Ligand-Induced Degradation of a CAR Permits Reversible Remote Control of CAR T Cell Activity In Vitro and In Vivo.

Chimeric antigen receptor (CAR)-modified T cells are endowed with novel antigen specificity and are most often administered to patients without an engineered mechanism to control the CAR T cells once infused. "Suicide switches" such as the small molecule-controlled, inducible caspase-9 (iCas9) system afford the ability to selectively eliminate engineered T cells; however, these approaches are designed for all-or-none, irreversible termination of an ongoing immune response. In order to permit reversible and adjustable modulation, we have created a CAR that is capable of on-demand downregulation by fusing the CAR to a previously developed ligand-induced degradation (LID) domain. Addition of a small molecule ligand triggers exposure of a cryptic degron within the LID domain, resulting in proteasomal degradation of the CAR-LID fusion protein and loss of CAR on the surface of T cells. This fusion construct allowed for reversible and "tunable" inhibition of CAR T cell activity in vitro. Delivery of the triggering molecule in CAR-LID-treated tumor-bearing mice temporarily reduced CAR activity through modulation of CAR surface expression. The ability to more flexibly modulate CAR T cell expression through a small molecule provides a platform for controlling possible adverse side effects, as well as preclinical investigations of CAR T cell biology.

HDAC5 controls the functions of Foxp3(+) T-regulatory and CD8(+) T cells.

Histone/protein deacetylases (HDACs) are frequently upregulated in human malignancies and have therefore become therapeutic targets in cancer therapy. However, inhibiting certain HDAC isoforms can have protolerogenic effects on the immune system, which could make it easier for tumor cells to evade the host immune system. Therefore, a better understanding of how each HDAC isoform affects immune biology is needed to develop targeted cancer therapy. Here, we studied the immune phenotype of HDAC5(-/-) mice on a C57BL/6 background. While HDAC5(-/-) mice replicate at expected Mendelian ratios and do not develop overt autoimmune disease, their T-regulatory (Treg) cells show reduced suppressive function in vitro and in vivo. Likewise, CD4(+) T-cells lacking HDAC5 convert poorly to Tregs under appropriately polarizing conditions. To test if this attenuated Treg formation and suppressive function translated into improved anticancer immunity, we inoculated HDAC5(-/-) mice and littermate controls with a lung adenocarcinoma cell line. Cumulatively, lack of HDAC5 did not lead to better anticancer immunity. We found that CD8(+) T cells missing HDAC5 had a reduced ability to produce the cytokine, IFN-γ, in vitro and in vivo, which may offset the benefit of weakened Treg function and formation. Taken together, targeting HDAC5 weakens suppressive function and de-novo induction of Tregs, but also reduces the ability of CD8(+) T cells to produce IFN-γ.

Changes in the local tumor microenvironment in recurrent cancers may explain the failure of vaccines after surgery.

Each year, more than 700,000 people undergo cancer surgery in the United States. However, more than 40% of those patients develop recurrences and have a poor outcome. Traditionally, the medical community has assumed that recurrent tumors arise from selected tumor clones that are refractory to therapy. However, we found that tumor cells have few phenotypical differences after surgery. Thus, we propose an alternative explanation for the resistance of recurrent tumors. Surgery promotes inhibitory factors that allow lingering immunosuppressive cells to repopulate small pockets of residual disease quickly. Recurrent tumors and draining lymph nodes are infiltrated with M2 (CD11b(+)F4/80(hi)CD206(hi) and CD11b(+)F4/80(hi)CD124(hi)) macrophages and CD4(+)Foxp3(+) regulatory T cells. This complex network of immunosuppression in the surrounding tumor microenvironment explains the resistance of tumor recurrences to conventional cancer vaccines despite small tumor size, an intact antitumor immune response, and unaltered cancer cells. Therapeutic strategies coupling antitumor agents with inhibition of immunosuppressive cells potentially could impact the outcomes of more than 250,000 people each year.

The receptor for advanced glycation end products mediates lung endothelial activation by RBCs.

