Estrogen receptor blockade and radiation therapy cooperate to enhance the response of immunologically cold ER+ breast cancer to immunotherapy

BACKGROUND

Most patients with estrogen receptor positive (ER+) breast cancer do not respond to immune checkpoint inhibition (ICI); the tumor microenvironment (TME) of these cancers is generally immunosuppressive and contains few tumor-infiltrating lymphocytes. Radiation therapy (RT) can increase tumor inflammation and infiltration by lymphocytes but does not improve responses to ICIs in these patients. This may result, in part, from additional effects of RT that suppress anti-tumor immunity, including increased tumor infiltration by myeloid-derived suppressor cells and regulatory T cells. We hypothesized that anti-estrogens, which are a standard of care for ER+ breast cancer, may ameliorate these detrimental effects of RT by reducing the recruitment/ activation of suppressive immune populations in the radiated TME, increasing anti-tumor immunity and responsiveness to ICIs.

METHODS

To interrogate the effect of the selective estrogen receptor downregulator, fulvestrant, on the irradiated TME in the absence of confounding growth inhibition by fulvestrant on tumor cells, we used the TC11 murine model of anti-estrogen resistant ER+ breast cancer. Tumors were orthotopically transplanted into immunocompetent syngeneic mice. Once tumors were established, we initiated treatment with fulvestrant or vehicle, followed by external beam RT one week later. We examined the number and activity of tumor infiltrating immune cells using flow cytometry, microscopy, transcript levels, and cytokine profiles. We tested whether fulvestrant improved tumor response and animal survival when added to the combination of RT and ICI.

RESULTS

Despite resistance of TC11 tumors to anti-estrogen therapy alone, fulvestrant slowed tumor regrowth following RT, and significantly altered multiple immune populations in the irradiated TME. Fulvestrant reduced the influx of Ly6C+Ly6G+ cells, increased markers of pro-inflammatory myeloid cells and activated T cells, and augmented the ratio of CD8+: FOXP3+ T cells. In contrast to the minimal effects of ICIs when co-treated with either fulvestrant or RT alone, combinatorial treatment with fulvestrant, RT and ICIs significantly reduced tumor growth and prolonged survival.

CONCLUSIONS

A combination of RT and fulvestrant can overcome the immunosuppressive TME in a preclinical model of ER+ breast cancer, enhancing the anti-tumor response and increasing the response to ICIs, even when growth of tumor cells is no longer estrogen sensitive.

In Situ Vaccination Following Intratumoral Injection of IL2 and Poly-l-lysine/Iron Oxide/CpG Nanoparticles to a Radiated Tumor Site

The in situ vaccine effect of radiation therapy (RT) has been shown to be limited in both preclinical and clinical settings, possibly due to the inadequacy of RT alone to stimulate in situ vaccination in immunologically "cold" tumor microenvironments (TMEs) and the mixed effects of RT in promoting tumor infiltration of both effector and suppressor immune cells. To address these limitations, we combined intratumoral injection of the radiated site with IL2 and a multifunctional nanoparticle (PIC). The local injection of these agents produced a cooperative effect that favorably immunomodulated the irradiated TME, enhancing the activation of tumor-infiltrating T cells and improving systemic anti-tumor T cell immunity. In syngeneic murine tumor models, the PIC+IL2+RT combination significantly improved the tumor response, surpassing the single or dual combinations of these treatments. Furthermore, this treatment led to the activation of tumor-specific immune memory and improved abscopal effects. Our findings suggest that this strategy can be used to augment the in situ vaccine effect of RT in clinical settings.

Abstract 2828: Impact of sequencing of immune checkpoint blockade and targeted radionuclide therapy on murine tumor response

Background: Sequencing of immune checkpoint inhibitors (ICI) and external beam radiation therapy (EBRT) for cancer treatment has been studied, but the optimal sequencing has yet to be determined. While some studies have noted therapeutic advantages of priming the tumor immune microenvironment with EBRT prior to ICI, others have described the benefit of modulating the tumor infiltrating lymphocyte (TIL) population with ICI before EBRT. Targeted radionuclide therapy (TRT) approaches allow investigation of how irradiation by a tumor-targeted radionuclide and differences in emission type, linear energy transfer, and dose rate affect optimal timing of ICI administration. NM600 is an alkylphosphocholine analog selectively taken up by tumors capable of chelating numerous radionuclides for comparative studies.

Objective: We use two immunologically cold tumor models, MOC2 head and neck squamous cell carcinoma and B78 melanoma, to describe the influence of dose rate on type I interferon (IFN1) signaling and the effect of ICI and 90Y-, 177Lu-, and 225Ac-NM600 TRT sequences on tumor response.

Methods: 90Y, 177Lu, or 225Ac were added to culture media in activities estimated using GEANT4 Monte Carlo to deliver 12 Gy to the cell monolayer. qPCR was performed on cDNA from cells irradiated with EBRT, 90Y, 177Lu, or 225Ac, and harvested on days 1, 3, or 7. In vivo dosimetry was performed using the Monte Carlo-based RAPID platform utilizing serial PET/CT or SPECT/CT imaging and/or longitudinal biodistribution. Differences over time (days 4, 7, 14, 21, 28 after RT) in TIL and systemic immune cell populations were measured by flow cytometry following no treatment, 12 Gy EBRT, or 90Y-, 177Lu-, or 225Ac-NM600 in MOC2 tumors. Mice bearing B78 tumors received 1.5 Gy 90Y-, 177Lu-, or 225Ac-NM600, or no radiation on day 1 +/- ICI (anti-CTLA4 + anti-PDL1) on days -3/0/3 (early), 4/7/10 (middle), or 11/14/17 (late). Mice were monitored for tumor growth and survival.

Results: TRT and EBRT induced IFN1 responses in MOC2 cells. MOC2 cells treated every 24h with EBRT-matched 90Y/225Ac dose rates led to upregulation of IFN1-associated Ifnb1 and Mx1, mimicking radionuclide-induced responses. Increased tumor CD8/Treg ratios and decreased Tregs were observed at day 7 following all RT forms in MOC2 tumors. Long half-life 225Ac-NM600 (90Y: 65h; 177Lu: 161h; 225Ac: 240h) induced similar TIL changes at day 21. For 1.5 Gy 90Y-, 177Lu-, and 225Ac-NM600, B78 tumor growth delay and statistically significant overall survival benefit over respective TRT monotherapy and control groups was observed with early (day -3/0/3) dual ICI administration.

Conclusions: These studies demonstrate novel immunomodulatory effects of α- and β- emitting TRT and the capacity to achieve substantial antitumor responses with appropriate TRT + ICI sequencing. These results may inform clinical trial design of TRT + ICI regimens for patients with metastatic cancers.

