Integrin-αvβ6 targeted peptide-toxin therapy in a novel αvβ6-expressing immunocompetent model of pancreatic cancer

Previously we reported that a novel αvβ6-specific peptide-drug conjugate (SG3299) could eliminate established human pancreatic ductal adenocarcinoma (PDAC) xenografts. However the development of effective therapies for PDAC, which is an essential need, must show efficacy in relevant immunocompetent animals. Previously we reported that the KPC mouse transgenic PDAC model that closely recapitulates most stages of development of human PDAC, unlike in humans, failed to express αvβ6 on their tumours or metastases. In this study we have taken the KPC-derived PDAC line TB32043 and engineered a variant line (TB32043mb6S2) that expresses mouse integrin αvβ6. We report that orthotopic implantation of the αvβ6 over-expressing TB32043mb6S2 cells promotes shorter overall survival and increase in metastases. Moreover, systemic treatment of mice with established TB32043mb6S2 tumours in the pancreas with SG2399 lived significantly longer (p < 0.001; mean OS 48d) compared with PBS or control SG3511 (mean OS 25.5d and 26d, respectively). Thus SG3299 is confirmed as a promising candidate therapeutic for the therapy of PDAC.

ADCT-602, a Novel PBD Dimer-containing Antibody-Drug Conjugate for Treating CD22-positive Hematologic Malignancies

Relapsed or refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) and lymphomas have poor patient outcomes; novel therapies are needed. CD22 is an attractive target for antibody-drug conjugates (ADCs), being highly expressed in R/R B-ALL with rapid internalization kinetics. ADCT-602 is a novel CD22-targeting ADC, consisting of humanized mAb hLL2-C220, site specifically conjugated to the pyrrolobenzodiazepine dimer-based payload tesirine. In preclinical studies, ADCT-602 demonstrated potent, specific cytotoxicity in CD22-positive lymphomas and leukemias. ADCT-602 was specifically bound, internalized, and trafficked to lysosomes in CD22-positive tumor cells; after cytotoxin release, DNA interstrand crosslink formation persisted for 48 hours. In the presence of CD22-positive tumor cells, ADCT-602 caused bystander killing of CD22-negative tumor cells. A single ADCT-602 dose led to potent, dose-dependent, in vivo antitumor activity in subcutaneous and disseminated human lymphoma/leukemia models. Pharmacokinetic analyses (rat and cynomolgus monkey) showed excellent stability and tolerability of ADCT-602. Cynomolgus monkey B cells were efficiently depleted from circulation after one dose. Gene signature association analysis revealed IRAK1 as a potential marker for ADCT-602 resistance. Combining ADCT-602 + pacritinib was beneficial in ADCT-602-resistant cells. Chidamide increased CD22 expression on B-cell tumor surfaces, increasing ADCT-602 activity. These data support clinical testing of ADCT-602 in R/R B-ALL (NCT03698552) and CD22-positive hematologic cancers.

Abstract 2638: Preclinical development of ADCT-212, a PSMA-targeted antibody-drug conjugate employing the pyrrolobenzodiazepine dimer SG2000 for PSMA-expressing cancers

Prostate-specific membrane antigen (PSMA) is a membrane-bound glutamate carboxypeptidase that is highly expressed in nearly all prostate cancers with the highest expression in metastatic castration-resistant prostate cancer. Moreover, PSMA is expressed in the neovasculature that supplies most non-prostatic solid tumors, including carcinomas of the lung, colon, breast, kidney, liver, and pancreas. ADCT-212 is an antibody-drug conjugate composed of the human IgG1 antibody 2A10 directed against human PSMA, site-specifically conjugated using GlycoConnectTM technology to PL1801, which contains HydraspaceTM, a valine-alanine cleavable linker and the pyrrolobenzodiazepine (PBD) dimer warhead SG2000 (drug-antibody ratio of ~1.8). The purpose of this study was to characterize the in vitro and in vivo anti-tumor activity of ADCT-212 in human cancer cell lines and xenograft models and to determine its tolerability and pharmacokinetic (PK) in the rat. In vitro, ADCT-212 demonstrated potent cytotoxicity in a panel of PSMA-positive prostate cancer cell lines, whereas its activity was greatly reduced in PSMA-negative cell lines. ADCT-212 was efficiently internalized by PSMA-expressing LNCaP cells. Trafficking to the lysosomes started as early as 30 minutes and peaked at 1-2 hours post treatment. In line with the mechanism of action of the PBD dimer, ADCT-212 produced DNA interstrand cross-links (ICLs) that peaked by 12 hours and persisted for up to 36 hours post-treatment. In contrast, the peak of DNA ICLs formation for SG2000, the PBD dimer warhead alone, was observed immediately after 2-hour incubation, while a non-targeted PBD-ADC did not yield any appreciable DNA ICLs. Moreover, ADCT-212 showed indirect bystander killing activity in PSMA-negative PC3 cells incubated with conditioned medium from ADCT-212-treated LNCaP cells. In vivo, ADCT-212 showed strong antitumor activity against CWR22Rv1 and LNCaP prostate cancer xenograft models. In the CWR22Rv1 model, a tumor with heterogeneous PSMA expression, ADCT-212 achieved dose-dependent antitumor activity when administered as single dose at 2, 4 or 6 mg/kg, which resulted in increased survival compared to the control animals. In the LNCaP model, a single dose of ADCT-212 at 5 or 10 mg/kg resulted in strong and specific antitumor activity. Conversely, in the PSMA-negative PC3 xenograft model, ADCT-212 did not show anti-tumor activity compared to the controls, highlighting its target-mediated antitumor activity. ADCT-212 was tolerated as a single 20 mg/kg dose in male rats, with exposure data being indicative of a linear PK profile with a half-life of approximately 12 days. In conclusion, ADCT-212 demonstrated potent and specific in vitro and in vivo anti-tumor activity while it was stable and well tolerated in the rat, warranting further development of ADCT-212 into the clinic.

Citation Format: Francesca Zammarchi, Karin Havenith, Lolke de Haan, Ian Kirby, Narinder Janghra, Veronica Gil, Pedro Alves, Kristina Zaitseva, Meghann Kerr, Ben Leatherdale, Afroze Patel, Marie Thoelke, Shiran Huang, John A Hartley, Patrick H van Berkel. Preclinical development of ADCT-212, a PSMA-targeted antibody-drug conjugate employing the pyrrolobenzodiazepine dimer SG2000 for PSMA-expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2638.

Comparison of Pyrrolobenzodiazepine Dimer Bis-imine versus Mono-imine: DNA Interstrand Cross-linking, Cytotoxicity, Antibody-Drug Conjugate Efficacy and Toxicity

Antibody-drug conjugates (ADC) delivering pyrrolobenzodiazepine (PBD) DNA cross-linkers are currently being evaluated in clinical trials, with encouraging results in Hodgkin and non-Hodgkin lymphomas. The first example of an ADC delivering a PBD DNA cross-linker (loncastuximab tesirine) has been recently approved by the FDA for the treatment of relapsed and refractory diffuse large B-cell lymphoma. There has also been considerable interest in mono-alkylating PBD analogs. We conducted a head-to-head comparison of a conventional PBD bis-imine and a novel PBD mono-imine. Key Mitsunobu chemistry allowed clean and convenient access to the mono-imine class. Extensive DNA-binding studies revealed that the mono-imine mediated a type of DNA interaction that is described as "pseudo cross-linking," as well as alkylation. The PBD mono-imine ADC demonstrated robust antitumor activity in mice bearing human tumor xenografts at doses 3-fold higher than those that were efficacious for the PBD bis-imine ADC. A single-dose toxicology study in rats demonstrated that the MTD of the PBD mono-alkylator ADC was approximately 3-fold higher than that of the ADC bearing a bis-imine payload, suggesting a comparable therapeutic index for this molecule. However, although both ADCs caused myelosuppression, renal toxicity was observed only for the bis-imine, indicating possible differences in toxicologic profiles that could influence tolerability and therapeutic index. These data show that mono-amine PBDs have physicochemical and pharmacotoxicologic properties distinct from their cross-linking analogs and support their potential utility as a novel class of ADC payload.

PANTHER: AZD8931, inhibitor of EGFR, ERBB2 and ERBB3 signalling, combined with FOLFIRI: a Phase I/II study to determine the importance of schedule and activity in colorectal cancer

BACKGROUND

Epidermal growth factor receptor (EGFR) is a therapeutic target to which HER2/HER3 activation may contribute resistance. This Phase I/II study examined the toxicity and efficacy of high-dose pulsed AZD8931, an EGFR/HER2/HER3 inhibitor, combined with chemotherapy, in metastatic colorectal cancer (CRC).

METHODS

Treatment-naive patients received 4-day pulses of AZD8931 with irinotecan/5-FU (FOLFIRI) in a Phase I/II single-arm trial. Primary endpoint for Phase I was dose limiting toxicity (DLT); for Phase II best overall response. Samples were analysed for pharmacokinetics, EGFR dimers in circulating exosomes and Comet assay quantitating DNA damage.

RESULTS

Eighteen patients received FOLFIRI and AZD8931. At 160 mg bd, 1 patient experienced G3 DLT; 160 mg bd was used for cohort expansion. No grade 5 adverse events (AE) reported. Seven (39%) and 1 (6%) patients experienced grade 3 and grade 4 AEs, respectively. Of 12 patients receiving 160 mg bd, best overall response rate was 25%, median PFS and OS were 8.7 and 21.2 months, respectively. A reduction in circulating HER2/3 dimer in the two responding patients after 12 weeks treatment was observed.

CONCLUSIONS

The combination of pulsed high-dose AZD8931 with FOLFIRI has acceptable toxicity. Further studies of TKI sequencing may establish a role for pulsed use of such agents rather than continuous exposure.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov number: NCT01862003.

