Recent Thymic Emigrants Require RBPJ-Dependent Notch Signaling to Transition into Functionally Mature Naive T Cells.

Recent thymic emigrant (RTE) cells are nascent T cells that continue their post-thymic maturation in the periphery and dominate T cell immune responses in early life and in adults having undergone lymphodepletion regimens. However, the events that govern their maturation and their functionality as they transition to mature naive T cells have not been clearly defined. Using RBPJind mice, we were able to identify different stages of RTE maturation and interrogate their immune function using a T cell transfer model of colitis. As CD45RBlo RTE cells mature, they transition through a CD45RBint immature naive T (INT) cell population that is more immunocompetent but shows a bias toward IL-17 production at the expense of IFN-γ. Additionally, the levels of IFN-γ and IL-17 produced in INT cells are highly dependent on whether Notch signals are received during INT cell maturation or during their effector function. IL-17 production by INT cells showed a total requirement for Notch signaling. Loss of Notch signaling at any stage of INT cells resulted in an impaired colitogenic effect of INT cells. RNA sequencing of INT cells that had matured in the absence of Notch signals showed a reduced inflammatory profile compared with Notch-responsive INT cells. Overall, we have elucidated a previously unknown INT cell stage, revealed its intrinsic bias toward IL-17 production, and demonstrated a role for Notch signaling in INT cell peripheral maturation and effector function in the context of a T cell transfer model of colitis.

Realization of the T Lineage Program Involves GATA-3 Induction of Bcl11b and Repression of Cdkn2b Expression.

The zinc-finger transcription factor GATA-3 plays a crucial role during early T cell development and also dictates later T cell differentiation outcomes. However, its role and collaboration with the Notch signaling pathway in the induction of T lineage specification and commitment have not been fully elucidated. We show that GATA-3 deficiency in mouse hematopoietic progenitors results in an early block in T cell development despite the presence of Notch signals, with a failure to upregulate Bcl11b expression, leading to a diversion along a myeloid, but not a B cell, lineage fate. GATA-3 deficiency in the presence of Notch signaling results in the apoptosis of early T lineage cells, as seen with inhibition of CDK4/6 (cyclin-dependent kinases 4 and 6) function, and dysregulated cyclin-dependent kinase inhibitor 2b (Cdkn2b) expression. We also show that GATA-3 induces Bcl11b, and together with Bcl11b represses Cdkn2b expression; however, loss of Cdkn2b failed to rescue the developmental block of GATA-3-deficient T cell progenitor. Our findings provide a signaling and transcriptional network by which the T lineage program in response to Notch signals is realized.

Thymus Reconstitution in Young and Aged Mice Is Facilitated by In Vitro-Generated Progenitor T Cells.

The prolonged lag in T cell recovery seen in older patients undergoing hematopoietic stem cell transplant (HSCT), after chemo-/radiotherapy, can lead to immune dysfunction. As a result, recovering patients may experience a relapse in malignancies and opportunistic infections, leading to high mortality rates. The delay in T cell recovery is partly due to thymic involution, a natural collapse in the size and function of the thymus, as individuals age, and partly due to the damage sustained by the thymic stromal cells through exposure to chemo-/radiotherapy. There is a clear need for new strategies to accelerate intrathymic T cell reconstitution when treating aged patients to counter the effects of involution and cancer therapy regimens. Adoptive transfer of human progenitor T (proT) cells has been shown to accelerate T cell regeneration in radiation-treated young mice and to restore thymic architecture in immunodeficient mice. Here, we demonstrate that the adoptive transfer of in vitro-generated proT cells in aged mice (18-24 months) accelerated thymic reconstitution after treatment with chemotherapy and gamma irradiation compared to HSCT alone. We noted that aged mice appeared to have a more limited expansion of CD4-CD8- thymocytes and slower temporal kinetics in the development of donor proT cells into mature T cells, when compared to younger mice, despite following the same chemo/radiation regimen. This suggests a greater resilience of the young thymus compared to the aged thymus. Nevertheless, newly generated T cells from proT cell engrafted aged and young mice were readily present in the periphery accelerating the reappearance of new naïve T cells. Accelerated T cell recovery was also observed in both aged and young mice receiving both proT cells and HSCT. The strategy of transferring proT cells can potentially be used as an effective cellular therapy in aged patients to improve immune recovery and reduce the risk of opportunistic infections post-HSCT.

