Response-adapted anti-PD-1-based salvage therapy for Hodgkin lymphoma with nivolumab alone or in combination with ICE.

This phase 2 trial evaluated PET-adapted nivolumab alone or in combination with ifosfamide, carboplatin, and etoposide (NICE) as first salvage therapy and bridge to autologous hematopoietic cell transplantation (AHCT) in relapsed/refractory (RR) classical Hodgkin lymphoma (cHL). Patients with RR cHL received 240 mg nivolumab every 2 weeks for up to 6 cycles (C). Patients in complete response (CR) after C6 proceeded to AHCT, whereas patients with progressive disease at any point or not in CR after C6 received NICE for 2 cycles. The primary endpoint was CR rate per the 2014 Lugano classification at completion of protocol therapy. Forty-three patients were evaluable for toxicity; 42 were evaluable for response. Thirty-four patients received nivolumab alone, and 9 patients received nivolumab+NICE. No unexpected toxicities were observed after nivolumab or NICE. After nivolumab, the overall response rate (ORR) was 81%, and the CR rate was 71%. Among 9 patients who received NICE, all responded, with 8 (89%) achieving CR. At the end of protocol therapy, the ORR and CR rates were 93% and 91%. Thirty-three patients were bridged directly to AHCT, including 26 after Nivo alone. The 2-year progression-free survival (PFS) and overall survival in all treated patients (n = 43) were 72% and 95%, respectively. Among 33 patients who bridged directly to AHCT, the 2-year PFS was 94% (95% CI: 78-98). PET-adapted sequential salvage therapy with nivolumab/nivolumab+NICE was well tolerated and effective, resulting in a high CR rate and bridging most patients to AHCT without chemotherapy. This trial was registered at www.clinicaltrials.gov #NCT03016871.

Antitumor efficacy of BAFF-R targeting CAR T cells manufactured under clinic-ready conditions.

B-cell malignancies can potentially be cured by CD19 chimeric antigen receptor (CAR) T-cell therapy. Although clinical response rates can be up to 93% in acute lymphoblastic leukemia, treatment-related antigen loss and lack of therapeutic persistence contribute to disease relapse. These shortcomings of current CAR T-cell therapy indicate the need for biologically relevant target selection and for improving the efficacy and persistence of the CAR T cells, which we have addressed by developing a novel B-cell activating factor receptor (BAFF-R) CAR T-cell therapy with improved therapeutic persistence. BAFF-R is a B-cell survival receptor and highly expressed in B-cell malignancies. We developed a prototype CAR T cell that efficiently and specifically eliminated BAFF-R expressing human B-cell tumors in several xenogeneic mouse models, including models of CD19 antigen loss. We proceeded with translational development and validation of BAFF-R CAR T cells produced under current good manufacturing practices (cGMP). cGMP-grade BAFF-R CAR T cells underwent in vitro and in vivo validation in established models to confirm that the potency and efficacy of our original research modeling was replicated. Food and Drug Administration required release testing was performed to ensure our BAFF-R CAR T cells meet specifications for new drug products. Completing and exceeding these requirements, the data fully support the initiation of a first-in-human Phase 1 trial for BAFF-R-positive relapsed/refractory (r/r) B-ALL.

Targeting myeloid-derived suppressor cells for cancer immunotherapy.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with an immune suppressive phenotype. They represent a critical component of the immune suppressive niche described in cancer, where they support immune escape and tumor progression through direct effects on both the innate and adaptive immune responses, largely by contributing to maintenance of a high oxidative stress environment. The number of MDSCs positively correlates with protumoral activity, and often diminishes the effectiveness of immunotherapies, which is particularly problematic with the emergence of personalized medicine. Approaches targeting MDSCs showed promising results in preclinical studies and are under active investigation in clinical trials in combination with various immune checkpoint inhibitors. In this review, we discuss MDSC targets and therapeutic approaches targeting MDSC that have the aim of enhancing the existing tumor therapies.

Phase I study of an active immunotherapy for asymptomatic phase Lymphoplasmacytic lymphoma with DNA vaccines encoding antigen-chemokine fusion: study protocol.

