Therapeutic potential of cladribine in combination with STAT3 inhibitor against multiple myeloma.
Bottom Line: Meanwhile, treatment with cladribine led to a remarkable reduction of the phosphorylated STAT3 (P-STAT3), but had little effect on STAT3 protein levels.Cladribine exhibited inhibitory effects on MM cells in vitro.Our data suggest that MM patients with the features of MM1.S cells may particularly benefit from cladribine monotherapy, whereas cladribine in combination with STAT3 inhibitor exerts a broader therapeutic potential against MM.
Affiliation: International Medical Centre of PLA General Hospital, Beijing, PR China.Show MeSH
Related in: MedlinePlus
Mentions: To explore whether cladribine might be a potential therapeutic agent against MM, we investigated its anti-proliferative/anti-survival effects on three MM cell lines: U266, RPMI8226 with mutant p53; and MM1.S which retains and expresses WT p53 . Although the three MM cell lines exhibited different sensitivities, cladribine was able to inhibit proliferation/survival of all cells in a dose-dependent manner (Figure 1). While U266 was the least sensitive cell line, MM1.S was the most sensitive one to cladribine. The IC50s of cladribine for U266, RPMI8226, MM1.S cells were approximately 2.43, 0.75, and 0.18 μmol/L, respectively. To determine the molecular mechanisms by which cladribine inhibited proliferation/survival of MM cells, we first investigated the effects of cladribine on cell cycle progression. Both U266 and RPMI8226 cells with mutant p53 were treated with cladribine at the same concentration (2 μmol/L). U266 cells were collected at different time points (24, 48, or 72 hrs), and then analyzed with flow cytometry. Treatment with cladribine gradually increased the percentage of cells in the G1 phase of the cell cycle and reduced the percentage of cells in S phase (Figure 2A). Similar results were obtained in RPMI8226 cells with the treatment of cladribine for 24 hrs (Figure 2B). Cladribine appeared to increase G2-M phase in U266 cells upon 24 hr-treatment, it had no significant effect on G2-M phase either in U266 cells with 48 or 72 hr-treatment or in RPMI8226 cells (Figure 2A &2B). It remains unclear why cladribine affected G2-M phase in U266 cells only by 24 hr-treatment. MM1.S cells were treated with cladribine at a much lower concentration (0.5 μmol/L) for 24 hrs. Cladribine induced a minor increase in G1 phase, decreased the percentage cells in S phase, and had no effect on G2-M phase in MM1.S cells (Figure 2C). Although our cell proliferation assays indicated that the IC50 of cladribine was much lower for MM1.S cells than the IC50s for U266 and RPMI8226 cells (Figure 1), it appeared G1 arrest-induced by cladribine in MM1.S cells was not as profound as that we observed in the other two cell lines (Figure 2). It is likely that the potent anti-proliferative/anti-survival effects of cladribine on MM1.S cells may be mainly due to its strong capability to induce apoptosis as we discovered in the following studies (Figures 3 &4). Collectively, our data suggest that induction of cell cycle G1 arrest contributes to cladribine-mediated growth inhibition in MM cells.
Affiliation: International Medical Centre of PLA General Hospital, Beijing, PR China.