Synthesis and biological evaluation of oral prodrugs based on the structure of gemcitabine

Advances in oral delivery of anti-cancer prodrugs

INTRODUCTION

Most anticancer drugs have poor aqueous solubility and low permeability across the gastrointestinal tract. Furthermore, extensive efflux by P-glycoproteins (P-gp) in the small intestine also limits the efficient delivery of anticancer drugs via oral route. Area covered: This review explores the prodrug strategy for oral delivery of anticancer drugs. Different categories of oral anticancer prodrugs along with recent clinical studies have been comprehensively reviewed here. Furthermore, novel anticancer prodrugs such as polymer-prodrugs and lipid-prodrugs have been discussed in detail. Finally, various nanocarrier-based approaches employed for oral delivery of anticancer prodrugs have also been discussed. Expert opinion: Premature degradation of anticancer prodrugs in the gastrointestinal tract could lead to variable pharmacokinetics and undesired toxicity. Despite their increased aqueous solubility, the oral bioavailability of several anticancer prodrugs are limited by their poor permeability across the gastrointestinal tract. These limitations can be overcome by the use of functional excipients (polymers, lipids, amino acids/dipeptides), which are specifically absorbed via transporters and receptor-mediated endocytosis. Oral delivery of anticancer prodrugs using nanocarrier-based drug delivery system is a recent development; however it should be justified based on the comparative advantages of encapsulating prodrug in a nanocarrier versus the use of anticancer prodrug molecule itself.

Characterization of permeability, stability and anti-HIV-1 activity of decitabine and gemcitabine divalerate prodrugs

BACKGROUND

Over 25 drugs have been approved for the treatment of HIV-1 replication. All but one of these drugs is delivered as an oral medication. Previous studies have demonstrated that two drugs, decitabine and gemcitabine, have potent anti-HIV-1 activities and can work together in synergy to reduce HIV-1 infectivity via lethal mutagenesis. For their current indications, decitabine and gemcitabine are delivered intravenously.

METHODS

As an initial step towards the clinical translation of these drugs for the treatment of HIV-1 infection, we synthesized decitabine and gemcitabine prodrugs in order to increase drug permeability, which has generally been shown to correlate with increased bioavailability in vivo. In the present study we investigated the permeability, stability and anti-HIV-1 activity of decitabine and gemcitabine prodrugs and selected the divalerate esters of each as candidates for further investigation.

RESULTS

Our results provide the first demonstration of divalerate prodrugs of decitabine and gemcitabine that are readily permeable, stable and possess anti-HIV-1 activity.

CONCLUSIONS

These observations predict improved oral availability of decitabine and gemcitabine, and warrant further study of their ability to reduce HIV-1 infectivity in vivo.

SL-01, an oral derivative of gemcitabine, inhibited human breast cancer growth through induction of apoptosis

SL-01 is an oral derivative of gemcitabine that was synthesized by introducing the moiety of 3-(dodecyloxycarbonyl) pyrazine-2-carbonyl at N4-position on cytidine ring of gemcitabine. We aimed to evaluate the efficacy of SL-01 on human breast cancer growth. SL-01 significantly inhibited MCF-7 proliferation as estimated by colorimetric assay. Flow cytometry assay indicated the apoptotic induction and cell cycle arrest in G1 phase. SL-01 modulated the expressions of p-ATM, p53 and p21 and decrease of cyclin D1 in MCF-7 cells. Further experiments were performed in a MCF-7 xenografts mouse model. SL-01 by oral administration strongly inhibited MCF-7 xenografts growth. This effect of SL-01 might arise from its roles in the induction of apoptosis. Immunohistochemistry assay showed the increase of TUNEL staining cells. Western blotting indicated the modulation of apoptotic proteins in SL-01-treated xenografts. During the course of study, there was no evidence of toxicity to mice. In contrast, the decrease of neutrophil cells in peripheral and increase of AST and ALT levels in serum were observed in the gemcitabine-treated mice.

CONCLUSION

SL-01 possessed similar activity against human breast cancer growth with gemcitabine, whereas, with lower toxicity to gemcitabine. SL-01 is a potent oral agent that may supplant the use of gemcitabine.

Pharmacokinetics and metabolism of SL-01, a prodrug of gemcitabine, in rats

PURPOSE

SL-01, dodecyl-3-((1-((2R,4R,5R)-3,3-difluoro-4-hydroxy-5-(hydroxymethyl)-tetrahydrofuran-2-yl)-2-oxo-1,2-dihydropyrimidin-4-yl) carbamoyl) pyrazine-2-carboxylate, is a prodrug of gemcitabine. Our previous reports suggested that SL-01 possesses superior bioavailability and anticancer activity to gemcitabine in mice. In this study, its pharmacokinetics and metabolisms were investigated in rats.

METHODS

The pharmacokinetics of SL-01 was studied following intravenous or oral administration of SL-01 to Sprague-Dawley rats. The metabolites profile of SL-01 was further determined in rats receiving intravenous administration of SL-01. Blood samples were analyzed by using LC-MS or LC-MS/MS assay.

RESULTS

Following administration with SL-01 intravenously or orally, SL-01, plasma gemcitabine released from SL-01 as well as the sum of gemcitabine (gemcitabine converted from SL-01 and plasma gemcitabine) exhibited higher values of V z /F and CL z /F, and longer MRT and t 1/2 than those of gemcitabine administered intravenously. The C max of gemcitabine produced by intravenous SL-01 was higher than that of gemcitabine dosed intravenously. The absolute bioavailability for the sum of gemcitabine was 32.2 % for intravenous and 22.2 % for oral administration with SL-01, respectively. After a single intravenous administration, a total of 5 components (M1, M2, M3, M4, and M5) were detected and identified as the metabolites of SL-01 in the plasma of rats. M1 and M2 were formed from the methylation and reduction of SL-01, respectively. Hydrolysis of the amide bond of SL-01 gave M3 and M4. M5 was produced from further dealkylation of M3.

CONCLUSIONS

SL-01 displayed improved absorption, good distribution, high clearance, long mean residence time, and moderate bioavailability after administered intravenously or orally to rats. The major metabolic pathways of SL-01 involved methylation, reduction, hydrolysis, and dealkylation. These results suggested that SL-01 acts as a prodrug of gemcitabine in rats.