Promotion of an Antitumor Immune Program by a Tumor-specific, Complement-activating Antibody.

Tumor-targeting Abs can be used to initiate an antitumor immune program, which appears essential to achieve a long-term durable clinical response to cancer. We previously identified an anti-complement factor H (CFH) autoantibody associated with patients with early-stage non-small cell lung cancer. We cloned from their peripheral B cells an mAb, GT103, that specifically recognizes CFH on tumor cells. Although the underlying mechanisms are not well defined, GT103 targets a conformationally distinct CFH epitope that is created when CFH is associated with tumor cells, kills tumor cells in vitro, and has potent antitumor activity in vivo. In the effort to better understand how an Ab targeting a tumor epitope can promote an effective antitumor immune response, we used the syngeneic CMT167 lung tumor C57BL/6 mouse model, and we found that murinized GT103 (mGT103) activates complement and enhances antitumor immunity through multiple pathways. It creates a favorable tumor microenvironment by decreasing immunosuppressive regulatory T cells and myeloid-derived suppressor cells, enhances Ag-specific effector T cells, and has an additive antitumor effect with anti-PD-L1 mAb. Furthermore, the immune landscape of tumors from early-stage patients expressing the anti-CFH autoantibody is associated with an immunologically active tumor microenvironment. More broadly, our results using an mAb cloned from autoantibody-expressing B cells provides novel, to our knowledge, mechanistic insights into how a tumor-specific, complement-activating Ab can generate an immune program to kill tumor cells and inhibit tumor growth.

Complement factor H: a novel innate immune checkpoint in cancer immunotherapy.

The elimination of cancer cells critically depends on the immune system. However, cancers have evolved a variety of defense mechanisms to evade immune monitoring, leading to tumor progression. Complement factor H (CFH), predominately known for its function in inhibiting the alternative pathway of the complement system, has recently been identified as an important innate immunological checkpoint in cancer. CFH-mediated immunosuppression enhances tumor cells' ability to avoid immune recognition and produce an immunosuppressive tumor microenvironment. This review explores the molecular underpinnings, interactions with immune cells, clinical consequences, and therapeutic possibilities of CFH as an innate immune checkpoint in cancer control. The difficulties and opportunities of using CFH as a target in cancer immunotherapy are also explored.

Antitumor Immune Mechanisms of the Anti-Complement Factor H Antibody GT103.

Development of novel therapeutic antibodies that not only kill tumor cells but modulate the adaptive immune response has the potential to produce long term anticancer immunity and a durable clinical response. We previously reported the discovery of anti-complement factor H (CFH) autoantibodies in patients with lung cancer that were associated with early-stage disease and exceptional outcomes. The human mAb GT103, produced from a single CFH autoantibody-expressing B cell of a patient with lung cancer, recognizes a conformationally distinct epitope on tumor cells, kills tumor cells, and inhibits tumor growth in animal studies. Recent experiments have shown that GT103 restructures the tumor microenvironment and initiates a robust antitumoral adaptive immune response. The current study further elucidates several mechanisms by which GT103 kills tumor cells and drives the immune program. Here we show GT103 has specificity for tumor cells without binding to native soluble CFH or normal tissues. GT103 causes complement C3 split product deposition on tumor cells in vitro and in vivo, triggers antibody-dependent cellular phagocytosis, and increases translocation of the danger-associated molecular pattern molecule calreticulin to the plasma membrane. We also demonstrate that GT103 causes B-cell activation in vitro and in vivo, and that GT103 antitumor activity in vivo is B-cell dependent. The complex mechanism of GT103, a tumor-specific antibody that kills tumor cells and stimulates an immune response, supports further development of this human-derived antibody as a novel therapeutic option for patients with lung cancer.

Prognostic significance of a complement factor H autoantibody in early stage NSCLC.

