Despite the promise of ribonucleic acid interference therapeutics, the delivery of oligonucleotides selectively to diseased tissues in the body, and specifically to the cellular location in the tissues needed to provide optimal therapeutic outcome, remains a significant challenge. Here, key material properties and biological mechanisms for delivery of short interfering RNAs (siRNAs) to effectively silence target-specific cells in vivo are identified. Using porous silicon nanoparticles as the siRNA host, tumor-targeting peptides for selective tissue homing, and fusogenic lipid coatings to induce fusion with the plasma membrane, it is shown that the uptake mechanism can be engineered to be independent of common receptor-mediated endocytosis pathways. Two examples of the potential broad clinical applicability of this concept in a mouse xenograft model of ovarian cancer peritoneal carcinomatosis are provided: silencing the Rev3l subunit of polymerase Pol ζ to impair DNA repair in combination with cisplatin; and reprogramming tumor-associated macrophages into a proinflammatory state.

APTO-253 is a small molecule with antiproliferative activity against cell lines derived from a wide range of human malignancies. We sought to determine the mechanisms of action and basis for resistance to APTO-253 so as to identify synthetic lethal interactions that can guide combination studies. The cellular pharmacology of APTO-253 was analyzed in Raji lymphoma cells and a subline selected for resistance (Raji/253R). Using LC/MS/ESI analysis, APTO-253 was found to convert intracellularly to a complex containing one molecule of iron and three molecules of APTO-253 [Fe(253)₃]. The intracellular content of Fe(253)₃ exceeded that of the native drug by approximately 18-fold, and Fe(253)₃ appears to be the most active form. Treatment of cells with APTO-253 caused DNA damage, which led us to ask whether cells deficient in homologous recombination (i.e., loss of BRCA1/2 function) were hypersensitive to this drug. It was found that loss of either BRCA1 or BRCA2 function in multiple isogenic paired cell lines resulted in hypersensitivity to APTO-253 of a magnitude similar to the effects of PARP inhibitors, olaparib. Raji cells selected for 16-fold acquired resistance had 16-fold reduced accumulation of Fe(253)₃ RNA-seq analysis revealed that overexpression of the ABCG2 drug efflux pump is a key mechanism of resistance. ABCG2-overexpressed HEK-293 cells were resistant to APTO-253, and inhibition of ABCG2 reversed resistance to APTO-253 in Raji/253R. APTO-253 joins the limited repertoire of drugs that can exploit defects in homologous recombination and is of particular interest because it does not produce myelosuppression. Mol Cancer Ther; 17(6); 1167-76. ©2018 AACR.

The molecular underpinnings of acquired resistance to carboplatin are poorly understood and often inconsistent between in vitro modeling studies. After sequential treatment cycles, multiple isogenic clones reached similar levels of resistance, but significant transcriptional heterogeneity. Gene-expression based virtual synchronization of 26,772 single cells from 2 treatment steps and 4 resistant clones was used to evaluate the activity of Hallmark gene sets in proliferative (P) and quiescent (Q) phases. Two behaviors were associated with resistance: (1) broad repression in the P phase observed in all clones in early resistant steps and (2) prevalent induction in Q phase observed in the late treatment step of one clone. Furthermore, the induction of IFNα response in P phase or Wnt-signaling in Q phase were observed in distinct resistant clones. These observations suggest a model of resistance hysteresis, where functional alterations of the P and Q phase states affect the dynamics of the successive transitions between drug exposure and recovery, and prompts for a precise monitoring of single-cell states to develop more effective schedules for, or combination of, chemotherapy treatments.

Phosphoenolpyruvate carboxykinase (PEPCK or PCK) catalyzes the first rate-limiting step in hepatic gluconeogenesis pathway to maintain blood glucose levels. Mammalian cells express two PCK genes, encoding for a cytoplasmic (PCPEK-C or PCK1) and a mitochondrial (PEPCK-M or PCK2) isoforms, respectively. Increased expressions of both PCK genes are found in cancer of several organs, including colon, lung, and skin, and linked to increased anabolic metabolism and cell proliferation. Here, we report that the expressions of both PCK1 and PCK2 genes are downregulated in primary hepatocellular carcinoma (HCC) and low PCK expression was associated with poor prognosis in patients with HCC. Forced expression of either PCK1 or PCK2 in liver cancer cell lines results in severe apoptosis under the condition of glucose deprivation and suppressed liver tumorigenesis in mice. Mechanistically, we show that the pro-apoptotic effect of PCK1 requires its catalytic activity. We demonstrate that forced PCK1 expression in glucose-starved liver cancer cells induced TCA cataplerosis, leading to energy crisis and oxidative stress. Replenishing TCA intermediate α-ketoglutarate or inhibition of reactive oxygen species production blocked the cell death caused by PCK expression. Taken together, our data reveal that PCK1 is detrimental to malignant hepatocytes and suggest activating PCK1 expression as a potential treatment strategy for patients with HCC.