Breast cancer 99mTc SM3 radioimmunoscintigraphy

Targeted radionuclide therapy for solid tumors: an overview

Although radioimmunotherapy (RIT) has been effective in non-Hodgkin's lymphoma (NHL) as a single agent, solid tumors have shown less clinically significant therapeutic response to RIT alone. The clinical impact of RIT or other forms of targeted radionuclide therapy for solid tumors depends on the development of a high therapeutic index (TI) for the tumor vs. normal tissue effect, and the implementation of RIT as part of synergistic combined modality therapy (CMRIT). Preclinical and clinical studies have provided a wealth of information, and new prototypes or paradigms have shed light on future possibilities in many instances. Evidence suggests that combination and sequencing of RIT in CMRIT appropriately can provide effective treatment for many solid tumors. Vascular targets provide RIT enhancement opportunities and nanoparticles may prove to be effective carriers for RIT combined with intracellular drug delivery or alternating magnetic frequency (AMF) induced thermal tumor necrosis. The sequence and timing of combined modality treatments will be of critical importance to achieve synergy for therapy while minimizing toxicity. Fortunately, the radionuclide used for RIT also provides a signal useful for nondestructive quantitation of the influence of sequence and timing of CMRIT on events in animals and patients. This can be readily accomplished clinically using quantitative high-resolution imaging (e.g., positron emission tomography [PET]).

Radioimmunodetection and therapy of breast cancer

Breast cancer is the second most-common cause of cancer death in women in the United States. Although more than 60% of patients can now be cured by initial treatment, the rest, although perhaps receiving palliation with currently available therapy, will die of their disease. Early detection of micrometastasis and improved treatment strategies are needed. Monoclonal antibody (mAb)-based imaging and tumor targeted therapy holds the potential to impact these problems. The most significant results of systemically administered antibody-based radiopharmaceuticals for detection and targeted therapy (radioimmunotherapy [RIT]) of breast cancer give strong evidence that this potential can be realized. Interest in immunoimaging recently has focused on small mAb modules used with 18F, 64Cu, or 124I to detect minimal disease in breast cancer by positron emission tomography or single-photon emission computed tomography. Reported therapy trials in advanced breast cancer have yielded objective responses and minimal toxicity. These studies have spanned several radionuclides as well as several mAb, fragments and approaches, including dose intensification with bone marrow support; combined therapy with other modalities (ie, CM-RIT); biodegradable peptide linkers; and pretargeting. RIT evaluated in clinical breast cancer trials has delivered as much as 4000 cGy to metastatic breast cancer per therapy dose with marrow stem cell support. Preclinical studies have demonstrated further promising strategies for breast cancer. RIT studies must address the key issue: enhancing the therapeutic index (tumor effect verses most sensitive normal tissue (bone marrow) effect). Approaches now include newly engineered mAb, scFv modular constructs, blood clearance on demand, enhanced pretargeting, applications of both alpha and beta emitting radionuclides, and combination therapy using molecular triggers for therapeutic synergy. These strategies for detection and treatment of metastatic breast cancer should lead to notable clinical impact on management and cure of breast cancer.

Clinical applications of 99mTc-sestamibi scintimammography

Mammography is the imaging modality of choice in detection of early, nonpalpable breast cancer. However, scintimammography may prove to be a very useful adjunct to a nondiagnostic or difficult mammography. Future prospective studies will have to be designed so that the specific clinical applications of scintimammography will be well defined. To be clinically relevant, each niche where scintimammography is potentially indicated should be clearly evaluated and incorporated into an algorithm of investigation of breast cancer, taking into consideration the relative advantages and limitations of scintimammography. Special care to obtain high-quality scintimammographic studies is mandatory. Because poor quality studies may be the major drawback, the nuclear medicine community should remind the lesson learned from radiologic mammography. Furthermore, it is also hoped that significant improvement in the scintigraphic equipment and data acquisition will be seen in a very near future to have more widespread clinical diagnostic applications of scintimammography.

Nuclear medicine in primary breast cancer imaging

The application of nuclear medicine techniques to study patients with breast cancer has recently raised its profile, particularly in the investigation 'indeterminate mammographic lesions'. This review briefly points out some of the difficulties encountered with other more conventional imaging modalities and describes the radionuclide techniques most frequently employed in the investigation of those patients with breast cancer. Both planar and single photon emission tomography methods are discussed including the use of monoclonal antibodies, perfusion ligands, receptor binding hormones and other specific radiotracers, non-specific tumour markers, as well as deoxyglucose and other amino acids labelled with positron emitting radionuclides.

