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Orthogonal targeting of EGFRvIII expressing glioblastomas through simultaneous EGFR and PLK1 inhibition.

Shen Y, Li J, Nitta M, Futalan D, Steed T, Treiber JM, Taich Z, Stevens D, Wykosky J, Chen HZ, Carter BS, Becher OJ, Kennedy R, Esashi F, Sarkaria JN, Furnari FB, Cavenee WK, Desai A, Chen CC - Oncotarget (2015)

Bottom Line: Accordingly, PLK1 inhibition enhanced the cytotoxic effects of the DNA damaging agent, temozolomide (TMZ).Although BI2536 significantly augmented the anti-neoplastic effect of EGFR inhibitors in the Ink4a/Arf(-/-) EGFRvIII model, durable response was not achieved until TMZ was added.Our results suggest that optimal therapeutic effect against glioblastomas requires a "multi-orthogonal" combination tailored to the molecular physiology associated with the target cancer genome.

View Article: PubMed Central - PubMed

Affiliation: Center for Theoretical and Applied Neuro-Oncology, Moores Cancer Center, Division of Neurosurgery, University of California San Diego, La Jolla, CA, USA.

ABSTRACT
We identified a synthetic lethality between PLK1 silencing and the expression of an oncogenic Epidermal Growth Factor Receptor, EGFRvIII. PLK1 promoted homologous recombination (HR), mitigating EGFRvIII induced oncogenic stress resulting from DNA damage accumulation. Accordingly, PLK1 inhibition enhanced the cytotoxic effects of the DNA damaging agent, temozolomide (TMZ). This effect was significantly more pronounced in an Ink4a/Arf(-/-) EGFRvIII glioblastoma model relative to an Ink4a/Arf(-/-) PDGF-β model. The tumoricidal and TMZ-sensitizing effects of BI2536 were uniformly observed across Ink4a/Arf(-/-) EGFRvIII glioblastoma clones that acquired independent resistance mechanisms to EGFR inhibitors, suggesting these resistant clones retain oncogenic stress that required PLK1 compensation. Although BI2536 significantly augmented the anti-neoplastic effect of EGFR inhibitors in the Ink4a/Arf(-/-) EGFRvIII model, durable response was not achieved until TMZ was added. Our results suggest that optimal therapeutic effect against glioblastomas requires a "multi-orthogonal" combination tailored to the molecular physiology associated with the target cancer genome.

No MeSH data available.


Related in: MedlinePlus

Context dependency of PLK1 inhibitionA. (left) Enhanced p-PLK1 and γH2AX in Ink4a/Arf(−/−) EGFRvIII tumors. 3 representative tissue samples resected from murine Ink4a/Arf(−/−), Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β, separately, were lysed and analyzed by immunoblotting using antibodies against p-PLK1, γH2AX, EGFRvIII and PDGF-β. Tubulin was loaded as loading control. (right) Quantitative densitometric assessment of pT210 PLK1 or γH2AX was normalized to tubulin and fold change represent the average of 3 samples, shown as mean±SD. *, p < 0.05; **, p < 0.01. B. BI2536 treatment exerted greater tumoricidal effect in Ink4a/Arf(−/−) EGFRvIII tumors compared to Ink4a/Arf(−/−) PDGF-β tumors. Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β cells were implanted into nu/nu mice and the treatment started when the tumor size was > 500 mm3. Tumor growth was monitored twice per week and represented separately to represent the comparison between BI2536 or TMZ treatment.
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Figure 5: Context dependency of PLK1 inhibitionA. (left) Enhanced p-PLK1 and γH2AX in Ink4a/Arf(−/−) EGFRvIII tumors. 3 representative tissue samples resected from murine Ink4a/Arf(−/−), Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β, separately, were lysed and analyzed by immunoblotting using antibodies against p-PLK1, γH2AX, EGFRvIII and PDGF-β. Tubulin was loaded as loading control. (right) Quantitative densitometric assessment of pT210 PLK1 or γH2AX was normalized to tubulin and fold change represent the average of 3 samples, shown as mean±SD. *, p < 0.05; **, p < 0.01. B. BI2536 treatment exerted greater tumoricidal effect in Ink4a/Arf(−/−) EGFRvIII tumors compared to Ink4a/Arf(−/−) PDGF-β tumors. Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β cells were implanted into nu/nu mice and the treatment started when the tumor size was > 500 mm3. Tumor growth was monitored twice per week and represented separately to represent the comparison between BI2536 or TMZ treatment.

