PI3K blockage synergizes with PLK1 inhibition preventing endoreduplication and enhancing apoptosis in anaplastic thyroid cancer

A polo-like kinase 1 inhibitor enhances erastin sensitivity in head and neck squamous cell carcinoma cells in vitro

BACKGROUND

Polo-like kinase 1 (PLK1) is a critical therapeutic target in the treatment of head and neck squamous cell carcinoma (HNSCC). The objective of this study was to investigate the therapeutic effect of the combination of BI 2536, a PLK1 inhibitor, and erastin, a ferroptosis inducer, in HNSCC.

METHODS

The proliferation, invasion, and migration abilities of Tu177 and FaDu cells upon exposure to BI 2536 and erastin, used in combination or alone, were tested. Fe2+, glutathione (GSH), and malondialdehyde (MDA) detection kits were used to determine whether the addition of BI 2536 enhanced the accumulation of Fe2+ and MDA, along with the depletion of GSH. Quantitative real-time PCR, western blot analyses were performed to investigate whether BI 2536 further altered the mRNA and expression level of ferroptosis genes. Furthermore, si PLK1 was used to investigate whether targeting PLK1 gene promoted erastin-induced ferroptosis.

RESULTS

The combination of BI 2536 and erastin exerted a stronger cytotoxicity than treatment with a single agent. Compared with erastin treatment alone, the combination of BI 2536 and erastin lowered the ability of tumor cells to self-clone, invade, and migrate. BI 2536 enhanced the accumulation of Fe2+ and MDA, and the depletion of GSH. BI 2536 increased erastin-induced changes in ferroptosis-related gene mRNA and expression. Importantly, targeting PKL1 enhanced the anti-cancer effect of erastin.

CONCLUSION

BI 2536 enhanced the sensitivity of HNSCC cells to erastin, which provides a new perspective for cancer treatment.

PLK1 and FoxM1 expressions positively correlate in papillary thyroid carcinoma and their combined inhibition results in synergistic anti-tumor effects

Polo-like kinase 1 (PLK1; also known as serine/threonine-protein kinase PLK1) serves as a central player in cell proliferation, exerting critical regulatory roles in mitotic processes and cell survival. We conducted an analysis of PLK1 protein expression in a large cohort of samples from papillary thyroid carcinoma (PTC) patients and examined its functional significance in PTC cell lines, both in vitro and in vivo. PLK1 overexpression was noted in 54.2% of all PTC and was significantly associated with aggressive clinicopathological parameters; it was also found to be an independent prognostic marker for shorter recurrence-free survival. Given the significant association between PLK1 and forkhead box protein M1 (FoxM1), and their concomitant overexpression in a large proportion of PTC samples, we explored their correlation and their combined inhibitions in PTC in vitro and in vivo. Inhibition of PLK1 expression indeed suppressed cell proliferation, leading to cell cycle arrest and apoptosis in PTC cell lines. Significantly, the downregulation of PLK1 reduced the self-renewal capability of spheroids formed from PTC cells. Immunoprecipitation analysis shows that PLK1 binds to FoxM1 and vice versa in vitro. Mechanistically, PLK1 knockdown suppresses FoxM1 expression, whereas inhibition of FoxM1 does not affect PLK1 expression, which suggests that PLK1 acts through the FoxM1 pathway. The combined treatment of a PLK1 inhibitor (volasertib) and a FoxM1 inhibitor (thiostrepton) demonstrated a synergistic effect in reducing PTC cell growth in vitro and delaying tumor growth in vivo. This study highlights the important role of PLK1 in PTC tumorigenesis and prognosis. It also highlights the synergistic therapeutic potential of dual-targeting PLK1 and FoxM1 in PTC, unveiling a potential innovative therapeutic strategy for managing aggressive forms of PTC.

Clinicopathological Significance of AKT1 and PLK1 Expression in Oral Squamous Cell Carcinoma

Purpose

Oral squamous cell carcinoma (OSCC) is the sixth leading cause of cancer-related death worldwide and is characterized by metastasis and recurrence. We aimed to evaluate the expression of AKT1 and PLK1 in OSCC and identify their correlation with the clinical and histological features and prognosis of patients with OSCC.

