[CANCER RESEARCH 62, 3893–3903, July 15, 2002] Review Mechanisms of Action of Arsenic Trioxide1 Wilson H. Miller, Jr.,2 Hyman M. Schipper, Janet S. Lee, Jack Singer, and Samuel Waxman Lady Davis Institute for Medical Research and Sir Mortimer B. Davis-Jewish General Hospital, McGill University, Montreal H3T 1E2, Quebec, Canada [W. H. M., H. M. S.]; Ingenix, Basking Ridge, New Jersey 07920 [J. S. L.]; Cell Therapeutics, Inc., Seattle, Washington 89119 [J. S.]; and Rochelle Belfer Chemotherapy Foundation Laboratory, Mt. Sinai School of Medicine, New York, New York 10029 [S. W.] Abstract or with symptom-based interventions and did not require suspension of treatment (1). Arsenic trioxide has shown substantial efficacy in treating both newly Additional studies conducted in the United States confirmed that diagnosed and relapsed patients with acute promyelocytic leukemia (APL). As a single agent, it induces complete remissions, causing few low doses of arsenic trioxide can induce complete remission in re- adverse effects and only minimal myelosuppression. These successes have lapsed APL patients. Twelve APL patients who had received exten- prompted investigations to elucidate the mechanisms of action underlying sive prior therapy were treated with arsenic trioxide in doses of these clinical responses. Substantial data show that arsenic trioxide pro- 0.06–0.2 mg/kg of body weight until visible leukemic blasts and duces remissions in patients with APL at least in part through a mecha- promyelocytes were eliminated from the bone marrow. Complete nism that results in the degradation of the aberrant PML-retinoic acid remissions occurred in 11 of the 12 patients, with 8 of those 11 ␣ receptor fusion protein. Studies have also investigated concerns about patients achieving molecular remissions as well (6). Adverse events the toxicity and potential carcinogenicity of long-term exposure to envi- associated with arsenic trioxide were mostly mild; they included rash, ronmental arsenic. Arsenic apparently affects numerous intracellular sig- nal transduction pathways and causes many alterations in cellular func- lightheadedness, fatigue, and musculoskeletal pain. These results were tion. These actions of arsenic may result in the induction of apoptosis, the confirmed in a follow-up multicenter trial, in which 34 of 40 patients inhibition of growth and angiogenesis, and the promotion of differentia- (85%) achieved complete responses; 31 of those patients also tion. Such effects have been observed in cultured cell lines and animal achieved cytogenetic remission (7). Additional trials are under way in models, as well as clinical studies. Because arsenic affects so many cellular patients with APL and in patients with other hematologic malignan- and physiological pathways, a wide variety of malignancies, including cies and solid tumors (8, 9). both hematologic cancer and solid tumors derived from several tissue The success of arsenic trioxide in inducing high rates of complete types, may be susceptible to therapy with arsenic trioxide. These multiple remission in patients who have relapsed with this aggressive, acute actions of arsenic trioxide also highlight the need for additional mecha- nistic studies to determine which actions mediate the diverse biological disease provides an impetus for uncovering the specific mechanisms effects of this agent. This information will be critical to realizing the of action underlying these dramatic clinical responses. This review potential for synergy between arsenic trioxide and other chemotherapeu- summarizes reports of the activity of arsenic in animal models and in tic agents, thus providing enhanced benefit in cancer therapy. the clinic. We will also address the explosion of literature describing many effects of arsenic on cancer cell growth, differentiation, and Introduction apoptosis, including its activation or inhibition of a variety of cellular signaling pathways. Finally, we draw potential links between the During the last decade, the efficacy of arsenic trioxide in both observed in vitro actions of arsenic and its potential future role in the newly diagnosed and relapsed patients with APL3 has been estab- lished. Arsenic trioxide can be used as a single agent and induces treatment of human cancer. complete remissions with only minimal myelosuppression (1). Inves- tigators in China introduced arsenic trioxide, alone and in combination Arsenicals and Their Metabolism chemotherapies, as a cancer therapeutic for patients with APL, achiev- Arsenic is a semimetal commonly found in soil, water, and air. ing notable rates of complete remission. In newly diagnosed patients, Common inorganic and organic forms of arsenic are listed in Table 1. complete remission rates have ranged from 