Abstract B222: Dicer substrate siRNAs to MYC, B-catenin, and other target genes effectively induce in vivo target gene knockdown and tumor inhibition

Although there are now multiple successful examples of targeted therapeutics in cancer, many key protein targets have remained largely ‘undruggable’, including transcription factors such as B-catenin (CTNNB1) and MYC. B-catenin mediates Wnt signaling, which is overactive in many cancers including hepatocarcinoma (HCC). RNAi offers a way to reach such undruggable targets by inhibiting their expression at the mRNA level. Dicer substrate siRNAs (“DsiRNAs”) can be particularly effective for gene silencing. DsiRNAs are longer than conventional siRNAs, and therefore are substrates for processing by Dicer, after which the product RNA duplexes are incorporated into RISC, leading to target mRNA knockdown. We have used DsiRNAs to target B-catenin, MYC, and other key genes in HCC and other cancers. Through large-scale DsiRNA screening, we have identified a series of high potency DsiRNAs with picomolar to sub-picomolar IC50 values for mRNA knockdown. Lead DsiRNAs fully tolerated extensive 2’-OMe modification, retaining high potency, and lacked detectable immunostimulatory activity. To test the effect of target gene knockdown on tumor growth in vivo, we used a lipid nanoparticle (LNP) delivery system. LNP/DsiRNA particles effectively delivered to tumors in mouse tumor models, leading to rapid knockdown of target gene mRNA and protein. Knockdown of B-catenin, MYC, and other target genes strongly inhibited tumor growth. B-catenin knockdown also strongly reduced expression of the B-catenin-regulated genes Axin2 and MYC, a potential mechanism for tumor inhibition. In summary, we have developed high potency DsiRNAs to cancer target genes, and effectively delivered these DsiRNAs to tumors in vivo, resulting in inhibition of target gene expression and inhibition of tumor growth. DsiRNA therapeutics show promise as novel agents for reaching traditionally undruggable target genes.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B222.

Citation Format: Hank Dudek, Kathleen Wortham, Rokhand Arvan, Anee Shah, Bo Ying, Wendy Cyr, Hailin Yang, Wei Zhou, Utsav Saxena, Yi Zhou, Rohan Diwanji, Ben Holmes, Ruchir Farkiwala, Aalok Shah, Bob Brown. Dicer substrate siRNAs to MYC, B-catenin, and other target genes effectively induce in vivo target gene knockdown and tumor inhibition. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B222.

The anti-Fn14 antibody BIIB036 inhibits tumor growth in xenografts and patient derived primary tumor models and enhances efficacy of chemotherapeutic agents in multiple xenograft models

Agonistic antibodies targeting Fn14, the receptor for TWEAK, have demonstrated anti-tumor activity in xenograft models. Herein, we further explore the therapeutic potential of the humanized anti-Fn14 agonistic antibody, BIIB036, as a single agent and in combination with standard of care cancer therapeutics. Pharmacokinetic studies of BIIB036 in tumor-bearing mice revealed a half-life of approximately three days suggesting twice a week dosing would be necessary to maintain efficacy. However, in multiple xenograft models, BIIB036 treatment resulted in extended tumor growth inhibition up to 40-50 d following cessation of dosing, suggesting that frequent administration of BIIB036 may not be necessary to maintain prolonged anti-tumor activity. Subsequent xenograft studies revealed that maximal efficacy was achieved with BIIB036 dosing once every two weeks, by either intraperitoneal or subcutaneous administration. Xenograft tumors that were initially treated with BIBI036 and then re-grew up to 1000 mm³ following cessation of the first cycle of treatment remained sensitive to a second cycle of treatment. BIIB036 was also evaluated in patient derived primary colon tumor models, where efficacy compared favorably with a standard of care agent. Lastly, BIIB036 enhanced the efficacy of several standard of care chemotherapeutics, including paclitaxel in MDA-MBA-231 breast tumor xenografts, paclitaxel or carboplatin in HOP62 non-small cell lung xenografts, and 5-FU in NCI-N87 gastric xenografts, with no overlapping toxicities. These studies thus establish BIIB036 as a promising therapeutic agent with durable anti-tumor activity in human xenografts as well as patient derived primary tumor models, and enhanced activity and tolerability in combination with standard of care chemotherapeutics. Taken together, the data presented herein suggest that BIIB036 warrants evaluation in the clinic.

