Head and neck squamous cell carcinoma (HNSCC) is the leading type of cancer, and anatomic subsites span the oral cavity, lips, nasal cavity, pharynx, and larynx. It is considered an aggressive and highly lethal cancer (Bray et al., 2018, Siegel et al., 2022, Sung et al., 2021). The prognosis is often compromised due to late diagnosis, and despite the use of multimodal treatments (including surgery, radiotherapy, and chemotherapy), these interventions often prove ineffective (Muzaffar et al., 2021, Pfister et al., 2020). Novel therapies like immunotherapy and targeted treatments for HNSCC are showing promise. (Galvis et al., 2020, Lau et al., 2020). Therapies targeting the mammalian target of rapamycin (mTOR) signaling, and utilizing inhibitors such as rapamycin and rapalogs, have been valuable as monotherapies, resulting in disease stabilization. The combination of an mTOR inhibitor with chemotherapy and radiation has also shown a positive impact on both partial response and survival rate. (Marques et al., 2016, Patel et al., 2020).

The phosphatidylinositol 3-kinase/mammalian target of rapamycin (PI3K/mTOR) pathway is frequently deregulated in HNSCC and plays a pivotal role in determining its aggressiveness. Molecular alterations within this pathway are typically observed from the early onset through to advanced TNM clinical stages (or Tumor, Nodes, Metastasis – A standardized system used for the cancer staging process). Thus, this pathway is an attractive target for therapeutic intervention (Moura et al., 2021, Tian et al., 2019). Furthermore, PI3K/mTOR pathway is negatively controlled by the phosphatase and tensin homolog (PTEN), a tumor suppressor gene that impacts HNSCC tumor burden and progression (Conciatori et al., 2022, Matsumoto et al., 2006, Squarize et al., 2013). PTEN and PI3K can be utilized to identify patients likely to respond to therapy, particularly when considering mutations and amplification in oncogenes such as the PIK3 gene or loss of function in tumor-suppressor genes like PTEN. Thus, stratifying patients based on these biomarkers for treatment responsiveness could offer meaningful benefits ( Squarize et al., 2013; Giudice & Squarize, 2013; Marques et al., 2016).

Cancer stem cells (CSCs) play a crucial role in tumor initiation, progression, and recurrence. CSCs exhibit an enhanced potential for multiplication, with the ability to self-renew and demonstrate resistance to current therapies (Almeida et al., 2016a, Barrandon and Green, 1987, Eun et al., 2017, Peiris-Pagès et al., 2016). PTEN may also regulate the CSC population (Squarize et al., 2013), and it remains unclear how PTEN synergizes or cooperates with CSCs, as well as how the pathway affects the different types of CSCs in HNSCC. Here, we investigate CSC response to PTEN modulation, its potential dependency on the mTOR signaling, and how they respond to therapy.