Antibody-based diagnostic and therapeutic innovations for human cancer

As adjuvants, antibody-based diagnostic and therapeutic innovations can potentially decrease morbidity and mortality associated with many human malignancies. Current strategies employing genetically modified constructs may improve tumor penetration and increase versatility.

Breast cancer imaging with radiolabeled antibodies

Over the past 2 decades, numerous anticancer antibodies against different molecular targets and labeled with different gamma-emitting radionuclides have been studied in human tumor xenografts and in clinical trials. In breast cancer, these molecular targets have included principally tumor-associated antigens, such as carcinoembryonic antigen (CEA) and the polymorphic epithelial mucin antigen, MUC1, and more recently the growth factor receptors, EGF-R and HER-2/neu. No antibody-based agent has yet been approved for clinical use in the diagnosis of mammary carcinoma, because few trials have addressed the issue of clinical use of these imaging agents in the management of breast cancer patients. Recently, the CEA antibody Fab' fragment approved for colorectal cancer detection, Arcitumomab (CEA-Scan, [Immunomedics, Morris Plains, NJ]), has been found to image both palpable and nonpalpable breast lesions that were suspicious on screening mammograms. Results to date indicate that Arcitumomab can complement mammography by providing a high specificity and positive predictive value, thus indicating when a patient with an abnormal mammogram may proceed directly to definitive surgery without an intermediate diagnostic biopsy. Breast cancer immunoscintigraphy holds promise for advancing toward immunoPET, which should combine the specificity of antibodies with the high sensitivity and resolution of PET. It is also the foundation of breast cancer radioimmunotherapy with humanized antibodies against CEA and MUC1, as well as other immunotherapy strategies.

Crystal structure at 1.95 A resolution of the breast tumour-specific antibody SM3 complexed with its peptide epitope reveals novel hypervariable loop recognition

The anti-breast tumour antibody SM3 has a high selectivity in reacting specifically with carcinoma-associated mucin. SM3 recognises the core repeating motif (Pro-Asp-Thr-Arg-Pro) of aberrantly glycosylated epithelial mucin MUC1, and has potential as a therapeutic and diagnostic tool. Here we report the crystal structure of the Fab fragment of SM3 in complex with a 13-residue MUC1 peptide antigen (Thr1P-Ser2P-Ala3P-Pro4P-Asp5P-Thr6P -Arg7P-Pro8P-Ala9P-Pro10P-Gly11P- Ser12P-Thr13P). The SM3-MUC1 peptide structure was solved by molecular replacement, and the current model is refined at 1.95 A resolution with an R-factor of 21.3% and R-free 28.3%. The MUC1 peptide is bound both by non-polar interactions and hydrogen bonds in an elongated groove in the antibody-combining site through interactions with Complimentarity Determining Regions (CDRs), three of the light chain (L1, L2, L3) and two of the heavy chain (H1 and H3). The conformation of the peptide is mainly extended with no discernable standard secondary structure. There is a single non-proline cis-peptide bond in H3 (Val95H-Gly96H-Gln97H-Phe98H-Ala101H-Ty r102H) between Gly96H and Gln97H, which appears to play a role in SM3-peptide antigen interactions, and represents the first such example within an antibody hypervariable loop. The SM3-MUC1 peptide structure has implications for rational therapeutic and diagnostic antibody engineering.

99mTc-labelled SM3 in the preoperative evaluation of axillary lymph nodes and primary breast cancer with change detection statistical processing as an aid to tumour detection

The extent of primary surgery for breast cancer could be tailored to the patient if previous information on the presence or absence of lymph node involvement could be reliably determined. Prospective radioimmunoscintigraphy in 29 patients with primary breast cancer that was found on screening has been undertaken with 555 MBq (15 mCi) 99mTc SM3, an Imperial Cancer Research Fund (ICRF) murine monoclonal antibody, 0.5 mg with images at 10 min and 22 h, and analysis using a change detection algorithm. Sites of significant change between the early and later images were displayed as a map of probabilities. Image-positive and -negative axillary lymph nodes were compared by histology in the 28 evaluable patients. The correct identification of the presence or absence of node involvement, even if impalpable, has been shown in 24 out of 28 patients (29 lymph node groups). Sensitivity was 90% (nine out of ten), specificity 84% (16 out of 19) and accuracy 86%. These results encourage further assessment of this technique.