Warrants

The Company accounts for common stock warrants as either equity instruments, derivative liabilities or liabilities depending on the specific terms of the warrant agreement. See Note 3 for further details on accounting policies related to the Company’s convertible instruments, including common stock warrants.

In connection with various financing transactions, the Company has issued warrants to purchase the Company’s common stock. In December 2017, the Company issued (i) pre-funded warrants to purchase an aggregate of 5,922,208 shares of the Company’s common stock and (ii) common stock purchase warrants to purchase up to an aggregate of 14,046,950 shares of the Company’s common stock including warrants to purchase up to 410,586 shares, issued pursuant to the partial exercise of the underwriters option to purchase additional common stock purchase warrants. Each pre-funded warrant was sold together with a common stock purchase warrant to purchase one share of the Company’s common stock at a combined effective price of $0.77 per share and accompanying warrant. Each common stock purchase warrant has an exercise price of $0.77 per share, was exercisable upon the date of issuance and expires five years from the date of issuance. As additional compensation, the Company issued warrants to the underwriter to purchase 436,364 shares of the Company’s common stock. Each such warrant has an exercise price of $0.9625 per share, and was exercisable as of the date of the underwriting agreement, and will expire five years after the date of the underwriting agreement.

In March 2017, the Company issued warrants to purchase 3,437,334 shares of its common stock in connection with the Company’s public offering of convertible preferred stock and warrants (each a Series A Warrant and collectively, the Series A Warrants), more fully described in Note 10. Each Series A Warrant has an exercise price of $2.54, will be exercisable six months after the date of issuance and will expire five years from the date of issuance.

The Company’s outstanding warrants consist of both liability-classified warrants and equity-classified warrants. The following table summarizes outstanding warrants to purchase the Company’s common stock:



	Number of warrants
	March 31, 2018	December 31, 2017	Exercise Price		Expiration Dates
Liability-classified Warrants
Issued with June 2012 Convertible Notes	375,194	375,194	$	7.50	Jun 2018
Issued in Series E Preferred Stock offering	523,045	523,045	$	22.50	Dec 2018
Issued with September 2016 Convertible Notes	6,029,174	6,029,174	$	4.50	Sep 2021
Total liability-classified warrants	6,927,413	6,927,413

Equity-classified Warrants
Issued in 2017 Series A Preferred Stock Offering	3,437,334	3,437,334	$	2.54	Mar 2022
Issued in December 2017 Common Stock Offering - common warrants	14,046,950	14,046,950	$	0.77	Dec 2022
Issued in December 2017 Common Stock Offering - underwriter warrants	436,364	436,364	$	0.9625	Dec 2022
Issued in December 2017 Common Stock Offering - pre-funded warrants	—	2,416,104	$	0.01	No exp
Total equity-classified warrants	17,920,648	20,336,752


Total outstanding warrants	24,848,061	27,264,165

The table below is a summary of the Company’s warrant activity during the three months ended March 31, 2018:



	Number of warrants					Weighted- average exercise price
	Liability-classified	Equity-classified		Total		Weighted- average exercise price
Outstanding at December 31, 2017	6,927,413	20,336,752		27,264,165		$	2.26
Granted	—	—		—		—
Exercised	—	(2,416,104	)	(2,416,104	)	0.01
Expired	—	—		—		—
Outstanding at March 31, 2018	6,927,413	17,920,648		24,848,061		$	2.48

Accounting for Liability-Classified Warrants

The Company’s liability-classified warrants were recorded as liabilities at their estimated fair value at the date of issuance, with the subsequent changes in estimated fair value recorded in warrant revaluation income (expense) in the Company’s Condensed Consolidated Statements of Operations in each subsequent period. The change in the estimated fair value of the warrant liability for the three months ended March 31, 2018 and March 31, 2017, resulted in non-cash income (expense) of approximately $0.2 million and ($0.1) million respectively.

Additionally, the liability-classified warrants are classified as either current or non-current on the Company’s Condensed Consolidated Balance Sheets based on their contractual expiration date. The Company utilizes a Monte Carlo simulation valuation method to value its liability-classified warrants.

Assumptions Used In Determining Fair Value of Liability-Classified Warrants

The estimated fair value of warrants is determined using Level 2 and Level 3 inputs (as described below). Inherent in the Monte Carlo simulation valuation method are the following assumptions:

Volatility. The Company estimates stock price volatility based on the Company’s historical stock price performance over a period of time that matches the volume-weighted average expected remaining life of the warrants.

Risk-free interest rate. The risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve in effect at the valuation date commensurate with the expected remaining life assumption.

Expected remaining life. The expected life of the warrants is assumed to be equivalent to their remaining contractual term.

Dividend rate. The dividend rate is based on the historical rate, which the Company anticipates will remain at zero.

Scenarios. The probability of complex features of the warrants being triggered is subjective (no observable inputs or available market data) and based on internal and external information known to management at the valuation date. Such assumptions include, among other inputs, probabilities related to a change of control and when it might occur as well as probabilities related to a default under the provisions of the Notes and when it might occur.

Changes to the key assumptions or to the scenarios used in the valuation model, including the probability of key events, such as a change of control transaction, could have a material impact to the overall valuation of the warrant liability.

The following table summarizes the calculated aggregate fair values, along with the inputs and assumptions utilized in each calculation:




($ in thousands except per share data)	March 31, 2018			December 31, 2017
Calculated aggregate value	$	838		$	1,073
Weighted average exercise price per share	$	6.02		$	6.02
Closing price per share of common stock	$	0.59		$	0.64
Volatility	93.0		%	92.2		%
Weighted average remaining expected life	3 years, 1 month			3 years, 4 months
Risk-free interest rate	2.34		%	2.00		%
Dividend yield	—			—