A Selective Mitochondrial-Targeted Chlorambucil with Remarkable Cytotoxicity in Breast and Pancreatic Cancers

Nitrogen mustards, widely used as chemotherapeutics, have limited safety and efficacy. Mitochondria lack a functional nucleotide excision repair mechanism to repair DNA adducts and are sensitive to alkylating agents. Importantly, cancer cells have higher intrinsic mitochondrial membrane potential (Δψ_mt) than normal cells. Therefore, selectively targeting nitrogen mustards to cancer cell mitochondria based on Δψ_mt could overcome those limitations. Herein, we describe the design, synthesis, and evaluation of Mito-Chlor, a triphenylphosphonium derivative of the nitrogen mustard chlorambucil. We show that Mito-Chlor localizes to cancer cell mitochondria where it acts on mtDNA to arrest cell cycle and induce cell death, resulting in a 80-fold enhancement of cell kill in a panel of breast and pancreatic cancer cell lines that are insensitive to the parent drug. Significantly, Mito-Chlor delayed tumor progression in a mouse xenograft model of human pancreatic cancer. This is a first example of repurposing chlorambucil, a drug not used in breast and pancreatic cancer treatment, as a novel drug candidate for these diseases

Suppression of Tumor Growth by Designed Dimeric Epidithiodiketopiperazine Targeting Hypoxia-Inducible Transcription Factor Complex

Hypoxia is a hallmark of solid tumors, is associated with local invasion, metastatic spread, resistance to chemo- and radiotherapy, and is an independent, negative prognostic factor for a diverse range of malignant neoplasms. The cellular response to hypoxia is primarily mediated by a family of transcription factors, among which hypoxia-inducible factor 1 (HIF1) plays a major role. Under normoxia, the oxygen-sensitive α subunit of HIF1 is rapidly and constitutively degraded but is stabilized and accumulates under hypoxia. Upon nuclear translocation, HIF1 controls the expression of over 100 genes involved in angiogenesis, altered energy metabolism, antiapoptotic, and pro-proliferative mechanisms that promote tumor growth. A designed transcriptional antagonist, dimeric epidithiodiketopiperazine (ETP <b>2</b>), selectively disrupts the interaction of HIF1α with p300/CBP coactivators and downregulates the expression of hypoxia-inducible genes. ETP <b>2</b> was synthesized via a novel homo-oxidative coupling of the aliphatic primary carbons of the dithioacetal precursor. It effectively inhibits HIF1-induced activation of <i>VEGFA</i>, <i>LOX</i>, <i>Glut1</i>, and <i>c-Met</i> genes in a panel of cell lines representing breast and lung cancers. We observed an outstanding antitumor efficacy of both (±)-ETP <b>2</b> and <i>meso</i>-ETP <b>2</b> in a fully established breast carcinoma model by intravital microscopy. Treatment with either form of ETP <b>2</b> (1 mg/kg) resulted in a rapid regression of tumor growth that lasted for up to 14 days. These results suggest that inhibition of HIF1 transcriptional activity by designed dimeric ETPs could offer an innovative approach to cancer therapy with the potential to overcome hypoxia-induced tumor growth and resistance

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