Murine Cancer Model Research Articles

Pan-PI3K inhibition with copanlisib overcomes Treg- and M2-TAM-mediated immune suppression and promotes anti-tumor immune responses

The PI3K pathway is one of the most frequently altered signaling pathways in human cancer. In addition to its function in cancer cells, PI3K plays a complex role in modulating anti-tumor immune responses upon immune checkpoint inhibition (ICI). Here, we evaluated the effects of the pan-Class I PI3K inhibitor copanlisib on different immune cell types in vitro and on tumor growth and immune cell infiltration in syngeneic murine cancer models. Intermittent treatment with copanlisib resulted in a strong in vivo anti-tumor efficacy, increased tumor infiltration of activated T cells and macrophages, and increased CD8+ T cell/regulatory T cell and M1/M2 macrophage ratios. The strong in vivo efficacy was at least partially due to immunomodulatory activity of copanlisib, as in vitro these murine cancer cells were resistant to PI3K inhibition. Furthermore, the combination of copanlisib with the ICI antibody anti-PD-1 demonstrated enhanced anti-tumor efficacy in both ICI-sensitive and insensitive syngeneic mouse tumor models. Importantly, in an ICI-sensitive model, combination therapy resulted in complete remission and prevention of tumor recurrence. Thus, the combination of ICIs with PI3K inhibition by intermittently dosed copanlisib represents a promising new strategy to increase sensitivity to ICI therapies and to treat human solid cancers.

Early T Cell Infiltration Correlates with Anti-CTLA4 Treatment Response in Murine Cancer Models.

Immune checkpoint inhibitor (ICI) Abs are a revolutionary class of cancer treatment, but only ∼30% of patients receive a lasting benefit from therapy. Preclinical studies using animals from the same genetic backgrounds, challenged with the same cancer models, also show nonuniform responses. Most mouse studies that have evaluated tumor-infiltrating leukocytes after ICI therapy cannot directly correlate their findings with treatment outcomes, because terminal methods were used to acquire immune infiltrate data. In the present study, we used fine-needle aspiration (a nonterminal sampling method) to collect multiple aspirates over several days from s.c. implanted P815, CT26, and 4T1 mouse cancer models treated with ICI Abs. These aspirates were then analyzed with flow cytometry to directly correlate tumor-infiltrating leukocyte populations with treatment success. We found that the P815 and CT26 models respond well to anti-CTLA4 therapies. Among P815-challenged animals, mice that regressed following anti-CTLA4 treatment showed significant increases in CD8+ T cells on days 3, 5, and 7 and in CD4+ T cells on days 5 and 7 and a decrease in macrophages and monocytes on days 3, 5, and 7 after treatment. Similar results were obtained in the CT26 model on day 11 posttreatment. Our study is the first, to our knowledge, to directly correlate early tumor infiltration of T cells with anti-CTLA4 treatment success, thus providing a mechanistic clue toward understanding why alloidentical mice challenged with identical tumors do not respond uniformly to ICI therapies.

P-279 - Pharmacokinetics, Dosimetry and Therapeutic efficacy of [225Ac] Ac-DOTA-TDA-Lipiodol® in a murine cancer model: The importance of considering the actinium-225 in vivo generated decay daughters for accurate treatment dosing

P-279 - Pharmacokinetics, Dosimetry and Therapeutic efficacy of [225Ac] Ac-DOTA-TDA-Lipiodol® in a murine cancer model: The importance of considering the actinium-225 in vivo generated decay daughters for accurate treatment dosing

Sini Decoction Inhibits Tumor Progression and Enhances the Anti-Tumor Immune Response in a Murine Model of Colon Cancer.

