PARP inhibitors have recently been approved as monotherapies for the treatment of recurrent ovarian cancer and metastatic BRCA-associated breast cancer, and ongoing studies are exploring additional indications and combinations with other agents. PARP inhibitors trap PARP onto damaged chromatin when combined with temozolomide and methyl methanesulfonate, but the clinical relevance of these findings remains unknown. PARP trapping has thus far been undetectable in cancer cells treated with PARP inhibitors alone. Here, we evaluate the contribution of PARP trapping to the tolerability and efficacy of PARP inhibitors in the monotherapy setting. We developed a novel implementation of the proximity ligation assay to detect chromatin-trapped PARP1 at single-cell resolution with higher sensitivity and throughput than previously reported methods. We further demonstrate that the PARP inhibitor-induced trapping appears to drive single-agent cytotoxicity in healthy human bone marrow, indicating that the toxicity of trapped PARP complexes is not restricted to cancer cells with homologous recombination deficiency. Finally, we show that PARP inhibitors with dramatically different trapping potencies exhibit comparable tumor growth inhibition at MTDs in a xenograft model of BRCA1-mutant triple-negative breast cancer. These results are consistent with emerging clinical data and suggest that the inverse relationship between trapping potency and tolerability may limit the potential therapeutic advantage of potent trapping activity. Implications: PARP trapping contributes to single-agent cytotoxicity of PARP inhibitors in both cancer cells and healthy bone marrow, and the therapeutic advantage of potent trapping activity appears to be limited.

Introduction Over-expression of the anti-apoptotic protein BCL-2 in MDS has been implicated in progression and drug resistance in MDS. Venetoclax (Ven), a selective, potent, orally bioavailable BCL-2 inhibitor, was recently approved in combination with HMAs or low dose cytarabine for the frontline management of older unfit pts with AML. In this study, we sought to evaluate the safety and efficacy of Ven in pts with R/R MDS. Methods This is an ongoing phase 1b, open-label, multicenter study in R/R MDS (NCT02966782). Key eligibility criteria include age ≥18 years, failure of HMA after receiving at least 4 cycles of Aza or 4 cycles of decitabine within the previous 5 years, marrow blasts <20%, and ECOG Performance status of ≤2. Cohort 1 (C1) pts received Ven monotherapy, either 400 mg (Arm A) or 800 mg (Arm B) per cycle (28 days) and Cohort 2 (C2) pts received Aza combined with escalating doses of Ven: 100, 200 and 400 mg daily for 14 of 28-day cycles. Aza was administered at the standard dose (75 mg/m2/day) for the first 7 days of each cycle. The primary objectives were to evaluate the safety profiles and the recommended Phase 2 dose (RP2D) of Ven monotherapy and Ven+Aza. Key secondary objectives included a preliminary assessment of overall response rate (ORR, defined as complete remission [CR]+marrow complete remission [mCR]+partial response [PR]) , time to first response (TTR), progression-free survival (PFS), and overall survival (OS). We used the modified International Working Group 2006 criteria for response assessment (Cheson et. al., Blood, 2006). Results As of April 9, 2019, 46 pts [87% male, median age 76 years (range 44-91)] were enrolled. C1 (Ven monotherapy) included 22 pts, C2 (combination therapy) included 24 pts. At baseline, 37 (80%) pts received at least one prior therapy, 2 (15%) pts received 2, and 1 (2%) patient received >3 therapies prior to enrollment in the study. Baseline bone marrow blasts were: ≤5% was observed in 16 (35%) pts, >5% and ≤10% in 23 (50%), and >10% in 7 (15%) pts respectively. Cytogenetics risk was evaluated in 27/46 pts and were as follows: Good 12 (44%), Intermediate 9 (33%), and Poor 6 (22%). Overall, 9 pts discontinued study therapy (8 deaths, 1 withdrew consent). The most frequent treatment-emergent adverse events (TEAEs) included neutropenia, thrombocytopenia, nausea, and diarrhea (Table ). Infectious TEAEs included febrile neutropenia and pneumonia. Predominant Grade 3 and 4 TEAEs were hematological and included neutropenia (41%), thrombocytopenia (30%), leukopenia (24%), and anemia (15%). Serious TEAEs occurring in ≥2 pts were febrile neutropenia (n=8), pneumonia (n=6), thrombocytopenia (n=2), and epistaxis (n=2). Death on study occurred in 8 (17%) pts, of whom 6 died of progressive disease. Other causes of death were septic shock (n=1) and pneumonia (n=1). Forty of 46 pts were response evaluable. Median follow-up time was 4.7 mos (range: 3.7-6.3 mos). In C1, ORR was 7% (1/16). Stable disease was observed in 75% (12/16) pts. Median TTR was 1.6 mos (range: 1.6-1.6 mos). Median PFS was 3.4 mos (95% CI: 1.9-5.2 mos) and 6-mos estimate for OS was 57% (95% CI: 22%, 81%). In C2, ORR was 50% (12/24 pts). Of those, 13% (3/24) had CR and 38% (9/24) had mCR. Stable disease was observed in 31% (10/24) pts. Median PFS, and OS were not reached. The 6-mos estimate for PFS was 76% (95% CI: 50%, 89%) and estimated OS at 9-mos was 83% (95% CI: 55%, 95%). Finally, 4 pts came off study to receive allogeneic stem cell transplantation. Conclusion Ven monotherapy and combination Ven+Aza were well tolerated in pts with R/R MDS and most AEs were manageable. Although the study is still ongoing, the 6-mos OS estimate of 57% in monotherapy pts compares favorably to historical controls. In addition, the ORR observed with combination therapy, and the observed 9-mos OS rate of 83% also compare favorably with historical data. Updated data on safety and efficacy, including data on RP2D, will be presented at the meeting. Disclosures Zeidan: Ariad: Honoraria; Agios: Honoraria; Abbvie: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Otsuka: Consultancy, Honoraria, Research Funding; ADC Therapeutics: Research Funding; Jazz: Honoraria; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria; Astellas: Honoraria; Daiichi Sankyo: Honoraria; Cardinal Health: Honoraria; Seattle Genetics: Honoraria; BeyondSpring: Honoraria; Acceleron Pharma: Consultancy, Honoraria, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Research Funding; Trovagene: Consultancy, Honoraria, Research Funding; Incyte: Consultancy, Honoraria, Research Funding; Celgene Corporation: Consultancy, Honoraria, Research Funding; Medimmune/AstraZeneca: Research Funding. Pollyea:Celyad: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Diachii Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Forty-Seven: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees. Garcia:Abbvie: Research Funding; Genentech: Research Funding. Brunner:Novartis: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Research Funding; Forty Seven Inc: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees. Roncolato:St. George Hospital: Employment. Borate:Novartis: Consultancy; Takeda: Consultancy; Pfizer: Consultancy; Daiichi Sankyo: Consultancy; AbbVie: Consultancy. Odenike:Astra Zeneca: Research Funding; Astex Pharmaceuticals: Research Funding; Agios: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI/Baxalta: Research Funding; NS Pharma: Research Funding; Gilead Sciences: Research Funding; Incyte: Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen Oncology: Research Funding; Oncotherapy: Research Funding. Bajel:Amgen: Honoraria, Speakers Bureau; Novartis: Honoraria; AbbVie: Honoraria; Pfizer: Honoraria. Watson:Amgen: Other: Travel grant; Roche: Other: Travel grant. Götze:AbbVie: Membership on an entity's Board of Directors or advisory committees. Nolte:Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Tan:AbbVie Inc: Other: Investigator in AbbVie funded trial. Hong:Roche: Equity Ownership; Genentech Inc.: Employment, Equity Ownership. Dunbar:AbbVie Inc: Employment, Other: Stock/stock options. Zhou:AbbVie Inc: Employment, Other: Stock/stock options. Gressick:AbbVie Inc: Employment, Other: Stock/stock options. Ainsworth:AbbVie Inc: Employment, Other: Stock/stock options. Harb:AbbVie Inc: Employment, Other: Stock/stock options. Salem:AbbVie: Employment, Other: Stock/stock options. Hayslip:AbbVie Inc: Employment, Other: Stock/stock options. Swords:AbbVie Inc: Employment, Other: Stock/stock options. Garcia-Manero:Amphivena: Consultancy, Research Funding; Helsinn: Research Funding; Novartis: Research Funding; AbbVie: Research Funding; Celgene: Consultancy, Research Funding; Astex: Consultancy, Research Funding; Onconova: Research Funding; H3 Biomedicine: Research Funding; Merck: Research Funding. OffLabel Disclosure: Venetoclax is a BCL-2 inhibitor that is FDA-approved in some indications. This presentation will focus on venetoclax for treatment in myelodysplastic syndromes, which is not an approved indication.

