Limits...
N-alkynyl derivatives of 5-fluorouracil: susceptibility to palladium-mediated dealkylation and toxigenicity in cancer cell culture.

Weiss JT, Fraser C, Rubio-Ruiz B, Myers SH, Crispin R, Dawson JC, Brunton VG, Patton EE, Carragher NO, Unciti-Broceta A - Front Chem (2014)

Bottom Line: Palladium-activated prodrug therapy is an experimental therapeutic approach that relies on the unique chemical properties and biocompatibility of heterogeneous palladium catalysis to enable the spatially-controlled in vivo conversion of a biochemically-stable prodrug into its active form.To provide additional insight on the properties of this system, we have investigated different N1-alkynyl derivatives of 5-fluorouracil and shown that the presence of substituents near the triple bond influence negatively on its sensitivity to palladium catalysis under biocompatible conditions.Comparative studies of the N1- vs. the N3-propargyl derivatives of 5-fluorouracil revealed that masking each or both positions equally led to inactive derivatives (>200-fold reduction of cytotoxicity relative to the unmodified drug), whereas the depropargylation process occurred faster at the N1 position than at the N3, thus resulting in greater toxigenic properties in cancer cell culture.

View Article: PubMed Central - PubMed

Affiliation: Edinburgh Cancer Research UK Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh Edinburgh, UK.

ABSTRACT
Palladium-activated prodrug therapy is an experimental therapeutic approach that relies on the unique chemical properties and biocompatibility of heterogeneous palladium catalysis to enable the spatially-controlled in vivo conversion of a biochemically-stable prodrug into its active form. This strategy, which would allow inducing local activation of systemically administered drug precursors by mediation of an implantable activating device made of Pd(0), has been proposed by our group as a way to reach therapeutic levels of the active drug in the affected tissue/organ while reducing its systemic toxicity. In the seminal study of such an approach, we reported that propargylation of the N1 position of 5-fluorouracil suppressed the drug's cytotoxic properties, showed high stability in cell culture and facilitated the bioorthogonal restoration of the drug's pharmacological activity in the presence of extracellular Pd(0)-functionalized resins. To provide additional insight on the properties of this system, we have investigated different N1-alkynyl derivatives of 5-fluorouracil and shown that the presence of substituents near the triple bond influence negatively on its sensitivity to palladium catalysis under biocompatible conditions. Comparative studies of the N1- vs. the N3-propargyl derivatives of 5-fluorouracil revealed that masking each or both positions equally led to inactive derivatives (>200-fold reduction of cytotoxicity relative to the unmodified drug), whereas the depropargylation process occurred faster at the N1 position than at the N3, thus resulting in greater toxigenic properties in cancer cell culture.

No MeSH data available.


Related in: MedlinePlus

Synthesis of compounds 3a-e (upper panel) and compounds 6, 7 (lower panel).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4114543&req=5

Figure 2: Synthesis of compounds 3a-e (upper panel) and compounds 6, 7 (lower panel).

Mentions: The clinical application and effective therapeutic response to several chemotherapeutics with a cytotoxic mechanism-of-action, including 5FU, is severely limited by numerous dose-limiting toxicities in patients. As previously reported (Weiss et al., 2014a), functionalization of the N1 position of 5FU with a propargyl group resulted in a bioorthogonal prodrug (3a) prone to conversion into 5FU in the presence of Pd0-resins both in PBS (biocompatible solution) and cell culture; a strategy that could allow for the reduction of systemic side effects of 5FU treatment. In order to investigate whether other alkynes could increase the rate of the dealkylation process, a set of N1-alkynyl derivatives of 5FU were synthesized following the procedure described in Figure 2. Subsequently, to study the susceptibility of derivatives 3b-e to palladium catalysis, Pd0-resins were used as the heterogeneous catalyst and palladium-labile 5-fluoro-1-propargyluracil (3a) as positive control (Figure 3A). Compounds 3a-e (100 μM) and Pd0-resins [1 mg/mL, (Pd0) = 400 μM] were dispersed in PBS (isotonic buffered solution at pH =7.4), incubated at 37°C for 24 h and the reaction crudes analyzed by HPLC using a UV detector. While compound 3a led to 100% conversion in less than 24 h, compounds 3b-e generated considerably lower levels of 5FU, 1 (see small table in Figure 3A). The susceptibility to palladium of compounds 3c-e (containing a methyl, ethyl and benzyl group at the terminal carbon of the triple bond, respectively) was inversely proportional to the size of the moiety, indicating that the lesser the accessibility to the triple bond, the slower the reaction occurs. 24 h reaction of compound 3b with Pd0-resins resulted in a 26% conversion into 5FU, a clear improvement over derivatives 3c-e but significantly inferior to the reactivity of 3a toward palladium. These results indicate that steric hindrance is a limiting factor in the reaction kinetics and, therefore, suggest that the non-substituted propargyl group is the optimal choice to generate palladium-labile bioorthogonal probes and prodrugs.


