Choline is an organic cation that plays a critical role in the structure and function of biological membranes. Intracellular choline accumulation through choline transporters is the rate-limiting step in phospholipid metabolism, and it is a prerequisite for cell proliferation. Choline PET/CT has been used to visualize various cancers, and high levels of choline accumulation have been observed in tumors. However, the uptake system for choline and the functional expression of choline transporters in pancreatic cancer are not completely understood. In this study, we examined the functional characterization of choline transporters in pancreatic cancer cells. Furthermore, we searched for compounds that inhibit choline uptake as well as cell proliferation in a plant-derived natural organic compound library.
We examined [3H]choline uptake in the pancreatic cancer cell line MIA PaCa-2. Cells were cultured in RPMI 1640 medium supplemented with 10 % fetal bovine serum and grown at 37 C in 5% CO2. The CellTiter-Glo Luminescent Cell Viability Assay is a homogeneous method of determining the number of viable cells. The caspase-Glo 3/7 Assay System is a homogeneous luminescent method used to measure caspase-3 and -7 activities.
Choline transporter-like protein 1 (CTL1) and CTL2 mRNA are highly expressed. CTL1 and CTL2 were located in the cell membrane and intracellular compartment, respectively. [3H]Choline uptake was mediated by a single Na+-independent, intermediate-affinity transport system. We found two hit compounds from 500 plant-derived natural organic compounds that inhibited choline uptake and cell viability. These hit compounds reduced cell survival and enhanced caspase-3/7 activity. One of the compounds inhibited tumor growth in MIA PaCa-2 cell xenograft model mice.
These results suggest that CTL1 is functionally expressed in pancreatic cancer cells and is also involved in abnormal proliferation. Identification of this CTL1-mediated choline transport system provides a potential new therapeutic target for the treatment of this disease.
Tokyo Medical University.
Has not received any funding.
All authors have declared no conflicts of interest.