Intracellular Released Payload Influences Potency and Bystander-Killing Effects of Antibody-Drug Conjugates in Preclinical Models

CD30 expression and survival in extranodal NK/T-cell lymphoma: a systematic review and meta-analysis

Background

The paradoxical reports about the prognostic value of the CD30 expression in extranodal NK/T-cell lymphoma (ENKTL) have restricted its further applications in clinical practice. To identify the common effects and the variation, we conducted this systematic review and meta-analysis.

Methods

PubMed, MEDLINE, Embase, and Web of Science were searched between January 1975 and 31 January 2017. The pooled hazard ratio was used to estimate the effect of the CD30 expression on overall survival. Bias was assessed by prespecified criteria referring to Reporting Recommendations for Tumor Marker Prognostic Studies and Newcastle-Ottawa Scale.

Results

Ten retrospective cohort studies with 310 patients are included. CD30 is associated with better overall survival significantly (HR 0.71, 95% CI 0.51 to 0.99, I² = 0%). A greater effect is observed among studies including participants predominant in regional involvement (HR 0.31, 95%CI 0.13 to 0.76, I² = 0%) compared with those in systemic involvement.

Conclusions

This study indicates that the CD30 expression is significantly associated with better prognosis in ENKTL, especially for patients with regional lymphoma involvement.

Current progress in innovative engineered antibodies

As of May 1, 2017, 74 antibody-based molecules have been approved by a regulatory authority in a major market. Additionally, there are 70 and 575 antibody-based molecules in phase III and phase I/II clinical trials, respectively. These total 719 antibody-based clinical stage molecules include 493 naked IgGs, 87 antibody-drug conjugates, 61 bispecific antibodies, 37 total Fc fusion proteins, 17 radioimmunoglobulins, 13 antibody fragments, and 11 immunocytokines. New uses for these antibodies are being discovered each year. For oncology, many of the exciting new approaches involve antibody modulation of T-cells. There are over 80 antibodies in clinical trials targeting T cell checkpoints, 26 T-cell-redirected bispecific antibodies, and 145 chimeric antigen receptor (CAR) cell-based candidates (all currently in phase I or II clinical trials), totaling more than 250 T cell interacting clinical stage antibody-based candidates. Finally, significant progress has been made recently on routes of delivery, including delivery of proteins across the blood-brain barrier, oral delivery to the gut, delivery to the cellular cytosol, and gene- and viral-based delivery of antibodies. Thus, there are currently at least 864 antibody-based clinical stage molecules or cells, with incredible diversity in how they are constructed and what activities they impart. These are followed by a next wave of novel molecules, approaches, and new methods and routes of delivery, demonstrating that the field of antibody-based biologics is very innovative and diverse in its approaches to fulfill their promise to treat unmet medical needs.

CD30 on extracellular vesicles from malignant Hodgkin cells supports damaging of CD30 ligand-expressing bystander cells with Brentuximab-Vedotin, in vitro

The goal of targeted immunotherapy in cancer is to damage both malignant and tumor-supporting cells of the microenvironment but spare unaffected tissue. The malignant cells in classical Hodgkin lymphoma (cHL) selectively express CD30. They release this receptor on extracellular vesicles (EVs) for the tumor-supporting communication with CD30 ligand (CD30L)-positive bystander cells. Here, we investigated how CD30-positive EVs influence the efficacy of the CD30 antibody drug conjugate (ADC) Brentuximab Vedotin (SGN-35). The malignant cells and the EVs expressed the active sheddase ADAM10. ADAM10 cleaved and released the CD30 ectodomain (sCD30), causing a gradual depletion of SGN-35 binding sites on EVs and creating a soluble competitor of the ADC therapy. In a 3D semi-solid tumor microenvironment model, the EVs were retained in the matrix whereas sCD30 penetrated readily into the surrounding culture medium. This resulted in a lowered ratio of EV-associated CD30 (CD30EV) to sCD30 in the surrounding medium in comparison to non-embedded cultures. A low percentage of CD30EV was also detected in the plasma of cHL patients, supporting the clinical relevance of the model. The adherence of CD30EV but not sCD30 to CD30-/CD30L+ mast cells and eosinophils allowed the indirect binding of SGN-35. Moreover, SGN-35 damaged CD30-negative cells, provided they were loaded with CD30+ EVs.

