Slaying the Dragon Nanomechanics opens a new route to the treatment of metastatic cancer. By Mauro Ferrari

nce cancers metastasize, they are Oalmost always fatal. Researchers are looking at the nanoscale mechanics of tumors to discover means to attack—and kill—all kinds of cancer cells. If successful, this will be a cure for even metastatic cancer.

Reprinted with permission, Mechanical Engineering magazine Vol. 137, No. 4, April 2015. Copyright ASME 2015.

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To reach and kill metastatic cancer cells, laying therapeutic vectors (gray disks) must S make it past enzymes (yellow bolts), immune system cells (white globs), and the endothelial layer (blue-gray barrier).

adverse e„ ect that the treatment gives to the patient. Simply put, the current treatments that are available to fi ght metastatic cancers have a therapeutic the Dragon index so low that they provide only days or weeks of extended life. And here is where nanotechnology and engineering mechanics come in. My colleagues and I are developing therapeutic drugs that can be tailored specifi cally to the weaknesses of these metastatic cancer cells and can be delivered to the cells directly, without poisoning the healthy tissues in the rest of the body. For instance, my colleague Haifa Shen at the Houston Methodist Re- search Institute has developed a multi- functional particle system that takes advantage of the mechanics of blood fl ow through capillaries to preferential- ly attack lung cancer cells. In labora- tory trials, Shen has had a 50 percent We have been at war against cancer ing to the healthy parts of the body, and success rate in curing metastatic lung for more than a generation—o cially therefore dosage cannot be increased at cancer in mice. since President Richard M. Nixon will without concern for major, poten- I will describe this approach in more signed the National Cancer Act of 1971, tially lethal adverse consequences for detail, below, but fi rst we need to take and for years before that as well. And the patients. a few steps back to frame the problem there have been many victories over The cancers which we cannot yet in fuller detail, and set the stage for the course of this war: Primary cancers cure with any level of confi dence are nanomechanics-based solution strate- are more and more often completely ones that have metastasized. That is, gies. Perhaps the narrative can be eased resolved, largely owing to advances in they have spread from the organ in by a metaphor—of the human body as surgical techniques. But because cancer which they originated to other organs. a medieval fortress, protected by mul- remains a leading cause of death in the Indeed, the rate at which metastatic tiple defensive systems: Its high walls, U.S. and other parts of the developed cancers, especially those that grow in encircled by a moat, with crocodiles to world, many people view the e„ ort the lungs, liver, and brain, are cured boot, archers on the walls, cauldrons of against the disease as a failure. remains abysmally low and they are boiling oil to be used against attackers As fearsome as cancers are, cancer responsible for the vast majority of scaling the walls (including meta- cells are easy to kill. All cancer drugs cancer deaths. phorical cancer drugs, mistaken for are e„ ective against cancer cells, as Medical researchers have a term, enemies). are many other substances—even tap “therapeutic index,” which is a mea- You get the idea, the human body water. The problem is that e„ ective sure of how much therapeutic benefi t comprises a sequence of built-in pro- cancer drugs are also extremely damag- we can achieve for a drug, per unit of tections against attack (a.k.a., “bio- Reprinted with permission, Mechanical Engineering magazine Vol. 137, No. 4, April 2015. Copyright ASME 2015.