Development of an Fn14 agonistic antibody as an anti-tumor agent

TWEAK, a TNF family ligand with pleiotropic cellular functions, was originally described as capable of inducing tumor cell death in vitro. TWEAK functions by binding its receptor, Fn14, which is up-regulated on many human solid tumors. Herein, we show that intratumoral administration of TWEAK, delivered either by an adenoviral vector or in an immunoglobulin Fc-fusion form, results in significant inhibition of tumor growth in a breast xenograft model. To exploit the TWEAK-Fn14 pathway as a therapeutic target in oncology, we developed an anti-Fn14 agonistic antibody, BIIB036. Studies described herein show that BIIB036 binds specifically to Fn14 but not other members of the TNF receptor family, induces Fn14 signaling, and promotes tumor cell apoptosis in vitro. In vivo, BIIB036 effectively inhibits growth of tumors in multiple xenograft models, including colon (WiDr), breast (MDA-MB-231), and gastric (NCI-N87) tumors, regardless of tumor cell growth inhibition response observed to BIIB036 in vitro. The anti-tumor activity in these cell lines is not TNF-dependent. Increasing the antigen-binding valency of BIB036 significantly enhances its anti-tumor effect, suggesting the contribution of higher order cross-linking of the Fn14 receptor. Full Fc effector function is required for maximal activity of BIIB036 in vivo, likely due to the cross-linking effect and/or ADCC mediated tumor killing activity. Taken together, the anti-tumor properties of BIIB036 validate Fn14 as a promising target in oncology and demonstrate its potential therapeutic utility in multiple solid tumor indications.

Stable IgG-like bispecific antibodies directed toward the type I insulin-like growth factor receptor demonstrate enhanced ligand blockade and anti-tumor activity

Bispecific antibodies (BsAbs) target multiple epitopes on the same molecular target or different targets. Although interest in BsAbs has persisted for decades, production of stable and active BsAbs has hindered their clinical evaluation. Here, we describe the production and characterization of tetravalent IgG-like BsAbs that combine the activities of allosteric and competitive inhibitors of the type-I insulin-like growth factor receptor (IGF-1R). The BsAbs, which were engineered for thermal stability, express well, demonstrate favorable biophysical properties, and recognize both epitopes on IGF-1R. Only one BsAb with a unique geometry, denoted BIIB4-5scFv, was capable of engaging all four of its binding arms simultaneously. All the BsAbs (especially BIIB4-5scFv) demonstrated enhanced ligand blocking over the single monoclonal antibodies (mAbs), particularly at high ligand concentrations. The pharmacokinetic profiles of two IgG-like BsAbs were tested in nude mice and shown to be comparable with that of the parental mAbs. The BsAbs, especially BIIB4-5scFv, demonstrated an improved ability to reduce the growth of multiple tumor cell lines and to inhibit ligand-induced IGF-1R signaling in tumor cells over the parental mAbs. BIIB4-5scFv also led to superior tumor growth inhibition over its parental mAbs in vivo. In summary, BsAbs that bridge multiple inhibitory mechanisms against a single target may generally represent a more effective strategy for intervention in oncology or other indications compared with traditional mAb therapy.

Protective effect of tonapofylline (BG9928), an adenosine A1 receptor antagonist, against cisplatin-induced acute kidney injury in rats

BACKGROUND/AIMS

Cisplatin (CIS) induces nephrotoxicity partly through renal vasoconstriction and decreased glomerular filtration effects thought to involve adenosine acting on adenosine A(1) receptors (A1Rs). We studied the effect of the orally active, A1R antagonist tonapofylline (BG9928) on biochemical measures of renal function in CIS-induced acute kidney injury (AKI) in rats.

METHODS

Tonapofylline, 1 mg/kg b.i.d., p.o., was administered on days 0-1 or 0-6 to rats treated with CIS 5.5 mg/kg i.v. Prednisolone (PRED) 5 mg/kg s.c. (day 0) served as a positive control. Serum creatinine and urea nitrogen (BUN) were measured in serial blood samples taken over the 13-day study period.

