Tetracycline-regulated intratumoral expression of interleukin-3 enhances the efficacy of radiation therapy for murine prostate cancer

Impacts of combining anti-PD-L1 immunotherapy and radiotherapy on the tumour immune microenvironment in a murine prostate cancer model

BACKGROUND

Radiotherapy enhances innate and adaptive anti-tumour immunity. It is unclear whether this effect may be harnessed by combining immunotherapy with radiotherapy fractions used to treat prostate cancer. We investigated tumour immune microenvironment responses of pre-clinical prostate cancer models to radiotherapy. Having defined this landscape, we tested whether radiotherapy-induced tumour growth delay could be enhanced with anti-PD-L1.

METHODS

Hypofractionated radiotherapy was delivered to TRAMP-C1 and MyC-CaP flank allografts. Tumour growth delay, tumour immune microenvironment flow-cytometry, and immune gene expression were analysed. TRAMP-C1 allografts were then treated with 3 × 5 Gy ± anti-PD-L1.

RESULTS

3 × 5 Gy caused tumour growth delay in TRAMP-C1 and MyC-CaP. Tumour immune microenvironment changes in TRAMP-C1 at 7 days post-radiotherapy included increased tumour-associated macrophages and dendritic cells and upregulation of PD-1/PD-L1, CD8+ T-cell, dendritic cell, and regulatory T-cell genes. At tumour regrowth post-3 × 5 Gy the tumour immune microenvironment flow-cytometry was similar to control tumours, however CD8+, natural killer and dendritic cell gene transcripts were reduced. PD-L1 inhibition plus 3 × 5 Gy in TRAMP-C1 did not enhance tumour growth delay versus monotherapy.

CONCLUSION

3 × 5 Gy hypofractionated radiotherapy can result in tumour growth delay and immune cell changes in allograft prostate cancer models. Adjuncts beyond immunomodulation may be necessary to improve the radiotherapy-induced anti-tumour response.

Gene Therapy with Tetracycline-Regulated Human Recombinant COLIA1 cDNA Direct Adenoviral Delivery Enhances Fracture Healing in Osteoporotic Rats

A number of previous studies have indicated that the genetic variation at the collage type I alpha 1 (COLIA1) gene locus influences susceptibility to osteoporosis. However, seldom have studies reported the effect of gene delivery using an adenovirus vector carrying human recombinant COLIA1 cDNA on stimulating osteogenic activity of osteoblasts and enhancing fracture healing of ovariectomized rats. The current study was performed to demonstrate whether direct gene delivery using an adenovirus vector carrying human recombinant COLIA1 cDNA could stimulate osteogenic activity of osteoblast in vitro and enhance fracture healing of ovariectomized rats in vivo. In vitro, the tet-on system regulated COLIA1 gene adenovirus was constructed and transfected to osteoblasts. COLIA1 mRNA and collagen type I levels were assessed by reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay to determine whether adenovirus transfected successfully. Osteogenic activity of the osteoblasts was assessed by alkaline phosphatase activity, immunohistochemical staining, immunofluorescent staining, mineralized matrix formation, and extracellular calcium levels. In vivo, adenovirus-delivered COLIA1 gene was injected into the fracture site of the tibia in an ovariectomized rat model of osteoporosis, and bone callus condition was assessed to determine whether the COLIA1 gene could accelerate osteoporotic fracture healing. In vitro, the results showed that COLIA1 gene adenovirus transfection could increase osteoblast COLIA1 gene expression and collagen type I protein synthesis, increase alkaline phosphatase activity, and stimulate calcium nodules formation, which exhibited a direct osteogenic effect on the osteoblasts. In vivo, local injection of COLIA1 gene adenovirus increased collagen type I expression, restored bone mineral density, and accelerated fracture healing in ovariectomized rats, without increasing serum collagen type I and liver COLIA1 mRNA levels. This study suggests direct gene delivery using an adenovirus carrying human COLIA1 cDNA can stimulate the osteogenic activity of osteoblasts in vitro and enhance bone fracture healing in vivo. The tet-on system is an ideal gene regulatory system for effective and safe regulation of the therapeutic gene.

A perspective on the impact of radiation therapy on the immune rheostat

The advent and success of immune checkpoint inhibitors (ICIs) in cancer treatment has broadened the spectrum of tumours that might be considered "immunogenic" and susceptible to immunotherapeutic (IT) intervention. Not all cancer types are sensitive, and not all patients with any given type respond. Combination treatment of ICIs with an established cytotoxic modality such as radiation therapy (RT) is a logical step towards improvement. For one, RT alone has been shown to be genuinely immunomodulatory and secondly pre-clinical data generally support combined ICI-RT approaches. This new integrated therapy for cancer treatment holds much promise, although there is still a lot to be learned about how best to schedule the treatments, manage the toxicities and determine what biomarkers might predict response, as well as many other issues. This review examines how RT alters the immune rheostat and how it might best be positioned to fully exploit IT.

