Adenosine A2A Receptor Activation Enhances Blood-Tumor Barrier Permeability in a Rodent Glioma Model.

The blood-tumor barrier (BTB) limits the entry of effective chemotherapeutic agents into the brain for treatment of malignant tumors like glioblastoma. Poor drug entry across the BTB allows infiltrative glioma stem cells to evade therapy and develop treatment resistance. Regadenoson, an FDA-approved adenosine A2A receptor (A2AR) agonist, has been shown to increase drug delivery across the blood-brain barrier in non-tumor-bearing rodents without a defined mechanism of enhancing BTB permeability. Here, we characterize the time-dependent impact of regadenoson on brain endothelial cell interactions and paracellular transport, using mouse and rat brain endothelial cells and tumor models. In vitro, A2AR activation leads to disorganization of cytoskeletal actin filaments by 30 minutes, downregulation of junctional protein expression by 4 hours, and reestablishment of endothelial cell integrity by 8 hours. In rats bearing intracranial gliomas, regadenoson treatment results in increase of intratumoral temozolomide concentrations, yet no increased survival noted with combined temozolomide therapy. These findings demonstrate regadenoson's ability to induce brain endothelial structural changes among glioma to increase BTB permeability. The use of vasoactive mediators, like regadenoson, which transiently influences paracellular transport, should further be explored to evaluate their potential to enhance central nervous system treatment delivery to aggressive brain tumors. IMPLICATIONS: This study provides insight on the use of a vasoactive agent to increase exposure of the BTB to chemotherapy with intention to improve glioma treatment efficacy.

Therapeutic targeting of ATR yields durable regressions in small cell lung cancers with high replication stress.

Small cell neuroendocrine cancers (SCNCs) are recalcitrant cancers arising from diverse primary sites that lack effective treatments. Using chemical genetic screens, we identified inhibition of ataxia telangiectasia and rad3 related (ATR), the primary activator of the replication stress response, and topoisomerase I (TOP1), nuclear enzyme that suppresses genomic instability, as synergistically cytotoxic in small cell lung cancer (SCLC). In a proof-of-concept study, we combined M6620 (berzosertib), first-in-class ATR inhibitor, and TOP1 inhibitor topotecan in patients with relapsed SCNCs. Objective response rate among patients with SCLC was 36% (9/25), achieving the primary efficacy endpoint. Durable tumor regressions were observed in patients with platinum-resistant SCNCs, typically fatal within weeks of recurrence. SCNCs with high neuroendocrine differentiation, characterized by enhanced replication stress, were more likely to respond. These findings highlight replication stress as a potentially transformative vulnerability of SCNCs, paving the way for rational patient selection in these cancers, now treated as a single disease.

Hypoxic Regulation of Gene Transcription and Chromatin: Cause and Effect.

Cellular responses to low oxygen (hypoxia) are fundamental to normal physiology and to the pathology of many common diseases. Hypoxia-inducible factor (HIF) is central to this by enhancing the transcriptional activity of many hundreds of genes. The cellular response to HIF is cell-type-specific and is largely governed by the pre-existing epigenetic landscape. Prior to activation, HIF-binding sites and the promoters of HIF-target genes are already accessible, in contact with each other through chromatin looping and display markers of activity. However, hypoxia also modulates the epigenetic environment, both in parallel to and as a consequence of HIF activation. This occurs through a combination of oxygen-sensitive changes in enzyme activity, transcriptional activation of epigenetic modifiers, and localized recruitment to chromatin by HIF and activated RNApol2. These hypoxic changes in the chromatin environment may both contribute to and occur as a consequence of transcriptional regulation. Nevertheless, they have the capacity to both modulate and extend the transcriptional response to hypoxia.

Metastasis-Specific Gene Expression in Autochthonous and Allograft Mouse Mammary Tumor Models: Stratification and Identification of Targetable Signatures.

