6. EQUITY COMPENSATION PLANS (Tables)

12 Months Ended

Apr. 30, 2016

Share-based compensation expense

	2016		2015		2014
Cost of contract manufacturing	$	41,000	$	59,000	$	68,000
Research and development		2,124,000		2,904,000		2,804,000
Selling, general and administrative		2,733,000		3,739,000		3,335,000
Total	$	4,898,000	$	6,702,000	$	6,207,000
Share-based compensation from:
Stock options	$	4,720,000	$	6,465,000	$	5,803,000
Restricted stock awards		–		–		139,000
ESPP		178,000		237,000		265,000
	$	4,898,000	$	6,702,000	$	6,207,000

Stock Options

Fair value valuation assumptions

	Year Ended April 30,
	2016		2015		2014
Risk-free interest rate		1.66%		1.95%		1.32%
Expected life (in years)		5.96		5.74		5.84
Expected volatility		104.74%		111.78%		113.92%
Expected dividend yield		–		–		–

Schedule of stock option transaction activity

Stock Options	Shares			Weighted Average Exercisable Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (1)
Outstanding, May 1, 2015		20,708,672			$1.54
Granted		4,173,260			$1.26
Exercised		(177,266	)		$0.79
Canceled or expired		(953,405	)		$1.87
Outstanding, April 30, 2016		23,751,261			$1.48		6.68	$	–
Exercisable and expected to vest		23,652,443			$1.48		6.67	$	–
Exercisable, April 30, 2016		20,153,764			$1.51		6.31	$	–

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⁽¹⁾ Aggregate intrinsic value represents the difference between the exercise price of an option and the closing market price of our common stock on April 29, 2016 (the last trading day of fiscal year 2016), which was $0.3541 per share.

Employee Stock Purchase Plan [Member]

Schedule of Share Based Payment Award Employee Stock Purchase Plan Valuation Assumptions Table Text Block

	Year Ended April 30,
	2016		2015		2014
Risk-free interest rate		0.18%		0.06%		0.08%
Expected life (in years)		0.50		0.50		0.50
Expected volatility		46.14%		63.54%		93.39%
Expected dividend yield		–		–		–