Fluorescence detection combined with either HPLC or HPTLC for pharmaceutical quality control in a hospital chemotherapy production unit: Application to camptothecin derivatives

In order to achieve the analytical assessment of the manufactured batches of chemotherapy preparations, post-production quality control has been developed. The common use of camptothecin derivatives (i.e. irinotecan (CPT-11) and topotecan (TPT)) as part of protocols in Institut Gustave Roussy (IGR) has led to develop an efficient analytical method that could assess an increasing number of samples with high throughput, good specificity and practicality. Due to the difference of concentration between batches containing irinotecan or topotecan, HPLC and HPTLC both combined with fluorescence detection were investigated. Those two techniques made identity, purity and quantitation assays possible. The chromatographic conditions that were chosen allowed identification of each drug through their rate of flow (Rf), 0.10 and 0.35, or their retention time (tR), 2 and 7 min for topotecan and irinotecan, respectively. A calibration curve was plotted for each molecule and validated by three quality controls (high, medium and low). Coefficients of variation of repeatability (CVr) and intermediate precision (CVi) were determined for both methods. Considering their values and the concentration ranges (from 100 to 500 mg/L for HPTLC and from 0.1 to 1 mg/L for HPLC), it was decided to perform analysis using HPTLC for irinotecan preparations and HPLC for topotecan preparations. These inferences seemed appropriate regarding the number of preparations to be assayed.

1,3-Dipolar Cycloaddition Chemistry for the Preparation of Novel Indolizinone-Based Compounds

[Chemical reaction: See text] Starting from methyl 5-oxo-6-trifluoromethanesulfonyloxy-1,2,3,5-tetrahydroindolizine-8-carboxylate, obtained by a Rh(II)-catalyzed 1,3-dipolar cycloaddition reaction of 1-(2-benzenesulfonyl-2-diazoacetyl)pyrrolidin-2-one and methyl acrylate, several indolo- and furano-fused indolizinones were efficiently prepared. In the first case, a palladium-mediated C-N coupling of the triflate with a variety of substituted anilines provided the desired methyl 5-oxo-6-(arylamino)-1,2,3,5-tetrahydroindolizine-8-carboxylates in high yield. Methyl 6-(2-bromophenylamino)-5-oxo-1,2,3,5-tetrahydroindolizine-8-carboxylate as well as its decarboxylated analogue, 6-(2-bromophenylamino)-2,3-dihydro-1H-indolizin-5-one, were synthesized in excellent yield and were found to undergo an intramolecular Heck cyclization to give 1,2,3,6-tetrahydroindolizino[6,7-b]indol-5-ones. To prepare furano-fused indolizinones, methyl 6-hydroxy-5-oxo-1,2,3,5-tetrahydroindolizine-8-carboxylate was etherified with different allyl halides, and the resultant allyl ethers were subjected to a thermal Claisen rearrangement to give the corresponding methyl 7-allyl-6-hydroxy-5-oxo-1,2,3,4-tetrahydroindolizine-8-carboxylates. Cyclization under Wacker oxidation conditions afforded methyl 2-methyl-8-oxo-5,6,7,8-tetrahydro-1-oxa-7a-aza-s-indacene-4-carboxylates in near-quantitative yield.

Synthesis and pharmacology of new camptothecin drugs

Camptothecin (CPT) drugs exhibit antineoplastic activity against colorectal, breast, lung and ovarian cancers. This review briefly summarizes the pharmacology of CPT drugs, examines four strategies and methods for the synthesis of camptothecins, and finally discusses homocamptothecins and silatecans, two new classes of CPT analog.

A Novel, Expeditious Synthesis of Racemic Camptothecin

[reaction: see text] A novel and efficient synthesis of racemic camptothecin, starting from a readily accessible hydroxy pyridone, is presented. Key steps include a Claisen rearrangement of a functionalized allylic ether, a hindered Heck coupling, and a Friedländer condensation.