Ontogenic timing, T cell receptor signal strength, and Notch signaling direct γδ T cell functional differentiation in vivo.

γδ T cells form an integral arm of the immune system and are critical during protective and destructive immunity. However, how γδ T cells are functionally programmed in vivo remains unclear. Here, we employ RBPJ-inducible and KN6-transgenic mice to assess the roles of ontogenic timing, T cell receptor (TCR) signal strength, and Notch signaling. We find skewing of Vγ1+ cells toward the PLZF+Lin28b+ lineage at the fetal stage. Generation of interleukin-17 (IL-17)-producing γδ T cells is favored during, although not exclusive to, the fetal stage. Surprisingly, Notch signaling is dispensable for peripheral γδ T cell IL-17 production. Strong TCR signals, together with Notch, promote IL-4 differentiation. Conversely, less strong TCR signals promote Notch-independent IL-17 differentiation. Single-cell transcriptomic analysis reveals differential programming instilled by TCR signal strength and Notch for specific subsets. Thus, our results precisely define the roles of ontogenic timing, TCR signal strength, and Notch signaling in γδ T cell functional programming in vivo.

Dose-dependent increases in circulating TGF-alpha and other EGFR ligands act as pharmacodynamic markers for optimal biological dosing of cetuximab and are tumor independent.

PURPOSE: The objective of this study was to characterize treatment-induced circulating ligand changes during therapy with epidermal growth factor receptor (EGFR) inhibitors and evaluate their potential as surrogate indicators of the optimal biological dose. EXPERIMENTAL DESIGN: Conditioned medium from human tumor cell lines, ascites fluid from tumor xenografts, and plasma samples from normal mice, as well as colorectal cancer patients, were assessed for ligand elevations using ELISA, following treatment with cetuximab (Erbitux), an anti-mouse EGFR neutralizing antibody, or a small-molecule EGFR tyrosine kinase inhibitor. RESULTS: A rapid elevation in human transforming growth factor alpha (TGF-alpha) was observed in all cell lines after treatment with cetuximab, but not with small-molecule inhibitors. The elevation showed a dose-response effect and plateau that corresponded to the maximal decrease in A431 proliferation in vitro and HT29 tumor growth in vivo. The TGF-alpha increase was exacerbated by ongoing ligand production and cleavage from the plasma membrane but did not involve transcriptional up-regulation of TGF-alpha or the matrix metalloproteinase tumor necrosis factor-alpha-converting enzyme/ADAM17. Elevations in plasma TGF-alpha, amphiregulin, and epiregulin were also detected in normal mice treated with an anti-mouse EGFR monoclonal antibody, illustrating a host tissue-dependent component of this effect in vivo. Finally, circulating TGF-alpha increased in the plasma of six patients with EGFR-negative colorectal tumors during cetuximab treatment. CONCLUSIONS: Treatment-induced increases in circulating ligands, particularly TGF-alpha, should be serially assessed in clinical trials of anti-EGFR therapeutic antibodies as potential biomarkers to aid in determination of the optimal biological dose.

Long-term progression and therapeutic response of visceral metastatic disease non-invasively monitored in mouse urine using beta-human choriogonadotropin secreting tumor cell lines.

