Breast cancer cells that preferentially metastasize to lung or bone are more glycolytic, synthesize serine at greater rates, and consume less ATP and NADPH than parent MDA-MB-231 cells

Table 1 ¹³C lactate labeling and model-optimized flux ratios with [1,2-¹³C] glucose

	Lactate ¹³C isotopologue content (%)				Modeled flux ratios (%)
	M	M1	M2	M3	\(\frac{\frac{2}{3}{J}_{3f}}{J_0+\frac{2}{3}{J}_{3f}}\) (R1)	\(\frac{J_{3f}}{J_{3r}}\) (R2)	\(\frac{J_7}{J_{2c}+{J}_7}\) (R3)	\(\frac{J_{6a}}{J_{6a}+{J}_{6b}}\) (R4)	Model error (%)
T47D	50.02±0.13 ^a (50.08±0.08)	3.20±0.06 ^a(3.29±0.11)	45.89±0.19 ^a (45.89±0.19)	0.89±0.04 ^a (0.74±0.02)	8.9±0.5 ^a	64±6 ^a	3.9±0.1 ^a	81±16 ^a	0.42±0.09
MDA231	49.30±0.20 ^b (49.30±0.20)	2.52±0.07 ^b (2.35±0.08)	47.49±0.20 ^b (47.49±0.20)	0.69±0.06 ^b (0.85±0.04)	3.2±0.4 ^b	40±380 ^a,b	5.1±0.3 ^b	100±0 ^a	0.33±0.06
BoM	49.04±0.17 ^b (49.15±0.08)	3.28±0.14 ^a (3.23±0.24)	46.59±0.33 ^a (46.59±0.33)	1.09±0.05 ^a,c (1.03±0.05)	5.5±0.7 ^c	30±43 ^a,b	5.9±0.3 ^b	83±17 ^a	0.37±0.19
LM	49.08±0.05 ^b (49.25±0.13)	3.03±0.05 ^a (3.18±0.13)	46.60±0.12 ^a (46.60±0.12)	1.29±0.05 ^c (0.97±0.07)	6.2±0.2 ^a,c	30±3 ^b	5.4±0.4 ^b	17±9 ^b	0.73±0.22

Cells were equilibrated in 2-well Lab-Tek chambers for approximately 6.5 h with 5.5 mM [1,2-¹³C] glucose as the sole exogenous substrate. Basal respiration rate was assessed from 5 to 6.5 h, followed by 2 × 1 h incubations to determine the rates of glucose uptake, lactate and serine efflux, and ¹³C enrichment in lactate and serine. Respiration rates averaged 3.7±0.2, 25±4, 15±3, and 4.3±0.5 nmol O/min × mg for T47D, MDA-MB-231, BoM, and LM cells, respectively (mean ± SEM, n=6). ¹³C lactate labeling (mean ± SEM, n=6) is expressed as percent contribution of each isotopologue to total extracellular lactate (M, M1, M2, and M3 denote lactate with none, one, two, two, or three ¹³C atoms, respectively). Data in parentheses are simulated lactate labeling (mean ± SEM, n=6) from Model 1-optimized flux ratios R1, R2, R3, and R4. Model error was calculated as the sum of the absolute values of the difference between the measured and simulated M-M3 lactate. Within a column, means sharing common superscripts do not significantly differ

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