Compared with follicular lymphoma, high PI3Kα expression was more prevalent in diffuse large B cell lymphoma (DLBCL), although both tumor types expressed substantial PI3Kδ. Simultaneous inhibition of PI3Kα and PI3Kδ dramatically enhanced the anti-tumor profile in ABC-DLBCL models compared with selective inhibition of PI3Kδ, PI3Kα, or BTK. The anti-tumor activity was associated with suppression of p-AKT and a mechanism of blocking nuclear factor-κB activation driven by CD79, CARD11, TNFAIP3, or MYD88. Inhibition of PI3Kα/δ resulted in tumor regression in an ibrutinib-resistant CD79B/MYD88 patient-derived ABC-DLBCL model. Furthermore, rebound activation of BTK and AKT was identified as a mechanism limiting CD79B-ABC-DLBCL to show a robust response to PI3K and BTK inhibitor monotherapies. A combination of ibrutinib with the PI3Kα/δ inhibitor copanlisib produced a sustained complete response in vivo in CD79B/MYD88 ABC-DLBCL models.

◥Purpose: Prostate-specific membrane antigen (PSMA) is an attractive target for radionuclide therapy of metastatic castrationresistant prostate cancer (mCRPC). PSMA-targeted alpha therapy (TAT) has shown early signs of activity in patients with prostate cancer refractory to beta radiation. We describe a novel, antibody-based TAT, the PSMA-targeted thorium-227 conjugate PSMA-TTC (BAY 2315497) consisting of the alpha-particle emitter thorium-227 complexed by a 3,2-HOPO chelator covalently linked to a fully human PSMA-targeting antibody.Experimental Design: PSMA-TTC was characterized for affinity, mode of action, and cytotoxic activity in vitro. Biodistribution, pharmacokinetics, and antitumor efficacy were investigated in vivo using cell line and patient-derived xenograft (PDX) models of prostate cancer.Results: PSMA-TTC was selectively internalized into PSMApositive cells and potently induced DNA damage, cell-cycle arrest, and apoptosis in vitro. Decrease in cell viability was observed dependent on the cellular PSMA expression levels. In vivo, PSMA-TTC showed strong antitumor efficacy with T/C values of 0.01 to 0.31 after a single injection at 300 to 500 kBq/kg in subcutaneous cell line and PDX models, including models resistant to standard-of-care drugs such as enzalutamide. Furthermore, inhibition of both cancer and cancer-induced abnormal bone growth was observed in a model mimicking prostate cancer metastasized to bone. Specific tumor uptake and efficacy were demonstrated using various PSMA-TTC doses and dosing schedules. Induction of DNA double-strand breaks was identified as a key mode of action for PSMA-TTC both in vitro and in vivo.Conclusions: The strong preclinical antitumor activity of PSMA-TTC supports its clinical evaluation, and a phase I trial is ongoing in mCRPC patients (NCT03724747).

Purpose: The catalytic function of BUB1 is required for chromosome arm resolution and positioning of the chromosomal passenger complex for resolution of spindle attachment errors and plays only a minor role in spindle assembly checkpoint activation. Here, we present the identification and preclinical pharmacologic profile of the first BUB1 kinase inhibitor with good bioavailability.Experimental Design: The Bayer compound library was screened for BUB1 kinase inhibitors and medicinal chemistry efforts to improve target affinity and physicochemical and pharmacokinetic parameters resulting in the identification of BAY 1816032 were performed. BAY 1816032 was characterized for kinase selectivity, inhibition of BUB1 signaling, and inhibition of tumor cell proliferation alone and in combination with taxanes, ATR, and PARP inhibitors. Effects on tumor growth in vivo were evaluated using human triple-negative breast xenograft models.Results: The highly selective compound BAY 1816032 showed long target residence time and induced chromosome mis-segregation upon combination with low concentrations of paclitaxel. It was synergistic or additive in combination with paclitaxel or docetaxel, as well as with ATR or PARP inhibitors in cellular assays. Tumor xenograft studies demonstrated a strong and statistically significant reduction of tumor size and excellent tolerability upon combination of BAY 1816032 with paclitaxel or olaparib as compared with the respective monotherapies.Conclusions: Our findings suggest clinical proof-of-concept studies evaluating BAY 1816032 in combination with taxanes or PARP inhibitors to enhance their efficacy and potentially overcome resistance.NOTE: Values represent the mean of at least two independent experiments with two technical replicates. In cases where SDs are not indicated, a single experiment with three or more replicates was conducted. Experimental details to the methods used are given in the Materials and Methods section. Siemeister et al. NOTE: CI 50 interpretation code: CI 50 < 0.8, synergism; 0.8 CI 50 1.2, additivity; CI 50 > 1.2, antagonism. Calculated combination indices for 50% inhibition (CI 50 ) from proliferation assays of cell lines treated with drug combinations as indicated. Monotreatment IC 50 values and the concentrations required in combination of the two test compounds to achieve the CI 50 are shown. All concentrations are given in mol/L.

