Melanoma Therapy with Rhenium-Cyclized Alpha Melanocyte Stimulating Hormone Peptide Analogs

Malignant melanoma is the 6th most commonly diagnosed cancer with increasing incidence in the United States. It is estimated that 54,200 cases of malignant melanoma will be newly diagnosed and 7,600 cases of death will occur in the United States in the year 2003 (1). At the present time, more than 1.3% of Americans will develop malignant melanoma during their lifetime (2). The average survival for patients with metastatic melanoma is about 6-9 months (3). Moreover, metastatic melanoma deposits are resistant to conventional chemotherapy and external beam radiation therapy (3). Systematic chemotherapy is the primary therapeutic approach to treat patients with metastatic melanoma. Dacarbazine is the only single chemotherapy agent approved by FDA for metastatic melanoma treatment (5). However, the response rate to Dacarbazine is only approximately 20% (6). Therefore, there is a great need to develop novel treatment approaches for metastatic melanoma. The global goal of this research program is the rational design, characterization and validation of melanoma imaging and therapeutic radiopharmaceuticals. Significant progress has been made in the design and characterization of metal-cyclized radiolabeled alpha-melanocyte stimulating hormone peptides. Therapy studies with {sup 188}Re-CCMSH demonstrated the therapeutic efficacy of the receptor-targeted treatment in murine and human melanoma bearing mice (previous progress report). Dosimetry calculations, based on biodistribution data, indicated that a significant dose was delivered to the tumor. However, {sup 188}Re is a very energetic beta-particle emitter. The longer-range beta-particles theoretically would be better for larger tumors. In the treatment of melanoma, the larger primary tumor is usually surgically removed leaving metastatic disease as the focus of targeted radiotherapy. Isotopes with lower beta-energies and/or shorter particle lengths should be better suited for targeting metastases. The {sup 177}Lu-DOTA-Re(Arg11)CCMSH and {sup 212}Pb-DOTA-Re(Arg11)CCMSH complexes were developed and synthesized to investigate its ability to target and deliver an effective dose to small melanoma tumors and metastatic deposits. Dosimetry calculations for {sup 188}Re-CCMSH and {sup 212}Pb/{sup 212}Bi[DOTA]-Re(Arg11)CCMSH were compared in the B16/F1 mouse melanoma flank tumor model to analyze the delivered dose to tumor and normal organs