Note 9 - Stockholders' Equity	3 Months Ended
Mar. 31, 2019
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	9. Stockholders’ Equity Series B Preferred Stock As of March 31, 2019, there are 100 shares of our Series B Convertible Preferred Stock (“Series B Preferred Stock”) outstanding. The Series B Preferred Stock may be converted at any time at the option of the holder into shares of our common stock at a conversion price of $175 per share. During the three months ended March 31, 2019, there were no conversions or other transactions involving our Series B Preferred Stock. Series F Preferred Stock On February 18, 2019, we entered into Exchange Agreements (the “Exchange Agreements”) with holders of our Series C and Series E Convertible Preferred Stock, pursuant to which the holders exchanged all shares of Series C and Series E Preferred Stock held by them for an aggregate of 2,763 shares of Series F Convertible Preferred Stock (“Series F Preferred Stock”). Each share of Series F Preferred Stock is entitled to a liquidation preference equal to its $1,000 stated value, has no voting rights, and is not entitled to a dividend. The Series F Preferred Stock is convertible at any time at the option of the holders into shares of our common stock, at a conversion price equal to the lesser of (i) $7.50 per share and (ii) 90% of the volume weighted average price of the common stock immediately preceding the delivery of a notice of conversion. The Series F Preferred Stock contains price adjustment provisions, which may, under certain circumstances reduce the conversion price to match if we sell or grant options to purchase, including rights to reprice, our common stock or common stock equivalents at a price lower than the then conversion price of the Series F Preferred Stock. During January and February 2019 ( prior to the exchange discussed above), the holders converted 587 shares of Series C Preferred Stock into 78,280 shares of our common stock. During March 2019 ( subsequent to the exchange), the holders converted 180 shares of Series F Preferred Stock into 40,000 shares of our common stock. As of March 31, 2019, there are no shares of our Series C or Series E Preferred Stock outstanding, and 2,583 shares of our Series F Preferred Stock outstanding. Series G Preferred Stock On February 25, 2019, we entered into a Securities Purchase Agreement (the “Securities Purchase Agreement”) with the purchasers identified therein (the “Purchasers”) providing for sale to the Purchasers of an aggregate of up to 1,000 shares of our Series G Convertible Preferred Stock (“Series G Preferred Stock”) and related warrants for gross proceeds of up to $1.0 million, to be funded at up to three different closings. Each share of Series G Preferred Stock is entitled to a liquidation preference equal to its $1,000 stated value, has no voting rights, and is not entitled to a dividend. The Series G Preferred Stock is convertible at any time at the option of the holders into shares of our common stock, at a conversion price equal to the lesser of (i) $7.50 per share and (ii) 90% of the volume weighted average price of the common stock immediately preceding the delivery of a notice of conversion. The Series G Preferred Stock contains price adjustment provisions, which may, under certain circumstances reduce the conversion price to match if we sell or grant options to purchase, including rights to reprice, our common stock or common stock equivalents at a price lower than the then conversion price of the Series G Preferred Stock. At the first closing, which occurred on February 26, 2019, we issued 500 shares of Series G Preferred Stock in exchange for the payment by the Purchasers of $250,000 in the aggregate, plus the cancellation of Term Notes held by the Purchasers (see Note 7 ) in the amount of $250,000. At the first closing we also issued the Purchasers Series I Warrants to purchase an aggregate of 33,334 shares of our common stock. The warrants have an exercise price of $7.50 per share, are exercisable six months from the issuance date, and have a term of exercise equal to five years from the date they first become exercisable. The warrants contain anti-dilution and price adjustment provisions, which may, under certain circumstances reduce the exercise price to match if we sell or grant options to purchase, including rights to reprice, our common stock or common stock equivalents at a price lower than the then exercise price of the warrants; in the event of such adjustment, the number of shares subject to the warrants will also increase so that the aggregate exercise price remains the same for each warrant. Within 50 to 60 days after the first closing, we may exercise the right to sell the Purchasers an aggregate of up to $250,000 of Series G Preferred Stock and related warrants at the second closing. Within 110 to120 days after the first closing, we may exercise the right to sell the Purchasers an aggregate of up to $250,000 of Series G Preferred Stock and related warrants at the third closing. At the second and third closings, assuming the sale of all of the Series G Preferred Stock that may be sold at those times, the Purchasers will receive aggregate additional Series I Warrants to purchase up to 66,668 shares of our common stock. During the three months ended March 31, 2019, there were no conversions or other transactions involving our Series G Preferred Stock. Common Stock Transactions As discussed above, during the three months ended March 31, 2019, we issued 118,280 shares of our common stock pursuant to conversions our Series C and Series F Preferred Stock. Stock Options During the three months ended March 31, 2019, there were no transactions involving our stock option plans. As of March 31, 2019, there are 29,441 stock options outstanding ( $53.19/share weighted-average exercise price), 13,585 of which are exercisable ( $93.92/share weighted-average exercise price). Stock Purchase Warrants During the three months ended March 31, 2019, we issued 33,334 stock purchase warrants in connection with the sale of our Series G Preferred Stock as discussed above. As of March 31, 2019, there are 148,032 stock purchase warrants outstanding ( $11.54/share weighted-average exercise price), 94,698 of which are exercisable ( $12.75/share weighted-average exercise price). Stock-Based Compensation Expense Stock-based compensation expense related to our stock option plans was $26,652 and $23,978 during the three -month periods ended March 31, 2019 and 2018, respectively. Stock-based compensation expense related to stock options is recognized on a straight-line basis over the requisite service period for the award and is allocated to research and development expense or general and administrative expense based upon the related employee classification. As of March 31, 2019, there was $183,731 of unrecognized compensation expense related to stock options, which we expect to recognize over a weighted average period of 2.0 years. Additionally, during the three -month periods ended March 31, 2019 and 2018 we recorded stock-based compensation expense of $126,572 and $28,571, respectively, associated with common stock issued for financial advisory services. As of March 31, 2019, there was $72,509 of unrecognized stock-based compensation expense associated with these arrangements, which we expect to recognize during the second quarter of 2019.