Citation Format: Caroline P. Kerr, Joseph J. Grudzinski, Carolina A. Ferreira, David Adam, Julia Sheehan-Klenk, Amber M. Bates, Won Jong Jin, Ohyun Kwon, Justin C. Jagodinsky, Maria Powers, Raghava N. Sriramaneni, Paul A. Clark, Luke Zangl, Thanh Phuong T. Nguyen, Anatoly N. Pinchuk, Cynthia Choi, Christopher F. Massey, Reinier Hernandez, Bryan Bednarz, Jamey P. Weichert, Zachary S. Morris. Impact of sequencing of immune checkpoint blockade and targeted radionuclide therapy on murine tumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2828.

Abstract 6407: Radionuclide-specific effects of90Y-,177Lu-, or225Ac-NM600 targeted radionuclide therapy on tumor immunomodulation and enhanced immunotherapy response in syngeneic murine tumors

Background: Targeted radionuclide therapy (TRT) delivers radiation treatment systemically to tumor sites via a therapeutic radionuclide-linked tumor-selective targeting vector. NM600 is an alkylphosphocholine analog selectively taken up and retained in murine and human tumor cells. We previously showed that low dose radiation delivery with 90Y-NM600 improves tumor response to immune checkpoint inhibitors (ICIs). Understanding the effect of different radionuclide physical properties (emission type, linear energy transfer (LET), half-life, and tissue range) on immunomodulation of metastatic cancers may guide therapy development. Here, we evaluated the type 1 interferon (IFN1) response elicited by 90Y-, 177Lu-, and 225Ac-NM600 in an immunologically cold syngeneic murine tumor model, B78 melanoma. We hypothesized that the unique physical properties of radionuclides will differentially impact immunomodulation by TRT.

Methods: Mice bearing B78 WT or Tmem173 -/- CRISPR deletion B78 (STING KO) tumors were randomized to receive 1.5 Gy external beam radiation (EBRT), an equivalent tumor dose of 90Y-, 177Lu-, or 225Ac-NM600 determined by the Monte Carlo-based RAPID platform, or no radiation on day 1. Tumors were harvested on days 4, 7, and 10 for RT-qPCR. Mice bearing two B78 WT or Tmem173 -/- CRISPR deletion B78 (STING KO) tumors were randomized to receive 4 Gy external beam radiation therapy (EBRT), an equivalent tumor dose of 90Y- or 177Lu-NM600, 0.5 μCi 225Ac-NM600, or no radiation +/- dual ICI (anti-CTLA4 and anti-PDL1). Mice were monitored for tumor growth and survival following these treatments.

Results: Both EBRT and TRT upregulated expression of IFN1 response-associated genes (Ifnβ1, Mx1) in B78 WT tumors. Only TRT induced upregulation of Ifnβ1 and Mx1 in STING KO B78 tumors. Ddx58, which encodes RIG-I, integral to an alternative IFN1 pathway, was upregulated in both B78 WT and STING KO tumors following 225Ac-NM600, but not other treatments. TRT in B78 STING KO tumors had earlier expression of IFN1 response-associated genes than B78 WT, 225Ac-NM600 in combination with dual ICI improved overall survival over 90Y- or 177Lu-NM600 + ICI and 225Ac-NM600 monotherapy.

Conclusions: The distinct physical properties of TRT radiation, γ, β or α, affect the timing, magnitude, and molecular pathways leading to this IFN1 response. Understanding TRT effects on the tumor microenvironment may optimize TRT and immunotherapy.

Citation Format: Thanh Phuong T. Nguyen, Caroline P. Kerr, Joseph J. Grudzinski, Carolina A. Ferreira, Julia Sheehan-Klenk, Ohyun Kwon, Maria Powers, Paul A. Clark, Raghava N. Sriramaneni, Reinier Hernandez, Bryan Bednarz, Jamey P. Weichert, Zachary S. Morris. Radionuclide-specific effects of90Y-,177Lu-, or225Ac-NM600 targeted radionuclide therapy on tumor immunomodulation and enhanced immunotherapy response in syngeneic murine tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6407.

Local TLR4 stimulation augments in situ vaccination induced via local radiation and anti-CTLA-4 checkpoint blockade through induction of CD8 T-cell independent Th1 polarization

BACKGROUND

Radiation therapy (RT) has been demonstrated to generate an in situ vaccination (ISV) effect in murine models and in patients with cancer; however, this has not routinely translated into enhanced clinical response to immune checkpoint inhibition (ICI). We investigated whether the commonly used vaccine adjuvant, monophosphoryl lipid A (MPL) could augment the ISV regimen consisting of combination RT and ICI.

MATERIALS/METHODS

We used syngeneic murine models of melanoma (B78) and prostate cancer (Myc-CaP). Tumor-bearing mice received either RT (12 Gy, day 1), RT+anti-CTLA-4 (C4, day 3, 6, 9), MPL (20 µg IT injection days 5, 7, 9), RT+C4+MPL, or PBS control. To evaluate the effect of MPL on the irradiated tumor microenvironment, primary tumor with tumor draining lymph nodes were harvested for immune cell infiltration analysis and cytokine profiling, and serum was collected for analysis of antitumor antibody populations.

RESULTS

Combination RT+C4+MPL significantly reduced tumor growth, increased survival and complete response rate compared with RT+C4 in both B78 and Myc-CaP models. MPL favorably reprogrammed the irradiated tumor-immune microenvironment toward M1 macrophage and Th1 TBET+CD4+ T cell polarization. Furthermore, MPL significantly increased intratumoral expression of several Th1-associated and M1-associated proinflammatory cytokines. In co-culture models, MPL-stimulated macrophages directly activated CD8 T cells and polarized CD4 cells toward Th1 phenotype. MPL treatment significantly increased production of Th1-associated, IgG2c antitumor antibodies, which were required for and predictive of antitumor response to RT+C4+MPL, and enabled macrophage-mediated antibody-dependent direct tumor cell killing by MPL-stimulated macrophages. Macrophage-mediated tumor cell killing was dependent on FcγR expression. In metastatic models, RT and MPL generated a systemic antitumor immune response that augmented response to ICIs. This was dependent on macrophages and CD4+ but not CD8+T cells.

CONCLUSIONS

We report the potential for MPL to augment the ISV effect of combination RT+C4 through FcγR, macrophage, and TBET+CD4+ Th1 cell dependent mechanisms. To our knowledge, this is the first report describing generation of a CD8+ T cell-independent, Th1 polarized, systemic antitumor immune response with subsequent generation of immunologic memory. These findings support the potential for vaccine adjuvants to enhance the efficacy of in situ tumor vaccine approaches.

