Other income was less than $0.1 million in the six months ended June 30, 2022 and 2021.
Interest expense— Interest expense was $0.2 million and less than $0.1 million in the three months ended June 30, 2022 and 2021, respectively. The $0.2 million increase was primarily related to an increase in the outstanding principal of the note payable during the three months ended June 30, 2022.
Interest expense was $0.4 million and $0.1 million in the six months ended June 30, 2022 and 2021, respectively. The $0.3 million increase was primarily related to an increase in the outstanding principal of the note payable during the six months ended June 30, 2022.
Loss on the extinguishment of debt—In May 2021, we entered into a new loan arrangement and repaid the outstanding principal balance under an existing outstanding term loan agreement prior to its maturity date. We also paid fees on behalf of the lender and we recorded a loss on extinguishment of debt of $0.2 million in connection with this transaction.
Income taxes—We did not incur material income tax expenses for the six months ended June 30, 2022 or 2021. Given our lack of prior earnings history, we have a full valuation allowance primarily related to our net operating loss and R&D credit carryforwards that we do not consider more likely than not to be realized.
Liquidity and Capital Resources
Since our inception, our primary sources of capital have been proceeds from sales of convertible preferred stock, payments received in connection with the Collaboration Agreement and proceeds from borrowings under various credit facilities.
For the years ended December 31, 2021 and 2020, we incurred net operating losses of $60.7 million and $25.4 million, respectively. For the six months ended June 30, 2022 and 2021, we incurred net operating losses of $44.1 million and $23.3 million, respectively.
As of December 31, 2021, we had an accumulated deficit of $226.1 million. As of December 31, 2021, we had outstanding debt of $6.4 million, net of debt issuance costs and debt discount. As of December 31, 2021, we had cash and cash equivalents of $76.9 million.
As of June 30, 2022, we had an accumulated deficit of $275.0 million. As of June 30, 2022, we had outstanding debt of $16.6 million, net of debt issuance costs and debt discount. As of June 30, 2022, we had cash and cash equivalents of $40.6 million and short-term investments of $5.0 million.
Our cash flows may fluctuate and are difficult to forecast and will depend on many factors. The revenue from the sale of EndeavorRx at the present time is not sufficient to cover operating costs incurred. Our ability to achieve sufficient revenue to cover our costs is highly dependent on achieving and maintaining broad market acceptance by patients and physicians and our patients having the ability to obtain reimbursement from third-party payers. We expect to continue to generate operating losses and negative operating cash flows for the foreseeable future.
Through December 31, 2021, we have received $228.3 million in gross cash proceeds from sales of preferred stock and gross proceeds of $10.0 million from corporate bonds and notes payable.
In May 2021, we entered into an Amended and Restated Loan and Security Agreement, by and between Silicon Valley Bank (“SVB”), SVB Innovation Credit Fund VIII, L.P., (together, with SCB, the “Lenders”) and Akili (such agreement, the “SVB Term Loan”), which consists of a secured term loan facility in an aggregate amount of up to $50.0 million, of which, $35.0 million became available at closing. As of June 30, 2022, there was $15.0 million outstanding under the term loan facility. Additionally, the corporate bond issued with Shionogi in March 2019 continues to have $5.0 million outstanding as of June 30, 2022.