitory activity.

Structural simplification of bioactive natural products with multicomponent synthesis. 3. Fused uracil-containing heterocycles as novel topoisomerase-targeting agents

After the initial discovery of antiproliferative and apoptosis-inducing properties of a camptothecin-inspired pentacycle based on a 1H-indeno[2',1':5,6]dihydropyrido[2,3-d]pyrimidine scaffold, a library of its analogues as well as their oxidized planar counterparts were prepared utilizing a practical multicomponent synthetic protocol. The synthesized compounds exhibited submicromolar to low micromolar antiproliferative potencies toward a panel of human cancer cell lines. Biochemical experiments are consistent with the dihydropyridine library members undergoing intracellular oxidation to the corresponding planar pyridines, which then inhibit topoisomerase II activity, leading to inhibition of proliferation and cell death. Because of facile synthetic preparation and promising antitopoisomerase activity, both the dihydropyridine and planar pyridine-based compounds represent a convenient starting point for anticancer drug discovery.

Overcoming tumor multidrug resistance using drugs able to evade P-glycoprotein or to exploit its expression

Multidrug resistance (MDR) is a major obstacle to the effective treatment of cancer. Cellular overproduction of P-glycoprotein (P-gp), which acts as an efflux pump for various anticancer drugs (e.g. anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and some of the newer antitumor drugs) is one of the more relevant mechanisms underlying MDR. P-gp belongs to the superfamily of ATP-binding cassette transporters and is encoded by the ABCB1 gene. Its overexpression in cancer cells has become a therapeutic target for circumventing MDR. As an alternative to the classical pharmacological strategy of the coadministration of pump inhibitors and cytotoxic substrates of P-gp and to other approaches applied in experimental tumor models (e.g. P-gp-targeting antibodies, ABCB1 gene silencing strategies, and transcriptional modulators) and in the clinical setting (e.g. incapsulation of P-gp substrate anticancer drugs into liposomes or nanoparticles), a more intriguing strategy for circumventing MDR is represented by the development of new anticancer drugs which are not substrates of P-gp (e.g. epothilones, second- and third-generation taxanes and other microtubule modulators, topoisomerase inhibitors). Some of these drugs have already been tested in clinical trials and, in most of cases, show relevant activity in patients previously treated with anticancer agents which are substrates of P-gp. Of these drugs, ixabepilone, an epothilone, was approved in the United States for the treatment of breast cancer patients pretreated with an anthracycline and a taxane. Another innovative approach is the use of molecules whose activity takes advantage of the overexpression of P-gp. The possibility of overcoming MDR using the latter two approaches is reviewed herein. 

DNA damage persistence as determinant of tumor sensitivity to the combination of Topo I inhibitors and telomere-targeting agents

PURPOSE

We previously reported that the G-quadruplex (G4) ligand RHPS4 potentiates the antitumor activity of camptothecins both in vitro and in tumor xenografts. The present study aims at investigating the mechanisms involved in this specific drug interaction.

EXPERIMENTAL DESIGN

Combination index test was used to evaluate the interaction between G4 ligands and standard or novel Topo I inhibitors. Chromatin immunoprecipitation was performed to study the presence at telomeres of various types of topisomerase, while immunolabeling experiments were performed to measure the activation of DNA damage both in vitro and in tumor xenografts.

RESULTS

We report that integration of the Topo I inhibitor SN-38, but not the Topo II poison doxorubicin with telomere-based therapy is strongly effective and the sequence of drug administration is critical in determining the synergistic interaction, impairing the cell ability to recover from drug-induced cytotoxicity. The synergistic effect of this combination was also observed by using novel camptothecins and, more interestingly, mice treated with ST1481/RHPS4 combination showed an inhibition and delay of tumor growth as well as an increased survival. The study of the mechanism(s) revealed that treatment with G4 ligands increased Topo I at the telomeres and the functional relevance of this observation was directly assessed by showing that standard and novel camptothecins stabilized DNA damage both in vitro and in xenografts.

CONCLUSIONS

Our results demonstrate an outstanding efficacy of Topo I inhibitors/G4 ligands combination, which likely reflects an enhanced and persistent activation of DNA damage response as a critical determinant of the therapeutic improvement.

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.

