Nanoprotrusion enlargement conducts cytocapsular tube elongation along the path of least resistance for metastasis initiation

Cancer metastasis is a major source of cancer lethality. Recently, we reported that the ATP-dependent calcium pump PMCA2 is enriched in cytocapsular membranes as biomarker of native malignant tumors. Cytocapsular tubes (CCTs) provide membrane-enclosed freeways for protected and bi-directional cancer metastasis in cytocapsular tumor network systems (CTNSs). It is obscure how CCTs initiate and elongate in heterogeneous human tissues and organs against diverse blocks of resistance. Here, we report that thin CCT nanoprotrusions (NPs) enlarge in directions of least resistance to grow into enlarged NPs. Subsequently, enlarged NPs develop into initial CCTs (ICCTs) followed by development into full CCTs. The full CCTs elongate in paths of least resistance over long distances, as observed in 34 kinds of human tissues and organs. Sideways CCT branching proceeds via a NP bifid format, which increases CCT numbers and expands 3D CCT networks in tissues. CCT regeneration additionally drives repeated cancer metastasis. CCT superstructures facilitate full cancer metastasis. This study demonstrated nanoprotrusion-conducted CCT elongation along the path of least resistance and branching morphogenesis in bifid branching style. The cytocapsular membrane system expansion mechanics of CCTs and CCT networks described here may open new avenues for native cancer research and CTNS-targeted effective cancer cure. (200 words) Significance statementThe recent identification of PMCA2 as a biomarker for malignant tumors, allows imaging very early native cancer growths on culture plates in vitro and in human bodies as revealed from snapshot images of numerous cancer biopsies in vivo. Aggressive cancer metastasis, cancer progression, repeated cancer relapse, limited cancer therapy outcomes, pan-cancer drug resistance, immune cell attack escape, and immunotherapy non-responsive "cold" tumors are unmet challenges in clinical cancer therapy. However, the cytocapsular tube (CCT) elongation mechanisms in human tissues/organs with heterogeneous resistances are still unclear. Here, we report that CCT nanoprotrusions (NPs) extend into enlarged NPs apparently towards tissue of least resistance and subsequently develop into initial CCTs. Intracytocapsular oncocells released cytocapsulasomes to fuse into the membranes of initial CCTs and increase cytocapsular membrane areas. This enables oncocells to push and deform initial CCT membranes and to generate new CCTs with new nanoprotrusion layers. Furthermore, CCT branching morphogenesis develops in a bifid format, significantly increasing CCT numbers and expanding 3D CCT networks in all kinds of human tissues. CCT superstructures promote complete cancer metastasis in AMCC complexes. Repeated CCT regeneration drives repeated cancer relapses. This study reveals the CCT elongation laws, and elucidates that CCT elongation and branching morphogenesis drives cytocapsular membrane protected cancer metastasis, and that repeated CCT regeneration promotes repeated tumor relapses in vivo.