Phase 0 Study of Vandetanib-Eluting Radiopaque Embolics as a Preoperative Embolization Treatment in Patients with Resectable Liver Malignancies

PURPOSE

To assess the safety and tolerability of a vandetanib-eluting radiopaque embolic (BTG-002814) for transarterial chemoembolization (TACE) in patients with resectable liver malignancies.

MATERIALS AND METHODS

The VEROnA clinical trial was a first-in-human, phase 0, single-arm, window-of-opportunity study. Eligible patients were aged ≥18 years and had resectable hepatocellular carcinoma (HCC) (Child-Pugh A) or metastatic colorectal cancer (mCRC). Patients received 1 mL of BTG-002814 transarterially (containing 100 mg of vandetanib) 7-21 days prior to surgery. The primary objectives were to establish the safety and tolerability of BTG-002814 and determine the concentrations of vandetanib and the N-desmethyl vandetanib metabolite in the plasma and resected liver after treatment. Biomarker studies included circulating proangiogenic factors, perfusion computed tomography, and dynamic contrast-enhanced magnetic resonance imaging.

RESULTS

Eight patients were enrolled: 2 with HCC and 6 with mCRC. There was 1 grade 3 adverse event (AE) before surgery and 18 after surgery; 6 AEs were deemed to be related to BTG-002814. Surgical resection was not delayed. Vandetanib was present in the plasma of all patients 12 days after treatment, with a mean maximum concentration of 24.3 ng/mL (standard deviation ± 13.94 ng/mL), and in resected liver tissue up to 32 days after treatment (441-404,000 ng/g). The median percentage of tumor necrosis was 92.5% (range, 5%-100%). There were no significant changes in perfusion imaging parameters after TACE.

CONCLUSIONS

BTG-002814 has an acceptable safety profile in patients before surgery. The presence of vandetanib in the tumor specimens up to 32 days after treatment suggests sustained anticancer activity, while the low vandetanib levels in the plasma suggest minimal release into the systemic circulation. Further evaluation of this TACE combination is warranted in dose-finding and efficacy studies.

Efficacy, Tolerability, and Pharmacokinetic Studies of Antibody-Drug Conjugates Containing a Low-Potency Pyrrolobenzodiazepine Dimer

Antibody-drug conjugate (ADC) research has typically focused on the release of highly potent cytotoxic agents to achieve antitumor efficacy. However, recently approved ADCs trastuzumab deruxtecan and sacituzumab govitecan release lower-potency topoisomerase inhibitors. This has prompted interest in ADCs that release lower-potency cytotoxic drugs to potentially enhance therapeutic index and reduce unwanted toxicity. Pyrrolobenzodiazepine (PBD) dimer ADCs have been widely investigated in human clinical trials, which have focused on high-potency PBDs. In this study, we evaluated five ADCs that release the low-potency PBD dimer SG3650. The relatively low cLogD for this agent facilitated higher drug-to-antibody ratio (DAR) conjugation without the need for antibody engineering or functionalization of the drug. The rank order of potency for DAR 2 site-specific ADCs (conjugated at the C239i position) matched the order for the corresponding free drugs in vitro. Despite free drug SG3650 being inactive in vivo, the DAR 2 ADCs derived from the corresponding drug-linker SG3584 showed antitumor efficacy in solid (anti-HER2) and hematological (anti-CD22) xenograft models. Antitumor activity could be enhanced by conjugating SG3584 to trastuzumab at higher DARs of 4 and 8 and by adjusting dosing and schedule. Higher-DAR conjugates were stable and displayed good rat pharmacokinetic profiles as measured by ELISA and LC-MS/MS. A single intravenous dose of isotype control SG3584 DAR 2 ADC resulted in no mortality in rats or monkeys at doses of up to 25 and 30 mg/kg, respectively. These findings suggest that further investigations of low-potency PBD dimers in ADCs that target hematological and solid tumors are warranted.

Preclinical Development of ADCT-601, a Novel Pyrrolobenzodiazepine Dimer-based Antibody-drug Conjugate Targeting AXL-expressing Cancers

AXL, a tyrosine kinase receptor that is overexpressed in many solid and hematologic malignancies, facilitates cancer progression and is associated with poor clinical outcomes. Importantly, drug-induced expression of AXL results in resistance to conventional chemotherapy and targeted therapies. Together with its presence on multiple cell types in the tumor immune microenvironment, these features make it an attractive therapeutic target for AXL-expressing malignancies. ADCT-601 (mipasetamab uzoptirine) is an AXL-targeted antibody-drug conjugate (ADC) comprising a humanized anti-AXL antibody site specifically conjugated using GlycoConnect technology to PL1601, which contains HydraSpace, a Val-Ala cleavable linker and the potent pyrrolobenzodiazepine (PBD) dimer cytotoxin SG3199. This study aimed to validate the ADCT-601 mode of action and evaluate its efficacy in vitro and in vivo, as well as its tolerability and pharmacokinetics. ADCT-601 bound to both soluble and membranous AXL, and was rapidly internalized by AXL-expressing tumor cells, allowing release of PBD dimer, DNA interstrand cross-linking, and subsequent cell killing. In vivo, ADCT-601 had potent and durable antitumor activity in a wide variety of human cancer xenograft mouse models, including patient-derived xenograft models with heterogeneous AXL expression where ADCT-601 antitumor activity was markedly superior to an auristatin-based comparator ADC. Notably, ADCT-601 had antitumor activity in a monomethyl auristatin E-resistant lung-cancer model and synergized with the PARP inhibitor olaparib in a BRCA1-mutated ovarian cancer model. ADCT-601 was well tolerated at doses of up to 6 mg/kg and showed excellent stability in vivo. These preclinical results warrant further evaluation of ADCT-601 in the clinic.

Osimertinib and anti-HER3 combination therapy engages immune dependent tumor toxicity via STING activation in trans

Over the past decade, immunotherapy delivered novel treatments for many cancer types. However, lung cancer still leads cancer mortality, and non-small-cell lung carcinoma patients with mutant EGFR cannot benefit from checkpoint inhibitors due to toxicity, relying only on palliative chemotherapy and the third-generation tyrosine kinase inhibitor (TKI) osimertinib. This new drug extends lifespan by 9-months vs. second-generation TKIs, but unfortunately, cancers relapse due to resistance mechanisms and the lack of antitumor immune responses. Here we explored the combination of osimertinib with anti-HER3 monoclonal antibodies and observed that the immune system contributed to eliminate tumor cells in mice and co-culture experiments using bone marrow-derived macrophages and human PBMCs. Osimertinib led to apoptosis of tumors but simultaneously, it triggered inositol-requiring-enzyme (IRE1α)-dependent HER3 upregulation, increased macrophage infiltration, and activated cGAS in cancer cells to produce cGAMP (detected by a lentivirally transduced STING activity biosensor), transactivating STING in macrophages. We sought to target osimertinib-induced HER3 upregulation with monoclonal antibodies, which engaged Fc receptor-dependent tumor elimination by macrophages, and STING agonists enhanced macrophage-mediated tumor elimination further. Thus, by engaging a tumor non-autonomous mechanism involving cGAS-STING and innate immunity, the combination of osimertinib and anti-HER3 antibodies could improve the limited therapeutic and stratification options for advanced stage lung cancer patients with mutant EGFR.

hMOB2 deficiency impairs homologous recombination-mediated DNA repair and sensitises cancer cells to PARP inhibitors

Monopolar spindle-one binder (MOBs) proteins are evolutionarily conserved and contribute to various cellular signalling pathways. Recently, we reported that hMOB2 functions in preventing the accumulation of endogenous DNA damage and a subsequent p53/p21-dependent G1/S cell cycle arrest in untransformed cells. However, the question of how hMOB2 protects cells from endogenous DNA damage accumulation remained enigmatic. Here, we uncover hMOB2 as a regulator of double-strand break (DSB) repair by homologous recombination (HR). hMOB2 supports the phosphorylation and accumulation of the RAD51 recombinase on resected single-strand DNA (ssDNA) overhangs. Physiologically, hMOB2 expression supports cancer cell survival in response to DSB-inducing anti-cancer compounds. Specifically, loss of hMOB2 renders ovarian and other cancer cells more vulnerable to FDA-approved PARP inhibitors. Reduced MOB2 expression correlates with increased overall survival in patients suffering from ovarian carcinoma. Taken together, our findings suggest that hMOB2 expression may serve as a candidate stratification biomarker of patients for HR-deficiency targeted cancer therapies, such as PARP inhibitor treatments.

Durable Responses and Low Toxicity After Fast Off-Rate CD19 Chimeric Antigen Receptor-T Therapy in Adults With Relapsed or Refractory B-Cell Acute Lymphoblastic Leukemia

PURPOSE

Prognosis for adult B-cell acute lymphoblastic leukemia (B-ALL) is poor, and there are currently no licensed CD19 chimeric antigen receptor (CAR) therapeutics. We developed a novel second-generation CD19-CAR (CAT19-41BB-Z) with a fast off rate, designed for more physiologic T-cell activation to reduce toxicity and improve engraftment. We describe the multicenter phase I ALLCAR19 (NCT02935257) study of autologous CAT19-41BB-Z CAR T cells (AUTO1) in relapsed or refractory (r/r) adult B-ALL.

METHODS

Patients age ≥ 16 years with r/r B-ALL were eligible. Primary outcomes were toxicity and manufacturing feasibility. Secondary outcomes were depth of response at 1 and 3 months, persistence of CAR-T, incidence and duration of hypogammaglobulinemia and B-cell aplasia, and event-free survival and overall survival at 1 and 2 years.

RESULTS

Twenty-five patients were leukapheresed, 24 products were manufactured, and 20 patients were infused with AUTO1. The median age was 41.5 years; 25% had prior blinatumomab, 50% prior inotuzumab ozogamicin, and 65% prior allogeneic stem-cell transplantation. At the time of preconditioning, 45% had ≥ 50% bone marrow blasts. No patients experienced ≥ grade 3 cytokine release syndrome; 3 of 20 (15%) experienced grade 3 neurotoxicity that resolved to ≤ grade 1 within 72 hours with steroids. Seventeen of 20 (85%) achieved minimal residual disease–negative complete response at month 1, and 3 of 17 underwent allogeneic stem-cell transplantation while in remission. The event-free survival at 6 and 12 months was 68.3% (42.4%-84.4%) and 48.3% (23.1%-69.7%), respectively. High-level expansion (Cmax 127,152 copies/µg genomic DNA) and durable CAR-T persistence were observed with B-cell aplasia ongoing in 15 of 20 patients at last follow-up.

