A Small Molecule–Drug Conjugate (SMDC) Consisting of a Modified Camptothecin Payload Linked to an αVß3 Binder for the Treatment of Multiple Cancer Types

To improve tumor selectivity of cytotoxic agents, we designed VIP236, a small molecule–drug conjugate consisting of an αVβ3 integrin binder linked to a modified camptothecin payload (VIP126), which is released by the enzyme neutrophil elastase (NE) in the tumor microenvironment (TME). The tumor targeting and pharmacokinetics of VIP236 were studied in tumor-bearing mice by in vivo near-infrared imaging and by analyzing tumor and plasma samples. The efficacy of VIP236 was investigated in a panel of cancer cell lines in vitro, and in MX-1, NCI-H69, and SW480 murine xenograft models. Imaging studies with the αVβ3 binder demonstrated efficient tumor targeting. Administration of VIP126 via VIP236 resulted in a 10-fold improvement in the tumor/plasma ratio of VIP126 compared with VIP126 administered alone. Unlike SN38, VIP126 is not a substrate of P-gp and BCRP drug transporters. VIP236 presented strong cytotoxic activity in the presence of NE. VIP236 treatment resulted in tumor regressions and very good tolerability in all in vivo models tested. VIP236 represents a novel approach for delivering a potent cytotoxic agent by utilizing αVβ3 as a targeting moiety and NE in the TME to release the VIP126 payload—designed for high permeability and low efflux—directly into the tumor stroma.

YK-4-279 Attenuates Progression of Pre-Existing Pigmented Lesions to Nodular Melanoma in a Mouse Model

More options are needed for the effective treatment of melanoma. In a previous study, we discovered the small molecule drug YK-4-279 almost completely inhibited tumor progression in the BrafCA;Tyr-CreERT2;Ptenflox/flox transgenic mouse model. YK-4-279 had no effect on tumor initiation but blocked progression of invasive melanoma. Our current study was designed as a treatment model, where YK-4-279 was administered during pigmented lesion formation. The study design included the use of three groups: (1) a control group that received only DMSO without a drug (MOCK), (2) mice following our prior studies with YK-4-279 administered at the time of tumor induction (YK-4-279), and (3) mice treated during tumor initiation (YK-4-279 delay). While the MOCK mice had progression of tumors, both YK-4-279 and YK-4-279 delay groups had a significant block or delay of progression. The majority of mice in the YK-4-279 groups had a block of progression, while the YK-4-279 delay group had either a partial block (60% in male mice or 29% in females) or a delay in disease progression in females (28 days in controls to 50 days in YK-4-279 delay group). Here, we demonstrate that YK-4-279 has a significant impact on blocking or delaying tumor progression in a pre-clinical treatment model of melanoma.

Alphataxin, a Small-Molecule Drug That Elevates Tumor-Infiltrating CD4+ T Cells, in Combination With Anti-PD-1 Therapy, Suppresses Murine Renal Cancer and Metastasis

By promoting the cytotoxic function of CD8+ T cells, immune checkpoint inhibitor therapy, e.g. programmed cell death protein-1 (PD-1), effectively inhibits tumor growth in renal cell carcinoma. Yet, as many as 87% of cancer patients do not respond to immune checkpoint therapy. Importantly, cytotoxic CD8+ T cell function crucially relies on CD4+ T helper cell cytokines, in particular, tumor necrosis factor beta (TNFβ) and its CD8+ T cell receptor (TNFR2) in the opposing manner as immune checkpoints and their receptors. Remarkably, despite advances in immunotherapy, there are no pharmaceutical treatments that increase circulating CD4+ T cell counts. Nor has there been much attention given to tumor-infiltrating CD4+ T cells. Using data from a clinical trial (NCT01731691), we discovered that the protein alpha-1 proteinase inhibitor (α1PI, alpha-1 antitrypsin) regulates the number of circulating CD4+ T cells. The orally available small-molecule drug Alphataxin acts as a surrogate for α1PI in this pathway. We aimed to examine how Alphataxin affected tumor growth in a murine model of renal cell carcinoma. Alphataxin, in combination with anti-PD-1 antibody, significantly elevated the ratio of circulating and tumor-infiltrating CD4+ T cells. In one study, following orthotopic implantation of syngeneic renal adenocarcinoma cells, combination treatment resulted in 100% regression of tumor growth. Moreover, in mice implanted orthotopically with one log more tumor cells, doubling Alphataxin dose in combination treatment led to 100% regression in one-third of mice and 81% suppression of tumor growth in the remaining two-thirds of mice. Lung metastasis was present in monotherapy, but significantly reduced in combination-treated mice. Orally available Alphataxin, the first and only drug developed to increase CD4+ T cells, in combination with anti-PD-1, is a powerful therapeutic method that provides long-term remission in renal cell carcinoma and potentially other T cell-responsive cancers by increasing the number of CD4+ tumor-infiltrating T cells.

