Faculty Bibliography

Recent clinical data in lung cancer suggests that epigenetically targeted therapy may selectively enhance chemotherapeutic sensitivity. There have been few if any studies rigorously evaluating this hypothesized priming effect. Here we describe a series of investigations testing whether epigenetic priming with azacitidine and entinostat increases sensitivity of NSCLC to cytotoxic agents. We noted no differences in chemosensitivity following treatment with epigenetic therapy in in vitro assays of viability and colony growth. Using cell line and patient derived xenograft (PDX) models, we also observed no change in responsiveness to cisplatin in vivo. In select models, we noted differential responses to irinotecan treatment in vivo. In vitro epigenetic therapy prior to tumor implantation abrogated response of H460 xenografts to irinotecan. Conversely, in vitro epigenetic therapy appeared to sensitize A549 xenografts (tumor growth inhibition 51%, vs. 22% in mock-pretreated control). In vivo epigenetic therapy enhanced the response of adenocarcinoma PDX to irinotecan. Taken together, these data do not support broadly applicable epigenetic priming in NSCLC. Priming effects may be context-specific, dependent on both tumor and host factors. Further preclinical study is necessary to determine whether, and in which contexts, priming with epigenetic therapy has potential to enhance chemotherapeutic efficacy in NSCLC patients.

The oncolytic picornavirus Seneca Valley Virus (SVV-001) demonstrates anti-tumor activity in models of small cell lung cancer (SCLC), but may ultimately need to be combined with cytotoxic therapies to improve responses observed in patients. Combining SVV-001 virotherapy with a peptide prodrug activated by the viral protease 3Cpro is a novel strategy that may increase the therapeutic potential of SVV-001. Using recombinant SVV-001 3Cpro, we measured cleavage kinetics of predicted SVV-001 3Cpro substrates. An efficient substrate, L/VP4 (kcat/KM = 1932 ± 183 M(-1)s(-1)), was further optimized by a P2' N→P substitution yielding L/VP4.1 (kcat/KM = 17446 ± 2203 M(-1)s(-1)). We also determined essential substrate amino acids by sequential N-terminal deletion and substitution of amino acids found in other picornavirus genera. A peptide corresponding to the L/VP4.1 substrate was selectively cleaved by SVV-001 3Cpro in vitro and was stable in human plasma. These data define an optimized peptide substrate for SVV-001 3Cpro, with direct implications for anti-cancer therapeutic development.

Overexpression of the antiapoptotic protein Bcl-2 is observed in the majority of small cell lung cancer (SCLC) cases and is associated with resistance to chemotherapy. While targeting Bcl-2 in hematologic malignancies continues to show signs of promise, translating the BH3 mimetic ABT-737 (or ABT-263; navitoclax) to the clinic for solid tumors has remained problematic, with limited single-agent activity in early-phase clinical trials. Here, we used patient-derived xenograft (PDX) models of SCLC to study ABT-737 resistance and demonstrated that responses to ABT-737 are short lived and coincide with decreases in HIF-1α-regulated transcripts. Combining the mTOR inhibitor rapamycin with ABT-737 rescued this resistance mechanism, was highly synergistic in vitro, and provided durable tumor regressions in vivo without notable hematologic suppression. In comparison, tumor regressions did not occur when ABT-737 was combined with etoposide, a gold-standard cytotoxic for SCLC therapy. Rapamycin exposure was consistently associated with an increase in the proapoptotic protein BAX, whereas ABT-737 caused dose-dependent decreases in BAX. As ABT-737 triggers programmed cell death in a BAX/BAK-dependent manner, we provide preclinical evidence that the efficacy of ABT-737 as a single agent is self-limiting in SCLC, but the addition of rapamycin can maintain or increase levels of BAX protein and markedly enhance the anticancer efficacy of ABT-737. These data have direct translational implications for SCLC clinical trials.

SUMMARY/CONCLUSIONS:In this issue of Cancer Discovery, Romero and colleagues identify somatic mutations and deletions of MAX, and also define what seem to be mutually exclusive alterations in MYC family members and other MYC-associated factors in small cell lung cancer. Taken together, these data highlight the importance of MYC signaling in small cell lung cancer and suggest possible avenues for therapeutic intervention.

We assessed the efficacy of Seneca Valley virus (SVV-001), a neuroendocrine cancer-selective oncolytic picornavirus, in primary heterotransplant mouse models of small cell lung cancer (SCLC), including three lines each of classic and variant SCLC. Half-maximal effective concentrations for cell lines derived from three variant heterotransplants ranged from 1.6×10(-3) (95% confidence interval [CI] = 1×10(-3) to 2.5×10(-3)) to 3.9×10(-3) (95% CI = 2.8×10(-3) to 5.5×10(-3)). Sustained tumor growth inhibition in vivo was only observed in variant lines (two-sided Student t test, P < .005 for each). Doses of 10(14) vp/kg were able to completely and durably eradicate tumors in a variant SCLC heterotransplant model in two of six mice. Gene expression profiling revealed that permissive lines are typified by lower expression of the early neurogenic transcription factor ASCL1 and, conversely, by higher expression of the late neurogenic transcription factor NEUROD1. This classifier demonstrates a sensitivity of .89, specificity of .92, and accuracy of .91. The NEUROD1 to ASCL1 ratio may serve as a predictive biomarker of SVV-001 efficacy.