BACKGROUND: There is now a renewed interest in cancer vaccines. Patients responding to immune checkpoint blockade usually bear tumors that are heavily infiltrated by T cells and express a high load of neoantigens, indicating that the immune system is involved in the therapeutic effect of these agents; this finding strongly supports the use of cancer vaccine strategies. Lymphoplasmacytic lymphoma (LPL) is a low grade, incurable disease featuring an abnormal proliferation of Immunoglobulin (Ig)-producing malignant cells. Asymptomatic patients are currently managed by a "watchful waiting" approach, as available therapies provide no survival advantage if started before symptoms develop. Idiotypic determinants of a lymphoma surface Ig, formed by the interaction of the variable regions of heavy and light chains, can be used as a tumor-specific marker and effective vaccination using idiotypes was demonstrated in a positive controlled phase III trial. METHODS: These variable region genes can be cloned and used as a DNA vaccine, a delivery system holding tremendous potential for streamlining vaccine production. To increase vaccination potency, we are targeting antigen-presenting cells (APCs) by fusing the antigen with a sequence encoding a chemokine (MIP-3α), which binds an endocytic surface receptor on APCs. Asymptomatic phase LPL is an excellent model to test our vaccine since patients have not received chemotherapeutics that interfere with innate immune function and have low tumor burden. We are evaluating the safety of this next-generation DNA vaccine in a first-in-human clinical trial currently enrolling asymptomatic LPL patients. To elucidate the mode of action of this vaccine, we will assess its ability to generate tumor-specific immune responses and examine changes in the immune profile of both the peripheral blood and bone marrow. DISCUSSION: This vaccine could shift the current paradigm of clinical management for patients with asymptomatic LPL and inform development of other personalized approaches. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT01209871; registered on September 24, 2010.

The Novel Ribonucleotide Reductase Inhibitor COH29 Inhibits DNA Repair In Vitro.

COH29 [N-(4-(3,4-dihydroxyphenyl)-5-phenylthiazol-2-yl)-3,4-dihydroxybenzamide], a novel antimetabolite drug developed at City of Hope Cancer Center, has anticancer activity that stems primarily from the inhibition of human ribonucleotide reductase (RNR). This key enzyme in deoxyribonucleotide biosynthesis is the target of established clinical agents such as hydroxyurea and gemcitabine because of its critical role in DNA replication and repair. Herein we report that BRCA-1-defective human breast cancer cells are more sensitive than wild-type BRCA-1 counterparts to COH29 in vitro and in vivo. Microarray gene expression profiling showed that COH29 reduces the expression of DNA repair pathway genes, suggesting that COH29 interferes with these pathways. It is well established that BRCA1 plays a role in DNA damage repair, especially homologous recombination (HR) repair, to maintain genome integrity. In BRCA1-defective HCC1937 breast cancer cells, COH29 induced more double-strand breaks (DSBs) and DNA-damage response than in HCC1937 + BRCA1 cells. By EJ5- and DR-green fluorescent protein (GFP) reporter assay, we found that COH29 could inhibit nonhomologous end joining (NHEJ) efficiency and that no HR activity was detected in HCC1937 cells, suggesting that repression of the NHEJ repair pathway may be involved in COH29-induced DSBs in BRCA1-deficient HCC1937 cells. Furthermore, we observed an accumulation of nuclear Rad51 foci in COH29-treated HCC1937 + BRCA1 cells, suggesting that BRCA1 plays a crucial role in repairing and recovering drug-induced DNA damage by recruiting Rad51 to damage sites. In summary, we describe here additional biologic effects of the RNR inhibitor COH29 that potentially strengthen its use as an anticancer agent.

Yttrium-90 Anti-CD25-BEAM-Conditioning for Autologous Hematopoietic Cell Transplantation in Peripheral T Cell Lymphoma.