N-alkynyl derivatives of 5-fluorouracil: susceptibility to palladium-mediated dealkylation and toxigenicity in cancer cell culture.

Weiss JT, Fraser C, Rubio-Ruiz B, Myers SH, Crispin R, Dawson JC, Brunton VG, Patton EE, Carragher NO, Unciti-Broceta A - Front Chem (2014)

Synthesis of compounds 3a-e (upper panel) and compounds 6, 7 (lower panel).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4114543&req=5

Figure 2: Synthesis of compounds 3a-e (upper panel) and compounds 6, 7 (lower panel).
Mentions: The clinical application and effective therapeutic response to several chemotherapeutics with a cytotoxic mechanism-of-action, including 5FU, is severely limited by numerous dose-limiting toxicities in patients. As previously reported (Weiss et al., 2014a), functionalization of the N1 position of 5FU with a propargyl group resulted in a bioorthogonal prodrug (3a) prone to conversion into 5FU in the presence of Pd0-resins both in PBS (biocompatible solution) and cell culture; a strategy that could allow for the reduction of systemic side effects of 5FU treatment. In order to investigate whether other alkynes could increase the rate of the dealkylation process, a set of N1-alkynyl derivatives of 5FU were synthesized following the procedure described in Figure 2. Subsequently, to study the susceptibility of derivatives 3b-e to palladium catalysis, Pd0-resins were used as the heterogeneous catalyst and palladium-labile 5-fluoro-1-propargyluracil (3a) as positive control (Figure 3A). Compounds 3a-e (100 μM) and Pd0-resins [1 mg/mL, (Pd0) = 400 μM] were dispersed in PBS (isotonic buffered solution at pH =7.4), incubated at 37°C for 24 h and the reaction crudes analyzed by HPLC using a UV detector. While compound 3a led to 100% conversion in less than 24 h, compounds 3b-e generated considerably lower levels of 5FU, 1 (see small table in Figure 3A). The susceptibility to palladium of compounds 3c-e (containing a methyl, ethyl and benzyl group at the terminal carbon of the triple bond, respectively) was inversely proportional to the size of the moiety, indicating that the lesser the accessibility to the triple bond, the slower the reaction occurs. 24 h reaction of compound 3b with Pd0-resins resulted in a 26% conversion into 5FU, a clear improvement over derivatives 3c-e but significantly inferior to the reactivity of 3a toward palladium. These results indicate that steric hindrance is a limiting factor in the reaction kinetics and, therefore, suggest that the non-substituted propargyl group is the optimal choice to generate palladium-labile bioorthogonal probes and prodrugs.

Bottom Line: Palladium-activated prodrug therapy is an experimental therapeutic approach that relies on the unique chemical properties and biocompatibility of heterogeneous palladium catalysis to enable the spatially-controlled in vivo conversion of a biochemically-stable prodrug into its active form.To provide additional insight on the properties of this system, we have investigated different N1-alkynyl derivatives of 5-fluorouracil and shown that the presence of substituents near the triple bond influence negatively on its sensitivity to palladium catalysis under biocompatible conditions.Comparative studies of the N1- vs. the N3-propargyl derivatives of 5-fluorouracil revealed that masking each or both positions equally led to inactive derivatives (>200-fold reduction of cytotoxicity relative to the unmodified drug), whereas the depropargylation process occurred faster at the N1 position than at the N3, thus resulting in greater toxigenic properties in cancer cell culture.

View Article: PubMed Central - PubMed

Affiliation: Edinburgh Cancer Research UK Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh Edinburgh, UK.

ABSTRACT
Palladium-activated prodrug therapy is an experimental therapeutic approach that relies on the unique chemical properties and biocompatibility of heterogeneous palladium catalysis to enable the spatially-controlled in vivo conversion of a biochemically-stable prodrug into its active form. This strategy, which would allow inducing local activation of systemically administered drug precursors by mediation of an implantable activating device made of Pd(0), has been proposed by our group as a way to reach therapeutic levels of the active drug in the affected tissue/organ while reducing its systemic toxicity. In the seminal study of such an approach, we reported that propargylation of the N1 position of 5-fluorouracil suppressed the drug's cytotoxic properties, showed high stability in cell culture and facilitated the bioorthogonal restoration of the drug's pharmacological activity in the presence of extracellular Pd(0)-functionalized resins. To provide additional insight on the properties of this system, we have investigated different N1-alkynyl derivatives of 5-fluorouracil and shown that the presence of substituents near the triple bond influence negatively on its sensitivity to palladium catalysis under biocompatible conditions. Comparative studies of the N1- vs. the N3-propargyl derivatives of 5-fluorouracil revealed that masking each or both positions equally led to inactive derivatives (>200-fold reduction of cytotoxicity relative to the unmodified drug), whereas the depropargylation process occurred faster at the N1 position than at the N3, thus resulting in greater toxigenic properties in cancer cell culture.

No MeSH data available.


Related in: MedlinePlus