Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Plant-derived natural compounds: A new frontier in inducing immunogenic cell death for cancer treatment

Immunogenic cell death (ICD) can activate adaptive immune response in the host with normal immune system. Some synthetic chemotherapeutic drugs and natural compounds have shown promising results in cancer treatment by triggering the release of damage-associated molecules (DAMPs) to trigger ICD. However, most chemotherapeutic drugs exhibit non-selective cytotoxicity and may also induce and promote metastasis, thereby significantly reducing their clinical efficacy. Among the natural compounds that can induce ICD, plant-derived compounds account for the largest proportion, which are of increasing value in the treatment of cancer. Understanding which plant-derived natural compounds can induce ICD and how they induce ICD is crucial for developing strategies to improve chemotherapy outcomes. In this review, we focus on the recent findings regarding plant-derived natural compounds that induce ICD according to the classification of flavonoids, alkaloids, glycosides, terpenoids and discuss the potential mechanisms including endoplasmic reticulum (ER) stress, DNA damage, apoptosis, necroptosis autophagy, ferroptosis. In addition, plant-derived natural compounds that can enhance the ICD induction ability of conventional therapies for cancer treatment is also elaborated. The rational use of plant-derived natural compounds to induce ICD is helpful for the development of new cancer treatment methods.

The crosstalk between DNA-damage responses and innate immunity

DNA damage is typically caused during cell growth by DNA replication stress or exposure to endogenous or external toxins. The accumulation of damaged DNA causes genomic instability, which is the root cause of many serious disorders. Multiple cellular organisms utilize sophisticated signaling pathways against DNA damage, collectively known as DNA damage response (DDR) networks. Innate immune responses are activated following cellular abnormalities, including DNA damage. Interestingly, recent studies have indicated that there is an intimate relationship between the DDR network and innate immune responses. Diverse kinds of cytosolic DNA sensors, such as cGAS and STING, recognize damaged DNA and induce signals related to innate immune responses, which link defective DDR to innate immunity. Moreover, DDR components operate in immune signaling pathways to induce IFNs and/or a cascade of inflammatory cytokines via direct interactions with innate immune modulators. Consistently, defective DDR factors exacerbate the innate immune imbalance, resulting in severe diseases, including autoimmune disorders and tumorigenesis. Here, the latest progress in understanding crosstalk between the DDR network and innate immune responses is reviewed. Notably, the dual function of innate immune modulators in the DDR network may provide novel insights into understanding and developing targeted immunotherapies for DNA damage-related diseases, even carcinomas.

When DNA-damage responses meet innate and adaptive immunity

When cells proliferate, stress on DNA replication or exposure to endogenous or external insults frequently results in DNA damage. DNA-Damage Response (DDR) networks are complex signaling pathways used by multicellular organisms to prevent DNA damage. Depending on the type of broken DNA, the various pathways, Base-Excision Repair (BER), Nucleotide Excision Repair (NER), Mismatch Repair (MMR), Homologous Recombination (HR), Non-Homologous End-Joining (NHEJ), Interstrand Crosslink (ICL) repair, and other direct repair pathways, can be activated separately or in combination to repair DNA damage. To preserve homeostasis, innate and adaptive immune responses are effective defenses against endogenous mutation or invasion by external pathogens. It is interesting to note that new research keeps showing how closely DDR components and the immune system are related. DDR and immunological response are linked by immune effectors such as the cyclic GMP-AMP synthase (cGAS)-Stimulator of Interferon Genes (STING) pathway. These effectors act as sensors of DNA damage-caused immune response. Furthermore, DDR components themselves function in immune responses to trigger the generation of inflammatory cytokines in a cascade or even trigger programmed cell death. Defective DDR components are known to disrupt genomic stability and compromise immunological responses, aggravating immune imbalance and leading to serious diseases such as cancer and autoimmune disorders. This study examines the most recent developments in the interaction between DDR elements and immunological responses. The DDR network's immune modulators' dual roles may offer new perspectives on treating infectious disorders linked to DNA damage, including cancer, and on the development of target immunotherapy.

