Differential effects of poly(ADP ribose) polymerase inhibitor-based metronomic therapy on programmed death-ligand 1 and matrix-associated factors in human myeloid cells

We recently showed that while partial poly(ADP-ribose) polymerase (PARP)-1 inhibition with a low metronomic sub-half-maximal inhibitory concentration/dose (IC50) of olaparib provides superior protection against colon cancer in mice compared to complete inhibition by blocking the suppressive function of myeloid-derived suppressor cells (MDSCs) and synergizing with anti-program cell death (PD)-1-based immunotherapy. Here, we examined whether PARP inhibitors (PARPi) exert effects on human myeloid cells that alter T cell function (e.g. PD-ligand (L)1) or metastasis/tumor microenvironment-associated factors (e.g. tissue inhibitor of matrix metalloproteinases (MMPs) (TIMP)-2 and MMPs activity). We show that olaparib-based metronomic therapy induced a marginal increase in PD-L1 expression in MDSCs-enriched cells, decreased its expression in dendritic cells (DCs)-enriched cells, and caused little to no effect on macrophage-enriched cells. Interestingly, MDSCs-enriched cells also expressed low levels of PARP-1 while dendritic cells and macrophages expressed high levels of the protein. Bone marrow progenitors expressed no PD-L1; however, when differentiated into MDSCs, the expression was high displaying higher glycosylation levels compared to those observed in peripheral blood mononuclear cells (PBMCs)-derived cells. Contrary to reported effects on cancer cells, the sub-IC50 or moderate olaparib concentration caused substantial decrease in PD-L1. A sub-IC50 concentration of other clinically used PARPi (rucaparib, niraparib, and talazoparib) as well as the failed PARPi, iniparib, exerted similar effects. Furthermore, PARPi-based metronomic therapy reprogramed myeloid cells with the potential to stabilize intratumoral matrix by increasing secreted-TIMP-2 with a differential reduction in MMP-2/MMP-9 activity. Thus, PARPi-based metronomic therapy may promote functional changes in myeloid cells that provide an additional rationale for combining it with immunotherapy. Our results also provide new opportunities for iniparib in cancer therapy.

Promotion of a synthetic degradation of activated STAT6 by PARP-1 inhibition: roles of poly(ADP-ribosyl)ation, calpains and autophagy

Background

We reported that PARP-1 regulates genes whose products are crucial for asthma, in part, by controlling STAT6 integrity speculatively through a calpain-dependent mechanism. We wished to decipher the PARP-1/STAT6 relationship in the context of intracellular trafficking and promoter occupancy of the transcription factor on target genes, its integrity in the presence of calpains, and its connection to autophagy.

Methods

This study was conducted using primary splenocytes or fibroblasts derived from wild-type or PARP-1^−/− mice and Jurkat T cells to mimic Th2 inflammation.

Results

We show that the role for PARP-1 in expression of IL-4-induced genes (e.g. gata-3) in splenocytes did not involve effects on STAT6 phosphorylation or its subcellular trafficking, rather, it influenced its occupancy of gata-3 proximal and distal promoters in the early stages of IL-4 stimulation. At later stages, PARP-1 was crucial for STAT6 integrity as its inhibition, pharmacologically or by gene knockout, compromised the fate of the transcription factor. Calpain-1 appeared to preferentially degrade JAK-phosphorylated-STAT6, which was blocked by calpastatin-mediated inhibition or by genetic knockout in mouse fibroblasts. The STAT6/PARP-1 relationship entailed physical interaction and modification by poly(ADP-ribosyl)ation independently of double-strand-DNA breaks. Poly(ADP-ribosyl)ation protected phosphorylated-STAT6 against calpain-1-mediated degradation. Additionally, our results show that STAT6 is a bonafide substrate for chaperone-mediated autophagy in a selective and calpain-dependent manner in the human Jurkat cell-line. The effects were partially blocked by IL-4 treatment and PARP-1 inhibition.

