4. Note Payable

On March 21, 2011, the Company executed a debt financing agreement whereby the Company had access to borrow up to $15,000,000 of senior loan financing through January 1, 2012. On December 30, 2011, the Company amended its credit facility to provide for an extension of its drawdown period through December 1, 2012, provided that it had drawn down at least $5,000,000 as of August 1, 2012. On July 23, 2012, the Company obtained an additional 60 day extension of the initial drawdown date from August 1, 2012 to October 1, 2012. For each draw, the Company shall make six months of interest only payments at a fixed rate of 11.5% followed by 30 months of interest and principal payments at a fixed rate of 8.5% and a final payment of 6% of the amount drawn. As of December 31, 2011, no amounts had been drawn. The debt is secured by all the Company's assets, except for the Company's intellectual property, which is subject to a negative pledge agreement.

On October 1, 2012 the Company drew $5,000,000 and, in November 2012, obtained an extension allowing for the draw of the remaining $10,000,000 in $5,000,000 increments by January 31, 2013 and February 28, 2013 (see further discussion in Note 12, "Subsequent Events").

Upon entry into the agreement, the Company issued warrants to purchase 34,000 shares of Series C redeemable convertible preferred stock ("Series C Preferred") at an exercise price of $13.3530. The estimated fair value of the warrants at issuance of approximately $345,000 was recorded as a deferred financing cost offsetting the note payable liability and is being amortized to warrant and other interest income (expense), net, over the expected term of the loan.

Upon extension of the credit facility in July 2012, the Company issued a warrant to purchase up to an additional 86,000 shares of its Series D redeemable convertible preferred stock ("Series D Preferred") at an exercise price of $13.9040. The estimated fair value of the warrant at issuance of approximately $1,074,000 was recorded as a deferred financing cost offsetting the note payable liability and is being amortized to warrant and other interest income (expense), net over the expected term of the loan.

Upon issuance, the Company classified the warrants to purchase convertible preferred stock as a liability and re-measured the liability to estimated fair value using the Black-Scholes option pricing model. Assumptions used to revalue the Series C Preferred warrants at December 31, 2011 were as follows: contractual life according to the remaining terms of the warrants, no dividend yield, risk-free interest rate of 1.75% and volatility of 80%. Assumptions used to revalue the Series D Preferred warrants at December 31, 2011 were as follows: contractual life according to the remaining terms of the warrants, no dividend yield, risk-free interest rate of 1.89% and volatility of 81%. Upon IPO in October of 2012, the warrants to purchase convertible preferred stock were converted to warrants to purchase common stock. Upon this conversion, the warrants ceased to be remeasured and the warrant liability was reclassified to equity.

The increase in the fair value of the Series C Preferred warrants from issuance in March 2011 through IPO in October of 2012, totaled $55,000 and has been recorded in warrant and other interest income (expense), net, in the statements of operations and comprehensive loss, and included interest expense of $91,000 and interest income of $36,000 for the years ended December 31, 2012 and 2011, respectively. The decrease in value of the Series D Preferred warrants from issuance in December 2011 through IPO in October of 2012 totaled $18,000 and has been recorded in warrant and other interest income (expense), net, in the statement of operations and comprehensive loss for the year ended December 31, 2012. There was no change in the fair value of the Series D Preferred warrants during the year ended December 31, 2011 due to the timing of issuance.

In December of 2012, the warrants to purchase 120,000 shares of common stock were net exercised on a cashless basis for 49,000 shares of common stock. There were no warrants outstanding as of December 31, 2012.

Included in warrant and other interest income (expense), net for the year ended December 31, 2012 was amortization of debt issuance costs of $272,000 and interest expense related to the note payable of $169,000. The balance of accrued interest expense at December 31, 2012 was $22,000. The remaining unamortized debt issuance cost at December 31, 2012 was $1,076,000.

The credit facility includes various covenants. As of December 31, 2011 and 2012, we were in compliance with all covenants associated with the credit facility.

Future maturities of the Note payable as of December 31, 2012 are as follows:


2013	$	1,500,000
2014		2,000,000
2015		1,500,000

		5,000,000
Unamortized debt issuance cost		(1,076,000	)

		3,924,000
Current portion		(1,160,000	)

Note payable—net of current portion	$	2,764,000