Targeting of histone methyltransferase DOT1L plays a dual role in chemosensitization of retinoblastoma cells and enhances the efficacy of chemotherapy

Abstract

Aberrant and exclusive expression of chromatin regulators in retinoblastoma (RB) in contrast to terminally differentiated normal retina presents a unique opportunity of selective targeting for RB. However, precise roles of these chromatin regulators in RB development and their potential as therapeutic targets have not been defined thoroughly. Here, we report that targeting of disruptor of telomeric silencing 1-like (DOT1L), a histone H3K79 methyltransferase, sensitizes RB cells to chemotherapeutic drugs by impairing the DNA damage response and thereby potentiating apoptosis while it is largely inefficacious as a single-agent therapy. Moreover, we identified high mobility group AT-hook 2 (HMGA2) as a novel DOT1L target gene in RB cells and found that its aberrant expression is dependent on DOT1L. As HMGA2 depletion reduced CHK1 phosphorylation during DNA damage response and augmented the drug sensitivity in RB cells, our results suggested that DOT1L targeting has a dual role in chemosensitization of RB cells by directly interfering with the immediate involvement of DOT1L in early DNA damage response upon genotoxic insults and also by downregulating the expression of HMGA2 as a rather late effect of DOT1L inhibition. Furthermore, we provide the first preclinical evidence demonstrating that combined therapy with a DOT1L inhibitor significantly improves the therapeutic efficacy of etoposide in murine orthotopic xenografts of RB by rendering the response to etoposide more potent and stable. Taken together, these results support the therapeutic benefits of DOT1L targeting in combination with other chemotherapeutic agents in RB, with mechanistic insights into how DOT1L targeting can improve the current chemotherapy in an RB cell-selective manner.

Genome maintenance in retinoblastoma: Implications for therapeutic vulnerabilities (Review)

“…Notably, DOT1L and H3K79 methylation have been demonstrated to be indispensable for ionizing radiation-induced tumor protein p53 binding protein 1 foci formation during G 1 /G 2 phase, and pharmacological inhibition of DOT1L in combination with DNA-damaging agents further decreased the proliferation of colorectal cancer cells and mixed-lineage leukemia (MLL)-rearranged leukemia cells (72)(73)(74). Consistent with the findings in other cancer cells, DOT1L targeting by EPZ5676 (pinometostat) sensitized RB cells to chemotherapeutic drugs by impairing the DNA damage response and thereby enhancing apoptosis, while it was largely inefficacious as a single-agent therapy in both RB cells and an orthotopic xenograft model (69). In addition to verifying the role of DOT1L in DNA damage response and chemosensitization in RB cells, the study also revealed that high mobility group AT-hook 2 (HMGA2) is a novel DOT1L target gene and its expression is epigenetically upregulated by DOT1L.…”

“…Similar to the case of UHRF1, disruptor of telomeric silencing 1-like (DOT1L) is highly and exclusively expressed in RB although it is thus far unknown whether DOT1L is also an E2F1 target (69). DOT1L is the only known histone methyltransferase catalyzing H3K79 methylation, which Upregulation of the listed genes is detected in primary human RB tumors relative to normal retina by gene expression profiling in the indicated references.…”

“…Notably, HMGA2 has been reported to promote RB cell proliferation and participate in the regulation of DNA damage response in cancer cells (75)(76)(77)(78). HMGA2 depletion reduces checkpoint kinase 1 phosphorylation during the etoposide-induced DNA damage response and potentiates the drug sensitivity in RB cells (69). The aforementioned study suggested that DOT1L targeting has a dual role in chemosensitization of RB cells by immediately hindering the early DNA damage response mediated by DOT1L itself upon genotoxic insults, and also by downregulating HMGA2 expression as a late effect of DOT1L inhibition (Fig.…”

An Epigenetic Role of Mitochondria in Cancer

“…The disruptor of telomeric silencing 1-like (DOT1L), a histone H3K79 methyltransferase, is a target for many diseases [ 509 ]. It sensitizes RB cells to chemotherapeutic drugs by impairing the DNA damage response, thereby potentiating apoptosis [ 510 ].…”

Histone Methyltransferase DOT1L as a Promising Epigenetic Target for Treatment of Solid Tumors

“…Finally, DOT1L inhibitors showed effects also in reducing retinoblastoma cells aggressiveness, where they enhanced sensitivity to chemotherapy and affected cell proliferation ( Mao et al, 2021 ). Moreover, combination therapy with DOT1L and SHP2 inhibitors was demonstrated to be effective in treating a specific subset of KRAS-mutant cancers characterized by a very poor prognosis ( Liu et al, 2021 ).…”