Methods

Tissue samples were collected from 70 patients with OSCC and 50 patients with normal oral mucosa. The expression levels of AKT1 and PLK1 in OSCC tissues and normal oral mucosa were detected by immunohistochemistry. The chi-square test was used to identify correlations between the expression levels of AKT1 and PLK1 with patients' clinicopathologic characteristics. Survival analysis was assessed by the Kaplan-Meier method. Spearman's rank correlation test was used to determine the relationships between AKT1 and PLK1 expressions. The bioinformatics database GEPIA was used to verify the experimental results.

Results

The chi-square test and Fisher's exact test showed that the positive expression rate of AKT1 and PLK1 in OSCC tissue was significantly higher than that in the normal oral mucosa (P < 0.05). PLK1 expression levels were significantly correlated with tumor stage and size (P < 0.05). Kaplan-Meier analysis showed that the survival time of AKT1 and PLK1 with high expression was significantly shorter than that of patients with low expression (P < 0.05). Spearman's rank correlation test showed a strong correlation between AKT1 and PLK1 expression in OSCC tissue (R = 0.53; P < 0.05). GEPIA bioinformatics database analysis results show that the expression and overall survival of AKT1 and PLK1 analysis and the correlation analysis of AKT1 and PLK1 were consistent with experimental results.

Conclusion

AKT1 and PLK1 expressions are associated with the occurrence and progression of OSCC and may be used as diagnostic and prognostic indicators of OSCC. There may be a correlation between AKT1 and PLK1 in OSCC tissue.

Navitoclax Enhances the Therapeutic Effects of PLK1 Targeting on Lung Cancer Cells in 2D and 3D Culture Systems

The efficacy of antimitotics is limited by slippage, whereby treated cells arrested in mitosis exit mitosis without cell division and, eventually, escape apoptosis, constituting a serious resistance mechanism to antimitotics. Strategies to overcome slippage should potentiate the cancer cell killing activity of these antimitotics. Such strategies should accelerate cell death in mitosis before slippage. Here, we undertook a mechanistic analysis to test whether the apoptosis activator Navitoclax potentiates apoptosis triggered by the antimitotic BI2536, a potent inhibitor of Polo-like kinase 1 (PLK1) with the goal of overcoming slippage. We found that cancer cells in 2D cultures treated with BI2536 alone accumulate in mitosis, but a significant fraction of arrested cells undergo slippage and survive. Remarkably, combining BI2536 with Navitoclax dramatically reduces slippage, shifting the cell fate to accelerated death in mitosis. The results are confirmed in 3D spheroids, a preclinical system that mimics in vivo tumor drug responses. Importantly, in 3D spheroids, the effect of the BI2536/Navitoclax combination requires a lower therapeutic dosage of each drug, underlying its potential to improve the therapeutic index. Our results highlight the relevance of apoptosis potentiators to circumvent slippage associated with antimitotics. The combination of BI2536 with Navitoclax shows in vitro synergy/additive effect, which warrants further clinical research.

PLK1 inhibition-based combination therapies for cancer management

Polo-like kinase I (PLK1), a cell cycle regulating kinase, has been shown to have oncogenic function in several cancers. Although PLK1 inhibitors, such as BI2536, BI6727 (volasertib) and NMS-1286937 (onvansertib) are generally well-tolerated with a favorable pharmacokinetic profile, clinical successes are limited due to partial responses in cancer patients, especially those in advanced stages. Recently, combination therapies targeting multiple pathways are being tested for cancer management. In this review, we first discuss structure and function of PLK1, role of PLK1 in cancers, PLK1 specific inhibitors, and advantages of using combination therapy versus monotherapy followed by a critical account on PLK1-based combination therapies in cancer treatments, especially highlighting recent advancements and challenges. PLK1 inhibitors in combination with chemotherapy drugs and targeted small molecules have shown superior effects against cancer both in vitro and in vivo. PLK1-based combination therapies have shown increased apoptosis, disrupted cell cycle, and potential to overcome resistance in cancer cells/tissues over monotherapies. Further, with successes in preclinical experiments, researchers are validating such approaches in clinical trials. Although PLK1-based combination therapies have achieved initial success in clinical studies, there are examples where they have failed to improve patient survival. Therefore, further research is needed to identify and validate novel biologically informed co-targets for PLK1-based combinatorial therapies. Employing a network-based analysis, we identified potential PLK1 co-targets that could be examined further. In addition, understanding the mechanisms of synergism between PLK1 inhibitors and other agents may lead to a better approach on which agents to pair with PLK1 inhibition for optimum cancer treatment.