Historically, the use of mouse models of metastatic disease to evaluate anticancer therapies has been hampered because of difficulties in detection and quantification of such lesions without sacrificing the mice, which in turn may also be dictated by institutional or ethical guidelines. Advancements in imaging technologies have begun to change this situation. A new method to non-invasively measure tumor burden, as yet untested to monitor spontaneous metastases, is the use of transplanted tumors expressing secretable human beta-chorionic gonadotropin (beta-hCG) that can be measured in urine. We describe examples of beta-hCG-transfected tumor cell lines for evaluating the effect of different therapies on metastatic disease, which in some cases involved monitoring tumor growth for >100 days. We used beta-hCG-tagged mouse B16 melanoma and erbB-2/Her-2-expressing human breast cancer MDA-MB-231 models, and drug treatments included metronomic low-dose cyclophosphamide chemotherapy with or without a vascular endothelial growth factor receptor 2-targeting antibody (DC101) or trastuzumab, the erbB-2/Her-2-targeting antibody. Both experimental and spontaneous metastasis models were studied; in the latter case, an increase in urine beta-hCG always foreshadowed the development of lung, liver, brain, and kidney metastases. Metastatic disease was unresponsive to DC101 or trastuzumab monotherapy treatment, as assessed by beta-hCG levels. Our results also suggest that beta-hCG levels may be set as an end point for metastasis studies, circumventing guidelines, which have often hampered the use of advanced disease models. Collectively, our data indicates that beta-hCG is an effective noninvasive preclinical marker for the long term monitoring of untreated or treated metastatic disease.

Highly efficacious nontoxic preclinical treatment for advanced metastatic breast cancer using combination oral UFT-cyclophosphamide metronomic chemotherapy.

Metronomic antiangiogenic chemotherapy, the prolonged administration of relatively low drug doses, at close regular intervals with no significant breaks, has been mainly studied at the preclinical level using single chemotherapeutic drugs, frequently in combination with a targeted antiangiogenic drug, and almost always evaluated on primary localized tumors. We tested a "doublet" combination metronomic chemotherapy treatment using two oral drugs, UFT, a 5-fluorouracil (5-FU) prodrug administered by gavage, and cyclophosphamide, for efficacy and toxicity in a new mouse model of advanced, terminal, metastatic human breast cancer. The optimal biological dose of each drug was first determined by effects on levels of circulating endothelial progenitor cells as a surrogate marker for angiogenesis, which was assessed to be 15 mg/kg for UFT and 20 mg/kg for cyclophosphamide. A combination treatment was then evaluated in mice with advanced metastatic disease using a serially selected metastatic variant of the MDA-MB-231 breast cancer-cell line, 231/LM2-4. UFT or cyclophosphamide treatment showed only very modest survival advantages whereas a combination of the two resulted in a remarkable prolongation of survival, with no evidence of overt toxicity despite 140 days of continuous therapy, such that a significant proportion of mice survived for over a year. In contrast, this striking therapeutic effect of the combination treatment was not observed when tested on primary orthotopic tumors. We conclude that combination oral low-dose daily metronomic chemotherapy, using cyclophosphamide and UFT, is superior to monotherapy and seems to be a safe and highly effective experimental antimetastatic therapy, in this case, for advanced metastatic breast cancer.

Tumor-Independent Host Secretomes Induced By Angiogenesis and Immune-Checkpoint Inhibitors.

