Warrants	12 Months Ended
Apr. 30, 2021
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. Each share of common stock was sold together with a warrant to purchase 0.35 of a share of common stock at a combined purchase price of $92.00. 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 April 30, 2021, none of the warrants had 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. Each share of common stock was sold together with a warrant to purchase 0.30 of a share of common stock at a combined purchase price of $135.00. 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 April 30, 2021, none of the warrants had 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. The pre-funded warrants have no expiration date. As of April 30, 2021, all of the pre-funded warrants had 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 April 30, 2021, warrants to purchase 732,500 shares of the common stock had been exercised. The Company accounts for warrants issued in connection with its June and July 2016 public offerings in accordance with the guidance on “Accounting for Certain Financial Instruments with Characteristics of Both Liabilities and Equity” 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 near zero at April 30, 2021 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

12 Months Ended

Apr. 30, 2021

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. Each share of common stock was sold together with a warrant to purchase 0.35 of a share of common stock at a combined purchase price of $92.00. 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 April 30, 2021, none of the warrants had 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. Each share of common stock was sold together with a warrant to purchase 0.30 of a share of common stock at a combined purchase price of $135.00. 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 April 30, 2021, none of the warrants had 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. The pre-funded warrants have no expiration date. As of April 30, 2021, all of the pre-funded warrants had 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 April 30, 2021, warrants to purchase 732,500 shares of the common stock had been exercised.

The Company accounts for warrants issued in connection with its June and July 2016 public offerings in accordance with the guidance on “Accounting for Certain Financial Instruments with Characteristics of Both Liabilities and Equity” 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 near zero at April 30, 2021 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.