operational costs increases. Stock-based compensation costs during the six month periods ended June 30, 2020 and 2019 were $0.3 million and $0.1 million, respectively.
Interest Income (Expense), net
Interest income for the six month period ended June 30, 2020 was $28,000 related to cash deposits. The Company did not incur interest expenses during the six months ended June 30, 2020 as there was no debt outstanding during the period.
Interest expense, net during the six month period ended June 30, 2019 included non-cash interest expense in connection with our convertible notes of $29,000 offset in part by interest income of $2,000 related to cash deposits. Non-cash interest expense during the six month period ended June 30, 2019 consisted of interest on principal in the amount of $13,000 and costs attributed to the underlying beneficial conversion features of the convertible notes in the form of discount amortization in the amount of $16,000.
Other Expense, net
Other expense, net was $1,000 during the six month period ended June 30, 2020, compared to a nominal amount during the six month period ended June 30, 2019. The net change of $1,000 was due to a fluctuations in realized foreign currency exchange gains and losses period over period.
Liquidity and Capital Resources
Prior to the Merger, Private NeuroBo funded operations with proceeds from sales of preferred stock and proceeds from the issuance of convertible debt. Prior to the Merger, Private NeuroBo received net proceeds of $40.9 million from sales of preferred stock and $0.5 million from the sales of convertible notes which were converted into shares of Private NeuroBo common stock, effective immediately prior to the closing of the Merger.
ln April 2018, Private NeuroBo issued an aggregate of 4,801,020 shares of Series A preferred stock (as adjusted for the exchange ratio (“Exchange Ratio”) in connection with the Merger), at a purchase price of $3.50 per share, for aggregate gross consideration of approximately $16.8 million. On December 30, 2019, each share of Series A preferred stock then outstanding was converted into common stock in accordance with the terms of the Merger Agreement.
ln August 2019, Private NeuroBo issued an aggregate of 3,463,593 shares of Series B preferred stock (as adjusted for the Exchange Ratio) at a purchase price of $7.00 per share, for aggregate gross consideration of approximately $24.2 million. On December 30, 2019, each share of Series B preferred stock then outstanding was converted into common stock in accordance with the terms of the Merger Agreement.
On April 13, 2020, we entered into a Securities Purchase Agreement with an institutional investor, pursuant to which we sold in a registered direct offering (the “Registered Offering”) 750,000 shares of our common stock, at an offering price of $10.00 per share. The Registered Offering resulted in gross proceeds of $7.5 million, before deducting the placement agent’s fees and related offering expenses.
Since inception, we have experienced significant losses and incurred negative cash flows from operations. We expect to incur further losses over the next several years as we develop our business. We have spent, and expect to continue to spend, a substantial amount of funds in connection with implementing our business strategy.
We will need substantial additional funding to support our continuing operations and to pursue our business strategy and, in the meantime, we have reduced scientific activity, as described under “Overview – Reduced Scientific Activity; Repurposing of NB-01” above, and we are carefully controlling expenses. In the first quarter of 2020, in connection with the reduced scientific activity, we directed our CRO partners and other vendors working on the Phase 3