70% to 90%, and in Often, arsenic is complexed with sulfur as red arsenic (As S ), also relapsed patients, rates of 65% to Ͼ90% have been reported (2–5). In 2 2 called realgar or sandaraca, or as yellow arsenic (As S ), also called one study (2), long-term follow-up revealed that 16 patients (50%) 2 3 orpiment or auripigment. White arsenic or arsenic trioxide (As O )is survived Ͼ5 years, with survival extending to Ͼ17 years. Myelosup- 2 3 produced by heating realgar (10). Arsenic is rarely found in a pure pression was minimal. The most common side effects of arsenic state; rather, it exists in both trivalent and pentavalent oxidation states trioxide were gastrointestinal. Adverse events subsided spontaneously as a chemically unstable sulfide or oxide, or as a salt of sodium, potassium, or calcium (11). Trivalent arsenicals, including sodium Received 11/28/01; accepted 5/9/02. The costs of publication of this article were defrayed in part by the payment of page arsenite and the more soluble arsenic trioxide, inhibit many enzymes charges. This article must therefore be hereby marked advertisement in accordance with by reacting with biological ligands that possess available sulfur 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported by the Canadian Institutes of Health Research (to W. H. M.), NIH Grant groups. Being pentavalent, arsenic is recognized as an uncoupler of R01 CA85748, and the Samuel Waxman Cancer Research Foundation (to S. W.). mitochondrial oxidative phosphorylation (12). W. H. M. is a scientist of the Canadian Institutes of Health Research. Although most inorganic arsenic that is ingested is eliminated fairly 2 To whom requests for reprints should be addressed, at Lady Davis Institute for Medical Research 3755 Cote Ste Catherine Road, Montreal H3T 1E2, Quebec, Canada. rapidly in the urine, a small amount may be modified by methylation 3 The abbreviations used are: APL, acute promyelocytic leukemia; ATRA, all-trans to monomethylarsonic acid and to dimethylarsinic acid, a process retinoic acid; GADD45, growth arrest- and DNA damage-inducible protein 45; IKK, I␬B referred to as biotransformation. Whereas these enzymatic reactions kinase; JNK, c-Jun NH2-terminal kinase; Hsp90, 90 Kd heat shock protein; MAP, mitogen-activated protein; NF␬B, nuclear factor ␬B; MEKK, mitogen-activated protein are considered to be detoxifying, some organic arsenic metabolites kinase/extracellular signal-regulated kinase kinase; PKC, protein kinase C; PML, pro- myelocytic leukemia; RAR, retinoic acid receptor; RA, retinoic acid; IL, interleukin; may actually contribute to the cytotoxicity of arsenic (reviewed in HO-1, Heme oxygenase-1. Ref. 13). 3893 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 2002 American Association for Cancer Research. MECHANISMS OF ACTION OF ARSENIC TRIOXIDE Table 1 Arsenic in nature the relationship between exposure to arsenic compounds via occupa- Chemical tion, ingestion, or medical use and skin cancer. In 1980, reevaluation Arsenic forms formula Other names of the data determined that exposure to arsenic and arsenic-containing Red arsenic As2S2 Realgar, sandaraca compounds was a cause of lung cancer in humans. Finally, in 1987, Yellow arsenic As2S3 Arsenikon, aurum pigmentum, orpiment support for arsenic as a cause of human cancers was judged as White arsenic (created by As2O3 heating realgar) adequate on the basis of “limited evidence of carcinogenicity in Phenylarsine oxide C6H5AsO experimental animals” (15). Dermatological manifestations of arsenic use were commonly ob- served in patients with prolonged arsenic exposure. Long-term inges- History of the Medicinal Use of Arsenic Derivatives tion of Fowler’s Solution produces signs of chronic arsenic intoxica- tion. In one study, palmar and plantar keratoses occurred in all of the Medicinal use of arsenic and its derivatives dates back more than patients evaluated, although the minimum time to onset was 15 years 2400 years to ancient Greece and Rome. Arsenic was viewed as both (median, 24 years) after beginning arsenic treatment. Basal cell car- a therapeutic agent and a poison (12). Hippocrates administered cinoma developed in a majority of these patients, with the same time orpiment (As2S3) and realgar (As2S2) as an ulcer remedy; Dioscorides to onset. Other manifestations included carcinoma in situ, squamous used orpiment as a depilatory. Arsenic has also been used to treat the cell carcinoma, breast adenocarcinoma, and colon carcinoma, all plague, malaria, and cancer and to promote sweating. Physicians appearing within a minimum of 28–63 years after treatment. The prescribed arsenic for both external and internal use throughout the precise amounts of arsenic these patients received over time is not 18th century. Arsenides