Theoretical premises of a "three in one" therapeutic approach to treat immunogenic and nonimmunogenic cancers: a narrative review

Abstract

Objective: We describe experimental and theoretical premises of a powerful cancer therapy based on the combination of three approaches. These include (I) in situ vaccination (intratumoral injections of CpG oligonucleotides and anti-OX40 antibody); (II) chronometric or metronomic low-dose cyclophosphamide (CMLD CP)-based chemotherapy; (III) cancer stem cell-eradicating therapy referred to as Karanahan (from the Sanskrit kāraṇa ["source"] + han ["to kill"]).

Background: In murine models, the first two approaches are particularly potent in targeting immunogenic tumors for destruction. In situ vaccination activates a fully fledged anticancer immune response via an intricate network of ligand-receptor-cytokine interactions. CMLD CP-based chemotherapy primarily targets the suppressive tumor microenvironment and activates tumor-infiltrating effectors. In contrast, Karanahan technology, being aimed at replicative machinery of tumor cells (both stem-like and committed), does not depend on tumor immunogenicity. With this technology, mice engrafted with ascites and/or solid tumors can be successfully cured. There is a significant degree of mechanistic and therapeutic overlap between these three approaches. For instance, the similarities shared between in situ vaccination and Karanahan technology include the therapeutic procedure, the cell target [antigen-presenting cells (APC) and dendritic cells (DC)], and the use of DNA-based preparations (CpG and DNAmix). Features shared between CMLD CP-based chemotherapy and Karanahan technology are the timing and the dose of the cytostatic drug administration, which lead to tumor regression.

Methods: The following keywords were used to search PubMed for the latest research reporting successful eradication of transplantable cancers in animal models that relied on approaches distinct from those used in the Karanahan technology: eradication of malignancy, cure cancer, complete tumor regression, permanently eradicating advanced mouse tumor, metronomic chemotherapy, in situ vaccination, immunotherapy, and others.

Conclusion: We hypothesize, therefore, that very potent anticancer activity can be achieved once these three therapeutic modalities are combined into a single approach. This multimodal approach is theoretically curative for any type of cancer that depends on the presence of tumor-inducing cancer stem cells, provided that the active therapeutic components are efficiently delivered into the tumor and the specific biological features of a given patient's tumor are properly addressed. We expect this multimodal approach to be primarily applicable to late-stage or terminal cancer patients who have exhausted all treatment options as well as patients with inoperable tumors.

Keywords: In situ vaccination; Karanahan technology; cancer stem cells; chronometric/metronome low-dose chemotherapy; immunity.

Figure 1

Cancer stem cells. (A) A model of cellular hierarchy within the tumor, with a self-perpetuating population of pluripotent cancer stem cells found on the top. (B) Various cancers encompass a subpopulation of DNA-internalizing cancer cells, referred to as TAMRA+ cancer stem cells (arrowheads): (I) sphere-forming cell line arising from human Epstein-Barr virus-induced lymphoma; (II) mouse Krebs-2 ascites; (III) a human lymphoma cell cluster. Cells (10⁶) were incubated with 0.1 mkg TAMRA-labeled DNA fragment (human Alu repeat, about 500 bp) for 1 hour at room temperature in the dark.

Figure 2

Side-by-side comparison of the three technologies. Shaded areas denote overlapping features of the approaches. αOX40, anti-OX40 antibodies; CpG, short synthetic single-stranded DNA molecules containing CpG motifs; CP, cyclophosphamide.

Figure 3

The progression of events induced by the integrated “three-in-one” technology. Successive intratumoral CP and DNAmix administration, strictly tied to the DNA repair timing, initiates the lysis of tumor cells that results in the formation of cellular debris consisting of apoptotic and necrotic components, elimination of cancer stem cells, disruption of the suppressive properties of tumor-associated stromal cells, development of local inflammation, and activation of the antigen-presenting properties of dendritic cells, which begin to secrete a wide range of cytokines (TNF-α, IFN-γ, IL-1RA, IL-1β, IL-6, IL-8, MCP-1, MIP-1β, IL-10, VEGF, G-CSF, and GM-CSF). These cytokines and direct cell–cell interactions activate tumor-infiltrating immune cells: effector T cells (Teff), NK, Neut, NKT, and Macr, which begin to express OX40 and FcR receptors on their surface. Anti-OX40 antibodies initiate a cascade of cellular and humoral reactions causing the development of adaptive immunity. CP, cyclophosphamide; NK, natural killer cells; Neut, neutrophils; NKT, natural killer T cells; Macr, OX40, macrophages; anti-OX40 antibodies.