The high frequency of activating RAS or BRAF mutations in cancer provides strong rationale for targeting the mitogen-activated protein kinase (MAPK) pathway. Selective BRAF and MAP-ERK kinase (MEK) inhibitors have shown clinical effi cacy in patients with melanoma. However, the majority of responses are transient, and resistance is often associated with pathway reactivation of the extracellular signal-regulated kinase (ERK) signaling pathway. Here, we describe the identifi cation and characterization of SCH772984, a novel and selective inhibitor of ERK1/2 that displays behaviors of both type I and type II kinase inhibitors. SCH772984 has nanomolar cellular potency in tumor cells with mutations in BRAF , NRAS , or KRAS and induces tumor regressions in xenograft models at tolerated doses. Importantly, SCH772984 effectively inhibited MAPK signaling and cell proliferation in BRAF or MEK inhibitor-resistant models as well as in tumor cells resistant to concurrent treatment with BRAF and MEK inhibitors. These data support the clinical development of ERK inhibitors for tumors refractory to MAPK inhibitors. SIGNIFICANCE: BRAF and MEK inhibitors have activity in MAPK-dependent cancers with BRAF or RAS mutations. However, resistance is associated with pathway alterations resulting in phospho-ERK reactivation. Here, we describe a novel ERK1/2 kinase inhibitor that has antitumor activity in MAPK inhibitor-naïve and MAPK inhibitor-resistant cells containing BRAF or RAS mutations. Cancer Discov; 3(7); 742-50.

The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes separated by one to seven A:T base pairs. The application of femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluorescence decay measurements permits detailed analysis of the formation and decay of the stilbene acceptor singlet state and of the charge-separated intermediates. When the donor and acceptor are separated by a single A:T base pair, charge separation occurs via a single-step superexchange mechanism. However, when the donor and acceptor are separated by two or more A:T base pairs, charge separation occurs via a multistep process consisting of hole injection, hole transport, and hole trapping. In such cases, hole arrival at the electron donor is slower than hole injection into the bridging A-tract. Rate constants for charge separation (hole arrival) and charge recombination are dependent upon the donor-acceptor distance; however, the rate constant for hole injection is independent of the donor-acceptor distance. The observation of crossover from a superexchange to a hopping mechanism provides a "missing link" in the analysis of DNA electron transfer and requires reevaluation of the existing literature for photoinduced electron transfer in DNA.

Whole scheme of things: The kinetics and efficiency of photoinduced hole transport across DNA A tracts with 1–7 base pairs have been determined from femtosecond transient absorption spectroscopic data. These values are strongly distance dependent over the first four base pairs, but are relatively insensitive to distance at longer distances. These kinetic results (□, ▪) parallel the DNA‐strand‐cleavage results of Giese et al. (○, •).

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Table S1. m/z values for oligomer sequences determined by MALDI-TOF mass spectrometry. Sequence Calculated Found Sequence Calculated Found APy-T 4886.3 4881.6 APy-1 Br U 4951.2 4948.2 APy-2 Br U 4951.2 4948.0 APy-2U 4872.3 4875.2 APy-3 Br U 4951.2 4948.3 APy-3U 4872.3 4869.5 APy-4 Br U 4951.2 4955.6 APy-4U 4872.3 4874.8 APy-5 Br U 5568.6 5576.7 APy-5U 5489.5 5489.1 APy-6 Br U 6186.0 6190.7 APy-6U 6107.1 6106.3 APy-7 Br U 6803.4 6805.4 APy-7U 6724.3 6726.9 APy-8 Br U 7420.9 7416.0 APy-8U 7341.8 7345.2 APy-2 I U 4998.3 4998.5 APy-2U 4872.3 4875.6 APy-3 I U 4998.3 4996.2 APy-3U 4872.3 4868.1 APy-4 I U 4998.3 4997.9 APy-4U 4872.3 4871.1 APy-5 I U 5615.7 5618.2 APy-5U 5489.6 5492.1

The mechanism and dynamics of charge separation and charge recombination in synthetic DNA hairpins possessing a stilbenedicarboxamide linker and a single guanine-cytosine base pair have been reinvestigated. The combination of femtosecond broad-band pump probe spectroscopy, nanosecond transient absorption experiments, and picosecond fluorescence decay measurements permits analysis of the formation and decay of the stilbene anion radical. Reversible hole injection resulting in the formation of the stilbene-adenine contact radical ion pair is found to occur on the picosecond time scale. The mechanism for charge separation across two or more base pairs is revised from single step superexchange to a multi-step process: hole injection followed by hole transport and hole trapping. The mechanism of charge recombination remains assigned to a superexchange process.

The structure, spectroscopy, and photophysical behavior of a series of hairpin-forming conjugates possessing a 5'-tethered N-alkylpyrenecarboxamide chromophore have been investigated. Comparison of the NMR spectra of the conjugates and analogs lacking the tethered pyrene indicates that the pyrene does not behave as an end-capping group but rather is intercalated between the two terminal hairpin base pairs. An intercalated structure is also consistent with the thermodynamic parameters for hairpin formation and the steady state and transient spectral properties of the conjugates. Quenching of the pyrene fluorescence and transient absorption spectra is observed only when guanine is located in one of the two terminal base pairs and is attributed to hole injection from singlet pyrene to guanine. The fast component of the transient decay is more rapid when guanine is located in the second vs first base pair, consistent with an intercalated but not an end-capped geometry. Spectral broadening of ultraviolet, fluorescence, and transient absorption spectra is attributed to multiple ground state conformations.

Stopover at G base: The efficiency of photoinduced charge separation between donor and acceptor chromophores separated by a polyadenine sequence containing a single guanine (G) is sensitive to the location of G and the total length of the polypurine sequence. Quantum yields provide support for a stepwise mechanism in which G serves as a temporary resting place in the overall process (Sa: stilbenedicarboxamide electron acceptor, Sd: stilbenediether electron donor).