Melanocortin subtype 1 receptor (MC1R) targeted-radionuclide therapy for melanoma
Creators: name: Li, Mengshi
Publisher: name: University of Iowa
Year: 2018

description: This thesis dissertation aims to (1) improve the therapeutic efficacy of melanocortin 1 receptor (MC1R)-targeted radionuclide therapy (MC1R-TRT) for metastatic melanoma; and (2) facilitate the clinical translation of MC1R-TRT by developing protocols that integrate Pb2+ radio-isotope purification with radiolabeling and separation of radiopharmaceuticals from precursors in an automated cassette-based system.
description: Chapter 1 reviews basic tumor biology of melanoma; currently available therapies in the clinical setting and MC1R-TRT for melanoma. Melanoma has been characterized with high somatic mutation, aggressive metastasis, and resistance to chemotherapies. MAPK pathway inhibitors and immune checkpoint inhibitors have significantly improved patient outcomes, but efficacy has been limited by acquired resistance, adverse side effects and low response rates. MC1R-TRT potentially circumvents the shortfalls of current therapies by directing radiation dose specifically to tumors. However, previous MC1R-TRT studies have beenb largely restricted to B16 murine melanoma models and lack evidence of the potential of the approach using human melanoma models. This is due to the heterogeneous expression of MC1R in available human melanoma cells. In chapter 2, I exploit the use of FDA-approved drugs to pharmacologically upregulate MC1R expression and thereby enhance delivery of radiation dose to human melanoma cells and tumors. MC1R expression was determined by qRT-PCR, immunoblotting, flowcytometry, radioligand-receptor binding, and immunohistochemistry. FDA-approved MAPK pathway inhibitors (both BRAFi and MEKi) and HDAC inhibitors (HDACi) robustly upregulated MC1R expression in vitro and in vivo. The elevated levels of MC1R led to enhanced accumulation of MC1R-targeted ligand DOTA-PEG-VMT-MC1R in melanoma tumors in mice. Significantly improved therapy outcomes were also demonstrated by combining [212Pb]DOTA-PEG-VMT-MC1R alpha-particle therapy with BRAFi and HDACi.
description: In Chapter 3, a production protocol was developed to efficiently purify and concentrate radioactive Pb2+ isotopes and radiolabel peptide precursors. This method successfully purified and recovered 203/212Pb2+ from generator eluate (212Pb) and carrier solution (203Pb) containing metal impurities (e.g., Fe3+, Cu2+). Purified 203/212Pb2+ successfully labeled chelator-functionalized precursor peptide ligands. Radiolabeled products were isolated from excess precursor by an in-line HPLC that afforts increased molar activity (MBq nmole-1). The method was adapted to a cassette-based automated prototype system that can be employed for routine clinical production of 203/212Pb radiopharmaceuticals and reduce occupational radiation exposure compared to manual methods for fluid handling through the radiolabeling procedure.
description: Chapter 4 outlines a proposal for future research (based on the results of this thesis) in which the feasibility of developing a regimen that combines MC1R-TRT and immune checkpoint inhibitor anti-PD1 for metastatic melanoma is presented. This proposal outline is based on the understanding that MC1R-TRT systemically delivers alpha-particle radiation to the tumor microenvironment. Therefore, MC1R-TRT possesses the potential of enhancing tumor antigen exposure and activating anti-tumor immunity independent of the “abscopal” effect upon which external beam radiation depends to provide for enhanced tumor-specific immune response. Preliminary biochemical assays will be performed in vitro in B16F10 cells to determine the immunophenotype after exposure to optimized lead compound M7-PSC[212Pb]. Immunogenic cell death and anti-tumor immunity from M7-PSC[212Pb] treatment will be determined using an in vivo tumor vaccination approach in C57BL/6 mice bearing B16F10 melanoma xenografts. Effectiveness of M7-PSC[212Pb] combined with anti-PD1 will be investigated by measurement of tumor growth rate in B16F10 xenograft model.