Conclusions

The results demonstrate that poly(ADP-ribosyl)ation plays a critical role in protecting activated STAT6 during Th2 inflammation, which may be synthetically targeted for degradation by inhibiting PARP-1.

Abstract 4211: Minocycline-based metronomic therapy as a novel approach to enhance anti-tumor immune responses and reduce tumor burden in mouse models of colorectal cancer

Despite the availability of numerous new therapies including immune checkpoint inhibitors, patients with colon cancer are faced with limited treatment options. We recently demonstrated that low metronomic dose of PARP inhibitor synergizes with anti-PD-1 immunotherapy, in part, by modulating the suppressive function of MDSCs via a reduction in Arg1 and iNOS but independently of DNA damage and STING (PMC7839867). The non-antibiotic properties of minocycline (Mc) include its ability to moderately inhibit PARP. We took advantage of Mc as a weak PARP inhibitor to explore its potential on tumorigenesis and immune suppression in colon cancer models. In this study, we show that Mc significantly reduced Arg1 and iNOS in bone marrow (BM)-derived MDSCs both at the mRNA and protein levels. Paradoxically, such strong effect did not culminate in a substantial modulation of MDSCs suppressive function as assessed by co-cultured anti-CD3/CD28-stimulated CFSE-labeled T cells proliferation. However and similarly to PARP inhibitors, Mc increased PD-L1 expression in several cell types. We thus speculated that the antibiotic might enhance anti-cancer immunotherapy and explored such potential in a MC-38 and CT-26 cell-based mouse models of colon cancer representing the MSI and MSS traits of the disease. Treatment of tumor-bearing mice with low metronomic doses of Mc (0.5 or 5mkg) promoted a substantial reduction in tumor size in the MC-38 cell-based model (MSI) without an apparent superiority of any of the two doses. Surprisingly, neither dose of Mc exerted appreciable effects on tumor size in the CT-26 cell-based model (MSS). The anti-tumor effect of Mc in the MSI model was associated with a significant reduction in intratumoral monocytic-MDSC population. While MDSCs harvested from tumors of control mice re-infiltrated ex vivo generated MC-38 cell-based organoids, MDSCs harvested from tumors of Mc-treated mice failed to re-infiltrate the organoids. This suggests that Mc may interfere with MDSCs intratumorally infiltration. The Mc concentrations used in this study exerted little to no effect on bacterial growth suggesting that the observed effects were independent of the antibiotic properties of the drug. Unlike the effects observed in vitro, Mc treatment reduced intratumoral PD-L1 while increasing IFNγ. The discrepancy may be associated with intratumoral stress condition as assessed by Chop protein levels and reproduced in vitro by serum starvation. Although the metronomic Mc dose and anti-PD1 administration caused a significant reduction in tumor size individually, the combination therapy promoted a 66.7% curing of the tumors. Our results propose repurposing Mc at metronomic doses as a new approach to enhance efficacy of immunotherapy for patients with MSI colon cancer.

Citation Format: Salome V. Ibba, Hanh H. Luu, Mohamed Ghonim, Cecilia Vittori, Matthew J. Dean, Giulia Monticone, Francesca Peruzzi, Augusto Ochoa, Lucio Miele, Hamid A. Boulares. Minocycline-based metronomic therapy as a novel approach to enhance anti-tumor immune responses and reduce tumor burden in mouse models of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4211.

Targeting PARP-1 with metronomic therapy modulates MDSC suppressive function and enhances anti-PD-1 immunotherapy in colon cancer

Background

Poly(ADP-ribose) polymerase (PARP) inhibitors (eg, olaparib) are effective against BRCA-mutated cancers at/near maximum tolerated doses by trapping PARP-1 on damaged chromatin, benefitting only small patient proportions. The benefits of targeting non-DNA repair aspects of PARP with metronomic doses remain unexplored.

