This Tender Offer Statement on Schedule TO (this Schedule TO) relates to
the offer by Appleseed Merger Sub LLC, a Maryland limited liability company (Purchaser), and a wholly owned direct subsidiary of Appleseed Holdco LLC, a Delaware limited liability company (Holdco), and a wholly owned indirect
subsidiary of American Tower Investments LLC, a California limited liability company (Parent), and a wholly owned indirect subsidiary of American Tower Corporation, a Delaware corporation (ATC), to purchase all of the
outstanding shares of common stock, $0.01 par value per share (Shares), of CoreSite Realty Corporation, a Maryland corporation (CoreSite), at a price of $170.00 per Share, without interest and subject to any applicable
withholding taxes, net to the seller in cash, upon the terms and subject to the conditions described in the Offer to Purchase dated November 29, 2021 (together with any amendments or supplements thereto, the Offer to Purchase) and
in the accompanying Letter of Transmittal (together with any amendments or supplements thereto and with the Offer to Purchase, the Offer), which are annexed to and filed with this Schedule TO as Exhibits (a)(1)(A) and
(a)(1)(B), respectively. This Schedule TO is being filed on behalf of ATC, Parent, Holdco and Purchaser. Unless otherwise indicated, references to sections in this Schedule TO are references to sections of the Offer to Purchase. A copy of
the Agreement and Plan of Merger, dated as of November 14, 2021, among Parent, Holdco, Purchaser, Appleseed OP Merger Sub LLC, a Delaware limited liability company, CoreSite, CoreSite, L.P., a Delaware limited partnership (the OP),
and ATC, is attached as Exhibit (d)(1) hereto and incorporated herein by reference with respect to Items 4 through 11 of this Schedule TO.
ITEM 1. SUMMARY TERM SHEET.
The
information set forth in the section of the Offer to Purchase titled Summary Term Sheet is incorporated herein by reference.
ITEM 2.
SUBJECT COMPANY INFORMATION.
(a) The subject company and the issuer of the securities subject to the Offer is CoreSite Realty
Corporation. Its principal executive office is located at 1001 17th Street, Suite 500, Denver, Colorado 80202, and its telephone number is
(866) 777-2673.
(b) This Schedule TO relates to the Shares. According to CoreSite, as
of the close of business on November 23, 2021, there were (i) 44,191,056 Shares issued and outstanding (including 518,419 Shares subject to restricted stock awards of CoreSite and performance stock awards of CoreSite); and (ii) 80,710 Shares
underlying outstanding restricted stock units of CoreSite.
(c) The information concerning the principal market, if any, in which the
Shares are traded and certain high and low sales prices for the Shares in the principal market in which the Shares are traded set forth in Section 6Price Range of Shares; Dividends of the Offer to Purchase is incorporated
herein by reference.
ITEM 3. IDENTITY AND BACKGROUND OF FILING PERSON.
(a)(c) The filing companies of this Schedule TO are ATC, Parent, Holdco and Purchaser. Each of ATCs, Parents,
Holdcos and Purchasers principal executive office is located at c/o American Tower Corporation, 116 Huntington Avenue, Boston, Massachusetts 02116, and the telephone number of each is (617)
375-7500. The information regarding ATC, Parent, Holdco and Purchaser set forth in Section 9Certain Information Concerning ATC, Parent, Holdco and Purchaser and Schedule A of the
Offer to Purchase is incorporated herein by reference.
ITEM 4. TERMS OF THE TRANSACTION.
The information set forth in the Offer to Purchase is incorporated herein by reference.
ITEM 5. PAST CONTACTS, TRANSACTIONS, NEGOTIATIONS AND AGREEMENTS.
(a), (b) The information set forth in Section 8Certain Information Concerning CoreSite,
Section 9Certain Information Concerning ATC, Parent, Holdco and Purchaser, Section 10Background of the Offer;