Lead compound profiling for small molecule inhibitors of the REV1-CT/RIR Translesion synthesis Protein-Protein interaction

Translesion synthesis (TLS) is a cellular mechanism through which actively replicating cells recruit specialized, low-fidelity DNA polymerases to damaged DNA to allow for replication past these lesions. REV1 is one of these TLS DNA polymerases that functions primarily as a scaffolding protein to organize the TLS heteroprotein complex and ensure replication occurs in the presence of DNA lesions. The C-Terminal domain of REV1 (REV1-CT) forms many protein-protein interactions (PPIs) with other TLS polymerases, making it essential for TLS function and a promising drug target for anti-cancer drug development. We utilized several lead identification strategies to identify various small molecules capable of disrupting the PPI between REV1-CT and the REV1 Interacting Regions (RIR) present in several other TLS polymerases. These lead compounds were profiled in several in vitro potency and PK assays to identify two scaffolds (1 and 6) as the most promising for further development. Both 1 and 6 synergized with cisplatin in a REV1-dependent fashion and demonstrated promising in vivo PK and toxicity profiles.

FANCJ promotes PARP1 activity during DNA replication that is essential in BRCA1 deficient cells

The effectiveness of poly (ADP-ribose) polymerase inhibitors (PARPi) in creating single-stranded DNA gaps and inducing sensitivity requires the FANCJ DNA helicase. Yet, how FANCJ relates to PARP1 inhibition or trapping, which contribute to PARPi toxicity, remains unclear. Here, we find PARPi effectiveness hinges on S-phase PARP1 activity, which is reduced in FANCJ deficient cells as G-quadruplexes sequester PARP1 and MSH2. Additionally, loss of the FANCJ-MLH1 interaction diminishes PARP1 activity; however, depleting MSH2 reinstates PARPi sensitivity and gaps. Indicating sequestered and trapped PARP1 are distinct, FANCJ loss increases PARPi resistance in cells susceptible to PARP1 trapping. However, with BRCA1 deficiency, the loss of FANCJ mirrors PARP1 loss or inhibition, with the detrimental commonality being loss of S-phase PARP1 activity. These insights underline the crucial role of PARP1 activity during DNA replication in BRCA1 deficient cells and emphasize the importance of understanding drug mechanisms for enhancing therapeutic response.

FANCJ promotes PARP1 activity during DNA replication that is essential in BRCA1 deficient cells

Single-stranded DNA gaps are postulated to be fundamental to the mechanism of anti-cancer drugs. Gaining insights into their induction could therefore be pivotal for advancing therapeutic strategies. For poly (ADP-ribose) polymerase inhibitors (PARPi) to be effective, the presence of FANCJ helicase is required. However, the relationship between FANCJ dependent gaps and PARP1 catalytic inhibition or trapping-both linked to PARPi toxicity in BRCA deficient cells-is yet to be elucidated. Here, we find that the efficacy of PARPi is contingent on S-phase PARP1 activity, which is compromised in FANCJ deficient cells because PARP1, along with MSH2, is "sequestered" by G-quadruplexes. PARP1's replication activity is also diminished in cells missing a FANCJ-MLH1 interaction, but in such cells, depleting MSH2 can release sequestered PARP1, restoring PARPi-induced gaps and sensitivity. Our observations indicate that sequestered and trapped PARP1 are different chromatin-bound forms, with FANCJ loss increasing PARPi resistance in cells susceptible to canonical PARP1 trapping. However, in BRCA1 null cells, the loss of FANCJ mirrors the effects of PARP1 loss or inhibition, with the common detrimental factor being the loss of PARP1 activity during DNA replication, not trapping. These insights underline the crucial role of PARP1 activity during DNA replication in BRCA deficient cells and emphasize the importance of understanding drug mechanisms for enhancing precision medicine.

Exploiting replication gaps for cancer therapy

Defects in DNA double-strand break repair are thought to render BRCA1 or BRCA2 (BRCA) mutant tumors selectively sensitive to PARP inhibitors (PARPis). Challenging this framework, BRCA and PARP1 share functions in DNA synthesis on the lagging strand. Thus, BRCA deficiency or "BRCAness" could reflect an inherent lagging strand problem that is vulnerable to drugs such as PARPi that also target the lagging strand, a combination that generates a toxic accumulation of replication gaps.

Replication gaps are a key determinant of PARP inhibitor synthetic lethality with BRCA deficiency

Mutations in BRCA1 or BRCA2 (BRCA) is synthetic lethal with poly(ADP-ribose) polymerase inhibitors (PARPi). Lethality is thought to derive from DNA double-stranded breaks (DSBs) necessitating BRCA function in homologous recombination (HR) and/or fork protection (FP). Here, we report instead that toxicity derives from replication gaps. BRCA1- or FANCJ-deficient cells, with common repair defects but distinct PARPi responses, reveal gaps as a distinguishing factor. We further uncouple HR, FP, and fork speed from PARPi response. Instead, gaps characterize BRCA-deficient cells, are diminished upon resistance, restored upon resensitization, and, when exposed, augment PARPi toxicity. Unchallenged BRCA1-deficient cells have elevated poly(ADP-ribose) and chromatin-associated PARP1, but aberrantly low XRCC1 consistent with defects in backup Okazaki fragment processing (OFP). 53BP1 loss resuscitates OFP by restoring XRCC1-LIG3 that suppresses the sensitivity of BRCA1-deficient cells to drugs targeting OFP or generating gaps. We highlight gaps as a determinant of PARPi toxicity changing the paradigm for synthetic lethal interactions.

Abstract IA-026: Gaps alone kill BRCA deficient cancer cells

Defects in DNA repair and/or the protection of stalled DNA replication forks are thought to underlie the chemosensitivity of tumors deficient in the hereditary breast cancer genes, BRCA1 and BRCA2 (BRCA). Challenging this assumption, recent findings indicate that chemotherapies such as cisplatin used to treat BRCA-deficient tumors do not initially cause DNA double-strand-breaks (DSBs). Here, we show that single stranded DNA (ssDNA) replication gaps underlie the hypersensitivity of BRCA-deficient cancer, and we propose that defects in homologous recombination (HR) or fork protection (FP) do not. Specifically, in BRCA-deficient cells, ssDNA gaps develop because replication is not effectively restrained in response to stress. Gap suppression by either restoration of fork restraint or gap filling confers therapy resistance in tissue culture and BRCA patient tumors. In contrast, restored FP and HR can be uncoupled from therapy resistance when gaps are present. Moreover, we find that DSBs are not detected after therapy when apoptosis is inhibited, supporting a framework in which DSBs are not directly induced by genotoxic agents, but rather from cell death nucleases. Together, this data indicate that ssDNA replication gaps underlie the BRCA cancer phenotype, “BRCAness,” and we propose are fundamental to the mechanism-of-action of genotoxic chemotherapies.

Citation Format: Sharon B. Cantor, Nicholas Panzarino. Gaps alone kill BRCA deficient cancer cells [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr IA-026.

