Human pharmacokinetics prediction with an in vitro–in vivo correction factor approach and in vitro drug-drug interaction profile of bictegravir, a potent integrase-strand transfer inhibitor component in approved biktarvy^® for the treatment of HIV-1 infection

Figures & data

Figure 1. Chemical structure of BIC.

Table 1. In vitro ADME properties of BIC.

Molecular weight	449.38 Da
pKa	8.3
LogD7.4	2.1
Kinetic Solubility (pH 7)	88 µM
Caco-2 Papp (× 10^-6cm/s)	BIC (10 µM): 6.2, 27.2, 4.4
AB, BA, ER	BIC (88 µM): 14.8, 22.6, 1.5
Biopharmaceutics Classification System	Class 2
	Rat	Dog	Cynomolgus Monkey	Rhesus Monkey	Human
Blood to plasma ratio (mean)	0.58	0.60	0.65	0.62	0.64
Plasma protein binding (fu,plasma; mean unbound %)	0.01	1.24	0.31	0.32	0.25
Liver microsomal protein binding (mean unbound %)	NA	NA	NA	NA	86.3
Rate of metabolism (t1/2, min)^a	49	108	63	76	194
CLint (l/h/kg)^a	1.72	0.35	0.59	0.49	0.19
Predicted hepatic extraction (%)	29	16	27	18	13

AB: apical to basolateral permeability; BA: basolateral to apical permeability; BIC: bictegravir; CL_int: intrinsic clearance; ER: efflux ratio; f_u,plasma: fraction unbound in plasma; NA: not applicable; P_app: apparent permeability coefficient.

^aDetermined in hepatic microsomes fortified with NADPH and UDPGA (see materials and methods).

Table 2. Summary of metabolites of BIC detected in cryopreserved hepatocytes.

Analyte^a	Identity	Fraction of Radiochromatogram (%)
		Rat	Dog	Monkey	Human
BIC	Parent	91.5	78.7	52.4	93.9
M305	N-dealkylation	1.7	8.7	2.4	1.2
M465a	Hydroxylation-1	1.2	1.4	2.7	ND
M465b	Hydroxylation-2	ND	0.2	11.6	0.6
M465c	Hydroxylation-3	ND	3.6	ND	ND
M611	Glucose conjugation	ND	0.8	4.4	ND
M625	Glucuronide conjugation	5.2	6.6	21.7	4.3
M641	Hydroxylation/glucuronidation	ND	ND	4.1	ND
Total	−	99.6	100	99.3	100

BIC: bictegravir; ND: not detected.

^aAnalyte metabolite identification numbers correspond to their molecular weight (e.g. M305 = metabolite with 305 Da molecular weight).

Figure 2. Plasma PK profile of BIC following a single-dose administration in rat, dog, and cynomolgus monkey (n = 3, mean ± S.D.). (A) Intravenous infusion (30 min) at a dose of 0.5 mg/kg; (B) oral solution administration at a dose of 0.5 mg/kg (rat) and 1 mg/kg (dog, monkey). Cyno: cynomolgus monkey.

Table 3. Nonclinical plasma PK parameters for BIC following a single-dose administration (n = 3, mean ± S.D.).

Species	Intravenous^a					Oral^b
	AUCinf (nM•h)	CL (L/hr/kg)	Vss (L/kg)	t1/2 (h)	MRT (h)	F (%)
Sprague-Dawley rat	549000 ± 45700	0.0020 ± 0.0002	0.13 ± 0.008	54.3 ± 14.4	62.0 ± 6.7	22.8 ± 7.8
Beagle dog	58,700 ± 17,700	0.022 ± 0.006	0.15 ± 0.02	5.34 ± 0.18	7.10 ± 1.32	41.8 ± 13.9
Cynomolgus monkey	49,400 ± 12,400	0.024 ± 0.007	0.095 ± 0.010	3.58 ± 0.23	4.16 ± 0.93	73.8 ± 40.3
Rhesus monkey	43,000 ± 5,050	0.026 ± 0.003	0.11 ± 0.02	3.76 ± 0.76	4.36 ± 1.30	NA

AUC_inf: area under the plasma concentration-time curve extrapolated to time infinity; CL: plasma clearance; F: oral bioavailability; MRT: mean residence time; NA: not applicable; t_1/2: estimated plasma elimination half-life; V_ss: volume of distribution at steady state.

^aIntravenous dose: 0.5 mg/kg infused over 30 min in all species.

^bOral dose: 0.5 mg/kg in rat; 1.0 mg/kg in dog and monkey.

Table 4. Comparisons between in vitro predicted clearance and in vivo measured clearance.

Species	fu,plasma (%)	In Vivo CL (L/hr/kg)		IVIV-CF^b
		Measured	Predicted^a
Rat	0.01	0.0020	1.21	605×
Dog	1.24	0.022	0.29	15×
Cynomolgus monkey	0.31	0.024	0.43	22×
Rhesus monkey	0.32	0.03	0.41	14×
Human	0.25	0.007 (projected)	0.17	25× (projected)

CL: clearance; f_u,plasma: fraction unbound in plasma; IVIV-CF: in vitro-in vivo correction factor.