CONCLUSION

AUTO1 demonstrates a tolerable safety profile, high remission rates, and excellent persistence in r/r adult B-ALL. Preliminary data support further development of AUTO1 as a stand-alone treatment for r/r adult B-ALL.

Low toxicity & high durability CD19CAR T without allo-SCT offers new possibility for refractory adult B-ALL

Atomic force microscopy-A tool for structural and translational DNA research

Atomic force microscopy (AFM) is a powerful imaging technique that allows for structural characterization of single biomolecules with nanoscale resolution. AFM has a unique capability to image biological molecules in their native states under physiological conditions without the need for labeling or averaging. DNA has been extensively imaged with AFM from early single-molecule studies of conformational diversity in plasmids, to recent examinations of intramolecular variation between groove depths within an individual DNA molecule. The ability to image dynamic biological interactions in situ has also allowed for the interaction of various proteins and therapeutic ligands with DNA to be evaluated-providing insights into structural assembly, flexibility, and movement. This review provides an overview of how innovation and optimization in AFM imaging have advanced our understanding of DNA structure, mechanics, and interactions. These include studies of the secondary and tertiary structure of DNA, including how these are affected by its interactions with proteins. The broader role of AFM as a tool in translational cancer research is also explored through its use in imaging DNA with key chemotherapeutic ligands, including those currently employed in clinical practice.

Whole-genome sequencing of single circulating tumor cells from neuroendocrine neoplasms

Single-cell profiling of circulating tumor cells (CTCs) as part of a minimally invasive liquid biopsy presents an opportunity to characterize and monitor tumor heterogeneity and evolution in individual patients. In this study, we aimed to compare single-cell copy number variation (CNV) data with tissue and define the degree of intra- and inter-patient genomic heterogeneity. We performed next-generation sequencing (NGS) whole-genome CNV analysis of 125 single CTCs derived from seven patients with neuroendocrine neoplasms (NEN) alongside matched white blood cells (WBC), formalin-fixed paraffin-embedded (FFPE), and fresh frozen (FF) samples. CTC CNV profiling demonstrated recurrent chromosomal alterations in previously reported NEN copy number hotspots, including the prognostically relevant loss of chromosome 18. Unsupervised hierarchical clustering revealed CTCs with distinct clonal lineages as well as significant intra- and inter-patient genomic heterogeneity, including subclonal alterations not detectable by bulk analysis and previously unreported in NEN. Notably, we also demonstrated the presence of genomically distinct CTCs according to the enrichment strategy utilized (EpCAM-dependent vs size-based). This work has significant implications for the identification of therapeutic targets, tracking of evolutionary change, and the implementation of CTC-biomarkers in cancer.

Prognostic Threshold for Circulating Tumor Cells in Patients With Pancreatic and Midgut Neuroendocrine Tumors

BACKGROUND

Circulating tumor cells (CTCs) are detectable in patients with neuroendocrine tumors (NETs) and are accurate prognostic markers although the optimum threshold has not been defined.

OBJECTIVE

This work aims to define optimal prognostic CTC thresholds in PanNET and midgut NETs.

PATIENTS AND METHODS

CellSearch was used to enumerate CTCs in 199 patients with metastatic pancreatic (PanNET) (90) or midgut NETs (109). Patients were followed for progression-free survival (PFS) and overall survival (OS) for a minimum of 3 years or until death.

RESULTS

The area under the receiver operating characteristic curve (AUROC) for progression at 12 months in PanNETs and midgut NETs identified the optimal CTC threshold as 1 or greater and 2 or greater, respectively. In multivariate logistic regression analysis, these thresholds were predictive for 12-month progression with an odds ratio (OR) of 6.69 (P < .01) for PanNETs and 5.88 (P < .003) for midgut NETs. The same thresholds were found to be optimal for predicting death at 36 months, with an OR of 2.87 (P < .03) and 5.09 (P < .005) for PanNETs and midgut NETs, respectively. In multivariate Cox hazard regression analysis for PFS in PanNETs, 1 or greater CTC had a hazard ratio (HR) of 2.6 (P < .01), whereas 2 or greater CTCs had an HR of 2.25 (P < .01) in midgut NETs. In multivariate analysis OS in PanNETs, 1 or greater CTCs had an HR of 3.16 (P < .01) and in midgut NETs, 2 or greater CTCs had an HR of 1.73 (P < .06).

CONCLUSIONS

The optimal CTC threshold to predict PFS and OS in metastatic PanNETs and midgut NETs is 1 and 2, respectively. These thresholds can be used to stratify patients in clinical practice and clinical trials.

The Role of Specific ATP-Binding Cassette Transporters in the Acquired Resistance to Pyrrolobenzodiazepine Dimer-Containing Antibody-Drug Conjugates

Antibody-drug conjugates (ADC) containing pyrrolobenzodiazepine (PBD) dimers are being evaluated clinically in both hematologic and solid tumors. These include ADCT-301 (camidanlumab tesirine) and ADCT-402 (loncastuximab tesirine) in pivotal phase II trials that contain the payload tesirine, which releases the PBD dimer warhead SG3199. An important consideration in future clinical development is acquired resistance. The aim was to generate and characterize PBD acquired resistant cell lines in both hematologic and solid tumor settings. Human Karpas-299 (ALCL) and NCI-N87 (gastric cancer) cells were incubated with increasing IC₅₀ doses of ADC (targeting CD25 and HER2, respectively) or SG3199 in a pulsed manner until stable acquired resistance was established. The level of resistance achieved was approximately 3,000-fold for ADCT-301 and 3-fold for SG3199 in Karpas-299, and 8-fold for ADCT-502 and 4-fold for SG3199 in NCI-N87. Cross-resistance between ADC and SG3199, and with an alternative PBD-containing ADC or PBD dimer was observed. The acquired resistant lines produced fewer DNA interstrand cross-links, indicating an upstream mechanism of resistance. Loss of antibody binding or internalization was not observed. A human drug transporter PCR Array revealed several genes upregulated in all the resistant cell lines, including ABCG2 and ABCC2, but not ABCB1(MDR1). These findings were confirmed by RT-PCR and Western blot, and inhibitors and siRNA knockdown of ABCG2 and ABCC2 recovered drug sensitivity. These data show that acquired resistance to PBD-ADCs and SG3199 can involve specific ATP-binding cassette drug transporters. This has clinical implications as potential biomarkers of resistance and for the rational design of drug combinations.

Antibody-drug conjugates (ADCs) delivering pyrrolobenzodiazepine (PBD) dimers for cancer therapy

INTRODUCTION

The rationally designed pyrrolobenzodiazepine (PBD) dimers emerged around ten years ago as a new class of drug component for antibody-drug conjugates (ADC). They produce highly cytotoxic DNA cross-links, exploiting a completely different cellular target to the auristatin and maytansinoid tubulin inhibitor classes and a different mode of DNA damage to other DNA interacting warheads such as calicheamicin.

AREAS COVERED

The properties which make the PBD dimers suitable warheads for ADCs, and the development of the two main payload structures talirine and tesirine, are discussed. The clinical experience with the twenty PBD dimer-containing ADCs to enter the clinic is reviewed, with a focus on vadastuximab talirine and rovalpituzumab tesirine, both of which were discontinued following pivotal studies, and loncastuximab tesirine and camidanlumab tesirine which are progressing towards approval.

EXPERT OPINION

Reviewing the clinical efficacy and safety data from almost forty clinical trials of PBD dimer-containing ADCs highlights the complexities and challenges of ADC early clinical development. It enables some conclusions to be made about reasons for failure and suggests strategies to optimise the future clinical development of this promising class of ADCs in a rapidly expanding field.

Integrin αvβ6-specific therapy for pancreatic cancer developed from foot-and-mouth-disease virus

Goals of investigation: The 5-year survival rate for pancreatic ductal adenocarcinoma (PDAC) has remained at <5% for decades because no effective therapies have been identified. Integrin αvβ6 is overexpressed in most PDAC and represents a promising therapeutic target. Thus, we attempted to develop an αvβ6-specific peptide-drug conjugate (PDC) for therapy of PDAC. Methodology: We conjugated the DNA-binding pyrrolobenzodiazepine (PBD)-based payload SG3249 (tesirine) to an αvβ6-specific 20mer peptide from the VP1 coat protein of foot-and-mouth-disease virus (FMDV) (forming conjugate SG3299) or to a non-targeting peptide (forming conjugate SG3511). PDCs were tested for specificity and toxicity on αvβ6-negative versus-positive PDAC cells, patient-derived cell lines from tumor xenografts, and on two different in vivo models of PDAC. Immunohistochemical analyses were performed to establish therapeutic mechanism. Results: The αvβ6-targeted PDC SG3299 was significantly more toxic (up to 78-fold) for αvβ6-expressing versus αvβ6-negative PDAC cell lines in vitro, and achieved significantly higher toxicity at equal dose than the non-targeted PDC SG3511 (up to 15-fold better). Moreover, SG3299 eliminated established (100mm3) Capan-1 PDAC human xenografts, extending the lifespan of mice significantly (P=0.005). Immunohistochemistry revealed SG3299 induced DNA damage and apoptosis (increased γH2AX and cleaved caspase 3, respectively) associated with significant reductions in proliferation (Ki67), β6 expression and PDAC tumour growth. Conclusions: The FMDV-peptide drug conjugate SG3299 showed αvβ6-selectivity in vitro and in vivo and can specifically eliminate αvβ6-positive cancers, providing a promising new molecular- specific therapy for pancreatic cancer.

