WARRANT AGREEMENT To Purchase Shares of the Series C Preferred Stock of TransOral Pharmaceuticals, Inc.

Exhibit 4.3

Execution 4/13/06

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS AMENDED, OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED, OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL FOR THE HOLDER THEREOF REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933 ACT AS AMENDED, OR ANY APPLICABLE STATE SECURITIES LAWS.

WARRANT AGREEMENT

To Purchase Shares of the Series C Preferred Stock of

TransOral Pharmaceuticals, Inc.

Dated as of April 13, 2006 (the “Effective Date”)

WHEREAS, TransOral Pharmaceuticals, Inc., a Delaware corporation (the “Company” ), has entered into a Senior Loan and Security Agreement of even date herewith (the “Loan Agreement” ) with Hercules Technology Growth Capital, Inc., a Maryland corporation (the “Warrantholder” );

WHEREAS, the Company desires to grant to Warrantholder, in consideration for, among other things, the financial accommodations provided for in the Loan Agreement, the right to purchase shares of its Series C Preferred Stock pursuant to this Warrant Agreement the “Agreement”);

NOW, THEREFORE, the Company and Warrantholder agree as follows:

For value received, the Company hereby grants to the Warrantholder, and the Warrantholder is entitled, upon the terms and subject to the conditions hereinafter set forth, to subscribe for and purchase, from the Company, fully paid and non-assessable shares of the Preferred Stock (as defined below) at a purchase price of $1.15 per share (the “Exercise price”). The number of Shares is equal to 5% of the aggregate Advances made under the Loan and Security Agreement dated as of the Effective Date between Company and Warrantholder divided by the Exercise Price. The number and Exercise Price of such shares are subject to adjustment as provided in Section 8. As used herein, the following terms shall have the following meanings:

“Act” means the Securities Exchange Act of 1933, as amended.

“Charter” means the Company’s Certificate of Incorporation, as may be amended from time to time.

“Common Stock” means the Company’s common stock;

1.

“Initial Public Offering” means the initial underwritten public offering of the Company’s Common Stock pursuant to a registration statement under the Act, which public offering has been declared effective by the Securities and Exchange Commission (“SEC”);

“Merger Event” means (i) a merger or consolidation involving the Company in which the Company is not the surviving entity, or in which the outstanding shares of the Company’s capital stock are otherwise converted into or exchanged for shares of capital stock of another entity, or (ii) the sale of all or substantially all of the assets of the Company.

“Preferred Stock” means the Series C Preferred Stock of the Company and any other stock into or for which the Series C Preferred Stock may be converted or exchanged, and upon and after the occurrences of an event which results in the automatic or voluntary conversion, redemption or retirement of all (but not less than all) of the outstanding shares of such Preferred Stock, including, without limitation, the consummation of an Initial Public Offering of the Common Stock in which such a conversion occurs, then from and after the date upon which such outstanding shares are so converted, redeemed or retired, “Preferred Stock” shall mean such Common Stock; and

“Purchase Price” means, with respect to any exercise of this Warrant, an amount equal to the Exercise Price as of the relevant time multiplied by the number of shares of Preferred Stock requested to be exercised under this Warrant pursuant to such exercise.

Except as otherwise provided for herein, the term of this Warrant and the right to purchase Preferred Stock as granted herein (the “Warrant”) shall commence on the Effective Date and shall be exercisable for a period ending upon the earliest to occur of (i) ten (10) years from the Effective Date; or (ii) five (5) years after the Initial Public Offering. Notwithstanding anything herein to the contrary, upon the consummation of a Merger Event where the consideration to the Company is cash or publicly traded securities, this Warrant shall automatically be exercised pursuant to Section 3 hereof, without any action by the holder of this Warrant.

(a) Exercise. The purchase rights set forth in this Warrant are exercisable by the Warrantholder, in whole or in part, at any time, or from time to time, prior to the expiration of the term set forth in Section 2, by tendering to the Company at its principal office a notice of exercise in the form attached hereto as Exhibit I (the “Notice of Exercise”), duly completed and executed, together with payment of the Purchase Price. Promptly upon receipt of the Notice of Exercise and the payment of the Purchase Price in accordance with the terms set forth below, and in no event later than ten (10) business days thereafter, the Company shall issue to the Warrantholder a certificate for the number of shares of Preferred Stock purchased and shall execute the acknowledgment of exercise in the form attached hereto as Exhibit II (the “Acknowledgment of Exercise”) indicating the number of shares which remain subject to future purchases, if any. The date which such certificate shall be deemed to have been issued shall be the date of exercise of the Warrant in the manner set forth herein.

2.