PSMA redirects cell survival signaling from the MAPK to the PI3K-AKT pathways to promote the progression of prostate cancer

Increased abundance of the prostate-specific membrane antigen (PSMA) on prostate epithelium is a hallmark of advanced metastatic prostate cancer (PCa) and correlates negatively with prognosis. However, direct evidence that PSMA functionally contributes to PCa progression remains elusive. We generated mice bearing PSMA-positive or PSMA-negative PCa by crossing PSMA-deficient mice with transgenic PCa (TRAMP) models, enabling direct assessment of PCa incidence and progression in the presence or absence of PSMA. Compared with PSMA-positive tumors, PSMA-negative tumors were smaller, lower-grade, and more apoptotic with fewer blood vessels, consistent with the recognized proangiogenic function of PSMA. Relative to PSMA-positive tumors, tumors lacking PSMA had less than half the abundance of type 1 insulin-like growth factor receptor (IGF-1R), less activity in the survival pathway mediated by PI3K-AKT signaling, and more activity in the proliferative pathway mediated by MAPK-ERK1/2 signaling. Biochemically, PSMA interacted with the scaffolding protein RACK1, disrupting signaling between the β₁ integrin and IGF-1R complex to the MAPK pathway, enabling activation of the AKT pathway instead. Manipulation of PSMA abundance in PCa cell lines recapitulated this signaling pathway switch. Analysis of published databases indicated that IGF-1R abundance, cell proliferation, and expression of transcripts for antiapoptotic markers positively correlated with PSMA abundance in patients, suggesting that this switch may be relevant to human PCa. Our findings suggest that increase in PSMA in prostate tumors contributes to progression by altering normal signal transduction pathways to drive PCa progression and that enhanced signaling through the IGF-1R/β₁ integrin axis may occur in other tumors.

The roles of macrophages and nitric oxide in interleukin-3-enhanced HSV-Sr39tk-mediated prodrug therapy

The herpes simplex virus thymidine kinase/ganciclovir (HSV-sr39tk/GCV) system is a well-established prodrug system used in cancer gene therapy. However, this system is currently not effective enough to eradicate malignant tumors completely. This study aimed to evaluate whether co-expression of interleukin-3 (IL-3) could enhance the anti-tumor activity of HSV-sr39tk/GCV prodrug gene therapy using a murine TRAMP-C1 prostate tumor model. In vitro results demonstrated that HSV-sr39tk-transfected cells exhibited enhanced sensitivity to the GCV prodrug, which was not affected by co-expression of the mIL-3 gene. However, in vivo studies showed that co-expression of the mIL-3 gene significantly increased the HSV-sr39tk/GCV-induced tumor growth delay and even cured the tumor. The TRAMP-C1-specific immune response of spleen lymphocytes from mice bearing HSV-sr39tk- and IL-3-expressing TRAMP-C1 tumors was measured by ELISA. Results showed that IL-3-activated IL-4-dominant lymphocytes became IFN-γ- dominant lymphocytes after combined HSV-sr39tk/GCV therapy. The efficacy of combined therapies on tumor regression was reduced when macrophages populations were depleted by carrageenan or NO production was inhibited by administration of the iNOS inhibitor, L-NAME. These results suggest that utilizing a bicistronic vector to express HSV-sr39tk and the IL-3 gene induced an enhanced macrophage- or NO-dependent anti-tumor effect.

Inhibition of pancreatic cancer cell growth in vivo using a tetracycline-inducible cyclin D1 antisense expression system

OBJECTIVES

Cyclin D1 is important for pancreatic cancer growth. Our aim was to determine the effects of cyclin D1 inhibition on the growth of established pancreatic tumors.

METHODS

PANC-1 cells harboring cyclin D1 antisense cDNA in a tetracycline-inducible vector system were prepared. The effects of cyclin D1 inhibition after tumor development were characterized in a mouse model.

RESULTS

In vitro removal of tetracycline induced cyclin D1 antisense cDNA expression and inhibited cyclin D1 expression and cyclin D1-associated kinase activity as well as anchorage-dependent and -independent growth. After establishment of xenograft tumors in the presence of tetracycline (2 mg/mL) in the drinking water, animals were assigned to either control (tetracycline remained in the drinking water) or to the group without tetracycline for which tetracycline was removed from the drinking water. Tumor growth was significantly inhibited after removal of tetracycline. Microscopic analysis revealed that the area of central necrosis was significantly increased in the group without tetracycline paralleled by a reduction of the vital peripheral area of proliferating cells.

CONCLUSIONS

Our results confirmed that cyclin D1 plays an important role in the growth of pancreatic cancer cells and may be an attractive molecular target for the treatment of human pancreatic cancer.