Targeting of EGFR by a combination of antibodies mediates unconventional EGFR trafficking and degradation

Antibody combinations targeting cell surface receptors are a new modality of cancer therapy. The trafficking and signalling mechanisms regulated by such therapeutics are not fully understood but could underlie differential tumour responses. We explored EGFR trafficking upon treatment with the antibody combination Sym004 which has shown promise clinically. Sym004 promoted EGFR endocytosis distinctly from EGF: it was asynchronous, not accompanied by canonical signalling events and involved EGFR clustering within detergent-insoluble plasma mebrane-associated tubules. Sym004 induced lysosomal degradation independently of EGFR ubiquitylation but dependent upon Hrs/Tsg101 that are required for the formation of intraluminal vesicles (ILVs) within late endosomes. We propose Sym004 cross-links EGFR physically triggering EGFR endocytosis and incorporation onto ILVs and so Sym004 sensitivity correlates with EGFR numbers available for binding, rather than specific signalling events. Consistently Sym004 efficacy and potentiation of cisplatin responses correlated with EGFR surface expression in head and neck cancer cells. These findings will have implications in understanding the mode of action of this new class of cancer therapeutics.

TR1801-ADC: a highly potent cMet antibody-drug conjugate with high activity in patient-derived xenograft models of solid tumors

cMet is a well‐characterized oncogene that is the target of many drugs including small molecule and biologic pathway inhibitors, and, more recently, antibody–drug conjugates (ADCs). However, the clinical benefit from cMet‐targeted therapy has been limited. We developed a novel cMet‐targeted ‘third‐generation’ ADC, TR1801‐ADC, that was optimized at different levels including specificity, stability, toxin–linker, conjugation site, and in vivo efficacy. Our nonagonistic cMet antibody was site‐specifically conjugated to the pyrrolobenzodiazepine (PBD) toxin–linker tesirine and has picomolar activity in cancer cell lines derived from different solid tumors including lung, colorectal, and gastric cancers. The potency of our cMet ADC is independent of MET gene copy number, and its antitumor activity was high not only in high cMet‐expressing cell lines but also in medium‐to‐low cMet cell lines (40 000–90 000 cMet/cell) in which a cMet ADC with tubulin inhibitor payload was considerably less potent. In vivo xenografts with low–medium cMet expression were also very responsive to TR1801‐ADC at a single dose, while a cMet ADC using a tubulin inhibitor showed a substantially reduced efficacy. Furthermore, TR1801‐ADC had excellent efficacy with significant antitumor activity in 90% of tested patient‐derived xenograft models of gastric, colorectal, and head and neck cancers: 7 of 10 gastric models, 4 of 10 colorectal cancer models, and 3 of 10 head and neck cancer models showed complete tumor regression after a single‐dose administration. Altogether, TR1801‐ADC is a new generation cMet ADC with best‐in‐class preclinical efficacy and good tolerability in rats.

VEROnA Protocol: A Pilot, Open-Label, Single-Arm, Phase 0, Window-of-Opportunity Study of Vandetanib-Eluting Radiopaque Embolic Beads (BTG-002814) in Patients With Resectable Liver Malignancies

BACKGROUND

Transarterial chemoembolization (TACE) is the current standard of care for patients with intermediate-stage hepatocellular carcinoma (HCC) and is also a treatment option for patients with liver metastases from colorectal cancer. However, TACE is not a curative treatment, and tumor progression occurs in more than half of the patients treated. Despite advances and technical refinements of TACE, including the introduction of drug-eluting beads-TACE, the clinical efficacy of TACE has not been optimized, and improved arterial therapies are required.

OBJECTIVE

The primary objectives of the VEROnA study are to evaluate the safety and tolerability of vandetanib-eluting radiopaque embolic beads (BTG-002814) in patients with resectable liver malignancies and to determine concentrations of vandetanib and the N-desmethyl metabolite in plasma and resected liver following treatment with BTG-002814.

METHODS

The VEROnA study is a first-in-human, open-label, single-arm, phase 0, window-of-opportunity study of BTG-002814 (containing 100 mg vandetanib) delivered transarterially, 7 to 21 days before surgery in patients with resectable liver malignancies. Eligible patients have a diagnosis of colorectal liver metastases, or HCC (Childs Pugh A), diagnosed histologically or radiologically, and are candidates for liver surgery. All patients are followed up for 28 days following surgery. Secondary objectives of this study are to evaluate the anatomical distribution of BTG-002814 on noncontrast-enhanced imaging, to evaluate histopathological features in the surgical specimen, and to assess changes in blood flow on dynamic contrast-enhanced magnetic resonance imaging following treatment with BTG-002814. Exploratory objectives of this study are to study blood biomarkers with the potential to identify patients likely to respond to treatment and to correlate the distribution of BTG-002814 on imaging with pathology by 3-dimensional modeling.

RESULTS

Enrollment for the study was completed in February 2019. Results of a planned interim analysis were reviewed by a safety committee after the first 3 patients completed follow-up. The recommendation of the committee was to continue the study without any changes to the dose or trial design, as there were no significant unexpected toxicities related to BTG-002814.

CONCLUSIONS

The VEROnA study is studying the feasibility of administering BTG-002814 to optimize the use of this novel technology as liver-directed therapy for patients with primary and secondary liver cancer.

TRIAL REGISTRATION

ClinicalTrial.gov NCT03291379; https://clinicaltrials.gov/ct2/show/NCT03291379.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/13696.

Potentiation of PBD Dimers by Lipophilicity Manipulation

Background & Introduction: Pyrrolobenzodiazepine (PBD) dimers are highly potent DNA cross-linking agents used as warheads in Antibody Drug Conjugates (ADCs) for cancer therapy. We propose to investigate the correlation existing between the lipophilicity of those molecules and their activity (both in vitro and in vivo) as well as any effect observed during conjugation.

MATERIALS AND METHODS

Reaction progress was monitored by Thin-Layer Chromatography (TLC) using Merck Kieselgel 60 F254 silica gel, with a fluorescent indicator on aluminium plates. Visualisation of TLC was achieved with UV light or iodine vapour unless otherwise stated. Flash chromatography was performed using Merck Kieselgel 60 F254 silica gel.

RESULTS

We have successfully designed and synthesized a novel PBD warhead (SG3312) with enhanced physicochemical properties. The warhead also displayed increased potency in vitro. After overcoming some epimerization issues, the synthesis of enantiomerically pure payload was achieved (SG3259) and fulfilled our criteria for a simplified and more efficient conjugation. No addition of propylene glycol was required, and high DAR and excellent monomeric purity were achieved.

CONCLUSION

The ADC (Herceptin-maia-SG3259) has been shown to release the active warhead (SG3312) upon exposure to Cathepsin B and demonstrated encouraging activity both in vitro and in vivo.

Abstract 225: TR1801-ADC, an optimized anti cMet PBD ADC with high efficacy in solid tumors of the GI tract and head & neck cancer

cMet is a well-characterized oncogene that is the target of many drugs including small molecule and biologic pathway inhibitors, and more recently, antibody drug conjugates (ADCs). However, clinical benefit from c-Met targeted therapy has been limited up to this point. We developed an optimized c-Met targeted antibody drug conjugate TR1801-ADC that utilized optimization at all steps including specificity, stability, internalization, toxin linkers, conjugation site, PK, and in vivo efficacy. The results were a highly potent c-Met ADC that was superior in comparison to a conventional MMAE (monomethylauristatin E) cMet ADC in potency, efficacy and duration of response. TR1801-ADC is site-specifically conjugated to a PBD-toxin linker and has low picomolar activity in multiple cancer cell lines derived from different solid tumors including lung cancer, colorectal cancer and gastric cancer. The potency of our cMet ADC is independent of MET gene copy number and its activity was high not only in high cMet cell lines but also in medium to low cell lines (100,000 to 40,000 cMet/cell). We identified potential Phase 1 cancer indications based on IHC and cMet H-score from tissue micro arrays (TMAs). 3 cancer indications (gastric, colorectal and head & neck cancer) were chosen based on high abundance of high cMet expression (&gt;20% abundance of H-Score higher than 150) and were used to assess the efficacy of our cMet ADC in PDX models. For each indication 10 PDX (patient-derived xenograft) models were chosen based on their cMet expression. TR1801-ADC was administered in all models as single i.v. dose at 1, 0.5, 0.25 and 0.125 mg/kg. Control ADC was administered at 1mg/kg. Tumor growth inhibition varying from &gt;100% to around 40% was seen in all gastric cancer PDX models with single dose injections of 1 mg/kg and 0.5 mg/kg. Complete tumor regression was seen in 70% of the 1 mg/kg group, in 50% of the 0.5 mg/kg group and in 40% of the 0.25 mg/kg group. TR1801-ADC produced statistically significant growth inhibition in comparison to untreated controls in 9 colorectal cancer PDX models. Complete tumor regression was observed in 40% (4/10) PDX models when treated with 1 mg/kg TR1801-ADC. The further 50% showed partial regression (5/10 models) and one showed no significant tumor response. The head & neck cancer PDX models were in general least sensitive to TR1801-ADC. TR1801-ADC produced statistically significant growth inhibition in comparison to untreated controls in 8/10 head & neck cancer PDX models. Complete tumor regression was observed in 30% (3/10) PDX models when treated with 1 mg/kg TR1801-ADC. 50% showed statistical significant partial regression while two models (20%) showed no significant tumor inhibition. Altogether, TR1801-ADC is a novel highly potent cMet ADC that shows very promising efficacy in PDX models of gastric, colorectal and head & neck cancer with long lasting anti-tumor effect with a single dose.

Citation Format: Marco Gymnopoulos, Oscar Betancourt, Vincent Blot, Ryo Fujita, Diana Ly, Sophie Nguyen, Jeanette Snedden, Jose Villicana, Jon Wojciak, Eley Wong, Neki Patel, Francois D'Hooge, Balakumar Vijayakrishnan, Conor Barry, John A. Hartley, Phil W. Howard, Roland Newman, Julia Coronella. TR1801-ADC, an optimized anti cMet PBD ADC with high efficacy in solid tumors of the GI tract and head & neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 225.