0415MEM_Ferarri.indd 37 2/27/2015 9:44:49 AM barriers”), which in biological reality the cancer and kill it on the spot will short: insu cient therapeutic index. comprise the surfaces lining the blood do the princess no good, unless they Second, in the last twenty years or vessels (vascular endothelium), the come with a sequence of passwords. so, all the rage has been on molecularly trapping organs that selectively fi lter Drugs without the required comple- targeted, biological therapies, mostly the content of the blood stream (e.g. ment of carrier passwords will end up monoclonal antibodies. These are re- liver and spleen, the reticulo-endothe- in the toilet, or worse, will mostly kill ally good at recognizing monsters from lial system), the membranes surround- innocent and helpful bystanders in princesses, and delivering their deadly ing the cells of the body, and their inner other rooms. payload against the captors, rather than organelles, and the safety pumps that Fourth, the very same poisons and the hostages. cells use to expel noxious substances weapons that kill the beast will also kill Great, but all of the biomolecular (multi-drug resistance e™ ux pumps). the princess—though some princesses equipment they need to carry in order In this medieval metaphor, let’s are indeed a bit stronger than the to achieve that bio-sniper capability imagine the beautiful princess, symbol- beasts, by a tiny bit that correlates with makes them big and bulky, and gener- izing life itself, chained in a room—one the therapeutic index. ally incapable of making it through the among the thousands of rooms in the Fifth, actually there are many prin- defenses: They are picked up by the fortress—and a hideous monster, sym- cesses, not only one, and they are all biological radars of the body, they are bolizing a cancer metastasis, creeping threatened by many di„ erent monsters, heard stumbling through the vaulted up to her, with deadly intent. symbolizing the heterogeneity of metas- halls, and killed; they are too heavy The good news is, the monster is tases deriving from a single primary to swim across the moat with rapid- easy to kill: Just about any substance or tumor. If any of the princesses dies, it’s ity, and succumb to the metaphorical weapon will kill it, as is true for cancer game over for all. And, di„ erent mon- crocodiles. Result: A modest survival cells, which can easily be killed with sters are vulnerable to di„ erent poisons advantage for metastatic patients, on tap water. and weapons, while all princesses are the order of weeks, certainly no cure. The bad news, however, is plentiful. harmed by all drugs. And, di„ erent Better therapeutic index, but still too First, we do not know in which room monsters can modify the biobarriers low, still needing to fl ood a patient with this tragedy is unfolding—and we need around them in di„ erent ways, each drugs to get enough past the crocodiles, to get there quick. Time is ticking away. with new and more complex passwords. and still too much damage to innocent Second, the monster has black magic Still surprised that metastatic disease and productive citizens of the body. powers, including the ability to modify is currently incurable? Third—here enters nanotechnology! the biobarriers around itself, so that So, what approaches have been used How about packing those chemo-drugs it will be protected against whatever to address this horrifying scenario? We in little tiny nano-containers that will poisons and weapons we want to use have four main lines of attack. preferentially be collected in the rooms where the princesses meet the beasts? Great I am optimistic that the day is coming, soon, when deadly metastatic diseases can idea, but you still need be definitively cured. And the approach that works will be based on the invaluable the biological passwords to advances that were recorded in all of the prior approaches, chemo- to bio- to nano-. get there. So, the fi rst genera- tion nanodrugs (starting about 20 years ago) were approved to treat against it. In reality, cancers have the First, the poisons that can get into cancers which were so stupid that they ability to grow protective tissue around every room of the human fortress—the did not even lock the doors behind themselves (stroma), plus an adverse classical approach of IV infusion of them. These cancers are very perme- pressure gradient, and express molecu- small molecule chemotherapeutics. able to nano-sized agents through the lar pumps that push poisons back to They will kill a lot of monsters indeed, so-called enhanced permeation and where they came from. but with this approach it is impossible retention e„ ect (EPR), which comes Third, the various barriers and to get them all without executing a with a greater leakiness of their vascu- protections in health and disease princess or two, even though the poi- lar walls. require special biological passwords to sons can be selected to act on processes The nanodrugs use nanoparticle get through. Thus, the ability for our that are more frequent in cancer than materials such as liposomes (imitation “prince charming drugs” to recognize health—such as cell duplication. In cell membrane) and albumin (a carrier Reprinted with permission, Mechanical Engineering magazine Vol. 137, No. 4, April 2015. Copyright ASME 2015.

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An illustration of a multi- stage vector designed to carry cancer drugs inside its nano-scale pores.

molecule of the body) as nano-scale “actively targeted” nanoparticles has ed that a new, multifunctional thera- drug containers and vectors, to be in- ever been approved for clinical use, peutic agent (MSV-pX) can completely jected into the bloodstream. Nanodrugs though several are in clinical trials. Tell cure about 50 percent of animals with in current clinical use have extended you a secret, I am not sure any ever breast cancers, metastatic to the lungs, the lives of many metastatic patients on will make to the clinic, and if they do, I in several di„ erent mouse models. For the order of weeks to months, which is doubt they will make much of a clinical the same situation in the clinic there is good, but not enough. impact. no cure, no expectation of survival. Thus, fourth came the idea of adding Any impact is good, don’t get me How did he do it? The key word to these nanoparticles a decoration of wrong—but my only surprise here is “multifunctional.” In turn, the key biomolecular recognition agents on the is that the vast majority of current foundations of his successes are engi- surfaces, such as antibodies that recog- nanomedicine projects deal with some neering mechanics and nanotechnol- nize cancer specifi cally, on the theory variant of this ill-fated approach. Dif- ogy. Let’s explore how. that this would keep the nanoparticle ferent materials, sizes, targeting agents, First, the vasculature feeding in the princess chambers longer, and drugs—but probably the same croco- metastatic lesion is di„ erent; it has away from the healthy parts of the diles in their future. characteristic fl ow dynamics, which body. Problem is, those metaphori- Still, I am optimistic that the day is also refl ect the organ in which they are cal crocodiles that get the biologically coming, soon, when deadly metastatic located. Employing mathematical mod- targeted therapies (second approach, diseases can be defi nitively cured. And els of multiphase fl ow, which we have above) have a fi eld day against these the approach that works will be based developed over the last 10 years, Shen molecularly targeted nanoparticles, on the invaluable advances that were was able to design particles that, upon which are much fatter, slower, and recorded in all of the prior approaches, reaching the lung cancer capillary bed, juicier! chemo- to bio- to nano-. tend to accentuate their drift toward Then, no surprise that none of these Haifa Shen has recently demonstrat- the vascular wall, and lodge there, or Reprinted with permission, Mechanical Engineering magazine Vol. 137, No. 4, April 2015. Copyright ASME 2015.

