Semisynthesis, cytotoxic activity, and oral availability of new lipophilic 9-substituted camptothecin derivatives

F10, a new camptothecin derivative, was identified as a new orally-bioavailable, potent antitumor agent

Topoisomerases are interesting targets for drug discovery. In the present study, we attached saturated carbon atoms to the 10-position of camptothecin and synthesized 10 new camptothecin derivatives from 10-HCPT or SN-38. The activities of new compounds were evaluated both in vitro and in vivo. The most promising compound F10, 7-ethyl-10-(2-oxo-2-(piperidin-1-yl)ethoxy)camptothecin, inhibited cancer cells growth with the IC₅₀ of 0.002, 0.003, 0.011 and 0.081 μM on Raji, HCT116, A549 and Lovo cells, respectively. Meanwhile, oral administration of F10 remarkably suppressed the HCT116-xenograft tumor growth in the nude-mice model at the dosage of 0.5, 2.0 and 8.0 mg/kg in vivo. Intraperitoneal administration of F10 can completely inhibit Raji-xenograft tumor growth in established NPG mouse model at 2.0 and 4.0 mg/kg. In addition, the minimum lethal doses of F10 and SN-38 in mice by intravenous administration were 80 and 40 mg/kg (or 0.155, 0.102 mmol/kg), respectively. The solubility of F10 reached 9.86 μg/mL in a buffer solution of pH 4.5. The oral bioavailability of F10 achieved 22.4% in mice. The molecular docking model revealed that F10 can interact with topoisomerase I-DNA complex. Our findings indicate that F10 is a new orally-oavailable antitumor agent with potent anticancer effect. Furthermore, attaching a ring hydrophobic moiety to the 10-position of camptothecin provides a favorable approach in the optimization of camptothecin.

Synthesis and Biological Evaluation of Paclitaxel and Camptothecin Prodrugs on the Basis of 2-Nitroimidazole

Due to the low esterase activity in human plasma, many ester and carbonate prodrugs tested in humans may be less effective than that in preclinical animals. In this letter, PTX and SN-38 were attached to the N-1 position of 2-nitroimidazole via a carbonate linker. Presumably, 2-aminoimidazole may help promote the intramolecular hydrolysis of the carbonate bond. The prodrugs exhibited a considerable stability in buffers at different pH values as well as in human plasma. Furthermore, a rapid reduction was exhibited in the presence of nitroreductase. An in vitro cytotoxicity assay demonstrated that hypoxic conditions could increase the toxicity of prodrugs. Potentially, the compound species may form a new class of promising antitumor agents.

Synthesis and biological evaluation of hypoxia-activated prodrugs of SN-38

We designed new hypoxia-activated prodrugs by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol with 7-ethyl-10-hydroxy camptothecin (SN-38). Initially, we improved the method of multi-gram scale synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which increased the yield to 42% compared to 8% by the original synthesis method. The improved method was used to synthesize evofosfamide (TH-302) and hypoxia-activated prodrugs of SN-38. Two different linkages between (1-methyl-2-nitro-1H-imidazol-5-yl)methanol and SN-38 were evaluated that afforded different hypoxia-selectivity and toxicity. Compound 16 (IOS), containing an ether linkage, was considered to be a promising hypoxia-selective antitumor agent.

Safe approaches for camptothecin delivery: Structural analogues and nanomedicines

Twenty-(S)-camptothecin is a strongly cytotoxic molecule with excellent antitumor activity over a wide spectrum of human cancers. However, the direct formulation is limited by its poor water solubility, low plasmatic stability and severe toxicity, which currently limits its clinical use. As a consequence, two strategies have been developed in order to achieve safe and efficient delivery of camptothecin to target cells: structural analogues and nanomedicines. In this review, we summarize recent advances in the design, synthesis and development of camptothecin molecular derivatives and supramolecular vehicles, following a systematic classification according to structure-activity relationships (structural analogues) or chemical nature (nanomedicines). A series of organic, inorganic and hybrid materials are presented as nanoplatforms to overcome camptothecin restrictions in administration, biodistribution, pharmacokinetics and toxicity. Nanocarriers which respond to a variety of stimuli endogenously (e.g., pH, redox potential, enzyme activity) or exogenously (e.g., magnetic field, light, temperature, ultrasound) seem the best positioned therapeutic materials for optimal spatial and temporal control over drug release. The main goal of this review is to be used as a source of relevant literature for others interested in the field of camptothecin-based therapeutics. To this end, final remarks on the most important formulations currently under clinical trial are provided.

Design of chalcogen-containing norepinephrines: efficient GPx mimics and strong cytotoxic agents against HeLa cells

AIM

Numerous chronic diseases exhibit multifactorial etiologies, so focusing on a single therapeutic target is usually an inadequate treatment; instead, multi-target drugs are preferred. Herein, a panel of phenolic thioureas and selenoureas were designed as new prototypes against multifactorial diseases concerning antioxidation and cytotoxicity, as a pro-oxidant environment is usually found in such diseases.

RESULTS

Selenoureas were excellent antiradical agents and biomimetic catalysts of glutathione peroxidase for the scavenging of H₂O₂. They were also potent and selective cytotoxic agents against cancer cells, in particular HeLa (IC₅₀ 2.77-6.13 μM), apoptosis being involved. Selenoureas also reduced oxidative stress in HeLa cells (IC₅₀= 3.76 μM).

CONCLUSION

Phenolic selenoureas are promising lead structures for the development of drugs targeting multifactorial diseases like cancer.

Tubulin acetylation promoting potency and absorption efficacy of deacetylase inhibitors

BACKGROUND AND PURPOSE

Histone deacetylase 6 (HDAC6) and silent information regulator 2 (SIRT2) control the dynamics of the microtubule network via their deacetylase activities. Tubulin polymerization promoting protein (TPPP/p25) enhances microtubule acetylation by its direct binding to HDAC6. Our objective was to characterize the multiple interactions of the deacetylases and to establish the inhibitory potency and the pharmacokinetic features of the deacetylase inhibitors, trichostatin A (TSA) and AGK2.

EXPERIMENTAL APPROACH

The interactions of deacetylases with tubulin and TPPP/p25 were quantified by elisa using human recombinant proteins. The effect of inhibitors on the tubulin acetylation was established in HeLa cells transfected with pTPPP and CG-4 cells expressing TPPP/p25 endogenously by celisa (elisa on cells), Western blot and immunofluorescence microscopy. The pharmacokinetic features of the inhibitors were evaluated by in situ kinetic modelling of their intestinal transport in rats.

KEY RESULTS

Deacetylases interact with both tubulin and TPPP/p25, notwithstanding piggy-back binding of HDAC6 or SIRT2 to the TPPP/p25-associated tubulin was established. Much higher inhibitory potency for TSA than for AGK2 was detected in both HeLa and CG-4 cells. Pioneer pharmacokinetic studies revealed passive diffusion and diffusion coupled with secretion for TSA and AGK2 respectively. Both inhibitors exhibited greater permeability than some other well-established drugs.

CONCLUSIONS AND IMPLICATIONS

TPPP/p25-directed deacetylase inhibition provides mechanisms for the fine control of the dynamics and stability of the microtubule network. Deacetylase inhibitors with chemical structures similar to TSA and AGK2 appear to be excellent candidates for oral drug absorption.