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Background Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) overexpression is linked to poor prognosis in various cancers, including astrocyte tumors, triple-negative breast cancer (TNBC), Ewing sarcoma, and osteosarcoma (OS). As the primary hydrolase of extracellular 2′3′-cGAMP—a cancer cell-derived immuno-transmitter that activates the anticancer STING pathway—ENPP1 suppresses immune activation by degrading cGAMP. Additionally, it produces immunosuppressive adenosine, enhancing tumor cell migration and hindering T-cell infiltration. RNAseq data highlight the highest ENPP1 expression in Ewing sarcoma, OS, and breast cancer. Proteomic analyses further identify ENPP1 as a promising immunotherapeutic target, particularly for rare cancers like sarcomas, underscoring its critical role in tumor progression and potential as a therapeutic focus.Methods The potency of AVA-NP-695, a small-molecule ENPP1 inhibitor, was validated through enzymatic assays using p-Nitrophenyl-5′-TMP and 2′3′-cGAMP substrates. Pharmacokinetic (PK) profiles were evaluated in mice, rats, and beagle dogs. In vivo efficacy was assessed in 4T1 tumor-bearing BALB/c mice, both as monotherapy and with anti-PD-L1, Olaparib (PARP inhibitor), or Paclitaxel. Further, ENPP1 expression and cGAMP export were evaluated after dsDNA stimulation, and ENPP1 activity was measured using a biochemical assay in OS cell lines, including OSPDX-cell lines. Activity varied significantly, with OS384 and OS526 showing the highest. Mono and combination effects of AVA-NP-695 and Olaparib were investigated in osteosarcoma (OS) and Ewing’s sarcoma models.Results AVA-NP-695 demonstrated potent and selective ENPP1 inhibition with no adverse effects in repeat-dose and dose-escalation toxicity studies in mice and beagle dogs. In the 4T1 breast cancer model, AVA-NP-695 (6 mg/kg BID) significantly outperformed Olaparib and anti-PD1, achieving superior TGI and reduced metastasis. In OS models, AVA-NP-695 induced tumor regression in both paratibial (orthotopic) and metastatic (lung) contexts. AVA-NP-695 effectively restored cGAMP levels, showing a notable rise (~2-3 fold) within 6 hours post-treatment. A targeted pharmacological screen revealed synthetic lethality between AVA-NP-695 and Olaparib in OS cell lines, enhancing intra- and extracellular cGAMP production. In-vivo, the AVA-NP-695/Olaparib combination promoted OS tumor regression and bolstered antitumor immune responses in both orthotopic and metastatic settings. Compassionate use in several canine patients resulted in >80% tumor volume reduction.Conclusions These findings underscore the therapeutic potential of AVA-NP-695 in solid tumors such as breast cancer and bone cancer. AVA-NP-695 exploits ENPP1 inhibition to exert a strong anti-tumor response and obliviates metastasis. Interestingly, AVA-NP-695 doesn’t restrict itself to a single combination modality and demonstrates cancer agnostic features both as monotherapy and also in combination with other existing standard of care treatment such as anti-PD-1 or Paclitaxel or PARP inhibitors.