Efficacy of SMIP-016, a novel CD37-directed biologic therapy, in human NHL tumor xenograft models

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Background: Small Modular Immuno-Pharmaceuticals (SMIP) biopharmaceuticals belong to a novel proprietary biologic compound class that retain Fc mediated effector functions and are smaller than monoclonal antibodies. SMIP-016 is a SMIP product candidate that binds to CD37 on human B cells and has potent ADCC and apoptotic activity in vitro. CD-37 is known to be over-expressed in non-Hodgkin’s lymphoma (NHL) and chronic lymphocytic leukemia (CLL). We have evaluated the activity of SMIP-016 in established human tumor xenograft models in nude mice. Methods: Nude mice were injected subcutaneously with either Ramos or Daudi tumor cells. At approximately 7 days post tumor inoculation the mice were randomized to groups with roughly equivalent mean tumor volumes (>200mm3) and were treated with SMIP-016 or rituximab as a comparator. Groups were evaluated for median survival time (MST), tumor volume and percentage of tumor-free animals. Results: In nude mice bearing Daudi tumors, SMIP-016 treated mice showed a significant improvement in MST compared to control mice (p < 0.0001). Nude mice bearing Ramos tumors treated with SMIP-016 also demonstrated a significant enhancement in their median survival time (MST) in comparison to control mice (p < 0.0001). In addition, mice receiving SMIP-016 administered in combination with rituximab in this model demonstrated improvements in survival time over either single agent therapy alone. Conclusions: SMIP-016 is effective in treating established tumors in these human tumor xenograft models. Addition of SMIP-016 to rituximab therapy resulted in enhanced survival times compared to animals treated with rituximab alone.

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The locus of tumor necrosis factor-alpha action in lung inflammation

The pulmonary host response to infection and inflammation appears, at least in part, to be compartmentalized from the systemic host response. Tumor necrosis factor-alpha (TNF-alpha) has been implicated in lung inflammation and injury, but its site(s) of action has not been clearly defined. To investigate this, transgenic mice (surfactant apoprotein C promotor/soluble TNF receptor type II-Fc fusion protein ([SPCTNFRIIFc] mice) were generated in which TNF-alpha was selectively antagonized in the distal lung through tissue-specific expression of sTNFRIIFc, a soluble TNF inhibitor. The lung inflammatory response in these mice to pulmonary challenge with Micropolyspora faeni antigen or lipopolysaccharide (LPS) was compared with the response of wild-type mice, wild-type mice treated with recombinant sTNFRIIFc intravenously, and type I TNF-receptor knockout mice. Recruitment of polymorphonuclear leukocytes (PMN) to the lung after challenge with M. faeni antigen was essentially abolished in the TNFRI knockout mice and markedly reduced in the SPCTNFRIIFc mice. Wild-type mice given sTNFRIIFc intravenously in amounts resulting in lung concentrations similar to those in SPCTNFRIIFc mice also showed significantly reduced lung PMN recruitment, whereas those given doses that achieved such concentrations in the blood but low levels in the lung did not. In contrast, PMN recruitment to the lung following aerosol challenge with LPS was reduced significantly in the TNFRI knockout mice and in mice given high-dose sTNFRIIFc intravenously, but was not reduced significantly in SPCTNFRIIFc mice. Thus, inhibition of PMN recruitment in response to M. faeni antigen correlated largely with the extent of intrapulmonary inhibition of TNF-alpha, whereas the response to LPS correlated best with the extent of extrapulmonary inhibition of TNF-alpha. These studies indicate that TNF-alpha may act at different loci to mediate lung inflammation, with the site of action depending in part on the nature of the inflammatory stimulus, and that SPCTNFRIIFc mice provide a tool by which the locus of TNF action can be addressed.

