Lipoplex mediated silencing of membrane regulators (CD46, CD55 and CD59) enhances complement-dependent anti-tumor activity of trastuzumab and pertuzumab

Complement in cancer: untangling an intricate relationship

In tumour immunology, complement has traditionally been considered as an adjunctive component that enhances the cytolytic effects of antibody-based immunotherapies, such as rituximab. Remarkably, research in the past decade has uncovered novel molecular mechanisms linking imbalanced complement activation in the tumour microenvironment with inflammation and suppression of antitumour immune responses. These findings have prompted new interest in manipulating the complement system for cancer therapy. This Review summarizes our current understanding of complement-mediated effector functions in the tumour microenvironment, focusing on how complement activation can act as a negative or positive regulator of tumorigenesis. It also offers insight into clinical aspects, including the feasibility of using complement biomarkers for cancer diagnosis and the use of complement inhibitors during cancer treatment.

Integrated MicroRNA-mRNA Analysis Reveals miR-204 Inhibits Cell Proliferation in Gastric Cancer by Targeting CKS1B, CXCL1 and GPRC5A

Gastric cancer (GC) is the second most frequent cause of cancer-related deaths worldwide. MicroRNAs are single-stranded RNA molecules of 21–23 nucleotides that regulate target gene expression through specific base-pairing interactions between miRNA and untranslated regions of targeted mRNAs. In this study, we generated a multistep approach for the integrated analysis of miRNA and mRNA expression. First, both miRNA and mRNA expression profiling datasets in gastric cancer from the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) identified 79 and 1042 differentially expressed miRNAs and mRNAs, respectively, in gastric cancer. Second, inverse correlations between miRNA and mRNA expression levels identified 3206 miRNA–mRNA pairs combined with 79 dysregulated miRNAs and their 774 target mRNAs predicted by three prediction tools, miRanda, PITA, and RNAhybrid. Additionally, miR-204, which was found to be down-regulated in gastric cancer, was ectopically over-expressed in the AGS gastric cancer cell line and all down-regulated targets were identified by RNA sequencing (RNA-seq) analysis. Over-expression of miR-204 reduced the gastric cancer cell proliferation and suppressed the expression of three targets which were validated by qRT-PCR and luciferase assays. For the first time, we identified that CKS1B, CXCL1, and GPRC5A are putative targets of miR-204 and elucidated that miR-204 acted as potential tumor suppressor and, therefore, are useful as a promising therapeutic target for gastric cancer.

Predicting the Efficacy of HER2-Targeted Therapies: A Look at the Host

HER2 is overexpressed in 20% of invasive breast cancers (BCs) and correlates with a more aggressive disease. Until the advent of targeted agents, HER2 was associated with worse outcomes. Rationally designed HER2-targeted agents have been developed and introduced into clinical practice for women with HER2-amplified BC, improving disease-free and overall survival for primary and metastatic tumors. Trastuzumab, a recombinant humanized anti-HER2 monoclonal antibody, combined with chemotherapy, remains the standard of care for patients with HER2-positive BCs. However, many patients do not respond to this agent, whereas newer drugs have proven to be efficacious in clinical trials. The identification of biomarkers that select sensitive tumors and patients who will benefit from these new agents would help the incorporation of these therapies, limiting the risk of side effects and overtreatment and improving the outcomes of all patients with early-stage HER2-positive BC. We review the mechanisms of action of HER2-targeting agents, focusing on the involvement of the immune system and related predictive biomarkers.

