Paediatric Strategy Forum for medicinal product development of DNA damage response pathway inhibitors in children and adolescents with cancer: ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration.

DNA damage response inhibitors have a potentially important therapeutic role in paediatric cancers; however, their optimal use, including patient selection and combination strategy, remains unknown. Moreover, there is an imbalance between the number of drugs with diverse mechanisms of action and the limited number of paediatric patients available to be enrolled in early-phase trials, so prioritisation and a strategy are essential. While PARP inhibitors targeting homologous recombination-deficient tumours have been used primarily in the treatment of adult cancers with BRCA1/2 mutations, BRCA1/2 mutations occur infrequently in childhood tumours, and therefore, a specific response hypothesis is required. Combinations with targeted radiotherapy, ATR inhibitors, or antibody drug conjugates with DNA topoisomerase I inhibitor-related warheads warrant evaluation. Additional monotherapy trials of PARP inhibitors with the same mechanism of action are not recommended. PARP1-specific inhibitors and PARP inhibitors with very good central nervous system penetration also deserve evaluation. ATR, ATM, DNA-PK, CHK1, WEE1, DNA polymerase theta and PKMYT1 inhibitors are early in paediatric development. There should be an overall coordinated strategy for their development. Therefore, an academia/industry consensus of the relevant biomarkers will be established and a focused meeting on ATR inhibitors (as proof of principle) held. CHK1 inhibitors have demonstrated activity in desmoplastic small round cell tumours and have a potential role in the treatment of other paediatric malignancies, such as neuroblastoma and Ewing sarcoma. Access to CHK1 inhibitors for paediatric clinical trials is a high priority. The three key elements in evaluating these inhibitors in children are (1) innovative trial design (design driven by a clear hypothesis with the intent to further investigate responders and non-responders with detailed retrospective molecular analyses to generate a revised or new hypothesis); (2) biomarker selection and (3) rational combination therapy, which is limited by overlapping toxicity. To maximally benefit children with cancer, investigators should work collaboratively to learn the lessons from the past and apply them to future studies. Plans should be based on the relevant biology, with a focus on simultaneous and parallel research in preclinical and clinical settings, and an overall integrated and collaborative strategy.

Phase 2 Study of Iodine-131 Tositumomab Plus Chemotherapy in Patients With Previously Untreated Mantle-Cell Lymphoma.

BACKGROUND: Mantle-cell lymphoma (MCL) is sensitive to radiotherapy, and the CD20 antigen is relatively highly expressed in MCL. Therefore, radioimmunotherapy using radiolabeled anti-CD20 monoclonal antibodies has the potential to treat MCL. The objective of this study was to investigate the efficacy, pharmacokinetics, and safety of tositumomab (TST) and iodine-131 tositumomab (I-131 TST) followed by 6 cycles of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) in patients with previously untreated MCL (ClinicalTrials.govNCT00022945). PATIENTS AND METHODS: In this phase 2 open-label study, patients received dosimetric (day 0: 450 mg TST, then 35 mg I-131 TST [5 mCi]) and therapeutic (between days 7 and 14: 450 mg TST, then an individualized dose of I-131 TST [65-75 cGy]) TST/I-131 TST, with CHOP treatment commencing approximately 13 weeks after the therapeutic dose. The primary end point was the MCL response rate to treatment; secondary end points included confirmed complete response rate and total body residence time. RESULTS: Twenty-six patients were enrolled, and 25 were included in the intent-to-treat population. The overall unconfirmed response rate was 84%, and the confirmed complete response rate was 44%. The median progression free-survival was 27.6 months. The median total body residence time was 94.5 hours. No new or unexpected safety signals were identified. CONCLUSION: Patients with previously untreated MCL who received radioimmunotherapy with TST/I-131 TST followed by CHOP had a high response rate and a long duration of response, indicating that radioimmunotherapy is a therapeutic option in this patient population.

CHOP Chemotherapy Followed by Tositumomab and Iodine-131 Tositumomab for Previously Untreated Diffuse Large B-cell Lymphoma.

The efficacy and safety of tositumomab/iodine-131 tositumomab (TST/I-131 TST) were evaluated in diffuse large B-cell lymphoma patients who responded to first-line cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP). Fifteen patients (median age, 52 years) received dosimetric and therapeutic doses of TST/I-131 TST. The most common Grade 3/4 hematologic adverse events were decreased absolute neutrophil count (47%), white blood cell count (40%), platelet count (27%), and hemoglobin (20%). The complete response (CR) rate increased from 60% post-CHOP to 80% post TST / I-131 TST. With a median follow-up of 120.0 months (range, 14-130 months), median duration of response (95% confidence intervals) was 58.4 months (12.0-not reached [NR]) for patients with confirmed complete response and 58.4 months (20.9-NR) for all confirmed responders. Median progression-free survival and time to treatment failure were 63.0 months (16.1-NR). Median overall survival was not reached; 2 patients died on study. CHOP and TST/I-131 TST demonstrated clinical activity with acceptable toxicity.

