C.	Debt Obligations

Deerfield Facility Agreement

June

2014,

the Company entered into a

$60

million facility agreement (the “Deerfield Facility Agreement”) with Deerfield Private Design Fund III, LP (“Deerfield”). The

first

payment to the Company under the terms of the Deerfield Facility Agreement consisted of a term loan of

$15

million (the “Term Note”) and a senior secured loan of

$10

million (the “Deerfield Convertible Note”). As of

June 30, 2016,

Deerfield was

longer obligated to provide the Company any additional disbursements under the Deerfield Facility Agreement. All loans issued under the Deerfield Facility Agreement bear interest at

9.75%

per annum. Deerfield

may

convert any portion of the outstanding principal and any accrued but unpaid interest on the Deerfield Convertible Note into shares of the Company’s common stock at an initial conversion price of

$5.85

per share (the "Deerfield Note Put Option").

The Company also issued to Deerfield a warrant to purchase

14,423,076

shares of Series D redeemable convertible preferred stock (“Series D Preferred”) at an exercise price of

$0.78

per share, which is exercisable until

June

2024

(the “Deerfield Warrant”). Upon completion of the Company's initial public offering (the "IPO"), the Deerfield Warrant automatically converted into a warrant to purchase

1,923,077

shares of the Company’s common stock at an exercise price of

$5.85

per share. This warrant qualifies as a participating security under ASC Topic

260,

Earnings per Share,

and is treated as such in the net loss per share calculation (Note I). If a Major Transaction occurs, as defined below, Deerfield

may

require the Company to redeem the Deerfield Warrant for a cash amount equal to the Black-Scholes value of the portion of the Deerfield Warrant to be redeemed (the “Warrant Put Option”). A Major Transaction is (i) a consolidation, merger, exchange of shares, recapitalization, reorganization, business combination or other similar event; (ii) the sale or transfer in

one

transaction or a series of related transactions of all or substantially all of the assets of the Company; (iii) a

third

-party purchase, tender or exchange offer made to the holders of outstanding shares, such that following such purchase, tender or exchange offer a change of control has occurred; (iv) the liquidation, bankruptcy, insolvency, dissolution or winding-up affecting the Company; (v) the shares of the Company’s common stock cease to be listed on any eligible market; and (vi) at any time, the shares of the Company’s common stock cease to be registered under Section

of the Securities Exchange Act of

1934,

as amended (the “Exchange Act”).

In addition, the Company issued to Deerfield

1,923,077

shares of Series D Preferred as consideration for the loans provided to the Company under the Deerfield Facility Agreement. Upon completion of the IPO, these shares automatically reclassified into

256,410

shares of the Company’s common stock. The Company recorded the fair value of the shares of Series D Preferred of

$1.5

million, to debt issuance costs on the date of issuance. The Company recorded the fair value of the Deerfield Warrant and the embedded Warrant Put Option to debt discount on the date of issuance. The debt issuance costs and debt discount are amortized over the term of the related debt and the expense is recorded as interest expense related to amortization of debt issuance costs and discount in the condensed statements of operations.

Pursuant to the Deerfield Facility Agreement, the Company

may

not

enter into specified transactions, including a debt financing in the aggregate value of

$750,000

or more, other than permitted indebtedness under the Deerfield Facility Agreement, a merger, an asset sale or any other change of control transaction or any joint venture, partnership or other profit sharing arrangement, without the prior approval of Deerfield. Additionally, if the Company were to enter into a major transaction, including a merger, consolidation, sale of substantially all of its assets or other change of control transaction, Deerfield would have the ability to demand that prior to consummation of such transaction the Company repay all outstanding principal and accrued interest of any notes issued under the Deerfield Facility Agreement. Under each warrant issued pursuant to the Deerfield Facility Agreement, Deerfield has the right to demand that the Company redeem the warrant for a cash amount equal to the Black-Scholes value of a portion of the warrant upon the occurrence of specified events, including a merger, an asset sale or any other change of control transaction.

The Company must repay

one

third

of the outstanding principal amount of all debt issued under the Deerfield Facility Agreement on the

fourth

and

fifth

anniversaries of the Deerfield Facility Agreement. The Company is then also obligated to repay the balance of the outstanding principal amount on

February

14,

2020.