PARP inhibitor plus radiotherapy reshape the immune suppressive microenvironment and potentiate the efficacy of immune checkpoint inhibitors in tumors with IDH1 mutation

Isocitrate dehydrogenase 1 mutant (IDH1mut) tumors respond poorly to immunotherapy, but are more sensitive to chemoradiotherapy and poly (ADP-ribose) polymerase inhibition (PARPi). Accordingly, some efforts have aimed to capitalize on the IDH1 mutation rather than reverse it. Moreover, radiotherapy (RT) and PARPi can stimulate antitumor immunity, raising the possibility of reversing the immunosuppression caused by IDH1 mutation while killing the tumor. To assess this possibility, we treated IDH1mut tumors and cells with RT + PARPi. RT + PARPi showed enhanced efficacy over either modality alone both in vitro and in vivo. RT + PARPi induced more DNA damage and activated the cGAS-STING pathway more. IFNβ, CXCL10, and CCL5 were also more highly expressed at both the mRNA and protein levels. In two different tumor models, RT + PARPi increased infiltration and cytolytic function of CD8+ T cells, with one model also showing increased CD8+T cell proliferation. RT+PARPi also increased PD-L1 expression and enhanced checkpoint inhibition. Knocking out cGAS reversed the increased CD8+ T cell infiltration and the antitumor effect of RT+PARPi. We conclude that RT + PARPi reshapes the IDH1mut tumor immunosuppressive microenvironment, thereby augmenting checkpoint inhibition.

Immunotherapy and Radiation Therapy Combinatorial Approaches in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), a prevalent and often fatal liver cancer, presents significant treatment challenges, especially in its advanced stages. This article delves into the promising approach of combining immunotherapy, particularly immune checkpoint inhibitors, with radiation therapy, a cornerstone of HCC management. Our review synthesizes current preclinical and clinical research, highlighting the potential synergistic effects of this combinational treatment. Emerging evidence suggests that this synergy enhances tumor control and improves patient survival rates. The combination leverages the localized, tumor-targeting ability of radiation therapy and the systemic, immune-boosting effects of immunotherapy, potentially overcoming the limitations inherent in each treatment modality when used separately. This integrative approach is especially promising in addressing the complex tumor microenvironment of HCC. However, the treatment landscape is nuanced, with challenges such as patient-specific response variability and potential resistance to therapies. Future research directions should focus on refining these combination strategies, tailoring them to individual patient profiles, and understanding the underlying mechanisms that govern the interaction between immunotherapy and radiation therapy. Such advancements could significantly improve HCC management, setting new standards for patient care and treatment efficacy.

Exploratory analysis of the cervix tumoral HPV antigen-specific T-cell repertoire during chemoradiation and after brachytherapy

BACKGROUND

Chemoradiation (CRT) may modulate the immune milieu as an in-situ vaccine. Rapid dose delivery of brachytherapy has unclear impact on T-cell repertoires. HPV-associated cancers express viral oncoproteins E6/E7, which enable tracking antigen/tumor-specific immunity during CRT.

METHODS

Thirteen cervical cancer patients on a multi-institutional prospective protocol from 1/2020-1/2023 underwent standard-of-care CRT with pulsed-dose-rate brachytherapy boost (2 fractions). Cervix swabs at various timepoints underwent multiplex DNA deep sequencing of the TCR-β/CDR3 region with immunoSEQ. Separately, HPV-responsive T-cell clones were also expanded ex vivo. Statistical analysis was via Mann-Whitney-U.

RESULTS

TCR productive clonality, templates, frequency, or rearrangements increased post-brachytherapy in 8 patients. Seven patients had E6/E7-responsive evolution over CRT with increased productive templates (ranges: 1.2-50.2 fold-increase from baseline), frequency (1.2-1.7), rearrangements (1.2-40.2), and clonality (1.2-15.4). Five patients had HPV-responsive clonal expansion post-brachytherapy, without changes in HPV non-responsive clones. Epitope mapping revealed VDJ rearrangements targeting cervical cancer-associated antigens in 5 patients. The only two patients with disease recurrence lacked response in all metrics. A lack of global TCR remodeling correlated with worse recurrence-free survival, p = 0.04.

