Development of radiolabelled plerixafor as a theranostic tool for malignant lymphomas

Lymphomas are a heterogeneous group of neoplasm comprising proliferating lymphoid cells or their precursors. The two main types are Hodgkin Lymphoma and Non- Hodgkin Lymphoma. The current treatment modalities include radiation therapy; chemotherapy; radio-immunotherapy and small-molecule inhibitors. Lymphoma cells over-express chemokine receptors that favor leukocyte infiltration and promote metastasis. Chemokine receptor 4 (CXCR4) antagonists disrupt the specific interaction of chemokines with its receptor and may elicit therapeutic potential. CXCR4 receptor over-expression in malignant lymphomas has been targeted using radiolabelled plerixafor. Standardization of conjugation of plerixafor with bifunctional chelating agents (DTPA, NOTA, etc.). Optimization includes radiolabelling of conjugated plerixafor with 68Ga and 177Lu for imaging and therapeutic purpose respectively. The quality control of radiolabelled plerixafor included radionuclide, radiochemical purity, sterility, pyrogenicity, and serum stability. CXCR4 binding efficacy and toxicity studies were performed on CXCR4 expressing cancer cell lines. The biodistribution studies were performed in normal rats. After obtaining clearance from the institutional ethics committee, 68Ga- plerixafor PET/CT was performed in lymphoma patients. DTPA conjugation of plerixafor (1087 Da) and NOTA conjugation (1014 Da) was confirmed with MALDI-TOF. The radionuclide and radiochemical purity of 68Ga and 177Lu plerixafor was >99%. The synthesized radiopharmaceuticals were sterile and pyrogen-free. Radio-ligand binding assay confirmed high specificity (Kd = 57.16 nM) towards CXCR4 expressing cancer cells. Furthermore, the cytotoxicity studies indicate a log absolute IC50 concentration of 2.628 nM. Immunocytochemistry depicted positive nuclear staining of CXCR4 receptors in cancer cells. In-vivo physiological biodistribution of 68Ga- plerixafor was found in the liver, lung, and spleen. The radiotracer showed faster renal clearance and low blood pool activity. High CXCR4 receptor affinity of radiolabelled plerixafor elicits theranostic potential for malignant lymphomas.