Methods

Colon epithelial cells or mouse or human bone marrow (BM)-derived-myeloid-derived suppressor cells (MDSCs) were stimulated to assess the effect of partial PARP-1 inhibition on inflammatory gene expression or immune suppression. Mice treated with azoxymethane/four dextran-sulfate-sodium cycles or APC^Min/+ mice bred into PARP-1^+/− or treated with olaparib were used to examine the role of PARP-1 in colitis-induced or spontaneous colon cancer, respectively. Syngeneic MC-38 cell-based (microsatellite instability, MSI^high) or CT-26 cell-based (microsatellite stable, MSS) tumor models were used to assess the effects of PARP inhibition on host responses and synergy with anti-Programmed cell Death protein (PD)-1 immunotherapy.

Results

Partial PARP-1 inhibition, via gene heterozygosity or a moderate dose of olaparib, protected against colitis-mediated/APC^Min-mediated intestinal tumorigenesis and APC^Min-associated cachexia, while extensive inhibition, via gene knockout or a high dose of olaparib, was ineffective or aggravating. A sub-IC50-olaparib dose or PARP-1 heterozygosity was sufficient to block tumorigenesis in a syngeneic colon cancer model by modulating the suppressive function, but not intratumoral migration or differentiation, of MDSCs, with concomitant increases in intratumoral T cell function and cytotoxicity, as assessed by granzyme-B/interferon-γ levels. Adoptive transfer of WT-BM-MDSCs abolished the protective effects of PARP-1 heterozygosity. The mechanism of MDSC modulation involved a reduction in arginase-1/inducible nitric oxide synthase/cyclo-oxygenase-2, but independent of PARP-1 trapping on chromatin. Although a high-concentration olaparib or the high-trapping PARP inhibitor, talazoparib, activated stimulator of interferon gene (STING) in BRCA-proficient cells and induced DNA damage, sub-IC50 concentrations of either drug failed to induce activation of the dsDNA break sensor. STING expression appeared dispensable for MDSC suppressive function and was not strictly required for olaparib-mediated effects. Ironically, STING activation blocked human and mouse MDSC function with no additive effects with olaparib. A metronomic dose of olaparib was highly synergistic with anti-PD-1-based immunotherapy, leading to eradication of MSI^high or reduction of MSS tumors in mice.

Conclusions

These results support a paradigm-shifting concept that expands the utility of PARP inhibitor and encourage testing metronomic dosing of PARP inhibitor to enhance the efficacy of checkpoint inhibitor-based immunotherapies in cancer.

Sulfated non-anticoagulant heparin blocks Th2-induced asthma by modulating the IL-4/signal transducer and activator of transcription 6/Janus kinase 1 pathway

BACKGROUND

The efficacy of heparins and low-MW-heparins (LMWH) against human asthma has been known for decades. However, the clinical utility of these compounds has been hampered by their anticoagulant properties. Much effort has been put into harnessing the anti-inflammatory properties of LMWH but none have been used as therapy for asthma. Sulfated-non-anticoagulant heparin (S-NACH) is an ultra-LMWH with no systemic anticoagulant effects.

OBJECTIVE

The present study explored the potential of S-NACH in blocking allergic asthma and examined the potential mechanism by which it exerts its effects.

METHODS

Acute and chronic ovalbumin-based mouse models of asthma, splenocytes, and a lung epithelial cell line were used. Mice were challenged with aerosolized ovalbumin and administered S-NACH or saline 30 min after each ovalbumin challenge.

RESULTS

Sulfated-non-anticoagulant heparin administration in mice promoted a robust reduction in airway eosinophilia, mucus production, and airway hyperresponsiveness even after chronic repeated challenges with ovalbumin. Such effects were linked to suppression of Th2 cytokines IL-4/IL-5/IL-13/GM-CSF and ovalbumin-specific IgE without any effect on IFN-γ. S-NACH also reduced lung fibrosis in mice that were chronically-exposed to ovalbumin. These protective effects of S-NACH may be attributed to modulation of the IL-4/JAK1 signal transduction pathway through an inhibition of STAT6 phosphorylation and a subsequent inhibition of GATA-3 and inducible NO synthase expression. The effect of the drug on STAT6 phosphorylation coincided with a reduction in JAK1 phosphorylation upon IL-4 treatment. The protective effects of S-NACH treatment was associated with reduction of the basal expression of the two isoforms of arginase ARG1 and ARG2 in lung epithelial cells.

