Oral antibiotics lower mycophenolate mofetil drug exposure, possibly by interfering with the enterohepatic recirculation: A case series.

Mycophenolate mofetil has an important role as immunosuppressive agent in solid organ transplant recipients. Exposure to the active mycophenolic acid (MPA) can be monitored using therapeutic drug monitoring. We present three cases in which MPA exposure severely decreased after oral antibiotic coadministration. By diminishing gut bacteria ß-glucuronidase activity, oral antibiotics can prevent deglucuronidation of the inactive MPA-7-O-glucuronide metabolite to MPA and thereby possibly prevent its enterohepatic recirculation. This pharmacokinetic interaction could result in rejection, which makes it clinically relevant in solid organ transplant recipients, especially when therapeutic drug monitoring frequency is low. Routine screening for this interaction, preferably supported by clinical decision support systems, and pragmatic close monitoring of the MPA exposure in cases is advised.

Ex vivo assays to predict enhanced chemosensitization by hyperthermia in urothelial cancer of the bladder.

INTRODUCTION: Bladder cancer (urothelial carcinoma) is a common malignancy characterized by high recurrence rates and intense clinical follow-up, indicating the necessity for more effective therapies. Current treatment regimens include intra-vesical administration of mitomycin C (MMC) for non-muscle invasive disease and systemic cisplatin for muscle-invasive or metastatic disease. Hyperthermia, heating a tumor to 40-44°C, enhances the efficacy of these chemotherapeutics by various modes of action, one of which is inhibition of DNA repair via homologous recombination. Here, we explore whether ex vivo assays on freshly obtained bladder tumors can be applied to predict the response towards hyperthermia. MATERIAL AND METHODS: The cytochrome C release assay (apoptosis) and the RAD51 focus formation assay (DNA repair) were first established in the bladder cancer cell lines RT112 and T24 as measurements for hyperthermia efficiency, and subsequently tested in freshly obtained bladder tumors (n = 59). RESULTS: Hyperthermia significantly increased the fraction of apoptotic cells after cisplatin or MMC treatment in both RT112 and T24 cells and in most of the bladder tumors (8/10). The RAD51 focus formation assay detected both morphological and numerical changes of RAD51 foci upon hyperthermia in the RT112 and T24 cell lines. In 64% of 37 analyzed primary bladder tumor samples, hyperthermia induced similar morphological changes in RAD51 foci. CONCLUSION: The cytochrome C assay and the RAD51 focus formation assay are both feasible on freshly obtained bladder tumors, and could serve to predict the efficacy of hyperthermia together with cytotoxic agents, such as MMC or cisplatin.

Functional Ex Vivo Assay Reveals Homologous Recombination Deficiency in Breast Cancer Beyond BRCA Gene Defects.

PURPOSE: Tumors of germline BRCA1/2 mutated carriers show homologous recombination (HR) deficiency (HRD), resulting in impaired DNA double-strand break (DSB) repair and high sensitivity to PARP inhibitors. Although this therapy is expected to be effective beyond germline BRCA1/2 mutated carriers, a robust validated test to detect HRD tumors is lacking. In this study, we therefore evaluated a functional HR assay exploiting the formation of RAD51 foci in proliferating cells after ex vivo irradiation of fresh breast cancer tissue: the recombination REpair CAPacity (RECAP) test. EXPERIMENTAL DESIGN: Fresh samples of 170 primary breast cancer were analyzed using the RECAP test. The molecular explanation for the HRD phenotype was investigated by exploring BRCA deficiencies, mutational signatures, tumor-infiltrating lymphocytes (TIL), and microsatellite instability (MSI). RESULTS: RECAP was completed successfully in 148 of 170 samples (87%). Twenty-four tumors showed HRD (16%), whereas six tumors were HR intermediate (HRi; 4%). HRD was explained by BRCA deficiencies (mutations, promoter hypermethylation, deletions) in 16 cases, whereas seven HRD tumors were non-BRCA related. HRD tumors showed an increased incidence of high TIL counts (P = 0.023) compared with HR proficient (HRP) tumors and MSI was more frequently observed in the HRD group (2/20, 10%) than expected in breast cancer (1%; P = 0.017). CONCLUSIONS: RECAP is a robust functional HR assay detecting both BRCA1/2-deficient and BRCA1/2-proficient HRD tumors. Functional assessment of HR in a pseudo-diagnostic setting is achievable and produces robust and interpretable results.

