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, employees and advisors. As of June 30, 2021, there were 10,472,864 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 June 30, 2021, there were 2,331,000 shares available for future grant under the Inducement Plan.

Total share-based compensation expense for all stock awards consists of the following, in thousands:


	Years Ended June 30,
	2021		2020		2019
Research and development	$	4,144	$	2,777	$	2,239
General and administrative		6,101		4,024		4,323
Total share-based compensation	$	10,245	$	6,801	$	6,562

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. As of June 30, 2021, there were a total of 16,668,542 options outstanding. Of the total outstanding options, 16,499,542 were granted under the Omnibus Plan and 169,000 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, 2020		11,252,976		$	2.81
Granted		6,201,300		$	3.39
Exercised		(141,907	)	$	2.34
Forfeited / Cancelled		(643,827	)	$	3.43
Outstanding at June 30, 2021		16,668,542		$	3.01		7.7	$	4,739,572
Vested and exercisable at June 30, 2021		8,416,964		$	2.78		6.6	$	3,954,990

As of June 30, 2021, the aggregate intrinsic value of outstanding options is calculated as the difference between the exercise price of the underlying options and the closing price of our common stock of $2.85 on that date. The total fair value of options that vested during the years ended June 30, 2021, 2020 and 2019 was $6.4 million, $5.4 million, and $3.4 million, respectively.

A summary of our non-vested stock option activity:


	Number of Options			Weighted-Average Grant Date Fair Value
Non-vested at June 30, 2020		5,777,907		$	2.05
Granted		6,201,300		$	2.30
Forfeited		(587,890	)	$	2.31
Vested		(3,139,739	)	$	2.04
Non-vested at June 30, 2021		8,251,578		$	2.23

Unrecognized compensation expense related to non-vested stock options totaled $8.3 million as of June 30, 2021. Such compensation expense is expected to be recognized over a weighted-average period of 1.8 years. As of June 30, 2021, we expect all outstanding options to vest.

We use a 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:


	Years Ended June 30,
	2021			2020			2019
Risk-free interest rate		0.5	%		1.7	%		2.7	%
Expected life (years)		6.0			6.0			6.0
Expected volatility		80.1	%		74.1	%		82.5	%
Dividend yield		0.0	%		0.0	%		0.0	%
Weighted-average grant date fair value	$	2.30		$	1.64		$	2.78

A summary of our RSU activity and related data follows:


	Number of RSUs			Weighted-Average Grant Date Fair Value
Non-vested at June 30, 2020		—		$	—
Granted		442,650		$	3.49
Forfeited		(42,000	)	$	3.49
Non-vested at June 30, 2021		400,650		$	3.49

Each RSU represents the contingent right to receive one share of our common stock. Under the terms of the Omnibus Plan, each of the RSUs is calculated as 1.25 shares of common stock for purposes of determining the number of shares available for future grant. As of June 30, 2021, unrecognized compensation expense related to the unvested portion of our RSUs was approximately $0.5 million and is expected to be recognized over approximately 1.0 year.