Observational Retrospective Study of Altered Biodistribution of Tositumomab and 131I-Tositumomab.

UNLABELLED: The tositumomab/(131)I-tositumomab radioimmunotherapy regimen is administered as a dosimetric dose followed by a therapeutic dose. The biodistribution of the dosimetric dose is assessed by quantitative calculations of whole-body residence time (TBRT) and visual examination of whole-body γ-camera images, to determine the administered radioactivity dose and whether a therapeutic dose can be administered. We investigated whether altered biodistribution of (131)I-tositumomab could be identified using quantitative TBRT. METHODS: BioClinica, Inc., provided γ-camera images to an independent reviewer to assess altered (131)I-tositumomab biodistribution in patients reported to a registry. RESULTS: Of 2,649 therapeutic doses, 5 (0.2%) were cancelled because of altered biodistribution as determined by γ-camera images and TBRT. Of these, 3 γ-camera images were assessed by the independent reviewer; one showed altered biodistribution (0.04%) and was in agreement with the TBRT on-site calculation. CONCLUSION: TBRT alone should be used to determine altered biodistribution and hence whether to administer the therapeutic dose.

Stimulation of polo-like kinase 3 mRNA decay by tristetraprolin.

Polo-like protein kinase 3 (Plk3) has been proposed to regulate entry into S phase and promote apoptosis in response to oxidative stress. Its mRNA contains three AU-rich elements (AREs) in its 3' untranslated region (3'-UTR) that can contribute to the rapid degradation of labile transcripts. We investigated the possibility that tristetraprolin (TTP), a tandem CCCH zinc finger protein, could promote the decay of Plk3 transcripts. TTP is known to stimulate the deadenylation and decay of mRNAs possessing one or more copies of the consensus nonamer motif UUAUUUAUU. In stable mouse fibroblast cell lines derived from wild-type and TTP knockout littermates, the decay of Plk3 transcripts after serum stimulation was slowed in the absence of TTP. The specificity of TTP for promoting the degradation of Plk3 was demonstrated by the unaltered decay of Plk3 mRNA in cell lines deficient in the TTP family members ZFP36L1 and ZFP36L2. We also found that the AREs present in the Plk3 transcript were essential for both the binding of TTP to the 3'-UTR and promoting the destruction of target transcripts in cotransfection experiments. The regulation of Plk3 mRNA stability by TTP may influence the control of the cell cycle by this protein kinase.

Phosphorylation of GRK1 and GRK7 by cAMP-dependent protein kinase attenuates their enzymatic activities.

Phosphorylation of G protein-coupled receptors is a critical step in the rapid termination of G protein signaling. In rod cells of the vertebrate retina, phosphorylation of rhodopsin is mediated by GRK1. In cone cells, either GRK1, GRK7, or both, depending on the species, are speculated to initiate signal termination by phosphorylating the cone opsins. To compare the biochemical properties of GRK1 and GRK7, we measured the K(m) and V(max) of these kinases for ATP and rhodopsin, a model substrate. The results demonstrated that these kinases share similar kinetic properties. We also determined that cAMP-dependent protein kinase (PKA) phosphorylates GRK1 at Ser(21) and GRK7 at Ser(23) and Ser(36) in vitro. These sites are also phosphorylated when FLAG-tagged GRK1 and GRK7 are expressed in HEK-293 cells treated with forskolin to stimulate the endogenous production of cAMP and activation of PKA. Rod outer segments isolated from bovine retina phosphorylated the FLAG-tagged GRKs in the presence of dibutyryl-cAMP, suggesting that GRK1 and GRK7 are physiologically relevant substrates. Although both GRKs also contain putative phosphorylation sites for PKC and Ca(2+)/calmodulin-dependent protein kinase II, neither kinase phosphorylated GRK1 or GRK7. Phosphorylation of GRK1 and GRK7 by PKA reduces the ability of GRK1 and GRK7 to phosphorylate rhodopsin in vitro. Since exposure to light causes a decrease in cAMP levels in rod cells, we propose that phosphorylation of GRK1 and GRK7 by PKA occurs in the dark, when cAMP levels in photoreceptor cells are elevated, and represents a novel mechanism for regulating the activities of these kinases.