Activation of the ERK pathway is a hallmark of cancer, and targeting of upstream signaling partners led to the development of approved drugs. Recently, SCH772984 has been shown to be a selective and ...potent ERK1/2 inhibitor. Here we report the structural mechanism for its remarkable selectivity. In ERK1/2, SCH772984 induces a so-far-unknown binding pocket that accommodates the piperazine-phenyl-pyrimidine decoration. This new binding pocket was created by an inactive conformation of the phosphate-binding loop and an outward tilt of helix αC. In contrast, structure determination of SCH772984 with the off-target haspin and JNK1 revealed two canonical but distinct type I binding modes. Notably, the new binding mode with ERK1/2 was associated with slow binding kinetics in vitro as well as in cell-based assay systems. The described binding mode of SCH772984 with ERK1/2 enables the design of a new type of specific kinase inhibitors with prolonged on-target activity.
G-quadruplex (G4)-forming genomic sequences, including telomeres, represent natural replication fork barriers. Stalled replication forks can be stabilized and restarted by homologous recombination ...(HR), which also repairs DNA double-strand breaks (DSBs) arising at collapsed forks. We have previously shown that HR facilitates telomere replication. Here, we demonstrate that the replication efficiency of guanine-rich (G-rich) telomeric repeats is decreased significantly in cells lacking HR. Treatment with the G4-stabilizing compound pyridostatin (PDS) increases telomere fragility in BRCA2-deficient cells, suggesting that G4 formation drives telomere instability. Remarkably, PDS reduces proliferation of HR-defective cells by inducing DSB accumulation, checkpoint activation, and deregulated G2/M progression and by enhancing the replication defect intrinsic to HR deficiency. PDS toxicity extends to HR-defective cells that have acquired olaparib resistance through loss of 53BP1 or REV7. Altogether, these results highlight the therapeutic potential of G4-stabilizing drugs to selectively eliminate HR-compromised cells and tumors, including those resistant to PARP inhibition.
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•G4 formation on the G-rich strand drives telomere fragility in HR-deficient cells•G4-stabilizing compounds reduce viability of cells lacking BRCA1, BRCA2, or RAD51•G4 toxicity stems from excessive replication stress and DNA damage accumulation•Olaparib-resistant, BRCA-defective cells are sensitive to G4-stabilizing compounds
Zimmer et al. discovered that homologous recombination activities of BRCA1 and BRCA2 facilitate replication of genomic regions with G-quadruplex-forming potential, including telomeres, and suppress genomic instability stemming from inefficient replication of these sites. G4-stabilizing compounds are toxic to BRCA1- and BRCA2-deficient cells, highlighting their therapeutic potential in targeting BRCA deficiency.
In 2018, there were 400,000 new cases of renal cell carcinoma (RCC) globally, with 175,000 deaths attributable to the disease. Three quarters of patients have potentially curable localised disease at ...diagnosis; however, recurrence rates are as high as 40% following surgery. There are currently no adjuvant therapies in routine clinical use which reliably improve outcomes. Effective adjuvant therapy is an urgent unmet need to reduce recurrence risk and improve outcomes. Early efforts explored chemotherapy, radiotherapy, cytokine therapy, hormonal treatments and tumour cell vaccines as adjuvant therapies, however, have yielded disappointing results. More recently, interest shifted to evaluating tyrosine kinase inhibitors (TKIs) in the adjuvant setting, as they improve outcomes in metastatic disease. Five phase III clinical trials testing adjuvant use of a range of TKIs have been performed, with the results of a sixth trial awaited. Unfortunately, these studies have thus far yielded conflicting and disappointing results, and there is currently no strong evidence for routine adjuvant TKI therapy. In parallel, novel immunotherapy treatment approaches have recently been developed, transforming the management of a range of malignancies, particularly through immune checkpoint inhibitors (ICIs). These approaches are well established in the metastatic context in RCC, as well as in the adjuvant treatment of melanoma. On this basis, five phase III trials are currently ongoing to test the efficacy of a range of ICIs in adjuvant RCC patients, with initial results expected over the next few years. In this article, we review the current evidence for adjuvant therapies in RCC, discuss ongoing clinical trials and suggest directions for future work to address this unmet need.
Abstract
BRCA1
or
BRCA2
germline mutations predispose to breast, ovarian and other cancers. High-throughput sequencing of tumour genomes revealed that oncogene amplification and
BRCA1/2
mutations are ...mutually exclusive in cancer, however the molecular mechanism underlying this incompatibility remains unknown. Here, we report that activation of β-catenin, an oncogene of the WNT signalling pathway, inhibits proliferation of BRCA1/2-deficient cells. RNA-seq analyses revealed β-catenin-induced discrete transcriptome alterations in BRCA2-deficient cells, including suppression of
CDKN1A
gene encoding the CDK inhibitor p21. This accelerates G1/S transition, triggering illegitimate origin firing and DNA damage. In addition, β-catenin activation accelerates replication fork progression in BRCA2-deficient cells, which is critically dependent on p21 downregulation. Importantly, we find that upregulated p21 expression is essential for the survival of BRCA2-deficient cells and tumours. Thus, our work demonstrates that β-catenin toxicity in cancer cells with compromised BRCA1/2 function is driven by transcriptional alterations that cause aberrant replication and inflict DNA damage.
