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Molecular Magnetic Resonance Imaging of Tumor Response to Therapy.

Shuhendler AJ, Ye D, Brewer KD, Bazalova-Carter M, Lee KH, Kempen P, Dane Wittrup K, Graves EE, Rutt B, Rao J - Sci Rep (2015)

Bottom Line: The poor sensitivity of MRI has limited the development of activatable molecular MR contrast agents.To overcome this limitation of molecular MRI, a novel implementation of our caspase-3-sensitive nanoaggregation MRI (C-SNAM) contrast agent is reported.Importantly, C-SNAM is inert to immune activation, permitting radiation therapy monitoring.

View Article: PubMed Central - PubMed

Affiliation: Molecular Imaging Program at Stanford, Stanford, California 94305, USA.

ABSTRACT
Personalized cancer medicine requires measurement of therapeutic efficacy as early as possible, which is optimally achieved by three-dimensional imaging given the heterogeneity of cancer. Magnetic resonance imaging (MRI) can obtain images of both anatomy and cellular responses, if acquired with a molecular imaging contrast agent. The poor sensitivity of MRI has limited the development of activatable molecular MR contrast agents. To overcome this limitation of molecular MRI, a novel implementation of our caspase-3-sensitive nanoaggregation MRI (C-SNAM) contrast agent is reported. C-SNAM is triggered to self-assemble into nanoparticles in apoptotic tumor cells, and effectively amplifies molecular level changes through nanoaggregation, enhancing tissue retention and spin-lattice relaxivity. At one-tenth the current clinical dose of contrast agent, and following a single imaging session, C-SNAM MRI accurately measured the response of tumors to either metronomic chemotherapy or radiation therapy, where the degree of signal enhancement is prognostic of long-term therapeutic efficacy. Importantly, C-SNAM is inert to immune activation, permitting radiation therapy monitoring.

No MeSH data available.


Related in: MedlinePlus

Structure, mechanism of action, and in vitro characterization of caspase 3-sensitive nano-aggregation MRI contrast agent (C-SNAM).(a) Schematic showing the structure of C-SNAM, including the DOTA-chelated Gd (blue sphere), the DEVD (green) and thioethyl (SEt, cyan) blocking groups, and the amine (red), thiol (orange), and cyano (yellow) click chemistry reactive groups. Upon removal of the capping groups, C-SNAM cyclizes and self-assembles into nanoparticles. The structure of the non-cyclizable control probe (NC-ctrl) lacks the cyano group and contains a methylated thiol, preventing cyclization upon removal of DEVD. (b) Scanning electron micrographs of C-SNAM alone (left) and after incubation with activated caspase-3 (right), showing self-assembled nano-aggregates (white arrows). (c) The activation of C-SNAM by caspase-3 results in an increase in relaxivity (r1) at 1T, but neither the activation of control probe (NC-ctrl) nor ProHance ®, suggesting that the change in ri is a result of the increase in contrast agent size following nano-aggregation. (d) Proposed mechanism of therapy response monitoring using C-SNAM. With ineffective therapy, caspase-3 remains inactive, failing to trigger C-SNAM self-assembly and resulting in rapid clearance of the probe. With successful tumor cell death, caspase-3 is activated and induces C-SNAM self-assembly, increasing signal retention and enhancing signal production to result in localized regions of MR signal enhancement (i.e. hotspots).
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f1: Structure, mechanism of action, and in vitro characterization of caspase 3-sensitive nano-aggregation MRI contrast agent (C-SNAM).(a) Schematic showing the structure of C-SNAM, including the DOTA-chelated Gd (blue sphere), the DEVD (green) and thioethyl (SEt, cyan) blocking groups, and the amine (red), thiol (orange), and cyano (yellow) click chemistry reactive groups. Upon removal of the capping groups, C-SNAM cyclizes and self-assembles into nanoparticles. The structure of the non-cyclizable control probe (NC-ctrl) lacks the cyano group and contains a methylated thiol, preventing cyclization upon removal of DEVD. (b) Scanning electron micrographs of C-SNAM alone (left) and after incubation with activated caspase-3 (right), showing self-assembled nano-aggregates (white arrows). (c) The activation of C-SNAM by caspase-3 results in an increase in relaxivity (r1) at 1T, but neither the activation of control probe (NC-ctrl) nor ProHance ®, suggesting that the change in ri is a result of the increase in contrast agent size following nano-aggregation. (d) Proposed mechanism of therapy response monitoring using C-SNAM. With ineffective therapy, caspase-3 remains inactive, failing to trigger C-SNAM self-assembly and resulting in rapid clearance of the probe. With successful tumor cell death, caspase-3 is activated and induces C-SNAM self-assembly, increasing signal retention and enhancing signal production to result in localized regions of MR signal enhancement (i.e. hotspots).