Multifunctional nanoparticle potentiates the in situ vaccination effect of radiation therapy and enhances response to immune checkpoint blockade

Radiation therapy (RT) activates an in situ vaccine effect when combined with immune checkpoint blockade (ICB), yet this effect may be limited because RT does not fully optimize tumor antigen presentation or fully overcome suppressive mechanisms in the tumor-immune microenvironment. To overcome this, we develop a multifunctional nanoparticle composed of polylysine, iron oxide, and CpG (PIC) to increase tumor antigen presentation, increase the ratio of M1:M2 tumor-associated macrophages, and enhance stimulation of a type I interferon response in conjunction with RT. In syngeneic immunologically "cold" murine tumor models, the combination of RT, PIC, and ICB significantly improves tumor response and overall survival resulting in cure of many mice and consistent activation of tumor-specific immune memory. Combining RT with PIC to elicit a robust in situ vaccine effect presents a simple and readily translatable strategy to potentiate adaptive anti-tumor immunity and augment response to ICB or potentially other immunotherapies.

Abstract 1304: Brachytherapy dose heterogeneity primes response to immune checkpoint blockade to generate anti-tumor immunity

Purpose: The immunologic effects of radiation (RT) are influenced by dose and each may be optimized over a unique dose range. We used brachytherapy (BT) to deliver a heterogeneous RT dose within a single tumor and compared the relative capacities of BT and homogenous dose external beam radiotherapy (EBRT) to enhance the anti-tumor immune response in combination with immune checkpoint inhibition (ICI).

Materials and Methods: We used syngeneic murine models of melanoma (B78) and prostate cancer (Myc-CaP). To evaluate the effect of BT on the microenvironment, mice bearing B78 tumors were randomized to receive BT (192Ir source, 2 Gy to tumor edge), sham insertion, or EBRT (2, 8, or 20 Gy). Tumors were harvested 3 days following RT and in the case of BT, punch excisions were taken from the dissected tumor 1, 3, and 5 mm from the source location for gene expression and immune cell infiltration analysis. To evaluate anti-tumor response, we randomized mice bearing B78 tumors on the right flank (~200 mm3) and left shoulder (~100 mm3) to BT alone, catheter insertion alone, BT + ICI (anti-PD-L1 and anti-CTLA-4, 200 µg IP injection days 3, 6, 9 after RT), EBRT (2 or 8 Gy) + ICI, or ICI alone. Mice bearing MyC-CaP tumors were randomized to sham insertion, BT (2 or 8 Gy to tumor edge), BT + ICI, EBRT (2, 8, or 20 Gy) + ICI, or ICI alone. Immediately following RT, mice were engrafted with a secondary tumor.

Results: Using qPCR analysis, we observed statistically significant differences in gene expression of Mhc-1, Ifnβ, and Vcam between tissue locations in BT treated tumors. Furthermore, in a single tumor BT optimally engaged all three pathways while each EBRT dose only optimally engaged one. Bulk RNAseq analysis revealed unique gene expression signatures between tissue locations in BT treated tumors. We observed significant differences in number of CD8+ and FOXP3+ cells between tissue locations. In B78 tumor bearing mice, we observed a greater anti-tumor response at the secondary untreated tumor with BT + ICI (63% CR) compared to EBRT + ICI (12.5% CR). In mice bearing Myc-CaP tumors treated with BT + ICI, we observed a significant reduction in tumor growth compared to other groups and no engraftment at the secondary tumor. This effect was dependent on both CD4+ and CD8+ cells and was sensitive to BT dose. Splenocytes harvested from disease-free mice co-cultured with tumor cells showed significant increases in expression of T cell activation markers in both CD4+ and CD8+ cell populations.

Conclusions: We report dose-dependent effects of RT on expression of immune susceptibility markers and immune cell infiltration in a murine tumor model. We observe that a heterogeneous dose of BT results in spatial differences in these effects within a single tumor. This spatial heterogeneity in activation of immune mechanisms may underlie a greater capacity of BT to augment anti-tumor immune response when combined with ICI, as compared to homogenous dose EBRT.

Citation Format: Justin C. Jagodinsky, Wonjong Jin, Jessica M. Vera, Raghava N. Sriramaneni, Paul A. Clark, Keng-Hsueh S. Lan, Ishan Chakravarty, Noah Siegel, Raad H. Allawi, Sarah E. Emma, Ian S. Arthur, Rupak K. Das, Irene M. Ong, Jessica R. Miller, Zachary S. Morris. Brachytherapy dose heterogeneity primes response to immune checkpoint blockade to generate anti-tumor immunity [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 1304.

Low-dose targeted radionuclide therapy renders immunologically cold tumors responsive to immune checkpoint blockade

Molecular and cellular effects of radiotherapy on tumor microenvironment (TME) can help prime and propagate antitumor immunity. We hypothesized that delivering radiation to all tumor sites could augment response to immunotherapies. We tested an approach to enhance response to immune checkpoint inhibitors (ICIs) by using targeted radionuclide therapy (TRT) to deliver radiation semiselectively to tumors. NM600, an alkylphosphocholine analog that preferentially accumulates in most tumor types, chelates a radioisotope and semiselectively delivers it to the TME for therapeutic or diagnostic applications. Using serial ⁸⁶Y-NM600 positron emission tomography (PET) imaging, we estimated the dosimetry of ⁹⁰Y-NM600 in immunologically cold syngeneic murine models that do not respond to ICIs alone. We observed strong therapeutic efficacy and reported optimal dose (2.5 to 5 gray) and sequence for ⁹⁰Y-NM600 in combination with ICIs. After combined treatment, 45 to 66% of mice exhibited complete response and tumor-specific T cell memory, compared to 0% with ⁹⁰Y-NM600 or ICI alone. This required expression of STING in tumor cells. Combined TRT and ICI activated production of proinflammatory cytokines in the TME, promoted tumor infiltration by and clonal expansion of CD8⁺ T cells, and reduced metastases. In mice bearing multiple tumors, combining TRT with moderate-dose (12 gray) external beam radiotherapy (EBRT) targeting a single tumor augmented response to ICIs compared to combination of ICIs with either TRT or EBRT alone. The safety of TRT was confirmed in a companion canine study. Low-dose TRT represents a translatable approach to promote response to ICIs for many tumor types, regardless of location.

Low-Dose Radiation Potentiates the Propagation of Anti-Tumor Immunity against Melanoma Tumor in the Brain after In Situ Vaccination at a Tumor outside the Brain