Treatment of CD30-Expressing Germ Cell Tumors and Sex Cord Stromal Tumors with Brentuximab Vedotin: Identification and Report of Seven Cases

BACKGROUND

Cytotoxic therapy for relapsed and refractory germ cell tumors or metastatic sex cord stromal tumors is rarely effective and is often accompanied by high adverse event rates. Expression of CD30 has been observed in testicular cancers, and patients with CD30-expressing embryonal carcinomas have worse progression-free survival and overall survival than those with CD30-negative tumors. The objective of this study (NCT01461538) was to characterize the antitumor activity of brentuximab vedotin in patients with CD30-expressing nonlymphomatous malignancies. Enrolled patients included seven patients with relapsed or refractory germ cell tumors or metastatic sex cord stromal tumors described in this case series.

MATERIALS AND METHODS

Forty patients with relapsed or refractory germ cell tumors, metastatic sex cord stromal tumors, or testicular tumors were screened for CD30 expression; 14 patients had tumors that expressed CD30. Seven patients with CD30-expressing testicular cancer were enrolled in the treatment study: five patients with germ cell tumors, one patient with a Leydig cell tumor, and one patient with a Sertoli cell tumor. Patients were treated with brentuximab vedotin at initial doses of 1.8 or 2.4 mg/kg every 3 weeks. Response assessments were performed at cycles 2 and 4 and every 4 cycles thereafter while the patient was receiving treatment.

RESULTS

Two of seven patients achieved an objective response, including one durable complete response and one partial response at a single time point. Both responding patients had germ cell tumors. Treatment with brentuximab vedotin was generally well tolerated.

CONCLUSION

Treatment of relapsed or refractory germ cell tumors with brentuximab vedotin can induce durable responses with a manageable toxicity profile.

IMPLICATIONS FOR PRACTICE

This case series of seven patients with relapsed or refractory CD30-expressing germ cell tumors (GCTs) or sex cord stromal tumors demonstrates that brentuximab vedotin has activity against GCTs and is well tolerated in heavily pretreated patients with these aggressive tumor types. One patient achieved a complete response that has been durable for almost 4 years since the discontinuation of treatment with brentuximab vedotin. Therefore, brentuximab vedotin may be a valuable option for physicians who care for this difficult-to-treat patient population.

Improved Tumor Penetration and Single-Cell Targeting of Antibody-Drug Conjugates Increases Anticancer Efficacy and Host Survival

Current antibody-drug conjugates (ADC) have made advances in engineering the antibody, linker, conjugation site, small-molecule payload, and drug-to-antibody ratio (DAR). However, the relationship between heterogeneous intratumoral distribution and efficacy of ADCs is poorly understood. Here, we compared trastuzumab and ado-trastuzumab emtansine (T-DM1) to study the impact of ADC tumor distribution on efficacy. In a mouse xenograft model insensitive to trastuzumab, coadministration of trastuzumab with a fixed dose of T-DM1 at 3:1 and 8:1 ratios dramatically improved ADC tumor penetration and resulted in twice the improvement in median survival compared with T-DM1 alone. In this setting, the effective DAR was lowered, decreasing the amount of payload delivered to each targeted cell but increasing the number of cells that received payload. This result is counterintuitive because trastuzumab acts as an antagonist in vitro and has no single-agent efficacy in vivo, yet improves the effectiveness of T-DM1 in vivo Novel dual-channel fluorescence ratios quantified single-cell ADC uptake and metabolism and confirmed that the in vivo cellular dose of T-DM1 alone exceeded the minimum required for efficacy in this model. In addition, this technique characterized cellular pharmacokinetics with heterogeneous delivery after 1 day, degradation and payload release by 2 days, and in vitro cell killing and in vivo tumor shrinkage 2 to 3 days later. This work demonstrates that the intratumoral distribution of ADC, independent of payload dose or plasma clearance, plays a major role in ADC efficacy.Significance: This study shows how lowering the drug-to-antibody ratio during treatment can improve the intratumoral distribution of a antibody-drug conjugate, with implications for improving the efficacy of this class of cancer drugs. Cancer Res; 78(3); 758-68. ©2017 AACR.

