CD8+ T cells maintain killing of MHC-I-negative tumor cells through the NKG2D-NKG2DL axis

The accepted paradigm for both cellular and anti-tumor immunity relies upon tumor cell killing by CD8+ T cells recognizing cognate antigens presented in the context of target cell major histocompatibility complex (MHC) class I (MHC-I) molecules. Likewise, a classically described mechanism of tumor immune escape is tumor MHC-I downregulation. Here, we report that CD8+ T cells maintain the capacity to kill tumor cells that are entirely devoid of MHC-I expression. This capacity proves to be dependent instead on interactions between T cell natural killer group 2D (NKG2D) and tumor NKG2D ligands (NKG2DLs), the latter of which are highly expressed on MHC-loss variants. Necessarily, tumor cell killing in these instances is antigen independent, although prior T cell antigen-specific activation is required and can be furnished by myeloid cells or even neighboring MHC-replete tumor cells. In this manner, adaptive priming can beget innate killing. These mechanisms are active in vivo in mice as well as in vitro in human tumor systems and are obviated by NKG2D knockout or blockade. These studies challenge the long-advanced notion that downregulation of MHC-I is a viable means of tumor immune escape and instead identify the NKG2D-NKG2DL axis as a therapeutic target for enhancing T cell-dependent anti-tumor immunity against MHC-loss variants.

Imaging prognostication and tumor biology in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy, and represents a significant global health burden with rising incidence rates, despite a more thorough understanding of the etiology and biology of HCC, as well as advancements in diagnosis and treatment modalities. According to emerging evidence, imaging features related to tumor aggressiveness can offer relevant prognostic information, hence validation of imaging prognostic features may allow for better noninvasive outcomes prediction and inform the selection of tailored therapies, ultimately improving survival outcomes for patients with HCC.

Risk of Tract Seeding Following Laser Interstitial Thermal Therapy for Brain Tumors

BACKGROUND

The management of intracranial oncological disease remains a significant challenge despite advances in systemic cancer therapy. Laser interstitial thermal therapy (LITT) represents a novel treatment for local control of brain tumors through photocoagulation with a stereotactically implanted laser fiber. Because the use of laser interstitial thermal therapy continues to increase within neurosurgery, characterization of LITT is necessary to improve outcomes.

OBJECTIVE

To quantify the risk of tumor seeding along the laser fiber tract in patients receiving LITT for primary or metastatic brain tumors at a high-volume treatment center.

METHODS

We retrospectively reviewed all patients receiving LITT from 2015 to 2021 at our medical center. Patients with biopsy-confirmed tumors were included in this study. Tract seeding was identified as discontinuous, newly enhancing tumor along the LITT tract.

RESULTS

Fifty-six patients received LITT for biopsy-confirmed tumors from 2015 to 2021, with tract seeding identified in 3 (5.4%). Twenty-nine (51.8%) patients had gliomas, while the remainder had metastases, of which lung was the most common histology (20 patients, 74%). Tract seeding was associated with ablation proceeding inward from superficial tumor margin closest to the cranial entry point ( P = .03). Patients with tract seeding had a shorter median time to progression of 1.1 (0.1-1.3) months vs 4.2 (2.2-8.6) months ( P = .03).

CONCLUSION

Although the risk of tract seeding after LITT is reassuringly low, it is associated with decreased progression-free survival. This risk may be related to surgical technique or experience. Follow-up radiosurgery to the LITT tract has the potential to prevent this complication.

Factors Associated with New-Onset Seizures Following Stereotactic Radiosurgery for Newly Diagnosed Brain Metastases

Purpose

Stereotactic radiosurgery (SRS) is a highly effective therapy for newly diagnosed brain metastases. Prophylactic antiepileptic drugs are no longer routinely used in current SRS practice, owing to a perceived low overall frequency of new-onset seizures and potential side effects of medications. It is nonetheless desirable to prevent unwanted side effects following SRS. Risk factors for new-onset seizures after SRS have not been well established. As such, we aimed to characterize variables associated with increased seizure risk.

