DNA double-strand breaks (DSB) are the most cytotoxic lesions induced by topoisomerase II poisons. Nonhomologous end joining (NHEJ) is a major pathway for DSB repair and requires DNA-dependent protein kinase (DNA-PK) activity. DNA-PK catalytic subunit (DNA-PKcs) is structurally similar to PI-3K, which promotes cell survival and proliferation and is upregulated in many cancers. KU-0060648 is a dual inhibitor of DNA-PK and PI-3K in vitro. KU-0060648 was investigated in a panel of human breast and colon cancer cells. The compound inhibited cellular DNA-PK autophosphorylation with IC 50 values of 0.019 mmol/L (MCF7 cells) and 0.17 mmol/L (SW620 cells), and PI-3K-mediated AKT phosphorylation with IC 50 values of 0.039 mmol/L (MCF7 cells) and more than 10 mmol/L (SW620 cells). Five-day exposure to 1 mmol/L KU-0060648 inhibited cell proliferation by more than 95% in MCF7 cells but only by 55% in SW620 cells. In clonogenic survival assays, KU-0060648 increased the cytotoxicity of etoposide and doxorubicin across the panel of DNA-PKcs-proficient cells, but not in DNA-PKcs-deficient cells, thus confirming that enhanced cytotoxicity was due to DNA-PK inhibition. In mice bearing SW620 and MCF7 xenografts, concentrations of KU-0060648 that were sufficient for in vitro growth inhibition and chemosensitization were maintained within the tumor for at least 4 hours at nontoxic doses. KU-0060648 alone delayed the growth of MCF7 xenografts and increased etoposide-induced tumor growth delay in both in SW620 and MCF7 xenografts by up to 4.5-fold, without exacerbating etoposide toxicity to unacceptable levels. The proof-of-principle in vitro and in vivo chemosensitization with KU-0060648 justifies further evaluation of dual DNA-PK and PI-3K inhibitors.

Purpose To investigate SGI-110 as a “chemosensitizer” in ovarian cancer (OC) and to assess its effects on tumor suppressor genes (TSG) and chemo-responsiveness associated genes silenced by DNA methylation in OC. Experimental Design Several OC cell lines were used for in vitro and in vivo platinum resensitization studies. Changes in DNA methylation and expression levels of TSG and other cancer-related genes in response to SGI-110 were measured by pyrosequencing and RT-PCR. Results We demonstrate in vitro that SGI-110 resensitized a range of platinum-resistant OC cells to cisplatin (CDDP) and induced significant demethylation and reexpression of TSG, differentiation-associated genes and putative drivers of OC cisplatin resistance. In vivo, SGI-110 alone or in combination with CDDP was well tolerated and induced anti-tumor effects in OC xenografts. Pyrosequencing analyses confirmed that SGI-110 caused both global (LINE1) and gene specific hypomethylation in vivo, including TSGs (RASSF1A), proposed drivers of OC cisplatin resistance (MLH1 and ZIC1), differentiation-associated genes (HOXA10 and HOXA11), and transcription factors (STAT5B). Furthermore, DNA damage induced by CDDP in OC cells was increased by SGI-110, as measured by ICP-mass spectrometry analysis of DNA adduct formation and repair of cisplatin-induced DNA damage. Conclusions These results strongly support further investigation of hypomethylating strategies in platinum-resistant OC. Specifically, SGI-110 in combination with conventional and/or targeted therapeutics warrants further development in this setting.

Emergence of clinical resistance to BRAF inhibitors, alone or in combination with MEK inhibitors, limits clinical responses in melanoma. Inhibiting HSP90 offers an approach to simultaneously interfere with multiple resistance mechanisms. Using the HSP90 inhibitor, AT13387, which is currently in clinical trials, we investigated the potential of HSP90 inhibition to overcome or delay the emergence of resistance to these kinase inhibitors in melanoma models. In vitro, treating vemurafenib-sensitive cells (A375 or SK-MEL-28) with a combination of AT13387 and vemurafenib prevented colony growth under conditions where vemurafenib treatment alone generated resistant colonies. In vivo, when AT13387 was combined with vemurafenib in a SK-MEL-28, vemurafenib-sensitive model, no regrowth of tumors was observed over 5 months, although 2 out of 7 tumors in the vemurafenib monotherapy group relapsed in this time. Together these data suggest that the combination of these agents can delay the emergence of resistance. Cell lines with acquired vemurafenib resistance, derived from these models (A375R, SK-MEL-28R) were also sensitive to HSP90 inhibitor treatment; key clients were depleted, apoptosis was induced and growth in 3D-culture was inhibited. Similar effects were observed in cell lines with acquired resistance to both BRAF and MEK inhibitors (SK-MEL-28RR, WM164RR, 1205LuRR). These data suggest that treatment with an HSP90 inhibitor, such as AT13387, is a potential approach for combatting resistance to BRAF and MEK inhibition in melanoma. Moreover, frontline combination of these agents with an HSP90 inhibitor could delay the emergence of resistance, providing a strong rationale for clinical investigation of such combinations in BRAF-mutated melanoma.

Purpose Therapy resistance and associated liver disease make hepatocellular cancers (HCC) difficult to treat with traditional cytotoxic therapies, while newer targeted approaches offer only modest survival benefit. We focused on DNA-dependent protein kinase, DNA-PKcs, encoded by PRKDC and central to DNA damage repair by non-homologous end joining. Our aim was to explore its roles in hepatocarcinogenesis and as a novel therapeutic candidate. Experimental Design PRKDC was characterised in liver tissues from of 132 patients (normal liver (n=10), cirrhotic liver (n=13), dysplastic nodules (n=18), HCC (n=91)) using Affymetrix U133 Plus 2.0 and 500K Human Mapping SNP arrays (cohort 1). In addition, we studied a case series of 45 patients with HCC undergoing diagnostic biopsy (cohort 2). Histological grading, response to treatment and survival were correlated with DNA-PKcs quantified immunohistochemically. Parallel in vitro studies determined the impact of DNA-PK on DNA repair and response to cytotoxic therapy. Results Increased PRKDC expression in HCC was associated with amplification of its genetic locus in cohort 1. In cohort 2, elevated DNA-PKcs identified patients with treatment-resistant HCC, progressing at a median of 4.5 months compared to 16.9 months, while elevation of activated pDNA-PK independently predicted poorer survival. DNA-PKcs was high in HCC cell lines, where its inhibition with NU7441 potentiated irradiation and doxorubicin-induced cytoxicity, while the combination suppressed HCC growth in vitro and in vivo. Conclusions These data identify PRKDC/DNA-PKcs as a candidate driver of hepatocarcinogenesis, whose biopsy characterisation at diagnosis may impact stratification of current therapies, and whose specific future targeting may overcome resistance.

Pex3p interacts with peroxisome retention factor Inp1p at the peroxisomal membrane and functions in the organelle’s segregation in addition to its biogenesis.