BACKGROUND: Biomarkers that predict which patients with early stage NSCLC will develop recurrent disease would be of clinical value. We previously discovered that an autoantibody to a complement regulatory protein, complement factor H (CFH), is associated with early stage, non-recurrent NSCLC, and hypothesized that the anti-CFH antibody inhibits metastasis. OBJECTIVES: The primary objective of this study was to evaluate the anti-CFH antibody as a prognostic marker for recurrence in stage I NSCLC. A secondary objective was to determine if changes in antibody serum level one year after resection were associated with recurrence. METHODS: Anti-CFH antibody was measured in the sera of 157 stage I NSCLC patients designated as a prognostic cohort: 61% whose cancers did not recur, and 39% whose cancers recurred following resection. Impact of anti-CFH antibody positivity on time to recurrence was assessed using a competing risk analysis. Anti-CFH antibody levels were measured before resection and one year after resection in an independent temporal cohort of 47 antibody-positive stage I NSCLC patients: 60% whose cancers did not recur and 40% whose cancers recurred following resection. The non-recurrent and recurrent groups were compared with respect to the one-year percent change in antibody level. RESULTS: In the prognostic cohort, the 60-month cumulative incidence of recurrence was 40% and 22% among antibody negative and positive patients, respectively; this difference was significant (Gray's test, P= 0.0425). In the temporal cohort, the antibody persisted in the serum at one year post-tumor resection. The change in antibody levels over the one year period was not statistically different between the non-recurrent and recurrent groups (Wilcoxon two-sample test, P= 0.4670). CONCLUSIONS: The anti-CFH autoantibody may be a useful prognostic marker signifying non-recurrence in early stage NSCLC patients. However, change in the level of this antibody in antibody-positive patients one year after resection had no association with recurrence.

Upregulation of complement proteins in lung cancer cells mediates tumor progression.

Introduction: In vivo, cancer cells respond to signals from the tumor microenvironment resulting in changes in expression of proteins that promote tumor progression and suppress anti-tumor immunity. This study employed an orthotopic immunocompetent model of lung cancer to define pathways that are altered in cancer cells recovered from tumors compared to cells grown in culture. Methods: Studies used four murine cell lines implanted into the lungs of syngeneic mice. Cancer cells were recovered using FACS, and transcriptional changes compared to cells grown in culture were determined by RNA-seq. Results: Changes in interferon response, antigen presentation and cytokine signaling were observed in all tumors. In addition, we observed induction of the complement pathway. We previously demonstrated that activation of complement is critical for tumor progression in this model. Complement can play both a pro-tumorigenic role through production of anaphylatoxins, and an anti-tumorigenic role by promoting complement-mediated cell killing of cancer cells. While complement proteins are produced by the liver, expression of complement proteins by cancer cells has been described. Silencing cancer cell-specific C3 inhibited tumor growth In vivo. We hypothesized that induction of complement regulatory proteins was critical for blocking the anti-tumor effects of complement activation. Silencing complement regulatory proteins also inhibited tumor growth, with different regulatory proteins acting in a cell-specific manner. Discussion: Based on these data we propose that localized induction of complement in cancer cells is a common feature of lung tumors that promotes tumor progression, with induction of complement regulatory proteins protecting cells from complement mediated-cell killing.

Genetic Variants of CLPP and M1AP Are Associated With Risk of Non-Small Cell Lung Cancer.

BACKGROUND: Single nucleotide polymorphisms (SNPs) are often associated with distinct phenotypes in cancer. The present study investigated associations of cancer risk and outcomes with SNPs discovered by whole exome sequencing of normal lung tissue DNA of 15 non-small cell lung cancer (NSCLC) patients, 10 early stage and 5 advanced stage. METHODS: DNA extracted from normal lung tissue of the 15 NSCLC patients was subjected to whole genome amplification and sequencing and analyzed for the occurrence of SNPs. The association of SNPs with the risk of lung cancer and survival was surveyed using the OncoArray study dataset of 85,716 patients (29,266 cases and 56,450 cancer-free controls) and the Prostate, Lung, Colorectal and Ovarian study subset of 1,175 lung cancer patients. RESULTS: We identified 4 SNPs exclusive to the 5 patients with advanced stage NSCLC: rs10420388 and rs10418574 in the CLPP gene, and rs11126435 and rs2021725 in the M1AP gene. The variant alleles G of SNP rs10420388 and A of SNP rs10418574 in the CLPP gene were associated with increased risk of squamous cell carcinoma (OR = 1.07 and 1.07; P = 0.013 and 0.016, respectively). The variant allele T of SNP rs11126435 in the M1AP gene was associated with decreased risk of adenocarcinoma (OR = 0.95; P = 0.027). There was no significant association of these SNPs with the overall survival of lung cancer patients (P > 0.05). CONCLUSIONS: SNPs identified in the CLPP and M1AP genes may be useful in risk prediction models for lung cancer. The previously established association of the CLPP gene with cancer progression lends relevance to our findings.

Complement factor H protects tumor cell-derived exosomes from complement-dependent lysis and phagocytosis.