The levels of various circulating blood proteins can change in response to cancer therapy. Monitoring therapy-induced secretomes (TIS) may have use as biomarkers for establishing optimal biological effect (such as dosing) or identifying sources of toxicity and drug resistance. Although TIS can derive from tumor cells directly, nontumor "host" treatment responses can also impact systemic secretory programs. For targeted inhibitors of the tumor microenvironment, including antiangiogenic and immune-checkpoint therapies, host TIS could explain unexpected collateral "side effects" of treatment. Here, we describe a comparative transcriptomic and proteomic analysis of host TIS in tissues and plasma from cancer-free mice treated with antibody and receptor tyrosine kinase inhibitors (RTKI) of the VEGF, cMet/ALK, and PD-1 pathways. We found that all cancer therapies elicit TIS independent of tumor growth, with systemic secretory gene change intensity higher in RTKIs compared with antibodies. Our results show that host TIS signatures differ between drug target, drug class, and dose. Notably, protein and gene host TIS signatures were not always predictive for each other, suggesting limitations to transcriptomic-only approaches to clinical biomarker development for circulating proteins. Together, these are the first studies to assess and compare "off-target" host secretory effects of VEGF and PD-1 pathway inhibition that occur independent of tumor stage or tumor response to therapy. Testing treatment impact on normal tissues to establish host-mediated TIS signatures (or "therasomes") may be important for identifying disease agnostic biomarkers to predict benefits (or limitations) of drug combinatory approaches. Mol Cancer Ther; 17(7); 1602-12. ©2018 AACR.

A Transient Pseudosenescent Secretome Promotes Tumor Growth after Antiangiogenic Therapy Withdrawal.

VEGF receptor tyrosine kinase inhibitors (VEGFR TKIs) approved to treat multiple cancer types can promote metastatic disease in certain limited preclinical settings. Here, we show that stopping VEGFR TKI treatment after resistance can lead to rebound tumor growth that is driven by cellular changes resembling senescence-associated secretory phenotypes (SASPs) known to promote cancer progression. A SASP-mimicking antiangiogenic therapy-induced secretome (ATIS) was found to persist during short withdrawal periods, and blockade of known SASP regulators, including mTOR and IL-6, could blunt rebound effects. Critically, senescence hallmarks ultimately reversed after long drug withdrawal periods, suggesting that the transition to a permanent growth-arrested senescent state was incomplete and the hijacking of SASP machinery ultimately transient. These findings may account for the highly diverse and reversible cytokine changes observed in VEGF inhibitor-treated patients, and suggest senescence-targeted therapies ("senotherapeutics")-particularly those that block SASP regulation-may improve outcomes in patients after VEGFR TKI failure.

Low-dose metronomic combined with intermittent bolus-dose cyclophosphamide is an effective long-term chemotherapy treatment strategy.

Metronomic chemotherapy refers to the close, regular administration of comparatively low doses of cytotoxic drugs, with minimal or no drug-free breaks, over prolonged periods. It is thought to have an antiangiogenic basis. However, whereas surprisingly durable and potent tumor responses have been observed in a number of preclinical tumor models, relapses usually eventually occur using this type of treatment strategy. We therefore decided to test modified metronomic chemotherapy regimens that might significantly delay such relapses, but still maintain modest and acceptable toxicity profiles. Here, we show that repeated administration of bolus doses (BDs) of cyclophosphamide every 3 or 6 weeks, combined with a daily oral low-dose metronomic (LDM) regimen (20 mg/kg/d cyclophosphamide), improves efficacy and significantly delays progression of transplanted PC-3 human prostate cancer xenografts, syngeneic transplanted EMT-6 breast tumors, and "spontaneous" murine erythroleukemia. Efficacy was superior whereas toxicity was mild and comparable to the LDM regimen, the latter assessed by body weight, neutrophil, lymphocyte, and total white blood counts. Antiangiogenic activity, measured by reduction in circulating endothelial precursor cells, revealed that the greatest degree of suppression occurred using the combination treatment. Overall, our results indicate that the administration of intermittent BD combined with chronic oral LDM cyclophosphamide is a potent treatment regimen for controlling tumor growth, which has a low toxicity profile, over prolonged periods of time.

Efficacy of Cotargeting Angiopoietin-2 and the VEGF Pathway in the Adjuvant Postsurgical Setting for Early Breast, Colorectal, and Renal Cancers.