The receptor for advanced glycation end products (RAGE) is a multiligand pattern recognition receptor implicated in multiple disease states. Although RAGE is expressed on systemic vascular endothelium, the expression and function of RAGE on lung endothelium has not been studied. Utilizing in vitro (human) and in vivo (mouse) models, we established the presence of RAGE on lung endothelium. Because RAGE ligands can induce the expression of RAGE and stored red blood cells express the RAGE ligand N(ε)-carboxymethyl lysine, we investigated whether red blood cell (RBC) transfusion would augment RAGE expression on endothelium utilizing a syngeneic model of RBC transfusion. RBC transfusion not only increased lung endothelial RAGE expression but enhanced lung inflammation and endothelial activation, since lung high mobility group box 1 and vascular cell adhesion molecule 1 expression was elevated following transfusion. These effects were mediated by RAGE, since endothelial activation was absent in RBC-transfused RAGE knockout mice. Thus, RAGE is inducibly expressed on lung endothelium, and one functional consequence of RBC transfusion is increased RAGE expression and endothelial activation.

Treating tumors with a vaccinia virus expressing IFNß illustrates the complex relationships between oncolytic ability and immunogenicity.

Since previous work using a nonreplicating adenovirus-expressing mouse interferon-ß (Ad.mIFNß) showed promising preclinical activity, we postulated that a vector-expressing IFNß at high levels that could also replicate would be even more beneficial. Accordingly a replication competent, recombinant vaccinia viral vector-expressing mIFNß (VV.mIFNß) was tested. VV.mIFNß-induced antitumor responses in two syngeneic mouse flank models of lung cancer. Although VV.mIFNß had equivalent in vivo efficacy in both murine tumor models, the mechanisms of tumor killing were completely different. In LKRM2 tumors, viral replication was minimal and the tumor killing mechanism was due to activation of immune responses through induction of a local inflammatory response and production of antitumor CD8 T-cells. In contrast, in TC-1 tumors, the vector replicated well, induced an innate immune response, but antitumor activity was primarily due to a direct oncolytic effect. However, the VV.mIFNß vector was able to augment the efficacy of an antitumor vaccine in the TC-1 tumor model in association with increased numbers of infiltrating CD8 T-cells. These data show the complex relationships between oncolytic viruses and the immune system which, if understood and harnessed correctly, could potentially be used to enhance the efficacy of immunotherapy.

Mesothelin, a novel immunotherapy target for triple negative breast cancer.

Mesothelin is a cell-surface glycoprotein present on mesothelial cells and elicits T cell responses in a variety of cancers including pancreatic, biliary and ovarian cancer. Breast cancer is not known to express mesothelin. We postulated that mesothelin may be a unique tumor-associated antigen in triple negative breast cancer (TNBC), a less common breast cancer subtype which may have been under-represented in prior studies that characterized mesothelin expression. Therefore, we screened 99 primary breast cancer samples by immunohistochemistry analysis using formalin-fixed paraffin-embedded archival tumor tissues and confirmed that mesothelin was overexpressed in the majority of TNBC (67 %) but only rarely in <5 % ER(+) or Her2-neu(+) breast cancer, respectively. To determine whether mesothelin may be exploited as a novel immunotherapy target in breast cancer, an in vitro cell killing assay was performed to compare the ability of genetically modified T cells expressing a chimeric antibody receptor (CAR) specific for mesothelin (mesoCAR T cells) or non-transduced T cells to kill mesothelin-expressing primary breast cancer cells. A significantly higher anti-tumor cytotoxicity by mesoCAR T cells was observed (31.7 vs. 8.7 %, p < 0.001). Our results suggest that mesothelin has promise as a novel immunotherapy target for TNBC for which effective targeted therapy is lacking to date.

Characterization of INCB086550: A Potent and Novel Small-Molecule PD-L1 Inhibitor.

