Telomerase inhibition by MST312 reduces tumor growth in vivo. A: Tumor growth shows strong reduction in mice that were treated for 3 weeks with MST312 (40 mg/kg, daily). Radiotherapy alone (10 Gys administrated locally at days 3 and 13) produced a similar effect. No significant improvement was obtained by combination of both therapies. B: H&E of untreated and MST312-treated mice (upper panel) show tumor cells with pyknotic nuclei upon treatment; immunohistochemistry for PCNA and cleaved-caspase 3 (middle panel) demonstrate a reduction in proliferation and increased apoptosis in mice injected with MST312, compared to controls; immunostaining for ALDH (lower panel) also reveals a reduction in the number of labeled cells after administration of the telomerase inhibitor.