That’s painting with too broad a brush, IMO. Clearly, not all purine nukes are toxic or companies wouldn't waste time developing them or waste money licensing them.
It's safe to say guanosine based nukes are a threatened class. IDIX continues to low dose IDX-184 after the failure of the IDX-320/184 combo. The FDA could potentially halt development of all guanosine nukes if more AE's are seen within this subgroup.
Speaking of wasting money, look no further than BMY.