Pre-clinically, phosphoinositide 3-kinase (PI3K) inhibition radiosensitises tumours by increasing intrinsic radiosensitivity and by reducing tumour hypoxia. We assessed whether buparlisib, a class 1 ...PI3K inhibitor, can be safely combined with radiotherapy in patients with non-small cell lung carcinoma (NSCLC) and investigated its effect on tumour hypoxia.
This was a 3 + 3 dose escalation and dose expansion phase I trial in patients with advanced NSCLC. Buparlisib dose levels were 50 mg, 80 mg and 100 mg once daily orally for 2 weeks, with palliative thoracic radiotherapy (20 Gy in 5 fractions) delivered during week 2. Tumour hypoxic volume (HV) was measured using 18F-fluoromisonidazole positron-emission tomography–computed tomography at baseline and following 1 week of buparlisib.
Twenty-one patients were recruited with 9 patients evaluable for maximum tolerated dose (MTD) analysis. No dose-limiting toxicity was reported; therefore, 100 mg was declared the MTD, and 10 patients received this dose in the expansion phase. Ninety-four percent of treatment-related adverse events were ≤grade 2 with fatigue (67%), nausea (24%) and decreased appetite (19%) most common per patient. One serious adverse event (grade 3 hypoalbuminaemia) was possibly related to buparlisib. No unexpected radiotherapy toxicity was reported. Ten (67%) of 15 patients evaluable for imaging analysis were responders with 20% median reduction in HV at the MTD.
This is the first clinical trial to combine a PI3K inhibitor with radiotherapy in NSCLC and investigate the effects of PI3K inhibition on tumour hypoxia. This combination was well tolerated and PI3K inhibition reduced hypoxia, warranting investigation into whether this novel class of radiosensitisers can improve radiotherapy outcomes.
•Buparlisib, a phosphoinositide 3-kinase (PI3K) inhibitor, is safe when combined with thoracic radiotherapy.•PI3K inhibition resulted in a rapid reduction in tumour hypoxia in non–small cell lung carcinoma.•This study supports the development of PI3K inhibitors as novel radiosensitisers.
Maintenance of genome integrity requires the functional interplay between Fanconi anemia (FA) and homologous recombination (HR) repair pathways. Endogenous acetaldehyde, a product of cellular ...metabolism, is a potent source of DNA damage, particularly toxic to cells and mice lacking the FA protein FANCD2. Here, we investigate whether HR‐compromised cells are sensitive to acetaldehyde, similarly to FANCD2‐deficient cells. We demonstrate that inactivation of HR factors BRCA1, BRCA2, or RAD51 hypersensitizes cells to acetaldehyde treatment, in spite of the FA pathway being functional. Aldehyde dehydrogenases (ALDHs) play key roles in endogenous acetaldehyde detoxification, and their chemical inhibition leads to cellular acetaldehyde accumulation. We find that disulfiram (Antabuse), an ALDH2 inhibitor in widespread clinical use for the treatment of alcoholism, selectively eliminates BRCA1/2‐deficient cells. Consistently, Aldh2 gene inactivation suppresses proliferation of HR‐deficient mouse embryonic fibroblasts (MEFs) and human fibroblasts. Hypersensitivity of cells lacking BRCA2 to acetaldehyde stems from accumulation of toxic replication‐associated DNA damage, leading to checkpoint activation, G2/M arrest, and cell death. Acetaldehyde‐arrested replication forks require BRCA2 and FANCD2 for protection against MRE11‐dependent degradation. Importantly, acetaldehyde specifically inhibits in vivo the growth of BRCA1/2‐deficient tumors and ex vivo in patient‐derived tumor xenograft cells (PDTCs), including those that are resistant to poly (ADP‐ribose) polymerase (PARP) inhibitors. The work presented here therefore identifies acetaldehyde metabolism as a potential therapeutic target for the selective elimination of BRCA1/2‐deficient cells and tumors.
Synopsis
Treatment with acetaldehyde or with the alcohol‐deterrent disulfiram, which enhances acetaldehyde levels, selectively eliminates BRCA1/2‐deficient cells and tumors. Increasing cellular acetaldehyde might thus benefit cancer patients with BRCA1/2 mutations.
Acetaldehyde and disulfiram increased the levels of RPA foci and decreased replication fork progression, leading to accumulation of replication‐associated DNA damage specifically in BRCA2‐deficient cells.
The Aldh2 gene encodes an aldehyde dehydrogenase with key roles in endogenous acetaldehyde detoxification.
Aldh2 gene deletion or its point mutation E487K associated with the ethanol‐induced flushing syndrome in humans causes proliferation arrest in cells lacking BRCA1/2 expression.
