Immunosuppressive drugs and their effect on experimental tumor growth

Achieving tolerance modifies cancer susceptibility profiles in liver transplant recipients

Long-term survival of transplant recipients is significantly impacted by malignancy. We aimed to determine whether calcineurin inhibitor (CNI)-treated recipients converted to and weaned off molecular target of rapamycin inhibitor (mTOR-I) therapy have favorable changes in their molecular profiles in regard to malignancy risk. We performed gene expression profiling from liver biopsy and blood (PBMC) specimens followed by network analysis of key dysregulated genes, associated diseases and disorders, molecular and cellular functions using IPA software. Twenty non-immune, non-viremic patients were included, and 8 of them achieved tolerance. Two comparisons were performed: (1) tolerance time point vs tacrolimus monotherapy and (2) tolerance time point vs sirolimus monotherapy. Upon achieving tolerance, IPA predicted significant activation of DNA damage response (p = 5.40e-04) and inhibition of DNA replication (p = 7.56e-03). Conversion from sirolimus to tolerance showed decrease in HCC (p = 1.30e-02), hepatic steatosis (p = 5.60e-02) and liver fibrosis (p = 2.91e-02) associated genes. In conclusion, this longitudinal study of patients eventually achieving tolerance reveals an evolving molecular profile associated with decreased cancer risk and improved hepatic steatosis and liver fibrosis. This provides a biological rationale for attempting conversion to mTOR-I therapy and tolerance following liver transplantation particularly in patients at higher risk of cancer incidence and progression post-transplant.

Increased Risk of Advanced Colonic Adenomas and Timing of Surveillance Colonoscopy Following Solid Organ Transplantation

BACKGROUND

Detection and removal of colonic adenomatous polyps (CAP) decreases colorectal cancer (CRC) development, particularly with more or larger polyps or polyps with advanced villous/dysplastic histology. Immunosuppression following solid organ transplantation (SOT) may accelerate CAP development and progression compared to average-risk population but the benefit of earlier colonoscopic surveillance is unclear.

AIMS

Study the impact of maintenance immunosuppression post-SOT on developmental timing, multiplicity and pathological features of CAP, by measuring incidence of advanced CAP (villous histology, size ≥ 10 mm, ≥ 3 polyps, presence of dysplasia) post-SOT and the incidence of newly diagnosed CRC compared to average-risk age-matched population.

METHODS

Single-center retrospective cohort study of SOT recipients.

RESULTS

295 SOT recipients were included and were compared with 291 age-matched average-risk controls. The mean interval between screening and surveillance colonoscopies between SOT and control groups was 6.3 years vs 5.9 years (p = 0.13). Post-SOT maintenance immunosuppression mean duration averaged 59.9 months at surveillance colonoscopy. On surveillance examinations, SOT recipients exhibited more advanced (≥ 10 mm) adenomas compared to matched controls (9.2% vs. 3.8%, p = 0.034; adjusted OR 2.38; 95% CI 1.07-5.30).

CONCLUSION

SOT recipients appear at higher risk for developing advanced CAP, suggesting that earlier surveillance should be considered.

Comprehensive Review on Colorectal Cancer and Transplant

Colorectal cancer (CRC) is a common malignancy worldwide. Some studies suggest that organ recipients are at a higher risk for CRC than the general population. The underlying transplant indications and their inherent risk factors for CRC may drive the variation in incidence rates that are seen in patients receiving different allografts. Recipients with cystic fibrosis are now recognized as a population at high risk for CRC at a young age. Transplant recipients have high mortality following a CRC diagnosis, even if it is detected at an early stage. Certain types of immunosuppression have been shown to accelerate cancer transformation and may contribute to the more aggressive phenotype seen in organ recipients. Given the high incidence and progressive nature of posttransplant CRC, shorter screening intervals with a modality that can detect early-stage polyps may be essential to prevent mortality. Future research is needed to better elucidate the role of immunosuppression in carcinogenesis. This comprehensive review examines CRC risk, screening, and management specific to organ transplant candidates and recipients.

Phosphorylation of ribosomal protein S6 attenuates DNA damage and tumor suppression during development of pancreatic cancer

The signaling pathways that mediate the development of pancreatic ductal adenocarcinoma (PDAC) downstream of mutant Kras remain incompletely understood. Here, we focus on ribosomal protein S6 (rpS6), an mTOR effector not implicated previously in cancer. Phosphorylation of rpS6 was increased in pancreatic acinar cells upon implantation of the chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) or transgenic expression of mutant Kras. To examine the functional significance of rpS6 phosphorylation, we used knockin mice lacking all five phosphorylatable sites in rpS6 (termed rpS6(P-/-) mice). Strikingly, the development of pancreatic cancer precursor lesions induced by either DMBA or mutant Kras was greatly reduced in rpS6(P-/-) mice. The rpS6 mutants expressing oncogenic Kras showed increased p53 along with increased staining of γ-H2AX and 53bp1 (Trp53bp1) in areas of acinar ductal metaplasia, suggesting that rpS6 phosphorylation attenuates Kras-induced DNA damage and p53-mediated tumor suppression. These results reveal that rpS6 phosphorylation is important for the initiation of pancreatic cancer.