Comprehensive Mutational Analysis of the BRCA1-Associated DNA Helicase and Tumor-Suppressor FANCJ/BACH1/BRIP1

FANCJ (BRIP1/BACH1) is a hereditary breast and ovarian cancer (HBOC) gene encoding a DNA helicase. Similar to HBOC genes, BRCA1 and BRCA2, FANCJ is critical for processing DNA inter-strand crosslinks (ICL) induced by chemotherapeutics, such as cisplatin. Consequently, cells deficient in FANCJ or its catalytic activity are sensitive to ICL-inducing agents. Unfortunately, the majority of FANCJ clinical mutations remain uncharacterized, limiting therapeutic opportunities to effectively use cisplatin to treat tumors with mutated FANCJ. Here, we sought to perform a comprehensive screen to identify FANCJ loss-of-function (LOF) mutations. We developed a FANCJ lentivirus mutation library representing approximately 450 patient-derived FANCJ nonsense and missense mutations to introduce FANCJ mutants into FANCJ knockout (K/O) HeLa cells. We performed a high-throughput screen to identify FANCJ LOF mutants that, as compared with wild-type FANCJ, fail to robustly restore resistance to ICL-inducing agents, cisplatin or mitomycin C (MMC). On the basis of the failure to confer resistance to either cisplatin or MMC, we identified 26 missense and 25 nonsense LOF mutations. Nonsense mutations elucidated a relationship between location of truncation and ICL sensitivity, as the majority of nonsense mutations before amino acid 860 confer ICL sensitivity. Further validation of a subset of LOF mutations confirmed the ability of the screen to identify FANCJ mutations unable to confer ICL resistance. Finally, mapping the location of LOF mutations to a new homology model provides additional functional information. IMPLICATIONS: We identify 51 FANCJ LOF mutations, providing important classification of FANCJ mutations that will afford additional therapeutic strategies for affected patients.

Targeting translesion synthesis (TLS) to expose replication gaps, a unique cancer vulnerability

Introduction: Translesion synthesis (TLS) is a DNA damage tolerance (DDT) mechanism that employs error-prone polymerases to bypass replication blocking DNA lesions, contributing to a gain in mutagenesis and chemo-resistance. However, recent findings illustrate an emerging role for TLS in replication gap suppression (RGS), distinct from its role in post-replication gap filling. Here, TLS protects cells from replication stress (RS)-induced toxic single-stranded DNA (ssDNA) gaps that accumulate in the wake of active replication. Intriguingly, TLS-mediated RGS is specifically observed in several cancer cell lines and contributes to their survival. Thus, targeting TLS has the potential to uniquely eradicate tumors without harming non-cancer tissues. Areas Covered: This review provides an innovative perspective on the role of TLS beyond its canonical function of lesion bypass or post-replicative gap filling. We provide a comprehensive analysis that underscores the emerging role of TLS as a cancer adaptation necessary to overcome the replication stress response (RSR), an anti-cancer barrier. Expert Opinion: TLS RGS is critical for tumorigenesis and is a new hallmark of cancer. Although the exact mechanism and extent of TLS dependency in cancer is still emerging, TLS inhibitors have shown promise as an anti-cancer therapy in selectively targeting this unique cancer vulnerability.

Replication Gaps Underlie BRCA Deficiency and Therapy Response

Defects in DNA repair and the protection of stalled DNA replication forks are thought to underlie the chemosensitivity of tumors deficient in the hereditary breast cancer genes BRCA1 and BRCA2 (BRCA). Challenging this assumption are recent findings that indicate chemotherapies, such as cisplatin used to treat BRCA-deficient tumors, do not initially cause DNA double-strand breaks (DSB). Here, we show that ssDNA replication gaps underlie the hypersensitivity of BRCA-deficient cancer and that defects in homologous recombination (HR) or fork protection (FP) do not. In BRCA-deficient cells, ssDNA gaps developed because replication was not effectively restrained in response to stress. Gap suppression by either restoration of fork restraint or gap filling conferred therapy resistance in tissue culture and BRCA patient tumors. In contrast, restored FP and HR could be uncoupled from therapy resistance when gaps were present. Moreover, DSBs were not detected after therapy when apoptosis was inhibited, supporting a framework in which DSBs are not directly induced by genotoxic agents, but rather are induced from cell death nucleases and are not fundamental to the mechanism of action of genotoxic agents. Together, these data indicate that ssDNA replication gaps underlie the BRCA cancer phenotype, "BRCAness," and we propose they are fundamental to the mechanism of action of genotoxic chemotherapies. SIGNIFICANCE: This study suggests that ssDNA replication gaps are fundamental to the toxicity of genotoxic agents and underlie the BRCA-cancer phenotype "BRCAness," yielding promising biomarkers, targets, and opportunities to resensitize refractory disease.See related commentary by Canman, p. 1214.

FANCJ compensates for RAP80 deficiency and suppresses genomic instability induced by interstrand cross-links

FANCJ, a DNA helicase and interacting partner of the tumor suppressor BRCA1, is crucial for the repair of DNA interstrand crosslinks (ICL), a highly toxic lesion that leads to chromosomal instability and perturbs normal transcription. In diploid cells, FANCJ is believed to operate in homologous recombination (HR) repair of DNA double-strand breaks (DSB); however, its precise role and molecular mechanism is poorly understood. Moreover, compensatory mechanisms of ICL resistance when FANCJ is deficient have not been explored. In this work, we conducted a siRNA screen to identify genes of the DNA damage response/DNA repair regime that when acutely depleted sensitize FANCJ CRISPR knockout cells to a low concentration of the DNA cross-linking agent mitomycin C (MMC). One of the top hits from the screen was RAP80, a protein that recruits repair machinery to broken DNA ends and regulates DNA end-processing. Concomitant loss of FANCJ and RAP80 not only accentuates DNA damage levels in human cells but also adversely affects the cell cycle checkpoint, resulting in profound chromosomal instability. Genetic complementation experiments demonstrated that both FANCJ's catalytic activity and interaction with BRCA1 are important for ICL resistance when RAP80 is deficient. The elevated RPA and RAD51 foci in cells co-deficient of FANCJ and RAP80 exposed to MMC are attributed to single-stranded DNA created by Mre11 and CtIP nucleases. Altogether, our cell-based findings together with biochemical studies suggest a critical function of FANCJ to suppress incompletely processed and toxic joint DNA molecules during repair of ICL-induced DNA damage.

Inhibition of the translesion synthesis polymerase REV1 exploits replication gaps as a cancer vulnerability

The replication stress response, which serves as an anticancer barrier, is activated not only by DNA damage and replication obstacles but also oncogenes, thus obscuring how cancer evolves. Here, we identify that oncogene expression, similar to other replication stress-inducing agents, induces single-stranded DNA (ssDNA) gaps that reduce cell fitness. DNA fiber analysis and electron microscopy reveal that activation of translesion synthesis (TLS) polymerases restricts replication fork slowing, reversal, and fork degradation without inducing replication gaps despite the continuation of replication during stress. Consistent with gap suppression (GS) being fundamental to cancer, we demonstrate that a small-molecule inhibitor targeting the TLS factor REV1 not only disrupts DNA replication and cancer cell fitness but also synergizes with gap-inducing therapies such as inhibitors of ATR or Wee1. Our work illuminates that GS during replication is critical for cancer cell fitness and therefore a targetable vulnerability.