Brain metastases develop in over 60% of advanced melanoma patients and negatively impact quality of life and prognosis. In a murine melanoma model, we previously showed that an in situ vaccination (ISV) regimen, combining radiation treatment and intratumoral (IT) injection of immunocytokine (IC: anti-GD2 antibody fused to IL2), along with the immune checkpoint inhibitor anti-CTLA-4, robustly eliminates peripheral flank tumors but only has modest effects on co-occurring intracranial tumors. In this study, we investigated the ability of low-dose radiation to the brain to potentiate anti-tumor immunity against a brain tumor when combined with ISV + anti-CTLA-4. B78 (GD2+, immunologically "cold") melanoma tumor cells were implanted into the flank and the right striatum of the brain in C57BL/6 mice. Flank tumors (50-150 mm3) were treated following a previously optimized ISV regimen [radiation (12 Gy × 1, treatment day 1), IT-IC (50 µg daily, treatment days 6-10), and anti-CTLA-4 (100 µg, treatment days 3, 6, 9)]. Mice that additionally received whole-brain radiation treatment (WBRT, 4 Gy × 1) on day 15 demonstrated significantly increased survival compared to animals that received ISV + anti-CTLA-4 alone, WBRT alone or no treatment (control) (P < 0.001, log-rank test). Timing of WBRT was critical, as WBRT administration on day 1 did not significantly enhance survival compared to ISV + anti-CTLA-4, suggesting that the effect of WBRT on survival might be mediated through immune modulation and not just direct tumor cell cytotoxicity. Modest increases in T cells (CD8+ and CD4+) and monocytes/macrophages (F4/80+) but no changes in FOXP3+ regulatory T cells (Tregs), were observed in brain melanoma tumors with addition of WBRT (on day 15) to ISV + anti-CTLA-4. Cytokine multiplex immunoassay revealed distinct changes in both intracranial melanoma and contralateral normal brain with addition of WBRT (day 15) to ISV + anti-CTLA-4, with notable significant changes in pro-inflammatory (e.g., IFNγ, TNFα and LIX/CXCL5) and suppressive (e.g., IL10, IL13) cytokines as well as chemokines (e.g., IP-10/CXCL10 and MIG/CXCL9). We tested the ability of the alkylphosphocholine analog, NM600, to deliver immunomodulatory radiation to melanoma brain tumors as a targeted radionuclide therapy (TRT). Yttrium-86 (86Y) chelated to NM600 was delivered intravenously by tail vein to mice harboring flank and brain melanoma tumors, and PET imaging demonstrated specific accumulation up to 72 h at each tumor site (∼12:1 brain tumor/brain and ∼8:1 flank tumor/muscle). When NM600 was chelated to therapeutic β-particle-emitting 90Y and administered on treatment day 13, T-cell infiltration and cytokine profiles were altered in melanoma brain tumor, like that observed for WBRT. Overall, our results demonstrate that addition of low-dose radiation, timed appropriately with ISV administration to tumors outside the brain, significantly increases survival in animals co-harboring melanoma brain tumors. This observation has potentially important translational implications as a treatment strategy for increasing the response of tumors in the brain to systemically administered immunotherapies.

Combination of Bempegaldesleukin and Anti-CTLA-4 Prevents Metastatic Dissemination After Primary Resection or Radiotherapy in a Preclinical Model of Non-Small Cell Lung Cancer

Surgical resection or hypo-fractionated radiation therapy (RT) in early-stage non-small cell lung cancer (NSCLC) achieves local tumor control, but metastatic relapse remains a challenge. We hypothesized that immunotherapy with anti-CTLA-4 and bempegaldesleukin (BEMPEG; NKTR-214), a CD122-preferential IL2 pathway agonist, after primary tumor RT or resection would reduce metastases in a syngeneic murine NSCLC model. Mice bearing Lewis Lung Carcinoma (LLC) tumors were treated with combinations of BEMPEG, anti-CTLA-4, and primary tumor treatment (surgical resection or RT). Primary tumor size, mouse survival, and metastatic disease at the time of death were assessed. Flow cytometry, qRT-PCR, and cytokine analyses were performed on tumor specimens. All mice treated with RT or surgical resection of primary tumor alone succumbed to metastatic disease, and all mice treated with BEMPEG and/or anti-CTLA-4 succumbed to primary tumor local progression. The combination of primary tumor RT or resection and BEMPEG and anti-CTLA-4 reduced spontaneous metastasis and improved survival without any noted toxicity. Flow cytometric immunoprofiling of primary tumors revealed increased CD8 T and NK cells and decreased T-regulatory cells with the combination of BEMPEG, anti-CTLA-4, and RT compared to RT alone. Increased expression of genes associated with tumor cell immune susceptibility, immune cell recruitment, and cytotoxic T lymphocyte activation were observed in tumors of mice treated with BEMPEG, anti-CTLA-4, and RT. The combination of BEMPEG and anti-CTLA-4 with primary tumor RT or resection enabled effective control of local and metastatic disease in a preclinical murine NSCLC model. This therapeutic combination has important translational potential for patients with early-stage NSCLC and other cancers.

Temporal analysis of type 1 interferon activation in tumor cells following external beam radiotherapy or targeted radionuclide therapy

Rationale: Clinical interest in combining targeted radionuclide therapies (TRT) with immunotherapies is growing. External beam radiation therapy (EBRT) activates a type 1 interferon (IFN1) response mediated via stimulator of interferon genes (STING), and this is critical to its therapeutic interaction with immune checkpoint blockade. However, little is known about the time course of IFN1 activation after EBRT or whether this may be induced by decay of a TRT source. Methods: We examined the IFN1 response and expression of immune susceptibility markers in B78 and B16 melanomas and MOC2 head and neck cancer murine models using qPCR and western blot. For TRT, we used 90Y chelated to NM600, an alkylphosphocholine analog that exhibits selective uptake and retention in tumor cells including B78 and MOC2. Results: We observed significant IFN1 activation in all cell lines, with peak activation in B78, B16, and MOC2 cell lines occurring 7, 7, and 1 days, respectively, following RT for all doses. This effect was STING-dependent. Select IFN response genes remained upregulated at 14 days following RT. IFN1 activation following STING agonist treatment in vitro was identical to RT suggesting time course differences between cell lines were mediated by STING pathway kinetics and not DNA damage susceptibility. In vivo delivery of EBRT and TRT to B78 and MOC2 tumors resulted in a comparable time course and magnitude of IFN1 activation. In the MOC2 model, the combination of 90Y-NM600 and dual checkpoint blockade therapy reduced tumor growth and prolonged survival compared to single agent therapy and cumulative dose equivalent combination EBRT and dual checkpoint blockade therapy. Conclusions: We report the time course of the STING-dependent IFN1 response following radiation in multiple murine tumor models. We show the potential of TRT to stimulate IFN1 activation that is comparable to that observed with EBRT and this may be critical to the therapeutic integration of TRT with immunotherapies.

A multipurpose brachytherapy catheter to enable intratumoral injection

PURPOSE

To create and test a multipurpose brachytherapy catheter prototype enabling intratumoral injection and brachytherapy after a single catheter insertion.

METHODS AND MATERIALS

The design of the prototype consists of an outer tube and an inner syringe tube that can be filled with injectable agent. The outer sheath and inner syringe tube were constructed using polytetrafluoroethylene tubing, and the other components were 3D printed using dental resin and polylactic acid material. To demonstrate functionality, we injected in vitro phantoms with dyed saline. For proof of concept, we demonstrated the potential for the prototype to deliver cell therapy, enhance tumor delineation, deliver tattoo ink for pathology marking, avoid toxicity through local delivery of chemotherapy, and facilitate combination brachytherapy and immunotherapy.

