142 



high concentrations of Con A (in excess of 100yg/ml) but 

 the mechanism of its resistance in unknown. If it is resis- 

 tant as a result of not being able to internalize Con A, 

 then it would be expected to be more resistant to ADGG- 

 Con A toxicity than the parent H-7 line. If it is resis- 

 tant at some step after internalization of bound Con A, 

 then the H-7Wcr would be expected to be as sensitive to 

 ADGG-Con A as the parent line. 



Both cell lines displayed comparable sensitivity to free 

 a-amanitin or ADGG over 48 hours of continuous exposure to 

 either inhibitor (Figure 27; Table 8) with ADGG being less 

 toxic chan a-amanitin by a ractor of six for both Knes. 

 This can be a reflection of the reduced affinity of ADGG for 



RNA polymerase II and/or impeded entry of the toxin to the 



-9 

 cell. With a K T for ADGG of 6.9 x 10 M and an ID cr . . „ n 



I 50 for H-7 



CHO cells of 3.0 x 10 M there is obviously a barrier to the 

 entry of ADGG to the cell with less than 0.25% of the inhi- 

 bitor entering the cell. 



Exposure of H-7 cells to ADGG, Con A or ADGG-Con A 

 for 15 minutes (Figure 26) resulted in little toxicity 

 from free ADGG. This could be a function of low permea- 

 bility of the cells to ADGG. ADGG-Con A caused a dramatic 

 inhibition with 50% inhibition of cell growth occurring at 

 2.1 x 10 M with respect to ADGG. Neither ADGG nor Con A 

 at concentrations equivalent to those present in the conju- 

 gate caused inhibition. This result indicates that the 

 ADGG-Con A conjugate is minimally 50 times more toxic than 

 the free ADGG following a 15 minute exposure. 