The Company prepaid all outstanding interest and principal on the Term Note in

February 2016. The outstanding principal amount due on the fourth anniversary of the Deerfield Facility Agreement and the related accrued but unpaid interest as of such date was converted in common stock of the Company in accordance with the provisions of the Deerfield Convertible Note, as amended. Refer to the section entitled Facility Agreement Waiver and Fifth Amendment to Senior Secured Convertible Note below.

Interest accrued on outstanding debt under the Deerfield Facility Agreement is due quarterly in arrears. Upon notice to Deerfield, the Company had the option to have

one

or more of the

first

eight

of such scheduled interest payments added to the outstanding principal amount of the debt issued under the Deerfield Facility Agreement, provided that all such interest was due on

July

2016.

The Company elected this option on all

eight

of the scheduled interest payments through

June 30, 2016.

The accrued interest added to outstanding principal, was paid to Deerfield on

July 1, 2016.

First Amendment to Facility Agreement, Senior Secured Convertible Note and Warrant

In connection with the IPO, in

March 2015,

the Company entered into a First Amendment (the “First Amendment) to the Deerfield Facility Agreement, the Deerfield Convertible Note and Deerfield Warrant, by and between the Company and Deerfield. The First Amendment, among other things, clarified that all references to the conversion of shares of Series D Preferred into the Company’s common stock in the Deerfield Facility Agreement, the Deerfield Convertible Note and Deerfield Warrant shall include any reclassification of the outstanding shares of Series D Preferred into shares of the Company’s common stock.

Second Amendment to Senior Secured Convertible Note and Warrant

January 2016,

the Company entered into a Second Amendment (the “Second Amendment”) to the Deerfield Convertible Note and Deerfield Warrant, by and between the Company and Deerfield. The Second Amendment, among other things, clarified the calculation of an anti-dilution adjustment of the conversion price and exercise price of the Deerfield Convertible Note and Deerfield Warrant, respectively, in the event that the Company effects a firm commitment underwritten public offering of its securities.

Issuance of

5.50%

Senior Convertible Notes and Third Amendment to Facility Agreement, Senior Secured Convertible Note and Warrant

February 2016,

the Company issued

$86.3

million aggregate principal amount of its

5.50%

Senior Convertible Notes due

2021

(the

“2021

Notes”) to Cowen and RBC Capital Markets, LLC, as representatives of the several initial purchasers (the “Initial Purchasers”), who subsequently resold the

2021

Notes to qualified institutional buyers (the “Note Offering”) in reliance on the exemption from registration provided by Rule

144A

under the Securities Act.

The net proceeds from the Note Offering were approximately

$82.8

million, after deducting the Initial Purchasers’ discount and estimated offering expenses. Concurrent with the Note Offering, the Company used approximately

$18.6

million of the net proceeds from the Note Offering to repay in full the Term Note, plus all accrued but unpaid interest, a make-whole interest payment and a prepayment premium on the Term Note.

The

2021

Notes were issued pursuant to an Indenture, dated as of

February

2016

(the “Indenture”), between the Company and U.S. Bank National Association, as trustee (the "Trustee"). Interest on the

2021

Notes is payable semi-annually in cash in arrears on

February

and

August

of each year, beginning on

August

2016,

at a rate of

5.50%

per year. The

2021

Notes mature on

February

2021

unless earlier converted or repurchased. The

2021

Notes are

not

redeemable prior to the maturity date, and

sinking fund is provided for the

2021

Notes.

The

2021

Notes are convertible at an initial conversion rate of

58.4454

shares of the Company’s common stock per

$1,000

principal amount of the

2021

Notes, subject to adjustment under the Indenture, which is equal to an initial conversion price of approximately

$17.11

per share of common stock. Upon conversion, the

2021

Notes will be settled in shares of the Company’s common stock, together with a cash payment in lieu of delivering any fractional share. The conversion rate will be subject to adjustment in some events but will

not

be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, the Company will increase the conversion rate for a holder who elects to convert its

2021

Notes in connection with such a corporate event in certain circumstances.

