Radiation sensitivity assay with a panel of patient-derived spheroids of small cell carcinoma of the cervix.

Small cell carcinoma of the uterine cervix (SCCC) is a rare cancer with a poor prognosis for which no standard treatment exists. Here, we successfully established panels of patient-derived spheroid cultures from six SCCC patient samples by cancer tissue-originated spheroids (CTOS) method. To assess the intrinsic radiosensitivity and mechanism of radioresistance in individual SCCC patients, we further developed an in vitro sensitivity assay for radiation. Radiation sensitivity in the CTOS assay varied among individual cases and was consistent with in vivo radiation sensitivity using CTOS-derived xenograft tumors in the examined cases. Furthermore, by comparing gene expression in CTOSs with different radiosensitivity, we found that expression of hypoxia-inducible factor-1α (HIF-1α) target genes was upregulated in resistant CTOSs. HIF-1α protein levels increased several hours after irradiation. In a radioresistant CTOS, an inhibitor of heat shock protein 90 (HSP90) suppressed radiation-induced HIF-1α expression. Suppression of HIF-1α by small hairpin RNA significantly enhanced the effect of radiation, at least in part by promoting radiation-induced apoptosis. HSP90 inhibitor also increased radiation sensitivity. Our results indicate that radiation-induced HIF-1α upregulation was one mechanism of radioresistance in a radioresistant SCCC CTOS. Accumulating CTOS lines may provide a good platform to study characters of rare cancers like SCCC.