Blocking the activity of the programmed cell death protein 1 (PD-1) inhibitory receptor with therapeutic antibodies against either the ligand (PD-L1) or PD-1 itself has proven to be an effective treatment modality for multiple cancers. Contrasting with antibodies, small molecules could demonstrate increased tissue penetration, distinct pharmacology, and potentially enhanced antitumor activity. Here, we describe the identification and characterization of INCB086550, a novel, oral, small-molecule PD-L1 inhibitor. In vitro, INCB086550 selectively and potently blocked the PD-L1/PD-1 interaction, induced PD-L1 dimerization and internalization, and induced stimulation-dependent cytokine production in primary human immune cells. In vivo, INCB086550 reduced tumor growth in CD34+ humanized mice and induced T-cell activation gene signatures, consistent with PD-L1/PD-1 pathway blockade. Preliminary data from an ongoing phase I study confirmed PD-L1/PD-1 blockade in peripheral blood cells, with increased immune activation and tumor growth control. These data support continued clinical evaluation of INCB086550 as an alternative to antibody-based therapies. SIGNIFICANCE: We have identified a potent small-molecule inhibitor of PD-L1, INCB086550, which has biological properties similar to PD-L1/PD-1 monoclonal antibodies and may represent an alternative to antibody therapy. Preliminary clinical data in patients demonstrated increased immune activation and tumor growth control, which support continued clinical evaluation of this approach. See related commentary by Capparelli and Aplin, p. 1413. This article is highlighted in the In This Issue feature, p. 1397.

Monocyte chemoattractant protein-1 blockade inhibits lung cancer tumor growth by altering macrophage phenotype and activating CD8+ cells.

The role of chemokines in the pathogenesis of lung cancer has been increasingly appreciated. Monocyte chemoattractant protein-1 (MCP-1, also known as CCL2) is secreted from tumor cells and associated tumor stromal cells. The blockade of CCL2, as mediated by neutralizing antibodies, was shown to reduce tumorigenesis in several solid tumors, but the role of CCL2 in lung cancer remains controversial, with evidence of both protumorigenic and antitumorigenic effects. We evaluated the effects and mechanisms of CCL2 blockade in several animal models of non-small-cell lung cancer (NSCLC). Anti-murine-CCL2 monoclonal antibodies were administered in syngeneic flank and orthotopic models of NSCLC. CCL2 blockade significantly slowed the growth of primary tumors in all models studied, and inhibited lung metastases in a model of spontaneous lung metastases of NSCLC. In contrast to expectations, no significant effect of treatment was evident in the number of tumor-associated macrophages recruited into the tumor after CCL2 blockade. However, a change occurred in the polarization of tumor-associated macrophages to a more antitumor phenotype after CCL2 blockade. This was associated with the activation of cytotoxic CD8(+) T lymphocytes (CTLs). The antitumor effects of CCL2 blockade were completely lost in CB-17 severe combined immunodeficient mice or after CD8 T-cell depletion. Our data from NSCLC models show that CCL2 blockade can inhibit the tumor growth of primary and metastatic disease. The mechanisms of CCL2 blockade include an alteration of the tumor macrophage phenotype and the activation of CTLs. Our work supports further evaluation of CCL2 blockade in thoracic malignancies.

Pharmacologic activation of the innate immune system to prevent respiratory viral infections.

Drugs that can rapidly inhibit respiratory infection from influenza or other respiratory pathogens are needed. One approach is to engage primary innate immune defenses against viral infection, such as activating the IFN pathway. In this study, we report that a small, cell-permeable compound called 5,6-di-methylxanthenone-4-acetic acid (DMXAA) can induce protection against vesicular stomatitis virus in vitro and H1N1 influenza A virus in vitro and in vivo through innate immune activation. Using the mouse C10 bronchial epithelial cell line and primary cultures of nasal epithelial cells, we demonstrate DMXAA activates the IFN regulatory factor-3 pathway leading to production of IFN-ß and subsequent high-level induction of IFN-ß-dependent proteins, such as myxovirus resistance 1 (Mx1) and 2',5'-oligoadenylate synthetase 1 (OAS1). Mice treated with DMXAA intranasally elevate mRNA/protein expression of Mx1 and OAS1 in the nasal mucosa, trachea, and lung. When challenged intranasally with a lethal dose of H1N1 influenza A virus, DMXAA reduced viral titers in the lungs and protected 80% of mice from death, even when given at 24 hours before infection. These data show that agents, like DMXAA, that can directly activate innate immune pathways, such as the IFN regulatory factor-3/IFN-ß system, in respiratory epithelial cells can be used to protect from influenza pneumonia and potentially in other respiratory viral infections. Development of this approach in humans could be valuable for protecting health care professionals and "first responders" in the early stages of viral pandemics or bioterror attacks.