Antiangiogenic tyrosine kinase inhibitors (TKI) that target VEGF receptor-2 (VEGFR2) have not been effective as adjuvant treatments for micrometastatic disease in phase III clinical trials. Angiopoietin-2 (Ang2) is a proangiogenic and proinflammatory vascular destabilizer that cooperates with VEGF. The purpose of this study was to test whether CVX-060 (an Ang2-specific CovX-body) can be combined with VEGFR2-targeting TKIs (sunitinib or regorafenib) to successfully treat postsurgical metastatic disease in multiple orthotopically implanted human tumor xenograft and syngeneic murine tumor models. In the MDA-MB-231.LM2-4 human breast cancer model, adjuvant sunitinib was ineffective, whereas adjuvant CVX-060 delayed the progression of pulmonary or distant lymphatic metastases; however, overall survival was only improved with the adjuvant use of a VEGF-A/Ang2-bispecific CovX-body (CVX-241) but not when CVX-060 is combined with sunitinib. Adjuvant CVX-241 also showed promise in the EMT-6/CDDP murine breast cancer model, with or without an immune checkpoint inhibitor (anti-PD-L1). In the RENCA model of mouse renal cancer, however, combining CVX-060 with sunitinib in the adjuvant setting was superior to CVX-241 as treatment for postsurgical lung metastases. In the HCT116 and HT29 xenograft models of colorectal cancer, both CVX-060 and regorafenib inhibited liver metastases. Overall, our preclinical findings suggest differential strategies by which Ang2 blockers can be successfully combined with VEGF pathway targeting in the adjuvant setting to treat micrometastatic disease-particularly, in combination with VEGF-A blockers (but not VEGFR2 TKIs) in resected breast cancer; in combination with VEGFR2 TKIs in resected kidney cancer; and as single agents or with VEGFR2 TKIs in resected colorectal cancer. Cancer Res; 76(23); 6988-7000. ©2016 AACR.

Co-option of Liver Vessels and Not Sprouting Angiogenesis Drives Acquired Sorafenib Resistance in Hepatocellular Carcinoma.

BACKGROUND: The anti-angiogenic Sorafenib is the only approved systemic therapy for advanced hepatocellular carcinoma (HCC). However, acquired resistance limits its efficacy. An emerging theory to explain intrinsic resistance to other anti-angiogenic drugs is 'vessel co-option,' ie, the ability of tumors to hijack the existing vasculature in organs such as the lungs or liver, thus limiting the need for sprouting angiogenesis. Vessel co-option has not been evaluated as a potential mechanism for acquired resistance to anti-angiogenic agents. METHODS: To study sorafenib resistance mechanisms, we used an orthotopic human HCC model (n = 4-11 per group), where tumor cells are tagged with a secreted protein biomarker to monitor disease burden and response to therapy. Histopathology, vessel perfusion assessed by contrast-enhanced ultrasound, and miRNA sequencing and quantitative real-time polymerase chain reaction were used to monitor changes in tumor biology. RESULTS: While sorafenib initially inhibited angiogenesis and stabilized tumor growth, no angiogenic 'rebound' effect was observed during development of resistance unless therapy was stopped. Instead, resistant tumors became more locally infiltrative, which facilitated extensive incorporation of liver parenchyma and the co-option of liver-associated vessels. Up to 75% (±10.9%) of total vessels were provided by vessel co-option in resistant tumors relative to 23.3% (±10.3%) in untreated controls. miRNA sequencing implicated pro-invasive signaling and epithelial-to-mesenchymal-like transition during resistance development while functional imaging further supported a shift from angiogenesis to vessel co-option. CONCLUSIONS: This is the first documentation of vessel co-option as a mechanism of acquired resistance to anti-angiogenic therapy and could have important implications including the potential therapeutic benefits of targeting vessel co-option in conjunction with vascular endothelial growth factor receptor signaling.

Preclinical Efficacy of Bevacizumab with CRLX101, an Investigational Nanoparticle-Drug Conjugate, in Treatment of Metastatic Triple-Negative Breast Cancer.