Opposing Roles of FANCJ and HLTF Protect Forks and Restrain Replication during Stress

The DNA helicase FANCJ is mutated in hereditary breast and ovarian cancer and Fanconi anemia (FA). Nevertheless, how loss of FANCJ translates to disease pathogenesis remains unclear. We addressed this question by analyzing proteins associated with replication forks in cells with or without FANCJ. We demonstrate that FANCJ-knockout (FANCJ-KO) cells have alterations in the replisome that are consistent with enhanced replication stress, including an aberrant accumulation of the fork remodeling factor helicase-like transcription factor (HLTF). Correspondingly, HLTF contributes to fork degradation in FANCJ-KO cells. Unexpectedly, the unrestrained DNA synthesis that characterizes HLTF-deficient cells is FANCJ dependent and correlates with S1 nuclease sensitivity and fork degradation. These results suggest that FANCJ and HLTF promote replication fork integrity, in part by counteracting each other to keep fork remodeling and elongation in check. Indicating one protein compensates for loss of the other, loss of both HLTF and FANCJ causes a more severe replication stress response.

Fork Protection and Therapy Resistance in Hereditary Breast Cancer

The BRCA-Fanconi anemia (FA) pathway preserves the genome and suppresses cancer and is a main determinant of chemotherapeutic efficacy. The hereditary breast cancer genes BRCA1 and BRCA2 function in DNA double-strand break repair mediating distinct steps of homologous recombination (HR). More recently, independent of DNA repair, functions in the replication stress response have come to light, providing insight as to how the BRCA-FA pathway also balances genome preservation with proliferation. The BRCA-FA proteins associate with the replisome and contribute to the efficiency and recovery of replication following perturbations that slow or arrest DNA replication. Although the full repertoire of functions in the replication stress response remains to be elucidated, the function of BRCA1 and BRCA2 in protecting stalled replication forks contributes along with HR to the sensitivity of BRCA-associated tumors to chemotherapy. Moreover, chemoresistance evolves from restoration of either HR and/or fork protection. Although mechanisms underlying the restoration of HR have been characterized, it remains less clear how restoration of fork protection is achieved. Here, we outline mechanisms of “rewired” fork protection and chemotherapy resistance in BRCA cancer. We propose that mechanisms are linked to permissive replication that limits fork remodeling and therefore opportunities for fork degradation. Combating this chemoresistance mechanism will require drugs that inactivate replication bypass mechanisms.

Replication fork stability confers chemoresistance in BRCA-deficient cells

Brca1- and Brca2-deficient cells have reduced capacity to repair DNA double-strand breaks (DSBs) by homologous recombination (HR) and consequently are hypersensitive to DNA damaging agents, including cisplatin and poly(ADP-ribose) polymerase (PARP) inhibitors. Here we show that loss of the MLL3/4 complex protein, PTIP, protects Brca1/2-deficient cells from DNA damage and rescues the lethality of Brca2-deficient embryonic stem cells. However, PTIP deficiency does not restore HR activity at DSBs. Instead, its absence inhibits the recruitment of the MRE11 nuclease to stalled replication forks, which in turn protects nascent DNA strands from extensive degradation. More generally, acquisition of PARPi and cisplatin resistance is associated with replication fork (RF) protection in Brca2-deficient tumor cells that do not develop Brca2 reversion mutations. Disruption of multiple proteins, including PARP1 and CHD4, leads to the same end point of RF protection, highlighting the complexities by which tumor cells evade chemotherapeutic interventions and acquire drug resistance.

What is wrong with Fanconi anemia cells?

Figuring out what is wrong in Fanconi anemia (FA) patient cells is critical to understanding the contributions of the FA pathway to DNA repair and tumor suppression. Although FA patients exhibit a wide range of disease manifestation as well as severity (asymptomatic to congenital abnormalities, bone marrow failure, and cancer), cells from FA patients share underlying defects in their ability to process DNA lesions that interfere with DNA replication. In particular, FA cells are very sensitive to agents that induce DNA interstrand crosslinks (ICLs). The cause of this pronounced ICL sensitivity is not fully understood, but has been linked to the aberrant activation of DNA damage repair proteins, checkpoints and pathways. Thus, regulation of these responses through coordination of repair processing at stalled replication forks is an essential function of the FA pathway. Here, we briefly summarize some of the aberrant DNA damage responses contributing to defects in FA cells, and detail the newly-identified relationship between FA and the mismatch repair protein, MSH2. Understanding the contribution of MSH2 and/or other proteins to the replication problem in FA cells will be key to assessing therapeutic options to improve the health of FA patients. Moreover, loss of these factors, if linked to improved replication, could be a key event in the progression of FA cells to cancer cells. Likewise, loss of these factors could synergize to enhance tumorigenesis or confer chemoresistance in tumors defective in FA-BRCA pathway proteins and provide a basis for biomarkers for disease progression and response.

Economic evaluation of DNA ploidy analysis vs liquid-based cytology for cervical screening

Background:

DNA ploidy analysis involves automated quantification of chromosomal aneuploidy, a potential marker of progression toward cervical carcinoma. We evaluated the cost-effectiveness of this method for cervical screening, comparing five ploidy strategies (using different numbers of aneuploid cells as cut points) with liquid-based Papanicolaou smear and no screening.

Methods:

A state-transition Markov model simulated the natural history of HPV infection and possible progression into cervical neoplasia in a cohort of 12-year-old females. The analysis evaluated cost in 2012 US$ and effectiveness in quality-adjusted life-years (QALYs) from a health-system perspective throughout a lifetime horizon in the US setting. We calculated incremental cost-effectiveness ratios (ICERs) to determine the best strategy. The robustness of optimal choices was examined in deterministic and probabilistic sensitivity analyses.

Results:

In the base-case analysis, the ploidy 4 cell strategy was cost-effective, yielding an increase of 0.032 QALY and an ICER of $18 264/QALY compared to no screening. For most scenarios in the deterministic sensitivity analysis, the ploidy 4 cell strategy was the only cost-effective strategy. Cost-effectiveness acceptability curves showed that this strategy was more likely to be cost-effective than the Papanicolaou smear.

Conclusion:

Compared to the liquid-based Papanicolaou smear, screening with a DNA ploidy strategy appeared less costly and comparably effective.

Resistance to therapy in BRCA2 mutant cells due to loss of the nucleosome remodeling factor CHD4

BRCA-associated cancers are sensitive to DNA-damaging agents such as cisplatin, but the efficacy of cisplatin is limited by the development of resistance. Guillemette et al. performed a genome-wide short hairpin (shRNA) screen and found that loss of the nucleosome remodeling factor CHD4 conferred cisplatin resistance. Cisplatin-resistant clones lacking genetic reversion of BRCA2 show de novo loss of CHD4 expression in vitro. BRCA2 mutant ovarian cancers with reduced CHD4 expression correlate with shorter progression-free survival and shorter overall survival.

Hereditary cancers derive from gene defects that often compromise DNA repair. Thus, BRCA-associated cancers are sensitive to DNA-damaging agents such as cisplatin. The efficacy of cisplatin is limited, however, by the development of resistance. One cisplatin resistance mechanism is restoration of homologous recombination (HR), which can result from BRCA reversion mutations. However, in BRCA2 mutant cancers, cisplatin resistance can occur independently of restored HR by a mechanism that remains unknown. Here we performed a genome-wide shRNA screen and found that loss of the nucleosome remodeling factor CHD4 confers cisplatin resistance. Restoration of cisplatin resistance is independent of HR but correlates with restored cell cycle progression, reduced chromosomal aberrations, and enhanced DNA damage tolerance. Suggesting clinical relevance, cisplatin-resistant clones lacking genetic reversion of BRCA2 show de novo loss of CHD4 expression in vitro. Moreover, BRCA2 mutant ovarian cancers with reduced CHD4 expression significantly correlate with shorter progression-free survival and shorter overall survival. Collectively, our findings indicate that CHD4 modulates therapeutic response in BRCA2 mutant cancer cells.