Mentions: EGFRvIII and PDGF-β are driver oncogenes for the classical and proneural subtypes of glioblastoma, respectively [20]. Characterization of murine glioblastomas formed in the Ink4a/Arf(−/−) EGFRvIII [30] and Gtv-a Ink4a/Arf(−/−) PDGF-β model [31] revealed significantly higher levels of DNA damage accumulation in the former, as evidenced by the levels of γH2AX (Figure 5A). If the therapeutic effect of PLK1 inhibition is related to the endogenous level of DNA damage, we would predict that BI2536 would be less effective in the Ink4a/Arf(−/−) PDGF-β model relative to the Ink4a/Arf(−/−) EGFRvIII model. To test this hypothesis, glioblastoma cells derived from these models were implanted into the flank of athymic nude mice. If the mice were treated while the tumor burden was < 100 mm3, no significant differences in response to BI2536 were noted (Figure 4C versus Supplemental Figure 4). However, when the tumors were allowed to reach the size > 500 mm3 before treatment, notable difference in response to BI2536 were found between the two models, as shown in Figure 5B. BI2536 induced tumor response (as measured by tumor shrinkage and dormancy) for a period of 15 days in the Ink4a/Arf(−/−) PDGF-β model, after which tumors rapidly increased in size. In the Ink4a/Arf(−/−) EGFRvIII model, BI2536 induced tumor response for a period of 30 days (p < 0.05). In contrast, the anti-neoplastic effects of TMZ treatment were comparable in both models. These results suggest that the therapeutic efficacy of PLK1 inhibition is dependent on the glioblastoma genetic context and correlates with the endogenous levels of DNA damage. TMZ is a more non-selective tumor ablative agent.


Orthogonal targeting of EGFRvIII expressing glioblastomas through simultaneous EGFR and PLK1 inhibition.

Shen Y, Li J, Nitta M, Futalan D, Steed T, Treiber JM, Taich Z, Stevens D, Wykosky J, Chen HZ, Carter BS, Becher OJ, Kennedy R, Esashi F, Sarkaria JN, Furnari FB, Cavenee WK, Desai A, Chen CC - Oncotarget (2015)

Context dependency of PLK1 inhibitionA. (left) Enhanced p-PLK1 and γH2AX in Ink4a/Arf(−/−) EGFRvIII tumors. 3 representative tissue samples resected from murine Ink4a/Arf(−/−), Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β, separately, were lysed and analyzed by immunoblotting using antibodies against p-PLK1, γH2AX, EGFRvIII and PDGF-β. Tubulin was loaded as loading control. (right) Quantitative densitometric assessment of pT210 PLK1 or γH2AX was normalized to tubulin and fold change represent the average of 3 samples, shown as mean±SD. *, p < 0.05; **, p < 0.01. B. BI2536 treatment exerted greater tumoricidal effect in Ink4a/Arf(−/−) EGFRvIII tumors compared to Ink4a/Arf(−/−) PDGF-β tumors. Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β cells were implanted into nu/nu mice and the treatment started when the tumor size was > 500 mm3. Tumor growth was monitored twice per week and represented separately to represent the comparison between BI2536 or TMZ treatment.
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Related In: Results  -  Collection

