Hedgehog pathway inhibitor saridegib (IPI-926) increases lifespan in a mouse medulloblastoma model.

The Sonic Hedgehog (Shh) pathway drives a subset of medulloblastomas, a malignant neuroectodermal brain cancer, and other cancers. Small-molecule Shh pathway inhibitors have induced tumor regression in mice and patients with medulloblastoma; however, drug resistance rapidly emerges, in some cases via de novo mutation of the drug target. Here we assess the response and resistance mechanisms to the natural product derivative saridegib in an aggressive Shh-driven mouse medulloblastoma model. In this model, saridegib treatment induced tumor reduction and significantly prolonged survival. Furthermore, the effect of saridegib on tumor-initiating capacity was demonstrated by reduced tumor incidence, slower growth, and spontaneous tumor regression that occurred in allografts generated from previously treated autochthonous medulloblastomas compared with those from untreated donors. Saridegib, a known P-glycoprotein (Pgp) substrate, induced Pgp activity in treated tumors, which likely contributed to emergence of drug resistance. Unlike other Smoothened (Smo) inhibitors, the drug resistance was neither mutation-dependent nor Gli2 amplification-dependent, and saridegib was found to be active in cells with the D473H point mutation that rendered them resistant to another Smo inhibitor, GDC-0449. The fivefold increase in lifespan in mice treated with saridegib as a single agent compares favorably with both targeted and cytotoxic therapies. The absence of genetic mutations that confer resistance distinguishes saridegib from other Smo inhibitors.

A biobank of patient-derived pediatric brain tumor models.

Brain tumors are the leading cause of cancer-related death in children. Genomic studies have provided insights into molecular subgroups and oncogenic drivers of pediatric brain tumors that may lead to novel therapeutic strategies. To evaluate new treatments, better preclinical models adequately reflecting the biological heterogeneity are needed. Through the Children's Oncology Group ACNS02B3 study, we have generated and comprehensively characterized 30 patient-derived orthotopic xenograft models and seven cell lines representing 14 molecular subgroups of pediatric brain tumors. Patient-derived orthotopic xenograft models were found to be representative of the human tumors they were derived from in terms of histology, immunohistochemistry, gene expression, DNA methylation, copy number, and mutational profiles. In vivo drug sensitivity of targeted therapeutics was associated with distinct molecular tumor subgroups and specific genetic alterations. These models and their molecular characterization provide an unprecedented resource for the cancer community to study key oncogenic drivers and to evaluate novel treatment strategies.

Voruciclib, a clinical stage oral CDK9 inhibitor, represses MCL-1 and sensitizes high-risk Diffuse Large B-cell Lymphoma to BCL2 inhibition.

Aberrant regulation of BCL-2 family members enables evasion of apoptosis and tumor resistance to chemotherapy. BCL-2 and functionally redundant counterpart, MCL-1, are frequently over-expressed in high-risk diffuse large B-cell lymphoma (DLBCL). While clinical inhibition of BCL-2 has been achieved with the BH3 mimetic venetoclax, anti-tumor efficacy is limited by compensatory induction of MCL-1. Voruciclib, an orally bioavailable clinical stage CDK-selective inhibitor, potently blocks CDK9, the transcriptional regulator of MCL-1. Here, we demonstrate that voruciclib represses MCL-1 protein expression in preclinical models of DLBCL. When combined with venetoclax in vivo, voruciclib leads to model-dependent tumor cell apoptosis and tumor growth inhibition. Strongest responses were observed in two models representing high-risk activated B-cell (ABC) DLBCL, while no response was observed in a third ABC model, and intermediate responses were observed in two models of germinal center B-cell like (GCB) DLBCL. Given the range of responses, we show that CIVO, a multiplexed tumor micro-dosing technology, represents a viable functional precision medicine approach for differentiating responders from non-responders to BCL-2/MCL-1 targeted therapy. These findings suggest that the combination of voruciclib and venetoclax holds promise as a novel, exclusively oral combination therapy for a subset of high-risk DLBCL patients.

