Species Differences in Troxacitabine Pharmacokinetics and Pharmacodynamics

Quantitative determination of talatisamine and its pharmacokinetics and bioavailability in mouse plasma by UPLC-MS/MS

Talatisamine, as the efficacy ingredient of Aconitum, was known as a novel specific blocker for the delayed rectifier K⁺ channels in rat hippocampal neurons. In this study, a rapid, selective and reproducible UPLC-MS/MS separation method was established and fully validated for the quantitative determination of talatisamine levels in ICR (Institute of Cancer Research) mouse blood. A total of 24 healthy male ICR mice were divided into four groups that was administered talatisamine via intravenous at a dose of 1 mg/kg and oral administration of three doses (2, 4, 8 mg/kg). All blood samples were protein precipitate by using acetonitrile with an internal standard (IS) deltaline. The effective chromatographic separation was carried out through an UPLC BEH C18 analytical column (2.1 mm × 50 mm, 1.7 μm) with an initial mobile phase that consisted of acetonitrile and 10 mmol/L ammonium acetate aqueous solution (containing 0.1% formic acid) with a gradient elution pumped at a flow rate of 0.4 mL/min. Also, an electrospray ionization (ESI) was applied to quantify the talatisamine in the positive ions mode. The method validation demonstrated good linearity over the range of 1-1000 ng/mL (r² ≥ 0.9993) for talatisamine in mouse blood with a lower limit of quantification (LLOQ) at 1 ng/mL. The accuracy values of the method were within 89.4% to 113.3%, and the matrix effects were between 103.2% and 106.3%. The mean extraction recoveries for talatisamine obtained from four concentrations of QC blood samples were exceeded 71.7%, and the relative standard deviation (RSD) both of intra- and inter-day precision values for replicate quality control samples did not exceed 15% respectively for all analytes during the assay validation. This method was successfully applied to the evaluation of the pharmacokinetic of talatisamine, regardless of intragastric or intravenous administration in mice. Based on the pharmacokinetics data, the bioavailability of talatisamine in mice was >65.0% after oral administration, exhibiting an excellent oral absorption.

Cordycepin Suppresses Endothelial Cell Proliferation, Migration, Angiogenesis, and Tumor Growth by Regulating Focal Adhesion Kinase and p53

Focal adhesion kinase (FAK) plays an important role in vascular development, including the regulation of endothelial cell (EC) adhesion, migration, proliferation, and survival. 3'-deoxyadenosine (cordycepin) is known to suppress FAK expression, cell migration, and the epithelial⁻mesenchymal transition in hepatocellular carcinoma (HCC). However, whether cordycepin affects FAK expression and cellular functions in ECs and the specific molecular mechanism remain unclear. In this study, we found that cordycepin suppressed FAK expression and the phosphorylation of FAK (p-FAK) at Tyr397 in ECs. Cordycepin inhibited the proliferation, wound healing, transwell migration, and tube formation of ECs. Confocal microscopy revealed that cordycepin significantly reduced FAK expression and decreased focal adhesion number of ECs. The suppressed expression of FAK was accompanied by induced p53 and p21 expression in ECs. Finally, we demonstrated that cordycepin suppressed angiogenesis in an in vivo angiogenesis assay and reduced HCC tumor growth in a xenograft nude mice model. Our study indicated that cordycepin could attenuate cell proliferation and migration and may result in the impairment of the angiogenesis process and tumor growth via downregulation of FAK and induction of p53 and p21 in ECs. Therefore, cordycepin may be used as a potential adjuvant for cancer therapy.

Pharmacokinetics and Bioavailability Study of Monocrotaline in Mouse Blood by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND AND AIMS

The present study aimed to develop a simple and sensitive method for quantitative determination of monocrotaline (MCT) in mouse blood employing ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI/MS/MS) using rhynchophylline as an internal standard.