RESULTS

The prototype enables accurate injection in vitro and in vivo without altering dosimetry. To illustrate the potential for delivery of cell therapies, we injected luciferase-expressing splenocytes and confirmed their delivery with bioluminescence imaging. To demonstrate feasibility of radiographically visualizing injected material, we delivered iohexol contrast intratumorally and confirmed tumor retention using Faxitron x-ray imaging. In addition, we show the potential of intratumoral administration to reduce toxicity associated with cyclophosphamide compared with systemic administration. To demonstrate feasibility, we treated tumor-bearing mice with brachytherapy (¹⁹²Ir source, 2 Gy to 5 mm) in combination with intratumoral injection of 375,000 U of interleukin 2 and observed no increased toxicity.

CONCLUSIONS

These results demonstrate that a prototype multipurpose brachytherapy catheter enables accurate intratumoral injection and support the feasibility of combining intratumoral injection with brachytherapy.

Tumor-Specific Antibody, Cetuximab, Enhances the In Situ Vaccine Effect of Radiation in Immunologically Cold Head and Neck Squamous Cell Carcinoma

In head and neck squamous cell carcinoma (HNSCC) tumors that over-expresses huEGFR, the anti-EGFR antibody, cetuximab, antagonizes tumor cell viability and sensitizes to radiation therapy. However, the immunologic interactions between cetuximab and radiation therapy are not well understood. We transduced two syngeneic murine HNSCC tumor cell lines to express human EGFR (MOC1- and MOC2-huEGFR) in order to facilitate evaluation of the immunologic interactions between radiation and cetuximab. Cetuximab was capable of inducing antibody-dependent cellular cytotoxicity (ADCC) in MOC1- and MOC2-huEGFR cells but showed no effect on the viability or radiosensitivity of these tumor cells, which also express muEGFR that is not targeted by cetuximab. Radiation enhanced the susceptibility of MOC1- and MOC2-huEGFR to ADCC, eliciting a type I interferon response and increasing expression of NKG2D ligands on these tumor cells. Co-culture of splenocytes with cetuximab and MOC2-huEGFR cells resulted in increased expression of IFNγ in not only NK cells but also in CD8+ T cells, and this was dependent upon splenocyte expression of FcγR. In MOC2-huEGFR tumors, combining radiation and cetuximab induced tumor growth delay that required NK cells, EGFR expression, and FcγR on host immune cells. Combination of radiation and cetuximab increased tumor infiltration with NK and CD8+ T cells but not regulatory T cells. Expression of PD-L1 was increased in MOC2-huEGFR tumors following treatment with radiation and cetuximab. Delivering anti-PD-L1 antibody with radiation and cetuximab improved survival and resulted in durable tumor regression in some mice. Notably, these cured mice showed evidence of an adaptive memory response that was not specifically directed against huEGFR. These findings suggest an opportunity to improve the treatment of HNSCC by combining radiation and cetuximab to engage an innate anti-tumor immune response that may prime an effective adaptive immune response when combined with immune checkpoint blockade. It is possible that this approach could be extended to any immunologically cold tumor that does not respond to immune checkpoint blockade alone and for which a tumor-specific antibody exists or could be developed.

Abstract 2256: Low dose brain radiotherapy enhances the efficacy of an extracranial in situ vaccine regimen against melanoma brain metastases in a pre-clinical murine model

Brain metastases develop in &gt;60% of advanced melanoma patients, resulting in considerable morbidity and mortality. We previously showed that a regimen combining radiation (RT) and intra-tumoral (IT) injection of immunocytokine (IC: αGD2 antibody fused to IL2) resulted in enhanced response to immune checkpoint inhibition (ICI: αCTLA4 Ab) in mice bearing immunologically cold murine melanoma tumors. Here, we used the immunologically cold B78 murine melanoma model to investigate the efficacy of this in situ vaccine (ISV) regimen (RT + IT-IC + ICI) in mice bearing melanoma tumors in the brain and at extracranial sites. B78 (GD2+) cells were implanted into the right and left flanks and the right striatum of the brain in syngeneic C57BL/6 mice. Right flank tumors (150-200 mm3) were treated following a previously optimized ISV regimen [RT (12Gy, day 1), IT-IC (days 6-10) and αCTLA4 (days 3, 6, 9)]. ISV eliminated both flank tumors [22/22 complete response (CR)] compared to αCTLA-4 alone (0/8 CR). However, ISV had only modest effect in prolonging survival in mice with a B78 brain melanoma tumor and all mice succumbed to progressive brain tumor burden. Comparing tumors from the left flank and brain of mice treated with ISV to a right flank tumor, qPCR demonstrated no difference in the expression of Mhc-1 or of various checkpoint receptors/ligands (including Ctla4, Tigit, Pd-L1, Lag3). Immunohistochemistry and flow cytometry at day 15 after ISV demonstrated decreased regulatory T cells (Tregs; CD4+, FOXP3+, CD25+) and a higher ratio of CD8+ T cells:Tregs in the left flank tumor compared to the brain tumor. In contrast, these levels did not differ between left flank and brain tumors in untreated mice. Following ISV, CD8+ T cell:Treg ratio at both the left flank and brain tumor sites significantly increased compared to these respective tumor sites in untreated mice. Multiplex profiling of 32 cytokines demonstrated indistinguishable cytokine expression between untreated tumors in the left flank and brain but showed a distinct pattern of response at these locations following right flank ISV with reduced activation of pro-inflammatory cytokines in the brain melanoma tumor. Given the capacity of low dose RT to temporarily deplete Tregs and increase production of pro-inflammatory cytokines, we hypothesized that low dose whole brain (WB) RT (4 Gy x 1) would enhance ISV response of melanoma brain tumors. Addition of WBRT at day 15 after ISV significantly increased survival of mice with a melanoma tumor in the brain compared to ISV or WBRT alone with 2/11 exhibiting durable CR compared to 0/10 with either ISV or WBRT alone. Interestingly, WBRT administered concurrently on day 1 with ISV had no survival benefit compared to ISV alone - suggesting a critical immunomodulatory role for WBRT at day 15. With WBRT + ISV, we observed an increased ratio of CD8+:FOXP3+ T cells in melanoma brain tumors compared to ISV alone. These results suggest that low dose brain RT may enhance the response to an extracranial ISV at immunologically cold brain metastases.

Citation Format: Raghava N. Sriramaneni, Paul A. Clark, Amber M. Bates, Bryce R. Anderson, Wonjong Jin, Justin C. Jagodinsky, Alexander L. Rakhmilevich, Zachary S. Morris. Low dose brain radiotherapy enhances the efficacy of an extracranial in situ vaccine regimen against melanoma brain metastases in a pre-clinical murine model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2256.

Abstract 1881: Immune mediated interaction between radiation and cetuximab in a syngeneic murine model of head and neck squamous cell carcinoma

Purpose: Patients with head and neck squamous cell carcinoma (HNSCC) treated with anti-EGFR (cetuximab) mAb-based immunotherapy often acquire therapy-resistance, reducing clinical benefit. We evaluated the efficacy of a combined modality in situ vaccination regimen aimed at overcoming resistance to cetuximab using a syngeneic tumor model.

