Six months ended June 30, 2023 and 2022
Collaboration revenue
In January 2023, we entered into the Collaboration Agreement with AbbVie and recognized collaboration revenue of $6.6 million for the six months ended June 30, 2023. No collaboration revenue was recognized for the six months ended June 30, 2022.
Research and development expenses
Research and development expenses were $9.6 million and $13.8 million for the six months ended June 30, 2023 and 2022, respectively.
Research and development expenses decreased by $4.2 million for the six months ended June 30, 2023. Of the $4.2 million decrease in research and development expenses, ONC-01 external program related expenses decreased by $3.4 million as a result of a decrease in product development activities. BCP-01 external program related expenses decreased by $3.2 million, net of contra expense, as a result of our decision to seek a partner in order to continue the BCP-01 trial and further development activities. These decreases were offset by an increase of $1.7 million in outsourced research and materials relating to the AbbVie collaboration. In addition, personnel related costs increased by $0.7 million for the six months ended June 30, 2023 primarily as a result of $0.6 million contra-expense to personnel related costs relating to the CARES Act employee retention credit recorded during the six months ended June 30, 2023.
General and administrative expenses
General and administrative expenses were $7.2 million and $6.8 million for the six months ended June 30, 2023 and 2022, respectively.
General and administrative expenses increased by $0.4 million for the three months ended June 30, 2023. The increase was primarily a result of a $1.2 million increase in professional fees, including consulting and legal related costs associated with the Merger, offset by a $0.8 million decrease in general expenses including insurance.
Interest income
Interest income was $0.4 million and $3,000 for the six months ended June 30, 2023 and 2022, respectively.
Interest income increased by $0.4 million for the six months ended June 30, 2023 as a result of increased interest rates on our cash balances held with a financial institution.
Liquidity and capital resources
Since our inception, we have incurred significant operating losses. We expect to incur significant expenses and operating losses for the foreseeable future as we continue advancement of our programs and development candidates. Through June 30, 2023, we raised an aggregate of $155.2 million in gross proceeds from sales of our common stock, Series A convertible preferred stock and warrants, warrant and stock option exercises, the issuance of convertible promissory notes, the Paycheck Protection Program, or PPP, loan that was forgiven in May 2021, and strategic partnerships with AbbVie Global Enterprises Ltd, or AbbVie. In January 2023, we received a $30.0 million upfront payment from AbbVie under the collaboration and option agreement, or the Collaboration Agreement. In addition, we received $17.6 million in expense reimbursement from the Department of Defense, or DoD under the Other Transaction Authority for Prototype Agreement, or the OTA Agreement, from inception through 2022.
On October 1, 2021, we entered into an Open Market Sale Agreement, or the ATM Agreement, with Jefferies Group LLC, which provides that, upon the terms and subject to the conditions and limitations in the ATM Agreement, we may elect, from time to time, to offer and sell shares of common stock under the registration statement having an aggregate offering price of up to $75.0 million through Jefferies Group LLC acting as sales agent. We filed a shelf registration