Antibody drug conjugates and bystander killing: is antigen-dependent internalisation required?

Antibody drug conjugates (ADCs) employ the exquisite specificity of tumour-specific monoclonal antibodies (mAb) for the targeted delivery of highly potent cytotoxic drugs to the tumour site. The chemistry of the linker, which connects the drug to the mAb, determines how and when the drug is released from the mAb. This, as well as the chemistry of the drug, can dictate whether the drug can diffuse into surrounding cells, resulting in 'bystander killing'. Initially, any bystander killing mechanism of action of an ADC was understood to involve an essential sequence of steps beginning with surface antigen targeting, internalisation, intracellular linker cleavage, drug release, and diffusion of drug away from the targeted cell. However, recent studies indicate that, depending on the linker and drug combination, this mechanism may not be essential and ADCs can be cleaved extracellularly or via other mechanisms. In this minireview, we will examine the role of bystander killing by ADCs and explore the emerging evidence of how this can occur independently of internalisation.

Targeted Delivery of Auristatin-Modified Toxins to Pancreatic Cancer Using Aptamers

Pancreatic cancer is one of the most lethal malignancies. Treatment with the first-line agent, gemcitabine, is often unsuccessful because it, like other traditional chemotherapeutic agents, is non-specific, resulting in off-target effects that necessitate administration of subcurative doses. Alternatively, monomethyl auristatin E (MMAE) and monomethyl auristatin F (MMAF) are highly toxic small molecules that require ligand-targeted delivery. MMAE has already received FDA approval as a component of an anti-CD30 antibody-drug conjugate, brentuximab vedotin. However, in contrast to antibodies, aptamers have distinct advantages. They are chemicals, which allows them to be produced synthetically and facilitates the rapid development of diagnostics and therapeutics with clinical applicability. In addition, their small size allows for enhanced tissue distribution and rapid systemic clearance. Here, we assayed the toxicity of MMAE and MMAF conjugated to an anti-transferrin receptor aptamer, Waz, and an anti-epidermal growth factor receptor aptamer, E07, on the pancreatic cancer cell lines Panc-1, MIA PaCa-2, and BxPC3. In vitro, our results indicate that these aptamers are a viable option for the targeted delivery of toxic payloads to pancreatic cancer cells.

Therapeutic potential of SGN-CD19B, a PBD-based anti-CD19 drug conjugate, for treatment of B-cell malignancies

Patients with relapsed/refractory B-cell malignancies such as non-Hodgkin lymphoma (B-NHL) or acute lymphoblastic leukemia have a poor prognosis. Despite measurable clinical activity with new targeted therapies, many patients do not achieve a complete or durable response suggesting an opportunity to improve upon existing therapies. Here we describe SGN-CD19B, a pyrrolobenzodiazepine (PBD)-based anti-CD19 antibody drug conjugate (ADC) being investigated for treatment of B-cell malignancies, which has improved potency compared with other ADCs. CD19-expressing tumor cells rapidly internalize SGN-CD19B, and the released PBD drug induces DNA damage, resulting in G2/M cell cycle arrest and cell death. SGN-CD19B demonstrated activity against a broad panel of malignant B-cell lines and induced durable regressions in mice bearing xenografts derived from these B-cell malignancies. A single dose of SGN-CD19B induced durable regressions at 300 μg/kg (3 μg/kg drug equivalents); combination with rituximab decreased the curative dose to 100 μg/kg (1 μg/kg drug equivalents). These doses are significantly lower than the level of drug required with other ADC payloads. In cynomolgus monkeys, SGN-CD19B effectively depleted CD20+ B lymphocytes in peripheral blood and lymphoid tissues confirming that SGN-CD19B is pharmacodynamically active at well-tolerated doses. In summary, preclinical studies show SGN-CD19B is a highly active ADC, which releases a DNA cross-linking agent rather than a microtubule inhibitor. The distinct mechanism of action, broad potency, and potential to combine with rituximab suggest that SGN-CD19B may offer unique clinical opportunities in B-cell malignancies. A phase 1 clinical trial is in progress to investigate the therapeutic potential of SGN-CD19B in relapsed/refractory B-NHL. This trial was registered at www.clinicaltrials.gov as #NCT02702141.