PLK1 Inhibition Sensitizes Breast Cancer Cells to Radiation via Suppressing Autophagy

PURPOSE

Polo-like kinase 1 (PLK1) is a protein kinase that is overexpressed in breast cancer and may represent an attractive target for breast cancer treatment. However, few studies have investigated the relationship between PLK1 and radiosensitivity in breast cancer. Here, we attempted to explore whether PLK1 inhibition could sensitize breast cancer cells to radiation.

METHODS AND MATERIALS

Breast cancer cells were treated with PLK1 small interference RNA or the PLK1-inhibitor, GSK461364. Cell proliferation was assessed using a colony formation assay. Cell cycle analyses were performed by flow cytometry. DNA damage, autophagy, and reactive oxygen species induced by ionizing radiation were detected by immunofluorescence, Western blot, and flow cytometry, respectively. Microtubule-associated protein 1 light chain 3 alpha (LC3) puncta were detected using an immunofluorescence assay. A clonogenic survival assay was used to determine the effect of PLK1 inhibition on cell radiosensitivity. A xenograft mouse model of breast cancer cells was used to investigate the potential synergistic effects of PLK1 inhibition and irradiation in vivo. Finally, the expression of PLK1 and LC3 in the breast cancer tissues was evaluated by immunohistochemistry.

RESULTS

PLK1 inhibition significantly suppressed the proliferation and increased the radiosensitivity of breast cancer cells. Pharmacologic inhibition of PLK1 by the selective inhibitor, GSK461364, enhanced the radiosensitivity of breast cancer cells in vivo (n = 4, P = .002). Mechanistically, PLK1 inhibition led to the downregulation of radiation-induced reactive oxygen species and autophagy, thereby increasing the radiosensitivity of breast cancer cells. Additionally, we detected a positive correlation between the expression of PLK1 and LC3 in human breast cancer samples (n = 102, R = 0.486, P = .005).

CONCLUSIONS

Our findings indicate that PLK1 inhibition enhances the radiosensitivity of breast cancer cells in a manner associated with the suppression of radiation-induced autophagy. The inhibition of PLK1 represents a promising strategy for radiosensitizing breast cancer.

Research update on the anticancer effects of buparlisib

Buparlisib is a highly efficient and selective PI3K inhibitor and a member of the 2,6-dimorpholinopyrimidine-derived family of compounds. It selectively inhibits four isomers of PI3K, PI3Kα, PI3Kβ, PI3Kγ and PI3Kδ, by competitively binding the lipid kinase domain on adenosine 5'-triphosphate (ATP), and serves an important role in inhibiting proliferation, promoting apoptosis and blocking angiogenesis, predominantly by antagonizing the PI3K/AKT pathway. Buparlisib has been confirmed to have a clinical effect in patients with solid tumors and hematological malignancies. A global, phase II clinical trial with buparlisib and paclitaxel in head and neck squamous cell carcinoma has now been completed, with a manageable safety profile. Buparlisib currently has fast-track status with the United States Food and Drug Administration. The present review examined the biochemical structure, pharmacokinetic characteristics, preclinical data and ongoing clinical studies of buparlisib. The various mechanisms of influence of buparlisib in tumors, particularly in preclinical research, were summarized, providing a theoretical basis and direction for basic research on and clinical treatment with buparlisib.

Therapeutic inhibition of polo-like kinases in anaplastic thyroid cancer

Polo‐like kinases (PLKs) are potent regulators of cell proliferation and cell survival. Polo‐like kinases are potential targets in the treatment of anaplastic thyroid cancer (ATC), a rare but deadly disease. The therapeutic effects of volasertib, a PLK inhibitor, was evaluated for the treatment of ATC either alone or in combination with sorafenib. Volasertib decreased cell viability in three ATC cell lines (8505C, 8305C, and KAT18) in a dose‐dependent manner. Volasertib caused ATC cells to accumulate in G₂/M phase, activated caspase‐3 activity, and induced apoptosis. Combination therapy using volasertib and sorafenib in ATC cells showed mostly synergistic effects. In vivo studies revealed that combination therapy of volasertib and sorafenib was effective in the treatment of 8505C xenografts. Single‐agent volasertib treatment was sufficient to retard 8305C tumor growth. No substantial morbidity was observed in animals that received either single‐agent or combination treatment. These preclinical findings suggest that volasertib could be an effective drug in treating ATC.