Poxvirus genomes encode a secreted, soluble protein that preferentially inhibits beta chemokine activity yet lacks sequence homology to known chemokine receptors

Poxvirus genomes encode several proteins which inhibit specific elements of the host immune response. We show the "35K" virulence gene in variola and cowpox viruses, whose vaccinia and Shope fibroma virus equivalents are strongly conserved in sequence, actually encodes a secreted soluble protein with high-affinity binding to virtually all known beta chemokines, but only weak or no affinity to the alpha and gamma classes. The viral protein completely inhibits the biological activity of monocyte chemotactic protein-1 (MCP-1) by competitive inhibition of chemokine binding to cellular receptors. As all beta chemokines are also shown to cross-compete with MCP1 binding to the viral protein, we conclude that this viral chemokine inhibitor (vCCI) not only interacts through a common binding site, but is likely a potent general inhibitor of beta chemokine activity. Unlike many poxvirus virulence genes to date, which are clearly altered forms of acquired cellular genes of the vertebrate immune system, this viral chemokine inhibitor (vCCI) shares no sequence homology with known proteins, including known cellular chemokine receptors, all of which are multiple membrane-spanning proteins. Thus, vCCI presumably has no cellular analogue and instead may be the product of unrelenting sequence variations which gave rise to a completely new protein with similar binding properties to native chemokine receptors. The proposed function of vCCI is inhibition of the proinflammatory (antiviral) activities of beta chemokines.

Treatment of rheumatoid arthritis with a recombinant human tumor necrosis factor receptor (p75)-Fc fusion protein

BACKGROUND

Tumor necrosis factor (TNF) is a proinflammatory cytokine involved in the pathogenesis of rheumatoid arthritis, and antagonism of TNF may reduce the activity of the disease. This study evaluated the safety and efficacy of a novel TNF antagonist - a recombinant fusion protein that consists of the soluble TNF receptor (p75) linked to the Fc portion of human IgG1 (TNFR:Fc).

METHODS

In this multicenter, double-blind trial, we randomly assigned 180 patients with refractory rheumatoid arthritis to receive subcutaneous injections of placebo or one of three doses of TNFR:Fc (0.25, 2, or 16 mg per square meter of body-surface area) twice weekly for three months. The clinical response was measured by changes in composite symptoms of arthritis defined according to American College of Rheumatology criteria.

RESULTS

Treatment with TNFR:Fc led to significant reductions in disease activity, and the therapeutic effects of TNFR:Fc were dose-related. At three months, 75 percent of the patients in the group assigned to 16 mg of TNFR:Fc per square meter had improvement of 20 percent or more in symptoms, as compared with 14 percent in the placebo group (P<0.001). In the group assigned to 16 mg per square meter, the mean percent reduction in the number of tender or swollen joints at three months was 61 percent, as compared with 25 percent in the placebo group (P<0.001). The most common adverse events were mild injection-site reactions and mild upper respiratory tract symptoms. There were no dose-limiting toxic effects, and no antibodies to TNFR:Fc were detected in serum samples.

CONCLUSIONS

In this three-month trial TNFR:Fc was safe, well tolerated, and associated with improvement in the inflammatory symptoms of rheumatoid arthritis.

Biological effects and fate of a soluble, dimeric, 80-kDa tumor necrosis factor receptor in renal transplant recipients who receive OKT3 therapy

A preliminary clinical study of renal allograft recipients revealed that a dimeric form of the human 80 kDa soluble receptor (sTNFR:Fc) for tumor necrosis factor (TNF) is well tolerated and attenuates the OKT3-induced acute clinical syndrome. The current study determined the in vivo biological effects and fate of sTNFR:Fc in these patients. Serial assessment of both antigenic and biological activities of circulating TNF and sTNFR:Fc have led to the following observations. (1) Although control patients typically responded to the first OKT3 injection with a rapid increase of biologically active TNFalpha, patients on sTNFR:Fc therapy had markedly higher serum TNFalpha antigenic levels, but no detectable bioactivity. Thus, sTNFR:Fc functioned as a potent antagonist, despite its cytokine-carrier effect. (2) Peak sTNFR:Fc levels averaging 800 and 2500 ng/ml were routinely achieved in vivo, using the low-dose (0.05 mg/kg) and high-dose (0.15 mg/kg) protocols. (3) The half-life of circulating sTNFR:Fc was estimated to be approximately 4.4 days, and levels of p80 receptors in treated patients remained significantly above those in control patients for at least 20 days. (4) In vitro blocking studies demonstrated that circulating sTNFR:Fc remained biologically active for 2 weeks. These results demonstrate that under current protocols, significant serum levels of sTNFR:Fc, capable of effectively neutralizing TNF activity over prolonged periods, can be achieved. The persistent OKT3 side effects observed, despite sTNFR:Fc therapy, are therefore likely to be caused by factors other than TNF.

