STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities
Net loss	$ (12,275)	$ (5,558)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	6	5
Stock-based compensation expense	771	47
Change in fair value of warrant liability		(397)
Amortization of debt issuance costs	4
Changes in operating assets and liabilities:
Prepaid expenses and other assets	219	854
Accounts payable and accrued expenses	2,097	1,535
Net cash used in operating activities	(9,178)	(3,514)
Cash flows from investing activities
Purchases of investments	(1,740)
Maturities of short-term investments	249
Deposit on equipment	(352)
Net cash used in investing activities	(1,843)
Cash flows from financing activities
Proceeds from exercise of stock options	234	28
Proceeds from issuance of convertible preferred stock, net of issuance costs		2,000
Net cash provided by (used in) financing activities	234	1,893
Financing costs		(135)
Net decrease in cash and cash equivalents	(10,787)	(1,621)
Cash and cash equivalents-beginning of year	49,720	10,037
Cash and cash equivalents-end of year	38,933	8,416
Supplemental disclosure of cash flow information
Cash paid for interest	$ 230	20
Issuance of Series C Preferred Stock		$ 500