Methods and Materials

Patients treated with SRS for newly diagnosed brain metastases between 2013 and 2016 were retrospectively reviewed at a single institution. Data on baseline demographics, radiation parameters, and clinical courses were collected.

Results

The cohort consisted of 305 patients treated with SRS without prior seizure history. Median age and baseline Karnofsky Performance Scale score were 64 years (interquartile range, 55-70) and 80 (interquartile range, 80-90), respectively. Twenty-six (8.5%) patients developed new-onset seizures within 3 months of SRS. There was no association between new-onset seizures and median baseline Karnofsky Performance Scale score, prior resection, or prior whole brain radiation therapy. There were significant differences in the combined total irradiated volume (12.5 vs 3.7 cm³, P < .001), maximum single lesion volume (8.8 vs 2.8 cm³, P = .003), lesion diameter (3.2 vs 2.0 cm, P = .003), and number of lesions treated (3 vs 1, P = .018) between patients with and without new-onset seizures, respectively. On multivariate logistic regression, total irradiated volume (odds ratio, 1.09 for every 1-cm¹ increase in total volume; confidence interval, 1.02-1.17; P = .016) and pre-SRS neurologic symptoms (odds ratio, 3.08; 95% confidence interval, 1.19-7.99; P = .020) were both significantly correlated with odds of seizures following SRS.

Conclusions

Our data suggest that larger total treatment volume and the presence of focal neurologic deficits at presentation are associated with new-onset seizures within 3 months of SRS. High-risk patients undergoing SRS may benefit from counseling or prophylactic antiseizure therapy.

Laser ablation: Heating up the anti-tumor response in the intracranial compartment

Immunotherapies, such as immune checkpoint inhibition (ICI), have had limited success in treating intracranial malignancies. These failures are due partly to the restrictive blood-brain-barrier (BBB), the profound tumor-dependent induction of local and systemic immunosuppression, and immune evasion exhibited by these tumors. Therefore, novel approaches must be explored that aim to overcome these stringent barriers. LITT is an emerging treatment for brain tumors that utilizes thermal ablation to kill tumor cells. LITT provides an additional therapeutic benefit by synergizing with ICI and systemic chemotherapies to strengthen the anti-tumor immune response. This synergistic relationship involves transient disruption of the BBB and local augmentation of immune function, culminating in increased CNS drug penetrance and improved anti-tumor immunity. In this review, we will provide an overview of the challenges facing immunotherapy for brain tumors, and discuss how LITT may synergize with the endogenous anti-tumor response to improve the efficacy of ICI.

CD8 T cells licensed with immune checkpoint blockade kill murine tumors lacking MHC-I

MHC-I downregulation is a well described mechanism of tumor immune escape. Thus, targeting tumors with low or no MHC-I expression remains a significant challenge for T cell-based immunotherapies, including immune checkpoint blockade (ICB).

We previously demonstrated that the combination of PD-1 blockade and 4-1BB agonism has marked efficacy against intracranial murine CT2A glioma in a CD8 T cell-dependent manner. Surprisingly, this combination therapy remained effective in a β2 microglobulin knockout CT2A line overexpressing TRP2 (CT2A-TRP2-β2mKO). These tumors lack MHC-I but retain the Trp2 rejection antigen. Remarkably, the persisting efficacy remained dependent on CD8 T cells, but independent of NK cells, CD4 T cells, and B cells. Furthermore, the efficacy was demonstrated to be antigen-specific in vivo, as adoptively transferred Trp2-specific T cells prolonged survival of mice bearing CT2A-TRP2-β2mKO tumors, but not those bearing CT2A-β2mKO, which lacked the TRP2 antigen.