Experimental Design: The murine HNSCC cell line MOC2 was transduced to express human EGFR (MOC2-huEGFR) and used as a syngeneic model of therapeutic resistance to cetuximab. The cells were tested for viability, radiosensitivity, and huEGFR-specific mAb binding efficacy in the presence of cetuximab. Antibody-dependent cellular cytotoxicity (ADCC) was tested by coculture of 51chromium-labeld MOC2-huEGFR with PBMC. Mice bearing these syngeneic tumors were treated with therapeutic regimens that included local radiation (RT), intratumoral (IT) cetuximab, and/or systemic immune checkpoint inhibitors, and tumor growth/survival rate were monitored.

Result: Cetuximab induced antibody-dependent cellular cytotoxicity (ADCC) in MOC2-huEGFR and PBMC co-cultures, but showed no effect on cell proliferation or radiosensitivity. Combined RT and IT-cetuximab treatment induced tumor growth delay, which required huEGFR expression, NK cells, and FcγR expression. In addition, combined RT+IT-cetuximab therapy greatly induced tumor infiltration by both CD8 T cells and NK cells. RT promoted NK cell-mediated ADCC effects against 51chromium-labeld MOC2-huEGFR with increased IFNγ expression. Proliferating tumor cells gradually increased Pd-l1 mRNA expression, and RT enhanced cell surface PD-L1 in MOC2-huEGFR cells. Systemic anti-PD-L1 antibody or IT-cetuximab alone did not show antitumor response against MOC2-huEGFR bearing mice; however, significant tumor growth inhibition was observed with combined anti-PD-L1, RT, and IT-cetuximab.

Conclusion: The MOC2-huEGFR HNSCC tumor model is immunologically “cold” and does not respond to either cetuximab or anti-PD-L1 therapies alone. In this model, we show that a combination of RT+cetuximab+anti-PD-L1 elicits a cooperative in situ vaccine effect. Combining RT, cetuximab and immune checkpoint blockade may enable anti-tumor immune response in HNSCC patients with immunologically cold, huEGFR-expressing tumors.

Citation Format: Wonjong Jin, Amy K. Erbe, Ciara Schwarz, Abigail Jaquish, Bryce R. Anderson, Raghava N. Sriramaneni, Justin C. Jagodinsky, Paul A. Clark, Zachary S. Morris. Immune mediated interaction between radiation and cetuximab in a syngeneic murine model of head and neck squamous cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1881.

In situ Vaccine Plus Checkpoint Blockade Induces Memory Humoral Response

In a syngeneic murine melanoma (MEL) model, we recently reported an in situ vaccination response to combined radiation (RT) and intra-tumoral (IT) injection of anti-GD2 hu14. 18-IL2 immunocytokine (IC). This combined treatment resulted in 71% complete and durable regression of 5-week tumors, a tumor-specific memory T cell response, and augmented response to systemic anti-CTLA-4 antibody checkpoint blockade. While the ability of radiation to diversify anti-tumor T cell response has been reported, we hypothesize that mice rendered disease-free (DF) by a RT-based ISV might also exhibit a heightened B cell response. C57BL/6 mice were engrafted with 2 × 10⁶ GD2+ B78 MEL and treated at a target tumor size of ~200 mm³ with 12 Gy RT, IT-IC on day (D)6-D10, and anti-CTLA-4 on D3, 6, and 9. Serum was collected via facial vein before tumor injection, before treatment, during treatment, after becoming DF, and following rejection of subcutaneous 2 × 10⁶ B78 MEL re-challenge on D90. Flow cytometry demonstrated the presence of tumor-specific IgG in sera from mice rendered DF and rejecting re-challenge with B78 MEL at D90 after starting treatment. Consistent with an adaptive endogenous anti-tumor humoral memory response, these anti-tumor antibodies bound to B78 cells and parental B16 cells (GD2-), but not to the unrelated syngeneic Panc02 or Panc02 GD2+ cell lines. We evaluated the kinetics of this response and observed that tumor-specific IgG was consistently detected by D22 after initiation of treatment, corresponding to a time of rapid tumor regression. The amount of tumor-specific antibody binding to tumor cells (as measured by flow MFI) did not correlate with host animal prognosis. Incubation of B16 MEL cells in DF serum, vs. naïve serum, prior to IV injection, did not delay engraftment of B16 metastases and showed similar overall survival rates. B cell depletion using anti-CD20 or anti-CD19 and anti-B220 did not impact the efficacy of ISV treatment. Thus, treatment with RT + IC + anti-CTLA-4 results in adaptive anti-tumor humoral memory response. This endogenous tumor-specific antibody response does not appear to have therapeutic efficacy but may serve as a biomarker for an anti-tumor T cell response.

In situ vaccination at a peripheral tumor site augments response against melanoma brain metastases

BACKGROUND

Immune checkpoint inhibition (ICI) alone is not efficacious for a large number of patients with melanoma brain metastases. We previously established an in situ vaccination (ISV) regimen combining radiation and immunocytokine to enhance response to ICIs. Here, we tested whether ISV inhibits the development of brain metastases in a murine melanoma model.

METHODS

B78 (GD2+) melanoma 'primary' tumors were engrafted on the right flank of C57BL/6 mice. After 3-4 weeks, primary tumors were treated with ISV (radiation (12 Gy, day 1), α-GD2 immunocytokine (hu14.18-IL2, days 6-10)) and ICI (α-CTLA-4, days 3, 6, 9). Complete response (CR) was defined as no residual tumor observed at treatment day 90. Mice with CR were tested for immune memory by re-engraftment with B78 in the left flank and then the brain. To test ISV efficacy against metastases, tumors were also engrafted in the left flank and brain of previously untreated mice. Tumors were analyzed by quantitative reverse transcription-PCR, immunohistochemistry, flow cytometry and multiplex cytokine assay.

RESULTS

ISV+α-CTLA-4 resulted in immune memory and rejection of B78 engraftment in the brain in 11 of 12 mice. When B78 was engrafted in brain prior to treatment, ISV+α-CTLA-4 increased survival compared with ICI alone. ISV+α-CTLA-4 eradicated left flank tumors but did not elicit CR at brain sites when tumor cells were engrafted in brain prior to ISV. ISV+α-CTLA-4 increased CD8+ and CD4+ T cells in flank and brain tumors compared with untreated mice. Among ISV + α-CTLA-4 treated mice, left flank tumors showed increased CD8+ infiltration and CD8+:FOXP3+ ratio compared with brain tumors. Flank and brain tumors showed minimal differences in expression of immune checkpoint receptors/ligands or Mhc-1. Cytokine productions were similar in left flank and brain tumors in untreated mice. Following ISV+α-CTLA-4, production of immune-stimulatory cytokines was greater in left flank compared with brain tumor grafts.