The Purchase Price may be paid at the Warrantholder’s election either (i) by cash or check, or (ii) if the fair market value of one share of the Preferred Stock is greater than the Exercise Price then in effect, by surrender of all or a portion of the Warrant for shares of Preferred Stock to be exercised under this Warrant and, if applicable, an amended Agreement representing the remaining number of shares purchasable hereunder, as determined below (“Net Issuance”). If the Warrantholder elects the Net Issuance method, the Company will issue Preferred Stock in accordance with the following formula:

For purposes of the above calculation, current fair market value of Preferred Stock shall mean with respect to each share of Preferred Stock:

(i) if the exercise is made concurrent with the closing of an Initial Public Offering, and if the Company’s Registration Statement relating to such Initial Public Offering has been declared effective by the SEC, then the fair market value per share shall be the product of (x) the initial “Price to Public” of the Common Stock specified in the final prospectus with respect to the offering and (y) the number of shares of Common Stock into which each share of Preferred Stock is convertible at the time of such exercise;

(ii) if the exercise is after, and not in connection with, an Initial Public Offering, and:

(1) if the Common Stock is traded on a securities exchange, the fair market value shall be deemed to be the product of (x) the average of the closing prices over a five (5) trading day period ending the first trading day before the day the current fair market value of the securities is being determined and (y) the number of shares of Common Stock into which each share of Preferred Stock is convertible at the time of such exercise; or

(2) if the Common Stock is traded over-the-counter, the fair market value shall be deemed to be the product of (x) the average of the closing bid and asked prices quoted on the NASDAQ system (or similar system) over the five (5) day trading day period ending the first trading day before the day the current fair market value of the securities is being determined and (y) the number of shares of Common Stock into which each share of Preferred Stock is convertible at the time of such exercise.

3.

(iii) if at any time the Common Stock is not listed on any securities exchange or quoted in the NASDAQ National Market or the over-the-counter market, the current fair market value of Preferred Stock shall be the product of (x) the highest price per share which the Company could obtain from a willing buyer (not a current employee or director) for shares of Common Stock sold by the Company, ‘from authorized but unissued shares, as most recently determined in good faith by its Board of Directors and (y) the number of shares of Common Stock into which each share of Preferred Stock is convertible at the time of such exercise, unless the exercise is made concurrent with a Merger Event pursuant to which the Company is not the surviving party, in which case the fair market value of Preferred Stock shall be deemed to be the per share value received by the holders of the Company’s Preferred Stock on a common equivalent basis pursuant to such Merger Event.

Upon partial exercise by either cash or Net Issuance, the Company shall promptly issue an amended Agreement representing the remaining number of shares purchasable hereunder. All other terms and conditions of such amended Agreement shall be identical to those contained herein, including, but not limited to the Effective Date hereof.

(b) Exercise Prior to Expiration. To the extent this Warrant is not previously exercised as to all Preferred Stock subject hereto, and if the fair market value of one share of the Preferred Stock is greater than the Exercise Price then in effect, this Warrant shall be deemed automatically exercised pursuant to Section 3(a) (even if not surrendered) immediately before its expiration. For purposes of such automatic exercise, the fair market value of on share of the Preferred Stock upon such expiration shall be determined pursuant to Section 3(a). To the extent this Warrant or any portion thereof is deemed automatically exercised pursuant to this Section 3(b), the Company agrees to promptly notify the Warrantholder of the number of shares of Preferred Stock, if any, the Warrantholder is to receive by reason of such automatic exercise.

During the term of this Warrant, the Company will at all times have authorized and reserved a sufficient number of shares of its Preferred Stock to provide for the exercise of the rights to purchase Preferred Stock as provided for herein, and shall have authorized and reserved a sufficient number of shares of its Common Stock to provide for the conversion of the preferred Shares available hereunder.

No fractional shares or scrip representing fractional shares shall be issued upon the exercise of this Warrant, but in lieu of such fractional shares the Company shall make a cash payment therefor upon the basis of the Exercise Price then in effect.

4.

The holder of this Warrant shall be made a party to that certain Amended and Restated Investor Rights Agreement (the “Investor Rights Agreement”) dated as of October 25, 2005, among the Company and the Stockholders, as defined therein, in accordance with that certain Joinder Agreement attached hereto as Exhibit IV.

The Company shall maintain a registry showing the name and address of the registered holder of this Warrant. Warrantholder’s initial address, for purposes of such registry, is set forth below Warrantholder’s signature on this Warrant. Warrantholder may change such address by giving written notice of such changed address to the Company.

The Exercise Price and the number of shares of Preferred Stock purchasable hereunder are subject to adjustment, as follows:

(a) Merger Event. Subject to the termination provisions contained in Section 2 hereof, if at any time there shall be a Merger Event, then, as a part of such Merger Event, lawful provision shall be made so that the Warrantholder shall thereafter be entitled to receive, upon exercise of this Warrant, the number of shares of preferred stock or other securities or property of the successor corporation resulting from such Merger Event that would have been issuable if Warrantholder had exercised this Warrant immediately prior to the Merger Event. In any such case, appropriate adjustment (as determined in good faith by the Company’s Board of Directors) shall be made in the application of the provisions of this Warrant with respect to the rights and interests of the Warrantholder after the Merger Event to the end that the provisions of this Warrant (including adjustments of the Exercise Price and number of shares of Preferred Stock purchasable) shall be applicable in their entirety, and to the greatest extent possible. Without limiting the foregoing, in connection with any Merger Event, upon the closing thereof, the successor or surviving entity shall assume the obligations of this Warrant.