Thyroid Hormone Receptor Beta Induces a Tumor-Suppressive Program in Anaplastic Thyroid Cancer

The thyroid hormone receptor beta (TRβ), a key regulator of cellular growth and differentiation, is frequently dysregulated in cancers. Diminished expression of TRβ is noted in thyroid, breast, and other solid tumors and is correlated with more aggressive disease. Restoration of TRβ levels decreased tumor growth supporting the concept that TRβ could function as a tumor suppressor. Yet, the TRβ tumor suppression transcriptome is not well delineated and the impact of TRβ is unknown in aggressive anaplastic thyroid cancer (ATC). Here, we establish that restoration of TRβ expression in the human ATC cell line SW1736 (SW-TRβ) reduces the aggressive phenotype, decreases cancer stem cell populations and induces cell death in a T3-dependent manner. Transcriptomic analysis of SW-TRβ cells via RNA sequencing revealed distinctive expression patterns induced by ligand-bound TRβ and revealed novel molecular signaling pathways. Of note, liganded TRβ repressed multiple nodes in the PI3K/AKT pathway, induced expression of thyroid differentiation markers, and promoted proapoptotic pathways. Our results further revealed the JAK1-STAT1 pathway as a novel, T3-mediated, antitumorigenic pathway that can be activated in additional ATC lines. These findings elucidate a TRβ-driven tumor suppression transcriptomic signature, highlight unexplored therapeutic options for ATC, and support TRβ activation as a promising therapeutic option in cancers. IMPLICATIONS: TRβ-T3 induced a less aggressive phenotype and tumor suppression program in anaplastic thyroid cancer cells revealing new potential therapeutic targets.

GPR120 promotes radiation resistance in esophageal cancer via regulating AKT and apoptosis pathway

The aim of the study is to investigate the role of GPR120 on the biological behavior of esophageal cancer cells in the setting of radiation and explore the mechanism. GPR120 knockdown was fulfilled by siRNA-mediated effects in two esophageal cancer cell lines Eca109 and EC9706. Colony formation, survival fraction calculation, viable cell evaluation by cell counting kit-8 assay and cell apoptosis analysis by phycoerythrin annexin V and 7-amino-actinomycin (7-AAD) staining and the flow cytometry examination was evaluated in Eca109 and EC9706 under the treatment of different radiation dosage. The mechanisms were explored by the evaluation of the Akt pathway and apoptosis protein level. Significantly decreased GPR120 mRNA and protein after GPR120 siRNA treatment compared to control siRNA treatment. Significantly decreased colony formation was found in GPR120 siRNA-treated Eca109 and EC9706 cells compared to control siRNA-treated cells at the radiation dosage of 2, 4, 6 and 8 Gy. Moreover, decreased survival fraction number with increased sensitive enhancing ratio was also found in GPR120 siRNA-treated Eca109 and EC9706 cells compared to control siRNA-treated cells. Decreased cell viability and increased cell apoptosis in GPR120 siRNA-treated esophageal cancer cells. GPR120 siRNA decreased the Akt phosphorylation and anti-apoptotic Bcl-2 expression level, but increased pro-apoptotic Bim expression level in esophageal cancer cell lines. GPR120 regulated the biological behavior of the esophageal cancer cells via affecting Akt pathway and apoptosis molecules. Moreover, GPR120 siRNA combined radiation treatment could be a therapeutic choice for esophageal cancer.

The Changing Face of in vitro Culture Models for Thyroid Cancer Research: A Systematic Literature Review

Background: Thyroid cancer is the most common endocrine malignancy worldwide. Primary treatment with surgery and radioactive iodine is usually successful, however, there remains a small proportion of thyroid cancers that are resistant to these treatments, and often represent aggressive forms of the disease. Since the 1950s, in vitro thyroid culture systems have been used in thyroid cancer research. In vitro culture models have evolved from 2-dimensional thyrocyte monolayers into physiologically functional 3-dimensional organoids. Recently, research groups have utilized in vitro thyroid cancer models to identify numerous genetic and epigenetic factors that are involved with tumorigenesis as well as test the efficacy of cytotoxic drugs on thyroid cancer cells and identify cancer stem cells within thyroid tumors.

Objective of Review: The objective of this literature review is to summarize how thyroid in vitro culture models have evolved and highlight how in vitro models have been fundamental to thyroid cancer research.

Type of Review: Systematic literature review.

Search Strategy: The National Institute for Health and Care Excellence (NICE) Healthcare and Databases Advanced Search (HDAS) tool was used to search EMBASE, Medline and PubMed databases. The following terms were included in the search: “in vitro” AND “thyroid cancer”. The search period was confined from January 2008 until June 2019. A manual search of the references of review articles and other key articles was also performed using Google Scholar.