Sini decoction (SND) is a widely used Traditional Chinese Medicine (TCM). The reports of SND application in colorectal cancer (CRC) is limited. The objective of this study is to investigate the anti-tumor activity of SND in the treatmeant of CRC. SND was analyzed using high-performance liquid chromatography. A CRC metastasis model was established using murine CT-26 cells. Whole-body fluorescence imaging was used to observe CRC liver metastasis. Liver morphology was determined using hematoxylin-eosin staining. Cytokine mRNA expression (interleukin-2 (IL-2), interleukin-10 (IL-10), interferon-gamma (IFN-γ), and tumor necrosis factor beta (TNF-β)) were determined using real-time reverse transcription polymerase chain reaction. Spectral flow cytometry was used to detect mouse tumor immune subgroups. Databases were used to find potential target genes of SND. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes were used to identify potential signaling pathways of target genes. SND suppressed CRC liver metastasis and alleviated liver injury in vivo. After SND treatment, IL-2 and IFN-γ were upregulated, whereas IL-10 and TGF-β were downregulated. Moreover, CD3+, CD8+T cells, natural killer T cells, and macrophages increased significantly after SND treatment, while CD4+CD25+T cells decreased significantly. Importantly, increasing the aconite concentration had a better anti-tumor effect. Fifty-50 compounds in SND were screened, and 611 potential target genes were identified. Functional analyses showed that the genes were associated with the PI3K-Akt signaling pathway, EGFR tyrosine kinase inhibitor resistance, and HIF-1 signaling pathway. SND exerts anti-tumor activity by inhibiting tumor progression and enhancing antitumor immunity in mice, suggesting its application to prevent and treat CRC.

Biogenic synthesis of gold nanoparticles using dual extract of tulsi-Vinca for breast cancer tumor regression in mice.

Aim: This work aims to synthesize the gold nanoparticles (GNPs) using a dual extract of tulsi and Vinca (T+V-Gold) for breast cancer tumor regression. Methods: The GNPs were synthesized and characterized for their microscopic, spectroscopicand crystalline properties. Further, the GNPs were investigated for invitro and invivo studies for the treatment of the 4T1-induced triple-negative breast cancer murine model. Results: The GNPs for 4T1 tumor-challenged mice resulted in delayed tumor development and lower tumor burden, with T+V-Gold demonstrating the highest prevention of tumor spread. The antitumor effect of T+V-Gold is highly significant in the glutathione family antioxidants glutathione S-transferase and glutathione in tumor tissue samples. Conclusion: The bioefficacy and anticancer outcomes of T+V-Gold nanoformulation can be used as therapeutic agents and drug-delivery vehicles.

EP02.03-01 ADAR1 Knockout Results in Loss of Tumorigenicity in a Syngeneic Murine Model of Non-small Cell Lung Cancer

EP02.03-01 ADAR1 Knockout Results in Loss of Tumorigenicity in a Syngeneic Murine Model of Non-small Cell Lung Cancer

Murine models of colorectal cancer: the azoxymethane (AOM)/dextran sulfate sodium (DSS) model of colitis-associated cancer.

Colorectal cancer (CRC) is the third most common cancer. It is a heterogeneous disease, including both hereditary and sporadic types of tumors. CRC results from complex interactions between various genetic and environmental factors. Inflammatory bowel disease is an important risk factor for developing CRC. Despite growing understanding of the CRC biology, preclinical models are still needed to investigate the etiology and pathogenesis of the disease, as well as to find new methods of treatment and prevention. The purpose of this review is to describe existing murine models of CRC with a focus on the models of colitis-associated CRC. This manuscript could be relevant for experimental biologists and oncologists. We checked PubMed and Google from 01/2018 to 05/2023 for reviews of CRC models. In addition, we searched PubMed from 01/2022 to 01/2023 for articles using the azoxymethane (AOM)/dextran sulfate sodium (DSS) CRC model. Existing murine models of CRC include spontaneous, genetically engineered, transplantation, and chemically induced models. For the study of colitis-associated cancer (CAC), the AOM/DSS model is predominantly used. This model is very similar in histological and molecular characteristics to the human CAC, and is highly reproducible, inexpensive, and easy to use. Despite its popularity, the AOM/DSS model is not standardized, which makes it difficult to analyze and compare data from different studies. Each model demonstrates particular advantages and disadvantages, and allows to reproduce different subtypes or aspects of the pathogenesis of CRC.

