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Tri-partite complex for axonal transport drug delivery achieves pharmacological effect.

Filler AG, Whiteside GT, Bacon M, Frederickson M, Howe FA, Rabinowitz MD, Sokoloff AJ, Deacon TW, Abell C, Munglani R, Griffiths JR, Bell BA, Lever AM - BMC Neurosci (2010)

Bottom Line: Intramuscular and intradermal injection proved effective for introducing pharmacologically effective doses into selected populations of CNS neurons.Pharmacological efficacy with gabapentin in a paw withdrawal latency model revealed a ten fold increase in half life and a 300 fold decrease in necessary dose relative to systemic administration for gabapentin when the drug was delivered by axonal transport using the tripartite vehicle.The pharmacologically efficacious drug delivery demonstrated here verify the fundamental feasibility of using axonal transport for targeted drug delivery.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Nerve Medicine, 2716 Ocean Park Blvd,, Suite 3082, Santa Monica, CA 90405, USA. afiller@nervemed.com

ABSTRACT

Background: Targeted delivery of pharmaceutical agents into selected populations of CNS (Central Nervous System) neurons is an extremely compelling goal. Currently, systemic methods are generally used for delivery of pain medications, anti-virals for treatment of dermatomal infections, anti-spasmodics, and neuroprotectants. Systemic side effects or undesirable effects on parts of the CNS that are not involved in the pathology limit efficacy and limit clinical utility for many classes of pharmaceuticals. Axonal transport from the periphery offers a possible selective route, but there has been little progress towards design of agents that can accomplish targeted delivery via this intraneural route. To achieve this goal, we developed a tripartite molecular construction concept involving an axonal transport facilitator molecule, a polymer linker, and a large number of drug molecules conjugated to the linker, then sought to evaluate its neurobiology and pharmacological behavior.

Results: We developed chemical synthesis methodologies for assembling these tripartite complexes using a variety of axonal transport facilitators including nerve growth factor, wheat germ agglutinin, and synthetic facilitators derived from phage display work. Loading of up to 100 drug molecules per complex was achieved. Conjugation methods were used that allowed the drugs to be released in active form inside the cell body after transport. Intramuscular and intradermal injection proved effective for introducing pharmacologically effective doses into selected populations of CNS neurons. Pharmacological efficacy with gabapentin in a paw withdrawal latency model revealed a ten fold increase in half life and a 300 fold decrease in necessary dose relative to systemic administration for gabapentin when the drug was delivered by axonal transport using the tripartite vehicle.

Conclusion: Specific targeting of selected subpopulations of CNS neurons for drug delivery by axonal transport holds great promise. The data shown here provide a basic framework for the intraneural pharmacology of this tripartite complex. The pharmacologically efficacious drug delivery demonstrated here verify the fundamental feasibility of using axonal transport for targeted drug delivery.

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Median nerve contrast study by solenoid coil high resolution, high field MRI. All images are from a single image slice of rabbit upper arm. Image (a) is collected with a STIR (short tau inversion recovery) sequence which suppresses signal from fat - it reduces the marrow signal (6), and also identifies structure (1) as the median nerve[44], structure (7) as the ulnar nerve, structure (8) as the flow void of he brachial artery and structure 9 as the flow void of the basilic vein. Images (b) & (c)are colorized spin echo studies obtained at 90 minutes and 360 minutes after injection, respectively. Note that the marrow (3) appears shifted out the humerus (partially overlapped dark circle) by chemical shift effects. The shift at 4.7 Tesla is 1.85 millimeters. Similar shifts are seen at (4), and serve at (5) to leave two bright structures in a gap between triceps and biceps. (a-m), (b-m), (c-m) are magnified views of the space between the biceps and triceps on the medial aspect of the upper arm. Structure (2) is a small amount of fatty tissue that is actually located on the inferior left surface of the brachial artery, but chemical shift has placed its fat image into the midst of the basilic vein. Structure (2) disappears in the STIR image due to fat suppression. Based on this identification, the median nerve (1/1a) is compared to the non-neural structure (2/2a) and is seen to lose intensity in the four and half hour interval between images (b) and (c) reflecting transport of the WGA-magnetite contrast agent injected in the forearm flexor muscles [24]. The image conspicuity of this structure was measured by multiplying its volume times the intensity in grayscale and this reveals a decrease of 52% in the 270 minute interval. Scale bars are 6 mm for (a), (b), and (c) and 3 mm for (am), (bm) and (cm).
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Figure 9: Median nerve contrast study by solenoid coil high resolution, high field MRI. All images are from a single image slice of rabbit upper arm. Image (a) is collected with a STIR (short tau inversion recovery) sequence which suppresses signal from fat - it reduces the marrow signal (6), and also identifies structure (1) as the median nerve[44], structure (7) as the ulnar nerve, structure (8) as the flow void of he brachial artery and structure 9 as the flow void of the basilic vein. Images (b) & (c)are colorized spin echo studies obtained at 90 minutes and 360 minutes after injection, respectively. Note that the marrow (3) appears shifted out the humerus (partially overlapped dark circle) by chemical shift effects. The shift at 4.7 Tesla is 1.85 millimeters. Similar shifts are seen at (4), and serve at (5) to leave two bright structures in a gap between triceps and biceps. (a-m), (b-m), (c-m) are magnified views of the space between the biceps and triceps on the medial aspect of the upper arm. Structure (2) is a small amount of fatty tissue that is actually located on the inferior left surface of the brachial artery, but chemical shift has placed its fat image into the midst of the basilic vein. Structure (2) disappears in the STIR image due to fat suppression. Based on this identification, the median nerve (1/1a) is compared to the non-neural structure (2/2a) and is seen to lose intensity in the four and half hour interval between images (b) and (c) reflecting transport of the WGA-magnetite contrast agent injected in the forearm flexor muscles [24]. The image conspicuity of this structure was measured by multiplying its volume times the intensity in grayscale and this reveals a decrease of 52% in the 270 minute interval. Scale bars are 6 mm for (a), (b), and (c) and 3 mm for (am), (bm) and (cm).