CONCLUSION

CRT and brachytherapy alters the cervical cancer microenvironment to facilitate the expansion of specific T-cell populations, which may contribute to treatment efficacy.

A Phase Ib Study of the DNA-PK Inhibitor Peposertib Combined with Neoadjuvant Chemoradiation in Patients with Locally Advanced Rectal Cancer

PURPOSE

Peposertib-an orally administered DNA-dependent protein kinase inhibitor-has shown potent radiosensitization in preclinical models. This dose-escalation study (NCT03770689) aimed to define the maximum tolerated dose (MTD) and recommended phase II dose (RP2D) of peposertib plus capecitabine-based chemoradiotherapy (CRT) and assessed its safety and efficacy in locally advanced rectal cancer.

PATIENTS AND METHODS

Patients were treated for 5 to 5.5 weeks with 50- to 250-mg peposertib once daily, capecitabine 825 mg/m2 twice daily, and radiotherapy (RT), 5 days per week. Following clinical restaging (8 weeks after CRT completion), patients with clinical complete response (cCR) could opt for surveillance. Total mesorectal excision was recommended upon incomplete response (IR).

RESULTS

Nineteen patients were treated with peposertib at doses of 50 mg (n = 1), 100 mg, 150 mg, and 250 mg (n = 6 each). Dose-limiting toxicities occurred in one out of five (100 mg), one out of six (150 mg), and three out of six (250 mg) evaluable patients. Peposertib ≤150 mg once daily was tolerable in combination with CRT. After 8 weeks of treatment with peposertib and CRT, the cCR was 15.8% (n = 3). Among the three patients with cCR, two underwent surgery and had residual tumors. Among the 16 patients with IR, seven underwent surgery and had residual tumors; five of the remaining nine patients opted for consolidative chemotherapy. The combined cCR/pathologic complete response (pCR) rate was 5.3% (n = 1, 100 mg cohort).

CONCLUSIONS

Peposertib did not improve complete response rates at tolerable dose levels. The study was closed without declaring the MTD/RP2D.

Progress in the treatment of anal cancer: an overview of the latest investigational drugs

INTRODUCTION

Anal cancer, a rare malignancy accounting for 2.5-3.0% of gastrointestinal cancers, primarily manifests as squamous cell carcinoma associated with HPV. Recent years have witnessed significant advancements in managing squamous cell carcinoma of the anus (SCCA), particularly with the introduction of immune checkpoint inhibitors (ICIs) and randomized data on front-line chemotherapy.

AREAS COVERED

This review discusses the current standard treatments for both early and advanced SCCA, based on published data. The authors then describe the new approaches, focusing on ICI combinations, targeted agents, T-cell adoptive therapy, and HPV-therapeutic vaccines.

EXPERT OPINION

The current standard treatment for SCCA includes front-line carboplatin and paclitaxel, with pembrolizumab and nivolumab as later-line options. While modified DCF has shown promise in single-arm studies, its role as a front-line therapy requires confirmation through randomized data. We eagerly anticipate the results of phase 3 trials investigating the front-line chemo-immunotherapy for metastatic SCCA and ICI consolidation following chemoradiation for early-stage SCCA. Novel approaches like T-cell adoptive therapy, HPV-therapeutic vaccines, and bifunctional antibodies combined with HPV vaccines are in early-stage trials for HPV-mediated tumors, including HPV-positive SCCA. These approaches targeting HPV epitopes may eventually gain tumor-agnostic approval, although their role in SCCA may take time to establish.

Phase I study of peposertib and avelumab with or without palliative radiotherapy in patients with advanced solid tumors

INTRODUCTION

We report results from a phase I, three-part, dose-escalation study of peposertib, a DNA-dependent protein kinase inhibitor, in combination with avelumab, an immune checkpoint inhibitor, with or without radiotherapy in patients with advanced solid tumors.