Activation of camptothecin derivatives by conjugation to triple helix-forming oligonucleotides

Topoisomerase I (topo I) is a ubiquitous DNA-cleaving enzyme and an important therapeutic target in cancer chemotherapy. Camptothecins (CPTs) reversibly trap topo I in covalent complex with DNA but exhibit limited sequence preference. The utilization of conjugates such as triplex-forming oligonucleotides (TFOs) to target a medicinal agent (like CPT) to a specific genetic sequence and orientation within the DNA has been accomplished successfully. In this study, different attachment points of the TFO to CPT (including positions 7, 9, 10, and 12) were investigated and our findings confirmed and extended previous conclusions. Interestingly, the conjugates induced specific DNA cleavage by topo I at the triplex site even when poorly active or inactive CPT derivatives were used. This suggests that the positioning of the drug in the cleavage complex by the sequence-specific DNA ligand is able to stabilize the ternary complex, even when important interactions between topo I and CPT are disrupted. Finally, certain TFO-CPT conjugates were able to induce sequence-specific DNA cleavage with the topo I mutants R364H and N722S that are resistant to camptothecin. The TFO-CPT conjugates are thus valuable tools to study the interactions involved in the formation of the ternary complex and also to enlarge the family of compounds that poison topo I. The fact that an inactive CPT analogue can act as a topo I poison when appropriately coupled to a TFO provides a new perspective at the level of drug design.

Synthesis and antitumor activity of 7-ethyl-9-alkyl derivatives of camptothecin

A series of new camptothecin derivatives, as topoisomerase I inhibitor, were synthesized to identify potent antitumor agents. The synthesis method was based on the Claisen rearrangement of 10-allyloxy-7-ethylcamptothecin. All of the compounds were assayed for cytotoxicity against two human tumor cell lines, Bel7402, HCT116, and showed good potency in vitro. Compounds 2, 4, 9, were assessed for the stability of lactone in human plasma. And then compound 2 was tested for antitumor activity in vitro against mouse tumor sarcoma-180. The results suggested that the small alkyl groups in the both 7- and 9-positions of camptothecin could promote liposolubility, antitumor activity in vitro and vivo, though did not bring much increase of the stability of lactone.

Synthesis and antitumor activity of A-ring modified hexacyclic analogues of camptothecin

AIM

To improve the biological activity of A-ring modified analogues of camptothecin.

METHODS

A-ring modified camptothecins were synthesized from 10-hydroxycamptothecin or 7-ethyl-10-hydroxycamptothecin (SN-38) in three or four steps. Their cytotoxicity was evaluated using MTY assay, and their in vivo antitumnor activity against mouse liver cancer H22 was tested. Results Five hexacyclic camptothecins (6a, 6b, 6c, 7a and 7b) are target compounds, and ten camptothecin derivatives are new compounds.

CONCLUSION

The modification of a 1,4-oxazine-2-one ring fused with positions 9 and 10 of A-ring will reduce the antitumor activity of camptothecins.

Synthesis of 14-Azacamptothecin, a Water-Soluble Topoisomerase I Poison

14-Azacamptothecin, a potent, water-soluble analogue of the antitumor agent camptothecin, has been prepared by a convergent synthesis. The key condensation of the AB and DE rings with concomitant formation of ring C of 14-aza CPT was carried out in two stages, the latter of which involved a radical cyclization strategy. [structure: see text]

Synthesis and anti-tumor activity of alkenyl camptothecin esters

AIM

To study the degrees of influence of changing side ester chains at position C20 of camptothecin on the anti-tumor activity of the molecules.

METHODS

The esterification reaction of camptothecin 1 and 9-nitrocamptothecin 2 with crotonic anhydride in pyridine gave the corresponding esters 3 and 4, respectively. The acylation of 1 and 2 with cinnamoyl chloride gave products 7 and 8. Epoxidation reaction of 3 and 4 with m-chloroperoxybenzoic acid in benzene solvent gave the products 5 and 6. Esters 3, 4, and 5 were tested for anti-tumor activity against 14 human cancer cell lines.

RESULTS

Both in vitro and in vivo anti-tumor activity studies for these esters were conducted and the data demonstrated positive results, that is, these esters were active against the tested tumor lines.

CONCLUSION

Alkenyl esters 3 and 4 showed strong anti-tumor activity in vitro against 14 different cancer cell lines. Ester 3 was active against human breast carcinoma in mice and the toxicity of the agent was not observed in mice during the treatment, implying that this agent is effective for treatment with low toxicity.

Synthesis and antitumor activity of 20-O-linked nitrogen-based camptothecin ester derivatives

A series of nitrogen-based 20S-hydroxyl camptothecin ester derivatives were prepared. 3-Aminopropionate of camptothecin was found more cytotoxic in vitro on several human tumor cell lines than 3-amidopropionate of camptothecin. Ester 16 showed best antitumor activity in vivo and in vitro in all esters we prepared.