CD55 and CD59 expression protects HER2-overexpressing breast cancer cells from trastuzumab-induced complement-dependent cytotoxicity

A large proportion (40-60%) of patients with human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancer do not benefit from trastuzumab treatment, potentially due to the lack of complement-dependent cytotoxicity (CDC) activation. In the present study, the effect of complement decay-accelerating factor (CD55) and CD59 glycoprotein precursor (CD59) expression on trastuzumab-induced CDC in HER2-positive breast cancer cell lines was investigated. The CD55 and CD59-overexpressing and HER2-positive cell lines SK-BR-3 and BT474 were selected for subsequent experiments. Blocking CD55 and CD59 function using targeting monoclonal antibodies significantly enhanced the cell lysis of SK-BR-3 and BT474 cells following treatment with trastuzumab. In addition, following treatment with 0.1 U/ml phosphatidylinositol-specific phospholipase C (PI-PLC) for 1 h, CD55 and CD59 surface expression was significantly decreased, and the cell lysis rate was further enhanced. Treatment of SK-BR-3 cells with short hairpin RNA (shRNA) targeting CD55 and CD59 downregulated CD55 and CD59 expression at the mRNA and protein levels, and resulted in significantly enhanced trastuzumab-induced CDC-dependent lysis. The data from the present study suggested that CD55 and CD59 serve roles in blocking trastuzumab-induced CDC, therefore strategies targeting CD55 and CD59 may overcome breast cancer cell resistance to trastuzumab. The results from the present study may provide a basis for developing suitable, personalized treatment strategies to improve the clinical efficacy of trastuzumab for patients with HER2-positive breast cancer.

A high-performance, non-radioactive potency assay for measuring cytotoxicity: A full substitute of the chromium-release assay targeting the regulatory-compliance objective

Standardized and biologically relevant potency assays are required by the regulatory authorities for the characterization and quality control of therapeutic antibodies. As critical mechanisms of action (MoA) of antibodies, the antibody-dependent cell-meditated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) must be characterized by appropriate potency assays. The current reference method for measuring cytotoxicity is the ⁵¹Cr-release method. However, radioactivity handling is difficult to implement in an industrial context because of environmental and operator protection constraints. Alternative non-radioactive methods suffer from poor validation performances and surrogate assays that measure FcγR-dependent functions do not comply with the regulatory requirement of biological relevance. Starting from these observations, we developed a non-radioactive luminescent method that is specific for target cell cytolysis. In adherent and non-adherent target cell models, the ADCC (using standardized effector cells) or CDC activities of rituximab, trastuzumab and adalimumab were compared in parallel using the ⁵¹Cr or luminescent methods. We demonstrated that the latter method is highly sensitive, with validation performances similar or better than the ⁵¹Cr method. This method also detected apoptosis following induction by a chemical agent or exposure to ultraviolet light. Moreover, it is more accurate, precise and specific than the concurrent non-radioactive calcein- and TR-FRET-based methods. The method is easy to use, versatile, standardized, biologically relevant and cost effective for measuring cytotoxicity. It is an ideal candidate for developing regulatory-compliant cytotoxicity assays for the characterization of the ADCC, CDC or apoptosis activities from the early stages of development to lot release.

Immuno-pharmacodynamics for evaluating mechanism of action and developing immunotherapy combinations

Immunotherapy has become a major modality of cancer treatment, with multiple new classes of immunotherapeutics recently entering the clinic and obtaining market approval from regulatory agencies. While the promise of these therapies is great, so is the number of possible combinations not only with each other but also with small molecule therapeutics. Furthermore, the observation of unusual dose-response relationships suggests a critical dependency of drug effectiveness on the dosage regimen (dose and schedule). Clinical pharmacodynamic (PD) biomarkers will be useful endpoints for confirming drug mechanism of action, evaluating combination therapies for synergy or antagonism, and identifying optimal dosage regimens. In contrast to conventional PD in which drug action occurs entirely within a single target cell (ie, is self-contained within the malignant cell), immunotherapy involves a complex mechanism of action with sequential steps that propagate through multiple cell types, both normal and malignant. Its intercellular pharmacology begins with molecular target engagement either on an immune effector cell or a malignant cell, followed by stimulatory biochemical and biological signals in immune effector cells, and then finally ends with activation of cell death mechanisms in malignant cells lying within a certain distance from the activated effector cells (immune cell-tumor cell proximity). Evaluating such "trans-cellular pharmacology," in which different steps of drug action are distributed across multiple cell types, requires novel microscopy and image analysis tools capable of quantifying PD-biomarker responses, mapping the responses onto the cellular geography of the tumor using phenotypic biomarkers to identify specific cell types, and finally analyzing the spatial relationships between biomarkers in the context of each cell's biological role. We have termed this form of nearest neighbor image analysis of drug action "proximity PD microscopy," to indicate the importance of the location of the PD-biomarker response within the cellular landscape of a tumor specimen. We discuss herein the major modes of immunotherapy, and lay out a blueprint for using PD assessment to optimize dosage regimens of single agents and guide development of combination immunotherapy regimens, using PD1/PD-L1 immune checkpoint inhibition as a case study.

