Interaction of plant cannabinoids with the multidrug transporter ABCC1 (MRP1)

Abstract

The ATP-binding cassette (ABC) transporter ABCC1, or multidrug resistance-related protein 1 (MRP1) is implicated in Phase II metabolism and multidrug resistance as it effluxes substrate anticancer drugs. As cannabinoids inhibit two related ABC transporters, P-glycoprotein and ABCG2, here we examined whether they also inhibit ABCC1. Indeed, the cannabinoids enhanced the intracellular accumulation of two ABCC1 substrates, Fluo3 and vincristine, in ovarian carcinoma cells over-expressing ABCC1 (2008/MRP1) with a rank order of potency: cannabidiol > cannabinol > Δ⁹-tetrahydrocannabinol. Cannabinoid inhibition of ABCC1 was confirmed using insect cell membrane MRP1 ATPase assays. These results demonstrate that cannabinoids inhibit ABCC1.

Introduction

ABCC1 or multidrug resistance-related protein 1 (MRP1) is a membrane-bound, energy-dependent efflux transporter belonging to the superfamily of ATP-binding cassette (ABC) transporters. With the notable exception of adult liver, ABCC1 is almost ubiquitously expressed, with high levels in lung, testes, kidney, skeletal muscle, epithelial and haematopoietic cells (Flens et al., 1996). In polarized epithelial cells, ABCC1 is expressed basolaterally, with the exception of the capillary endothelial cells within the brain, where it is expressed apically (Peng et al., 1999, Zhang et al., 2004). Physiologically, ABCC1 contributes to Phase II metabolism by transporting a range of glutathione, glucuronide and sulfate conjugates (Keppler et al., 1997), and limits the toxicity of such metabolites in the central nervous system and other sanctuary tissue sites (Wijnholds et al., 2000, Wijnholds et al., 1998). Importantly, ABCC1 transports a range of clinically employed cancer drugs, including folate based anti-metabolites, anthracyclines, plant-derived Vinca alkaloids and anti-androgens (Cole et al., 1994, Grzywacz et al., 2003, Hooijberg et al., 1999). Energy-dependent efflux of such drugs reduces intracellular concentrations in tumour cells, thereby conferring resistance. ABCC1 expression has been shown to correlate with clinical drug resistance and poor treatment response in some cancer types such as neuroblastoma and acute myeloid leukemia (Karaszi et al., 2001, Norris et al., 1996).

Cannabis and cannabinoid preparations, such as Marinol^® (dronabinol) and Cesamet™ (nabilone), are used to palliate nausea and vomiting induced by cancer chemotherapy (Slatkin, 2007). Furthermore, there is mounting pre-clinical evidence that cannabinoid compounds exert direct anti-proliferative effects in some tumour types (Guzman, 2003). Recently, we and others have identified plant cannabinoids as novel modulators of the ABC transporters, P-glycoprotein and ABCG2 (Holland et al., 2007, Zhu et al., 2006). Due to the over-lapping substrate specificities of the multidrug transporters, compounds which have affinity for one are more likely to interact with the others (Matsson et al., 2007). Therefore we have examined whether cannabinoids similarly affect ABCC1. This is important given the use of cannabinoids in the treatment of cancer, where they are likely to be co-administered with a range of conventional cancer drugs, many of which are substrates for ABCC1, creating the potential for ABCC1 mediated drug–drug interactions. Here we present data describing the effects of the three most abundant plant cannabinoids on ABCC1 function, the principal psychoactive constituent, Δ⁹-tetrahydrocannabinol (Δ⁹-THC), cannabinol and the non-psychoactive cannabidiol.