Note 10 - Common Stock and Stock-based Compensation	6 Months Ended
Jun. 30, 2019
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	10. Common Stock and Stock-Based Compensation Reverse Stock Split Following approval by our shareholders at a meeting held on April 15, 2019, on April 30, 2019, we effected a one -for- five hundred reverse split of our common stock by the filing of an amendment to our certificate of incorporation with the State of Delaware. All share and per share information in our condensed consolidated financial statements and notes that relate to our common stock has been retroactively restated to reflect the reverse stock split. Common Stock Transactions As discussed in Note 9, during the three -month and six -month periods ended June 30, 2019, we issued 253,300 and 371,580 shares, respectively, of our common stock pursuant to conversions our Series C and Series F Preferred Stock. During the three -month and six -month periods ended June 30, 2018, we issued 46,000 and 106,000 shares, respectively, of our common stock pursuant to conversions our Series D Preferred Stock. During the three -month and six -month periods ended June 30, 2019, we issued 4,127 shares of our common stock in exchange for consulting services. During the three -month and six -month periods ended June 30, 2018, we issued - 0 - and 10,000 shares, respectively, of our common stock in exchange for investment banking and financial advisory services. See “Stock-Based Compensation Expense” below. Stock Options During the six months ended June 30, 2019, there were no transactions involving our stock option plans. As of June 30, 2019, there are 29,441 stock options outstanding ( $53.19/share weighted-average exercise price), 13,585 of which are exercisable at that date ( $93.92/share weighted-average exercise price). Stock Purchase Warrants During the six months ended June 30, 2019, we issued an aggregate of 100,002 stock purchase warrants in connection with the sale of our Series G Preferred Stock as discussed above. As of June 30, 2019, there are 294,302 stock purchase warrants outstanding ( $7.50/share weighted-average exercise price), 194,300 of which are exercisable at that date ( $7.50/share weighted-average exercise price). Stock-Based Compensation Expense Stock-based compensation expense related to our stock option plans was $26,664 and $53,316 during the three -month and six -month periods ended June 30, 2019, respectively, as compared to $23,221 and $47,199, respectively, during the same periods of 2018. 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 June 30, 2019, there was $157,067 of unrecognized compensation expense related to stock options, which we expect to recognize over a weighted average period of 1.9 years. During the three -month and six -month periods ended June 30, 2019 we recorded stock-based compensation expense of $78,509 and $205,080, respectively, associated with common stock issued for consulting and financial advisory services, as compared to $57,143 and $85,714, respectively, during the same periods of 2018.

10.

Common Stock and Stock-Based Compensation

Reverse Stock Split

Following approval by our shareholders at a meeting held on

April 15, 2019,

April 30, 2019,

we effected a

one

-for-

five hundred

reverse split of our common stock by the filing of an amendment to our certificate of incorporation with the State of Delaware. All share and per share information in our condensed consolidated financial statements and notes that relate to our common stock has been retroactively restated to reflect the reverse stock split.

Common Stock Transactions

As discussed in Note

during the

three

-month and

six

-month periods ended

June 30, 2019,

we issued

253,300

and

371,580

shares, respectively, of our common stock pursuant to conversions our Series C and Series F Preferred Stock. During the

three

-month and

six

-month periods ended

June 30, 2018,

we issued

46,000

and

106,000

shares, respectively, of our common stock pursuant to conversions our Series D Preferred Stock.

During the

three

-month and

six

-month periods ended

June 30, 2019,

we issued

4,127

shares of our common stock in exchange for consulting services. During the

three

-month and

six

-month periods ended

June 30, 2018,

we issued -

- and

10,000

shares, respectively, of our common stock in exchange for investment banking and financial advisory services. See “Stock-Based Compensation Expense” below.

Stock Options

During the

six

months ended

June 30, 2019,

there were

transactions involving our stock option plans. As of

June 30, 2019,

there are

29,441

stock options outstanding (

$53.19/share

weighted-average exercise price),

13,585

of which are exercisable at that date (

$93.92/share

weighted-average exercise price).

Stock Purchase Warrants

During the

six

months ended

June 30, 2019,

we issued an aggregate of

100,002

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

June 30, 2019,

there are

294,302

stock purchase warrants outstanding (

$7.50/share

weighted-average exercise price),

194,300

of which are exercisable at that date (

$7.50/share

weighted-average exercise price).

Stock-Based Compensation Expense

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

$26,664

and

$53,316

during the

three

-month and

six

-month periods ended

June 30, 2019,

respectively, as compared to

$23,221

and

$47,199,

respectively, during the same periods of

2018.

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

June

30,

2019,

there was

$157,067

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

1.9

years.

During the

three

-month and

six

-month periods ended

June 30, 2019

we recorded stock-based compensation expense of

$78,509

and

$205,080,

respectively, associated with common stock issued for consulting and financial advisory services, as compared to

$57,143

and

$85,714,

respectively, during the same periods of

2018.