Brentuximab vedotin exerts profound antiproliferative and pro-apoptotic efficacy in CD30-positive as well as cocultured CD30-negative germ cell tumour cell lines

Prognosis in patients suffering from high‐risk, refractory and relapsed germ cell tumours (GCT) often comprising of CD30‐positive embryonal carcinoma (EC) components remains poor. Thus, novel treatment strategies are warranted. The antibody‐drug conjugate (ADC) brentuximab vedotin delivers the potent antimitotic drug monomethyl auristatin E (MMAE) to CD30‐expressing tumour cells. After CD30 binding, internalization and intracellular linker cleavage cytotoxic MMAE can efflux and eradicate neighbouring CD30‐negative cells. To analyse cytotoxicity and a potential bystander effect of brentuximab vedotin in GCT, we established an in vitro coculture model mimicking GCT of heterogeneous CD30 positivity and measured cell viability, proliferation and apoptosis after exposure to brentuximab vedotin and unbound MMAE by MTS‐ and flow cytometry‐based CFSE/Hoechst assay. CD30 expression being assessed by quantitative RT‐PCR and immunohistochemistry was apparent in all EC cell lines with different intensity. Brentuximab vedotin abrogates cell viability of CD30‐positive GCT27 EC line exerting marked time‐dependent antiproliferative and pro‐apoptotic activity. CD30‐negative JAR cultured alone barely responds to brentuximab vedotin, while in coculture with GCT27 brentuximab vedotin induces clear dose‐dependent cytotoxicity. Cellular proliferation and cell death are significantly enhanced in CD30‐negative JAR cocultured with CD30‐positive GCT27 compared to JAR cultured alone in proof of substantial bystander activity of brentuximab vedotin in CD30‐negative GCT. We present first evidence that in an in vitro model mimicking GCT of heterogeneous histology, brentuximab vedotin exerts potent antiproliferative and pro‐apoptotic activity against both CD30‐positive as well as CD30‐negative GCT subsets. Our results strongly support translational efforts to evaluate clinical efficacy of brentuximab vedotin in high‐risk GCT of heterogeneous CD30 positivity.

A non-internalizing antibody-drug conjugate based on an anthracycline payload displays potent therapeutic activity in vivo

Antibody-drug conjugates are generally believed to crucially rely on internalization into cancer cells for therapeutic activity. Here, we show that a non-internalizing antibody-drug conjugate, based on the F16 antibody specific to the alternatively spliced A1 domain of tenascin-C, mediates a potent therapeutic activity when equipped with the anthracycline PNU159682. The peptide linker, connecting the F16 antibody in IgG format at a specific cysteine residue to the drug, was stable in serum but could be efficiently cleaved in the subendothelial extracellular matrix by proteases released by the dying tumor cells. The results indicate that there may be a broader potential applicability of non-internalizing antibody-drug conjugates for cancer therapy than what had previously been assumed.

Featured Article: Delivery of chemotherapeutic vcMMAE using tobacco mosaic virus nanoparticles