METHODS

Proteins present in the blood samples were precipitated using acetonitrile. MCT was separated using a 1.7-μm ethylene bridged hybrid (BEH) C18 column (2.1 mm × 50 mm) with a gradient elution program and a constant flow rate of 0.4 mL/min. The LC mobile phase consisted of 10 mmol/L ammonium acetate (containing 0.1% formic acid) and acetonitrile. The total elution time was 4.0 min. The analytes were detected on a UPLC-ESI mass spectrometer in multiple reaction monitoring (MRM) mode and quantified.

RESULTS

The new method for the determination of MCT has a satisfactory linear detection range of 1-2000 ng/mL and excellent linearity (r = 0.9971). The lower limit of quantification (LLOQ) of MCT is 1.0 ng/mL. Intra- and interassay precisions of MCT were ≤13% with an accuracy from 96.2% to 106.6%. The average recovery of the new method was >75.0%, and matrix effects were between 89.0% and 94.3%. Based on the pharmacokinetics data, the bioavailability of MCT in mice was 88.3% after oral administration.

CONCLUSIONS

The results suggest that the newly standardized method for quantitative determination of MCT in whole blood is fast, reliable, specific, sensitive, and suitable for pharmacokinetic studies of MCT after intravenous or intragastric administration.

Troxacitabine in acute leukemia

Troxacitabine (Troxatyl; BCH-4556; (-)-2'-deoxy-3'-oxacytadine) is the first synthetic l-nucleoside enantiomer to demonstrate broad spectrum cytotoxic activity. It was obtained by exchanging the sulphur endocyclic atom with oxygen in the structure of lamivudine, following the discovery that this agent had cytotoxic, as well as anti-viral activity. The unique "unnatural" stereochemistry of troxacitabine has produced impressive cytotoxic potency against a wide range of malignancies in the laboratory which led to its selection for clinical development. The initial trials with troxacitabine have established its efficacy in both solid and haematological malignancies, including those resistant to ara-C (cytarabine). This review will consider troxacitabine in terms of its pharmacology, mode of action, pharmacokinetics, tolerability and clinical efficacy.

Novel tubulin polymerization inhibitors overcome multidrug resistance and reduce melanoma lung metastasis

PURPOSE

To evaluate abilities of 2-aryl-4-benzoyl-imidazoles (ABI) to overcome multidrug resistance (MDR), define their cellular target, and assess in vivo antimelanoma efficacy.

METHODS

MDR cell lines that overexpressed P-glycoprotein, MDR-associated proteins, and breast cancer resistance protein were used to evaluate ABI ability to overcome MDR. Cell cycle analysis, molecular modeling, and microtubule imaging were used to define ABI cellular target. SHO mice bearing A375 human melanoma xenograft were used to evaluate ABI in vivo antitumor activity. B16-F10/C57BL mouse melanoma lung metastasis model was used to test ABI efficacy to inhibit tumor lung metastasis.

RESULTS

ABIs showed similar potency to MDR cells compared to matching parent cells. ABIs were identified to target tubulin on the colchicine binding site. After 31 days of treatment, ABI-288 dosed at 25 mg/kg inhibited melanoma tumor growth by 69%; dacarbazine at 60 mg/kg inhibited growth by 52%. ABI-274 dosed at 25 mg/kg showed better lung metastasis inhibition than dacarbazine at 60 mg/kg.

CONCLUSIONS

This new class of antimitotic compounds can overcome several clinically important drug resistant mechanisms in vitro and are effective in inhibiting melanoma lung metastasis in vivo, supporting their further development.