Molecular and cellular functions of the FANCJ DNA helicase defective in cancer and in Fanconi anemia

The FANCJ DNA helicase is mutated in hereditary breast and ovarian cancer as well as the progressive bone marrow failure disorder Fanconi anemia (FA). FANCJ is linked to cancer suppression and DNA double strand break repair through its direct interaction with the hereditary breast cancer associated gene product, BRCA1. FANCJ also operates in the FA pathway of interstrand cross-link repair and contributes to homologous recombination. FANCJ collaborates with a number of DNA metabolizing proteins implicated in DNA damage detection and repair, and plays an important role in cell cycle checkpoint control. In addition to its role in the classical FA pathway, FANCJ is believed to have other functions that are centered on alleviating replication stress. FANCJ resolves G-quadruplex (G4) DNA structures that are known to affect cellular replication and transcription, and potentially play a role in the preservation and functionality of chromosomal structures such as telomeres. Recent studies suggest that FANCJ helps to maintain chromatin structure and preserve epigenetic stability by facilitating smooth progression of the replication fork when it encounters DNA damage or an alternate DNA structure such as a G4. Ongoing studies suggest a prominent but still not well-understood role of FANCJ in transcriptional regulation, chromosomal structure and function, and DNA damage repair to maintain genomic stability. This review will synthesize our current understanding of the molecular and cellular functions of FANCJ that are critical for chromosomal integrity.

Crosstalk between BRCA-Fanconi anemia and mismatch repair pathways prevents MSH2-dependent aberrant DNA damage responses

Several proteins in the BRCA-Fanconi anemia (FA) pathway, such as FANCJ, BRCA1, and FANCD2, interact with mismatch repair (MMR) pathway factors, but the significance of this link remains unknown. Unlike the BRCA-FA pathway, the MMR pathway is not essential for cells to survive toxic DNA interstrand crosslinks (ICLs), although MMR proteins bind ICLs and other DNA structures that form at stalled replication forks. We hypothesized that MMR proteins corrupt ICL repair in cells that lack crosstalk between BRCA-FA and MMR pathways. Here, we show that ICL sensitivity of cells lacking the interaction between FANCJ and the MMR protein MLH1 is suppressed by depletion of the upstream mismatch recognition factor MSH2. MSH2 depletion suppresses an aberrant DNA damage response, restores cell cycle progression, and promotes ICL resistance through a Rad18-dependent mechanism. MSH2 depletion also suppresses ICL sensitivity in cells deficient for BRCA1 or FANCD2, but not FANCA. Rescue by Msh2 loss was confirmed in Fancd2-null primary mouse cells. Thus, we propose that regulation of MSH2-dependent DNA damage response underlies the importance of interactions between BRCA-FA and MMR pathways.

FANCJ localization by mismatch repair is vital to maintain genomic integrity after UV irradiation

Nucleotide excision repair (NER) is critical for the repair of DNA lesions induced by UV radiation, but its contribution in replicating cells is less clear. Here, we show that dual incision by NER endonucleases, including XPF and XPG, promotes the S-phase accumulation of the BRCA1 and Fanconi anemia-associated DNA helicase FANCJ to sites of UV-induced damage. FANCJ promotes replication protein A phosphorylation and the arrest of DNA synthesis following UV irradiation. Interaction defective mutants of FANCJ reveal that BRCA1 binding is not required for FANCJ localization, whereas interaction with the mismatch repair (MMR) protein MLH1 is essential. Correspondingly, we find that FANCJ, its direct interaction with MLH1, and the MMR protein MSH2 function in a common pathway in response to UV irradiation. FANCJ-deficient cells are not sensitive to killing by UV irradiation, yet we find that DNA mutations are significantly enhanced. Thus, we considered that FANCJ deficiency could be associated with skin cancer. Along these lines, in melanoma we found several somatic mutations in FANCJ, some of which were previously identified in hereditary breast cancer and Fanconi anemia. Given that, mutations in XPF can also lead to Fanconi anemia, we propose collaborations between Fanconi anemia, NER, and MMR are necessary to initiate checkpoint activation in replicating human cells to limit genomic instability.

Fanconi anemia group J helicase and MRE11 nuclease interact to facilitate the DNA damage response

FANCJ mutations are linked to Fanconi anemia (FA) and increase breast cancer risk. FANCJ encodes a DNA helicase implicated in homologous recombination (HR) repair of double-strand breaks (DSBs) and interstrand cross-links (ICLs), but its mechanism of action is not well understood. Here we show with live-cell imaging that FANCJ recruitment to laser-induced DSBs but not psoralen-induced ICLs is dependent on nuclease-active MRE11. FANCJ interacts directly with MRE11 and inhibits its exonuclease activity in a specific manner, suggesting that FANCJ regulates the MRE11 nuclease to facilitate DSB processing and appropriate end resection. Cells deficient in FANCJ and MRE11 show increased ionizing radiation (IR) resistance, reduced numbers of γH2AX and RAD51 foci, and elevated numbers of DNA-dependent protein kinase catalytic subunit foci, suggesting that HR is compromised and the nonhomologous end-joining (NHEJ) pathway is elicited to help cells cope with IR-induced strand breaks. Interplay between FANCJ and MRE11 ensures a normal response to IR-induced DSBs, whereas FANCJ involvement in ICL repair is regulated by MLH1 and the FA pathway. Our findings are discussed in light of the current model for HR repair.

FANCJ/BACH1 acetylation at lysine 1249 regulates the DNA damage response

BRCA1 promotes DNA repair through interactions with multiple proteins, including CtIP and FANCJ (also known as BRIP1/BACH1). While CtIP facilitates DNA end resection when de-acetylated, the function of FANCJ in repair processing is less well defined. Here, we report that FANCJ is also acetylated. Preventing FANCJ acetylation at lysine 1249 does not interfere with the ability of cells to survive DNA interstrand crosslinks (ICLs). However, resistance is achieved with reduced reliance on recombination. Mechanistically, FANCJ acetylation facilitates DNA end processing required for repair and checkpoint signaling. This conclusion was based on the finding that FANCJ and its acetylation were required for robust RPA foci formation, RPA phosphorylation, and Rad51 foci formation in response to camptothecin (CPT). Furthermore, both preventing and mimicking FANCJ acetylation at lysine 1249 disrupts FANCJ function in checkpoint maintenance. Thus, we propose that the dynamic regulation of FANCJ acetylation is critical for robust DNA damage response, recombination-based processing, and ultimately checkpoint maintenance.

The BRCA1–Fanconi anemia (FA) pathway is required for both tumor suppression and cell survival, particularly following treatment with DNA damaging agents that induce DNA interstrand crosslinks (ICLs). ICL processing by the BRCA–FA pathway includes promotion of homologous recombination (HR) and DNA damage tolerance through translesion synthesis. However, little is known about how the BRCA–FA pathway or these ICL processing mechanisms are regulated. Here, we identify acetylation as a DNA damage–dependent regulator of the BRCA–FA protein, FANCJ. FANCJ acetylation at lysine 1249 is enhanced by expression of the histone acetyltransferase CBP and reduced by expression of histone deacetylases HDAC3 or SIRT1. Furthermore, acetylation on endogenous FANCJ is induced upon treatment of cells with agents that generate DNA lesions. Consistent with this post-translation event regulating FANCJ function during cellular DNA repair, preventing FANCJ acetylation skews ICL processing. Cells have reduced reliance on HR factor Rad54 and greater reliance on translesion synthesis polymerase polη. Our data indicate that FANCJ acetylation contributes to DNA end processing that is required for HR. Furthermore, resection-dependent checkpoint maintenance relies on the dynamic regulation of FANCJ acetylation. The implication of these findings is that FANCJ acetylation contributes to DNA repair choice within the BRCA–FA pathway.

