The redeployed drug combination of bezafibrate and medroxyprogesterone acetate (designated BaP) has potent in vivo anticancer activity in acute myeloid leukemia (AML) and endemic-Burkitt’s lymphoma (eBL) patients; however its mechanism-of-action is unclear. Given that elevated fatty acid biosynthesis is a hallmark of many cancers and that these drugs can affect lipid metabolism, we hypothesized that BaP exerts anticancer effects by disrupting lipogenesis. We applied mass spectrometry-based lipidomics and gene and protein expression measurements of key lipogenic enzymes [acetyl CoA carboxylase 1 (ACC1), fatty acid synthase (FASN) and stearoyl-CoA desaturase 1 (SCD1)] to AML and eBL cell lines treated with BaP. BaP treatment decreased fatty acid and phospholipid biosynthesis from glucose. The proportion of phospholipid species with saturated and monounsaturated acyl chains were also decreased after treatment, while those with polyunsaturated chains increased. BaP decreased SCD1 protein levels in each cell line (0.46 – 0.62-fold, p<0.023) and decreased FASN protein levels across all cell lines (0.87-fold decrease, p=1.7×10-4). Changes to ACC1 protein levels were mostly insignificant. Supplementation with the SCD1 enzymatic product, oleate, rescued AML and e-BL cells from BaP cell killing and decreased levels of BaP-induced reactive oxygen species whereas supplementation with the SCD1 substrate (and FASN product), palmitate, did not rescue cells. In conclusion, these data suggest that the critical anticancer actions of BaP are decreases in SCD1 levels and monounsaturated fatty acid synthesis. To our knowledge, this is the first time that clinically available anti-leukemic and anti-lymphoma drugs targeting SCD1 have been reported.

The product of the Brca1 tumor-suppressor gene is involved in multiple aspects of the cellular DNA damage response (DDR), including activation of cell-cycle arrests and DNA double-stranded break (DSB) repair by homologous recombination. Prior reports demonstrated that BRCA1 recruitment to areas of DNA breakage depended on RAP80 and the RNF8/RNF168 E3 ubiquitin ligases. Here, we extend these findings by showing that RAP80 is only required for the binding of BRCA1 to regions flanking the DSB, whereas BRCA1 binding directly to DNA breaks requires Nijmegen breakage syndrome 1 (NBS1). These differential recruitment mechanisms differentially affect BRCA1 functions: (i) RAP80-dependent recruitment of BRCA1 to chromatin flanking DNA breaks is required for BRCA1 phosphorylation at serine 1387 and 1423 by ATM and, consequently, for the activation of S and G2 checkpoints; and (ii) BRCA1 interaction with NBS1 upon DSB induction results in an NBS1-dependent recruitment of BRCA1 directly to the DNA break and is required for nonhomologous end-joining repair. Together, these findings illustrate that spatially distinct fractions of BRCA1 exist at the DSB site, which are recruited by different mechanisms and execute different functions in the DDR. Cancer Res; 75(13); 1–9. ©2015 AACR.

The product of the Brca1 tumor-suppressor gene is involved in multiple aspects of the cellular DNA damage response (DDR), including activation of cell cycle arrests and DNA double-stranded break (DSB) repair by homologous recombination (HR). Prior reports demonstrated that Brca1 recruitment to areas of DNA breakage depended on Rap80 and the RNF8/RNF168 E3 ubiquitin ligases. Here we extend these findings by showing that Rap80 is only required for the binding of Brca1 to regions flanking the DSB, while Brca1 binding directly to DNA breaks requires Nbs1. These differential recruitment mechanisms differentially affect Brca1 functions: 1) Rap80-dependent recruitment of Brca1 to chromatin flanking DNA breaks is required for Brca1 phosphorylation at serine 1387 and 1423 by ATM and, consequently, for the activation of S and G2 checkpoints; and 2) Brca1 interaction with Nbs1 upon DSB induction results in an Nbs1-dependent recruitment of Brca1 directly to the DNA break and is required for non-homologous end-joining repair. Together, these findings illustrate that spatially distinct fractions of Brca1 exist at the DSB site, which are recruited by different mechanisms and execute different functions in the DDR.

Predictive biomarkers can play a key role in individualized disease monitoring. Unfortunately, the use of biomarkers in clinical settings has thus far been limited. We have previously shown that mechanism-based pharmacokinetic/pharmacodynamic modeling enables integration of nonvalidated biomarker data to provide predictive model-based biomarkers for response classification. The biomarker model we developed incorporates an underlying latent variable (disease) representing (unobserved) tumor size dynamics, which is assumed to drive biomarker production and to be influenced by exposure to treatment. Here, we show that by integrating CT scan data, the population model can be expanded to include patient outcome. Moreover, we show that in conjunction with routine medical monitoring data, the population model can support accurate individual predictions of outcome. Our combined model predicts that a change in disease of 29.2% (relative standard error 20%) between two consecutive CT scans (i.e., 6–8 weeks) gives a probability of disease progression of 50%. We apply this framework to an external dataset containing biomarker data from 22 small cell lung cancer patients (four patients progressing during follow-up). Using only data up until the end of treatment (a total of 137 lactate dehydrogenase and 77 neuron-specific enolase observations), the statistical framework prospectively identified 75% of the individuals as having a predictable outcome in follow-up visits. This included two of the four patients who eventually progressed. In all identified individuals, the model-predicted outcomes matched the observed outcomes. This framework allows at risk patients to be identified early and therapeutic intervention/monitoring to be adjusted individually, which may improve overall patient survival. Cancer Res; 75(12); 1–10. ©2015 AACR.

Millions of DNA-damaging lesions occur every day in each cell of our bodies due to various stresses. The failure to detect and accurately repair these lesions can give rise to cells with high levels of endogenous DNA damage, deleterious mutations, or genomic aberrations. Such genomic instability can lead to the activation of specific signaling pathways, including the DNA damage response (DDR) pathway. Constitutive activation of DDR proteins has been observed in human tumor specimens from different cancer stages, including precancerous and metastatic cancers, although not in normal tissues. The tumor-suppressive role of DDR activity during the premalignant stage has been studied, and strong evidence is emerging for an oncogenic role for DDR proteins such as DNA-PK and CHK1 during the later stages of tumor development. However, the majority of current cancer therapies induce DNA damage, potentially exacerbating protumorigenic genomic instability and enabling the development of resistance. Therefore, elucidating the molecular basis of DNA damage–mediated genomic instability and its role in tumorigenesis is critical. Finally, I discuss the potential existence of distinct DNA damage thresholds at various stages of tumorigenesis and what the ramifications of such thresholds would be, including the ambiguous role of the DDR pathway in human cancers, therapy-induced malignancies, and enhanced therapies. Cancer Res; 75(11); 1–6. ©2015 AACR.