Rabacfosadine (GS-9219)

Kinase experiment:

Twenty million PHA-stimulated T cells are incubated with 10 μM[14C]GS-9219 for 24 h. Cells are washed once with tissue culture medium and twice with PBS, incubated in 80% methanol overnight, and centrifuged at 14,000 rpm for 15 min to remove denatured proteins. The methanol extracts are lyophilized and dissolved in the high-performance liquid chromatography (HPLC) loading buffer. A portion of each sample is used for scintillation counting to calculate the total pmoles, and the rest is used for HPLC analysis to calculate the ratio of metabolites. HPLC analysis is done by gradient elution using a Phenomenex Prodigy column (5 μm, ODS3 150×4 mm), where buffer A is 25 mM K2HPO4 (pH 6.0) and 5 mM Tetrabutylammonium bromide and buffer B is 25 mM K2HPO4 (pH 6.0), 70% Acetonitrile, and 5 mM Tetrabutylammonium bromide[1].

Animal experiment:

Dogs[2] Dogs are given alternating doses of Rabacfosadine and Doxorubicin every 3 weeks. Rabacfosadine is administered at a dosage of 1.0 mg/kg as a 30-minute IV infusion on weeks 0, 6, and 12. Doxorubicin is administered at a dosage of 30 mg/m2 (1.0 mg/kg for dogs weighing <15 kg) as an approximately 20-minute IV infusion on weeks 3, 9, and 15. Concurrent cytotoxic chemotherapy of any kind and concurrent corticosteroids are not allowed. A CBC is performed 1 week after the first Rabacfosadine and Doxorubicin treatments (weeks 1 and 4). All dogs have a physical examination with lymph node measurements, owner history, CBC, serum biochemistry profile (SBC), and urinalysis performed at each chemotherapy visit. Thoracic radiographs are recommended at week 15 and approximately every 2 months thereafter in responding dogs. Dose delays, reductions, or both, and supportive treatment for AEs are carried out at the discretion of the attending clinician. Dogs that experienced a complete response (CR) are followed with monthly physical examinations after week 15 until relapse, when they are considered off study. Dogs that experienced partial response (PR) or stable disease (SD) at week 15 are considered off study and censored from analysis at that time. At the time of study withdrawal, dogs are eligible for additional treatment at the discretion of the attending clinician.

References:

[1]. Reiser H, et al. GS-9219--a novel acyclic nucleotide analogue with potent antineoplastic activity in dogs with spontaneous non-Hodgkin's lymphoma. Clin Cancer Res. 2008 May 1;14(9):2824-32.
[2]. Thamm DH, et al. Alternating Rabacfosadine/Doxorubicin: Efficacy and Tolerability in Naïve Canine Multicentric Lymphoma. J Vet Intern Med. 2017 May;31(3):872-878.