Mentions: The relaxivity experiments (Figure 7) taken together with distribution studies showed that the concentration of magnetite delivered to the axon by the tripartite was sufficient to affect the T2 relaxation rate of nerve. The observation of a decrease of T2 relaxation time in nerves transporting superparamagnetic nanoparticles in both the micro-MRI nerve channel studies (Figure 8) and in the high resolution MRI experiments (Figure 9) confirmed that the carrier particles were not degraded. Any hydrolysis of the sub-domain sized particles would have eradicated their superparamagnetic effect on T2 relaxation time in nerve as transport progressed. The relaxivity effect far exceeded that which would result from free iron or ferritin at the doses administered.


Tri-partite complex for axonal transport drug delivery achieves pharmacological effect.

Filler AG, Whiteside GT, Bacon M, Frederickson M, Howe FA, Rabinowitz MD, Sokoloff AJ, Deacon TW, Abell C, Munglani R, Griffiths JR, Bell BA, Lever AM - BMC Neurosci (2010)

Median nerve contrast study by solenoid coil high resolution, high field MRI. All images are from a single image slice of rabbit upper arm. Image (a) is collected with a STIR (short tau inversion recovery) sequence which suppresses signal from fat - it reduces the marrow signal (6), and also identifies structure (1) as the median nerve[44], structure (7) as the ulnar nerve, structure (8) as the flow void of he brachial artery and structure 9 as the flow void of the basilic vein. Images (b) & (c)are colorized spin echo studies obtained at 90 minutes and 360 minutes after injection, respectively. Note that the marrow (3) appears shifted out the humerus (partially overlapped dark circle) by chemical shift effects. The shift at 4.7 Tesla is 1.85 millimeters. Similar shifts are seen at (4), and serve at (5) to leave two bright structures in a gap between triceps and biceps. (a-m), (b-m), (c-m) are magnified views of the space between the biceps and triceps on the medial aspect of the upper arm. Structure (2) is a small amount of fatty tissue that is actually located on the inferior left surface of the brachial artery, but chemical shift has placed its fat image into the midst of the basilic vein. Structure (2) disappears in the STIR image due to fat suppression. Based on this identification, the median nerve (1/1a) is compared to the non-neural structure (2/2a) and is seen to lose intensity in the four and half hour interval between images (b) and (c) reflecting transport of the WGA-magnetite contrast agent injected in the forearm flexor muscles [24]. The image conspicuity of this structure was measured by multiplying its volume times the intensity in grayscale and this reveals a decrease of 52% in the 270 minute interval. Scale bars are 6 mm for (a), (b), and (c) and 3 mm for (am), (bm) and (cm).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 9: Median nerve contrast study by solenoid coil high resolution, high field MRI. All images are from a single image slice of rabbit upper arm. Image (a) is collected with a STIR (short tau inversion recovery) sequence which suppresses signal from fat - it reduces the marrow signal (6), and also identifies structure (1) as the median nerve[44], structure (7) as the ulnar nerve, structure (8) as the flow void of he brachial artery and structure 9 as the flow void of the basilic vein. Images (b) & (c)are colorized spin echo studies obtained at 90 minutes and 360 minutes after injection, respectively. Note that the marrow (3) appears shifted out the humerus (partially overlapped dark circle) by chemical shift effects. The shift at 4.7 Tesla is 1.85 millimeters. Similar shifts are seen at (4), and serve at (5) to leave two bright structures in a gap between triceps and biceps. (a-m), (b-m), (c-m) are magnified views of the space between the biceps and triceps on the medial aspect of the upper arm. Structure (2) is a small amount of fatty tissue that is actually located on the inferior left surface of the brachial artery, but chemical shift has placed its fat image into the midst of the basilic vein. Structure (2) disappears in the STIR image due to fat suppression. Based on this identification, the median nerve (1/1a) is compared to the non-neural structure (2/2a) and is seen to lose intensity in the four and half hour interval between images (b) and (c) reflecting transport of the WGA-magnetite contrast agent injected in the forearm flexor muscles [24]. The image conspicuity of this structure was measured by multiplying its volume times the intensity in grayscale and this reveals a decrease of 52% in the 270 minute interval. Scale bars are 6 mm for (a), (b), and (c) and 3 mm for (am), (bm) and (cm).
