The analysis of organic anion transporting polypeptide (OATP) mRNA and protein patterns in primary and metastatic liver cancer

Abstract

Organic anion transporting polypeptides (OATP, SLCO genes) mediate the uptake of endobiotics and drugs. Thus, their expression levels and pattern could be of relevance for cancer therapy. This prompted us to investigate the expression of poorly characterized OATPs, namely OATP2A1, OATP3A1, OATP4A1 and OATP5A1 in hepatic cancer of different origin. First, mRNA levels of all eleven OATPs were determined in paired (cancerous and adjacent non-cancerous) specimens from 43 patients with primary liver cancer (hepatocellular carcinoma, HCC; cholangiocellular carcinoma, CCC) and liver metastases from colon tumors (MLT). Real-time RT-PCR analysis revealed that all OATPs, except OATP1C1 and OATP6A1, are extensively expressed in nearly all samples. In contrast to downregulated OATP1B1, OATP1B3, OATP1A2 and OATP2B1 in cancerous vs. non-cancerous samples, an increase in OATP2A1, OATP3A1, OATP4A1 and OATP5A1 mRNA levels was seen in tumors (up to 40-fold for OATP5A1 in the MLT group). Therefore, OATP2A1, OATP3A1, OATP4A1 and OATP5A1 were further investigated by immunofluorescence microscopy on paraffin-embedded cancerous and non-cancerous sections (seven per group). OATP-derived immunoreactivity was observed in plasma membranes and cytosol of hepatic tumor cells, and additionally, in various cytokeratin 19 positive bile ducts. An increased percentage of immunoreactive cells and a higher staining intensity in cancerous vs. non-cancerous paraffin sections paralleled higher mRNA levels of OATP2A1, OATP3A1, OATP4A1 and OATP5A1 in cancerous tissues of HCC, CCC and MLT patients. The extensive expression of OATP2A1, OATP3A1, OATP4A1 and OATP5A1 in hepatic tumors of different origin suggests that these transporters might be further exploited for the discovery of novel anticancer agents.

Role of Organic Anion-Transporting Polypeptides (OATPs) in Cancer Therapy

“…Immunohistochemical analyses confirmed that OATP5A1 is expressed on the membrane and in the cytoplasm of breast cancer cells (89). OATP5A1 at both the mRNA and protein levels was found to be upregulated in liver cancer (80) and small cell lung cancer (SCLC) (5). As a potential marker of chemotherapy resistance, HEK-293 cells transfected with OATP5A1 showed resistance to satraplatin treatment (5).…”

“…Certain (60) ↑ in prostate cancer cells (6) qRT-PCR Kidney (64) ↑ in bone cancer (65) RT-PCR OATP1B1 Liver (2,66) ↓ in liver cancer (37)(38)(39)67,68) RT-PCR, IF, IB ↑ in colon polyps and colon cancer (63) RT-PCR ↑ in ovarian cancer (69) RT-PCR OATP1B3 Liver (3,70) ↓ in liver cancer (41) qRT-PCR, IB ↑ in colon cancer (4,71,72) RT-PCR, qRT-PCR, IB, IHC ↑ in pancreatic cancer (71)(72)(73) RT-PCR, qRT-PCR, IB, IHC ↑ in lung cancer (38) RT-PCR, qRT-PCR, IF ↑ in prostate cancer (16,17,68,74) qRT-PCR, IF ↑ in breast cancer (75) qRT-PCR, IHC ↑ in testicular cancer (68) qRT-PCR, IF ↑ in ovarian cancer (69) RT-PCR OATP1C1 Brain (76) ↑ in bone cancers (65) RT-PCR Testes (76) Ciliary body (77) OATP2A1 Ubiquitous (78) ↑ in breast cancer (79) qRT-PCR ↑ in liver cancer (80) qRT-PCR, IF ↑ in bone metastases from kidney cancer (65) qRT-PCR, IB ↓ in cancers of bowel, stomach, ovary, lung, and kidney (81) RT-PCR OATP2B1 Blood-brain barrier (82) ↑ in bone cancer (65) RT-PCR Heart (83) ↑ in breast cancers (79,84) qRT-PCR, IF, IB Enterocytes (85) ↓ in liver and pancreatic cancers (68) qRT-PCR Liver (86) Placenta (87) OATP3A1 Ubiquitous (88) ↑ in bone cysts …”

“…Similar to OATP3A1, OATP4A1 is also overexpressed in multiple cancer cell lines, aneurysmal bone cysts, liver cancers, and breast cancers (65,79,80,90). In colorectal neoplasia specimens, OATP4A1 mRNA levels were reported to be elevated (91).…”

“…In breast cancer, OATP3A1 is localized both on the plasma membrane and in the cytoplasm (89). Wleck et al showed that OATP3A1 levels were increased in primary and metastatic liver cancers (80).…”

Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

“…In lowering the intracellular amount of drug (MOC-1) 6 , an important part is played by reduced uptake (MOC-1a) through solute carrier (SLC) transporters, such as organic anion-transporting poly peptides (OATPs). Substrates of OATP1A2, which is highly expressed in cholangiocytes, include methotrexate, taxanes and imatinib, whose uptake by CCA cells in vitro can be impaired by OATP1A2 downregulation 272 or the expression of less active genetic variants 273 . Uptake of cationic drugs (for example, platinum derivatives and tyrosine kinase inhibitors) is mediated in part by organic cationic transporters (OCT), which are downregulated (OCT3) 274 or very poorly expressed (OCT1) 275 in CCA.…”