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&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;b&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold;" size="2"&gt;5. Note Payable&lt;/font&gt;&lt;/b&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;On March&amp;#160;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&amp;#160;1, 2012. On December&amp;#160;30, 2011, the Company amended its credit facility to provide for an extension of its drawdown period through December&amp;#160;1, 2012, provided that it had drawn down at least $5,000,000 as of August&amp;#160;1, 2012. On July&amp;#160;23, 2012, the Company obtained an additional 60 day extension to the initial drawdown date from August&amp;#160;1, 2012 to October&amp;#160;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. The debt is secured by all the Company&amp;#8217;s assets, except for the Company&amp;#8217;s intellectual property, which is subject to a negative pledge agreement.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-ALIGN: center; MARGIN: 0in 0in 0pt;" align="center"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Upon entry into the agreement, the Company issued warrants to purchase 34,000 shares of Series&amp;#160;C redeemable convertible preferred stock (&amp;#8220;Series&amp;#160;C Preferred&amp;#8221;) 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 interest expense over the expected term of the loan.&lt;/font&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Upon extension of the credit facility in December&amp;#160;2011, the Company issued a warrant to purchase up to an additional 86,000 shares of its Series&amp;#160;D redeemable convertible preferred stock (&amp;#8220;Series&amp;#160;D Preferred&amp;#8221;) 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 interest expense over the expected term of the loan. As of June&amp;#160;30, 2013 and December&amp;#160;31, 2012, $15,000,000 and $5,000,000 respectively had been drawn. There is no further borrowing capacity under this facility as of June&amp;#160;30, 2013.&lt;/font&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Effective immediately prior to the closing of the Company&amp;#8217;s IPO, the warrants for convertible preferred stock became warrants for common stock and were reclassified to stockholders&amp;#8217; equity. Prior to the IPO, the Company had classified the warrants 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 June&amp;#160;30, 2012 were as follows: contractual life according to the remaining terms of the warrants, no dividend yield, risk-free interest rate of 1.43% and volatility of 76%. Assumptions used to revalue the Series&amp;#160;D Preferred warrants at June&amp;#160;30, 2012 were as follows: contractual life according to the remaining terms of the warrants, no dividend yield, risk-free interest rate of 1.58% and volatility of 77%.&lt;/font&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;The increase in the fair value of the Series&amp;#160;C Preferred warrants from issuance in March&amp;#160;2011 through the IPO in October&amp;#160;of 2012, totaled $55,000 and was recorded in warrant and other income (expense), net, in the statement of operations and comprehensive loss, and included expense of $105,000 and $97,000 for the three and six months ended June&amp;#160;30, 2012. The decrease in value of the Series&amp;#160;D Preferred warrants from issuance in December&amp;#160;2011 through the IPO in October&amp;#160;of 2012 totaled $18,000 and was recorded in warrant and other income (expense), net, in the statement of operations and comprehensive loss, including expense of $5,000 and income of $2,000 for the three and six months ended June&amp;#160;30, 2012.&lt;/font&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;All warrants were exercised on a cashless basis in December&amp;#160;of 2012 resulting in the net issuance of 49,000 shares of common stock and no warrants are outstanding as of June&amp;#160;30, 2013.&lt;/font&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Included in interest expense for the three and six months ended June&amp;#160;30, 2013 and 2012 was amortization of debt issuance costs of $85,000, $170,000, $52,000 and $104,000, respectively, and interest expense of $469,000 and $779,000 related to the note payable for the three and six months ended June&amp;#160;30, 2013. No interest expense was recorded for the three and six months ended June&amp;#160;30, 2012 as no amounts had yet been drawn under the credit facility. The balance of accrued interest expense at June&amp;#160;30, 2013 was $120,000. The remaining unamortized debt issuance cost at June&amp;#160;30, 2013 was $906,000.&lt;/font&gt;&lt;/p&gt;
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