Peripheral T cell lymphomas (PTCL) have a poor prognosis with current treatments. High-dose chemotherapy followed by autologous hematopoietic cell transplant (AHCT) is used as a consolidation strategy after achieving clinical remission with first-line therapy, as well as in chemosensitive relapse if allogeneic transplant is not an option. CD25 is a targetable protein often highly expressed in PTCL. In this phase 1 clinical trial, we tested the addition of beta-emitting 90Y-labeled chimeric anti-CD25 basiliximab (aTac) to BEAM (carmustine, etoposide, cytarabine, melphalan) as conditioning for AHCT in patients with PTCL. Twenty-three AHCT-eligible patients were enrolled, and 20 received therapeutic 90Y-aTac-BEAM AHCT. Radiation doses of 0.4, 0.5 and 0.6 mCi/kg were tested. With no observed dose-limiting toxicities, 0.6 mCi/kg was deemed the recommended phase 2 dose. The most prevalent adverse effect, grade 2 mucositis, was experienced by 80% of patients. As of this report, 6 (30%) of the treated patients had died, 5 due to progressive disease and 1 due to multiple organ failure [median time of death 17 mo (range: 9-21 mo)] post-AHCT. Median follow-up was 24 mo (range: 9-26 mo) overall and 24 mo (range: 13-26 mo) for surviving patients. For patients who received therapeutic 90Y-aTac-BEAM AHCT, the 2-year progression-free and overall survival were 59% (95% CI: 34-77%) and 68% (95% CI: 42-84%), respectively. 90Y-aTac-BEAM appears to be safe as an AHCT conditioning regimen for PTCL, with no increased toxicity over the toxicities historically seen with BEAM alone in this patient population. This trial was registered at www.clinicaltrials.gov as # NCT02342782.

Blockade of the Immune Checkpoint CD47 by TTI-621 Potentiates the Response to Anti-PD-L1 in Cutaneous T-Cell Lymphoma.

Cutaneous T-cell lymphoma (CTCL) is an incurable and cosmetically disfiguring disease associated with microenvironmental signals. We investigated the effects of CD47 and PD-L1 immune checkpoint blockades, as a strategy for targeting both innate and adaptive immunity. CIBERSORT analysis identified the immune-cell composition in the CTCL tumor microenvironment and the immune checkpoint expression profile for each immune-cell gene cluster from CTCL lesions. We investigated the relationship between MYC and CD47 and PD-L1 expression and found that MYC short hairpin RNA knockdown and MYC functional suppression by TTI-621 (SIRPαFc) and anti-PD-L1 (durvalumab) in CTCL cell lines reduced the expression of CD47 and PDL1 mRNA and protein as measured by qPCR and flow cytometry, respectively. In vitro, blockade of the CD47-SIRPα interaction with TTI-621 increased the phagocytic activity of macrophages against CTCL cells and enhanced CD8+ T-cell-mediated killing in a mixed leucocyte reaction. Moreover, TTI-621 synergized with anti-PD-L1 in macrophages reprogram to M1-like phenotypes and inhibited CTCL cell growth. These effects were mediated by cell death-related pathways, including apoptosis, autophagy, and necroptosis. Collectively, our findings show that CD47 and PD-L1 are critical regulators of immune surveillance in CTCL and that dual targeting of CD47 and PD-L1 will provide insight into tumor immunotherapy for CTCL.

Generation of a humanized afucosylated BAFF-R antibody with broad activity against human B-cell malignancies.

B-cell activating factor receptor (BAFF-R) is a mature B-cell survival receptor, which is highly expressed in a wide variety of B-cell malignancies but with minimal expression in immature B cells. These properties make BAFF-R an attractive target for therapy of B-cell lymphomas. We generated a novel humanized anti BAFF-R monoclonal antibody (mAb) with high specificity and potent in vitro and in vivo activity against B-cell lymphomas and leukemias. The humanized variants of an original chimeric BAFF-R mAb retained BAFF-R binding affinity and antibody-dependent cellular cytotoxicity (ADCC) against a panel of human cell lines and primary lymphoma samples. Furthermore, 1 humanized BAFF-R mAb clone and its afucosylated version, glycoengineered to optimize the primary mechanism of action, prolonged survival of immunodeficient mice bearing human tumor cell lines or patient-derived lymphoma xenografts in 3 separate models, compared with controls. Finally, the tissue specificity of this humanized mAb was confirmed against a broad panel of normal human tissues. Taken together, we have identified a robust lead-candidate BAFF-R mAb for clinical development.

Emerging CAR T Cell Strategies for the Treatment of AML.