Cytotoxic mechanisms of immunotherapy: Harnessing complement in the action of anti-tumor monoclonal antibodies

Several mAbs that have been approved for the treatment of cancer make use of complement-dependent cytotoxicity (CDC) to eliminate tumor cells. Comprehensive investigations, based on in vitro studies, mouse models and analyses of patient blood samples after mAb treatment have provided key insights into the details of individual steps in the CDC reaction. Based on the lessons learned from these studies, new and innovative approaches are now being developed to increase the clinical efficacy of next generation mAbs with respect to CDC. These improvements include engineering changes in the mAbs to enhance their ability to activate complement. In addition, mAb dosing paradigms are being developed that take into account the capacity as well as the limitations of the complement system to eliminate a substantial burden of mAb-opsonized cells. Over the next few years it is likely these approaches will lead to mAbs that are far more effective in the treatment of cancer.

Cytotoxic activity against human neuroblastoma and melanoma cells mediated by IgM antibodies derived from peripheral blood of healthy donors

A small percentage of healthy donors identified in the Western population carry antibodies in their peripheral blood which convey cytotoxic activity against certain human melanoma and neuroblastoma cell lines. We measured the cytotoxic activity of sera and plasmas from healthy donors on the human neuroblastoma cell line Kelly and various melanoma cell lines. Antibodies of IgM isotype, presumably belonging to the class of naturally occurring antibodies, exerted cytotoxic activity in a complement-dependent fashion. Apart from complement-dependent tumor cell lysis, we observed C3 opsonization in all tumor cell lines upon treatment with cytotoxic plasmas. Cell lines tested primarily expressed membrane complement regulatory proteins (mCRP) CD46, CD55 and CD59 to various extents. Blocking of mCRPs by monoclonal antibodies enhanced cell lysis and opsonization, though some melanoma cells remained resistant to complement attack. Epitopes recognized by cytotoxic antibodies were represented by gangliosides such as GD2 and GD3, as evidenced by cellular sialidase pretreatment and enhanced expression of distinct gangliosides. It remains to be clarified why only a small fraction of healthy persons carry these antitumor cytotoxic antibodies.

The complement system in cancer: Ambivalence between tumour destruction and promotion

Constituting a part of the innate immune system, the complement system consists of over 50 proteins either acting as part of a 3-branch activation cascade, a well-differentiated regulatory system in fluid phase or on each tissue, or as receptors translating the activation signal to multiple cellular effector functions. Complement serves as first line of defence against infections from bacteria, viruses and parasites by orchestrating the immune response through opsonisation, recruitment of immune cells to the site of infection and direct cell lysis. Complement is generally recognised as a protective mechanism against the formation of tumours in humans, but is often limited by various resistance mechanisms interfering with its cytotoxic action, now considered as a great barrier of successful antibody-based immunotherapy. However, recent studies also indicate a pro-tumourigenic potential of complement in certain cancers and under certain conditions. In this review, we present recent findings on the possible dual role of complement in destroying cancer, especially if resistance mechanisms are blocked, but also under certain inflammatory conditions-promoting tumour development.