0415MEM_Ferarri.indd 39 2/27/2015 9:44:51 AM Breast cancer cells are shown in dark pink in this micrograph. A nano-based, multi- stage therapy has shown good results.

even penetrate across a line of cancer endothelial cells into the cancer tissue. This process of drifting (margin- ation), lodging (fi rm adhesion) and penetration (EPR, transcytosis, and paracytosis) is fundamentally en- abled by the shape (disks, resembling platelets), size (3-micrometer diameter, 200 nm thickness), surface charge, and density. It is a physics-based choice of optimal design parameters, obtained in keeping with the principles of engineering mechanics that gives the preferential concentration at the tumor with smaller (second-stage) carriers these drug-carrying nanoparticles – a site, or: Mechanics begets therapeutic and molecules? Multi-Stage Vector (the “MSV”). index. Di„ erent choices of physical de- As we saw, these by themselves if in- Why not just carry polymeric sign variables enable preferential con- jected in the blood stream would never nanoparticles to start with, you ask? centration at other crucial metastatic concentrate at the target site, but the Too big for the nanopores of the fi rst sites, such as liver and bone marrow. idea here is they can be carried there stage vector. Over a hundred years ago, the Wright by the “fi rst-stage” Haifa Shen carrier. Why do you need nanoparticles, brothers tried a few designs to see if Sure, to accomplish this all you have to rather than just the polymer molecules any of their contraptions would fl y. do is to make the fi rst-stage particles with their linked drugs? Because the Now, we design airplanes with the suitably nanoporous (easy, done, pat- polymer with drug simply will not be benefi t of engineering mechanics ented) and load the “stage two” in the taken in by the cancer cells. and computer simulation for optimal nanopores. The nanoparticle, on the other hand, design. Tell you what—I think the time The solution that works against lung has Trojan horse-like properties, and has come that we do exactly the same metastases is to load a second stage that gets engulfed by the target cells by thing with drugs, designing them for is a molecule of a polymer (the “p” in phagocytic processes. I suspect that the optimal concentration at target sites, MSV-pX), which is linked to a con- Trojans of old would not have taken based on the quantitative approaches of ventional “anti-duplication” chemo- into their city just any old, shapeless engineering mechanics. therapeutic drug (the “X”) by means of mass of wood. It had to look like a Tell you more: If di„ erent cancers a chemical group which is cleaved in horse, right? So, we need nanoparticles, have di„ erent vascular and blood fl ow high-acidity environments (Don’t ask not polymeric strands—same idea. characteristics, how about we deter- me why now; you will see later). This Now, part three of this perilous mine these fi rst by radiological imaging stage-two molecule is spewed out from journey through the cancer jungle (this is easy) and then we design the the fi rst-stage vector by di„ usion, and swamps, plus crocodiles: Once the most suitable drug in a way that will during the chemical disintegration of nanoparticles are picked up by the optimize transport to the needed sites? the fi rst stage carrier in the body—and cancer cells, what happens to them is In other words: Personalizing therapy by thermodynamic forces it forms what happens to anything (nutrients, by optimizing the engineering mechan- nanoparticles, upon exiting the pores. signaling molecules, etc.) that is picked ics of its transport? So, at this point you have a biode- up by receptor-mediated endocytosis Alas, concentrate preferentially gradable microparticle for injection in cells: They are enveloped in a lipid- though they may at desired metastatic in the bloodstream, which can act as bound container (vesicle, phagosome, lesion sites, the Haifa Shen vectors do nanoparticle generator, can concentrate then transforming into an endosome or not penetrate through the cancer deep preferentially at the target cancer be- lysosome during transport) and carried enough. They are simply too big. But cause of its physical characteristics, and actively by transporter molecules along then—ah-ha!—how about we load them upon getting there forms and spews out train-tracks (microtubules) that direct Reprinted with permission, Mechanical Engineering magazine Vol. 137, No. 4, April 2015. Copyright ASME 2015.