Seneca Valley virus (SVV-001) is an oncolytic picornavirus with selective tropism for a subset of human cancers with neuroendocrine differentiation. To characterize further the specificity of SVV-001 and its patterns and kinetics of intratumoral spread, bacterial plasmids encoding a cDNA clone of the full-length wild-type virus and a derivative virus expressing GFP were generated. The full-length cDNA of the SVV-001 RNA genome was cloned into a bacterial plasmid under the control of the T7 core promoter sequence to create an infectious cDNA clone, pNTX-09. A GFP reporter virus cDNA clone, pNTX-11, was then generated by cloning a fusion protein of GFP and the 2A protein from foot-and-mouth disease virus immediately following the native SVV-001 2A sequence. Recombinant GFP-expressing reporter virus, SVV-GFP, was rescued from cells transfected with in vitro RNA transcripts from pNTX-11 and propagated in cell culture. The proliferation kinetics of SVV-001 and SVV-GFP were indistinguishable. The SVV-GFP reporter virus was used to determine that a subpopulation of permissive cells is present in small-cell lung cancer cell lines previously thought to lack permissivity to SVV-001. Finally, it was shown that SVV-GFP administered to tumour-bearing animals homes in to and infects tumours whilst having no detectable tropism for normal mouse tissues at 1×10(11) viral particles kg(-1), a dose equivalent to that administered in ongoing clinical trials. These infectious clones will be of substantial value in further characterizing the biology of this virus and as a backbone for the generation of additional oncolytic derivatives.

Small-cell lung cancer (SCLC) is an exceptionally aggressive disease with poor prognosis. Here, we obtained exome, transcriptome and copy-number alteration data from approximately 53 samples consisting of 36 primary human SCLC and normal tissue pairs and 17 matched SCLC and lymphoblastoid cell lines. We also obtained data for 4 primary tumors and 23 SCLC cell lines. We identified 22 significantly mutated genes in SCLC, including genes encoding kinases, G protein-coupled receptors and chromatin-modifying proteins. We found that several members of the SOX family of genes were mutated in SCLC. We also found SOX2 amplification in approximately 27% of the samples. Suppression of SOX2 using shRNAs blocked proliferation of SOX2-amplified SCLC lines. RNA sequencing identified multiple fusion transcripts and a recurrent RLF-MYCL1 fusion. Silencing of MYCL1 in SCLC cell lines that had the RLF-MYCL1 fusion decreased cell proliferation. These data provide an in-depth view of the spectrum of genomic alterations in SCLC and identify several potential targets for therapeutic intervention.

PURPOSE/OBJECTIVE:Seneca Valley Virus (SVV-001) is a novel naturally occurring replication-competent picornavirus with potent and selective tropism for neuroendocrine cancer cell types, including small cell lung cancer. We conducted a first-in-human, first-in-class phase I clinical trial of this agent in patients with cancers with neuroendocrine features, including small cell lung cancer. EXPERIMENTAL DESIGN/METHODS:Clinical evaluation of single intravenous doses in patients with cancers with neuroendocrine features was performed across five log-increments from 10(7) to 10(11) vp/kg. Toxicity, viral titers and clearance, neutralizing antibody development, and tumor response were assessed. RESULTS:A total of 30 patients were treated with SVV-001, including six with small cell carcinoma at the lowest dose of 10(7) vp/kg. SVV-001 was well tolerated, with no dose-limiting toxicities observed in any dose cohort. Viral clearance was documented in all subjects and correlated temporally with development of antiviral antibodies. Evidence of in vivo intratumoral viral replication was observed among patients with small cell carcinoma, with peak viral titers estimated to be >10(3)-fold higher than the administered dose. One patient with previously progressive chemorefractory small cell lung cancer remained progression-free for 10 months after SVV-001 administration, and is alive over 3 years after treatment. CONCLUSIONS:Intravenous SVV-001 administration in patients is well tolerated at doses up to 10(11) vp/kg, with predictable viral clearance kinetics, intratumoral viral replication, and evidence of antitumor activity in patients with small cell lung cancer. Phase II clinical evaluation in small cell lung cancer is warranted, and has been initiated.

Amplification of the HER2 (ErbB2, c-Neu) proto-oncogene in breast cancer is associated with poor prognosis and high relapse rates. HER2/ErbB2, in conjunction with ErbB3, signals through the Akt/phosphatidylinositol 3-kinase pathway and leads to the activation of mammalian target of rapamycin (mTOR), a critical mRNA translation regulator that controls cell growth. Gene expression analysis of mammary tumors collected from mouse mammary tumor virus-c-Neu transgenic mice revealed that mRNA levels of several mTOR pathway members were either up-regulated (p85/phosphatidylinositol 3-kinase and p70S6 kinase) or down-regulated (eIF-4E-BP1) in a manner expected to enhance signaling through this pathway. Treatment of these mice with the mTOR inhibitor rapamycin caused growth arrest and regression of primary tumors with no evidence of weight loss or generalized toxicity. The treatment effects were due to decreased proliferation, associated with reduced cyclin D1 expression, and increased cell death in primary tumors. Whereas many of the dead epithelial cells had the histopathologic characteristics of ischemic necrosis, rapamycin treatment was not associated with changes in microvascular density or apoptosis. Rapamycin also inhibited cellular proliferation in lung metastases. In summary, data from this preclinical model of ErbB2/Neu-induced breast cancer show that inhibition of the mTOR pathway with rapamycin blocks multiple stages of ErbB2/Neu-induced tumorigenic progression.