Activation of the nucleotide oligomerization domain signaling pathway by the non-bacterially derived xanthone drug 5'6-dimethylxanthenone-4-acetic acid (Vadimezan).

The cytosolic nucleotide-binding oligomerization domain 1 (NOD1)/CARD4 and NOD2/CARD15 proteins are members of NOD-like receptors recognizing specific motifs within peptidoglycans of both Gram-negative and Gram-positive bacteria. NOD1 and NOD2 signal via the downstream adaptor serine/threonine kinase RIP2/CARDIAK/RICK to initiate NF-kappaB activation and the release of inflammatory cytokines/chemokines. In this report, we show that 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a cell-permeable, small molecule that has anti-tumor activity, can also activate NOD1 and NOD2. This was demonstrated: 1) by using human embryonic kidney epithelial (HEK) 293 cells transfected with a NF-kappaB reporter plasmid in combination with NOD1 or NOD2 expression plasmids; 2) by inhibiting DMXAA-induced chemokine (CXCL10) mRNA and protein production in the AB12 mesothelioma cell line using a pharmacological inhibitor of RICK kinase, SB20358; and 3) by using small interfering RNA to knock down NOD2 and lentiviral short hairpin RNA to knock down RICK. These findings expand the potential ligands for the NOD-like receptors, suggesting that other xanthone compounds may act similarly and could be developed as anti-tumor agents. This information also expands our knowledge on the mechanisms of action of the anti-tumor agent DMXAA (currently in clinical trials) and may be important for its biological activity.

A human CD137×PD-L1 bispecific antibody promotes anti-tumor immunity via context-dependent T cell costimulation and checkpoint blockade.

Immune checkpoint inhibitors demonstrate clinical activity in many tumor types, however, only a fraction of patients benefit. Combining CD137 agonists with these inhibitors increases anti-tumor activity preclinically, but attempts to translate these observations to the clinic have been hampered by systemic toxicity. Here we describe a human CD137xPD-L1 bispecific antibody, MCLA-145, identified through functional screening of agonist- and immune checkpoint inhibitor arm combinations. MCLA-145 potently activates T cells at sub-nanomolar concentrations, even under suppressive conditions, and enhances T cell priming, differentiation and memory recall responses. In vivo, MCLA-145 anti-tumor activity is superior to immune checkpoint inhibitor comparators and linked to recruitment and intra-tumor expansion of CD8 + T cells. No graft-versus-host-disease is observed in contrast to other antibodies inhibiting the PD-1 and PD-L1 pathway. Non-human primates treated with 100 mg/kg/week of MCLA-145 show no adverse effects. The conditional activation of CD137 signaling by MCLA-145, triggered by neighboring cells expressing >5000 copies of PD-L1, may provide both safety and potency advantages.

Intra-tumoral delivery of CXCL11 via a vaccinia virus, but not by modified T cells, enhances the efficacy of adoptive T cell therapy and vaccines.

