Books, Articles, and Information

Paul Carter

Magic Bullets Fly Again

Molecular guided missiles called monoclonal antibodies were poised to shoot down cancer and a host of other diseases--until they crashed and burned. Now a new generation is soaring to market
By Carol Ezzell

The unbridled optimism that surrounded monoclonal antibodies in the 1980s was infectious. You had to be the world's toughest cynic not to be dazzled. Got cancer? No problem. Like heat-seeking missiles, monoclonal antibodies tipped with poisons or radioactive isotopes would home in on malignant cells and deliver their deadly payloads, wiping out cancer while leaving normal cells intact. How about an infectious disease? All would be well. Monoclonals would surround marauding viruses and bacteria like goombahs from Tony Soprano's crew, muscling them into secluded byways where killer cells of the immune system would make them an offer they couldn't refuse.

A novel alpha-particle emitting monoclonal antibody (mAb) construct targeting the external domain of Prostate Specific Membrane Antigen (PSMA) was prepared and evaluated in vitro and in vivo.  The chelating agent, N-[2-amino-3-(p-isothiocyanatophen-yl)propyl] -trans-cyclohexane-1,2-diamine-N,N’,N’,N’’,N’’-pentaacetic acid, was appended to J591 mAb to stably bind the ²¹³Bi radiometal ion.  Bismuth-213 is a short-lived (t_1/2 = 46 min.) radionuclide that emits high energy alpha-particles with an effective range of 0.07-0.10 mm which are ideally suited to treating single celled neoplasms and micrometastatic carcinomas.  The LNCaP prostate cancer cell line had an estimated 180,000 molecules of PSMA per cell; J591 bound to PSMA with a 3 nM affinity.  After binding, the radiolabeled construct-antigen complex was rapidly internalized into the cell, carrying the radiometal inside.  [²¹³Bi]J591 was specifically cytotoxic to LNCaP.

Prostate specific membrane antigen (PSMA) is a well characterized cell surface antigen expressed by virtually all prostate cancers (PCa). PSMA has been successfully targeted in vivo with ¹¹¹In-labeled 7E11 mAb (ProstaScint®, Cytogen, Princeton, NJ), which binds to an intracellular epitope of PSMA. This work reports the in vitro characterization of three recently developed mAbs that bind the extracellular domain of PSMA (PSMAext). Murine mAbs J415, J533, J591 and 7E11 were radiolabeled with 131I and evaluated in competitive and saturation binding studies with substrates derived from LNCaP cells. 

Prostate-specific membrane antigen (PSMA), a Type II transmembrane protein, was originally thought to be strictly expressed in prostatic tissue, but recent studies have demonstrated PSMA protein expression in non-prostatic tumor neovasculature as well.  Utilizing immunohistochemistry, RT-PCR assays, and in situ hybridization, we have demonstrated PSMA mRNA transcripts and protein expression in the endothelium of tumor-associated neovasculature of multiple non-prostatic solid malignancies.  In addition, we found no PSMA mRNA or protein expression in the vascular endothelial cells of corresponding benign tissue examples.

Prostate-specific membrane antigen (PSMA) is a type II integral membrane glycoprotein initially characterized by the monoclonal antibody (mAb) 7E11.  PSMA is highly expressed in prostate secretory-acinar epithelium and prostate cancer as well as in several extra-prostatic tissues.  Recent evidence suggests that PSMA is also expressed in tumor-associated neovasculature.  We examined the immunohistochemical characteristics of 7E11 and those of four recently developed anti-PSMA mAbs (J591, J415, and Hybritech Incorporated PEQ226.5 and PM2J004.5), each of which binds a distinct epitope of PSMA.  We evaluated these mAbs in viable prostate cancer cell lines and various fresh-frozen benign and malignant tissue specimens.  In the latter, we compared the localization of the anti-PSMA mAbs to that of the anti-endothelial cell mAb CD34. 

Geldanamycin (GM) is an antitumor antibiotic that binds to a specific pocket in the Hsp90 chaperone and alters its function, thus causing the degradation of an important subset of cellular signaling proteins, including steroid receptors and HER2, Raf1 and IGF kinases. This causes the growth arrest and apoptosis of tumor cells. However, the important normal functions of the proteins destroyed by the drug suggest that its use will be limited by significant toxicity. We have now attached over 40 molecules of GM to an anti-prostate specific membrane antigen (PSMA) monoclonal antibody by means of a linker that is cleaved intracellularly. PSMA is a membrane protein that is selectively expressed on the surface of prostate cancer cells and on the vasculature of other tumors, but not in normal tissues. This conjugate selectively binds to and is taken up by prostate cancer cells that express the PSMA protein. Additionally, it induces the degradation of HER2 kinase and is toxic to PSMA-expressing prostate cancer cells with an IC₅₀=0.7nM. Although this is an order of magnitude less than GM, the conjugate has no effect on PSMA-negative cells at these concentrations. The conjugate may represent a targeted GM that is selectively toxic to prostate cancer and to tumor vasculature.

