Expanding a large dynamic expression involving roots of a degree 4 polynomial

Question

I am trying to find the eigenvalues of a 4x4 Matrix symbolically. Below is the code I am using,

P = (3 Subscript[a, 0]^2 - 125)/(Subscript[a, 0]^2 + 25);
Q = (20 Subscript[a, 0])/(Subscript[a, 0]^2 + 25);
R = (2 Subscript[a, 0]^2 Subscript[b, 0 ] c)/(
  Subscript[a, 0]^2 + 25);
S = (5  Subscript[a, 0] Subscript[b, 0 ] c)/(Subscript[a, 0]^2 + 25);
Subscript[\[Theta], 1] = (2 Subscript[a, 0]^2 c)/(
  Subscript[a, 0]^2 + 25);
Subscript[\[Theta], 2] = (5 Subscript[a, 0] c)/(
  Subscript[a, 0]^2 + 25);
M = ( {
    {P, Q, 0, 0},
    {R, S, Subscript[\[Theta], 1], Subscript[\[Theta], 2]},
    {0, 0 , P - \[Lambda], Q},
    {\[Sigma] Subscript[\[Theta], 1], \[Sigma] Subscript[\[Theta], 2],
      R, S - \[Lambda]}
   } );
x = Eigenvalues[M];
e1 = x[[1]] // ToRadicals

The element e1 represents the first eigenvalue of the matrix; I want it in the form of nested radicals instead of the Root function.Thus I have used the ToRadicals command.

I realize that the full expression is going to be extremely large, but I still require the full expression as I need to explicitly give it as a supporting information of an article. So when I try to to get the full expression by clicking the Show All button, I get the Abort Dynamic Updating popup. Is there any way to avoid this problem ? Even if it means waiting for an extended period of time?