|Molar mass||445.03 g/mol|
|Appearance||White to pale beige crystalline solid or powder|
|Density||1.56 g/cm3, solid|
|Melting point||220 °C (decomposes)|
|Solubility in water||24(2) mM; 10.7(9) mg/mL (25 °C)|
|Crystal structure||Orthorhombic; space group Pbca|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Gallium maltolate is a coordination complex consisting of a trivalent gallium cation coordinated to three maltolate ligands. The compound is undergoing clinical and preclinical testing as a potential therapeutic agent for cancer, infectious disease, and inflammatory disease. It appears to have low toxicity when administered orally, without the renal toxicity observed for intravenously administered gallium nitrate. The lower toxicity probably results because gallium absorbed into the body from oral gallium maltolate becomes nearly entirely protein bound, whereas gallium from intravenous gallium nitrate tends to form anionic gallium hydroxide (Ga(OH)4-; gallate) in the blood, which is rapidly excreted in the urine and may be renally toxic. Topical gallium maltolate, which is administered to the skin at a dose of approximately one-thousandth that of the safe oral dose, has had no reported adverse effects. A cosmetic skin cream containing gallium maltolate is marketed under the name Gallixa.
In aqueous solutions, gallium maltolate has neutral charge and pH, and is stable between about pH 5 and 8. It has significant solubility in both water and lipids (octanol:water partition coefficient = 0.41).
Gallium maltolate is able to deliver gallium with high oral bioavailability: the bioavailability is several times higher than that of gallium salts such as gallium nitrate and gallium trichloride. Gallium is antiproliferative to pathologically proliferating cells, particularly cancer cells and some bacteria, due primarily to its ability to mimic ferric iron (Fe3+). Ferric iron is essential for DNA synthesis, as it is present in the active site of the enzyme ribonucleotide reductase, which catalyzes the conversion of ribonucleotides to the deoxyribonucleotides required for DNA. Gallium is taken up by the rapidly proliferating cells, but it is not functional for DNA synthesis, so the cells cannot reproduce and they ultimately die by apoptosis. Normally reproducing cells take up little gallium (as is known from gallium scans), and gallium is not incorporated into hemoglobin, accounting for the relatively low toxicity of gallium.
The anti-inflammatory activity of gallium appears to involve the down-regulation of inflammatory T cells and macrophages, as well as possible interference with matrix metalloproteinases. Because many iron compounds are pro-inflammatory, the ability of gallium to act as a non-functional iron mimic may contribute to its anti-inflammatory activity.
Analgesic activity has also been reported for gallium maltolate. Orally administered gallium maltolate has alleviated cancer-related pain, and topically applied gallium maltolate, at doses one-thousandth those of the safe oral doses, has been effective against refractory neuropathic pain (severe postherpetic neuralgia). The analgesic activity likely derives from gallium's observed anti-inflammatory mechanisms, and possibly from its interactions with certain matrix metalloproteinases and substance P, whose activities are zinc-mediated and which have been implicated in the etiology of pain.
Christopher Chitambar and his associates at the Medical College of Wisconsin have found that gallium maltolate is active against several lymphoma cell lines, including those resistant to gallium nitrate.
Gallium maltolate is being studied as a potential treatment for primary liver cancer (hepatocellular carcinoma; HCC). In vitro experiments demonstrated efficacy against all HCC cell lines tested  and a clinical case study produced very encouraging results in a patient with advanced HCC who had not responded to therapy with sorafenib 
The activity of gallium against infection-related biofilms, particularly those caused by Pseudomonas aeruginosa, is being studied by Pradeep Singh at the University of Washington, and by others, who have reported encouraging results in mice. Pulmonary P. aeruginosa biofilms are responsible for many fatalities in cystic fibrosis and immunocompromised patients; in general, bacterial biofilms are responsible for significant morbidity and mortality. In related research, locally administered gallium maltolate has shown potent efficacy against P. aeruginosa in a mouse burn/infection model.
Oral gallium maltolate is also being investigated as a treatment for Rhodococcus equi foal pneumonia, a common and often fatal disease of newborn horses. R. equi can also infect humans with AIDS or who are otherwise immunocompromized. The veterinary studies are being conducted by researchers at Texas A&M University, led by Ronald Martens, Noah Cohen, and M. Keith Chaffin.
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- Wirtz, U.F.; Kadurugamuwa, J.; Bucalo, L.R.; Sreedharan, S.P. (2006). "Efficacy of gallium maltolate in a mouse model for Pseudomonas aeruginosa chronic urinary tract infection". American Society for Microbiology 106th general meeting. Orlando, Florida. pp. poster A–074.
- Parsek, M.; Singh, P. (2003). "Bacterial biofilms: an emerging link to disease pathogenesis". Annu. Rev. Microbiol. 57: 677–701. doi:10.1146/annurev.micro.57.030502.090720. PMID 14527295.
- DeLeon K.; Balldin F.; Watters C.; Hamood A.; Griswold J.; Sreedharan S.; Rumbaugh K.P. (2009). "Gallium maltolate treatment eradicates Pseudomonas aeruginosa infection in thermally injured mice". Antimicrobial Agents and Chemotherapy 53 (4): 1331–1337. doi:10.1128/AAC.01330-08. PMC 2663094. PMID 19188381.
- Harrington, J.R.; Martens, R.J.; Cohen, N.D.; Bernstein, L.R. (2006). "Antimicrobial activity of gallium against virulent Rhodococcus equi in vitro and in vivo". J. Vet. Pharmacol. Ther. 29 (2): 121–127. doi:10.1111/j.1365-2885.2006.00723.x. PMID 16515666.
- Martens, R.J.; Mealey, K.; Cohen, N.D.; Harrington, J.R.; Chaffin, M.K.; Taylor, R.J.; Bernstein, L.R. (2007). "Pharmacokinetics of gallium maltolate after intragastric administration in neonatal foals". Am. J. Vet. Res. 68 (10): 1041–1044. doi:10.2460/ajvr.68.10.1041. PMID 17916007.