Citations

Abstract Malignant transformation is commonly associated with dysregulated ribosome biogenesis and for more than 100 years, pathologists have utilized the increase in size and number of nucleoli, the site of ribosome biogenesis, as a marker for aggressive malignancies (Hein et al., Trends in Molecular Medicine, 2013). Recently we demonstrated that hyperactivated RNA Polymerase I (Pol I) transcription, a rate limiting step in ribosome biogenesis, can be specifically targeted by the small molecule inhibitor, CX-5461 (Drygin et al., Cancer Research, 2011; Bywater et al. Cancer Cell, 2012). When evaluated for its anti-proliferative activity against a panel of genetically diverse human cancer cell lines, those derived from p53 wild type hematological malignancies were the most sensitive (Drygin et al., Cancer Research, 2011). Evaluation of whether Pol I transcription inhibition could serve as therapeutic strategy in vivo revealed that CX-5461 administration significantly prolongs the overall survival of Em-Myc lymphoma bearing mice. This survival advantage was associated with rapid activation of the ribosomal protein (Rp)-MDM2-p53 nucleolar stress response (Deisenroth et al., Oncogene, 2010) and subsequent induction of tumour cell-specific p53-dependent apoptosis; importantly the wild type B-cell population was maintained and did not activate p53 pathways (Bywater et al. Cancer Cell, 2012). To explore the therapeutic potential of Pol I transcription inhibition via CX-5461 in hematological malignancies refractory to standard chemotherapy, we employed mouse models of highly aggressive MLL-driven Acute Myeloid Leukemia (AML) (MLL/AF9 + Nras and MLL/ENL + Nras) (Zuber et al., Genes Dev, 2009) and V*κ-Myc-driven Multiple Myeloma (MM) (Chesi et al. Cancer Cell, 2009). CX-5461 administration significantly increased the overall survival time of AML-bearing mice (MLL/ENL Nras median 17 days for vehicle vs 36 days for drug, P<0.0001 (Figure 1); MLL/AF9 Nras median 15 days for vehicle vs 23 days for drug, P 0.0009) without severe adverse effects. The extended survival of MLL-driven AML bearing mice was associated with acute activation of p53, induction of cell death and an aberrant G2/M cell cycle progression, which consequently delayed tumour progression as monitored by bioluminescence-imaging and white blood cell counts (WBC). In contrast to CX-5461, standard-therapy with a regime containing Cytarabine/Doxorubicin (5:3) failed to induce p53 in MLL/ENL Nras AML-bearing mice, resulting in a significantly lower survival advantage as compared to animals treated with CX-5461 therapy. Figure 1Figure 1. In ongoing experiments with MM-bearing mice, chronic CX-5461 administration robustly reduced the secretion of serum monoclonal Ig, as detected by serum protein electrophoresis (SPEP), and significantly prolonged the overall survival time (Figure 2) (V*κ-Myc median >160 days for drug vs, 103.5 days for vehicle, ongoing) demonstrating that CX-5461 exhibits potent anti-tumour activity in MM model. Analysis of the molecular mechanism responsible for the therapeutic benefit of CX-5461 in MM is ongoing but appears to involve both p53 mediated apoptosis and aberrant cell cycle progression. Figure 2Figure 2. These data demonstrate that hyperactivated Pol I transcription can be successfully targeted through small molecule inhibitors to treat models of human AML and MM that are refractory to standard therapy. Based on these and previously published results (Bywater et al., Cancer Cell, 2012), we have recently initiated a first-in-human, phase I, dose escalation clinical trial of this first-in-class drug, CX-5461 in patients with advanced hematological malignancies. The toxicity, response, pharmacokinetic and co-relative data from this trial will offer valuable insights as to whether inhibition of ribosome synthesis might offer a new non-genotoxic therapeutic approach in the fight against cancers, which are highly refractory to standard therapies. Disclosures: O'Brien: Senhwa Biosciences, Inc: Employment.