CONCLUSIONS

Our study demonstrates that S-NACH constitutes an opportunity to benefit from the well-known anti-asthma properties of heparins/LMWH while bypassing the risk of bleeding. Our results show, for the first time, that such anti-asthma effects may be associated with reduction of the IL-4/JAK1/STAT6 pathway.

Overexpression of Ad5 precursor terminal protein accelerates recombinant adenovirus packaging and amplification in HEK-293 packaging cells

Recombinant adenoviruses are one of the most common vehicles for efficient in vitro and in vivo gene deliveries. Here, we investigate whether exogenous precursor terminal protein (pTP) expression in 293 cells improves the efficiency of adenovirus packaging and amplification. We used a piggyBac transposon-based vector and engineered a stable 293 line that expresses high level of Ad5 pTP, designated as 293pTP. Using the AdBMP6-GLuc that expresses green fluorescent protein (GFP), BMP6 and Gaussia luciferase, we found that the infectivity of AdBMP6-GLuc viral samples packaged in 293pTP cells was titrated up to 19.3 times higher than that packaged in parental 293 cells. AdBMP6-GLuc viral samples packaged in 293pTP cells exhibited significantly higher transduction efficiency in 143B and immortalized mouse embryonic fibroblast (iMEF) cells, as assessed by fluorescence-activated cell sorting analysis of GFP-positive cells, the luciferase activity assay and BMP6-induced osteogenic marker alkaline phosphatase activities in iMEFs. When adenovirus amplification efficiency was analyzed, we found that 293pTP cells infected with AdBMP6-GLuc yielded up to 12.6 times higher titer than that in parental 293 cells, especially at lower multiplicities of infection. These results strongly suggest that exogenous pTP expression may accelerate the packaging and amplification of recombinant adenoviruses. Thus, the engineered 293pTP cells should be a superior packaging line for efficient adenovirus production.

Characterization of the distinct orthotopic bone-forming activity of 14 BMPs using recombinant adenovirus-mediated gene delivery

Efficacious bone regeneration could revolutionize the clinical management of bone and musculoskeletal disorders. Although several bone morphogenetic proteins (BMPs) (mostly BMP-2 and BMP-7) have been shown to induce bone formation, it is unclear whether the currently used BMPs represent the most osteogenic ones. Until recently, comprehensive analysis of osteogenic activity of all BMPs has been hampered by the fact that recombinant proteins are either not biologically active or not available for all BMPs. In this study, we used recombinant adenoviruses expressing the 14 types of BMPs (AdBMPs), and demonstrated that, in addition to currently used BMP-2 and BMP-7, BMP-6 and BMP-9 effectively induced orthotopic ossification when either AdBMP-transduced osteoblast progenitors or the viral vectors were injected into the quadriceps of athymic mice. Radiographic and histological evaluation demonstrated that BMP-6 and BMP-9 induced the most robust and mature ossification at multiple time points. BMP-3, a negative regulator of bone formation, was shown to effectively inhibit orthotopic ossification induced by BMP-2, BMP-6, and BMP-7. However, BMP-3 exerted no inhibitory effect on BMP-9-induced bone formation, suggesting that BMP-9 may transduce osteogenic signaling differently. Our findings suggest that BMP-6 and BMP-9 may represent more effective osteogenic factors for bone regeneration.

The unsatisfactory margin in breast cancer surgery

BACKGROUND

Surgical margin involvement with breast cancer usually results in obligatory reexcision or mastectomy. While unalterable occult host and pathologic factors may interfere with margin clearance during the initial excision, it is possible that alterations in surgical technique might increase the likelihood of obtaining satisfactory margins.

METHODS

Two hundred and thirty-five patients who were candidates for breast conservation therapy were identified for 1991 and 1996 using the Tumor Registry. Margins were defined as "unsatisfactory" if there was microscopic involvement with tumor or the margin was close at initial excisional biopsy and the surgeon opted for reexcision. Multiple logistic regression analyses of factors associated with margin status were performed.

