Motexafin Gadolinium (Xcytrin): A Comprehensive Monograph on a Novel Theranostic Radiosensitizer

Section 1: Molecular Profile and Chemical Rationale

1.1 Identification and Physicochemical Properties

Motexafin gadolinium is an investigational small molecule drug developed by Pharmacyclics, Inc., as a novel anti-cancer agent.[1] It is identified by the DrugBank accession number DB05428 and the Chemical Abstracts Service (CAS) registry number 246252-06-2.[1] Throughout its development, the compound has been referred to by a variety of synonyms and code names that reflect its progression from a preclinical entity to a clinical candidate. These include the chemical descriptor

gadolinium texaphyrin, the internal company code PCI-0120, and other research identifiers such as Gd-Tex, GdT2B2, API-GP 3, NSC 695238, and IND 55583.[1] The proposed trade name for the final drug product was

Xcytrin.[6] This nomenclature trail provides a historical map of its journey from laboratory discovery to its near-market status.

The molecule's chemical formula is consistently reported as C52​H72​GdN5​O14​, with a corresponding average molecular weight of approximately 1148.4 g/mol.[1] Some sources report slight variations in the formula, such as

C48​H66​N5​O10​⋅2C2​H3​O2​⋅Gd, which explicitly accounts for the two acetate ligands coordinated to the central gadolinium ion.[13] The structural complexity of the molecule is reflected in its formal IUPAC name: (PB-7-11-233'2'4)-bis(acetato-kappaO)(9,10-diethyl-20,21-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-4,15-dimethyl-8,11-imino-3,6:16,13-dinitrilo-1,18-benzodiazacycloeicosine-5,14-dipropanolato-kappaN(1),kappaN(18),kappaN(23),kappaN(24),kappaN(25))gadolinium.[2]