VEGF pathway-targeting antiangiogenic drugs, such as bevacizumab, when combined with chemotherapy have changed clinical practice for the treatment of a broad spectrum of human cancers. However, adaptive resistance often develops, and one major mechanism is elevated tumor hypoxia and upregulated hypoxia-inducible factor-1α (HIF1α) caused by antiangiogenic treatment. Reduced tumor vessel numbers and function following antiangiogenic therapy may also affect intratumoral delivery of concurrently administered chemotherapy. Nonetheless, combining chemotherapy and bevacizumab can lead to improved response rates, progression-free survival, and sometimes, overall survival, the extent of which can partly depend on the chemotherapy backbone. A rational, complementing chemotherapy partner for combination with bevacizumab would not only reduce HIF1α to overcome hypoxia-induced resistance, but also improve tumor perfusion to maintain intratumoral drug delivery. Here, we evaluated bevacizumab and CRLX101, an investigational nanoparticle-drug conjugate containing camptothecin, in preclinical mouse models of orthotopic primary triple-negative breast tumor xenografts, including a patient-derived xenograft. We also evaluated long-term efficacy of CRLX101 and bevacizumab to treat postsurgical, advanced metastatic breast cancer in mice. CRLX101 alone and combined with bevacizumab was highly efficacious, leading to complete tumor regressions, reduced metastasis, and greatly extended survival of mice with metastatic disease. Moreover, CRLX101 led to improved tumor perfusion and reduced hypoxia, as measured by contrast-enhanced ultrasound and photoacoustic imaging. CRLX101 durably suppressed HIF1α, thus potentially counteracting undesirable effects of elevated tumor hypoxia caused by bevacizumab. Our preclinical results show pairing a potent cytotoxic nanoparticle chemotherapeutic that complements and improves concurrent antiangiogenic therapy may be a promising treatment strategy for metastatic breast cancer. Cancer Res; 76(15); 4493-503. ©2016 AACR.

Effects of Sorafenib Dose on Acquired Reversible Resistance and Toxicity in Hepatocellular Carcinoma.

Acquired evasive resistance is a major limitation of hepatocellular carcinoma (HCC) treatment with the tyrosine kinase inhibitor (TKI) sorafenib. Recent findings suggest that resistance to sorafenib may have a reversible phenotype. In addition, loss of responsiveness has been proposed to be due to a gradual decrease in sorafenib plasma levels in patients. Here, the possible mechanisms underlying reversible sorafenib resistance were investigated using a Hep3B-hCG orthotopic human xenograft model of locally advanced HCC. Tissue and plasma sorafenib and metabolite levels, downstream antitumor targets, and toxicity were assessed during standard and dose-escalated sorafenib treatment. Drug levels were found to decline significantly over time in mice treated with 30 mg/kg sorafenib, coinciding with the onset of resistance but a greater magnitude of change was observed in tissues compared with plasma. Skin rash also correlated with drug levels and tended to decrease in severity over time. Drug level changes appeared to be partially tumor dependent involving induction of tumoral CYP3A4 metabolism, with host pretreatment alone unable to generate resistance. Escalation from 30 to 60 mg/kg sorafenib improved antitumor efficacy but worsened survival due to excessive body weight loss. Microvessel density was inhibited by sorafenib treatment but remained suppressed over time and dose increase. In conclusion, tumor CYP3A4 induction by sorafenib is a novel mechanism to account for variability in systemic drug levels; however, declining systemic sorafenib levels may only be a minor resistance mechanism. Escalating the dose may be an effective treatment strategy, provided toxicity can be controlled.

Vasculotide reduces endothelial permeability and tumor cell extravasation in the absence of binding to or agonistic activation of Tie2.

