I'd wager they spent it. Crunchbase reports they had 60 employees at some update in the past, so it was probably higher than that at the peak. 60 employees alone probably cost them $6 to $8 million per year depending on all the perks. You could easily vaporize $25 to $35 million over four years in San Francisco on 60 employees.

But keep in mind that $45 million wasn't raised in the past four years.

On 9/08 they raised $28.7 million, and then another $5 million on 7/11. So they've raised $33.7m over the last four years.