Exosomes are a class of extracellular vesicles (EVs) that are mediators of normal intercellular communication, but exosomes are also used by tumor cells to promote oncogenesis and metastasis. Complement factor H (CFH) protects host cells from attack and destruction by the alternative pathway of complement-dependent cytotoxicity (CDC). Here we show that CFH can protect exosomes from complement-mediated lysis and phagocytosis. CFH was found to be associated with EVs from a variety of tumor cell lines as well as EVs isolated from the plasma of patients with metastatic non-small cell lung cancer. Higher levels of CFH-containing EVs correlated with higher metastatic potential of cell lines. GT103, a previously described antibody to CFH that preferentially causes CDC of tumor cells, was used to probe the susceptibility of tumor cell-derived exosomes to destruction. Exosomes were purified from EVs using CD63 beads. Incubation of GT103 with tumor cell-derived exosomes triggered exosome lysis primarily by the classical complement pathway as well as antibody-dependent exosome phagocytosis by macrophages. These results imply that GT103-mediated exosome destruction can be triggered by antibody Fc-C1q interaction (in the case of lysis), and antibody-Fc receptor interactions (in the case of phagocytosis). Thus, this work demonstrates CFH is expressed on tumor cell derived exosomes, can protect them from complement lysis and phagocytosis, and that an anti-CFH antibody can be used to target tumor-derived exosomes for exosome destruction via innate immune mechanisms. These findings suggest that a therapeutic CFH antibody has the potential to inhibit tumor progression and reduce metastasis promoted by exosomes.

Enhanced CDC of B cell chronic lymphocytic leukemia cells mediated by rituximab combined with a novel anti-complement factor H antibody.

Rituximab therapy for B cell chronic lymphocytic leukemia (B-CLL) has met with mixed success. Among several factors to which resistance can be attributed is failure to activate complement dependent cytotoxicity (CDC) due to protective complement regulatory proteins, including the soluble regulator complement factor H (CFH). We hypothesized that rituximab killing of non-responsive B-CLL cells could be augmented by a novel human monoclonal antibody against CFH. The B cells from 11 patients with B-CLL were tested ex vivo in CDC assays with combinations of CFH monoclonal antibody, rituximab, and a negative control antibody. CDC of rituximab non-responsive malignant B cells from CLL patients could in some cases be augmented by the CFH monoclonal antibody. Antibody-mediated cytotoxicity of cells was dependent upon functional complement. In one case where B-CLL cells were refractory to CDC by the combination of rituximab plus CFH monoclonal antibody, additionally neutralizing the membrane complement regulatory protein CD59 allowed CDC to occur. Inhibiting CDC regulatory proteins such as CFH holds promise for overcoming resistance to rituximab therapy in B-CLL.

A Therapeutic Antibody for Cancer, Derived from Single Human B Cells.

Some patients with cancer never develop metastasis, and their host response might provide cues for innovative treatment strategies. We previously reported an association between autoantibodies against complement factor H (CFH) and early-stage lung cancer. CFH prevents complement-mediated cytotoxicity (CDC) by inhibiting formation of cell-lytic membrane attack complexes on self-surfaces. In an effort to translate these findings into a biologic therapy for cancer, we isolated and expressed DNA sequences encoding high-affinity human CFH antibodies directly from single, sorted B cells obtained from patients with the antibody. The co-crystal structure of a CFH antibody-target complex shows a conformational change in the target relative to the native structure. This recombinant CFH antibody causes complement activation and release of anaphylatoxins, promotes CDC of tumor cell lines, and inhibits tumor growth in vivo. The isolation of anti-tumor antibodies derived from single human B cells represents an alternative paradigm in antibody drug discovery.

Complement Factor H Antibodies from Lung Cancer Patients Induce Complement-Dependent Lysis of Tumor Cells, Suggesting a Novel Immunotherapeutic Strategy.

Characterization of the humoral immune response in selected patients with cancer who uniformly do well may lead to the development of novel therapeutic strategies. We have previously shown an association between patients with early-stage nonmetastatic lung cancer and autoantibodies to complement factor H (CFH). CFH protects normal and tumor cells from destruction by the alternative complement pathway by inactivating C3b, a protein that is essential for formation of a lytic complex on the cell surface. Here, we show that CFH autoantibodies in lung cancer patients recognize a conformationally distinct form of CFH in vitro, are IgG3 subclass, and epitope map to a crucial functional domain of CFH known to interact with C3b. Purified CFH autoantibodies inhibited binding of CFH to A549 lung tumor cells, increased C3b deposition, and caused complement-dependent tumor cell lysis. This work demonstrates that CFH autoantibodies isolated from patients with lung cancer can kill tumor cells in vitro, suggesting that they may perform this function in vivo as well. Development of specific antibodies to the conformationally distinct epitope of CFH may lead to a useful biologic therapy for lung cancer.

