Contract analysis

I. EXECUTIVE SUMMARY A. Purpose This Legal Due Diligence Report (this "Report") summarizes the principal findings and observations of Calderwood & Harkness LLP ("Calderwood & Harkness" or "C&H") arising from its review of the legal due diligence materials made available in connection with the proposed acquisition (the "Proposed Transaction") of Caliston BioSciences, Inc. ("Caliston" or the "Company") by Penterra Phar

II. CORPORATE ORGANIZATION AND GOOD STANDING A. Formation and Jurisdiction Caliston BioSciences, Inc. was incorporated in the State of Delaware on September 12, 2017. The Company's full legal name is Caliston BioSciences, Inc. The Company's federal Employer Identification Number (EIN) is 84-4219063. The Company's registered agent in the State of Delaware is Pemberton Industries, located at 251 Little Falls Drive, Wil

1. Dr. Nadia Sorensen — Co-Founder and Chief Executive Officer of Caliston. Dr. Sorensen has served as CEO and as a member of the Board since the Company's founding in 2017. She holds an approximately 14.2% equity interest in the Company on a fully-diluted basis.

2. Dr. Evan Whitmore — Head of Clinical Development. Dr. Whitmore joined Caliston in 2019 and has served on the Board since 2020. The Special Committee should note that Dr. Whitmore is the spouse of Angela Whitmore, who serves as Executive Vice President, Commercial Operations of Penterra and as a member of Penterra's Board of Directors. Ms. Whitmore has been recused from all Special Committee proceedings and all Pen

3. Ava Lindström — Managing Partner, Ridgeline Ventures, LP. Ms. Lindström was designated to the Board by Ridgeline Ventures, LP pursuant to the investor rights provisions of the Series C stockholder agreements. Ridgeline Ventures served as the lead investor in the Series C round and holds an approximately 22.3% equity interest in the Company.

4. Tomás Reyes — Managing Partner, Meridian Life Sciences Fund III, LP. Mr. Reyes was designated to the Board by Meridian Life Sciences Fund III, LP pursuant to the investor rights provisions of the Series B stockholder agreements. Meridian III served as the lead investor in the Series B round and holds an approximately 18.7% equity interest in the Company.

5. One additional independent director — Identified in the Data Room as an independent director who does not hold an institutional investor designation right. This individual was appointed to the Board in 2020 and serves on the Audit Committee and Compensation Committee of the Board. In addition to the five voting directors, Dr. Marcus Hale, Chairman and Chief Executive Officer of Penterra, holds a non-voting board o

III. CAPITALIZATION A. Authorized and Outstanding Capital Stock Under the Restated Certificate of Incorporation, as filed in connection with the Series C financing in October 2021, the Company is authorized to issue shares of common stock and four series of preferred stock: Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock. The specific number of authorized

IV. MATERIAL CONTRACTS A. Overview Calderwood & Harkness reviewed all contracts identified by Caliston's management as material or having an annualized value in excess of $500,000, as well as all contracts containing change-of-control, assignment, consent, or notification provisions that may be triggered by the Proposed Transaction. In total, we reviewed the material contracts described below, along with additional a

V. INTELLECTUAL PROPERTY A. Patent Portfolio — CLT-4019 CLT-4019 is a selective CDK4/6 inhibitor being developed by Caliston for the treatment of HR+/HER2– metastatic breast cancer. The compound represents the Company's lead clinical-stage asset and the primary driver of the Company's enterprise value. Calderwood & Harkness, in coordination with outside patent counsel, reviewed the patent portfolio associated with CL

VI. REGULATORY STATUS A. IND Status — CLT-4019 Caliston submitted an Investigational New Drug Application (IND) for CLT-4019 to the U.S. Food and Drug Administration (the "FDA") in March 2020. The IND is designated as IND 158429. Based on our review of the FDA correspondence in the Data Room, the IND is active and in good standing. We did not identify any clinical holds, partial clinical holds, refusal-to-file commun

VII. LITIGATION A. Pending Litigation Caliston represented to Calderwood & Harkness, through its counsel and through officer certifications provided in the Data Room, that there is no pending litigation, arbitration, or administrative proceeding in which the Company is a party or to which any of the Company's assets are subject. Calderwood & Harkness conducted litigation searches in the jurisdictions in which the Com

VIII. ANTITRUST AND REGULATORY APPROVALS The Proposed Transaction will require compliance with the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the "HSR Act"). A detailed analysis of the HSR Act filing requirements and the substantive antitrust considerations applicable to the Proposed Transaction has been prepared separately in the Memorandum on Antitrust / HSR Act Analysis, dated August 10, 202

IX. EMPLOYMENT MATTERS A. Employee Headcount As of the most recent data provided in the Data Room, Caliston employs 94 individuals. The majority of the Company's employees are based at its principal office in Cambridge, Massachusetts. The employee base includes scientific researchers, clinical development personnel, regulatory affairs professionals, corporate and administrative staff, and senior management. No employ

X. TAX MATTERS Calderwood & Harkness reviewed the tax-related materials provided in the Data Room, including federal and state income tax returns, correspondence with taxing authorities, and information relating to the Company's net operating loss carryforwards. The following principal observations are noted: (a) Tax Filings. Caliston has filed all required federal and state income tax returns for all open tax years.