Seeing double can be a good thing: Many human breast cancers harbor activating mutations in PIK3CA , the gene coding for the catalytic subunit of phosphoinositide 3-kinase (PI3K). Clinical trials are underway to evaluate the efficacy of PI3K inhibitors in cancer patients. Vasan et al. found unexpectedly that a subset of breast cancers harbor not one—but two— PIK3CA mutations, and the mutations occur on the same allele (see the Perspective by Toker). In model systems, the double mutations hyperactivate PI3K signaling and enhance tumor growth. Preliminary analysis of clinical trial data suggests that breast cancers with double mutations are more responsive to PI3K inhibitors than those with a single mutation. PIK3CA mutational status could help identify the breast cancer patients most likely to benefit from these drugs. Science , this issue p. 714 ; see also p. 685

Although platinum‐based drugs are widely used chemotherapeutics for cancer treatment, the determinants of tumor cell responsiveness remain poorly understood. We show that the loss of subunits LRRC8A and LRRC8D of the heteromeric LRRC8 volume‐regulated anion channels (VRACs) increased resistance to clinically relevant cisplatin/carboplatin concentrations. Under isotonic conditions, about 50% of cisplatin uptake depended on LRRC8A and LRRC8D, but neither on LRRC8C nor on LRRC8E. Cell swelling strongly enhanced LRRC8‐dependent cisplatin uptake, bolstering the notion that cisplatin enters cells through VRAC. LRRC8A disruption also suppressed drug‐induced apoptosis independently from drug uptake, possibly by impairing VRAC‐dependent apoptotic cell volume decrease. Hence, by mediating cisplatin uptake and facilitating apoptosis, VRAC plays a dual role in the cellular drug response. Incorporation of the LRRC8D subunit into VRAC substantially increased its permeability for cisplatin and the cellular osmolyte taurine, indicating that LRRC8 proteins form the channel pore. Our work suggests that LRRC8D‐containing VRACs are crucial for cell volume regulation by an important organic osmolyte and may influence cisplatin/carboplatin responsiveness of tumors. Synopsis LRRC8 proteins were recently shown to constitute the elusive volume‐regulated anion channel VRAC. This study shows that VRAC subunits LRRC8A and LRRC8D regulate both cell volume and uptake of anti‐cancer drugs, thus modulating cellular tumour drug responses. Substrate selectivity of the volume‐regulated anion channel VRAC depends on LRRC8 subunit composition, suggesting that these proteins form the channel pore. VRAC mediates cellular uptake of the cancer drugs cisplatin and carboplatin. By mediating drug uptake and by independently facilitating apoptosis, VRAC plays a dual role in tumor drug response. In addition to enabling cisplatin transport, LRRC8D facilitates cell volume regulation by the organic osmolyte taurine.

Current methods for detection of copy number variants (CNV) and aberrations (CNA) from targeted sequencing data are based on the depth of coverage of captured exons. Accurate CNA determination is complicated by uneven genomic distribution and non-uniform capture efficiency of targeted exons. Here we present CopywriteR, which eludes these problems by exploiting ‘off-target’ sequence reads. CopywriteR allows for extracting uniformly distributed copy number information, can be used without reference, and can be applied to sequencing data obtained from various techniques including chromatin immunoprecipitation and target enrichment on small gene panels. CopywriteR outperforms existing methods and constitutes a widely applicable alternative to available tools.

Pan- or multidrug resistance is a central problem in clinical oncology. Here, we use a genetically engineered mouse model of BRCA2-associated hereditary breast cancer to study drug resistance to several types of chemotherapy and PARP inhibition. We found that multidrug resistance was strongly associated with an EMT-like sarcomatoid phenotype and high expression of the Abcb1b gene, which encodes the drug efflux transporter P-glycoprotein. Inhibition of P-glycoprotein could partly resensitize sarcomatoid tumors to the PARP inhibitor olaparib, docetaxel, and doxorubicin. We propose that multidrug resistance is a multifactorial process and that mouse models are useful to unravel this. Cancer Res; 75(4); 732–41. ©2014 AACR.