If the Company undergoes a “fundamental change” (as defined in the Indenture), holders

may

require that the Company repurchase for cash all or any portion of their

2021

Notes at a fundamental change repurchase price equal to

100%

of the principal amount of the

2021

Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, holders who convert their

2021

Notes on or after the date that is

one

year after the last date of original issuance of the

2021

Notes

may

also be entitled to receive, under certain circumstances, an interest make-whole payment payable in shares of the Company’s common stock. The Company is bifurcating the fundamental change and make-whole interest payment provisions as embedded derivatives and marking them to fair value each reporting period (Note H).

The Indenture includes customary terms and covenants, including certain events of default after which the

2021

Notes

may

be due and payable immediately.

In connection with the Note Offering, in

February 2016,

the Company entered into a Third Amendment (the “Third Amendment”) to the Deerfield Facility Agreement, Deerfield Convertible Note and Deerfield Warrant with Deerfield. The Third Amendment, among other things, eliminated the Company’s ability to require Deerfield to convert the Deerfield Convertible Note into Company common stock. In addition, pursuant to the Third Amendment, Deerfield consented to the prepayment of the Term Note and the issuance of the

2021

Notes.

Refer to the section entitled Exchange Agreement below for a further discussion of an exchange of a certain portion of the

2021

Notes for shares of the Company's Series A Convertible Preferred Stock, par value

$0.0001

per share (the "Series A Preferred Stock").

Fourth Amendment to Senior Secured Convertible Note and Warrant

In connection with entering into the First ATM Agreement, in

October 2016,

the Company entered into a Fourth Amendment (the “Fourth Amendment”) to the Deerfield Convertible Note and the Deerfield Warrant with Deerfield. The Fourth Amendment, among other things, clarifies the calculation of an anti-dilution adjustment of the conversion price and exercise price of the Deerfield Convertible Note and Deerfield Warrant, respectively, in the event that the Company effects an “at the market offering” as defined in Rule

415

of the Securities Act of its common stock.

Facility Agreement Waiver and Fifth Amendment to Senior Secured Convertible Note

June 2018,

the Company entered into the Facility Agreement Waiver and Fifth Amendment (the "Fifth Amendment") to the Deerfield Convertible Note with Deerfield. The Fifth Amendment, among other things, provided that (i)

$3,333,333

of the principal amount, plus

$168,288

of accrued interest, of the Deerfield Convertible Note issued pursuant to the terms of the Deerfield Facility Agreement was converted into

598,568

shares of the Company’s common stock, with such principal conversion amount being applied against and in full satisfaction of the amortization payment due

June 2, 2018; (

ii) Deerfield waived specified rights under the Deerfield Facility Agreement with regards to such principal and interest amount; and (iii) amended specified provisions of the Deerfield Convertible Note as they relate to the delivery of shares of the Company’s common stock in connection with any conversion of the Deerfield Convertible Note.

Exchange Agreement

October 2018,

the Company entered into an Exchange Agreement (the “Exchange Agreement”) with Deerfield and Deerfield Special Situations Fund, L.P. (the “Holders”). Under the Exchange Agreement, the Holders exchanged an aggregate of

$9,577,000

principal amount of the

2021

Notes for an aggregate of

9,577

shares of Series A Preferred Stock,. The Company also agreed to pay the Holders an amount of

$95,105

in cash, which represented the amount of accrued and unpaid interest on the exchanged notes. The Exchange Agreement contains customary representations, warranties and covenants made by the Company and the Holders. The Exchange Agreement required the Company to reimburse the Holders for up to

$25,000

of expenses relating to the exchange.

As a condition to closing of the Exchange Agreement, the Company filed a Certificate of Designation of Preferences, Rights and Limitations of Series A Convertible Preferred Stock (the “Certificate of Designation”) with the Secretary of State of the State Delaware, setting forth the preferences, rights and limitations of the Series A Preferred Stock.

Each share of Series A Preferred Stock has an aggregate stated value of

$1,000

and is convertible into shares of common stock at a price equal to

$3.00

per share (subject to adjustment to reflect stock splits and similar events). Immediately following the exchange, there were an aggregate of

3,192,334

shares of common stock issuable upon conversion of the Series A Preferred Stock (without giving effect to the limitation on conversion described below). The Series A Preferred Stock is convertible at any time at the option of the Holders, provided that the Holders are prohibited from converting shares of Series A Preferred Stock into shares of common stock if, as a result of such conversion, such Holders (together with certain affiliates and “group” members) would beneficially own more than

