The understanding of biological functions of miRNAs in patients with PC will significantly help the development of new targeted anticancer drugs and testing of novel therapies. Most investigators agree that miRNA expression profiling is an accurate method for the analysis of archived surgical specimens from tumours including PC (Li et al, 2007
; Doleshal et al, 2008
; Szafranska et al, 2008a
; Goswami et al, 2010
). We previously identified miRNA expression from plasma samples that were characteristic of PCs (Ali et al, 2010b
). The primary objective of this study was to determine the feasibility of performing miRNA arrays and qRT–PCR from FFPE cell blocks obtained from diagnostic FNAs.
To the best of our knowledge this is the first study to determine miRNA expression from FNAs of FFPE cell blocks in patients with PC. We found 228 miRNAs that were differentially expressed in the PC patients compared with normal controls. Consistent with published literature using surgical specimens, we found higher expression of miR-451 and miR-486-5p, and lower expression of let-7c, let-7d, let-7f, and miR-200c in the FNA samples of PC patients. Further analyses revealed marked downregulation of the let-7 family that is well known for its tumour suppressive characteristics and consistent with previous independent studies showing that let-7 is underexpressed in PC (Li et al, 2009
; Torrisani et al, 2009
; Watanabe et al, 2009
; Oh et al, 2010
; Ngi-Garimella et al, 2011
). We confirmed the expression of let-7c, let-7d, and let-7f in PC individually and compared with controls by qRT–PCR. We found that the expression of let-7c and let-7f was significantly reduced in all PC specimens, whereas the expression of let-7d was differentially expressed between these samples.
Emerging evidence indicates that EMT has a crucial role in cancer progression and drug resistance and is associated with loss of miR-200c expression (Burk et al, 2008
; Li et al, 2009
; Wellner et al, 2009
; Yu et al, 2010
). A recent study from our group showed that re-expression of miR-200 suppressed pulmonary metastases of breast cancer cells in vivo
, whereas anti-miR-200 treatment in vivo
resulted in increased metastases (Ahmad et al, 2011
). Here, we report that the expression of miR-200c is significantly reduced in all PC patients tested compared with controls. In addition to downregulated miRNAs in PC, our results also demonstrated a significant upregulation of miR-486-5p, miR-451, and miR-423-5p. These findings are in concordance with the findings of another recent study in gastric cancer where a significant increase in serum miR-423-5p was demonstrated by Solexa sequencing. Furthermore, miR-423-5p expression level showed a substantial increase in patients with metastatic disease compared with those with stages I or II (Liu et al, 2011
It is obvious that with a molecularly very complex disease such as pancreatic adenocarcinoma a single gene product or pathway is unlikely neither to be a robust target for therapy nor to predict biology of disease. A systems biology approach provides a unique strategy to study networks of molecular events that drive various signalling pathways resulting from the deregulations of miRNAs (Azmi et al, 2011
). The miRNAs and their targets are arranged in complex regulatory networks ( and ), but as the functional roles of miRNAs in PC are better defined, it will improve the sub-classification of PC with respect to prognosis and patterns of response to specific therapies.
In conclusion, this study demonstrates the feasibility of undertaking analyses of miRNAs in very small diagnostic specimens from FNAs of PC that may provide an invaluable research tool to individualise therapy and develop rationally based targeted therapies. Moreover, a unique group of miRNAs were identified that can serve as a tool for investigating the biology of PC with respect to prognosis and response to therapy at the individual level. Prospective clinical trials will be needed to better understand the functions of these miRNAs. The role of miRNAs may also be extended to in vivo monitoring of targeted therapies.