The Human Carnitine Transporter SLC22A16 Mediates High Affinity Uptake of the Anticancer Polyamine Analogue Bleomycin-A5

Abstract

Bleomycin is used in combination with other antineoplastic agents to effectively treat lymphomas, testicular carcinomas, and squamous cell carcinomas of the cervix, head, and neck. However, resistance to bleomycin remains a persistent limitation in exploiting the full therapeutic benefit of the drug with other types of cancers. Previously, we documented that the Saccharomyces cerevisiae L-carnitine transporter Agp2 is responsible for the high affinity uptake of polyamines and of the polyamine analogue bleomycin-A5. Herein, we document that the human L-carnitine transporter hCT2 encoded by the SLC22A16 gene is involved in bleomycin-A5 uptake, as well as polyamines. We show that NT2/D1 human testicular cancer cells, which highly express hCT2, are extremely sensitive to bleomycin-A5, whereas HCT116 human colon carcinoma cells devoid of detectable hCT2 expression or MCF-7 human breast cancer cells that only weakly express the permease showed striking resistance to the drug. NT2/D1 cells accumulated fluoresceinlabeled bleomycin-A5 to substantially higher levels than HCT116 cells. Moreover, L-carnitine protected NT2/D1 cells from the lethal effects of bleomycin-A5 by preventing its influx, and siRNA targeted to hCT2 induced resistance to bleomycin-A5-dependent genotoxicity. Furthermore, hCT2 overexpression induced by transient transfection of a functional hCT2-GFP fusion protein sensitized HCT116 cells to bleomycin-A5. Collectively, our data strongly suggest that hCT2 can mediate bleomycin-A5 and polyamine uptake, and that the rate of bleomycin-A5 accumulation may account for the differential response to the drug in patients.

Carnitine transporter CT2 (SLC22A16) is over-expressed in acute myeloid leukemia (AML) and target knockdown reduces growth and viability of AML cells

“…The CT2 transporter mediates the uptake of the chemotherapeutic agent bleomycin [15]. Therefore, as an additional approach to assess the impact of CT2 shRNA knockdown on the function of the transporter, we knocked down CT2 in OCI-AML2 cells and treated them with bleomycin.…”

Histatin 5 Uptake by Candida albicans Utilizes Polyamine Transporters Dur3 and Dur31 Proteins

“…A specialized form of bleomycin called bleomycin-A5 is transported into S. cerevisaie cells by the polyamine permease Agp2, because this bleomycin variant contains a spermidine residue as its terminal amine substituent (49). The therapeutic utility of bleomycin-A5 in cancer patients is based upon the functional similarity of the human high affinity L-carnitine transporter hCT2 with S. cerevisaie Agp2, both of which transport bleomycin-A5 intracellularly to damage DNA (50). This raises the interesting possibility that adding a spermidine or spermine moiety to Hst 5 or other antifungal drugs may improve intracellular delivery through polyamine transporters.…”

Distribution, Molecular Structure and Functional Analysis of Carnitine Transporter (SLC22A5) in Canine Lens Epithelial Cells

“…Butyrobetaine reduced only 30% of the carnitine transport activity of LEC. There was reportedly other carnitine transporters, for example SLC22A16 [1]. Therefore, other carnitine transporters may possibly exist in LECs.…”