^aPredicted without plasma or liver microsomal protein binding correction.

^bIVIV-CF = predicted CL/measured CL.

Table 5. Correlations between in vitro predicted clearance with plasma and liver microsomal protein binding applied and in vivo measured clearance.

Species	fu,plasma (%)	In Vivo CL (l/h/kg)
		Measured	Predicted with Plasma Binding^a	Predicted with Plasma and Liver Microsomal Binding^b
Rat	0.01	0.0020	0.00042	0.00049
Dog	1.24	0.022	0.02097	0.02407
Cynomolgus monkey	0.31	0.024	0.00492	0.00569
Rhesus monkey	0.32	0.03	0.00725	0.00838
Human	0.25	0.007 (projected)	0.00320	0.00369

CL: clearance; f_u,plasma: fraction unbound in plasma.

^aPredicted with plasma protein binding correction.

^bPredicted with plasma and liver microsomal protein binding correction. Human liver microsomal protein binding (unbound, 86.3%; Table 1) applied across all species.

Figure 3. Clinical steady state mean PK profile following repeat dosing of BIC 100 mg once daily for 7 days in healthy subjects. Projected PK (dashed line) and observed PK (solid line) are shown (n = 6, mean ± S.D.).

Table 6. Plasma PK summary of BIC following single- and multiple-dose administration of BIC 100 mg in healthy subjects.

Parameter	Observed PK (n = 6, mean ± S.D.)			Projected PK
	Single Dose	Multiple Dose		Multiple Dose
		Day 1	Day 7	Day 7
Cmax (ng/ml)	6998 ± 2529	6248 ± 1676	9397 ± 1954	5890
Ctau (ng/ml)	NA	NA	3145 ± 820	2754
AUCinf (h•ng/ml)	163,028 ± 39,549	NA	NA	NA
AUCtau (h•ng/ml)	NA	NA	126,786 ± 30,010	102,403
AUC0-24h (h•ng/ml)	NA	79,774 ± 15,062	NA	NA
Tmax (h)^a	2.3 (1.5, 3.0)	2.5 (2.0, 3.0)	1.8 (1.5, 3.0)	1.8
t1/2 (h)^a	18.9 (18.0, 20.1)	NA	NA	19.8
CL/F (l/h)^b	0.656 ± 0.216	NA	NA	NR
Vz/F (l)^b	19.8 ± 11.409	NA	NA	NR
Accumulation ratio of AUC (%)^c	NA	NA	159 ± 19	NR

AUC: area under the plasma concentration-time curve; AUC_0-24h: area under the plasma concentration-time curve from time 0 to 24 h following the 1^st dose; AUC_inf: AUC from time 0 to infinity; AUC_tau: area under the plasma concentration-time curve over the dosing interval (24 h) following the Day 7 dose; CL/F: apparent oral clearance; C_max: observed peak plasma concentration; C_tau: observed concentration at the end of the dosing interval; NA: not applicable; NR: not reported; T_max: time to C_max; V_z/F: apparent volume of distribution.

^aData presented as median (quartile 1, 3).

^bAssuming F = 50% and a body weight of 70 kg, the predicted human CL and V_ss is 0.980 L/h and 28 L respectively.

^cAccumulation ratio of AUC = AUC_tau on Day 7/AUC_0-24h on Day 1.

Table 7. In vitro PK drug interaction assessment of BIC.

Assessment	Protein
Inhibition – reversible	CYPs 1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 3 A: IC50 > 100 µM
	UGT1A1: IC50 = 176 µM
Inhibition – time dependent	CYPs 1A2, 2B6, 2C8, 2C9, 2C19, or 2D6: none
	CYP3A: KI > 100 μM
Induction – mRNA expression	CYPs 1A2, 2C8, 2C9: none; P-gp: 5.76-fold at 60 µM BIC
	CYP2B6: EC50 = 103 μM; CYP3A4: EC50 = 19 μM
Transporter – substrate	P-gp and BCRP: yes
Transporter – inhibition	P-gp, BCRP, BSEP: IC50 > 80 µM
	OATP1B1, OATP1B3, OCT1, OAT1: IC50 > 80 µM
	OCT2: IC50 = 0.42 µM; OAT3: IC50 = 55 µM; MATE1: IC50 = 8.0 µM

BCRP: breast cancer resistance protein; BSEP, bile salt export pump; CYP: cytochrome P450 enzyme; EC₅₀: half-maximal effective concentration; IC₅₀: half-maximal inhibitory concentration; K_I: kinetic inhibition constant; MATE: multidrug and toxin extrusion; OAT: organic anion transporter; OATP: organic anion-transporting polypeptide; OCT: organic cation transporter; P-gp: P-glycoprotein; UGT: UDP-glucuronosyltransferase.