Abstract Results from the Phase I portion of this study in high risk chronic lymphocytic leukemia (CLL) patients (pts) (NCT01269385) showed that the combination of Imprime PGG (IPGG) at doses up to 4 mg/kg, with alemtuzumab (ALM) and rituximab (RTX), was well tolerated and associated with a 73% complete response (CR) rate (Blood 120: Abstr 1792, 2013). IPGG is a yeast-derived beta 1,3/1,6 glucan that engages innate immune cells, enhancing anti-tumor activity in combination with complement activating monoclonal antibodies (mAb) via a mechanism involving complement receptor 3 (J Immunol 177:1661, 2006). Endogenous anti-beta glucan antibodies (ABA) are required for IPGG binding to complement receptors and modulation of innate immune cell function. In pts with stage IV non-small cell lung cancer (NSCLC), correlation between serum ABA concentrations and response to an IPGG-containing frontline regimen has been observed (J Clin Oncol 32: 15S; Abstr 3045, 2014). Here we report clinical and translational results at the end of the Phase II portion of this CLL study. Methods: The primary endpoint of the Phase II study was the proportion of pts experiencing CR 3 months after completing 5 weeks of treatment with IPGG 4 mg/kg, ALM and RTX. Eligible pts (n=14) had a diagnosis of CLL by standard criteria (IWCLL-NCI 2008), no prior treatment for CLL, high risk CLL based on molecular markers (17p13-; 11q22-; unmutated [<2%] IGHV and/or use of VH3-21 AND CD38+ [³30%] and/or ZAP70+ [³20%]), no standard indication for initiation of CLL therapy, and adequate performance status and organ function. Planned enrollment was up to 39 pts but the study was terminated early due to slow accrual. Translational studies evaluated baseline serum ABA levels and in vitro binding of IPGG to immune cell subsets in whole blood. Results: The median age was 63.5 (range 47-77); 71% were male; and 6 (43%), 5 (36%) and 3 (21%) pts had Rai Stage 0, 1 and 2, respectively. CLL high-risk parameters were 17p13- in 3 (21%), 11q22- in 5 (36%), and unmutated IGHV or use of VH3-21 together with either expression of ZAP70 and/or CD38 in 6 (43%) pts. Grade 3 AEs were diarrhea (n=3) and increased transaminase levels, dehydration, gastritis, hypertension, hyponatremia, and hypertension (each n=1). Grade 4 AEs were neutropenia (n=2) and febrile neutropenia (n=1). Thirteen (93%) patients responded to therapy, with 7 CR, 2 CR with incomplete marrow recovery, 1 nodular PR and 3 PR (IWCLL-NCI 2008 criteria). Median follow-up was 12.7 mo (range 6.7 - 28.0). The overall median duration of response cannot be determined, as only 5/13 responders have progressed (median of 5.6 mo; range: 2.9 - 8.5) and the other 8 remain progression-free after a median of 8.0 mo (range 5.6 - 21.0). Four progressing pts were retreated after a median of 14.2 mo (range 12.4 - 20.5). There were no deaths during or after treatment. Translational studies demonstrated a correlation between ABA concentrations and binding of IPGG to neutrophils, monocytes and B-cells. However, there was no correlation between ABA concentrations and response to treatment. Potential functional implications of binding of IPGG to leukemic B cells, including direct and indirect enhancement of the antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis mediated by anti-tumor mAbs are under investigation. Discussion: The combination of IPGG with ALM and RTX appeared safe and well tolerated overall with an ORR of 93% and a 64% CR/CRi rate. ABA concentrations did not correlate with clinical response to an IPGG containing regimen in these CLL patients. Data on functional implications of IPGG binding to leukemic B cells will be presented. Disclosures Bose: Biothera: Corporate stock options Other, Employment, Research Funding. Zent:Biothera: Research Funding. Ottoson:Biothera: Corporate stock options Other, Employment. Leonardo:Biothera: Corporate stock options Other, Employment. Ansell:Biothera: Research Funding.

PURPOSE Evidence-based treatments for metastatic, human epidermal growth factor receptor 2 (HER2)–positive breast cancer to the CNS are limited. We previously reported modest activity of neratinib monotherapy for HER2-positive breast cancer brain metastases. Here we report the results from additional study cohorts. PATIENTS AND METHODS Patients with measurable, progressive, HER2-positive brain metastases (92% after receiving CNS surgery and/or radiotherapy) received neratinib 240 mg orally once per day plus capecitabine 750 mg/m 2 twice per day for 14 days, then 7 days off. Lapatinib-naïve (cohort 3A) and lapatinib-treated (cohort 3B) patients were enrolled. If nine or more of 35 (cohort 3A) or three or more of 25 (cohort 3B) had CNS objective response rates (ORR), the drug combination would be deemed promising. The primary end point was composite CNS ORR in each cohort separately, requiring a reduction of 50% or more in the sum of target CNS lesion volumes without progression of nontarget lesions, new lesions, escalating steroids, progressive neurologic signs or symptoms, or non-CNS progression. RESULTS Forty-nine patients enrolled in cohorts 3A (n = 37) and 3B (n = 12; cohort closed for slow accrual). In cohort 3A, the composite CNS ORR = 49% (95% CI, 32% to 66%), and the CNS ORR in cohort 3B = 33% (95% CI, 10% to 65%). Median progression-free survival was 5.5 and 3.1 months in cohorts 3A and 3B, respectively; median survival was 13.3 and 15.1 months. Diarrhea was the most common grade 3 toxicity (29% in cohorts 3A and 3B). Neratinib plus capecitabine is active against refractory, HER2-positive breast cancer brain metastases, adding additional evidence that the efficacy of HER2-directed therapy in the brain is enhanced by chemotherapy. For optimal tolerance, efforts to minimize diarrhea are warranted.