Engineered T cells expressing chimeric antigen receptors (CARs) on their cell surface can redirect antigen specificity. This ability makes CARs one of the most promising cancer therapeutic agents. CAR-T cells for treating patients with B cell hematological malignancies have shown impressive results. Clinical manifestation has yielded several trials, so far five CAR-T cell therapies have received US Food and Drug Administration (FDA) approval. However, emerging clinical data and recent findings have identified some immune-related toxicities due to CAR-T cell therapy. Given the outcome and utilization of the same proof of concept, further investigation in other hematological malignancies, such as leukemias, is warranted. This review discusses the previous findings from the pre-clinical and human experience with CAR-T cell therapy. Additionally, we describe recent developments of novel targets for adoptive immunotherapy. Here we present some of the early findings from the pre-clinical studies of CAR-T cell modification through advances in genetic engineering, gene editing, cellular programming, and formats of synthetic biology, along with the ongoing efforts to restore the function of exhausted CAR-T cells through epigenetic remodeling. We aim to shed light on the new targets focusing on acute myeloid leukemia (AML).

Anti-CD25 radioimmunotherapy with BEAM autologous hematopoietic cell transplantation conditioning in Hodgkin lymphoma.

High-risk relapsed or refractory (R/R) classical Hodgkin lymphoma (HL) is associated with poor outcomes after conventional salvage therapy and autologous hematopoietic cell transplantation (AHCT). Post-AHCT consolidation with brentuximab vedotin (BV) improves progression-free survival (PFS), but with increasing use of BV early in the treatment course, the utility of consolidation is unclear. CD25 is often expressed on Reed-Sternberg cells and in the tumor microenvironment in HL, and we hypothesized that the addition of 90Y-antiCD25 (aTac) to carmustine, etoposide, cytarabine, melphalan (BEAM) AHCT would be safe and result in a transplantation platform that is agnostic to prior HL-directed therapy. Twenty-five patients with high-risk R/R HL were enrolled in this phase 1 dose-escalation trial of aTac-BEAM. Following an imaging dose of 111In-antiCD25, 2 patients had altered biodistribution, and a third developed an unrelated catheter-associated bacteremia; therefore, 22 patients ultimately received therapeutic 90Y-aTac-BEAM AHCT. No dose-limiting toxicities were observed, and 0.6 mCi/kg was deemed the recommended phase 2 dose, the dose at which the heart wall would not receive >2500 cGy. Toxicities and time to engraftment were similar to those observed with standard AHCT, though 95% of patients developed stomatitis (all grade 1-2 per Bearman toxicity scale). Seven relapses (32%) were observed, most commonly in patients with ≥3 risk factors. The estimated 5-year PFS and overall survival probabilities among 22 evaluable patients were 68% and 95%, respectively, and non-relapse mortality was 0%. aTac-BEAM AHCT was tolerable in patients with high-risk R/R HL, and we are further evaluating the efficacy of this approach in a phase 2 trial. This trial was registered at www.clinicaltrials.gov as #NCT01476839.

CAR T cells targeting BAFF-R can overcome CD19 antigen loss in B cell malignancies.

CAR T cells targeting CD19 provide promising options for treatment of B cell malignancies. However, tumor relapse from antigen loss can limit efficacy. We developed humanized, second-generation CAR T cells against another B cell-specific marker, B cell activating factor receptor (BAFF-R), which demonstrated cytotoxicity against human lymphoma and acute lymphoblastic leukemia (ALL) lines. Adoptively transferred BAFF-R-CAR T cells eradicated 10-day preestablished tumor xenografts after a single treatment and retained efficacy against xenografts deficient in CD19 expression, including CD19-negative variants within a background of CD19-positive lymphoma cells. Four relapsed, primary ALLs with CD19 antigen loss obtained after CD19-directed therapy retained BAFF-R expression and activated BAFF-R-CAR, but not CD19-CAR, T cells. BAFF-R-CAR, but not CD19-CAR, T cells also demonstrated antitumor effects against an additional CD19 antigen loss primary patient-derived xenograft (PDX) in vivo. BAFF-R is amenable to CAR T cell therapy, and its targeting may prevent emergence of CD19 antigen loss variants.

Novel BAFF-Receptor Antibody to Natively Folded Recombinant Protein Eliminates Drug-Resistant Human B-cell Malignancies In Vivo.