MA12.11 A Novel 89Zr-anti-PD1 immunoPET-CT May Predict Response to PD-1 Inhibitors in a Lung Cancer Murine Model Receiving Immunotherapy

MA12.11 A Novel 89Zr-anti-PD1 immunoPET-CT May Predict Response to PD-1 Inhibitors in a Lung Cancer Murine Model Receiving Immunotherapy

Anti-cancer Potential of Hydatid Cyst-Derived Antigens: In Vivo Insights

The global healthcare challenge of cancer remains challenging, requiring innovative approaches to identify potential anticancer agents. The intriguing anti-tumor properties of hydatid cysts produced in their larval stage by Echinococcus granulosus (E. granulosus) have attracted the attention of many scientists in recent years. This review aimed to delve deeper into the in vivo anticancer effects of hydatid cyst-derived antigens and shed light on their mechanisms of action and therapeutic implications for various cancer types. Several bioactive molecules in E. granulosus antigens have shown significant anti-cancer activity in vivo. Several studies have shown that administering these antigens reduced tumor size while increasing overall survival in breast cancer models. The immune response against tumor cells in lung cancer murine models has also been enhanced by E. granulosus antigens, such as antigen B, leading to the regression of tumors and enhanced immunity. Colon cancer cells are sensitized to these antigens as indicated by in vivo studies, rendering standard chemotherapy more effective at inhibiting tumor growth. E. granulosus antigens also reduce tumor metastasis when applied to in vivo melanoma models. E. granulosus antigens have demonstrated in vivo efficacy as a potential anticancer agent, underscoring their potential as valuable therapeutic agents. There is still much to be discovered about the exact mechanisms of these antigens and their clinical applicability. However, the impressive results observed across a wide range of cancer types underscore the significance of further research into the antigens to overcome cancer in vivo. In conclusion, animal model studies reveal the promising potential of E. granulosus antigens, particularly hydatid cyst fluid, in inhibiting tumor growth in colon, breast, melanoma, and lung cancers through immune-mediated mechanisms and apoptosis induction. These findings open up new avenues for cancer therapy and immunotherapy research, emphasizing the role of parasite antigens in combatting various cancer types.

Ultrasound targeted microbubble destruction using docetaxel and Rose Bengal loaded Microbubbles for targeted Chemo-Sonodynamic therapy treatment of prostate cancer

Docetaxel (DTX) chemotherapy is commonly used in the treatment of patients with advanced prostate cancer demonstrating modest improvements in survival. As these patients are often elderly and the chemotherapy treatment is not targeted, it is often poorly tolerated. More targeted approaches that increase therapeutic efficacy yet reduce the amount of toxic chemotherapy administered are needed. In this manuscript, we investigate the potential of ultrasound targeted microbubble destruction (UTMD) to deliver a combination of docetaxel chemotherapy and Rose Bengal mediated sonodynamic therapy (SDT) in pre-clinical prostate cancer models. A Rose Bengal modified phospholipid was synthesized and used as a component lipid to prepare a microbubble (MB) formulation that was also loaded with DTX. The DTX-MB-RB formulation was used in the UTMD mediated treatment of androgen sensitive and androgen resistant 3D spheroid and murine models of prostate cancer. Results from the 3D spheroid experiments showed UTMD mediated DTX-MB-RB chemo-sonodynamic therapy to be significantly more effective at reducing cell viability than UTMD mediated DTX or SDT treatment alone. In an androgen sensitive murine model of prostate cancer, UTMD mediated DTX-MB-RB chemo-sonodynamic therapy was as effective as androgen deprivation therapy (ADT) at controlling tumour growth. However, when both treatments were combined, a significant improvement in tumour growth delay was observed. In an androgen resistant murine model, UTMD mediated DTX-MB-RB chemo-sonodynamic therapy was significantly more effective than standard DTX monotherapy. Indeed, the DTX dose administered using the DTX-MB-RB formulation was 91% less than standard DTX monotherapy. As a result, UTMD mediated DTX-MB-RB treatment was well tolerated while animals treated with DTX monotherapy displayed significant weight loss which was attributed to acute toxic effects. These results highlight the potential of UTMD mediated DTX-MB-RB chemo-sonodynamic therapy as a targeted, well tolerated alternative treatment for advanced prostate cancer.

Plasmodium immunotherapy combined with gemcitabine has a synergistic inhibitory effect on tumor growth and metastasis in murine Lewis lung cancer models.