Hereditary breast cancer and the BRCA1-associated FANCJ/BACH1/BRIP1

It is clear that FANCJ, also known as BACH1 or BRIP1, is an essential tumor suppressor gene based on the identification of clinically relevant mutations not only in breast cancer, but also the childhood cancer syndrome, Fanconi anemia. This conclusion is further supported by the direct and functional interaction between FANCJ and the hereditary breast cancer-associated gene product BRCA1. In the absence of the FANCJ DNA helicase or its interaction with BRCA1, cells have defects in several aspects of the DNA damage response. In particular, the BRCA1-FANCJ interaction is essential for promoting error-free repair, checkpoint control and for limiting DNA damage tolerance. As the number of FANCJ clinical mutations and affected patients accumulate, it will be critical to understand whether the associated tumors resemble BRCA-associated tumors. If so, FANCJ patients could also benefit from new therapies that selectively sensitize DNA repair-defective tumors and spare healthy cells. In this article, we summarize the breast cancer-associated FANCJ mutations and discuss functional outcomes for DNA repair and tumor suppression.

Interaction between the helicases genetically linked to Fanconi anemia group J and Bloom's syndrome

Bloom's syndrome (BS) and Fanconi anemia (FA) are autosomal recessive disorders characterized by cancer and chromosomal instability. BS and FA group J arise from mutations in the BLM and FANCJ genes, respectively, which encode DNA helicases. In this work, FANCJ and BLM were found to interact physically and functionally in human cells and co-localize to nuclear foci in response to replication stress. The cellular level of BLM is strongly dependent upon FANCJ, and BLM is degraded by a proteasome-mediated pathway when FANCJ is depleted. FANCJ-deficient cells display increased sister chromatid exchange and sensitivity to replication stress. Expression of a FANCJ C-terminal fragment that interacts with BLM exerted a dominant negative effect on hydroxyurea resistance by interfering with the FANCJ-BLM interaction. FANCJ and BLM synergistically unwound a DNA duplex substrate with sugar phosphate backbone discontinuity, but not an 'undamaged' duplex. Collectively, the results suggest that FANCJ catalytic activity and its effect on BLM protein stability contribute to preservation of genomic stability and a normal response to replication stress.

An MLH1 mutation links BACH1/FANCJ to colon cancer, signaling, and insight toward directed therapy

Defects in MLH1, as with other mismatch repair (MMR) proteins, are the primary cause of hereditary nonpolyposis colon cancer (HNPCC). Mutations in MMR genes often disrupt mismatch repair and MMR signaling functions. However, some HNPCC-associated mutations have unknown pathogenicity. Here, we uncover an MLH1 clinical mutation with a leucine (L)-to-histidine (H) amino acid change at position 607 that ablates MLH1 binding to FANCJ. Given that a DNA helicase is not essential for mammalian MMR in vitro, we considered that loss of MLH1 binding to FANCJ could alter MMR signaling. Consistent with this hypothesis, FANCJ-deficient cells exhibit delayed MMR signaling and apoptotic responses that generate resistance to agents that induce O(6)-methylguanine lesions. Our data indicate that the delay in MMR signaling provides time for the methylguanine methyltransferase (MGMT) enzyme to reverse DNA methylation. In essence, FANCJ deficiency alters the competition between two pathways: MGMT-prosurvival versus MMR-prodeath. This outcome could explain the HNPCC familial cancers that present as microsatellite stable and with intact MMR, such as MLH(L607H). Importantly, the link between FANCJ and HNPCC provides insight toward directed therapies because loss of the FANCJ/MLH1 interaction also uniquely sensitizes cells to DNA cross-linking agents.

Assessing the link between BACH1/FANCJ and MLH1 in DNA crosslink repair

FANCJ (also known as BRIP1 or BACH1) is a DNA helicase that was originally identified by its direct interaction with the hereditary breast cancer protein, BRCA1. Similar to BRCA1, FANCJ function is essential for DNA repair and breast cancer suppression. FANCJ is also mutated in the cancer prone syndrome Fanconi anemia, for which patient cells are characterized by extreme sensitivity to agents that generate DNA interstand crosslinks. Unexpectedly, correction of the interstrand crosslink sensitivity of FANCJ-null patient cells did not require the FANCJ/BRCA1 interaction. Instead, FANCJ binding to the mismatch repair protein, MLH1 was required. Given this finding, we address the role of FANCJ and MLH1 in DNA crosslink processing and how their functions could be linked in checkpoint and/or recombination pathways. We speculate that after DNA crosslink processing and repair, the FANCJ/MLH1 interaction is critical for recovery and restart of replication. These ideas are considered and summarized in this review.

FANCJ uses its motor ATPase to destabilize protein-DNA complexes, unwind triplexes, and inhibit RAD51 strand exchange

Mutations in the FANCJ helicase predispose individuals to breast cancer and are genetically linked to the Fanconi anemia (FA) complementation group J. FA is a chromosomal instability disorder characterized by multiple congenital anomalies, progressive bone marrow failure, and high cancer risk. FANCJ has been proposed to function downstream of FANCD2 monoubiquitination, a critical event in the FA pathway. Evidence supports a role for FANCJ in a homologous recombination pathway of double strand break repair. In an effort to understand the molecular functions of FANCJ, we have investigated the ability of purified FANCJ recombinant protein to use its motor ATPase function for activities in addition to unwinding of conventional duplex DNA substrates. These efforts have led to the discovery that FANCJ ATP hydrolysis can be used to destabilize protein-DNA complexes and unwind triple helix alternate DNA structures. These novel catalytic functions of FANCJ may be important for its role in cellular DNA repair, recombination, or resolving DNA structural obstacles to replication. Consistent with this, we show that FANCJ can inhibit RAD51 strand exchange, an activity that is likely to be important for its role in controlling DNA repair through homologous recombination.

BRCA-FA pathway as a target for anti-tumor drugs

Promising research on DNA repair signaling pathways predicts a new age of anti-tumor drugs. This research was initiated through the discovery and characterization of proteins that functioned together in signaling pathways to sense, respond, and repair DNA damage. It was realized that tumor cells often lacked distinct DNA repair pathways, but simultaneously relied heavily on compensating pathways. More recently, researchers have begun to manipulate these compensating pathways to reign in and kill tumor cells. In a striking example it was shown that tumors derived from mutations in the DNA repair genes, of BRCA-FA pathway, were selectively sensitive to inhibition of the base excision repair pathway. These findings suggest that tumors derived from defects in DNA repair genes will be easier to treat clinically, providing a streamlined and targeted therapy that spares healthy cells. In the future, identifying patients with susceptible tumors and discovering additional DNA repair targets amenable to anti-tumor drugs will have a major impact on the course of cancer treatment.

