By David N. Leff
Editor¿s note: Science Scan is a roundup of recently published biotechnology-related research.
Squalamine, the anti-angiogenic molecule discovered in the dogfish shark (Squalus acanthiasis), scored twice at last week¿s meeting of the American Association for Cancer Research (AACR) in Philadelphia.
The drug, developed by Magainin Pharmaceuticals Inc. (MPI), of Plymouth Meeting, Pa., proved ¿extremely effective¿ in treating mice with prostate and lung cancers, company collaborating scientists reported to the meeting. ¿We are pleased by the activity we continue to see with squalamine,¿ said MPI president and CEO Michael Dougherty, adding, ¿We expect to begin Phase II clinical studies of squalamine later this quarter.¿ (See BioWorld Today, July 8, 1998, p. 1.)
On Tuesday, April 13, Michael Sokoloff, of the University of Virginia, in Charlottesville, which collaborates with MPI, reported to an AACR mini-symposium on prostate cancer approaches that squalamine by itself ¿had complete eradication of human prostate cancer lesions¿ in eight mice carrying the tumors. In seven of the eight, blood levels of the cancer monitor prostate-specific antigen remained undetectable for the 12-week duration of the in vivo experiment.
Also Tuesday, at a poster session on new antitumor agents, C. M. Gonzalez, of the Institute for Drug Development, in San Antonio, another MPI collaborating center, reported that squalamine added to paclitaxel/carboplatin, a front-line chemotherapy combination for non-small-cell lung cancer, enhanced the combo¿s anticancer effect. In three of 10 mice bearing the chemoresistant tumor, the triple-drug regimen brought about tumor growth inhibition of 95.7 percent, and in four of the 10 animals, tumor shrinkage of 54.8 percent. Without the squalamine additive, the double-drug treatment scored percentages of 55.9 percent and zero, respectively.
MPI currently synthesizes the shark-derived squalamine molecule, which preclinical studies have shown acts to interrupt angiogenesis and tumor growth early in the blood vessel-forming cascade.
Expressing Endostatin Gene In Muscle, Instead Of Injecting Its Protein, Is Way To Go
One of the two more celebrated tumor-throttling proteins, angiostatin and endostatin, has also chalked up preclinical success. Both agents had their 15 minutes of fame a year ago, also at AACR¿s annual meeting. Associates of anti-angiogenesis pioneer Judah Folkman told that gathering on April 1, 1998, that gene therapy had transferred and expressed angiostatin and endostatin in mice. No April Fool Day joke, this news triggered a media and investment scramble.
Actually, Folkman had announced discovery of naturally occurring murine angiostatin and endostatin four months earlier, on November 27, 1997. But there was no immediate in vivo follow-up; apparently, biosynthesis of the two substances in sufficient quantity made preclinical testing problematic.
Now, scientists at GeneMedicine Inc., of The Woodlands, Texas, have designed and tested a stratagem to sidestep injecting the anti-angiogenic endostatin protein into mice by expressing the molecule¿s gene in their muscles. Their paper reporting this feat, in Nature Biotechnology for April 1999, bears the title: ¿Systemic inhibition of tumor growth and tumor metastasis by intramuscular administration of the endostatin gene.¿
Murine endostatin is a C-terminal fragment of collagen 18a.The co-authors developed a nonviral gene therapy system in an expression plasmid. It encoded a secretable form of mouse endostatin with a synthetic polymer, for gene delivery to skeletal muscle tissue. The construct inhibited not only the growth of distant primary tumors, but the development of metastases as well.
In one preclinical trial, the co-authors first implanted murine renal cell carcinoma cells under the skin of laboratory mice. Seven days later, when these tumors had begun to grow, the team started intramuscular injection of the endostatin plasmid. The resulting inhibition of tumor growth, they reported, was still statistically significant at day 13 post-treatment.
Those animals produced, on average, more than 300 metastases per lung surface in a control mouse. Results showed that this pulmonary dissemination was reduced six-fold in number and 32 percent in weight, following a single gene injection. ¿The primary tumors,¿ their article pointed out, ¿were already of a large size prior to intramuscular administration of the gene; however, the amount of transgene in the bloodstream was sufficient to reduce tumor growth.¿
Currently, the GeneMedicine team is seeking to improve efficacy of the gene by increasing frequency of administration and longer duration of expression
Tweaking Human Immune System Leads To Malaria Vaccine Aimed At Protecting Whole World
A one-type-fits-all malaria vaccine is being tested in preclinical trials at San Diego-based Epimmune Inc., as reported in the first March 1999 issue of the twice-monthly journal Vaccine. The paper¿s title is, ¿Pan DR binding sequence provides T-cell help for induction of protective antibodies against Plasmodium yoelii sporozoites.¿ (See BioWorld Today, March 3, 1998, p. 1.)
The universal reach of Epimmune¿s immunization technology derives from a proprietary molecule named PADRE, which mobilizes both antibody-producing B cells and T-cell pathogen-slaying cytotoxic lymphocytes.
¿PADRE stands for Pan-DR-Epitope,¿¿ explained Epimmune¿s vice president of research and development, immunologist Robert Chesnut. ¿Pan as in universal,¿ and DR [is] the Class II major histocompatibility molecule in humans. PADRE is a synthetic designer peptide, 13 amino acids long, designed to bind with high affinity to many, many human DR molecules.
¿In the human,¿ Chesnut told BioWorld Today, ¿these molecules have evolved to present antigens to the immune system in order to combat diseases, and they¿re fairly heterogeneous in their structure. Therefore, a wide variety of different antigens can be presented.
¿What we¿ve done,¿ he went on, ¿is to design a non-natural peptide that binds universally to most human DR molecules. So, we are now able to link to that PADRE peptide an antigen to which B lymphocytes can direct antibodies. We have used one of the repeating segments of the Plasmodium falciparum malarial parasite,¿ Chesnut continued. ¿And when we administer that as a vaccine, those B cells actually bind to that malarial antigen. This brings in the T helper cells that are specific for PADRE. And because it¿s able to function in individuals who have different DR types, this one vaccine construct will be able to stimulate a strong immune response in virtually all ethnic groups in the world. Most peptides, which are not designed this way, would only be able to stimulate T cells in a much smaller segment of the human population.¿
Epimmune is working closely with Capt. Stephen Hoffman, who directs the malaria vaccine program at the U.S. Naval Medical Center, in Bethesda, Md.
¿He is a co-author of the article in Vaccine,¿ Chesnut observed, ¿and we¿re looking at using PADRE coupled to malaria antigens, to induce both antibody and CTL responses.
¿It¿s possible,¿ Chesnut concluded, ¿that Hoffman could be testing it on human volunteers within a year or two. The proof is in the human.¿