4. INTANGIBLES

All of our intangible assets are subject to amortization and are amortized using the straight-line method over their estimated useful life.

We acquired license agreements, related to OncoGenex’s product candidate apatorsen, upon the acquisition of OncoGenex on August 1, 2017. As at the date of the acquisition, the agreements were determined to have a fair value of $8.6 million with an estimated useful life of 6 years. (Note 2—Reverse Merger)

In August 2017, we discontinued further development of apatorsen. We provided a notice of discontinuance to our former development partners for apatorsen, Ionis Pharmaceuticals, Inc., or Ionis, and a letter of termination to the University of British Columbia, or UBC, notifying them that we have discontinued development of apatorsen resulting in termination of all licensing agreements related to this product candidate. We believe that all financial obligations, other than continuing mutual indemnification obligations and our requirement to pay for out-of-pocket patent expenses incurred up to the date of termination and for abandoning the apatorsen patents and patent applications, under all apatorsen related agreements with Ionis and UBC, are no longer owed and no further payments are due. We recognized a loss on disposition of apatorsen of $8.6 million and a deferred income tax recovery of $2.9 million as a result of discontinuing the development program and providing a notice of discontinuance of the license agreements with Ionis.

We acquired license and supply agreements, in relation to cytisine upon the acquisition of Extab Corporation, or Extab, on May 18, 2015. The agreements were determined to have a fair value of $3.1 million with an estimated useful life of 14 years (Note 5— Extab Acquisition).

The components of intangible assets were as follows:

For the three months ended March 31, 2018 we recorded license agreement amortization expense of $0.1 million. For the three months ended March 31, 2017 we recorded license agreement amortization expense of $0.1 million. The following table outlines the estimated future amortization expense related to intangible assets held as of March 31, 2018:

We evaluate the carrying amount of intangible assets periodically by taking into account events or circumstances that may warrant revised estimates of useful life or that indicate the asset may be impaired. We conducted an impairment analysis for long lived assets, including the license and supply agreements for the active pharmaceutical ingredient cytisine, and concluded no impairment has occurred as of March 31, 2018.