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Unaudited Statements of Cash Flows - USD ($)
6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Operating activities    
Net loss $ (21,741,633) $ (29,913,712)
Adjustments to reconcile net loss to net cash used in operating activities:    
Depreciation 135,872 141,631
Non-cash lease expense 332,413 302,843
Stock-based compensation expense 3,583,822 2,901,839
Changes in assets and liabilities:    
Prepaid expenses and other current assets 812,917 (34,547)
Accounts payable (70,944) 363,167
Accrued expenses (1,230,997) 844,026
Noncurrent accrued expenses 515,144  
Operating lease liabilities (388,646) (347,744)
Net cash used in operating activities (18,052,052) (25,742,497)
Investing activities    
Purchases of property and equipment (14,519) (114,305)
Net cash used in investing activities (14,519) (114,305)
Financing activities    
Proceeds from issuance of common stock, net of issuance costs 9,574,137  
Proceeds from exercise of stock options 135,583 106,321
Net cash provided by financing activities 9,709,720 106,321
Net change in cash and cash equivalents (8,356,851) (25,750,481)
Cash and cash equivalents, beginning of period 158,201,441 209,917,595
Cash and cash equivalents, end of period 149,844,590 $ 184,167,114
Non-cash investing and financing activities    
Property acquisition costs included in accounts payable $ 6,592