Sequence-specific targeting of IGF-I and IGF-IR genes by camptothecins

We and others have clearly demonstrated that a topoisomerase I (Top1) inhibitor, such as camptothecin (CPT), coupled to a triplex-forming oligonucleotide (TFO) through a suitable linker can be used to cause site-specific cleavage of the targeted DNA sequence in in vitro models. Here we evaluated whether these molecular tools induce sequence-specific DNA damage in a genome context. We targeted the insulin-like growth factor (IGF)-I axis and in particular promoter 1 of IGF-I and intron 2 of type 1 insulin-like growth factor receptor (IGF-IR) in cancer cells. The IGF axis molecules represent important targets for anticancer strategies, because of their central role in oncogenic maintenance and metastasis processes. We chemically attached 2 CPT derivatives to 2 TFOs. Both conjugates efficiently blocked gene expression in cells, reducing the quantity of mRNA transcribed by 70-80%, as measured by quantitative RT-PCR. We confirmed that the inhibitory mechanism of these TFO conjugates was mediated by Top1-induced cleavage through the use of RNA interference experiments and a camptothecin-resistant cell line. In addition, induction of phospho-H2AX foci supports the DNA-damaging activity of TFO-CPT conjugates at specific sites. The evaluated conjugates induce a specific DNA damage at the target gene mediated by Top1.

Efficacy of ST1968 (namitecan) on a topotecan-resistant squamous cell carcinoma

ST1968 (namitecan), a novel 7-modified hydrophilic camptothecin, was found to be effective against tumor models relatively resistant to topotecan and irinotecan. Based on this observation, this study was designed to investigate the cellular and antitumor effects of ST1968 in a subline of A431, squamous cell carcinoma, selected for resistance to topotecan (A431/TPT). This model was characterized by a slow growth rate, associated with downregulation of EGFR and topoisomerase I. In contrast to other camptothecins (SN38 and gimatecan), ST1968 was able to overcome almost completely the resistance at cellular level. The cellular pharmacokinetics indicated a comparable accumulation and retention of ST1968 in sensitive and resistant cells, in spite of expression of the efflux transporter, P-glycoprotein, in resistant cells. The uptake and retention of topotecan were dramatically reduced in both tumor cell lines, but more evident in the resistant one. In contrast to topotecan, ST1968 retained an outstanding efficacy in vivo against the resistant tumor (A431/TPT). The results are consistent with the interpretation that ST1968 was able to overcome the most relevant mechanisms associated with the development of topotecan resistance (i.e., slow proliferation and target downregulation) owing to its peculiar pharmacokinetic behaviour.

Phase I and pharmacokinetic study of gimatecan given orally once a week for 3 of 4 weeks in patients with advanced solid tumors

PURPOSE

A phase I study was conducted to determine the dose-limiting toxicities (DLT) and maximum tolerated dose (MTD) of gimatecan, a lipophilic camptothecin analogue, administered orally once a week for 3 weeks.

EXPERIMENTAL DESIGN

Adult patients with advanced solid tumors with good performance status and adequate hematologic, hepatic, and renal function were eligible for the study. The plasma pharmacokinetics of the drug was characterized during the initial 28-day cycle.

RESULTS

A total of 33 patients were evaluated at 7 dose levels ranging from 0.27 to 3.20 mg/m(2)/wk. Anemia, fatigue, neutropenia, nausea, and vomiting were the principal toxicities. DLTs experienced by 3 of 7 patients in dose level 7 (3.20 mg/m(2)) were grade 2 hyperbilirubinemia and grade 3 to 4 fatigue. DLT (anorexia and nausea) occurred in only 1 of 11 patients evaluated at the MTD of 2.40 mg/m(2). There were no objective responses, although disease stabilization was observed in 4 patients. Gimatecan has a very long apparent biological half-life (mean +/- SD, 77 +/- 37 h) and exists in plasma almost entirely as the pharmacologically active intact lactone form. At the MTD, mean peak concentrations of the drug in plasma ranged from 67 to 82 ng/mL for the 3 weekly doses and the mean concentration 7 days after dosing was 15 +/- 18 ng/mL.

CONCLUSIONS

Administration of gimatecan orally once a week at doses that are well tolerated provides continuous exposure to potentially effective plasma concentrations of the biologically active form of the drug. This regimen deserves further evaluation to define its antitumor activity in specific tumor types either alone or in combination with other agents.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.

E-ring-modified 7-oxyiminomethyl camptothecins: Synthesis and preliminary in vitro and in vivo biological evaluation

In contrast to five-membered E-ring analogues, 7-oxyiminomethyl derivatives of homocamptothecins showed ability to form stable ternary complexes with DNA and topoisomerase I. The 7-oxyiminomethyl derivatives of homocamptothecins were evaluated as a racemic mixture. Following the isolation of the two enantiomers, the 20 (R)-hydroxy isomer confirms the best activity. By using a panel of human tumor cells, all tested homocamptothecins showed a potent antiproliferative activity, correlating to the persistence of the cleavable complex. No significant difference was observed between the natural scaffold and the corresponding homocamptothecin homologue. A selected compound of this series exhibited an excellent antitumor activity against human gastrointestinal tumor xenografts.