Bioreduction activated prodrugs of camptothecin: molecular design, synthesis, activation mechanism and hypoxia selective cytotoxicity

Several water-soluble derivatives (CPT3, CPT3a-d) of camptothecin (CPT) were synthesized, among which CPT3 bearing an N,N'-dimethyl-1-aminoethylcarbamate side-chain was further conjugated with reductively eliminating structural units of indolequinone, 4-nitrobenzyl alcohol and 4-nitrofuryl alcohol to produce novel prodrugs of camptothecin (CPT4-6). All CPT derivatives were of lower cytotoxicity than their parent compound of CPT. In contrast, CPT4 and CPT6 showed higher hypoxia selectivity of cytotoxicity towards tumor cells than CPT. A mechanism by which a representative prodrug CPT4 is activated in the presence of DT-diaphorase to release CPT was also discussed. The bioreduction activated CPT prodrugs including CPT4 and CPT6 are identified to be promising for application to the hypoxia targeting tumor chemotherapy.

Camptothecin: current perspectives

This review provides a detailed discussion of recent advances in the medicinal chemistry of camptothecin, a potent antitumor antibiotic. Two camptothecin analogues are presently approved for use in the clinic as antitumor agents and several others are in clinical trials. Camptothecin possesses a novel mechanism of action involving the inhibition of DNA relaxation by DNA topoisomerase I, and more specifically the stabilization of a covalent binary complex formed between topoisomerase I and DNA. This review summarizes the current status of studies of the mechanism of action of camptothecin, including topoisomerase I inhibition and additional cellular responses. Modern synthetic approaches to camptothecin and several of the semi-synthetic methods are also discussed. Finally, a systematic evaluation of novel and important analogues of camptothecin and their contribution to the current structure-activity profile are considered.

Camptothecin analogs with bulky, hydrophobic substituents at the 7-position via a Grignard reaction

By developing a new synthetic procedure for introduction of side chains onto the camptothecin ring system, we were able to achieve the preparation of a number of analogs bearing bulky, hydrophobic groups directly attached to the 7-position. These include 7-tert-butylcamptothecin, 7-benzylcamptothecin and the corresponding 10,11-methylenedioxycamptothecins. This method involves the reaction of an appropriate orthoaminobenzonitrile with various Grignard reagents to give the corresponding orthoaminoketones. Friedlander condensation of the latter with the key tricyclic ketone leads to 7-substituted camptothecin analogs. We report the activity of these compounds as topoisomerase I poisons and their ability to inhibit growth of selected tumor cell lines.

Combined Directed Ortho Metalation/Cross-Coupling Strategies: Synthesis of the Tetracyclic A/B/C/D Ring Core of the Antitumor Agent Camptothecin

A convergent synthesis of the A/B/C/D ring fragment 5 of camptothecin using a combination of directed ortho metalation and Negishi cross-coupling is described. The key features of the synthetic sequence are an anionic ortho-Fries rearrangement (10 --> 12), a Negishi cross-coupling (7 --> 6), and a terminal modified von Braun reaction (16 --> 5) that leads to tetracyclic derivative 5 in 7 steps and 11% overall yield.

Synthesis of a Macromolecular Camptothecin Conjugate with Dual Phase Drug Release

A water soluble macromolecular conjugate of camptothecin (CPT) with a new, dual phase hydrolytic drug release mechanism was prepared on the basis of a 60 kDa biodegradable hydrophilic "stealth" polyacetal, poly(1-hydroxymethylethylene hydroxy-methyl formal). Succinamido-glycinate was used as a prodrug releasing group. A model preparation with 7.5% CPT content w/w was water soluble. The lipophilic camptothecin prodrug, camptothecin-(O20)-succinimidoglycinate, was released from the conjugate with t(1/2) = 2.2 +/- 0.1 h in rodent plasma. The blood clearance in a rodent model as measured by CPT was release limited, t(1/2) = 2.1 +/- 0.2 h, while the conjugate half-life was 14.2 +/- 1.7 h. In a xenograft tumor model, the conjugate demonstrated higher antineoplastic efficacy than CPT at a less than equitoxic dose. This improved therapeutic window is in line with the modified drug pharmacokinetics and with camptothecin release in a stabilized lipophilic prodrug form. Regulation of prodrug release and hydrolysis rates through linker structure modification will open the way to further improve both pharmacokinetics and pharmacodynamics.