Mentions: C-SNAM is composed of a flexible aminoluciferin-based linker connecting two biocompatible reactive moieties, D-cysteine on one end (Fig. 1a, red and orange) and 2-cyano-6-hydroxyquinoline (Fig. 1a, yellow) on the other. In order to control the bioorthogonal reaction and self-assembly, the reactive groups of D-cysteine are reversibly blocked: the thiol is blocked by a disulfide bond to a thioethyl group (cyan oval) reducible by glutathione upon entry into a cell. The amine is blocked by an acetyl-Asp-Glu-Val-Asp (DEVD, green bar) group, a substrate of caspase-3 that is removed upon activation of the enzyme during successful radiation or chemotherapy1718. When unblocked, these reactive groups undergo rapid intramolecular condensation under physiological conditions (first order rate constant = 5.8 × 10−3 s−1)19 to form a cyclic compound, C-SNAM-cycl, whose high rigidity favors self-assembly through π-π stacking, ultimately forming a nanoparticle at a typical size of approximately 400 nm (Fig. 1b)141519. In addition to C-SNAM, a non-cyclizable control probe (NC-ctrl) was prepared lacking the cyano moiety and having a methylated thiol, preventing cyclization even after removal of the DEVD blocking group to abrogate self-assembly (Fig. 1a).


Molecular Magnetic Resonance Imaging of Tumor Response to Therapy.

Shuhendler AJ, Ye D, Brewer KD, Bazalova-Carter M, Lee KH, Kempen P, Dane Wittrup K, Graves EE, Rutt B, Rao J - Sci Rep (2015)

Structure, mechanism of action, and in vitro characterization of caspase 3-sensitive nano-aggregation MRI contrast agent (C-SNAM).(a) Schematic showing the structure of C-SNAM, including the DOTA-chelated Gd (blue sphere), the DEVD (green) and thioethyl (SEt, cyan) blocking groups, and the amine (red), thiol (orange), and cyano (yellow) click chemistry reactive groups. Upon removal of the capping groups, C-SNAM cyclizes and self-assembles into nanoparticles. The structure of the non-cyclizable control probe (NC-ctrl) lacks the cyano group and contains a methylated thiol, preventing cyclization upon removal of DEVD. (b) Scanning electron micrographs of C-SNAM alone (left) and after incubation with activated caspase-3 (right), showing self-assembled nano-aggregates (white arrows). (c) The activation of C-SNAM by caspase-3 results in an increase in relaxivity (r1) at 1T, but neither the activation of control probe (NC-ctrl) nor ProHance ®, suggesting that the change in ri is a result of the increase in contrast agent size following nano-aggregation. (d) Proposed mechanism of therapy response monitoring using C-SNAM. With ineffective therapy, caspase-3 remains inactive, failing to trigger C-SNAM self-assembly and resulting in rapid clearance of the probe. With successful tumor cell death, caspase-3 is activated and induces C-SNAM self-assembly, increasing signal retention and enhancing signal production to result in localized regions of MR signal enhancement (i.e. hotspots).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594000&req=5