RESULTS

One hundred thirty-two (56%) patients had positive or close (unsatisfactory) margins; this rate increased from 51% in 1991 to 59% in 1996. Patients with unsatisfactory margins underwent more procedures (mean 2.0 versus 1.2; P <0.0001) than patients whose margins were satisfactory. The breast conservation rate for patients with unsatisfactory margins was 64% compared with 99% for patients with satisfactory margins. A multiple logistic regression demonstrated that patients with unsatisfactory margins were 67 times more likely to have a mastectomy than patients whose margins were satisfactory after adjusting for other significant factors (P <0.0001). The practice of fine needle aspiration biopsy, orientation of specimen margins by the surgeon, and reexcision of tumor at the first operation were statistically significant technical factors in obtaining satisfactory margins. Significant pathology factors were extensive intraductal component (EIC), lobular or ductal extension, and tumor size.

CONCLUSION

These data show that technical factors in the surgical management of breast cancer, as well as biological factors such as EIC, can influence the success of breast conservation.

Chromosome 17-mediated dormancy of AT6.1 prostate cancer micrometastases

To improve the diagnosis and treatment of cancer, an increased understanding of the molecular and cellular changes that regulate metastatic ability is required. We have recently demonstrated a prostate cancer metastasis-suppressor activity encoded by a discontinuous approximately 70-cM region of human chromosome. The presence of this region suppresses the spontaneous metastatic ability of AT6.1 rat prostatic cancer cells by greater than 30-fold (M. A. Chekmareva et al., Prostate, 33: 271-280, 1997). Interestingly, a number of potentially important genes which have been mapped to human chromosome 17, including TP53, NM23, and BRCA1, are not retained (M. A. Chekmareva et al., cited above) or are not expressed in these microcell hybrids (B. A. Yoshida et al., In Vivo, in press), which suggests the presence of a novel metastasis-suppressor gene(s) or novel function of a known gene(s) encoded by this region(s). We hypothesize that identification of the "step" in the metastatic cascade that is inhibited by the presence of the approximately 70-cM metastasis-suppressor region will facilitate the identification of candidate metastasis-suppressor genes. For a cancer cell to metastasize, it must escape from the primary tumor, enter the circulation, arrest in the microcirculation, extravasate into a tissue compartment, and grow. This suppression of spontaneous macroscopic lung metastases could be due to the inhibition of a number of steps within this cascade. Results of the current study demonstrate that AT6.1 cells containing the approximately 70-cM region (AT6.1-17-4 cells) escape from the primary tumor and arrest in the lung but are growth-inhibited unless the metastasis-suppressor region is lost. This growth inhibition seems to result from an effect of one or more genes at the metastatic site and not from a circulating angiogenesis inhibitor. Our findings suggest that the approximately 70-cM region of human chromosome 17 may encode a gene(s) that regulates the "dormancy" of AT6.1-17-4 micrometastases.