Critical Review of Preclinical Approaches to Evaluate the Potential of Immunosuppressive Drugs to Influence Human Neoplasia

Many immunosuppressive drugs are associated with an increased risk of B-cell lymphoma, squamous cell carcinoma, and Kaposi sarcoma. Thirteen immunosuppressive drugs have been tested in 2-year carcinogenicity studies (abatacept; azathioprine; busulfan; cyclophosphamide; cyclosporine; dexamethasone; everolimus; leflunomide; methotrexate; mycophenolate mofetil; prednisone; sirolimus; and tacrolimus) and in additional models including neonatal and genetically modified mice; chemical, viral, ultraviolet, and ionizing radiation co-carcinogenesis, and in models with transplanted tumor cells. The purpose of this review is to outline the mechanisms by which immunosuppressive drugs can influence neoplasia, to summarize the available preclinical data on the 13 drugs, and to critically review the performance of the models. A combination of primary tumor and metastasis assays conducted with transplanted cells may provide the highest value for hazard identification and can be applied on a case-by-case basis. However, for both small molecules and therapeutic proteins, determining the relative risk to patients from preclinical data remains problematic. Classifying immunosuppressive drugs based on their mechanism of action and hazard identification from preclinical studies and a prospective pharmacovigilance program to monitor carcinogenic risk may be a feasible way to manage patient safety during the clinical development program and postmarketing.

Pro- and anti-cancer effects of immunosuppressive agents used in organ transplantation

Development of cancer is a feared, and increasingly apparent, complication of long-term immunosuppressive therapy in transplant recipients. In addition to the need to reduce cancer occurrence in these patients, therapeutic protocols are lacking to simultaneously attack the malignancy and protect the allograft when neoplasms do occur. In this overview, we present the current literature regarding the pro- and anti-neoplastic effects of immunosuppressive agents on cancer growth and development. Recent experimental findings are paving the way for new therapeutic strategies aimed at both protecting an allograft from immunologic rejection and addressing the problem of cancer in this high-risk population.

Mycophenolate mofetil impairs healing of left-sided colon anastomoses

INTRODUCTION

Inadequate healing and consequent leakage from bowel anastomoses are a significant cause of postoperative morbidity and mortality. Immunosuppressive drugs are known to disturb healing processes and to impair the mechanical stability of bowel anastomosis. Mycophenolate mofetil (MMF) is an immunosuppressive agent that selectively inhibits the proliferation of T and B lymphocytes and has been shown to be effective in preventing allograft rejection after organ transplantation. Adverse effects are few; however, nothing is known in regard to possible adverse effects of MMF administration on the healing of bowel anastomosis. The aim of the present study was to evaluate the effect of systemic MMF administration on the healing of colon anastomoses in rats.

METHODS

Rats underwent laparotomy, division of the left colon, and sigmoidostomy. MMF (25 mg/kg) or vehicle was administered intraperitoneally in two groups (n=21 per group) 3 days before surgery and then once daily until euthanization (7 animals per group; 2, 4, and 6 days after surgery). Bursting pressure measurements, histologic evaluation, morphometric analysis, mucin and collagen staining, and BrdU immunohistochemistry of the anastomotic site were performed. Furthermore, matrix protein expression at the anastomotic site was determined by collagen I and fibronectin Western blots.

RESULTS

Administration of MMF significantly decreased anastomotic bursting pressure postoperatively. Accordingly, histology, mucin staining, and BrdU immunohistochemistry and measurements of the colonic crypt depth showed more extended inflammation, a significantly lower proliferation rate, and a significantly thinned mucosal layer in the MMF-treated groups when compared to control animals, whereas matrix synthesis at the anastomotic site was not different.

CONCLUSIONS

The administration of the immunosuppressive agent MMF significantly impairs healing and mechanical stability of colon anastomosis in rats during the early postoperative period. MMF act to disturb host reparative processes mainly by impairment of reparative colonic epithelium proliferation and less by a disturbance of matrix synthesis.

Liver transplantation and hepatocellular carcinoma

Liver transplantation for advanced hepatocellular carcinoma (HCC) continues to be a subject of debate mostly due to a uniformly high failure rate secondary to recurrence. However, accumulating experiences have enabled detailed analysis of the prognostic factors affecting patient outcome. Clinicopathological factors affecting survival have been reported to include tumor size, number, lobar distribution, vascular invasion, lymphnode metastasis, and histologic type such as fibrolamellar variant of HCC. Poor prognosis has been associated with advanced stage of the tumor, particularly pTNM stage IV. Many transplant centers now use a protocol of adjuvant chemotherapy with reasonable success, although experiences are limited. Better understanding in tumor biology, particularly of the role of immunosuppression affecting tumor growth, will provide further success in the treatment of HCC by liver transplantation.