The radiosensitizing effect of fluorocyclopentenyl-cytosine (RX-3117) in ovarian and lung cancer cell lines

Abstract

RX-3117 (fluorocyclopentenyl-cytosine) is a novel cytidine analog currently being evaluated in a Phase Ib clinical trial in cancer patients with solid tumors. The radiosensitizing effect of RX-3117 was studied in A2780 ovarian cancer cells and non-small cell lung cancer cell lines and related to cell survival and the effect on cell cycle and cell cycle proteins. RX-3117 has a schedule-dependent radiosensitizing effect, but only at pre-incubation (dose modifying factors: 1.4-1.8), observed at pulse and fractionated irradiation. Radiosensitizion was also seen in a three-dimensional spheroid model. At the low radiosensitizing concentration, RX-3117 in combination with radiation led to an accumulation of cells in S-phase, which was accompanied with an increase of cell cycle proteins such as p-Chk2 and p-cdc25C. In addition, RX-3117 caused DNA damage and increased apoptosis. In conclusion, our in vitro experiments showed a radiosensitizing effect of RX-3117.

RX-3117 (fluorocyclopentenyl cytosine): a novel specific antimetabolite for selective cancer treatment

“…RX-3117 and radiation were also used to investigate the cell cycle distribution. RX-3117 and irradiation led to accumulation of cells in G2 and S phase [29]. RX-3117 might be an effective radiosensitizing agent for NSCLC.…”

“…RX-3117 has also been evaluated for its radiosensitizing potential. Firstly, using a clonogenic assay, it was demonstrated that pre-incubation of cells with RX-3117 led to a radiosensitizing effect in the majority of the analyzed cell lines [29]. Moreover, RX-3117 had a significant effect on radiation induced-DNA damage with a delayed DNA repair in irradiated cells, after RX-3117 treatment.…”

“…According to this evidence, RX-3117 mechanism of action was compared with aza-CR, which can be incorporated both to RNA and DNA, but exerts its cytotoxic effect due to its incorporation in the DNA, not affecting RNA integrity as well [12]. The incorporation of RX-3117 into DNA led to DNA damage as found with positive staining for the DNA damage marker gamma H2AX, accumulation of cells in the S-phase, causing apoptosis as shown by increased annexin-5 staining [29] (Figure 4).…”

RX-3117 (Fluorocyclopentenyl-Cytosine)-Mediated Down-Regulation of DNA Methyltransferase 1 Leads to Protein Expression of Tumor-Suppressor Genes and Increased Functionality of the Proton-Coupled Folate Carrier

“…Since DNMT1 expression is cell cycle regulated, this raises the question whether RX-3117 induced DNMT1 down-regulation might be a cell cycle effect. Indeed RX-3117 induces some cell cycle proteins (e.g., CHK2 and cdc25), with an arrest in the S and G2M phase), [33] but whether this is related to DNMT1 down-regulation is unlikely because of the different time-span. Altogether re-activation of TSGs may contribute to the elimination of tumor cells, by inhibition of tumor growth, invasion, and controlling metastasis.…”

“…In addition, this study underlines the relevance of DNA methylation as a potential biomarker for RX-3117 s anti-tumor activity. However, RX-3117 is also known to cause DNA damage by its incorporation into DNA [4,33]. Usually the induction of DNA damage by a nucleoside analog takes more time, so that the effects on DNA methylation may occur earlier then the DNA damage.…”