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 September 30, 2021, there were 7,106,383 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 September 30, 2021, there were 1,772,000 shares available for future grant under the Inducement Plan.

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


	Three Months Ended September 30,
	2021		2020
Research and development	$	622	$	1,129
General and administrative		1,917		1,813
Total share-based compensation	$	2,539	$	2,942

Stock option activity for the three months ended September 30, 2021 was as follows:


	Number of Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at June 30, 2021		16,668,542		$	3.01
Granted		5,051,400			2.93
Forfeited / Cancelled		(1,078,419	)		3.10
Outstanding at September 30, 2021		20,641,523			2.98		7.9	$	4,131,984
Vested and exercisable at September 30, 2021		9,748,144			2.86		6.6	$	3,610,815

The fair value of each stock option granted during the three months ended September 30, 2021 is estimated on the grant date under the fair value method using a Black-Scholes valuation model. Stock options granted to employees during the three months ended September 30, 2021 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 during the three months ended September 30, 2021 vest ratably each month for a period of 12 months from the date of grant and expire ten years from the date of grant. The estimated fair values of the stock options, including the effect of estimated forfeitures, are expensed over the service period.

The following weighted-average assumptions were used to determine the fair value of options granted during the period:


	Three Months Ended September 30,
	2021			2020
Risk-free interest rate		1.1	%		0.4	%
Expected life (years)		6.1			6.0
Expected volatility		67.8	%		80.6	%
Dividend yield		0.0	%		0.0	%
Weighted-average grant date fair value	$	1.78		$	2.35

As of September 30, 2021, there was $13.0 million of unrecognized compensation expense related to the unvested portion of stock options. Such compensation expense is expected to be recognized over a weighted-average period of 1.8 years.

RSU activity for the three months ended September 30, 2021 was as follows:


	Number of RSUs			Weighted-Average Grant Date Fair Value
Non-vested at June 30, 2021		400,650		$	3.49
Vested		(130,000	)	$	3.49
Forfeited / Cancelled		(38,000	)	$	3.49
Non-vested at September 30, 2021		232,650		$	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. During the three months ended September 30, 2021, 130,000 RSUs vested. We issued 63,855 shares of common stock to RSU holders; 66,145 shares were surrendered to us by RSU holders as payment for the employee portion of the required withholding of associated payroll taxes. As of September 30, 2021, unrecognized compensation expense related to the unvested portion of our RSUs was approximately $0.3 million and is expected to be recognized over approximately nine months.