Our previous studies have demonstrated that Plasmodium immunotherapy (infection) has antitumor effects in mice. However, as a new form of immunotherapy, this therapy has a weakness: its specific killing effect on tumor cells is relatively weak. Therefore, we tested whether Plasmodium immunotherapy combined with gemcitabine (Gem), a representative chemotherapy drug, has synergistic antitumor effects. We designed subcutaneously and intravenously implanted murine Lewis lung cancer (LLC) models to test the antitumor effect of Plasmodium chabaudi ASS (Pc) infection in combination with Gem treatment and explored its underlying mechanisms. We found that both Pc infection alone and Gem treatment alone significantly inhibited tumor growth in the subcutaneous model, and combination therapy was more effective than either monotherapy. Monotherapy only tended to prolong the survival of tumor-bearing mice, while the combination therapy significantly extended the survival of mice, indicating a significant synergistic effect of the combination. In the mechanistic experiments, we found that the combination therapy significantly upregulated E-cadherin and downregulated Snail protein expression levels, thus inhibiting epithelial-mesenchymal transition (EMT) of tumor cells, which may be due to the blockade of CXCR2/TGF-β-mediated PI3K/Akt/GSK-3β signaling pathway. The combination of Pc and Gem plays a synergistic role in inhibiting tumor growth and metastasis, and prolonging mice survival in murine lung cancer models. These effects are partially attributed to the inhibition of EMT of tumor cells, which is potentially due to the blockade of CXCR2/TGF-β-mediated PI3K/Akt/GSK-3β/Snail signaling pathway. The clinical transformation of Plasmodium immunotherapy combined with Gem for lung cancer is worthy of expectation.

CR5/CCL5 axis is linked to a poor outcome, and inhibition reduces metastasis in oral squamous cell carcinoma.

The CCR5/CCL5 axis is essential for interactions between malignant cells and microenvironment components, promoting tumor progression in oral squamous cell carcinoma (OSCC). This study aims to evaluate the association of CCL5 and CCR5 with the behavior of oral cancer and assess the therapeutic potential of a CCR5 antagonist. A retrospective study to analyze CCR5 and CCL5 expression on paraffin-embedded tissues was performed. In cell lines, rhCCL5 was added to induce CCR5-related pathways, and Maraviroc and shRNA against CCR5 were used to neutralize the receptor. Finally, an in vivo murine orthotopic xenograft model of tongue cancer was used to evaluate Maraviroc as an oncologic therapy. After 15days, the mice were killed, and the primary tumors and cervical lymph nodes were analyzed. The expression of CCR5 was associated with clinical stage and metastasis, and CCL5 was related to overall survival. Adding rhCCL5 induced cell proliferation, while shRNA and Maraviroc reduced it in a dose-dependent manner. Maraviroc treatment also increased apoptosis and modified cytoskeletal organization. In vivo, Maraviroc reduced neck metastasis. The effects of CCR5 antagonists in OSCC have been poorly studied, and this study reports in vitro and in vivo evidence for the effects of Maraviroc in OSCC. Our results suggest that the CCR5/CCL5 axis plays a role in oral cancer behavior, and that its inhibition is a promising new therapy alternative.

Targeting myeloid-derived suppressor cells with gemcitabine to enhance efficacy of adoptive cell therapy in bladder cancer.

New therapeutics in development for bladder cancer need to address the recalcitrant nature of the disease. Intravesical adoptive cell therapy (ACT) with tumor infiltrating lymphocytes (TIL) can potentially induce durable responses in bladder cancer while maximizing T cells at the tumor site. T cells infused into the bladder directly encounter immunosuppressive populations, such as myeloid derived suppressor cells (MDSCs), that can attenuate T cell responses. Intravesical instillation of gemcitabine can be used as a lymphodepleting agent to precondition the bladder microenvironment for infused T cell products. Urine samples from bladder cancer patients and healthy donors were analyzed by flow cytometry and cytometric bead array for immune profiling and cytokine quantification. MDSCs were isolated from the urine and cocultured with stimulated T cells to assess effects on proliferation. An orthotopic murine model of bladder cancer was established using the MB49-OVA cell line and immune profiling was performed. MDSCs from tumor-bearing mice were cocultured with OT-I splenocytes to assess T cell proliferation. Mice received intravesical instillation of gemcitabine and depletion of immune cells was measured via flow cytometry. Bladder tumor growth of mice treated with intravesical gemcitabine, OT-I transgenic T cells, or combination was monitored via ultrasound measurement. In comparison to healthy donors, urine specimen from bladder cancer patients show high levels of MDSCs and cytokines associated with myeloid chemotaxis, T cell chemotaxis, and inflammation. T cells isolated from healthy donors were less proliferative when cocultured with MDSCs from the urine. Orthotopic murine bladder tumors also presented with high levels of MDSCs along with enrichment of cytokines found in the patient urine samples. MDSCs isolated from spleens of tumor-bearing mice exerted suppressive effects on the proliferation of OT-I T cells. Intravesical instillation of gemcitabine reduced overall immune cells, MDSCs, and T cells in orthotopic bladder tumors. Combination treatment with gemcitabine and OT-I T cells resulted in sustained anti-tumor responses in comparison to monotherapy treatments. MDSCs are enriched within the microenvironment of bladder tumors and are suppressive to T cells. Gemcitabine can be used to lymphodeplete bladder tumors and precondition the microenvironment for intravesical ACT.