MATERIALS AND METHODS

Peposertib 100-400 mg twice daily (b.i.d.) or 100-250 mg once daily (q.d.) was administered in combination with avelumab 800 mg every 2 weeks in Part A or avelumab plus radiotherapy (3 Gy/fraction × 10 days) in Part B. Part FE assessed the effect of food on the pharmacokinetics of peposertib plus avelumab. The primary endpoint in Parts A and B was dose-limiting toxicity (DLT). Secondary endpoints were safety, best overall response per RECIST version 1.1, and pharmacokinetics. The recommended phase II dose (RP2D) and maximum tolerated dose (MTD) were determined in Parts A and B.

RESULTS

In Part A, peposertib doses administered were 100 mg (n = 4), 200 mg (n = 11), 250 mg (n = 4), 300 mg (n = 6), and 400 mg (n = 4) b.i.d. Of DLT-evaluable patients, one each had DLT at the 250-mg and 300-mg dose levels and three had DLT at the 400-mg b.i.d. dose level. In Part B, peposertib doses administered were 100 mg (n = 3), 150 mg (n = 3), 200 mg (n = 4), and 250 mg (n = 9) q.d.; no DLT was reported in evaluable patients. Peposertib 200 mg b.i.d. plus avelumab and peposertib 250 mg q.d. plus avelumab and radiotherapy were declared as the RP2D/MTD. No objective responses were observed in Part A or B; one patient had a partial response in Part FE. Peposertib exposure was generally dose proportional.

CONCLUSIONS

Peposertib doses up to 200 mg b.i.d. in combination with avelumab and up to 250 mg q.d. in combination with avelumab and radiotherapy were tolerable in patients with advanced solid tumors; however, antitumor activity was limited.

CLINICALTRIALS

GOV IDENTIFIER

NCT03724890.

Impaired activation of plasmacytoid dendritic cells via toll-like receptor 7/9 and STING is mediated by melanoma-derived immunosuppressive cytokines and metabolic drift

Introduction

Plasmacytoid dendritic cells (pDCs) infiltrate a large set of human cancers. Interferon alpha (IFN-α) produced by pDCs induces growth arrest and apoptosis in tumor cells and modulates innate and adaptive immune cells involved in anti-cancer immunity. Moreover, effector molecules exert tumor cell killing. However, the activation state and clinical relevance of pDCs infiltration in cancer is still largely controversial. In Primary Cutaneous Melanoma (PCM), pDCs density decreases over disease progression and collapses in metastatic melanoma (MM). Moreover, the residual circulating pDC compartment is defective in IFN-α production.

Methods

The activation of tumor-associated pDCs was evaluated by in silico and microscopic analysis. The expression of human myxovirus resistant protein 1 (MxA), as surrogate of IFN-α production, and proximity ligation assay (PLA) to test dsDNA-cGAS activation were performed on human melanoma biopsies. Moreover, IFN-α and CXCL10 production by in vitro stimulated (i.e. with R848, CpG-A, ADU-S100) pDCs exposed to melanoma cell lines supernatants (SN-mel) was tested by intracellular flow cytometry and ELISA. We also performed a bulk RNA-sequencing on SN-mel-exposed pDCs, resting or stimulated with R848. Glycolytic rate assay was performed on SN-mel-exposed pDCs using the Seahorse XFe24 Extracellular Flux Analyzer.

Results

Based on a set of microscopic, functional and in silico analyses, we demonstrated that the melanoma milieu directly impairs IFN-α and CXCL10 production by pDCs via TLR-7/9 and cGAS-STING signaling pathways. Melanoma-derived immunosuppressive cytokines and a metabolic drift represent relevant mechanisms enforcing pDC-mediated melanoma escape.

Discussion

These findings propose a new window of intervention for novel immunotherapy approaches to amplify the antitumor innate immune response in cutaneous melanoma (CM).