f1: Structure, mechanism of action, and in vitro characterization of caspase 3-sensitive nano-aggregation MRI contrast agent (C-SNAM).(a) Schematic showing the structure of C-SNAM, including the DOTA-chelated Gd (blue sphere), the DEVD (green) and thioethyl (SEt, cyan) blocking groups, and the amine (red), thiol (orange), and cyano (yellow) click chemistry reactive groups. Upon removal of the capping groups, C-SNAM cyclizes and self-assembles into nanoparticles. The structure of the non-cyclizable control probe (NC-ctrl) lacks the cyano group and contains a methylated thiol, preventing cyclization upon removal of DEVD. (b) Scanning electron micrographs of C-SNAM alone (left) and after incubation with activated caspase-3 (right), showing self-assembled nano-aggregates (white arrows). (c) The activation of C-SNAM by caspase-3 results in an increase in relaxivity (r1) at 1T, but neither the activation of control probe (NC-ctrl) nor ProHance ®, suggesting that the change in ri is a result of the increase in contrast agent size following nano-aggregation. (d) Proposed mechanism of therapy response monitoring using C-SNAM. With ineffective therapy, caspase-3 remains inactive, failing to trigger C-SNAM self-assembly and resulting in rapid clearance of the probe. With successful tumor cell death, caspase-3 is activated and induces C-SNAM self-assembly, increasing signal retention and enhancing signal production to result in localized regions of MR signal enhancement (i.e. hotspots).
Mentions: C-SNAM is composed of a flexible aminoluciferin-based linker connecting two biocompatible reactive moieties, D-cysteine on one end (Fig. 1a, red and orange) and 2-cyano-6-hydroxyquinoline (Fig. 1a, yellow) on the other. In order to control the bioorthogonal reaction and self-assembly, the reactive groups of D-cysteine are reversibly blocked: the thiol is blocked by a disulfide bond to a thioethyl group (cyan oval) reducible by glutathione upon entry into a cell. The amine is blocked by an acetyl-Asp-Glu-Val-Asp (DEVD, green bar) group, a substrate of caspase-3 that is removed upon activation of the enzyme during successful radiation or chemotherapy1718. When unblocked, these reactive groups undergo rapid intramolecular condensation under physiological conditions (first order rate constant = 5.8 × 10−3 s−1)19 to form a cyclic compound, C-SNAM-cycl, whose high rigidity favors self-assembly through π-π stacking, ultimately forming a nanoparticle at a typical size of approximately 400 nm (Fig. 1b)141519. In addition to C-SNAM, a non-cyclizable control probe (NC-ctrl) was prepared lacking the cyano moiety and having a methylated thiol, preventing cyclization even after removal of the DEVD blocking group to abrogate self-assembly (Fig. 1a).

Bottom Line: The poor sensitivity of MRI has limited the development of activatable molecular MR contrast agents.To overcome this limitation of molecular MRI, a novel implementation of our caspase-3-sensitive nanoaggregation MRI (C-SNAM) contrast agent is reported.Importantly, C-SNAM is inert to immune activation, permitting radiation therapy monitoring.

View Article: PubMed Central - PubMed

Affiliation: Molecular Imaging Program at Stanford, Stanford, California 94305, USA.

ABSTRACT
Personalized cancer medicine requires measurement of therapeutic efficacy as early as possible, which is optimally achieved by three-dimensional imaging given the heterogeneity of cancer. Magnetic resonance imaging (MRI) can obtain images of both anatomy and cellular responses, if acquired with a molecular imaging contrast agent. The poor sensitivity of MRI has limited the development of activatable molecular MR contrast agents. To overcome this limitation of molecular MRI, a novel implementation of our caspase-3-sensitive nanoaggregation MRI (C-SNAM) contrast agent is reported. C-SNAM is triggered to self-assemble into nanoparticles in apoptotic tumor cells, and effectively amplifies molecular level changes through nanoaggregation, enhancing tissue retention and spin-lattice relaxivity. At one-tenth the current clinical dose of contrast agent, and following a single imaging session, C-SNAM MRI accurately measured the response of tumors to either metronomic chemotherapy or radiation therapy, where the degree of signal enhancement is prognostic of long-term therapeutic efficacy. Importantly, C-SNAM is inert to immune activation, permitting radiation therapy monitoring.

No MeSH data available.


Related in: MedlinePlus