The first-line treatment for non-Hodgkin's lymphoma is chemotherapy. While generally well tolerated, off-target effects and chemotherapy-associated complications are still of concern. To overcome the challenges associated with systemic chemotherapy, we developed a biology-inspired, nanoparticle drug delivery system (nanoDDS) making use of the nucleoprotein components of the tobacco mosaic virus (TMV). Virus-based nanoparticles, including the high-aspect ratio soft nanorods formed by TMV, are growing in popularity as nanoDDS due to their simple genetic and chemical engineerability, size and shape tunability, and biocompatibility. In this study, we used bioconjugation to modify TMV as a multivalent carrier for delivery of the antimitotic drug valine-citrulline monomethyl auristatin E (vcMMAE) targeting non-Hodgkin's lymphoma. We demonstrate successful synthesis of the TMV-vcMMAE; data indicate that the TMV-vcMMAE particles remained structurally sound with all of the 2130 identical TMV coat proteins modified to carry the therapeutic payload vcMMAE. Cell uptake using Karpas 299 cells was confirmed with TMV particles trafficking to the endolysosomal compartment, likely allowing for protease-mediated cleavage of the valine-citrulline linker for the release of the active monomethyl auristatin E component. Indeed, effective cell killing of non-Hodgkin's lymphoma in vitro was demonstrated; TMV-vcMMAE was shown to exhibit an IC50 of ∼250 nM. This study contributes to the development of viral nanoDDS. Impact statement Due to side effects associated with systemic chemotherapy, there is an urgent need for the development of novel drug delivery systems. We focus on the high-aspect ratio nanotubes formed by tobacco mosaic virus (TMV) to deliver antimitotic drugs targeted to non-Hodgkin's lymphoma. Many synthetic and biologic nanocarriers are in the development pipeline; the majority of systems are spherical in shape. This may not be optimal, because high-aspect ratio filaments exhibit enhanced tumor homing, increased target cell interactions and decreased immune cell uptake, and therefore have favorable properties for drug delivery compared to their spherical counterparts. Nevertheless, the synthesis of high-aspect ratio materials at the nanoscale remains challenging; therefore, we turned toward the nucleoprotein components of TMV as a biologic nanodrug delivery system. This work presents groundwork for the development of plant virus-based vehicles for use in cancer treatment.

Protease-Cleavable Linkers Modulate the Anticancer Activity of Noninternalizing Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) represent an attractive class of biopharmaceutical agents, with the potential to selectively deliver potent cytotoxic agents to tumors. It is generally assumed that ADC products should preferably bind and internalize into cancer cells in order to liberate their toxic payload, but a growing body of evidence indicates that also ADCs based on noninternalizing antibodies may be potently active. In this Communication, we investigated dipeptide-based linkers (frequently used for internalizing ADC products) in the context of the noninternalizing F16 antibody, specific to a splice isoform of tenascin-C. Using monomethyl auristatin E (MMAE) as potent cytotoxic drug, we observed that a single amino acid substitution of the Val-Cit dipeptide linker can substantially modulate the in vivo stability of the corresponding ADC products, as well as the anticancer activity in mice bearing the human epidermoid A431 carcinoma. In these settings, the linker based on the Val-Ala dipeptide exhibited better performances, compared to Val-Cit, Val-Lys, and Val-Arg analogues. Mass spectrometric analysis revealed that the four linkers displayed not only different stability in vivo but also differences in cleavage sites. Moreover, the absence of anticancer activity for a F16-MMAE conjugate featuring a noncleavable linker indicated that drug release modalities, based on proteolytic degradation of the immunoglobulin moiety, cannot be exploited with noninternalizing antibodies. ADC products based on the noninternalizing F16 antibody may be useful for the treatment of several human malignancies, as the cognate antigen is abundantly expressed in the extracellular matrix of several tumors, while being virtually undetectable in most normal adult tissues.

Eradication of Tumors through Simultaneous Ablation of CD276/B7-H3-Positive Tumor Cells and Tumor Vasculature

Targeting the tumor vasculature with antibody-drug conjugates (ADCs) is a promising anti-cancer strategy that in order to be realized must overcome several obstacles, including identification of suitable targets and optimal warheads. Here, we demonstrate that the cell-surface protein CD276/B7-H3 is broadly overexpressed by multiple tumor types on both cancer cells and tumor-infiltrating blood vessels, making it a potentially ideal dual-compartment therapeutic target. In preclinical studies CD276 ADCs armed with a conventional MMAE warhead destroyed CD276-positive cancer cells, but were ineffective against tumor vasculature. In contrast, pyrrolobenzodiazepine-conjugated CD276 ADCs killed both cancer cells and tumor vasculature, eradicating large established tumors and metastases, and improving long-term overall survival. CD276-targeted dual-compartment ablation could aid in the development of highly selective broad-acting anti-cancer therapies.

