Extended Data Figure 2: Magnetic loading, iron oxide quantification by electronic spin resonance and strain compression calculation of magnetized wild-type and Apc+/1638N colon distal samples.
From: Mechanical induction of the tumorigenic β-catenin pathway by tumour growth pressure
a, Magnetizing mouse colon. Subcutaneous insertion of the 3 mm diameter magnet (in red) on the back of the mice 7 mm in front of the distal colon, following UML injection in the lateral caudal vein of the mouse tail. Acoustic elastography probe in green. b, UML detection and localization in the colon. Rhodamine-labelled UML observed 1 week after injection in wild-type colon explants, in contrast to non-injected controls (measured in n = 10 images, in six mice for each condition). c, Iron oxide quantification by electronic spin resonance in wild-type mice, injected with UML or magnetic liposomes loaded with an equivalent of 120 moles and 2.2 moles of Fe(III) per mole of lipids, respectively. Iron oxide concentration in the distal colon was measured by electronic spin resonance (5% precision) from lyophilized colon explants at 1 week (magnetic liposomes: 79 ± 12 nmole g−1 (measured in n = 6 mice); UML: 183 ± 48 nmole g−1 (measured in n = 3 mice), 2 weeks (271 ± 64 nmole g−1 (measured in n = 3 mice)) and 1 month (299 ± 157 nmole g−1 (measured in n = 3 mice)) after administration. Control sample was not injected with UML and was used to set up background of iron oxide concentration. A Mann–Whitney–Wilcoxon test concluded no significant difference in iron oxide concentration during 1 month (P ≥ 0.2) in the case of the mice injected with UML. This supports the maintaining of the number and local containment of the delivered magnetic particles into the distal colon over this period of time, in agreement with the very slow biotransformation of such nanomagnets recently revealed in vivo51. The iron oxide concentration at 1 week in the distal colon of wild-type mice injected with magnetic liposomes was found around twice lower compared to samples injected with UML while the residual content tends to vanish from 2 weeks (results not shown). d, Magnetized wild-type colon samples injected with magnetic liposomes show no difference of local strain compression compared to non-injected samples or injected with magnetic liposomes without magnet (measured in n = 2 for each condition). e, Schematic representation of the ultrasound measurement setup and biomechanical imaging techniques. Left, shear wave elastography. Right, strain imaging. f, Ultrasound imaging of magnetically induced deformation of the mouse colon. Representative B-mode acoustic image (right) of a magnetically loaded colon explant and the corresponding displacement map (left) after magnet moved from 10 mm to 7 mm towards the colon (Methods). The mean value of displacement within the colon and the rest of the phantom were 35 μm and 16.9 μm, respectively (measured in n = 12 mice). g, Stiffness measurements of control (in 3 mice) and magnetized colon explants (in 6 mice) remained on the order of E = 30–35 kPa, n = 6 measurements by mice. h, Apc+/1638N mice show poor deformation at 1 week (mean elastic modulus control E = 24 ± 2 kPa, measured in n = 3 mice; UML + magnet E = 23 ± 2 kPa, measured in n = 4 mice) compared to wild type at 1 week (Fig. 1b) with similar iron oxide loading concentration of 265 ± 80 nmole g−1 (see i, n = 3) compared to the 183 ± 48 nmole g−1 of wild type (see c). Deformation decreases at 2 weeks compared to 1 week in both the Apc+/1638N (mean elastic modulus control E = 21 ± 5 kPa, measured in n = 3 mice; UML + magnet E = 33 ± 2 kPa, measured in n = 2 mice) and wild type (mean elastic modulus control E = 30 ± 8 kPa, measured in n = 3 mice; UML + magnet E = 35 ± 5 kPa, measured in n = 3 mice). i, The mean Fe(III) concentration in magnetized Apc+/1638N colon, of 258 ± 80 nmole g−1 on one month, remains on the order of magnitude of the mean concentration in wild-type colons, of 250 ± 50 nmole g−1, meaning that the magnetically induced stress remains on the same order of magnitude during 1 month in Apc+/1638N compared to wild-type mice (measured in n = 3 mice for each condition).
