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Includes supplementary methods, figures, and tables.

Purpose:PI3K–Akt–mTOR and androgen receptor (AR) signaling are commonly aberrantly activated in metastatic castration-resistant prostate cancer (mCRPC), with PTEN loss associating with poor prognosis. We therefore conducted a phase Ib/II study of the combination of ipatasertib, an Akt inhibitor, with the CYP17 inhibitor abiraterone in patients with mCRPC.Patients and Methods: Patients were randomized 1:1:1 to ipatasertib 400 mg, ipatasertib 200 mg, or placebo, with abiraterone 1,000 mg orally. Coprimary efficacy endpoints were radiographic progression-free survival (rPFS) in the intent-to-treat population and in patients with PTEN-loss tumors.Results:rPFS was prolonged in the ipatasertib cohort versus placebo, with similar trends in overall survival and time-to-PSA progression. A larger rPFS prolongation for the combination was demonstrated in PTEN-loss tumors versus those without. The combination was well tolerated, with no treatment-related deaths.Conclusions:In mCRPC, combined blockade with abiraterone and ipatasertib showed superior antitumor activity to abiraterone alone, especially in patients with PTEN-loss tumors.See related commentary by Zhang et al., p. 901

3081 Background: Zotatifin (eFT226) is a first in class, potent and sequence selective inhibitor of RNA helicase eIF4A1 that promotes stable mRNA:eIF4A:drug ternary complex at specific polypurine motifs within the 5’-UTR, preventing ribosome docking and thus, efficient translation of select transcripts. In preclinical models zotatifin treatment simultaneously down-regulated translation of numerous oncogenes with complex 5’ mRNA structures, including ERBB2, FGFR1/2, EGFR, KRAS, and CCND1. Methods: Patients (pts) with select advanced solid tumors harboring mutations/amplification of ERBB2, FGFR1, FGFR2, EGFR, or KRAS or with pancreatic cancer were enrolled into 3+3 dose escalation portion of the protocol (Part 1), and indication specific expansions continue to enroll at recommended phase 2 dose (RP2D; Part 2). The primary endpoints of Part 1 include determination of safety, tolerability, and maximum tolerated dose (MTD)/RP2D; additional endpoints include characterization of pharmacokinetic, pharmacodynamic (including from blood-based assay during escalation and from pre- and on-treatment biopsy at/near MTD with reverse phase protein array (RPPA)), and initial efficacy. Results: As of cut-off date Jan 13, 2022, Dose escalation phase (Part 1) included 37 patients treated with zotatifin at dose levels: 0.005, 0.01, 0.02, 0.035 mg/Kg IV weekly, and 0.035, 0.05, 0.07, 0.1 mg/kg IV 2 weeks-on and 1 week-off. DLTs were observed in 3 patients: Gr 2 thrombocytopenia (0.035 mg/kg weekly), Gr 3 anemia (0.1 mg/kg) and Gr 3 gastrointestinal bleed resulting in anemia (0.1 mg/kg). MTD/RP2D is 0.07 mg/Kg IV 2 weeks-on and 1 week-off. The most common treatment emergent adverse events (TEAEs) in Part 1 include: fatigue, anemia, diarrhea and dyspnea. The most common AEs at RP2D (n = 16 pts; Part 1 and Part 2) include: anemia (25% all gr 1 or 2), fatigue (25% all gr 1 or 2) and dyspnea (19%; 13% Gr 3) diarrhea (13%, all Gr 1 or 2). Pharmacokinetics were generally linear and dose proportional and exposures at MTD/RP2D are consistent with target pharmacologic levels in preclinical models. Blood based biomarkers showed dose- and time- dependent evidence of target engagement. Pre- and on-treatment biopsy data in expansion patients showed decreased expression of target proteins. No patient in dose escalation experienced an objective tumor response; initial efficacy data from Part 2 and at RP2D will be presented. Conclusions: eIF4A inhibitor zotatifin achieves pharmacologically relevant exposures with on-target AEs that are manageable at the MTD, with evidence of target knockdown from on-treatment biopsies. Part 2 indication-specific expansions (including in ER+ FGFR-amplified MBC as single agent, ER+ MBC in combination with fulvestrant and abemaciclib, and KRAS NSCLC in combination with sotorasib) are on-going. Clinical trial information: NCT04092673.

Inheritance of a defective copy of the von Hippel-Lindau (VHL) gene leads to the most common cause of inherited renal cell carcinoma (RCC). In addition, most patients with sporadic RCC have aberrant VHL. In the absence of VHL, hypoxia-inducible factor α accumulates, leading to production of several growth factors, including vascular endothelial growth factor and platelet-derived growth factor. We review here the biology of RCC and how a combination of proximal and distal block of VHL/hypoxia-inducible factor α pathway by novel targeted agents, including sunitinib, sorafenib, bevacizumab, everolimus, and temsirolimus, has led to significant improvements in progression-free survival.