Tumor-Associated Macrophages Can Contribute to Antitumor Activity through FcγR-Mediated Processing of Antibody-Drug Conjugates

The primary mechanism of antibody-drug conjugates (ADC) is targeted delivery of a cytotoxic payload to tumor cells via cancer-associated membrane receptors. However, the tumor microenvironment likely plays a role in ADC penetration, distribution, and processing and thus impacts the overall antitumor activity. Here, we report on the potential contribution of Fc-FcγR interactions between ADCs and tumor-associated macrophages (TAM) to the preclinical antitumor activities of ADCs. In the CD30⁺ L-428 Hodgkin lymphoma model, anti-CD30-vcMMAE and a non-binding control (hIgG-vcMMAE) demonstrated similar antitumor activity as well as similar payload release in the tumors. IHC analysis revealed L-428 tumors contained highly abundant TAMs, which were confirmed to bind ADCs by IHC and flow cytometry. The infiltration of TAMs was further found to correlate with the antitumor activity of the non-binding hIgG-vcMMAE in five additional xenograft models. hIgG1V1-vcMMAE, bearing a mutation in the Fc region which ablates Fc gamma receptor (FcγR) binding, lost antitumor activity in three TAM-high xenograft models, suggesting Fc-FcγR interactions modulate the TAM-ADC interaction. Our results suggest that TAMs can contribute to ADC processing through FcγR interaction in preclinical tumor models and may represent an important additional mechanism for drug release from ADCs. Correlative studies in clinical trials will further shed light on whether TAMs play a role in patients' response to ADC therapies. Mol Cancer Ther; 16(7); 1347-54. ©2017 AACR.

Trastuzumab emtansine versus taxane use for previously treated HER2-positive locally advanced or metastatic gastric or gastro-oesophageal junction adenocarcinoma (GATSBY): an international randomised, open-label, adaptive, phase 2/3 study

BACKGROUND

Although trastuzumab plus chemotherapy is the standard of care for first-line treatment of HER2-positive advanced gastric cancer, there is no established therapy in the second-line setting. In GATSBY, we examined the efficacy and tolerability of trastuzumab emtansine in patients previously treated for HER2-positive advanced gastric cancer (unresectable, locally advanced, or metastatic gastric cancer, including adenocarcinoma of the gastro-oesophageal junction).

METHODS

This is the final analysis from GATSBY, a randomised, open-label, adaptive, phase 2/3 study, done at 107 centres (28 countries worldwide). Eligible patients had HER2-positive advanced gastric cancer and progressed during or after first-line therapy. In stage one of the trial, patients were randomly assigned to treatment groups (2:2:1) to receive intravenous trastuzumab emtansine (3·6 mg/kg every 3 weeks or 2·4 mg/kg weekly) or physician's choice of a taxane (intravenous docetaxel 75 mg/m² every 3 weeks or intravenous paclitaxel 80 mg/m² weekly). In stage two, patients were randomly assigned to treatment groups (2:1) to receive the independent data monitoring committee (IDMC)-selected dose of trastuzumab emtansine (2·4 mg/kg weekly) or a taxane (same regimen as above). We used permuted block randomisation, stratified by world region, previous HER2-targeted therapy, and previous gastrectomy. The primary endpoint (overall survival) was assessed in the intention-to-treat population. This study is registered with ClinicalTrials.gov, number NCT01641939.

FINDINGS

Between Sept 3, 2012, and Oct 14, 2013, 70 patients were assigned to receive trastuzumab emtansine 3·6 mg/kg every 3 weeks, 75 to receive trastuzumab emtansine 2·4 mg/kg weekly, and 37 to receive a taxane in the stage 1 part of the trial. At the pre-planned interim analysis (Oct 14, 2013), the IDMC selected trastuzumab emtansine 2·4 mg/kg weekly as the dose to proceed to stage 2. By Feb 9, 2015, a further 153 patients had been randomly assigned to receive trastuzumab emtansine 2·4 mg/kg weekly and a further 80 to receive a taxane. At data cutoff, median follow-up was 17·5 months (IQR 12·1-23·0) for the trastuzumab emtansine 2·4 mg/kg weekly group and 15·4 months (9·2-18·1) in the taxane group. Median overall survival was 7·9 months (95% CI 6·7-9·5) with trastuzumab emtansine 2·4 mg/kg weekly and 8·6 months (7·1-11·2) with taxane treatment (hazard ratio 1·15, 95% CI 0·87-1·51, one-sided p=0·86). The trastuzumab emtansine 2·4 mg/kg group had lower incidences of grade 3 or more adverse events (134 [60%] of 224 patients treated with trastuzumab emtansine vs 78 [70%] of 111 patients treated with a taxane), and similar incidences of adverse events leading to death (eight [4%] vs four [4%]), serious adverse events (65 [29%] vs 31 [28%]), and adverse events leading to treatment discontinuation (31 [14%] vs 15 [14%]) than did taxane treatment. The most common grade 3 or more adverse events in the trastuzumab emtansine 2·4 mg/kg weekly group were anaemia (59 [26%]) and thrombocytopenia (25 [11%]) compared with neutropenia (43 [39%]), and anaemia (20 [18%]), in the taxane group. The most common serious adverse events were anaemia (eight [4%]), upper gastrointestinal haemorrhage (eight [4%]), pneumonia (seven [3%]), gastric haemorrhage (six [3%]), and gastrointestinal haemorrhage (five [2%]) in the trastuzumab emtansine 2·4 mg/kg weekly group compared with pneumonia (four [4%]), febrile neutropenia (four [4%]), anaemia (three [3%]), and neutropenia (three [3%]) in the taxane group.