Etoposide and navitoclax as triggers of senescence and senolysis: in vitro and in vivo studies in murine pancreatic cancer models

Etoposide and navitoclax as triggers of senescence and senolysis: in vitro and in vivo studies in murine pancreatic cancer models

Chemoresistant fibroblasts dictate neoadjuvant chemotherapeutic response of head and neck cancer via TGFα-EGFR paracrine signaling

Conventional chemotherapy targets malignant cells without evaluating counter protection from the tumor microenvironment that often causes treatment failure. Herein, we establish chemoresistant fibroblasts (rCAFs) as regulators of neoadjuvant chemotherapeutic (NACT) response in head and neck squamous cell carcinoma (HNSCC). Clinically, high expression of CAF-related gene signature correlates with worse prognosis and chemotherapeutic response in multiple cancers, while the population of CAFs in the residual tumors of chemoresistant HNSCC patients remains unchanged after NACT treatment, compared to chemosensitive patients. Using a murine cancer model or patient-derived organoid, and primary CAFs isolated from chemo-sensitive (sCAFs) or -resistant patients, we show that rCAFs, but not sCAFs, are resistant to chemotherapy-induced apoptosis while reducing HNSCC cell chemosensitivity via paracrine signals. Combined multi-omics and biochemical analyses indicate an elevated PI3K/AKT/p65 driven cell survival and cytokine production in rCAFs, while rCAF-secreted TGFα promotes cancer cell chemoresistance by activating EGFR/Src/STAT3 survival signaling axis. Treatment with anti-EGFR cetuximab restores the chemosensitivity of tumors derived from co-injection of cancer cells and rCAFs in vivo, while the serum level of TGFα determines NACT response in HNSCC patients. Overall, our findings uncover a novel insight whereby the crosstalk between tumor cell and rCAF determines chemotherapeutic response and prognosis in cancer patients.

SIRP-alpha-IL-6 axis induces immunosuppressive macrophages in non-small-cell lung cancer

Signal regulatory protein-alpha (SIRPα) and IL-6 participate in the induction of tumor immune suppressive environment and facilitate tumor growth. In this study, we found that SIRPα was significantly elevated in macrophages of non-small cell lung cancer (NSCLC) tissues, which was positively correlated to the expression of CD163, PD-1, IL-6, and lung cancer progression. SIRPα in peripheral blood mononuclear cells (PBMCs) of NSCLC patients was also associated with CD163, PD-1, and plasma IL-6. Blockade of SIRPα signaling in SIRPα ± and SIRPα−/− mice attenuated lung cancer growth and reduced IL-6 expression in LLC cells-transplanted murine lung cancer model. Co-targeting SIRPα and IL-6 additively suppressed the expression of IL-6 and activation of STAT3, accompanied with a reduced population of pro-tumorigenic CD206+ M2 subtype of macrophages, PD-1+ tumor-associated macrophages (TAMs), and PD-1+CD8+ T cells in tumor tissues of anti-IL-6 antibody (aIL-6)-treated mice deficient in SIRPα. Further in vitro studies showed that blockade of SIRPα signaling by anti-SIRPα effectively improved phagocytosis of human PBMCs. IL-6 treatment improved polarization of M2 subtypes and the expression of PD-1 in bone marrow-derived macrophages (BMDMs); whereas both aIL-6 and STAT3 inhibitor C188-9 suppressed the expression of PD-1 and SIRPα in BMDMs. M2 cell-biased polarization was also reduced in aIL-6 or C188-9 treated BMDMs. Thereby, SIRPα and IL-6 form a positive feedback loop and regulate each other through STAT3 signaling in macrophages. The increased SIRPα/IL-6 axis may promote immune suppressive environment and lung cancer growth, which may be a potential target for clinical treatment.

