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Molecular processes that could contribute to di erences in chemo-and radioresistance include variations in DNA repair mechanisms. In mammalian cells, the product of the rad51 gene mediates DNA repair via homologous recombination. We describe that in contrast to conventional monolayer cell systems Rad51 protein accumulates to high-levels in three-dimensional cell culture models as well as in orthotopic xeno-transplants of human pancreatic cancer cells. Strikingly, over-expression of wild-type Rad51 was also found in 66% of human pancreatic adenocarcinoma tissue specimens. Functional analysis revealed that Rad51 over-expression enhances survival of cells after induction of DNA double strand breaks. These data suggest that perturbations of Rad51 expression contribute to the malignant phenotype of pancreatic cancer.

Background This multicenter, open‐label, phase Ib study investigated the safety and efficacy of binimetinib (MEK inhibitor) in combination with buparlisib (phosphatidylinositol 3‐kinase [PI3K] inhibitor) in patients with advanced solid tumors with RAS/RAF alterations. Materials and Methods Eighty‐nine patients were enrolled in the study. Eligible patients had advanced solid tumors with disease progression after standard therapy and/or for which no standard therapy existed. Evaluable disease was mandatory, per RECIST version 1.1 and Eastern Cooperative Oncology Group performance status 0‐2. Binimetinib and buparlisib combinations were explored in patients with KRAS‐, NRAS‐, or BRAF‐mutant advanced solid tumors until the maximum tolerated dose and recommended phase II dose (RP2D) were defined. The expansion phase comprised patients with epidermal growth factor receptor (EGFR)‐mutant, advanced non‐small cell lung cancer, after progression on an EGFR inhibitor; advanced RAS‐ or BRAF‐mutant ovarian cancer; or advanced non‐small cell lung cancer with KRAS mutation. Results At data cutoff, 32/89 patients discontinued treatment because of adverse events. RP2D for continuous dosing was buparlisib 80 mg once daily/binimetinib 45 mg twice daily. The toxicity profile of the combination resulted in a lower dose intensity than anticipated. Six (12.0%) patients with RAS/BRAF‐mutant ovarian cancer achieved a partial response. Pharmacokinetics of binimetinib were not altered by buparlisib. Pharmacodynamic analyses revealed downregulation of pERK and pS6 in tumor biopsies. Conclusion Although dual inhibition of MEK and the PI3K pathways showed promising activity in RAS/BRAF ovarian cancer, continuous dosing resulted in intolerable toxicities beyond the dose‐limiting toxicity monitoring period. Alternative schedules such as pulsatile dosing may be advantageous when combining therapies. Implications for Practice Because dysregulation of the mitogen‐activated protein kinase (MAPK) and the phosphatidylinositol 3‐kinase (PI3K) pathways are both frequently involved in resistance to current targeted therapies, dual inhibition of both pathways may be required to overcome resistance mechanisms to single‐agent tyrosine kinase inhibitors or to treat cancers with driver mutations that cannot be directly targeted. A study investigating the safety and efficacy of combination binimetinib (MEK inhibitor) and buparlisib (PI3K inhibitor) in patients harboring alterations in the RAS/RAF pathway was conducted. The results may inform the design of future combination therapy trials in patients with tumors harboring mutations in the PI3K and MAPK pathways.

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Nuclear DNA helicase II (NDH II) unwinds both DNA and RNA (Zhang, S., and Grosse, F. (1994) Biochemistry 33, 3906-3912). Here, we report on the molecular cloning and sequence determination of the complementary DNA (cDNA) coding for this DNA and RNA helicase. The full-length cDNA sequence was derived from overlapping clones that were detected by immunoscreening of a calf thymus cDNA library in bacteriophage lambda gt11. This cDNA was 4,528 bases in length, which corresponded well with a 4.5-4.7-kilobase-long mRNA as detected by Northern blot analysis. The open reading frame of NDH II cDNA predicts a polypeptide of 1287 amino acids and a calculated molecular mass of 141,854 daltons. NDH II is related to a group of nucleic acid helicases from the DEAD/H box family II, with the signature motif DEIH in domain II. Two further proteins of this family, i.e. human RNA helicase A and Drosophila Maleless (Mle) protein, were found to be highly homologous to NDH II. With RNA helicase A, there was 91.5% identity and 95.5% similarity between the amino acid residues; with Mle protein, we observed a 50% identity and an 85% similarity. Antibodies against human RNA helicase A cross-reacted with NDH II, further supporting that NDH II is the bovine homologue of human RNA helicase A. Immunofluorescence studies revealed a mainly nuclear localization of NDH II. A role for NDH II in nuclear DNA and RNA metabolism is suggested.