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

Immunogenic cell death after combined treatment with radiation and ATR inhibitors is dually regulated by apoptotic caspases

Introduction

Inhibitors of the ATR kinase act as radiosensitizers through abrogating the G2 checkpoint and reducing DNA repair. Recent studies suggest that ATR inhibitors can also increase radiation-induced antitumor immunity, but the underlying immunomodulating mechanisms remain poorly understood. Moreover, it is poorly known how such immune effects relate to different death pathways such as caspase-dependent apoptosis. Here we address whether ATR inhibition in combination with irradiation may increase the presentation of hallmark factors of immunogenic cell death (ICD), and to what extent caspase activation regulates this response.

Methods

Human lung cancer and osteosarcoma cell lines (SW900, H1975, H460, U2OS) were treated with X-rays and ATR inhibitors (VE822; AZD6738) in the absence and presence of a pan-caspase inhibitor. The ICD hallmarks HMGB1 release, ATP secretion and calreticulin surface-presentation were assessed by immunoblotting of growth medium, the CellTiter-Glo assay and an optimized live-cell flow cytometry assay, respectively. To obtain accurate measurement of small differences in the calreticulin signal by flow cytometry, we included normalization to a barcoded control sample.

Results

Extracellular release of HMGB1 was increased in all the cell lines at 72 hours after the combined treatment with radiation and ATR inhibitors, relative to mock treatment or cells treated with radiation alone. The HMGB1 release correlated largely - but not strictly - with loss of plasma membrane integrity, and was suppressed by addition of the caspase inhibitor. However, one cell line showed HMGB1 release despite caspase inhibition, and in this cell line caspase inhibition induced pMLKL, a marker for necroptosis. ATP secretion occurred already at 48 hours after the co-treatment and did clearly not correlate with loss of plasma membrane integrity. Addition of pan-caspase inhibition further increased the ATP secretion. Surface-presentation of calreticulin was increased at 24-72 hours after irradiation, but not further increased by either ATR or caspase inhibition.

Conclusion

These results show that ATR inhibition can increase the presentation of two out of three ICD hallmark factors from irradiated human cancer cells. Moreover, caspase activation distinctly affects each of the hallmark factors, and therefore likely plays a dual role in tumor immunogenicity by promoting both immunostimulatory and -suppressive effects.

Radiation-induced tumor immune microenvironments and potential targets for combination therapy

As one of the four major means of cancer treatment including surgery, radiotherapy (RT), chemotherapy, immunotherapy, RT can be applied to various cancers as both a radical cancer treatment and an adjuvant treatment before or after surgery. Although RT is an important modality for cancer treatment, the consequential changes caused by RT in the tumor microenvironment (TME) have not yet been fully elucidated. RT-induced damage to cancer cells leads to different outcomes, such as survival, senescence, or death. During RT, alterations in signaling pathways result in changes in the local immune microenvironment. However, some immune cells are immunosuppressive or transform into immunosuppressive phenotypes under specific conditions, leading to the development of radioresistance. Patients who are radioresistant respond poorly to RT and may experience cancer progression. Given that the emergence of radioresistance is inevitable, new radiosensitization treatments are urgently needed. In this review, we discuss the changes in irradiated cancer cells and immune cells in the TME under different RT regimens and describe existing and potential molecules that could be targeted to improve the therapeutic effects of RT. Overall, this review highlights the possibilities of synergistic therapy by building on existing research.

Effective therapy with Bismuth-212 labeled macroaggregated albumin in orthotopic mouse breast tumor models