Pharmacokinetic parameters and biodistribution of soluble cytokine receptors

The potential use of soluble cytokine receptors as therapeutics in disease states when excessive or prolonged cytokine expression leads to pathogenesis is just beginning (Van Brunt, 1989). The inhibitory effects of soluble receptors have been found to be highly potent and specific for their respective cytokines (Maliszewski and Fanslow, 1990; Maliszewski et al., 1990). Recent in vivo data have shown that exogenously administered soluble receptors can function as cytokine antagonists and suppress autoimmune inflammatory responses (Jacobs et al., 1991a), allograft rejection, and alloreactivity (Fanslow et al., 1990b). The proposed frequency of administration and dosage of a therapeutic agent is dependent on the half-life of the agent and the route of administration. The elimination or half-life of a drug usually depends on its physiochemical properties (molecular size, glycosylation, isoelectric point, and hydrophobic/hydrophilic properties) (DiPalma and DiGregorio, 1990; Katzung, 1984). The half-life will also depend on the mechanism of clearance for that specific receptor. Once pharmacokinetic data are available for soluble receptors, the therapeutic potential of these molecules can be better evaluated. Only limited pharmacokinetic data are currently available for soluble cytokine receptors (Jacobs et al., 1991b). For sIL-1R, the majority of an intravenously administered dose was cleared in the second elimination phase, with a reasonably long half-life (6.3 hr), such that the entire dose was not eliminated until 35 hr. If administration is by subcutaneous injection, the half-life was even more prolonged. One explanation for the prolonged half-life is the minimal distribution to liver and kidneys and thus low levels of clearance by these organs. In contrast, elimination of intravenously administered sIL-4R was relatively rapid, with a short half-life (2.3 hr). This appeared mainly due to liver distribution and clearance, which has been the highest observed for any soluble cytokine receptor. Administering sIL-4R by subcutaneous injection significantly prolonged the half-life. This was most likely due to delaying the rate of liver distribution by slowing the rate of sIL-4R absorption into the circulation. Thus, subcutaneous injection would be the recommended route of administration for this receptor. Construction of a larger dimeric sIL-4R fusion protein did not prolong the i.v. half-life compared to that of the monomer, as the sIL-4R fusion protein was distributed to, and was cleared by, the liver to a greater degree.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanisms of neonatal transplantation tolerance

Although our analysis is very incomplete, our data indicate that a complete explanation of tolerance induced neonatally to H-2 encoded alloantigens will include elements of clonal deletion and active suppression. Background genes not encoded in H-2 play an important role in determining the extent to which clonal reduction occurs. In mice of B10 background genotype, extensive elimination of clones capable of recognizing class I and class II antigens is accomplished. Tolerance to class I alloantigens alone seems to be maintained almost exclusively by this mechanism. In B10 background mice tolerant of class II antigens alone or in consort with class I alloantigens, peripherally maintained (post-thymic) active suppression exists, that is dependent upon donor I-J expression, and is superimposed on clonal reduction. As a consequence, the activities of class II alloantigen-specific cells appear to be reduced to background, a level insufficient to activate specific effector precursors, even in the presence of relevant alloantigens. Donor alloantigens expressed on chimeric cells that exist among central (bone marrow, thymus) and peripheral (spleen, lymph nodes) lymphoid cells are undoubtedly crucial both to the process of ongoing clonal elimination as well as of active suppression. The role of clonal reduction in the maintenance of class II alone tolerance in mice of A/J background is more obscure. If the class II alloreactive cells that provide helper/inducer activity are identical to the cells that provide effector function (cytotoxic T cells, TDTH cells), then clonal reduction seems not to occur. Instead, class II tolerogen reactive cells remain within the peripheral lymphoid tissues of the tolerant mice, but appear to be incapable of differentiating beyond the initial steps of antigen-driven activation. We know little about the process by which such cells could be placed under these differentiation strictures, nor why they are retained within the tolerant animal's lymphoid mass. However, the absence of detectable chimerism in alloclass II tolerant animals of A/J background may offer an important clue to solving this mystery.