A phase II multicenter study of troxacitabine in relapsed or refractory lymphoproliferative neoplasms or multiple myeloma

Options for patients with relapsed/refractory lymphoproliferative disorders and multiple myeloma are currently limited. Troxacitabine has shown promise in preclinical studies in a variety of malignancies; hence, the current study was conducted to evaluate the activity of troxacitabine in relapsed or refractory lymphoid malignancies. This was a phase II, open-label, multinational, multicenter study of patients with relapsed or refractory lymphoproliferative disorders or multiple myeloma. Thirty-four adults were enrolled in the study and received the study drug at either 5.4 mg/m2 (n = 16) or 4.3 mg/m2 (n = 18). The dose was decided in a phase I study, during which dose escalation was carried to reach a maximum tolerated dose with an acceptable toxicity profile. Two separate phase I studies were performed in Europe and the US. Troxacitabine was administered by intravenous infusion over 30 min daily for days 1 - 5 every 4 weeks. Treatment was continued to disease progression or until the subjects met criteria for withdrawal or unacceptable toxicities were evident as outlined in the protocol. Two patients had a partial response (PR) to treatment with troxacitabine to yield an overall response rate of 13%. There were no complete responses seen with the drug. Stable disease was achieved in 15 patients (44%). All patients had at least one treatment related adverse event, which led to six withdrawals from the study. Hematologic toxicity constituted the most common adverse events. Serious adverse effects were seen in 62% of patients. None of the 13 deaths were attributed directly to troxacitabine. As a single agent, troxacitabine has limited benefit in patients with advanced lymphoproliferative disorders or multiple myeloma. Future studies will be needed to address modified dosing according to emerging pharmacokinetic and pharmacodynamic data and combination therapy which may lead to improved clinical benefit for troxacitabine in hematologic malignancies.

Effect of hypoxia on the expression of phosphoglycerate kinase and antitumor activity of troxacitabine and gemcitabine in non-small cell lung carcinoma

Beta-L-dioxolane-cytidine (L-OddC; BCH-4556; troxacitabine), a novel L-configuration deoxycytidine analogue, was under clinical trials for treating cancer. The cytotoxicity of L-OddC is dependent on its phosphorylation to L-OddCTP by phosphoglycerate kinase (PGK) and its subsequent addition into nuclear DNA. Because PGK is induced with hypoxia, the expression of hypoxia-inducible factor-1alpha and PGK of H460 cells (human non-small cell lung carcinoma) in vitro and in vivo was studied. In culture, hypoxic treatment induced the protein expression of PGK by 3-fold but had no effect on the protein expression of other L-OddC metabolism-associated enzymes such as apurinic/apyrimidinic endonuclease-1, deoxycytidine kinase, CMP kinase, and nM23 H1. Using a clonogenic assay, hypoxic treatment of H460 cells rendered cells 4-fold more susceptible to L-OddC but not to gemcitabine (dFdC) following exposure to drugs for one generation. Using hypoxia response element-luciferase reporter system, Western blotting, and immunohistochemistry, it was found that hypoxia-inducible factor-1alpha and PGK expression increased and could be correlated to tumor size. Despite dFdC being more toxic than L-OddC in cell culture, L-OddC (300 mg/kg i.p.) had a stronger antitumor activity than dFdC in H460 xenograft-bearing nude mice. Furthermore, L-OddC retained approximately 50% of its antitumor activity with oral gavage compared with i.p. delivery. Oral administration of L-OddC (600 mg/kg p.o.) had a similar area under the curve value compared with i.p. injection of dFdC (300 mg/kg i.p.). In conclusion, the hypoxia, which commonly exists in non-small cell lung carcinoma or other solid tumors resistant to radiotherapy or chemotherapy, is a favorable determinant to enhance the antitumor activity of L-OddC in vivo.

Phase I study of troxacitabine administered by continuous infusion in subjects with advanced solid malignancies

BACKGROUND

Troxacitabine is a novel L-nucleoside analogue. Preclinical studies showed improved activity with infusions of at least 3 days compared with bolus regimens, especially at concentrations >20 ng/ml. This phase I study tested the feasibility of achieving a troxacitabine steady-state concentration of 20 ng/ml for at least 72 h in patients with solid tumors.

PATIENTS AND METHODS

Patients with solid tumors received troxacitabine as a progressively longer infusion on days 1-4 of a 28-day cycle. The initial length of infusion and infusion rate were 48 h and 3 mg/m(2)/day.