T cell trafficking into tumors depends on a "match" between chemokine receptors on effector cells (e.g., CXCR3 and CCR5) and tumor-secreted chemokines. There is often a chemokine/chemokine receptor "mismatch", with tumors producing minute amounts of chemokines, resulting in inefficient targeting of effectors to tumors. We aimed to alter tumors to produce higher levels of CXCL11, a CXCR3 ligand, to attract more effector cells following immunotherapy. Mice bearing established subcutaneous tumors were studied. In our first approach, we used modified chimeric antigen receptor (CAR)-transduced human T cells to deliver CXCL11 (CAR/CXCL11) into tumors. In our second approach, we intravenously (iv) administered a modified oncolytic vaccinia virus (VV) engineered to produce CXCL11 (VV.CXCL11). The effect of these treatments on T cell trafficking into the tumors and anti-tumor efficacy after subsequent CAR T cell injections or anti-tumor vaccines was determined. CAR/CXCL11 and VV.CXCL11 significantly increased CXCL11 protein levels within tumors. For CAR/CXCL11, injection of a subsequent dose of CAR T cells did not result in increased intra-tumoral trafficking, and appeared to decrease the function of the injected CAR T cells. In contrast, VV.CXCL11 increased the number of total and antigen-specific T cells within tumors after CAR T cell injection or vaccination and significantly enhanced anti-tumor efficacy. Both approaches were successful in increasing CXCL11 levels within the tumors; however, only the vaccinia approach was successful in recruiting T cells and augmenting anti-tumor efficacy. VV.CXCL11 should be considered as a potential approach to augment adoptive T cell transfer or vaccine immunotherapy.

Synthesis and biological activity of azido analogues of 5,6-dimethylxanthenone-4-acetic acid for use in photoaffinity labeling.

5,6-Dimethylxanthenone-4-acetic acid (1) is scheduled for phase III clinical trials as a vascular disrupting agent. However, its biochemical receptor(s) have yet to be identified. In this report, the synthesis of azido analogues of 1 that could be used for photoaffinity labeling of proteins as an approach toward identifying its molecular targets is described. While 5-azidoxanthenone-4-acetic acid (2) and 5-azido-6-methylxantheone-4-acetic acid (3) were found to have biological activities similar to that of 1, 6-azido-5-methylxanthenone-4-acetic acid (4) was unstable and could not be evaluated. Both azido compounds 2 and 3 activated NF-kappaB, induced the production of tumor necrosis factor in cultured mouse splenocytes, and induced hemorrhagic necrosis of colon 38 tumors in mice. Photoreaction of lysates from spleen cells with tritiated 2 resulted in two radiolabeled protein bands at 50 and 14 kDa that could be competitively inhibited with cold 1 and cold 2. The azido compounds 2 and 3 exhibit all the requirements for use in photoaffinity labeling of potential receptor(s) for 1.

Inhibition of DMXAA-induced tumor necrosis factor production in murine splenocyte cultures by NF-kappaB inhibitors.

The induction of cytokine synthesis within tumor tissue is a key component of the antivascular action of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in murine tumors. We previously showed that DMXAA alone induced only low amounts of tumor necrosis factor (TNF) in cultured spleen cells, but the addition of suboptimal concentrations of lipopolysaccharide (LPS) provided a costimulatory signal that resulted in 6-10-fold increase in secreted TNF. In this study we investigated the molecular pathway involved, and showed that the addition of NF-kappaB inhibitors salicylate and parthenolide reduced the levels of TNF secreted into the culture supernatants induced with DMXAA (10 microg/ml) alone or in combination with LPS (10 microg/ml). Results from gene arrays, confirmed with RT-PCR, showed that the TNF gene was not upregulated with DMXAA alone, and was only slightly increased above the level of significance when LPS was added simultaneously. This contrasted with secreted TNF protein levels, which increased 5- and 48-fold, respectively, above that in untreated cultures with DMXAA alone or in combination with LPS. In addition to TNF, protein arrays showed IL-6, IL-10, MIP-1alpha, MIP-2, and RANTES were also secreted following treatment with 10 microg/ml DMXAA alone, and IL-4, IFN-gamma, MCP-5, and TIMP-1 were additionally induced using a higher dose of 300 microg/ml DMXAA. The drug is currently showing promise in phase II combination trials, and these studies suggest that DMXAA-induced TNF production in the splenocyte cultures was not due to increased expression of the TNF gene, but through effects on NF-kappaB-dependent posttranscriptional regulation.