Multidrug Analyses in Patients Distinguish Efficacious Cancer Agents Based on Both Tumor Cell Killing and Immunomodulation.

The vision of a precision medicine-guided approach to novel cancer drug development is challenged by high intratumor heterogeneity and interpatient diversity. This complexity is rarely modeled accurately during preclinical drug development, hampering predictions of clinical drug efficacy. To address this issue, we developed Comparative In Vivo Oncology (CIVO) arrayed microinjection technology to test tumor responsiveness to simultaneous microdoses of multiple drugs directly in a patient's tumor. Here, in a study of 18 canine patients with soft tissue sarcoma (STS), CIVO captured complex, patient-specific tumor responses encompassing both cancer cells and multiple immune infiltrates following localized exposure to different chemotherapy agents. CIVO also classified patient-specific tumor resistance to the most effective agent, doxorubicin, and further enabled assessment of a preclinical autophagy inhibitor, PS-1001, to reverse doxorubicin resistance. In a CIVO-identified subset of doxorubicin-resistant tumors, PS-1001 resulted in enhanced antitumor activity, increased infiltration of macrophages, and skewed this infiltrate toward M1 polarization. The ability to evaluate and cross-compare multiple drugs and drug combinations simultaneously in living tumors and across a diverse immunocompetent patient population may provide a foundation from which to make informed drug development decisions. This method also represents a viable functional approach to complement current precision oncology strategies. Cancer Res; 77(11); 2869-80. ©2017 AACR.

A Platform for Rapid, Quantitative Assessment of Multiple Drug Combinations Simultaneously in Solid Tumors In Vivo.

While advances in high-throughput screening have resulted in increased ability to identify synergistic anti-cancer drug combinations, validation of drug synergy in the in vivo setting and prioritization of combinations for clinical development remain low-throughput and resource intensive. Furthermore, there is currently no viable method for prospectively assessing drug synergy directly in human patients in order to potentially tailor therapies. To address these issues we have employed the previously described CIVO platform and developed a quantitative approach for investigating multiple combination hypotheses simultaneously in single living tumors. This platform provides a rapid, quantitative and cost effective approach to compare and prioritize drug combinations based on evidence of synergistic tumor cell killing in the live tumor context. Using a gemcitabine resistant model of pancreatic cancer, we efficiently investigated nine rationally selected Abraxane-based combinations employing only 19 xenografted mice. Among the drugs tested, the BCL2/BCLxL inhibitor ABT-263 was identified as the one agent that synergized with Abraxane® to enhance acute induction of localized apoptosis in this model of human pancreatic cancer. Importantly, results obtained with CIVO accurately predicted the outcome of systemic dosing studies in the same model where superior tumor regression induced by the Abraxane/ABT-263 combination was observed compared to that induced by either single agent. This supports expanded use of CIVO as an in vivo platform for expedited in vivo drug combination validation and sets the stage for performing toxicity-sparing drug combination studies directly in cancer patients with solid malignancies.

Efficacy of cabazitaxel in mouse models of pediatric brain tumors.

BACKGROUND: There is an unmet need in the treatment of pediatric brain tumors for chemotherapy that is efficacious, avoids damage to the developing brain, and crosses the blood-brain barrier. These experiments evaluated the efficacy of cabazitaxel in mouse models of pediatric brain tumors. METHODS: The antitumor activity of cabazitaxel and docetaxel were compared in flank and orthotopic xenograft models of patient-derived atypical teratoid rhabdoid tumor (ATRT), medulloblastoma, and central nervous system primitive neuroectodermal tumor (CNS-PNET). Efficacy of cabazitaxel and docetaxel were also assessed in the Smo/Smo spontaneous mouse medulloblastoma tumor model. RESULTS: This study observed significant tumor growth inhibition in pediatric patient-derived flank xenograft tumor models of ATRT, medulloblastoma, and CNS-PNET after treatment with either cabazitaxel or docetaxel. Cabazitaxel, but not docetaxel, treatment resulted in sustained tumor growth inhibition in the ATRT and medulloblastoma flank xenograft models. Patient-derived orthotopic xenograft models of ATRT, medulloblastoma, and CNS-PNET showed significantly improved survival with treatment of cabazitaxel. CONCLUSION: These data support further testing of cabazitaxel as a therapy for treating human pediatric brain tumors.

