The mammalian target of rapamycin (mTOR) kinase is a master regulator of protein synthesis that couples nutrient sensing to cell growth and cancer. However, the downstream translationally regulated nodes of gene expression that may direct cancer development are poorly characterized. Using ribosome profiling, we uncover specialized translation of the prostate cancer genome by oncogenic mTOR signalling, revealing a remarkably specific repertoire of genes involved in cell proliferation, metabolism and invasion. We extend these findings by functionally characterizing a class of translationally controlled pro-invasion messenger RNAs that we show direct prostate cancer invasion and metastasis downstream of oncogenic mTOR signalling. Furthermore, we develop a clinically relevant ATP site inhibitor of mTOR, INK128, which reprograms this gene expression signature with therapeutic benefit for prostate cancer metastasis, for which there is presently no cure. Together, these findings extend our understanding of how the ‘cancerous’ translation machinery steers specific cancer cell behaviours, including metastasis, and may be therapeutically targeted.

KRAS was recently identified to be potentially druggable by allele-specific covalent targeting of Cys-12 in vicinity to an inducible allosteric switch II pocket (S-IIP). Success of this approach requires active cycling of KRAS between its active-GTP and inactive-GDP conformations as accessibility of the S-IIP is restricted only to the GDP-bound state. This strategy proved feasible for inhibiting mutant KRAS in vitro; however, it is uncertain whether this approach would translate to in vivo. Here, we describe structure-based design and identification of ARS-1620, a covalent compound with high potency and selectivity for KRAS. ARS-1620 achieves rapid and sustained in vivo target occupancy to induce tumor regression. We use ARS-1620 to dissect oncogenic KRAS dependency and demonstrate that monolayer culture formats significantly underestimate KRAS dependency in vivo. This study provides in vivo evidence that mutant KRAS can be selectively targeted and reveals ARS-1620 as representing a new generation of KRAS-specific inhibitors with promising therapeutic potential.

KRAS gain-of-function mutations occur in approximately 30% of all human cancers. Despite more than 30 years of KRAS-focused research and development efforts, no targeted therapy has been discovered for cancers with KRAS mutations. Here, we describe ARS-853, a selective, covalent inhibitor of KRAS G12C that inhibits mutant KRAS-driven signaling by binding to the GDP-bound oncoprotein and preventing activation. Based on the rates of engagement and inhibition observed for ARS-853, along with a mutant-specifi c mass spectrometry-based assay for assessing KRAS activation status, we show that the nucleotide state of KRAS G12C is in a state of dynamic fl ux that can be modulated by upstream signaling factors. These studies provide convincing evidence that the KRAS G12C mutation generates a "hyperexcitable" rather than a "statically active" state and that targeting the inactive, GDP-bound form is a promising approach for generating novel anti-RAS therapeutics. SIGNIFICANCE:A cell-active, mutant-specifi c, covalent inhibitor of KRAS G12C is described that targets the GDP-bound, inactive state and prevents subsequent activation. Using this novel compound, we demonstrate that KRAS G12C oncoprotein rapidly cycles bound nucleotide and responds to upstream signaling inputs to maintain a highly active state. Cancer Discov; 6(3); 316-29.

Targeting the mammalian target of rapamycin (mTOR) is a promising strategy for cancer therapy. However, the mTOR kinase functions in two complexes, TORC1 and TORC2, neither of which is fully inhibited by the allosteric inhibitor rapamycin or analogs. We compared rapamycin with the active-site TORC1/2 inhibitor PP242, in acute leukemia models harboring the Philadelphia chromosome (Ph) translocation. We demonstrate that PP242, but not rapamycin, causes death of mouse and human leukemia cells. In vivo, PP242 delays leukemia onset and augments the effects of current front-line tyrosine kinase inhibitors, more effectively than rapamycin. Surprisingly, PP242 has much weaker effects than rapamycin on proliferation and function of normal lymphocytes. PI-103, a less selective TORC1/2 inhibitor that also targets phosphoinositide 3-kinase, is more immunosuppressive than PP242. These findings establish that Ph+ transformed cells are more sensitive than normal lymphocytes to selective TORC1/2 inhibitors, and support the development of such inhibitors for leukemia therapy.

Deregulation of the phosphoinositide 3-kinase (PI3K) pathway has been implicated in numerous pathologies like cancer, diabetes, thrombosis, rheumatoid arthritis and asthma. Recently, small molecule and ATP-competitive PI3K inhibitors with a wide range of selectivities have entered clinical development. In order to understand mechanisms underlying isoform selectivity of these inhibitors, we developed a novel expression strategy that enabled us to determine the first crystal structure of the catalytic subunit of the class IA PI3K p110δ. Structures of this enzyme in complex with a broad panel of isoform- and pan-selective class I PI3K inhibitors reveal that selectivity towards p110δ can be achieved by exploiting its conformational flexibility and the sequence diversity of active-site residues that do not contact ATP. We have used these observations to rationalize and synthesize highly selective inhibitors for p110δ with greatly improved potencies.