Rationale for immunotoxin therapy of metastatic prostate carcinoma formatted as a multi-stage delivery system

Bispecific antibody-mediated detection of the Staphylococcus aureus thermonuclease

We report a novel fluorescence-based immunoassay which enables qualitative detection of the Staphylococcus aureus Thermonuclease (TNase) enzyme, thus providing confirmation of the presence of the S. aureus bacterium in vitro. The biomedical problem of chronic wound healing and the continuing emergence of antibiotic-resistant species is addressed in the development of a detection system capable of the rapid, real-time assessment of bacterial load and diversity. The use of bispecific antibodies (BsAb) provides integration of the molecular detection and signal response components of a standard immunoassay due to steric hindrance-mediated release of prebound fluorescent reporter molecules upon specific binding of TNase to adjacent sites. Rhodamine and fluorescein-labeled hemocyanin from Megathura crenulata (KLH) were prepared as effective immunoconjugates containing a sensitive fluorescent reporter moiety. BsAb that both specifically quenched the fluorescence of the reporter conjugate and bound the TNase target antigen were produced using cell fusion techniques. Assays were then performed to analyze the properties attributable to the steric hindrance-mediated release of the fluorescent reporter molecules upon adjacent TNase binding. This was performed by monitoring the intensity of fluorescence emission of the immunogenic reporter conjugate released into an aqueous environment at 578 and 520 nm, respectively.

Antibody immunoglobulin G (IgG) against human prostatic specific antigen (PSA) as a carrier protein for chemotherapeutic drugs to human prostate tumors: Part 1. A double immunofluorescence analysis

BACKGROUND

Adenocarcinoma of the prostate (CaP) is the the second highest cause of cancer deaths in U.S. males. Current chemotherapeutic and/or endocrine treatments do not specifically and selectively target tumor cells of prostate cancer and benign prostatic hyperplasia (BPH). We hypothesized that because of the specific binding characteristics of antibody immunoglobulin G (IgG) to human prostatic-specific antigen (PSA), PSA-IgG could function as a carrier protein for conjugated chemotherapeutic drugs and that the immunoconjugate would selectively bind to prostatic epithelial cells and their tumors, but not to epithelial cells of unrelated organs. Our objective was to test the hypothesis using human prostatectomy specimens.

METHODS

WE used several derivatives of 5'-fluorouracil, namely, 5'-fluoro- 2'-deoxyuridine (5'-Fu-2'-d), 5'-fluoro-2'-deoxyuridine-5' monophosphate (5'-Fu-2'-d-5'-mp), 5'-fluoro-2'-deoxyuridine-5'-(p-aminophenyl) monophosphate (5'-Fu-2'-d'-5'-amp), to conjugate with rabbit anti-PSA-IgG together with fluorescent markers (such as rhodamine and fluorescein or fluorescein isothiocyanate: FITC). Prostate specimens were obtained from prostatectomy patients who had not been treated with cytotoxic drugs before surgery. We evaluated formalin-fixed and paraffin-embedded sections as well as cryostat sections of frozen specimens for localization of PSA-IgG alone and PSA-IgG-drug immunoconjugate using immunoperoxidase (IP) and single and/or double immunofluorescence (IF) localization techniques.

RESULTS

Our study showed that the immunoconjugate (PSA-IgG-5'-Fu-2'-d) bound to PSA (molecular size of approximately 34 KDa) on nitrocellulose sheets in Western immunoblots of extracts of BPH and CaP tissues. This binding of immunoconjugate to PSA on immunoblots was similar to that of the unconjugated PSA-IgG. Immunostaining patterns for rabbit anti-PSA-IgG and PSA-IgG-5'-Fu-2'-d immunoconjugate were similar and specific for prostate epithelial cells and their tumors, as revealed by IP techniques. To demonstrate that both the antibody and drug localized in the same group of prostatic epithelial cells, we used an immunoconjugate in which the PSA-IgG was labeled with rhodamine and 5'-Fu-2'-d-5'-amp with FITC. Our study showed that fluorescence for rhodamine and FITC was present in the same group of prostatic epithelial cells. Phase contrast microscopy demonstrated details of prostatic glandular epithelium and connective tissues. Our study showed that fluorescence for rhodamine and FITC and immunostaining by IP techniques were not observed in prostate sections incubated with normal rabbit serum.

CONCLUSIONS

We have shown that conjugation of 5'-Fu derivatives to PSA-IgG did not affect either the selectivity or specificity of the antibody for prostatic epithelial cells. Differential immunofluorescence study has shown that PSA-IgG may function as a carrier protein for chemotherapeutic drugs to prostate epithelial cells and their tumors. Furthermore, FITC-labeled 5'-Fu-2'-d did not specifically localize in prostatic glands, kidney, lungs, bladder, or colon. Because of the specificity and selectivity of the immunoconjugate for prostatic epithelial cells and their tumors, the immunoconjugate could be used in small dosages to treat prostatic tumors and such treatment would greatly reduce many unpleasant side effects in patients. This is the first report to show that PSA-IgG can function as an organ specific carrier protein for chemotherapeutic drugs to human prostate epithelium and its tumors.

Characterization of a new model of human prostatic cancer: the multicellular tumor spheroid

Multicellular tumor spheroids (MTS) provide a closer in vitro correlate to in vivo malignancy than do conventional monolayer cultures; while simulating many parameters of in vivo growth, MTS systems provide those perquisites (i.e., experimental control, economy, expediency) associated with in vitro evaluation of preclinical therapeutic strategies. For these reasons, we exploited the proclivity of the highly metastatic human prostatic carcinoma subline I-LN-PC3-IA to spontaneously assume a spheroid morphology under routine culture conditions. I-LN spheroids demonstrate salient features described in other spheroid systems and exhibit histologic characteristics of human prostate carcinoma. Cells encompassed in the I-LN spheroid format demonstrated functional divergence from their monolayer counterparts with respect to immunoreactivity for prostatic acid phosphatase, positional dependence of prostate-restricted p40 antigen expression, and chemotherapeutic drug response. This new in vitro-in vivo transition model of human prostatic carcinoma should provide a valuable in vitro context to expediently evaluate in vivo correlates of oncolytic protocols on a malignancy that remains refractive to therapy.

Bispecific antibody: a tool for diagnosis and treatment of disease

Antibodies with two distinct binding specificities have great potential for a wide range of clinical applications as targeting agents for in vitro and in vivo immunodiagnosis and therapy, and for improving immunoassays. They have shown great promise for targeting cytotoxic effector cells, delivering radionuclides, toxins or cytotoxic drugs to specific targets, particularly tumour cells. We discuss potential applications of bispecific antibodies, the theoretical basis and problems associated with their production and purification, cell fusion and chemical conjugation techniques, and propose a new manufacturing strategy by genetic engineering. This approach has enormous potential applications for producing tailor-made bispecific antibodies, and will enable widespread clinical uses of these antibodies both for diagnostic purposes and therapy.