Evaluation Method: All experimental studies and review articles that explicitly mentioned the use of in vitro models for thyroid cancer research in the title and/or abstract were considered. Full-text versions of all selected articles were evaluated. Experimental studies were reviewed and grouped according to topic: genetics/epigenetics, drug testing/cancer treatment, and side populations (SP)/tumor microenvironment (TME).

Results: Three thousand three hundred and seventy three articles were identified through database and manual searches. One thousand two hundred and sixteen articles remained after duplicates were removed. Five hundred and eighty nine articles were excluded based on title and/or abstract. Of the remaining 627 full-text articles: 24 were review articles, 332 related to genetic/epigenetics, 240 related to drug testing/treatments, and 31 related to SP/TME.

Conclusion:In vitro cell culture models have been fundamental in thyroid cancer research. There have been many advances in culture techniques- developing complex cellular architecture that more closely resemble tumors in vivo. Genetic and epigenetic factors that have been identified using in vitro culture models can be used as targets for novel drug therapies. In the future, in vitro systems will facilitate personalized medicine, offering bespoke treatments to patients.

Inhibition of Polo-like kinase 1 (PLK1) facilitates the elimination of HIV-1 viral reservoirs in CD4+ T cells ex vivo

Although combination antiretroviral therapy is effective in controlling HIV-1 infection, latent HIV-1 proviruses cannot be eliminated. HIV-1 reactivation induced by the mere use of latency-reversing agents is insufficient to render death of reservoir cells, indicating that certain intrinsic survival mechanisms exist. We report that Polo-like kinase 1 (PLK1) plays a critical role in survival of CD4+ T cells that undergo HIV-1 reactivation from latency or de novo infection. PLK1 is elevated in both scenarios, which requires HIV-1 Nef. HIV-1 enhances PLK1 SUMOylation, causing its nuclear translocation and protein stabilization. Inhibition or knockdown of PLK1 markedly facilitates death of HIV-1-infected CD4+ T cells. Furthermore, PLK1 inhibitors strikingly reduce the size of HIV-1 latent reservoirs in primary CD4+ T cells. Our findings demonstrate that HIV-1 infection hijacks PLK1 to prevent cell death induced by viral cytopathic effects, and that PLK1 is a promising target for chemical "killing" of HIV-1 reservoir cells.

Identification of PLK1 as a New Therapeutic Target in Mucinous Ovarian Carcinoma

Mucinous epithelial ovarian cancer (mEOC) is a rare subset of epithelial ovarian cancer. When diagnosed at a late stage, its prognosis is very poor, as it is quite chemo-resistant. To find new therapeutic options for mEOC, we performed high-throughput screening using a siRNA library directed against human protein kinases in a mEOC cell line, and polo-like kinase1 (PLK1) was identified as the kinase whose downregulation interfered with cell proliferation. Both PLK1 siRNA and two specific PLK1 inhibitors (onvansertib and volasertib) were able to inhibit cell growth, induce apoptosis and block cells in the G2/M phase of the cell cycle. We evaluated, in vitro, the combinations of PLK1 inhibitors and different chemotherapeutic drugs currently used in the treatment of mEOC, and we observed a synergistic effect of PLK1 inhibitors and antimitotic drugs. When translated into an in vivo xenograft model, the combination of onvansertib and paclitaxel resulted in stronger tumor regressions and in a longer mice survival than the single treatments. These effects were associated with a higher induction of mitotic block and induction of apoptosis, similarly to what was observed in vitro. These data suggest that the combination onvansertib/paclitaxel could represent a new active therapeutic option in mEOC.

Targeting PLKs as a therapeutic approach to well-differentiated thyroid cancer

Polo-like kinases (PLKs) are pivotal regulators of cell proliferation and cell survival; therefore, PLKs may be potential targets in the treatment of malignancy. The therapeutic effects of volasertib, a PLKs inhibitor for papillary and follicular thyroid cancer (known as well-differentiated thyroid cancer (WDTC)), were evaluated in this study. Volasertib inhibited cell proliferation in two papillary and two follicular thyroid cancer cell lines in a dose-dependent manner. Volasertib treatment reduced cells in the S phase and increased cells in the G2/M phase. Volasertib activated caspase-3 activity and induced apoptosis. Drug combinations of volasertib and sorafenib showed mostly synergism in four well-differentiated thyroid carcinoma cell lines in vitro. Volasertib treatment in vivo retarded the growth of a papillary thyroid tumor model. Furthermore, the combination of volasertib with sorafenib was more effective than a single treatment of either in a follicular thyroid cancer xenograft model. Promising safety profiles appeared in animals treated with either volasertib alone or volasertib and sorafenib combination therapy. These findings support volasertib as a potential drug for the treatment of patients with WDTC.