A technology platform to assess multiple cancer agents simultaneously within a patient's tumor.

A fundamental problem in cancer drug development is that antitumor efficacy in preclinical cancer models does not translate faithfully to patient outcomes. Much of early cancer drug discovery is performed under in vitro conditions in cell-based models that poorly represent actual malignancies. To address this inconsistency, we have developed a technology platform called CIVO, which enables simultaneous assessment of up to eight drugs or drug combinations within a single solid tumor in vivo. The platform is currently designed for use in animal models of cancer and patients with superficial tumors but can be modified for investigation of deeper-seated malignancies. In xenograft lymphoma models, CIVO microinjection of well-characterized anticancer agents (vincristine, doxorubicin, mafosfamide, and prednisolone) induced spatially defined cellular changes around sites of drug exposure, specific to the known mechanisms of action of each drug. The observed localized responses predicted responses to systemically delivered drugs in animals. In pair-matched lymphoma models, CIVO correctly demonstrated tumor resistance to doxorubicin and vincristine and an unexpected enhanced sensitivity to mafosfamide in multidrug-resistant lymphomas compared with chemotherapy-naïve lymphomas. A CIVO-enabled in vivo screen of 97 approved oncology agents revealed a novel mTOR (mammalian target of rapamycin) pathway inhibitor that exhibits significantly increased tumor-killing activity in the drug-resistant setting compared with chemotherapy-naïve tumors. Finally, feasibility studies to assess the use of CIVO in human and canine patients demonstrated that microinjection of drugs is toxicity-sparing while inducing robust, easily tracked, drug-specific responses in autochthonous tumors, setting the stage for further application of this technology in clinical trials.

A distinct Smoothened mutation causes severe cerebellar developmental defects and medulloblastoma in a novel transgenic mouse model.

Deregulated developmental processes in the cerebellum cause medulloblastoma, the most common pediatric brain malignancy. About 25 to 30% of cases are caused by mutations increasing the activity of the Sonic hedgehog (Shh) pathway, a critical mitogen in cerebellar development. The proto-oncogene Smoothened (Smo) is a key transducer of the Shh pathway. Activating mutations in Smo that lead to constitutive activity of the Shh pathway have been identified in human medulloblastoma. To understand the developmental and oncogenic effects of two closely positioned point mutations in Smo, we characterized NeuroD2-SmoA2 mice and compared them to NeuroD2-SmoA1 mice. While both SmoA1 and SmoA2 transgenes cause medulloblastoma with similar frequencies and timing, SmoA2 mice have severe aberrations in cerebellar development, whereas SmoA1 mice are largely normal during development. Intriguingly, neurologic function, as measured by specific tests, is normal in the SmoA2 mice despite extensive cerebellar dysplasia. We demonstrate how two nearly contiguous point mutations in the same domain of the encoded Smo protein can produce striking phenotypic differences in cerebellar development and organization in mice.

Rapid pharmacokinetic and biodistribution studies using cholorotoxin-conjugated iron oxide nanoparticles: a novel non-radioactive method.

BACKGROUND: Recent advances in nanotechnology have led to the development of biocompatible nanoparticles for in vivo molecular imaging and targeted therapy. Many nanoparticles have undesirable tissue distribution or unacceptably low serum half-lives. Pharmacokinetic (PK) and biodistribution studies can help inform decisions determining particle size, coatings, or other features early in nanoparticle development. Unfortunately, these studies are rarely done in a timely fashion because many nanotechnology labs lack the resources and expertise to synthesize radioactive nanoparticles and evaluate them in mice. METHODOLOGY/PRINCIPAL FINDINGS: To address this problem, we developed an economical, radioactivity-free method for assessing serum half-life and tissue distribution of nanoparticles in mice. Iron oxide nanoparticles coated with chitosan and polyethylene glycol that utilize chlorotoxin as a targeting molecule have a serum half-life of 7-8 hours and the particles remain stable for extended periods of time in physiologic fluids and in vivo. Nanoparticles preferentially distribute to spleen and liver, presumably due to reticuloendothelial uptake. Other organs have very low levels of nanoparticles, which is ideal for imaging most cancers in the future. No acute toxicity was attributed to the nanoparticles. CONCLUSIONS/SIGNIFICANCE: We report here a simple near-infrared fluorescence based methodology to assess PK properties of nanoparticles in order to integrate pharmacokinetic data into early nanoparticle design and synthesis. The nanoparticles tested demonstrate properties that are excellent for future clinical imaging strategies and potentially suitable for targeted therapy.

