Table 3.
Comparison of warfarin inhibition for hVKORC1 variants determined by in vitro assays of vitamin K 2,3-epoxide reductase (VKOR) in cell fractions or in cultured cells.
| hVKORC1 Variant | Mean Patient Dosage in HDT Multiples [Drug] for n = Number of Reported Patients [11] | Warfarin IC50 by DTT-Driven VKOR Assay [8,12] | Warfarin IC50 by Cell Based Assay [23] | Warfarin Phenotypes by Cell Based Assay [36] |
|---|---|---|---|---|
| Wild-type | 1.0 [W, P] (n = 77) | |||
| Ala26Pro | >3.0 [W] (n = 1) | 11.2-fold increased Ki[12] | 49.6-fold increased IC50 | n.d. |
| Ala26Thr | >2.0 [P] (n = 1) | sensitive as wt [12] | 3.0-fold increased IC50 | n.d. |
| Leu27Val | >3.0 [F], 1.0 [W] (n = 1) * | sensitive as wt [12] | 2.5-fold increased IC50 | n.d. |
| His28Gln | 3.5 [P] (n = 1) | more sensitive than wt [ 12] | 2.9-fold increased IC50 | n.d. |
| Val29Leu | 2.0 [W] (n = 1) | absence of expression [12]/low VKOR activity and more sensitive than wt [8] | 5.5-fold increased IC50 | n.d. |
| Ala34Pro | 3.8 [W] (n = 1) | n.d. | n.d. | n.d. |
| Asp36Gly | 3.0 [W] (n = 1) | more sensitive than wt [ 12] | 3.2-fold increased IC50 | n.d. |
| Asp36Tyr | 1.5–3.5 [W] (n = 10) | sensitive as wt [12] | 3.8-fold increased IC50 | n.d. |
| Val45Ala | >2.0 [W] (n = 1) | low VKOR activity [ 8], more sensitive than wt [8,12] | 6.2-fold increased IC50 | n.d. |
| Ser52Leu | >3.0 [P] (n = 1) | low VKOR activity, Ki determination not possible [ 12] | 7.4-fold increased IC50 | moderate resistance |
| Ser52Trp | 3.5 [P] (n = 1) | low VKOR activity, Ki determination not possible [ 12] | 5.7-fold increased IC50 | sensitive as wt |
| Val54Leu | 1.5–5.5 [W] (n = 2) | 4.6-fold increased Ki[12] | 4.5-fold increased IC50 | n.d. |
| Ser56Phe | >5.0 [P] (n = 1) | more sensitive than wt [12] | 6.8-fold increased IC50 | n.d. |
| Arg58Gly | 5.0 [W] (n = 1) | low VKOR activity [8], more sensitive than wt [8 and 12] | 3.4-fold increased IC50 | n.d. |
| Trp59Arg | 7.0 [P] (n = 1) | low VKOR activity, Ki determination not possible [12] | 17.5-fold increased IC50 | high resistance |
| Trp59Cys | >3.5 [P] (n = 1) | more sensitive than wt [12] | 7.6-fold increased IC50 | n.d. |
| Trp59Leu | >5.0 [P] (n = 1) | low VKOR activity, Ki determination not possible [12] | 75.2-fold increased IC50 | high VKOR activity, high resistance |
| Val66Gly | 2.5 [P] (n = 1) | low VKOR activity, Ki determination not possible [12] | 2.8-fold increased IC50 | sensitive as wt |
| Val66Met | 3.0–6.0 [W] (n = 7) | low VKOR activity, Ki determination not possible [12] | 5.4-fold increased IC50 | sensitive as wt |
| Gly71Ala | >2.0 [P] (n = 1) | low VKOR activity, Ki determination not possible [12] | 5.1-fold increased IC50 | sensitive as wt |
| Asn77Ser | >3.0 [P] (n = 1) | low VKOR activity, Ki determination not possible [12] | 5.3-fold increased IC50 | moderate resistance |
| Asn77Tyr | 3.5 [W] (n = 1) | low VKOR activity, Ki determination not possible [12] | 3.9-fold increased IC50 | sensitive as wt |
| Ile123Asn | >7.0 [P] (n = 1) | 2.4-fold increased Ki[12] | 8.5-fold increased IC50 | n.d. |
| Leu128Arg | >4.0–7.0 [W] (n = 5) | low VKOR activity [8,12], Ki determination not possible [12]/more sensitive than wt [8] | 49.7-fold increased IC50 | high VKOR activity, high resistance |
| Tyr139His | >3.0 [W] (n = 1) | 3.6-fold increased Ki[12] | 4.6-fold increased IC50 | n.d. |
This table shows patient data as well as in vitro results from the DTT-driven and cell culture-based VKOR assays for VKORC1 variants reported to cause resistance to VKA. Patient data from Watzka et al. [11] and Hodroge et al. [12], with [P] = phenprocoumon, [W] = warfarin; HDT = High Dosage Threshold which is equivalent to the mean patient population dosage divided by that for the control group (homozygous wild-type VKORC1 alleles with VKORC1:c.-1639GG haplotype). The patient marked with an asterisk (*) and Leu27Val mutation had additionally the CYP2C9*2*3 haplotype which results in a reduced warfarin dosage requirement to achieve a stable, therapeutic INR compared to patients with wild-type CYP2C9*1*1 haplotype. Variants investigated by the DTT-driven assay by Hodroge et al. [12] and Rost et al. [8] were summarized in one column, followed by data from Czogalla et al. [23] and Tie et al. [36]. n.d. = not determined.