EACH: A randomised phase II study evaluating the safety and anti-tumour activity of the combination of avelumab and cetuximab relative to avelumab monotherapy in recurrent/metastatic head and neck squamous cell cancer

TPS6091

Background: Patients with recurrent/metastatic head and neck squamous cell carcinoma (R/M HNSCC) have low response rates to licensed second line therapies, including PD-1 inhibitors nivolumab and pembrolizumab, and represent an area of unmet clinical need. The chimeric IgG1 epithelial growth factor receptor (EGFR) monoclonal antibody cetuximab potentiates the activity of radiotherapy in locally advanced HNSCC and chemotherapy in R/M HNSCC and is also licensed with modest activity as a single agent. Cetuximab initiates Natural Killer (NK) cell antibody-dependent cell-mediated cytotoxicity (ADCC), resulting in an anti-tumour immune response and the potential to augment the activity of PD-1/PD-L1 inhibition. EACH aims to examine the safety and efficacy of the potentially synergistic interaction between cetuximab and avelumab, a fully human IgG1 anti-PD-L1 monoclonal antibody in R/M HNSCC. Methods: EACH is a randomised phase II trial preceded by a safety run-in phase. Eligible patients have histologically or cytologically confirmed measurable recurrent or metastatic squamous cell carcinoma of any site in the safety run-in phase, and HNSCC in phase II, that is considered incurable by local therapies. The safety run-in has a single arm de-escalating design, aiming to establish the safety of cetuximab with avelumab and determine the optimal dose of cetuximab within this combination. The safety run-in has a dosing schedule of avelumab (10 mg/kg) + cetuximab (500 mg/m2) intravenously every 2 weeks, with de-escalation of cetuximab to 400 mg/m2 and 300 mg/m2 if necessary. The safety run-in phase commenced recruitment in July 2018 and is ongoing. The phase II component will randomize 114 HNSCC patients between either avelumab + cetuximab at the dose determined by the safety run-in phase or avelumab (10 mg/kg) alone. Treatment will be in 4-week cycles for up to one year. The primary endpoint in the safety run-in phase is the occurrence of dose limiting toxicities, and in phase II is Disease Control Rate at 24 weeks, using iRECIST. Blood and fresh tissue will be collected for exploratory translational studies, which will focus on the identification of potential novel predictive biomarkers for response. Clinical trial information: NCT03494322.

Circulating tumour cells and their association with bone metastases in patients with neuroendocrine tumours

Background

Bone metastases are associated with a worse outcome in patients with neuroendocrine tumours (NETs). Tumour overexpression of C-X-C chemokine receptor 4 (CXCR4) appears predictive of skeletal involvement. We investigated the role of circulating tumour cells (CTCs) and CXCR4 expression on CTCs as potential predictors of skeleton invasion.

Methods

Blood from patients with metastatic bronchial, midgut or pancreatic NET (pNET) was analysed by CellSearch. CXCR4 immunohistochemistry was performed on matched formalin-fixed paraffin-embedded (FFPE) samples.

Results

Two hundred and fifty-four patients were recruited with 121 midgut and 119 pNETs, of which 51 and 36% had detectable CTCs, respectively. Bone metastases were reported in 30% of midgut and 23% of pNET patients and were significantly associated with CTC presence (p = 0.003 and p < 0.0001). In a subgroup of 40 patients, 85% patients with CTCs had CTCs positive for CXCR4 expression. The proportion of CXCR4-positive CTCs in patients with bone metastases was 56% compared to 35% in those without (p = 0.18) it. Staining for CXCR4 on matched FFPE tissue showed a trend towards a correlation with CXCR4 expression on CTCs (p = 0.08).

Conclusions

CTC presence is associated with bone metastases in NETs. CXCR4 may be involved in CTC osteotropism and present a therapeutic target to reduce skeletal morbidity.

Abstract A004: MEDI3726 (ADCT-401), a novel antibody-drug conjugate targeting PSMA, has potent in vivo antitumor activity in prostate cancer patient-derived xenograft models

Prostate specific membrane antigen (PSMA), a type II membrane glycoprotein, is highly expressed in nearly all prostate cancers, with the highest expression in metastatic castration-resistant prostate cancer (mCRPC). The prevalence, increased surface expression in prostate tumors, and constitutive internalization make PSMA an attractive target for an antibody-drug conjugate (ADC) approach in anticancer treatment of patients with mCRPC.

MEDI3726 (previously known as ADCT-401) is an ADC consisting of an engineered version of anti-PSMA antibody J591, site-specifically conjugated with DNA cross-linking pyrrolobenzodiazepine (PBD) dimer SG3249 for targeting prostatic cancer cells. Using prostate cancer cell line models, we have previously shown that MEDI3726 specifically binds to the extracellular domain of PSMA and, once internalized, releases the PBD dimer to cross link DNA and achieve potent in vitro and in vivo cytotoxicity.

Here we investigated the in vivo activity of MEDI3726 in a series of LuCaP prostate cancer patient-derived xenograft (PDX) models. The selected LuCaP models had varying PSMA expression and heterogeneous genetic and phenotypic backgrounds. In agreement with the earlier cell line xenograft data, dose-dependent antitumor activity was observed in PSMA-positive PDX models with durable tumor regressions in models with high PSMA expression. In the PSMA-negative LuCaP 35CR PDX model, MEDI3726 did not have significant antitumor activity, thus highlighting target-mediated in vivo activity. Increased phosphorylation of histone H2AX was observed in xenografts dosed with MEDI3726, confirming DNA damage induced by interstrand cross-linking PBD dimer as the mechanism of antitumor activity of MEDI3726.

In summary, MEDI3726 demonstrated potent and specific in vivo antitumor activity, concurrent with DNA damage, in clinically relevant prostate cancer PDX models. MEDI3726 is being evaluated in phase 1 clinical trial as an anticancer treatment in patients with metastatic castrate-resistant prostate cancer (NCT02991911).

Citation Format: Song Cho, Francesca Zammarchi, Noel R. Monks, Kapil Vashisht, Ravinder Tammali, Kevin Schifferli, Patrick Strout, Wanda King, Karma Dacosta, Ryan Fleming, David G. Williams, Karin Havenith, Mary Jane Masson Hinrichs, Simon Chivers, Nazzareno Dimasi, Phil W. Howard, John A. Hartley, Steve Coats, Ronald Herbst, Patrick H. van Berkel, David A. Tice. MEDI3726 (ADCT-401), a novel antibody-drug conjugate targeting PSMA, has potent in vivo antitumor activity in prostate cancer patient-derived xenograft models [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A004.

DNA-Binding Properties of New Fluorescent AzaHx Amides: Methoxypyridylazabenzimidazolepyrroleimidazole/pyrrole

DNA minor groove binding polyamides have been extensively developed to control abnormal gene expression. The establishment of novel, inherently fluorescent 2-(p-anisyl)benzimidazole (Hx) amides has provided an alternative path for studying DNA binding in cells by direct observation of cell localization. Because of the 2:1 antiparallel stacking homodimer binding mode of these molecules to DNA, modification of Hx amides to 2-(p-anisyl)-4-azabenzimidazole (AzaHx) amides has successfully extended the DNA-recognition repertoire from central CG [recognized by Hx-I (I=N-methylimidazole)] to central GC [recognized by AzaHx-P (P=N-methylpyrrole)] recognition. For potential targeting of two consecutive GG bases, modification of the AzaHx moiety to 2- and 3-pyridyl-aza-benzimidazole (Pyr-AzaHx) moieties was explored. The newly designed molecules are also small-sized, fluorescent amides with the Pyr-AzaHx moiety connected to two conventional five-membered heterocycles. Complementary biophysical methods were performed to investigate the DNA-binding properties of these molecules. The results showed that neither 3-Pyr-AzaHx nor 2-Pyr-AzaHx was able to mimic I-I=N-methylimidazole-N-methylimidazole to target GG dinucleotides specifically. Rather, 3-Pyr-AzaHx was found to function like AzaHx, f-I (f=formamide), or P-I as an antiparallel stacked dimer. 3-Pyr-AzaHx-PI (2) binds 5'-ACGCGT'-3' with improved binding affinity and high sequence specificity in comparison to its parent molecule AzaHx-PI (1). However, 2-Pyr-AzaHx is detrimental to DNA binding because of an unfavorable steric clash upon stacking in the minor groove.

Pre-clinical pharmacology and mechanism of action of SG3199, the pyrrolobenzodiazepine (PBD) dimer warhead component of antibody-drug conjugate (ADC) payload tesirine

Synthetic pyrrolobenzodiazepine (PBD) dimers, where two PBD monomers are linked through their aromatic A-ring phenolic C8-positions via a flexible propyldioxy tether, are highly efficient DNA minor groove cross-linking agents with potent cytotoxicity. PBD dimer SG3199 is the released warhead component of the antibody-drug conjugate (ADC) payload tesirine (SG3249), currently being evaluated in several ADC clinical trials. SG3199 was potently cytotoxic against a panel of human solid tumour and haematological cancer cell lines with a mean GI₅₀ of 151.5 pM. Cells defective in DNA repair protein ERCC1 or homologous recombination repair showed increased sensitivity to SG3199 and the drug was only moderately susceptible to multidrug resistance mechanisms. SG3199 was highly efficient at producing DNA interstrand cross-links in naked linear plasmid DNA and dose-dependent cross-linking was observed in cells. Cross-links formed rapidly in cells and persisted over 36 hours. Following intravenous (iv) administration to rats SG3199 showed a very rapid clearance with a half life as short as 8 minutes. These combined properties of cytotoxic potency, rapid formation and persistence of DNA interstrand cross-links and very short half-life contribute to the emerging success of SG3199 as a warhead in clinical stage ADCs.

