The emerging role of homologous recombination repair and PARP inhibitors in genitourinary malignancies.

As cells age and are exposed to genotoxic stress, preservation of the genomic code requires multiple DNA repair pathways to remove single-strand or double-strand breaks. Loss of function somatic genomic aberrations or germline deficiency in genes involved in DNA repair can result in acute cell death or, after a latency period, cellular transformation. Therapeutic exploitation of DNA repair by inhibition of poly (adenosine diphosphate [ADP]) ribose polymerases (PARP), a family of enzymes involved in the repair of single-strand and in some cases double-strand breaks, has become a novel cancer treatment. Although the application of PARP inhibitors (PARPis) initially focused on tumors with BRCA1 or BRCA2 deficiencies, synthetic susceptibilities to PARPis have been expanded due to the identification of tumors with mutations pathways involved in DNA damage repair, in particular those that repair double-strand breaks using homologous recombination (HR). There is an increasing appreciation that genitourinary (GU) malignancies, including bladder cancer and especially prostate cancer, contain subsets of patients with germline and somatic alterations in HR genes that may reflect an increased response to PARPis. In this review, the authors describe the mechanisms and rationale of the use of PARPis in patients with GU cancers, summarize previously reported preclinical and clinical trials, and identify ongoing trials to determine how PARPis and strategies targeted at HR repair can have widespread application in patients with GU cancers. Cancer 2017;123:1912-1924. © 2017 American Cancer Society.

Changes in Lean Muscle Mass Associated with Neoadjuvant Platinum-Based Chemotherapy in Patients with Muscle Invasive Bladder Cancer.

BACKGROUND: Baseline sarcopenia or severe lean muscle deficiency is independently associated with increased mortality after cystectomy for muscle-invasive urothelial carcinoma of the bladder (MIUC). The impact of chemotherapy on muscle mass in MIUC patients remains undefined. OBJECTIVES: To describe preoperative changes in body composition in MIUC patients receiving platinum-based neoadjuvant chemotherapy (NC). METHODS: Patients with cT2-4 N0-1 M0 UC of the bladder who received NC were identified. Lumbar skeletal muscle index (SMI, cm2/m2), visceral adipose index (VAI, cm2/m2), and the subcutaneous and intramuscular adipose index (SAI, cm2/m2) were calculated using validated methodology (cross sectional area of skeletal muscle/height2 at L3) from measurement of soft tissue areas on pre- (pre-NC) and post-NC (post-NC) computed tomography. Patients were classified as sarcopenic according to consensus definitions: Male: SMI <55 cm2/m2, Female: SMI <38.5 cm2/m2. Pre-NC and post-NC median body mass index (BMI kg/m2), SMI, and adipose indices were compared. RESULTS: The study cohort consisted of 26 patients, with a median age 70 years, including 7 females (27%). Chemotherapy regimens included dose-dense methotrexate, vinblastine, doxorubicin and cisplatin (31%), gemcitabine/cisplatin (62%) and gemcitabine/carboplatin (3.8%) with a median of 3.5 (range 2-6) cycles. Median pre- and post-NC BMI were 27.1 kg/m2 and 27.2 kg/m2 (p = 0.36). Median pre- and post-NC SMI were 49.1 cm2/m2 and 44.5 (p < 0.001) respectively. Median percent change in SMI was -6.4% (range -30% to 10%). Pre-NC, 18 (69%) patients were sarcopenic vs. 21 (81%, p = 0.002) post-NC. Median time between initiation of chemotherapy and cystectomy was 110 days. CONCLUSIONS: We observed a significant decrease in lean muscle mass among MIUC patients treated with platinum-based NC prior to cystectomy, with an associated increase in the prevalence of sarcopenia. Patients undergoing NC may benefit from pre-habilitative interventions to mitigate lean muscle loss prior to cystectomy.

APOBEC-mediated mutagenesis in urothelial carcinoma is associated with improved survival, mutations in DNA damage response genes, and immune response.

APOBEC enzymes are responsible for a mutation signature (TCW>T/G) implicated in a wide variety of tumors. We explore the APOBEC mutational signature in bladder cancer and the relationship with specific mutations, molecular subtype, gene expression, and survival using sequencing data from The Cancer Genome Atlas (n = 395), Beijing Genomics Institute (n = 99), and Cancer Cell Line Encyclopedia. Tumors were split into "APOBEC-high" and "APOBEC-low" based on APOBEC enrichment. Patients with APOBEC-high tumors have better overall survival compared to those with APOBEC-low tumors (38.2 vs. 18.5 months, p = 0.005). APOBEC-high tumors are more likely to have mutations in DNA damage response genes (TP53, ATR, BRCA2) and chromatin regulatory genes (ARID1A, MLL, MLL3), while APOBEC-low tumors are more likely to have mutations in FGFR3 and KRAS. APOBEC3A and APOBEC3B expression correlates with mutation burden, regardless of bladder tumor molecular subtype. APOBEC mutagenesis is associated with increased expression of immune signatures, including interferon signaling, and expression of APOBEC3B is increased after stimulation of APOBEC-high bladder cancer cell lines with IFNγ. In summary, APOBEC-high tumors are more likely to have mutations in DNA damage response and chromatin regulatory genes, potentially providing more substrate for APOBEC enzymes, leading to a hypermutational phenotype and the subsequent enhanced immune response.

A Carcinogen-induced mouse model recapitulates the molecular alterations of human muscle invasive bladder cancer.

The N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) mouse model is an attractive model system of muscle-invasive bladder cancer (MIBC) as it recapitulates the histology of human tumors in a background with intact immune system. However, it was unknown whether this carcinogen-induced model also mimicked human MIBC at the molecular and mutational level. In our study, we analyzed gene expression and mutational landscape of the BBN model by next-generation sequencing followed by a bioinformatic comparison to human MIBC using data from The Cancer Genome Atlas and other repositories. BBN tumors showed overexpression of markers of basal cancer subtype, and had a high mutation burden with frequent Trp53 (80%), Kmt2d (70%), and Kmt2c (90%) mutations by exome sequencing, similar to human MIBC. Many variants corresponded to human cancer hotspot mutations, supporting their role as driver mutations. We extracted two novel mutational signatures from the BBN mouse genomes. The integrated analysis of mutation frequencies and signatures highlighted the contribution of aberrations to chromatin regulators and genetic instability in the BBN tumors. Together, our study revealed several similarities between human MIBC and the BBN mouse model, providing a strong rationale for its use in molecular and drug discovery studies.