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them toward the cell nucleus. they fi nd them, they actively expel Tasciotti again hijack some cells in the As this happens, the interior of them from the inside of the cell, where body so that they will carry MSV thera- the vesicles becomes more and more they can hurt, to the outside, where peutics deepest inside of cancers. Car- acidic. It’s part of the normal garbage they can be safely dealt with. lotta Borsoi uses MSV systems to build disposal processes of our cells. As they Free chemodrug di„ using into the a metaphorical road across the cancer get to the immediate vicinity of the cell will be spewed out most e„ ectively. jungle, so that conventional drugs can nucleus (which is the ultimate target Chemodrug inside of polymer nanopar- get there with greatest e cacy. Haifa of the anti-duplication chemotherapy ticle, on the other hand, is taken up Shen has developed multifunctional drug), the interior of the transporter by the vesicles and ferried far away MSV cancer therapeutic vaccines. I biovesicle reaches a trigger point of acidity, which results in the pH- sensitive linker to be cleaved, Cancer cells, especially those that are hardest to kill and that repopulate the cancer and the therapeutic moiety to after most of it is wiped out by therapy, have this exceptionally powerful defense be freed from the polymer mechanism of multi-drug resistance enabled by a great many molecular pumps. backbone. In this free form it can di„ use out of the vesicle, and travel from these e™ ux pumps, right by the have been focusing primarily on using the very short distance to get into the nucleus where it can carry out its mis- MSVs as components of a therapeutic nucleus, where it e„ ectively kills the sion impossible, past the defense of the strategy that suppresses the actions of target cell. Victory. Haifa cured about dark-star cancer cell. the key driver genes of cancer. 50 percent of the animals with lung Again, all elements of this exquisitely All of these approaches could not metastases, which otherwise would designed multi-component drug—the succeed without the multi-disciplinary have died in days to weeks. MSV, the p, the X—are all necessary for palette of clinical oncology, nanotech- Again, why don’t we just inject the its success, and they are all based on nology, cancer biology, mathematics, drug by itself? Can’t reach enough the mechanics of transport. And, please materials sciences, pharmaceutical concentration in the right place, result- do not talk to me about mere “drug de- methods, physics of transport, imaging ing in bad therapeutic index. This is the livery systems.” What we have here is a technology, chemistry, biotechnol- classical chemotherapy approach. new generation of multi-tasking drugs, ogy—and the necessary foundations of Why not inject the chemo+polymer? and any component by itself is incom- engineering mechanics! Will not enter the cell as e„ ectively. plete, exactly like those we use every So, I reckon it’s time that engineer- Why not just fi nd another way to day on thousands of cancer patients. ing mechanics join forces with all of marinate the cancer cells into a large Other colleagues of mine are explor- these disciplines, to fi nally win the fi ght dose of chemo, somehow delivered ing further frontiers of multistage against metastases. What say you? Hai- at the right site, rather than using the pharmaceuticals: Ennio Tasciotti strips fa Shen and his colleagues have shown polymer backbone-turned nanoparticle some immune cells of their membranes, the way. There are prairies worth of to transport across the train tracks of and uses them to cloak MSV carriers so space for other strategies and designs the cells, toward the nucleus? Now, that they will not be captured as readily that will conquer di„ erent beasts in dif- that’s a good question to ask! Here by the fi ltering organs of the body. To ferent fortresses. goes the explanation—very, very clever use paratrooper analogies, if you are Many lives to save, and we can do of Dr. Shen: Cancer cells, especially going to be dropped behind enemy it, if we join forces and work together. those that are hardest to kill and that lines, you might avoid capture longer to Let’s all get busy! ME repopulate the cancer after most of it is carry out your mission, if you wear the wiped out by therapy (these are known uniform of the enemy. MAURO FERRARI, an ASME Fellow, is the Ernest as cancer stem cells), have this excep- Elvin Blanco deploys second stages Cockrell Jr. Presidential Distinguished Chair, tionally powerful defense mechanism that carry more than one drug, with president, and chief executive officer of the Houston of multi-drug resistance enabled by a prescribed concentration ratios, to Methodist Research Institute in Texas. He is also the great many molecular pumps that sit at optimize their synergy. He can even get executive vice president of the Houston Methodist or by their outer cell membranes. them to release at di„ erent, prescribed Hospital System and senior associate dean and pro- The pumps look for toxic agents that times. fessor of medicine at Weill Cornell Medical College may have penetrated the cell, and when Kenji Yokoi, Biana Godin, and Ennio in New York City. Reprinted with permission, Mechanical Engineering magazine Vol. 137, No. 4, April 2015. Copyright ASME 2015.

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