The immunohistochemical analysis of membrane-bound CD55, CD59 and fluid-phase FH and FH-like complement inhibitors in cancers of ovary and corpus uteri origin

One of the potential therapeutic methods of cancer treatment is the immunotherapy with monoclonal antibodies. This kind of therapy, although devoid of serious side effects, has often insufficient efficacy. The presence of complement inhibitors on the cancer cells, which are able to inactivate complement-mediated immune response represents one of the main reasons for the inefficiency of such therapy. In our studies we investigated the expression of main membrane–bound and fluid-phase complement regulators: CD55, CD59 and factor H/factor H-like in tumour samples of ovarian and corpus uteri cancer. Tissue samples were collected from 50 patients and stained immunohistochemically, with the use of peroxidase-based immunodetection system. Immunohistochemical analysis revealed that complement inhibitors are present in examined tumors although their presence is heterogenous. The most prevalent is the presence of factor H/H-like, localized mostly in tumor stroma and within vascular structures. Membrane bound complement inhibitors are less prominently expressed by cancer cells. CD55 was detected in low percentage of cells, predominantly within cancer tubules. CD59 immunoreactivity was more prevalent in cancer cells, and was localized particularly at the margin of cancer cell tubules. Our results demonstrate that the most prominent complement inhibitor in cancer of ovary and corpus uteri origin is factor H/factor H-like. Blocking or downregulation of this inhibitor should be taken into consideration with regards to improving the efficiency of immunotherapy with monoclonal antibodies.

CD55, CD59, factor H and factor H-like 1 gene expression analysis in tumors of the ovary and corpus uteri origin

The expression level of complement regulators in ovarian and corpus uteri tumors was not fully established so far. In current manuscript we performed gene expression analysis by the real-time PCR approach to investigate both membrane bound - CD55 and CD59 and fluid phase - factor H and factor H-like 1 complement regulators. We found increased CD55 expression in corpus uteri tumors when compared to control tissues, whereas in ovarian cancer CD55 expression was lower than in control sections. Additionally we found CD59 expression to be more prominent in ovarian cancer than in corpus uteri tumor samples. We observed also the strong positive correlation between the level of expression of the whole group of regulators, which was particularly significant between the expression of factor H and factor H- like 1. In conclusion we present novel results which implicates different role of particular complement inhibitors in the regulation of the complement system in two cancer types examined. Strong positive correlation between examined proteins implicates similar pattern of the regulation which should be taken into consideration with regards to the possible immunotherapy applied as adjuvant therapeutic approach in these two indications. The inhibition of complement regulation may serve as a strategy to potentiate the efficacy of such treatment.

Complement receptor 1 genetic variants contribute to the susceptibility to gastric cancer in chinese population

As the receptor for C3b/C4b, type 1 complement receptor (CR1/CD35) plays an important role in the regulation of complement activity and is further involved in carcinogenesis. This study aimed to elucidate the association of CR1 genetic variants with the susceptibility to gastric cancer in Chinese population. Based on the NCBI database, totally 13 tag single nucleotide polymorphisms (SNPs) were selected by Haploview program and genotyped using iPlex Gold Genotyping Assay and Sequenom MassArray among 500 gastric cancer cases and 500 healthy controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression to evaluate the association of each SNP with gastric cancer. Of all selected Tag SNPs , CR1 rs9429942 T > C was found to confer to the risk of developing gastric cancer. Compared with the carriers with rs9429942 TT genotype, those with CT genotype had 88% decreased risk of developing gastric cancer with OR (95%CI) of 0.12 (0.03-0.50). Generalized multifactor dimensionality reduction (GMDR) analysis revealed a significant three-way interaction among rs75422544 C > A, rs10494885 C > T and rs7525160 G > C in the development of gastric cancer with a maximum testing balance accuracy of 56.07% and a cross-validation consistency of 7/10 (P = 0.011). In conclusion, our findings demonstrated the genetic role of CR1 gene in the development of gastric cancer in Chinese population.