RESULTS

CIS produced significant elevations in creatinine, reduction in body weight and marked proximal tubular injury throughout the renal cortex and outer medulla. Tonapofylline, days 0-1 or 0-6 and PRED all produced sustained reductions in post-CIS serum creatinine and BUN levels compared with controls, improved body weight recovery and significant attenuation of CIS-induced kidney pathology scores.

CONCLUSION

These data support the involvement of A1Rs in CIS-induced AKI in rats. Tonapofylline may be useful in the clinical setting for the prevention of kidney failure induced by nephrotoxic agents such as CIS.

Targeting the lymphotoxin-beta receptor with agonist antibodies as a potential cancer therapy

The lymphotoxin-beta receptor (LT beta R) is a tumor necrosis factor receptor family member critical for the development and maintenance of various lymphoid microenvironments. Herein, we show that agonistic anti-LT beta R monoclonal antibody (mAb) CBE11 inhibited tumor growth in xenograft models and potentiated tumor responses to chemotherapeutic agents. In a syngeneic colon carcinoma tumor model, treatment of the tumor-bearing mice with an agonistic antibody against murine LT beta R caused increased lymphocyte infiltration and necrosis of the tumor. A pattern of differential gene expression predictive of cellular and xenograft response to LT beta R activation was identified in a panel of colon carcinoma cell lines and when applied to a panel of clinical colorectal tumor samples indicated 35% likelihood a tumor response to CBE11. Consistent with this estimate, CBE11 decreased tumor size and/or improved long-term animal survival with two of six independent orthotopic xenografts prepared from surgical colorectal carcinoma samples. Targeting of LT beta R with agonistic mAbs offers a novel approach to the treatment of colorectal and potentially other types of cancers.

Design, synthesis, and analysis of a polyethelene glycol-modified (PEGylated) small molecule inhibitor of integrin {alpha}4{beta}1 with improved pharmaceutical properties

Integrin alpha4beta1 plays an important role in inflammatory processes by regulating the migration of leukocytes into inflamed tissues. Previously, we identified BIO5192 [2(S)-{[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino}-4-[4-methyl-2(S)-(methyl-{2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl}-amino)-pentanoylamino]-butyric acid], a highly selective and potent (K(D) of 9 pM) small molecule inhibitor of alpha4beta1. Although BIO5192 is efficacious in various animal models of inflammatory disease, high doses and daily treatment of the compound are needed to achieve a therapeutic effect because of its relatively short serum half-life. To address this issue, polyethylene glycol modification (PEGylation) was used as an approach to improve systemic exposure. BIO5192 was PEGylated by a targeted approach in which derivatizable amino groups were incorporated into the molecule. Two sites were identified that could be modified, and from these, five PEGylated compounds were synthesized and characterized. One compound, 2a-PEG (K(D) of 19 pM), was selected for in vivo studies. The pharmacokinetic and pharmacodynamic properties of 2a-PEG were dramatically improved relative to the unmodified compound. The PEGylated compound was efficacious in a rat model of experimental autoimmune encephalomyelitis at a 30-fold lower molar dose than the parent compound and required only a once-a-week dosing regimen compared with a daily treatment for BIO5192. Compound 2a-PEG was highly selective for alpha4beta1. These studies demonstrate the feasibility of PEGylation of alpha4beta1-targeted small molecules with retention of activity in vitro and in vivo. 2a-PEG, and related compounds, will be valuable reagents for assessing alpha4beta1 biology and may provide a new therapeutic approach to treatment of human inflammatory diseases.

An assessment of the mechanistic differences between two integrin alpha 4 beta 1 inhibitors, the monoclonal antibody TA-2 and the small molecule BIO5192, in rat experimental autoimmune encephalomyelitis

