Table 1. Parameters of the non-linear regression analysis of the viability (V) decay upon incubation of cells with SP.

Time, assay	Cell line	Parameters of the viability decay regression
		V0	Vfast	Vslow	kfast, mM−1	kslow, mM−1	Plateau
96 h, MTT	SK-NA-S	98	8	33	14	0.12	53
	A549	100	9	64	8	0.12	27
	C6	101	11	89	112	0.03	0*
	N2A	94	-	19	-	0.1	75*
	U87	100	19	82	~2*105	0.01	0*
	HSF	96	21	36	9	0.24	39
	T98G	98	23	51	3	0.14	24
	MOGGCCM	99	26	53	1.6	0.13	20
5 h, MTT	Primary rat astrocytes	100	20	80	90	0.09	0
24 h, CTB	LN405	103	-	103	-	0.004	0*
	1321N1	105	-	105	-	0.001	0*
	U87	105	7	-	0.8	-	98*
	T98G	105	-	76	-	0.02	28*
	52/11	102	24	78	1.1	0.02	0*
	85/13	102	-	56	-	0.01	46*

Experimental curves in Figures 1 and 3 with significant viability decays were best approximated by the biphasic exponential equation: V_SP=V_fast*e^−k_fast^*[SP] + V_slow*e^−k_slow^*[SP] + Plateau, where V_fast=(V₀-Plateau)*PercentFast*0.01; V_slow=(V₀-Plateau)*(100-PercentFast)*0.01. Plateau is V at infinite times; PercentFast is the fast fraction of the span from V₀ to Plateau. For the SP-resistant cell lines exhibiting low amplitude of decay under experimental conditions, plateau could not be defined. In these cases (marked as *) the decay equations were simplified by manual setting the plateau value to zero. Then, if the regression constant k_slow approached zero, the corresponding V_slow was considered as plateau. The residual fraction (V_fast) was considered as the fast or slow step according to the value of the regression constant k_fast. The highly variable k_fast and differences between the regression parameter V₀ and 100%, comparable to V_fast, result from insufficient resolution of the fast process by regression analysis due to experimental limitations.