Phase I dose-escalating study of TAS-106 in combination with carboplatin in patients with solid tumors

Background TAS-106 was designed to inhibit RNA synthesis by blocking RNA polymerases I, II, and III. Methods This was a single-center, open-label, phase I study to identify the maximum tolerated dose (MTD), pharmacokinetics, and biologic effects of the combination of TAS-106 and carboplatin, following a standard 3 + 3 design. This phase I trial was comprised of a regimen of a 60-min IV infusion of carboplatin on day 1 of each 21-day cycle followed by a 24-h infusion of TAS-106, also on day 1 of each cycle. Results 39 patients were treated (21 male, 18 female, median age 62 years, range 21–80 years). Median number of prior therapies was 4. Maximum Tolerated Dose (MTD) was 3 mg/m² TAS-106 with AU 4 carboplatin. Dose-limiting toxicities were neutropenia and thrombocytopenia, with and without growth factor support. While no patients achieved a complete or partial response, four patients had stable disease lasting ≥4 months, including one patient each with ovarian, non-small cell lung, basal cell and colorectal cancer. Conclusions In summary, the combination of TAS-106 and carboplatin was well-tolerated, and further studies in non-small cell lung and ovarian cancer are warranted to assess the efficacy of this drug combination.

An RNA-directed nucleoside anti-metabolite, 1-(3-C-ethynyl-beta-d-ribo-pentofuranosyl)cytosine (ECyd), elicits antitumor effect via TP53-induced Glycolysis and Apoptosis Regulator (TIGAR) downregulation

1-(3-C-ethynyl-beta-d-ribo-pentofuranosyl)cytosine (ECyd) is a ribose-modified nucleoside analog of cytidine with potent anticancer activity in several cancers. The main antitumor mechanism of this promising RNA-directed nucleoside anti-metabolite is efficient blockade of RNA synthesis in cancer cells. Here, we examined the therapeutic potential of this RNA-directed anti-metabolite in in vitro models of nasopharyngeal cancer (NPC). In a panel of 6 NPC cell lines, ECyd effectively inhibited cellular proliferation at nM concentrations (IC(50): approximately 13-44nM). Moreover, cisplatin-resistant NPC cells were highly sensitive to ECyd (at nM concentration). The ECyd-mediated growth inhibition was associated with G(2)/M cell cycle arrest, PARP cleavage (a hallmark of apoptosis) and Bcl-2 downregulation, indicating induction of apoptosis by ECyd in NPC cells. Unexpectedly, ECyd-induced significant downregulation of TIGAR, a newly described dual regulator of apoptosis and glycolysis. More importantly, this novel action of ECyd on TIGAR was accompanied by marked depletion of NADPH, the major reducing power critically required for cell proliferation and survival. We hypothesized that ECyd-induced TIGAR downregulation was crucially involved in the antitumor activity of ECyd. Indeed, overexpression of TIGAR was able to rescue NPC cells from ECyd-induced growth inhibition, demonstrating a novel mechanistic action of ECyd on TIGAR. We demonstrated for the first time that an RNA-directed nucleoside analog, ECyd, exerts its antitumor activity via downregulation of a novel regulator of apoptosis, TIGAR. Moreover, ECyd may represent a novel therapy for NPC.