To analyze the mechanism driving antigen-dependent killing of tumor cells lacking MHC-I, we performed a series of in vitro cytotoxicity experiments using Trp2-specific T cells in the presence or absence of Trp2 antigen-loaded bone marrow-derived macrophages (BMDM). These studies demonstrated that in the absence of BMDM, Trp2-specific T cells efficiently killed MHC-I-expressing CT2A-Trp2, but failed to kill MHC-I deficient CT2A-Trp2-B2mKO tumors. However, killing was restored in the presence of Trp2 loaded BMDMs; the latter of which possessed little to no cytotoxic effect alone. These findings suggest a novel role for myeloid populations in mediating the influence of ICB on T cell function and challenge the traditional model of T cell tumor killing.

Pushing Past the Blockade: Advancements in T Cell-Based Cancer Immunotherapies

Successful cancer immunotherapies rely on a replete and functional immune compartment. Within the immune compartment, T cells are often the effector arm of immune-based strategies due to their potent cytotoxic capabilities. However, many tumors have evolved a variety of mechanisms to evade T cell-mediated killing. Thus, while many T cell-based immunotherapies, such as immune checkpoint inhibition (ICI) and chimeric antigen receptor (CAR) T cells, have achieved considerable success in some solid cancers and hematological malignancies, these therapies often fail in solid tumors due to tumor-imposed T cell dysfunctions. These dysfunctional mechanisms broadly include reduced T cell access into and identification of tumors, as well as an overall immunosuppressive tumor microenvironment that elicits T cell exhaustion. Therefore, novel, rational approaches are necessary to overcome the barriers to T cell function elicited by solid tumors. In this review, we will provide an overview of conventional immunotherapeutic strategies and the various barriers to T cell anti-tumor function encountered in solid tumors that lead to resistance. We will also explore a sampling of emerging strategies specifically aimed to bypass these tumor-imposed boundaries to T cell-based immunotherapies.

Control of myeloid differentiation and survival by Stats

Hematopoiesis involves a complex array of growth factors that regulate the survival and proliferation of immature progenitors, influence differentiation commitment, and modulate end-stage cell functions. This mini-review is focused on the role of Stat activation in the development of myeloid cells in response to hematopoietic cytokines. Much of the evidence implicating Stats in these cellular processes comes from studies of mutant cytokine receptors selectively uncoupled from Stat activation, dominant-inhibitory Stat mutants, and mice with targeted disruptions of Stat genes. Together these approaches provide strong evidence that Stat activation, particularly of Stat3 and Stat5, plays an important role in myeloid differentiation and survival. Oncogene (2000).

The nonreceptor protein-tyrosine kinase c-Fes is involved in fibroblast growth factor-2-induced chemotaxis of murine brain capillary endothelial cells

Fibroblast growth factor-2 (FGF-2)-induced migration of endothelial cells is involved in angiogenesis in vivo. However, signal transduction pathways leading to FGF-2-induced chemotaxis of endothelial cells are largely unknown. Previous studies have shown that the cytoplasmic protein-tyrosine kinase c-Fes is expressed in vascular endothelial cells and may influence angiogenesis in vivo. To investigate the contribution of c-Fes to FGF-2 signaling, we expressed wild-type or kinase-inactive human c-Fes in the murine brain capillary endothelial cell line, IBE (Immortomouse brain endothelial cells). Wild-type c-Fes was tyrosine-phosphorylated upon FGF-2-stimulation in transfected cells, whereas kinase-inactive c-Fes was not. Overexpression of wild-type c-Fes promoted FGF-2-independent tube formation of IBE cells. Tube formation was not observed with endothelial cells expressing kinase-inactive c-Fes, indicating a requirement for c-Fes kinase activity in this biological response. Expression of kinase-defective c-Fes suppressed endothelial cell migration following FGF-2 treatment, suggesting that activation of endogenous c-Fes may be required for the chemotactic response. Expression of either wild-type c-Fes or the kinase-inactive mutant did not affect the tyrosine phosphorylation FRS2, Shc, or phospholipase C-gamma, nor did it influence the kinetics of mitogen-activated protein kinase activation. These results implicate c-Fes in FGF-2-induced chemotaxis of endothelial cells through signaling pathways not linked to mitogenesis.