Response of preclinical medulloblastoma models to combination therapy with 13-cis retinoic acid and suberoylanilide hydroxamic acid (SAHA).

PURPOSE: Current medulloblastoma therapy, surgery, radiation, and chemotherapy, is unacceptably toxic. However, 13-cis retinoic acid (RA) and SAHA, a histone deacetylase inhibitor, have each been shown to induce apoptosis in medulloblastoma cultures and mouse models. Both drugs cross the blood brain barrier, have been given safely to children, and achieve brain concentrations that are at or near therapeutic levels. Retinoic acid acts by transcriptionally activating bone morphogenetic protein-2 (BMP-2) and SAHA facilitates transcriptional activity through chromatin accessibility. We tested the hypothesis that these drugs additively induce BMP-2 transcription and apoptosis. EXPERIMENTAL DESIGN: RA + SAHA induction of BMP-2 transcription and apoptosis in medulloblastoma cultures was evaluated. Subsequently the response of mouse medulloblastomas to these two agents in the presence and absence of cisplatin was evaluated. RESULTS: BMP-2 transcription multiplied 3-fold with addition of RA to culture, and 7-fold with both agents. The IC50 of SAHA was reduced by 40% when low dose RA was added. Interestingly, a p38 MAP kinase inhibitor that partially blocks RA-induced apoptosis did not inhibit the activity of RA + SAHA. Flank D283 tumors in athymic mice had slower growth in the RA + SAHA arm than single drug or control arms. Intracranial tumors in ND2:SmoA1 mice treated with RA + SAHA + cisplatin showed a 4-fold increase in apoptosis over controls, and a 2-fold increase over animals receiving only SAHA or RA + SAHA. CONCLUSIONS: RA + SAHA additively induce BMP-2 transcription and medulloblastoma apoptosis. The combination may act through a p38 MAPK independent mechanism. Efficacy increased with cisplatin, which has implications for clinical trial design.

The Smo/Smo model: hedgehog-induced medulloblastoma with 90% incidence and leptomeningeal spread.

Toward the goal of generating a mouse medulloblastoma model with increased tumor incidence, we developed a homozygous version of our ND2:SmoA1 model. Medulloblastomas form in 94% of homozygous Smo/Smo mice by 2 months of age. Tumor formation is, thus, predictable by age, before the symptomatic appearance of larger lesions. This high incidence and early onset of tumors is ideal for preclinical studies because mice can be enrolled before symptom onset and with a greater latency period before late-stage disease. Smo/Smo tumors also display leptomeningeal dissemination of neoplastic cells to the brain and spine, which occurs in many human cases. Despite an extended proliferation of granule neuron precursors (GNP) in the postnatal external granular layer (EGL), the internal granular layer formed normally in Smo/Smo mice and tumor formation occurred only in localized foci on the superficial surface of the molecular layer. Thus, tumor formation is not simply the result of over proliferation of GNPs within the EGL. Moreover, Smo/Smo medulloblastomas were transplantable and serially passaged in vivo, demonstrating the aggressiveness of tumor cells and their transformation beyond a hyperplastic state. The Smo/Smo model is the first mouse medulloblastoma model to show leptomeningeal spread. The adherence to human pathology, high incidence, and early onset of tumors thus make Smo/Smo mice an efficient model for preclinical studies.