A phase Ib dose-finding, pharmacokinetic study of the focal adhesion kinase inhibitor GSK2256098 and trametinib in patients with advanced solid tumours.

BACKGROUND: Combined focal adhesion kinase (FAK) and MEK inhibition may provide greater anticancer effect than FAK monotherapy. METHODS: This dose-finding phase Ib study (adaptive 3 + 3 design) determined the maximum tolerated dose (MTD) of trametinib and the FAK inhibitor GSK2256098 in combination. Eligible patients had mesothelioma or other solid tumours with probable mitogen activated protein kinase pathway activation. Adverse events (AEs), dose-limiting toxicities, disease progression and pharmacokinetics/pharmacodynamics were analysed. RESULTS: Thirty-four subjects were enrolled. The GSK2256098/trametinib MTDs were 500 mg twice daily (BID)/0.375 mg once daily (QD) (high/low) and 250 mg BID/0.5 mg QD (low/high). The most common AEs were nausea, diarrhoea, decreased appetite, pruritus, fatigue and rash; none were grade 4. Systemic exposure to trametinib increased when co-administered with GSK2256098, versus trametinib monotherapy; GSK2256098 pharmacokinetics were unaffected by concomitant trametinib. Median progression-free survival (PFS) was 11.8 weeks (95% CI: 6.1-24.1) in subjects with mesothelioma and was longer with Merlin-negative versus Merlin-positive tumours (15.0 vs 7.3 weeks). CONCLUSIONS: Trametinib exposure increased when co-administered with GSK2256098, but not vice versa. Mesothelioma patients with loss of Merlin had longer PFS than subjects with wild-type, although support for efficacy with this combination was limited. Safety profiles were acceptable up to the MTD.

Correlation of BRAF Mutation Status in Circulating-Free DNA and Tumor and Association with Clinical Outcome across Four BRAFi and MEKi Clinical Trials.

PURPOSE: Tumor-derived circulating cell-free DNA (cfDNA) is a potential alternative source from which to derive tumor mutation status. cfDNA data from four clinical studies of the BRAF inhibitor (BRAFi) dabrafenib or the MEK inhibitor (MEKi) trametinib were analyzed to determine the association between BRAF mutation status in cfDNA and tumor tissue, and the association of BRAF cfDNA mutation status with baseline factors and clinical outcome. EXPERIMENTAL DESIGN: Patients with BRAF V600 mutation-positive melanoma were enrolled in each study after central confirmation of BRAF status in tumor using a PCR-based assay. BRAF mutation status in cfDNA from patient plasma collected at baseline, 732 of 836 (88%) enrolled patients in total, was determined. RESULTS: BRAF mutations were detectable in cfDNA in 76% and 81% of patients with BRAF V600E/V600K-positive tumors, respectively. Patients negative for BRAF mutations in cfDNA had longer progression-free survival (PFS) and overall survival in each of the four studies, compared with patients with detectable cfDNA BRAF mutations. The presence of BRAF-mutant cfDNA was an independent prognostic factor for PFS after multivariate adjustment for baseline factors in three of four studies. Patients negative for BRAF mutation-positive cfDNA in plasma had higher response rates to dabrafenib and trametinib. CONCLUSIONS: BRAF mutations in cfDNA are detectable in >75% of late-stage melanoma patients with BRAF mutation-positive tumors. The lack of circulating, BRAF mutation-positive cfDNA is clinically significant for metastatic melanoma patients, and may be a prognostic marker for better disease outcome.

Phase II trial (BREAK-2) of the BRAF inhibitor dabrafenib (GSK2118436) in patients with metastatic melanoma.

PURPOSE: Dabrafenib (GSK2118436) is a potent inhibitor of mutated BRAF kinase. Our multicenter, single-arm, phase II study assessed the safety and clinical activity of dabrafenib in BRAF(V600E/K) mutation-positive metastatic melanoma (mut(+) MM). PATIENTS AND METHODS: Histologically confirmed patients with stage IV BRAF(V600E/K) mut(+) MM received oral dabrafenib 150 mg twice daily until disease progression, death, or unacceptable adverse events (AEs). The primary end point was investigator-assessed overall response rate in BRAF(V600E) mut(+) MM patients. Secondary end points included progression-free survival (PFS) and overall survival (OS). Exploratory objectives included the comparison of BRAF mutation status between tumor-specific circulating cell-free DNA (cfDNA) and tumor tissue, and the evaluation of cfDNA as a predictor of clinical outcome. RESULTS: Seventy-six patients with BRAF(V600E) and 16 patients with BRAF(V600K) mut(+) MM were enrolled onto the study. In the BRAF(V600E) group, 45 patients (59%) had a confirmed response (95% CI, 48.2 to 70.3), including five patients (7%) with complete responses. Two patients (13%) with BRAF(V600K) mut(+) MM had a confirmed partial response (95% CI, 0 to 28.7). In the BRAF(V600E) and BRAF(V600K) groups, median PFS was 6.3 months and 4.5 months, and median OS was 13.1 months and 12.9 months, respectively. The most common AEs were arthralgia (33%), hyperkeratosis (27%), and pyrexia (24%). Overall, 25 patients (27%) experienced a serious AE and nine patients (10%) had squamous cell carcinoma. Baseline cfDNA levels predicted response rate and PFS in BRAF(V600E) mut(+) MM patients. CONCLUSION: Dabrafenib was well tolerated and clinically active in patients with BRAF(V600E/K) mut(+) MM. cfDNA may be a useful prognostic and response marker in future studies.

