Bladder cancer pharmacogenomics: recent insights and future perspectives

Diagnostic Microdosing Approach to Study Gemcitabine Resistance

Gemcitabine metabolites cause the termination of DNA replication and induction of apoptosis. We determined whether subtherapeutic "microdoses" of gemcitabine are incorporated into DNA at levels that correlate to drug cytotoxicity. A pair of nearly isogenic bladder cancer cell lines differing in resistance to several chemotherapy drugs were treated with various concentrations of ¹⁴C-labeled gemcitabine for 4-24 h. Drug incorporation into DNA was determined by accelerator mass spectrometry. A mechanistic analysis determined that RRM2, a DNA synthesis protein and a known resistance factor, substantially mediated gemcitabine toxicity. These results support gemcitabine levels in DNA as a potential biomarker of drug cytotoxicity.

Clinical Evaluation of Cisplatin Sensitivity of Germline Polymorphisms in Neoadjuvant Chemotherapy for Urothelial Cancer

BACKGROUND

Level 1 evidence has demonstrated increased overall survival with cisplatin-based neoadjuvant chemotherapy for patients with muscle-invasive urothelial cancer. Usage remains low, however, in part because neoadjuvant chemotherapy will not be effective for every patient. To identify the patients most likely to benefit, we evaluated germline pharmacogenomic markers for association with neoadjuvant chemotherapy sensitivity in 2 large cohorts of patients with urothelial cancer.

PATIENTS AND METHODS

Patients receiving neoadjuvant cisplatin-based chemotherapy for muscle-invasive urothelial cancer were eligible. Nine germline single nucleotide polymorphisms (SNPs) potentially conferring platinum sensitivity were tested for an association with a complete pathologic response to neoadjuvant chemotherapy (pT0) or elimination of muscle-invasive cancer (<pT2).

RESULTS

The data from 205 patients were analyzed-59 patients were included in the discovery set and 146 in an independent replication cohort-from 3 institutions. The stage pT0 (26%) and < pT2 (50%) rates were consistent across the discovery and replication populations. Using a multivariate recessive genetic model, rs244898 in RARS (odds ratio, 6.8; 95% confidence interval, 1.8-28.9; P = .006) and rs7937567 in GALNTL4 (odds ratio, 4.8; 95% confidence interval, 1.1-22.6; P = .04) were associated with pT0 in the discovery set. Despite these large effects, neither were associated with achievement of pT0 in the replication set. A third SNP, rs10964552, was associated with stage < pT2 in the discovery set but also failed to replicate.

CONCLUSION

Germline SNPs previously associated with platinum sensitivity were not associated with the neoadjuvant chemotherapy response in a large replication cohort of patients with urothelial cancer. These results emphasize the need for replication when evaluating pharmacogenomic markers and demonstrate that multi-institutional efforts are feasible and will be necessary to achieve advances in urothelial cancer pharmacogenomics.

Pharmacogenomics in bladder cancer

Bladder cancer is a common cancer worldwide. For patients presenting with muscle-invasive disease, the 5-year survival rate is approximately 50%. Cisplatin-based combination chemotherapy is recommended in the neoadjuvant setting before cystectomy and is also the first line in the metastatic setting. However, the survival benefit of such therapy is modest. The identification of pharmacogenomic biomarkers would enable the rational and personalized treatment of patients by selecting those patients that would benefit most from such therapies sparing others the unnecessary toxicity. Conventional therapies would be recommended for an expected responder, whereas a nonresponder would be considered for alternative therapies selected on the basis of the individual's molecular profile. Although few effective bladder cancer therapies have been introduced in the past 30 years, several targeted therapies against the molecular drivers of bladder cancer appear promising. This review summarizes pharmacogenomic biomarkers that require further investigation or prospective evaluation or both, and publicly available tools for drug discovery and biomarker identification from in vitro data.