Endocrine Abstracts

Introduction:Anaplastic thyroid carcinoma has a very poor prognosis because it is a highly aggressive and extremely lethal human cancer with poor therapeutic responses due to intrinsic resistance to chemotherapy.One of the reasons is DNA methylation which causes silencing of tumour suppressor genes (TSGs).To improve the prognosis of patients with anaplastic thyroid Ca,a better understanding of the molecular changes involved in its pathogenesis is essential.

Methods:Anaplastic thyroid Ca cells from a patient were obtained by biopsy pre-and post treatment.Pre-treated tumour cells were analysed by IHC,SSCP,ChiP assay,MS-PCR,RTTT-PCR,RT-PCR,flow cytometry and NB.There was 5'CpG island methylation of TSGs p53,Gadd45 and Rb defining this tumour as CIMP+.Furthermore,we detected upregulation of DNA-MeTase mRNA.The anaplastic thyroid Ca was treated with chimeric LNA/DNA antisense oligonucleotides against DNA MeTase and vinorelbine-tartrate encapsulated in pegylated liposomes termed as liposomal antisense vinorelbine (LAV).

Results:Post-treatment,RNaseH assay exhibited activation of RNaseH cleavage of DNA MeTase mRNA leading to its downregulation.This inhibited the 5'CpG island methylation of TSGs resulting to upregulation of their mRNA.Furthermore,there was hyperacetylation of histones H3 and H4 reactivating the silenced TSGs.Overexpression of the TTTSGs combined with the microtubule depolymerizing action of vinorelbine inhibited metabolic activity and DNA synthesis of tumour cells according to MTT and BrdU.Flow cytometry has blocked cell cycle at phase G2/M.There was induction of apoptosis in tumour cells according to TUNEL,DNA laddering and TEM.The majority of tumor cells exhibited condensed chromatin and membrane bound small bodies which were phagocytosed by adjacent tumour cells and phagocytic cells.

Conclusion:This therapeutic approach with pegylated liposomal formulation of chimeric LNA/DNA antisense oligonucleotides against DNA MeTas and vinorelbine may revolutionise anaplastic thyroid Ca treatment adding significantly to the current clinical armamentarium due to potential advantages offered by antisense therapy and conventional therapy such as well-defined mode of action,safety profile,selectivity and circumvention of biological milieu interactions such as RES elimination enhancing therapeutic index.