FANCJ (BACH1) helicase forms DNA damage inducible foci with replication protein A and interacts physically and functionally with the single-stranded DNA-binding protein

The BRCA1 associated C-terminal helicase (BACH1, designated FANCJ) is implicated in the chromosomal instability genetic disorder Fanconi anemia (FA) and hereditary breast cancer. A critical role of FANCJ helicase may be to restart replication as a component of downstream events that occur during the repair of DNA cross-links or double-strand breaks. We investigated the potential interaction of FANCJ with replication protein A (RPA), a single-stranded DNA-binding protein implicated in both DNA replication and repair. FANCJ and RPA were shown to coimmunoprecipitate most likely through a direct interaction of FANCJ and the RPA70 subunit. Moreover, dependent on the presence of BRCA1, FANCJ colocalizes with RPA in nuclear foci after DNA damage. Our data are consistent with a model in which FANCJ associates with RPA in a DNA damage-inducible manner and through the protein interaction RPA stimulates FANCJ helicase to better unwind duplex DNA substrates. These findings identify RPA as the first regulatory partner of FANCJ. The FANCJ-RPA interaction is likely to be important for the role of the helicase to more efficiently unwind DNA repair intermediates to maintain genomic stability.

The FANCJ/MutLalpha interaction is required for correction of the cross-link response in FA-J cells

FANCJ also called BACH1/BRIP1 was first linked to hereditary breast cancer through its direct interaction with BRCA1. FANCJ was also recently identified as a Fanconi anemia (FA) gene product, establishing FANCJ as an essential tumor suppressor. Similar to other FA cells, FANCJ-null (FA-J) cells accumulate 4N DNA content in response to DNA interstrand crosslinks (ICLs). This accumulation is corrected by reintroduction of wild-type FANCJ. Here, we show that FANCJ interacts with the mismatch repair complex MutLalpha, composed of PMS2 and MLH1. Specifically, FANCJ directly interacts with MLH1 independent of BRCA1, through its helicase domain. Genetic studies reveal that FANCJ helicase activity and MLH1 binding, but not BRCA1 binding, are essential to correct the FA-J cells' ICL-induced 4N DNA accumulation and sensitivity to ICLs. These results suggest that the FANCJ/MutLalpha interaction, but not FANCJ/BRCA1 interaction, is essential for establishment of a normal ICL-induced response. The functional role of the FANCJ/MutLalpha complex demonstrates a novel link between FA and MMR, and predicts a broader role for FANCJ in DNA damage signaling independent of BRCA1.

Inhibition of BACH1 (FANCJ) helicase by backbone discontinuity is overcome by increased motor ATPase or length of loading strand

The BRCA1 associated C-terminal helicase (BACH1) associated with breast cancer has been implicated in double strand break (DSB) repair. More recently, BACH1 (FANCJ) has been genetically linked to the chromosomal instability disorder Fanconi Anemia (FA). Understanding the roles of BACH1 in cellular DNA metabolism and how BACH1 dysfunction leads to tumorigenesis requires a comprehensive investigation of its catalytic mechanism and molecular functions in DNA repair. In this study, we have determined that BACH1 helicase contacts with both the translocating and the non-translocating strands of the duplex are critical for its ability to track along the sugar phosphate backbone and unwind dsDNA. An increased motor ATPase of a BACH1 helicase domain variant (M299I) enabled the helicase to unwind the backbone-modified DNA substrate in a more proficient manner. Alternatively, increasing the length of the 5′ tail of the DNA substrate allowed BACH1 to overcome the backbone discontinuity, suggesting that BACH1 loading mechanism is critical for its ability to unwind damaged DNA molecules.

BACH1 is a DNA repair protein supporting BRCA1 damage response

The link between defects in BRCA1 and breast cancer development may be best understood by deciphering the role of associated proteins. BRCA1 associated C-terminal helicase (BACH1) interacts directly with the BRCA1 C-terminal BRCT repeats, which are important for BRCA1 DNA repair and are mutated in the majority of BRCA1 familial cancers. Thus, BACH1 is a likely candidate for mediating BRCA1 DNA repair and tumor suppression functions. Although previous evidence using overexpression of a dominant negative BACH1 has suggested that BACH1 is involved in BRCA1-DNA repair function, our results using BACH1 deficient cells provide direct evidence for involvement of BACH1 in DNA repair as well as for localizing BRCA1. Following DNA damage BACH1 is modified by phosphorylation, displays a BRCA1-like nuclear foci pattern and colocalizes with gamma-H2AX. Given that the BACH1/BRCA1 complex is unaltered by DNA damage and the intensity of BRCA1 foci is diminished in BACH1 deficient cells, BACH1 may serve to not only facilitate DNA repair, but also maintain BRCA1 in DNA damage foci.

Multifactorial contributions to an acute DNA damage response by BRCA1/BARD1-containing complexes

The BRCA1 gene product and its stoichiometric binding partner, BARD1, play a vital role in the cellular response to DNA damage. However, how they acquire specific biochemical functions after DNA damage is poorly understood. Following exposure to genotoxic stress, DNA damage-specific interactions were observed between BRCA1/BARD1 and the DNA damage-response proteins, TopBP1 and Mre11/Rad50/NBS1. Two distinct DNA damage-dependent super complexes emerged; their activation was dependent, in part, on the actions of specific checkpoint kinases, and each super complex contributed to a distinctive aspect of the DNA damage response. The results support a new, multifactorial model that describes how genotoxic stress enables BRCA1 to execute a diverse set of DNA damage-response functions.

Assessing the Link between BACH1 and BRCA1 in the FA Pathway

The BACH1 helicase was initially identified by its direct binding to BRCA1 and, thus, was linked to hereditary breast cancer. More recently, BACH1 was identified as the gene defective in the J complementation group of Fanconi anemia (FA). FA is a multigenetic disorder characterized by cellular sensitivity to crosslinkers and chromosome instability. Because FANCD2 monoubiquitination is intact in BACH1 deficient cells, BACH1 appears to act downstream in the FA pathway akin to BRCA2/FANCD1. Interestingly, while BRCA1 has various interactions with FA proteins it has not been identified as an FA gene. As the race to uncover the last few unknown FA complementation groups comes to an end, future work will be required to uncover how these gene products function to combat the effects of DNA damage and maintain genomic stability. In particular, it remains elusive whether BRCA1 is functionally linked to the FA pathway through its interaction with BACH1/FANCJ. This review focuses on a model for the connection of BRCA1 to BACH1 in the FA pathway. We predict that BRCA1 regulates the BACH1 helicase activity to coordinate the timely displacement of Rad51 from nucleofilaments, promoting error free repair and ultimately maintaining chromosomal integrity.

BACH1 is critical for homologous recombination and appears to be the Fanconi anemia gene product FANCJ

We showed in this study that cells deficient of the BRCA1-associated BACH1 helicase, also known as BRIP1, failed to elicit homologous recombination (HR) after DNA double-stranded breaks (DSBs). BACH1-deficient cells were also sensitive to mitomycin C (MMC) and underwent MMC-induced chromosome instability. Moreover, we identified a homozygous nonsense mutation in BACH1 in a FA-J patient-derived cell line and could not detect BACH1 protein in this cell line. Expression of wild-type BACH1 in this cell line reduced the accumulation of cells at G2/M phases following exposure to DNA crosslinkers, a characteristic of Fanconi anemia (FA) cells. These results support the conclusion that BACH1 is FANCJ.