CD11b+Ly6G+ cells inhibit tumor growth by suppressing IL-17 production at early stages of tumorigenesis.

Neutrophils are important innate immune cells involved in microbial clearance at the sites of infection. However, their role in cancer development is unclear. We hypothesized that neutrophils mediate antitumor effects in early tumorigenesis. To test this, we first studied the cytotoxic effects of neutrophils in vitro. Neutrophils were cytotoxic against tumor cells, with neutrophils isolated from tumor-bearing mice trending to have increased cytotoxic activities. We then injected an ELR+ CXC chemokine-producing tumor cell line into C57BL/6 and Cxcr2-/- mice, the latter lacking the receptors for neutrophil chemokines. We observed increased tumor growth in Cxcr2-/- mice. As expected, tumors from Cxcr2-/- mice contained fewer neutrophils. Surprisingly, these tumors also contained fewer CD8+ T cells, but more IL-17-producing cells. Replenishment of functional neutrophils was correlated with decreased IL-17-producing cells, increased CD8+ T cells, and decreased tumor size in Cxcr2-/- mice, while depletion of neutrophils in C57BL/6 mice showed the opposite effects. Results from a non-ELR+ CXC chemokine producing tumor further supported that functional neutrophils indirectly mediate tumor control by suppressing IL-17A production. We further studied the correlation of IL-17A and CD8+ T cells in vitro. IL-17A suppressed proliferation and IFNγ production of CD8+ T cells, while CD11b+Ly6G+ neutrophils did not suppress CD8+ T cell function. Taken together, these data demonstrate that, while neutrophils could control tumor growth by direct cytotoxic effects, the primary mechanism by which neutrophils exert antitumor effects is to regulate IL-17 production, through which they indirectly promote CD8+ T cell responses.

Generation of Potent T-cell Immunotherapy for Cancer Using DAP12-Based, Multichain, Chimeric Immunoreceptors.

Chimeric antigen receptors (CAR) bearing an antigen-binding domain linked in cis to the cytoplasmic domains of CD3ζ and costimulatory receptors have provided a potent method for engineering T-cell cytotoxicity toward B-cell leukemia and lymphoma. However, resistance to immunotherapy due to loss of T-cell effector function remains a significant barrier, especially in solid malignancies. We describe an alternative chimeric immunoreceptor design in which we have fused a single-chain variable fragment for antigen recognition to the transmembrane and cytoplasmic domains of KIR2DS2, a stimulatory killer immunoglobulin-like receptor (KIR). We show that this simple, KIR-based CAR (KIR-CAR) triggers robust antigen-specific proliferation and effector function in vitro when introduced into human T cells with DAP12, an immunotyrosine-based activation motifs-containing adaptor. T cells modified to express a KIR-CAR and DAP12 exhibit superior antitumor activity compared with standard first- and second-generation CD3ζ-based CARs in a xenograft model of mesothelioma highly resistant to immunotherapy. The enhanced antitumor activity is associated with improved retention of chimeric immunoreceptor expression and improved effector function of isolated tumor-infiltrating lymphocytes. These results support the exploration of KIR-CARs for adoptive T-cell immunotherapy, particularly in immunotherapy-resistant solid tumors.

Tumor-Promoting Desmoplasia Is Disrupted by Depleting FAP-Expressing Stromal Cells.

Malignant cells drive the generation of a desmoplastic and immunosuppressive tumor microenvironment. Cancer-associated stromal cells (CASC) are a heterogeneous population that provides both negative and positive signals for tumor cell growth and metastasis. Fibroblast activation protein (FAP) is a marker of a major subset of CASCs in virtually all carcinomas. Clinically, FAP expression serves as an independent negative prognostic factor for multiple types of human malignancies. Prior studies established that depletion of FAP(+) cells inhibits tumor growth by augmenting antitumor immunity. However, the potential for immune-independent effects on tumor growth have not been defined. Herein, we demonstrate that FAP(+) CASCs are required for maintenance of the provisional tumor stroma because depletion of these cells, by adoptive transfer of FAP-targeted chimeric antigen receptor (CAR) T cells, reduced extracellular matrix proteins and glycosaminoglycans. Adoptive transfer of FAP-CAR T cells also decreased tumor vascular density and restrained growth of desmoplastic human lung cancer xenografts and syngeneic murine pancreatic cancers in an immune-independent fashion. Adoptive transfer of FAP-CAR T cells also restrained autochthonous pancreatic cancer growth. These data distinguish the function of FAP(+) CASCs from other CASC subsets and provide support for further development of FAP(+) stromal cell-targeted therapies for the treatment of solid tumors.