Regulation of UDP-glucuronosyltransferase 1A1 expression and activity by microRNA 491-3p.

The UDP-glucuronosyltransferase (UGT) 1A enzymes are involved in the phase II metabolism of many important endogenous and exogenous compounds. The nine UGT1A isoforms exhibit high interindividual differences in expression, but their epigenetic regulation is not well understood. The purpose of the present study was to examine microRNA (miRNA) regulation of hepatic UGT1A enzymes and determine whether or not that regulation impacts enzymatic activity. In silico analysis identified miRNA 491-3p (miR-491-3p) as a potential regulator of the UGT1A gene family via binding to the shared UGT1A 3'-untranslated region common to all UGT1A enzymes. Transfection of miR-491-3p mimic into HuH-7 cells significantly repressed UGT1A1 (P < 0.001), UGT1A3 (P < 0.05), and UGT1A6 (P < 0.05) mRNA levels. For UGT1A1, this repression correlated with significantly reduced metabolism of raloxifene into raloxifene-6-glucuronide (ral-6-gluc; P < 0.01) and raloxifene-4'-glucuronide (ral-4'-gluc; P < 0.01). In HuH-7 cells with repressed miR-491-3p expression, there was a significant increase (~80%; P < 0.01) in UGT1A1 mRNA and a corresponding increase in glucuronidation of raloxifene into ral-6-gluc (50%; P < 0.05) and ral-4'-gluc (22%; P < 0.01). Knockdown of endogenous miR-491-3p in HepG2 cells did not significantly alter UGT1A1 mRNA levels but did increase the formation of ral-6-gluc (50%; P < 0.05) and ral-4'-gluc (34%; P < 0.001). A significant inverse correlation between miR-491-3p expression and both UGT1A3 (P < 0.05) and UGT1A6 (P < 0.01) mRNA levels was observed in a panel of normal human liver specimens, with a significant (P < 0.05) increase in UGT1A3 and UGT1A6 mRNA levels observed in miR-491-3p nonexpressing versus expressing liver specimens. These results suggest that miR-491-3p is an important factor in regulating the expression of UGT1A enzymes in vivo.

Importance of UDP-glucuronosyltransferases 2A2 and 2A3 in tobacco carcinogen metabolism.

UDP-glucuronosyltransferase A1 (UGT2A1) is expressed in the lung and exhibits activity against polycyclic aromatic hydrocarbons (PAHs), suggesting UGT2A1 involvement in the local metabolism of PAH tobacco carcinogens. The goal of the present study was to investigate the importance of two additional UGT2A enzymes, UGT2A2 and UGT2A3, in tobacco carcinogen metabolism. Real-time polymerase chain reaction suggested that wild-type UGT2A2 had the highest expression in the breast, followed by trachea > larynx > kidney. A novel splice variant of UGT2A2 lacking exon 3 (termed UGT2A2Δexon3) was investigated, with UGT2A2Δexon3 expression determined to be 25-50% that of wild-type UGT2A2 in all tissues examined. UGT2A3 was determined to be well expressed in the liver and colon, followed by pancreas > kidney > lung > tonsil > trachea > larynx. Cell homogenates prepared from human embryonic kidney (HEK)293 cells overexpressing wild-type UGT2A2 (termed UGT2A2_i1) exhibited glucuronidation activity, as observed by reverse-phase ultra-pressure liquid chromatography, against 1-hydroxy-(OH)-pyrene, 1-naphthol, and hydroxylated benzo(a)pyrene metabolites, whereas homogenates prepared from HEK293 cells overexpressing UGT2A3 only showed activity against simple PAHs like 1-OH-pyrene and 1-naphthol. Activity assays showed the UGT2A2Δexon3 protein (termed UGT2A2_i2) exhibited no detectable glucuronidation activity against all substrates examined; however, coexpression studies suggested that UGT2A2_i2 negatively modulates UGT2A2_i1 activity. Both UGT2A2 and UGT2A3 exhibited no detectable activity against complex PAH proximate carcinogens, tobacco-specific nitrosamines, or heterocyclic amines. These data suggest that, although UGT2A1 is the only UGT2A enzyme active against PAH proximate carcinogens (including PAH diols), both UGTs 2A1 and 2A2 play an important role in the local detoxification of procarcinogenic monohydroxylated PAH metabolites.

