As filed with the Securities and Exchange Commission on December 11, 2025 Registration No. 333-291628 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-1 (Amendment No. 1) REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 SHUTTLE PHARMACEUTICALS HOLDINGS, INC. (Exact name of registrant as specified in its charter) David E. Danovitch, Esq. Aaron M. Schleicher, Esq. Sullivan & Worcester LLP 1251 Avenue of the Americas, 19 Floor New York, NY 10020 (212) 660-3060 From time to ...