Design, synthesis, nuclear localization, and biological activity of a fluorescent duocarmycin analog, HxTfA

HxTfA 4 is a fluorescent analog of a potent cytotoxic and antimalarial agent, TfA 3, which is currently being investigated for the development of an antimalarial vaccine, PlasProtect®. HxTfA contains a p-anisylbenzimidazole or Hx moiety, which is endowed with a blue emission upon excitation at 318 nm; thus enabling it to be used as a surrogate for probing the cellular fate of TfA using confocal microscopy, and addressing the question of nuclear localization. HxTfA exhibits similar selectivity to TfA for A-tract sequences of DNA, alkylating adenine-N3, albeit at 10-fold higher concentrations. It also possesses in vitro cytotoxicity against A549 human lung carcinoma cells and Plasmodium falciparum. Confocal microscopy studies showed for the first time that HxTfA, and by inference TfA, entered A549 cells and localized in the nucleus to exert its biological activity. At biologically relevant concentrations, HxTfA elicits DNA damage response as evidenced by a marked increase in the levels of γH2AX observed by confocal microscopy and immunoblotting studies, and ultimately induces apoptosis.

ADCT-402, a PBD dimer-containing antibody drug conjugate targeting CD19-expressing malignancies

Human CD19 antigen is a 95-kDa type I membrane glycoprotein in the immunoglobulin superfamily whose expression is limited to the various stages of B-cell development and differentiation and is maintained in the majority of B-cell malignancies, including leukemias and non-Hodgkin lymphomas of B-cell origin. Coupled with its differential and favorable expression profile, CD19 has rapid internalization kinetics and is not shed into the circulation, making it an ideal target for the development of antibody-drug conjugates (ADCs) to treat B-cell malignancies. ADCT-402 (loncastuximab tesirine) is a novel CD19-targeted ADC delivering SG3199, a highly cytotoxic DNA minor groove interstrand crosslinking pyrrolobenzodiazepine (PDB) dimer warhead. It showed potent and highly targeted in vitro cytotoxicity in CD19-expressing human cell lines. ADCT-402 was specifically bound, internalized, and trafficked to lysosomes in CD19-expressing cells and, following release of the PBD warhead, resulted in formation of DNA crosslinks that persisted for 36 hours. Bystander killing of CD19- cells by ADCT-402 was also observed. In vivo, single doses of ADCT-402 resulted in highly potent, dose-dependent antitumor activity in several subcutaneous and disseminated human tumor models with marked superiority to comparator ADCs delivering tubulin inhibitors. Dose-dependent DNA crosslinks and γ-H2AX DNA damage response were measured in tumors by 24 hours after single dose administration, whereas matched peripheral blood mononuclear cells showed no evidence of DNA damage. Pharmacokinetic analysis in rat and cynomolgus monkey showed excellent stability and tolerability of ADCT-402 in vivo. Together, these impressive data were used to support the clinical testing of this novel ADC in patients with CD19-expressing B-cell malignancies.

MEK inhibition leads to BRCA2 downregulation and sensitization to DNA damaging agents in pancreas and ovarian cancer models

Targeting the DNA damage response (DDR) in tumors with defective DNA repair is a clinically successful strategy. The RAS/RAF/MEK/ERK signalling pathway is frequently deregulated in human cancers. In this study, we explored the effects of MEK inhibition on the homologous recombination pathway and explored the potential for combination therapy of MEK inhibitors with DDR inhibitors and a hypoxia-activated prodrug. We studied effects of combining pimasertib, a selective allosteric inhibitor of MEK1/2, with olaparib, a small molecule inhibitor of poly (adenosine diphosphate [ADP]-ribose) polymerases (PARP), and with the hypoxia-activated prodrug evofosfamide in ovarian and pancreatic cancer cell lines. Apoptosis was assessed by Caspase 3/7 assay and protein expression was detected by immunoblotting. DNA damage response was monitored with γH2AX and RAD51 immunofluorescence staining. In vivo antitumor activity of pimasertib with evofosfamide were assessed in pancreatic cancer xenografts. We found that BRCA2 protein expression was downregulated following pimasertib treatment under hypoxic conditions. This translated into reduced homologous recombination repair demonstrated by levels of RAD51 foci. MEK inhibition was sufficient to induce formation of γH2AX foci, suggesting that inhibition of this pathway would impair DNA repair. When combined with olaparib or evofosfamide, pimasertib treatment enhanced DNA damage and increased apoptosis. The combination of pimasertib with evofosfamide demonstrated increased anti-tumor activity in BRCA wild-type Mia-PaCa-2 xenograft model, but not in the BRCA mutated BxPC3 model. Our data suggest that targeted MEK inhibition leads to impaired homologous recombination DNA damage repair and increased PARP inhibition sensitivity in BRCA-2 proficient cancers.

Corrigendum: Phylogenetic ctDNA analysis depicts early-stage lung cancer evolution

This corrects the article DOI: 10.1038/nature22364.

The emerging role of anti-CD25 directed therapies as both immune modulators and targeted agents in cancer

CD25 (also termed IL2RA) forms one component of the high-affinity heterotrimeric interleukin 2 (IL2) receptor on activated T cells. Its affinity for IL2 and cellular function are tightly regulated and vary in different cell types. The high frequency of CD25 on the surface of many different haematological tumour cells is now well established and, apart from its prognostic significance, CD25 may be present on leukaemic stem cells and enable oncogenic signalling pathways in leukaemic cells. Additionally, high CD25 expression in activated circulating immune cells and Tregs is a factor that has already been exploited by IL2 immunotherapies for treatment of tumours and autoimmune disease. The relative clinical safety and efficacy of administering anti-CD25 radioimmunoconjugates and immunotoxins in various haematological tumour indications has been established and clinical trials of a novel CD25-directed antibody drug conjugate are underway.

Abstract 52: Mechanistic and benchmarking studies of ADCT-502, a pyrrolobenzodiazepine (PBD) dimer-containing antibody-drug conjugate (ADC) targeting HER2-expressing solid tumors

ADCT-502 is an ADC composed of an engineered version of humanized IgG1 trastuzumab, directed against human HER2, site-specifically conjugated to the highly cytotoxic PBD-based linker-drug tesirine (drug-antibody ratio of 1.7). In vitro, ADCT-502 has highly potent and targeted cytotoxicity against various solid cancer cell lines. In vivo, ADCT-502 demonstrates strong and durable antitumor activity in mouse xenografts with various levels of HER2, but is inactive in a HER2-negative xenograft. ADCT-502 is stable, well tolerated and has a favorable PK profile both in rat and cynomolgus monkey. The current study aimed to define further the mechanism of action of ADCT-502 and to benchmark its activity in xenograft models against ado-trastuzumab emtansine (T-DM1), the ADC currently approved for the treatment of HER2+ metastatic breast cancers. ADCT-502 bound and internalized efficiently in JIMT-1 cells (HER2+) and co-localized with lysosomes within 2 hours. PBD dimers bind in the DNA minor groove and exert cytotoxicity via the formation of DNA interstrand cross-links. Following a 2-hour exposure to ADCT-502, DNA interstrand cross-linking peaked between 12 and 24 hours, after which cross-links persisted at least 36 hours. In contrast, cross-link formation by an equimolar concentration of warhead alone, peaked immediately following drug exposure and a non-targeted ADC did not produce DNA crosslinks in these cells. Moreover, ADCT-502 showed indirect bystander killing activity in HER2-negative MDA-MB-468 cells incubated with conditioned medium from ADCT-502-treated HER2+ SK-BR-3 cells. In vivo, antitumor activity of ADCT-502 was compared to T-DM1 in both cell line- and patient-derived-xenograft (PDX) models. For example, in a HER2 1+, FISH- breast cancer PDX, ADCT-502 showed dose-dependent antitumor activity resulting in 1/8 and 8/8 TFS after a single dose at 0.1 and 0.2 mg/kg, respectively. Conversely, a single dose of T-DM1 at 30 mg/kg showed only marginal activity compared to the control. Similarly, in a HER2 1+, FISH- esophageal cancer PDX, while a single dose of ADCT-502 at 0.44 mg/kg resulted in strong and durable antitumor activity, single doses of T-DM1 at either 10 or 30 mg/kg showed no activity compared to the control. These data confirm that the mechanism of cell killing of ADCT-502 is via target-specific internalization and subsequent cross-linking of DNA. They also show superior in vivo antitumor activity of ADCT-502 compared to T-DM1 in various tumor xenografts, including those with low HER2 levels. Taken together, these results support the development of ADCT-502 not only in patients that have become resistant/refractory to T-DM1, but also in patients whose tumors express low levels of HER2, and are not eligible for treatment with T-DM1.