Clinical Trials and the FDA

By Zeke Ashton (TMF Centaur)
April 5, 2000 

The biotechnology sector has emerged as one of the hottest of the past year. More and more investors are pouring their money into this sector, hoping that companies will translate flashy new technologies into revenue-producing drugs. While biotechnology has come of age, and the number of profitable companies with products on the market has continued to swell, the vast majority of companies are still pinning their hopes on the positive outcomes and subsequent FDA approval of the drugs being tested in clinical trials. This article is for those investors who are interested in learning a little more about the FDA and the clinical trial process.

Constitutive and Antibody-Induced Internalization of Prostate Specific Membrane Antigen by He Liu et. al.

Prostate specific membrane antigen (PSMA) is a cell surface glycoprotein expressed predominantly by prostate cancer cells. We have characterized four monoclonal antibodies that bind to the extracellular domain of PSMA (Liu et al., Cancer Res. 57;3629-3634, 1997). Here we report that viable LNCaP cells internalize these antibodies. Laser scanning confocal microscopy reveals that the internalized antibodies accumulate in endosomes and immunoelectron microscopy reveals that endocytosis of PSMA-antibody complex occur via clathrin coated pits. In addition, a quantitative cell surface biotinylation assay demonstrates that PSMA is constititively endocytosed in LNCaP cells and that anti-PSMA antibodies increases the rate of internalization of PSMA.

Monoclonal Antibodies to the Extracellular Domain of Prostate-specific Membrane Antigen Also React with Tumor Vascular Endothelium by He Liu et. al.

Prostate specific membrane antigen (PSMA), initially defined by monoclonal antibody (mAb) 7E11, is a now well-characterized type 2 integral membrane glycoprotein expressed in a highly restricted manner by prostate epithelial cells. 7E11 has been shown to bind an intracellular epitope of PSMA which, in viable cells, is not available for binding. We herein report the initial characterization of the first 4 reported IgG mAbs which bind the external domain of PSMA. Competitive binding studies indicate these antibodies define 2 distinct, non-competing epitopes on the extracellular domain of PSMA. In contrast to 7E11, these mAbs bind to viable LNCaP cells in vitro. In addition, they show strong immunohistochemical reactivity to tissue sections of prostate epithelia, including prostate cancer. These mAbs were also strongly reactive with vascular endothelium within a wide variety of carcinomas (including lung, colon, breast and others), but not with normal vascular endothelium. These antibodies should prove useful for in vivo targeting to prostate cancer as well as to the vascular compartment of a wide variety of carcinomas.

Monoclonal Antibodies by Karol Sikora and Howard M. Smedley

The immune system...Antibody-antigen interaction...Producing a monoclonal antibody...Complex antigens...Specificity...Antibody characteristics...Choice of animal for antibody production...Monoclonal antibodies for cancer localization...Antibodies to cancer cells...Tumor-associated antigens...Scanning technique...Cancer treatment...Problems in cancer treatment...Production of the antibody...Tumor-specific antibodies...Screening...Specificity...Arming monoclonal antibodies...Physical agents...Passive radioactive administration...Toxins...Further reading.

Current Status of Monoclonal Antibodies for Imaging and Therapy of Prostate Cancer by Neil H. Bander

Introduction...Imaging...Therapy...Conclusion

Monoclonal Antibodies in Diagnosis and Therapy by Thomas A. Waldmann

Genetically engineered antibodies...Radiolabeled monoclonal antibodies

Reengineered Monoclonal Antibodies Step Up to the Plate in Cancer Studies by Joan Stephenson

Magic bullets?...Hematologic cancers...Residual disease...Synergy with chemotherapy

A New Generation of Monoclonal Antibodies Arrives at the Clinic by Caroline McNeil

Good responses...Biggest step forward...Some success

Monoclonal Antibodies at Age 20: The Promise at Last? by Stephen S. Hall

Big guns...New targets...Smarter bullets

Monoclonal Antibody Technology--The Basics from Genentech

Monoclonal antibody production

Antibody Animations

• Quicktime Movie of antibody binding to epitope by Thomas J. Smith 
• Animation of antibody
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