Complement in monoclonal antibody therapy of cancer

Monoclonal antibodies (mAb) have been used as targeted treatments against cancer for more than a decade, with mixed results. Research is needed to understand mAb mechanisms of action with the goal of improving the efficacy of currently used mAbs and guiding the design of novel mAbs. While some mAb-induced tumor cell killing is a result of direct effects on tumor cell signaling, mAb opsonization of tumor cells also triggers activation of immune responses due to complement activation and engagement of antibody receptors on immune effector cells. In fact, complement has been shown to play an important role in modulating the anti-tumor activity of many mAb through complement-dependent cytotoxicity, antibody-dependent cytotoxicity, and through indirect effects by modulating the tumor microenvironment. Complement activity can have both agonistic and antagonistic effects on these processes. How the balance of such effects impacts on the clinical efficacy of mAb therapy remains unclear. In this review, we discuss the mAbs currently approved for cancer treatment and examine how complement can impact their efficacy with a focus on how this information might be used to improve the clinical efficacy of mAb treatment.

Neutralization of membrane complement regulators improves complement-dependent effector functions of therapeutic anticancer antibodies targeting leukemic cells

Complement-dependent cytotoxicity (CDC) is one of the effector mechanisms mediated by therapeutic anticancer monoclonal antibodies (mAbs). However, the efficacy of antibodies is limited by the resistance of malignant cells to complement attack, primarily due to the over-expression of one or more membrane complement regulatory proteins (mCRPs) CD46, CD55, and CD59. CD20-positive Burkitt lymphoma Raji cells and primary CLL cells are resistant to rituximab (RTX)-induced CDC whereas ofatumumab (OFA) proved to be more efficient in cell killing. Primary CLL cells but not CD52-positive acute lymphoblastic leukemia (ALL) REH cells were sensitive to alemtuzumab (ALM)-induced CDC. Upon combined inhibition on Raji and CLL cells by mCRPs-specific siRNAs or neutralizing antibodies, CDC induced by RTX and by OFA was augmented. Similarly, CDC of REH cells was enhanced after mCRPs were inhibited upon treatment with ALM. All mAbs induced C3 opsonization, which was significantly augmented upon blocking mCRPs. C3 opsonization led to enhanced cell-mediated cytotoxicity of leukemia cells exposed to PBLs or macrophages. Furthermore, opsonized CLL cells were efficiently phagocytized by macrophages. Our results provide conclusive evidence that inhibition of mCRPs expression sensitizes leukemic cells to complement attack thereby enhancing the therapeutic effect of mAbs targeting leukemic cells.

Regulation of complement and modulation of its activity in monoclonal antibody therapy of cancer

The complement system is a powerful tool of the innate immune system to eradicate pathogens. Both in vitro and in vivo evidence indicates that therapeutic anti-tumor monoclonal antibodies (mAbs) can activate the complement system by the classical pathway. However, the contribution of complement to the efficacy of mAbs is still debated, mainly due to the lack of convincing data in patients. A beneficial role for complement during mAb therapy is supported by the fact that cancer cells often upregulate complement-regulatory proteins (CRPs). Polymorphisms in various CRPs were previously associated with complement-mediated disorders.

In this review the role of complement in anti-tumor mAb therapy will be discussed with special emphasis on strategies aiming at modifying complement activity. In the future, clinical efficacy of mAbs with enhanced effector functions together with comprehensive analysis of polymorphisms in CRPs in mAb-treated patients will further clarify the role of complement in mAb therapy.

Where does radioimmunotherapy fit in the management of breast cancer?

Breast cancer is one of the most commonly diagnosed malignancies and is the main cause of death in women aged 40-49 years. Metastatic breast cancer is a heterogeneous disease that has a variety of different clinical presentations, ranging from solitary metastatic lesion to diffuse and multiple organ involvement. The biological heterogeneity of metastatic breast cancer has led to its unpredictable clinical behavior. One of the major challenges, therefore, is to identify predictive and prognostic models facilitating the selection of patients who can benefit from more aggressive and potentially curative options. This article provides an overview of the current management of metastatic breast cancer with focused emphasis on radioimmunotherapy.