Background: Patients with acute myeloid leukemia (AML) who are older or ineligible for intensive induction chemotherapy have limited treatment options and poor survival. In the VIALE-A study, venetoclax (Ven) + azacitidine (Aza) improved overall survival and response rates compared with placebo (Pbo) + Aza in older or unfit patients with newly diagnosed AML (DiNardo et al. N Engl J Med. 2020). Although cytopenia is common in AML, Ven+Aza was associated with hematologic adverse events in 83% of patients in the VIALE-A study (vs 69% in the Pbo+Aza arm). Here, the frequency and management of cytopenia are analyzed in patients achieving a best response of complete remission (CR) or CR with partial hematologic recovery (CRh) in the VIALE-A study. Methods: This double-blind, Pbo-controlled, multicenter Phase 3 study (NCT02993523) enrolled patients with newly diagnosed AML who were ineligible for intensive chemotherapy due to age ≥75 years or comorbidities. Patients were randomized 2:1 to receive 75 mg/m2 Aza (Days 1-7 of each 28-day cycle) plus either daily 400 mg Ven (Ven+Aza) or Pbo (Pbo+Aza). Disease response was assessed via bone marrow aspirate and biopsy at the end of Cycle 1 and at least every 3 cycles thereafter. After patients achieved blast clearance (bone marrow blasts <5%), various dosing modifications were implemented to manage cytopenia (Table 1). Cytopenia, defined here as Grade 4 neutropenia (absolute neutrophil count <500/μL) or Grade 4 thrombocytopenia (platelet count <25×103/μL) lasting ≥7 days, was assessed using laboratory data. Results: In total, 186 of 283 (66%) Ven+Aza-treated patients and 33 of 144 (23%) Pbo+Aza-treated patients achieved a best response of CR or CRh (CR/CRh). Of patients with a best response of CR/CRh in the Ven+Aza arm, 77% achieved blast clearance by the end of Cycle 1, 88% by the end of Cycle 2, 92% by the end of Cycle 3, and 98% by the end of Cycle 4. Of patients with a best response of CR/CRh in the Pbo+Aza arm, 33% achieved blast clearance by the end of Cycle 1, 55% by the end of Cycle 2, 76% by the end of Cycle 3, and 91% by the end of Cycle 4. After achieving blast clearance, 75% and 67% of patients in the Ven+Aza and Pbo+Aza arms, respectively, had a delay of the next cycle, with a median duration per cycle delay post-blast clearance (range) of 9.0 (1-39) and 5.5 (1-21) days. Among CR/CRh patients, more patients receiving Ven+Aza versus Pbo+Aza had post-remission cytopenia (87% vs 45%; Table 2). A similar percentage of CR/CRh patients in both arms (Ven+Aza, 26%; Pbo+Aza, 24%) had in-cycle dose interruptions (ie, days without Ven/Pbo exposure between a cycle's first and last Ven/Pbo dose), with a median duration (range) of 2.0 days (1-20) for Ven+Aza and 1.0 (1-13) for Pbo+Aza. A greater proportion of CR/CRh patients experienced post-remission cycle delays due to cytopenia in the Ven+Aza arm (77%) than in the Pbo+Aza arm (30%). Furthermore, a higher percentage of CR/CRh patients had post-remission cycles with a reduction in Ven/Pbo dosing days and/or cycle delays totaling ≥7 days due to cytopenia in the Ven+Aza arm (75%) than in the Pbo+Aza arm (27%). Among these patients, the median percentage of days without Ven/Pbo administration while in remission (out of the total number of days in remission) was 18% (range, 1-69) in the Ven+Aza arm and 13% (3-44) in the Pbo+Aza arm. Ultimately, 129 CR/CRh patients (69%) in the Ven+Aza arm and 10 (30%) in the Pbo+Aza arm received ≤21-day Ven/Pbo dosing post-remission, with a median time from remission to first ≤21-day cycle (range) of 92.0 days (1-480) for Ven+Aza and 74.0 days (6-405) for Pbo+Aza. Conclusion: In the VIALE-A study of older or unfit patients with newly diagnosed AML, the majority of responding patients in the Ven+Aza arm required dosing modifications to manage cytopenia, of which delays between cycles or within-cycle reductions of Ven dosing days were most common. Post-remission cytopenia and dosing modifications were more frequent with Ven+Aza versus Pbo+Aza treatment. The impact of cytopenia and dosing modifications on patient outcomes with Ven+Aza is currently being analyzed and will be reported at a future date. Disclosures Pratz: AbbVie: Other: Scientific Advisory Board, Research Funding; Boston BioMedical: Consultancy; Astellas: Other: Scientific Advisory Board, Research Funding; Jazz Pharmaceutical: Consultancy; Millennium: Research Funding; Daiichi Sankyo: Research Funding; Agios: Other: Scientific Advisory Board, Research