Angiopoietin-1 (Ang1) activation of Tie2 receptors on endothelial cells (ECs) reduces adhesion by tumor cells (TCs) and limits junctional permeability to TC diapedesis. We hypothesized that systemic therapy with Vasculotide (VT)-a purported Ang1 mimetic, Tie2 agonist-can reduce the extravasation of potentially metastatic circulating TCs by similarly stabilizing the host vasculature. In vitro, VT and Ang1 treatments impeded endothelial hypermeability and the transendothelial migration of MDA-MB-231∙LM2-4 (breast), HT29 (colon), or SN12 (renal) cancer cells to varying degrees. In mice, VT treatment inhibited the transit of TCs through the pulmonary endothelium, but not the hepatic or lymphatic endothelium. In the in vivo LM2-4 model, VT monotherapy had no effect on primary tumors, but significantly delayed distant metastatic dissemination to the lungs. In the post-surgical adjuvant treatment setting, VT therapeutically complemented sunitinib therapy, an anti-angiogenic tyrosine kinase inhibitor which limited the local growth of residual disease. Unexpectedly, detailed investigations into the putative mechanism of action of VT revealed no evidence of Tie2 agonism or Tie2 binding; alternative mechanisms have yet to be determined.

Postsurgical adjuvant or metastatic renal cell carcinoma therapy models reveal potent antitumor activity of metronomic oral topotecan with pazopanib.

Renal cell carcinoma (RCC), normally considered an intrinsically chemotherapy-resistant cancer, is currently treated with targeted biologic therapies, including antiangiogenic tyrosine kinase inhibitors (TKIs), such as pazopanib. The efficacy of these agents is limited by both intrinsic and acquired resistance. Death is almost always due to advanced metastatic disease, a treatment circumstance seldom modeled in preclinical (mouse) drug testing. Similarly, therapy results using postsurgical adjuvant therapy models of microscopic disease have not been reported. Using in vivo selection and transfection of established human RCC cell lines (786-0 and SN12-PM6), we derived clonal luciferase-expressing variants capable of spontaneous metastasis from an orthotopic primary tumor to organs typical of clinical RCC, including bone, lungs, and brain. The bioluminescence and consistent metastatic spread of von Hippel-Lindau-wild type SN12-PM6-1 cells allowed for the establishment of perioperative therapy models of RCC. We report that the combination of daily low-dose metronomic topotecan with pazopanib has highly potent antiprimary tumor as well as both postsurgical adjuvant and metastatic therapy efficacy despite lack of an antimetastatic effect of pazopanib monotherapy. The combination therapy resulted in sustained metastatic tumor cell dormancy, but tumor progression occurred upon treatment cessation. We also obtained evidence for a direct effect of pazopanib on RCC cells, resulting in increased intracellular concentration of topotecan. Our results suggest that this type of treatment combination should be considered for clinical evaluation in early- or late-stage metastatic disease, even for tumors seemingly intrinsically "resistant" to antiangiogenic TKIs or chemotherapy.

Translational impact of nanoparticle-drug conjugate CRLX101 with or without bevacizumab in advanced ovarian cancer.

PURPOSE: Increased tumor hypoxia and hence elevated hypoxia-inducible factor-1α (HIF1α) is thought to limit the efficacy of vascular endothelial growth factor (VEGF) pathway-targeting drugs by upregulating adaptive resistance genes. One strategy to counteract this is to combine antiangiogenic drugs with agents able to suppress HIF1α. One such possibility is the investigational drug CRLX101, a nanoparticle-drug conjugate (NDC) containing the payload camptothecin, a known topoisomerase-I poison. EXPERIMENTAL DESIGN: CRLX101 was evaluated both as a monotherapy and combination with bevacizumab in a preclinical mouse model of advanced metastatic ovarian cancer. These preclinical studies contributed to the rationale for undertaking a phase II clinical study to evaluate CRLX101 monotherapy in patients with advanced platinum-resistant ovarian cancer. RESULTS: Preclinically, CRLX101 is highly efficacious as a monotherapy when administered at maximum-tolerated doses. Furthermore, chronic low-dose CRLX101 with bevacizumab reduced bevacizumab-induced HIF1α upregulation and resulted in synergistic efficacy, with minimal toxicity in mice. In parallel, initial data reported here from an ongoing phase II clinical study of CRLX101 monotherapy shows measurable tumor reductions in 74% of patients and a 16% RECIST response rate to date. CONCLUSIONS: Given these preclinical and initial clinical results, further clinical studies are currently evaluating CRLX101 in combination with bevacizumab in ovarian cancer and warrant the evaluation of this therapy combination in other cancer types where HIF1α is implicated in pathogenesis, as it may potentially be able to improve the efficacy of antiangiogenic drugs.