Identification of a novel metastasis-suppressor region on human chromosome 12

There is a critical need for markers that can be used to predict accurately the malignant potential of histological prostate cancers (J. T. Isaacs. Am. J. Pathol., 150: 1511-1521, 1997). Metastasis-suppressor genes are attractive candidates for marker development because, by definition, their loss should be associated with the acquisition of metastatic ability. In an effort to identify such genes, a single copy of human chromosome 12, tagged with the neomycin resistance gene, was introduced into highly metastatic Dunning AT6.1 prostate cancer cells by microcell-mediated chromosomal transfer. Thirty-two AT6.1-12 clonal cell lines were established and the region(s) of chromosome 12 retained was determined by sequence tagged site-based PCR analysis. Representative AT6.1-12 clones containing overlapping regions of chromosome 12 were characterized cytogenetically and were shown to have a normal complement of parental AT6.1 rat chromosomes. Fluorescence in situ hybridization, performed on representative AT6.1-12 hybrids, demonstrated a single human chromosome 12-specific signal. The metastatic ability of six representative clones was tested in immunodeficient mice. All of the AT6.1-12 clones showed the same in vivo growth rates as the control AT6.1-neo cells. Clonal cell lines that contained a conserved approximately 70-cM portion of chromosome 12 (e.g., AT6.1-12-8, -8-1, and -8-3), showed a >30-fold suppression in the number of macroscopic surface lung metastases. Mice that received injections of these cells developed a mean number 4 lung metastases whereas mice that received injections of other AT6.1-12 hybrids (lacking the approximately 70-cM region) or AT6.1-neo control cells, developed a mean number of 140 metastases. Interestingly, histological examination of the lungs of the mice that received injections of AT6.1-12-8 cells showed essentially no microscopic metastases. These findings suggest that a gene(s) encoded by the approximately 70-cM portion of human chromosome 12 suppresses an early step in the metastatic cascade.

Posttranslational regulation of plakoglobin expression. Influence of the desmosomal cadherins on plakoglobin metabolic stability

Desmosomes are adhesive intercellular junctions that act as cell surface attachment sites for intermediate filaments. The desmosomal glycoproteins, desmogleins and desmocollins, are members of the cadherin family of adhesion molecules. In addition, desmoglein has been shown to coimmunoprecipitate with the junctional protein plakoglobin. To characterize further the interaction between plakoglobin and the desmosomal cadherins, stable mouse fibroblast (L-cells) cell lines were generated that express plakoglobin, desmoglein and plakoglobin, or desmocollin and plakoglobin. L-cell lines transfected with a plasmid encoding human plakoglobin expressed plakoglobin mRNA but very little plakoglobin protein. However, plakoglobin protein was expressed at high levels in L-cells coexpressing either desmoglein or desmocollin. In addition, both desmocollin and desmoglein were found to coimmunoprecipitate with plakoglobin. The transient expression of desmoglein in L-cell lines expressing plakoglobin mRNA resulted in the formation of a complex between plakoglobin and desmoglein and in the accumulation of plakoglobin protein. Furthermore, the rate of plakoglobin protein degradation was decreased by 15-20-fold in cell lines expressing either desmoglein or desmocollin. These results demonstrate that the desmosomal cadherins posttranslationally regulate plakoglobin expression by decreasing the rate of plakoglobin degradation.

Functional analysis of desmoplakin domains: specification of the interaction with keratin versus vimentin intermediate filament networks

We previously demonstrated that truncated desmoplakin I (DP I) molecules containing the carboxyl terminus specifically coalign with and disrupt both keratin and vimentin intermediate filament (IF) networks when overexpressed in tissue culture cells (Stappenbeck, T. S., and K. J. Green. J. Cell Biol. 116:1197-1209). These experiments suggested that the DP carboxyl-terminal domain is involved either directly or indirectly in linking IF with the desmosome. Using a similar approach, we have now investigated the behavior of ectopically expressed full-length DP I in cultured cells. In addition, we have further dissected the functional sequences in the carboxyl terminus of DP I that facilitate the interaction with IF networks. Transient transfection of a clone encoding full-length DP I into COS-7 cells produced protein that appeared in some cells to associate with desmosomes and in others to coalign with and disrupt IF. Deletion of the carboxyl terminus from this clone resulted in protein that still appeared capable of associating with desmosomes but not interacting with IF networks. As the amino terminus appeared to be dispensable for IF interaction, we made finer deletions in the carboxyl terminus of DP based on blocks of sequence similarity with the related molecules bullous pemphigoid antigen and plectin. We found a sequence at the very carboxyl terminus of DP that was necessary for coalignment with and disruption of keratin IF but not vimentin IF. Furthermore, the coalignment of specific DP proteins along keratin IF but not vimentin IF was correlated with resistance to extraction by Triton. The striking uncoupling resulting from the deletion of specific DP sequences suggests that the carboxyl terminus of DP interacts differentially with keratin and vimentin IF networks.