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Figure 5: Context dependency of PLK1 inhibitionA. (left) Enhanced p-PLK1 and γH2AX in Ink4a/Arf(−/−) EGFRvIII tumors. 3 representative tissue samples resected from murine Ink4a/Arf(−/−), Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β, separately, were lysed and analyzed by immunoblotting using antibodies against p-PLK1, γH2AX, EGFRvIII and PDGF-β. Tubulin was loaded as loading control. (right) Quantitative densitometric assessment of pT210 PLK1 or γH2AX was normalized to tubulin and fold change represent the average of 3 samples, shown as mean±SD. *, p < 0.05; **, p < 0.01. B. BI2536 treatment exerted greater tumoricidal effect in Ink4a/Arf(−/−) EGFRvIII tumors compared to Ink4a/Arf(−/−) PDGF-β tumors. Ink4a/Arf(−/−) EGFRvIII or Ink4a/Arf(−/−) PDGF-β cells were implanted into nu/nu mice and the treatment started when the tumor size was > 500 mm3. Tumor growth was monitored twice per week and represented separately to represent the comparison between BI2536 or TMZ treatment.
Mentions: EGFRvIII and PDGF-β are driver oncogenes for the classical and proneural subtypes of glioblastoma, respectively [20]. Characterization of murine glioblastomas formed in the Ink4a/Arf(−/−) EGFRvIII [30] and Gtv-a Ink4a/Arf(−/−) PDGF-β model [31] revealed significantly higher levels of DNA damage accumulation in the former, as evidenced by the levels of γH2AX (Figure 5A). If the therapeutic effect of PLK1 inhibition is related to the endogenous level of DNA damage, we would predict that BI2536 would be less effective in the Ink4a/Arf(−/−) PDGF-β model relative to the Ink4a/Arf(−/−) EGFRvIII model. To test this hypothesis, glioblastoma cells derived from these models were implanted into the flank of athymic nude mice. If the mice were treated while the tumor burden was < 100 mm3, no significant differences in response to BI2536 were noted (Figure 4C versus Supplemental Figure 4). However, when the tumors were allowed to reach the size > 500 mm3 before treatment, notable difference in response to BI2536 were found between the two models, as shown in Figure 5B. BI2536 induced tumor response (as measured by tumor shrinkage and dormancy) for a period of 15 days in the Ink4a/Arf(−/−) PDGF-β model, after which tumors rapidly increased in size. In the Ink4a/Arf(−/−) EGFRvIII model, BI2536 induced tumor response for a period of 30 days (p < 0.05). In contrast, the anti-neoplastic effects of TMZ treatment were comparable in both models. These results suggest that the therapeutic efficacy of PLK1 inhibition is dependent on the glioblastoma genetic context and correlates with the endogenous levels of DNA damage. TMZ is a more non-selective tumor ablative agent.

Bottom Line: Accordingly, PLK1 inhibition enhanced the cytotoxic effects of the DNA damaging agent, temozolomide (TMZ).Although BI2536 significantly augmented the anti-neoplastic effect of EGFR inhibitors in the Ink4a/Arf(-/-) EGFRvIII model, durable response was not achieved until TMZ was added.Our results suggest that optimal therapeutic effect against glioblastomas requires a "multi-orthogonal" combination tailored to the molecular physiology associated with the target cancer genome.

View Article: PubMed Central - PubMed

Affiliation: Center for Theoretical and Applied Neuro-Oncology, Moores Cancer Center, Division of Neurosurgery, University of California San Diego, La Jolla, CA, USA.

ABSTRACT
We identified a synthetic lethality between PLK1 silencing and the expression of an oncogenic Epidermal Growth Factor Receptor, EGFRvIII. PLK1 promoted homologous recombination (HR), mitigating EGFRvIII induced oncogenic stress resulting from DNA damage accumulation. Accordingly, PLK1 inhibition enhanced the cytotoxic effects of the DNA damaging agent, temozolomide (TMZ). This effect was significantly more pronounced in an Ink4a/Arf(-/-) EGFRvIII glioblastoma model relative to an Ink4a/Arf(-/-) PDGF-β model. The tumoricidal and TMZ-sensitizing effects of BI2536 were uniformly observed across Ink4a/Arf(-/-) EGFRvIII glioblastoma clones that acquired independent resistance mechanisms to EGFR inhibitors, suggesting these resistant clones retain oncogenic stress that required PLK1 compensation. Although BI2536 significantly augmented the anti-neoplastic effect of EGFR inhibitors in the Ink4a/Arf(-/-) EGFRvIII model, durable response was not achieved until TMZ was added. Our results suggest that optimal therapeutic effect against glioblastomas requires a "multi-orthogonal" combination tailored to the molecular physiology associated with the target cancer genome.

No MeSH data available.


Related in: MedlinePlus