Synthesis and biological evaluation of bis and monocarbonate prodrugs of 10-hydroxycamptothecins

In an effort to improve the stability of labile lactone ring of camptothecins, the bis and mono-alkyl carbonate prodrugs of 10-hydroxycamptothecins were synthesized and their chemical and enzymatical stability as well as antitumor activity were studied. The in vitro evaluation of the stability of these carbonates indicates that the 10,20-biscarbonates are firstly hydrolyzed to afford the stable 20-monocarbonates. And the 10-carbonates are not stable in human plasma, mouse plasma and pH7.4 phosphate buffer, while the 20-carbonates are relatively stable in the three media and can be readily cleaved by porcine liver esterase. The overall toxicity of the tested carbonate against mice bearing S180 sarcoma is much lower when compared with the parent compound, and the antitumor activity is maintained.

[Synthesis and antitumor activity of 20-O-linked camptothecin ester derivatives]

AIM

To improve the profile of 20 (S)-camptothecin, a series of 20-O-linked camptothecin phenoxyacetic acid ester derivatives have been designed.

METHODS

These derivatives were synthesized by the method of acylation. Their chemical structures were confirmed with 1HNMR, IR, MS, and HRMS. The cytotoxicities of the compounds were tested by MTT assay. The in vivo antitumor activities of these esters were evaluated against mouse liver tumor H22 in mice.

RESULTS

Twelve derivatives of camptothecin ester are new compounds.

CONCLUSION

In vitro and in vivo antitumor activity has indicated that some derivatives appeared significantly more effective than topotecan in the H22 mouse liver tumoral model.

Synthesis and cytotoxicity of water soluble quaternary salt derivatives of camptothecin

In an effort to improve the water solubility of camptothecin, 16 water soluble 10-substituted quaternary ammonium salt derivatives of camptothecin were prepared. Their antitumor activity was evaluated on cancer cells in vitro. All of these salts possess lower cytotoxicities than CPT in comparison. The camptothecin salts 16, 20 showed similar cytotoxic activity to topotecan. Especially the salts 21 showed similar cytotoxic activity to CPT in vitro.

[Synthesis and antitumor activities of 10-hydroxy camptothecin derivatives]

AIM

To find new anticancer drug based on the structure of 10-hydroxy camptothecin.

METHODS

Seven camptothecin derivatives (3 -9) were synthesized and the antitumor activities of these derivatives were evaluated.

RESULTS

Structures of seven new compounds were determined by 1HNMR, IR, MS. Seven compounds showed inhibitory effects on Hela, BEL-7402, 7901 cell lines in vitro. Especially, compound 4 showed high bioactivities to all of the tumor cells in vitro, its anticancer activity against human cervical carcinoma Hela was much higher than that of 10-hydroxy camptothecin.

CONCLUSION

Some compounds are worth further studying.

A method to determine the incorporation capacity of camptothecin in liposomes

The purpose of this study was to establish a new experimental approach to determine the maximum amount of camptothecin (CPT) that can be incorporated in liposomes, and to use this method to compare the CPT-incorporation capacity of various liposome formulations. Small, CPT-saturated liposomes were prepared by dispersing freeze-dried blends of lipids and drug in phosphate buffer, and subsequent probe-sonication. Excess precipitated CPT could be separated from the liposomes by ultracentrifugation. The small and homogeneous liposome size obtained gave a good and reproducible recovery of liposomes in the supernatant (>80%), whereas the acidic pH (pH 6.0) kept CPT in its hydrophobic lactone form, which is poorly soluble in the buffer. The maximum CPT-incorporation capacity of 12 different liposome formulations was investigated, using the described method, and was found to vary widely. With liposomes made of neutral and anionic phospholipids, the solubility of CPT in the buffer was improved by approximately a factor of 10 (from 2.7 to 15-50 microg/mL) as compared with buffer. With cationic liposomes containing 1,2-dioleoyl-3-trimethyl-ammonium-propane (DOTAP), a maximum CPT-solubilization of 100-fold, the buffer solubility was reached, probably owing to an electrostatic interaction between the cationic lipids and the carboxylate-CPT isomer. Increasing DOTAP fractions within egg-phosphatidylcholine (EPC)/DOTAP liposomes reached a CPT-incorporation plateau at 20 mol% DOTAP. The presented approach appears suitable to study the incorporation capacity of any drug component within small vesicles as long as the liposome incorporation is high relative to the intrinsic water solubility of the drug.