RESULTS

Twenty-one patients were treated at infusion lengths that increased from 48 to 72 h and then 96 h. The infusion rate was decreased from 3 to 1.88 mg/m(2)/day due to toxicity. Dose-limiting toxicities consisted of grade 4 neutropenia (three) and grade 3 constipation (one). The maximum tolerated dose of continuous infusion troxacitabine in patients with solid tumors is 7.5 mg/m(2) administered over 96 h. This dose level resulted in steady-state drug concentration of at least 20 ng/ml for 72 h.

CONCLUSIONS

Administration of troxacitabine by continuous infusion achieved the prospectively defined target plasma concentration. Pharmacokinetics (PK) modeling coupled with real-time PK assessment was an efficient approach to conduct hypothesis-driven phase I trials.

Troxacitabine in leukemia

Troxacitabine (Troxatyl; BCH-4556; (-)-2'-deoxy-3'-oxacytadine) is the first synthetic l-nucleoside enantiomer to demonstrate broad spectrum cytotoxic activity. It was obtained by exchanging the sulphur endocyclic atom with oxygen in the structure of lamivudine, following the discovery that this agent had cytotoxic, as well as anti-viral activity. The unique "unnatural" stereochemistry of troxacitabine has produced impressive cytotoxic potency against a wide range of malignancies in the laboratory which led to its selection for clinical development. The initial trials with troxacitabine have established its efficacy in both solid and haematological malignancies, including those resistant to ara-C (cytarabine). This review will consider troxacitabine in terms of its pharmacology, mode of action, pharmacokinetics, toxicities, and clinical efficacy.

The Impact of Hypoxic Treatment on the Expression of Phosphoglycerate Kinase and the Cytotoxicity of Troxacitabine and Gemcitabine

beta-L-Dioxolane-cytidine (L-OddC, Troxacitabine, BCH-4556), a novel L-configuration deoxycytidine analog, is under clinical trials for treating cancer. The cytotoxicity of L-OddC is dependent on the amount of the triphosphate form (L-OddCTP) in nuclear DNA. Phosphoglycerate kinase (PGK), a downstream protein of hypoxia-inducible-factor-1alpha (HIF-1alpha), is responsible for the phosphorylation of the diphosphate to the triphosphate of L-OddC. In this study, we studied the impact of hypoxia on the metabolism and the cytotoxicity of L-OddC and beta-d-2',2'-difluorodeoxycytidine (dFdC) in several human tumor cell lines including HepG2, Hep3B, A673, Panc-1, and RKO. Hypoxic treatment induced the protein expression of PGK 3-fold but had no effect on the protein expression of APE-1, dCK, CMPK, and nM23 H1. Hypoxic treatment increased L-OddCTP formation and incorporation of L-OddC into DNA, but it decreased the uptake and incorporation of dFdC, which correlated with the reduction of hENT1, hENT2, and hCNT2 expression. Using a clonogenic assay, hypoxic treatment of cells made them 2- to 3-fold more susceptible to L-OddC but not to dFdC after exposure to drugs for one generation. Dimethyloxallyl glycine enhanced the cytotoxicity of L-OddC but not dFdC in Panc-1 cells under normoxic conditions. Overexpression or down-regulation of PGK using transient transfection of pcDNA5-PGK or inducible shRNA in RKO cells affected the cytotoxicity of L-OddC but not that of dFdC. The knockdown of HIF-1alpha in inducible shRNA in RKO cells reduced the cytotoxicity of L-OddC but not dFdC under hypoxic conditions. In conclusion, hypoxia is an important factor that may potentiate the activity of L-OddC.

Phase I/II Study of Continuous-Infusion Troxacitabine in Refractory Acute Myeloid Leukemia

Purpose

Troxacitabine is a non-natural nucleoside analog with unique structural and metabolic features. Bolus intravenous (IV) troxacitabine regimens have shown significant activity in patients with refractory acute myeloid leukemia (AML) and preclinical data suggest that administration via continuous infusion may result in enhanced antitumor activity.