Identification and functional characterization of a novel UDP-glucuronosyltransferase 2A1 splice variant: potential importance in tobacco-related cancer susceptibility.

UDP-glucuronosyltransferase (UGT) 2A1 is a respiratory and aerodigestive tract-expressing phase II detoxifying enzyme that metabolizes various xenobiotics including polycyclic aromatic hydrocarbons (PAHs). In the present study, a novel exon 3 deletion splice variant was identified for UGT2A1 (UGT2A1Δexon3). As determined by reverse transcription-polymerase chain reaction (PCR), UGT2A1Δexon3 was shown to be expressed in various tissues including lung, trachea, larynx, tonsil, and colon. The ratio of UGT2A1Δexon3/wild-type UGT2A1 expression was highest in colon (0.79 ± 0.08) and lung (0.42 ± 0.12) as determined by real-time PCR; an antibody specific to UGT2A1 showed splice variant protein (UGT2A1_i2) to wild-type protein (UGT2A1_i1) ratios in the range of 0.5 to 0.9 in these tissues. Using ultra-pressure liquid chromatography, we found that homogenates prepared from UGT2A1_i2-overexpressing human embryonic kidney 293 cells exhibited no glucuronidation activity against PAHs, including benzo[a]pyrene-7,8-dihydrodiol (B[a]P-7,8-diol). An inducible in vitro system was created to determine the effect of UGT2A1_i2 expression on UGT2A1_i1 activity. Increasing UGT2A1_i2 levels resulted in a significant (p < 0.01) decrease in the UGT2A1_i1 V(max) against 1-hydroxy (OH)-pyrene, 3-OH-benzo[a]pyrene, and B[a]P-7,8-diol; no significant changes in K(M) were observed for any of the three substrates. Coimmunoprecipitation experiments suggested the formation of UGT2A1_i1 and UGT2A1_i2 hetero-oligomers and UGT2A1_i1 homo-oligomers; coexpression of UGT2A1_i1 or UGT2A1_i2 with other UGT1A or UGT2B enzymes caused no change in UGT1A or UGT2B glucuronidation activity. These data suggest that a novel UGT2A1 splice variant regulates UGT2A1-mediated glucuronidation activity via UGT2A1-specific protein-protein interactions, and expression of this variant could play an important role in the detoxification of carcinogens within target tissues for tobacco carcinogenesis.

Characterization of UDP-glucuronosyltransferase 2A1 (UGT2A1) variants and their potential role in tobacco carcinogenesis.

OBJECTIVE: To examine UGT2A1 expression in human tissues, determine its glucuronidation activity against tobacco carcinogens, and assess the potential functional role of UGT2A1 missense single nucleotide polymorphisms on UGT2A1 enzyme activity. METHODS: Reverse transcription polymerase chain reaction and real time polymerase chain reaction were used to assess UGT2A1 gene expression in various human tissues. A glucuronidation assay measured by reverse phase ultra-performance liquid chromatography was used to determine UGT2A1 activity. RESULTS: UGT2A1 was expressed in aerodigestive tract tissues including trachea, larynx, tonsil, lung, and colon; no expression was observed in breast, whole brain, pancreas, prostate, kidney, liver, or esophagus. UGT2A1 exhibited highest expression in the lung, followed by trachea >tonsil >larynx >colon >olfactory tissue. Cell homogenates prepared from wildtype UGT2A1(75Lys308Gly) overexpressing HEK293 cells showed significant glucuronidation activity against a variety of polycyclic aromatic hydrocarbons including, 1-hydroxy-benzo(a)pyrene, benzo(a)pyrene-7,8-diol, and 5-methylchrysene-1,2-diol. No activity was observed in UGT2A1 overexpressing cell homogenate against substrates that form N-glucuronides, such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), nicotine, or N-OH-2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (N-OH PhIP). A significant (P<0.05) decrease (approximately 25%) in glucuronidation activity (Vmax/KM) was observed against all polycyclic aromatic hydrocarbons substrates for the UGT2A1(75Lys308Gly) variant compared with homogenates from wildtype UGT2A1(75Lys308Gly); no activity was observed for cell homogenates overexpressing the UGT2A1 variant for all substrates tested. CONCLUSION: These data suggest that UGT2A1 is an important detoxification enzyme in the metabolism of polycyclic aromatic hydrocarbons within target tissues for tobacco carcinogens and functional polymorphisms in UGT2A1 may play a role in tobacco-related cancer risk.