In millions, except per share items | Jun-30-23 | Mar-31-23 | Dec-31-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 | Jun-30-21 |
| 10-Q | 10-Q | | 10-Q | 10-Q | 10-K | 10-Q | 10-Q |
Assets | | | | | | | | |
Current assets: | | | | | | | | |
Cash and cash equivalents | 25.8 | 30.8 | | 42.9 | 47.5 | 53.8 | 53.5 | 56.9 |
Restricted cash | 0.2 | 0.2 | | | | | | |
Accounts receivable | 0.4 | 0.7 | | 0.6 | 1.1 | 0.1 | 0.0 | 1.8 |
Prepaid expenses and other current assets | 1.0 | 1.2 | | 2.1 | 2.0 | 0.9 | 0.9 | 1.6 |
Total current assets | 27.4 | 32.8 | | 45.8 | 50.6 | 54.8 | 54.4 | 60.5 |
Property and equipment, net | 0.3 | 0.2 | | 0.3 | 0.3 | 0.3 | 0.3 | 0.4 |
Operating lease right-of-use asset | 0.3 | 0.7 | | 1.4 | 1.8 | 2.1 | 0.8 | 1.0 |
Long-term restricted cash | 1.5 | 1.5 | | 1.5 | 1.6 | 1.6 | 0.2 | |
Other long-term assets | 2.0 | 0.9 | | 0.4 | | | | |
Total assets | 31.4 | 36.1 | | 49.4 | 54.3 | 58.8 | 55.7 | 65.4 |
|
Liabilities and stockholders’ equity | | | | | | | | |
Current liabilities: | | | | | | | | |
Accounts payable | 0.9 | 0.6 | | 0.7 | 1.2 | 0.8 | 0.9 | 1.5 |
Accrued expenses and other current liabilities | 1.2 | 1.7 | | 1.6 | 1.1 | 1.2 | 1.4 | 1.2 |
Operating lease liability | 0.4 | 0.8 | | 1.7 | 1.6 | 1.4 | 0.9 | 1.2 |
Deferred revenue | 1.1 | 1.7 | | 1.6 | 1.5 | 0.9 | 2.0 | 3.0 |
Total current liabilities | 3.6 | 4.7 | | 5.6 | 5.4 | 4.4 | 5.1 | 6.9 |
Deferred revenue, net of current portion | 4.3 | 4.3 | | 5.4 | 5.7 | 6.1 | 5.4 | 5.4 |
Total liabilities | 7.9 | 9.0 | | 11.0 | 11.5 | 11.4 | 10.6 | 12.3 |
|
Commitments and contingencies (Note 11) | | | | | | | | |
Stockholders’ equity: | | | | | | | | |
Preferred stock, $0.0001 par value — 500,000 shares authorized; 6,746 shares designated Series A convertible preferred stock; no shares issued and outstanding at June 30, 2023 and December 31, 2022 | | | | | | | | |
Common stock, $0.0001 par value — 200,000,000 shares authorized; 3,652,285 and 3,639,185 shares issued and outstanding at June 30, 2023 and December 31, 2022, respectively | | | | | | | | |
Additional paid-in capital | 305.2 | 304.9 | | 302.6 | 301.8 | 301.0 | 295.8 | 295.5 |
Accumulated deficit | -281.7 | -277.9 | | -264.2 | -259.6 | -254.6 | -250.6 | -242.4 |
Total stockholders’ equity | 23.4 | 27.0 | | 38.4 | 42.8 | 47.4 | 45.2 | 53.1 |
Total liabilities and stockholders’ equity | 31.4 | 36.1 | | 49.4 | 54.3 | 58.8 | 55.7 | 65.4 |