Background UCART19 is a genetically modified T-cell product manufactured from non-HLA matched healthy donor cells. Lentiviral-transduced CAR T-cells express (1) an anti-CD19 CAR (anti-CD19 scFv- 41BB- CD3ζ) and (2) an RQR8 "safety switch" that is intended to allow targeted elimination of RQR8+ cells by rituximab. UCART19 has been additionally modified to disrupt the T-cell receptor alpha constant (TRAC) and CD52 genes. The preliminary results of this "off-the-shelf" allogeneic CAR T-cell therapy in a phase I, dose-escalation trial of UCART19 in CD19+ R/R B-ALL adult patients (pts) are described. Methods The primary objective of this study is to determine the maximum tolerated dose of UCART19 by investigating up to four dose levels (DL) in separate sequential cohorts. Adult pts (age ≥16 years) with CD19+ R/R B-ALL who have exhausted available treatment options are eligible. Disease burden must be quantifiable morphologically or with a minimal residual disease (MRD) load ≥1x10-3 at the end of the last anti-leukemic treatment. The lymphodepletion regimen combines cyclophosphamide and fludarabine, with or without alemtuzumab (FC or FCA). A single dose of UCART19 is administered on Day 0, and pts are closely monitored for safety and anti-leukemic activity until the end of study, 3 months after UCART19 administration. Pts are then rolled-over into a 15-years long-term follow-up study. The dose escalation follows a modified Toxicity Probability Interval (mTPI) design based on the occurrence of dose-limiting toxicity (DLT) assessed at the end of the 28-day evaluation period post UCART19 (D28). Results As of 24 June 2017, the 2 first cohorts (3 pts each) who received the first DL (DL1=6x106 total CAR+ cells) have been completed. Median age was 22.5 years (range 18-42). Pts received 1 to 5 previous lines of treatment with 5 out of 6 pts having undergone an allogeneic stem cell transplant (allo-SCT). Four of them had relapsed within 4-6 months post-transplant. Prior to UCART19 infusion, 4 pts had low disease burden ( All pts experienced cytokine release syndrome (CRS): 1 G1, 4 G2 and 1 G4. CRS G1 and G2 were manageable by supportive care ± tocilizumab. CRS G4, assessed as a DLT, occurred in the context of neutropenic sepsis, and was considered to be a contributory factor in the patient's death from multiple organ failure at D15. Time to onset of first CRS symptoms ranged between D5 and D10. CRS correlated with serum cytokine increase (IL-6; IL-10 and INFγ) and UCART19 expansion in the blood. One patient was reported to have probable skin GvHD G1. Only G1 neurotoxic events were observed in 1 patient. Asymptomatic viral reactivations (CMV and/or adenovirus) were seen in 3 pts and resolved with antiviral therapy. Among the 6 pts, 4 achieved a CRi with MRD negativity at D28 (MRD-ve, defined as a tumor burden All 4 pts achieving MRD-ve remission underwent a subsequent allo-SCT, 3 of them within 3 months of UCART19 infusion and 1 following retreatment with FC lymphodepletion and the same dose of UCART19, this patient having relapsed with CD19+ disease 2 months post initial UCART19 infusion. Post allo-SCT, 1 patient relapsed at 100 days with CD19+ disease, 1 died from infection and 2 remain in complete remission. Three pts remain alive at 2.4, 5.3 and 10.2 months respectively post UCART19 treatment. UCART19 (both cells and transgene levels) peaked between D12 and D17 in blood (flow cytometry [figure 1] and qPCR, respectively). UCART19 was detectable in blood from D10 to D28 (up to D42 in 1 patient) and in BM aspirates performed at D14 and D28. In-vivo cell expansion in BM occurred in all but the refractory patient. Conclusion Preliminary results of this first-in-human trial of UCART19 treatment in a high risk R/R B-ALL adult population revealed no unexpected toxicities. Asymptomatic lymphodepletion-related viral reactivations and a probable skin GvHD G1 were encountered. CRi with MRD-ve was achieved in 4 out of 5 pts who reached D28. The 2 first cohorts treated at DL1 have been completed and DL2 will now be investigated on which further results may be presented. The study is active in the UK and will be expanded to other EU countries and the US (NCT 02746952). Disclosures Graham: Servier: Research Funding; Pfizer: Other: Educational meeting attendance; Gilead: Other: Educational meeting attendance; Sanofi: Other: Educational meeting attendance. Yallop: Jazz Pharmaceuticals: Honoraria; Amgen: Honoraria; Pfizer: Other: Advisory board. Jozwik: Servier: Research Funding. Patten: Gilead Inc: Honoraria, Research Funding; Roche: Honoraria; Abbvie: Honoraria. Ellard: Moldmed: Honoraria. Potter: Pfizer: Other: Advisory board; Jazz: Honoraria. Devereux: AbbVie: Consultancy, Honoraria; MSD: Consultancy, Honoraria; Roche: Consultancy, Other: travel expenses; GSK: Consultancy; Gilead: Consultancy, Honoraria, Other: travel expenses, Speakers Bureau; Janssen: Consultancy, Honoraria, Other: travel expenses, Speakers Bureau; Servier: Other: Advisory board. Pagliuca: Jazz: Honoraria; Merck: Honoraria, Research Funding; Bluebird: Honoraria; Pfizer: Honoraria; Basilea: Honoraria; Astellas: Consultancy, Speakers Bureau; Gilead: Honoraria. Zinai: Servier: Employment. Binlich: Servier: Employment. Dupouy: Servier: Employment. Philippe: Servier: Employment. Balandraud: Servier: Employment. Dubois: Servier: Employment. Konto: Bristol-Myers Squibb: Employment, Equity Ownership; Pfizer: Employment, Equity Ownership. Patel: Pfizer: Employment, Equity Ownership. Benjamin: Pfizer: Other: Participated in Adboard meeting, Research Funding; Servier: Research Funding; Celgene: Honoraria.