4.985%

of the total number of shares of the Company’s common stock then issued and outstanding. The Series A Preferred Stock is

not

redeemable. In the event of the Company’s liquidation, dissolution or winding up, the Holders will receive an amount equal to

$0.0001

per share of Series A Preferred Stock, plus any declared but unpaid dividends, and thereafter will share ratably in any distribution of the Company’s assets with holders of common stock on an as-converted basis. With respect to rights upon liquidation, the Series A Preferred Stock ranks senior to the common stock and junior to existing and future indebtedness. Except as otherwise required by law (or with respect to approval of certain actions involving the Company’s organizational documents that materially and adversely affect the holders of Series A Preferred Stock), the Series A Preferred Stock does

not

have voting rights. The Series A Preferred Stock is

not

subject to any price-based anti-dilution protections and does

not

provide for any accruing dividends, but provides that holders of Series A Preferred Stock will participate in any dividends on the common stock on an as-converted basis (without giving effect to the limitation on conversion described above). The Certificate of Designation also provides for partial liquidated damages in the event that the Company fails to timely convert shares of Series A Preferred Stock into common stock in accordance with the Certificate of Designation.

First Supplemental Indenture, Sixth Amendment to Deerfield Convertible Note and Fifth Amendment to Deerfield Warrant

November 2018,

the Company entered into a First Supplemental Indenture (the “Supplemental Indenture”) with the Trustee. Pursuant to the Supplemental Indenture, the Indenture was amended to allow each Holder (as defined in the Indenture) or any beneficial holder of any

2021

Notes to, at its option, elect a limit on beneficial ownership as to such Holder or beneficial owner (but

not

as to any other Holder or beneficial owner) that is less than or equal to the

9.985%

Cap (as defined in the Indenture) or any other limit previously elected and then applicable to such Holder or beneficial owner upon written notice delivered to the Company at least

three

(

) business days prior to the date of effectiveness of such beneficial ownership limit (or such shorter period as

may

be agreed upon by the Company), specifying the percentage of shares of the Company’s common stock outstanding for the beneficial ownership limit that shall apply to such Holder or beneficial owner.

Also in

November 2018,

in connection with entering into the Supplemental Indenture, the Company entered into an amendment (the “Sixth Amendment”) with Deerfield to the Deerfield Convertible Note and Deerfield Warrant. The Sixth Amendment, among other things, lowers the beneficial ownership limit under both the Deerfield Convertible Note and Deerfield Warrant to

4.985%

of the Company’s outstanding common stock. The Sixth Amendment also includes a notice from Deerfield that it has elected to lower the beneficial ownership limit under the

2021

Notes, as to Deerfield and its affiliates, to

4.985%.

Seventh Amendment to Deerfield Convertible Note and Sixth Amendment to Deerfield Warrant

February 2019,

in connection with entering into the Purchase Agreement, the Company entered into an amendment (the “Seventh Amendment”), with Deerfield to the Deerfield Convertible Note and Deerfield Warrant. The Seventh Amendment, among other things, clarified that the anti-dilution protections contained in the Deerfield Convertible Note and Deerfield Warrant would

not

apply to sales made under the Purchase Agreement or Second ATM Agreement. The Seventh Amendment also included a waiver from Deerfield regarding any registration rights it

may

have under the Company’s amended and restated investor rights agreement in connection with the Registration Rights Agreement.

Except as modified by the First Amendment, Second Amendment, Third Amendment, Fourth Amendment, Fifth Amendment, Sixth Amendment and Seventh Amendment, all terms and conditions of the Deerfield Facility Agreement, Deerfield Warrant and Deerfield Convertible Note remained in full force and effect.

Line of Credit

During the

second

quarter of

2016,

the Company opened a line of credit with a total borrowing capacity of

$1.1

million with City National Bank of Florida (the "Line of Credit Agreement") to support several irrevocable letters of credit issued by the bank on behalf of the Company. The line of credit had an original maturity date of

January 31, 2018.

January 31, 2018,

the line of credit was renewed for an additional two-year term and was set to mature on

January 31, 2020.

The Line of Credit Agreement was collateralized by a restricted money market account, equal to the total amount of the letters of credit outstanding which are supported by the line of credit. In

March 2019,

the line of credit was closed

The irrevocable letters of credit and associated money market account remain and the money market account is reported as restricted cash on the condensed balance sheets.