Activation of the PI3K/mTOR signaling pathway is recurrent in different lymphoma types, and pharmacologic inhibition of the PI3K/mTOR pathway has shown activity in lymphoma patients. Here, we extensively characterized the and activity and the mechanism of action of PQR309 (bimiralisib), a novel oral selective dual PI3K/mTOR inhibitor under clinical evaluation, in preclinical lymphoma models. This study included preclinical activity screening on a large panel of cell lines, both as single agent and in combination, validation experiments on models and primary cells, proteomics and gene-expression profiling, and comparison with other signaling inhibitors. PQR309 had antilymphoma activity as single agent and in combination with venetoclax, panobinostat, ibrutinib, lenalidomide, ARV-825, marizomib, and rituximab. Sensitivity to PQR309 was associated with specific baseline gene-expression features, such as high expression of transcripts coding for the BCR pathway. Combining proteomics and RNA profiling, we identified the different contribution of PQR309-induced protein phosphorylation and gene expression changes to the drug mechanism of action. Gene-expression signatures induced by PQR309 and by other signaling inhibitors largely overlapped. PQR309 showed activity in cells with primary or secondary resistance to idelalisib. On the basis of these results, PQR309 appeared as a novel and promising compound that is worth developing in the lymphoma setting. .

Phosphoinositide 3-kinase (PI3K) is deregulated in a wide variety of human tumors and triggers activation of protein kinase B (PKB/Akt) and mammalian target of rapamycin (mTOR). Here we describe the preclinical characterization of compound 1 (PQR309, bimiralisib), a potent 4,6-dimorpholino-1,3,5-triazine-based pan-class I PI3K inhibitor, which targets mTOR kinase in a balanced fashion at higher concentrations. No off-target interactions were detected for 1 in a wide panel of protein kinase, enzyme, and receptor ligand assays. Moreover, 1 did not bind tubulin, which was observed for the structurally related 4 (BKM120, buparlisib). Compound 1 is orally available, crosses the blood-brain barrier, and displayed favorable pharmacokinetic parameters in mice, rats, and dogs. Compound 1 demonstrated efficiency in inhibiting proliferation in tumor cell lines and a rat xenograft model. This, together with the compound's safety profile, identifies 1 as a clinical candidate with a broad application range in oncology, including treatment of brain tumors or CNS metastasis. Compound 1 is currently in phase II clinical trials for advanced solid tumors and refractory lymphoma.

BKM120 (Buparlisib) is one of the most advanced phosphoinositide 3-kinase (PI3K) inhibitors for the treatment of cancer, but it interferes as an off-target effect with microtubule polymerization. Here, we developed two chemical derivatives that differ from BKM120 by only one atom. We show that these minute changes separate the dual activity of BKM120 into discrete PI3K and tubulin inhibitors. Analysis of the compounds cellular growth arrest phenotypes and microtubule dynamics suggest that the antiproliferative activity of BKM120 is mainly due to microtubule-dependent cytotoxicity rather than through inhibition of PI3K. Crystal structures of BKM120 and derivatives in complex with tubulin and PI3K provide insights into the selective mode of action of this class of drugs. Our results raise concerns over BKM120's generally accepted mode of action, and provide a unique mechanistic basis for next-generation PI3K inhibitors with improved safety profiles and flexibility for use in combination therapies.

Mechanistic target of rapamycin (mTOR) promotes cell proliferation, growth, and survival and is overactivated in many tumors and central nervous system disorders. PQR620 (3) is a novel, potent, selective, and brain penetrable inhibitor of mTORC1/2 kinase. PQR620 (3) showed excellent selectivity for mTOR over PI3K and protein kinases and efficiently prevented cancer cell growth in a 66 cancer cell line panel. In C57BL/6J and Sprague−Dawley mice, maximum concentration (C max ) in plasma and brain was reached after 30 min, with a half-life (t 1/2 ) > 5 h. In an ovarian carcinoma mouse xenograft model (OVCAR-3), daily dosing of PQR620 (3) inhibited tumor growth significantly. Moreover, PQR620 (3) attenuated epileptic seizures in a tuberous sclerosis complex (TSC) mouse model. In conclusion, PQR620 (3) inhibits mTOR kinase potently and selectively, shows antitumor effects in vitro and in vivo, and promises advantages in CNS indications due to its brain/plasma distribution ratio.

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