When the single-stranded RNA genome of HIV-1 is copied into double-stranded DNA, the viral enzyme reverse transcriptase (RT) catalyzes the addition of approximately 20,000 nucleotides; however, the precise mechanism of nucleotide addition is unknown. In this study, we attempt to integrate the genetic data and biochemical mechanism of DNA polymerization with the structure of HIV-1 RT complexed with a dsDNA template-primer. The first step of polymerization involves the physical association of a polymerase with its nucleic acid substrate. A comparison of the structures of HIV-1 RT in the presence and absence of DNA indicates that the tip of the p66 thumb moves approximately 30 A upon DNA binding. This conformational change permits numerous interactions between residues of alpha-helices H and I in the thumb subdomain and the DNA. Measurements of DNA binding affinity for nucleic acids with double-stranded DNAs that have an increasing number of bases in the template overhang and molecular modeling suggest that portions of beta 3 and beta 4 within the fingers subdomain bind single-stranded regions of the template. Measurements of nucleotide incorporation efficiency (kcat/Km) show that the binding and incorporation of the next complementary nucleotide are not dependent on the length of the template overhang. Molecular modeling of an incoming nucleotide triphosphate (dTTP), based in part on the position of mercury atoms in a RT/DNA/Hg-UTP/Fab structure, suggests that portions of secondary structural elements alpha C-beta 6, alpha E, beta 11b, and beta 9-beta 10 determine the topology of the dNTP-binding site. These results also suggest that nucleotide incorporation is accompanied by a protein conformational change that positions the dNTP for nucleophilic attack. Nucleophilic attack by the oxygen atom of the 3'-OH group of the primer strand could be metal-mediated, and Asp185 may be directly involved in stabilizing the transition state. The translocation step may be characterized by rotational as well as translational motions of HIV-1 RT relative to the DNA double helix. Some of the energy required for translocation could be provided by dNTP hydrolysis and could be coupled with conformational changes within the nucleic acid. A structural comparison of HIV-1 RT, Klenow fragment, and T7 RNA polymerase identified regions within T7 RNA polymerase which are not present in the other two polymerases that might help this polymerase to remain bound with nucleic acids and contribute to the ability of the T7 RNA polymerase to polymerize processively.

3079Background: Stimulating effector T cells is an attractive anti-cancer therapeutic strategy. PF-8600 is a novel fully human IgG2 agonistic mAb specific for human OX40, a tumor necrosis factor re...

Lenalidomide (CC-5013) is a structural derivative of thalidomide, with antiangiogenic and immunomodulatory effects. Fourteen patients with metastatic renal cell carcinoma (RCC) were enrolled on a phase 2 trial of lenalidomide administered orally at 25 mg daily for 21 days followed by a rest period of 7 days. The best response was stable disease in eight patients (57%) of the 14 evaluable patients. Toxicities included fatigue, hyperglycemia, dyspnea, and myelosuppression with decreased hemoglobin, lymphopenia, and neutropenia. Lenalidomide is tolerable, but no objective responses were observed in this clinical trial.

Human immunodeficiency virus type 1 (HIV-1) is genetically highly variable. This is attributed to the error-prone nature of HIV-1 replication and its proclivity for recombination. During replication and recombination, reverse transcriptase (RT) must polymerize DNA to the 5' ends of multiple RNA and DNA template termini while converting HIV-1 RNA to double-stranded DNA. We have determined the fidelity of HIV-1 RT in vitro during polymerization to the 5' ends of HIV-1 long terminal repeat DNA template sequences and to the end of a partial HIV-1 genomic RNA template that mimics a recombination intermediate. HIV-1 RT readily extended recessed DNA primers to form full-length blunt-end DNA-DNA and DNA-RNA duplexes. In addition, HIV-1 RT catalyzed high yields of products with one to four extra nucleotides at the 3' ends of the nascent DNAs. These products were formed processively via a nontemplated mechanism that is highly specific for the addition of purine nucleotides (A > G >> T > or = C). Thus, HIV-1 RT is extremely unfaithful at both DNA and RNA template ends, introducing errors (extra nucleotides) in one out of every two or three nascent strands processively polymerized. This error rate is 1000 times higher than for HIV-1 RT-catalyzed errors at internal template positions. Blunt-end additions were also catalyzed by other retroviral RTs at relative rates of HIV-1 approximately Moloney murine leukemia virus > avian myeloblastosis virus. These data suggest a potentially important mechanism for retroviral mutation mediated by nontemplated blunt-end addition of purines prior to forced copy-choice recombination.