Induction of tumour necrosis factor and interferon-gamma in cultured murine splenocytes by the antivascular agent DMXAA and its metabolites.

The induction of haemorrhagic necrosis by 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in transplantable murine tumours depends on the in situ synthesis of cytokines, particularly tumour necrosis factor (TNF). Since the in vivo action of DMXAA would be greatly clarified by the development of an in vitro model, we investigated whether DMXAA could induce cytokines in cultured murine splenocytes. DMXAA alone induced low amounts of TNF with an optimal concentration of 10 microg/mL and an optimal time of 4 hr. When combined with low concentrations of lipopolysaccharide, deactivated-lipopolysaccharide (dLPS) or phorbol-12-myristate-13-acetate that did not elicit TNF production alone, synergistic TNF production was obtained. DMXAA also induced interferon-gamma at an optimal dose of 300 microg/mL, but the addition of dLPS had no further effect. Decreasing culture pH, although not changing the optimal concentrations for stimulation, increased both TNF and interferon-gamma production in response to DMXAA. The major DMXAA metabolites, DMXAA-glucuronide and 6-hydroxy-5-methylxanthenone-4-acetic acid, did not induce either cytokine alone, in combination with dLPS or at low pH. The results indicate that DMXAA rather than a metabolite is responsible for cytokine induction and suggest that the microenvironment of the tumour may be responsible for the observed selective induction of cytokines in tumour tissue.

Modulation of thalidomide pharmacokinetics by cyclophosphamide or 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in mice: the role of tumour necrosis factor.

PURPOSE: There is considerable current interest in the use of thalidomide as a single agent or in combination with drugs such as cyclophosphamide in the treatment of multiple myeloma and other cancers. Our previous work has shown that thalidomide potentiates the antitumour activity of both cyclophosphamide and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) against murine Colon 38 tumours. In both of these cases, thalidomide extends the half-life (t(1/2)) of the other drug. We wished to determine whether cyclophosphamide and DMXAA altered the t(1/2) of thalidomide. Since both thalidomide and DMXAA modulate tumour necrosis factor (TNF), we also wished to determine the role of TNF in this interaction. METHODS: Mice with Colon 38 tumours were treated with cyclophosphamide (220 mg/kg) and/or thalidomide (20 mg/kg) or DMXAA (25 mg/kg) and thalidomide (100 mg/kg), combinations that have previously demonstrated synergistic activity. Plasma and tumour tissue drug concentrations were analysed by high-performance liquid chromatography. To determine the role of TNF, similar experiments were performed using mice defective in the TNF gene (TNF(-/-)) or the TNF receptor-1 gene (TNFR1(-/-)). RESULTS: Coadministration of cyclophosphamide increased the thalidomide t(1/2) by 3.9- and 3.6-fold, respectively, in plasma and tumour tissue, with a corresponding increase in the concentration-time curve (AUC). The corresponding values following coadministration of DMXAA were 3.0- and 4.6-fold, respectively. Coadministration of cyclophosphamide had similar effects on thalidomide t(1/2) in C57Bl/6, TNF(-/-) and TNFR1(-/-) mice, while coadministration of DMXAA did not alter the t(1/2) or AUC in TNF(-/-) and TNFR1(-/-) mice. CONCLUSIONS: Both cyclophosphamide and DMXAA have a pharmacokinetic interaction with thalidomide, increasing t(1/2) and AUC. TNF mediates the effect of DMXAA on thalidomide pharmacokinetics but not that of cyclophosphamide.