Analysis of the DNA substrate specificity of the human BACH1 helicase associated with breast cancer

We have investigated the DNA substrate specificity of BACH1 (BRCA1-associated C-terminal helicase). The importance of various DNA structural elements for efficient unwinding by purified recombinant BACH1 helicase was examined. The results indicated that BACH1 preferentially binds and unwinds a forked duplex substrate compared with a duplex flanked by only one single-stranded DNA (ssDNA) tail. In support of its DNA substrate preference, helicase sequestration studies revealed that BACH1 can be preferentially trapped by forked duplex molecules. BACH1 helicase requires a minimal 5 ' ssDNA tail of 15 nucleotides for unwinding of conventional duplex DNA substrates; however, the enzyme is able to catalytically release the third strand of the homologous recombination intermediate D-loop structure irrespective of DNA tail status. In contrast, BACH1 completely fails to unwind a synthetic Holliday junction structure. Moreover, BACH1 requires nucleic acid continuity in the 5 ' ssDNA tail of the forked duplex substrate within six nucleotides of the ssDNA-dsDNA junction to initiate efficiently DNA unwinding. These studies provide the first detailed information on the DNA substrate specificity of BACH1 helicase and provide insight to the types of DNA structures the enzyme is likely to act upon to perform its functions in DNA repair or recombination.

A pilot study for a screening trial of cervical fluorescence spectroscopy

Fluorescence spectroscopy is a promising technology for detection of epithelial precancers and cancers. In preparation for a multicenter phase II screening trial, a pilot trial was conducted to test data collection and patient examination procedures, use data forms, time procedures, and identify problems with preliminary data analysis. Women 18 years of age and older underwent a questionnaire, a complete history, and a physical examination, including a pan-colposcopy of the lower genital tract. A fiber-optic probe measured fluorescence excitation-emission matrices at 1-3 cervical sites for 58 women. The data collection procedures, data forms, and procedure times worked well, although collection times for all the clinical data take an average of 28 min. The clinical team followed procedures well, and the data could be retrieved from the database at all sites. The multivariate analysis algorithm correctly identified squamous normal tissue 99% of the time and columnar normal tissue only 7%. The assessment of ploidy from monolayer samples was not accurate in this small sample. The study was successful as a pilot trial. We learned who participated, who withdrew, how often abnormalities were present, and that algorithms that have worked extremely well in previous studies do not work as well when a few study parameters are changed. The current algorithm for diagnosis identified squamous normal tissue very accurately and did less well for columnar normal tissue. Inflammation may be an explanation for this phenomenon. Fluorescence spectroscopy is a promising technology for the detection of epithelial precancers and cancers. The screening trial of fluorescence and reflectance spectroscopy was successful.

Structure of the 53BP1 BRCT region bound to p53 and its comparison to the Brca1 BRCT structure

Brca1 C-terminal (BRCT) domains are a common protein-protein interaction motif in proteins involved in the DNA damage response and DNA repair. The DNA-damage response protein 53BP1 has two BRCT domains that bind to the DNA-binding domain of p53. The 53BP1 tandem-BRCT region is homologous to the tandem-BRCT region of Brca1, which is involved in double-strand break repair and homologous recombination and which binds BACH1, a member of the DEAH helicase family. Here we report the structures of a human 53BP1-p53 complex and of the rat Brca1 BRCT repeats. The 53BP1-p53 structure shows that the two BRCT repeats are arranged tandemly and pack extensively through an interface that also involves the inter-repeat linker. The first BRCT repeat and the linker together bind p53 on a region that overlaps with the DNA-binding surface of p53 and involves p53 residues that are mutated in cancer and are important for DNA binding. Comparison with the structure of the tandem-BRCT region of Brca1 shows a remarkable conservation of the repeat arrangement and of the inter-BRCT repeat interface. Analysis of human BRCA1 tumor-derived mutations and conservation identifies a potential protein-binding site that we show through mutagenesis is involved in BACH1 binding. The BACH1-binding region of Brca1 consists of a unique insertion in the first BRCT repeat and the inter-repeat linker and is analogous to the region of 53BP1 that binds p53.

Clinical and economic impact of multiple gated acquisition scan monitoring during anthracycline therapy

The clinical and economic impacts of monitoring cardiac function in patients given doxorubicin have yet to be determined, especially in relation to patient age, cumulative doxorubicin dose, and the relative efficacies of doxorubicin-based vs alternative regimens. We developed a decision analysis model that includes these factors to estimate the incremental survival benefit and cost-effectiveness of using multiple gated acquisition scans to measure left-ventricular ejection fraction before and during doxorubicin chemotherapy. Probability distributions for the incidences of abnormal left-ventricular ejection fraction findings and congestive heart failure were derived from a retrospective review of 227 consecutive cases at The University of Michigan Medical Center and published findings. Multiple gated acquisition-scan monitoring minimally improved the probability of 5-year survival (<1.5% in the base--case scenario). For patients who received up to 350 mg m(-2) of doxorubicin, multiple gated acquisition-scan screening had an incremental cost of $425 402 per life saved for patients between the ages of 15--39. This incremental cost markedly decreased to $138 191, for patients between the ages of 40--59, and to $86 829 for patients older than 60 years. The small gain in 5-year survival probability secondary to multiple gated acquisition scan monitoring doubled for all age groups when the average cumulative dose for doxorubicin reached 500 mg m(-2). Variations in the cure rate differences between the doxorubicin and alternative regimens had insignificant effects on the improvement in 5-year survival rates from multiple gated acquisition-scan screening. The use of multiple gated acquisition scans for pretreatment screening appears to be more cost-effective for patients who are 40 years or older, when cumulative doxorubicin dose is 350 mg m(-2) or less.

Optimal treatment strategy in patients with papillary thyroid cancer: a decision analysis

BACKGROUND

The management of patients with papillary thyroid carcinoma (PTC) remains controversial. We used decision analysis to identify the optimal treatment strategy for patients with PTC, stratified by risk-group classification.

METHODS

We designed a Markov model to compare thyroid lobectomy and total thyroidectomy (with adjuvant radioiodine therapy) in low- and high-risk patients with PTC. Morbidity, recurrence, and mortality estimates were obtained from the literature. Outcomes were quality-adjusted by using health state preferences.

RESULTS

In low-risk patients, lobectomy and total thyroidectomy resulted in 31.7 and 32.9 quality-adjusted life years (QALYs). Total thyroidectomy was the optimal strategy as long as the relative risk of recurrence after lobectomy was greater than 1.3. Lobectomy became the preferred strategy if subjects were willing to give up 1.5 years of life to avoid thyroid hormone dependency and a remote risk of radioiodine-induced malignancy. In high-risk patients, lobectomy and total thyroidectomy resulted in 11.2 and 16.5 QALYs. Model results were robust to varying the permanent complication rates of initial or completion thyroidectomy, the efficacy of adjuvant radioiodine therapy, and the impact of complications and cancer recurrence on quality of life, irrespective of risk-group classification.

CONCLUSIONS

Total thyroidectomy maximized quality-adjusted life expectancy in low- and high-risk patients with PTC.

Utility of chest computed tomography for staging in patients with T1 extremity soft tissue sarcomas

BACKGROUND

National Cancer Center Network (NCCN) and Society of Surgical Oncology (SSO) practice guidelines recommend chest computed tomography (CT) as part of the staging evaluation of patients with extremity soft tissue sarcoma (STS). In the current study, the authors evaluated the use and yield of chest roentgenography (CXR) and selective chest CT to screen for pulmonary metastases in patients with T1 STS.