(b) Reclassification of Shares. Except as set forth in Section 8(a), if the Company at any time shall, by combination, reclassification, exchange or subdivision of securities or otherwise, change any of the securities as to which purchase rights under this Warrant exist into the same or a different number of securities of any other class or classes, this Warrant shall thereafter represent the right to acquire such number and kind of securities as would have been issuable as the result of such change with respect to the securities which were subject to the purchase rights under this Warrant immediately prior to such combination, reclassification, exchange, subdivision or other change.

(c) Subdivision or Combination of Shares. If the Company at any time shall combine or subdivide its Preferred Stock, (i) in the case of a subdivision, the Exercise price shall be proportionately decreased, and the number of shares of Preferred Stock issuable upon exercise of this Warrant shall be proportionately increased, or (ii) in the case of a combination, the Exercise Price shall be proportionately increased, and the number of shares of Preferred Stock issuable upon the exercise of this Warrant shall be proportionately decreased.

5.

(d) Stock Dividends. If the Company at any time while this Warrant is outstanding and unexpired shall:

(i) pay a dividend with respect to the Preferred Stock payable in preferred Stock, then the Exercise Price shall be adjusted, from and after the date of determination of shareholders entitled to receive such dividend or distribution, to that price determined by multiplying the Exercise Price in effect immediately prior to such date of determination by a fraction (A) the numerator of which shall be the total number of shares of Preferred Stock outstanding immediately prior to such dividend or distribution, and (B) the denominator of which shall be the total number of shares of Preferred Stock outstanding immediately after such dividend or distribution; or

(ii) make any other distribution with respect to Preferred Stock (or stock into which the Preferred Stock is convertible), except any distribution specifically provided for in any other clause of this Section 8, then, in each such case, provision shall be made by the Company such that the Warrantholder shall receive upon exercise or conversion of this Warrant a proportionate share of any such distribution as though it were the holder of the preferred Stock (or other stock for which the Preferred Stock is convertible) as of the record date fixed for the determination of the shareholders of the Company entitled to receive such distribution.

(e) Antidilution Rights. Additional antidilution rights applicable to the preferred Stock purchasable hereunder are as set forth in the Company’s Charter and shall be applicable with respect to the Preferred Stock issuable hereunder. The Company shall promptly provide the Warrantholder with any restatement, amendment, modification or waiver of the Charter that materially affects the rights of the Preferred Stock; provided, that no such amendment, modification or waiver shall impair or reduce the antidilution rights applicable to the Preferred Stock as of the date hereof unless such amendment, modification or waiver affects the rights of Warrantholder with respect to the Preferred Stock in the same manner as it affects all other holders of Preferred Stock. For the avoidance of doubt, there shall be no duplicate anti-dilution adjustment pursuant to this subsection (f), the forgoing subsection (d) and the Company’s Charter.

(f) Notice of Adjustments. Whenever an adjustment to the Exercise price or the number of shares of Preferred Stock issuable upon exercise of this Warrant is made pursuant to this Section 8, the Company shall send to the Warrantholder a notice setting forth, in reasonable detail, (i) the event requiring the adjustment, (ii) the amount of such adjustment, (iii) the method by which such adjustment was calculated, (iv) the adjusted Exercise Price (if the Exercise price has been adjusted), and (v) the number of shares subject to purchase hereunder after giving effect to such adjustment, and shall cause such notice to be mailed (by first class mail, postage. prepaid, or by reputable overnight courier with all charges prepaid) within thirty (30) days of such adjustment addressed to the Warrantholder at the address for Warrantholder set forth in the registry referred to in Section 7.

6.

(a) Reservation of Preferred Stock. The Preferred Stock issuable upon exercise of the Warrantholder’s rights has been duly and validly reserved and, when issued in accordance with the provisions of this Warrant, will be validly issued, fully paid and non-assessable, and will be free of any taxes, liens, charges or encumbrances of any nature whatsoever; provided, that the Preferred Stock issuable pursuant to this Warrant may be subject to restrictions on transfer under state and/or federal securities laws and applicable agreements to which the Company or its security holders are parties. The Company has made available to the Warrantholder true, correct and complete copies of its Charter and current bylaws. The issuance of certificates for shares of Preferred Stock upon exercise of this Warrant shall be made without charge to the Warrantholder for any issuance tax in respect thereof, or other cost incurred by the Company in connection with such exercise and the related issuance of sha