We use equity-based compensation programs to provide long-term performance incentives for our employees. These incentives consist primarily of stock options and RSUs. In December 2008, we adopted the MEI Pharma, Inc. 2008 Stock Omnibus Equity Compensation Plan (“Omnibus Plan”), as amended and restated from time-to-time, under which 29,014,794 shares of common stock are authorized for issuance. The Omnibus Plan provides for the grant of options and/or other stock-based or stock-denominated awards to our non-employee directors, officers, and employees. As of December 31, 2022, there were 3,335,415 shares available for future grant under the Omnibus Plan. In January 2023, our stockholders approved the increase of 8,000,000 additional shares available for future grant under the Omnibus Plan.

In May 2021, we adopted the 2021 Inducement Plan ("Inducement Plan"), under which 2,500,000 shares of common stock are authorized for issuance. The Inducement Plan is intended to assist us in attracting and retaining selected individuals to serve as employees who are expected to contribute to our success, by providing an inducement for such individuals to enter into employment with us, and to achieve long-term objectives that will benefit stockholders of the Company. As of December 31, 2022, there were 491,397 shares available for future grant under the Inducement Plan.

Total share-based compensation expense for all stock awards consisted of the following for the periods presented (in thousands):


	Three Months Ended December 31,				Six Months Ended December 31,
	2022		2021		2022		2021
Research and development	$	201	$	658	$	850	$	1,280
General and administrative		612		1,666		1,522		3,583
Total share-based compensation expense	$	813	$	2,324	$	2,372	$	4,863

Stock options granted to employees vest 25% one year from the date of grant and ratably each month thereafter for a period of 36 months and expire ten years from the date of grant. Stock options granted to directors vest ratably each month for a period of 12 months from the date of grant and expire ten years from the date of grant. Of the total options outstanding of 25,404,860 as of December 31, 2022, 23,396,257 were granted under the Omnibus Plan and 2,008,603 were granted under the Inducement Plan.

A summary of our stock option activity and related data follows:


	Number of Options			Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at June 30, 2022		19,934,007		$	2.85
Granted		9,220,410			0.53
Expired		(156,667	)		2.63
Forfeited/Cancelled		(3,592,890	)		2.05
Outstanding at December 31, 2022		25,404,860			2.12		7.7	$	—
Vested and exercisable at December 31, 2022		12,242,063			2.89		6.3	$	—

As of December 31, 2022, the aggregate intrinsic value of outstanding options was calculated as the difference between the exercise price of the underlying options and the closing price of our common stock of $0.24 on that date.

Unrecognized compensation expense related to non-vested stock options totaled $5.2 million as of December 31, 2022. Such compensation expense is expected to be recognized over a weighted average period of 1.6 years. As of December 31, 2022, we expect all options to vest.

We use the Black-Scholes valuation model to estimate the grant date fair value of stock options. To calculate these fair values, the following weighted average assumptions were used for the periods presented:


	Six Months Ended December 31,
	2022			2021
Risk-free interest rate		2.9	%		1.1	%
Expected life (years)		6.0			6.0
Expected volatility		84.1	%		68.0	%
Dividend yield		0.0	%		0.0	%
Weighted average grant date fair value	$	0.39		$	1.78

A summary of our RSU activity and related data for the six months ended December 31, 2022 was as follows:


	Number of RSUs			Weighted Average Grant Date Fair Value
Non-vested at June 30, 2022		184,400		$	3.49
Vested		(184,400	)	$	3.49
Non-vested at December 31, 2022		—		$	—