First-in class selective AXL inhibitor bemcentinib (BGB324) in combination with LDAC or decitabine exerts anti-leukaemic activity in AML patients unfit for intensive chemotherapy: Phase II open-label study

7043

Background: The RTK AXL represents a therapeutic target promoting AML cell proliferation and survival by pleiotropic mechanisms and is a negative regulator of anti-tumour immunity. Bemcentinib is a first-in-class, highly selective, oral AXL inhibitor that has previously shown encouraging anti-leukaemic activity as a monotherapy in r/r AML and hr-MDS. Methods: A monotherapy dose-escalation and expansion part of this trial is complete. In this second, phase II part of the study, 11 and 15 AML pts unfit for intensive chemotherapy received bemcentinib at RP2D (200 mg po/d) in combination with low-dose cytarabine (LDAC) and decitabine, respectively. Median age was 77 yr (range: 50-83), median screen myeloblast count 39% (3-95%) and 2/19 (11%) of pts evaluable for FLT3 were FLT3+. Plasma protein biomarker levels were measured using the DiscoveryMap v3.3 panel (Myriad RBM) at screen and following treatment. Results: The most common TRAEs (≥ 15% of pts) were ECG QT prolongation (35%) and diarrhoea (15%). Among these, 3 were Grade 3, and none 4 or 5. All TRAEs were manageable and/or reversible. As of Feb ‘19, 9 pts (2 de novo, 1 secondary, 6 r/r) in the bemcentinib + LDAC group were evaluable for response and 4 (44%; 2 de novo + 2 relapsed) achieved rapid CRi at C2D1. Responses were durable (range: 7 – 11 cycles) in 3 of the 4 responders. A further 2 pts (22%, 1 secondary + 1 relapsed) achieved durable SD (5 and 6 cycles). mPFS among the 5 pts with durable CRi or SD was 5 months (range: 3.5-7.7). Further, at the time of writing, 11 pts (8 de novo, 3 r/r) in the bemcentinib + decitabine group were evaluable for response of which 4 (36%, all de novo) achieved CRi after ≥ 4 cycles. One additional de novo pt achieved durable SD lasting for 5 cycles. Conclusions: Bemcentinib in combination with LDAC exerted early durable responses in patients with both de novo and relapsed AML whilst the combination of bemcentinib + decitabine exerted comparably fewer and later responses in de novo AML. Soluble biomarker correlations will be presented at the meeting. Both combinations were generally well-tolerated and further exploration is warranted. Clinical trial information: NCT02488408.

BET-inhibition by JQ1 promotes proliferation and self-renewal capacity of hematopoietic stem cells

Although inhibitors of bromodomain and extra terminal domain (BET) proteins show promising clinical activity in different hematologic malignancies, a systematic analysis of the consequences of pharmacological BET inhibition on healthy hematopoietic (stem) cells is urgently needed. We found that JQ1 treatment decreases the numbers of pre-, immature and mature B cells while numbers of early pro-B cells remain constant. In addition, JQ1 treatment increases apoptosis in T cells, all together leading to reduced cellularity in thymus, bone marrow and spleen. Furthermore, JQ1 induces proliferation of long-term hematopoietic stem cells, thereby increasing stem cell numbers. Due to increased numbers, JQ1-treated hematopoietic stem cells engrafted better after stem cell transplantation and repopulated the hematopoietic system significantly faster after sublethal myeloablation. As quantity and functionality of hematopoietic stem cells determine the duration of life-threatening myelosuppression, BET inhibition might benefit patients in myelosuppressive conditions.

Axl blockade in vitro and in patients with high-risk MDS by the small molecule inhibitor BGB324

7059

Background: The interplay with bone marrow stroma plays an important role in the pathobiology of MDS. Gas6 is secreted by mesenchymal bone marrow stroma cells and promotes survival and therapy resistance of AML cells expressing the Axl receptor. We hypothesized that inhibiting Axl by the small molecule inhibitor BGB324 might hold therapeutic potential in MDS. Methods: We investigated the inhibitory effect of BGB324 on primary bone marrow mononucleated cells (BMMNC) and mesenchymal stroma cells (MSC) from MDS patients in comparison to healthy donors. In the ongoing first-in-patient Phase 1a/b trial BGBC003 A standard 3 + 3 dose escalation study was performed to identify the maximum tolerated dose of BGB324 in patients with previously treated high risk MDS or AML. BGB324 was administered as an oral loading dose on days one and two followed by a reduced daily maintenance. Three dose levels were explored 400/100mg, 600/200mg and 900/300mg. Results: We found that BGB324 inhibited BMMNC from low- and high-risk MDS patients with an IC50 of 2.1 µM and 3.8 µM, respectively (n = 5). In comparison, BMNNC from healthy donors were resistant to BGB324 (IC50 9.4 µM, p < 0.05, n = 10). Axl expression was present in MSC isolated from the BM of MDS patients and BGB324 inhibited the proliferation of MSC from low- and high-risk MDS patients (IC50 2.5 µM and 2.7 µM, respectively; n = 7/5).To date, 3 patients with MDS were treated with 400 mg loading dose and 100 mg maintenance dose of BGB324. Therapy has been well-tolerated and the MTD has not yet been reached. The majority of adverse events reported have been Grade 1 and 2. The most common related adverse events are diarrhea and fatigue. One patient with MDS was treated for 80 weeks and experienced a PR. Evidence of target inhibition was demonstrated by almost complete inhibition of Axl phosphorylation accompanied by reduction in phosphoErk and phosphoAkt signalling at day 21 of treatment. Conclusions: BGB324 is well-tolerated and might represent a promising novel treatment approach in MDS. Safety and efficacy of BGB324 will be explored further in clinical trials. Clinical trial information: NCT02488408.