Affinity of Src family kinase SH3 domains for HIV Nef in vitro does not predict kinase activation by Nef in vivo

Nef is an HIV accessory protein required for high-titer viral replication and AIDS progression. Previous studies have shown that the SH3 domains of Hck and Lyn bind to Nef via proline-rich sequences in vitro, identifying these Src-related kinases as potential targets for Nef in vivo. Association of Nef with Hck causes displacement of the intramolecular interaction between the SH3 domain and the SH2-kinase linker, leading to kinase activation both in vitro and in vivo. In this study, we investigated whether interaction with Nef induces activation of other Src family kinases (Lyn, Fyn, Src, and Lck) following coexpression with Nef in Rat-2 fibroblasts. Coexpression with Nef induced Hck kinase activation and fibroblast transformation, consistent with previous results. In contrast, coexpression of Nef with Lyn was without effect, despite equivalent binding of Nef to full-length Lyn and Hck. Furthermore, Nef was found to suppress the kinase and transforming activities of Fyn, the SH3 domain of which exhibits low affinity for Nef. Coexpression with Nef did not alter c-Src or Lck tyrosine kinase or transforming activity in this system. Differential modulation of Src family members by Nef may produce unique downstream signals depending on the profile of Src kinases expressed in a given cell type.

Inhibition of the prenylation of K-Ras, but not H- or N-Ras, is highly resistant to CAAX peptidomimetics and requires both a farnesyltransferase and a geranylgeranyltransferase I inhibitor in human tumor cell lines

The farnesyltransferase (FTase) inhibitor FTI-277 is highly effective at blocking oncogenic H-Ras but not K-Ras4B processing and signaling. While inhibition of processing and signaling of oncogenic K-Ras4B is more sensitive to the geranylgeranyltransferase I (GGTase I) inhibitor GGTI-286 than it is to FTI-277 in K-Ras4B-transformed NIH3T3 cells, the sensitivity of K-Ras as well as H- and N-Ras to the CAAX peptidomimetics in human tumor cell lines is not known. Here, we report that a panel of five human carcinoma cell lines from pancreatic, pulmonary, and bladder origins all express H-, N-, and K-Ras, and their respective prenylation sensitivities to the FTase and GGTase I inhibitors is variable. In all of the cell lines investigated, the prenylation of N-Ras was highly sensitive to FTI-277, and in two of the cell lines, N-Ras showed slight sensitivity to GGTI-298, an analog of GGTI-286. Although the prenylation of H-Ras was also sensitive to FTI-277, complete inhibition of H-Ras processing even at high concentrations of FTI-277 and/or GGTI-298 was never achieved. The prenylation of K-Ras, on the other hand, was highly resistant to FTI-277 and GGTI-298. Most significantly, treatment of human tumor cell lines with both inhibitors was required for inhibition of K-Ras prenylation. In one cell line, the human lung adenocarcinoma A-549, prenylation of K-Ras was highly resistant even when co-treated with both inhibitors. Furthermore, soft agar experiments demonstrated that in all the human tumor cell lines tested inhibition of K-Ras prenylation was not necessary for inhibition of anchorage-independent growth. In addition, although GGTI-298 had very little effect on soft agar growth, the combination of FTI-277 and GGTI-298 resulted in significant growth inhibition. Therefore, the results demonstrate that while FTI-277 inhibits N-Ras and H-Ras processing in the human tumor cell lines evaluated, inhibition of K-Ras processing requires both an FTase inhibitor as well as a GGTase I inhibitor, and that inhibition of human tumor growth in soft agar does not require inhibition of oncogenic K-Ras processing.

Inhibition of Ras prenylation: a signaling target for novel anti-cancer drug design

The cancer-causing activity of Ras requires the prenylation of a cysteine fourth from its carboxyl terminus. Rational design of peptidomimetics of the carboxyl terminal tetrapeptide prenylation site on Ras resulted in pharmacological agents capable of inhibiting Ras processing, selectively antagonizing oncogenic signaling and suppressing human tumor growth in mouse models without side effects. This mini-review describes the efforts of several groups to design, synthesize and evaluate the biological activities of farnesyltransferase and geranylgeranyltransferase I inhibitors. Among the important issues that will be discussed are the mechanism of action of these inhibitors and the potential mechanisms of resistance to inhibition of K-Ras farnesylation.

