Punctate LC3B Expression Is a Common Feature of Solid Tumors and Associated with Proliferation, Metastasis, and Poor Outcome

Abstract

Purpose Measurement of autophagy in cancer and correlation with histopathologic grading or clinical outcomes has been limited. Accordingly, we investigated LC3B as an autophagosome marker by analyzing nearly 1400 tumors from 20 types of cancer, focussing on correlations with clinical outcomes in melanoma and breast cancer. Experimental Design Staining protocols were developed for automated quantitative analysis (AQUA) using antibodies vs LC3 isoform B (LC3B) and Ki-67. Clinically annotated breast and melanoma TMA’s and a multitumor array were employed. An AQUA program was developed to quantitate LC3B distribution in punctate and diffuse compartments of the cell. Results LC3B staining was moderate to high in the large majority of tumors. The % area occupied by punctate LC3B was elevated 3–5 fold at high LC3B intensities. In breast cancer and melanoma TMAs, LC3B and Ki-67 showed strong correlations (p < 0.0001) and in multitumor TMAs mitotic figures were most often seen in tumors with highest LC3B expression (p < 0.002). In breast cancer, LC3B expression was elevated in node-positive vs node-negative primaries and associated with increased nuclear grade and shortened survival. In a melanoma TMA with no survival data, LC3B levels were highest in nodal, visceral and cutaneous metastases. Conclusions The results reveal a common expression of LC3B in malignancy and support emerging evidence that autophagy plays a significant role in cancer progression. High LC3B was associated proliferation, invasion and metastasis, high nuclear grade and worse outcome. Thus autophagy presents a key target of therapeutic vulnerability in solid tumors.

Combined autophagy and HDAC inhibition

“…Our findings are in agreement with a recent study that reported high basal MAP1LC3B expression in various advanced solid tumors. 27 At this time, CQ and its analog HCQ are the only clinically relevant autophagy inhibitors and they are currently being evaluated in more than 20 clinical trials for cancer therapy. 6 Our study provides one of the first reports of the clinical safety and preliminary efficacy of the inhibition of autophagy as a novel approach to augment the efficacy of conventional anticancer agents.…”

Autophagy Is a Protective Mechanism for Human Melanoma Cells under Acidic Stress

“…Interestingly, acidic stress caused inhibition of the mTOR pathway also in MCF-7 cells (data not shown), suggesting that the capacity of cancer cells to modulate autophagy following acidic stress may not be dependent only on mTOR inhibition but likely on their ability to restore their physiological pH i by extruding acids via pH-regulating systems. On the other hand, human melanoma cells rely on functional autophagy for survival and invasion (48) and increased autophagy in several human cancers, including melanoma is associated to metastasis and poor outcome (69). Interestingly, the melanoma cell line Me30966 maintained an increased autophagic flux even after a long-term (24 -72 h) cul-ture in acidic conditions.…”

Glutaminolysis and autophagy in cancer

“…73 Moreover, the expression of the core autophagy gene MAP1LC3 (a marker of the autophagy process) is increased in samples of aggressive tumors and correlates with the risk of metastatic disease and with a poor patient outcome. 77,78 Autophagy promotes metastasis by limiting detachment-induced cell death (anoikis) during extracellular matrix detachment of cancer cells. 79 Autophagy also contributes to the survival of dormant disseminated tumor cells for extremely prolonged periods.…”