Ablation of nectin4 binding compromises CD46 usage by a hybrid vesicular stomatitis virus/measles virus

Measles virus (MV) immunosuppression is due to infection of SLAM-positive immune cells, whereas respiratory shedding and virus transmission are due to infection of nectin4-positive airway epithelial cells. The vaccine lineage MV strain Edmonston (MV-Edm) acquired an additional tropism for CD46 which is the basis of its oncolytic specificity. VSVFH is a vesicular stomatitis virus (VSV) encoding the MV-Edm F and H entry proteins in place of G. The virus spreads faster than MV-Edm and is highly fusogenic and a potent oncolytic. To determine whether ablating nectin4 tropism from VSVFH might prevent shedding, increasing its safety profile as an oncolytic, or might have any effect on CD46 binding, we generated VSVFH viruses with H mutations that disrupt attachment to SLAM and/or nectin4. Disruption of nectin4 binding reduced release of VSVFH from the basolateral side of differentiated airway epithelia composed of Calu-3 cells. However, because nectin4 and CD46 have substantially overlapping receptor binding surfaces on H, disruption of nectin4 binding compromised CD46 binding and greatly diminished the oncolytic potency of these viruses on human cancer cells. Thus, our results support continued preclinical development of VSVFH without ablation of nectin4 binding.

Trastuzumab mediates antibody-dependent cell-mediated cytotoxicity and phagocytosis to the same extent in both adjuvant and metastatic HER2/neu breast cancer patients

Background

Monoclonal antibodies (mAb), such as trastuzumab are a valuable addition to breast cancer therapy. Data obtained from neoadjuvant settings revealed that antibody-dependent cell-mediated cytotoxicity (ADCC) is a major mechanism of action for the mAb trastuzumab. Conflicting results still call into question whether disease progression, prolonged treatment or concomitant chemotherapy influences ADCC and related immunological phenomena.

Methods

We analyzed the activity of ADCC and antibody-dependent cell-mediated phagocytosis (ADCP) of peripheral blood mononuclear cells (PBMCs) from human epidermal growth factor receptor 2 (HER2/neu) positive breast cancer patients receiving trastuzumab therapy either in an adjuvant (n = 13) or metastatic (n = 15) setting as well as from trastuzumab treatment-naive (t-naive) HER2/neu negative patients (n = 15). PBMCs from healthy volunteers (n = 24) were used as controls. ADCC and ADCP activity was correlated with the expression of antibody binding Fc-gamma receptor (FcγR)I (CD64), FcγRII (CD32) and FcγRIII (CD16) on CD14+ (monocytes) and CD56+ (NK) cells, as well as the expression of CD107a+ (LAMP-1) on CD56+ cells and the total amount of CD4+CD25+FOXP3+ (T_reg) cells. In metastatic patients, markers were correlated with progression-free survival (PFS).

Results

ADCC activity was significantly down regulated in metastatic, adjuvant and t-naive patient cohorts as compared to healthy controls. Reduced ADCC activity was inversely correlated with the expression of CD107a on CD56+ cells in adjuvant patients. ADCC and ADCP activity of the patient cohorts were similar, regardless of treatment duration or additional chemotherapy. PFS in metastatic patients inversely correlated with the number of peripheral T_reg cells.

Conclusion

The reduction of ADCC in patients as compared to healthy controls calls for adjuvant strategies, such as immune-enhancing agents, to improve the activity of trastuzumab. However, efficacy of trastuzumab-specific ADCC and ADCP appears not to be affected by treatment duration, disease progression or concomitant chemotherapy. This finding supports the application of trastuzumab at any stage of the disease.

Rebmab200, a humanized monoclonal antibody targeting the sodium phosphate transporter NaPi2b displays strong immune mediated cytotoxicity against cancer: a novel reagent for targeted antibody therapy of cancer