Muscarinic receptor agonist-induced βPix binding to β-catenin promotes colon neoplasia

M3 muscarinic receptors (M3R) modulate β-catenin signaling and colon neoplasia. CDC42/RAC guanine nucleotide exchange factor, βPix, binds to β-catenin in colon cancer cells, augmenting β-catenin transcriptional activity. Using in silico, in vitro, and in vivo approaches, we explored whether these actions are regulated by M3R. At the invasive fronts of murine and human colon cancers, we detected co-localized nuclear expression of βPix and β-catenin in stem cells overexpressing M3R. Using immunohistochemistry, immunoprecipitation, proximity ligand, and fluorescent cell sorting assays in human tissues and established and primary human colon cancer cell cultures, we detected time-dependent M3R agonist-induced cytoplasmic and nuclear association of βPix with β-catenin. βPix knockdown attenuated M3R agonist-induced human colon cancer cell proliferation, migration, invasion, and expression of PTGS2, the gene encoding cyclooxygenase-2, a key player in colon neoplasia. Overexpressing βPix dose-dependently augmented β-catenin binding to the transcription factor TCF4. In a murine model of sporadic colon cancer, advanced neoplasia was attenuated in conditional knockout mice with intestinal epithelial cell deficiency of βPix. Expression levels of β-catenin target genes and proteins relevant to colon neoplasia, including c-Myc and Ptgs2, were reduced in colon tumors from βPix-deficient conditional knockout mice. Targeting the M3R/βPix/β-catenin axis may have therapeutic potential.

Tandem Isotope Therapy with 225Ac- and 177Lu-PSMA-617 in a Murine Model of Prostate Cancer.

Radionuclide therapy targeting prostate-specific membrane antigen (PSMA) is a promising option for metastatic castration-resistant prostate cancer. Clinical experience using 177Lu or 225Ac has demonstrated encouraging treatment responses; however, responses are not durable. Dual-isotope combinations, or "tandem" approaches, may improve tolerability while retaining a high tumor dose. In this study, we directly compared α- versus β-particle treatment, as well as a combination thereof, at different stages of disease in a murine model of disseminated prostate cancer. Methods: First, to determine comparable injected activities from 177Lu- and 225Ac-PSMA-617, ex vivo biodistribution studies were performed at 5 time points after treatment of C4-2 subcutaneous tumor-bearing NSG mice. To establish a more representative model of metastatic prostate cancer, NSG mice were inoculated with luciferase-expressing C4-2 cells in the left ventricle, leading to disseminated visceral and bone lesions. At either 3 or 5 wk after inoculation, the mice were treated with equivalent tumor dose-depositing activities of 177Lu- or 225Ac-PSMA-617 alone or in combination (35 MBq of 177Lu, 40 kBq of 225Ac, or 17 MBq of 177Lu + 20 kBq 225Ac; 10/group). Disease burden was assessed by weekly bioluminescence imaging. Treatment efficacy was evaluated using whole-body tumor burden and overall survival. Results: The ex vivo biodistribution studies revealed that 35 MBq of 177Lu and 40 kBq of 225Ac yield equivalent absorbed tumor doses in a subcutaneous C4-2 model. The disease burden of mice treated at 3 wk after inoculation (microscopic disease) with 177Lu was not significantly different from that of untreated mice. However, 225Ac-PSMA-617 both as a single agent and in combination with 177Lu (17 MBq of 177Lu + 20 kBq of 225Ac) were associated with significant whole-body tumor growth retardation and survival benefit (overall survival, 8.3 wk for nontreatment, 9.4 wk for 177Lu, 15.3 wk for 225Ac alone, and 14.1 wk for tandem therapy). When treated at 5 wk after inoculation (macroscopic disease), all treatment groups showed retarded tumor growth and improved survival, with no significant differences between 225Ac alone and administration of half the 225Ac activity in tandem with 177Lu (overall survival, 7.9 wk for nontreatment, 10.3 wk for 177Lu, 14.6 wk for 225Ac alone, and 13.2 wk for tandem therapy). Conclusion: Treatment of a disseminated model of prostate cancer with simultaneous 225Ac- and 177Lu-PSMA-617 results in significantly decreased tumor growth compared with 177Lu, which was ineffective as a single agent against microscopic lesions. Mice treated later in the disease progression and bearing macroscopic, millimeter-sized lesions experienced significant tumor growth retardation and survival benefit in both monoisotopic and tandem regimens of 177Lu and 225Ac. Although the greatest benefits were observed with the single agent 225Ac, the tandem arm experienced no significant difference in disease burden or survival benefit, suggesting that the reduced activity of 225Ac was adequately compensated in the tandem arm. The superior therapeutic efficacy of 225Ac in this model suggests a preference for α-emitters alone, or possibly in combination, in the microscopic disease setting.