INTERPRETATION

Trastuzumab emtansine was not superior to taxane in patients with previously treated, HER2-positive advanced gastric cancer. There is still an unmet need in this patient group and therapeutic options remain limited.

FUNDING

F Hoffmann-La Roche.

Novel anti-Sialyl-Tn monoclonal antibodies and antibody-drug conjugates demonstrate tumor specificity and anti-tumor activity

Targeted therapeutics that can differentiate between normal and malignant tumor cells represent the ideal standard for the development of a successful anti-cancer strategy. The Sialyl-Thomsen-nouveau antigen (STn or Sialyl-Tn, also known as CD175s) is rarely seen in normal adult tissues, but it is abundantly expressed in many types of human epithelial cancers. We have identified novel antibodies that specifically target with high affinity the STn glycan independent of its carrier protein, affording the potential to recognize a wider array of cancer-specific sialylated proteins. A panel of murine monoclonal anti-STn therapeutic antibodies were generated and their binding specificity and efficacy were characterized in vitro and in in vivo murine cancer models. A subset of these antibodies were conjugated to monomethyl auristatin E (MMAE) to generate antibody-drug conjugates (ADCs). These ADCs demonstrated in vitro efficacy in STn-expressing cell lines and significant tumor growth inhibition in STn-expressing tumor xenograft cancer models with no evidence of overt toxicity.

Marine Antibody-Drug Conjugates: Design Strategies and Research Progress

Antibody-drug conjugates (ADCs), constructed with monoclonal antibodies (mAbs), linkers, and natural cytotoxins, are innovative drugs developed for oncotherapy. Owing to the distinctive advantages of both chemotherapy drugs and antibody drugs, ADCs have obtained enormous success during the past several years. The development of highly specific antibodies, novel marine toxins' applications, and innovative linker technologies all accelerate the rapid R&D of ADCs. Meanwhile, some challenges remain to be solved for future ADCs. For instance, varieties of site-specific conjugation have been proposed for solving the inhomogeneity of DARs (Drug Antibody Ratios). In this review, the usages of various natural toxins, especially marine cytotoxins, and the development strategies for ADCs in the past decade are summarized. Representative ADCs with marine cytotoxins in the pipeline are introduced and characterized with their new features, while perspective comments for future ADCs are proposed.

From Anthramycin to Pyrrolobenzodiazepine (PBD)-Containing Antibody-Drug Conjugates (ADCs)

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a family of sequence-selective DNA minor-groove binding agents that form a covalent aminal bond between their C11-position and the C2-NH2 groups of guanine bases. The first example of a PBD monomer, the natural product anthramycin, was discovered in the 1960s, and the best known PBD dimer, SJG-136 (also known as SG2000, NSC 694501 or BN2629), was synthesized in the 1990s and has recently completed Phase II clinical trials in patients with leukaemia and ovarian cancer. More recently, PBD dimer analogues are being attached to tumor-targeting antibodies to create antibody-drug conjugates (ADCs), a number of which are now in clinical trials, with many others in pre-clinical development. This Review maps the development from anthramycin to the first PBD dimers, and then to PBD-containing ADCs, and explores both structure-activity relationships (SARs) and the biology of PBDs, and the strategies for their use as payloads for ADCs.

