"An army," Napoleon said, "marches on its belly."
So the savviest strategy for making an enemy force go belly-up is totarget its troops' food supply. This nutrient-denying maneuver alsoshould work to defeat the armies of solid-tumor cells that multiplyand metastasize in cancer patients.
A tumor's nourishment arrives via a spreading network of new bloodvessels _ the process of angiogenesis. Besides striving to kill off themalignant cells by surgery, radiation and chemotherapy, oncologistsare now deploying a host of biological counter forces aimed atblowing up these expanding pipelines of malignancy, and throttlingtheir proliferation. (See BioWorld Today, Jan. 4, 1995, p. 1.)
This is no simple one-shot assault. First of all, dissolve the basalmembrane underpinning the endothelial cells that form blood vessels.Then, search out and destroy the moving targets presented by thosecells' migration, invasion, adhesion and proliferation.
Surgeon Judah Folkman, the acknowledged Napoleon of anti-angiogenesis strategy, tactics and logistics, holds an endowed chair atHarvard Medical School. He and his associates have just completedan extensive experiment to determine whether the cytokine,interleukin 12 (IL 12), an experimental cytotoxic anti-cancer drug,can also inhibit tumors by cutting off their angiogenesis.
The title of the Harvard researchers' report in the current Journal ofthe National Cancer Institute (JNCI), dated April 19, says as much:"Inhibition of angiogenesis in vivo by interleukin 12."
Testing An Immuno-Zoo Of Mice
Angiogenesis testing in live animal models takes place in themammalian eyeball, because its cornea grows no blood vessels of itsown. Folkman's co-authors, in collaboration with the oncologydepartment of Hoffmann-La Roche Inc., of Nutley, N.J., implanted apellet of basic fibroblast growth factor _ a sure-fire blood-vesselproliferator _ in the cornea of mice. These animals then receivedfive-day infusions of recombinant murine IL 12, to see if thiscytokine could curb or cripple the sprouting blood vessels in theircorneas.
It could and did _ in an immunological assortment of rodents. Thismini-zoo included normal, immuno-competent mice, immuno-compromised severe combined immune deficient (SCID) mice, beigemice that lack natural killer cells, and nude mice devoid of Tlymphocytes.
The IL 12 treatment, Folkman's paper reports, "almost completelyinhibited corneal neovascularization" in normal, beige and SCIDmice. But "this potent suppression of angiogenesis was prevented bythe administration of interferon-gamma-neutralizing antibodies[which] totally abolished the anti-angiogenic properties of IL 12."
This strongly suggested that IL 12 works against blood vessels byinducing gamma interferon (IFN g). In fact, when the teamadministered IFN g alone, it too damped down angiogenesis.
Control mice, which received dummy infusions, "had blood vesselsthat reached the pellet within five days of its implantation."
The multi-mouse-strain experiment implied that IL 12 achievesangiogenesis by mechanisms that by-pass the mammalian immunesystem. In its results, Folkman's group saw "evidence that inhibitionof angiogenesis is a previously unrecognized biological activity of IL12, [resulting] in an optimum anti-tumor effect."
To Canadian oncologist Robert Kerbel, it suggests that attackinggenetically stable endothelial blood-vessels rather than tumor cellsper se would obviate the flaw in current chemotherapy of generatingdrug-resistance in tumor cells. Kerbel, who is at Toronto'sSunnybrook Regional Cancer Center, wrote an accompanyingcomment on Folkman's report in the current JNCI.
Until now, oncologists and immunologists alike have viewedinterleukin 12 solely as acting on natural killer and cytotoxic T cells.Besides the cytokine's potent antitumor and antimetastatic activitiesin mouse models, (but less successful so far in human cancerpatients), it looked like a likely adjuvant for infectious-diseasevaccines. (see BioWorld for Jan. 18, 1994, p. 1.)
One co-author of the JNCI paper is tumor biologist Gary Truitt ofRoche's oncology department. The director of cell biology in thatunit is experimental oncologist Alexander Wood.
He told BioWorld Today that the genesis of the IL 12 anti-angiogenesis project was Truitt's noticing in preclinical animalstudies of IL 12 "that tumors excised from animals at the end oftherapy were not only smaller in size but paler in color than untreatedtumors from untreated mice."
The Roche scientists wondered whether this in vivo-in vitrodichotomy meant that the cytokine had reduced the tumor cells, thusdiminishing their blood supply, or had affected blood vesselformation directly.
"To distinguish between those two possibilities," Wood said, "andevaluate anti-angiogenic activity of the compound, if it had any,Truitt turned to the world expert and pioneer in the field, JudahFolkman. That began our collaborative effort."
Roche is now conducting Phase I clinical trials with recombinanthuman IL 12 in the U.S. and Europe. "Knowing it's angiogenic,"Wood said, "will help us decide additional indications with respect tofurther clinical trials of the cytokine.
Moving Ahead With Angigenesis Therapies
"Then," he added, "we'll have to wait and see what the safety profileof IL 12 is. That information will tell us whether we can pursue otherangiogenesis-type therapies."
Folkman told BioWorld that the paper's first author, post-doctoraloncologist Emile Voest, "has just gone back to the Netherlands. "Weare collaborating, and the laboratory side is going to be to find outexactly how IL 12 works.
"It looks so far as if it up-regulates gamma interferon," Folkmanadded. "Gamma interferon itself may not be the direct inhibitor ofendothelial cells, but it may induce another protein that then inhibitsendothelial cells. And we're going to try to find that."
"IL 12 packs a double punch," he said. "It seems to tell the T cells tobe increased in their activity against tumors. And the second thing isit tells the endothelial cells that are growing to stop. Not to die but tostop."
Anent the difference between IL 12's in vivo and in vitroperformance, Folkman concluded: "It's a funny paradox _ IL 12works in the animal, not in the dish. That's a red flag to look forangiogenesis inhibition." n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.