Stockholders’ Equity

Series B Preferred Stock

As of

March 31, 2019,

there are

100

shares of our Series B Convertible Preferred Stock (“Series B Preferred Stock”) outstanding. The Series B Preferred Stock

may

be converted at any time at the option of the holder into shares of our common stock at a conversion price of

$175

per share. During the

three

months ended

March

31,

2019,

there were

conversions or other transactions involving our Series B Preferred Stock.

Series F Preferred Stock

February 18, 2019,

we entered into Exchange Agreements (the “Exchange Agreements”) with holders of our Series C and Series E Convertible Preferred Stock, pursuant to which the holders exchanged all shares of Series C and Series E Preferred Stock held by them for an aggregate of

2,763

shares of Series F Convertible Preferred Stock (“Series F Preferred Stock”). Each share of Series F Preferred Stock is entitled to a liquidation preference equal to its

$1,000

stated value, has

voting rights, and is

not

entitled to a dividend. The Series F Preferred Stock is convertible at any time at the option of the holders into shares of our common stock, at a conversion price equal to the lesser of (i)

$7.50

per share and (ii)

90%

of the volume weighted average price of the common stock immediately preceding the delivery of a notice of conversion. The Series F Preferred Stock contains price adjustment provisions, which

may,

under certain circumstances reduce the conversion price to match if we sell or grant options to purchase, including rights to reprice, our common stock or common stock equivalents at a price lower than the then conversion price of the Series F Preferred Stock.

During

January

and

February 2019 (

prior to the exchange discussed above), the holders converted

587

shares of Series C Preferred Stock into

78,280

shares of our common stock. During

March 2019 (

subsequent to the exchange), the holders converted

180

shares of Series F Preferred Stock into

40,000

shares of our common stock. As of

March 31, 2019,

there are

shares of our Series C or Series E Preferred Stock outstanding, and

2,583

shares of our Series F Preferred Stock outstanding.

