Bladder cancer is the 9th most common cancer worldwide, with around 429.800 new cases diagnosed in 2012 and the 5th most common cancer in Europe, with more than 151.000 new cases diagnosed in 2012. Relating mortality figures, bladder cancer is the 13th most common cause of cancer death worldwide, with around 165.100 deaths from bladder cancer in 2012 and the 9th in Europe, with around 52.400.

Cisplatin-based chemotherapy remains the standard treatment in patients with metastatic urothelial carcinoma (UC).This regimen has been associated with a median survival of 14-15 months. The prognosis of patients who progress after a platinum-based regimen is dismal. Several chemotherapy drugs tested in the second-line setting, such as taxanes, vinflunine and pemetrexed, have demonstrated limited activity, with response rates of 5-20%, median progression-free survival (PFS) of 2-4 months, and median survival of 6-8 months. Thus, there are significant unmet medical needs in the second-line setting. New therapeutic targets should be tested in urothelial carcinoma to improve these results.

Therapies targeting DNA repair pathways can exploit DNA repair defects in cancer cells to generate synthetic lethality. Alterations in DNA repair pathways have been associated with response to DNA-damaging agents. For example, defective homologous recombination (HR) plays a crucial role in tumors where platinum agents are involved in therapeutic management, as well as in those treated with PARP inhibitors, which have synthetic lethal effects when applied to cells with defective HR. Targeted mutational profiling of HR genes using next-generation sequencing has been used to identify mutations of key HR genes. Furthermore, HR-defective tumors exhibit genomic instability, including loss of heterozygosity (LOH), telomeric allelic imbalance (TAI) and large-scale state transitions (LST). A combined HR deficiency score (myChoice homologous recombination deficiency (HRD) test from Myriad Genetics) defined as the sum of LOH, TAI and LST has been developed. This score has been associated with response to platinum-based chemotherapy and in ovarian cancer with the efficacy of niraparib in patients without germline breast cancer gene (gBRCA) mutations.

In patients with muscle-invasive bladder cancer (MIBC), the Cancer Genome Atlas project found 31% of alterations in BRCA1-2 genes, mainly related to copy number and overexpression. In addition, a high percentage of tumors had alterations in other DNA repair genes. Recently, in platinum-treated UC patients, 47% of mutations in DNA repair genes have been found, including 50% of mutations in HR, Fanconi anemia, and DNA-damage-response checkpoint pathways. The presence of these mutations has been associated with survival. These results suggest a potential role for PARP inhibitors in UC. Niraparib is a highly selective inhibitor of poly (adenosine diphosphate \[ADP\]-ribose) polymerase (PARP)1/2 nuclear protein. PARP enzymes are involved in DNA repair through activation of the base excision repair (BER) pathway and alternative end-joining pathways and inhibition of non-homologous end-joining. PARP inhibition in cells with HR deficiency causes accumulation of unrepaired DNA double-strand breaks, leading to cell death. For these reasons, PARP inhibitors are selectively lethal in tumor cells with defective HR. Niraparib at the recommended oral dose of 300 mg daily has demonstrated efficacy in platinum- sensitive recurrent ovarian cancer with defective HR. The most significant toxicity was hematologic (thrombocytopenia, neutropenia, and anemia). Among non-hematologic toxicities, hypertension was detected in 8% of patients.

c-Met receptor tyrosine kinase (RTK) is activated by its ligand, hepatocyte growth factor (HGF), and induces increased proliferation, migration, motility, and invasion of bladder cancer cells. c-Met is overexpressed in more than 60% of metastatic bladder cancer patients and is linked to poor outcome. Furthermore, in bladder cancer, c-Met is co-expressed with other RTKs, such as AXL and PDGFR. Some evidence suggests a relationship between c-Met and AXL expression with DNA damage response and resistance to chemotherapy. For example, Balaji et al have demonstrated that AXL inhibition leads to a defect in the HR pathway, sensitizing cells to PARP inhibition. In a recently published study, a significant interaction between c-Met and Poly \[ADP-ribose\] polymerase 1 (PARP1) was detected in breast cancer cell lines. c-Met activity can decrease response to PARP inhibitors, whereas treatment with c-Met inhibitors renders cells more sensitive to PARP inhibition. Likewise, in in vivo models with xenograft tumors, the combination of c-Met and PARP inhibitors showed a significant reduction in tumor growth compared to either inhibitor alone. This interaction can be explained because c-Met mediates PARP1 function through phosphorylation of PARP1 at Y907. These results raise the possibility that bladder cancer patients with tumors overexpressing c-Met can benefit from the combination of c-Met inhibitors and PARP inhibitors.

Cabozantinib is an oral, small-molecule tyrosine kinase inhibitor. Its primary targets are MET, VEGFR1-3, RET, AXL, FLT3 and KIT. Cabozantinib has been approved by the FDA for clinical treatment of progressive, metastatic medullary thyroid cancer. The recommended dose of cabozantinib has been established in phase I trials at 60 mg/day in 28-day cycles. Recently published trials have demonstrated activity for cabozantinib in patients with advanced renal cell carcinoma and metastatic castration-resistant prostate cancer (mCRPC). Furthermore, in preclinical models of UC of the bladder, cabozantinib has demonstrated the ability to inhibit tumor xenograft growth. It has been suggested that levels of soluble Met ectodomain (sMet) can be measured in the urine as a useful biomarker to monitor the efficacy of c-Met therapy in bladder cancer patients. Moreover, cabozantinib has demonstrated activity in heavily pretreated, advanced bladder cancer patients, with a response rate of 19.5% and manageable toxicities.

In the phase I of this study it is proposed to evaluate DLTs of niraparib and cabozantinib combination and determine MTD in patients with advanced urothelial or renal cell carcinoma. In the phase II it is proposed to make a preliminary evaluation of the efficacy of this combination in patients with urothelial cell carcinoma. Efficacy results will be correlated with genomic alterations related to c-Met and PARP inhibitor activity.