OR05-05 A Novel Model Of Prostate Cancer Suggests Enzalutamide Functions Through The Immune System To Diminish Castration Resistant And Metastatic Growth

Abstract Disclosure: S. Kregel: None. Background: There exists a tremendous need for establishing prostate cancer (PCa) murine models capable of recapitulating the progress of human PCa. By itself, the murine prostate does not form sporadic tumors and is anatomically and developmentally different from the human prostate. Engineered mouse models, however, lack the heterogeneity of human disease, are often driven in a contrived manner, and rarely (if ever) establish metastatic growth. Human xenografts represent an alternative, but they rely on tumor growth in an immunocompromised host, thus preventing the study of tumor-immune interactions and immunotherapies. Accordingly, we generated PCa xenograft models in a murine system with an intact human immune system (huNOG mice) to test the hypothesis that humanizing tumor-immune interactions would improve modeling of metastatic PCa as well as our ability to model the impact of hormonal and immunotherapies. Methods: Male huNOG and huNOG-EXL mice were produced at Taconic Biosciences by engrafting juvenile NOG mice with human CD34+ hematopoietic stem cells. These mice stably maintained multiple human cell lineages, including functional human T-cells. We utilized two human PCa xenograft cell line models transduced with luciferase to assay organ-specific metastatic growth. First, castrated and intact control mice were injected subcutaneously with 22Rv1 cells. When tumors reached >100 mm3, half of the castrated mice were treated with enzalutamide (enza), and tumor growth was then monitored to endpoint. Additionally, VCaP tumor-bearing mice were castrated when the tumors reached ∼200 mm3, and once the tumor grew back, they were randomized and treated with enza and/or the anti-PD-1 antibody, pembrolizumab (pembro) as well as with vehicle controls. At sacrifice, organs were ex vivo analyzed for metastatic growth, tumor infiltrating lymphocytes, and splenic immune reconstitution. Results: In 22Rv1 tumor-bearing mice, subcutaneous tumor size was not significantly altered across conditions. However, the extent and growth at the secondary sites differed markedly in castrate huNOG vs conventional NOG mice treated with enza. VCaP xenograft tumors showed marked decreases in growth with enza and pembro treatments in huNOG mice, while no effect was observed with either of these treatments in NOG mice. Furthermore, immune responses to enza treatment in huNOG and NOG mice were distinct, as enza treatment only increased intra-tumor CD3+ T-cells as well as CD3+ T-cell activation in huNOG mice. Conclusions: These results illustrate, to the best of our knowledge, the first model of human PCa that metastasizes to clinically relevant locations, has an intact human immune system, and responds to standard-of-care hormonal therapies in a manner similar to responses observed under clinical settings. Presentation: Thursday, June 15, 2023

Impact of ultrasonic inertial cavitation on the pancreatic tumor stiffness in mice

Pancreatic ductal adenocarcinoma (PDAC) is among the fastest-growing cancers and is predicted to become the second leading cause of cancer-related deaths worldwide by 2030. Ultrasound-induced inertial cavitation (IC) is an emerging therapeutic strategy with promise for treating patients with unresectable tumors. However, the physical impact of IC on tumors remains unclear. In this study, we used orthotopic murine models of pancreatic cancer and employed passive elastography to measure elasticity before and after applying IC to the whole tumor volume. The IC was generated using two focused confocal transducers (center frequency, 1.1 MHz). The output level was adjusted with a real-time feedback loop based on broadband signal acquired with a passive cavitation detector. Cavitation clouds were visualized during treatment using an imaging probe. The results from eight treated mice showed a 24% decrease (p < 0.05) in tumor stiffness after the IC treatment, indicating that the chosen IC sequence can soften the tumor environment. After sacrifice, we utilized second-harmonic imaging microscopy to visualize the collagen network within the tumor, a known contributor to tissue stiffness, and correlated various features of this network (length, width, curvature) with the measured elasticity.