Let's first start by expanding the expressions:

(2x-5)(2x+5) = 4x^2 - 25

(2x+3)^3 = (2x+3)(2x+3)(2x+3)
= (4x^2 + 12x + 9)(2x+3)
= 8x^3 + 24x^2 + 18x + 12x^2 + 36x + 27
= 8x^3 + 36x^2 + 54x + 27

Now we can substitute these expanded expressions back into the original equation and simplify:

4x^2 - 25 - (8x^3 + 36x^2 + 54x + 27) = -1
4x^2 - 25 - 8x^3 - 36x^2 - 54x - 27 = -1
-4x^3 - 32x^2 - 54x - 52 = -1
-4x^3 - 32x^2 - 54x - 51 = 0

So the simplified equation is -4x^3 - 32x^2 - 54x - 51 = 0.