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Biomedical subjects

Hans W Scheeren

Publications and source records attributed to Hans W Scheeren.

9 recordsLinked to original sources
PubMed2004

A methylester of the glucuronide prodrug DOX-GA3 for improvement of tumor-selective chemotherapy.

The glucuronide prodrug of doxorubicin, DOX-GA3, can be selectively activated in tumors by extracellular human beta-glucuronidase, resulting in a better therapeutic index than doxorubicin. DOX-GA3, however, is rapidly excreted by the kidney. We hypothesized that slow release of DOX-GA3 from its methylester, DOX-mGA3, by esterase activity in blood would result in improved circulation half-life (t(1/2)) of DOX-GA3. DOX-mGA3 was synthesized more efficiently with an overall yield of 60% as compared to 37% in the case of DOX-GA3. We showed that DOX-mGA3 was enzymatically converted to DOX-GA3 with a t(1/2) of approximately 0.5 min in mouse plasma to 2.5 h in human plasma, which was in agreement with differences in esterase activity between species. DOX-mGA3, similar to DOX-GA3, was at least 37-fold less potent than the parent drug doxorubicin in growth inhibition of four different human malignant cell lines in vitro. Incubation of OVCAR-3 cells with DOX-mGA3 in combination with an excess of human beta-glucuronidase (0.05 U mL(-1)) resulted in a similar growth inhibition to that of doxorubicin. Intravenous administration of DOX-mGA3 in FMa-bearing mice resulted in an area under the concentration versus time curve (AUC) of DOX-GA3 in tumor and most normal tissues that was 2.5- to 3-fold higher than after the same dose of DOX-GA3 itself. In tumor tissue, this was accompanied by a 2.7-fold increase in the AUC of doxorubicin from DOX-mGA3 than from DOX-GA3. In conclusion, an advantage of DOX-mGA3 over DOX-GA3 is that this prodrug can be produced with a higher yield. Another important advantage is the improved pharmacokinetics of the lipophilic DOX-mGA3 as compared to that of the hydrophilic DOX-GA3. This effect may even be more pronounced in man, because of the lower plasma esterase activity than measured in mice.

Animals↗
PubMed2004

Plasmin-activated doxorubicin prodrugs containing a spacer reduce tumor growth and angiogenesis without systemic toxicity.

To generate doxorubicin (Dox) specifically at the tumor site, the chemotherapeutic agent was incorporated into a prodrug by linkage to a peptide specifically recognized by plasmin, which is overproduced in many cancers. ST-9905, which contains an elongated self-elimination spacer, is activated more rapidly in vitro by plasmin than is ST-9802. Prodrug activation in vitro depended on the level of urokinase produced by tumor cells and was inhibited by aprotinin, a plasmin inhibitor. Comparison of equimolar concentrations of ST-9905, ST-9802, and Dox in EF43.fgf-4 and MCF7 models revealed that both prodrugs, in sharp contrast to Dox, displayed antiproliferative and antiangiogenic activities without discernible toxicity. Although MCF7 cells are poor urokinase producers in vitro, prodrug efficacy in this model may be explained by production of plasmin by tumor-infiltrating host cells. Mice treated with equitoxic concentrations (maximum tolerated doses) of prodrugs showed 100% survival and negligible body weight loss, in contrast to results after Dox treatment. ST-9905 was substantially more effective than ST-9802 and induced similar tumor growth inhibition as Dox but without apparent toxicity. This finding may be explained by the elongated spacer, which facilitates enzymatic prodrug activation. These data validate both the use of elongated spacers in vivo and the concept of targeting anticancer prodrugs to tumor-associated plasmin.

Adenocarcinoma↗
PubMed2003

High pressure: a promising tool for multicomponent reactions.

In this paper the application of high pressure in multicomponent reactions is discussed. Using high pressure the scope of certain multicomponent reactions can be increased. Reactions are described that can only be performed in a multicomponent fashion when high pressure catalysis is applied. An overview of high pressure catalysed multicomponent reactions is presented with special attention to the domino [4 + 2]/[3 + 2] cycloaddition reaction.

Chemistry, Organic↗
PubMed2002

Novel 20-carbonate linked prodrugs of camptothecin and 9-aminocamptothecin designed for activation by tumour-associated plasmin.

The first prodrugs of camptothecin and 9-aminocamptothecin that are activated by the tumour-associated protease plasmin are reported. The tripartate prodrugs consist of a tripeptide sequence recognised by plasmin, which is linked to the 20-hydroxyl group of the camptothecins via a 1,6-elimination spacer. After selective N-protection of 9-aminocamptothecin with an Aloc group, the promoiety (tripeptide-spacer conjugate) was linked to camptothecin or 9-Aloc-9-aminocamptothecin via a 20-carbonate linkage by reacting parent drugs with the p-nitrophenyl carbonate activated promoiety in the presence of DMAP. Both prodrugs showed to be stable in buffer solution and both parent drugs were released upon incubation in the presence of plasmin. Furthermore, the prodrugs showed an average 10-fold decreased cytotoxicity with respect to their parent drugs upon incubation in seven human tumour cell lines.

Camptothecin↗
PubMed2002

Synthesis of novel paclitaxel prodrugs designed for bioreductive activation in hypoxic tumour tissue.