Purpose: mAbs such as anti-CD20 rituximab are proven therapies in B-cell malignancies, yet many patients develop resistance. Novel therapies against alternative targets are needed to circumvent resistance mechanisms. We sought to generate mAbs against human B-cell-activating factor receptor (BAFF-R/TNFRSF13C), which has not yet been targeted successfully for cancer therapy.Experimental Design: Novel mAbs were generated against BAFF-R, expressed as a natively folded cell surface immunogen on mouse fibroblast cells. Chimeric BAFF-R mAbs were developed and assessed for in vitro and in vivo monotherapy cytotoxicity. The chimeric mAbs were tested against human B-cell tumor lines, primary patient samples, and drug-resistant tumors.Results: Chimeric antibodies bound with high affinity to multiple human malignant B-cell lines and induced potent antibody-dependent cellular cytotoxicity (ADCC) against multiple subtypes of human lymphoma and leukemia, including primary tumors from patients who had relapsed after anti-CD20 therapy. Chimeric antibodies also induced ADCC against ibrutinib-resistant and rituximab-insensitive CD20-deficient variant lymphomas, respectively. Importantly, they demonstrated remarkable in vivo growth inhibition of drug-resistant tumor models in immunodeficient mice.Conclusions: Our method generated novel anti-BAFF-R antibody therapeutics with remarkable single-agent antitumor effects. We propose that these antibodies represent an effective new strategy for targeting and treating drug-resistant B-cell malignancies and warrant further development. Clin Cancer Res; 24(5); 1114-23. ©2017 AACR.

Phase I/II trial of nonpegylated liposomal doxorubicin, cyclophosphamide, vincristine, and prednisone in the treatment of newly diagnosed aggressive non-Hodgkin's lymphoma.

BACKGROUND: The toxicity and efficacy of nonpegylated liposomal doxorubicin (TLC D-99) when substituted for conventional doxorubicin in the CHOP (doxorubicin/cyclophosphamide/vincristine/prednisone) regimen were evaluated in the treatment of newly diagnosed patients with aggressive non-Hodgkin's lymphoma. Liposomal doxorubicin at doses of 40 mg/m2, 50 mg/m2, 60 mg/m2, and 80 mg/m2 was given with fixed doses of cyclophosphamide, vincristine, and prednisone. Chemotherapy cycles were repeated every 21 days. PATIENTS AND METHODS: Forty-seven patients with a median age of 55 years (range, 25-83 years) were studied. RESULTS: No dose-limiting toxicities were observed at any level. Reversible grade 3/4 neutropenia was the most common toxicity (95.8%). Most nonhematologic side effects were grade 1/2 in severity. Complete remissions were documented in 31 of 46 evaluable patients (67.4%) and partial remissions in 7 (15.2%), for an overall major response rate of 82.6%. The median duration of complete remission is > or = 27.7 months (range, 2.4 months to > or = 59.8 months). An exploratory objective was to correlate multidrug resistance-1 (MDR-1) expression with outcome. Immunohistochemistry for MDR-1-related p-glycoprotein was assessed in lymphoma tissues from 27 patients. Of the 27 lymphoma tissues studied, 8 (30%) were MDR-1 positive at diagnosis. The complete response rate was 63% in MDR-1-positive lymphomas and 74% in the MDR-1-negative cases (P = 0.66). CONCLUSION: Nonpegylated liposomal doxorubicin in combination with cyclophosphamide, vincristine, and prednisone is an active regimen for patients with newly diagnosed, aggressive non-Hodgkin's lymphoma. The regimen is relatively well tolerated, with hematologic suppression as the major toxicity. Liposomal encapsulation might evade resistance caused by MDR-1 expression.

A small-molecule blocking ribonucleotide reductase holoenzyme formation inhibits cancer cell growth and overcomes drug resistance.

