Shareholder Equity (Tables)

6 Months Ended

Jun. 30, 2019

Summary of Warrants Outstanding and Warrant Activity

Warrants outstanding and warrant activity for the six-month period ended June 30, 2019 is as follows:



Description	Classification	Issuance Date	Exercise Price	Expiration Date	Balance December 31, 2018	Warrants Issued	Warrants Exercised	Warrants Expired	Balance June 30, 2019
Non-tradeable warrants	Equity	06/21/19	$1.47	June 2020	—	20,410,000	—	—	20,410,000
Non-tradeable warrants	Equity	03/23/18	$1.20	Mar. 2023	7,210,945	—	1,861,115	—	5,349,830
Non-tradeable warrants	Equity	11/01/17	$0.80	Nov. 2022	1,991,687	—	1,500,000	—	491,687
Non-tradeable warrants	Equity	05/11/15	$11.83	May 2025	27,500	—	—	—	27,500
Non-tradeable warrants	Equity	11/25/14	$11.04	Nov. 2024	27,500	—	—	—	27,500
					9,257,632	20,410,000	3,361,115	—	26,306,517

Summary of Stock-Based Compensation Expense

Stock-based compensation expense by award type was as follows (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock options	$	355	$	283	$	680	$	659
Restricted stock	—		—		$	—	22
Employee stock purchase plan	—		2		2		5
	$	355	$	285	$	682	$	686

The Company allocated stock-based compensation expense as follows in the condensed consolidated statements of operations and comprehensive loss (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development expense	$	86	$	123	$	139	$	288
General and administrative expense	269		162		$	543	$	398
	$	355	$	285	$	682	$	686

Summary of Stock Option Activity and Related Information

A summary of the stock option activity is presented below:



	Shares		Weighted-Average Exercise Price
Outstanding at December 31, 2018	3,941,947		$	2.12
Granted	2,425,115		0.93
Exercised	(30,000	)	1.50
Cancelled or forfeited	(558,018	)	2.30
Outstanding at June 30, 2019	5,779,044		$	1.60
Exercisable at June 30, 2019	1,189,418		$	2.86