Growth of BRCA1/2‐defective tumors, including those that have acquired resistance to PARP inhibitors, is suppressed by acetaldehyde treatment.
Treatment with acetaldehyde or with the alcohol‐deterrent disulfiram, which enhances acetaldehyde levels, selectively eliminates BRCA1/2‐deficient cells and tumors. Increasing cellular acetaldehyde might thus benefit cancer patients with BRCA1/2 mutations.
Telomeres protect the ends of linear chromosomes against loss of genetic information and inappropriate processing as damaged DNA and are therefore crucial to the maintenance of chromosome integrity. ...In addition to providing a pathway for genome-wide DNA repair, homologous recombination (HR) plays a key role in telomere replication and capping. Consistent with this, the genomic instability characteristic of HR-deficient cells and tumours is driven in part by telomere dysfunction. Here, we discuss the mechanisms by which HR modulates the response to intrinsic cellular challenges that arise during telomere replication, as well as its impact on the assembly of telomere protective structures. How normal and tumour cells differ in their ability to maintain telomeres is deeply relevant to the search for treatments that would selectively eliminate cells whose capacity for HR-mediated repair has been compromised.
Due to compromised homologous recombination (HR) repair, BRCA1‐ and BRCA2‐mutated tumours accumulate DNA damage and genomic rearrangements conducive of tumour progression. To identify drugs that ...target specifically BRCA2‐deficient cells, we screened a chemical library containing compounds in clinical use. The top hit was chlorambucil, a bifunctional alkylating agent used for the treatment of chronic lymphocytic leukaemia (CLL). We establish that chlorambucil is specifically toxic to BRCA1/2‐deficient cells, including olaparib‐resistant and cisplatin‐resistant ones, suggesting the potential clinical use of chlorambucil against disease which has become resistant to these drugs. Additionally, chlorambucil eradicates BRCA2‐deficient xenografts and inhibits growth of olaparib‐resistant patient‐derived tumour xenografts (PDTXs). We demonstrate that chlorambucil inflicts replication‐associated DNA double‐strand breaks (DSBs), similarly to cisplatin, and we identify ATR, FANCD2 and the SNM1A nuclease as determinants of sensitivity to both drugs. Importantly, chlorambucil is substantially less toxic to normal cells and tissues in vitro and in vivo relative to cisplatin. Because chlorambucil and cisplatin are equally effective inhibitors of BRCA2‐compromised tumours, our results indicate that chlorambucil has a higher therapeutic index than cisplatin in targeting BRCA‐deficient tumours.
Synopsis
BRCA1/2‐deficient tumours accumulate DNA damage and genomic rearrangements conducive for tumour progression, which is exploited in the clinic by targeted therapies against the BRCA1/2‐mutated tumour subset. Chlorambucil is identified as the most effective drug in eliminating BRCA2‐deficient cells.
The bi‐functional alkylator chlorambucil was specifically toxic to BRCA1/2‐deficient cells and tumours, but not to wild type controls.
Chlorambucil effectively eliminated cisplatin‐resistant and olaparib‐resistant BRCA1/2‐deficient cells and tumours.
Mechanistically, chlorambucil toxicity is mediated by accumulation of replication‐associated DNA damage, similarly to cisplatin.
ATR, FANCD2 and SNM1A nuclease are determinants of cellular sensitivity to both drugs.
Chlorambucil is substantially less toxic to normal cells and tissues than cisplatin.
BRCA1/2‐deficient tumours accumulate DNA damage and genomic rearrangements conducive for tumour progression, which is exploited in the clinic by targeted therapies against the BRCA1/2‐mutated tumour subset. Chlorambucil is identified as the most effective drug in eliminating BRCA2‐deficient cells.
Due to compromised homologous recombination (HR) repair, BRCA1‐ and BRCA2‐mutated tumours accumulate DNA damage and genomic rearrangements conducive of tumour progression. To identify drugs that ...target specifically BRCA2‐deficient cells, we screened a chemical library containing compounds in clinical use. The top hit was chlorambucil, a bifunctional alkylating agent used for the treatment of chronic lymphocytic leukaemia (CLL). We establish that chlorambucil is specifically toxic to BRCA1/2‐deficient cells, including olaparib‐resistant and cisplatin‐resistant ones, suggesting the potential clinical use of chlorambucil against disease which has become resistant to these drugs. Additionally, chlorambucil eradicates BRCA2‐deficient xenografts and inhibits growth of olaparib‐resistant patient‐derived tumour xenografts (PDTXs). We demonstrate that chlorambucil inflicts replication‐associated DNA double‐strand breaks (DSBs), similarly to cisplatin, and we identify ATR, FANCD2 and the SNM1A nuclease as determinants of sensitivity to both drugs. Importantly, chlorambucil is substantially less toxic to normal cells and tissues in vitro and in vivo relative to cisplatin. Because chlorambucil and cisplatin are equally effective inhibitors of BRCA2‐compromised tumours, our results indicate that chlorambucil has a higher therapeutic index than cisplatin in targeting BRCA‐deficient tumours.
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