Radioimmunodetection and radioimmunotherapy of malignant melanoma. A review

Targeting melanoma with 211At/131I-methylene blue: preclinical and clinical experience

The increasing incidence of melanoma and a lack of effective therapy have stimulated a search for new methods of early detection and treatment of the disease. Melanin synthesized in melanoma cells presents a unique target to which the treatment can be selectively addressed, provided the pigment is recognized by a suitable drug. Methylene blue possesses a high affinity for melanin and, therefore, accumulates preferentially in melanoma cells. Since not directly toxic to the tumor, methylene blue serves as a carrier for radioisotopes and, once taken up by melanoma cells, acts as a selectively localized source of radiation. Hence, radioderivatives of the compound can be used for diagnosis and therapy of disseminated melanoma. 131I-methylene blue in conjunction with gamma camera imaging has already proved in clinical studies to be a useful tool for the detection of early melanoma dissemination. 211At-methylene blue exceptional efficacy in treating melanoma and preventing its metastatic spread without damaging normal structures when administered systemically to human melanoma-bearing mice led to the approval of this alpha-particle emitting methylene blue derivative for the Phase I clinical trial.

Scintigraphic visualization of ocular melanoma with Tc-99m glutathione

In a patient with ocular melanoma scintigraphy obtained with 99mTc-GSH clearly demonstrated the histologically proven ocular lesion both in planar and SPECT images. 99mTc-sestamibi study obtained in the same patient three days later was negative. 99mTc-GSH is a potential alternative to the currently used radiopharmaceuticals for imaging both cutaneous and ocular melanomas and their metastases.

Visualization of uveal amelanotic melanoma with technetium-99m(V) dimercaptosuccinic acid

The possibility of using technetium-99m(V) dimercaptosuccinic acid, Tc-99m DMSA, in the evaluation of uveal amelanotic melanoma was assessed in this study. Both planar and SPECT images clearly demonstrated the tumor. Following confirmation of our results by contemporaneous ultrasonography and MRI the patient was treated with Iodine-125 brachytherapy. In combination with other diagnostic tests, Tc-99m(V) DMSA scintigraphy may play a role in the detection of uveal melanoma and its possible systemic metastases.

[Immunoscintigraphy in oncology]

In vivo immunotargeting of specific antigens with radiolabeled monoclonal antibodies is a new method of diagnosis which has largely improved over the past 15 years. It has been especially developed in the oncologic field. Although it is not yet a daily procedure, immunoscintigraphy has been proven a useful diagnostic tool in many situations. It gives information about the presence of lesions and their neoplastic nature. For this reason, immunoscintigraphy appears as very complementary to morphological imaging and is mainly indicated when lesions have insufficient anatomical definition. Early detection of recurrences is actually the best indication of immunoscintigraphy. However, some problems still exist, concerning the tumor/tissues uptake ratio which is not sufficient for an optimal imaging contrast, and the apparition of human anti-mouse antibodies (HAMA) in the patients. At present, many works are in progress which could resolve these problems. Ultimately, well-performed clinical trials are necessary to establish the right place for immunoscintigraphy in the diagnostic and therapeutic strategies in oncology.

Radioimmunodetection of malignant solid tumours

An increased clinical utility of radiolabelled monoclonal antibodies (MoAb), recognizing a variety of different antigens expressed preferentially in malignant tissue, for localizing primary, metastatic and recurrent cancer has been documented in many recent investigations. This review focuses on both basic and practical aspects of radioimmunodetection in oncology and is a status report on the performance and limitations of radiolabelled antibody procedures currently applied to the clinical detection of malignant solid tumours. At this time clinically validated radioimmunodetection methods are available for colorectal, ovarian, breast, lung, thyroid medullary, and head and neck carcinoma, and melanoma. Recent advances in humanization of MoAb significantly improve the prospects of effective antibody-guided radiotherapy in the near future.