Combined inhibition of PLK1 and NOTCH for melanoma management

The overall objective of this study is to determine the therapeutic efficacy of concomitant inhibition of PLK1
and NOTCH against melanoma progression and drug resistance as well as to identify novel signaling
mechanisms associated with drug response using two human-relevant melanoma mouse models.
The available therapeutic strategies against melanoma have either failed to achieve >25% response in
patients, or the responses are short-lived with developing resistance to therapy. For example, BRAF inhibitors
Vemurafenib and Dabrafenib were found to achieve significant improvement over chemotherapy and were
FDA-approved for melanomas with BRAF-mutations. Even with a combination of Dabrafenib with MEK inhibitor
Trametinib (also FDA approved), the patients develop acquired resistance. More recently advancements in
immunotherapy have improved melanoma treatment outcomes. Despite the success of immune checkpoint
inhibitors durable responses are not seen in all patients due to drug resistance. Therefore, novel mechanism-
based combinatorial approaches are needed for an effective management of this neoplasm. Polo-like kinase 1
(PLK1) is a serine/threonine protein kinase that plays a key role in cell proliferation. We have previously
reported that PLK1 is significantly overexpressed in melanoma and can be therapeutically targeted. Further,
the NOTCH pathway, an evolutionally conserved pathway, which plays important roles in cell fate
determination, proliferation, differentiation and survival, has been shown to regulate many aspects of
melanomagenesis. NOTCH1 is considered a primary oncogenic factor in melanoma and activation of NOTCH1
and its target genes is linked with metastatic melanoma. Moreover, inhibition of PLK1 or NOTCH has been
shown to modulate markers of epithelial mesenchymal transition (EMT) and metastasis. Interestingly, both
PLK1 and NOTCH are also linked with drug resistance. Our recently published data suggest that PLK1 and
NOTCH expressions have significant positive correlation in melanoma clinical tissues and simultaneous small
molecule inhibition of PLK1 and NOTCH by BI 6727 (specific inhibitors of PLK1) and MK-0752 (γ-secretase
inhibitor), respectively, caused a significant anti-proliferative response in multiple melanoma cell lines,
warranting further pre-clinical testing in in vivo melanoma models. This data together with other published
studies provide a strong scientific premise for our proposed hypothesis that combined inhibition of PLK1 and
NOTCH will be therapeutically superior for the management of melanoma. We will challenge this hypothesis in
two specific aims. In Aim 1, we will determine the in vivo therapeutic efficacy and mechanism of concomitant
inhibition of PLK1 (by BI 6727 or PCM-075) and NOTCH (by MK-0752) on melanoma progression and
metastasis in genetically engineered Braf-Pten melanoma mouse model, which recapitulates human disease
progression from localized to metastatic disease. In Aim 2, we will determine therapeutic efficacy and
mechanism of concomitant inhibition of PLK1 and NOTCH against melanoma drug resistant using patient
derived xenograft (PDX) model, which conserve original tumor characteristics and offer relevant predictive
insights into clinical outcomes, for direct relevance to clinical management of melanoma. Additionally, we will
determine the novel mechanisms associated with treatment response using mutiple techniques such as
Nanostring PanCancer Progression Panel, global proteomics and RNA-seq analyses in tumor samples
followed by validation using RT-qPCR and ProteinSimple analyses. Overall, our study is expected to provide
mechanistic insights and rationale for clinical testing of the combined PLK1-NOTCH inhibition to obtain
superior anti-melanoma response and overcome resistance. Our proposed work is relevant and significant to
the Veterans because melanoma is the fifth most diagnosed malignancy among Veterans, and the fact that the
US military has been engaged, in missions all over the world, many US military personnel, who are deployed to
high ultraviolet (UV) climates in tropical and subtropical zones are potentially at a higher risk for melanoma.

Grant Number: 5I01BX005917-03
NIH Institute/Center: VA
Principal Investigator: Nihal Ahmad