Funding; Celgene: Other: Scientific Advisory Board. DiNardo:MedImmune: Honoraria; Agios: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Jazz: Honoraria; Takeda: Honoraria; AbbVie: Consultancy, Honoraria, Research Funding; Syros: Honoraria; Notable Labs: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; ImmuneOnc: Honoraria; Novartis: Consultancy; Calithera: Research Funding. Selleslag:Amgen: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Astellas: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria, Speakers Bureau; Janssen Cilag: Consultancy, Honoraria, Speakers Bureau; AbbVie: Consultancy, Honoraria, Speakers Bureau; Belgian College: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Speakers Bureau; MSD: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria; Alexion: Consultancy, Honoraria; GSK: Consultancy, Honoraria; Teva: Consultancy, Honoraria, Speakers Bureau; Sanofi: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Speakers Bureau. Yamamoto:AbbVie: Consultancy, Honoraria, Research Funding; Astra-Zeneca: Consultancy, Research Funding; Zenyaku: Research Funding; Sumitomo Dainippon: Honoraria; Sanofi: Honoraria; Pfizer: Honoraria; Otsuka: Consultancy, Honoraria, Research Funding; Ono: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Nippon Shinyaku: Honoraria, Research Funding; Mundipharma: Consultancy, Honoraria, Research Funding; MSD: Consultancy, Honoraria, Research Funding; Mochida: Honoraria; Meiji Seika Pharma: Consultancy, Honoraria; Kyowa Kirin: Honoraria; Janssen: Honoraria; Gilead Sciences: Research Funding; IQIVA/Incyte: Research Funding; HUYA: Consultancy; IQIVA/HUYA: Honoraria; Daiichi Sankyo: Consultancy; Eisai: Consultancy, Honoraria, Research Funding; Chugai: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Yakult: Research Funding; Stemline Therapeutics: Consultancy; Solasia Pharma: Research Funding; SymBio: Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Bayer: Research Funding; Aichi Cancer Center: Current Employment. Konopleva:AbbVie: Consultancy, Research Funding; Cellectis: Research Funding; Agios: Research Funding; Sanofi: Research Funding; Amgen: Consultancy; Reata Pharmaceutical Inc.;: Patents & Royalties: patents and royalties with patent US 7,795,305 B2 on CDDO-compounds and combination therapies, licensed to Reata Pharmaceutical; Ascentage: Research Funding; Eli Lilly: Research Funding; Stemline Therapeutics: Consultancy, Research Funding; Calithera: Research Funding; Forty-Seven: Consultancy, Research Funding; Ablynx: Research Funding; Rafael Pharmaceutical: Research Funding; F. Hoffmann La-Roche: Consultancy, Research Funding; Kisoji: Consultancy; AstraZeneca: Research Funding; Genentech: Consultancy, Research Funding. McDonald:venetoclax advisory board in South Africa (in CLL context): Consultancy; Alberts Cellular Therapy: Current Employment. Babu:Genentech, Inc./ F. Hoffmann-La Roche: Research Funding; Novartis: Research Funding; Janssen Oncology: Research Funding; Syndax: Research Funding; Nektar: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Alexion Pharmaceuticals: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding, Speakers Bureau; Lilly: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Bayer: Honoraria; AstraZeneca: Consultancy, Honoraria; AstraZeneca/MedImmune: Research Funding; Argenx: Consultancy, Research Funding; Boehringer Ingelheim: Consultancy; Merck: Research Funding; AbbVie: Research Funding; TG Therapeutics: Research Funding; Amgen: Research Funding; Lutheran Hospital: Other; Fort Wayne Medical Oncology & Hematology: Current Employment, Current equity holder in publicly-traded company; Sanofi: Research Funding. Stevens:Amgen, MorphoSys: Consultancy. Kantarjian:BioAscend: Honoraria; Delta Fly: Honoraria; Abbvie: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Ascentage: Research Funding; Janssen: Honoraria; Adaptive biotechnologies: Honoraria; Aptitute Health: Honoraria; Oxford Biomedical: Honoraria; Daiichi-Sankyo: Honoraria, Research Funding; BMS: Research Funding; Jazz: Research Funding; Immunogen: Research Funding; Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Sanofi: Research Funding; Actinium: Honoraria, Membership on an entity's Board of Directors or advisory committees. Traina:University of São Paulo at Ribeirão Preto Medical School: Current Employment; AbbVie: Other: Principal Investigator for Protocol Number M15-656 . Venditti:Jazz: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AbbVie: Consultancy, Honoraria, Other: TRAVEL, ACCOMODATIONS, EXPENSES (paid by any for-profit health care company); Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMODATIONS, EXPENSES (paid by any for-profit health care company); Amgen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Pfizer: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Speakers Bureau; Novartis: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Mayer:AbbVie: Research Funding; Principia Biopharma: Research Funding. Montez:F. Hoffmann-La Roche: Current equity holder in publicly-traded company; Genentech, Inc.: Current Employment. Ramsingh:Roche: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Genentech: Current Employment, Current equity holder in publicly-traded company. Jin:Genentech: Current Employment. Ainsworth:AbbVie: Current Employment, Current equity holder in publicly-traded company. Duan:AbbVie: Current Employment, Other: may hold stock or options. Svensson:AbbVie: Current Employment, Current equity holder in publicly-traded company. Werner:AbbVie: Current Employment, Current equity holder in publicly-traded company. Potluri:AbbVie: Current Employment, Other: may hold stock or stock options. Jonas:AbbVie: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Amgen: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; GlycoMimetics: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Celgene: Consultancy, Research Funding; Jazz: Consultancy, Research Funding; Takeda: Consultancy; Tolero: Consultancy; Treadwell: Consultancy; Forty Seven: Research Funding; Accelerated Medical Diagnostics: Research Funding; AROG: Research Funding; Daiichi Sankyo: Research Funding; F. Hoffmann-La Roche: Research Funding; Forma: Research Funding; Genentech/Roche: Research Funding; Hanmi: Research Funding; Incyte: Research Funding; LP Therapeutics: Research Funding; Pfizer: Research Funding; Pharmacyclics: Research Funding; Sigma Tau: Research Funding.

The evolutionarily conserved MEC1 checkpoint pathway mediates cell cycle arrest and induction of genes including the RNR (Ribonucleotide reductase) genes and HUG1 (Hydroxyurea, ultraviolet, and gamma radiation) in response to DNA damage and replication arrest. Rnr complex activity is in part controlled by cytoplasmic localization of the Rnr2p-Rnr4p subunits and inactivation of negative regulators Sml1p and Dif1p upon DNA damage and hydroxyurea (HU) treatment. We previously showed that a deletion of HUG1 rescues lethality of mec1Δ and suppresses dun1Δ strains. In this study, multiple approaches demonstrate the regulatory response of Hug1p to DNA damage and HU treatment and support its role as a negative effector of the MEC1 pathway. Consistent with our hypothesis, wild-type cells are sensitive to DNA damage and HU when HUG1 was overexpressed. A Hug1 polyclonal antiserum reveals that HUG1 encodes a protein in budding yeast and its MEC1-dependent expression is delayed compared to the rapid induction of Rnr3p in response to HU treatment. Cell biology and subcellular fractionation experiments show localization of Hug1p-GFP to the cytoplasm upon HU treatment. The cytoplasmic localization of Hug1p-GFP is dependent on MEC1 pathway genes and coincides with the cytoplasmic localization of Rnr2p-Rnr4p. Taken together, the genetic interactions, gene expression, and localization studies support a novel role for Hug1p as a negative regulator of the MEC1 checkpoint response through its compartmentalization with Rnr2p-Rnr4p.

Monitoring promoter response to environmental changes using reporter systems has provided invaluable information regarding cellular state. With the development of in vivo luciferase reporter systems, inexpensive, sensitive and accurate promoter assays have been developed without the variability reported between in vitro samplings. Current luciferase reporter systems, however, are largely inflexible to modifications to the promoter of interest. To overcome problems in flexibility and stability of these expression vectors, we report the creation of a novel vector system which introduces a cytosol-localized Photinus pyralis luciferase [LUC*(ÀSKL)] capable of one-step, in vivo measurements into a promoter-reporter system via PCR-based gene deletion and fusion. After introduction of the reporter under HUG1 promoter control, cytosolic localization was confirmed by fluorescence microscopy. The dose-response of this novel construct was then compared with that of a similar HUG1Δ::yEGFP1 promoter-reporter system and shown to give a similar response pattern.