Here, we investigated the possibility of clinical DDIs via inhibitory effects of eight small-molecule TKIs on the transport activity of human OCT1, OCT2, OCT3, MATE1, and MATE2-K. Our results showed that imatinib, nilotinib, gefitinib and erlotinib exerted selectively potent inhibitory effects with unbound Cmax,sys,p/IC50 ≥ 0.1 on MATE1, OCT3, MATE2-K and OCT1, respectively. In particular, unbound Cmax,sys,p/IC50 was greater than 1 for the inhibition of MATE1 by imatinib and of OCT1 by erlotinib, suggesting a high probability of a DDI if the compounds are administered with metformin.
Because drug concentrations at the inlet of the liver after oral administration are generally expected to be higher than in the systemic circulation (39
), actual risks of DDI may be underestimated by unbound Cmax,sys,p
. Therefore, unbound Cmax,portal,p
values (Supplementary Table S1
) may be used as [I] to predict potential DDIs with transporters in the liver (hOCT1) to avoid false-negative predictions. Prevalence of type 2 diabetes ranges from 2%-10% in industrialized countries, with rates on the rise (41
). Because cancer and type 2 diabetes are two common diseases that may share risk factors (41
), many present and future patients will likely undergo concomitant treatment with TKIs and metformin. Importantly, because metformin appears to have some efficacy in cancer management, clinical studies with TKIs and metformin are ongoing. Though relatively safe, at high concentrations, metformin can cause lactic acidosis, a life-threatening adverse reaction. DDIs with TKIs may result in increased levels of metformin and therefore, increase patient susceptibility to lactic acidosis. Such DDIs may be particularly problematic in patients with widespread metastases who are at increased risk for lactic acidosis. Our study strongly supports the need for clinical DDI studies between metformin and TKIs.
Methods used in the in vitro
assessment of drug transporter interactions are important to obtain accurate predictions of potential clinical DDIs. The current standard in vitro
method of evaluating a drug as an inhibitor of an uptake transporter involves simultaneous addition of the test drug inhibitor and model substrate and determination of uptake of the substrate. In real clinical situations, however, a drug may be metabolized into several distinct chemical species, and the transporter may be exposed to the inhibitor drug for a long period of time before a substrate is administered (28
). We found that preincubation of erlotinib with the cells before initiation of metformin uptake enhanced the inhibitory effects of erlotinib on OCT1 (). This suggest that the interaction of erlotinib with the lipophilic and negatively charged cell membrane, which is supposed to be crucial step in achieving OCT1 inhibition (11
), or other steps required for erlotinib to reach its binding domain on OCT1 may be slow. We also observed that the inhibition potency of erlotonib was increased for the M420del (), a common polymorphism of OCT1 found at allele frequencies of about 20% in white Americans (13
). Our data are consistent with a previous study showing that M420del is more sensitive to drug inhibition by glibenclamine, simvastatin, and verapamil, with IC50
values up to eight times lower for the variant than those observed for the reference OCT1 (28
Major metabolites of TKIs showed IC50
values similar to those for unchanged TKIs. Plasma concentrations of O-desmethyl gefitinib in CYP2D6 extensive metabolizers are higher than for unchanged gefitinib (42
). Therefore, O-desmethyl gefitinib may contribute to potential clinical DDIs that may occur following concomitant metformin and gefitinib administration. Given that plasma concentrations of N-desmethyl imatinib are approximately 10-fold lower than those of the unchanged imatinib (43
), and the unbound fractions of N-desmethyl imatinib and imatinib are nearly equal (44
), the inhibitory effects of N-desmethyl imatinib on the tested transporters may be negligible at therapeutic doses of imatinib. O-desmethyl erlotinib is a 10-fold weaker inhibitor of OCT1 than erlotinib (Supplementary Table S3
), and the metabolite concentration in plasma is more than 10-fold lower than that of the unchanged erlotinib (45
), suggesting little inhibitory effects at normal doses.
To determine whether mice could be used as animal models to study transporter based human DDIs between TKIs and OCTs and MATEs, we investigated the inhibition potency of TKIs for mouse orthologs of OCTs and MATEs. Our data showed striking species differences in the interaction of erlotinib, nilotinib, and imatinib, with mouse orthologs of OCT1, OCT3 and MATE1, respectively in comparison to the human orthologs (). All three compounds had weaker interactions with the mouse transporters in comparison to the human orthologs. This finding suggests that mice are unlikely to be suitable animal models for in vivo DDI studies of TKIs and OCTs/MATEs, The structural basis for the reduced potency of interaction of the TKIs with the mouse orthologs of the transporters is not known and needs investigation. Because high resolution crystal structures of OCTs and MATEs are not available for construction of molecular models, it is difficult to explain the structural basis for the striking interspecies differences that were observed in the interaction of TKIs with OCTs and MATEs.
In this study, we observed that the cellular uptake of platinum was reduced after oxaliplatin treatment in the presence of clinically relevant concentrations of erlotinib and nilotinib (). These experiments suggest that combination therapy involving oxaliplatin and these TKIs may not be optimal, particularly for tumors in which OCTs are involved in the uptake of oxaliplatin. Co-administration of erlotonib or nilotinib may reduce the anti-cancer effects of oxaliplatin by inhibiting the drug's uptake into such tumors. Nilotinib appears to be a more potent inhibitor of oxalplatin transport by hOCT1, hOCT2 and hOCT3 than of metformin transport. This may suggest that the inhibition potency of TKIs on OCTs may be different depending on the substrate and/or that experimental condition such as incubation time may affect the results of in vitro assessment.
Negative correlations between lipophilicity (ClogP and ClogDpH7.4
) and negative log10
) of the TKIs for human OCT1 and OCT2 () suggest that excessive lipophilicity weakens the inhibitory effects of TKIs on metformin uptake by OCT1 and OCT2. These data are not in agreement with studies demonstrating that high lipophilicity is one of the key physicochemical properties for OCT1 inhibition (11
). Excessive lipophilicity may make it difficult for a drug to access the substrate binding region of OCT1 that is in contact with the aqueous phase (46
). ClogP values of the tested TKIs (Supplementary Table S1
) met the minimum requirement of lipophilicity needed for OCT1 inhibition (11
). Our study also suggests that positive charge may be one of key factors for MATE1 inhibition (). Because the number of tested compounds is small, further studies are needed for accurate drug-structure-based prediction of transporter inhibitory effects.
In the present study, we investigated the possibility of clinical DDIs in response to the inhibitory effects of eight small-molecule TKIs on the transport activity of human OCT1, OCT2, OCT3, MATE1, and MATE2-K. Results showed the potential for clinical DDIs when certain TKIs were used concomitantly with drugs that are transported by organic cation transporters, such as metformin or oxaliplatin. The results of this study provide the basis for further clinical studies investigating the transporter-based DDI potential of TKIs.