O2 regulates stem cells through Wnt/ß-catenin signalling.

Stem cells reside in specialized microenvironments or 'niches' that regulate their function. In vitro studies using hypoxic culture conditions (<5% O2) have revealed strong regulatory links between O2 availability and functions of stem and precursor cells. Although some stem cells are perivascular, others may occupy hypoxic niches and be regulated by O2 gradients. However, the underlying mechanisms remain unclear. Here, we show that hypoxia inducible factor-1α (HIF-1α), a principal mediator of hypoxic adaptations, modulates Wnt/ß-catenin signalling in hypoxic embryonic stem (ES) cells by enhancing ß-catenin activation and expression of the downstream effectors LEF-1 and TCF-1. This regulation extends to primary cells, including isolated neural stem cells (NSCs), and is not observed in differentiated cells. In vivo, Wnt/ß-catenin activity is closely associated with low O2 regions in the subgranular zone of the hippocampus, a key NSC niche. Hif-1α deletion impairs hippocampal Wnt-dependent processes, including NSC proliferation, differentiation and neuronal maturation. This decline correlates with reduced Wnt/ß-catenin signalling in the subgranular zone. O2 availability, therefore, may have a direct role in stem cell regulation through HIF-1α modulation of Wnt/ß-catenin signalling.

HIF-2alpha deletion promotes Kras-driven lung tumor development.

Non-small cell lung cancer (NSCLC) is the leading cause of cancer deaths worldwide. The oxygen-sensitive hypoxia inducible factor (HIF) transcriptional regulators HIF-1alpha and HIF-2alpha are overexpressed in many human NSCLCs, and constitutive HIF-2alpha activity can promote murine lung tumor progression, suggesting that HIF proteins may be effective NSCLC therapeutic targets. To investigate the consequences of inhibiting HIF activity in lung cancers, we deleted Hif-1alpha or Hif-2alpha in an established Kras(G12D)-driven murine NSCLC model. Deletion of Hif-1alpha had no obvious effect on tumor growth, whereas Hif-2alpha deletion resulted in an unexpected increase in tumor burden that correlated with reduced expression of the candidate tumor suppressor gene Scgb3a1 (HIN-1). Here, we identify Scgb3a1 as a direct HIF-2alpha target gene and demonstrate that HIF-2alpha regulates Scgb3a1 expression and tumor formation in human Kras(G12D)-driven NSCLC cells. AKT pathway activity, reported to be repressed by Scgb3a1, was enhanced in HIF-2alpha-deficient human NSCLC cells and xenografts. Finally, a direct correlation between HIF-2alpha and SCGB3a1 expression was observed in approximately 70% of human NSCLC samples analyzed. These data suggest that, whereas HIF-2alpha overexpression can contribute to NSCLC progression, therapeutic inhibition of HIF-2alpha below a critical threshold may paradoxically promote tumor growth by reducing expression of tumor suppressor genes, including Scgb3a1.

Hypoxia-inducible factors in stem cells and cancer.

Cellular properties are influenced by complex factors inherent to their microenvironments. While oxygen deprivation (hypoxia) occurs in tumours because of rapid cell proliferation and aberrant blood vessel formation, embryonic cells develop in a naturally occurring hypoxic environment. Cells respond to hypoxia by stabilizing hypoxia-inducible factors (HIFs), which are traditionally viewed to function by altering cellular metabolism and blood vessel architecture. Recently, HIFs have been shown to modulate specific stem cell effectors, such as Notch, Wnt and Oct4 that control stem cell proliferation, differentiation and pluripotency. Direct molecular links have also been established between HIFs and critical cell signalling pathways such as cMyc and p53. These novel links suggest a new role for HIFs in stem cell and tumour regulation.

Apicoplast fatty acid synthesis is essential for organelle biogenesis and parasite survival in Toxoplasma gondii.

Apicomplexan parasites are the cause of numerous important human diseases including malaria and AIDS-associated opportunistic infections. Drug treatment for these diseases is not satisfactory and is threatened by resistance. The discovery of the apicoplast, a chloroplast-like organelle, presents drug targets unique to these parasites. The apicoplast-localized fatty acid synthesis (FAS II) pathway, a metabolic process fundamentally divergent from the analogous FAS I pathway in humans, represents one such target. However, the specific biological roles of apicoplast FAS II remain elusive. Furthermore, the parasite genome encodes additional and potentially redundant pathways for the synthesis of fatty acids. We have constructed a conditional null mutant of acyl carrier protein, a central component of the FAS II pathway in Toxoplasma gondii. Loss of FAS II severely compromises parasite growth in culture. We show FAS II to be required for the activation of pyruvate dehydrogenase, an important source of the metabolic precursor acetyl-CoA. Interestingly, acyl carrier protein knockout also leads to defects in apicoplast biogenesis and a consequent loss of the organelle. Most importantly, in vivo knockdown of apicoplast FAS II in a mouse model results in cure from a lethal challenge infection. In conclusion, our study demonstrates a direct link between apicoplast FAS II functions and parasite survival and pathogenesis. Our genetic model also offers a platform to dissect the integration of the apicoplast into parasite metabolism, especially its postulated interaction with the mitochondrion.