Correlation of Platinum Cytotoxicity to Drug-DNA Adduct Levels in a Breast Cancer Cell Line Panel

Abstract

Platinum drugs, including carboplatin and oxaliplatin, are commonly used chemotherapy drugs that kill cancer cells by forming toxic drug-DNA adducts. These drugs have a proven, but modest, efficacy against several aggressive subtypes of breast cancer but also cause several side effects that can lead to the cessation of treatment. There is a clinical need to identify patients who will respond to platinum drugs in order to better inform clinical decision making. Diagnostic microdosing involves dosing patients or patient samples with subtherapeutic doses of radiolabeled platinum followed by measurement of platinum-DNA adducts in blood or tumor tissue and may be used to predict patient response. We exposed a panel of six breast cancer cell lines to 14C-labeled carboplatin or oxaliplatin at therapeutic and microdose (1% therapeutic dose) concentrations for a range of exposure lengths and isolated DNA from the cells. The DNA was converted to graphite, and measurement of radiocarbon due to platinum-DNA adduction was quantified via accelerator mass spectrometry (AMS). We observed a linear correlation in adduct levels between the microdose and therapeutic dose, and the level of platinum-DNA adducts corresponded to cell line drug sensitivity for both carboplatin and oxaliplatin. These results showed a clear separation in adduct levels between the sensitive and resistant groups of cell lines that could not be fully explained or predicted by changes in DNA repair rates or mutations in DNA repair genes. Further, we were able to quantitate oxaliplatin-DNA adducts in the blood and tumor tissue of a metastatic breast cancer patient. Together, these data support the use of diagnostic microdosing for predicting patient sensitivity to platinum. Future studies will be aimed at replicating this data in a clinical feasibility trial.

Genome-wide single-nucleotide resolution of oxaliplatin–DNA adduct repair in drug-sensitive and -resistant colorectal cancer cell lines

“…Platinating anticancer drugs kill cells by binding to DNA. In light of our results showing that differences in DNA repair do not account for the cellular resistance we observed, it makes sense that this resistance is related to lower net influx of drug, as has been found in other studies and now is strongly supported by this study (23,(49)(50)(51). Low initial platinum levels in resistant cells are thought to arise from reduced influx and/or increased efflux of drug, and several membrane proteins have been implicated in transmembrane transport of platinum drugs (34)(35)(36).…”

Small extracellular vesicles ameliorate peripheral neuropathy and enhance chemotherapy of oxaliplatin on ovarian cancer

“…These data suggest that the combination of CEC‐sEVs with oxaliplatin reduces EMT. The DNA/platinum adducts induce cytotoxicity (Johnson et al., 1994; Wang et al., 2018). We thus examined the effect of CEC‐sEVs on oxaliplatin‐DNA interstrand crosslinks.…”

DNA Adducts in Cancer Chemotherapy

“…It is worth noting that early quantitative studies using Pt-DNA enzyme-linked immunosorbent assays (ELISA) could result in an underestimation of 10–300-fold lower levels of adducts in human samples than mass spectrometry approaches . A new approach using 14 C-labeled carboplatin or oxaliplatin under diagnostic microdosing conditions has been explored for predicting patient sensitivity to platinum drugs in cancer patients. − …”