Cetuximab Resistance in Head and Neck Cancer Is Mediated by EGFR-K521 Polymorphism

Head and neck squamous cell carcinomas (HNSCC) exhibiting resistance to the EGFR-targeting drug cetuximab poses a challenge to their effective clinical management. Here, we report a specific mechanism of resistance in this setting based upon the presence of a single nucleotide polymorphism encoding EGFR-K₅₂₁ (K-allele), which is expressed in >40% of HNSCC cases. Patients expressing the K-allele showed significantly shorter progression-free survival upon palliative treatment with cetuximab plus chemotherapy or radiation. In several EGFR-mediated cancer models, cetuximab failed to inhibit downstream signaling or to kill cells harboring a high K-allele frequency. Cetuximab affinity for EGFR-K₅₂₁ was reduced slightly, but ligand-mediated EGFR activation was intact. We found a lack of glycan sialyation on EGFR-K₅₂₁ that associated with reduced protein stability, suggesting a structural basis for reduced cetuximab efficacy. CetuGEX, an antibody with optimized Fc glycosylation targeting the same epitope as cetuximab, restored HNSCC sensitivity in a manner associated with antibody-dependent cellular cytotoxicity rather than EGFR pathway inhibition. Overall, our results highlight EGFR-K₅₂₁ expression as a key mechanism of cetuximab resistance to evaluate prospectively as a predictive biomarker in HNSCC patients. Further, they offer a preclinical rationale for the use of ADCC-optimized antibodies to treat tumors harboring this EGFR isoform. Cancer Res; 77(5); 1188-99. ©2016 AACR.

Abstract 3253: Mast cell-derived granzyme b contributes to resistance against anti-angiogenic therapy

Significance: Targeted therapies have revolutionized the treatment of cancer. However, efficacy of anti-angiogenic therapies is limited due to significant resistance.

Recent studies showed that the tumor microenvironment is involved in resistance towards targeted anti-angiogenic treatment. Based on the correlation of mast cell (MC) density with tumor growth and angiogenesis we put forward the hypothesis that MC might be implicated in anti-angiogenic therapy resistance.

Methods: C57BL/6J, NSG or MC-deficient KitW-sh (Wsh) mice were subcutaneously injected with 5×105 (Panc02 and EL4) or 1×106 (TD2) cells +/- bone marrow derived MC. Tumors were treated with 20 mg/kg anti-VEGFR2 antibody (DC101) or 25 mg/kg cromoglicic acid (Cromo). BrdU was injected 12 h before sacrifice.

Results: We show that MC alter the proliferative and organizational state of endothelial cells (EC). MC dose-dependently induced EC-proliferation (158 ± 12%; *p&lt;0.05) and tube formation (290 ± 12%; *p&lt;0.05). Furthermore, MC increased HUVEC migration by 1.4-fold (*p&lt;0.05) and protected them from AAT in vitro. In MC-deficient mice, tumor growth was reduced by 36% (*p&lt;0.05) and the efficacy of AAT was increased (WT + DC101: 1420 ± 134 mg; Wsh + DC101: 599 ± 107 mg; *p&lt;0.05). Histomorphometric analyses unraveled that MC-deficiency decreased the numbers of mature pericyte-covered vessels by 80% (*p&lt;0.05) rendering them more prone for therapy. Indeed, an additive anti-angiogenic effect of MC-deficiency and AAT was observed resulting in reduced microvessel density (MVD) and tumor cell proliferation. This “angiosensitizing” effect could be abrogated by adoptive transfer of bone marrow-derived MC into MC-deficient mice.

