Faculty Bibliography

A critical benchmark in the development of antibody-based therapeutics is demonstration of efficacy in preclinical mouse models of human disease, many of which rely on immunodeficient mice. However, relatively little is known about how the biology of various immunodeficient strains impacts the in vivo fate of these drugs. Here we used immunoPET radiotracers prepared from humanized, chimeric, and murine mAbs against four therapeutic oncologic targets to interrogate their biodistribution in four different strains of immunodeficient mice bearing lung, prostate, and ovarian cancer xenografts. The immunodeficiency status of the mouse host as well as both the biological origin and glycosylation of the antibody contributed significantly to the anomalous biodistribution of therapeutic monoclonal antibodies in an Fc receptor-dependent manner. These findings may have important implications for the preclinical evaluation of Fc-containing therapeutics and highlight a clear need for biodistribution studies in the early stages of antibody drug development.Significance: Fc/FcγR-mediated immunobiology of the experimental host is a key determinant to preclinical in vivo tumor targeting and efficacy of therapeutic antibodies. Cancer Res; 78(7); 1820-32. ©2018 AACR.

Purpose: Small cell lung cancer (SCLC) is an aggressive malignancy with a critical need for novel therapies. Our goal was to determine whether PARP inhibition could sensitize SCLC cells to ionizing radiation (IR) and if so, to determine the contribution of PARP trapping to radiosensitization.Experimental Design: Short-term viability assays and clonogenic survival assays (CSA) were used to assess radiosensitization in 6 SCLC cell lines. Doses of veliparib and talazoparib with equivalent enzymatic inhibitory activity but differing PARP trapping activity were identified and compared in CSAs. Talazoparib, IR, and their combination were tested in three patient-derived xenograft (PDX) models.Results: Talazoparib radiosensitized 5 of 6 SCLC cell lines in short-term viability assays and confirmed in 3 of 3 cell lines by CSAs. Concentrations of 200 nmol/L talazoparib and 1,600 nmol/L veliparib similarly inhibited PAR polymerization; however, talazoparib exhibited greater PARP trapping activity that was associated with superior radiosensitization. This observation further correlated with an increased number of double-stranded DNA breaks induced by talazoparib as compared with veliparib. Finally, a dose of 0.2 mg/kg talazoparib in vivo caused tumor growth inhibition in combination with IR but not as a single agent in 3 SCLC PDX models.Conclusions: PARP inhibition effectively sensitizes SCLC cell lines and PDXs to IR, and PARP trapping activity enhances this effect. PARP inhibitors, especially those with high PARP trapping activity, may provide a powerful tool to improve the efficacy of radiotherapy in SCLC. Clin Cancer Res; 24(20); 5143-52. ©2018 AACR.

Insufficient chemotherapy response and rapid disease progression remain concerns for small-cell lung cancer (SCLC). Oncologists rely on serial CT scanning to guide treatment decisions, but this cannot assess in vivo target engagement of therapeutic agents. Biomarker assessments in biopsy material do not assess contemporaneous target expression, intratumoral drug exposure, or drug-target engagement. Here, we report the use of PARP1/2-targeted imaging to measure target engagement of PARP inhibitors in vivo. Using a panel of clinical PARP inhibitors, we show that PARP imaging can quantify target engagement of chemically diverse small molecule inhibitors in vitro and in vivo. We measure PARP1/2 inhibition over time to calculate effective doses for individual drugs. Using patient-derived xenografts, we demonstrate that different therapeutics achieve similar integrated inhibition efficiencies under different dosing regimens. This imaging approach to non-invasive, quantitative assessment of dynamic intratumoral target inhibition may improve patient care through real-time monitoring of drug delivery.

The Notch ligand DLL3 has emerged as a novel therapeutic target expressed in small cell lung cancer (SCLC) and high-grade neuroendocrine carcinomas. Rovalpituzumab teserine (Rova-T; SC16LD6.5) is a first-in-class DLL3-targeted antibody-drug conjugate with encouraging initial safety and efficacy profiles in SCLC in the clinic. Here we demonstrate that tumor expression of DLL3, although orders of magnitude lower in surface protein expression than typical oncology targets of immunoPET, can serve as an imaging biomarker for SCLC. We developed ⁸⁹Zr-labeled SC16 antibody as a companion diagnostic agent to facilitate selection of patients for treatment with Rova-T based on a noninvasive interrogation of the in vivo status of DLL3 expression using PET imaging. Despite low cell-surface abundance of DLL3, immunoPET imaging with ⁸⁹Zr-labeled SC16 antibody enabled delineation of subcutaneous and orthotopic SCLC tumor xenografts as well as distant organ metastases with high sensitivity. Uptake of the radiotracer in tumors was concordant with levels of DLL3 expression and, most notably, DLL3 immunoPET yielded rank-order correlation for response to SC16LD6.5 therapy in SCLC patient-derived xenograft models. Cancer Res; 77(14); 3931-41. ©2017 AACR.