Citation Format: Francesca Zammarchi, Halla W. Reinert, Narinder Janghra, Simon Corbett, Maria Mellinas-Gomez, Sajidah Chowdhury, Neha Arora, Peter Tyrer, Francois Bertelli, David G. Williams, Philip W. Howard, John A. Hartley, Patrick H. van Berkel. Mechanistic and benchmarking studies of ADCT-502, a pyrrolobenzodiazepine (PBD) dimer-containing antibody-drug conjugate (ADC) targeting HER2-expressing solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 52. doi:10.1158/1538-7445.AM2017-52

Abstract 3111A: ADCT-401/MEDI3726, a novel pyrrolobenzodiazepine (PBD)-based antibody-drug conjugate (ADC) targeting PSMA-expressing prostate cancers

Prostate-specific membrane antigen (PSMA) is an attractive target for an ADC approach as it is over-expressed by virtually all prostate cancers and its expression is highest in poorly-differentiated, metastatic and castration-resistant cases. PSMA has limited expression in non-prostatic tissues, it is not secreted or cleaved by PSMA-expressing cells, and it is constitutively internalized, a process that may be accelerated by specific antibody binding. ADCT-401/MEDI3726 is an ADC composed of a monoclonal antibody (J591), directed against human PSMA, site-specifically conjugated (drug-to-antibody ratio of 1.8) to a highly cytotoxic DNA cross-linking PBD dimer with a valine-alanine dipeptide linker. In vitro, ADCT-401/MEDI3726 demonstrated potent and specific cytotoxicity in a panel of PSMA-expressing prostate cancer cell lines, whereas its activity was greatly reduced in PSMA-negative cell lines. In vivo, ADCT-401/MEDI3726 showed strong antitumor activity against CWR22Rv1 and LNCaP human-derived prostate cancer xenograft models. In the CWR22Rv1 model, a tumor with low, heterogeneous PSMA expression, ADCT-401/MEDI3726 achieved dose-dependent antitumor activity when administered as single dose at either 0.33 or 1 mg/kg, which resulted in significant increase in survival compared to the vehicle-treated animals. Moreover, a single dose of ADCT-401/MEDI3726 showed remarkable superior antitumor activity compared to multiple doses of another PSMA-targeted ADC stochastically conjugated to the auristatin payload vcMMAE with a DAR of ~4. In the LNCaP model, ADCT-401/MEDI3726 resulted in dose-dependent antitumor activity when dosed once at 0.11, 0.33 or 1 mg/kg. In the PSMA-negative prostate cancer-derived PC3 xenograft model, ADCT-401/MEDI3726 and an isotope-control ADC showed limited tumor growth inhibition highlighting target-mediated antitumor activity. ADCT-401/MEDI3726 demonstrated potent and specific in vitro and in vivo antitumor activity in prostate cancer-derived models of differing levels of PSMA and this warrants further development of this ADC into the clinic.

Citation Format: Francesca Zammarchi, Simon Chivers, Karin Havenith, David G. Williams, Lauren Adams, Maria Mellinas-Gomez, Simon Corbett, Peter Tyrer, Francois D'Hooge, Song Cho, Nazzareno Dimasi, Mary Jane Hinrichs, Phil W. Howard, John A. Hartley, Patrick H. van Berkel. ADCT-401/MEDI3726, a novel pyrrolobenzodiazepine (PBD)-based antibody-drug conjugate (ADC) targeting PSMA-expressing prostate cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3111A. doi:10.1158/1538-7445.AM2017-3111A

Tracking the Evolution of Non-Small-Cell Lung Cancer

BACKGROUND

Among patients with non-small-cell lung cancer (NSCLC), data on intratumor heterogeneity and cancer genome evolution have been limited to small retrospective cohorts. We wanted to prospectively investigate intratumor heterogeneity in relation to clinical outcome and to determine the clonal nature of driver events and evolutionary processes in early-stage NSCLC.

METHODS

In this prospective cohort study, we performed multiregion whole-exome sequencing on 100 early-stage NSCLC tumors that had been resected before systemic therapy. We sequenced and analyzed 327 tumor regions to define evolutionary histories, obtain a census of clonal and subclonal events, and assess the relationship between intratumor heterogeneity and recurrence-free survival.

RESULTS

We observed widespread intratumor heterogeneity for both somatic copy-number alterations and mutations. Driver mutations in EGFR, MET, BRAF, and TP53 were almost always clonal. However, heterogeneous driver alterations that occurred later in evolution were found in more than 75% of the tumors and were common in PIK3CA and NF1 and in genes that are involved in chromatin modification and DNA damage response and repair. Genome doubling and ongoing dynamic chromosomal instability were associated with intratumor heterogeneity and resulted in parallel evolution of driver somatic copy-number alterations, including amplifications in CDK4, FOXA1, and BCL11A. Elevated copy-number heterogeneity was associated with an increased risk of recurrence or death (hazard ratio, 4.9; P=4.4×10-4), which remained significant in multivariate analysis.

CONCLUSIONS

Intratumor heterogeneity mediated through chromosome instability was associated with an increased risk of recurrence or death, a finding that supports the potential value of chromosome instability as a prognostic predictor. (Funded by Cancer Research UK and others; TRACERx ClinicalTrials.gov number, NCT01888601 .).

Modulation of topoisomerase IIα expression and chemosensitivity through targeted inhibition of NF-Y:DNA binding by a diamino p-anisyl-benzimidazole (Hx) polyamide

BACKGROUND

Sequence specific polyamide HxIP 1, targeted to the inverted CCAAT Box 2 (ICB2) on the topoisomerase IIα (topo IIα) promoter can inhibit NF-Y binding, re-induce gene expression and increase sensitivity to etoposide. To enhance biological activity, diamino-containing derivatives (HxI*P 2 and HxIP* 3) were synthesised incorporating an alkyl amino group at the N1-heterocyclic position of the imidazole/pyrrole.

METHODS

DNase I footprinting was used to evaluate DNA binding of the diamino Hx-polyamides, and their ability to disrupt the NF-Y:ICB2 interaction assessed using EMSAs. Topo IIα mRNA (RT-PCR) and protein (Immunoblotting) levels were measured following 18h polyamide treatment of confluent A549 cells. γH2AX was used as a marker for etoposide-induced DNA damage after pre-treatment with HxIP* 3 and cell viability was measured using Cell-Titer Glo®.

RESULTS

Introduction of the N1-alkyl amino group reduced selectivity for the target sequence 5'-TACGAT-3' on the topo IIα promoter, but increased DNA binding affinity. Confocal microscopy revealed both fluorescent diamino polyamides localised in the nucleus, yet HxI*P 2 was unable to disrupt the NF-Y:ICB2 interaction and showed no effect against the downregulation of topo IIα. In contrast, inhibition of NF-Y binding by HxIP* 3 stimulated dose-dependent (0.1-2μM) re-induction of topo IIα and potentiated cytotoxicity of topo II poisons by enhancing DNA damage.

CONCLUSIONS

Polyamide functionalisation at the N1-position offers a design strategy to improve drug-like properties. Dicationic HxIP* 3 increased topo IIα expression and chemosensitivity to topo II-targeting agents.

GENERAL SIGNIFICANCE

Pharmacological modulation of topo IIα expression has the potential to enhance cellular sensitivity to clinically-used anticancer therapeutics. This article is part of a Special Issue entitled: Nuclear Factor Y in Development and Disease, edited by Prof. Roberto Mantovani.

Phylogenetic ctDNA analysis depicts early-stage lung cancer evolution

The early detection of relapse following primary surgery for non-small-cell lung cancer and the characterization of emerging subclones, which seed metastatic sites, might offer new therapeutic approaches for limiting tumour recurrence. The ability to track the evolutionary dynamics of early-stage lung cancer non-invasively in circulating tumour DNA (ctDNA) has not yet been demonstrated. Here we use a tumour-specific phylogenetic approach to profile the ctDNA of the first 100 TRACERx (Tracking Non-Small-Cell Lung Cancer Evolution Through Therapy (Rx)) study participants, including one patient who was also recruited to the PEACE (Posthumous Evaluation of Advanced Cancer Environment) post-mortem study. We identify independent predictors of ctDNA release and analyse the tumour-volume detection limit. Through blinded profiling of postoperative plasma, we observe evidence of adjuvant chemotherapy resistance and identify patients who are very likely to experience recurrence of their lung cancer. Finally, we show that phylogenetic ctDNA profiling tracks the subclonal nature of lung cancer relapse and metastasis, providing a new approach for ctDNA-driven therapeutic studies.

Synthesis and in vitro evaluation of SG3227, a pyrrolobenzodiazepine dimer antibody-drug conjugate payload based on sibiromycin

A novel pyrrolobenzodiazepine dimer payload, SG3227, was rationally designed based on the naturally occurring antitumour compound sibiromycin. SG3227 was synthesized from a dimeric core in an efficient fashion. An unexpected room temperature Diels-Alder reaction occurred during the final step of the synthesis and was circumvented by use of an iodoacetamide conjugation moiety in place of a maleimide. The payload was successfully conjugated to trastuzumab and the resulting ADC exhibited potent activity against a HER2-expressing human cancer cell line in vitro.

Expression of somatostatin receptors 2 and 5 in circulating tumour cells from patients with neuroendocrine tumours

BACKGROUND

Neuroendocrine tumours (NET) overexpress somatostatin receptors (SSTR) that can be targeted for therapy. Somatostatin receptor expression is routinely measured by molecular imaging but the resolution is insufficient to define heterogeneity. We hypothesised that SSTR expression could be measured on circulating tumour cells (CTCs) and used to investigate heterogeneity of expression and track changes during therapy.

METHODS

MCF-7 cells were transfected with SSTR2 or 5 and spiked into donor blood for analysis by CellSearch. Optimum anti-SSTR antibody concentration and exposure time were determined, and flow cytometry was used to evaluate assay sensitivity. For clinical evaluation, blood was analysed by CellSearch, and SSTR2/5 immunohistochemistry was performed on matched tissue samples.

RESULTS

Flow cytometry confirmed CellSearch was sensitive and that detection of SSTR was unaffected by the presence of somatostatin analogue up to a concentration of 100 ng ml-l. Thirty-one NET patients were recruited: grade; G1 (29%), G2 (45%), G3 (13%), primary site; midgut (58%), pancreatic (39%). Overall, 87% had SSTR-positive tumours according to somatostatin receptor scintigraphy or 68-Ga-DOTATE PET/CT. Circulating tumour cells were detected in 21 out of 31 patients (68%), of which 33% had evidence of heterogeneous expression of either SSTR2 (n=5) or SSTR5 (n=2).

CONCLUSIONS

Somatostatin receptors 2 and 5 are detectable on CTCs from NET patients and may be a useful biomarker for evaluating SSTR-targeted therapies and this is being prospectively evaluated in the Phase IV CALMNET trial (NCT02075606).