Orthogonal Cysteine Protection Enables Homogeneous Multi-Drug Antibody-Drug Conjugates

A strategy for the preparation of homogeneous antibody–drug conjugates (ADCs) containing multiple payloads has been developed. This approach utilizes sequential unmasking of cysteine residues with orthogonal protection to enable site‐specific conjugation of each drug. In addition, because the approach utilizes conjugation to native antibody cysteine residues, it is widely applicable and enables high drug loading for improved ADC potency. To highlight the benefits of ADC dual drug delivery, this strategy was applied to the preparation of ADCs containing two classes of auristatin drug‐linkers that have differing physiochemical properties and exert complementary anti‐cancer activities. Dual‐auristatin ADCs imparted activity in cell line and xenograft models that are refractory to ADCs comprised of the individual auristatin components. This work presents a facile method for construction of potent dual‐drug ADCs and demonstrates how delivery of multiple cytotoxic warheads can lead to improved ADC activities. Lastly, we anticipate that the conditions utilized herein for orthogonal cysteine unmasking are not restricted to ADCs and can be broadly utilized for site‐specific protein modification.

Mechanisms of Resistance to Antibody-Drug Conjugates

Drug resistance limits the effectiveness of cancer therapies. Despite attempts to develop curative anticancer treatments, tumors evolve evasive mechanisms limiting durable responses. Hence, diverse therapies are used to attack cancer, including cytotoxic and targeted agents. Antibody-drug conjugates (ADC) are biotherapeutics designed to deliver potent cytotoxins to cancer cells via tumor-specific antigens. Little is known about the clinical manifestations of drug resistance to this class of therapy; however, recent preclinical studies reveal potential mechanisms of resistance. Because ADCs are a combination of antibody and small molecule cytotoxin, multifactorial modes of resistance are emerging that are inherent to the structure and function of the ADC. Decreased cell-surface antigen reduces antibody binding, whereas elevated drug transporters such as MDR1 and MRP1 reduce effectiveness of the payload. Inherent to the uniqueness of the ADC, other novel resistance mechanisms are emerging, including altered antibody trafficking, ADC processing, and intracellular drug release. Most importantly, the modular nature of the ADC allows components to be switched and replaced, enabling development of second-generation ADCs that overcome acquired resistance. This review is intended to highlight recent progress in our understanding of ADC resistance, including approaches to create preclinical ADC-refractory models and to characterize their emerging mechanisms of resistance. Mol Cancer Ther; 15(12); 2825-34. ©2016 AACR.

Multiscale Modeling of Antibody-Drug Conjugates: Connecting Tissue and Cellular Distribution to Whole Animal Pharmacokinetics and Potential Implications for Efficacy

Antibody-drug conjugates exhibit complex pharmacokinetics due to their combination of macromolecular and small molecule properties. These issues range from systemic concerns, such as deconjugation of the small molecule drug during the long antibody circulation time or rapid clearance from nonspecific interactions, to local tumor tissue heterogeneity, cell bystander effects, and endosomal escape. Mathematical models can be used to study the impact of these processes on overall distribution in an efficient manner, and several types of models have been used to analyze varying aspects of antibody distribution including physiologically based pharmacokinetic (PBPK) models and tissue-level simulations. However, these processes are quantitative in nature and cannot be handled qualitatively in isolation. For example, free antibody from deconjugation of the small molecule will impact the distribution of conjugated antibodies within the tumor. To incorporate these effects into a unified framework, we have coupled the systemic and organ-level distribution of a PBPK model with the tissue-level detail of a distributed parameter tumor model. We used this mathematical model to analyze new experimental results on the distribution of the clinical antibody-drug conjugate Kadcyla in HER2-positive mouse xenografts. This model is able to capture the impact of the drug-antibody ratio (DAR) on tumor penetration, the net result of drug deconjugation, and the effect of using unconjugated antibody to drive ADC penetration deeper into the tumor tissue. This modeling approach will provide quantitative and mechanistic support to experimental studies trying to parse the impact of multiple mechanisms of action for these complex drugs.