Theranostics: Cancer imaging and therapy using injectable radionuclide-labeled ligands

Abstract

Cytotoxic chemotherapy, a mainstay of non-surgical cancer therapy for many decades and often combined with external beam radiotherapy, can be viewed as a “carpet bombing” therapeutic approach, often resulting in substantial side effects and recurring cancer cells. In the last decade, a new molecular oncology model has evolved that includes genomics, proteomics and immune system modulation. Targeted therapies and immunotherapies have offered new, albeit more expensive, therapeutic modalities. However, these typically benefit only a subset of patients with immunohistochemistry-identified markers (e.g., CTLA-4 or PD-L1) or specific gene mutations (e.g., EGFR, ALK, BRAF, PIK3CA) and tend to suppress rather than eradicate tumors. Targeted precision cancer therapy using injectable radionuclide-labeled ligands has opened up new horizons to treat resistant or widely scattered cancers by delivering cytotoxic ionizing radiation directly and specifically to tumor cells. This therapeutic approach is termed radioligand theranostics (RT), a combination of thera peutics + diag nostics . This two-step process first uses molecular imaging to identify a specific receptor or biomarker expressed on a particular tumor cell type and then uses a therapeutic version of the radioligand that is internalized by cancer cells via specific receptors to achieve cell death with minimal damage to neighboring healthy tissue. One of the most successful examples of RT development includes octreotide radionuclide scintigraphy and therapy for neuroendocrine tumors (NETS). 68 Ga DOTATOC (DOTA-Phe-Tyr octreotide) injection is now available for PET imaging of somatostatin- positive gastroenteropancreatic NETs and 177 Lu-DOTA-Tyr 3 -octreotate was approved by both the FDA and EMA to treat patients with progressive somatostatin-receptor–positive midgut NETs. However, RT has widespread therapeutic implications beyond NETS and has served as a beacon for the conception of theranostic treatments for other cancer types, for example multiple myeloma, leukemia, non-Hodgkin lymphoma, metastatic castrate-resistant ovarian