Immunity to the Vacuolar ATPase Complex Accessory Unit ATP6S1 in Patients with Malignant Melanoma

Abstract

The augmentation of high-titer antibodies to ATP6S1 is associated with favorable clinical outcomes in patients who received vaccination with autologous, irradiated tumor cells engineered to secrete GM-CSF and allogeneic bone marrow transplantation. Cellular immune responses to ATP6S1 are unknown. To define its role as an immune target, examination of cellular responses to ATP6S1 and immunity related to current therapies such as checkpoint blockade is needed. We used an overlapping peptide library representing the full-length ATP6S1 protein to screen for cellular responses from the peripheral blood of patients with stage III and IV melanoma. Reactive peptide pools were used to determine the individual peptide activity and epitopes. Recombinant ATP6S1 protein was used in an ELISA to assess potential correlation with humoral immune responses and changes in immunity related to CTLA-4 blockade with ipilimumab in these patients. We observed a broad array of CD4 þ and CD8 þ cellular responses against ATP6S1, including the identification of several MHC class I and II ATP6S1 epitopes. The generation of specific CD4 þ and cytotoxic T cells revealed potent functional capability elicited by ipilimumab treatment in patients with metastatic melanoma, which revealed potent functional capability, including cytokine production, proliferation responsiveness to melanoma cell lines, and tumor-cell killing. Furthermore, the augmented humoral immune responses to ATP6S1 as a function of ipilimumab treatment were associated with beneficial clinical outcomes. These results support the continued development of ATP6S1 as a biomarker and therapeutic target. Cancer Immunol Res; 3(1); 59-67. Ó2014 AACR.

Discovery of a Small-Molecule Probe for V-ATPase Function

“… 6 Mutations in various subunits of the V-ATPase complex have been linked to osteopetrosis, 7 , 8 x-linked myopathy, 9 distal renal tubular acidosis, sensorineural deafness, 10 , 11 and pulmonary tuberculosis, 12 and the complex has been studied as a potential dependency of certain cancer cells. 6 , 13 , 14 …”

“…6 Mutations in various subunits of the V-ATPase complex have been linked to osteopetrosis, 7,8 x-linked myopathy, 9 distal renal tubular acidosis, sensorineural deafness, 10,11 and pulmonary tuberculosis, 12 and the complex has been studied as a potential dependency of certain cancer cells. 6,13,14 Beyond its degradative function, recent studies have identified the lysosome as a critical component of various signaling pathways. For example, amino acids in the lysosomal lumen promote the recruitment of the mechanistic target of rapamycin (mTOR) to the lysosomal membrane and the activation of mTOR signaling in a V-ATPase-and ragulatordependent manner, 15,16 leading to enhancement of cell growth and protein synthesis and inhibition of autophagy.…”

“…The acidic pH in the lysosomal lumen (pH = 4.5–5.0), which is required for optimal hydrolase activity, is generated and maintained by the vacuolar-type H + -ATPase (V-ATPase), a protein complex on lysosomal membranes that hydrolyzes ATP to drive protons into lysosomes . Mutations in various subunits of the V-ATPase complex have been linked to osteopetrosis, , x-linked myopathy, distal renal tubular acidosis, sensorineural deafness, , and pulmonary tuberculosis, and the complex has been studied as a potential dependency of certain cancer cells. ,, …”

Trametinib in metastatic melanoma

“…As responses are often slow, patients may not benefit clinically when presenting with rapidly progressing clinical symptoms. Currently, there are no biomarkers to predict who may benefit from ipilimumab, hence patients can undergo treatment and some associated risk without reduction or stabilization of their disease [16][17][18][19][20]. Notably ipilimumab can be used in patients regardless of their BRAF status.…”