TABLE 4

Summary of CES activity for gemcitabine esters

Values listed are the mean ± S.E. When the kinetic constants K_m and V_max were determined for a substrate and enzyme combination, the intrinsic clearance (CL_int) is V_max/K_m; otherwise, the initial clearance (CL_ini) was calculated. Units for K_m are micromolar concentration, for V_max are nanomoles of product per minute per milligram of protein, and for CL_int/CL_ini are microliters per second per milligram of protein, respectively.

	Kinetic Constants	hCES1	cCES1	dCES1	hCES2	cCES2	dCES2
Prodrugs at R1 position and –OH at R2 position
01	K_m	N.A.	N.A.	N.A.	273 ± 5	41.1 ± 1.4	N.A.
	V_max	N.A.	N.A.	N.A.	4037 ± 26	12266 ± 74	N.A.
	CL_ini/int	2.58 ± 0.02	12.2 ± 0.1	11.3 ± 0.0	246 ± 5	4969 ± 167	0.320 ± 0.001
02	K_m	N.A.	303 ± 49	399 ± 19	407 ± 6	69.5 ± 2.2	N.A.
	V_max	N.A.	2662 ± 163	6189 ± 134	22440 ± 138	36726 ± 200	N.A.
	CL_ini/int	18.3 ± 0.1	146 ± 25	259 ± 14	918 ± 14	8813 ± 281	8.56 ± 0.04
03	K_m	242 ± 3	130 ± 2	289 ± 3	107 ± 0	36.5 ± 1.9	N.A.
	V_max	617 ± 2	1141 ± 4	3946 ± 16	4175 ± 1	15201 ± 149	N.A.
	CL_ini/int	42.6 ± 0.5	147 ± 3	228 ± 3	652 ± 0	6949 ± 364	1.71 ± 0.01
04	K_m	N.A.	N.A.	N.A.	N.A.	187 ± 13	N.A.
	V_max	N.A.	N.A.	N.A.	N.A.	2912 ± 56	N.A.
	CL_ini/int	0.109 ± 0.001	0.507 ± 0.005	0.840 ± 0.005	5.88 ± 0.01	260 ± 18	0.253 ± 0.001
05	K_m	212 ± 9	431 ± 25	235 ± 77	316 ± 14	37.7 ± 2.3	145 ± 3
	V_max	44.7 ± 0.6	124 ± 3	59.9 ± 6.4	389 ± 7	2385 ± 28	40.2 ± 0.2
	CL_ini/int	3.52 ± 0.15	4.81 ± 0.31	4.24 ± 1.46	20.5 ± 1.0	1056 ± 66	4.63 ± 0.09
06	K_m	92.9 ± 2.9	N.A.	N.A.	N.A.	26.4 ± 1.6	250 ± 12
	V_max	14.6 ± 0.1	N.A.	N.A.	N.A.	1093 ± 14	22.6 ± 0.4
	CL_ini/int	2.63 ± 0.08	2.67 ± 0.03	2.67 ± 0.03	4.30 ± 0.05	690 ± 44	1.51 ± 0.08
07	K_m	338 ± 8	N.A.	N.A.	119 ± 2	44.9 ± 5.8	N.A.
	V_max	788 ± 7	N.A.	N.A.	592 ± 2	4632 ± 107	N.A.
	CL_ini/int	38.8 ± 1.0	13.3 ± 0.2	9.72 ± 0.10	83.0 ± 1.5	1717 ± 224	0.558 ± 0.001
08	K_m	N.A.	N.A.	N.A.	N.A.	72.1 ± 1.0	N.A.
	V_max	N.A.	N.A.	N.A.	N.A.	700 ± 2	N.A.
	CL_ini/int	0.118 ± 0.001	1.14 ± 0.01	1.96 ± 0.02	1.34 ± 0.01	162 ± 2	0.283 ± 0.001
09	K_m	85.0 ± 5.4	279 ± 11	139 ± 3	82.2 ± 0.2	43.1 ± 0.2	398 ± 14
	V_max	3.16 ± 0.04	12.9 ± 0.2	14.2 ± 0.1	27.8 ± 0.0	123 ± 0	18.2 ± 0.3
	CL_ini/int	0.620 ± 0.040	0.769 ± 0.033	1.69 ± 0.04	5.63 ± 0.02	47.4 ± 0.2	0.761 ± 0.030
10	K_m	16.5 ± 2.8	378 ± 12	3.57 ± 4.44	349 ± 5	15.3 ± 3.4	147 ± 12
	V_max	0.348 ± 0.014	7.25 ± 0.10	0.178 ± 0.046	6.85 ± 0.04	3.40 ± 0.18	2.75 ± 0.05
	CL_ini/int	0.351 ± 0.061	0.320 ± 0.011	0.834 ± 1.060	0.327 ± 0.005	3.72 ± 0.85	0.312 ± 0
11	K_m	158 ± 2	132 ± 1	119 ± 3	153 ± 4	41.7 ± 0.8	N.A.
	V_max	9.45 ± 0.03	21.3 ± 0.0	16.1 ± 0.1	21.3 ± 0.1	146 ± 1	N.A.
	CL_ini/int	0.994 ± 0.013	2.69 ± 0.01	2.25 ± 0.06	2.31 ± 0.07	58.5 ± 1.2	0.0577 ± 0.0005
12	K_m	137 ± 7	N.A.	430 ± 4	25.5 ± 0.2	7.78 ± 1.98	N.A.
	V_max	8.11 ± 0.10	N.A.	43.1 ± 0.2	378 ± 1	2136 ± 127	N.A.
	CL_ini/int	0.987 ± 0.054	0.373 ± 0.004	1.67 ± 0.02	247 ± 2	4575 ± 1195	0.0299 ± 0.0001
13	K_m	437 ± 18	N.A.	N.A.	80.8 ± 1.8	22.9 ± 1.8	N.A.
	V_max	23.3 ± 0.5	N.A.	N.A.	590 ± 2	5520 ± 96	N.A.
	CL_ini/int	0.888 ± 0.041	0.202 ± 0.001	1.17 ± 0.01	122 ± 3	4018 ± 328	1.02 ± 0.00
14	K_m	82.2 ± 0.6	181 ± 0	284 ± 9	40.0 ± 0.1	3.67 ± 0.66	N.A.
	V_max	5.93 ± 0.01	25.3 ± 0.0	149 ± 2	11.9 ± 0.0	668 ± 25	N.A.
	CL_ini/int	1.20 ± 0.01	2.34 ± 0.00	8.73 ± 0.29	4.97 ± 0.02	3035 ± 556	0.0156 ± 0.0002
Prodrugs at R2 position and −OH at R1 position
15	K_m	362 ± 63	N.A.	N.A.	278 ± 57	N.A.	N.A.
	V_max	22.5 ± 1.7	N.A.	N.A.	884 ± 66	N.A.	N.A.
	CL_ini/int	1.04 ± 0.20	1.17 ± 0.01	1.02 ± 0.00	53.0 ± 11.6	8.91 ± 0.11	N.D.
16	K_m	316 ± 11	N.A.	N.A.	48.6 ± 0.4	220 ± 7	N.A.
	V_max	19.0 ± 0.2	N.A.	N.A.	917 ± 1	294 ± 3	N.A.
	CL_ini/int	1.00 ± 0.04	0.711 ± 0.000	2.09 ± 0.01	315 ± 3	22.3 ± 0.8	0.430 ± 0.001

N.A., not applicable.