The syntheses and preliminary evaluation of the first potential bioreductive paclitaxel prodrugs are described. These prodrugs were designed as potential candidates in more selective chemotherapy by targeting hypoxic tumour tissue. Aromatic nitro and azide groups were used as the bioreductive trigger. Generation of paclitaxel occurs after reduction and subsequent 1,6-elimination or 1,8-elimination. All prodrugs are stable in buffer and indeed give paclitaxel after chemical reduction of the aromatic nitro or azide functionality. In aerobic cytotoxicity assays several prodrugs exhibit diminished cytotoxicity. These compounds are interesting candidates for further biological evaluation.

Antineoplastic Agents↗
PubMed2002

Beta-glucuronidase-mediated drug release.

The selective activation of a relatively non-toxic prodrug by an enzyme present only in the tumour should enhance the drug concentration at the tumour site and result in a better anti-tumour effect and a reduction in systemic toxicity as compared to conventional chemotherapy. beta-Glucuronidase is such an enzyme. It is normally expressed in the lysosomes of cells. In larger tumours, however, high levels of the enzyme are present in necrotic areas. Several glucuronide prodrugs have been synthesised that can be activated by beta-glucuronidase. They are relatively non-toxic due to their hydrophilic nature, which prevents them from entering cells and thus from contact with lysosomal beta-glucuronidase. The main problem of glucuronide prodrugs for clinical use is their fast renal clearance. Special attention should be paid to the development of new less hydrophilic prodrugs with slower clearance, as this would result in a prolonged exposure to beta-glucuronidase at the site of the tumour and a reduction of the amount of prodrug needed. A number of interesting anthracyclin-based glucuronide prodrugs have been synthesised and have shown favourable therapeutic effects compared to treatment with the parent drug. The tumoural levels of beta-glucuronidase can even be enhanced by two-step approaches, in which exogenous enzyme is targeted to the tumour by an antibody (ADEPT) or by the gene encoding the enzyme in transduced tumour cells (GDEPT). The ADEPT and GDEPT approaches in combination with glucuronide prodrugs have shown enhanced efficacy in experimental tumour models. Further improvement of ADEPT and GDEPT is warranted to optimise the tumour uptake and retention of antibody-enzyme fusion proteins and the efficiency and safety of current gene delivery methods. In conclusion, it is clear that glucuronide prodrugs hold promise for future use in the treatment of cancer in patients as monotherapy. Enhancement of the therapeutic effects of glucuronide prodrugs, also in patients with small tumour lesions, may possibly be achieved by techniques that target beta-glucuronidase specifically to the site of the tumour.

Animals↗
PubMed2002

Design, synthesis, and biological evaluation of a dual tumor-specific motive containing integrin-targeted plasmin-cleavable doxorubicin prodrug.

The design, synthesis, and initial biological evaluation of a doxorubicin prodrug that contains a dual tumor specific moiety, which allows enhanced tumor recognition potential, is reported. Both a tumor-specific recognition site and a tumor selective enzymatic activation sequence are incorporated in the prodrug. The first tumor-specific sequence is the bicyclic CDCRGDCFC (RGD-4C) peptide that selectively binds alpha v beta 3 and alpha v beta 5 integrins. These integrins are highly overexpressed on invading tumor endothelial cells. The second tumor-specific sequence is a D-Ala-Phe-Lys tripeptide that is selectively recognized by the tumor-associated protease plasmin, which is involved in tumor invasion and metastasis. An aminocaproyl residue was incorporated as a spacer between the two peptide sequences, whereas a self-eliminating 4-aminobenzyl alcohol spacer was inserted between the plasmin substrate and doxorubicin. Although the prodrug showed a decreased binding affinity as compared with the unconjugated reference peptide, it was still a potent ligand for alpha v beta 3 and alpha v beta 5 integrin receptors. The synthesized construct also possessed plasmin substrate properties as demonstrated by doxorubicin release from 1 upon incubation with plasmin. The release of doxorubicin from 1 was not complete, possibly related to low prodrug solubility. In vitro prodrug 1 showed plasmin-dependent cytotoxicity for endothelial cells and HT1080 fibrosarcoma cells. On the basis of these in vitro results, derivatives of 1 with improved water solubility are considered good candidates for additional development and in vivo evaluation of this dual targeting concept.

Amino Acid Sequence↗
PubMedDate not supplied

Synthesis of spirohydantoins and spiro-2,5-diketopiperazines via resin-bound cyclic alpha,alpha-disubstituted alpha-amino esters.

A seven-step solid-phase synthesis of spirohydantoins and an eight-step solid-phase synthesis of spiro-2,5-diketopiperazines is reported. Key intermediate in the synthesis of both compound libraries is the resin-bound cyclic alpha,alpha-disubstituted alpha-amino ester, which can be obtained after selective homogeneous reduction of the aliphatic nitro ester using tin(II) chloride dihydrate. Nitro ester, in turn, is synthesized by a high-pressure-assisted [4 + 2] cycloaddition of resin-bound nitro alkene and butadiene, whereas nitro alkene is obtained by a Knoevenagel condensation of resin-bound nitro acetate with an imine. Novel spirohydantoins are obtained by isocyanate coupling with the resin-bound amino ester 5, followed by cyclization cleavage using a base. Novel spiro-2,5-diketopiperazines are obtained by PyBOP coupling of a Fmoc-protected amino acid with resin-bound amino ester, followed by Fmoc deprotection and an acid-assisted cyclization cleavage. After preparation of seven different resin-bound alpha,alpha-disubstituted alpha-amino esters, a 7 x 8 compound library of spirohydantoins was synthesized using eight different isocyanates, and a 7 x 8 compound library of spiro-2,5-diketopiperazines was synthesized using eight different Fmoc amino acids.

Amino Acids↗