| Explanation of Responses: |
| (1) | This Form 3 is filed jointly by Biotechnology Value Fund, L.P. ("BVF"), Biotechnology Value Fund II, L.P. ("BVF2"), Biotechnology Value Trading Fund OS LP ("Trading Fund OS"), BVF Partners OS Ltd. ("Partners OS"), BVF I GP LLC ("BVF GP"), BVF II GP LLC ("BVF2 GP"), BVF GP Holdings LLC ("BVF GPH"), BVF Partners L.P. ("Partners"), BVF Inc. and Mark N. Lampert (collectively, the "Reporting Persons"). Each of the Reporting Persons is a member of a group for purposes of Section 13(d) of the Securities Exchange Act of 1934 (the "Exchange Act") that collectively beneficially owns over 10% of the Issuer's outstanding shares of Common Stock (the "Common Stock"). Each of the Reporting Persons disclaims beneficial ownership of the securities reported herein except to the extent of his or its pecuniary interest therein. |
| (2) | Securities owned directly by BVF. As the general partner of BVF, BVF GP may be deemed to beneficially own the securities owned directly by BVF. As the sole member of BVF GP, BVF GPH may be deemed to beneficially own the securities owned directly by BVF. As the investment manager of BVF, Partners may be deemed to beneficially own the securities owned directly by BVF. As the investment adviser and general partner of Partners, BVF Inc. may be deemed to beneficially own the securities owned directly by BVF. As a director and officer of BVF Inc., Mr. Lampert may be deemed to beneficially own the securities owned directly by BVF. |
| (3) | Securities owned directly by BVF2. As the general partner of BVF2, BVF2 GP may be deemed to beneficially own the securities owned directly by BVF2. As the sole member of BVF2 GP, BVF GPH may be deemed to beneficially own the securities owned directly by BVF2. As the investment manager of BVF2, Partners may be deemed to beneficially own the securities owned directly by BVF2. As the investment adviser and general partner of Partners, BVF Inc. may be deemed to beneficially own the securities owned directly by BVF2. As a director and officer of BVF Inc., Mr. Lampert may be deemed to beneficially own the securities owned directly by BVF2. |
| (4) | Securities owned directly by Trading Fund OS. As the general partner of Trading Fund OS, Partners OS may be deemed to beneficially own the securities owned directly by Trading Fund OS. As the investment manager of Trading Fund OS and the sole member of Partners OS, Partners may be deemed to beneficially own the securities owned directly by Trading Fund OS. As the investment adviser and general partner of Partners, BVF Inc. may be deemed to beneficially own the securities owned directly by Trading Fund OS. As a director and officer of BVF Inc., Mr. Lampert may be deemed to beneficially own the securities owned directly by Trading Fund OS. |
| (5) | The Reporting Persons hold an aggregate of 85 shares of Series A Convertible Preferred Stock (the "Series A Preferred Stock"), which are convertible into an aggregate of 85,000 shares of Common Stock. Each share of Series A Preferred Stock is convertible at any time, at the holder's option, into 1,000 shares of Common Stock, except that the Series A Preferred Stock may not be converted if, after such conversion, the holder thereof (together with such holder's affiliates, and any other person whose beneficial ownership of Common Stock would be aggregated with the holder's ownership for purposes of Section 13(d) of the Exchange Act and the applicable regulations of the SEC, including any "group" of which the holder is a member) would beneficially own a number of shares of Common Stock in excess of 9.99% of the number of shares of Common Stock outstanding immediately after giving effect to the issuance of the Common Stock. The Series A Preferred Stock has no expiration date. |
| (6) | The Reporting Persons hold an aggregate of 4,026 shares of Series B Convertible Preferred Stock (the "Series B Preferred Stock"), which are convertible into an aggregate of 4,026,000 shares of Common Stock. Each share of Series B Preferred Stock is convertible at any time, at the holder's option, into 1,000 shares of Common Stock, except that the Series B Preferred Stock may not be converted if, after such conversion, the holder thereof (together with such holder's affiliates, and any other person whose beneficial ownership of Common Stock would be aggregated with the holder's ownership for purposes of Section 13(d) of the Exchange Act and the applicable regulations of the SEC, including any "group" of which the holder is a member) would beneficially own shares of Common Stock in excess of 9.99% of the number of shares of Common Stock outstanding immediately after giving effect to the issuance of the Common Stock. The Series B Preferred Stock has no expiration date. |