In WT mice, AAT only initially reduced the proliferation of tumor vessels by 60% (*p&lt;0.05), a process that got reverted after long-term treatment as a result of therapy resistance. Intriguingly, this pro-angiogenic rescue phenotype did not occur in MC-deficient mice. By blocking MC degranulation with Cromo we could increase the efficacy of AAT (DC101: 703 ± 48 mg; Cromo + DC101: 386 ± 92 mg; *p&lt;0.05), leading to reduced vessel proliferation, MVD and tumor cell proliferation.

Microarray analysis of tumor-resident MC unraveled increased expression levels of ECM-degrading granzyme b (gzmb) in response to therapy. MC-specific knock down of gzmb rendered tumors more susceptible for AAT and lowered the levels of alternative, pro-angiogenic mediators beside the VEGF-VEGFR2-axis in the tumor microenvironment.

Conclusions: Our results indicate that tumor-resident MC interfere with AAT. We provide evidence that MC-derived gzmb liberates ECM-bound pro-angiogenic factors besides the targeted VEGF-VEGFR2 axis, thereby fine-tuning vessel maturation and proliferation, which ultimately decreases therapeutic efficacy. Importantly, knock down of gzmb and pharmacological inhibition of MC degranulation improved the therapeutic response towards AAT.

Citation Format: Mark A. Wroblewski, Raimund Bauer, Miguel Cubas Córdova, Florian Udonta, Isabel Ben Batalla, Victoria Gensch, Stefanie Sawall, Jonas S. Waizenegger, Julian Pardo Jimeno, Klaus Pantel, Carsten Bokemeyer, Sonja Loges. Mast cell-derived granzyme b contributes to resistance against anti-angiogenic therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3253.

Abstract 1161: COX-2 blockade improves efficacy of VEGF-targeting drugs

Efficacy of anti-angiogenic drugs is hampered by hypoxia-induced resistance. Because cyclooxygenase-2 (Cox-2) is upregulated in hypoxic conditions we analyzed mRNA expression levels of cyclooxygenase-1 (Cox-1) and Cox-2 in GFP+ FACS-sorted tumor cells from 4T1 tumors after treatment with anti-VEGFR2 antibodies (DC101) or with sunitinib. Cox-2 but not Cox-1 mRNA was upregulated by 2.3-fold upon anti-angiogenic treatment. In addition we found 5.2-fold increased prostaglandin E2 levels in 4T1 tumors after anti-angiogenic therapy. We hypothesized that concomitant blockade of Cox-2 could increase efficacy of anti-angiogenic agents. Therefore we treated 4T1 tumor-bearing mice with sunitinib or DC101 alone and in combination with acetylsalicyclic acid (ASA). We found that single treatment with ASA or angiogenesis inhibitors inhibited tumor growth and that combined inhibition of Cox-2 and VEGF(R) signaling exerted additive therapeutic efficacy (n=5; 1142±84 (ASS); 1148±78 (Sunitnib) vs. 63±5 mg (combination); p&lt;0.0001). Similar effects were achieved upon combining the specific Cox2 inhibitor SC-236 with anti-angiogenic therapy (n=6; 985±147 (SC-326); 1123±61 (Sunitnib) vs. 680±76 mg (combination); p&lt;0.05) and in the 6CCL4 orthotopic breast cancer model (data not shown). We carried out an extensive profiling of the tumor cells and their microenvironment upon concomitant blockade of Cox-2 and VEGF signaling in order to elucidate the underlying mechanism. We found no changes in tumor cell proliferation or upon combined Cox-2 inhibition and anti-angiogenic therapies. Also combined Cox-2 and VEGF-signaling inhibition did not change the quantitative composition of the inflammatory tumor infiltrate. However, upon analyzing polarization of FACS-sorted TAMs we found that mRNA of the M1 markers iNOS, MHCII, IL1β and TNFα were upregulated upon treatment with ASA alone and/or in combination with anti-angiogenic agents compared to controls or monotherapy with anti-angiogenic agents. In contrast, the M2 markers Arg1 and YM1 were downregulated upon treatment with Cox2-inhibitors and anti-angiogenic agents. Therefore, Cox-2 inhibitors skew TAMs towards an anti-tumoral M1 phenotype while the pro-angiogenic, tumor promoting M2-phenotype is suppressed.

In addition, Cox-2 and PGE2 can promote tumor angiogenesis. This alternative pro-angiogenic pathway would be enhanced by increased Cox-2 expression and PGE2 levels and could contribute to resistance against anti-angiogenic treatments. In line with this hypothesis the MVD was decreased 4T1 tumors treated with combined Cox-2 and VEGF blockade compared to the respective monotherapy (n=7; 31±2.4 (Sunitinib); 28.58±0.83 (ASS) vs. 9.67±1.71 (combination); p&lt;0.001). In conclusion concomitant Cox2 inhibition and anti-angiogenic therapies exert pronounced additive effects, which are at least partially due to increased M1 polarization and additive anti-angiogenic effects.

