Effect of S9788 on the efficiency of doxorubicin in vivo and in vitro in medullary thyroid carcinoma xenograft

Incretin receptors in non-neoplastic and neoplastic thyroid C cells in rodents and humans: relevance for incretin-based diabetes therapy

While incretins are of great interest for the therapy of diabetes 2, the focus has recently been brought to the thyroid, since rodents treated with glucagon-like peptide-1 (GLP-1) analogs were found to occasionally develop medullary thyroid carcinomas. Incretin receptors for GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) were therefore measured in various rodent and human thyroid conditions. In vitro GLP-1 and GIP receptor autoradiography were performed in normal thyroids, C-cell hyperplasia and medullary thyroid carcinomas in rodents. Receptor incidence and density were assessed and compared with the receptor expression in human thyroids, medullary thyroid carcinomas, and TT cells. GLP-1 receptors are expressed in C cells of normal rat and mice thyroids. Their density is markedly increased in rat C-cell hyperplasia and medullary thyroid carcinomas, where their incidence amounts to 100%. GIP receptors are neither detected in normal rodent thyroids nor in C-cell hyperplasia, but are present in all rat medullary thyroid carcinomas. No GLP-1 or GIP receptors are detected in normal human thyroids. Whereas only 27% of all human medullary thyroid carcinomas express GLP-1 receptors, up to 89% express GIP receptors in a high density. TT cells lack GLP-1 receptors but express GIP receptors. GLP-1 receptors are frequently expressed in non-neoplastic and neoplastic C cells in rodents while they are rarely detected in human C-cell neoplasia, suggesting species differences. Conversely, GIP receptors appear to be massively overexpressed in neoplastic C cells in both species. The presence of incretin receptors in thyroid C cell lesions suggests that this organ should be monitored before and during incretin-based therapy of diabetes.

Effect of all-trans retinoic acid and sodium butyrate in vitro and in vivo on thyroid carcinoma xenografts

Histone deacetylase (HDAC) inhibitors have been shown to reverse repression of some genes, including retinoic acid (RA) receptor beta2. In this work, we studied the effects of RA alone or combined with the HDAC inhibitor sodium butyrate (NaB) in a poorly differentiated thyroid carcinoma cell line (FTC-133) cultured in vitro or transplanted into nude mice. In vitro, the action of the xenobiotics on cell differentiation was evaluated by the measurement of alkaline phosphatase (ALP) activity. In vivo, FTC cells were injected in nude mice divided into four groups: controls, RA (1 mg/kg), NaB (50 mg/kg) in two daily injections or both RA plus NaB. Body weight, tumoral volume (TV), doubling time of the tumor, specific growth delay and inhibition of tumoral growth at day 35 were determined in each group. In vitro, RA increased the NaB-induced increase in ALP activity. In vivo, body weight and TV decreased with RA or NaB. Specific growth delay significantly increased with RA (72.5%; P < 0.001) and with NaB (31.3%; 0.02 <P <0.01). Inhibition of tumoral growth significantly fell to 50.3% (0.02 < P < 0.01) and 42.9% (0.05 < P < 0.02) with RA and NaB, respectively. The combination of RA with NaB induced no significant change in the different parameters observed in mice treated with RA alone. In conclusion, a synergistic effect between RA and NaB was observed in vitro on cell differentiation. The addition of NaB to RA induces no change in growth inhibition observed with RA alone in nude xenografts.

Effect of sodium butyrate on doxorubicin resistance and expression of multidrug resistance genes in thyroid carcinoma cells

ATP-binding cassette (ABC) transporters [P-glycoprotein and multidrug resistance (MDR)-associated proteins (MRPs)] confer MDR to tumor cells. In this work, we investigated doxorubicin resistance in three thyroid carcinoma cell lines. The effects of sodium butyrate (NaB) on doxorubicin-induced cytotoxicity and on transcription of three MDR genes were also studied. Thyroid cell lines established from anaplastic (8505C) and two poorly differentiated follicular (FTC 238 and FTC 133) cancers were cultured for 24 or 48 h in the presence of NaB (0, 0.25, 0.5 and 1 mM) alone or combined with increased doses of doxorubicin. Cytotoxicity was assessed using the MTT test. MDR1, MRP1 and MRP2 mRNA expression was studied by RT-PCR. After a 24- or 48-h incubation, doxorubicin alone induced cytotoxicity in the three cell lines. NaB significantly (p<0.0001) increased the doxorubicin-induced cytotoxicity. MRP1 transcripts were expressed in the three non-treated cell lines. MDR1 and MRP2 mRNAs were both present in 8505C, but absent in FTC 133 or FTC 238 cell lines, respectively. Treatment with NaB for 24 or 48 h induced no change in MRP1 and MRP2 levels, but increased MDR1 expression in 8505C and FTC 238 cell lines comparably to alkaline phosphatase activity. In conclusion, MRP1 and sometimes MDR1 and MRP2 are expressed in the tested cell lines. NaB potentiates doxorubicin-induced cytotoxicity independently of the ABC transporters. The combination of doxorubicin and NaB might have clinical implications for thyroid cancer therapy.