Targeted alpha therapy (TAT) offers the potential for the targeted delivery of potent a-particle-emitting radionuclides that emit high linear energy transfer radiation. This leads to a densely ionizing radiation track over a short path. Localized radiation induces cytotoxic, difficult-to-repair, clustered DNA double-strand breaks (DSBs). To date, radium-223 (223 Ra) is the only TAT approved for the treatment of patients with metastatic castration-resistant prostate cancer. Thorium-227 (227 Th), the progenitor nuclide of 223 Ra, offers promise as a wider-ranging alternative due to the availability of efficient chelators, such as octadentate 3,2-hydroxypyridinone (3,2-HOPO). The 3,2-HOPO chelator can be readily conjugated to a range of targeting moieties, enabling the generation of new targeted thorium-227 conjugates (TTCs). This review provides a comprehensive overview of the advances in the preclinical development of TTCs for hematological cancers, including CD22-positive B cell cancers and CD33-positive leukemia, as well as for solid tumors overexpressing renal cell cancer antigen CD70, membrane-anchored glycoprotein mesothelin in mesothelioma, prostate-specific membrane antigen in prostate cancer, and fibroblast growth factor receptor 2. As the mechanism of action for TTCs is linked to the formation of DSBs, the authors also report data supporting combinations of TTCs with inhibitors of the DNA damage response pathways, including those of the ataxia telangiectasia and Rad3-related protein, and poly-ADP ribose polymerase. Finally, emerging evidence suggests that TTCs induce immunogenic cell death through the release of danger-associated molecular patterns. Based on encouraging preclinical data, clinical studies have been initiated to investigate the safety and tolerability of TTCs in patients with various cancers.

Combination therapy has improved the quality of life for patients with squamous cell carcinomas of the head and neck (HNSCCs) but has not decisively changed prognosis. Targeted therapies, which enhance accumulation of the drug in the tumor, may be realized using tumor-specific binding peptides. This paper identifies and characterizes an HNSCC affine peptide. Methods: From a phage library comprising 10 9 different displayed peptides, 1 peptide was enriched after 5 in vitro selection rounds on HNO223 tumor cells. Subsequently, the gained peptide sequence H 2 N-SPRGDLAVLGHKY-CONH 2 (HBP-1) was synthesized as an amide and labeled with 125 I. In vitro studies for binding kinetics and competition were performed with 5 different HNSCC cell lines. Furthermore, the stability of the peptide was evaluated in human serum. The in vivo biodistribution of 131 Ilabeled peptide was determined in HNSCC tumor-bearing nude mice. The results were further validated in human HNSCC tumor tissue sections using fluorescence-labeled HBP-1. Competition experiments were performed to determine the binding sequence and validate the target. Results: The HBP-1 motif was enriched in 62% of all phages sequenced. Labeled 125 I-HBP-1 showed binding to 5 different HNSCC cell lines and a maximum binding to HNO97 cells, with 11% of the applied dose per 10 6 cells and an inhibitory concentration of 50% of 38.9 nM. Stability experiments in human serum showed a half-life of 55 min. In 2 different HNSCC tumor xenografts, 131 I-HBP-1 accumulated rapidly, with stable uptake until 45 min after intravenous application. Peptide immunohistochemistry of HNSCC tissue sections exhibited tumor staining by HBP-1, whereas normal tissue remained negative. Sequence mutation and competition experiments revealed that the intrinsic RGD motif in combination with the intrinsic LXXL motif is responsible for the binding ability of HBP1. The RGDLXXL sequence within this peptide is known and indicates that binding occurs via the a v b 6 rather than the a v b 3 integrin. Conclusion: Within the sequence of HBP-1 is a RGDLXXL motif, and most likely it is targeting the a v b 6 receptor of the integrin family of cell adhesion receptors. HBP-1 represents a promising lead structure for the development of targeted therapies or diagnostic procedures in patients with HNSCC. More than 5% of all malignant tumors worldwide are head and neck cancer, with more than 100,000 cases diagnosed in Europe each year. In the Western world, squamous cell carcinoma of the head and neck (HNSCC) accounts for more than 90% of all head and neck cancers (1). Most cases are diagnosed in patients who are between 50 and 70 y old, with a 5 times higher rate for men than for women. The 5-y survival rate of less than 30% is due to a high lymphogenic metastatic tendency, a high recurrence rate, and an increased occurrence of secondary tumors. Treatment strategies for advanced HNSCC have evolved from less effective monotherapy to an integrated, more effective multidisciplinary approach. A new field under investigati...