Seneca Valley virus (SVV) is an oncolytic picornavirus with selective tropism for neuroendocrine cancers. It has shown promise as a cancer therapeutic in preclinical studies and early-phase clinical trials. Here, we have identified anthrax toxin receptor 1 (ANTXR1) as the receptor for SVV using genome-wide loss-of-function screens. ANTXR1 is necessary for permissivity in vitro and in vivo. However, robust SVV replication requires an additional innate immune defect. We found that SVV interacts directly and specifically with ANTXR1, that this interaction is required for SVV binding to permissive cells, and that ANTXR1 expression is necessary and sufficient for infection in cell lines with decreased expression of antiviral IFN genes at baseline. Finally, we identified the region of the SVV capsid that is responsible for receptor recognition using cryoelectron microscopy of the SVV-ANTXR1-Fc complex. These studies identify ANTXR1, a class of receptor that is shared by a mammalian virus and a bacterial toxin, as the cellular receptor for SVV.

PURPOSE/OBJECTIVE:PARP inhibitors (PARPi) are a novel class of small molecule therapeutics for small cell lung cancer (SCLC). Identification of predictors of response would advance our understanding, and guide clinical application, of this therapeutic strategy. EXPERIMENTAL DESIGN/METHODS:Efficacy of PARP inhibitors olaparib, rucaparib, and veliparib, as well as etoposide and cisplatin in SCLC cell lines, and gene expression correlates, was analyzed using public datasets. HRD genomic scar scores were calculated from Affymetrix SNP 6.0 arrays. In vitro talazoparib efficacy was measured by cell viability assays. For functional studies, CRISPR/Cas9 and shRNA were used for genomic editing and transcript knockdown, respectively. Protein levels were assessed by immunoblotting and immunohistochemistry (IHC). Quantitative synergy of talazoparib and temozolomide was determined in vitro In vivo efficacy of talazoparib, temozolomide, and the combination was assessed in patient-derived xenograft (PDX) models. RESULTS:We identified SLFN11, but not HRD genomic scars, as a consistent correlate of response to all three PARPi assessed, with loss of SLFN11 conferring resistance to PARPi. We confirmed these findings in vivo across multiple PDX and defined IHC staining for SLFN11 as a predictor of talazoparib response. As temozolomide has activity in SCLC, we investigated combination therapy with talazoparib and found marked synergy in vitro and efficacy in vivo, which did not solely depend on SLFN11 or MGMT status. CONCLUSIONS:SLFN11 is a relevant predictive biomarker of sensitivity to PARP inhibitor monotherapy in SCLC and we identify combinatorial therapy with TMZ as a particularly promising therapeutic strategy that warrants further clinical investigation. Clin Cancer Res; 23(2); 523-35. ©2016 AACR.

Small cell lung cancer is initially highly responsive to cisplatin and etoposide but in almost every case becomes rapidly chemoresistant, leading to death within 1 year. We modeled acquired chemoresistance in vivo using a series of patient-derived xenografts to generate paired chemosensitive and chemoresistant cancers. Multiple chemoresistant models demonstrated suppression of SLFN11, a factor implicated in DNA-damage repair deficiency. In vivo silencing of SLFN11 was associated with marked deposition of H3K27me3, a histone modification placed by EZH2, within the gene body of SLFN11, inducing local chromatin condensation and gene silencing. Inclusion of an EZH2 inhibitor with standard cytotoxic therapies prevented emergence of acquired resistance and augmented chemotherapeutic efficacy in both chemosensitive and chemoresistant models of small cell lung cancer.

Inactivation of NF2/Merlin causes the autosomal-dominant cancer predisposition syndrome familial neurofibromatosis type 2 (NF2) and contributes to the development of malignant pleural mesothelioma (MPM). To develop a targeted therapy for NF2-mutant tumors, we have exploited the recent realization that Merlin loss drives tumorigenesis by activating the E3 ubiquitin ligase CRL4^DCAF1, thereby inhibiting the Hippo pathway component Lats. Here, we show that MLN4924, a NEDD8-activating enzyme (NAE) inhibitor, suppresses CRL4^DCAF1 and attenuates activation of YAP in NF2-mutant tumor cells. In addition, MLN4924 sensitizes MPM to traditional chemotherapy, presumably as a result of collateral inhibition of cullin-RING ubiquitin ligases (CRL) involved in DNA repair. However, even in combination with chemotherapy, MLN4924 does not exhibit significant preclinical activity. Further analysis revealed that depletion of DCAF1 or treatment with MLN4924 does not affect mTOR hyperactivation in NF2-mutant tumor cells, suggesting that loss of Merlin activates mTOR independently of CRL4^DCAF1 Intriguingly, combining MLN4924 with the mTOR/PI3K inhibitor GDC-0980 suppresses the growth of NF2-mutant tumor cells in vitro as well as in mouse and patient-derived xenografts. These results provide preclinical rationale for the use of NAE inhibitors in combination with mTOR/PI3K inhibitors in NF2-mutant tumors. Mol Cancer Ther; 16(8); 1693-704. ©2017 AACR.