Disruption of oncogenic K-Ras4B processing and signaling by a potent geranylgeranyltransferase I inhibitor

Prenylation of the carboxyl-terminal CAAX (C, cysteine; A, aliphatic acid; and X, any amino acid) of Ras is required for its biological activity. We have designed a CAAX peptidomimetic, GGTI-287, which is 10 times more potent toward inhibiting geranylgeranyltransferase I (GGTase I) in vitro (IC50 = 5 nM) than our previously reported farnesyltransferase inhibitor, FTI-276. In whole cells, the methyl ester derivative of GGTI-287, GGTI-286, was 25-fold more potent (IC50 = 2 microM) than the corresponding methyl ester of FTI-276, FTI-277, toward inhibiting the processing of the geranylgeranylated protein Rap1A. Furthermore, GGTI-286 is highly selective for geranylgeranylation over farnesylation since it inhibited the processing of farnesylated H-Ras only at much higher concentrations (IC50 > 30 microM). While the processing of H-Ras was very sensitive to inhibition by FTI-277 (IC50 = 100 nM), that of K-Ras4B was highly resistant (IC50 = 10 microM). In contrast, we found the processing of K-Ras4B to be much more sensitive to GGTI-286 (IC50 = 2 microM). Furthermore, oncogenic K-Ras4B stimulation inhibited potently by GGTI-286 (IC50 = 1 microM) but weakly by FTI-277 (IC50 = 30 microM). Significant inhibition of oncogenic K-Ras4B stimulation of MAP kinase by GGTI-286 occurred at concentrations (1-3 microM) that did not inhibit oncogenic H-Ras stimulation of MAP kinase. The data presented in this study provide the first demonstration of selective disruption of oncogenic K-Ras4B processing and signaling by a CAAX peptidomimetic. The higher sensitivity of K-Ras4B toward a GGTase I inhibitor has a tremendous impact on future research directions targeting Ras in anticancer therapy.

Ras CAAX peptidomimetic FTI-277 selectively blocks oncogenic Ras signaling by inducing cytoplasmic accumulation of inactive Ras-Raf complexes

Ras-induced malignant transformation requires Ras farnesylation, a lipid posttranslational modification catalyzed by farnesyltransferase (FTase). Inhibitors of this enzyme have been shown to block Ras-dependent transformation, but the mechanism by which this occurs remains largely unknown. We have designed FTI-276, a peptide mimetic of the COOH-terminal Cys-Val-Ile-Met of K-Ras4B that inhibited potently FTase in vitro (IC50 = 500 pM) and was highly selective for FTase over geranylgeranyltransferase I (GGTase I) (IC50 = 50 nM). FTI-277, the methyl ester derivative of FTI-276, was extremely potent (IC50 = 100 nM) at inhibiting H-Ras, but not the geranylgeranylated Rap1A processing in whole cells. Treatment of H-Ras oncogene-transformed NIH 3T3 cells with FTI-277 blocked recruitment to the plasma membrane and subsequent activation of the serine/threonine kinase c-Raf-1 in cells transformed by farnesylated Ras (H-RasF), but not geranylgeranylated, Ras (H-RasGG). FTI-277 induced accumulation of cytoplasmic non-farnesylated H-Ras that was able to bind Raf and form cytoplasmic Ras/Raf complexes in which Raf kinase was not activated. Furthermore, FTI-277 blocked constitutive activation of mitogen-activated protein kinase (MAPK) in H-RasF, but not H-RasGG, or Raf-transformed cells. FTI-277 also inhibited oncogenic K-Ras4B processing and constitutive activation of MAPK, but the concentrations required were 100-fold higher than those needed for H-Ras inhibition. The results demonstrate that FTI-277 blocks Ras oncogenic signaling by accumulating inactive Ras/Raf complexes in the cytoplasm, hence preventing constitutive activation of the MAPK cascade.