how to interpret an antepost market

I just cannot get my head around a market to interpret the likelihood of a horse running in a particular race. For example, in the antepost market for the Nat Hunt chase at Cheltenham, for Don Poli, there is £150 available to back at 6 and £15 at 6.2. However to lay, there is £10 at 30.
How do I interpret that market strength/weakness to try and decide if a horse is likely to run or not (Don Poli is just an example)?