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. .

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The cytotoxic activity of ecteinascidin 743 (ET-743), a natural product derived from the marine tunicate Ecteinascidia turbinata that exhibits potent anti-tumor activity in pre-clinical systems and promising activity in phase I and II clinical trials, was investigated in a number of cell systems with well-defined deficiencies in DNA-repair mechanisms. ET-743 binds to N2 of guanine in the minor groove, but its activity does not appear to be related to DNA-topoisomerase I poisoning as the drug is equally active in wild-type yeast and in yeast with a deletion in the DNA-topoisomerase I gene. Defects in the mismatch repair pathway, usually associated with increased resistance to methylating agents and cisplatin, did not affect the cytotoxic activity of ET-743. However, ET-743 did show decreased activity (from 2-to 8-fold) in nucleotide excision repair ( Ecteinascidin 743 (ET-743) is a natural product derived from the marine tunicate Ecteinascidia turbinata, selected for its significant anti-tumor activity in different in vitro and in vivo models. [1][2][3] Currently, ET-743 is undergoing phase II clinical trials after having shown activity in phase I clinical studies with responses observed in different human tumors, including soft tissue sarcoma, osteosarcoma, melanoma and breast cancer. 4,5 The mechanism of action of ET-743 has yet to be fully defined, but DNA appears to be the primary target. Indeed, it has been shown to bind in the minor groove of DNA and to alkylate the N2 position of guanine with some degree of specificity. 6,7 Such ET-743 minor-groove alkylation induces a bend in the DNA helix toward the major groove, a finding not common to the other minor groove-alkylating agents, which bend DNA into the minor groove. 8 No single-strand breaks, double-strand breaks or DNAprotein cross-links could be found by alkaline elution in cells exposed to IC 50 concentrations of ET-743. 9 However, Takebayashi et al. 10 showed that ET-743 was able to induce DNA-topoisomerase I cross-linking but that high concentrations were required to produce the effect.To provide some insight into the mechanism of action of ET-743, we have evaluated its cytotoxic activity using a panel of different cellular systems characterized by well-defined deficiencies in different mammalian repair pathways. Our data indicate that ET-743 has a unique mechanism of interaction with DNA. MATERIAL AND METHODS Cells and drugsYeast strains and the isogenic derivatives CY2823 (⌬rad52) and CY2278 (⌬topI) (kindly provided by Dr. M. Lopes, Instituto F.I.R.C. di Oncologia Molecolare, Milan, Italy) were grown in YPD plates (1% yeast extract, 2% bacto-peptone, 2% glucose) with or without the drugs.The Chinese hamster ovary (CHO) parental cell line CHO-AA8 and the UV-sensitive DNA repair-deficient mutant cell lines CHO-UV23, CHO-UV61 and CHO-UV96 (hereafter named UV23, UV61 and UV96) 11 were kindly provided by Dr. M. Stefanini (CNR IGBE, Pavia, Italy). The UV96 cell line was transfected by the calcium phosphate technique using 10 g of a CMV-ERCC1 plasmid enc...

Mammalian Chk1 and Chk2 protein kinases are two important components of the G 2 DNA damage checkpoint. They are activated by upstream kinases (ataxia telangectasia mutated gene and ATM and Rad 3 related gene) and interfere with the activity of the cdc2/cyclinB1 complex, necessary for the G 2-M transition, through the inactivation of the cdc25 phosphatases (cdc25A and cdc25C). To understand the role of Chk1 and Chk2 in the cellular response to different anticancer agents, we knocked down the expression of each protein or simultaneously of both proteins by using the small interfering RNA technique in the HCT-116 colon carcinoma cell line and in its isogenic systems in which p53 and p21 have been inactivated by targeted homologous recombination. We here show that inhibition of Chk1 but not of Chk2 in p21-/and p53-/cells caused a greater abrogation of G 2 block induced by ionizing radiation and cis-diamine-dichloroplatinum treatments and a greater sensitization to the same treatments than in the parental cell line with p53 and p21 wild type proteins. These data further emphasise the role of Chk1 as a molecular target to inhibit in tumors with a defect in the G 1 checkpoint with the aim of increasing the selectivity and specificity of anticancer drug treatments.

Mantle cell lymphoma (MCL) is an aggressive, incurable disease, characterized by a deregulated cell cycle. Chk1 and Wee1 are main regulators of cell cycle progression and recent data on solid tumors suggest that simultaneous inhibition of these proteins has a strong synergistic cytotoxic effect. The effects of a Chk1 inhibitor (PF-00477736) and a Wee1 inhibitor (MK-1775) have been herein investigated in a large panel of mature B-cell lymphoma cell lines. We found that MCL cells were the most sensitive to the Chk1 inhibitor PF-00477736 and Wee1 inhibitor MK-1775 as single agents. Possible involvement of the translocation t(11;14) in Chk1 inhibitor sensitivity was hypothesized. The combined inhibition of Chk1 and Wee1 was strongly synergistic in MCL cells, leading to deregulation of the cell cycle, with increased activity of CDK2 and CDK1, and activation of apoptosis. In vivo treatment with the drug combination of mice bearing JeKo-1 xenografts (MCL) had a marked antitumor effect with tumor regressions observed at non-toxic doses (best T/C%=0.54%). Gene expression profiling suggested effect on genes involved in apoptosis. The strong synergism observed by combining Chk1 and Wee1 inhibitors in preclinical models of MCL provides the rationale for testing this combination in the clinical setting.

Posttranslational modifications of p53 induced by two widely used anticancer agents, cisplatinum (DDP) and taxol were investigated in two human cancer cell lines. Although both drugs were able to induce phosphorylation at serine 20 (Ser20), only DDP treatment induced p53 phosphorylation at serine 15 (Ser15). Moreover, both drug treatments were able to increase p53 levels and consequently the transcription of waf1 and mdm-2 genes, although DDP treatment resulted in a stronger inducer of both genes. Using two ataxia telangiectasia mutated (ATM) cell lines, the role of ATM in drug-induced p53 phosphorylations was investigated. No differences in drug-induced p53 phosphorylation could be observed, indicating that ATM is not the kinase involved in these phosphorylation events. In addition, inhibition of DNA-dependent protein kinase activity by wortmannin did not abolish p53 phosphorylation at Ser15 and Ser20, again indicating that DNA-PK is unlikely to be the kinase involved. After both taxol and DDP treatments, an activation of hCHK2 was found and this is likely to be responsible for phosphorylation at Ser20. In contrast, only DDP was able to activate ATR, which is the candidate kinase for phosphorylation of Ser15 by this drug. This data clearly suggests that differential mechanisms are involved in phosphorylation and activation of p53 depending on the drug type.

The checkpoint kinase 1 (Chk1) is one of the major players in the signal transduction pathway set in motion in response to DNA damage which activates different cell cycle checkpoints including the G 1/S, the intra-S, G 2-M and the mitotic spindle checkpoint, contributing to the maintenance of genomic stability. Chk1 is considered a good molecular target to inhibit, in combination with other anticancer agents, to increase the sensitivity of treatment, especially in tumors with a defective G 1 checkpoint. Experimental evidence highlights the essential role of Chk1 in normal and cancer cells even under unstressed conditions, especially in controlling DNA replication and cell division. This review looks at the main functions of Chk1 and the data on Chk1 inhibitors at their preclinical and clinical development are reported. This information may suggest novel approaches for new treatments with Chk1 inhibitors in combination with anticancer agents or as single agents. The emergent synthetic lethality approach may help define the genetic background features where Chk1 inhibitors alone could be very effective.