NaPi2b, a sodium-dependent phosphate transporter, is highly expressed in ovarian carcinomas and is recognized by the murine monoclonal antibody MX35. The antibody had shown excellent targeting to ovarian cancer in several early phase clinical trials but being murine the antibody's full therapeutic potential could not be explored. To overcome this impediment we developed a humanized antibody version named Rebmab200, expressed in human PER.C6® cells and cloned by limiting dilution. In order to select a clone with high therapeutic potential clones were characterized using a series of physicochemical assays, flow cytometry, real-time surface plasmon resonance, glycosylation analyses, immunohistochemistry, antibody-dependent cell-mediated cytotoxicity, complement-dependent-cytotoxicity assays and quantitative PCR. Comparative analyses of Rebmab200 and MX35 monoclonal antibodies demonstrated that the two antibodies had similar specificity for NaPi2b by flow cytometry with a panel of 30 cell lines and maintained similar kinetic parameters. Robust and high producer cell clones potentially suitable for use in manufacturing were obtained. Rebmab200 antibodies were assessed by immunohistochemistry using a large panel of tissues including human carcinomas of ovarian, lung, kidney and breast origin. An assessment of its binding towards 33 normal human organs was performed as well. Rebmab200 showed selected strong reactivity with the tested tumor types but little or no reactivity with the normal tissues tested confirming its potential for targeted therapeutics strategies. The remarkable cytotoxicity shown by Rebmab200 in OVCAR-3 cells is a significant addition to the traits of stability and productivity displayed by the top clones of Rebmab200. Antibody-dependent cell-mediated toxicity functionality was confirmed in repeated assays using cancer cell lines derived from ovary, kidney and lung as targets. To explore use of this antibody in clinical trials, GMP production of Rebmab200 has been initiated. As the next step of development, Phase I clinical trials are now planned for translation of Rebmab200 into the clinic.

The role of complement in mAb-based therapies of cancer

The ability of complement to promote lysis of antibody-opsonized cells is well-established. Virtually all of the molecular details of this reaction have been elucidated and numerous points of regulation have also been delineated. Use of this information, along with the techniques that were first applied in the fundamental studies of complement, has allowed for investigations of the role of complement in mAb-based immunotherapies of cancer. These studies, which have often combined in vitro investigations with parallel correlative clinical measurements, have revealed that several FDA-approved mAbs make use of complement as an effector function in promoting opsonization and killing of targeted malignant cells. We describe the key methods used in this work, and discuss how the results of these studies provide rational approaches for making more effective use of complement in mAb-based cancer immunotherapy.

Lipoplex mediated silencing of membrane regulators (CD46, CD55 and CD59) enhances complement-dependent anti-tumor activity of trastuzumab and pertuzumab

The therapeutic potential of anticancer antibodies is limited by the resistance of tumor cells to complement-mediated attack, primarily through the over-expression of membrane complement regulatory proteins (mCRPs: CD46, CD55 and CD59). Trastuzumab, an anti- HER2 monoclonal antibody, approved for the treatment of HER2-positive breast and gastric cancers, exerts only minor complement-mediated cytotoxicity (CDC). Pertuzumab is a novel anti-HER2 monoclonal antibody, which blocks HER2 dimerization with other ligand-activated HER family members. Here, we explored the complement-mediated anti-tumor effects of trastuzumab and pertuzumab on HER2-positive tumor cells of various histological origins. Delivery of chemically stabilized anti-mCRP siRNAs using cationic lipoplexes, AtuPLEXes, to HER2-over-expressing BT474, SK-BR-3 (breast), SKOV3 (ovarian) and Calu-3 (lung) cancer cells reduced mCRPs expression by 85-95%. Knockdown of individual complement regulators variably led to increased CDC only upon combined treatment with trastuzumab and pertuzumab. The combined down-regulation of all the three regulators augmented CDC by 48% in BT474, 46% in SK-BR-3 cells, 78% in SKOV3 cells and by 30% in Calu-3 cells and also increased complement-induced apoptosis and caspase activity on mCRP neutralized tumor cells. In addition, antibody-induced C3 opsonization of tumor cells was significantly enhanced after mCRP silencing and further augmented tumor cell killing by macrophages. Our findings suggest that siRNA-induced inhibition of complement regulator expression clearly enhances complement- and macrophage-mediated anti-tumor activity of trastuzumab and pertuzumab on HER2-positive tumor cells. Thus - if selectively targeted to the tumor - siRNA-induced inhibition of complement regulation may serve as an innovative strategy to potentiate the efficacy of antibody-based immunotherapy.