Intravascularly administered radiation therapy using beta (β-)-emitting radioisotopes has relied on either intravenously injected radiolabeled peptides that target cancer or radiolabeled microspheres that are trapped in the tumor following intra-arterial delivery. More recently, targeted intravenous radiopeptide therapies have explored the use of alpha (α)-particle emitting radioisotopes, but microspheres radiolabeled with α-particle emitters have not yet been studied. Here, FDA-approved macroaggregated albumin (MAA) particles were radiolabeled with Bismuth-212 (Bi-212-MAA) and evaluated using clonogenic and survival assays in vitro and using immune-competent mouse models of breast cancer. The in vivo biodistribution of Bi-212-MAA was investigated in Balb/c and C57BL/6 mice with 4T1 and EO771 orthotopic breast tumors, respectively. The same orthotopic breast cancer models were used to evaluate the treatment efficacy of Bi-212-MAA. Our results showed that macroaggregated albumin can be stably radiolabeled with Bi-212 and that Bi-212-MAA can deliver significant radiation therapy to reduce the growth and clonogenic potential of 4T1 and EO771 cells in vitro. Additionally, Bi-212-MAA treatment upregulated γH2AX and cleaved Caspase-3 expression in 4T1 cells. Biodistribution analyses showed 87-93% of the Bi-212-MAA remained in 4T1 and EO771 tumors 2 and 4 h after injection. Following single-tumor treatments with Bi-212-MAA there was a significant reduction in the growth of both 4T1 and EO771 breast tumors over the 18-day monitoring period. Overall, these findings showed that Bi-212-MAA was stably radiolabeled and inhibited breast cancer growth. Bi-212-MAA is an exciting platform to study α-particle therapy and will be easily translatable to larger animal models and human clinical trials.

The Cytokine Network in Colorectal Cancer: Implications for New Treatment Strategies

Colorectal cancer (CRC) is one of the most frequent tumor entities worldwide with only limited therapeutic options. CRC is not only a genetic disease with several mutations in specific oncogenes and/or tumor suppressor genes such as APC, KRAS, PIC3CA, BRAF, SMAD4 or TP53 but also a multifactorial disease including environmental factors. Cancer cells communicate with their environment mostly via soluble factors such as cytokines, chemokines or growth factors to generate a favorable tumor microenvironment (TME). The TME, a heterogeneous population of differentiated and progenitor cells, plays a critical role in regulating tumor development, growth, invasion, metastasis and therapy resistance. In this context, cytokines from cancer cells and cells of the TME influence each other, eliciting an inflammatory milieu that can either enhance or suppress tumor growth and metastasis. Additionally, several lines of evidence exist that the composition of the microbiota regulates inflammatory processes, controlled by cytokine secretion, that play a role in carcinogenesis and tumor progression. In this review, we discuss the cytokine networks between cancer cells and the TME and microbiome in colorectal cancer and the related treatment strategies, with the goal to discuss cytokine-mediated strategies that could overcome the common therapeutic resistance of CRC tumors.

Targeted Therapy with PI3K, PARP, and WEE1 Inhibitors and Radiotherapy in HPV Positive and Negative Tonsillar Squamous Cell Carcinoma Cell Lines Reveals Synergy while Effects with APR-246 Are Limited

Human papillomavirus positive (HPV⁺) tonsillar and base of tongue cancer (TSCC/BOTSCC) is rising in incidence, but chemoradiotherapy is not curative for all. Therefore, targeted therapy with PI3K (BYL719), PARP (BMN-673), and WEE1 (MK-1775) inhibitors alone or combined was pursued with or without 10 Gy and their effects were analyzed by viability, proliferation, and cytotoxicity assays on the TSCC/BOTSCC cell lines HPV⁺ UPCI-SCC-154 and HPV^- UT-SCC-60A. Effective single drug/10 Gy combinations were validated on additional TSCC lines. Finally, APR-246 was assessed on several TSCC/BOTSCC cell lines. BYL719, BMN-673, and MK-1775 treatments induced dose dependent responses in HPV⁺ UPCI-SCC-154 and HPV^- UT-SCC-60A and when combined with 10 Gy, synergistic effects were disclosed, as was also the case upon validation. Using BYL719/BMN-673, BYL719/MK-1775, or BMN-673/MK-1775 combinations on HPV⁺ UPCI-SCC-154 and HPV^- UT-SCC-60A also induced synergy compared to single drug administrations, but adding 10 Gy to these synergistic drug combinations had no further major effects. Low APR-246 concentrations had limited usefulness. To conclude, synergistic effects were disclosed when complementing single BYL719 BMN-673 and MK-1775 administrations with 10 Gy or when combining the inhibitors, while adding 10 Gy to the latter did not further enhance their already additive/synergistic effects. APR-246 was suboptimal in the present context.