Patients and Methods

Patients with refractory AML initially received troxacitabine 10.1 mg/m2 by continuous IV infusion (CIVI) for 48 hours. Infusion duration and daily dose were increased in subsequent patient cohorts.

Results

Forty-eight patients, median age 58 years (range, 21 to 81 years), were treated. Dose-limiting toxicities were mucositis and hand-foot syndrome, and 12.0 mg/m2/d for 5 days was established as the maximum-tolerated dose. Seven patients (15%) achieved complete remission (CR) or CR with incomplete platelet recovery (CRp), with a median survival among responders of 12 months. Steady-state concentrations of troxacitabine were found to be linearly and inversely proportionally related to calculated creatinine clearance at doses of 10.1 and 12.0 mg/m2/d. All patients responding to troxacitabine had steady-state serum drug concentration of more than approximately 80 ng/mL. In 27 patients achieving target troxacitabine plasma concentrations (ie, approximately 80 ng/mL) the CR + CRp rate was 26%.

Conclusion

Troxacitabine administered as a CIVI allows a significant increase in dose-intensity in comparison to IV bolus regimens, has antileukemic activity, and warrants additional investigation in patients with refractory AML. The recommended phase II study dose is 12.0 mg/m2 daily CIVI for 5 days.

l-Nucleoside enantiomers as antivirals drugs: A mini-review

The discovery that some nucleoside analogues endowed with the unnatural L-configuration can possess biological activities has been a significant breakthrough in antiviral chemotherapy. In this regard, lamivudine (3TC) was the first L-nucleoside enantiomer approved against HIV and HBV, and several other L-nucleosides are currently under clinical development as antiviral agents.

Apurinic/apyrimidinic endonuclease-1 protein level is associated with the cytotoxicity of L-configuration deoxycytidine analogs (troxacitabine and beta-L-2',3'-dideoxy-2',3'-didehydro-5-fluorocytidine) but not D-configuration deoxycytidine analogs (gemcitabine and beta-D-arabinofuranosylcytosine)

Beta-L-dioxolane-cytidine (L-OddC, BCH-4556, Troxacitabine), a novel L-configuration deoxycytidine analog, is under phase III clinical trial for cancer treatment. We showed that human apurinic/apyrimidinic endonuclease (APE-1) has exonuclease activity for preferentially removing L-OddC and other L-configuration nucleosides over D-configuration nucleosides from the 3' terminus of DNA in vitro. In this study, we examined whether APE-1 protein plays a role in the cytotoxicity of L-OddC. We established RKO (human colorectal carcinoma) cell lines that can be induced by doxycycline to overexpress 4- to 5-fold either APE-1 wild type (wt), C65A (redox deficient), E96A (exonuclease deficient), or E96Q (exonuclease deficient) mutants and to down-regulate endogenous APE-1 by short hairpin RNA to 10% of the original level. Clonogenic results indicated that the induction of wt or C65A, but not E96A or E96Q, made cells approximately 2-fold resistant to L-OddC and beta-L-2',3'-dideoxy-2',3'-didehydro-5-fluorocytidine (L-Fd4C), whereas the down-regulation of APE-1 sensitized cells by approximately 2-fold to L-OddC and L-Fd4C. The alteration of APE-1 in cells did not change the sensitivity of these cells to beta-D-2',2'-difluorodeoxycytidine (dFdC; gemcitabine) and beta-D-arabinofuranosylcytosine (AraC), both of which are D-configuration deoxycytidine analogs. The DNA incorporation of L-OddC, but not that of dFdC, was decreased by the induction of wt APE-1 but not E96A mutant and was increased by the down-regulation of APE-1. The rate of retention of L-OddC was inversely correlated to the level of APE-1 in isolated nuclei; however, this was not the case for dFdC. In conclusion, this study supports the hypothesis that APE-1 plays a critical role in the actions of L-configuration but not D-configuration nucleoside analogs.