Mentions: The relaxivity experiments (Figure 7) taken together with distribution studies showed that the concentration of magnetite delivered to the axon by the tripartite was sufficient to affect the T2 relaxation rate of nerve. The observation of a decrease of T2 relaxation time in nerves transporting superparamagnetic nanoparticles in both the micro-MRI nerve channel studies (Figure 8) and in the high resolution MRI experiments (Figure 9) confirmed that the carrier particles were not degraded. Any hydrolysis of the sub-domain sized particles would have eradicated their superparamagnetic effect on T2 relaxation time in nerve as transport progressed. The relaxivity effect far exceeded that which would result from free iron or ferritin at the doses administered.

Bottom Line: Intramuscular and intradermal injection proved effective for introducing pharmacologically effective doses into selected populations of CNS neurons.Pharmacological efficacy with gabapentin in a paw withdrawal latency model revealed a ten fold increase in half life and a 300 fold decrease in necessary dose relative to systemic administration for gabapentin when the drug was delivered by axonal transport using the tripartite vehicle.The pharmacologically efficacious drug delivery demonstrated here verify the fundamental feasibility of using axonal transport for targeted drug delivery.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Nerve Medicine, 2716 Ocean Park Blvd,, Suite 3082, Santa Monica, CA 90405, USA. afiller@nervemed.com

ABSTRACT

Background: Targeted delivery of pharmaceutical agents into selected populations of CNS (Central Nervous System) neurons is an extremely compelling goal. Currently, systemic methods are generally used for delivery of pain medications, anti-virals for treatment of dermatomal infections, anti-spasmodics, and neuroprotectants. Systemic side effects or undesirable effects on parts of the CNS that are not involved in the pathology limit efficacy and limit clinical utility for many classes of pharmaceuticals. Axonal transport from the periphery offers a possible selective route, but there has been little progress towards design of agents that can accomplish targeted delivery via this intraneural route. To achieve this goal, we developed a tripartite molecular construction concept involving an axonal transport facilitator molecule, a polymer linker, and a large number of drug molecules conjugated to the linker, then sought to evaluate its neurobiology and pharmacological behavior.

Results: We developed chemical synthesis methodologies for assembling these tripartite complexes using a variety of axonal transport facilitators including nerve growth factor, wheat germ agglutinin, and synthetic facilitators derived from phage display work. Loading of up to 100 drug molecules per complex was achieved. Conjugation methods were used that allowed the drugs to be released in active form inside the cell body after transport. Intramuscular and intradermal injection proved effective for introducing pharmacologically effective doses into selected populations of CNS neurons. Pharmacological efficacy with gabapentin in a paw withdrawal latency model revealed a ten fold increase in half life and a 300 fold decrease in necessary dose relative to systemic administration for gabapentin when the drug was delivered by axonal transport using the tripartite vehicle.

Conclusion: Specific targeting of selected subpopulations of CNS neurons for drug delivery by axonal transport holds great promise. The data shown here provide a basic framework for the intraneural pharmacology of this tripartite complex. The pharmacologically efficacious drug delivery demonstrated here verify the fundamental feasibility of using axonal transport for targeted drug delivery.

Show MeSH
Related in: MedlinePlus