Ribonucleotide reductase (RNR) is an attractive target for anticancer agents given its central function in DNA synthesis, growth, metastasis, and drug resistance of cancer cells. The current clinically established RNR inhibitors have the shortcomings of short half-life, drug resistance, and iron chelation. Here, we report the development of a novel class of effective RNR inhibitors addressing these issues. A novel ligand-binding pocket on the RNR small subunit (RRM2) near the C-terminal tail was proposed by computer modeling and verified by site-directed mutagenesis and nuclear magnetic resonance (NMR) techniques. A compound targeting this pocket was identified by virtual screening of the National Cancer Institute (NCI) diverse small-molecule database. By lead optimization, we developed the novel RNR inhibitor COH29 that acted as a potent inhibitor of both recombinant and cellular human RNR enzymes. COH29 overcame hydroxyurea and gemcitabine resistance in cancer cells. It effectively inhibited proliferation of most cell lines in the NCI 60 human cancer panel, most notably ovarian cancer and leukemia, but exerted little effect on normal fibroblasts or endothelial cells. In mouse xenograft models of human cancer, COH29 treatment reduced tumor growth compared with vehicle. Site-directed mutagenesis, NMR, and surface plasmon resonance biosensor studies confirmed COH29 binding to the proposed ligand-binding pocket and offered evidence for assembly blockade of the RRM1-RRM2 quaternary structure. Our findings offer preclinical validation of COH29 as a promising new class of RNR inhibitors with a new mechanism of inhibition, with broad potential for improved treatment of human cancer.

Phase I study of antisense oligonucleotide against vascular endothelial growth factor: decrease in plasma vascular endothelial growth factor with potential clinical efficacy.

PURPOSE: Vascular endothelial growth factor antisense (VEGF-AS) is an antisense oligonucleotide that targets VEGF, inhibiting angiogenesis and tumor cell proliferation. This study established the safety, biologic effects, and pharmacokinetics of VEGF-AS in 51 patients with advanced malignancies. METHODS: VEGF-AS was administered as a 2-hour infusion daily for 5 consecutive days for only one cycle on the first four dose levels, and then administered daily for 5 days every other week for up to 4 months on subsequent levels. Pharmacokinetics, tumor response, and the effect on plasma VEGF levels were determined. RESULTS: The maximum-tolerated dose was 200 mg/m2. Dose-limiting toxicities included grade 4 fever, and pulmonary embolism in one patient each at 250 mg/m2. Mild anemia, fever, fatigue, and gastrointestinal complaints were the most common adverse events. VEGF-AS t(1/2beta) (beta-phase terminal half-life of drug concentration) was 2.25 hours (range, 1.97 to 2.95 hours). Mean plasma VEGF-A (P = .002) and VEGF-C (P = .01) levels decreased 24 hours postinfusion, with a trend towards greater decreases at higher dose levels. At the maximum-tolerated dose, five of six patients demonstrated reductions in plasma VEGF. Clinical responses included complete remission in one patient with AIDS-Kaposi's sarcoma, a mixed but dramatic response in one patient with cutaneous T-cell lymphoma, and prolongation of progression-free survival compared with that obtained on the immediate prior regimen in six patients (12%) with renal cell, bronchoalveolar, small cell lung, thyroid, and ovarian carcinomas, and chondrosarcoma, respectively. CONCLUSION: VEGF-AS was well tolerated, with biologic effects and preliminary evidence of clinical efficacy.

Ephrin B2 expression in Kaposi sarcoma is induced by human herpesvirus type 8: phenotype switch from venous to arterial endothelium.

Kaposi sarcoma (KS) is an angioproliferative tumor derived from endothelial cells in which tumor cells form aberrant vascular structures. Ephrin B2 and ephrin B4 (EphB4) are artery- and vein-specific proteins, respectively, with critical roles in vessel maturation. We investigated whether the disorganized KS vasculature was due to unbalanced expression of ephrin B2 and EphB4. Secondly, we wished to determine if human herpesvirus type 8 (HHV-8), the viral agent associated with KS, regulates ephrin B2 and EphB4. An arterial phenotype was observed in KS tissue and cell lines, as shown by abundant expression of ephrin B2 with little or no EphB4. Infection of venous endothelial cells with HHV-8 resulted in a phenotype switch from EphB4 to ephrin B2, similar to that seen with vascular endothelial growth factor (VEGF). The HHV-8 effect on ephrin B2 expression was reproduced with the HHV-8-specific viral G-protein-coupled receptor. We also showed that ephrin B2 expression is required for KS cell viability by knock down with siRNA. KS is the first example of a human tumor with a predominantly arterial phenotype. This predominance can be attributed to expression of HHV-8 proteins and their downstream effects. Ephrin B2 is thus an important novel factor in KS biology and a potential target for therapy.