Synthesis and cytotoxic activity of substituted 7-aryliminomethyl derivatives of camptothecin

A series of imines derived from camptothecin-7-aldehyde (CPT-CHO) and aromatic amines were synthesised and tested for their cytotoxicity against tumour cell line H460, that expresses a high level of topoisomerase I. In general ortho-substituted compounds showed higher cytotoxic potency than the corresponding para-substituted imines. This effect was dependent on the nature of the substituent. Structure-activity relationships were studied by calculation of docking energy with a model of the ternary complex camptothecin-DNA-topoisomerase I. The ability of selected compounds to stimulate the topoisomerase I-mediated DNA cleavage and the persistence of the cleavable complex were consistent with the cytotoxic activity.

Synthesis, Characterization, and Preliminary in Vivo Tests of New Poly(ethylene glycol) Conjugates of the Antitumor Agent 10-Amino-7-ethylcamptothecin

Despite the high antitumor activity of camptothecins, few derivatives have been developed and tested for human treatment of solid tumors, due to unpredictable toxicity mainly connected to their poor water solubility. We report the conjugation of the antitumor agent 10-amino-7-hydroxy camptothecin (SN-392) to linear or branched poly(ethylene glycol)s (PEGs) of different loading capacity through a tri- or tetrapeptide spacer selectively cleaved by lysosomal enzymes (cathepsins). A synthetic strategy based on the chemoselective acylation of the aromatic amino group in the presence of the unprotected C20 tertiary alcohol allowed high overall yields. Two conjugates demonstrated good stability at physiological pH and in mouse plasma (nonspecific proteases) but slowly released the drug payload in the presence of the lysosomal enzyme cathepsin B1. Compound 3, selected for in vivo experiments, was very active against P388, P388/ADM leukaemia, and Meth A fibrosarcoma cell lines, scoring T/C% values comparable with the camptothecin derivative CPT-11. Pharmacokinetic studies indicated that 3 acts as a reservoir of 10-amino-7-ethylcamptothecin, as the mean residence time (MRT) is about 3-fold higher than that of the free drug.

Regioselective synthesis and cytotoxicities of camptothecin derivatives modified at the 7-, 10- and 20-positions

A series of 7-acyloxymethylcamptothecin and 20-O-acyl-7-acyloxymethylcamptothecin derivatives were regioselectively prepared on different solvents. 7-Acyloxymethylcamptothecins possess more efficacy than 20-O-acyl-7-acyloxymethylcamptothecins against six human cancer cell lines in vitro.

Synthesis of linear, beta-cyclodextrin-based polymers and their camptothecin conjugates

6(A),6(D)-Bis-(2-amino-2-carboxylethylthio)-6(A),6(D)-dideoxy-beta-cyclodextrin 1, a diamino acid derivative of beta-cyclodextrin, is synthesized and condensed with difunctionalized PEG comonomers to give linear, high molecular weight (M(w) over 50 kDa) beta-cyclodextrin-based polymers (2-4) with pendant functionality (carboxylate). 2-4 are all highly soluble in aqueous solutions (over 200 mg/mL). 20-O-trifluoroglycinylcamptothecin, 5a, and 20-O-trifluoroglycinylglycinylglycinylcamptothecin, 5b, are synthesized and conjugated to 2 to give polymer-camptothecin (CPT) prodrugs. The solubility of CPT is increased by more than three orders of magnitude when it is conjugated to 2. The rates of CPT release from the conjugates HGGG6 (high molecular weight polymer (M(w) 97 kDa), glyglygly linker and 6 wt % CPT loading) and HG6 (high MW polymer (M(w) 97 kDa), gly linker and 6 wt % CPT loading) in either mouse or human plasma are dramatically accelerated over the rates of pure hydrolysis at pH = 7.4, indicating the presence of enzymatic cleavage as a rate-determining step at this pH in the release of the CPT. The pH of aqueous solution has a large effect on hydrolysis rate of CPT from HGGG6 and HG6; the lower the pH, the slower the rate in the range at 4.1 <or= pH <or= 13.1. The IC(50)'s of polymer 2e, CPT, and the CPT conjugates HG6 and HGGG6 are found to be cell-line dependent with LS174T, HT29, A2780, and PC3 cells using in vitro MTT assays. The parent polymer 2e has very low toxicity to all cultured cells tested.