Breast cancer metastasis is a leading cause of cancer-related death of women in the United States. A hurdle in advancing metastasis-targeted intervention is the phenotypic heterogeneity between primary and secondary lesions. To identify metastasis-specific gene expression profiles we performed RNA-sequencing of breast cancer mouse models; analyzing metastases from models of various drivers and routes. We contrasted the models and identified common, targetable signatures. Allograft models exhibited more mesenchymal-like gene expression than genetically engineered mouse models (GEMM), and primary culturing of GEMM-derived metastatic tissue induced mesenchymal-like gene expression. In addition, metastasis-specific transcriptomes differed between tail vein and orthotopic injection of the same cell line. Gene expression common to models of spontaneous metastasis included sildenafil response and nicotine degradation pathways. Strikingly, in vivo sildenafil treatment significantly reduced metastasis by 54%, while nicotine significantly increased metastasis by 46%. These data suggest that (i) actionable metastasis-specific pathways can be readily identified, (ii) already available drugs may have great potential to alleviate metastatic incidence, and (iii) metastasis may be influenced greatly by lifestyle choices such as the choice to consume nicotine products. In summary, while mouse models of breast cancer metastasis vary in ways that must not be ignored, there are shared features that can be identified and potentially targeted therapeutically. IMPLICATIONS: The data we present here exposes critical variances between preclinical models of metastatic breast cancer and identifies targetable pathways integral to metastatic spread. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/18/9/1278/F1.large.jpg.

Local and Systemic Antitumor Effects of Photo-activatable Paclitaxel Prodrug on Rat Breast Tumor Models.

We demonstrated that a large primary and a small untreated distant breast cancer could be controlled by local treatment with our light-activatable paclitaxel (PTX) prodrug. We hypothesized that the treated tumor would be damaged by the combinational effects of photodynamic therapy (PDT) and locally released PTX and that the distant tumor would be suppressed by systemic antitumor effects. Syngeneic rat breast cancer models (single- and two-tumor models) were established on Fischer 344 rats by subcutaneous injection of MAT B III cells. The rats were injected with PTX prodrug (dose: 1 umole kg-1 , i.v.), and tumors were treated with illumination using a 690-nm laser (75 or 140 mW cm-1 for 30 min, cylindrical light diffuser, drug-light interval [DLI] 9 h). Larger tumors (~16 mm) were effectively ablated (100%) without recurrence for >90 days. All cured rats rejected rechallenged tumor for up to 12 months. In the two-tumor model, the treatment of the local large tumor (~16 mm) also cured the untreated tumor (4-6 mm) through adaptive immune activation. This is our first demonstration that local treatment with our PTX prodrug produces systemic antitumor effects. Further investigations are warranted to understand mechanisms and optimal conditions to achieve clinically translatable systemic antitumor effects.

Phase I/II Study of the Mesothelin-targeted Immunotoxin LMB-100 with Nab-Paclitaxel for Patients with Advanced Pancreatic Adenocarcinoma.

PURPOSE: LMB-100 is a recombinant immunotoxin (iTox) consisting of a mesothelin-binding Fab for targeting and a modified Pseudomonas exotoxin A payload. Preclinical studies showed that combining taxanes with iTox results in synergistic antitumor activity. The objectives of this phase I/II study were to determine the MTD of LMB-100 when administered with nanoalbumin bound (nab)-paclitaxel to patients with previously treated advanced pancreatic adenocarcinoma and to assess the objective response rate. PATIENTS AND METHODS: Patients (n = 20) received fixed-dose nab-paclitaxel (125 mg/m2 on days 1 and 8) with LMB-100 (65 or 100 µg/kg on days 1, 3, and 5) in 21-day cycles for 1-3 cycles. RESULTS: Fourteen patients were treated on the dose escalation and an additional six in the phase II expansion. MTD of 65 µg/kg was established for the combination. Dose-limiting toxicity resulting from capillary leak syndrome (CLS) was seen in two of five patients treated at 100 µg/kg and one of six evaluable phase I patients receiving the MTD. Severity of CLS was associated with increases in apoptotic circulating endothelial cells. LMB-100 exposure was unaffected by anti-LMB-100 antibody formation in five of 13 patients during cycle 2. Seven of 17 evaluable patients experienced >50% decrease in CA 19-9, including three with previous exposure to nab-paclitaxel. One patient developed an objective partial response. Patients with biomarker responses had higher tumor mesothelin expression. CONCLUSIONS: Although clinical activity was observed, the combination was not well tolerated and alternative drug combinations with LMB-100 will be pursued.

