Monoamine Oxidase A Inhibitor–Near-Infrared Dye Conjugate Reduces Prostate Tumor Growth

Development of anti-cancer agents with high tumor-targeting specificity and efficacy is critical for modern multidisciplinary cancer research. Monoamine oxidase A (MAOA), a mitochondria-bound enzyme, degrades monoamine neurotransmitters and dietary monoamines. Recent evidence suggests a correlation between increased MAOA expression and prostate cancer (PCa) progression with poor outcomes for patients. MAOA induces epithelial–mesenchymal transition (EMT) and augments hypoxic effects by producing excess reactive oxygen species. Thus, development of MAOA inhibitors which selectively target tumors becomes an important goal in cancer pharmacology. Here we describe the design, synthesis, and <i>in vitro</i> and <i>in vivo</i> evaluation of <b>NMI</b>, a conjugate that combines a near-infrared dye for tumor targeting with the moiety derived from the MAOA inhibitor clorgyline. <b>NMI</b> inhibits MAOA with low micromolar IC₅₀, suppresses PCa cell proliferation and colony formation, and reduces migration and invasion. In mouse PCa xenografts, <b>NMI</b> targets tumors with no detectable accumulation in normal tissues, providing effective reduction of the tumor burden. Analysis of tumor specimens shows reduction in Ki-67⁺ and CD31⁺ cells, suggesting a decrease of cell proliferation and angiogenesis and an increase in M30⁺ cells, indicating increased apoptosis. Gene expression profiles of tumors treated with <b>NMI</b> demonstrate reduced expression of oncogenes <i>FOS</i>, <i>JUN</i>, <i>NFKB</i>, and <i>MYC</i> and cell cycle regulators <i>CCND1</i>, <i>CCNE1</i>, and <i>CDK4/6</i>, along with increases in the levels of tumor suppressor gene <i>TP53</i>, cell cycle inhibitors <i>CDKN1A</i> and <i>CDKN2A</i>, and MAOA-downstream genes that promote EMT, tumor hypoxia, cancer cell migration, and invasion. These data suggest that <b>NMI</b> exerts its effect through tumor-targeted delivery of a MAOA-inactivating group, making <b>NMI</b> a valuable anti-tumor agent