METHODS

The utility of these staging studies was evaluated retrospectively in a cohort of 125 consecutive patients who presented to a tertiary care cancer center with T1 primary (nonrecurrent) extremity STS. Two diagnostic strategies (CXR alone vs. CXR plus chest CT) were evaluated using an incremental cost-effectiveness ratio.

RESULTS

The majority of tumors (70%) were high grade. The median sarcoma size was 3.0 cm; 64 of the tumors (51%) were located deep to the investing fascia of the extremity. All patients underwent staging CXR; 1 CXR (< 1%) was suspicious for metastatic disease. Fifty-one patients (41%) also underwent chest CT; 1 chest CT, performed in the patient with a suspicious CXR, revealed metastatic disease. With a median follow-up of 76 months, 19 patients (15%) developed metachronous pulmonary metastases. The relatively low yield resulted in an incremental cost-effectiveness ratio of $59,772 per case of synchronous pulmonary metastasis detected by CXR plus chest CT.

CONCLUSIONS

Less than 1% of patients with T1 primary extremity STS were found to have pulmonary metastases that were detectable using a staging algorithm that employs routine CXR with the selective use of chest CT. The findings of the current study do not support current NCCN or SSO practice guidelines for patients with high-grade T1 STS.

BACH1, a novel helicase-like protein, interacts directly with BRCA1 and contributes to its DNA repair function

BRCA1 interacts in vivo with a novel protein, BACH1, a member of the DEAH helicase family. BACH1 binds directly to the BRCT repeats of BRCA1. A BACH1 derivative, bearing a mutation in a residue that was essential for catalytic function in other helicases, interfered with normal double-strand break repair in a manner that was dependent on its BRCA1 binding function. Thus, BACH1/BRCA1 complex formation contributes to a key BRCA1 activity. In addition, germline BACH1 mutations affecting the helicase domain were detected in two early-onset breast cancer patients and not in 200 matched controls. Thus, it is conceivable that, like BRCA1, BACH1 is a target of germline cancer-inducing mutations.

Incidence, cost, and outcomes of bleeding and chemotherapy dose modification among solid tumor patients with chemotherapy-induced thrombocytopenia

PURPOSE

To describe the incidence and outcomes of bleeding and chemotherapy dose modifications associated with chemotherapy-induced thrombocytopenia (platelets < 50,000/microL).

PATIENTS AND METHODS

Six hundred nine patients with solid tumors or lymphoma were followed-up during 1,262 chemotherapy cycles complicated by thrombocytopenia for development of bleeding, delay or dose reduction of the subsequent cycle, survival, and resource utilization. The association between survival and bleeding or dose modification was examined using the Cox proportional hazards model. Predisposing factors were identified by logistic regression.

RESULTS

Bleeding occurred during 9% of cycles among patients with previous bleeding episodes (P <.0001), baseline platelets less than 75,000/microL (P <.0001), bone marrow metastases (P =.001), poor performance status (P =.03), and cisplatin, carboplatin, carmustine or lomustine administration (P =.0002). Major bleeding episodes resulted in shorter survival and higher resource utilization (P <.0001). Chemotherapy delays occurred during 6% of cycles among patients with more than five previous cycles (P =.003), radiotherapy (P =.03), and disseminated disease (P =.04). They experienced similar clinical outcomes but used significantly more resources. Dose reductions occurred during 15% of cycles but were not associated with poor clinical outcomes or excess resource utilization. Significantly shorter survival and higher resource utilization were observed among the 20% of patients who failed to achieve an adequate response to platelet transfusion.

CONCLUSION

The incidence of bleeding is low among solid tumor patients overall but exceeds 20% in some subgroups. These subgroups are easily identifiable using routinely available clinical information. A clinical prediction rule is being developed. Poor response to platelet transfusion is a clinically and financially significant downstream effect of thrombocytopenia and warrants further investigation.

Quality of life and cost effectiveness analysis of therapy for locally recurrent rectal cancer

PURPOSE

This study was performed to determine the quality of life and cost-effectiveness of therapeutic options for patients with locally recurrent rectal carcinoma, determined from the perspectives of patients and health care providers.

METHODS

We reviewed the records of patients (N = 68) with locally recurrent rectal carcinoma evaluated from 1992 through 1995. We constructed a decision-analytic model incorporating outcomes, survival, and costs. Utilities were elicited from convenience samples of health care providers and patients using the standard gamble technique.

RESULTS

The median survival for patients undergoing surgical resection (n = 40) was 42 months, compared with 16.8 months for patients undergoing diagnostic or palliative surgery (n = 16) and 18.3 months for patients treated nonoperatively (n = 12; P < 0.005). The mean cost of treatment per patient was $19,283 for the nonoperative group, $45,647 for the diagnostic or palliative surgery group, and $70,878 for the surgical resection group. The diagnostic or palliative surgical strategy was dominated by the nonoperative strategy because the former had greater costs with fewer health benefits. The incremental cost-utility ratio of surgical resection compared with nonoperative management using health care provider utilities was $109,777 per quality-adjusted life year gained; it was reduced to $56,698 using per quality-adjusted life year using mean patient utilities.

CONCLUSIONS

Patients with recurrent rectal carcinoma view surgery and morbidity to be less severe than health care providers. Diagnostic or palliative surgery is expensive and affects quality-adjusted survival adversely compared with nonoperative therapy. Surgical resection may be a cost-effective use of resources, particularly when cost-effectiveness is calculated using patient preferences.

Identifying risk factors for imminent death in cancer patients with acute dyspnea

A substantial proportion of cancer patients presenting to an emergency center (EC) or clinic with acute dyspnea survives fewer than 2 weeks. If these patients could be identified at the time of admission, physicians and patients would have additional information on which to base decisions to continue therapy to extend life or to refocus treatment efforts on palliation and/or hospice care alone. The purpose of this study was to identify risk factors for imminent death (survival </= 2 weeks) and short-term survival (1, 3, or 6 months) in cancer patients presenting to an EC with acute dyspnea and to combine these factors into a model to help clinicians identify patients with short life expectancies. A random sample of 122 patients presenting to an EC with acute dyspnea was selected for a retrospective analysis. Data that were available to physicians during the initial EC visit included patient histories, triage and discharge vital signs, chest radiographs, and laboratory results. These variables were used in univariate and logistic regression models to develop predictive models for imminent death and short-term survival. Variables and interactions meeting a univariate criterion of P < 0.10 were included in stepwise regression by using forward and backward stepping. Models were compared with the use of Hosmer-Lemeshow statistics and receiver operating characteristics curves. Underlying cancers were 30% breast, 37% lung, and 34% other cancers. Triage respiration greater than 28/min., triage pulse greater than or equal to 110 bpm, uncontrolled progressive disease, and history of metastasis were found to be statistically significant predictors (alpha </= 0.05) of imminent death. Patients with uncontrolled progressive disease had a relative risk of imminent death of 21.93. Relative risks for triage respiration, pulse, and metastases were 12.72, 4.92, and 3.85, respectively. Cancer diagnosis was not predictive of imminent death but was predictive when longer time periods were modeled. It may be possible to identify patients whose death is imminent from a group of cancer patients with acute dyspnea. Some factors that predict imminent death (triage pulse and respiration) differ from those (cancer diagnosis) that predict short-term survival. Extent of disease/response to treatment is common to all models. These factors need further examination and validation. If these findings are confirmed, this quantified information can help physicians in making difficult end-of-life decisions.