Nuclear localization

As all roads lead to Rome, all routes lead to the nucleus

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One of the most known events that took place along the Appian Way involved the gladiator Spartacus. Spartacus was a Thracian who was taken prisoner by the Romans and subjected into gladiator school (ludus gladiatorius).  In 73 B.C. Spartacus and 80 of his fellow gladiators rebelled and escaped and began what is known as the third Servile War. Showing leadership, Spartacus managed to fight the Romans for more than two years. Finally, pinned down and out numbered, Spartacus on the banks of the Sele River (SouthWest Italy) mad his last stand. He killed his horse reasoning if he won, the Romans would have more horses for him to ride. If he died, he would not need a horse. After the defeat, the more than 6,000 slaves that survived were crucified along the 200-kilometer Appian Way from Capua to Rome. As the Appian Way was the most important Roman road as it was the main artery that lead to Rome, arguably the center of the everything for ancient Rome.

The nucleus is the major susceptibility center for many in therapeutics  for it controls the expression of gene products with functions necessary for cellular survival. Thus, the biomedical field widely investigates the application of nuclear localization signal (NLS)-tagging for nonviral transfer of oligonucleotides, proteins, and drugs as therapeutics. Examples include nuclear targeting for DNA vaccines to improve the expression of immunogenic peptides, and for theranostic radionuclides to localize short-range radiation-emitting radionuclides to ionize the DNA . Enabling a mAb to target cell surface receptors on diseased cells and then deliver cytotoxic payloads to the nucleus would be a promising approach to develop effective therapies. Thus, all roads lead to Rome, all the major cellular transport routes lead to the nucleus. 

endosome escape

Escape from the endosome

Acatraz movie.jpg
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I love this movie and still remember as a boy taking the tour of Alcatraz, the notorious prison that housed America's worse felons, including Al Capone. Alcatraz was deemed inescapable. Until, on June 11th 1962 Frank Morris and John and Clarence Anglin vanished from Alcatraz. Some say their makeshift inflatable boat sank in dangerous waters of San Francisco Bay, others (including myself) like to believe they escaped.

Similarly, the endosome has been an Alcatraz for ADCs and therapeutics that aim to localize to the nucleus. Proteins, such as antibodies cannot penetrate the greasy shell of endosomes. However, to get inside the cell they must enter through a processes that encapsulates them inside these notorious endosomes. Finding an approach to breakout of endosomes could be a key to unlocking the next-generation of effective biopharmaceuticals.

Leyton lab platform technology

Cell Accumulator (Accum)

We have developed a technology (termed Cell Accumulator [Accum]) that enables mAbs to escape endosome entrapment and then localize to the nucleus in target cells. 

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Figure. Schematic of mAb modified with Accum (blue curved line) binding to it target receptor. Upon binding to the receptor, the complex undergoes receptor-mediated internalization and is entrapped inside endosomes. Accum contains a nuclear localization signal sequence that is recognized by nuclear transport receptors. The nucleus becomes a reservoir for increased intracellular accumulation of attached molecular payloads. Testing in vivo models of cancer, Accum-modified mAbs improve tumor targeting and increases the cellular concentration of the conjugated molecular payload. 

Key papers:

Pharmaceutical Applications: 

1. Antibody-drug conjugates (ADCs)

2. Drugging intracellular "undruggable" targets

3. Radioimmunoconjugates