Radiation enhances regulatory T cell representation

PURPOSE

Immunotherapy could be a useful adjunct to standard cytotoxic therapies such as radiation in patients with micrometastatic disease, although successful integration of immunotherapy into treatment protocols will require further understanding of how standard therapies affect the generation of antitumor immune responses. This study was undertaken to evaluate the impact of radiation therapy (RT) on immunosuppressive T regulatory (Treg) cells.

METHODS AND MATERIALS

Treg cells were identified as a CD4(+)CD25(hi)Foxp3(+) lymphocyte subset, and their fate was followed in a murine TRAMP C1 model of prostate cancer in mice with and without RT.

RESULTS

CD4(+)CD25(hi)Foxp3(+) Treg cells increased in immune organs after local leg or whole-body radiation. A large part, but not all, of this increase after leg-only irradiation could be ascribed to radiation scatter and Treg cells being intrinsically more radiation resistant than other lymphocyte subpopulations, resulting in their selection. Their functional activity on a per-cell basis was not affected by radiation exposure. Similar findings were made with mice receiving local RT to murine prostate tumors growing in the leg. The importance of the Treg cell population in the response to RT was shown by systemic elimination of Treg cells, which greatly enhanced radiation-induced tumor regression.

CONCLUSIONS

We conclude that Treg cells are more resistant to radiation than other lymphocytes, resulting in their preferential increase. Treg cells may form an important homeostatic mechanism for tissues injured by radiation, and in a tumor context, they may assist in immune evasion during therapy. Targeting this population may allow enhancement of radiotherapeutic benefit through immune modulation.

Local irradiation of murine melanoma affects the development of tumour-specific immunity

Radiation therapy affects the immune system. In addition to killing radiosensitive immune cells, it can induce functional changes in those cells that survive. Our recent studies showed that the exposure of dendritic cells (DCs) to radiation in vitro influences their ability to present tumour antigen in vivo. Here we show that local radiation therapy of B16 melanoma tumours inhibits the development of systemic immunity to the melanoma antigen MART-1. This inhibition could not be overcome by intratumoral injection of DCs expressing human MART-1 after radiation therapy, suggesting that a form of immune suppression might have developed. On the other hand, injection of MART-expressing DCs prior to tumour irradiation was able to prevent inhibition from developing. These results suggest that local radiation therapy may block the generation of immunity under some circumstances and that strategies may be required to prevent this and allow radiation-induced cell death to translate fully into the development of systemic immunity.

Strategies of Gene Transfer and Silencing, and Technical Considerations

Cancer gene therapy is a relatively new modality that might ultimately revolutionize oncology. The basic principle is to alter the tumor genetically to enhance more traditional chemo- and radiation therapy schema. The last decade has seen tremendous progress and development of new technologies in the areas of vector delivery, tumor targeting, and numerous clever ways to increase tumor killing, including early attempts to modulate tumor gene expression by RNA interference. In recent years, attempts to image affected cells have also been part of these efforts. Many studies have proceeded to the preclinical stage and a fair number to early clinical testing with some showing encouraging results. However, real impact on patient survival remains to be seen. One major problem still to be overcome is the quantitative delivery of the vector into the tumor mass. The next decade is expected to resolve many of these technical issues and improve the treatment of patients. This chapter will discuss new technologies and provide a brief overview of the field.

Macrophages from irradiated tumors express higher levels of iNOS, arginase-I and COX-2, and promote tumor growth

PURPOSE

To investigate the effects of single and fractionated doses of radiation on tumors and tumor-associated macrophages (TAMs), and to elucidate the potential of TAMs to influence tumor growth.

METHODS AND MATERIALS

A murine prostate cell line, TRAMP-C1, was grown in C57Bl/6J mice to 4-mm tumor diameter and irradiated with either 25 Gy in a single dose, or 60 Gy in 15 fractions. The tumors were removed at the indicated times and assessed for a variety of markers related to TAM content, activation status, and function.

RESULTS

In tumors receiving a single radiation dose, arginase (Arg-I), and cycloxygenase-2 (COX-2) mRNA expression increased as a small transient wave within 24 h and a larger persistent wave starting after 3 days. Inducible nitric oxide synthase (iNOS) mRNA was elevated only after 3 days and continued to increase up to 3 weeks. After fractionated irradiation, Arg-1 and COX-2 mRNA levels increased within 5 days, whereas iNOS was increased only after 10 fractions of irradiation had been given. Increased levels of Arg-I, COX-2, and, to a lesser extent, iNOS protein were found to associate with TAMs 1-2 weeks after tumor irradiation. Function of TAMs were compared by mixing them with TRAMP-C1 cells and injecting them into mice; TRAMP-C1 cells mixed with TAMs from irradiated tumors appeared earlier and grew significantly faster than those mixed with TAMs from unirradiated tumors or TRAMP-C1 alone.

CONCLUSIONS

Tumor-associated macrophages in the postirradiated tumor microenvironment express higher levels of Arg-1, COX-2, and iNOS, and promote early tumor growth in vivo.