The role of aurora A and polo-like kinases in high-risk lymphomas

High-risk lymphomas (HRLs) are associated with dismal outcomes and remain a therapeutic challenge. Recurrent genetic and molecular alterations, including c-myc expression and aurora A kinase (AAK) and polo-like kinase-1 (PLK1) activation, promote cell proliferation and contribute to the highly aggressive natural history associated with these lymphoproliferative disorders. In addition to its canonical targets regulating mitosis, the AAK/PLK1 axis directly regulates noncanonical targets, including c-myc. Recent studies demonstrate that HRLs, including T-cell lymphomas and many highly aggressive B-cell lymphomas, are dependent upon the AAK/PLK1 axis. Therefore, the AAK/PLK1 axis has emerged as an attractive therapeutic target in these lymphomas. In addition to reviewing these recent findings, we summarize the rationale for targeting AAK/PLK1 in high-risk and c-myc-driven lymphoproliferative disorders.

Discovery and evaluation of ZT55, a novel highly-selective tyrosine kinase inhibitor of JAK2V617F against myeloproliferative neoplasms

BACKGROUND

The JAK2-STAT signaling pathway plays a critical role in myeloproliferative neoplasms (MPN). An activating mutation in JAK2 (V617F) is present in ~ 95% of polycythemia vera, essential thrombocythemia, and primary myelofibrosis cases. This study aims to explore the selective JAK2^V617F inhibitor, evaluate the efficacy and possible mechanism of ZT55 on MPN.

METHODS

HTRF assays were conducted to evaluate the selective inhibition of ZT55 for JAKs. Cell apoptosis, proliferation, and cycle arrest assays were performed to examine the effect of ZT55 on HEL cell line with JAK2^V617F mutation in vitro. Western analysis was used to monitor the expression and activity of proteins on JAK2/STAT pathway. A mice xenograft model was established to evaluate the antitumor efficacy of ZT55 in vivo. Peripheral blood samples from patients with the JAK2^V617F mutation were collected to estimate the effect of ZT55 on erythroid colony formation by colony-forming assay.

RESULTS

We found that ZT55 showed a selective inhibition of a 0.031 μM IC₅₀ value against JAK2. It exhibited potent effects on the cellular JAK-STAT pathway, inhibiting tyrosine phosphorylation in JAK2^V617F and downstream STAT3/5 transcription factors. ZT55 inhibited the proliferation of the JAK2^V617F-expressing HEL cell line, leading to cell cycle arrest at the G₂/M phase and induction of caspase-dependent apoptosis. Notably, ZT55 also significantly suppressed the growth of HEL xenograft tumors in vivo. Further evaluation indicated that ZT55 blocked erythroid colony formation of peripheral blood hematopoietic progenitors from patients carrying the JAK2^V617F mutation.

CONCLUSION

These results suggest that ZT55 is a highly-selective JAK2 inhibitor that can induce apoptosis of human erythroleukemia cells by inhibiting the JAK2-STAT signaling.

PLK1: a promising and previously unexplored target in double-hit lymphoma

Inhibitors that target specific kinases or oncoproteins have become popular additions to or replacements for cytotoxic chemotherapies to treat many different types of cancer. However, many tumors lack a discernable target kinase and an amplified oncoprotein and/or rely on several cooperating mechanisms for progression. Thus, combinations of targeted therapies are essential for treating many cancers to avoid the rapid emergence of resistance. In this issue of the JCI, Ren et al. use an elegant kinase activity-profiling method and identify activity of the oncogene polo-like kinase-1 (PLK1) as an important driver of double-hit lymphoma (DHL), an aggressive subgroup of B cell lymphoma characterized by chromosomal translocations involving c-MYC and BCL2 or BCL6. Moreover, PLK1 activity was associated with MYC expression and poor prognosis in DHL patients. PLK1 inhibition with volasertib, alone and in combination with the BCL-2 inhibitor venetoclax, was efficacious in multiple DHL models, including mice harboring DHL patient-derived xenografts. Together, these data support PLK1 as a promising prognostic marker and therapeutic target for DHL.