CONCLUSION

ISV augmented response to ICIs in murine melanoma at brain and extracranial tumor sites. Although baseline tumor-immune microenvironments were similar at brain and extracranial tumor sites, response to ISV+α-CTLA-4 was divergent with reduced infiltration and activation of immune cells in brain tumors. Additional therapies may be needed for effective antitumor immune response against melanoma brain metastases.

Combining brachytherapy and immunotherapy to achieve in situ tumor vaccination: A review of cooperative mechanisms and clinical opportunities

As immunotherapies continue to emerge as a standard component of treatment for a variety of cancers, the imperative for testing these in combination with other standard cancer therapies grows. Radiation therapy may be a particularly well-suited partner for many immunotherapies. By modulating immune tolerance and functional immunogenicity at a targeted tumor site, radiation therapy may serve as a method of in situ tumor vaccination. In situ tumor vaccination is a therapeutic strategy that seeks to convert a patient's own tumor into a nidus for enhanced presentation of tumor-specific antigens in a way that will stimulate and diversify an antitumor T cell response. The mechanisms whereby radiation may impact immunotherapy are diverse and include its capacity to simultaneously elicit local inflammation, temporary local depletion of suppressive lymphocyte lineages, enhanced tumor cell susceptibility to immune response, and immunogenic tumor cell death. Emerging data suggest that each of these mechanisms may display a distinct dose-response profile, making it challenging to maximize each of these effects using external beam radiation. Conversely, the highly heterogenous and conformal dose distribution achieved with brachytherapy may be optimal for enhancing the immunogenic capacity of radiation at a tumor site while minimizing off-target antagonistic effects on peripheral immune cells. Here, we review the immunogenic effects of radiation, summarize the clinical rationale and data supporting the use of radiation together with immunotherapies, and discuss the rationale and urgent need for further preclinical and clinical investigation specifically of brachytherapy in combination with immunotherapies. Harnessing these immunomodulatory effects of brachytherapy may offer solutions to overcome obstacles to the efficacy of immunotherapies in immunologically "cold" tumors while potentiating greater response in the context of immunologically "hot" tumors.

Tumor-Specific Inhibition of In Situ Vaccination by Distant Untreated Tumor Sites

In situ vaccination is an emerging cancer treatment strategy that uses local therapies to stimulate a systemic antitumor immune response. We previously reported an in situ vaccination effect when combining radiation (RT) with intratumor (IT) injection of tumor-specific immunocytokine (IC), a fusion of tumor-specific antibody and IL2 cytokine. In mice bearing two tumors, we initially hypothesized that delivering RT plus IT-IC to the "primary" tumor would induce a systemic antitumor response causing regression of the "secondary" tumor. To test this, mice bearing one or two syngeneic murine tumors of B78 melanoma and/or Panc02 pancreatic cancer were treated with combined external beam RT and IT-IC to the designated "primary" tumor only. Primary and secondary tumor response as well as animal survival were monitored. Immunohistochemistry and quantitative real-time PCR were used to quantify tumor infiltration with regulatory T cells (Treg). Transgenic "DEREG" mice or IgG2a anti-CTLA-4 were used to transiently deplete tumor Tregs. Contrary to our initial hypothesis, we observed that the presence of an untreated secondary tumor antagonized the therapeutic effect of RT + IT-IC delivered to the primary tumor. We observed reciprocal tumor specificity for this effect, which was circumvented if all tumors received RT or by transient depletion of Tregs. Primary tumor treatment with RT + IT-IC together with systemic administration of Treg-depleting anti-CTLA-4 resulted in a renewed in situ vaccination effect. Our findings show that untreated tumors can exert a tumor-specific, Treg-dependent, suppressive effect on the efficacy of in situ vaccination and demonstrate clinically viable approaches to overcome this effect. Untreated tumor sites antagonize the systemic and local antitumor immune response to an in situ vaccination regimen. This effect is radiation sensitive and may be mediated by tumor-specific regulatory T cells harbored in the untreated tumor sites. Cancer Immunol Res; 6(7); 825-34. ©2018 AACR.

Transcriptional-mediated effects of radiation on the expression of immune susceptibility markers in melanoma

BACKGROUND AND PURPOSE

We recently reported a time-sensitive, cooperative, anti-tumor effect elicited by radiation (RT) and intra-tumoral-immunocytokine injection in vivo. We hypothesized that RT triggers transcriptional-mediated changes in tumor expression of immune susceptibility markers at delayed time points, which may explain these previously observed time-dependent effects.

MATERIALS AND METHODS

We examined the time course of changes in expression of immune susceptibility markers following in vitro or in vivo RT in B78 murine melanoma and A375 human melanoma using flow cytometry, immunoblotting, and qPCR.

RESULTS

Flow cytometry and immunoblot revealed time-dependent increases in expression of death receptors and T cell co-stimulatory/co-inhibitory ligands following RT in murine and human melanoma. Using high-throughput qPCR, we observed comparable time courses of RT-induced transcriptional upregulation for multiple immune susceptibility markers. We confirmed analogous changes in B78 tumors irradiated in vivo. We observed upregulated expression of DNA damage response markers days prior to changes in immune markers, whereas phosphorylation of the STAT1 transcription factor occurred concurrently with changes following RT.

CONCLUSION

This study highlights time-dependent, transcription-mediated changes in tumor immune susceptibility marker expression following RT. These findings may help in the design of strategies to optimize sequencing of RT and immunotherapy in translational and clinical studies.

In-vitro assessment and pharmacodynamics of nimesulide incorporated Aloe vera transemulgel

The aim of the investigation was to prepare nimesulide emulsion for incorporation in Aloe vera gel base to formulate 'nimesulide - Aloe vera transemulgel' (NAE) and to carryout in-vitro assessment and in-vivo anti-inflammatory studies of the product. Although the use of nimesulide is banned for oral administration, due to its potential for inducing hepatotoxicity and thrombocytopenia, the use of nimesulide for topical delivery is prominent in the treatment of many inflammatory conditions including rheumatoid arthritis. The drug loading capacity of transdermal gels is low for hydrophobic drugs such as nimesulide. Nimesulide can be effectively incorporated into emulgels (a combination of emulsion and gel). Aloe vera has a mild anti-inflammatory effect and in the present study Aloe vera gel was formulated and used as a gel base to prepare NAE. The emulgels thus prepared were evaluated for viscosity, pH, in-vitro permeation, stability and skin irritation test. In-vivo anti-inflammatory studies were performed using carrageenan induced hind paw edema method in Wistar rats. The results were compared with that of commercial nimesulide gel (CNG). From the in-vitro studies, effective permeation of nimesulide from NAE (53.04 %) was observed compared to CNG (44.72 %) at 30 min indicating better drug release from NAE. Topical application of the emulgel found no skin irritation. Stability studies proved the integrity of the formulation. The percentage of inhibition of edema was highest for the prepared NAE (67.4 % inhibition after 240 min) compared to CNG (59.6 %). From our results, it was concluded that the Aloe vera gel acts as an effective gel base to prepare nimesulide emulgel with high drug loading capacity (86.4 % drug content) compared to CNG (70.5 % drug content) with significant anti-inflammatory effect.

