Warrants	6 Months Ended
Oct. 31, 2020
Warrants and Rights Note Disclosure [Abstract]
Warrants	(8) Warrants Liability Classified Warrants On June 2, 2016, the Company entered into a securities purchase agreement, which was amended on June 7, 2016 (as amended, the “June Purchase Agreement”) with certain institutional purchasers (the “June Purchasers”). Pursuant to the terms of the June Purchase Agreement, the Company sold an aggregate of 20,850 shares of Common Stock together with warrants to purchase up to an aggregate of 7,298 shares of Common Stock. The warrants have an exercise price of $121.60 per share, became exercisable on December 3, 2016 (“Initial Exercise Date”), and will expire five years following the Initial Exercise Date. As of October 31, 2020, none of the warrants have been exercised. On July 22, 2016, the Company entered into a Second Amendment to the Purchase Agreement (the “Second Amended Purchase Agreement”) with certain institutional purchasers (the “July Purchasers”). Pursuant to the terms of the Second Amended Purchase Agreement, the Company sold an aggregate of 29,750 shares of Common Stock together with warrants to purchase up to an aggregate of 8,925 shares of Common Stock. The Warrants were exercisable immediately at an exercise price of $187.20 per share. The Warrants will expire on the fifth (5th) anniversary of the initial date of issuance. As of October 31, 2020, none of the warrants have been exercised. Equity Classified Warrants On April 8, 2019, the Company issued and sold 1,542,000 shares of common stock and pre-funded warrants to purchase up to 3,385,680 shares of common stock and common warrants to purchase up to 4,927,680 shares of our common stock in an underwritten public offering. The public offering price for the pre-funded warrants was equal to the public offering price of the common stock, less the $0.01 per share exercise price of each warrant. As of October 31, 2020, all of the pre-funded warrants have been exercised. The common stock warrants have an exercise price of $3.85 per share and expire five years from the issuance date. As of October 31, 2020, none of the common stock warrants have been exercised. The Company accounted for the warrants issued in connection with its June and July 2016 public offerings in accordance with the guidance in Topic 480 which provides that the Company classify the warrant instruments as a liability at its fair value. The warrant liabilities are subject to re-measurement at each balance sheet date using the Black-Scholes option pricing model. The June and July 2016 warrants contain a feature whereby they could require the transfer of assets and therefore are classified as a liability award in accordance with the guidance in Topic 480. The warrants have a value close to zero at October 31, 2020 and April 30, 2020 and are reflected within “Warrant liabilities” in the Consolidated Balance Sheets. The pre-funded and common warrants issued in the Company’s April 8, 2019 public offering did not meet the criteria to be classified as a liability award and therefore were treated as an equity award and recorded as a component of stockholders’ equity in the Consolidated Balance Sheets.

Warrants

6 Months Ended

Oct. 31, 2020

Warrants and Rights Note Disclosure [Abstract]

(8) Warrants

Liability Classified Warrants

On June 2, 2016, the Company entered into a securities purchase agreement, which was amended on June 7, 2016 (as amended, the “June Purchase Agreement”) with certain institutional purchasers (the “June Purchasers”). Pursuant to the terms of the June Purchase Agreement, the Company sold an aggregate of 20,850 shares of Common Stock together with warrants to purchase up to an aggregate of 7,298 shares of Common Stock. The warrants have an exercise price of $121.60 per share, became exercisable on December 3, 2016 (“Initial Exercise Date”), and will expire five years following the Initial Exercise Date. As of October 31, 2020, none of the warrants have been exercised.

On July 22, 2016, the Company entered into a Second Amendment to the Purchase Agreement (the “Second Amended Purchase Agreement”) with certain institutional purchasers (the “July Purchasers”). Pursuant to the terms of the Second Amended Purchase Agreement, the Company sold an aggregate of 29,750 shares of Common Stock together with warrants to purchase up to an aggregate of 8,925 shares of Common Stock. The Warrants were exercisable immediately at an exercise price of $187.20 per share. The Warrants will expire on the fifth (5th) anniversary of the initial date of issuance. As of October 31, 2020, none of the warrants have been exercised.

Equity Classified Warrants

On April 8, 2019, the Company issued and sold 1,542,000 shares of common stock and pre-funded warrants to purchase up to 3,385,680 shares of common stock and common warrants to purchase up to 4,927,680 shares of our common stock in an underwritten public offering. The public offering price for the pre-funded warrants was equal to the public offering price of the common stock, less the $0.01 per share exercise price of each warrant. As of October 31, 2020, all of the pre-funded warrants have been exercised. The common stock warrants have an exercise price of $3.85 per share and expire five years from the issuance date. As of October 31, 2020, none of the common stock warrants have been exercised.

The Company accounted for the warrants issued in connection with its June and July 2016 public offerings in accordance with the guidance in Topic 480 which provides that the Company classify the warrant instruments as a liability at its fair value. The warrant liabilities are subject to re-measurement at each balance sheet date using the Black-Scholes option pricing model. The June and July 2016 warrants contain a feature whereby they could require the transfer of assets and therefore are classified as a liability award in accordance with the guidance in Topic 480. The warrants have a value close to zero at October 31, 2020 and April 30, 2020 and are reflected within “Warrant liabilities” in the Consolidated Balance Sheets. The pre-funded and common warrants issued in the Company’s April 8, 2019 public offering did not meet the criteria to be classified as a liability award and therefore were treated as an equity award and recorded as a component of stockholders’ equity in the Consolidated Balance Sheets.