Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Stockholders' Equity

Schedule of warrants outstanding and exercisable for purchase of common stock

	Number of Shares
	June 30,	December 31,	Weighted-Average
Description	2019	2018	Exercise Price		Expiration Date
Issued in May 2013 financing (pre-funded)	1,977,041	1,977,041		$ 0.08	May 2020
Issued in September 2013 financing (pre-funded)	521,997	521,997		$ 0.08	Sep 2020
Issued in February 2014 financing (pre-funded)	269,844	269,844		$ 0.08	Feb 2021
Total	2,768,882	2,768,882

Summary of warrant activity

	Number of	Weighted-Average
	Warrants	Exercise Price
Outstanding at December 31, 2018	2,768,882	$	0.08
Issued	—		—
Exercised	—		—
Expired	—		—
Outstanding at June 30, 2019	2,768,882	$	0.08