Importance Patterns-of-failure studies suggest that in metastatic non–small-cell lung cancer (NSCLC) sites of gross disease at presentation are the first to progress when treated with chemotherapy. This knowledge has led to increased adoption of local ablative radiation therapy in patients with stage IV NSCLC, though prospective randomized evidence is limited. Objective To determine if intervening with noninvasive stereotactic ablative radiotherapy (SAbR) prior to maintenance chemotherapy in patients with non–progressive limited metastatic NSCLC after induction therapy led to significant improvements in progression-free survival (PFS). Design, Setting, and Participants This is a single-institution randomized phase 2 study of maintenance chemotherapy alone vs SAbR followed by maintenance chemotherapy for patients with limited metastatic NSCLC (primary plus up to 5 metastatic sites) whose tumors did not possessEGFR-targetable orALK-targetable mutations but did achieve a partial response or stable disease after induction chemotherapy. Interventions Maintenance chemotherapy or SAbR to all sites of gross disease (including SAbR or hypofractionated radiation to the primary) followed by maintenance chemotherapy. Main Outcomes and Measures The primary end point was PFS; secondary end points included toxic effects, local and distant tumor control, patterns of failure, and overall survival. Results A total of 29 patients (9 women and 20 men) were enrolled; 14 patients (median [range] age, 63.5 [51.0-78.0] years) were allocated to the SAbR-plus-maintenance chemotherapy arm, and 15 patients (median [range] age, 70.0 [51.0-79.0] years) were allocated to the maintenance chemotherapy–alone arm. The trial was stopped to accrual early after an interim analysis found a significant improvement in PFS in the SAbR-plus-maintenance chemotherapy arm of 9.7 months vs 3.5 months in the maintenance chemotherapy–alone arm (P = .01). Toxic effects were similar in both arms. There were no in-field failures with fewer overall recurrences in the SAbR arm while those patients receiving maintenance therapy alone had progression at existing sites of disease and distantly. Conclusions and Relevance Consolidative SAbR prior to maintenance chemotherapy appeared beneficial, nearly tripling PFS in patients with limited metastatic NSCLC compared with maintenance chemotherapy alone, with no difference in toxic effects. The irradiation prevented local failures in original disease, the most likely sites of first recurrence. Furthermore, PFS for patients with limited metastatic disease appeared similar to those patients with a greater metastatic burden, further arguing for the potential benefits of local therapy in limited metastatic settings. Trial Registration clinicaltrials.gov Identifier:NCT02045446

KRAS mutations are the most common genetic abnormalities in cancer, but the distribution of specific mutations across cancers and the differential responses of patients with specific KRAS mutations in therapeutic clinical trials suggest that different KRAS mutations have unique biochemical behaviors. To further explain these high-level clinical differences and to explore potential therapeutic strategies for specific KRAS isoforms, we characterized the most common KRAS mutants biochemically for substrate binding kinetics, intrinsic and GTPase-activating protein (GAP)–stimulated GTPase activities, and interactions with the RAS effector, RAF kinase. Of note, KRAS G13D shows rapid nucleotide exchange kinetics compared with other mutants analyzed. This property can be explained by changes in the electrostatic charge distribution of the active site induced by the G13D mutation as shown by X-ray crystallography. High-resolution X-ray structures are also provided for the GDP-bound forms of KRAS G12V, G12R, and Q61L and reveal additional insight. Overall, the structural data and measurements, obtained herein, indicate that measurable biochemical properties provide clues for identifying KRAS-driven tumors that preferentially signal through RAF. Implications: Biochemical profiling and subclassification of KRAS-driven cancers will enable the rational selection of therapies targeting specific KRAS isoforms or specific RAS effectors. Mol Cancer Res; 13(9); 1325–35. ©2015 AACR.

A quantitative high-throughput screen identified an inhibitor of phosphoglycerate dehydrogenase (PHGDH), a key enzyme for serine synthesis. This inhibitor limits one-carbon unit availability for nucleotide synthesis. Serine is both a proteinogenic amino acid and the source of one-carbon units essential for de novo purine and deoxythymidine synthesis. In the canonical pathway of glucose-derived serine synthesis, Homo sapiens phosphoglycerate dehydrogenase (PHGDH) catalyzes the first, rate-limiting step. Genetic loss of PHGDH is toxic toward PHGDH-overexpressing breast cancer cell lines even in the presence of exogenous serine. Here, we used a quantitative high-throughput screen to identify small-molecule PHGDH inhibitors. These compounds reduce the production of glucose-derived serine in cells and suppress the growth of PHGDH-dependent cancer cells in culture and in orthotopic xenograft tumors. Surprisingly, PHGDH inhibition reduced the incorporation into nucleotides of one-carbon units from glucose-derived and exogenous serine. We conclude that glycolytic serine synthesis coordinates the use of one-carbon units from endogenous and exogenous serine in nucleotide synthesis, and we suggest that one-carbon unit wasting thus may contribute to the efficacy of PHGDH inhibitors in vitro and in vivo.

The structure of the general transcription factor IIB (TFIIB) in a complex with RNA polymerase II reveals three features crucial for transcription initiation: an N-terminal zinc ribbon domain of TFIIB that contacts the “dock” domain of the polymerase, near the path of RNA exit from a transcribing enzyme; a “finger” domain of TFIIB that is inserted into the polymerase active center; and a C-terminal domain, whose interaction with both the polymerase and with a TATA box–binding protein (TBP)–promoter DNA complex orients the DNA for unwinding and transcription. TFIIB stabilizes an early initiation complex, containing an incomplete RNA-DNA hybrid region. It may interact with the template strand, which sets the location of the transcription start site, and may interfere with RNA exit, which leads to abortive initiation or promoter escape. The trajectory of promoter DNA determined by the C-terminal domain of TFIIB traverses sites of interaction with TFIIE, TFIIF, and TFIIH, serving to define their roles in the transcription initiation process.