Characterization of the Possible Mechanisms Underlying the Hypotensive and Spasmogenic Effects of Loranthus ferrugineus Methanolic Extract

In the present study, L. ferrugineus methanol extract (LFME) was evaluated for its blood pressure lowering effect in anesthetized normotensive Sprague Dawley (SD) rats and its spasmogenic effect in isolated guinea pig ileum. The possible mechanism(s) of action were also investigated. LFME was obtained by Soxhlet extraction. The rats were fasted overnight and anesthetized with sodium pentobarbitone (60 mg/kg i.p.). LFME was administered in i.v. boluses in the concentrations of 25, 50, 100 and 200 mg/kg respectively, with concomitant monitoring of mean arterial pressure (MAP). It was found that LFME dose-dependently reduced MAP. An i.v. bolus injection of atropine significantly decreased the blood pressure lowering effect of LFME. Similarly, L-NAME (Nω-nitro-L-arginine methyl ester) significantly lowered both the MAP and the action duration. Conversely, no significant change in MAP was seen following i.v. injections of neostigmine, hexamethonium, prazosin and propranolol. LFME also produced a dose-dependent contractile effect in guinea pig ileum. This contraction was significantly reduced in atropine pre-incubated tissue segments, yet it was significantly enhanced in the presence of neostigmine. No appreciable change in the ability of LFME to contract guinea pig ileum was seen in the presence of hexamethonium. Accordingly, it can be postulated that LFME possesses a marked hypotensive effect that can be attributed to stimulation of muscarinic receptors and/or stimulation of nitric oxide (NO) release. Moreover, LFME retains a considerable spasmogenic action due to its cholinergic properties. The hypotensive and spasmogenic effects of LFME justify its traditional uses.

Vasorelaxant effect of diterpenoid lactones from Andrographis paniculata chloroform extract on rat aortic rings

BACKGROUND

The aim of the present study is to evaluate the possible mechanism of the vasorelaxant effect of the Andrographis paniculata chloroform extract (APCE) and diterpenoids, such as, 14-deoxyandrographolide (DA) and 14-deoxy-11, 12-didehydroandrographolide (DDA), on rat aortic rings.

METHODS

DA and DDA (10 μM to 40 μM) induce relaxation in the aortic rings pre-contracted with KCl (80 mM).

RESULTS

The IC(50) values are 40.47 ± 1.44 and 37.43 ± 1.41%, respectively, and this inhibition is antagonized by increasing the Ca(2+) concentration in the Kreb's medium. The results indicate that APCE, DA, and DDA may have a calcium anatgonist property. APCE, DA, and DDA also relax norepinephrene (NE)-induced sustained contractions with IC(50) values 41.63 ± 1.19, 49.22 ± 2.76, and 37.46 ± 1.41% and this relaxant effect is unaffected by the removal of the endothelium or by the presence of indomethacin and Nω-nitro-L-arginine (L-NAME). Moreover, DA and DDA inhibit the phasic and tonic contractions induced by NE in a concentration-dependent manner and show the most potent inhibition on phasic contraction (P < 0.01).

CONCLUSION

This study shows that APCE, DA, and DDA pre-treatment presents a more potent inhibition compared to post-treatment, after the tension has reached a steady state. These results suggest that the vasorelaxation of APCE, DA, and DDA direct the inhibition of the calcium influx. The vasorelaxant effect is more active in the calcium independent pathway and more sensitive in the intial stage of contraction.

Cardiovascular activity of the n-butanol fraction of the methanol extract of Loranthus ferrugineus Roxb

We investigated the vascular responses and the blood pressure reducing effects of different fractions obtained from the methanol extract of Loranthus ferrugineus Roxb. (F. Loranthaceae). By means of solvent-solvent extraction, L. ferrugineus methanol extract (LFME) was successively fractionated with chloroform, ethyl acetate and n-butanol. The ability of these LFME fractions to relax vascular smooth muscle against phenylephrine (PE)- and KCl-induced contractions in isolated rat aortic rings was determined. In another set of experiments, LFME fractions were tested for blood pressure lowering activity in anesthetized adult male Sprague-Dawley rats (250-300 g, 14-18 weeks). The n-butanol fraction of LFME (NBF-LFME) produced a significant concentration-dependent inhibition of PE- and KCl-induced aortic ring contractions compared to other fractions. Moreover, NBF-LFME had a significantly higher relaxant effect against PE- than against high K+-induced contractions. In anesthetized Sprague-Dawley rats, NBF-LFME significantly lowered blood pressure in a dose-dependent manner and with a relatively longer duration of action compared to the other fractions. HPLC, UV and IR spectra suggested the presence of terpenoid constituents in both LFME and NBF-LFME. Accordingly, we conclude that NBF-LFME is the most potent fraction producing a concentration-dependent relaxation in vascular smooth muscle in vitro and a dose-dependent blood pressure lowering activity in vivo. The cardiovascular effects of NBF-LFME are most likely attributable to its terpenoid content.

Pharmacological mechanisms underlying the vascular activities of Loranthus ferrugineus Roxb. in rat thoracic aorta

AIM OF THE STUDY

The present study was aimed to investigate the pharmacological basis for the use of Loranthus ferrugineus in hypertension.

MATERIALS AND METHODS

Loranthus ferrugineus methanol extract (LFME) was obtained using Soxhelt extractor and then successively fractionated using chloroform, ethyl acetate and n-butanol. The n-butanol fraction of LFME (NBF-LFME) was studied using isolated rat thoracic aorta.

RESULTS

NBF-LFME (1.0 x 10(-5) to 3.0mg/ml) was found to be the most potent to concentration-dependently relax the endothelium-intact phenyephrine (PE, 1 microM)- and high K(+) (80 mM)-precontracted rat aortic rings. Removal of the endothelium completely abolished the vascular relaxing properties of NBF-LFME. Pretreatment with atropine (1 microM), L-NAME (10 microM), indomethacin (10 microM) and methylene blue (10 microM) significantly blocked NBF-LFME-mediated relaxation. Endothelium-dependent and -independent relaxations induced by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly enhanced in aortic rings pretreated with NBF-LFME when compared to those observed in control aortic rings. On the contrary, glibenclamide (10 microM), propranolol (1 microM) and prazosin (0.01 microM) did not alter NBF-LFME-induced relaxation.

CONCLUSIONS

The results suggest that NBF-LFME induced vascular relaxation by stimulating muscarinic receptors, activating the endothelium-derived nitric oxide-cGMP-relaxant pathway, promoting prostacyclin release and/or possibly through its ability to lengthen the released nitric oxide half-life. The present data further supports previous in vivo findings and explain the traditional use of Loranthus ferrugineus as an anti-hypertensive agent.