Citation Format: Isabel Ben Batalla, Miguel Cubas-Cordova, Florian Udonta, Mark Wroblewski, Stefanie Sawall, Victoria Gensch, Klaus Pantel, Carsten Bokemeyer, Sonja Loges. COX-2 blockade improves efficacy of VEGF-targeting drugs. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1161. doi:10.1158/1538-7445.AM2014-1161

Use of Axl, a therapeutic target in AML, to mediate stroma-induced chemoresistance

7027

Background: Axl, the receptor for Growth Arrest-specific protein 6 (Gas6) plays a role in AML pathobiology (Blood Suppl. Nov 2011; 118: 940). Here, we investigated whether Axl represents a therapeutic target in AML. Methods: Gas6 levels were measured by ELISA and immunohistochemistry. Axl expression was detected by flow cytometry. Co-cultures of (murine) BM stroma cells (primary, OP9, S17) with Mv4-11 and OCI-AML5 cell lines were performed. Results: We found (i) higher expression of Axl in AML BM compared to healthy BM donors (66.20 ± 10.87 vs. 0.65 ± 0.10 %; n=8/6; p<0.05); (ii) Axl expression by 68 ± 31% of AML blasts and (iv) higher expression of Axl by CD34+CD38- AML stem cells compared to healthy CD34+CD38- BM stem cells (58.43 ± 4.63 % vs. 6.00 ± 2.01 %; n=7/6; p<0.05). The Axl inhibitor BGB324 dose-dependently inhibited proliferation of primary AML cells with a mean IC50 of 1.8 µM. Sensitivity to BGB324 (i.e. a lower IC50) correlated with Axl expression on leukemia cells (Pearson’s r = -0.9656, p<0.05). Combination therapy with BGB324 and cytarabine exerted an additive therapeutic effect and BGB324 could chemosensitize cytarabine-resistant AML cells. Analyses of BM sections revealed that Gas6 expression was low in AML cells, similar to healthy hematopoietic cells while it was abundantly expressed in AML BM stromal cells with fibroblastic/mesenchymal morphology (BMDSCs). Gas6 expression was considerably lower in control BMDSCs (86 ± 14 % vs. 20 ± 20 %; n=5/7; p<0.05) thus suggesting a possible paracrine interaction between AML cells and BMDSCs leading to Gas6 upregulation in the stroma compartment. Co-culture experiments indicated specific upregulation of murine (m)Gas6 in BMDSCs via leukemia-cell derived IL-10 and M-CSF. This stroma-derived Gas6 could mediate chemoresistance of AML cells in co-culture, which was abrogated by sAxl or by BGB324. Thus, interaction between stroma-derived Gas6 and Axl+leukemia cells forms a chemoprotective niche for leukemia cells. In line with these findings Axl blockade chemosensitizes Mv4-11 cells for treatment with doxorubicine in vivo. Conclusions: Axl represents a therapeutic target in AML and Axl inhibition by BGB324 holds potential to treat chemosensitive and chemoresistant AML.

VEGFR-1 expression levels predict occurrence of disseminated tumor cells in the bone marrow of patients with esophageal carcinoma

Blocking angiogenesis by inhibiting VEGF represents an established therapeutic strategy in many cancers. The role of placental growth factor (PlGF) and of its receptor VEGFR-1 in tumor biology remain more elusive. Currently, humanized monoclonal antibodies against PlGF are studied in early phase clinical trials because PlGF inhibition blocked murine tumor growth and angiogenesis. In contrast to mice exclusively expressing one PlGF isoform (PlGF-2), humans can produce four PlGF isoforms (PlGF1-4). Surprisingly nothing is yet known about expression of all four PlGF isoforms in human cancer, because until now mostly total PlGF levels or PlGF-1/2 were analyzed without discriminating further. In this study we determined mRNA expression levels of PlGF1-4 and of VEGFR-1 by QRT-PCR in human esophageal tumor tissue and investigated whether gene expression levels correlate with clinical data. PlGF-1 and -2 were expressed in virtually all analyzable tumors, whereas PlGF-3 and -4 were present in tumors of 59 and 74 % of patients, respectively. MRNA Expression levels of all four splice variants correlated with each other. In contrast, PlGF-1 and -2 mRNA expression was lower in esophageal control tissue and PlGF-3 and -4 mRNA were undetectable. VEGFR-1 was expressed by more than 80 % of patients. Interestingly, VEGFR-1 expression levels significantly correlate with presence of disseminated tumor cells (DTCs) in bone marrow. Patients with DTCs exhibit lower VEGFR-1 mRNA expression than patients without DTCs. Pending validation in other types of cancer, expression levels of VEGFR-1 might be useful as surrogate marker for DTCs.