Design and Synthesis of Tesirine, a Clinical Antibody-Drug Conjugate Pyrrolobenzodiazepine Dimer Payload

Pyrrolobenzodiazepine dimers are an emerging class of warhead in the field of antibody-drug conjugates (ADCs). Tesirine (SG3249) was designed to combine potent antitumor activity with desirable physicochemical properties such as favorable hydrophobicity and improved conjugation characteristics. One of the reactive imines was capped with a cathepsin B-cleavable valine-alanine linker. A robust synthetic route was developed to allow the production of tesirine on clinical scale, employing a flexible, convergent strategy. Tesirine was evaluated in vitro both in stochastic and engineered ADC constructs and was confirmed as a potent and versatile payload. The conjugation of tesirine to anti-DLL3 rovalpituzumab has resulted in rovalpituzumab-tesirine (Rova-T), currently under evaluation for the treatment of small cell lung cancer.

ADCT-301, a Pyrrolobenzodiazepine (PBD) Dimer-Containing Antibody-Drug Conjugate (ADC) Targeting CD25-Expressing Hematological Malignancies

Despite the many advances in the treatment of hematologic malignancies over the past decade, outcomes in refractory lymphomas remain poor. One potential strategy in this patient population is the specific targeting of IL2R-α (CD25), which is overexpressed on many lymphoma and leukemic cells, using antibody-drug conjugates (ADC). ADCT-301 is an ADC composed of human IgG1 HuMax-TAC against CD25, stochastically conjugated through a dipeptide cleavable linker to a pyrrolobenzodiazepine (PBD) dimer warhead with a drug-antibody ratio (DAR) of 2.3. ADCT-301 binds human CD25 with picomolar affinity. ADCT-301 has highly potent and selective cytotoxicity against a panel of CD25-expressing human lymphoma cell lines. Once internalized, the released warhead binds in the DNA minor groove and exerts its potent cytotoxic action via the formation of DNA interstrand cross-links. A strong correlation between loss of viability and DNA cross-link formation is demonstrated. DNA damage persists, resulting in phosphorylation of histone H2AX, cell-cycle arrest in G2-M, and apoptosis. Bystander killing of CD25-negative cells by ADCT-301 is also observed. In vivo, a single dose of ADCT-301 results in dose-dependent and targeted antitumor activity against both subcutaneous and disseminated CD25-positive lymphoma models. In xenografts of Karpas 299, which expressed both CD25 and CD30, marked superiority over brentuximab vedotin (Adcetris) is observed. Dose-dependent increases in DNA cross-linking, γ-H2AX, and PBD payload staining were observed in tumors in vivo indicating a role as relevant pharmacodynamic assays. Together, these data support the clinical testing of this novel ADC in patients with CD25-expressing tumors. Mol Cancer Ther; 15(11); 2709-21. ©2016 AACR.

Sequence Selective Molecular Recognition of Long DNA Sequences by Oligomethylene-Linked Oligoimidazole Analogs of Distamycin

We have studied a series of homologous N-to-N oligomethylene linked bis(diimidazole) analogs 4a-f (number of methylene groups = 1 to 6, re spectively) and a dipicolinamide congener 4g that bind to long GC-containing sequences of DNA. Results from an ethidium binding assay reveal that, for 4a-f, the compounds with an even number of methylene groups have larger ap parent binding constants, Kapp, than those with an odd number. The Kapp values of the compounds with an odd number of methylene groups are close to that of their monomeric analog 3 suggesting that they may be binding to DNA in a monodentate fashion. The binding of these compounds to T4 DNA and their larger binding constants for poly(dG-dC) over poly(dA-dT) indicated minor groove binding selectivity and tolerance for GC sequences. The ability of com pounds 4b-f to bind selectively to DNA was illustrated by an MPE-Fe(II) foot printing study which showed that compound 4f gave the most distinct foot prints. CD titration studies on compounds 4b, d, and f further demonstrated the GC tolerance of these compounds and that they can bind to 7 ~ 8 base pairs of DNA in a bidentate fashion. The minor groove and bidentate bind ing of the ethylene linked compound 4b on the underlined sequence of

Abstract 3755: Genome-wide transcriptome analysis reveals the distinct gene expression profiles and specific biological effects of fluorescent polyamides, HxIP and azaHxPI

DNA-binding polyamides target predetermined sequences to inhibit specific transcription factor-DNA interactions and modulate gene expression. Inherently non-genotoxic, these non-covalent binding small molecules exert their biological activity without inflicting DNA damage and provide the basis for potentially less toxic DNA-targeting anticancer therapeutics. However, the genome-wide specificity of polyamide binding remains an outstanding issue in delivering the desired biological response without inducing widespread off-target effects.

In this study, we used RNA-seq transcriptome analysis to assess the global effects of fluorescent polyamides HxIP and azaHxPI, having previously shown that they bind with high affinity and selectivity to their respective target DNA sequences 5’-WWCGWW-3’ and 5’-WCGCGW-3’ (W = A/T)1,2. Changes to the MDA-MB-231 breast adenocarcinoma transcriptome were measured following 24 h treatment with 2 and 5 μM HxIP or azaHxPI. At 5 μM, HxIP affected 349 genes by two-fold (p&lt;0.05), corresponding to 1.72% of the Ensembl coding gene assembly, of which 171 genes were downregulated and 178 were upregulated. AzaHxPI caused the differential expression of 496 genes (2.44%), with 176 of these genes downregulated and 320 genes upregulated. Both HxIP and azaHxPI affected only a small number of the total gene set without significantly perturbing the rest of the transcriptome, demonstrating the specific nature of polyamide induced biological effects. Only 26 genes were affected by both polyamides (3.1% overlap), suggesting that HxIP and azaHxPI stimulate unique transcriptome profiles as a result of targeting different DNA sequences.

Following a 96 h treatment HxIP had no effect on cell growth (GI50 &gt; 100 μM), whereas azaHxPI causes growth inhibition (GI50 = 20.3 μM) and induces apoptosis. Immunoblotting analysis of γ;H2AX showed no evidence of DNA damage, further corroborated by the absence of chk2 phosphorylation. In addition, no ATR-chk1 activation was detected suggesting that azaHxPI does not induce replication stress, despite inhibiting DNA synthesis as shown using the BrdU incorporation assay. Levels of phospho-AKT (Ser472) decreased in response to polyamide treatment, whilst p21 is significantly upregulated and both may be implicated in the mechanism of azaHxPI induced-apoptosis. Taken together these results emphasise the potential application of polyamides as apoptosis-inducing DNA-targeting agents benefiting from enhanced sequence selectivity which in turn confers specific biological activity.

References:

1. Kiakos. et al Chem. Biol. (2015) 22(7):862-75.

2. Satam. et al Bioorg. Med. Chem. Lett. (2015) 25(17):3681-5.

Citation Format: Luke Pett, Vijay Satam, Pravin Patil, Moses Lee, John A. Hartley, Konstantinos Kiakos. Genome-wide transcriptome analysis reveals the distinct gene expression profiles and specific biological effects of fluorescent polyamides, HxIP and azaHxPI. [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 3755.

Role of Reactive Oxygen Species in the Abrogation of Oxaliplatin Activity by Cetuximab in Colorectal Cancer

BACKGROUND

The antibody cetuximab, targeting epidermal growth factor receptor (EGFR), is used to treat metastatic colorectal cancer (mCRC). Clinical trials suggest reduced benefit from the combination of cetuximab with oxaliplatin. The aim of this study was to investigate potential negative interactions between cetuximab and oxaliplatin.

METHODS

Thiazolyl blue tetrazolium bromide (MTT) assay and Calcusyn software were used to characterize drug interactions. Reactive oxygen species (ROS) were measured by flow cytometry and real-time polymerase chain reaction oxidative stress arrays identified genes regulating ROS production. Chromatin immunoprecipitation (ChIP) measured signal transducer and activator of transcription 1 (STAT-1) binding to dual oxidase 2 (DUOX2) promoter. SW48, DLD-1 KRAS wild-type cell lines and DLD-1 xenograft models exposed to cetuximab, oxaliplatin, or oxaliplatin + cetuximab (control [saline]; n = 3 mice per treatment group) were used. Statistical tests were two-sided.

RESULTS

Cetuximab and oxaliplatin exhibited antagonistic effects on cellular proliferation and apoptosis (caspase 3/7 activity reduced by 1.4-fold, 95% confidence interval [CI] = 0.78 to 2.11, P = .003) as opposed to synergistic effects observed with the irinotecan metabolite 7-Ethyl-10-hydroxycamptothecin (SN-38). Although both oxaliplatin and SN-38 produced ROS, only oxaliplatin-mediated apoptosis was ROS dependent. Production of ROS by oxaliplatin was secondary to STAT1-mediated transcriptional upregulation of DUOX2 (3.1-fold, 95% CI = 1.75 to 2.41, P < .001). Inhibition of DUOX2 induction and p38 activation by cetuximab reduced oxaliplatin cytotoxicity.

CONCLUSIONS

Inhibition of STAT1 and DUOX2-mediated ROS generation by cetuximab impairs p38-dependent apoptosis by oxaliplatin in preclinical models and may contribute to reduced efficacy in clinical settings. Understanding the rationale for unexpected trial results will inform improved rationales for combining EGFR inhibitors with chemotherapeutic agents in future therapeutic use.

NF-Y activates genes of metabolic pathways altered in cancer cells

The trimeric transcription factor NF-Y binds to the CCAAT box, an element enriched in promoters of genes overexpressed in tumors. Previous studies on the NF-Y regulome identified the general term metabolism as significantly enriched. We dissect here in detail the targeting of metabolic genes by integrating analysis of NF-Y genomic binding and profilings after inactivation of NF-Y subunits in different cell types. NF-Y controls de novo biosynthetic pathways of lipids, teaming up with the master SREBPs regulators. It activates glycolytic genes, but, surprisingly, is neutral or represses mitochondrial respiratory genes. NF-Y targets the SOCG (Serine, One Carbon, Glycine) and Glutamine pathways, as well as genes involved in the biosynthesis of polyamines and purines. Specific cancer-driving nodes are generally under NF-Y control. Altogether, these data delineate a coherent strategy to promote expression of metabolic genes fuelling anaerobic energy production and other anabolic pathways commonly altered in cancer cells.