Assessment of AI-based Protein Structure Prediction for the NLRP3 Target

The recent success of AlphaFold and RoseTTAFold has demonstrated the values of AI methods in predicting highly accurate protein structures. Despite the advances, their roles in the context of small-molecule drug discovery need to be thoroughly explored. In this study, we evaluated the possibility whether the AI-based models can lead to reliable 3D structures of protein-ligand complexes. With the AI-generated protein structure, we were able to confidently predict the binding modes of small-molecule inhibitors for NLRP3, a challenging protein target in terms of obtaining the 3D model both experimentally and computationally. We therefore concluded that through careful evaluation, AI-predicted protein structures can be trusted and useful for small-molecule drug discovery projects.

STEM-12. THE SMALL MOLECULE DRUG CBL0137 INCREASES THE LEVEL OF DNA DAMAGE AND THE EFFICACY OF RADIOTHERAPY FOR GLIOBLASTOMA

Glioblastoma (GBM) is a fatal and incurable brain tumor, with an average life expectancy after diagnosis of only 12-15 months. A main reason for the lethality of GBM is inevitable recurrence, caused by a small population of the tumor cells, called cancer stem cells (CSCs). These cells are aggressive, infiltrative, and resistant to current GBM treatments of chemotherapy and radiotherapy. We use a small molecule drug, CBL0137, which inhibits the FACT (facilitates chromatin transcription) complex leading to cancer cell specific cytotoxicity. Here, we show that CBL0137 sensitized GBM CSCs to radiotherapy and hence lead to increased CSC death and prolonged survival in preclinical models. Clonogenic assays were used to show that CSCs were radiosensitized after CBL0137 treatment. We saw increased DNA damage when GBM CSCs were treated with CBL0137, as well as a decrease in foci resolution over time, when CBL0137 was combined with irradiation. In order to elucidate if the increase in DNA damage was directly due to the inhibition of the FACT complex, we depleted the level of FACT in our GBM CSCs. FACT depletion also led to increased DNA damage, and even more so when combined with irradiation. To validate whether combination therapy sensitized CSCs to radiotherapy in vivo, we used a subcutaneous mouse model and showed combination treatment decreased CSCs frequency in these tumors as well as decreased tumor volume. With an orthotopic model of GBM, we showed that CBL0137 treatment followed by radiotherapy significantly increased survival of mice bearing tumors over either treatment alone. Together, this work establishes a new treatment paradigm for GBM, which sensitizes radio-resistant GBM CSCs to irradiation, a critical component of patient care. Radio-sensitizing agents, including CBL0137, pose an exciting new therapeutic capable of increasing the efficacy of irradiation, by inclusively targeting CSCs.

Potential of Farnesyl Transferase Inhibitors in Combination Regimens in Squamous Cell Carcinomas

Current therapies for recurrent and metastatic SCC are associated with poor outcomes, and options for later lines of treatment are limited. Insights into potential therapeutic targets, as well as mechanisms of resistance to available therapies, have begun to be elucidated, creating the basis for exploration of combination approaches to drive better patient outcomes. Tipifarnib, a farnesyl transferase inhibitor (FTI), is a small molecule drug that has demonstrated encouraging clinical activity in a genetically-defined subset of head and neck squamous cell carcinoma (HNSCC)–specifically, tumors that express a mutation in the HRAS protooncogene. More recently, bioinformatic analyses and results from patient-derived xenograft modeling indicate that HRAS pathway dependency may extend to a broader subpopulation of SCCs beyond HRAS mutants in the context of combination with agents such as cisplatin, cetuximab, or alpelisib. In addition, tipifarnib can also inactivate additional farnesylated proteins implicated in resistance to approved therapies, including immunotherapies, through a variety of distinct mechanisms, suggesting that tipifarnib could serve as an anchor for combination regimens in SCCs and other tumor types.