A population pharmacokinetic analysis of the oral CYP17 lyase and androgen receptor inhibitor seviteronel in patients with advanced/metastatic castration-resistant prostate cancer or breast cancer.

PURPOSE: Seviteronel is an orally-administered selective cytochrome P450c17a 17,20-lyase and androgen receptor inhibitor with anti-tumor activity in vitro and in vivo, and clinical activity in men with advanced castration-resistant prostate cancer (CRPC) and men and women with advanced breast cancer. The purpose of this study was to assess the pharmacokinetics (PK) of seviteronel across the aforementioned populations. METHODS: This report describes the PK of seviteronel (50-750 mg, QD or BID) using noncompartmental and population approaches from 243 patients with advanced breast or prostate cancer pooled across 4 clinical studies. First dose and steady-state PK were examined, as well as covariates including prandial status, sex and concomitant dexamethasone. RESULTS: Seviteronel PK can be characterized by transit absorption and a bi-phasic first-order elimination while accounting for covariance between random effects. Prandial status did not significantly affect any parameters to a clinically-relevant extent. Both sex and body weight were significant covariates on clearance, explaining 37% of the interindividual variability on that parameter. There were no significant effects from the race or the presence of a corticosteroid (either dexamethasone or prednisone). CONCLUSIONS: Seviteronel demonstrates linear PK over the dose range of 50-750 mg given either BID or QD in men with advanced CRPC or men and women with breast cancer. The disposition of seviteronel following oral administration is well described by this population PK model and can be used for accurate simulations for future studies with body weight and sex affecting clearance, but not to a clinically-meaningful degree requiring a change in the current dosing scheme.

PBPK modeling-based optimization of site-specific chemo-photodynamic therapy with far-red light-activatable paclitaxel prodrug.

Photodynamic therapy (PDT) is a clinically approved therapeutic modality to treat certain types of cancers. However, incomplete ablation of tumor is a challenge. Visible and near IR-activatable prodrug, exhibiting the combined effects of PDT and local chemotherapy, showed better efficacy than PDT alone, without systemic side effects. Site-specifically released chemotherapeutic drugs killed cancer cells surviving from rapid PDT damage via bystander effects. Recently, we developed such a paclitaxel (PTX) prodrug that targets folate receptors. The goals of this study were to determine the optimal treatment conditions, based on modeling, for maximum antitumor efficacy in terms of drug-light interval (DLI), and to investigate the impact of rapid PDT effects on the pharmacokinetic (PK) profiles of the released PTX. PK profiles of the prodrug were determined in key organs and a quantitative systems pharmacology (QSP) model was established to simulate PK profiles of the prodrug and the released PTX. Three illumination time points (DLI = 0.5, 9, or 48 h) were selected for the treatment based on the plasma/tumor ratio of the prodrug to achieve V-PDT (vascular targeted-PDT, 0.5 h), C-PDT (cellular targeted-PDT, 48 h), or both V- and C-PDT (9 h). The anti-tumor efficacy of the PTX prodrug was greatly influenced by the DLI. The 9 h DLI group, when both tumor and plasma concentrations of the prodrug were sufficient, showed the best antitumor effect. The clearance of the released PTX from tumor seemed to be largely impacted by blood circulation. Here, QSP modeling was an invaluable tool for rational optimization of the treatment conditions and for a deeper mechanistic understanding of the positive physiological effect of the combination therapy.