LDH-A Knockdown: Changes in The LDH Isoenzyme Profile and Variability in Glioma Response

Background: Lactate metabolism in tumors is now recognized as a major energy source and a major gluconeogenic precursor for many tumors, as well as shown to exhibit signaling properties. There is less information on the role of the LDH/lactate axis in brain tumors, although lactate formation in gliomas is associated with poor survival. Methods: Three murine glioma cell lines (GL261, CT2A, and ALTS1C1) were transduced to knockdown (KD) expression of the murine LDH-A gene. The effects of the LDH-A KD were compared to those in control (NC) cells and tumors. Results: Differences in the expression of LDH-A and LDH-B mRNA, protein, and enzymatic activity were observed in the six cell lines. LDH zymography showed a major difference in LDH subunit distribution between GL261 LDH-A KD and NC tumors, whereas little or no effect of LDH-A KD was observed in CT2A and ALTS1C1 tumors. Tumors LDH-A and LDH-B immunohistochemistry and a Weka segmentation analysis were consistent with isoenzyme patterns and the above analyses. An “inverse” LDH-A/LDH-B staining relationship (high vs low) was observed in many local GL261 tumor regions. In contrast, CT2A tumors showed a more “direct” local LDH-A/LDH-B staining relationship. LDH-A KD prolonged the doubling time of GL261 cells in culture and prevented the formation of subcutaneous flank tumors in immune-competent C57BL/6 mice (GL261 NC tumors had a prolonged growth delay). In nude mice, both LDH-A KD and NC GL261 tumors grew more rapidly than GL261 NC tumors in C57BL/6 mice. No differences between NC and KD cell proliferation (in vitro) and tumor growth in C57BL/6 mice (doubling time) were observed for CT2A and ALTS1C1 cells and tumors, consistent with the absence of a difference in their LDH isoenzyme profiles. Conclusions: These results show the combined impact of a genetic alteration (LDH-A depletion) on the LDH isoenzyme profile, expression of LDH-A vs LDH-B and LDH enzymatic activity, and the immune system (C57BL/6 vs nude mice) on the growth of s.c. located tumors.

Correlation of lactate dehydrogenase (LDH) isoenzyme profile with outcome in advanced colorectal cancer (CRC) patients (pts) treated with chemotherapy and bevacizumab (BEV) or cediranib (CED).

e13541 Background: There is a clinical need for predictive biomarkers of efficacy of VEGF signaling inhibitors (VSIs). LDH is a tetramer that can include any combination of the M and H subunits. LDH4 and 5 isoenzymes are composed mostly of the M subunit and are more abundant in hypoxic conditions. We speculated that the levels of LDH isoenzymes in pts serum may correlate with outcome of pts treated with VSIs. HORIZON I trial enrolled pts that were randomized to mFOLFOX6 with BEV or CED. A retrospective exploratory analysis was performed on baseline serum samples of these pts. Methods: Total serum LDH was tested on fresh samples during the conduct of the trial. About 2 years after the trial, frozen samples stored at -70 degrees were tested for total serum LDH and LDH isoenzymes, measured by agarose electrophoresis and a colorimetric enzymatic assay. Relative levels of M and H subunits were derived based on the known structure of each isoenzyme. Progression free survival (PFS) and overall survival (OS) were compared by subgroups of total LDH and LDH isoenzyme levels. P values were not calculated for these exploratory analyses. Results: Baseline total LDH levels from fresh serum were available for 207 pts. Total and isoenzyme LDH levels were available for frozen serum samples of 189 pts. Total LDH in the frozen and fresh samples correlated (R=0.9). Distant isoenzymes (e.g. LDH1 and 5) were negatively correlated. High M/H subunits ratio correlated with poor OS (HR=1.804, 95%CI 1.24-2.620). A non-significant trend for better OS to CED-treated vs. BEV-treated pts was seen in pts with high M/H ratio (e.g., CED 30mg vs BEV HR=0.685, 95%CI 0.382-1.23). Conclusions: Evaluation of LDH isoenzymes is feasible using serum samples kept frozen for 2 years. A negative correlation is seen between hypoxic-related and oxic-related isoenzymes. In CRC pts treated with a VSI, LDH isoenzyme hypoxia-associated profile correlates with poorer outcome. LDH isoenzyme profile as a possible predictive biomarker for benefit from CED vs. BEV requires further investigation.