Tumor slice culture system to assess drug response of primary breast cancer.

BACKGROUND: The high incidence of breast cancer has sparked the development of novel targeted and personalized therapies. Personalization of cancer treatment requires reliable prediction of chemotherapy responses in individual patients. Effective selection can prevent unnecessary treatment that would mainly result in the unwanted side effects of the therapy. This selection can be facilitated by characterization of individual tumors using robust and specific functional assays, which requires development of powerful ex vivo culture systems and procedures to analyze the response to treatment. METHODS: We optimized culture methods for primary breast tumor samples that allowed propagation of tissue ex vivo. We combined several tissue culture strategies, including defined tissue slicing technology, growth medium optimization and use of a rotating platform to increase nutrient exchange. RESULTS: We could maintain tissue cultures for at least 7 days without losing tissue morphology, viability or cell proliferation. We also developed methods to determine the cytotoxic response of individual tumors to the chemotherapeutic treatment FAC (5-FU, Adriamycin [Doxorubicin] and Cyclophosphamide). Using this tool we designated tumors as sensitive or resistant and distinguished a clinically proven resistant tumor from other tumors. CONCLUSION: This method defines conditions that allow ex vivo testing of individual tumor responses to anti-cancer drugs and therefore might improve personalization of breast cancer treatment.

Attenuated XPC expression is not associated with impaired DNA repair in bladder cancer.

Bladder cancer has a high incidence with significant morbidity and mortality. Attenuated expression of the DNA damage response protein Xeroderma Pigmentosum complementation group C (XPC) has been described in bladder cancer. XPC plays an essential role as the main initiator and damage-detector in global genome nucleotide excision repair (NER) of UV-induced lesions, bulky DNA adducts and intrastrand crosslinks, such as those made by the chemotherapeutic agent Cisplatin. Hence, XPC protein might be an informative biomarker to guide personalized therapy strategies in a subset of bladder cancer cases. Therefore, we measured the XPC protein expression level and functional NER activity of 36 bladder tumors in a standardized manner. We optimized conditions for dissociation and in vitro culture of primary bladder cancer cells and confirmed attenuated XPC expression in approximately 40% of the tumors. However, NER activity was similar to co-cultured wild type cells in all but one of 36 bladder tumors. We conclude, that (i) functional NER deficiency is a relatively rare phenomenon in bladder cancer and (ii) XPC protein levels are not useful as biomarker for NER activity in these tumors.

Functional ex vivo assay to select homologous recombination-deficient breast tumors for PARP inhibitor treatment.

PURPOSE: Poly(ADP-ribose) polymerase (PARP) inhibitors are promising targeted treatment options for hereditary breast tumors with a homologous recombination (HR) deficiency caused by BRCA1 or BRCA2 mutations. However, the functional consequence of BRCA gene mutations is not always known and tumors can be HR deficient for other reasons than BRCA gene mutations. Therefore, we aimed to develop a functional test to determine HR activity in tumor samples to facilitate selection of patients eligible for PARP inhibitor treatment. EXPERIMENTAL DESIGN: We obtained 54 fresh primary breast tumor samples from patients undergoing surgery. We determined their HR capacity by studying the formation of ionizing radiation induced foci (IRIF) of the HR protein RAD51 after ex vivo irradiation of these organotypic breast tumor samples. Tumors showing impaired RAD51 IRIF formation were subjected to genetic and epigenetic analysis. RESULTS: Five of 45 primary breast tumors with sufficient numbers of proliferating tumor cells were RAD51 IRIF formation deficient (11%, 95% CI, 5%-24%). This HR defect was significantly associated with triple-negative breast cancer (OR, 57; 95% CI, 3.9-825; P = 0.003). Two of five HR-deficient tumors were not caused by mutations in the BRCA genes, but by BRCA1 promoter hypermethylation. CONCLUSION: The functional RAD51 IRIF assay faithfully identifies HR-deficient tumors and has clear advantages over gene sequencing. It is a relatively easy assay that can be performed on biopsy material, making it a powerful tool to select patients with an HR-deficient cancer for PARP inhibitor treatment in the clinic.