Human herpesvirus-8-transformed endothelial cells have functionally activated vascular endothelial growth factor/vascular endothelial growth factor receptor.

Kaposi's sarcoma is a vascular tumor commonly associated with human immunodeficiency virus (HIV)-1 and human herpesvirus (HHV-8) also known as Kaposi's sarcoma-associated herpesvirus. The principal features of this tumor are abnormal proliferation of vascular structures lined with spindle-shaped endothelial cells. HHV-8 may transform a subpopulation of endothelial cells in vitro via viral and cellular gene expression. We hypothesized that among the cellular genes, vascular endothelial growth factors (VEGFs) and their cognate receptors may be involved in viral-mediated transformation. We have shown that HHV-8-transformed endothelial cells (EC-HHV-8) express higher levels of VEGF, VEGF-C, VEGF-D, and PlGF in addition to VEGF receptors-1, -2, and -3. Furthermore, antibodies to VEGF receptor-2 inhibited cell proliferation and viability. Similarly, inhibition of VEGF gene expression with antisense oligonucleotides inhibited EC-HHV-8 cell proliferation/viability. The growth and viability of primary endothelial cells and a fibroblast cell line however were unaffected by either the VEGF receptor-2 antibody or the VEGF antisense oligodeoxynucleotides. VEGF and VEGF receptors are thus induced in EC-HHV-8 and participate in the transformation. Inhibitors of VEGF may thus modulate the disease process during development and progression.

Natural killer cell cytolytic activity is necessary for in vivo antitumor activity of the dipeptide L-glutamyl-L-tryptophan.

A dipeptide, L-glutamyl L-tryptophan (L-glu-L-trp), was identified in a screen for immunomodulators in the soluble fraction of the thymus. L-glu-L-trp inhibits tumor growth in mice without showing direct cellular toxicity in a variety of human tumor cell lines. L-glu-L-trp antitumor activity in vivo requires the presence of natural killer (NK) cells. Defective trafficking of cytoplasmic granules caused by the Lyst mutation also resulted in loss of antitumor activity of the dipeptide. The effect of L-glu-L-trp on tumor growth in mice with targeted gene mutations demonstrated the absolute requirement for perforin for antitumor activity. The requirement of 2 major modulators of NK cell activity, gamma interferon (IFNgamma) and interleukin (IL)-12, were also tested. L-glu-L-trp had full antitumor activity in IFNgamma knockout mice, but had significantly diminished activity in IL-12 knockout mice. These data show that L-glu-L-trp antitumor activity in mice is dependent on cytolytic cell activity of NK or NKT cells. L-glu-L-trp in vivo regulates NK cell function independent of IFNgamma but partly dependent on IL-12.

Malignant mesothelioma growth inhibition by agents that target the VEGF and VEGF-C autocrine loops.

Malignant mesothelioma (MM) is a locally aggressive tumor that originates from the mesothelial cells of the pleural and sometimes peritoneal surface. Conventional treatments for MM, consisting of chemotherapy or surgery give little survival benefit to patients, who generally die within 1 year of diagnosis. Hence, there is an urgent need for the development of alternative therapies. Vascular endothelial growth factor (VEGF) is an autocrine growth factor for MM. The closely related molecule, VEGF-C, is also implicated in malignant mesothelioma growth. VEGF-C and its cognate receptor VEGFR-3 are co-expressed in mesothelioma cell lines. A functional VEGF-C autocrine growth loop was demonstrated in mesothelioma cells by targeting VEGF-C expression and binding to VEGFR-3. The ability of novel agents that reduce the levels of VEGF and VEGF-C to inhibit mesothelioma cell growth in vitro was assessed. Antisense oligonucleotide (ODN) complementary to VEGF that inhibited VEGF and VEGF-C expression simultaneously specifically inhibited mesothelioma cell growth. Similarly, antibodies to VEGF receptor (VEGFR-2) and VEGF-C receptor (VEGFR-3) were synergistic in inhibiting mesothelioma cell growth. In addition, a diphtheria toxin-VEGF fusion protein (DT-VEGF), which is toxic to cells that express VEGF receptors was very effective in inhibiting mesothelioma cell growth in vitro. These results indicate that targeting VEGF and VEGF-C simultaneously may be an effective therapeutic approach for malignant mesothelioma.