Integrin alpha 4 beta 1 plays an important role in inflammatory processes by regulating the migration of lymphocytes into inflamed tissues. Here we evaluated the biochemical, pharmacological, and pharmacodynamic properties and efficacy in experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, of two types of alpha 4 beta 1 inhibitors, the anti-rat alpha 4 monoclonal antibody TA-2 and the small molecule inhibitor BIO5192 [2(S)-[[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino]-4-[4-methyl-2(S)-(methyl-[2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl]-amino)-pentanoylamino]-butyric acid]. TA-2 has been extensively studied in rats and provides a benchmark for assessing function. BIO5192 is a highly selective and potent (KD of <10 pM) inhibitor of alpha 4 beta 1. Dosing regimens were identified for both inhibitors, which provided full receptor occupancy during the duration of the study. Both inhibitors induced leukocytosis, an effect that was used as a pharmacodynamic marker of activity, and both were efficacious in the EAE model. Treatment with TA-2 caused a decrease in alpha 4 integrin expression on the cell surface, which resulted from internalization of alpha 4 integrin/TA-2 complexes. In contrast, BIO5192 did not modulate cell surface alpha 4 beta 1. Our results with BIO5192 indicate that alpha 4 beta 7 does not play a role in this model and that blockade of alpha 4 beta 1/ligand interactions without down-modulation is sufficient for efficacy in rat EAE. BIO5192 is highly selective and binds with high affinity to alpha 4 beta 1 from four of four species tested. These studies demonstrate that BIO5192, a novel, potent, and selective inhibitor of alpha 4 beta 1 integrin, will be a valuable reagent for assessing alpha 4 beta 1 biology and may provide a new therapeutic for treatment of human inflammatory diseases.

Malignant melanocytic neural crest tumor in a young chicken (Gallus domesticus)

A malignant melanocytic tumor was found in an 8-week-old chicken. The tumor, which was composed of melanocytes, ganglion cells, nerves, and primitive pressure receptors, was examined by light microscopy, transmission electron microscopy, and immunohistochemistry. Antibodies to neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP), and S-100 protein variably stained nerves, but melanocytes were only rarely immunolabelled by NSE antibodies and there was no specific staining of these cells for S-100 or GFAP. Ultrastructurally, neoplastic melanocytes contained melanin within melanosomes and premelanosomes and did not resemble Schwann cells.

The effect of ibuprofen on microvascular thrombosis in an experimental rabbit model

The efficacy of ibuprofen in reducing microvascular thrombosis in a well-established experimental model was studied. Bilateral 2-mm arterial inversion grafts were constructed in the femoral arteries of New Zealand White rabbits. The experimental group (n = 40 grafts) received subcutaneous injections of ibuprofen 15 mg/kg t.i.d. beginning 1 day preoperatively and continued for 7 days postoperatively. The control group (n = 42 grafts) received injections of an equivalent volume of saline three times per day. Patency was evaluated at 7 days by the distal milking test. Seventy-three percent of the ibuprofen grafts were patent at 7 days, whereas 57% of the control grafts remained open. This difference in microvascular patency was not statistically significant. Representative scanning electron micrographs revealed a moderate reduction in aggregated platelets and overall clot density in the patent ibuprofen arterial inversion grafts compared with the patent control specimens. Although the use of ibuprofen as a sole antithrombotic agent cannot be recommended as the result of this study, it may be efficacious when used in conjunction with other agents such as dextran 40.

Prostacyclin production by vein grafts in the arterial circulation: a study in rats

The in vitro production of prostacyclin by vein grafts was measured using vascular rings followed by radioimmunoassay of the medium. The grafts were prepared by interposing a segment of epigastric vein in a gap in the ipsilateral femoral artery of the rat. Measurements made over a period of 1 to 42 days showed a progressive rise from venous levels (less than 0.2 ng/ml) to values close to the arterial controls (10.9 +/- 2.2 ng/ml). This deficiency of prostacyclin synthesis during the "arterialization" of the graft may account for some of the early failures which can occur in vein grafting and suggests the possibility of pharmacological intervention to improve the success rate.

Vascular labelling with monastral blue B

Vascular labelling is an established technique of experimental pathology whereby leaky vessels can be identified in vivo. A suspension of a suitable colloidal pigment is injected intravenously; the pigment is then trapped in the wall of the leaky vessels. The colloidal preparation of carbon black, which has been used for many years for this purpose, is no longer commercially available. This communication introduces a substitute: Monastral blue B which gives beautiful preparations in whole mounts, is readily visible in paraffin and plastic embedded histologic sections, has a distinctive appearance in electron micrographs, and is nontoxic in the required dosage.