Science1 publisher2 min readPublished Updated
Kyushu chemists make one metal-free molecule that glows in cells and brightens MRI phantoms
Kyushu University chemists made two metal-free radicals that fluoresce deep red and lift MRI phantom contrast about 2.5 to 4.5 times over earlier versions. The design is a possible route to MRI contrast without gadolinium, but it has not yet been tried in an animal.
The Scientist · Science desk
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What happened
- The two molecules, TTM-trisTP3B and TTM-trisTP9B, each have water-soluble groups attached in three directions around a TTM radical core.
- In living cells, TTM-trisTP3B fluoresced around the nucleus and kept glowing for at least 24 hours.
- Fluorescence imaging resolves single cells but cannot see deep into the body, while MRI sees deep but lacks single-cell resolution.
- The Kyushu University team, led by associate professor Ken Albrecht, published the work in the journal Advanced Science.
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Why it matters
- capability A probe that both methods can detect could let researchers pair fluorescence's cell-level detail with MRI's depth while tracking one agent.
- constraint The fluorescence evidence comes from cells and the MRI evidence from phantoms, so the two halves have not yet been shown working together in one living sample.
- precedent Other groups working on luminescent radicals now have a demonstrated way to make them water-soluble. Poor solubility had kept this class out of biological use.
The 2.5 to 4.5 times contrast gain is measured against previously reported water-soluble TTM radicals, on MRI phantom images [3]. So the comparison stays within one family of organic radicals. The published account does not include a gadolinium agent run through the same test [3].
Ken Albrecht, the Kyushu associate professor who led the study, said building one molecule for both methods "is challenging because the functional mechanisms of the two technologies differ" [10]. "In FI, a molecule absorbs and reemits certain wavelengths of light that we then detect," he said. "MRI works by detecting the molecular spin of the hydrogen atoms in water molecules in the body." [11]
Luminescent organic radicals both fluoresce and carry a molecular spin, so in principle one of them can serve both methods [5]. Earlier ones were hydrophobic, and that limited their use in biological systems [5]. TTM, short for tris(2,4,6-trichlorophenyl) methyl, is one such radical [12]. The group reworked it over more than one generation to make it dissolve in water and fluoresce more brightly [13]. "The first generation of molecules we made showed good MRI activity but had extremely weak fluorescence," Albrecht said [6].
The appeal of the design is that it contains no metal. MRI contrast agents contain paramagnetic metals such as gadolinium, and those metals can potentially cause adverse side effects, according to the phys.org account [8]. Removing the metal removes that concern. It does not by itself show that the radicals are safe. I think the evidence supports a narrower claim than a replacement for gadolinium: one water-soluble organic radical can do both imaging jobs at the bench [3][4]. Albrecht describes it in similar terms. "We will have to perform animal studies to further examine the viability of these molecules, but the present results establish important proof of concept for metal-free fluorescence/MRI dual-modal imaging," he said [7].
What to watch
- Animal results showing whether TTM-trisTP3B's MRI contrast holds in living tissue at a dose an animal tolerates.
- Cell data for TTM-trisTP9B, which has so far been reported in water and phantom images but not in living cells.
- Toxicity and clearance data for the radicals, the evidence a safety case for metal-free contrast would rest on.