Series G Preferred Stock

February 25, 2019,

we entered into a Securities Purchase Agreement (the “Securities Purchase Agreement”) with the purchasers identified therein (the “Purchasers”) providing for sale to the Purchasers of an aggregate of up to

1,000

shares of our Series G Convertible Preferred Stock (“Series G Preferred Stock”) and related warrants for gross proceeds of up to

$1.0

million, to be funded at up to

three

different closings. Each share of Series G Preferred Stock is entitled to a liquidation preference equal to its

$1,000

stated value, has

voting rights, and is

not

entitled to a dividend. The Series G Preferred Stock is convertible at any time at the option of the holders into shares of our common stock, at a conversion price equal to the lesser of (i)

$7.50

per share and (ii)

90%

of the volume weighted average price of the common stock immediately preceding the delivery of a notice of conversion. The Series G Preferred Stock contains price adjustment provisions, which

may,

At the

first

closing, which occurred on

February 26, 2019,

we issued

500

shares of Series G Preferred Stock in exchange for the payment by the Purchasers of

$250,000

in the aggregate, plus the cancellation of Term Notes held by the Purchasers (see Note

) in the amount of

$250,000.

At the

first

closing we also issued the Purchasers Series I Warrants to purchase an aggregate of

33,334

shares of our common stock. The warrants have an exercise price of

$7.50

per share, are exercisable

six

months from the issuance date, and have a term of exercise equal to

five

years from the date they

first

become exercisable. The warrants contain anti-dilution and price adjustment provisions, which

may,

under certain circumstances reduce the exercise price to match if we sell or grant options to purchase, including rights to reprice, our common stock or common stock equivalents at a price lower than the then exercise price of the warrants; in the event of such adjustment, the number of shares subject to the warrants will also increase so that the aggregate exercise price remains the same for each warrant.

Within

days after the

first

closing, we

may

exercise the right to sell the Purchasers an aggregate of up to

$250,000

of Series G Preferred Stock and related warrants at the

second

closing. Within

110

to120

days after the

first

closing, we

may

exercise the right to sell the Purchasers an aggregate of up to

$250,000

of Series G Preferred Stock and related warrants at the

third

closing. At the

second

and

third

closings, assuming the sale of all of the Series G Preferred Stock that

may

be sold at those times, the Purchasers will receive aggregate additional Series I Warrants to purchase up to

66,668

shares of our common stock.

During the

three

months ended

March

31,

2019,

there were

conversions or other transactions involving our Series G Preferred Stock.

Common Stock Transactions

As discussed above, during the

three

months ended

March 31, 2019,

we issued

118,280

shares of our common stock pursuant to conversions our Series C and Series F Preferred Stock.

Stock Options

During the

three

months ended

March 31, 2019,

there were

transactions involving our stock option plans. As of

March 31, 2019,

there are

29,441

stock options outstanding (

$53.19/share

weighted-average exercise price),

13,585

of which are exercisable (

$93.92/share

weighted-average exercise price).

Stock Purchase Warrants

During the

three

months ended

March 31, 2019,

we issued

33,334

stock purchase warrants in connection with the sale of our Series G Preferred Stock as discussed above. As of

March 31, 2019,

there are

148,032

stock purchase warrants outstanding (

$11.54/share

weighted-average exercise price),

94,698

of which are exercisable (

$12.75/share

weighted-average exercise price).

Stock-Based Compensation Expense

Stock-based compensation expense related to our stock option plans was

$26,652

and

$23,978

during the

three

-month periods ended

March 31, 2019

and

2018,

respectively. Stock-based compensation expense related to stock options is recognized on a straight-line basis over the requisite service period for the award and is allocated to research and development expense or general and administrative expense based upon the related employee classification. As of

March

31,

2019,

there was

$183,731

of unrecognized compensation expense related to stock options, which we expect to recognize over a weighted average period of

2.0

years.

Additionally, during the

three

-month periods ended

March 31, 2019

and

2018

we recorded stock-based compensation expense of

$126,572

and

$28,571,

respectively, associated with common stock issued for financial advisory services. As of

March 31, 2019,

there was

$72,509

of unrecognized stock-based compensation expense associated with these arrangements, which we expect to recognize during the

second

quarter of

2019.