13. Commitments and Contingencies Operating Leases In May 2013, the Company entered into a lease for office space in Burlington, Massachusetts. The lease is for a 42-month term with minimum monthly lease payments beginning at $17,588 per month and escalating over the lease term. The Company provided a letter of credit to the lessor in the amount of $98,000 as a security deposit pursuant to the lease agreement to secure its obligations under the lease. During January 2015, this letter of credit was reduced to $74,000 pursuant to the original lease agreement. The Company incurred rent expense of $242,946, $227,381, and $123,023 for the years ended December 31, 2014, 2013 and 2012, respectively . Future minimum lease payments under operating leases as of December 31, 2014, together with the new Burlington lease, were as follows: Year Ending December 31, 2015 289,972 2016 243,532 Total $ 533,504 AstraZeneca License Agreements On September 3, 2010, the Company entered into an exclusive license agreement with AstraZeneca for FX007. The agreement grants the Company an exclusive, royalty-bearing right and license to the patent rights detailed in the agreement. Per the terms of the license agreement, the Company was required to pay a nonrefundable fee of $1,000,000: $500,000 within thirty days of the execution of the agreement and $500,000 six months after the execution of the agreement. The Company recorded $1,000,000 as research and development expense during 2010. The agreement includes terms for potential future milestone payments including up to an aggregate of $21 million upon the achievement of certain regulatory and development milestones for a first licensed product for OA indications, or up to an aggregate of $15 million upon the achievement of certain regulatory and development milestones for a first-licensed product for non-OA indications. Upon commercialization of a product that results from the technology licensed under the agreement, the Company will owe AstraZeneca tiered royalty payments on net sales base