Friend virus-induced erythroleukemias: a unique and well-defined mouse model for the development of leukemia.

Retroviruses lacking oncogenes have been known to induce various types of cancer when inoculated into animals. Among these, Friend virus, discovered by Charlotte Friend in 1957, is capable of inducing erythroleukemias when injected into susceptible strains of mice. Since its discovery, this murine model of leukemogenesis has been extensively used to study the multistage nature of cancer. In the past two decades, several oncogenes and tumour suppressor genes, which play critical roles in the induction and progression of Friend erythroleukemia, have been identified. Retroviral insertional activation of Fli-1 and Spi-1/PU.1, as well as loss of tumour suppressor genes such as p53 or p45 NFE2 have been shown to be critical for the induction and progression of Friend virus-induced erythroleukemias. The majority of these genetic changes have also been implicated in various types of human neoplastic transformations. In this review we will discuss the genetic changes associated with Friend Disease, the temporal order during induction and progression of disease, and the function of these genes in both normal erythroid development as well as malignant transformation.

Modeling spontaneous metastatic renal cell carcinoma (mRCC) in mice following nephrectomy.

One of the key challenges to improved testing of new experimental therapeutics in renal cell carcinoma (RCC) is the development of models that faithfully recapitulate early- and late-stage metastatic disease progression. Typical tumor implantation models utilize ectopic or orthotopic primary tumor implantation, but few include systemic spontaneous metastatic disease that mimics the clinical setting. This protocol describes the key steps to develop RCC disease progression stages similar to patients. First, it uses a highly metastatic mouse tumor cell line in a syngeneic model to show orthotopic tumor cell implantation. Methods include superficial and internal implantation into the sub-capsular space with cells combined with matrigel to prevent leakage and early spread. Next it describes the procedures for excision of tumor-bearing kidney (nephrectomy), with critical pre- and post- surgical mouse care. Finally, it outlines the steps necessary to monitor and assess micro-and macro-metastatic disease progression, including bioluminescent imaging as well provides a detailed visual necropsy guide to score systemic disease distribution. The goal of this protocol description is to facilitate the widespread use of clinically relevant metastatic RCC models to improve the predictive value of future therapeutic testing. 

Neoadjuvant antiangiogenic therapy reveals contrasts in primary and metastatic tumor efficacy.

Thousands of cancer patients are currently in clinical trials evaluating antiangiogenic therapy in the neoadjuvant setting, which is the treatment of localized primary tumors prior to surgical intervention. The rationale is that shrinking a tumor will improve surgical outcomes and minimize growth of occult micrometastatic disease-thus delaying post-surgical recurrence and improving survival. But approved VEGF pathway inhibitors have not been tested in clinically relevant neoadjuvant models that compare pre- and post-surgical treatment effects. Using mouse models of breast, kidney, and melanoma metastasis, we demonstrate that primary tumor responses to neoadjuvant VEGFR TKI treatment do not consistently correlate with improved post-surgical survival, with survival worsened in certain settings. Similar negative effects did not extend to protein-based VEGF pathway inhibitors and could be reversed with altered dose, surgical timing, and treatment duration, or when VEGFR TKIs are combined with metronomic 'anti-metastatic' chemotherapy regimens. These studies represent the first attempt to recapitulate the complex clinical parameters of neoadjuvant therapy in mice and identify a novel tool to compare systemic antiangiogenic treatment effects on localized and disseminated disease.