| (7) | The Reporting Persons hold an aggregate of 3,506 shares of Series C Convertible Preferred Stock (the "Series C Preferred Stock"), which are convertible into an aggregate of 3,506,000 shares of Common Stock. Each share of Series C Preferred Stock is convertible at any time, at the holder's option, into 1,000 shares of Common Stock, except that the Series C Preferred Stock may not be converted if, after such conversion, the holder thereof (together with such holder's affiliates, and any other person whose beneficial ownership of Common Stock would be aggregated with the holder's ownership for purposes of Section 13(d) of the Exchange Act and the applicable regulations of the SEC, including any "group" of which the holder is a member) would beneficially own shares of Common Stock in excess of 9.99% of the number of shares of Common Stock outstanding immediately after giving effect to the issuance of the Common Stock. The Series C Preferred Stock has no expiration date. |
| (8) | The Reporting Persons hold an aggregate of 3,000 shares of Series D Convertible Preferred Stock (the "Series D Preferred Stock"), which are convertible into an aggregate of 3,000,000 shares of Common Stock. Each share of Series D Preferred Stock is convertible at any time, at the holder's option, into 1,000 shares of Common Stock, except that the Series D Preferred Stock may not be converted if, after such conversion, the holder thereof (together with such holder's affiliates, and any other person whose beneficial ownership of Common Stock would be aggregated with the holder's ownership for purposes of Section 13(d) of the Exchange Act and the applicable regulations of the SEC, including any "group" of which the holder is a member) would beneficially own shares of Common Stock in excess of 9.99% of the number of shares of Common Stock outstanding immediately after giving effect to the issuance of the Common Stock. The Series D Preferred Stock has no expiration date. |
| (9) | The Reporting Persons hold an aggregate of 5,000 shares of Series E Convertible Preferred Stock (the "Series E Preferred Stock"), which are convertible into an aggregate of 5,000,000 shares of Common Stock. Each share of Series E Preferred Stock is convertible at any time, at the holder's option, into 1,000 shares of Common Stock, except that the Series E Preferred Stock may not be converted if, after such conversion, the holder thereof (together with such holder's affiliates, and any other person whose beneficial ownership of Common Stock would be aggregated with the holder's ownership for purposes of Section 13(d) of the Exchange Act and the applicable regulations of the SEC, including any "group" of which the holder is a member) would beneficially own shares of Common Stock in excess of 9.99% of the number of shares of Common Stock outstanding immediately after giving effect to the issuance of the Common Stock. The Series E Preferred Stock has no expiration date. |
| (10) | The Reporting Persons hold an aggregate of 3,522,000 Tranche C Warrants (the "C Warrants"), which are exercisable into an aggregate of 3,522,000 shares of Common Stock. If (i) the Issuer's initial public disclosure of its Phase 2a Study of PRS-060/AZD1402 that includes the "p" value achieved for the primary endpoint of such study reveals top-line data on the primary efficacy endpoint in the Phase 2a Study with a "p" value below 0.05 (i.e., p < 0.05) in at least one dose level; and (ii) the 10-day volume weighted average Common Stock price commencing on the trading day immediately after the initial data disclosure is at least 3% more than the exercise price of the C Warrants, then the C Warrants will be exercisable for a period of 60 days from the date of the initial data disclosure and may only be exercised for cash. Otherwise, the C Warrants will be exercisable for a period of 5 years from the date of issuance. |
| (11) | However, the C Warrants may not be exercised if, after such exercise, the total number of shares of Common Stock then beneficially owned by the holder of the C Warrants (together with such holder's affiliates, and any other person whose beneficial ownership of Common Stock would be aggregated with the holder's ownership for purposes of Section 13(d) of the Exchange Act and the applicable regulations of the SEC, including any "group" of which the holder is a member) would exceed 9.99% of the total number of then issued and outstanding shares of Common Stock (including for such purposes the Common Stock issuable upon such exercise). |